Recent advances in nanoformulation-based delivery for cancer immunotherapy

ABSTRACT

Cancer is one of the leading causes of mortality worldwide, and its treatment faces several challenges. Phytoconstituents derived from recently discovered medicinal plants through nanotechnology potentially target cancer cells via PI3K/Akt/mTOR pathways and exert their effects selectively through the generation of reactive oxygen species through β-catenin inhibition, DNA damage, and increasing caspase 3/9 and p53 expression. These nanocarriers act specifically against different cancer cell lines such as HT-29, MOLT-4 human leukemia cancer and MCF-7 cell lines SKOV-3, Caov-3, SW-626, HepG2, A-549, HeLa, and MCF-7. This review comprehensively elaborates on the cellular and molecular mechanisms, and therapeutic prospects of various plant-mediated nanoformulations to attain a revolutionary shift in cancer immunotherapy.

Plain language summary

Article Highlights.

Background & approaches for nanoformulations design

• Drug nanofabrication using the multidisciplinary field of nanotechnology may be a possible solution for the treatment of cancer.

• Medicinal plants as natural sources of anticancer compounds are the most suitable, safe, and cost-effective alternatives to traditional chemical drugs, and nanoencapsulation of plant bioactive compounds could effectively improve cancer treatment.

• The main approaches for the proper synthesis of nanoformulated drugs are top-down and bottom-up methods, considering the key features of particle size, shape, structure as well as particle size distribution.

Modes of delivery routes

• An efficient drug-delivery system is site-specific with minimum loss in blood circulation, improved bioavailability and biocompatibility and without harmful effects on noncancerous cells.

• The nanocarriers are capable of crossing diverse biological barriers and improve bioaccessability of anticancer drugs when administered orally.

• The transdermal, intravenous, and pulmonary administration of nanoparticles (NPs) avoid first-pass metabolism, reduce systemic toxicity, and improve bioavailability of drugs through passive and active targeting of cancerous tissues.

Plant-mediated nanoformulations for cancer therapy

• Natural antitumor agents are of great importance with more than 60% of cancer treatments using natural sources, focusing on green synthesis of NPs. Plants have been preferred for this purpose.

Hydrophilic & hydrophobic nature of NPs

• An important parameter for risk considerations of biological interactions of NPs is their relative hydrophobicity.

• Hydrophobic NPs attach to and interact with cell lipid bilayer membrane and exhibit enhanced uptake compared with hydrophilic NPs.

Clinical trials

• Many clinical and preclinical studies have proved the effectiveness of nanoformulated drugs, but unfortunately not many nanodrugs have received approval for clinical application. At present, ~16 anticancer nanodrugs have been approved by the US FDA, 75 are in clinical trials, and five are available in market.

Current challenges

• The main limitation to medical application of naturally synthesized NPs is their toxicity in tissues and determining how to obtain the ideal size and monodispersion of particles.

Future perspective

• Using properly regulated methods, adjustment of parameters during NP synthesis and co-delivery of combinative natural nanodrugs can improve cancer immunotherapy in the future.

1. Introduction

Cancer is one of the leading causes of mortality worldwide, with 10 million deaths reported in 2020. It is mainly caused by an uncontrolled and rapid proliferation of cells that grow beyond the usual limits, form a microenvironment, and thus promote the development of metastasis [1]. This unusual cell behavior may be the consequence of transmissible mutations or nongenetic alterations in oncogenes that are involved in cell cycle regulation, homeostasis and apoptosis, tumor suppressor gene inactivation, and inhibition of DNA repair machinery. The characteristics of cancer cells are the downregulation of programmed cell death and the abnormal behavior of microtubules in mitosis. Cancer risks include smoking and alcohol consumption, obesity, lack of physical activity, poor diet, exposure to environmental pollutants, ionizing radiation, and infections, in combination with genetic factors. The most common cancers identified in different organs of the human body are lung, breast, colorectal, prostate, endometrial, bladder, thyroid, leukemia, lymphoma, melanoma, kidney (pelvis and renal cells), liver, and pancreatic cancers [2].

Traditional cancer treatments include radiation, surgery, and chemotherapy used either alone or combined clinically. Chemotherapy involves the administration of anticancer drugs to the patient, but they adversely interact with DNA and block its replication during cell proliferation through the formation of cross-linked nitrogenous bases. Several commonly used anticancer drugs, such as doxorubicin, tamoxifen, methotrexate, and cyclophosphamide, cause high risk for several complications such as cardiac toxicity, intestinal mucositis, neutropenia, embolism, leukopenia, cardiomyopathy, and hepatic toxicity [3]. These anticancer drugs act by weakening the immune system and make the patient suffer from infections rather than the cancer itself. The chemical drugs provide only temporary improvement and help patients live longer but also cause loss of healthy, rapidly dividing cells; loss of hair and weight; nausea; and diarrhea generally. The drugs used in chemotherapy have limited water solubility with low biocompatibility and are administered at higher doses to accomplish therapeutic levels, which causes high systemic toxicity. Therefore, drug nanofabrication is a promising possible solution for cancer immunotherapy [4].

Nanotechnology is a broad, multidisciplinary field due to its role in targeting cancer cells and is a rapidly emerging worldwide area of study in recent years [5]. Nanoparticle (NP) size is exceptionally small at 1–100 nm, which improves their biological and physicochemical properties compared with traditional materials. Nanotechnology is applied in cancer immunotherapy for the manufacturing of nano-drugs and nanocompounds targeting tumor cells. Different types of nanocarriers currently being examined include organic polymers or nanocapsules (micelles, liposomes, dendrimers, and ferritin); inorganic materials, including metal and metal oxides; and carbon-based products, such as carbon black, nano-tubes, nanofibers, graphene, and fullerene [6]. Greater drug load with lower dose requirements; lower toxicity; various administration routes, such as ocular, oral, pulmonary, and parenteral; and passive targeting are the advantages of nanosuspensions. The use of nanostructures is a novel approach to developing a cancer-targeted delivery system that reduces drug side effects through controlled drug release and enhancement of their in vivo efficacy as well as their ability to pass across blood vessels and other body barriers [7,8].

