Multifunctional Nanocarriers-Mediated Synergistic Combination of Immune Checkpoint Inhibitor Cancer Immunotherapy and Interventional Oncology Therapy

Abstract

Immune checkpoint inhibitor (ICI) cancer immunotherapies are becoming one of the standard therapies for cancer patients. However, ICI cancer immunotherapy’s overall response rate is still moderate and even combinational ICI cancer immunotherapies are not showing significant improvement in therapeutic outcomes. Only a subset of patients responds to the therapy due to the resistance and ignorance to the ICI cancer immunotherapy. Following immune-related adverse events (irAEs) are also limiting the whole therapeutic regimens. New approaches that can increase the immunotherapeutic efficacy and reduce systemic irAEs are required. Recently, multifunctional nanocarriers, which can extend the half-life of ICIs and modulate tumor microenvironment (TME), have shown a substantial opportunity to enhance ICI cancer immunotherapies. Interventional oncology (IO) allowing simultaneous diagnosis, immunogenic loco-regional therapeutic delivery, and real-time monitoring of the treatment efficacy have advanced to demonstrate the effective conversion of TME. The use of multifunctional nanocarriers with the IO therapies amplify the image guidance capability and immunogenic therapeutic localization for the potential combinational ICI cancer immunotherapy. This article will discuss the emerging opportunity of multifunctional nanocarriers mediated synergistic combination of ICI cancer immunotherapy and IO local therapy.

Graphical Abstract

This review gives an overview of the current and future application of multifunctional nanocarriers mediated synergistic combination of interventional oncology (IO) therapy and immune checkpoint inhibitor (ICI) cancer immunotherapy. Immune suppressive tumor microenvironment (TME) and systemic irAEs of ICI cancer immunotherapy are the main hurdles. Local delivery of ICI immunotherapy using nanocarriers endows the increase of overall therapeutic outcomes with minimized irAEs. Recent development of nanocarriers also allows highly localized immunogenic IO therapeutics that change the TME. Multifunctional nanocarriers mediated combinational IO and ICI cancer immunotherapy should be a promising option for the effective clinical ICI cancer immunotherapy.

1. Introduction

Accumulating tumor mutational burden (TMB) facilitate tumor development. The host immune surveillance possibly recognizes the genetic and epigenetic changes of TMB with the detection of unique tumor-associated antigens (TAAs) for the tumor immunization.^[1] However, cancer cells manage to escape the immune surveillance and break down the “cancer-immunity cycle” to resist.^[2] Neoplastic tumors in the immune surveillance develop multiple defensive mechanisms, including immune checkpoint (IC) expression, immune-suppressive cytokines, and immune-modulatory cell production.^[3] Cancer immunotherapy is activating the pooled patients’ immune system to kill cancer cells. It has emerged as a powerful strategy to treat cancers.^[4] Recent progress in understanding the cancer-immunity and immune-modulating molecules has initiated a broad range of pre-clinical research and clinical trials of cancer immunotherapy. Immune checkpoint inhibitors (ICI) cancer immunotherapy among approximately two-thousands of immunotherapeutic agents^[5] has received more considerable and broad interest because of as-demonstrated significant overall survival improvement in several randomized trials.^[6] Since cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) blocking ipilimumab ICI was firstly approved by the US Food and Drug Administration (FDA) for metastatic melanoma treatment in 2011, other types of ICI received the FDA approval for the treatment of various types of cancer. Recent promising advancement of ICI cancer immunotherapy and underlying research on immuno-oncology successfully promoted the 2018 Nobel Prize in Medicine.^[6] Further development of ICI cancer immunotherapy with careful consideration of immunotherapy’s efficiency and safety is urgently needed to control the historic cancer pandemic.

2. Immune checkpoint inhibitor cancer immunotherapy

Sophisticate harmonization of a variety of immune cells and microenvironment execute immune regulation and activation.^[7] ICs that work for co-stimulatory and co-inhibitory molecules are the central modulators in maintaining immune balance.^[8] During tumor progression, cancer cells overexpresses the ICs to decrease antitumor T cell proliferation and activation, TAA presentation, inflammatory mediator release to develop the immune-suppressive tumor microenvironment (TME).^[9] Consequently, the infiltration of tumor favorable immune suppressor cells, including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) is gradually increased within the TME to avoid the immune surveillance and promote the tumor growth.^[10] Thus, ICI cancer immunotherapy targeting the ICs such as indoleamine 2,3-dioxygenase-1 (IDO1), lymphocyte-activation gene 3 (LAG 3), CTLA-4, programmed death-ligand 1 (PD-L1), and programmed cell death protein 1 (PD-1) should be an effective approach to remove the defense system of cancer cells.^[9]

Recent advance of immunotherapy proves that the blockage of ICs efficiently enhances and recovers T cell-mediated adaptive immune responses. When ICIs disrupt the expressed ICs in TME, suppressed immune cells are unleashed to eliminate tumor cells.^[11] Immune suppressive TME frequently shows PD-1 expression on activated T cells and infiltration of PD-L1 expressed Tregs and MDSCs.^[12] The immunoglobulin superfamily PD-1 is a specialized immunomodulatory transmembrane receptor that is specifically bound to its ligand PD-L1. PD-1/PD-L1 axis interaction reduces the proliferation, cytotoxicity, and inflammatory cytokine release and induces the anergy of tumor specific T cells.^[13] Recently, PD-1/PD-L1 ICIs immunotherapy inhibiting the PD-1/PD-L1 axis binding demonstrated an improved long-term survival rate.^[14] The FDA has approved various types of PD-1/PD-L1 ICIs, including Pembrolizumab, Nivolumab, Durvalumab, Atezolizumab, Avelumab, and Cemiplimab for a broad range of cancers including non–small cell lung cancer (NSCLC), metastatic melanoma, head and neck squamous cell cancer (HNSCC), hepatocellular carcinoma (HCC), urothelial carcinoma, gastric cancer, and cervical cancer.^[15] The number of clinical trials using the FDA approved ICIs significantly increased every year between 2017 to 2020 (Figure 1a and 1b).^[16] 4,400 clinical trials based on PD-1/PD-L1 ICIs are on-going in 2020.

