Enhancement of tumour penetration by nanomedicines through strategies based on transport processes and barriers

Tumor microenvironment reprogramming combined with immunogenic enhancement by nanoemulsions potentiates immunotherapy

The combination of immune checkpoint inhibitors and immunogenic cell death (ICD) inducers has become a promising strategy for the treatment of various cancers. However, its efficacy remains unmet because of the dense stroma and defective vasculatures in the tumor microenvironment (TME) that restricts the intratumoral infiltration of cytotoxic T lymphocytes (CTLs). Herein, cancer-associated fibroblasts (CAFs)-targeted nanoemulsions are tailored to combine the ICD induction and the TME reprogramming to sensitize checkpoint blockade immunotherapy. Melittin, as an ICD inducer and an antifibrotic agent, is efficiently encapsulated into the nanoemulsion accompanied by a nitric oxide donor to improve its bioavailability and tumor targeting. The nanoemulsions exhibited dual functionality by directly inducing direct cancer cell death and enhancing the tumoral immunogenicity, while also synergistically reprogramming the TME through reversing the activated CAFs, decreasing collagen deposition and restoring tumor vessels. Consequently, these nanemulsions successfully facilitated the CTLs infiltration and suppressing the recruitment of immunosuppressive cells. A combination of AE-MGNPs and anti-CTLA-4 antibody greatly elicited a striking level of antitumor T-cell response to suppress tumor growth in CAFs-rich colorectal tumor models. Our work emphasized the integration of the ICD induction with simultaneous modulation of the TME to enhance the sensitivity of patients to checkpoint blockade immunotherapy.

Nano-enhanced immunotherapy: Targeting the immunosuppressive tumor microenvironment

The tumor microenvironment (TME), which is mostly composed of tumor cells, immune cells, signaling molecules, stromal tissue, and the vascular system, is an integrated system that is conducive to the formation of tumors. TME heterogeneity makes the response to immunotherapy different in different tumors, such as "immune-cold" and "immune-hot" tumors. Tumor-associated macrophages, myeloid-derived suppressor cells, and regulatory T cells are the major suppressive immune cells and their different phenotypes interact and influence cancer cells by secreting different signaling factors, thus playing a key role in the formation of the TME as well as in the initiation, growth, and metastasis of cancer cells. Nanotechnology development has facilitated overcoming the obstacles that limit the further development of conventional immunotherapy, such as toxic side effects and lack of targeting. In this review, we focus on the role of three major suppressive immune cells in the TME as well as in tumor development, clinical trials of different drugs targeting immune cells, and different attempts to combine drugs with nanomaterials. The aim is to reveal the relationship between immunotherapy, immunosuppressive TME and nanomedicine, thus laying the foundation for further development of immunotherapy.

Progress and challenges in the translation of cancer nanomedicines

With the booming development of nanotechnology, nanomedicines have made considerable progress in the pharmaceutical field. However, the number of nanodrugs approved for clinical treatment is very limited. The main obstacles stem from the complexity of nanomedicine composition, tumor heterogeneity, complexity and incomplete understanding of nanotumor interactions, uncontrollable scaling, high production costs, and uncertainty of regulations and standards. This review article described the current stage of nanomedicines and highlighted the challenges, strategies, and opportunities for clinical translation of nanomedicines.

Recent advances in nano/micro systems for improved circulation stability, enhanced tumor targeting, penetration, and intracellular drug delivery: a review

In recent years, nanoparticles (NPs) have been extensively developed as drug carriers to overcome the limitations of cancer therapeutics. However, there are several biological barriers to nanomedicines, which include the lack of stability in circulation, limited target specificity, low penetration into tumors and insufficient cellular uptake, restricting the active targeting toward tumors of nanomedicines. To address these challenges, a variety of promising strategies were developed recently, as they can be designed to improve NP accumulation and penetration in tumor tissues, circulation stability, tumor targeting, and intracellular uptake. In this Review, we summarized nanomaterials developed in recent three years that could be utilized to improve drug delivery for cancer treatments.

Promoting Intratumoral Drug Accumulation by Bio-Membrane Regulated Active Targeting for Tumor Photothermal Therapy

Introduction

Insufficient tumor permeability and inadequate nanoparticle retention continue to be significant limitations in the efficacy of anti-tumor drug therapy. Numerous studies have focused on enhancing tumor perfusion by improvement of tumor-induced endothelial leakage, often known as the enhanced permeability and retention (EPR) effect. However, these approaches have produced suboptimal therapeutic outcomes and have been associated with significant side effects. Therefore, in this study, we prepared tumor cell membrane-coated gold nanorods (GNR@TM) to enhance drug delivery in tumors through homogeneous targeting of tumor cell membranes and in situ real-time photo-controlled therapy.

Methods

Here, we fabricated GNR@TM, and characterized it using various techniques including Ultraviolet-Visible (UV-Vis) spectrophotometer, particle size analysis, potential measurement, and transmission electron microscopy (TEM). The cellular uptake and cytotoxicity of GNR@TM were analyzed by flow cytometry, confocal laser scanning microscopy (CLSM), TEM, CCK8 assay and live/dead staining. Tissue drug distribution was determined by inductively coupled plasma mass spectrometry (ICP-MS) and immunofluorescence staining. Furthermore, to evaluate the therapeutic effect, mice bearing MB49 tumors were intravenously administered with GNR@TM. Subsequently, near-infrared (NIR) laser therapy was performed, and the mice's tumor growth and body weight were monitored.