Medicinal plants are the most suitable alternatives to chemotherapeutic drugs because they are cost-effective and safe for clinical treatments [9]. The bioactive compounds derived from medicinal plants such as amino acids, proteins, enzymes, polysaccharides, flavones, phenolics, terpenoids, and alkaloids are potent capping agents that stabilize and control the structure of NPs. The NPs act by the activation of substrates to attain electrostatic, steric, hydration, depletion, and Van der Waals stability [10]. The nanotechnology field can provide an eco-friendly process for the synthesis of NPs used in many pharmaceutical and cosmetic applications. However, the application of green production of NPs has gained significant attention in cancer therapy. The plant species used for the production of NPs having anticancer potential include Acalypha indica, Azadirachta indica, Aloe vera, Calliandra haematocephala, Cinnamomum camphora, Datura metel, Eucalyptus procera, Geranium leaf, Madhuca longifolia, Nelumbo nucifera, Rhododedendron dauricam, Gloriosa superba, Moringa oleifera, Punica granatum, Teucrium polium, and Tropaeolum majus [4,11]. However, the clinical application of plant products in cancer therapy is limited due to their low biocompatibility and untargeted delivery. Therefore, carrying out encapsulation of secondary metabolites could effectively reduce their adverse effects and improve their anticancer activities [12].

This review attempts to highlight the innovative aspects and recent literature on cellular and molecular mechanisms, elaborating on the pharmacological actions of different types of nanoformulations from recently discovered medicinal plants targeting cancerous cells. The data presented in this review has been obtained through searching of literature available on different web sources, such as Google Scholar, ScienceDirect, PubMed, and Web of Science, focusing on the keywords: anticancer NPs, medicinal plants with cytotoxicity potential, reactive oxygen species causing cell cycle arrest and apoptosis or cell death; to fully elucidate therapeutic suggestions to this serious health issue. The novel NPs possess anticancer properties for the targeting of proliferating cells and tumors. They also possess cytotoxicity potential through activation of reactive oxygen species (ROS) by arresting the cell cycle. These cellular events eventually lead to apoptosis and induce cell death and thus are proposed as delivery for therapeutic purposes.

2. Different approaches for nanoformulation design

The key features for the synthesis of NPs are particle size, shape, structure (crystalline or amorphous), and distribution of particle size as monodispersity or polydispersity, with particles of the same or different sizes, respectively. The main approaches for the synthesis of NPs are top-down and bottom-up approaches involving the assembly of atoms or molecules to produce NPs, respectively. The top-down approach uses complex analysis in which larger NPs are produced and later a mechanical method or acid treatment is used to decrease their size; the bottom-up method initiates at the atomic level through the formation of molecules [13]. Mechanical milling, sputtering, electron beam lithography, photolithography, thermal, anodization, etching, and laser ablation are commonly used top-down methods, and solid, fluid, and gas state methods; molecular condensation; chemical reduction and green synthesis of NPs by pyrolysis; the sol-gel method; and spinning are bottom-up methods [14].

2.1. Methods for NP synthesis

Carbide and oxide-strengthened aluminum (Al) alloys, copper/magnesium/nickel/aluminum-based nanoalloys and wear-resistant spray coatings are produced by mechanical milling or ball milling that grinds the particles to smaller sizes and mixes them well. The arc discharge method and chemical vapor deposition (bottom-up) are used to produce carbon-based NPs [15]. In the arc column, two graphite rods are adjusted in a chamber with maintained helium pressure to avoid oxygen or moisture and carbon rod vaporization occurs between the ends of the rods and in an oven where a substrate is heated and hydrocarbon gas as a precursor decomposes and releases carbon atoms that recombine in the form of carbon nanotubes [16]. The advantage of this technique is the formation of fine powder and milling of toxic and coarse materials, but it is time-consuming and has a high risk of contamination and noise production from the collision of milling balls in a metal cylinder. For instance, carbon nanotube-fabricated ginsenoside from Panax ginseng with polymethacrylic acid increased the solubility and stability of ginsenoside against cancer cells at much lower concentrations [17].

Laser ablation uses a powerful beam of laser that hits the target material and causes its vaporization; this is useful in the formation of metal oxides, carbon-based NPs, and nanosuspensions. The average size and distribution of colloidal NPs can be adjusted through wavelength, fluence, and laser salt addition. The sol-gel method, with reaction steps of hydrolysis and condensation, dissolves the metal alkoxide in alcohol or water and converts it to a gel containing metal oxide NPs (Figure 1). Specific amounts of aqueous solution of metal salt and plant extract are mixed, and the metals are reduced to a zero oxidation state to be converted to metal NPs when the technique is used in green synthesis. The advantage of this method is a comparatively low-temperature requirement and easy control of the process parameters [18].

Figure 1.

Green synthesis of nanoparticles.

NP: Nanoparticle.

Reproduced with permission from Moritz M, Geszke-Moritz M. The newest achievements in synthesis, immobilization, and practical applications of antibacterial nanoparticles. Chem. Engin. J. 2013;228:596–613. © 2013 Elsevier B.V.

Preparation of polymers is based on the polymerization of monomers or using preformed polymers through two-step processes involving an emulsification preparation following NP synthesis or one-step processes with no emulsification step required. PLGA-NPs are designed by a single emulsion-solvent evaporation method that is suitable for encapsulating hydrophobic drugs in oil–water emulsion using polyvinyl alcohol as an emulsifier or stabilizer [19]. Liposomes are made up of phospholipids of an amphiphilic nature in a storage compartment in which NPs are embedded in a spherical bilayer structure of phospholipids. NPs and anticancer drugs such as doxorubicin entrapped in PEGylated liposomes were successfully delivered to organisms. Dendrimers are made by convergent and divergent methods in which branches are produced first and then linked to the core and vice versa, respectively [20].

2.2. NPs in cancer treatment

Chemotherapy is a critical and widely used method for the complete treatment of cancer, and nanotechnology can counteract the adverse effects of existing chemotherapeutic drugs, including low bioavailability, high toxicity, multidrug resistance, and poor cancer site recognition and penetration. Encapsulation of drugs with nanostructures prevents their degradation in biological systems, ensures direct delivery to the target cancerous site, controls their diffusion and release into the affected cells and maximizes their therapeutic effects. Polymeric NPs, liposomes, and metallic NPs have been applied to develop various types of drug-delivery systems to target cancer cells with antiproliferative and cell-toxic compounds or plant extracts [21]. Biocompatible polymeric NPs provide a harmless and effective means of drug delivery, whereas metallic NPs, such as gold or silver, with their unique physical and optical properties, are used for targeted drug delivery as well as imaging. The surface characteristics of these NPs allow for coating with specific proteins or antibodies that can interact with and bind to cancer cell receptors, ensuring targeted drug transport. They can also be used to detect and monitor the cancer progression in real time using imaging techniques such as photoacoustic imaging. Nanocapsules or polymeric NPs are now important in the formulation of carriers for anticancer drugs due to their responsiveness and ability to be conjugated with drugs. Nevertheless, despite a variety of nanoformulations designed for this purpose, only some liposomes and polymeric NPs have been clinically approved and are preferred over other formulations [22]. Inorganic NPs such as CuO NPs with specific electrical, optical, magnetic, catalytic, and biological properties are of considerable importance among metal oxide NPs in the treatment of cancer. ZnO NPs coupled with anticancer drug daunorubicin and UV radiation exhibited synergistic apoptotic effects against leukemia cancer cells in a dose-dependent manner [23].