Figure 1. ICI cancer immunotherapy clinical trials from 2017 to 2020.

a. Number of clinical trials using ICI molecules in 2017 and 2020. b. Changes of total clinical trials of ICI cancer immunotherapy from 2017 to 2020. Reproduced with permission.^[16] 2020, Springer Nature.

3. Limitation of immune checkpoint inhibitor cancer immunotherapy

Despite the potential cure-like survival benefit of ICI cancer immunotherapy over the last decade, acquired resistance and ignorance against the ICIs, and immune related adverse effects (irAEs) resulted in small percentage of patients experienced a positive therapeutic response.^[17–19] The moderate therapeutic response rate hinders further application of ICI cancer immunotherapy. Considerable efforts are required to overcome the limitation and develop novel strategies to advance ICI cancer immunotherapy for treating cancers more effectively and safely.

3.1. Moderate response rate and combinational immune checkpoint inhibitor cancer immunotherapy

Moderate levels of progression-free and OS of ICI monotherapy in a large number of patients^[17] are mostly associated with the resistance or ignorance induced by intrinsic and extrinsic factors of immunologically “cold” TME (Figure 2).^[18] Intrinsic factors represent low TMB or other immune-suppressive TME, including poor TAA presentation. Extrinsic factors include low T cell infiltration, suppressive immune cells, and IC mediated T cell exhaustion.^{[18, 20]} The lack of TAA significantly impedes the tumoricidal effect of functional T cells, resulting in the failure of ICI cancer immunotherapy. On the other hand, a high level of tumor immunogenicity “hot’ TME is positively correlated with the activity of T cells to recognize TAA expressing cancer cells, which is essential for the effective tumor regression (Figure 2). The other fundamental components in ICI cancer immunotherapy is the expression level of IC.^{[21, 22]} Kowanetz et al. reported an importance of PD-L1 expression on tumor cells that during the atezolizumab (aPD-L1) ICI immunotherapy. High PD-L1 expression on tumor cells alone reported 40% of objective response rate (ORR) in patients whereas high PD-L1 expression on immune cells alone reported 22%.^[23] This result shows the functional importance of PD-L1 expression level in regulating the PD-1/PD-L1 axis dependent T cell response. Thus, the PD-L1 expression of tumor cells from biopsy samples is usually tested to predict the immunological response and therapeutic outcome.^[21]

Figure 2. TME change and ICI cancer immunotherapy.

Therapeutic outcome of ICI cancer immunotherapy is dependent on the immunological status of TME. Immunologically “cold” TME induces the resistance or ignorance of ICI cancer therapy. Low TMB, poor TAA presentation, low immune cell infiltration, unfavorable anti-inflammatory cytokines, and low IC expression represent “cold” TME. However, “hot” tumor with high TMB expresses TAAs, which induce immune cell infiltration. Concurrent overexpression of pro-inflammatory cytokines develops the tumor specific immune responses with increased T cell accumulation in tumor. Then, tumors overexpresses ICs to attenuate the immune response, as a survival signal. ICI cancer immunotherapy in “hot” tumor facilitates the anti-cancer immune responses.

To enhance the ICI cancer immuno-therapeutic response rate, additional procedures that can induce “hot” TME are frequently combined with the ICI cancer immunotherapy.^[24] A phase I clinical study reported that 85% of patients treated with the proinflammatory cytokine IFN-γ, which alters the “cold” TME to “hot” TME, showed the increased T cell infiltration to a solid tumor in serum (Figure 2).^[25] Importantly, patients expressing low PD-L1 (less than 5%) showed a significant increase of PD-L1 (40%) after the IFN-γ treatment and the response efficacy of anti-PD-L1 antibody (aPD-L1) ICI cancer immunotherapy was enhanced. This clinical trial proves that modulating “cold” TME for “hot” is critical for the response to ICI cancer immunotherapy (Figure 2). Thus, multiple combinational approaches to build up “hot” TME to enhance the ORR of ICI cancer immunotherapy have been extensively studied along with various immunogenic cancer therapies.^{[24, 26]} In 2017–2020, over 2,900 clinical trials related with combination PD-1/PD-L1 ICI cancer immunotherapy with immunogenic therapies were conducted (Figure 3a). Newly launched 724 clinical trials in 2020 are including the combination PD-1/PD-L1 ICI cancer immunotherapy with immunogenic chemotherapy, VEGF/R, radiotherapy, oncolytic virus, targeted therapy, and other immunotherapies (Figure. 3b). The ratio and number of combination ICI cancer immunotherapy in 2020 (53%, 1694 trials) was significantly increased compared to that of 2017 (43%, 494 trials) (Figure. 3c).

Figure 3. Increase of clinical trials of combination PD-1/PD-L1 cancer immunotherapy in 2020 and 2017.

a. Number of clinical trials of combination PD-1/PD-L1 cancer immunotherapy with other therapies in 2017 and 2020. b. Newly launched clinical trials of combination PD-1/PD-L1 cancer immunotherapy with other therapies (724 trials) starting in the year of 2020. c. Ratio of clinical trials of mono PD-1/PD-L1 cancer immunotherapy and combination PD-1/PD-L1 cancer immunotherapy in 2017 and 2020, respectively. Reproduced with permission.^[16] 2020, Springer Nature.

3.2. Immune-related adverse events

Although ICI cancer immunotherapy changes the paradigm of cancer treatment, excessive systemic immune responses followed by ICI cancer immunotherapy have been noticed as a form of irAEs.^[27] The therapeutic IC blockade results in a disruption of the immune balance. The unbalanced immune tolerance and immunity can trigger an innate immune response leading to the over-activation of self-reactive immune cells, which can manifest as irAEs.^[28] The irAEs are accompanied by pneumonitis, colitis, hepatitis, myocarditis.^[29] Symptoms of irAEs are mostly handled by steroid-based immunosuppressive treatment. However, those concurrent use of immunosuppressive therapy is inevitably associated with reduced efficacy of ICI immunotherapy. It is one of the main limitation of ICI cancer immunotherapy as witnessed increasing incident rate and mortality of irAEs.^[30]

