Cooperative Self-Assembled Nanoparticle Induces Sequential Immunogenic Cell Death and Toll-Like Receptor Activation for Synergistic Chemo-immunotherapy

Shifting cold to hot tumors by nanoparticle-loaded drugs and products

Cold tumors lack antitumor immunity and are resistant to therapy, representing a major challenge in cancer medicine. Because of the immunosuppressive spirit of the tumor microenvironment (TME), this form of tumor has a low response to immunotherapy, radiotherapy, and also chemotherapy. Cold tumors have low infiltration of immune cells and a high expression of co-inhibitory molecules, such as immune checkpoints and immunosuppressive molecules. Therefore, targeting TME and remodeling immunity in cold tumors can improve the chance of tumor repression after therapy. However, tumor stroma prevents the infiltration of inflammatory cells and hinders the penetration of diverse molecules and drugs. Nanoparticles are an intriguing tool for the delivery of immune modulatory agents and shifting cold to hot tumors. In this review article, we discuss the mechanisms underlying the ability of nanoparticles loaded with different drugs and products to modulate TME and enhance immune cell infiltration. We also focus on newest progresses in the design and development of nanoparticle-based strategies for changing cold to hot tumors. These include the use of nanoparticles for targeted delivery of immunomodulatory agents, such as cytokines, small molecules, and checkpoint inhibitors, and for co-delivery of chemotherapy drugs and immunomodulatory agents. Furthermore, we discuss the potential of nanoparticles for enhancing the efficacy of cancer vaccines and cell therapy for overcoming resistance to treatment.

Engineering nanomedicines for immunogenic eradication of cancer cells: Recent trends and synergistic approaches

Resistance to cancer immunotherapy is mainly attributed to poor tumor immunogenicity as well as the immunosuppressive tumor microenvironment (TME) leading to failure of immune response. Numerous therapeutic strategies including chemotherapy, radiotherapy, photodynamic, photothermal, magnetic, chemodynamic, sonodynamic and oncolytic therapy, have been developed to induce immunogenic cell death (ICD) of cancer cells and thereby elicit immunogenicity and boost the antitumor immune response. However, many challenges hamper the clinical application of ICD inducers resulting in modest immunogenic response. Here, we outline the current state of using nanomedicines for boosting ICD of cancer cells. Moreover, synergistic approaches used in combination with ICD inducing nanomedicines for remodeling the TME via targeting immune checkpoints, phagocytosis, macrophage polarization, tumor hypoxia, autophagy and stromal modulation to enhance immunogenicity of dying cancer cells were analyzed. We further highlight the emerging trends of using nanomaterials for triggering amplified ICD-mediated antitumor immune responses. Endoplasmic reticulum localized ICD, focused ultrasound hyperthermia, cell membrane camouflaged nanomedicines, amplified reactive oxygen species (ROS) generation, metallo-immunotherapy, ion modulators and engineered bacteria are among the most innovative approaches. Various challenges, merits and demerits of ICD inducer nanomedicines were also discussed with shedding light on the future role of this technology in improving the outcomes of cancer immunotherapy.

Molecule engineering strategy of toll-like receptor 7/8 agonists designed for potentiating immune stimuli activation

Toll-like receptor 7/8 (TLR-7/8) agonists serve as a promising class of pattern recognition receptors that effectively evoke the innate immune response, making them promising immunomodulatory agents for tumor immunotherapy. However, the uncontrollable administration of TLR-7/8 agonists frequently leads to the occurrence of severe immune-related adverse events (irAEs). Thus, it is imperative to strategically design tumor-microenvironment-associated biomarkers or exogenous stimuli responsive TLR-7/8 agonists in order to accurately evaluate and activate innate immune responses. No comprehensive elucidation has been documented thus far regarding TLR-7/8 immune agonists that are specifically engineered to enhance immune activation. In this feature article, we provide an overview of the advancements in TLR-7/8 agonists, aiming to enhance the comprehension of their mechanisms and promote the clinical progression through nanomedicine strategies. The current challenges and future directions of cancer immunotherapy are also discussed, with the hope that this work will inspire researchers to explore innovative applications for triggering immune responses through TLR-7/8 agonists.

Advances in Nanomaterials for Immunotherapeutic Improvement of Cancer Chemotherapy

Immuno-stimulative effect of chemotherapy (ISECT) is recognized as a potential alternative to conventional immunotherapies, however, the clinical application is constrained by its inefficiency. Metronomic chemotherapy, though designed to overcome these limitations, offers inconsistent results, with effectiveness varying based on cancer types, stages, and patient-specific factors. In parallel, a wealth of preclinical nanomaterials holds considerable promise for ISECT improvement by modulating the cancer-immunity cycle. In the area of biomedical nanomaterials, current literature reviews mainly concentrate on a specific category of nanomaterials and nanotechnological perspectives, while two essential issues are still lacking, i.e., a comprehensive analysis addressing the causes for ISECT inefficiency and a thorough summary elaborating the nanomaterials for ISECT improvement. This review thus aims to fill these gaps and catalyze further development in this field. For the first time, this review comprehensively discusses the causes of ISECT inefficiency. It then meticulously categorizes six types of nanomaterials for improving ISECT. Subsequently, practical strategies are further proposed for addressing inefficient ISECT, along with a detailed discussion on exemplary nanomedicines. Finally, this review provides insights into the challenges and perspectives for improving chemo-immunotherapy by innovations in nanomaterials.

