Tumor-Acidity-Cleavable Maleic Acid Amide (TACMAA): A Powerful Tool for Designing Smart Nanoparticles To Overcome Delivery Barriers in Cancer Nanomedicine

Bioresponsive nanomedicines based on dynamic covalent bonds

Trends in the development of modern medicine necessitate the efficient delivery of therapeutics to achieve the desired treatment outcomes through precise spatiotemporal accumulation of therapeutics at the disease site. Bioresponsive nanomedicine is a promising platform for this purpose. Dynamic covalent bonds (DCBs) have attracted much attention in studies of the fabrication of bioresponsive nanomedicines with an abundance of combinations of therapeutic modules and carrier function units. DCB-based nanomedicines could be designed to maintain biological friendly synthesis and site-specific release for optimal therapeutic effects, allowing the complex to retain an integrated structure before accumulating at the disease site, but disassembling into individual active components without compromising function in the targeted organs or tissues. In this review, we focus on responsive nanomedicines containing dynamic chemical bonds that can be cleaved by various specific stimuli, enabling achievement of targeted drug release for optimal therapy in various diseases.

A Tumor-Penetrating Nanomedicine Improves the Chemoimmunotherapy of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most malignant tumors with a low survival rate. The therapeutic effect of chemotherapy and immunotherapy for PDAC is disappointing due to the presence of dense tumor stroma and immunosuppressive cells in the tumor microenvironment (TME). Herein, a tumor-penetrating nanoparticle is reported to modulate the deep microenvironment of PDAC for improved chemoimmunotherapy. The tumor pH-sensitive polymer is synthesized by conjugating N,N-dipentylethyl moieties and monomethoxylpoly(ethylene glycol) onto PAMAM dendrimer, into whose cavity a hydrophobic gemcitabine (Gem) prodrug is accommodated. They self-assemble into nanoparticles (denoted as SPN@Pro-Gem) with the size around 120 nm at neutral pH, but switch into small particles (≈8 nm) at tumor site to facilitate deep delivery of Gem into the tumor parenchyma. In addition to killing cancer cells that resided deeply in the tumor tissue, SPN@Pro-Gem could modulate the TME by reducing the abundance of tumor-associated macrophages and myeloid-derived suppressor cells as well as upregulating the expression level of PD-L1 of tumor cells. This collectively facilitates the infiltration of cytotoxic T cells into the tumors and renders checkpoint inhibitors more effective in previously unresponsive PDAC models. This study reveals a promising strategy for improving the chemoimmunotherapy of pancreatic cancer.

Innovations in Biomaterial Design toward Successful RNA Interference Therapy for Cancer Treatment

Gene regulation using RNA interference (RNAi) therapy has been developed as one of the frontiers in cancer treatment. The ability to tailor the expression of genes by delivering synthetic oligonucleotides to tumor cells has transformed the way scientists think about treating cancer. However, its clinical application has been limited due to the need to deliver synthetic RNAi oligonucleotides efficiently and effectively to target cells. Advances in nanotechnology and biomaterials have begun to address the limitations to RNAi therapeutic delivery, increasing the likelihood of RNAi therapeutics for cancer treatment in clinical settings. Herein, innovations in the design of nanocarriers for the delivery of oligonucleotides for successful RNAi therapy are discussed.

Protein nanogels with enhanced pH-responsive dynamics triggered by remote NIR for systemic protein delivery and programmable controlled release

Therapeutic proteins represent promising treatments in medical applications; however, direct administration of native proteins frequently suffers from in vivo enzymatic degradation or denaturation in hostile environments. Engineering proteins into biocompatible formulations can be used to solve these problems. Despite years of effort, efficient systemic delivery followed by successful release from the formulation remains a challenge. Herein, we describe a pH-responsive nanogel (PI825@PDC/protein NGs) formed by host-guest recognition of 6-arm PEGylated crystalline β-cyclodextrin (β-CD) and near-infrared IR825 dye, which affords highly efficient encapsulation of proteins during their self-assembly. PI825@PDC/protein NGs are robust enough to withstand hostile physiological conditions both in vitro and in vivo and could be slightly disassociated from protein release in acidic environments due to the anchored pH-responsive 2,3-dimethylmaleic anhydride (DMA) linker. Furthermore, the pH-responsive dynamics can be greatly enhanced by elevated temperature upon remote (Near-infrared spectroscopy) NIR irradiation of the IR825 within NGs, generating programmable release of loaded proteins for enhanced cancer treatment. This study describes a general method to load proteins with high efficiency for systemic delivery, followed by programmable protein release by remote NIR irradiation and offers new insights for protein engineering and potential medical applications.