Based on the global meta-analysis, CTLA-4 ICI cancer immunotherapy (Ipilimumab) showed the most extensive irAEs data. 80 to 90% of patient treated with ipilimumab showed any-grade of irAEs. 35% of patient were eventually treated with immunosuppressive therapy with glucocorticoids. Although PD-1/PD-L1 ICI cancer immunotherapy showed relatively less irAEs compared CTLA-4, 26% of patient treated with PD-1 ICIs (Nivolumab, Pembrolizumab, and Cemiplimab), and 14% of patient treated with PD-L1 ICIs (Atezolizumab, Avelumab, and Durvalumab) experienced irAEs (Table 1) and received immunosuppressive therapy for the management of irAEs.^[31] Recent studies have shown that the combination use of ICIs also led to severe irAEs.^{[32, 33]} The incidence of total irAEs was 96%, and severe irAEs with grade 3/4 were observed in 44 to 59% of patient during the combinational Nivolumab-plus-Ipilimumab treatment group (Table 1).^[34] 22% of patients discontinued the immunotherapy because of the severe irAEs. Once irAEs is happened with systemic over-immune reaction, discontinued ICI cancer immunotherapies could not be resumed with the immunological memory response.^[35] Indeed, intensive investigation of minimizing irAEs is required to improve the therapeutic response of ICI cancer immunotherapy.

Table 1. irAEs after ICI monotherapy and combination ICI cancer immunotherapy.

Excessive development of immune response of ICI cancer immunotherapy induces the off-target toxicity to the healthy tissues and cells.^[50] Severity and diversity of irAEs are different from the mechanism of ICIs.

irAEs compared to monotherapy with combination therapy
Targets	Treatments	Cancer type	Dose	Any grade	Grade 3/4	Discontinuation
CTLA-4	Ipilimumab[36]	Melanoma	10 mg/kg p3w	90.4%	41.6%	53.3%
	Ipilimumab[37]	Melanoma	3 mg/kg p3w	80.2%	22.9%	-
PD-1	Nivolumab[38]	Melanoma	3 mg/kg p2w	93.2%	34.0%	5.8%
	Pembrolizumab[39]	Melanoma	200 mg p3w	93.3%	31.6%	13.8%
PD-L1	Avelumab[40]	NSCLC	10 mg/kg p2w	65.9%	6.8%	9.1%
	Atezolizumab[41]	NSCLC	1200 mg p3w	64.0%	15.0%	8.0%
	Durvalumab[42]	NSCLC	10 mg/kg p2w	57.7%	9.5%	2.2%
CTLA-4 & PD-1	Ipilimumab + Nivolumab[32]	Melanoma	3 mg/kg Ipilimumab p3w, 1 mg/kg Nivolumab p3w	96.0%	59.0%	39.3%
	Ipilimumab + Pembrolizumab[43]	NSCLC	2mg/kg Pembrolizumab p3w, 1 mg/kg Ipilimumab p3w	64.0%	29.0%	22.2%
PD-1 & NK	Pembrolizumab + NK cells[44]	NSCLC	10 mg/kg Pembrolizumab p3w, 109 NK cells p3w	60.0%	10.0%	1.8%
PD-1 & Thermal ablation	Pembrolizumab + Thermal ablation[45]	HCC	3 mg/kg Pembrolizumab p3w	82.0%	14.0%	8.0%
PD-1 & kinase	Nivolumab + Deucravacitinib[46]	Solid tumor	240 mg of Deucravacitinib p4w, 240 mg of Nivolumab p4w	65.8%	9.4%	1.5%
	Pembrolizumab + Acalabrutinib[47]	metastatic urothelial cancer	200 mg Pembrolizumab p3w, 100 mg Acalbrutinib(oral) twice a day	47.5%	20.0%	40.0%
PD-L1 & kinase	Durvalumab + Trametinib[48]	Melanoma	10 mg/kg Durvalumab p2w, 2 mg Trametinib (oral) per day	85.0%	40.0%	-
	Durvalumab + Darafenib + Trametinib[48]	Melanoma	10 mg/kg Durvalumab p2w, 150 mg Darafenib (oral) per day, 2 mg Trametinib (oral) per day	100.0%	17.0%	-
PD-L1 & EGFR	Durvalumab + Osimertinib[49]	EGFR-mutant lung cancer	10 mg/kg Durvalumab p2w, 80 mg Osimertinib (oral) per day	100.0%	38.5%	39.0%

Abbreviations: CTLA-4, cytotoxic T-lymphocyte-associated protein 4;PD-1, programmed death protein 1; PD-L1, programmed death-ligand 1; NSCLC, non–small cell lung cancer; HCC, hepatocellular carcinoma; irAE, immune-related adverse event; p2w, per 2 weeks; p3w, per 3 weeks; p4w, per 4 weeks.

4. Advanced approaches for immune checkpoint inhibitor cancer immunotherapy

Recent advances of multifunctional nanocarriers and interventional oncology (IO) therapy for the ICI cancer immunotherapy allow the improved therapeutic efficacy of ICI cancer immunotherapy.^[51–53]

4.1. Multifunctional nanocarriers for immune checkpoint inhibitor cancer immunotherapy

Nanocarriers have demonstrated excellence in improving the pharmacokinetics of various therapeutic agents in cancer therapy. Over the last decades, 45 nanocarriers and nano-formulations have been approved by the FDA, and over 80 clinical trials are being investigated for clinical trials.^{[54, 55]} As increasing demands for local ICI cancer immunotherapy, nanocarriers incorporating ICI molecules have intensively tested to improve ICI cancer immunotherapy’s therapeutic efficacy. Many investigations have provided a clear perception of the nanocarriers-mediated ICI local delivery and sustained release to the local tumors. The current therapeutic interval of systemic ICI cancer immunotherapy is usually 2 to 3 weeks.^[56] Within this period, most systemically administered ICIs are attenuated or excluded by biological clearance resulting in multiple injections and systemic irAEs.^[57] The maintaining therapeutic dose of ICI in the targeted region is essential for long-lasting cancer immunization. A multifunctional nanocarrier system might be a key technology to address the above issues by offering targeted delivery of ICI cancer immunotherapy. Recent progress of organic, inorganic and hybrid nanocarriers for the ICI cancer immunotherapies is summarized below.