Results

The tumor cell membrane coating endowed GNR@TM with extended circulation time in vivo and homotypic targeting to tumor, thereby enhancing the accumulation of GNR@TM within tumors. Upon 780 nm laser, GNR@TM exhibited excellent photothermal conversion capability, leading to increased tumor vascular leakage. This magnification of the EPR effect induced by NIR laser further increased the accumulation of GNR@TM at the tumor site, demonstrating strong antitumor effects in vivo.

Conclusion

In this study, we successfully developed a NIR-triggered nanomedicine that increased drug accumulation in tumor through photo-controlled therapy and homotypic targeting of the tumor cell membrane. GNR@TM has been demonstrated effective suppression of tumor growth, excellent biocompatibility, and significant potential for clinical applications.

"Ice and Fire" Supramolecular Cell-Conjugation Drug Delivery Platform for Deep Tumor Ablation and Boosted Antitumor Immunity

Cancer recurrence and metastasis are two major challenges in the current clinical therapy. In this work, a novel diketopyrrolopyrrole-based photothermal reagent (DCN) with unique J-aggregation-induced redshift is synthesized to achieve efficient tumor thermal ablation under safe power (0.33 W cm-2 ). Meanwhile, S-nitroso-N-acetylpenicillamine (SNAP) is co-loaded with near-infrared-absorbing DCN in amphiphilic polymers to realize heat-induced massive release of nitric oxide (NO), which can form oxidant peroxynitrite (ONOO- ) to active matrix metalloproteinases (MMPs), thereby degrading the compact tumor extracellular matrix to improve the ablation depth and infiltration of immune cells. Through a facile supramolecular assembly method, the DCN/SNAP nanoparticles are anchored to liquid-nitrogen-frozen cancer cells, achieving enhanced antitumor immune responses and effective inhibition of distant tumors and pulmonary metastases after only one treatment. The safety and effectiveness of this supramolecular cell-conjugation platform are verified by 2D/3D cellular experiments and bilateral tumor model, confirming the thermal-ablation-gas-permeation-antigen-presentation therapeutic mode has promising anticancer prospects.

Normalizing Tumor Blood Vessels to Improve Chemotherapy and Inhibit Breast Cancer Metastasis by Multifunctional Nanoparticles

The abnormal tumor blood vessels with high leakage can promote tumor cells to infiltrate into the systemic circulation and increase the risk of tumor metastasis. In addition, chemotherapy may destroy tumor blood vessels and further aggravate metastasis. Normalizing tumor blood vessels can reduce vascular leakage and increase vascular integrity. The simultaneous administration of vascular normalization drugs and chemotherapy drugs may resist the blood vessels' destruction of chemotherapy. Here, multifunctional nanoparticles (CCM@LMSN/DOX&St), which combined chemotherapy with tumor blood vessel normalization, were prepared for the treatment of breast cancer. The results showed that CCM@LMSN/DOX&St-loaded sunitinib (St) promoted the expression of junction proteins Claudin-4 and VE-cadherin of endothelial cells, reversed the destruction of DOX to the endothelial cell layer, protected the integrity of the endothelial cell layer, and inhibited the migration of 4T1 tumor cells across the endothelial cell layer. In vivo experiments showed that CCM@LMSN/DOX&St effectively inhibited tumor growth in situ; what is exciting was that it also inhibited distal metastasis of breast cancer. CCM@LMSN/DOX&St encapsulated with St can normalize tumor blood vessels, reverse the damage of DOX to tumor blood vessels, increase the integrity of blood vessels, and prevent tumor cell invasion into blood vessels, which can inhibit breast cancer spontaneous metastasis and reduce chemotherapy-induced metastasis. This drug delivery platform effectively inhibited the progression of tumors and provided a promising solution for effective tumor treatment.

Synchronous targeted delivery of TGF-β siRNA to stromal and tumor cells elicits robust antitumor immunity against triple-negative breast cancer by comprehensively remodeling the tumor microenvironment

The poor permeability of therapeutic drugs, limited T-cell infiltration, and strong immunosuppressive tumor microenvironment of triple-negative breast cancer (TNBC) acts as a prominent barrier to the delivery of drugs and immunotherapy including programmed cell death ligand-1 antibody (anti-PD-L1). Transforming growth factor (TGF)-β, an important cytokine produced by cancer-associated fibroblasts (CAFs) and tumor cells contributes to the pathological vasculature, dense tumor stroma and strong immunosuppressive tumor microenvironment (TME). Herein, a nanomedicine platform (HA-LSL/siTGF-β) employing dual-targeting, alongside hyaluronidase (HAase) and glutathione (GSH) triggered release was elaborately constructed to efficiently deliver TGF-β small interference RNA (siTGF-β). It was determined that this system was able to improve the efficacy of anti-PD-L1. The siTGF-β nanosystem efficiently silenced TGF-β-related signaling pathways in both activated NIH 3T3 cells and 4T1 cells in vitro and in vivo. This occurred firstly, through CD44-mediated uptake, followed by rapid escape mediated by HAase in endo/lysosomes and release of siRNA mediated by high GSH concentrations in the cytoplasm. By simultaneous silencing of TGF-β in stromal and tumor cells, HA-LSL/siTGF-β dramatically reduced stroma deposition, promoted the penetration of nanomedicines for deep remodeling of the TME, improved oxygenation, T cells infiltration and subsequent anti-PD-L1 deep penetration. The double suppression of TGF-β has been demonstrated to promote blood vessel normalization, inhibit an epithelial-to-mesenchymal transition (EMT), and further modify the immunosuppressive TME, which was supported by an overall increase in the proportion of dendritic cells and cytotoxic T cells. Further, a reduction in the proportion of immunosuppression cells such as regulatory T cells and myeloid-derived suppressor cells was also observed in the TME. Based on the comprehensive remodeling of the tumor microenvironment by this nanosystem, subsequent anti-PD-L1 therapy elicited robust antitumor immunity. Specifically, this system was able to suppress the growth of both primary and distant tumor while preventing tumor metastasis to the lung. Therefore, the combination of the dual-targeted siTGF-β nanosystem, alongside anti-PD-L1 may serve as a novel method to enhance antitumor immunotherapy against stroma-rich TNBC.