Nanomedicine Remodels Tumor Microenvironment for Solid Tumor Immunotherapy

Although immunotherapy is relatively effective in treating hematological malignancies, their efficacy against solid tumors is still suboptimal or even noneffective presently. Compared to hematological cancers, solid tumors exhibit strikingly different immunosuppressive microenvironment, severely deteriorating the efficacy of immunotherapy: (1) chemical features such as hypoxia and mild acidity suppress the activity of immune cells, (2) the pro-tumorigenic domestication of immune cells in the microenvironment within the solid tumors further undermines the effectiveness of immunotherapy, and (3) the dense physical barrier of solid tumor tissues prevents the effective intratumoral infiltration and contact killing of active immune cells. Therefore, we believe that reversing the immunosuppressive microenvironment are of critical priority for the immunotherapy against solid tumors. Due to their unique morphologies, structures, and compositions, nanomedicines have become powerful tools for achieving this goal. In this Perspective, we will first briefly introduce the immunosuppressive microenvironment of solid tumors and then summarize the most recent progresses in nanomedicine-based immunotherapy for solid tumors by remodeling tumor immune-microenvironment in a comprehensive manner. It is highly expected that this Perspective will aid in advancing immunotherapy against solid tumors, and we are highly optimistic on the future development in this burgeoning field.

Proton-Gradient-Driven Porphyrin-Based Liposome Remote-Loaded with Imiquimod as In Situ Nanoadjuvants for Synergistically Augmented Tumor Photoimmunotherapy

Cancer immunotherapy is expected to achieve tumor treatment mainly by stimulating the patient's own immune system to kill tumor cells. However, the low immunogenicity of the tumor and the poor efficiency of tumor antigen presentation result in a variety of solid tumors that do not respond to immunotherapy. Herein, we designed a proton-gradient-driven porphyrin-based liposome (PBL) with highly efficient Toll-like receptor 7 (TLR7) agonist (imiquimod, R837) encapsulation (R837@PBL). R837@PBL rapidly released R837 in the acid microenvironment to activate the TLR in the endosome inner membrane to promote bone-marrow-derived dendritic cell maturation and enhance antigen presentation. R837@PBL upon laser irradiation triggered immunogenic cell death of tumor cells and tumor-associated antigen release after subcutaneous injection, activated TLR7, formed in situ tumor nanoadjuvants, and enhanced the antigen presentation efficiency. Photoimmunotherapy promoted the infiltration of cytotoxic T lymphocytes into tumor tissues, inhibited the growth of the treated and abscopal tumors, and exerted highly effective photoimmunotherapeutic effects. Hence, our designed in situ tumor nanoadjuvants are expected to be an effective treatment for treated and abscopal tumors, providing a novel approach for synergistic photoimmunotherapy of tumors.

Tumor Microenvironment-Responsive Nanoparticles Amplifying STING Signaling Pathway for Cancer Immunotherapy

Insufficient activation of the stimulator of interferon genes (STING) signaling pathway and profoundly immunosuppressive microenvironment largely limits the effect of cancer immunotherapy. Herein, tumor microenvironment (TME)-responsive nanoparticles (PMM NPs) are exploited that simultaneously harness STING and Toll-like receptor 4 (TLR4) to augment STING activation via TLR4-mediated nuclear factor-kappa B signaling pathway stimulation, leading to the increased secretion of type I interferons (i.e., 4.0-fold enhancement of IFN-β) and pro-inflammatory cytokines to promote a specific T cell immune response. Moreover, PMM NPs relieve the immunosuppression of the TME by decreasing the percentage of regulatory T cells, and polarizing M2 macrophages to the M1 type, thus creating an immune-supportive TME to unleash a cascade adaptive immune response. Combined with an anti-PD-1 antibody, synergistic efficacy is achieved in both inflamed colorectal cancer and noninflamed metastatic breast tumor models. Moreover, rechallenging tumor-free animals with homotypic cells induced complete tumor rejection, indicating the generation of systemic antitumor memory. These TME-responsive nanoparticles may open a new avenue to achieve the spatiotemporal orchestration of STING activation, providing a promising clinical candidate for next-generation cancer immunotherapy.

Stimuli-responsive nanodelivery systems for amplifying immunogenic cell death in cancer immunotherapy

Immunogenic cell death (ICD) is a special pattern of tumor cell death, enabling to elicit tumor-specific immune response via the release of damage-associated molecular patterns and tumor-associated antigens in the tumor microenvironment. ICD-induced immunotherapy holds the promise for completely eliminating tumors and long-term protective antitumor immune response. Increasing ICD inducers have been discovered for boosting antitumor immunity via evoking ICD. Nonetheless, the utilization of ICD inducers remains insufficient owing to serious toxic reactions, low localization efficiency within the tumor microenvironmental niche, etc. For overcoming such limitations, stimuli-responsive multifunctional nanoparticles or nanocomposites with ICD inducers have been developed for improving immunotherapeutic efficiency via lowering toxicity, which represent a prospective scheme for fostering the utilization of ICD inducers in immunotherapy. This review outlines the advances in near-infrared (NIR)-, pH-, redox-, pH- and redox-, or NIR- and tumor microenvironment-responsive nanodelivery systems for ICD induction. Furthermore, we discuss their clinical translational potential. The progress of stimuli-responsive nanoparticles in clinical settings depends upon the development of biologically safer drugs tailored to patient needs. Moreover, an in-depth comprehending of ICD biomarkers, immunosuppressive microenvironment, and ICD inducers may accelerate the advance in smarter multifunctional nanodelivery systems to further amplify ICD.

The spatiotemporal journey of nanomedicines in solid tumors on their therapeutic efficacy

The rapid development of nanomedicines is revolutionizing the landscape of cancer treatment, while effectively delivering them into solid tumors remains a formidable challenge. Currently, there is a huge disconnect on therapeutic response between regulatory approved nanomedicines and laboratory reported nanoparticles. The discrepancy is mainly resulted from the failure of using the classic overall pharmacokinetics behaviors of nanomedicines in tumors to predict the antitumor efficacy. Increasing evidence has revealed that the therapeutic efficacy predominantly relies on the intratumoral spatiotemporal distribution of nanomedicines. This review focuses on the spatiotemporal distribution of systemically administered chemotherapeutic nanomedicines in solid tumor. Firstly, the intratumoral biological barriers that regulate the spatiotemporal distribution of nanomedicines are described in detail. Next, the influences on antitumor efficacy caused by the spatial distribution and temporal drug release of nanomedicines are emphatically analyzed. Then, current methodologies for evaluating the spatiotemporal distribution of nanomedicines are summarized. Finally, the advanced strategies to positively modulate the spatiotemporal distribution of nanomedicines for an optimal tumor therapy are comprehensively reviewed.