4.1.1. Inorganic nanocarriers

Various physical functionality of nanoscale inorganic materials would endow the potential for the multifunctional nanocarrier that can perform ICIs local delivery and additional imaging or immunogenic therapeutics. Well-established inorganic nanocarriers are considered to circumvent systemic inflammatory responses and overstimulation of self-reactive T cells caused by the systematic circulation of ICIs. Luo and their colleagues suggested an insightful study of local delivery ICI for the combinational ICI immunotherapy. Suggested anti-PD-1 peptide (APP) and hollow gold nanoshell (HAuNS) bearing poly(lactic-co-glycolic acid) (PLGA) nanoparticles (AA@PN) enhanced the near infrared laser (NIR) mediated photothermal ablation of malignant tumors and the destruction of PLGA nanoparticles by plasmon absorption of HAuNS (Figure 4a(i)). Released free APP inhibited the suppressive tumor immunity and induced tumor infiltration of functional cytotoxic T lymphocytes (CTLs) with increased abscopal effect (Figure 4a(ii)).^[58] Liu et al. synthesized the biodegradable indocyanine green (ICG) and PD-L1 specific siRNA loaded CaCO₃/MnO₂ nanoplatform (Mn@CaCO₃/ICG@siRNA) to improve the efficiency of combination ICI cancer immunotherapy. After systemic administration, enhanced permeation and retention (EPR) mediated tumor accumulation stimulated the turnover of tumor hypoxia to normoxia. Application of local PDT enhanced the tumor killing and the PDT triggered siRNA release assisted the tumor immunization. As a result, combinational PDT and ICI immunotherapy increased the dendritic cell (DC) maturation and CTL accumulation to tumor by Mn@CaCO₃/ICG@siRNA.^[59] Banstola et al also published an interesting research related to local combination of chemo-photothermal therapy and ICI cancer immunotherapy to overcome the resistance and ignorance of immunotherapy. They synthesized aPD-L1 and doxorubicin (DOX) loaded hollow gold nanoshell (T-HGNS-DOX). After intratumoral injection, NIR laser was applied to induce hyperthermia and simultaneous DOX and aPD-L1 release was demonstrated near TME. Synergized with aPD-L1 ICI cancer immunotherapy with chemo-hyperthermia, significant tumor apoptosis was observed along with downregulation of proliferation and angiogenesis of TME.^[60]

Figure 4. Nanocarriers for ICI cancer immunotherapy.

a. i) WSP NPs were synthesized to increase the RT and PTT efficiency. Nanoparticles mediated PTT induced ICD and increased the DC maturation, resulting in CTL accumulation within the tumor. ii) WSP NP sensitizer improved the tumor regression in both primary and distant tumors with PTT/RT and aPD-L1 combination. Reproduced with permission.^[58] 2018, Elsevier. b. i) aPD-1 encapsulated CpG DNA nano-cocoon (DNC) achieved the combinational delivery of immune-adjuvant and ICI at local tumor after surgery. ii) Proinflammation after surgical tumor resection promoted TAA presentation and maturation of APCs by CpG component of DNC. Concurrently delivered aPD-1 enhanced adaptive immunity. iii) Synergistic combination of adjuvant/ICI nanocarrier suppressed the tumor recurrence with the powerful tumor immunization and activation of the adaptive immune responses in the local tumor area. Reproduced with permission.^[61] 2016, Wiley-VCH. c. i) Zeolitic imidazolate frameworks (ZIFs) were synthesized for the controlled delivery of Nivolumab. Cancer cell membrane was utilized to encapsulate the NV-ZIF (NV-ZIF_MCF) for tumor-specific affinity. ii) The pH responsive property of NV-ZIF_MCF allowed the tumor specific release of Nivolumab by low pH of tumor. iii) NV-ZIF_MCF was targeted to local tumor because of tumor homing and EPR effect for sustainable Nivolumab cancer immunotherapy. Reproduced with permission.^[67] 2021, American Association for the Advancement of Science.

4.1.2. Organic nanocarriers

PLGA, polyethylene glycol (PEG), lipid, protein, and cell membrane, such as biocompatible organic nanocarriers, also have been developed as an efficient delivery platform for the ICI delivery. aPD-1 encapsulated CpG DNA nano-cocoon (DNC) achieved the combinational delivery of immune-adjuvant and ICI at local tumor after surgery (Figure 4b (i)). Inflammatory processes following tumor resection promoted the survival mechanism of adjacent healthy cells, even residual cancer cells. CpG component of DNC induced TAA presentation and maturation of antigen presenting cells (APCs). Concurrently delivered aPD-1 blocked the immune-suppressive mechanism of TME for enhanced adaptive immunity (Figure 4b (ii)). This synergistic combination of adjuvant/ICI nanocarrier suppressed the tumor recurrence with the powerful tumor immunization and activation of the adaptive immune responses in the local tumor area (Figure 4b (iii)).^[61] Ishihara et al. utilized the extracellular matrix (ECM) binding nanotag, the placenta growth factor-2 (PlGF-2) to deliver the aCTLA-4 in the tumor. Cancer protects itself from the outer immune system by expression of ECM. They administered PlGF-2 tagged aCTLA-4 systemically, and the ICIs successfully accumulated to the tumor and sustained the tumor development. Cell membrane-derived nanocarriers such as platelets and hematopoietic stem cells (HSCs)-based nanocarriers also attracted interest in the delivery of ICIs to the tumors.^[62] A pioneer work reported by Gu Z group, engineered aPD-L1 decorated nanoparticles by utilizing platelet’s cell membranes to capture aPD-L1 on the surface of nanoparticles. Their follow-up works further utilized HSCs to load ICIs for cancer treatment. This nanocarrier construction modality takes advantages of HSCs and platelets’ properties, such as homing capability and the benefit for the local release of ICI molecules. The modulated pharmacokinetics of ICIs finally inhibited the growth and recurrence of tumors in mice. Researchers also designed a nanocarrier mediated codelivery of ICIs and costimulatory immunomodulators to overcome the resistance and limited ORR of mono ICI cancer immunotherapy. Wang et al. utilized PLGA nanocarrier to achieve the spatiotemporal codelivery of antagonistic antibodies (aPD-1) and agonistic antibodies (anti-OX40 antibody, aOX40). The nanocarrier mediated simultaneous delivery of aPD-1 and aOX40 exhibited a significant increase of IFN-γ production and IFN-γ producing T cells than a simple mixture of free aPD-1 and aOX40. A direct local ICI cancer immunotherapy using a biodegradable microneedle coupling with ICI-loaded nanocarrier was also developed for controlled delivery of aPD-1 toward melanoma.^[63] ICI was encapsulated by pH-sensitive dextran nanoparticles, and then it was integrated with biocompatible hyaluronic acid formed microneedle patch. The sustained release of ICIs over 3 days in vitro was confirmed with self-dissociated nanoparticles distributed inside the microneedle patch. In vivo test demonstrated that one microneedle patch enhanced the retention of ICIs in the tumor and finally induced robust immune responses against B16F10 mouse melanoma compared to free aPD-1. Another report in the same group tested the combination of aPD-1 and immunosuppressive enzyme IDO-1 inhibitor (IDOi) to treat melanoma through the microneedle-based transcutaneous delivery approach.^[64] The nanocomposite carriers demonstrated the sustained release and enhanced retention of ICIs in the TME resulting in enhanced anticancer therapeutic and minimized irAEs.