Mesoporous silica nanoparticles (MSNPs) are a recently introduced form of inorganic NPs. They are ideal anticancer drug carriers with variable, highly ordered mesoporous pore sizes of 2 to 50 nm, large specific surface area and pore volume, favorable biodegradability and biocompatibility, and many modifiable hydroxyl groups on their surface. Hollow MSNPs, with an internal network of pores surrounded by a mesoporous shell, core-shell MSNPs, with integrated nanocores within mesoporous shells, such as magnetic NPs and gold and silver NPs, are specific types of such NPs. Magnetic MSNPs are dominant among other types because their mesopores are open and exhibit a controlled release of drug-loaded within the pores by implying hydrogen bonds, electrostatic interactions, or covalent grafting through opening and closure in response to endogenous and exogenous stimuli [24].

3. Modes of delivery routes

For an efficient drug-delivery system, site-specific targeting with minimal loss in blood circulation and efficient killing of cancer cells without any harmful effects are required. The probable administration routes for drug delivery are oral, transdermal, subcutaneous, intravenous, and nasal, among others. However, nanocarriers should cross diverse biological barriers before reaching the selected target [25]. The oldest drug administration route is oral because it is easy, cost-effective and patient-amenable but not in cancer therapy due to the physiological conditions in the gastrointestinal (GI) tract. Some chemotherapeutic agents are less soluble and are degraded in the GI tract, and their bioavailability is reduced. The NPs help increase the solubility of anticancer drugs in aqueous medium and their bioaccessibility when administered orally [26–28].

The transdermal strategy for drug delivery also avoids first-pass metabolism and GI degradation, which improves drug bioavailability. NPs enter the skin through intercellular spaces in the stratum corneum (dead keratinocytes), the transcellular pathway (through keratinocytes), and the transappendageal pathway (hair follicles, sweat ducts, and sebaceous glands) [29]. The intravenous administration of anticancer NPs of proper dose via needle injection is the most common and direct route to systemic blood circulation through the skin. However, the intravenous route may still create some problems, including the recognition of NPs by the immune system and their elimination or accumulation in the spleen or liver. NPs may also react with some proteins in body fluids. These drawbacks have led to the development of new approaches for tumor-targeting nanocompounds as engineered particles, compatible with the standard in vivo clearance pathways and decreased potential systemic toxicity after injection [30]. Monoclonal antibodies are the first ideal class of targeting molecules because they increase the uptake and toxic potential of NPs in cancer cells. Recently, researchers encapsulated the chemotherapeutic drugs into NPs and functionalized their surface with antibodies to maintain targeting efficacy. Pulmonary administration of NPs also reduces the systemic toxicity of chemotherapeutic agents. Lung cancer can be cured efficiently by long-term delivery of anticancer nanoencapsulations as an inhalable powder. For instance, inhaled doxorubicin NPs showed less cardiac toxicity and paclitaxel–polyglutamic acid conjugate was well tolerated by mice after intratracheal administration. Once present in circulation, NPs are coated with protein opsonin (opsonization) and aggregate in reticuloendothelial or mononuclear phagocyte systems, but the physicochemical properties of NPs usually determine if they will be cleared out or taken up by cancer cells through either passive targeting or receptor-mediated active targeting pathways [31].

Passive targeting takes advantage of tumor tissue permeability. Cancerous tissue has a leaky and defective vasculature through which NPs can pass because of their improved permeation and retention effect, but active targeting is achieved by conjugating NPs to a targeting substrate and allowing accumulation of the drug within the cancer cells, intracellular organelles, or specific molecules in cancer cells (Figure 2). This approach is used to direct NPs to cell surface carbohydrates, receptors, and antigens [32]. When the NPs are administered through any route, they enter the blood and penetrate the cancer vasculature to reach the target cells and release the drug uptake. This occurs through a process called endocytosis. It occurs either through ligand-NP–receptor interaction or a nonspecific interaction of NPs–cell membrane, pinocytosis, and phagocytosis. Cellular uptake of NPs increases with decreasing particle size and NPs can skip the endo-lysosomal pathway and get into the cytosol, the active site for most of the drugs [33].

Figure 2.

Enhanced permeation and retention effect of nanoparticles in cancer tissues.

NP: Nanoparticle.

Reproduced with permission from Chang J-H, Chandrasekar N, Shen S-Y, et al. Biomedical applications. In: S. Thomas, TA Nguyen, M Ahmadi, G Yasin, N Joshi, editors. Silicon-Based Hybrid Nanoparticles: Fundamentals, Properties, and Applications. Elsevier; 2022. p. 277–323. © 2022 Elsevier Inc. Amsterdam, Netherlands.

4. Plant-mediated nanoformulations as promising anticancer potentials

Natural antitumor agents are of great importance in the enhancement of cancer therapy, and more than 60% of cancer therapeutics available are based on natural compounds that have largely been focused on NP synthesis because they are controllable and appropriate for the development of stable and eco-friendly processes. The green synthesis of NPs uses economical and safe raw materials, such as bacteria, fungi, algae, and plant extracts, among which, plants have been preferred because they do not require microbial culture maintenance [34].

4.1. Treatment by phytocompounds

Compared with many other chemotherapeutic agents, phytocompounds derived from natural sources are believed to have fewer side effects. Plants and herbs have been considered traditional and primary therapeutic agents for cancer treatment in several parts of the world, including the global East and West, particularly India and Europe. According to WHO reports, various countries use medicinal plants for treatment of cancer, and among herbs used for this purpose, only 10 to 15% have been examined thoroughly for their unique anticancer potential. Phytocompounds are alternative and safe compounds that reduce resistance to chemotherapy within cancerous tissues and enhance the antitumor action of chemical drugs. Nearly two-thirds of cancer treatments are achieved through plant processing and the phytochemicals they possess [23].

4.2. Targeting cancer cells

Deactivation of the tumor suppressor gene and promotion of oncogenic reactions transform normal cells to cancerous ones. This conversion reaction is controlled by the release of free radicals and inflammatory cytokines and causes DNA damage and upregulation of apoptosis. The absence of cell cycle arrest is an obvious reason for abnormal division in cancerous tissues, along with the downregulation of tumor suppressor genes associated with alteration of PI3K/Akt/mTOR, MAPK/ERK, and JAK/STAT signaling cascades. Phytochemicals possess antiproliferative properties such as free radical scavenging and anti-inflammatory exhibited in in vitro studies. With such anticancer abilities, phytocompounds can alter cancer-promoting effects, prevent DNA damage, stop uncontrollable cell divisions and cellular signaling pathways, and induce cellular apoptotic reactions and cell death [23].