Liposomal nanocarriers containing siRNA as small molecule-based drugs to overcome cancer drug resistance

This review discusses the application of nanoliposomes containing siRNA/drug to overcome multidrug resistance for all types of cancer treatments. As drug resistance-associated factors are overexpressed in many cancer cell types, pumping chemotherapy drugs out of the cytoplasm leads to an inadequate therapeutic response. The siRNA/drug-loaded nanoliposomes are a promising approach to treating multidrug-resistant cancer, as they can effectively transmit a small-molecule drug into the target cytoplasm, ensuring that the drug binds efficiently. Moreover, nanoliposome-based therapeutics with advances in nanotechnology can effectively deliver siRNA to cancer cells. Overall, nanoliposomes have the potential to effectively deliver siRNA and small-molecule drugs in a targeted manner and are thus a promising tool for the treatment of cancer and other diseases.

Breaking Tumor Immunosuppressive Network by Regulating Multiple Nodes with Triadic Drug Delivery Nanoparticles

Inside the tumor microenvironment, a complicated immunosuppressive network is constituted by tumor cells and suppressive immune cells as its nodes, including myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), and regulatory T cells, which have mutual promotion on each other and superimposed inhibition on natural killer (NK) cells and cytotoxic T cells. Breaking the whole balance of this web is critical to tumor immunotherapy since modulation on a single node may be diluted by other factors in the network. To achieve multifaceted regulation on antitumor immunity against triple-negative breast cancer, in this work, a micelle, termed BEM, co-delivering the MDSC inhibitor, entinostat (ENT), and the immune checkpoint inhibitor, BMS-1, was constructed with pH-sensitive amphiphilic poly(β-amino ester) derivatives. Then, BEM and the scavenger receptor A (SR-A) ligand dextran sulfate (DXS) formed a negatively charged nanoparticle (BEN). DXS detached from BEN in the weakly acidic tumor microenvironment and blocked SR-A on TAMs, reprogramming TAMs toward the M1 type. The positively charged BEM with facilitated intratumoral penetration and cellular uptake dissociated in the lysosomes, accompanied by the release of ENT and BMS-1 to suppress MDSCs and block the programmed cell death protein (PD)-1/PD-ligand 1 pathway, respectively. As a result, NK cells and CD8+ T cells in tumors were increased, as were their effector cytokines. The activated innate and adaptive antitumor immune responses suppressed the growth and metastasis of tumors and prolonged survival of 4T1 tumor-bearing mice. BEN provides a reliable approach for improving cancer immunotherapy by destroying the immunosuppression web in tumors via multinode regulation.

Progress on the pathological tissue microenvironment barrier-modulated nanomedicine

Imbalance in the tissue microenvironment is the main obstacle to drug delivery and distribution in the human body. Before penetrating the pathological tissue microenvironment to the target site, therapeutic agents are usually accompanied by three consumption steps: the first step is tissue physical barriers for prevention of their penetration, the second step is inactivation of them by biological molecules, and the third step is a cytoprotective mechanism for preventing them from functioning on specific subcellular organelles. However, recent studies in drug-hindering mainly focus on normal physiological rather than pathological microenvironment, and the repair of damaged physiological barriers is also rarely discussed. Actually, both the modulation of pathological barriers and the repair of damaged physiological barriers are essential in the disease treatment and the homeostasis maintenance. In this review, we present an overview describing the latest advances in the generality of these pathological barriers and barrier-modulated nanomedicine. Overall, this review holds considerable significance for guiding the design of nanomedicine to increase drug efficacy in the future.

Prophylactic consequences of sodium salicylate nanoparticles in cisplatin-mediated hepatotoxicity

Unintended side effects linked to the antineoplastic drug cisplatin are a major drawback in its clinical application. The underlying source of these side effects include the generation of reactive oxygen species which are toxic and damaging to tissues and organs. In the present study the anti-inflammatory and antioxidant potential of sodium salicylate was assessed against cisplatin-induced hepatotoxicity in albino rats. Sodium salicylate was used as a model drug and loading into hollow structured porous silica using ultrasound-assisted sol-gel method to produce a nanoemulsion. Transmission Electron Microscopy and Dynamic Light scattering analysis were employed to assess the structural properties and stability of this model. Liver function was assessed by measuring biomarkers including ALT, AST & GGT and oxidant/antioxidant markers including MDA, NO, PON, GSH, MCP1 & AVP in serum or liver tissue. Additionally, blood leukocyte DNA damage was evaluated. Cisplatin significantly altered the normal levels of all biomarkers confirming its hepatotoxic effects. In contrast, treatment with sodium salicylate-loaded silica nanoemulsion significantly restored the levels of these markers. The finding suggests the protective effects of this model drug in preventing cisplatin-induced hepatotoxicity, and therefore may have implications in attenuating cisplatin-induced hepatotoxicity.