Biomaterials-Based Delivery of Therapeutic Antibodies for Cancer Therapy

Considerable breakthroughs in the treatment of malignant tumors using antibody drugs, especially immunomodulating monoclonal antibodies (mAbs), have been made in the past decade. Despite technological advancements in antibody design and manufacture, multiple challenges face antibody-mediated cancer therapy, such as instability in vivo, poor tumor penetration, limited response rate, and undesirable off-target cytotoxicity. In recent years, an increasing number of biomaterials-based delivery systems have been reported to enhance the antitumor efficacy of antibody drugs. This review summarizes the advances and breakthroughs in integrating biomaterials with therapeutic antibodies for enhanced cancer therapy. A brief introduction to the principal mechanism of antibody-based cancer therapy is first established, and then various antibody immobilization strategies are provided. Finally, the current state-of-the-art in biomaterials-based antibody delivery systems and their applications in cancer treatment are summarized, highlighting how the delivery systems augment the therapeutic efficacy of antibody drugs. The outlook and perspective on biomaterials-based delivery of antitumor antibodies are also discussed.

Recent progress on charge-reversal polymeric nanocarriers for cancer treatments

Nanocarriers (NCs) for delivery anticancer therapeutics have been under development for decades. Although great progress has been achieved, the clinic translation is still in the infancy. The key challenge lies in the biological barriers which lie between the NCs and the target spots, including blood circulation, tumor penetration, cellular uptake, endo-/lysosomal escape, intracellular therapeutics release and organelle targeting. Each barrier has its own distinctive microenvironment and requires different surface charge. To address this challenge, charge-reversal polymeric NCs have been a hot topic, which are capable of overcoming each delivery barrier, by reversing their charges in response to certain biological stimuli in the tumor microenvironment. In this review, the triggering mechanisms of charge reversal, including pH, enzyme and redox approaches are summarized. Then the corresponding design principles of charge-reversal NCs for each delivery barrier are discussed. More importantly, the limitations and future prospects of charge-reversal NCs in clinical applications are proposed.

Recent Advances in pH- or/and Photo-Responsive Nanovehicles

The combination of nanotechnology and chemotherapy has resulted in more effective drug design via the development of nanomaterial-based drug delivery systems (DDSs) for tumor targeting. Stimulus-responsive DDSs in response to internal or external signals can offer precisely controlled delivery of preloaded therapeutics. Among the various DDSs, the photo-triggered system improves the efficacy and safety of treatment through spatiotemporal manipulation of light. Additionally, pH-induced delivery is one of the most widely studied strategies for targeting the acidic micro-environment of solid tumors. Accordingly, in this review, we discuss representative strategies for designing DDSs using light as an exogenous signal or pH as an endogenous trigger.

Co-inhibition of the TGF-β pathway and the PD-L1 checkpoint by pH-responsive clustered nanoparticles for pancreatic cancer microenvironment regulation and anti-tumor immunotherapy

Pancreatic ductal adenocarcinoma (PDAC) has a dense extracellular matrix (ECM) surrounding tumor cells to sequester CD8+ T cell infiltration and prevent drug penetration. Concomitant inhibition of both the TGF-β pathway and the PD-1/PD-L1 checkpoint is a viable strategy to increase T cell infiltration and cytotoxicity. Here, we used an acidic tumor extracellular pH (pHe) responsive clustered nanoparticle (LYiClustersiPD-L1) to deliver TGF-β receptor inhibitors (LY2157299) and siRNA targeting PD-L1 (siPD-L1) for PDAC stroma microenvironment regulation and antitumor immunotherapy. LY2157299 encapsulated in the hydrophobic core of the nanoparticle can effectively inhibit the activation of pancreatic stellate cells (PSCs) and result in a reduction in type I collagen. siPD-L1 adsorbed on the surface of the nanoparticle was released with small size poly(amidoamine) (PAMAM) at the surface of LYiClustersiPD-L1 under pHe and penetrated into the tumors to silence PD-L1 gene expression in tumor cells. Compared to monotherapy, LYiClustersiPD-L1 significantly increased tumor infiltrating CD8+ T cells and provoked antitumor immunity to synergistically suppress tumor growth in both a subcutaneous Panc02 xenograft model and an orthotopic tumor model.