4.3. Pathways targeted by phytochemicals

Phytochemicals can control cancer progression via several cell pathways. They alter cell growth and survival (MAPK and ERK) pathways. Genistein, isothiocyanates, gingerol, resveratrol, kaempferol, ursolic acid, and sulforaphane are some phytocompounds reported in the literature that induce apoptosis via MAPK and ERK pathways. Akt/PI3K pathway plays a vital role in the progression and control of cancer. The levels of EGF manage inflammation via NF-kB stimulation and phosphorylation of Akt, and hence are resistance to apoptosis. It also downregulates rapamycin (mTOR), caspases, glycogen synthase kinase 3-β, and Bcl-2. Alkaloids, phenolics, resveratrol, curcumin, flavone, luteolin, sulforaphane, and apigenin with antiproliferation ability can control these processes and inhibit Akt/ PI3K signaling. JAK/STAT pathway also regulates the transcription of p53 necessary for apoptosis. Phytochemicals quercetin, apigenin, kaempferol, and luteolin can limit JAK/STAT signaling and induce apoptosis [23,24].

4.4. Mechanism of action of phytochemicals in green synthesis

The initiating factor in programmed cell death is a high concentration of ROS within the cell and across the mitochondrial membrane through uncoupling of cellular respiration and upregulation of p53 protein induced by plant-based NPs. The size and shape of plant-based NPs also affect their level of toxicity toward cancer cells, and studies indicate that spherical NPs possess stronger anticancer ability compared to other shapes. For example, human lung epithelial (A549) cells are more susceptible to cytotoxicity when exposed to 100- to 160-nm spherical NPs. Production of new blood vessels from existing ones through the process of angiogenesis also can cause the formation of solid tumors according to Folkman's theory. Angiogenesis promotes tumor growth by providing cancer cells with sufficient oxygen and nutrients to penetrate and spread throughout the body. Biosynthesized NPs with antiangiogenesis properties could alleviate retinal neovascularization-like disorders by suppressing VEGFR-2 and activating ERK1 by its phosphorylation and dephosphorylation [35]. Biosynthesized NPs have a longer half-life and can change the morphology of cancer cells by reducing their size, changing their shapes, formation of apoptotic blebs, and altering intracellular vacuole arrangement and chromatin structure [36].

The results from an MTT assay and real-time PCR showed that biosynthesized zinc oxide NPs of Lepidium sativum L. were significantly toxic to colon cancer cell lines HT-29, Caco-2, and SW480 in a dose-dependent manner through inhibition of Bcl-2 gene expression and activating p53 and Bax genes expression. Plant NPs are capable of functionalization by which they can selectively target malignant cells and attach to them through several molecules such as antibodies, proteins, and aptamers. The high cellular penetration ability and DNA binding of NPs might be due to the presence of metal ions. Plant bioactive compounds can attach to the surface of NPs and improve their bioavailability and cytotoxicity potential. For instance, encapsulation of Spondias pinnata extract by NPs reduced the migratory and clonogenic abilities of colorectal cancer and caused the release of intracellular calcium leading to oxidative stress damage, genotoxicity, and apoptosis onset, proved by results of reverse transcription quantitative PCR, revealing upregulation of caspase 3, 8, and 9 [37].

Much research suggests that the antitumor activities of NPs occur through increasing ROS production within cancer cells. After cancer cells are exposed to NPs, a high concentration of ROS leads to cell toxicity and reduced cell growth and division rate. ROS damages cell macromolecules such as lipids, proteins, and DNA, and cell organelles by binding to them and eventually causes cell death. A research team treated HepG2-human hepatocarcinoma cells with 10-nm citrate-packed Ag-NPs and observed a reduction in proteins and cell death as a result of decreased glutathione metabolism while such changes did not happen in the normal cells exposed to the same NPs. Similar results were obtained in experiments with pancreatic tumor cells exposed to small-sized Ag-NPs of diameter 2.6 nm with higher cytotoxic effects than large ones with a diameter of 18 nm. Additionally, NPs also affect other characteristics of cancers such as energy metabolism, mitochondrial function and electron transport chain, and drug resistance, as a result of which electrons and ROS generated in the mitochondrial space leak out and cause oxidative stress interfering with cellular pathways leading to apoptosis and cancer cell death [38].

5. Hydrophilic & hydrophobic nature of NPs

Once spent, NPs are released and meet complex and dynamic environments that alter their surface characteristics. A useful and important parameter for the risk assessment and biological interactions of NPs is their relative hydrophobicity when in aqueous environments, partitioned into physiological systems and their bioavailability. Hydrophilic NPs are more likely to remain in the aqueous medium, possibly with increased mobility, whereas hydrophobic NPs tend to remain attached to organic materials. Studies suggest that hydrophobic NPs interact with the cell membrane and exhibit increased uptake compared with hydrophilic NPs. After uptake, the surface hydrophobicity directly affects circulation time, bioaccumulation, and toxicity of NPs. Additionally, hydrophobicity directs the interaction of the NP surface with biomolecules, which are adsorbed to the surface and influence the transformation, affinity, uptake, and ultimate fate of NPs. Nanostructure-specific characteristics such as size and shape also affect the complexity of hydrophobicity measurements and NPs interactions in the biological environments. According to some studies, NP size affects how rapidly they are distributed to the lipid bilayer membrane, and surface features and solution chemistry determine the concentration states of NPs. The presence of specific surface coatings also alters the hydrophobicity and functionality of NPs; for example, the attachment of Ag-NPs to hydrophobic surfaces is directly proportional to the hydrophobic nature of coatings such as polyvinylpyrrolidone, citrate, and gibberellic acid. Consequently, a suitable measure of hydrophobicity will accurately determine the nature of the behavior and interaction of NPs within living systems [39].

Researchers have synthesized different potent plant-mediated anticancer NPs such as nickel oxide (NiO), copper oxide (CuO), and zinc oxide (ZnO) NPs against colon cancer (HT-29), human lung carcinoma (A549), epithelioma (Hep-2), cervical cancer cells (HeLa), epidermoid carcinoma (A431), human hepatocellular carcinoma cells (HepG2), and breast cancer cell lines (MDA-MB-231, MCF-7) [40] (Figure 3). Table 1 provides a detailed description and tabular presentation of selected plants and their parts used for NP synthesis, the types of NPs, characterization methods, anticancer assessments, and outcomes of the reviewed studies.

Figure 3.

The mechanisms leading to cell death by nanostructures in cancer cells.

ROS: Reactive oxygen species.