Injectable hydrogel loaded with lysed OK-432 and doxorubicin for residual liver cancer after incomplete radiofrequency ablation

OBJECTIVE

To investigate the efficacy of an injectable hydrogel loaded with lysed OK-432 (lyOK-432) and doxorubicin (DOX) for residual liver cancer after incomplete radiofrequency ablation (iRFA) of hepatocellular carcinoma (HCC), and explore the underlying mechanism.

MATERIALS AND METHODS

The effect of OK-432 and lyOK-432 was compared in activating dendritic cells (DCs). RADA16-I (R) peptide was dissolved in a mixture of lyOK-432 (O) and DOX (D) to develop an ROD hydrogel. The characteristics of ROD hydrogel were evaluated. Tumor response and mice survival were measured after different treatments. The number of immune cells and cytokine levels were measured, and the activation of cGAS/STING/IFN-I signaling pathway in DC was evaluated both in vitro and in vivo.

RESULTS

LyOK-432 was more effective than OK-432 in promoting DC maturation and activating the IFN-I pathway. ROD was an injectable hydrogel for effectively loading lyOK-432 and DOX, and presented the controlled-release property. ROD treatment achieved the highest tumor necrosis rate (p < 0.001) and the longest survival time (p < 0.001) compared with the other therapies. The ROD group also displayed the highest percentages of DCs, CD4+ T cells and CD8+ T cells (p < 0.001), the lowest level of Treg cells (p < 0.001), and the highest expression levels of IFN-γ and TNF-α (p < 0.001) compared with the other groups. The expression levels of pSTING, pIRF3, and IFN-β in DCs were obviously higher after treatment of lyOK-432 in combination with DOX than the other therapies. The surviving mice in the ROD group showed a growth inhibition of rechallenged subcutaneous tumor.

CONCLUSION

The novel ROD peptide hydrogel induced an antitumor immunity by activating the STING pathway, which was effective for treating residual liver cancer after iRFA of HCC.

Polyprodrugs for tumor chemotherapy: from molecular structure to drug release performance

Polyprodrugs have been recognized as promising carrier-free drug delivery systems (DDSs) for tumor chemotherapy in recent years, showing distinct superiority in comparison with the conventional polymer prodrugs. In the present work, the structure-property relationship of polyprodrugs was explored from the perspective of molecular structure, by discussing the effects of the conjugations and linkers on their drug content and drug releasing performance, including drug releasing rate and drug releasing selectivity, as well as the anti-tumor performance of the released drugs. Moreover, the future challenges in the design of polyprodrug-based DDSs with high anti-tumor efficacy were also highlighted.

Injectable biocompatible nanocomposites of Prussian blue nanoparticles and bacterial cellulose as a safe and effective photothermal cancer therapy

Photothermal therapy (PTT) is a novel cancer treatment using a photoabsorber to cause hyperthermia to kill tumors by laser irradiation. Prussian blue nanoparticles (PB NPs) are considered as next-generation photothermal agents due to the facile synthesis and excellent absorption of near-infrared light. Although PB NPs demonstrate remarkable PTT capabilities, their clinical application is limited due to their systemic toxicity. Bacterial cellulose (BC) has been applied to various bio-applications based on its unique properties and biocompatibility. Herein, we design composites with PB NPs and BC as an injectable, highly biocompatible PTT agent (IBC-PB composites). Injectable bacterial cellulose (IBC) is produced through the trituration of BC, with PB NPs synthesized on the IBC surface to prepare IBC-PB composites. IBC-PB composites show in vitro and in vivo photothermal therapeutic effects similar to those of PB NPs but with significantly greater biocompatibility. Specifically, in vitro therapeutic index of IBC-PB composites is 26.5-fold higher than that of PB NPs. Furthermore, unlike PB NPs, IBC-PB composites exhibit no overt toxicity in mice as assessed by blood biochemical analysis and histological images. Hence, it is worth pursuing further research and development of IBC-PB composites as they hold promise as safe and efficacious PTT agents for clinical application.

Supramolecular Biomaterials for Cancer Immunotherapy

Cancer immunotherapy has achieved tremendous successful clinical results and obtained historic victories in tumor treatments. However, great limitations associated with feeble immune responses and serious adverse effects still cannot be neglected due to the complicated multifactorial etiology and pathologic microenvironment in tumors. The rapid development of nanomedical science and material science has facilitated the advanced progress of engineering biomaterials to tackle critical issues. The supramolecular biomaterials with flexible and modular structures have exhibited unparalleled advantages of high cargo-loading efficiency, excellent biocompatibility, and diversiform immunomodulatory activity, thereby providing a powerful weapon for cancer immunotherapy. In past decades, supramolecular biomaterials were extensively explored as versatile delivery platforms for immunotherapeutic agents or designed to interact with the key moleculars in immune system in a precise and controllable manner. In this review, we focused on the crucial role of supramolecular biomaterials in the modulation of pivotal steps during tumor immunotherapy, including antigen delivery and presentation, T lymphocyte activation, tumor-associated macrophage elimination and repolarization, and myeloid-derived suppressor cell depletion. Based on extensive research, we explored the current limitations and development prospects of supramolecular biomaterials in cancer immunotherapy.

