Magnetic nanoparticles for ferroptosis cancer therapy with diagnostic imaging

Abstract

Ferroptosis offers a novel method for overcoming therapeutic resistance of cancers to conventional cancer treatment regimens. Its effective use as a cancer therapy requires a precisely targeted approach, which can be facilitated by using nanoparticles and nanomedicine, and their use to enhance ferroptosis is indeed a growing area of research. While a few review papers have been published on iron-dependent mechanism and inducers of ferroptosis cancer therapy that partly covers ferroptosis nanoparticles, there is a need for a comprehensive review focusing on the design of magnetic nanoparticles that can typically supply iron ions to promote ferroptosis and simultaneously enable targeted ferroptosis cancer nanomedicine. Furthermore, magnetic nanoparticles can locally induce ferroptosis and combinational ferroptosis with diagnostic magnetic resonance imaging (MRI). The use of remotely controllable magnetic nanocarriers can offer highly effective localized image-guided ferroptosis cancer nanomedicine. Here, recent developments in magnetically manipulable nanocarriers for ferroptosis cancer nanomedicine with medical imaging are summarized. This review also highlights the advantages of current state-of-the-art image-guided ferroptosis cancer nanomedicine. Finally, image guided combinational ferroptosis cancer therapy with conventional apoptosis-based therapy that enables synergistic tumor therapy is discussed for clinical translations.

Graphical abstract

Highlights

• •Recent advances in the use of magnetic nanoparticles for ferroptosis cancer nanomedicine are summarized.
• •The advantages of image-guided ferroptosis cancer nanomedicine are overviewed.
• •The rational design and fabrication of magnetic nanoparticles to enhance local ferroptosis induction are described.
• •Challenges and opportunities for image-guided ferroptosis cancer nanomedicine in clinical applications are provided.

1. Introduction

Cancer is the 2nd most common cause of death that is rising each year (1.95 million new cases are projected in 2023) [1]. Most of conventional major cancer therapies have utilized the caspase-dependent apoptotic cancer cell death. However, the apoptosis associated therapeutic resistance of cancer cells significantly attributed to the continuous increase of mortality in cancer patients [[2], [3], [4], [5], [6], [7]]. Established apoptosis-based therapeutic approaches could be reconsidered with other alternative pathways regulating cancer cell death to make a transformative breakthrough in cancer treatment [8]. Ferroptosis-based cancer therapeutics provide a new strategy for preventing resistance to conventional cancer therapies. Ferroptosis is a recently discovered type of programmed cell death that is genetically and biochemically distinct from caspase-based apoptosis, pyroptosis, or necrosis. Increases in iron-dependent lipid peroxidation (LPO) and hydroxyl radicals are the major processes for ferroptosis through the Fenton reaction, which is mediated by excess iron ions and intracellular hydrogen peroxide (H₂O₂). Ferroptosis is characterized by the accumulation of iron-dependent cellular reactive oxygen species (ROS) leading to the failure of cell redox homeostasis that results in oxidative damage to cells. Recently, exploiting ferroptosis as a new effective approach has been considered to overcome the limitations of conventional apoptotic cell death-based cancer therapies. In preclinical studies, the ferroptosis process has shown potential for treating therapeutically resistant cancer cells with outstanding treatment outcomes compared to conventional chemotherapy, which frequently results in therapeutic resistance and tumor regrowth. X_c⁻ transporter system (system X_c⁻) inhibitors (e.g., erastin and its analogs, sulfasalazine, and sorafenib), glutathione peroxidase 4 (GPX4) inhibitors (e.g., RSL3, FIN 56, and FINO2), and ROS producers (e.g., artesunate and ruscogenin) are ferroptosis-associated antitumor agents [[9], [10], [11], [12], [13]]. The multifaceted impact of ferroptosis on tumor treatment and development extends beyond its direct cellular effects. It is intricately influenced not only by oncogenes and tumor suppressors but also by the complex TME. As a result, targeting ferroptotic pathways is implicated in augmenting chemotherapeutic, immunotherapeutic, and radiotherapeutic outcomes.

However, there is not yet any clinical evidence of ferroptosis-augmenting agents showing substantial tumor therapeutic outcomes. Currently, various approaches for efficient ferroptosis induction and its combination with conventional cancer therapies are being continually studied. Despite this, currently available ferroptosis inducers have been found to not only treat cancer but also promote cancer and other diseases. Thus, treating cancers based on ferroptosis requires further consideration. Various routes toward pathological cell death and the cause of many diseases are related to ferroptosis. Degenerative pathological changes can also occur due to the reduced ability to repair the damage caused by LPO [14,15]. The specificity and optimal dose of ferroptosis inducers should be further explored to reduce their side effects and damage to normal cells. In addition, the heterogeneity and plasticity of tumor cells affect their sensitivity to ferroptosis inducers differently, while the subsequent specific functionality of signals released from cancer cells in the TME has not yet been determined [16]. Furthermore, translational ferroptosis inducing agents have shown poor bioavailability and low tumor specificity. Thus, exploiting the ferroptosis mechanism and the tumor-specific induction of ferroptosis is currently under investigation.

A promising approach for image-guided ferroptosis-induction and combinational ferroptosis-induction cancer therapies is using magnetically manipulable nanoparticles (MNPs) (Fig. 1). Specifically, the localized delivery and catalytic effect of MNPs for conventional and combinational cancer therapy have been demonstrated and established in the field of translational medicine [[17], [18], [19], [20], [21], [22], [23], [24], [25]]. These MNPs could become a next-generation tool for treating cancer. Their use could help to achieve targeted ferroptosis induction with additional imaging in emerging ferroptosis-induction cancer therapeutics. Representatively, iron oxide NPs, ROS-generating polymeric and inorganic NPs, and multifunctional nano-cargoes combining an imaging component and ferroptosis induction have shown high efficacy in treating tumors [26]. The imaging component is essential for targeting the tumor and localizing the ferroptosis therapy. Image guidance in ferroptosis or ferroptosis-based combinational therapies allows the safe and effective use of ferroptosis for the treatment of therapeutically resistant cancers. Herein, the latest developmental trends of image-guided ferroptosis-induction cancer nanomedicine using MNPs as a future form of cancer medicine are summarized and their advantages and limitations are discussed.

Fig. 1.

Schematic illustrations of various magnetic nanoparticles and their multifunction including iron metabolism mediated ferroptosis induction, magnetic manipulation, magnetic energy transduction, and magnetic resonance imaging for synergistic ferroptosis cancer nanomedicine.

2. Ferroptosis in cancer cells

Metabolic dysfunction related to LPO is the main cause of ferroptosis induction in cancer cells. Therefore, the increases in free ROS radicals, fatty acid supply, and enzymatic LPO are the main effectors of ferroptosis. Although the link between ferroptosis and human disease is still under investigation, validation of the therapeutic efficacy of ferroptosis inhibitors in various disease animal models has contributed to our understanding of the involvement of ferroptosis in cancer and degenerative diseases (Fig. 2). Specifically, the outcomes of recent studies have revealed that iron, lipids, ROS, and cell metabolism play a critical role in ferroptosis induction in cells. Ferroptosis inducers can kill highly metabolic cancer cells. Various strategies to unbalance key regulators of iron, antioxidant, mitochondrial, and lipid metabolism have been developed for ferroptosis-based cancer therapy. Here, the ferroptosis mechanism and key regulators for potential cancer therapy applications are briefly summarized. Since the promise of ferroptosis in cancer research has been recognized, extensive review papers on the ferroptosis mechanism and perspectives on this new cancer therapy opportunity have been published [[27], [28], [29]].

Fig. 2.

Ferroptosis related human diseases demonstrating the impact of ferroptosis for treating various tumors and diseases. Reproduced with permission [30]. Copyright 2021, Elsevier B.V.

2.1. Iron metabolism

Iron is a key component in regulating metabolism and proliferation of cancer cells. In general, enhancing the antioxidant level upregulates the DNA repair of cancer cells, while the high ROS tolerance of cancer cells makes them more sensitive to iron-induced stress. Thus, various types of cancer cells can finely regulate the more intracellular iron level via tumor-specific iron transportation systems such as ferroportin (FPN), transferrin receptor (TFR), transferrin (TF), ferritin, and ceruloplasmin (Fig. 3). In the iron homeostasis pathway, Fe²⁺ is captured by C-reactive protein and oxidized to Fe³⁺, which binds to TF and TFRs in the blood circulatory system. Meanwhile, excess iron in cells is exported via the FPN cellular efflux channel, thereby balancing the intracellular iron level. Recently, it has been reported that the iron homeostasis pathway contributes to cancer development, therapeutic resistance, and metastasis [31]. Interference in iron metabolism pathways can induce the LPO-mediated ferroptosis of cancer cells. Various molecules targeting iron-transportation components for the treatment of cancer cells have been studied [[32], [33], [34], [35]].

Fig. 3.

Ferroptosis mechanism associated with iron metabolism, lipid metabolism and ROS metabolism in cancer cells.

2.2. Lipids metabolism - antioxidants

Glutathione (GSH), which is generated from glutamate, cysteine, and glycine, is the predominant intracellular antioxidant in most living cells. GSH production is a two-step process involving adenosine triphosphate (ATP)-dependent cytosolic enzymes glutamate-cysteine ligase (GCL) and glutathione synthetase (GSS). Therefore, GSH synthesis is strongly dependent on the availability of cystine and cysteine. Ferroptosis is triggered by depleting or inhibiting GSH synthesis (Fig. 3) [36]. The redox status of the extracellular compartment modulates cystine-cystathionine exchange activity across the cellular membrane. The alanine-serine-cysteine system induces the influx of cysteine under certain redox conditions. The cellular balance of cystine-cystathionine is controlled by the system X_c⁻ comprising cystine-glutamate antiporters SLC3A2 and SLC7A11. Cystine and glutamic acid influx into cells through system X_c⁻ in the cell membranes. Subsequently, the synthesis of GSH as the substrate for GPX4 occurs through γ-glutamyl cysteine ligase and GSH synthase [37]. GPX4 converts GSH into oxidized GSH and reduces lipid peroxides to their corresponding alcohols. In general, membrane lipid metabolism is maintained by both GPX4 and GSH-associated functionality. GPX4, a main reductase in the ferroptosis, is involved in the breakdown of lipid membranes, and inactivating it can trigger cancer cell ferroptosis [38,39]. Another ferroptosis-inducing molecule that is related to lipid metabolism, coenzyme Q (CoQ10), is a representative of a ubiquitously expressed family of coenzymes that are regulated by apoptosis-inducing factor mitochondria-associated 2 (AIFM2) recently renamed as ferroptosis suppressor protein 1 (FSP1). Apoptosis and ferroptosis can be inhibited according to the location of CoQ10. The translocation of AIFM2 from the mitochondria to the plasma membrane by enzymatically reducing non-mitochondrial CoQ10 changes its pro-apoptotic activity into anti-ferroptotic activity. The AIFM2-regulated CoQ10 reduction process runs in parallel with the GPX4 pathway for reducing lipid peroxides. Targeting these antioxidant pathways can induce an imbalance in lipid metabolism leading to the ferroptosis of cancer cells.

2.3. ROS metabolism

ROS include peroxides, superoxide, singlet oxygen, and free radicals containing unpaired electrons. Excess as the by-product of oxidative phosphorylation can damage the mitochondria, proteins, DNA, and lipids [[40], [41], [42]]. Ferroptosis is frequently promoted by ROS derived from mitochondrial respiration, a pathway that can be subverted by inhibitors of mitochondrial electron-transfer complexes such as the NADPH oxidase (NOX) family, including NOX1, CYBB/NOX2, and NOX4 (Fig. 3). Besides mitochondrial ROS, ferroptosis-mitigated ROS production can occur from various sources, and the accumulation of oxidative products is considered as a maker of ferroptosis [43]. Polyunsaturated fatty acids (PUFAs), which are highly susceptible to LPO, comprise a key marker for ferroptosis [44,45]. Free PUFAs can be esterified by the activation of acyl-CoA synthetase long-chain family member 4 (ACSL4). Esterified PUFAs are incorporated into phospholipid membranes via the lysophosphatidyl choline acyltransferase 3 (LPCAT3). Thus, upregulating ACSL4 can induce ferroptosis [46,47]. Phosphatidyle-thanolamines (PEs) containing arachidonoyl (AA) or adrenoyl (AdA) are a class of phospholipids that predominantly undergo oxidation during ferroptosis [48]. ROS generation by decomposing lipid peroxides depletes nucleic acids and proteins and induces ferroptosis [49]. Intensive work to investigate the interactions between various ROS and the regulation of ferroptosis is ongoing.