Prospects of Using Protein Engineering for Selective Drug Delivery into a Specific Compartment of Target Cells

A large number of proteins are successfully used to treat various diseases. These include natural polypeptide hormones, their synthetic analogues, antibodies, antibody mimetics, enzymes, and other drugs based on them. Many of them are demanded in clinical settings and commercially successful, mainly for cancer treatment. The targets for most of the aforementioned drugs are located at the cell surface. Meanwhile, the vast majority of therapeutic targets, which are usually regulatory macromolecules, are located inside the cell. Traditional low molecular weight drugs freely penetrate all cells, causing side effects in non-target cells. In addition, it is often difficult to elaborate a small molecule that can specifically affect protein interactions. Modern technologies make it possible to obtain proteins capable of interacting with almost any target. However, proteins, like other macromolecules, cannot, as a rule, freely penetrate into the desired cellular compartment. Recent studies allow us to design multifunctional proteins that solve these problems. This review considers the scope of application of such artificial constructs for the targeted delivery of both protein-based and traditional low molecular weight drugs, the obstacles met on the way of their transport to the specified intracellular compartment of the target cells after their systemic bloodstream administration, and the means to overcome those difficulties.

Exosomes as Rheumatoid Arthritis Diagnostic Biomarkers and Therapeutic Agents

Rheumatoid arthritis (RA) is a chronic inflammatory joint disorder that causes systemic inflammation, autoimmunity, and joint abnormalities that result in permanent disability. Exosomes are nanosized extracellular particles found in mammals (40–100 nm). They are a transporter of lipids, proteins, and genetic material involved in mammalian cell–cell signaling, biological processes, and cell signaling. Exosomes have been identified as playing a role in rheumatoid arthritis-related joint inflammation (RA). Uniquely functioning extracellular vesicles (EVs) are responsible for the transport of autoantigens and mediators between distant cells. In addition, paracrine factors, such as exosomes, modulate the immunomodulatory function of mesenchymal stem cells (MSCs). In addition to transporting genetic information, exosomes convey miRNAs between cells and have been studied as drug delivery vehicles. In animal models, it has been observed that MSCs secrete EVs with immunomodulatory properties, and promising results have been observed in this area. By understanding the diversity of exosomal contents and their corresponding targets, it may be possible to diagnose autoimmune diseases. Exosomes can be employed as diagnostic biomarkers for immunological disorders. We here discuss the most recent findings regarding the diagnostic, prognostic, and therapeutic potential of these nanoparticles in rheumatoid arthritis and provide an overview of the evidence pertaining to the biology of exosomes in RA.

Synthesis and characterization of silica nanoparticles from rice ashes coated with chitosan/cancer cell membrane for hepatocellular cancer treatment

Dual pH-sensitive smart nanocarriers based on silica nanoparticles (SNPs) extracted from rice husk ashes (RHAs) to effectively inhibit liver cancer cell proliferation were investigated. The SNPs were coated with chitosan (CH) and loaded with doxorubicin (DOX), then functionalized with cell membrane (CM) for homologous targeting ability. The FTIR spectra showed an absorption wave number at 1083 cm^-1 which confirmed the existence of the SiOSi group, ratifying that the nanocarriers belong to silica species. The Korsmeyer-Peppas kinetic model reported R² values of 0.996 and 0.931 for pH = 5.4 and pH = 7.4, respectively, demonstrating pH-responsive behavior of the nanocarriers. The cytotoxicity test confirmed that the HepG2 cell line treated with different SNP-CH-CM concentrations had no detectable significant cell toxicity, however, SNP-CH-DOX-CM induced greater cell death. In vivo tests revealed that SNP-CH-DOX-CM suppressed liver cancer growth in nude mice, demonstrating high pharmaceutical capability. Histological examination of vital organs showed that the targeted drug delivery system (DDS) had minor in vivo toxicity. In the light of its high treatment efficacy and minimal side effects, the investigated DDS is promising for the therapy of liver cancer.

Hypoxia-Triggered Bioreduction of Poly(N-oxide)-Drug Conjugates Enhances Tumor Penetration and Antitumor Efficacy

PEGylation prolongs the blood circulation time of drugs; however, it simultaneously reduces the tumor penetration of drugs due to the nonfouling function and bulky hydrodynamic volume of PEG, leading to unsatisfactory outcomes in the treatment of solid tumors. Herein, we report the in situ growth of a bioreducible polymer of poly(N-oxide) from an important protein drug of interferon alpha (IFN) to generate site-specific IFN-poly(N-oxide) conjugates with higher bioactivity than a clinically used PEGylated IFN of PEGASYS. An IFN-poly(N-oxide) conjugate is screened out to have a circulating half-life as long as 51 h, which is similar to that of PEGASYS but 96-fold greater than that of IFN. However, the conjugate greatly outperforms PEGASYS and IFN in tumor penetration and antitumor efficacy in mice bearing melanoma. This enhanced tumor penetration is ascribed to the adsorption-mediated transcytosis of the conjugate whose poly(N-oxide) is biologically reduced into poly(tertiary amine), under hypoxia, which can be further protonated in the acidic tumor microenvironment. These novel findings demonstrate that poly(N-oxide)s are not only long-circulating but also bioreducible under hypoxia and are of great promise as next-generation carriers to deliver drugs into the interior of solid tumors to enhance their antitumor efficacy.