Multi-stimuli responsive hollow MnO2-based drug delivery system for magnetic resonance imaging and combined chemo-chemodynamic cancer therapy

The exploration and application of hollow manganese dioxide nanoparticle (HMDN) for biosensing and biomedicine has gained significant research attention in the past decade. In this study, a type of biodegradable HMDN is prepared for multi-stimuli responsive tumor-targeted drug delivery, which was successfully loaded with doxorubicin hydrochloride (DOX). Then, the drug-loaded HMDN is functionalized with polyethyleneimine (PEI) as a gatekeeper followed by citraconic anhydride (cit) functionalized poly-_L-lysine (PLL(cit)) as a charge reversal moiety successively to yield the resultant DOX@HMDN-PEI-PLL(cit) nanoparticles. In vitro study showed that DOX@HMDN-PEI-PLL(cit) exhibited a ''stealthy'' property under physiological conditions and enhanced cellular uptake activity in response to the mild acidic tumor microenvironment due to the departure of cit. In vitro release profiles proved that the decomposition of HMDN to Mn²⁺ under acidic condition/high glutathione (GSH) concentration triggered the release of DOX and Fenton-like reaction for improved therapeutic effect. And Mn²⁺ could also act as a T₁-weighted magnetic resonance imaging (MRI) contrast agent. In vivo studies further proved with both the charge reversal and combined therapy properties, DOX@HMDN-PEI-PLL(cit) showed a good tumor enrichment ability and therapeutic effect with few side effects to the mice. These results demonstrate that DOX@HMDN-PEI-PLL(cit) nanoparticles are promising drug delivery systems for targeted cancer therapy. STATEMENT OF SIGNIFICANCE: Traditional chemotherapy based on anticancer drugs such as doxorubicin hydrochloride (DOX) shows limited efficacy with serious side effects. We employed hollow manganese dioxide nanoparticle (HMDN) to loaded DOX and coated it with polyethyleneimine and then citraconic anhydride functionalized poly-_L-lysine to endow it with a charge reversal property to obtain a multi-stimuli responsive drug delivery system named DOX@HMDN-PEI-PLL(cit). It was ''stealthy'' with low cellular uptake capability by normal cells, but could be "acid-activated" in tumors for endocytosis by cancer cells to reduce side effects. HMDN could be decomposed to Mn²⁺ under acidic conditions/high glutathione concentration to release DOX intracellular. DOX and Mn²⁺ catalyzed Fenton-like reaction could achieve a combined chemo-chemodynamic therapy. And Mn²⁺ could be used for T₁-weighted magnetic resonance imaging.

Human serum albumin-based doxorubicin prodrug nanoparticles with tumor pH-responsive aggregation-enhanced retention and reduced cardiotoxicity

Doxorubicin (DOX) is a widely-used anticancer drug, but its cardiotoxicity severely hampers its potency in chemotherapy. Herein, human serum albumin (HSA) is engaged as a biocompatible nanocarrier to load a pH-sensitive DOX prodrug, DMDOX, generating HSA-DMDOX nanoparticles via self-assembly driven by hydrophobic interactions. HSA-DMDOX disperses well in a physiological environment (∼40 nm) but aggregates in a tumor acidic microenvironment (pH 6.5, ∼140 nm) owing to the hydrophobicity increase of DMDOX by protonation of carboxylic groups. In vitro anticancer study showed that HSA-DMDOX exhibited enhanced cellular uptake by 4T1 cells and superior cytotoxicity in comparison to HSA-DOX nanoparticles. In vivo study suggested that HSA-DMDOX achieved long blood circulation, aggregation enhanced tumor retention, comparable antitumor efficacy and reduced cardiotoxicity relative to free DOX. Our work presents a facile and effective approach to delivering anthracyclines by HSA-based tumor pH-responsive nanoparticles with aggregation-enhanced tumor retention and reduced toxicity.