2.4. Tumor suppressor genes

Tumor suppressor genes, including TP53, BRCA1-associated protein 1 (BAP1), alternative reading frame (ARF), and beclin1, suppress system X_c⁻ activity. TP53 is involved in the cancer development, including cell cycle arrest, senescence, and apoptosis [50]. It has recently been reported that p53 is a key component in modulating cancer cell ferroptosis [[51], [52], [53]]. TP53 transcriptional targets (p533KR (3 KR: K117R + K161R + K162R)) significantly promote ferroptosis via the downregulation of SLC7A11 [54]. At the same time, the loss of an additional acetylation site at K98 (4 KR: K98R + 117R + K161R + K162R) abrogates the ferroptosis activity of p53 [55]. The outcomes from another study infer that interferon-gamma secreted by CD8⁺ T cells sensitizes tumor cells for ferroptosis by suppressing system X_c⁻, suggesting including ferroptosis might be an effective tumor-suppression regimen [56]. BAP1 can induce ferroptosis in a similar process to TP53 by downregulating SLC7A11 [57]. It is frequently deleted or mutated in human cancers such as renal cell carcinoma, uveal melanoma, cholangiocarcinoma, and mesothelioma. It has been reported that the inactivation of BAP1 upregulates SLC7A11 and suppresses ferroptosis, resulting in tumor development. Although the precise mechanism by which BAP1 induces SLC7A11 suppression needs to be further investigated, it could regulate the H2A ubiquitination (H2Aub) level on the SLC7A11 promoter, which suppresses the expression of SLC7A11 [58]. Developing NP-mediated gene editing techniques could make these genes an effective target for ferroptosis-mediated cancer therapy.

3. Ferroptosis inducers for ferroptosis cancer therapy

Since highly metabolic cancer cells could be particularly susceptible to ferroptosis, ferroptosis-induction cancer medicines that can kill therapeutically resistant cancer cells open a new field of cancer therapy research [59]. Extensive research has been conducted to find target signals and molecules that can induce cancer cell ferroptosis. As mentioned earlier, intervention in iron, lipid, and ROS metabolism, as well as upregulating tumor suppressor genes, in cancer cells, can directly induce cancer cell ferroptosis. Various chemotherapeutic agents and nano-materials that are ferroptosis inducers and their potential for the treatment of cancers have been shown (Table 1) [60]. Their action mechanisms and possible applications for cancer therapy are described here.

Table 1.

Conventional ferroptosis inducers that are available in the clinical trials or the market.

Mechanism of action	Agent	Tumor type	Clinical development phase	Ref.
GSH inhibition	Cisplatin	Ovarian cancer, pancreatic cancer, urothelial cancer)	Marketed	NCT04574960
				NCT01561586
				NCT03649321
GPX4 inhibition	Altretamine	Lymphoma, sarcoma	Marketed	NCT00002936
	Withaferin A	Breast cancer, osteosarcoma	Phase II	NCT04092647
				NCT00689195
Iron activation	Neratinib	Breast cancer, colorectal cancer	Marketed	NCT04366713
				NCT03377387
				NCT03457896
	Salinomycin	Various solid tumor	Marketed (antibacterial drug) preclinical (anticancer activity)
	Lapatinib	Breast cancer	Marketed	NCT03085368
				NCT00356811
				NCT00667251
SLC7A11 inhibition	Erastin analog (PRLX 93936s)	Multiple myeloma	Phase I/II	NCT01695590
	SRF	Acute myeloid leukemia, hepatocellular carcinoma, non-small-cell lung cancer, renal cell carcinoma	Marketed	NCT03247088
				NCT02559778
				NCT00064350
	Sulfasalazine	Breast cancer, glioblastoma	Marketed (anti-inflammatory agent) phase I (cancer treatment)
DNA stress induction	Zalcitabine	AIDS-related Kaposi's sarcoma	Marketed (HIV treatment) preclinical (cancer treatment)	NCT00000954
GCL inhibition	Buthionine, sulfoximine	Melanoma, neuroblastoma	Phase I	NCT00002730
				NCT00005835
				NCT00661336
HMGCR inhibition	Fluvastatin	Breast cancer	Marketed (lipid-lowering agent) phase I (oncology)	NCT00416403
	Pravastatin	Acute myeloid leukemia, hepatocellular carcinoma	Marketed (lipid-lowering agent) phase I (oncology)
	Lovastatin	Multiple myeloma	Marketed (lipid-lowering agent) phase I (oncology)
	Simvastatin	Multiple myeloma	Marketed (lipid-lowering agent) phase I (oncology)

3.1. General ferroptosis inducers

The synthesis of GSH, the main antioxidant within cells, is dependent on system X_c⁻-mediated cysteine uptake. Erastin and its derivatives such as piperazine erastin and imidazole ketone erastin have been known to inhibit system X_c⁻ and induce ferroptosis [61]. Recently, researchers have found that multi-targeted kinase inhibitor sorafenib (SRF) and anti-inflammatory sulfasalazine (SAS) can also block system X_c⁻ and cause ferroptosis in both hepatocellular carcinoma and glioma cells, respectively [62,63]. GPX4 inhibition is another effective target that can lead directly to the accumulation of LPO. Electrophilic chloroacetamides (RSL3) and nitrile oxide electrophiles (ML210, JKE-1674, and JKE-1716) can initiate ferroptosis by inhibiting selenocysteine activity in the active site of GPX4 [38,64,65]. Iron-based FINO2 can directly oxidize lipids and indirectly inhibit GPX4 activity resulting in ferroptosis [66]. FIN56, a novel ferroptosis inducer, promotes the breakdown of GPX4, which results in increased intracellular ROS [67]. Various organic peroxide compounds containing one or more oxygen bonds (ROOR) have easily breakable O–O bonds, which can produce RO⋅ radicals leading to ferroptosis induction (Table 1).

3.2. Clinically applicable ferroptosis inducers

Drug-resistant cancer cells commonly present epithelial-to-mesenchymal transition (i.e. upregulation of mesenchymal markers and downregulation of epithelial markers), which makes them more sensitive to ferroptosis [68,69]. Thus, various conventional chemotherapeutic agents against which cancer cells are resistant have been re-evaluated as clinical ferroptosis inducers (Table 1). Representatively, cisplatin, artemisinins, neratinib, lapatinib, statin, sulfasalazine, SRF, withaferin A, and zalcitabine are being tested in clinical trials for potential repurposing as ferroptosis inducers. At the same time, clinical studies in which several proven ferroptosis inducers are being used in combination with these clinical chemotherapeutic agents to promote ferroptosis of cancer cells are also being conducted.

3.3. The limitation of ferroptosis inducers: their side effects and cancer therapeutic efficacy

The therapeutic efficacy of ferroptosis inducers, as well as other cancer therapeutic agents, is based on the selective targeting and destruction of tumor cells over normal cells, and considering their potential side effects is vital for maximizing their therapeutic benefit (Fig. 4). However, unfortunately, most currently used clinical ferroptosis inducers have poor bioavailability, low solubility, and poor metabolic stability. In a recent preclinical study, it was shown that erastin intraperitoneally injected into healthy mice significantly induced metabolic changes in several tissues [38]. Although erastin increased serum iron and malondialdehyde and decreased GSH and GPX4, it also enhanced iron deposition in the brain, duodenum, kidney, and spleen. The blood index values post-erastin injection also indicate mild cerebral infarction of the brain and enlarged glomerular volume of the kidneys, while pathological analysis showed ferroptosis-mediated growth of the duodenal epithelium. These findings infer that ferroptosis inducers induce pathological changes of healthy tissues in addition to the ferroptosis of cancer cells. Meanwhile, ferroptosis inducers can cause intestinal ischemia/reperfusion, ulcerative colitis and cystic fibrosis, and the enhanced iron level could be involved in abnormal limb development [[70], [71], [72], [73]]. Indeed, erastin and its analogs, system X_c⁻ inhibitors, and GPX4 inhibitors have also shown side effects in clinical trials (NCT03745716) (Fig. 4) [74]. Thus, targeted ferroptosis-induction cancer medicine is essential for achieving the greatest clinical benefit for cancer patients.

Fig. 4.

The potential side effects associated with systemically administered conventional ferroptosis-inducing agents that lack tumor targeting and imaging capabilities.

3.4. Nano-ferroptosis inducers

NPs with intrinsic physicochemical properties provide additional options for ferroptosis induction [75]. Iron-based NPs are the representative form of ferroptosis-inducing NPs [76,77]. Approved for clinical use as an iron supplement by the US Food and Drug Administration (FDA), they can induce the Fenton reaction and the ferroptosis of cells. Fe ions from the iron oxide NPs can generate considerable levels of ROS in cells, resulting in LPO, iron accumulation, and GPX4-mediated ferroptosis induction [78,79]. Various iron-doped and iron-based hybrid nanostructures, iron-organic frameworks, and iron-based nanocomposites have been reported. Other lipid-based NPs could promote the PUFA level in the cancer cells, which induces ferroptosis by disrupting the activity of iron receptors/channels on the cell membrane.

3.5. Magnetic nanomedicines for ferroptosis cancer therapy

As previously mentioned, ferroptosis influences several oncogenic pathways, and cancer cells can have a higher susceptibility to ferroptosis than normal cells due to their high metabolic activity. To enhance iron-dependent ferroptosis induction, regulating iron and/or lipid metabolism can effectively modulate the sensitivity of cancer cells toward ferroptosis. At the same time, the composition of the cellular antioxidant system depends on amino acid metabolism and the mevalonate pathway. Moreover, cancer metastasis can be controlled by using ferroptosis-induction cancer medication in combination with immunotherapy. However, as shown by the high failure rate of most small-molecule drugs in clinical trials, it is usually difficult to achieve adequate efficacy in the treatment of cancer using currently available ferroptosis inducers. Non-targeted ferroptosis induction can interfere with iron homeostasis and cause excessive ROS production, which can affect the immune system and cause neurodegenerative conditions such as Huntington's and Parkinson's disease, heart failure, and leukemia (Fig. 4) [[80], [81], [82], [83], [84], [85], [86]]. Ferroptosis induction in healthy cells can also activate tumorigenesis associated with iron-donating tumor-associated macrophages.

Various MNPs have been considered for the carriers of chemotherapeutic drugs due to their advantages of enhanced bioavailability, minimal side effects, appropriate degradation, and targeted delivery [[87], [88], [89], [90], [91], [92], [93], [94], [95], [96]]. Ferroptosis-induction cancer nanomedicines utilizing MNPs have been produced and tested, a summary of which is provided in Table 2. Emerging nanomedicines that promote LPO or ROS accumulation in cancer cells can control the expression of GPX4 in cancer cells, subsequently resulting in the Fenton reaction and exogenous regulation of peroxidation (Fig. 5) [97,98]. NPs that enhance the intracellular ROS can mediate intracellular chemical reactions and intervene in cancer cellular ferroptosis pathways. Another approach is to increase the uptake of exogeneous lipids by cancer cells to boost ferroptosis induction via intracellular lipid peroxide accumulation [45,99,100].

Table 2.

Summary of nano/micromaterials used to induce ferroptosis, including magnetic nanomedicine, tumor model, ferroptotic cargos, mechanism of action (ferroptosis), and compatible imaging type.