Reproduced with permission from Das CGA, Kumar VG, Dhas TS, et al. Nanomaterials in anticancer applications and their mechanism of action – a review. Nanomedicine. 2023;47:102613. © 2023 Elsevier Inc.

Table 1.

List of biosynthesized nanoparticles using different plants.

Plant	Plant part	NP type	Characterization method	Cancer targeted	Anticancer mechanism	Ref.
Crocus sativus	Dried stigmas	Cu-, N-doped CDs	UV-Vis, TEM, FTIR, EDX, and AO/PI staining	Colorectal cancer cells	Increased ROS, lipotoxicity, decreased cell viability, upregulation of apoptotic genes	[41]
Sargassum vulgare	Alginate extract	Ag-NPs	Apoptosis detection, TEM, XRD, AFM, and FTIR	Myeloblastic leukemia cells, cervical cancer cells	Cytotoxic, DNA fragmentation, apoptosis	[42]
Matricaria chamomilla	Flower extract	Ag-NPs	UV-Vis, XRD, and TEM	Breast cancer, cervical cancer, human lung carcinoma cells	Growth inhibition	[43]
Moringa oleifera	Stem bark Leaf extract Flower extract	Ag-NPs Au-NPs CuO-NPs, ZnO-NPs, Fe2O3-NPs, La2O3-NPs	UV-Vis, DLS, TEM, FTIR, H-NMR, and EDX	Cervical cancer cells Breast cancer cells Hepatocellular cancer cells Colorectal cancer cells Human Kasumi-1 (leukemia cells) Breast, liver and lung fibroblast cell lines	Apoptosis, reduced cell viability, inhibition of cell growth, strong cytotoxicity	[44,45]
Mentha piperita Citrus lemon	Leaf extract	ZnO/Ag NPs	UV-Vis, FESEM, XRD, EDX, and FTIR	Cervical cancer cells	Reduced cell viability	[46]
Peganum harmala	Smoke extract Seed harmine	Ag-, ZnO NPs H/p-SC6 Pt-, Pd- and Pt/Pd NPs PLGA-NPs	XRD, DLS, FESEM, and FTIR DLS, Doppler velocimetry, TEM, FTIR, and SBA UV-Vis, XRD, TEM, and FTIR SEM, DLS, and FESEM	Prostate, ovarian, and liver malignant cells Human breast cancer and ovarian cancer cells Lung cancer cells, breast adenocarcinoma cells, hepatocellular, and colorectal cancer cells	ROS generation Growth inhibition Cytotoxicity Strong cytotoxicity and reduced cell viability Strong growth inhibition	[47,48]
Nigella sativa	Seed extract	PdPt NPs	UV-Vis, TEM, XRD, and FTIR	Ishikawa, breast and cervical cancer	Reduced cell viability	[49]
Camellia sinensis	Leaves	Ag NPs Cu2O NPs ZnO NPs	UV-Vis, NTA, XRD, SEM, TEM, and FTIR XRD, FTIR, FESEM, EDX, TEM, and XEDS UV-Vis, XRD, SEM, TEM, and FTIR XRD, SEM, EDS, DLS, and FTIR	Colon, breast and leukemia cancer cell lines Ovarian cancer cell lines Breast cancer cells Cervical cancer cells	Cytotoxicity Cell death Reduced cell viability	[50]
Coffea Coffea arabica	Coffee beans Green beans	PLGA NPs Ag NPs	DLS, FTIR, and FESEM UV-Vis, FTIR, and FESEM	Breast, cervical, lung and hepatocellular cancer cell lines	Inhibition of efflux transport (p-glycoprotein), cytotoxicity	[19,51]
Centella asiatica	Leaf extract	Ag NPs MgO NPs	UV-Vis, TEM, SEM, XRD, and FTIR UV-Vis, TEM, XRD, EDX, FTIR, and AFM	Breast cancer cells Prostate cancer cells	Upregulated caspase 3/9 genes Reduction in migration and mitochondrial transmembrane potential, ROS generation, cell cycle arrest, DNA damage	[52]
Solanum nigrum	Fruit extract	Se NPs ZnO NPs	UV-Vis, FTIR, XRD, DLS, zeta potential, SEM, and TEM	Breast cancer cells Cervical cancer cells	β-catenin inhibition and increasing caspase 3/9 and p53 levels	[53]

AFM: Atomic force microscopy; AO/PI: Acridine orange/propidium iodide staining; CD: Carbon dot; DLS; Dynamic light scattering; EDS: Energy dispersive spectroscopy; EDX: Energy-dispersive x-ray; FESEM: Field emission scanning electron microscopy; FTIR; Fourier transform infrared spectroscopy; H-NMR: Proton nuclear magnetic resonance spectroscopy; NP: Nanoparticle; ROS: Reactive oxygen species; SBA: Sulforhodamine B assay; SEM: Scanning electron microscopy; TEM: Transmission electron microscopy; UV-Vis: UV-visible spectroscopy; XEDS: x-ray elemental mapping; XRD: x-ray diffraction.

Crocus sativus L. (dried stigmas, saffron), a spice of the Iridaceae family, has extensively been used in folk and modern medicines. The major active components of saffron are safranal, crocetin, crocin, and picrocrocin [54–56]. The discrete quasispherical Cu- and N-doped carbon dots <10 nm from C. sativus notably decreased cell viability of HCT-116 and HT-29 in a dose- and time-dependent manner at an IC₅₀ in the range of 0.52–0.54 mg/ml. Apoptosis was increased in association with upregulation of apoptotic genes (p < 0.05) [41]. Uniform, stable, and spherical gold crocin NPs of 4–10 nm synthesized also effectively (p < 0.05) reduced human breast cancer cell growth in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) and lactate dehydrogenase assays and conjugated saffron to PEG/SeNPs that exhibited pH-dependent release of crocin with improved cytotoxic effect towards lung cancer cells through apoptosis induction in vivo [57]. Apoptosis induced by crocin-conjugated PEG-SeNPs in treated A549 cells was confirmed by Western blot analysis of apoptotic-related gene expressions. The decreased expression of Bcl-2 and increased expression of Bax, cytosolic caspases-3, and cytochrome c were detected after treatment with crocin-conjugated PEG-SeNPs. Similarly, encapsulated doxorubicin and saffron with chitosan-laponite RD-NPs efficiently (83 and 60%) and found that the NPs released the drug notably controllable and pH-responsive. The NPs were highly biocompatible and cytotoxic to MDA-MB-231 cells [58].