Mitochondrion-specific dendritic lipopeptide liposomes for targeted sub-cellular delivery

The mitochondrion is an important sub-cellular organelle responsible for the cellular energetic source and processes. Owing to its unique sensitivity to heat and reactive oxygen species, the mitochondrion is an appropriate target for photothermal and photodynamic treatment for cancer. However, targeted delivery of therapeutics to mitochondria remains a great challenge due to their location in the sub-cellular compartment and complexity of the intracellular environment. Herein, we report a class of the mitochondrion-targeted liposomal delivery platform consisting of a guanidinium-based dendritic peptide moiety mimicking mitochondrion protein transmembrane signaling to exert mitochondrion-targeted delivery with pH sensitive and charge-reversible functions to enhance tumor accumulation and cell penetration. Compared to the current triphenylphosphonium (TPP)-based mitochondrion targeting system, this dendritic lipopeptide (DLP) liposomal delivery platform exhibits about 3.7-fold higher mitochondrion-targeted delivery efficacy. Complete tumor eradication is demonstrated in mice bearing 4T1 mammary tumors after combined photothermal and photodynamic therapies delivered by the reported DLP platform.

pH-Triggered Copper-Free Click Reaction-Mediated Micelle Aggregation for Enhanced Tumor Retention and Elevated Immuno-Chemotherapy against Melanoma

Natural killer (NK) cell-based immunotherapy presents a promising antitumor strategy and holds potential for combination with chemotherapy. However, the suppressed NK cell activity and poor tumor retention of therapeutics hinder the efficacy. To activate NK cell-based immuno-chemotherapy and enhance the tumor retention, we proposed a pH-responsive self-aggregated nanoparticle for the codelivery of chemotherapeutic doxorubicin (DOX) and the transforming growth factor-β (TGF-β)/Smad3 signaling pathway inhibitor SIS3. Polycaprolactone-poly(ethylene glycol) (PCL-PEG₂₀₀₀) micelles modified with dibenzylcyclooctyne (DBCO) or azido (N₃) and coated with acid-cleavable PEG₅₀₀₀ were established. This nanoplatform, namely, M-DN@DOX/SIS3, could remain well dispersed in the neutral systemic circulation, while quickly respond to the acidic tumor microenvironment and intracellular lysosomes, triggering copper-free click reaction-mediated aggregation, leading to the increased tumor accumulation and reduced cellular efflux. In addition, the combination of DOX with SIS3 facilitated by the aggregation strategy resulted in potent inhibition of melanoma tumor growth and significantly increased NK cells, NK cell cytokines, and antitumor T cells in the tumor. Taken together, our study offered a new concept of applying copper-free click chemistry to achieve nanoparticle aggregation and enhance tumor retention, as well as a promising new combined tumor treatment approach of chemotherapy and immunotherapy.

Charge-reversal nanomedicine based on black phosphorus for the development of A Novel photothermal therapy of oral cancer

Driven by the lifestyle habits of modern people, such as excessive smoking, drinking, and chewing betel nut and other cancer-causing foods, the incidence of oral cancer has increased sharply and has a trend of becoming younger. Given the current mainstream treatment means of surgical resection will cause serious damage to many oral organs, so that patients lose the ability to chew, speak, and so on, it is urgent to develop new oral cancer treatment methods. Based on the strong killing effect of photothermal therapy on exposed superficial tumors, we developed a pH-responsive charge reversal nanomedicine system for oral cancer which is a kind of classic superficial tumor. With excellent photothermal properties of polydopamine (PDA) modified black phosphorus nanosheets (BP NSs) as basal material, then used polyacrylamide hydrochloride-dimethylmaleic acid (PAH-DMMA) charge reversal system for further surface modification, which can be negatively charged at blood circulation, and become a positive surface charge in the tumor site weakly acidic conditions due to the breaking of dimethylmaleic amide. Therefore, the uptake of oral cancer cells was enhanced and the therapeutic effect was improved. It can be proved that this nanomedicine has excellent photothermal properties and tumor enrichment ability, as well as a good killing effect on oral cancer cells through in vitro cytotoxicity test and in vivo photothermal test, which may become a very promising new model of oral cancer treatment.