A ROS-responsive biomimetic nano-platform for enhanced chemo-photodynamic-immunotherapy efficacy

Due to the complex bloodstream components, tumor microenvironment and tumor heterogeneity, traditional nanoparticles have a limited effect (low drug delivery efficiency and poor penetration to the deeper tumor) on eradicating tumors. To solve these challenges, novel platelet membrane-coated nanoparticles (PCDD NPs) were constructed for combined chemo-photodynamic- and immunotherapy of melanoma. The platelet membrane imparted the PCDD nanoparticles with an excellent long circulation effect and tumor targeting ability, which solved the issues of low drug delivery efficiency. After reaching the tumor cells, it releases the drug-loaded CDD micelles, becoming positively charged and facilitating the deep penetration of tumors. Cytotoxic and apoptosis experiments showed that PCDD nanoparticles have the strongest tumor cell killing ability. Based on the excellent results in vitro, PCDD was used to assess anti-tumor and distal tumor inhibition in rat models. The results revealed that the PCDD combined PDT, immunotherapy and chemotherapy could not only inhibit the primary tumor growth (inhibition rate: 92.0%) but also suppress the distant tumor growth (inhibition rate: 90.7%) and lung metastasis, which is far more effective compared to the commercial Taxotere®. Exploration of the molecular mechanism showed that in vivo immune response induced an increase in positive immune responders, suppressed negative immune suppressors, and established an inflammatory tumor immune environment, leading to excellent results in tumor suppression and lung metastasis. In conclusion, this novel multifunctional PCDD nanoparticle is a promising platform for tumor combined chemotherapy, photodynamic therapy (PDT) and immunotherapy.

Immunogenic Cell Death Activates the Tumor Immune Microenvironment to Boost the Immunotherapy Efficiency

Tumor immunotherapy is only effective in a fraction of patients due to a low response rate and severe side effects, and these challenges of immunotherapy in clinics can be addressed through induction of immunogenic cell death (ICD). ICD is elicited from many antitumor therapies to release danger associated molecular patterns (DAMPs) and tumor-associated antigens to facilitate maturation of dendritic cells (DCs) and infiltration of cytotoxic T lymphocytes (CTLs). The process can reverse the tumor immunosuppressive microenvironment to improve the sensitivity of immunotherapy. Nanostructure-based drug delivery systems (NDDSs) are explored to induce ICD by incorporating therapeutic molecules for chemotherapy, photosensitizers (PSs) for photodynamic therapy (PDT), photothermal conversion agents for photothermal therapy (PTT), and radiosensitizers for radiotherapy (RT). These NDDSs can release loaded agents at a right dose in the right place at the right time, resulting in greater effectiveness and lower toxicity. Immunotherapeutic agents can also be combined with these NDDSs to achieve the synergic antitumor effect in a multi-modality therapeutic approach. In this review, NDDSs are harnessed to load multiple agents to induce ICD by chemotherapy, PDT, PTT, and RT in combination of immunotherapy to promote the therapeutic effect and reduce side effects associated with cancer treatment.

Extracellular vesicles for improved tumor accumulation and penetration

Extracellular vesicles (EVs), including microparticles and exosomes, have emerged as potential tools for tumor targeting delivery during the past years. Recently, mass of strategies are applied to assist EVs to accumulate and penetrate into deep tumor sites. In this review, EVs from different cells with unique innate characters and engineered approaches (e.g. chemical engineering, genetical engineering and biomimetic engineering) as drug delivery systems to enhance tumor accumulation and penetration are summarized. Meanwhile, efficient biological function modulation (e.g. extracellular matrix degradation, mechanical property regulation and transcytosis) is introduced to facilitate tumor accumulation and penetration of EVs. Finally, the prospects and challenges on further clinical applications of EVs are discussed.

Combination of tumor vessel normalization and immune checkpoint blockade for breast cancer treatment via multifunctional nanocomplexes

Tumor vessel normalization can alleviate hypoxia, reduce the intratumoral infiltration of immunosuppressive cells and increase the intratumoral infiltration of immune effector cells (CD8⁺ T cells), further reversing the immunosuppressive microenvironment. Here, nanocomplexes (lipo/St@FA-COSA/BMS-202) which can accurately deliver drugs to tumor tissues and release different drugs at different sites with different rates were prepared to combine tumor vessel normalization with immune checkpoint blockade. The results of drug release in vitro showed that in a pH 6.5 release medium, lipo/St@FA-COSA/BMS-202 rapidly released the vascular normalizing drug (sunitinib, St) and slowly released the PD-1/PD-L1-blocking drug (BMS-202). The results of in vivo experiments showed that the rapidly released St normalized tumor vessels and formed an immunosupportive microenvironment which improved the anti-tumor efficacy of BMS-202. In conclusion, the drug delivery strategy significantly inhibited tumor growth and had excellent anti-tumor efficacy, which can provide a potential approach for effective tumor treatment.