4.1.3. Hybrid nanocarriers

Nanoscale metal-organic frameworks (nMOFs) are hybrid porous materials composed of metal ions or clusters with organic bridging ligands. Porous structure of nMOFs exhibits extra high surface area that have a potential for stable loading of ICIs.^[65] Lu et al. suggested a 5,15-di(p-benzoato)porphyrin-hafnium (DBP-Hf) nMOF as a radiosensitizer and IDOi delivery nanocarrier. Secondary building units (SBUs) of Hf of DBP-Hf absorbed the X-ray energy and produced the ROS by the ionizing radiation treatment for radio-dynamic therapy of targeted tumor. In murine caner models, intratumorally injected IDOi loaded DBP-hf boosted the radiation damage upon low doses of X-ray irradiation. Simultaneously, co-loaded IDOi synergized the ICI cancer immunotherapy. Also, the regression of distal and recurrent tumors was observed because of the abscopal effect.^[66] Another outstanding research using hybrid nanocarriers was reported by Alsaiari et al. They synthesized zeolitic imidazolate frameworks (ZIFs) for the controlled delivery of Nivolumab. Sustained release of ICIs from NV-ZIF presented efficient T cell activation in HCC compared to free ICIs (Figure 4c(i)). To enhance the delivery efficiency, cancer cell membrane was utilized to encapsulate the NV-ZIF (NV-ZIF_MCF) for tumor-specific affinity during the systemic injection procedure. The pH responsive property of NV-ZIF_MCF allowed the tumor specific release of loaded Nivolumab by low pH of tumor (Figure 4c(ii)). In patient samples, this camouflaged nMOF showed the powerful CTL activation and proliferation with Treg accumulation within the TME. Therefore, NV-ZIF_MCF was delivered to local tumor because of homing effect of tumor and EPR for sustainable Nivolumab cancer immunotherapy (Figure 4c(iii)).^[67]

These studies utilizing multifunctional nanocarriers offer an effective strategy to combine ICI cancer immunotherapy with other immunogenic therapies in a localized manner. It is evident that nanocarrier mediated ICI cancer immunotherapy gives a potential for the enhanced ICI immunotherapies with increased therapeutic dose in the local tumor area. However, biological and technological barriers are still challenging, and the actual efficient delivery of ICI loaded nanocarriers to the target tumors are not guaranteed.^[68] The potential low tumor targeting/uptake efficiency of systemically applied nanocarriers are still one of the clinical translation concerns. Thus, many investigations still have provided a perception of nanocarriers to deliver ICIs locally to the targeted tissues, tumors, tumor- draining lymph node, and spleen to enhance therapeutic efficacy and minimize irAEs.^[69] Consequently, IO clinical practices that can deliver therapeutics and those nanocarriers to local tumors with image guidance have been intensively considered for the integration with ICI cancer immunotherapies and multifunctional nanocarriers in clinical and preclinical trials.^[69–71]

4.2. Interventional oncology for immune checkpoint inhibitor cancer immunotherapy

IO is a rapidly expanding field of clinical interventional radiology. IO constitutes a pioneering specialty in the field of minimally invasive and precision medicine, allowing simultaneous diagnosis, therapy, and real-time monitoring of treatment efficacy. IO catheter-based intra-arterial therapies delivering embolization/chemotherapies^{[72, 73]}, image-guided ablation therapies,^[74–76] and percutaneous interventions have been performed for the treatment of targeted tumors (Figure 5a). IO using the most cutting-edge imaging technologies and medical tools has been one of the promising options to selectively target and treat cancers in the management of cancer patients.^[77] Recent studies reveal that IO image-guided local therapies treat the primary tumor and lead to the shrinkage of untreated tumors elsewhere in the body as known as abscopal effect. The immune reaction and immunogenicity of the IO therapies are now in the great interest of the combination ICI cancer immunotherapy. Indeed, IO local therapies induce IC overexpression and antigen-presenting cells to be recognized by the dendritic cells, potentially leading to anti-cancer immune responses throughout the body. Preclinical and clinical data have confirmed the immunogenicity of IO local therapy for the combination with ICI cancer immunotherapies.

Figure 5.

a. Representative IO cancer therapies (TACE, TARE, RFA, IRE, cryoablation, HIFU, and etc.). Catheter-based intra-arterial therapies localize therapeutics (chemo-agents, embolization, radiation and so on) in the tumor region. Percutaneous tumor ablations are performed with MRI, CT, or ultrasound image guidance for the local ablation of tumor. b. IO cancer therapies induce ICD. ICD turnovers the “cold” TME to “hot” TME and supports the tumor specific ICI cancer immunotherapies by increased immune cell accumulation and pro-inflammatory cytokines.