Cyclic Anhydrides as Powerful Tools for Bioconjugation and Smart Delivery

Cyclic anhydrides are potent tools for bioconjugation; therefore, they are broadly used in the functionalization of biomolecules and carriers. The pH-dependent stability and reactivity, as well as the physical properties, can be tuned by the structure of the cyclic anhydride used; thus, their application in smart delivery systems has become very important. This review intends to cover the last updates in the use of cyclic anhydrides as pH-sensitive linkers, their differences in reactivity, and the latest applications found in bioconjugation chemistry or chemical biology, and when possible, in drug delivery.

Smart transformable nanomedicines for cancer therapy

Despite that great progression has been made in nanoparticulate drug delivery systems (nano-DDS), multiple drug delivery dilemmas still impair the delivery efficiency of nanomedicines. Rational design of smart transformable nano-DDS based on the in vivo drug delivery process represents a promising strategy for overcoming delivery obstacle of nano-DDS. In recent years, tremendous efforts have been devoted to developing smart transformable anticancer nanomedicines. Herein, we provide a review to outline the advances in this emerging field. First, smart size-reducible nanoparticles (NPs) for deep tumor penetration are summarized, including carrier degradation-induced, protonation-triggered and photobleaching-induced size reduction. Second, emerging transformable nanostructures for various therapeutic applications are discussed, including prolonging tumor retention, reversing drug-resistance, inhibiting tumor metastasis, preventing tumor recurrence and non-pharmaceutical therapy. Third, shell-detachable nanocarriers are introduced, focusing on chemical bonds breaking-initiated, charge repulsion-mediated and exogenous stimuli-triggered shell detachment approaches. Finally, the future perspectives and challenges of transformable nanomedicines in clinical cancer therapy are highlighted.

Hierarchical responsive micelle facilitates intratumoral penetration by acid-activated positive charge surface and size contraction

Integrating these features of acid-activated positively charged surface and size contraction into single nanoparticle would be an effective strategy for enhancing cellular uptake, intratumoral penetration and accumulation. Here, hierarchical responsive micelle (HVDMs) was developed via RAFT reaction as multifunctional polymer-drug conjugate for maximizing penetration and therapeutic effect against MCF-7 tumor by combining positively charged surface with size contraction: surface zeta-potential reversal (-2 to +12 mV) by protonation of PHEME and size contraction (~81-~41 nm) by simultaneous hydrophobic/hydrophilic conversion (pH ≈ 6.7); the disintegration of hydrazone bond between hydrophobic PVB and DOX triggered drug release (pH ≈ 5.0). The in vitro structural stabilization, cellular uptake and anti-proliferative efficiency were significantly higher than other control groups (CVDMs and HSDMs) at pH 6.7. The markedly increased penetration depth, cellular internalization and anti-tumor efficiency were confirmed in 3D MCSs spheroids at pH 6.7, and the ex vivo DOX fluorescence images further verified obvious penetration and accumulation in internal region of solid tumor. The antitumor effect in vivo demonstrated that HVDMs accelerated tumor atrophy, induced intratumoral cells apoptosis and alleviated system toxicity.

Hypoxia-responsive nanogel as IL-12 carrier for anti-cancer therapy

In the past two decades, protein drugs have evolved to become the most successful and important strategy in cancer therapy. However, systematical administration of protein drugs may cause serious side effects. In order to prepare a new promising hydrophilic drugs carrier, we constructed a PEGylated hyaluronic acid nanogel (NI-MAHA-PEG nanogel) with hypoxia and enzymatic responsiveness, which can selectively release hydrophilic drugs interleukin-12 (IL-12) on demand in a tumor microenvironment. We observed that release of IL-12 from nanogels by hypoxia-responsive stimulation, nanogels have anti-tumor effects on melanoma. Compared with physiological conditions, the IL-12 release rate has achieved remarkable growth under hypoxic conditions. Similarly, the drug release rate increased significantly with the addition of 500 U ml^-1 hyaluronidase. We provide a novel strategy to allow efficient delivery, on-demand release, and enhanced access of proteins to hypoxic tumor regions. The rational design of this nanogels drug delivery system can further explore the use of various drugs to treat many cancers.