	Magnetic nanoparticles	Tumor model	Ferroptotic cargos	Mechanism of action	Diagnostic imaging	Ref.
Magnetic field targeted ferroptosis	Fe3O4@mSiO2-ANG exosome	Brain cancer	Fe3O4 NPs	DHODH disruption	FI	[104]
				GPX4 inhibition
Magnetic field triggered ferroptosis	PLGA-Fe3O4 NPs with AA	Prostate cancer	Fe3O4 NPs	Fenton reaction	MRI (T2)	[105]
MRI-guided ferroptosis	Engineered magnetosomes	Breast cancer	Fe3O4 NPs	Fenton reaction	MRI (T2)	[106]
	Fe3+/Gd3+-chelated polymer	Breast cancer	Fe3+ ions	Fenton reaction	MRI (T1)	[107]
	Cisplatin- Fe3O4/Gd2O3 hybrid NPs	Brain cancer	Fe3O4 NPs	Fenton reaction	MRI (T1)	[108]
	DOX-tannic acid-Fe3+	Melanoma	Fe3+ ions	Fenton reaction	MRI (T1)	[109]
	DOX-Gd2O3–Fe3O4 NPs	Breast cancer	Fe3O4 NPs	Fenton reaction	MRI (T1&T2)	[110]
	Gemcitabine-loaded carbonaceous NPs	Pancreatic cancer	MnFe2O4	Fenton reaction, GPX4 inhibition	MRI (T2)	[111]
	Fe3O4 NPs-gelatin microsphere	Hepatocellular carcinoma	Fe3O4 NPs	Fenton reaction	MRI (T2)	[112]
	Arginine-rich manganese silicate nanobubbles	Liver cancer	MnOx	GSH depletion, GPX4 inhibition	MRI (T1)	[113]
	FePt-MOF	Breast cancer	Fe ions	Fenton reaction	MRI (T2), CT	[114]
	SRF/Fe3O4 NPs-PDA NPs	Rectal cancer	Fe3O4 NPs	Fenton reaction, GPX4 inhibition	MRI (T2)	[115]
	Fe3O4–Gd2O3 nanopeanuts	Prostate cancer	Fe3O4 NPs	Fenton reaction	MRI (T1)	[116]
Magnetic ferroptosis nanomedicine with immunotherapy	iTGF-β-aPD-1 magnetosomes	Melanoma, breast cancer	Fe3O4 NPs	Fenton reaction	MRI (T2)	[106]
	MnOx nanospikes	Breast cancer	Mn2+ ions	GSH depletion	MRI (T1), PAI	[117]
	Fe3O4-SAS@PLT	Breast cancer	Fe3O4 NPs	Fenton reaction	MRI (T2)	[118]
	FePt/BP nanoplatforms	Breast cancer	FePt NPs	Fenton reaction	MRI (T2), NIR	[119]
	Ferumoxytol	Prostate cancer	Fe3O4 NPs	Fenton reaction	MRI (T2)	[120]
Magnetic ferroptosis with synergistic diagnostic imaging	Fe3O4@Cu1.77Se-PEG	Breast cancer	Fe3O4 NPs, Cu2+	Fenton reaction, GSH depletion	MRI (T2), PAI	[121]
	GBP@Fe3O4 polypeptide	Prostate cancer	Fe3O4 NPs	Fenton reaction, GSH depletion	MRI (T2), PAI	[122]
	FCSP@DOX	Breast cancer	DOX, Fe and Cu ions	GSH depletion	MRI (T2), PAI	[123]
	MOF@DOX
	Cro-Fe@BSA NP	Breast cancer	Fe3+ ions	Fenton reaction	MRI (T1), PAI	[124]
	RGD/Pt-GFNP	Brain cancer	Pt (IV), Fe2+	Fenton reaction, GSH depletion	MRI (T2)	[125]
	Fe3O4-PLGA-Ce6	Breast cancer	Fe3O4 NPs	Fenton reaction	MRI (T2), FI	[126]
	Fe3O4@PGL	Colon cancer	Fe3O4	Fenton reaction	MRI (T2), FI	[127]

Fe₃O₄ NPs, IONPs, iron oxide nanoparticles; ANG, angiopep-2 (TFFYGGSRGKRNNFKTEEYC); DHODH, dihydroorotate dehydrogenase; SS, 3′-dithiodipropionic anhydride; GSH, glutathione; GPX4, GSH peroxidase 4; FI, Fluorescence imaging; PLGA, poly(lactic-co-glycolic acid); AA, ascorbic acid; MRI, magnetic resonance imaging; DOX: doxorubicin; MOF, metal organic framework; SRF, sorafenib; PDA, polydopamine; iTGF-β, transforming growth factor-β inhibitor; Fe₃O₄ NCs, iron oxide nanoclusters; aPD-1, programmed death-1 antibody; SAS, sulfasalazine; PLT, platelet; BP, black phosphorous nanosheet; NIR, Near-infrared imaging; GBP. Polypeptide-modified and 1H-perfluoropentane-encapsulated Fe₃O₄ containing nanoformulation; FCSP, PEGylated Fe–Cu MOF; GFNP, Gallic acid/Fe nanomaterial; Cro, croconaine; BSA, bovine serum albumin; PGL, porphyrin grafted lipid.

Fig. 5.

Various types of nano-ferroptosis inducers categorized by iron based magnetic nanoparticles and non-iron based nanoparticles. Nano-ferroptosis inducers can be utilized for the image guided local ferroptosis induction and triggered ferroptosis induction.

Synergistic ferroptotic nanomedicines with diagnostic imaging are critical for improving their efficacy, and the development of effective MNPs for this has been widely studied in recent years [[101], [102], [103]]. In this review, various MNPs for image-guided ferroptosis induction in cancer cells and innovative possibilities are summarized. Validating the effectiveness of ferroptosis-induction cancer nanomedicines using the MNPs will warrant their successful clinical translation for the treatment of cancer.

4. Magnetic nanoparticles for image-guided ferroptosis cancer nanomedicine

Maximizing the therapeutic efficiency and minimizing the side effects of tumor-specific ferroptosis-induction nanomedicine are challenging issues. The employment of MNPs provides a promising approach for localizing cancer cell ferroptosis [128,129]. MNPs with intrinsic anticancer activity and remote controllable via an external magnetic field have attracted extensive attention [130,131]. Iron-based MNPs have shown effective ferroptosis induction as a result of the Fe²⁺ or Fe³⁺ ions released during the endocytosis process. The subsequent Fenton reaction can produce intracellular ROS, LPO, and macromolecular damage caused by ferroptosis induction. In addition, the unique magnetic properties of iron-based MNPs such as superparamagnetism, high magnetic susceptibility, and magnetization enable them to respond to an externally applied magnetic field [[132], [133], [134]]. Thus, various magnetic targeting and external field triggered behaviors can conduct targeted ferroptosis cancer nanomedicine. The motion of MNPs under an external magnetic field can be converted to mechanical, thermal, or chemical energy. Meanwhile, interaction with the magnetic field enables targeted ferroptosis-induction cancer therapy with T₁ or T₂ magnetic resonance imaging (MRI) contrast capability (Fig. 6) [135]. Indeed, multifunctional MNPs can provide non-invasive localized ferroptosis-inducing nanomedicines for the effective treatment of cancers.

Fig. 6.

Multifunctional theranostic magnetic nanoparticles mediated ferroptosis cancer nanomedicines. Nano-engineered magnetic nanoparticles and their nanocomposites can be equipped for the image guided ferroptosis cancer nanomedicine.

4.1. Magnetic nanoparticles for the fenton reaction

Iron oxide MNPs provide an excellent contrast material for MRI [136,137]. At the same time, recent studies have proved that iron oxide MNPs can induce ferroptosis of cancer cells through ROS generation via the Fenton reaction [[138], [139], [140]]. Iron oxide MNP-based ferroptosis-induction cancer nanomedicines have become increasingly attractive and investigated extensively [141,142]. Moreover, it was found that iron oxide MNP-induced ferroptosis in cancer cells could eliminate all of the neighboring cancer cells in a fast propagating wave [143]. Cancer cells are highly sensitive to iron concentration, and a slight fluctuation in iron concentration in the process of intracellular iron homeostasis can cause a great impact on the fate of the cancer cells [[144], [145], [146], [147], [148]]. Cancer cells can effectively store and export excess intracellular iron ions released from endocytosed iron oxide MNPs. Moreover, the meso-2,3-dimercaptosuccinic acid (DMSA)-coated Fe₃O₄ NPs treatment of cancer cells significantly upregulates the transcription of genes responsible for exporting intracellular iron ions [149]. Xiaolian Sun's group utilized ultrasmall single-crystal Fe NPs for targeted ferroptosis-induction cancer therapy [150]. Ultrasmall body-centered-cubic (BCC) Fe NPs comprising 2 nm Fe core and a 0.7 nm iron oxide shell were synthesized via a one-step method (Fig. 7a). The ultrathin shell protects the Fe (0) core from oxidation and escaping from the endosome during cellular uptake. The synthesized bcc-Fe NPs showed high Fenton catalytic activity, thereby inducing oxidative stress and ferroptosis of cancer cells (Fig. 7b). The ultrasmall single-crystal Fe NPs were stable in the physiological environment whereas they were selectively active in the TME because of lysosomal acidic etching of the Fe₃O₄ shell and subsequent exposure of the Fe core. Finally, a low dose of ultrasmall single-crystal Fe NPs efficiently induced tumor cell ferroptosis and immunogenetic cell death. Due to their small size, renal clearance of the NPs was rapid, thereby demonstrating their suitability for potential clinical translation. Furthermore, the cancer cell-targeted delivery of iron enhanced the therapeutic efficacy of the ferroptosis nanomedicine without severe side effects. Thus, the iRGD-labeled ultrasmall single-crystal Fe NPs and the combinational therapy approach provide an effective cancer cell-targeting treatment.

Fig. 7.

Rapidly renal clearable ultrasmall iron nanoparticles (USINPs) as a selective ferroptosis inducer. (a) Characterization of the bcc-USINPs. (b) A schematic illustration of the pH-activated Fe release from the bcc-USINPs. Reproduced with permission [150]. Copyright 2021, American Chemical Society.

In another report related to iron oxide MNP-based ferroptosis from Gao et al., the authors deduced that the NP-mediated inhibition of the genes associated with exporting intracellular iron ions, which they named this therapy gene-interference ferroptosis therapy (GIFT), could be effective at inducing cancer cell ferroptosis [151]. DMSA-coated Fe₃O₄ NP (FeNP) was combined with DMP-controlled gene-interference tools (Fig. 8a and b). DNA-mimicking protein (DMP)-controlled CRISPR/Cas13a and microRNA (miRNA) specifically knock down the expression of two iron metabolic genes encoding FPN and lipocalin 2 (LCN 2) in cancer cells. Co-treatment with FeNPs induced significant cancer cell ferroptosis in both hematologic and solid tumors with minimal side effects (Fig. 8a). The growth of different xenografted tumors in mice was significantly inhibited by GIFT therapy (Fig. 8c and d). As iron metabolic genes were successfully knocked down, cancer cells failed to maintain homeostasis by pumping out iron ions, resulting in a significant increase in intracellular ROS levels. This result suggested that intracellular Fe contents could be maximized in target cancer cells by integrating specific gene transfer with Fe source administration, while there is no damage to normal cells.

Fig. 8.

Gene-interference ferroptosis therapy (GIFT). (a) A schematic diagram of CRISPR/cas13a- and miRNA-based GIFT. (b) Stability of the DMSA-coated Fe₃O₄ nanoparticles over 90 days. (c–d) The in vivo antitumor effect of GIFT in (c) WEHI-3-xenografted mice and (d) CT-26-xenografted mice. Data are presented as the mean ± standard deviation (n = 10 mice). Reproduced with permission [151]. Copyright 2021, Springer Nature.