Self-Immolated Nanoadjuvant for In Situ Vaccination Immunotherapy of Colorectal Cancer

Vaccination immunotherapy has revolutionized cancer treatment modalities. Although the immunomodulatory adjuvant generally employs for potentiating vaccine response, systemic administration may drive immune-related side effects, even immune tolerance. Therefore, tunable immunoadjuvants are highly desirable to simultaneously stimulate the immune response and mitigate systemic toxicity. Self-immolated nanoadjuvants are herein reported to potentiate vaccination immunotherapy of cancer. The nanoadjuvants are engineered by co-assembling an intracellular acidity-ionizable polymeric agonist of toll-like receptor 7/8 resiquimod (R848) and polymeric photosensitizer pyropheophorbide a (PPa). The resultant nanoadjuvants specifically accumulate at the tumor site via passive targeting and are dissociated in the acidic endosome versicles to activate PPa via protonation of the polymer backbone. Upon 671 nm laser irradiation, PPa performed photodynamic therapy to induce immunogenic cell death of tumor cells and subsequently releases R848 in a customized manner, which synergistically activates dendritic cells (DCs), promotes antigen cross-presentation, and eventually recruits cytotoxic T lymphocytes for tumor regression. Furthermore, the synergistic in situ vaccination immunotherapy with immune checkpoint blockade induce sustained immunological memory to suppress tumor recurrence in the rechallenged colorectal tumor model.

Promotion of ICD via Nanotechnology

Immunotherapy represents the most promising treatment strategy for cancer, but suffers from compromised therapeutic efficiency due to low immune activity of tumor cells and an immunosuppressive microenvironment, which significantly hampers the clinical translations of this treatment strategy. To promote immunotherapy with desired therapeutic efficiency, immunogenic cell death (ICD), a particular type of death capable of reshaping body's antitumor immune activity, has drawn considerable attention due to the potential to stimulate a potent immune response. Still, the potential of ICD effect remains unsatisfactory because of the intricate tumor microenvironment and multiple drawbacks of the used inducing agents. ICD has been thoroughly reviewed so far with a general classification of ICD as a kind of immunotherapy strategy and repeated discussion of the related mechanism. However, there are no published reviews, to the authors' knowledge, providing a systematic summarization on the enhancement of ICD via nanotechnology. For this purpose, this review first discusses the four stages of ICD according to the development mechanisms, followed by a comprehensive description on the use of nanotechnology to enhance ICD in the corresponding four stages. The challenges of ICD inducers and possible solutions are finally summarized for future ICD-based enhanced immunotherapy.

Nanodelivery of scutellarin induces immunogenic cell death for treating hepatocellular carcinoma

Hepatocellular carcinoma (HCC) causes the immunosuppressive tumor microenvironment (TME) resistant to current immunotherapy. The immunogenic apoptosis (currently termed immunogenic cell death, ICD) of cancer cells may induce the adaptive immunity against tumors, thereby providing great potential for treating HCC. In this study, we have confirmed the potential of scutellarin (SCU, a flavonoid found in Erigeron breviscapus) for triggering ICD in HCC cells. To facilitate in vivo application of SCU for HCC immunotherapy, an aminoethyl anisamide-targeted polyethylene glycol-modified poly(lactide-co-glycolide) (PLGA-PEG-AEAA) was produced to facilitate SCU delivery in this study. The resultant nanoformulation (PLGA-PEG-AEAA.SCU) remarkably promoted blood circulation and tumor delivery in the orthotopic HCC mouse model. Consequently, PLGA-PEG-AEAA.SCU reversed the immune suppressive TME and achieved the immunotherapeutic efficacy, resulting in significantly longer survival of mice, without inducing toxicity. These findings uncover the ICD potential of SCU and provide a promising strategy for HCC immunotherapy.

Activating Nanomedicines with Electromagnetic Energy for Deep-Tissue Induction of Immunogenic Cell Death in Cancer Immunotherapy

Immunotherapy is an attractive approach for cancer therapy, while its antitumor efficacy is still limited, especially for non-immunogenic tumors. Nanomedicines can be utilized to convert the non-immunogenic "cold" tumors to immunogenic "hot" tumors via inducing immunogenic cell death (ICD), thereby promoting the antitumor immune response. Some nanomedicines that can produce local heat and reactive oxygen species upon the stimulation of electromagnetic energy are the main candidates for inducing the ICD effect. However, their applications are often restricted due to the poor tissue penetration depths of electromagnetic energy, such as light. By contrast, ultrasound, X-ray, alternating magnetic field, and microwave show excellent tissue penetration depths and thereby can be used for sonodynamic therapy, radiotherapy, magnetic hyperthermia therapy, and microwave ablation therapy, all of which can effectively induce ICD. Herein, the combination of deep-tissue electromagnetic energy with nanomedicines for inducing ICD and cancer immunotherapy are summarized. In particular, the designs of nanomedicines to amplify ICD effect in the presence of deep-tissue electromagnetic energy and sensitize tumors to various immunotherapies will be discussed. At the end of this review, a brief conclusion and discussion of current challenges and further perspectives in this subfield are provided.

Nano Delivery of Chemotherapeutic ICD Inducers for Tumor Immunotherapy

Immunogenic cell death (ICD, also known as immunogenic apoptosis) of malignant cells is confirmed to activate the host immune system to prevent, control, and eliminate tumors. Recently, a range of chemotherapeutic drugs have been repurposed as ICD inducers and applied for tumor immunotherapy. However, several hurdles to the widespread application of chemotherapeutic ICD inducers remain, namely poor water solubility, short blood circulation, non-specific tissue distribution, and severe toxicity. Recent advances in nanotechnology and pharmaceutical formulation foster the development of nano drug delivery systems to tackle the aforementioned hurdles and expedite safe, effective, and specific delivery. This review will describe delivery barriers to chemical ICD inducers and highlight recent nanoformulations for these drugs in tumor immunotherapy.