4.2.1. Combination immune checkpoint inhibitor cancer immunotherapy and interventional oncology local therapy

Immunogenicity and immunogenic cell death (ICD) of IO local therapy hold great potential for the synergistic combination with ICI cancer immunotherapies. ICD induced by IO local therapies is commonly applied to the low immunogenic tumor for re-programming the immunogenicity of TME to a “hot” tumor. ICD refers to the cancer cell death accompanying the antitumor immune responses. ICD releases the TAAs, high mobility group protein 1 (HMGB1), and ATP to recruit the immune cells to the TME and expresses the surface calreticulin (CRT) as an “eat-me” signal. Subsequent accumulation of circulating phagocytic APCs synergizes with ICI cancer immunotherapy (Figure 5b).^[78] Therefore, various combinations of ICI cancer immunotherapy with immunogenic IO local cancer therapies are now on clinical trials to evaluate the OS and ORR compared to the mono ICI cancer immunotherapy.^[79–81]

Cryoablation, one of IO local therapies, is highly immunogenic with the secretion of IFN-γ and TNFα.^{[82, 83]} A combinational treatment of aCTLA-4 ICI cancer immunotherapy and cryoablation showed an increased survival rate and decreased size of secondary distal tumor in murine prostate cancer model.^[84] Clinical trials are ongoing to evaluate the benefits of combinational ICI cancer immunotherapy with cryoablation in HCC, biliary tract carcinoma, breast cancer, metastatic kidney cancer, metastatic melanoma, and metastatic colorectal cancer.(NCT02821754, NCT03457948, NCT02833233, NCT02626130, NCT03290677, and NCT01853618) Even though those clinical trials are mostly focused on safety, the combination of highly immunogenic IO cryoablation and ICI cancer immunotherapy is promising to show the synergistic combination therapeutic effect in metastatic tumors. Radiofrequency ablation (RFA) is another representative IO local ablation therapy that can be used for the combinational ICI cancer immunotherapy. RFA ablates local tumors or assists the tumor resection to prevent a recurrence.^[85] Recent reports show that RFA procedures induce TAA exposure, numerous T cell/DC infiltration to TME and IFN-γ secretion.^{[85, 86]} Combination of RFA and aPD-1 ICI cancer immunotherapy in murine HCC model demonstrated 25% of complete tumor regression and 63% of partial tumor regression.^[87] Because incompletely ablated tumors boost tumor malignancy, another preclinical study evaluated the feasibility of combinational aPD-1 ICI cancer immunotherapy to eliminate the RFA survived tumor cells.^[88] One of most recent IO local ablation therapy is irreversible electroporation (IRE) ablation therapy. IRE uses short high-voltage electric pulses to induce cell death through permanent membrane lysis or loss of homeostasis to kill tumor cells. Recent studies on immunocompetent rodent tumor models have shown a significantly improved ICD after an optimized IRE treatment.^[89] Thereby, IRE promotes the immune cell infiltration in tumor and prolongs tumor-specific immunological memory.^[90] In the clinical analysis of IRE treated pancreatic ductal adenocarcinoma, an intensive decrease of Treg population was observed after 24 hours of IRE treatment. Moreover, a decreased Treg population was correlated to the overall survival rates.^[91] Based on these clues, there is an increasing demand to combine the IRE and ICI cancer immunotherapy to achieve synergistic combination therapeutic outcomes. Recently, Zhao et al. proved that combination of IRE and aPD-1 immunotherapy could overcome the ICI resistance of murine PDAC tumor. Interestingly, IRE reserves vessels during the ablation and allows the functional CTLs infiltration to a tumor and APC maturation. These features provide more benefits for the combination IRE and ICI cancer immunotherapy.^[92] Duffy et al. also proved enhanced CTLs accumulation in the tumor after a synergistic combination of aCTLA-4 immunotherapy with various IO local therapy techniques, TACE, RFA, and cryoablation.^{[93, 94]} Now IO local therapies are one of the important partners for enhancing the therapeutic efficacy of emerging combination ICI cancer immunotherapy. However, current standard clinical approaches to combine IO local therapies with ICI cancer immunotherapy are based on the systemic administration of ICI molecules after IO therapies. Despite the enhanced therapeutic efficacy of the combination of ICI and IO cancer therapy, irAEs induced by the systemic ICI cancer immunotherapy still occurred frequently. Severe irAEs (grade 3 or 4) incidence is reported as high as 90% due to systemic ICIs immunotherapies following an IO local therapies.^[95] Local delivery of ICI during the image-guided local IO therapies will improve their efficiency while avoiding the side effects. Evaluation of the synergistic therapeutic effect and feasibility of combinational IO local therapy and local ICI delivery would be the next step for a new class of ICI cancer immunotherapy (NCT01853618).^[53]

4.3. Combination immune checkpoint inhibitor cancer immunotherapy and interventional oncology therapy using multifunctional nanocarriers

Multifunctional nanocarriers are the versatile tool that can achieve the synergistic combination image-guided immunogenic IO therapy and ICI cancer immunotherapy.^[51–53] Imaging contrast effect, delivery, and various therapeutic physical properties of nanocarriers provide unique features supporting the procedures and tumor localization of IO image-guided therapies. The modification of physicochemical properties of multifunctional nanocarriers also allows the local delivery of various single or multiple ICI molecules with the intensive ICI loading capacity.^[96–99] As proven the effectiveness of multifunctional nanocarriers on each nano-immunotherapy and nanoparticles-mediated IO local therapies, well-designed multifunctional nanocarriers would be an effective mediator that can enhance overall therapeutic outcomes of the combination IO local therapy and ICI cancer immunotherapy with minimizing irAEs. As a therapeutic catalyst, ICI loaded multifunctional nanocarrier induces even stronger ICD of IO local therapy to overcome immune suppressive TME, and simultaneous ICI local release synergizes the tumor specific immune responses. Subsequently, the educated circulating immune cells, including CTLs, effectively infiltrates to distal tumors for abscopal effect (Figure 6).

Figure 6. Concepts of nanocarrier mediated combination of ICI cancer immunotherapy and IO cancer therapy.

Nanocarrier medicated IO local cancer therapies facilitate enhanced local ICD resulting in intense and local “hot” immunogenic TME, which effectively unleash the suppressed tumor specific immune responses. Simultaneous nanocarrier mediated local ICI delivery synergizes to immunize the tumor with minimized irAEs. Educated CTLs circulate in the blood streams and infiltrate to other distal tumor for abscopal effect.