Next, utilizing iron with conventional chemoagents to become prodrugs for combined apoptosis and ferroptosis-induction cancer therapy is explored. Optimizing the targeting of ferroptosis can be achieved by combining the approach with pH-responsive degradable amorphous calcium carbonate (ACC). Xue et al. reported localized tumor ferroptosis agents that can be combined with apoptosis-based cancer therapy [152]. Doxorubicin (DOX) was chelated with Fe²⁺ ions and co-encapsulated with calcium-silica precursors in a one-step approach (Fig. 9a). The complexation of DOX and Fe²⁺ ions enabled their efficient loading into the nano-assembly and prevented the early release of Fe²⁺ ions in the cancer cells. A thin layer of silica-ACC (CaSi) hybrid was then deposited onto the surface of the nanocomplex. Subsequently, folate-modified and PEGylated polyamidoamine (PAMAM) dendrimers were conjugated to confer the targeting function for the selective treatment of cancer cells. Elevated expression of matrix metalloproteinase-2 (MMP-2) in the extracellular TME targets the cancer cell membranes and TME. MMP-2-cleavable peptides (GPLGVRGDGG) added to the PEG parts of the PAMAM dendrimer provided effective cancer targeting. The prepared nano-formulation could activate selective cancer cell death through combined ferroptosis and apoptosis, while DOX-Fe²⁺ complexation within the nano-formulation protected Fe²⁺ from cellular oxidative stress, which prevented its premature release and enhanced the therapeutic efficacy. In the MMP-2-rich TME, the PEG segments of nano-formulation were shed at the GPLGVRGDGG peptide linker, which exposed the tumor-targeting folate moieties and enhanced their uptake by the cancer cells. The proton sponge effect of PAMAM in the nano-formulation subsequently enabled the nano-formulation to release the therapeutic DOX-Fe complex into the cytosolic matrix (Fig. 9b). Finally, ROS generation by DOX-associated NOX activation acted in synergy with the Fe²⁺-mediated ferroptosis. The ferroptosis-apoptosis combination treatment significantly inhibited tumor growth (Fig. 9c). This strategy offers an effective ferroptosis-induction cancer nanomedicine approach that can overcome the limitations of conventional apoptosis-based anticancer modalities.

Fig. 9.

TME-responsive ferroptosis induction. (a) Schematic diagrams of the synthesis of ACC@DOX.Fe²⁺-CaSi-PAMAM-folic acid (FA)/mPEG and its mechanism of therapeutic action in the TME. (b) Impact of pH (left, pH 7.4; right, pH 5.5) on the release of DOX-Fe²⁺ from the ACC substrate. (c) The in vivo therapeutic efficacy of the nano-formulation using the 4T1 tumor-bearing mice model (n = 6). Reproduced with permission [152]. Copyright 2020, American Association for the Advancement of Science.

Iron-based MNPs are a natural choice for ferroptotic inducers given the role of iron ions in ferroptosis. All iron-based MNPs follow the common principle of the redox reaction to generate Fe²⁺ ions to start the Fenton reaction. Fe₃O₄ NPs can be reduced under acidic conditions which the lysosomes in cells without requiring an external reducing agent. Li et al. showed that Fe³⁺ ions in the Fe₃O₄ NPs were reduced to Fe²⁺ ions in the cells, which then reacted with H₂O₂ to create free radicals via the Fenton reaction that induced ferroptosis [153]. However, the endogenous reduction of iron in the cells might not be sufficient to trigger ferroptosis. Hence, novel approaches such as combining ferroptosis with other treatment regimens to boost the Fenton reaction or enhance ferroptosis via multiple pathways including GSH depletion, and GPX4 inhibition are needed. Further attempts to enhance ferroptosis from the intracellular reduction of iron were reported by Zhou et al. concurrent sonodynamic therapy (SDT) with ferumoxytol-protoporphyrin IX (PPIX)-loaded nanoliposomes produced enhanced ferroptosis via the Fenton reaction with the ferumoxytol iron oxide core while photosensitization of PPIX via SDT which inhibited ferritin and GPX4 activity [154]. Also, a ferrous ion-croconium dye complex for the controllable delivery of ferrous ions was recently reported to regulate metallomodulation cell death strategies [155].

4.2. Magnetic nanoparticles for targeted ferroptosis cancer nanomedicine

Precise targeting of cells in which to induce ferroptosis is an essential consideration to effectively use ferroptosis for cancer treatment, and magnetically responsive NPs can be used to achieve this [156]. Various magnetic field types can precisely steer the MNPs to the targeted region [157]. Recently, Li et al. reported an approach that can enhance localized ferroptosis in glioblastoma multiforme (GBM) cells [104]. In this study, engineered exosome-conjugated MNPs induced ferroptosis by disintegrating dihydroorotate dehydrogenase (DHODH) and GPX4 (Fig. 10a). The platform was composed of two components: magnetic Fe₃O₄ NPs coated with a mesoporous SiO₂ shell containing brequinar (BQR; an FDA-approved DHODH inhibitor) and functionalized with CD63 antibodies and human mesenchymal stem cell (hMSC)-derived exosomes with angiopep-2 (ANG) and CD63 embedded in their membranes. In Addition, small interfering RNA of GPX4 (siGPX4) was enveloped in the exosomes via electroporation. The two components were conjugated via antigen-antibody interaction (Fig. 10b). ANG enabled the exosome-conjugated MNPs to cross the blood-brain barrier (BBB) and specifically target GBM cells, while BQR become subsequently localized in the TME (Fig. 10c). Furthermore, the exosome-conjugated MNPs were effectively delivered to the tumor region due to them having 3D-printed magnetic NdFeB helmets (Fig. 10d and e). As a result, the exosome-conjugated MNPs localized within the TME provided a combinational therapeutic effect against GBM cells by distinguishing DHODH, the localized delivery of siGPX4, and the release of Fe²⁺ ions that then induced the Fenton reaction. Thus, magnetic field-targeted ferroptosis induction provides an exciting approach for treating GBM. Furthermore, Wang and co-workers reported that the intratumoral implantation of micromagnet successfully employed 50% more MNPs in a tumor via enhanced permeability and retention (EPR) [158].

Fig. 10.

Ferroptosis-inducing platform using MNPs for magnetic targeting and drug delivery. (a) A schematic illustration of the design and synthesis of MNP@BQR@ANG-EXO-siGPX4. (b) Representative transmission electron microscopy (TEM) images of Fe₃O₄ NPs (top left), MNPs (top right), and the MNP-exosome conjugate (bottom). (c) The mechanism underlying the induction of GBM cell ferroptosis. (d) Luminescence images of orthotopic LN229-Luc + human GBM tumor-bearing nude mice. (e) Quantitative analysis of luminescence images. Reproduced with permission [104]. Copyright 2022, John Wiley & Sons.

4.3. Magnetic nanoparticles for magnetic field-triggered ferroptosis cancer nanomedicine

Among various types of MNPs, Fe₃O₄ NPs comprise a strong candidate for ferroptosis induction owing to their biocompatibility and unique magnetic properties. However, in terms of ROS productivity, Fe₃O₄ may not be a top priority due to its chemical structure comprising two Fe³⁺ and one Fe²⁺ ion. The Fenton-like reaction involving Fe³⁺ ions has a much lower reaction constant than the Fenton reaction involving Fe²⁺ ions, thus Fe₃O₄ is usually combined with a complementary source for reducing Fe³⁺ ions to Fe²⁺ ions to maximize ROS production in catalytic processes (i.e., the photo-Fenton and electro-Fenton processes) [159]. Yu et al. hypothesized that if a reducing agent is released under an external magnetic field, it would be able to utilize reactive Fe²⁺ ions and thereby enhance ferroptosis [105]. They synthesized a hybrid core-shell vesicle (HCSV) composed of ascorbic acid in the core and Fe₃O₄ NPs embedded in a poly(lactic-co-glycolic acid) (PLGA) shell (Fig. 11a). A circularly polarized magnetic field (CPMF) at 2 Hz induced circular back-and-forth vibration of the iron oxide NPs, resulting in the gradual degradation of the PLGA shell and consequential release of ascorbic acid and Fe₃O₄ NPs in the TME (Fig. 11b). Fe²⁺ and Fe³⁺ ions were released from Fe₃O₄ NPs in the acidic TME, and ascorbic acid reduced the Fe³⁺ ions, thereby increasing the Fe²⁺ ions (Fig. 11c). The Fe²⁺ ions in TME boosted iron metabolism and ROS production, leading to the downregulation of GPX4. Calreticulin (CRT) expression was also upregulated due to the triggered oxidative stress (Fig. 11d). An intratumoral injection of HCSVs and CPMF treatment significantly inhibited tumor growth (Fig. 11e). Moreover, the reduction of Fe³⁺ ions made the MRI R2* signal change, which could be used to provide the progress of ferroptosis (Fig. 11f). Thus, an exogenous magnetic field can be used to trigger ferroptosis and combinational immunotherapy applications.

Fig. 11.

Magnetic field-mediated ferroptosis induction. (a) A schematic illustration of using an exogenous magnetic field (MF) to boost Fenton reaction. (b) TEM images of HCSVs treated with a circularly polarized MF (2 Hz). (c) The time-dependent relative concentration of Fe²⁺ ions. (d) A flow cytometry histogram of CRT expression on the surfaces of TrampC1 cells after treatment. (e) Tumor response after treatments. (f) R2* mapping and changes after intratumoral injection of HCSVs. The red circle indicates the tumor region. Reproduced with permission [105]. Copyright 2022, Springer Nature.

4.4. Magnetic resonance image (MRI)-guided ferroptosis cancer medicine

MRI is the first option for monitoring ferroptosis nano-inducers due to the magnetic moment originating from the iron ions dephasing the dipole moment of adjacent protons via T₂ (spin-spin) relaxation [160,161]. Compared to other imaging modalities such as computed tomography (CT) [162], photoacoustic imaging (PAI) [163], and ultrasound [[164], [165], [166], [167]], MRI has some unique characteristics: non-invasive imaging without radiation, deep tissue penetration, and high resolution for soft tissue. Besides, NP ferroptosis inducers can provide time-dependent MRI contrast changes via the Fenton reaction. Recently, novel strategies for MRI-guided ferroptosis-induction cancer therapy have been reported. Zhang et al. created MRI-guided ferroptosis-induction magnetosomes using magnetic Fe₃O₄ nanoclusters (NCs) coated with a leukocyte membrane [106]. After injection the magnetosomes intravenously, they could be efficiently localized within the TME by applying an external magnetic field owing to the high magnetism of the NCs. Meanwhile, the superparamagnetic property of the magnetosomes enabled their non-invasive T₂ MRI-guided delivery that consequentially induced ferroptosis and immunomodulation within the TME. Yu and coworkers reported an image-guided ferroptosis inducer comprising hybrid core-shell vesicles that can release ascorbic acid and iron oxide nanocubes under CPMF [105]. They focused on monitoring the Fe³⁺: Fe²⁺ ratio via MRI R2* because the two ions exhibited significantly different magnetic relaxation behaviors (Fig. 11f). The progress of the reduction of Fe³⁺ to Fe²⁺ (indicating the progress of Fenton reaction-mediated ferroptosis) was correlated with a decrease in the MRI R2* signal. Therefore, MRI can be utilized to confirm the localization of the nanomedicine as well as track its therapeutic effects. Luo et al. synthesized a theranostic platform composed of Fe³⁺/Gd³⁺ chelated polyphenol, an amphiphilic polymer skeleton, and cinnamaldehyde as a prodrug [107]. The nanoplatform became depolymerized in the TME due to the high level of GSH, resulting in the activation of the prodrug. Furthermore, increased intracellular H₂O₂ boosted the Fenton reaction that induced ferroptosis and was subsequently followed by the release of Gd³⁺ ions within the tumor. The T₁ MR contrast was significantly enhanced by the free Gd³⁺ ions that accelerated the relaxation of water protons, thereby enabling visualization of the progress of the therapeutic effect and providing the ability to post-operative monitor tumor lesions. Shen et al. fabricated Fenton-reaction-accelerable nanomedicine based on Fe₃O₄/Gd₂O₃ hybrid NP [108]. T₁-weighted MRI of a brain tumor indicated that the hybrid NPs successfully transported across the BBB. Furthermore, they adopted diffusion-weighted MRI to monitor their therapeutic efficacy because it is sensitive to the movement of water protons and so is especially useful for monitoring the progress of ferroptosis via the apparent diffusion coefficient change at the molecular scale. In contrast, T₁-weighted MRI can be used to visualize the therapeutic progress via morphological changes in the tumor at the tissue scale. Xu et al. employed a pH-responsive tannic acid-Fe³⁺ complex as an MRI-guided ferroptosis-induction cancer nanomedicine [109]. Tannic acid releases Fe³⁺ in the acidic TME, thereby increasing the T₁-weighted MR contrast effect originating from the increase in Fe²⁺ ions in the tumor cells as the tannic acid-Fe³⁺ complex dissociates. Koo et al. suggested Cu–Fe bimetallic peroxide NPs as a TME-sensitive Fenton reaction inducer [168]. Cu–Fe peroxide NPs decompose into free Cu and Fe ions via cyclic redox reactions within the acidic TME. The release of Fe ions caused s 20-fold increase in T₁ relaxivity compared to that at neutral pH. The low r₂/r₁ ratio of the Cu–Fe NPs (1.46) indicates they efficiently improved the T₁ contrast effect and marked the tumor region with a much brighter T₁-weighted MR signal compared to normal tissue. Zhu et al. developed T₁-T₂ dual modal MRI-guided ferroptosis nanomedicine based on incorporating Gd species within iron oxide MNPs [110]. Dual-modal T₁-T₂ MRI offered accurate tumor diagnosis by the cross-checking because T₂-weighted MR contrast effect from iron oxide MNPs could be affected by material-dependent properties such as calcification, bleeding, or metal deposits. Zhang and colleagues reported a MnFe₂O₄ NP-based nanozyme for real-time MR monitoring and ferroptosis-chemotherapy toward pancreatic adenocarcinoma [111]. Manganese-doped iron oxide NPs exhibited enhanced magnetic susceptibility and shortened T₂ relaxivity. Significant T₂-contrast effect of MnFe₂O₄ NPs appeared in the tumor region 30 min after intravenous injection and lasted for 4 h. Chen et al. employed superparamagnetic Fe₃O₄ NPs-loaded PLGA particles as an MRI-guided ferroptosis inducer [126]. The acidic TME induced the degradation of PLGA and the release of Fe₃O₄ NPs in the tumor. The Fe₃O₄ NPs exhibited a similar T₂ contrast effect as commercial contrast agents Feridex and Resovist. The authors evaluated the tumor-targeting efficiency and retention in the tumor region of their nanomedicine via T₂-weighted MRI intensity. Additionally, the assembly of γ-Fe₂O₃ nanocrystals could be disassembled under acidic TME, resulting in the switching from T₂-weighted MRI to T₁-weighted MRI [169].