Anticancer nanomedicines harnessing tumor microenvironmental components

INTRODUCTION

Small-molecular drugs are extensively used in cancer therapy, while they have issues of nonspecific distribution and consequent side effects. Nanomedicines that incorporate chemotherapeutic drugs have been developed to enhance the therapeutic efficacy of these drugs and reduce their side effects. One of the promising strategies is to prepare nanomedicines by harnessing the unique tumor microenvironment (TME).

AREAS COVERED

The TME contains numerous cell types that specifically express specific antibodies on the surface including tumor vascular endothelial cells, tumor-associated adipocytes, tumor-associated fibroblasts, tumor-associated immune cells and cancer stem cells. The physicochemical environment is characterized with a low pH, hypoxia, and a high redox potential resulting from tumor-specific metabolism. The intelligent nanomedicines can be categorized into two groups: the first group which is rapidly responsive to extracellular chemical/biological factors in the TME and the second one which actively and/or specifically targets cellular components in the TME.

EXPERT OPINION

In this paper, we review recent progress of nanomedicines by harnessing the TME and illustrate the principles and advantages of different strategies for designing nanomedicines, which are of great significance for exploring novel nanomedicines or translating current nanomedicines into clinical practice. We will discuss the challenges and prospects of preparing nanomedicines to utilize or alter the TME for achieving effective, safe anticancer treatment.

Intracellular Self-Immolative Polyprodrug with Near-Infrared Light Guided Accumulation and in Vivo Visualization of Drug Release

The selective accumulation and real-time monitoring of drug release at tumor site are the key bottlenecks to the clinical translation of polyprodrug. Herein, an intracellular self-immolative polyprodrug (PMTO) is exploited, which not only shows the enhanced cellular internalization and selective accumulation in tumor site under the mild hyperthermia triggered by laser irradiation, but also possesses the self-monitoring drug release ability in vivo. The polyprodrug amphiphiles are synthesized by sequential esterification reaction, and hydrophilic poly(ethylene glycol) serves as blocking agent. On account of the mild hyperthermia produced by PMTO under the laser irradiation at tumor site, the cell membranous permeability increases, resulting in the enhanced cellular internalization and drug accumulation in tumor. After internalized by cells, the self-immolative PMTO nanoparticles can release free mitoxantrone (MTO) in intracellular reductive environment, and ratiometric photoacoustic imaging based on distinct signals between MTO and PMTO is presented to trace the drug release in vivo. Finally, this self-monitoring polyprodrug presents significant tumor suppression efficacy, which exhibits great potential for guiding the clinical medication in cancer treatment.

An NIR Discrete Metallacycle Constructed from Perylene Bisimide and Tetraphenylethylene Fluorophores for Imaging-Guided Cancer Radio-Chemotherapy

To promote the clinical theranostic performances of platinum-based anticancer drugs, imaging capability is urgently desired, and their chemotherapeutic efficacy needs to be upgraded. Herein, a theranostic metallacycle (M) is developed for imaging-guided cancer radio-chemotherapy using perylene bisimide fluorophore (PPy) and tetraphenylethylene-based di-Pt(II) organometallic precursor (TPE-Pt) as building blocks. The formation of this discrete supramolecular coordination complex facilitates the encapsulation of M by a glutathione (GSH)-responsive amphiphilic block copolymer to prepare M-loaded nanoparticles (MNPs). TPE-Pt acts as a chemotherapeutic drug and also an excellent radiosensitizer, thus incorporating radiotherapy into the nanomedicine to accelerate the therapeutic efficacy and overcome drug resistance. The NIR-emission of PPy is employed to detect the intracellular delivery and tissue distribution of MNPs in real time. In vitro and in vivo investigations demonstrate the excellent anticancer efficacy combining chemotherapy and radiotherapy; the administration of this nanomedicine effectively inhibits the tumor growth and greatly extends the survival rate of cisplatin-resistant A2780CIS-tumor-bearing mice. Guided by in vivo fluorescence imaging, radio-chemotherapy is precisely carried out, which facilitates boosting of the therapeutic outcomes and minimizing undesired side effects. The success of this theranostic system brings new hope to supramolecular nanomedicines for their potential clinical translations.

Engineered strategies to enhance tumor penetration of drug-loaded nanoparticles

Nanocarriers have been widely employed in preclinical studies and clinical trials for the delivery of anticancer drugs. The most important causes of failure in clinical translation of nanocarriers is their inefficient accumulation and penetration which arises from special characteristics of tumor microenvironment such as insufficient blood supply, dense extracellular matrix, and elevated interstitial fluid pressure. Various strategies such as engineering extracellular matrix, optimizing the physicochemical properties of nanocarriers have been proposed to increase the depth of tumor penetration; however, these strategies have not been very successful so far. Novel strategies such as transformable nanocarriers, transcellular transport of peptide-modified nanocarriers, and bio-inspired carriers have recently been emerged as an advanced generation of drug carriers. In this study, the latest developments of nanocarrier-based drug delivery to solid tumor are presented with their possible limitations. Then, the prospects of advanced drug delivery systems are discussed in detail.