4.3.1. Inorganic multifunctional nanocarrier

In a recent study, an aPD-L1 decorated DOX loaded AuNP was developed for local combinational ICI cancer immunotherapy.^[100] The local delivery of aPD-L1 and DOX loaded AuNP with CT image guidance demonstrated a pronounced cancer cell death (66% apoptosis) in colorectal cancer CT-26 cells. Further combination with NIR irradiation and aPD-L1-AuNP-DOX treatment significantly and synergistically suppressed the in vitro proliferation of CT-26 cells by increasing apoptosis and cell cycle arrest. The study demonstrates that aPD-L1-AuNP-DOX combined with synergistic image-guided chemo-photothermal local ablation therapy has considerable potential for treating localized colorectal cancer. Another novel approach combining IO IRE ablation and ICIs immunotherapy using iron oxide nanocarriers was reported in 2020.^[101] A simple overlay of IO local ablation and ICI immunotherapies often results in poor therapeutic outcomes with unexpected immune tolerance. Careful design of synergistic combination of IO local therapy is strongly required for developing a robust combinational ICI cancer immunotherapy. This project developed IDOi ICI loaded iron-oxide-nanocube clusters (IDOi-IONCs) for the enhanced cancer cell killing and immunogenic TME modulation of IRE. A relatively new IRE in IO area has shown promising results to control local tumors. Researchers found MRI visible IONCs were responsive to the IRE electric pulses. IDOi-IONCs was highly responsive upon the IRE electric pulse application. The IRE responsiveness of IDOi-IONCs also allowed a triggered release of IDOi ICI (Figure 7a(i)). In vitro and in vivo studies confirmed significantly enhanced cancer cell-killing efficiency with IDOi-IONCs mediated IRE. Finally, the MR image-guided combinational IRE + IDOi-IONCs demonstrated a synergistic tumor regression with immunogenic conversion of immunosuppressive TME. The increase of infiltrated CD8+ T cells and the ratio of CD8+ T cells to Tregs were followed by the IRE with IDOi-IONCs. Importantly, synergistic combination IRE and IDOi-IONCs resulted in an enhanced elimination of both primary and secondary tumors (Figure 7a(ii)). Another study showed aPD-L1 loaded MRI visible ultra-large pore mesoporous nanoparticles (UPMSNPs) for a sequential local image guided chemo-immunotherapy.^[58] aPD-L1 was loaded into the large pores in the silica carriers, and MRI visible ferumoxytol iron oxide nanoparticles were used as a cap for the sustained local release of aPD-L1 (Figure 7b(i)). Localized chemotherapy induced the ICD by expression of CRT and the release of HMGB1 to manipulate immune favorable TME. The followed sustainable release of aPD-L1 from UPMSNPs led to strong cancer-specific immunization (Figure 7b(ii)). More recently, our group developed snowflake-like gold-silver alloy nanocarriers (S-AuNC) for a synergistic combination of radiation therapy (RT) and ICI cancer immunotherapy in the low immunogenic prostate cancer (PC) (Figure 7c(i)).^[102] CT contrast properties of aPD-L1 loaded S-AuNC allowed an image-guided intratumoral injection for high-efficient ICI local delivery. The radiosensitizing effect of S-AuNC increased the production of reactive oxygen species (ROS) in response to a single session of radiation, resulting in an enhanced ICD of local PC. Abundant ROS production dissolved the silver components from S-AuNC. Subsequently, aPD-L1 in the S-AuNC was released to immunogenic “hot” TME of PC resulting in an outstanding tumoricidal immune response (Figure 7c(ii)). S-AuNC mediated local delivery and release of aPD-L1 minimized the irAEs (Figure 7c(iii)). These studies utilizing multifunctional inorganic nanoparticles offer an effective strategy to combine ICI cancer immunotherapy with immunogenic IO local therapies. It is evident that well-designed inorganic nanocarriers give a potential for synergistic therapeutic efficacy of the combination of IO local therapy and ICI cancer immunotherapy with circumventing systemic inflammatory responses and overstimulation of self-reactive T cells caused by the systematic circulation of ICIs.

Figure 7. Combination of IO and ICI cancer immunotherapy by nanomedicine.

a. i) IDOi-IONCs enhanced the therapeutic efficacy of IRE and ICI combinational cancer immunotherapy. IRE electric pulse responsive IDOi-IONCs showed enhanced IRE cell-killing efficiency. IRE triggered release of IDOi from IDOi-IONCs synergize the combinational ICI cancer immunotherapy. ii) Synergistic combination IRE and IDOi-IONCs also showed abscopal effect treating both primary and secondary tumors. Reproduced with permission.^[101] 2020, American Chemical Society. b. i) Sequential chemo-ICI cancer immunotherapy that contains aPD-L1 loaded UPMSNPs after a standard Cbz chemotherapy of PC. ii) Localized chemotherapy induced ICD and synergized with the sustainable release of aPD-L1 from UPMSNPs for strong cancer-specific immunization. Reproduced with permission.^[97] 2019, Wiley-VCH. c. i) aPD-L1 loaded S-AuNC for synergistic combination of RT and ICI cancer immunotherapy of low immunogenic PC. ii-iii) CT-guided intratumoral delivery of aPD-L1 loaded S-AuNC allowed radiosensitization and RT-responsive aPD-L1 release to PC tumor resulted in enhanced tumoricidal immune response with minimized the irAEs. Reproduced with permission.^[102] 2020, American Chemical Society. d. i) Hybrid nanovesicles composed by AA core and IONC incorporated PLGA shell induced magnetic field triggered ferroptosis-like cell-death. ii) Hybrid nanovesicles mediated ROS generation with the Fenton reaction led to DC maturation and the CTL infiltration to TME. iii) The concentration changes of ferric ion during the treatment allowed to monitor the hybrid nanovesicle mediated ferroptosis by MRI scan. Reproduced with permission.^[104] 2020, Springer Nature.

4.3.2. Hybrid multifunctional nanocarrier

Because the most mechanisms of IO therapies are relying on the physical energy, the usage of only organic material based nanocarriers is very limited. Multifunctional hybrid nanocarriers have been tested more for the combinational IO and ICI cancer immunotherapy. Zhang et al. recently suggested a hybrid ICI, perfluoropentane and iron oxide nanoparticles loaded PLGA for the combination of ICI cancer immunotherapy with photothermal therapy (PTT) to treat the melanoma.^[103] The aPD-1 loaded hybrid PLGA nanocarriers were modified with PEG and Gly-Arg-Gly-Asp-Ser (GRGDS) peptides (GOP@aPD1). Targeting peptides of PLGA nanocarriers (GOP@aPD-1) facilitated the active accumulation and localized PTT in the tumor. Released aPD-1 to immunogenic TME from thermosensitive GOP@aPD-1 increased the retention time of aPD-1 and relieved the toxicity. Subsequently, active T cells were infiltrated into the tumor, resulting in high tumor rejection. Recently, our group reported a hybrid nanovesicle for an image-guided ferroptosis based ICI immunotherapies.^[104] Hybrid nanovesicles were synthesized by loading ascorbic acid (AA) in the core and PLGA shell incorporating IONCs. A circularly polarized magnetic field triggered AA release induced the increase of ferrous ions through the redox reaction between AA and IONCs (Figure 7d (i)). Fenton reaction of the hybrid nanovesicles under the magnetic field successfully induced ferroptosis-like cell-death. The oxidative stress during the Fenton reaction led to the CRT expression of tumor cells as an “eat me” signal. Followed DC maturation and TAA presentation to naïve T cells succeeded to induce the tumor specific CTL infiltration in TME (Figure 7d(ii)). Additionally, the concentration change of ferric ions during the treatment allowed the MRI monitoring of ferroptosis (Figure 7d(iii)). The ferroptosis based immune reaction showed a new perspective to the use of ferroptosis-based immunotherapy combined with image-guided medicine.