Among the various clinical intraosseous practices, transcatheter arterial chemoembolization (TACE) can be used as a minimally invasive procedure for treating advanced hepatocellular carcinoma (HCC) and is conducted using MRI guidance. Thus, ferroptosis-inducing nanomedicines combined with TACE offer great potential for cancer treatment. Drug-eluting microspheres comprise a commonly used clinical chemoembolization agent with moderate therapeutic outcomes. Recently, Chen et al. developed gelatin microspheres containing Adriamycin (ADM) and Fe₃O₄ NPs (ADM/Fe₃O₄-MS) for localized ferroptosis-induction cancer therapy (Fig. 12a) [112]. ADM/Fe₃O₄-MSs were homogeneously synthesized via a high-voltage electrospray method (Fig. 12b). With angiographic guidance, the microspheres were used to completely block the hepatic artery (Fig. 12c). Consequently, the HCC tumor cells were deprived of essential oxygen and nutrients and ADM was locally released. The Fe₃O₄ NPs provided both T₂-weighted MR contrast and ferroptosis-inducing cancer therapy in combination with microwave-induced hyperthermia (Fig. 12d). When microwaves irradiated ADM/Fe₃O₄-MS, Fe₃O₄ NPs generated enough heat to make the tumor cells sensitive to the released ADM and microspheres. Moreover, iron oxide NPs released Fe³⁺ and Fe²⁺ ions into the TME and successfully induced ferroptosis, as confirmed by significant decreases in ferroptosis markers GPX4 and ACSL4 (Fig. 12e and f). This study is an excellent demonstration of using MRI-guided ferroptosis-induction nanomedicine with clinically interventional oncology procedures.

Fig. 12.

MRI-guided TACE and ferroptosis induction. (a) A schematic diagram of ADM/Fe₃O₄-MS and TACE treatment. (b) A representative microscopic image of ADM/Fe₃O₄-MS. (c) Digital subtraction angiography before (left) and after (right) embolization. (d) T₂-weighted MR images of tumor-bearing rabbits before and 2 weeks after treatment. (e) Tumor volume and (f) tumor growth rates in each rabbit group. Reproduced with permission [112]. Copyright 2022, Springer Nature.

Recently, the unique characteristics of Mn and its derivatives such as pH-responsiveness and degradability have led to their widespread application in cancer therapy [170]. Wang et al. created Mn silicate NPs via bubble formation due to the decomposition of ethanol to CO₂ during the synthesis process [113]. The bubble structures were less stable and degraded more rapidly than their solid NP counterparts. Degradation of the nanobubbles caused the fast reduction of Mn oxides to Mn²⁺ ions by GSH, which increased the r₁ relaxivity for T₁ MRI. Hence, greater GSH depletion and subsequently enhanced ferroptosis and MRI contrast were seen with the Mn silicate nanobubbles than with solid silica NPs.

Metal-organic frameworks (MOFs) in which metal ions and organic ligands form periodic and coordinative bonds with each other have emerged as a new class of NPs. The distinct feature of MOFs is their structure; around 90% of their volume is free, into which small molecules can be loaded. Furthermore, their coordinatively bonded structure makes them sensitive to the acidic TME, thereby enabling the release of drugs and metal ions. Fe-based MOFs have attracted attention as competitive ferroptosis inducers. Meng et al. reported a novel FePt-MOF nanocomplex as a theranostic agent for cancer therapy [114]. They encapsulated FePt NPs into a hexagram-shaped MIL-101(Fe) MOF and decorated its surface with a tumor-homing peptide (tLyp-1) to enhance its tumor targetability (Fig. 13a and b). As the MOF degraded in the acidic TME, it released drugs and metal ions leading to the accumulation of LPO. Moreover, the Fe and Pt components offered dual MRI and CT capability, thereby enabling precise image-guided drug delivery (Fig. 13c and d); the released Fe ions generated highly reactive hydroxyl radicals in the TME via the Fenton reaction and consequently contributed to the inhibition of tumor growth via ferroptosis (Fig. 13e). Xu and coworkers studied similar concept utilizing the localized release of iron ions [171]. They synthesized a MOF comprising Fe²⁺ and 2-aminoterephthalic acid (BCD) and coated it with hyaluronic acid (HA) to make it hydrophilic and enhance the drug retention time. The Fe²⁺-BCD MOF maintained its structural stability under physiological conditions but degraded in the acidic TME. Besides, synergistic ferroptosis nanomedicines with diagnostic imaging utilizing fluorescent dyes, upconverting NPs, and PAI have been reported [172].

Fig. 13.

MRI/CT-guided FePt MOF ferroptosis nanomedicine. (a) A schematic diagram of FePt-MOFs-tLyp-1 NCs and their mechanism of pH-responsive action for ferroptosis therapy and MRI/CT imaging. (b) TEM image of FePt-MOF NCs. (c) Iron concentration dependent T₂ relaxation times. (d) Pt concentration dependent CT intensity (Hounsfield intensity). (e) In vivo T₂-weighted MRI (axial plane), and (f) in vivo CT imaging (axial plane) of 4T1 tumor-bearing mice after intravenous injection of FePt-MOF-tLyp-1 NCs. (g) Tumor response after treatment (I, PBS; II, MOF-tLyp-1; III, FePt(R)-MOF-tLyp-1; and IV, FePt(S)-MOF-tLyp-1). Reproduced with permission [114]. Copyright 2020, American Chemical Society.

Iron oxide NPs release iron ions in the acidic TME that can provide T₂-weighted MR contrast owing to their magnetic property. Guan et al. suggested superparamagnetic iron oxide NPs and SRF-incorporated mesoporous polydopamine (MPDA) NPs (SRF@MPDA-SPIO) as a ferroptosis nanomedicine (Fig. 14a and b) [115]. MPDA NPs were formed through π−π interactions between SRF and polydopamine (PDA). Since PDA is amphiphilic, the SPIO NPs clustered on the MDPA via hydrophobic interactions could interact with their neighbors, leading to a relatively decreased T₂ relaxation time (Fig. 14c). Intravenously injected SRF@MPDA-SPIO was efficiently accumulated to the tumor. After confirming the localization of NPs by time-dependent MRI (Figs. 14d), 808 nm NIR laser irradiation was applied to boost the release of iron ions. Released SRF, Fe²⁺, and Fe³⁺ successfully induced ferroptosis (Fig. 14e–i).

Fig. 14.

MRI-guided ferroptosis induction with photothermal therapy (PTT). (a) Schematic diagram of MRI-guided ferroptosis/PTT combinational therapy using SRF@MPDA-SPIO. (b) A representative TEM image of SRF@MPDA-SPIO. (c) The T₂ relaxation rate of SRF@MPDA-SPIO. (d) In vivo pseudo-colored T₂-weighted MR image. (e) Photothermal conversion of SRF@MPDA-SPIO after NIR laser irradiation (808 nm, 1 W cm⁻²). (f) Temperature elevation of SRF@MPDA-SPIO solution with various NP concentrations. (g) Infrared thermal images after laser irradiation. (h, i) The anticancer effect of SRF@MPDA-SPIO in vivo. Reproduced with permission [115]. Copyright 2020, Elsevier B.V.

In an approach to add the MRI contrast effect to a novel ferroptosis nanoagent, Zhang and coworkers developed porous nanopeanuts composed of Gd-oxide and Fe-oxide (GINP) [116]. To synthesize the porous GINPs, they utilized a solvothermal method to first form anisotropic nanowires and the allowed the reaction to proceed for 4 days to sufficiently grow the internal lumen (Fig. 15a). The GINPs were able to store oxygen and Pt (IV) prodrug in the free space therein. Tf-labeled amino polyethylene glycol (Tf-PEG-NH₂) was conjugated to the GINPs to enhance their tumor-targeting ability, biocompatibility, dispersion stability under physiological conditions, and GSH responsiveness. According to inductively coupled plasma mass spectrometry (ICP-MS) results, the GINPs loaded more Pt⁴⁺ content than other nanozymes. They also confirmed that the GINPs were composed of superparamagnetic Fe₃O₄ and paramagnetic Gd₂O₃ by attaining magnetic hysteresis loops at 3 and 300 K. Moreover, the GINPs exhibited better T₁ MR contrast ability than other Gd-based clinical contrast agents. In a tumor-bearing mice model, the GINPs provided obvious T₁ MR contrast 30 min after injection (Fig. 15b). After the GINPs were taken up by cancer cells, they released oxygen, the Pt prodrug, as well as Fe²⁺, and Fe³⁺ ions in acidic TME. Released Pt (IV) prodrug depleted intracellular GSH and was reduced to Pt (II). Consecutively, Pt (II) contents activated members of the nitric oxide synthase family resulting in a significant increase in the intracellular H₂O₂ level by converting oxygen into superoxide anions. Here, the porous GINP-Pt nanodrug system effectively inhibited tumor growth by inducing ferroptosis and apoptosis (Fig. 15c).

Fig. 15.

T₁-weighted MRI-guided ferroptosis. (a) Representative TEM and elemental mapping images of the GINPs. (b) T₁-weighted MR images of tumor-bearing mice before and after injection of Gd-DTPA (clinical T₁ contrast agent), PGINP (porous Fe₃O₄/Gd₂O₃ nanopeanut), and Tf-GINP-Pt (Transferrin-coated PGINP loaded with Pt (IV) prodrugs). (c) The in vivo anticancer activity of Tf-GINP-Pt. Reproduced with permission [116]. Copyright 2020, Elsevier B.V.