Cancer Immunotherapy Elicited by Immunogenic Cell Death Based on Smart Nanomaterials

Cancer immunotherapy has been a revolutionary cancer treatment modality because it can not only eliminate primary tumors but also prevent metastases and recurrent tumors. Immunogenic cell death (ICD) induced by various treatment modalities, including chemotherapy, phototherapy, and radiotherapy, converts dead cancer cells into therapeutic vaccines, eliciting a systemic antigen-specific antitumor. However, the outcome effect of cancer immunotherapy induced by ICD has been limited due to the low accumulation efficiency of ICD inducers in the tumor site and concomitant damage to normal tissues. The boom in smart nanomaterials is conducive to overcoming these hurdles owing to their virtues of good stability, targeted lesion site, high bioavailability, on-demand release, and good biocompatibility. Herein, the design of targeted nanomaterials, various ICD inducers, and the applications of nanomaterials responsive to different stimuli, including pH, enzymes, reactive oxygen species, or dual responses are summarized. Furthermore, the prospect and challenges are briefly outlined to provide reference and inspiration for designing novel smart nanomaterials for immunotherapy induced by ICD.

Polymeric nanoparticle-based nanovaccines for cancer immunotherapy

Therapeutic cancer vaccines, which are designed to amplify tumor-specific T cell responses, have been envisioned as one of the most powerful tools for effective cancer immunotherapy. However, increasing the potency, quality and durability of the vaccine response remains a big challenge. In recent years, materials-based delivery systems focusing on the co-delivery of antigens and adjuvants to enhance cancer vaccination therapy have attracted increasing interest. Among various materials, polymeric nanoparticles (NPs) with different physicochemical properties which can incorporate multiple immunological cues are of great interest. In this review, the recent progress in the design and construction of both ex vivo subunit and in situ cancer vaccines using polymeric NPs is summarized. Especially, we will focus on how these NPs improve the adjuvanticity of vaccines. The design principles of polymeric NPs for ex vivo subunit cancer vaccines and in situ cancer vaccination are also discussed. Finally, we want to briefly discuss molecular chaperones in cancer immunity and the applications of our unique self-assembly mixed shell polymeric micelle-based nanochaperones for cancer vaccines.

Rethinking nanoparticulate polymer-drug conjugates for cancer theranostics

Polymer-drug conjugates (PDCs) fabricated as nanoparticles have hogged the limelight in cancer theranostics in the past decade. Many researchers have devoted to developing novel and efficient polymeric drug delivery system since the first generation of poly(N-[2-hydroxypropyl]methacrylamide) copolymer-drug conjugates. However, none of them has been approved for chemotherapy in clinic. An ideal PDC nanoparticle for cancer theranostics should possess several properties, including prolonged circulation in blood, sufficient accumulation and internalization in tumors, and efficient drug release in target sites. To achieve these goals, it is important to rationally design the nanoparticulate PDCs based on circulation, accumulation, penetration, internalization, and drug release (CAPIR) cascade. Specifically, CAPIR cascades are divided into five steps: (1) circulation in the vascular compartment without burst release, (2) accumulation in tumors via enhanced permeability and retention effect, (3) subsequent penetration into the deep regions of tumors, (4) internalization into tumor cells, and (5) release of drugs as free molecules to exert their pharmacological effects. In this review, we focus on the development and novel approaches of nanoparticulate PDCs based on CAPIR cascade, and provide an outlook on future clinical application. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Lysosomal-mediated drug release and activation for cancer therapy and immunotherapy

The development of carrier systems that are able to transport and release therapeutics to target cells is an emergent strategy to treat cancer; however, they following endocytosis are usually trapped in the endo/lysosomal compartments. The efficacy of drug conjugates and nanotherapeutics relies critically on their intracellular drug release ability, for which advanced systems responding to the unique lysosomal environment such as acidic pH and abundant enzymes (e.g. cathepsin B, sulfatase and β-glucuronidase) or equipped with photochemical internalization property have been energetically pursued. In this review, we highlight the recent designs of smart systems that promote efficient lysosomal release and/or escape of anticancer agents including chemotherapeutics (e.g. doxorubicin, platinum, chloroquine and hydrochloroquine) and biotherapeutics (e.g. proteins, siRNA, miRNA, mRNA and pDNA) to cancer cells or immunotherapeutic agents (e.g. antigens, mRNA and immunoadjuvants) to antigen-presenting cells (APCs), thereby boosting cancer therapy and immunotherapy. Lysosomal-mediated drug release presents an appealing approach to develop innovative cancer therapeutics and immunotherapeutics.

Engineering metal‐phenolic networks for enhancing cancer therapy by tumor microenvironment modulation

The complicated tumor microenvironment (TME) is featured by low pH values, high redox status, and hypoxia, which greatly supports the genesis, development, and metastasis of tumors, leading to drug resistance and clinical failure. Moreover, a lot of immunosuppressive cells infiltrate in such TME, resulting in depressing immunotherapy. Therefore, the development of TME-responsive nanoplatforms has shown great significance in enhancing cancer therapeutics. Metal-phenolic networks (MPNs)-based nanosystems, which self-assemble via coordination of phenolic materials and metal ions, have emerged as excellent TME theranostic nanoplatforms. MPNs have unique properties including fast preparation, tunable morphologies, pH response, and biocompatibility. Besides, functionalization and surface modification can endow MPNs with specific functions for application requirements. Here, the representative engineering strategies of various polyphenols are first introduced, followed by the introduction of the engineering mechanisms of polyphenolic nanosystems, fabrication, and distinct properties of MPNs. Then, their advances in TME modulation are highlighted, such as antiangiogenesis, hypoxia relief, combination therapy sensitization, and immunosuppressive TME reversion. Finally, we will discuss the challenges and future perspectives of MPNs-based nanosystems for enhancing cancer therapy. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Combining immune checkpoint blockade with ATP-based immunogenic cell death amplifier for cancer chemo-immunotherapy