5. Conclusions and Outlook

ICI cancer immunotherapy has been one of the most powerful approaches killing primary, metastatic tumors and recurred tumors. However, immunological resistance, therapeutic ignorance and the potential irAEs are still significant issues for the broad application of ICI cancer immunotherapy in the clinic. Recent studies revealed that most of image guided IO local therapies induce “hot” TME modulation such as up-regulation of ICI, ICD, TAA release and so on. The combination of image-guided IO therapy and ICI cancer immunotherapy is made for each other to enhance the therapeutic efficacy. Nanocarriers mediated TME changes and ICI delivery have been tested to overcome the ICI therapeutic tumor resistance, ignorance, and off target side effect (irAEs). Clinical interventional therapies are performed with a form of image guided local therapies. Nanoparticles have been shown excellent potential for imaging contrast effect and various physical cancer therapies using heat, chemical reaction, radiation and so on. Although nanoparticles mediated interventional therapies are relatively a new area, the multifunctional nanoparticles can be conveniently added to the interventional procedures for the enhanced tumor targeting efficiency and additional therapeutic monitoring features. Advanced MRI, CT, DSA and PET image guided delivery, monitoring and quantification of multifunctional nanoparticles for the interventional local therapies could achieve higher therapeutic efficacy compared to conventional clinical interventional therapies such as thermal-, electric-, cryo-ablations, and radiation therapy. Indeed, the use of multifunctional nanocarriers reforms the clinical interventional therapy applications. Thus, well-tailored multifunctional nanocarrier mediated combinational image guided IO cancer therapy and ICI cancer immunotherapy will be potentiated for superior synergistic outcomes compared to conventional cancer therapies (Figure 8). This process is different with conventional multifunctional nanoparticles based overlayed combination ICI immunotherapy studies. Those studies are more focusing on the searching new possible nanoparticles mediated combinational ICI immunotherapies. The proposed multifunctional nanocarriers mediated combination IO and ICI cancer immunotherapy is an advanced strategy utilizing clinical tumor localization procedure of image guided IO therapies and current clinical ablation technique for a specific type of tumors. It should take a position for next generation ICI cancer immunotherapy. An intensive understanding of the correlation among the features of IO local therapy, ICI cancer immunotherapy, and multifunctional nanocarriers is needed for a new class of cancer therapy. The research areas of IO, immuno-oncology and nanocarrier have been dynamically evolving. New opportunities for an innovative cancer therapeutic efficacy will be generated by the integration of those areas. However, there are also several challenges to be considered. First, ICI local delivery showed a promising result for the enhanced therapeutic efficacy with minimized irAEs. Detail dosing strategy for the local ICI delivery needs to be established. Based on the optimal ICI dose and pharmacokinetics for the local ICI treatment, nanocarriers should be designed to control the ICI loading capacity and local release rate to maintain the effective ICI concentration through the therapeutic regimen. Second, more effort to finding the most efficient multifunctional nanocarrier mediated combination of IO local therapy and ICI cancer immunotherapy is required to achieve synergistic the immunogenic conversion of treated tumor and activation of anti-cancer immune response. Third, the proper combination sequence and timeline should be studied to maximize the therapeutic outcome. ICD, APC and the maturation and activation of immune cells are all time-dependent and there are sequences. By investigating immune sequences, multifunctional nanocarriers and sequence of ICI delivery and IO local therapy should be determined. Lastly, the delivery of multifunctional nanocarriers could be conducted with the image guidance that is using for IO local therapy. Image-guided delivery through tumor specific vessels has shown exceptional delivery efficacy of nanocarriers compared to systemic delivery of nanocarriers.^[105–108] Image guidance during the IO local therapies should be utilized for the local delivery of multifunctional nanocarriers for the combination ICI and IO cancer immunotherapy. With those consideration, more effort on the validation the synergistic efficacy of multifunctional nanocarriers mediated combination of IO and ICI cancer immunotherapy is necessary for the clinical translation (Figure 8). Close collaboration of interventional oncologist and immunooncologist with materials engineers and chemists is critical from the beginning of the effective future ICI cancer immunotherapy design process (Figure 8). Further, this effort to integrate them into the cancer treatment should further reinforce each area’s potential and deliver meaningful impact for treatment of cancer in the clinic.

Figure 8.

Perspective of multifunctional nanocarriers mediated synergistic combination of ICI cancer immunotherapy and IO cancer therapies.

Biographies

Bongseo Choi is Postdoctoral research associate in the Department of Radiology at Northwestern University. He has Ph.D. in Biological science at Ulsan National Institute of Science and Technology in Republic of Korea. He studied about the application of organic/inorganic nanomaterials to cancer immunotherapy. Currently, his research focused on the translational combination of conventional cancer treatment and cancer immunotherapy by utilizing interventional oncology and biocompatible nanomaterials in Prof. Dong-Hyun. Kim’s Lab.

Dong-Hyun Kim is an Associate Professor of Radiology and Biomedical Engineering at the Northwestern University and the director of Biomaterials for Image Guided MEDicine lab at Northwestern University. He received his B.S. degree in Materials Science & Engineering and Ph.D. degree in Medical Science, Yonsei University. He got postdoc trainings in Chemical & Biological Engineering at University of Alabama and Materials Science Division at Argonne National Laboratory. He and his group research are focusing on the therapeutic nanocarriers, image guided medicine and new cancer therapy research, which can overcome the limitation of the conventional cancer therapies.