Matricaria chamomilla (chamomile), a roadside perennial plant of the Compositae family, is used as a traditional sedative [59]. Lately, the toxicity effect of Ag-NPs with chamomile extracts on MCF-7, HeLa, and A549 cancer cell lines through MTT assay has been investigated. The synthesized NPs were as small as 19 nm and exhibited a notable (50%) inhibitory effect on selected cell lines at 50 μg/ml concentration. Such therapeutic effect is associated with the coating of secondary metabolites and their controlled release along with silver ions. Moringa oleifera, a plant of the family Moringaceae, is used to cure cardiovascular diseases. Its extract is rich in quercetin, phenols, caffeoylquinic acid, kaempferol, and β-sitosterol and can modulate immunity and regulate blood cholesterol and sugar [60]. Surprisingly, M. oleifera extract inhibits the proliferation of human alveolar and pancreatic cancer cells [44]. Researchers synthesized stable spherical and pentagon Ag-NPs of <40 nm using M. oleifera stem bark and found that the viability of HeLa cells in contact with these NPs was significantly reduced (94% apoptosis) with characteristic membrane blebbing. Recently, in support of a previous study, researchers discovered that among ZnO/Ag-NPs synthesized with M. oleifera, Mentha piperita, and Citrus lemon (119 ± 36 nm), M. oleifera was an excellent reducing agent of NPs, with notable anticancer effect against HeLa cells with 60% cell viability at 2.5 μg/ml concentration. The findings showed that ZnO/Ag-NPs are stronger anticancer agents compared to Ag-NPs or ZnO-NPs alone.

The cytotoxic effect of CuO-NPs from the leaves of Azadirachta indica and Rosa sinensis has been shown to be due to the presence of phenols, flavonoids, carbohydrates, glycosides, amino acids, and proteins. Characterization techniques revealed the presence of biomolecules, elements, and formation of stable NPs and the toxicity effect of NPs against MCF-7, A549, HeLa, and Hep-2 cells was highly significant. These findings showed that green chemistry is far more effective than the chemical method of NPs synthesis [61]. The cytotoxic effect of NPs (Ag, CuO, ZnO, iron oxide Fe₂O₃, and La₂O₃) synthesized using aqueous leaf extract of M. oleifera on (HepG2, A549, breast-T47D, and fibroblast-Wi38) cell lines was also investigated. The cytotoxic effect of NPs was dose- and time-dependent and potent against A549 and T47D cell lines with IC₅₀ (26–115 and 38–210 μg/ml), respectively [45].

Peganum harmala, a perennial and glabrous salt-tolerant herb of the family Zygophillaceae (Nitrariaceae), commonly known as Harmal is a small wild shrub that grows in sandy soil. Its seeds contain alkaloids – chiefly, harmine, β-carboline, and quinazoline. The efficacy of H/p-SC6 (harmine/p-sulfonato-calix[n]arenes (p-SC4 and p-SC6) nanocapsules toxicity against MCF-7 and ovarian cancer (SKOV-3) cells has been investigated. The average size of 264.77 ± 10.56 nm in the range of 200–600 nm was ideal for drug carriers with enhanced passive accumulation into the permeable vasculature of tumor cells. The NPs with high negative surface charge and spherical shape were stable and amphiphilic, suitable for encapsulation of water-insoluble harmala alkaloids supporting constant drug release at pH 7.4. The H/p-SC6 nanocapsules were remarkably toxic to MCF-7 and SKOV-3 in vitro with high biocompatibility and bioavailability [62].

In another experiment, the bioreduction of metals into platinum (Pt)–palladium/(Pd) and Pt/Pd NPs containing P. harmala seed extract, their spherical shape, average ideal size, and stability were confirmed by the characterization methods listed in Table 1. Pt/Pd-NPs demonstrated notable cytotoxic effects on MCF-7 and A549 cells, related to the synergistic influence of both metals [63]. The cytotoxic potential of PLGA polymers containing Brassica napus extract and smoke extract of P. harmala on MCF-7 only and human cancer cell lines (MCF-7, A549, A2780, PC3, HT-29, HepG2, and MDA-MB-231), respectively, was evaluated. NPs were 71.07 and 216.33 nm, and they restricted growth of all cancer cell lines with IC₅₀ 170.94 μg/ml and 208.62–3467.5 μg/ml, respectively, through early necroptosis, late apoptosis, upregulation of caspase 3, p53, and TNF-α genes, the effects that relate to the biocompatibility of NPs. Mitochondrial targeting P. harmala harmine-loaded liposomes containing a peptide carrying legumain-recognition site (Ala-Ala-Asn) and folic acid nanographene-harmine particles of ideal sizes also exhibited controlled drug release and remarkable toxicity to hepatocellular carcinoma (SK-Hep-1) and MCF-7 cells in vitro and in vivo by approximately 67 and 60%, respectively, with outstanding biocompatibility [64].

P. harmala extract dual loaded on (harmine-tannic acid polyamidoamine (PAMAM)-OH) dendrimers of generations (3, 4, and 5) against breast cancer cells were synthesized [65]. G3 dendrimers were the smallest and most stable at pH 7.4 (192 ± 1.9 nm) and exhibited high encapsulation efficiencies and targeted drug-release ability at pH 5.5. The NPs were notably toxic to MCF-7 cells at IC₅₀ 1.7 ± 0.6 μg/ml compared with free drugs and induced a high percentage of apoptosis in cancer cells. Folic acid/chitosan-coated PLGA-NPs (276.16 nm, ζ-potential +32.31 mV) loaded with smoke extract of P. harmala reduced cell viability and induced apoptosis in MCF-7 cells at IC₅₀ 75.65 μg/ml through upregulation of caspase 3, 9, p53 genes, and ROS generation [66].

Nigella sativa, black cumin from the Ranunculaceae family, is a rich source of phytochemicals specifically quinines, due to which it exerts antioxidant, analgesic, antibacterial, and anticancer effects [67]. Recently, stable cubic ~30 nm PdPt NPs were synthesized, and their anticancer potential on MDA-MB-231, Ishikawa, and HeLa cell lines were evaluated as increasing with increasing concentration of NPs and calculated IC₅₀ in the range 9.1744 ± 1.566 to 18.1963 ± 1.730 μg/ml [49].

Bruceae fructus fruit has been used for the treatment of inflammation, malaria, dysentery, and cancer in Chinese medicine [68]. Natural alkaloids are poorly soluble but have higher bioavailability and absorption than chemical drugs for cancer therapy. B. fructus oil emulsive nanostructures as antitumor agents carrying evodiamine with the same effect were fabricated and increased lung cancer cells' sensitivity to alkaloids. Sesbania grandiflora (Linn) from the Fabaceae family has been widely used as an antibacterial, anti-inflammatory, analgesic, and antitumor agent. Ag-NPs from its leaf extract as a reducing agent were characterized as stable and spherical (22 nm) and showed toxic effects against MCF-7 cell lines through disruption of cell membrane integrity, ROS generation, and apoptosis [69].