Rapid pH-responsive self-disintegrating nanoassemblies balance tumor accumulation and penetration for enhanced anti-breast cancer therapy

The dilemma of tumor accumulation and deep penetration has always been a barrier in antitumor therapy. Stimuli-responsive size changeable drug delivery systems provide possible solutions. Nevertheless, the low size-shrinkage efficiency limited the antitumor effects. In this study, an instant pH-responsive size shrinkable nanoassemblies named self-aggregated DOX@HA-CD (SA-DOX@HA-CD) was formulated using small-sized hyaluronic acid modified carbon dots (HA-CD) as monomers, which could self-aggregate into raspberry-like structure via hydrophobicity force in neutral pH and rapidly disassemble into shotgun-like DOX-loaded CD monomer in simulated tumor microenvironment (pH 6.5), owing to the transformation in electrical charge and hydrophobicity/hydrophilicity of this system. The transmission electron microscopy showed that the clustered SA-DOX@HA-CD had a diameter of ~150 nm, and thoroughly disassembled into ~30 nm nanoparticles in response to acidic environment. The disassemble efficiency was approximately 100%. Attributed to this property, SA-DOX@HA-CD led to enhanced cellular internalization and accumulation in 4T1 cells in simulated tumor microenvironment, as well as deep tumor penetration in 3D tumor spheroid model. Besides, the imine bond between DOX and HA-CD endowed DOX with pH-responsive release profile in the acidic lysosome environment. Furthermore, in the orthotopic 4T1 tumor-bearing mouse model, SA-DOX@HA-CD demonstrated higher tumor accumulation than non-aggregated DOX-HA-CD. Meanwhile, in response to the acid tumor microenvironment, the dissociated DOX-HA achieved deep tumor penetration, which consequently resulted in 2.5-fold higher antitumor efficiency. The formulation of self-aggregated SA-DOX@HA-CD provides a simple and effective alternative to prepare pH-responsive size-shrinkable nanodrug delivery systems. STATEMENT OF SIGNIFICANCE: The heterogeneity of tumor vasculature and the high tumor interstitial pressure lead to the barriers in tumor accumulation and deep penetration, which calls for opposite properties (e.g. size) of drug delivery systems. To address this dilemma, various size changeable nanoparticles have been developed utilizing special features of tumor microenvironment, such as pH, enzyme and reactive oxygen species. Nevertheless, the current strategies face the problems of incomplete hydrolysis of chemical bonds or insufficient enzyme degradation, which result in only partial size shrinkage, hindering the tumor deep penetration effects. Here we developed a self-assembled nanocluster, which could respond to acidic pH rapidly and thoroughly disassemble into small nanodots due to the alteration of hydrophobicity/hydrophilicity/charge, leading to approximately 100% dissociation. This strategy provides a new concept for design of size changeable drug delivery systems.

Charge-reversal biodegradable MSNs for tumor synergetic chemo/photothermal and visualized therapy

Given the difficulties of biodegradation of mesoporous silica nanoparticles (NPs), enrichment and penetration of tumor sites, and real-time monitoring of the treatment process, we developed a kind of mannose-doping doxorubicin-loading mesoporous silica nanoparticle (MSN-Man-DOX) and coated by polydopamine-Gd³⁺ (PDAGd) metal-phenolic networks, as well as modified by poly (2-Ethyl-2-Oxazoline) (PEOz), constructing a novel nanomedicine MSN-Man-DOX@PDA-Gd-PEOz. Its pH-responsive charge reversal, photothermal, biodegradation, drug release, and magnetic resonance imaging (MRI) properties were evaluated in vitro. Cellular uptake, tumor penetration, lysosomal escape properties, as well as cell safety and toxicity of the nanoplatform were investigated through cell experiments. Finally, the MRI, organ distribution, photothermal condition, and comprehensive anti-tumor therapy in vivo were evaluated comprehensively through animal experiments. Research results showed that MSN-Man-DOX@PDA-Gd-PEOz had outstanding tumor enrichment and penetration abilities, which can produce excellent treatment effects through the synergistic effect of chemotherapy and photothermal therapy (PTT) with the function of magnetic resonance imaging contrast agent for disease monitoring. Besides, after finishing the therapeutic effect MSN-Man-DOX@PDA-Gd-PEOz can be biodegraded, so it had a good prospect of clinical application.

Emerging strategies based on nanomaterials for ionizing radiation-optimized drug treatment of cancer

Drug-radiotherapy is a common and effective combinational treatment for cancer. This study aimed to explore the ionizing radiation-optimized drug treatment based on nanomaterials so as to improve the synergistic efficacy of drug-radiotherapy against cancer and limit the adverse effect on healthy organs. In this review, these emerging strategies were divided into four parts. First, the delivery of the drug-loaded nanoparticles was optimized owing to the strengthened passive targeting process, active targeting process, and cell targeting process of nanoparticles after ionizing radiation exposure. Second, nanomaterials were designed to respond to the ionizing radiation, thus leading to the release of the loading drugs controllably. Third, radiation-activated pro-drugs were loaded onto nanoparticles for radiation-triggered drug therapy. In particular, nontoxic nanoparticles with radiosensitization capability and innocuous radio-dynamic contrast agents can be considered as radiation-activated drugs, which were discussed in this review. Fourth, according to the various synergetic mechanisms, radiotherapy could improve the drug response of cancer, obtaining optimized drug-radiotherapy. Finally, relative suggestions were provided to further optimize these aforementioned strategies. Therefore, a novel topic was selected and the emerging strategies in this region were discussed, aiming to stimulate the inspiration for the development of ionizing radiation-optimized drug treatment based on nanomaterials.