Amplifying "eat me signal" during tumor immunogenic cell death (ICD) cascade is crucial for tumor immunotherapy. Inspired by the indispensable role of adenosine triphosphate (ATP, a necessary "eat me signal" for ICD), a versatile ICD amplifier was developed for chemotherapy-sensitized immunotherapy. Doxorubicin (DOX), ATP and ferrous ions (Fe²⁺) were co-assembled into nanosized amplifier (ADO-Fe) through π‒π stacking and coordination effect. Meanwhile, phenylboric acid-polyethylene glycol-phenylboric acid (PBA-PEG-PBA) was modified on the surface of ADO-Fe (denoted as PADO-Fe) by the virtue of d-ribose unit of ATP. PADO-Fe could display active targetability against tumor cells via sialic acid/PBA interaction. In acidic microenvironment, PBA-PEG-PBA would dissociate from amplifier. Moreover, high H₂O₂ concentration would induce hydroxyl radical (·OH) and oxygen (O₂) generation through Fenton reaction by Fe²⁺. DOX and ATP would be released from the amplifier, which could induce ICD effect and "ICD adjuvant" to amplify this process. Together with programmed death ligands 1 (PD-L1) checkpoint blockade immunotherapy, PADO-Fe could not only activate immune response against primary tumor, but also strong abscopal effect against distant tumor. Our simple and multifunctional ICD amplifier opens a new window for enhancing ICD effect and immune checkpoint blockade therapy.

Black Phosphorus-Synergic Nitric Oxide Nanogasholder Spatiotemporally Regulates Tumor Microenvironments for Self-Amplifying Immunotherapy

The lack of tumor immunogenicity coupled with the presence of tumor immunosuppression severely hinders antitumor immunity, especially in the treatment of "immune cold" tumors. Here, we have developed a drug-free and NIR-enabled nitric oxide (NO)-releasing nanogasholder (NO_PS@BP) composed of an outer cloak of nitrate-containing polymeric NO donor and an inner core of black phosphorus (BP) as the energy converter to spatiotemporally regulate NO-mediated tumor microenvironment remodeling and achieve multimodal therapy. Following NIR-irradiation, BP-induced photothermia and its intrinsic reducing property accelerate NO release from the outer cloak, by which the instantaneous NO burst concomitant with mild photothermia, on the one hand, induces immunogenic cell death (ICD), thereby provoking antitumor responses such as the maturation of dendritic cells (DCs) and the infiltration of cytotoxic T lymphocytes (CTLs); on the other hand, it reverses tumor immunosuppression via Treg inhibition, M2 macrophage restraint, and PD-L1 downregulation, further strengthening antitumor immunity. Therefore, this drug-free NO_PS@BP by means of multimodal therapy (NO gas therapy, immune therapy, photothermal therapy) realizes extremely significant curative effects against primary and distant tumors and even metastasis in B16F10 tumor models, providing a new modality to conquer immune cold tumors by NO-potentiated ICD and immunosuppression reversal.

When Natural Compounds Meet Nanotechnology: Nature-Inspired Nanomedicines for Cancer Immunotherapy

Recent significant strides of natural compounds in immunomodulation have highlighted their great potential against cancer. Despite many attempts being made for cancer immunotherapy, the biomedical application of natural compounds encounters a bottleneck because of their unclear mechanisms, low solubility and bioavailability, and limited efficacy. Herein, we summarize the immune regulatory mechanisms of different natural compounds at each step of the cancer-immunity cycle and highlight their anti-tumor potential and current limitations. We then propose and present various drug delivery strategies based on nanotechnology, including traditional nanoparticles (NPs)-based delivery strategies (lipid-based NPs, micelles, and polysaccharide/peptide/protein-based NPs) and novel delivery strategies (cell-derived NPs and carrier-free NPs), thus providing solutions to break through existing bottlenecks. Furthermore, representative applications of nature-inspired nanomedicines are also emphasized in detail with the advantages and disadvantages discussed. Finally, the challenges and prospects of natural compounds for cancer immunotherapy are provided, hopefully, to facilitate their far-reaching development toward clinical translation.

A phenolic based tumor-permeated nano-framework for immunogenic cell death induction combined with PD-L1 immune checkpoint blockade

A critical obstacle for programmed death ligand 1 (PD-L1) immune checkpoint blockade immunotherapy is the insufficient T cell infiltration and low immunogenicity of tumor cells. Improving tumor immunogenicity through immunogenic cell death (ICD) can make tumor sensitive to PD-L1 checkpoint blockade immunotherapy. Herein, a phenolic based tumor-permeated nano-framework (EGPt-NF) was fabricated by cross-linking phenylboric acid modified platinum nanoparticles (PBA-Pt, ICD inducer) and epigallocatechin-3-O-gallate (EGCG, PD-L1 inhibitor) via pH-reversible borate ester. In particular, PBA-Pt could not only induce ICD cascade but also relieve tumor hypoxia. Consequently, EGPt-NF could effectively promote dendritic cell maturation and downregulate PD-L1 expression in tumor cells. Furthermore, EGPt-NF could also relieve tumor hypoxia to facilitate cytotoxic T lymphocyte infiltration and IFN-γ secretion. The synergistic effect of EGPt-NF could effectively improve tumor immunogenicity and amplify the therapeutic outcomes of cancer immunotherapy, resulting in a strong antitumor immune response in primary tumor and metastasis inhibition. Our simple approach expands the application of platinum-based drug delivery systems for cancer immunotherapy.