Houttuynia cordata, an herb of the family Saururaceae grows in moist areas and is used as food and medicine. CuO-NPs synthesized from H. cordata (40 nm) were toxic (50%- IC₅₀ of 5 mg/ml) to HeLa cells, contributing to ROS generation, increase in apoptotic gene (Bax, Bad) expression (p ≤ 0.05), and suppression of cell cycle regulatory proteins PI3K/AKT/m-TOR expression [70]. Ocimum sanctum (tulsi), a member of the Lamiaceae family, is known as the ‘Queen of Herbs’ and holds marvelous medicinal potential in Ayurveda, Greek, Unani, and Roman medicine systems. Au-NPs using its leaf extract were spherical in shape (200 nm) and stabilized by biomolecules of O. sanctum. Dalton's lymphoma cell viability and nuclear morphology were altered and apoptosis was induced at IC₅₀ <50 ng/ml of NPs. Quercetin-conjugated Ni-NPs and PEG-Ni-NPs from leaf extract of O. sanctum showed anti-MCF-7 activity at IC₅₀ of 6.25 μg/ml and contributed to ROS production with mitochondrial membrane potential loss, active caspases 7 and 9, and apoptosis with hexagonal irregular NPs sized 27.3–40.4 nm [71].

Camellia sinensis (tea), the popular world beverage, is used to reduce blood pressure, oxidative damage, and cure cancer. Polyphenols as the main active constituents of tea regulate the cell cycle, induce apoptosis, and control invasion and metastasis [72]. It was also found that Cu₂O-NPs with C. sinensis leaf extract had a high cell death effect on ovarian cancer cell lines SKOV-3, Caov-3, and SW-626. Spherical, crystallite Ag-NPs and graphene oxide/Ag-NPs sized 35–42 nm of C. sinensis leaf extract also reduced cell viability of MCF-7 cells in vitro. Similarly, spherical ZnO-NPs sized 6–112 nm were highly active against HeLa cells but nontoxic to normal cells, confirming their biocompatibility – a characteristic ideal for anticancer application [50].

Taxus brevifolia and Taxus wallichiana are sources of Taxol (paclitaxel) with antimitotic activity against various cancers [73]. Ni-NPs (53 nm, hexagonal) synthesized by T. brevifolia leaf extract exhibited enhanced cytotoxic effect against MCF-7 cells and crystalline, cubic (29 nm) Ag-NPs showed toxicity against U251 brain cancer cells at 10 μg/ml [74].

Coffea (Rubiaceae), a beverage used worldwide, contains phenolics, coumaric acids, ferulic acids, caffeic acids, and alkaloids (caffeine) as its active constituents. It was encapsulated with biopolymeric nanoparticulate (PLGA-NPs) [19]. The stable particles (318.60 ± 5.65 nm) with encapsulation efficiency of 85.92 ± 4.01% showed greater anticancer effect than free Coffea against cell lines HepG2 (84.84%), A-549 (78.17%), HeLa (85.84%), and MCF-7 (86.78%) and slow in vitro release at pH 5.5 and 7.4. Similarly, C. arabica Ag-NPs (20–70 nm) were toxic to brain cancer (A172) (significant p < 0.001), MCF-7, and embryonic kidney (Hek293) cell lines at CC₅₀ of 72.9, 116.8, and 437.2 μg/ml, respectively [51].

Centella asiatica, known as the ‘life elixir’, is a member of the family Apiaceae. The spherical Ag-NPs of C. asiatica (19.17 nm) exhibited anticancer, cytotoxicity, apoptosis induction, and upregulated caspase 3/9 expression in MCF-7 cells [75]. The C. asiatica magnesium oxide (MgO)-NPs inhibited the proliferation of PC3 cells at IC₅₀ 123.65 ± 4.82 μg/ml through a reduction in migration and mitochondrial transmembrane potential, ROS generation, cell cycle arrest at S-phase, and DNA damage. The plant extract acts as a reducing and stabilizing agent to produce stable and efficient NPs, as confirmed by previous study. Solanum nigrum, a black night shade, belongs to the family Solanaceae. It was recently reported that spherical Se-NPs (87 nm) were active against triple-negative breast cancer cells at 19 μg/ml IC₅₀ and ZnO-NPs destructed HeLa cells through β-catenin inhibition, DNA damage, and increasing caspase 3/9 and p53 expression exhibiting targeted drug delivery. According to the existing data across different Internet sources, various biological NPs, mostly metal NPs, have been leading the treatment of cancer through similar mechanisms that lead to mitochondrial dysfunction and apoptosis for the benefit of healthy tissues [76] (Figure 4).

Figure 4.

Reactions caused by biosynthesized nanoparticles in cancer cells.

NP: Nanoparticle; ROS: Reactive oxygen species.

Reproduced with permission from Sanati M, Afshari AR, Kesharwani P, et al. Recent trends in the application of nanoparticles in cancer therapy: the involvement of oxidative stress. J. Control. Rel. 2022;348:287–304. © 2022 Elsevier B.V.

6. Clinical trials

Similar to regular medicines, nanodrugs require approval and evidence for their safety, quality, and efficacy, and these processes are time-consuming, costly, and rigorous. Still, the successful application of nanomedicines significantly changes the course of diagnostics and treatment of life-threatening diseases such as cancer, but it is often restricted by the complexity of the design that averts their economic and large-scale production [77]. NPs have been excellent forms of anticancer drug delivery because they do not pass through normal capillaries and accumulate at higher concentrations in tumor tissues through their enhanced permeability and retention effect, resulting from leaky tumor linings with decreased lymphatic drainage. Targeting NPs to specific sites can be enhanced with the conjugation of specific molecular tags to the particle's surface. Many clinical and preclinical studies have demonstrated that nanoformulated drugs can enhance tumor accumulation and decrease normal tissue exposure to drugs; unfortunately, not many basic and preclinical studies have been successful for application in clinical practice [78].

Recently, the effective production and introduction of various novel nanoformulated products into clinical trials, and even at commercial levels, have shown promising outcomes of fundamental research in clinics. According to a survey of available data, few nanoformulations have received approval for cancer treatment; ~16 anticancer nanodrugs are approved by the US FDA, whereas ~75 are in clinical trials, and five major anticancer nanodrugs are available on the market [78]. Table 2 provides a snapshot of selected anticancer-encapsulated drugs in NPs that have recently received regulatory approval and the current status of those undergoing different phases of clinical trials.

Table 2.

Clinical trials using nanocarriers for the treatment of different cancers.