4.5. Magnetic ferroptosis nanomedicine with immunotherapy

Cancer immunotherapy, which activates and modulates the patients’ immune system to kill cancer cells, has emerged as a powerful strategy to treat cancer [173]. Recently, it has been reported that cytotoxic T cells utilize ferroptosis for killing cancer cells. The JAK-STAT1 pathway is activated by cytotoxic T cells and leads to the downregulation of SLC7A11 and SLC3A2, which subsequently stimulates ferroptosis in cancer cells [56]. Downregulation of SLC3A2 in cancer cells is positively related to the efficacy of immune checkpoint inhibitor (ICI) immunotherapy [174]. Ferroptosis can be exploited in cancer therapy by linking it to various ligands that can activate STAT1. For example, transforming growth factor β1 (TGFβ1) can cause ferroptosis by downregulating SLC7A11 and upregulating zinc finger E-box binding homeobox1 (ZEB1) through SMAD signaling [175]. Ferroptotic cells release damage-associated molecular patterns (DAMPs), which can underlie antitumor immunity by arousing immunogenic cell death (ICD) [176]. Interplay between ferroptosis and the immune system is not always positively correlated (e.g., ferroptosis in melanoma is hindered by the increased monounsaturated fatty acid due to acyl-coenzyme A synthetase long-chain family member 3 (ACSL3). ICI immunotherapy has shown promising therapeutic outcomes in various cancers, while ferroptosis induction in combination with ICI immunotherapy is of great interest for cancer therapy since they may synergistically induce tumor growth inhibition. Recently, a combination of immunotherapy with ferroptosis using a TGF-β inhibitor and anti-PD-L1 loaded onto Fe₃O₄ NCs produced a synergistic antitumor effect in mice models for melanoma and breast cancer [106]. Ferroptosis was effectively induced via the reduction of the Fe₃O₄ NCs. The concurrent release of the immunotherapeutic resulted in an increase in the M1/M2 macrophage, CD4⁺/T_reg, and CD8⁺/T_reg ratios in the TME. In other cases, co-delivery of anti-TGF-β antibody and SRF using Fe₃O₄/Gd₂O₃ hybrid NP could induce ferroptosis as well as convert cold TME into hot TME [177]. Thus, the synergistic combination of ferroptosis and immunotherapy has been widely demonstrated. Here, recently published representative findings are discussed.

Ding et al. produced mixed MnO_x nanospikes (NSs) for cancer vaccine-based immunotherapy (Fig. 16a) [117]. They have a large lumen inside which antigens can be loaded (average pore size: 4.3 nm, total pore volume: 2.5 cm³g^-1) (Fig. 16b–d). Intracellular GSH degraded the MnO_x NSs to produce Mn²⁺ ions, leading to escaping Mn²⁺ ions from the endo/lysosomes and GSH depletion. Moreover, intracellular ROS was enhanced, resulting in endosomal membrane oxidation and rupturing, as well as depletion of GPX4 and upregulation of LPO. On the other hand, high-mobility group box 1 (HMGB1) and ATP were increased after chemodynamic therapy (CDT). As a result, MnO_x NSs successfully employed mature DCs (Fig. 16e). Interestingly, MnO_x NSs had TME-sensitive imaging ability, exhibiting photoacoustic contrasting via the MnO_x phase and T₁ MR contrasting via the production of Mn²⁺ (Fig. 16f). The MnO_x cancer vaccine exhibited not only effective inhibition of tumor growth by utilizing ferroptosis and CDT via DC immunotherapy but also dual MRI/PAI for therapeutic procedure tracking.

Fig. 16.

Dual MRI/PAI-guided ferroptosis and cancer immunotherapy. (a) An illustration of the MnO_x-OVA/tumor cell fragment cancer immunotherapy vaccine with dual MRI/PAI. (b) TEM, (c) STEM, and (d) elemental mapping of MnO_x nanovaccines. (e) In vivo flow cytometry analysis of the DC, CD8 T cell, and CD4 T cell populations in tumor-bearing mice after treatment with various vaccine formulations. (f) In vivo MRI/PAI and (g) the relative tumor-growth curves of distant tumors. ANOVA was used to assess statistical significance: ***p < 0.001. Reproduced with permission [117]. Copyright 2020, John Wiley & Sons.

One of the primary challenges in current immunotherapy is that immunogenicity can arouse cytokine-release syndrome and/or an abnormal inflammatory response. Jiang et al. reported SAS-loaded mesoporous Fe₃O₄ NPs and platelet (PLT) membrane (Fe₃O₄-SAS@PLT) for inducing ferroptosis and controlled immunogenicity (Fig. 17a) [118]. SAS, a commercial drug for treating rheumatoid arthritis, hinders inflammatory cell migration, blocks the IκB kinase pathway, and obstructs cysteine uptake, resulting in tumor growth inhibition and ferroptosis [178]. Fe₃O₄ NPs were synthesized via a polyol method using ammonium acetate and poly (γ-glutamic acid) and SAS was physically incorporated into the pores of mesoporous Fe₃O₄ NPs via mechanical stirring. A PLT membrane was coated with Fe₃O₄-SAS via an extrusion method to produce an immunosurveillance-stealthy ferroptosis inducer. The PLT membrane formed a 10 nm thick shell and exhibited a higher negative surface zeta potential than Fe₃O₄-SAS (Fig. 17b). Fe₃O₄-SAS@PLT was successfully delivered to the cancer cells by evading the immunosurveillance system and mediated LPO by releasing iron ions, thereby downregulating system X_c⁻ and GPX4 in 4T1 cells (Fig. 17c). Consequently, the cells undergoing ferroptosis released abundant tumor antigens and stimulated DC maturation (Fig. 17d and e). Fe₃O₄-SAS@PLT could effectively target metastatic tumors and thereby produce a higher mature/immature DC ratio than other treatment groups. After treating Fe₃O₄-SAS@PLT, the significant upregulation of tumor necrosis factor- α (TNF-α), interleukin (IL)-6, and IL-12p70 was observed 48 h after intravenous injection (Fig. 17f). The authors suggested that Fe₃O₄-SAS@PLT-mediated ferroptosis could release moderate levels of tumor antigens and effectively induce activation of the immune system. Fe₃O₄-SAS@PLT also repolarized M2 macrophages to the M1 phenotype. Thus, it provides a novel approach for synergistic ferroptosis mediated immunotherapy for metastatic tumors.

Fig. 17.

Ferroptosis-enhanced cancer immunotherapy. (a) An illustration of Fe₃O₄-SAS@PLT nanoparticles. (b) Dispersion stability of Fe₃O₄-SAS@PLT in 10% fetal bovine serum (FBS)/phosphate-buffered saline (PBS) over a week and protein composition analysis of the PLT membrane. (c) A schematic diagram of Fe₃O₄-SAS@PLT-induced ferroptosis. (d) The mechanisms of Fe₃O₄-SAS@PLT-mediated ferroptosis-induced immunotherapy for metastatic tumors. (e) In vivo flow cytometry analysis of mature DCs in the lymph nodes of 4T1 metastatic tumor-bearing mice at 24 h after receiving various treatment regimens. (f) Secretion of TNF-α, IL-6, and IL-12p70 in the serum after treatment; n = 5; ns represented no significance, ***p < 0.001. Reproduced with permission [118]. Copyright 2020, John Wiley & Sons.

Yao et al. developed FePt NPs embedded on ultrathin black phosphorous nanosheets (FePt/BP) for photothermal therapy (PTT), photodynamic therapy (PDT), CDT, ferroptosis, and immunotherapy [119]. First, they synthesized FePt NPs via thermal decomposition and then coated them with DMSA. After that, they modified the surface of BP with polyethylenimine (PEI) via electrostatic interaction. Subsequently, folic acid (FA) was conjugated with the BP to enhance tumor targetability (Fig. 18a). The FePt/BP-PEI-FA nanocomposite could be armed with versatile tumor therapeutic options: generating heat under 808 nm laser irradiation, singlet oxygen under 660 nm laser irradiation, specific cytotoxicity toward tumor cell displaying FA receptors, and lipid ROS accumulation via the Fenton reaction (Fig. 18b). In addition, the superparamagnetic properties originating from the small FePt NPs provided T₂-weighted MR contrasting. As a result of the multimodal tumor therapies, the number of mature DCs was increased and TNF-α, IFN-γ, and IL-12 were upregulated. Furthermore, they administered a cytotoxic T lymphocyte-associated protein 4 (CTLA-4) checkpoint inhibitor via the FePt/BP-PEI-FA nanocomposite that consequentially inhibited both primary and distant tumor growth (Fig. 18c–h). The experimental results suggest that FePt/BP-PEI-FA NCs mediate ferroptosis and in combination with the ICI, is an effective approach for treating both primary and secondary tumors.

Fig. 18.

Combinational PTT, PDT, CDT, and ferroptosis therapy. (a) A TEM image of the FePt/BP NCs. (b) A schematic diagram of the dual-mode imaging-guided synergistic PTT/PDT/CDT cancer therapies. (c, d) The antitumor effects toward primary (c) and distant (d) tumors under various treatment regimens: PBS, anti-CTLA4, FePt/BT-PEI-FA, FePt/BP-PEI-FA with laser irradiation (808 nm, 1.75 W cm⁻², 5 min), and FePt/BP-PEI-FA + anti-CTLA4 with laser irradiation (n = 3, *p < 0.05). (e) Body weight changes during the treatment. (f, g) T cells in distant tumors with the above-mentioned treatment regimens. (h) Cytokine levels for TNF-α. Reproduced with permission [119]. Copyright 2020, Royal Society of Chemistry.

Ferroptosis can activate innate immunity as well as adaptive immunity for cancer treatment. Our group (Kim et al.) reported that iron oxide-mediated ferroptosis induction can activate natural killer (NK) cells to kill cancer cells (Fig. 19a) [120]. We focused on the immune response after ferroptosis, especially the release of NK cell-activating surface molecules, due to ferroptosis-induced ICD. The anticancer cytotoxicity of NK cells could be activated by the recognition of stress-inducible protein by activating receptors on the NK cell surface for NKG2D (natural killer group 2D). The stress-inducible molecules for NKG2D are UL16 binding proteins (ULBPs) and MHC class I chain-related protein A and B (MICA/B). Ferumoxytol (a clinical treatment for Fe-deficiency anemia using iron oxide NPs) successfully induced ferroptosis in prostate cancer PC-3 cells. Moreover, when PC-3 cells were co-treated with iron oxide NPs and NK cells, the degree of lipid ROS accumulation was significantly increased. Interestingly, the secretion of IFN-γ and the lysis of cancer cells due to the anticancer activity of the NK cells increased, and degranulation was also observed. Furthermore, UL16BP1, ULB16P2, and UL16BP3 were upregulated on the PC-3 cell surface after iron oxide NPs treatment (Fig. 19b). The UL16BPs on the cancer cells bound to the NKG2D ligand on the NK cells, which subsequently enhanced the anticancer efficacy of the latter. Since NK cells are innate immune cells, they have PD-1 receptors. Thus, adding anti-PD-L1 to the combinational NK cell and ferroptosis-inducing therapy is a novel strategy for treating cancer (Fig. 19c).

Fig. 19.

Ferroptosis-mediated innate immunity. (a) A schematic diagram of combinational NK cell and iron oxide NP-mediated ferroptosis cancer therapy. (b) The expression of UL16BPs and MHC class I and II expression in PC-3 prostate cancer cells after iron oxide NP treatment. (c) Tumor-size curves for each treatment group: DPBS, NK-92MI, NK-92MI + Fer, NK-92MI + Fer-aPDL1. Reproduced with permission [120]. Copyright 2022, Springer Nature.

4.6. Synergistic magnetic ferroptosis combination therapy with multi-modal imaging

Molecular mechanism regulating ferroptosis in cancer cells has been commonly involved with various cellular signals of cancer cells [[179], [180], [181]]. Combinational ferroptosis cancer therapy by finding synergistic biochemical pathways might be an effective way to maximize the anti-cancer therapeutic efficacy [182,183]. Those synergistic effects of combinational magnetic ferroptosis cancer medicine will be achieved by rational designing of MNPs or MNPs based hybrid nano-structures. MNPs based hybrid structures can possess extended options for the additional opportunity of ferroptosis based cancer therapy combined with various other cancer therapies along with additional medical imaging contrasts. In this section, we review synergistic ferroptosis combination therapy using MNPs based hybrid nanostructures.