Tumor-associated macrophage membrane-camouflaged pH-responsive polymeric micelles for combined cancer chemotherapy-sensitized immunotherapy

The low immunogenicity and tumor immunosuppressive microenvironment (TIM) are two major obstacles for cancer immunotherapy. Synergistically immunogenic cell death induction and tumor-associated macrophages depletion could perfectly overcome this limitation. Herein, a tumor-associated macrophage (TAMs) membrane-camouflaged pH-responsive doxorubicin (DOX) loaded hyaluronic acid (HA)-g-poly (histidine) polymeric micelles (DHP@M2) was fabricated for the first time. DHP@M2 could effectively accumulated into tumor regions via TAMs membrane mediated immune camouflage. In acidic tumor microenvironment, particle size of DHP was enlarged due to decrease hydrophobic interaction of inner core, which caused a "membrane escape effect" to expose inner HA residue. Together high expression of α4β1 integrin, DHP@M2 could reach CD44/VCAM-1 dual-targetability to facilitate intracellular DOX accumulation for efficient ICD induction. Meanwhile, TAMs membrane could absorb colony stimulating factor 1(CSF1) through high expression of its receptor (CSF1R) on TAMs membrane to deplete TAMs in tumor tissues and relieved TIM. This strategy could efficiently induce cytotoxic T lymphocyte (CTLs) infiltration for antitumor immune response and inhibit tumor progression in 4T1 tumor bearing Balb/c mice. Therefore, DHP@M2 is suitable for cancer chemotherapy-sensitized immunotherapy.

Non-cytotoxic Nanoparticles Re-educating Macrophages Achieving both Innate and Adaptive Immune Responses for Tumor Therapy

Macrophages are important antigen-presenting cells to combat tumor via both innate and adaptive immunity, while they are programmed to M2 phenotype in established tumors and instead promote cancer development and metastasis. Here, we develop a nanomedicine that can re-educate M2 polarized macrophages to restore their anti-tumor activities. The nanomedicine has a core-shell structure to co-load IPI549, a PI3Kγ inhibitor, and CpG, a Toll-like receptor 9 agonist. Specifically, the hydrophobic IPI549 is self-assembled into a pure drug nano-core, while MOF shell layer is coated for CpG encapsulation, achieving extra-high total drugs loading of 44%. Such nanosystem could facilitate intracellular delivery of the payloads but without any cytotoxicity, displaying excellent biocompatibility. After entering macrophages, the released IPI549 and CpG exert a synergistic effect to switch macrophages from M2 to M1 phenotype, which enables anti-tumor activities via directly engulfing tumor cells or excreting tumor killing cytokines. Moreover, tumor antigens released from the dying tumor cells could be effectively presented by the re-educated macrophages owing to the up-regulation of various antigen presenting mediators, resulting in infiltration and activation of cytotoxic T lymphocytes. As a result, the nanosystem triggers a robust anti-tumor immune response in combination with PD-L1 antibody to inhibit tumor growth and metastasis. This work provides a non-cytotoxic nanomedicine to modulate tumor immune microenvironment by reprograming macrophages.

A pH-/Enzyme-Responsive Nanoparticle Selectively Targets Endosomal Toll-like Receptors to Potentiate Robust Cancer Vaccination

Toll-like receptor (TLR) agonists are potent immune-stimulators that hold great potential in vaccine adjuvants as well as cancer immunotherapy. However, TLR agonists in free form are prone to be eliminated quickly by the circulatory system and cause systemic inflammation side effects. It remains a challenge to achieve precise release of TLR7/8 agonist in the native form at the receptor site in the endosomal compartments while keeping stable encapsulation and inactive in nontarget environment. Here, we report a pH-/enzyme-responsive TLR7/8 agonist-conjugated nanovaccine (TNV), which responds intelligently to the acidic environment and cathepsin B in the endosome, precisely releases TLR7/8 agonist to activate its receptor signaling at the endosomal membrane, stimulates DCs maturation, and provokes specific cellular immunity. In vivo experiments demonstrate outstanding prophylactic and therapeutic efficacy of TNV in mouse melanoma and colon cancer. The endosome-targeted responsive nanoparticle strategy provides a potential delivery toolbox of adjuvants to advance the development of tumor nanovaccines.

Tumor microenvironment-responsive size-switchable drug delivery nanosystems

INTRODUCTION

Compared with ordinary chemotherapeutic drugs, the variable-size nanoparticles (NPs) have better therapeutic effects and fewer side effects.

AREAS COVERED

This review mainly summarizes the strategies used to construct smart, size-tunable nanocarriers based on characteristic factors of tumor microenvironment (TME) to dramatically increase the penetration and retention of drugs within tumors.

EXPERT OPINION

Nanosystems with changeable sizes based on the TME have been extensively studied in the past decade, and their permeability and retention have been greatly improved, making them a very promising treatment for tumors.

Inhibition of post-surgery tumour recurrence via a sprayable chemo-immunotherapy gel releasing PD-L1 antibody and platelet-derived small EVs

Background

Melanoma is the most serious type of skin cancer, and surgery is an effective method to treat melanoma. Unfortunately, local residual micro-infiltrated tumour cells and systemic circulating tumour cells (CTCs) are significant causes of treatment failure, leading to tumour recurrence and metastasis.

Methods

Small EVs were isolated from platelets by differential centrifugation, and doxorubicin-loaded small EVs (PexD) was prepared by mixing small EVs with doxorubicin (DOX). PexD and an anti-PD-L1 monoclonal antibody (aPD-L1) were co-encapsulated in fibrin gel. The synergistic antitumour efficacy of the gel containing PexD and aPD-L1 was assessed both in vitro and in vivo.

Results

Herein, we developed an in situ-formed bioresponsive gel combined with chemoimmunotherapeutic agents as a drug reservoir that could effectively inhibit both local tumour recurrence and tumour metastasis. In comparison with a DOX solution, PexD could better bind to tumour cells, induce more tumour immunogenic cell death (ICD) and promote a stronger antitumour immune response. PexD could enter the blood circulation through damaged blood vessels to track and eliminate CTCs. The concurrent release of aPD-L1 at the tumour site could impair the PD-1/PD-L1 pathway and restore the tumour-killing effect of cytotoxic T cells. This chemoimmunotherapeutic strategy triggered relatively strong T cell immune responses, significantly improving the tumour immune microenvironment.