Nucleic Acid Delivery with Red-Blood-Cell-Based Carriers

Gene therapy has the potential to become a staple of 21st-century medicine. However, to overcome the limitations of existing gene-delivery therapies, that is, poor stability and inefficient and delivery and accumulation of nucleic acids (NAs), safe drug-delivery systems (DDSs) allowing the prolonged circulation and expression of the administered genes in vivo are needed. In this review article, the development of DDSs over the past 70 years is briefly described. Since synthetic DDSs can be recognized and eliminated as foreign substances by the immune system, new approaches must be found. Using the body's own cells as DDSs is a unique and exciting strategy and can be used in a completely new way to overcome the critical limitations of existing drug-delivery approaches. Among the different circulatory cells, red blood cells (RBCs) are the most abundant and thus can be isolated in sufficiently large quantities to decrease the complexity and cost of the treatment compared to other cell-based carriers. Therefore, in the second part, this article describes 70 years of research on the development of RBCs as DDSs, covering the most important RBC properties and loading methods. In the third part, it focuses on RBCs as the NA delivery system with advantages and drawbacks discussed to decide whether they are suitable for NA delivery in vivo.

Nanodrug Delivery Systems Modulate Tumor Vessels to Increase the Enhanced Permeability and Retention Effect

The use of nanomedicine for antitumor therapy has been extensively investigated for a long time. Enhanced permeability and retention (EPR) effect-mediated drug delivery is currently regarded as an effective way to bring drugs to tumors, especially macromolecular drugs and drug-loaded pharmaceutical nanocarriers. However, a disordered vessel network, and occluded or embolized tumor blood vessels seriously limit the EPR effect. To augment the EPR effect and improve curative effects, in this review, we focused on the perspective of tumor blood vessels, and analyzed the relationship among abnormal angiogenesis, abnormal vascular structure, irregular blood flow, extensive permeability of tumor vessels, and the EPR effect. In this commentary, nanoparticles including liposomes, micelles, and polymers extravasate through the tumor vasculature, which are based on modulating tumor vessels, to increase the EPR effect, thereby increasing their therapeutic effect.

Pre- and Post-Transcriptional Regulation of cFLIP for Effective Cancer Therapy Using pH-Ultrasensitive Nanoparticles

Cellular FLIP (cFLIP) is a crucial player of apoptosis-regulated pathways that is frequently overexpressed in solid cancers. To inhibit c-FLIP, pre- and post-transcriptionally, a multifunctional nanoparticle (NP) was created to deliver cFLIP-specific small interfering RNA (siRNA) into cancer cells. Specifically, Vorinostat (Vor)-loaded mesoporous silica nanoparticles (MSN) were conjugated with polyethylenimine-biotin (PB), followed by electrostatically binding with cFLIP siRNA (Vor/siR@MSN-PB). To stabilize and prolong the circulation time of nanoparticles, a bialdehyde-modified poly(ethylene glycol) (PEG) was cross-linked onto the polyethylenimine (PEI) backbone via the formation of the imine linkage (Schiff base) (Vor/siR@MSN-PB-PEG). The Schiff base is highly stable at physiological pH 7.4 but labile under slightly acidic pH conditions. In the acidic tumor microenvironment (TME), the PEG outer layer could be rapidly cleaved, resulting in the switching of the nanoparticle surface charge to positive, which specifically enhances internalization of the NPs to the biotin-positive tumor cells. Our results demonstrated the successful preparation of Vor/siR@MSN-PB-PEG NPs, in which the siRNA was effectively protected in serum and regulated the expression of cFlip, post-transcriptionally. The presence of the PEG layer resulted in high tumor accumulation and high efficacy in tumor inhibition, which was a result of the efficient cFLIP suppression. Furthermore, in the low-dose regimen of Vorinostat-the pre-transcriptional cFLIP suppressor, treatment with Vor/siR@MSN-PB-PEG NPs was found to be safe with the treated mice, indicating a promising combination regimen for cancer therapy.

Development of Non-Porous Silica Nanoparticles towards Cancer Photo-Theranostics

Nanoparticles have demonstrated several advantages for biomedical applications, including for the development of multifunctional agents as innovative medicine. Silica nanoparticles hold a special position among the various types of functional nanoparticles, due to their unique structural and functional properties. The recent development of silica nanoparticles has led to a new trend in light-based nanomedicines. The application of light provides many advantages for in vivo imaging and therapy of certain diseases, including cancer. Mesoporous and non-porous silica nanoparticles have high potential for light-based nanomedicine. Each silica nanoparticle has a unique structure, which incorporates various functions to utilize optical properties. Such advantages enable silica nanoparticles to perform powerful and advanced optical imaging, from the in vivo level to the nano and micro levels, using not only visible light but also near-infrared light. Furthermore, applications such as photodynamic therapy, in which a lesion site is specifically irradiated with light to treat it, have also been advancing. Silica nanoparticles have shown the potential to play important roles in the integration of light-based diagnostics and therapeutics, termed "photo-theranostics". Here, we review the recent development and progress of non-porous silica nanoparticles toward cancer "photo-theranostics".