Drug name	Indication	Nanoformulation	Status	ClinicalTrials.gov Identifier	Ref.
Nano-Ayurvedic medicine (Dnanostanna)	Breast cancer	Nano Swarna Bhasma gold NPs	Applicable (AYUSH, India)	Application no. 3623279	[79]
IMX-110 (Immix Biopharma)	Advanced solid tumors	Curcumin encapsulated doxorubicin	Approved (US FDA, phase I/II), Australia	NCT03382340	[80]
CRLX101 (UNC Lineberger Comprehensive Cancer Center)	Rectal cancer	Polymeric NPs of camptothecin	Phase I/II	NCT02010567	[81]
Lipocurc (SignPath Pharma)	Solid tumors	Liposomal curcumin	Phase I/II (Completed, Austria)	NCT02138955	[82]
VYXEOS CPX-351 (Jazz Pharmaceuticals)	Various leukemias	Liposomal formulation of cytarabine	Approved (US FDA, 2017), (EMA, 2018)	NCT03575325	[83]
NBTXR3 (Nanobiotix)	Adult squamous cell carcinoma	Hafnium oxide NPs stimulated with external radiation	Phase I (Completed)	NCT01433068	[84]
Onivyde MM-398 (Merrimack)	Pancreatic cancer	Nanoliposomal Irinotecan	Approved (US FDA, 2015)	NCT01494506	[85]
Marqibo (Talon Therapeutics)	Acute lymphoblastic leukemia	Vincristine sulfate liposome	Approved (US FDA, phase II)	NCT00495079	[86]
Paclitaxel (Abraxane)	Pancreatic cancer	Albumin-bound NPs	Approved (US FDA, 2013)	NCT01770795	[87]
Magnablate I (University College London)	Prostate cancer	Iron oxide NPs	Early phase I (Incomplete)	NCT02033447	[88]

AYUSH: Ayurveda, Yoga and Naturopathy, Unani, Siddha and Homoeopathy, Government of India; NP: Nanoparticle; NSCLC: Non-small-cell lung cancer; UNC: University of North Carolina.

7. Current challenges

The wide-ranging applications of NPs in therapeutics are a certainty for the future, but some challenges remain to be overcome for successful production and application of NPs in clinical practice. To date, most nanodrugs have been under examination by researchers for cancer therapy and a large number have been successfully tested against many cancer cell lines through preclinical experiments [89].

The main limitation of employing biogenic NPs for medical purposes is their toxicity. There is no typical method defined for the assessment of NPs toxicity. They may accumulate in the tissues over time and cause toxicity related to their time and dose exposure to the systems. At above-threshold limits, they may distort the cell membrane and DNA through oxidative damage and hinder the electron transport chain because they can enter cells and organelles [90]. Nonetheless, the exact mechanism of cell destruction by NPs has not yet been discovered due to the limited availability of data on their biological activity. Improving the technology for the synthesis and commercialization of anticancer NPs also plays an important role and remains a challenge to overcome. The green synthesis of NPs is also slower than chemical synthesis, and due to the presence of various phytoconstituents in plant extracts, it is difficult to isolate the exact biologically active compound responsible for the effectiveness of NPs. If large-scale biosynthesis of NPs is conducted, an ecological imbalance may occur due to the overemployment of different natural species, and microbial toxins may be present in natural sources used for biosynthesis. Another challenge of NPs biosynthesis is to determine the ideal size, shape, and monodispersed NPs because these features influence their effectiveness [91].

8. Future perspective

To ensure the safe and guaranteed future of anticancer plant NPs, the adjustment of parameters during the synthesis of NPs is of utmost importance. There is a need for proper regulatory methods when NPs are used for medical applications. Currently, researchers are highly focused on using biopolymeric NPs for biomedical applications with improved efficiency and reduced toxicity. To overcome the limitations and for successful synthesis and application of NPs in preclinical and clinical trials, they must be biocompatible, nontoxic, and free from side effects. The co-delivery of nanoformulated combinative drugs with NPs can improve treatment efficacy synergistically, manage drug resistance, and provisionally control the drug release at the tumor site. Such treatment is likely to solve problems of drug toxicity and dose control by using the simultaneous advantages of existing NPs and combination therapy. Plant extracts greatly affect the shape and size of NPs. Using different plant extracts and proper methodology for the biosynthesis of NPs is important to optimize and standardize the synthesis protocol to produce NPs with appropriate shape, size, and surface characteristics. Researchers have used different extraction methods and precursor concentrations as stabilizing agents to obtain ideal NPs for medical use, especially cancer therapy [92]. In the future, research groups may focus on the synthesis of different types of plant NPs to be used safely and thus develop the application to more cancerous conditions. The outcomes of this review enlighten future research directions in the green synthesis of nanostructures and their development in biomedical aspects [13].

9. Conclusion

Medicinal plants are rich sources of natural compounds for the development of novel nontoxic and effective anticancer drugs. Nanotechnology is an effective means for the production of safe and targeted drug delivery and uses physical, chemical, and biological approaches in NP synthesis. Green synthesis has been proved to be the most effective, efficient, ecofriendly, cost-effective, and nontoxic method to prepare NPs from natural sources. Plant bioactive compounds with anti-inflammatory, antioxidant, and cytotoxic capabilities have shown unlimited antitumor and antiproliferative effects on different types of cancers in vitro and in vivo. The development of nanostructures using phytochemicals has reached a high level, and many experiments have been conducted to take advantage of the great power of nature against cancer by its ability to interfere with many cellular signaling pathways.

Various types of plant-based nanoformulations have shown enhanced anticancer therapy through the generation of ROS, inhibition of cell proliferation, DNA damage, activation of caspases, and upregulation of apoptotic and antitumor genes. Biosynthesized NPs also target the PI3K/Akt/mTOR pathway, disrupt cell membrane integrity, and inhibit efflux transport in tumor cells. The improved anticancer activity of nanofabrications due to their nanosize, increased biocompatibility, accurate delivery, and enhanced permeation and retention effect in cancer tissues make them successful substitutes for conventional anticancer approaches. These therapeutic NPs with phytoconstituents can be combined to explore novel anticancer agents with different anticancer effects. In summary, this review provides new insights into enzyme, organelle, and gene responsive therapy, leading to cell death in the future of cancer treatment.

Author contributions

SS Bokhari: conceptualization, validation, writing – original draft. T Ali: conceptualization, validation, data curation, project administration, writing – review & editing. M Naeem: validation, data curation, writing – review & editing. F Hussain: validation, project administration, supervision A Nasir: validation, visualization, writing – review & editing.

Financial disclosure

The authors have no financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Competing interests disclosure

The authors have no competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Writing disclosure

No writing assistance was utilized in the production of this manuscript.