Polypeptide-modified Fe₃O₄-containing 1H-PFP NPs (GBP@Fe₃O₄) to target prostate cancer cells were synthesized by encapsulating Fe₃O₄ NPs and 1H-PFP with PEG-PLGA. GBP@Fe₃O₄ mediated ferroptosis after light irradiation by first producing heat and then by releasing Fe₃O₄ via 808 nm laser irradiation. The release of Fe₃O₄ induced the production of ROS, leading to ferroptosis. In addition, the photothermic effect induced GSH depletion and limited the antioxidant response, which enhanced ROS-mediated ferroptosis [38,[184], [185], [186]]. The photothermal effect also enabled 1H-PFP phase transformation and Fe₃O₄ release by producing a large amount of LPO by facilitating the Fenton reaction, leading to ferroptosis [187]. The photothermal effect sustained the tumor antioxidant response through GSH depletion, leading to LPO overproduction and acetyl-CoA synthetase bubblegum family member 1 (ACSBG1)-dependent ferroptosis, which is an important component for the ferroptosis-mediated therapy in castration-resistant prostate cancer cell lines (Fig. 20a) [122]. Several imaging modalities were enabled by GBP@Fe₃O₄ and Fe release-based T₂-weighted MRI and photothermal effect-mediated PAI and ultrasound imaging. Accumulation of GBP@Fe₃O₄ at the tumor sites was indicated through PAI (Fig. 20b). Furthermore, T₂-weight MRI showed tumor site accumulation after injection of GBP@Fe₃O₄, with 2-phosphonomethylpentanedioic acid, a PSMA (prostate-specific membrane antigen) receptor antagonist, blocking its accumulation along with MP@Fe₃O₄ aggregation (Fig. 20c). To confirm the ferroptosis of tumor cells, ferroptosis inhibitor ferrostatin 1 (Fer-1) was used, which interfered with the tumor growth inhibition by GBP@Fe₃O₄ (Fig. 20d). However, GBP@Fe₃O₄ with laser irradiation provided a noticeable reduction in tumor volume without any cytotoxic effects in vivo. These results suggested synergistic effects of PTT and ferroptosis that moderate heat supply to local tumor successfully led to burst release of GBP@Fe₃O₄, resulting in significant LPO. Furthermore, heat stress hindered the synthesis of GSH, consequently, cancer cells became much more vulnerable to oxidative stress.

Fig. 20.

Photo-triggered ferroptosis cancer nanomedicine with PAI/MRI guidance. (a) Schematic diagrams of the synthesis and therapeutic mechanism of GBP@Fe₃O₄. (b) PAI and (c) T₂-weighted MRI results after the injection of various nanoformulations. (d) Relative tumor volume changes after various treatment regimens (%ID/g: percentage injected dose per gram, *p < 0.05, **p < 0.01, ***p < 0.001). Reproduced with permission [122]. Copyright 2021, American Chemical Society.

PTT can synergistically affect chemotherapy. PEGylated Fe-Cu-SS MOF (FCSP)@DOX was first synthesized by using a hydrothermal method via bridging Fe and Cu ions with disulfide bonds to form the FCSP MOF followed by the hydrophobic interaction-mediated loading of DOX. Furthermore, C18PMH-mPEG was used to enhance hydrophilicity and biocompatibility, and to support the EPR effect. FCSP@DOX induced ferroptosis based on the release of Fe and Cu ions and the downregulation of GSH [188]. The depletion of GSH provided a large amount of ROS through the Fenton reaction using Fe and Cu ions [[189], [190], [191], [192]]. Furthermore, DOX released inside the NPs produced H₂O₂, which induced ferroptosis [193]. This mediated the chemotherapy and enhanced ferroptosis. Owing to strong NIR absorption of FCSF MOFs, it exhibited effective photothermal conversion. The photothermal effect increased ROS production and the temperature in the TME, thereby causing cancer cell death (Fig. 21a) [123,194]. They confirmed mild hyperthermia contributed to about 20% more hydroxyl radical generation compared to control group without photothermal heating. TEM analysis showed that the FCSP MOF comprised flower-like shapes around 127.53 nm in size (Fig. 21b). Both MRI and PAI were enabled by using FCSP@DOX. To be specific, T₂-weighted MRI showed increased T₂ relaxivity as the FCSP@DOX concentration was increased (Fig. 21c). In vivo MR images showed significant changes before and after injection of FCSP@DOXs (Fig. 21e). Likewise, PAI provided a linear relationship between FCSP@DOX concentration and the photoacoustic intensity (Fig. 21d). A significant increase in the photoacoustic signal intensity in vivo after FCSP@MOF injection into the tumor sites further validates the PAI modality of FCSP@DOX (Fig. 21f). As expected, significant tumor volume reduction after FCSP@DOX + NIR laser therapy was observed (Fig. 21g) with no distinct cytotoxic effects in treated mice. This paper suggested that co-delivery of DOX and FCSP induces apoptosis and ferroptosis at local tumor and furthermore provides synergistic effect by generating H₂O₂ for Fenton reaction. Additionally, moderate heating by PTT can boost the Fenton reaction efficiency.

Fig. 21.

MRI/PAI-guided ferroptosis cancer nanomedicine accelerated by PTT. (a) A schematic diagram of the therapeutic mechanism of FCSP@DOX. (b) A TEM image and elemental mapping of the FCSP MOF. (c) T₂-weighted MR images and the T₂ relaxivity rate according to the concentration of FCSP@DOX. (d) PAI results and intensity according to the concentration of FCSP@DOX. (e) MRI results of 4T1 tumor-bearing mice after injection of FCSP@DOX. (f) PAI results of 4T1 tumor-bearing mice after injection of FCSP@DOX into the tumor sites (n = 3). (g) Relative tumor volume changes after various treatment regimens (*p < 0.05, **p < 0.01, ***p < 0.001). Reproduced with permission [123]. Copyright 2021, Elsevier B.V.

Another combinational approach for delivering Fe³⁺ ions to enhance the Fenton reaction in cancer cells was reported by Zeng et al. After the interaction between croconaine (Cro) and Fe³⁺ to produce Cro-Fe, BSA was then added to encapsulate Cro-Fe, which enhanced the biocompatibility of the NPs named Cro-Fe@BSA [124]. When heat stress applied to cancer cells, heat shock proteins usually were upregulated as a self-defense mechanism of cancer cells. However, as Fe³⁺ ions were released in an acidic condition, ROS production was boosted and consequently hindered the production of heat shock protein, leading to ferroptosis. The photothermal effect enhanced the Fenton reaction through the production of •OH and LPO. Upon irradiation, the Fe²⁺ level also increased, which enhanced ferroptosis (Fig. 22a). PAI and T₁-weighted MRI were used to track the Cro-Fe@BSA after injection in vivo, the results of which show that the concentration of Cro-Fe@BSA reached its maximum 24 h post-injection (Fig. 22b and d). The results imply that the EPR effect mediated the efficient internalization of the NPs by the tumor cells. Thermal images were taken to determine the photothermal effect after irradiation. The temperature increased in mice treated with Cro-Fe@BSA and Cro@BSA to 55.2 °C and 50.1 °C, respectively (Fig. 22c). The difference is due to the lower accumulation rate of Cro@BSA at the tumor sites due to its larger size. The tumor volume and inhibition rate are measured after various treatment regimens (Fig. 22e); efficient tumor growth reduction was observed after treatment with Cro-Fe@BSA and laser irradiation. The Cro-Fe@BSA NPs provided a responsive combinational ferroptosis and photothermal effect. The release of Fe³⁺ ions generated Fe²⁺ ions in the reaction with GSH for the ferroptosis induction. Additional photothermal effect enhanced the Fenton reaction rate for the formation of ROS and LPO. This study provides insight into designing Fe-based ferroptosis agents that can perform enhanced synergetic combinational cancer therapy.

Fig. 22.

Synergistic PTT and ferroptosis cancer nanomedicine with MRI/PAI/US guidance. (a) Schematic illustrations of the synthesis and therapeutic mechanism of Cro-Fe@BSA. (b) PAI/US images of tumor-bearing mice after injection of Cro-Fe@BSA. (c) Thermal images of tumor-bearing mice after 10 min of laser irradiation. (d) T₁-weighted MRI results of tumor-bearing mice after injection of Cro-Fe@BSA. (e) Tumor volume changes after various treatment regimens (Group I: Control, Group II: Cro@BSA, Group III: Cro@BSA + laser, Group IV: Cro-Fe@BSA, Group V: Cro-Fe@BSA + laser). Reproduced with permission [124]. Copyright 2021, John Wiley & Sons.

The cRGD/Pt + DOX@GFNPs (RPDGs) can activate the Fenton reaction, with Pt (IV) downregulating the level of GSH and upregulating the level of ROS. After NIR irradiation, the Fenton reaction was increased via the gallic acid/Fe²⁺ NPs (GFNPs) and Pt (IV) enhanced the depletion of GSH. In addition, the GFNPs provided the photothermal effect and the release of Fe²⁺ from the NPs was accelerated (Fig. 23a) [125]. TEM analysis of RPDG showed that it is 60.4 nm in size, with DLS data showing a uniform size distribution (68.06 nm) (Fig. 23b and c). As Fe²⁺ from the GFNPs provide T₂-weighted MRI capability, MR images were taken according to the RPDG concentration (Fig. 23d). Furthermore, the r₂ value was further measured according to the Fe concentration (81.0 mM⁻¹ s⁻¹) (Fig. 23e). MR images were taken after administering various treatment regimens: GFNPs, Pt (IV)@GFNPs, Pt (IV) + DOX@GFNPs, and RPDGs. Among them, the RPDGs provided an obvious signal reduction, which supports the assumption that they provide an efficient diagnostic method (Fig. 23f). To observe the tumor-specific targeting ability, fluorescent Cy7 was loaded onto the RPDGs and showed significant accumulation at the tumor sites (Fig. 23g). The photothermal effect after NIR irradiation with each treatment regimen provided a temperature increase (Fig. 23h and i), with that employing the RPGDs being the highest. Finally, bioluminescence was measured to examine the therapeutic effect of the RPDGs. It was reduced dramatically, which indicates that tumor therapy via the RPDGs is effective. This paper suggested that RPDGs provided a combinational approach to chemotherapy, ferroptosis, and PTT. Locally elevated temperature not only accelerates the Fenton reaction but also increases the local blood flow to the tumor tissue leading to enhanced drug delivery overcoming the blood-brain barrier.

Fig. 23.

MRI/FI-guided ferroptosis nanomedicine. (a) Schematic illustrations of the synthesis and therapeutic mechanism of RPDGs. (b) TEM images and (c) DLS data of the GFNPs and RPDGs. (d) T₂-weighted MRI results according to the Fe concentration in the RPDGs. (e) The transverse relaxation coefficients of the RPDGs. (f) T₂-weighted MRI results of tumor-bearing mice 24 h after injection of various components. (g) FI results of tumor-bearing mice, their major organs, and tumors after injection of Pt (IV) + DOX@GFNPs or RPDGs. (h) Thermal images of mice and (i) temperature changes 8 h post-injection of Pt (IV) + DOX@GFNPs or RPDGs. Reproduced with permission [125]. Copyright 2021, Elsevier B.V.

Ce6, a common photosensitizer for PDT, enhances ROS production and GSH or GPX4 depletion, leading to the ferroptosis of cancer cells. NIR fluorescence imaging (FI) is commonly enabled by conjugating or encapsulating NPs with photosensitizers such as Ce6 whereas MRI is enabled by Fe-containing NPs [[195], [196], [197], [198]].

Fe₃O₄-PLGA-Ce6 NPs provided ferroptosis and PDT via NIR irradiation. Fe²⁺, Fe³⁺, and Ce6 are released from PLGA under the acidic conditions of the TME and facilitate Fenton reaction-mediated ROS production [108,199]. Upon NIR irradiation, Ce6-mediated PDT supported both apoptosis- and ferroptosis-mediated cell death [200]. Fe₃O₄-PLGA-Ce6 NPs were synthesized by loading Ce6 and citric acid-coated Fe₃O₄ (CA-Fe₃O₄) onto PLGA NPs (Fig. 24a) [126]. Ce6-mediated FI was conducted to observe the enhanced penetration and retention in subcutaneous tumors (Fig. 24b). In addition, the major organs and tumors were harvested 72 h after injection and Fe₃O₄-PLGA-Ce6 NPs accumulation at the tumor sites was observed (Fig. 24c). T₂-weighted MRI was enabled by the loaded Fe₃O₄ [116,201]. The MRI signals could be observed up to 72 h after injection (Fig. 24d). Thus, they administrated Fe₃O₄-PLGA-Ce6 NPs every 3 days and a day after administration they conducted PDT. These therapeutic cycles were repeated total 3 times. Fe₃O₄-PLGA-Ce6+laser treatment showed the most dramatic tumor size reduction and inhibition owing to the combination of ferroptosis and PDT (Fig. 24e). They also mentioned that the synergism between ferroptosis and PDT is large amounts of oxygen as a result of the Fenton reaction relieved hypoxia in the malignant TME and supplied PDT sources simultaneously.