Conclusion

Our findings indicated that the immunotherapeutic fibrin gel could “awaken” the host innate immune system to inhibit both local tumour recurrence post-surgery and metastatic potential, thus, it could serve as a promising approach to prevent tumour recurrence.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01270-7.

Nanomedicine-enabled chemotherapy-based synergetic cancer treatments

Chemotherapy remains one of the most prevailing regimens hitherto in the fight against cancer, but its development has been being suffering from various fatal side effects associated with the non-specific toxicity of common chemical drugs. Advances in biomedical application of nanomedicine have been providing alternative but promising approaches for cancer therapy, by leveraging its excellent intrinsic physicochemical properties to address these critical concerns. In particular, nanomedicine-enabled chemotherapy has been established as a safer and promising therapeutic modality, especially the recently proposed nanocatalytic medicine featuring the capabilities to generate toxic substances by initiating diverse catalytic reactions within the tumor without directly relying on highly toxic but non-selective chemotherapeutic agents. Of special note, under exogenous/endogenous stimulations, nanomedicine can serve as a versatile platform that allows additional therapeutic modalities (photothermal therapy (PTT), photodynamic therapy (PDT), chemodynamic therapy (CDT), etc.) to be seamlessly integrated with chemotherapy for efficacious synergistic treatments of tumors. Here, we comprehensively review and summarize the representative studies of multimodal synergistic cancer treatments derived from nanomedicine and nanocatalytic medicine-enabled chemotherapy in recent years, and their underlying mechanisms are also presented in detail. A number of existing challenges and further perspectives for nanomedicine-synergized chemotherapy for malignant solid tumor treatments are also highlighted for understanding this booming research area as comprehensively as possible.

Magnetic hyperthermia induces effective and genuine immunogenic tumor cell death with respect to exogenous heating

This study systematically verified that magnetic hyperthermia (MH) with intracellular heating can induce genuine immunogenic tumor cell death for effective antitumor therapy, while exogenous heating fails to elicit this effect.

Cascade-Responsive Hierarchical Nanosystems for Multisite Specific Drug Exposure and Boosted Chemoimmunotherapy

The precise delivery of multiple drugs to their distinct destinations plays a significant role in safe and efficient combination therapy; however, it is highly challenging to simultaneously realize the targets and overcome the intricate biological hindrances using an all-in-one nanosystem. Herein, a cascade-responsive hierarchical nanosystem containing checkpoint inhibitor anti-PD-L1 antibody (αPD-L1) and paclitaxel (PTX) is developed for spatially programed delivery of multiple drugs and simultaneously overcoming biological pathway barriers. The hierarchical nanoparticles (MPH-NP@A) are composed of pH-sensitive hyaluronic acid-acetal-PTX prodrugs (HA-ace-PTX(SH)) chaperoned by αPD-L1 and metalloproteinase-9 (MMP-9)-responsive outer shells, which could be fast cleaved to release αPD-L1 in the tumor microenvironment (TME). The released αPD-L1 sequentially synergizes with PTX released in the cytoplasm for boosted chemoimmunotherapy due to direct killing of PTX and intensified immune responses through immunogenic cell death (ICD) as well as suppression of immune escape by blocking the PD-1/PD-L1 axis. The in vitro and in vivo studies demonstrate that MPH-NP@A evokes distinct ICD, enhanced cytotoxic T lymphocytes infiltration, as well as significant tumor inhibition, thus providing a promising therapeutic nano-platform for safe and efficient combination therapy.

Type I macrophage activator photosensitizer against hypoxic tumors

Photodynamic immunotherapy has emerged as a promising strategy to treat cancer. However, the hypoxic nature of most solid tumors and notoriously immunosuppressive tumor microenvironment could greatly compromise the efficacy of photodynamic immunotherapy. To address this challenge, we rationally synthesized a type I photosensitizer of TPA-DCR nanoparticles (NPs) with aggregation-enhanced reactive oxygen species generation via an oxygen-independent pathway. We demonstrated that the free radicals produced by TPA-DCR NPs could reprogram M0 and M2 macrophages into an anti-tumor state, which is not restricted by the hypoxic conditions. The activated M1 macrophages could further induce the immunogenic cell death of cancer cells by secreting pro-inflammatory cytokines and phagocytosis. In addition, in vivo anti-tumor experiments revealed that the TPA-DCR NPs could further trigger tumor immune response by re-educating tumor-associated macrophages toward M1 phenotype and promoting T cell infiltration. Overall, this work demonstrates the design of type I organic photosensitizers and mechanistic investigation of their superior anti-tumor efficacy. The results will benefit the exploration of advanced strategies to regulate the tumor microenvironment for effective photodynamic immunotherapy against hypoxic tumors.

Self-adjuvanting photosensitizer nanoparticles for combination photodynamic immunotherapy

Combination cancer immunotherapy that synergizes the advantages of multiple therapeutic agents has shown great potential in tumor treatment. Herein, we report the one-step assembly of therapeutic nanoparticles (NPs) to co-deliver photosensitizers and adjuvants for combination photodynamic therapy (PDT) and immunotherapy. The NPs are obtained via self-assembly of chlorin e6 (Ce6) and imidazoquinoline-based TLR7 agonists (IMDQ), which results in a high loading efficacy of 72.2% and 27.8% for Ce6 and IMDQ, respectively. Upon laser irradiation, the resulting NPs could not only effectively induce photodynamic immunogenic cancer cell death, but also elicit robust antitumor immunity, leading to significant inhibition of both primary and distant tumors in a bilateral tumor model. This study demonstrates the potential of self-assembled NPs in co-delivering multiple therapeutics for potential immunotherapy to enhance the antitumor efficacy.