Fig. 24.

MRI/FI-guided ferroptosis nanomedicine enhanced by PDT. (a) Schematic illustrations of the synthesis and therapeutic mechanism of Fe₃O₄-PLGA-Ce6 NPs. (b) FI results of tumor-bearing mice after injection of free Ce6 or Fe₃O₄-PLGA-Ce6 NPs. (c) FI results of the major organs and tumors 72 h after injection of free Ce6 or Fe₃O₄-PLGA-Ce6 NPs. (d) T₂-weighted MRI results after injection of Fe₃O₄ or Fe₃O₄-PLGA-Ce6 NPs. (e) The tumor inhibition rate after various treatment regimens. Reproduced with permission [126]. Copyright 2021, The Royal Society of Chemistry.

Liang et al. reported combinational ferroptosis and PDT approach using iron oxide MNPs loaded with porphyrin-lipids [127]. Porphyrin-grafted lipid (PGL) and DSPE-polyethylene glycols (DSPE-PEG) self-assembled on the surface of oleic acid capped Fe₃O₄ NPs (Fe₃O₄@PGL NPs) (Fig. 25a). Porphyrin photosensitizers were then covalently conjugated on the NPs to avoid their uncontrolled release. In vitro testing on macrophage cell line RAW 264.7 shows that the Fe₃O₄@PGL NPs could generate a large amount of ROS via the Fenton reaction, as shown in the FI (Fig. 25b). Thus, the ROS generation activated tumor associated macrophages, leading to ferroptosis-mediated cell death of human colon cancer cells (HT-29 cell line). To observe the tumor-targeting ability of the Fe₃O₄@PGL NPs, PGL-mediated FI was taken, showing that the fluorescence signals at the tumor sites reached the maximum 24 h after injection. In addition, fluorescence signals measured after harvesting the major organs and tumors clearly reveal that Fe₃O₄@PGL NPs had well accumulated at the tumor sites. T₂-weighted was also possible with the Fe₃O₄@PGL NPs; darkening according to the concentration of NPs was. The measured r₂ was 628.6 mM⁻¹s⁻¹ (Fig. 25c). The Fenton reaction and oxidative stress of macrophages were effectively accelerated via PDT treatment. The relatively small-sized Fe₃O₄@ PGL NPs showed a high porphyrin photosensitizer-loading efficacy and excellent biocompatibility. Cancer cells were effectively killed by using a small amount of the Fe₃O₄@PGL NPs with PDT treatment. An in vivo animal study further demonstrated complete tumor growth inhibition after treatment with the Fe₃O₄@PGL NPs and PDT (Fig. 25d). This result suggested that the combination of Fenton reaction, PDT and stimulation of tumor-associated macrophage successively induce ferroptosis-mediated cell death. This work contributes to the current emerging context of combinational ferroptosis and PDT therapy where magnetic Fe-oxide NPs can be used together with conventional porphyrin photosensitizers to maximize ROS generation for cancer therapy.

Fig. 25.

PDT-mediated ferroptosis cancer nanomedicine with MRI/FI guidance. (a) Preparation and characterization of Fe₃O₄@PGL NPs. (b) Real-time FI using Fe₃O₄@PGL NPs and their biodistribution. (c) MR contrast enhancing property of Fe₃O₄@PGL NPs. (d) In vivo PDT of Fe₃O₄@PGL NPs. Reproduced with permission [127]. Copyright 2021, American Chemical Society.

5. Conclusion

Despite the remarkable strides made in the advancement of cancer therapy via a heightened comprehension of cancer biology and molecular biology, cancer is still a leading cause of mortality, largely due to the apoptosis-based cancer therapy and subsequent therapeutic resistance of cancers. Typically, the apoptotic pathways of cancers are evaded by numerous mutations such as overexpression of antiapoptotic proteins (BCL-2, BCL-XL, BCL-W, MCL-1, BFL-1/A1) and under-expression of proapoptotic proteins (BAX, BAK, BAD, BID, etc), or tumor suppressing p53 protein [[202], [203], [204]]. Many of these changes associated with the apoptosis cause the therapeutic resistance to the most common anticancer therapies. Thus, there is an imminent need to explore alternative strategies that leverage non-apoptotic cancer cell death as a means of improving therapeutic outcomes. Ferroptosis-based cancer therapy can bypass the common apoptosis based therapeutic resistance mechanisms. Ferroptosis can serve as an alternative or complementary pathway to conventional apoptosis-based cancer treatment. Here beforehand introduced research on ferroptosis-mediated cancer cell death highlights the great potential for new ferroptosis based cancer therapy approaches. As demonstrated the effectiveness of ferroptosis based cancer therapies, the importance of ferroptosis in cancer treatment is rapidly growing and attracting attention as a new clinical cancer treatment approach. However, the therapeutic efficacy of conventional small-molecule ferroptosis agents in the clinical setting can be significantly limited with the lack of tumor-specificity, as witnessed by the side effects and failure of numerous chemotherapy trials. The next frontier in the advancement of ferroptosis-based cancer therapeutics lies in the effective ferroptosis induction of cancer cells with minimized side effects. An effective mean of harnessing the clinical potential of ferroptosis-mediated cancer therapy is local image guided ferroptosis- and combinational ferroptosis-cancer therapy regimen [[205], [206], [207], [208]]. As considering combinational ferroptosis cancer therapy, the rational design of the combination for the synergistic anticancer effects is of significant importance [[209], [210], [211], [212], [213]]. Further, additional efforts on investigating the ferroptosis targeting mechanism, feasible clinical targeted ferroptosis approaches, and optimized synergistic combinational ferroptosis cancer therapy, and ideas for constructing ferroptosis nanocarriers are required for the successful clinical translation of this approach.

MNPs are one of the most extensively studied NPs in biomedical applications. Their innate magnetic properties of MNPs originate from unpaired spins/electrons of the atom. Advanced nanotechnology found their remote dynamic control such as remote steering, heat generation, mechanical force generation, and MRI contrast with an external magnetic field. For the biomedical applications, highly magnetic field responsive MNPs are commonly composed of iron, which is one of essential component in human body. Non-ionizing external magnetic fields can pass through the human body without harmful effects. Magnetic field response MNPs can be precisely localized to specific sites of the human or trigger the mechanical force or heat [214,215]. The presence of MNPs in the human body is easily detected by diagnostic MRI. Indeed, magnetic field responsive MNPs are the most versatile option for the future nanomedicine. In association with ferroptosis, iron metabolism is easily affected by the iron oxide MNPs and iron oxide MNPs become one of the key targets for the ferroptosis cancer treatment. Iron oxide MNPs can be dissolved in acidic TME and release ROS-generating Fe²⁺ and Fe³⁺ ions, resulting in ferroptosis induction of cancer cells. Enhancing the ferroptosis catalytic process of iron oxide MNPs in the TME has been one of the main strategies for the ferroptosis cancer nanomedicine. Various types of iron oxide MNPs such as anisotropic, porous, or hierarchical morphologies have been studied for the multifunctional ferroptosis nanomedicine agents [103,216,217]. Forming a hybrid MNP nanostructures composed of iron oxide MNPs and other transition metal oxides also provides a strategy to sustain the multivalent metal ion redox cycle [218,219]. Further, the magnetic field responsive mechanical or thermal energy of iron oxide MNPs which are related to lipid peroxidation and ferroptosis pathways provide an opportunity for the triggered and local ferroptosis induction [220,221]. Those approaches allow precise spatial and temporal regulation of ferroptosis induction, contributing to personalized cancer treatment. Multimodal imaging characters of MNPs and hybrid MNPs also provide real-time feedback on treatment progress and tumor response. Finally, the therapeutic multifunctionality of MNPs and hybrid MNPs further allows combinational synergistic ferroptosis approaches such as ferroptosis/chemotherapy, ferroptosis/pyroptosis, ferroptosis/radiation, ferroptosis/ablations, and ferroptosis/immunotherapies [219,222]. Especially, combining MNP-mediated ferroptosis induction with immunotherapy has shown great promise. Ferroptosis mediated DAMP release and PD-L1 upregulation strongly suggest that combinational ferroptosis induction and immunotherapy using MNPs could be a highly efficient method of killing cancer cells and enhancing the overall therapeutic outcomes.

One challenge for ferroptosis-induction cancer nanomedicine is inconsistent therapeutic outcomes depending on the tumor type. For instance, the molecular features of prostate cancer involve Fe dysmetabolism, including Fe-ion influx, intracellular Fe-ion distribution, and Fe-ion flux. Diffuse large B cell lymphomas and renal cell carcinomas have been shown to be more susceptible to erastin-induced ferroptosis compared to other cancer cell lines from six different tissue types (breast, lung, colon, melanocytes, central nervous system, and ovary) [223]. This variability in the sensitivity of different cell lines to ferroptosis could be attributed to differences in their underlying metabolic states. Additionally, TME varies significantly across different cancer types. For example, tumor makes acidic TME via increased glycolysis, but the degree of glycolysis may vary with their type, size, and stage [224,225]. The acidity difference in TME affects to the tendency of iron ions dissolution, resulting in a difference in ferroptosis induction. Thus, a specific tumor type focused MNPs ferroptosis cancer nanomedicine should be developed. MNP that can trigger the ferroptosis cycle remotely might control the ferroptosis induction behaviors for each type of cancer along with their imaging capabilities. To advance MNPs mediated ferroptosis cancer nanomedicine to the clinical translation, interdisciplinary cooperation between material scientists and clinicians is required to determine the suitability of MNPs for the treatment of specific cancer types.

In this review, the mechanism of ferroptosis and various ideas for the design and development of ferroptosis therapeutic nanoplatforms were examined, and innovative possibilities were proposed along with a summary of previous findings. This information should expand the horizon of MNP platforms for ferroptosis-induction cancer nanomedicine applications. Although the NP platforms are still under investigation for clinical translation, their consideration should be the top priority for the successful deployment of ferroptosis-induction cancer nanomedicine. Immunotherapy is a relatively new and emerging approach for treating cancer. Further studies on ferroptosis combined with immunotherapy involving MNPs are needed to clarify the molecular mechanisms and to provide an opportunity for designing new therapeutic interventions. Addressing these issues will deepen our understanding of ferroptosis-based cancer nanomedicine and advance its clinical applicability. Additionally, there is a gap between cutting-edge pre-clinical research of MNPs ferroptosis cancer nanomedicine and their clinical translation. Innovative MNPs ferroptosis cancer nanomedicine should be validated for superior cancer therapy based on the thorough investigation of ferroptosis regulating molecules and signaling pathways. Consistent efforts on evaluating the safety of MNPs or MNPs based hybrid nanostructures and developing image guided localized approaches of ferroptosis nanomedicine are required for the clinical translation of MNPs mediated ferroptosis cancer nanomedicine. Multidisciplinary and interdisciplinary collaborations are critically needed. At the same time, additional attention on economic feasibility, regulatory considerations, safety assessments, relevance with clinical unmet needs, and public perspective will be essential for the successful translation of promising ferroptosis magnetic cancer nanomedicine.

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This review article does not require any ethical approval or allied consents for publication.

CRediT authorship contribution statement

Min Jun Ko: Visualization, Conceptualization, Writing-Original Draft, Investigation. Sunhong Min: Visualization, Investigation, Conceptualization. Hyunsik Hong: Validation, Conceptualization. Woojung Yoo: Investigation, Resources, Visualization. Jinmyoung Joo: Investigation, Project administration. Yu Shrike Zhang: Supervision, Project administration, Resources. Heemin Kang: Conceptualization, Funding acquisition, Project administration, Supervision, Writing-Review & Editing. Dong-Hyun Kim: Conceptualization, Funding acquisition, Supervision, Project administration, Writing-Original Draft, Writing-Review & Editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.