Gold nanoparticle-guarded large-pore mesoporous silica nanocomposites for delivery and controlled release of cytochrome c

Efficient delivery of active proteins to specific cells and organs is one of the most important issues in medical applications. However, in most cases, proteins without appropriate carriers face numerous barriers when delivered to the target, due to their unsatisfied properties, such as poor stability, short half-life, and low membrane permeability. Herein, we have presented a large-pore mesoporous silica nanoparticle (LPMSN)-based protein delivery system. LPMSNs were obtained with ethyl acetate as a pore expander. A 2,3-dimethylmaleamic acid-containing silane coupling agent was modified on LPMSNs to provide pH-triggered charge reversal. After Cytochrome c (CC) was encapsulated in the large pores of LPMSNs, amino-terminated polyethylene glycol-modified gold nanoparticles (AuNPs) served as gateguards to cap the tunnels of LPMSNs and to avoid the leakage of CC. Above nanocomposites exhibited the capability to deliver active CC into cancer cells, charge reversal-induced protein release, as well as to initiate the apoptosis machinery of cancer cells in vitro. Importantly, the nanocomposites significantly inhibited tumor growth and extended survival rate without obvious side effects. This study provides a smart and efficient protein delivery platform with good safety profiles for efficacious tumor protein therapy in vivo.

Chemo-physical Strategies to Advance the in Vivo Functionality of Targeted Nanomedicine: The Next Generation

The past few decades have witnessed an evolution of nanomedicine from biologically inert entities to more smart systems, aimed at advancing in vivo functionality. However, we should recognize that most systems still rely on reasonable explanation-including some over-explanation-rather than definitive evidence, which is a watershed radically determining the speed and extent of advancing nanomedicine. Probing nano-bio interactions and desirable functionality at the tissue, cellular, and molecular levels is most frequently overlooked. Progress toward answering these questions will provide instructive insight guiding more effective chemo-physical strategies. Thus, in the next generation, we argue that much effort should be made to provide definitive evidence for proof-of-mechanism, in lieu of creating many new and complicated systems for similar proof-of-concept.

A Sequentially Responsive Nanosystem Breaches Cascaded Bio-barriers and Suppresses P-Glycoprotein Function for Reversing Cancer Drug Resistance

Cancer chemotherapy is challenged by multidrug resistance (MDR) mainly attributed to overexpressed transmembrane efflux pump P-glycoprotein (P-gp) in cancer cells. Improving drug delivery efficacy while co-delivering P-gp inhibitors to suppress drug efflux is an often-used nanostrategy for combating MDR, which is however challenged by cascaded bio-barriers en route to cancer cells and P-gp inhibitors' adverse effects. To effectively breach the cascaded bio-barriers while avoiding P-gp inhibitors' adverse effects, a stealthy, sequentially responsive doxorubicin (DOX) delivery nanosystem (RCMSNs) is fabricated, composed of an extracellular-tumor-acidity-responsive polymer shell (PEG-b-PLLDA), pH/redox dual-responsive mesoporous silica nanoparticle-based carriers (MSNs-SS-Py), and cationic β-cyclodextrin-PEI (CD-PEI) gatekeepers. The PEG-b-PLLDA corona makes RCMSNs stealthy with prolonged blood circulation time. Once tumors are reached, extracellular acidity degrades PEG-b-PLLDA, reversing nanosystem's surface charges to be positive, which drastically improves RCMSNs' tumor accumulation, penetration, and cellular internalization. Within cancer cells, CD-PEI gatekeepers detach to allow DOX unloading in response to intracellular acidity and glutathione and functionally act as a P-gp inhibitor, dampening P-gp's efflux activity by impairing ATP production. Thus, the resultant high-efficacy drug delivery along with reduced P-gp function cooperatively reverses MDR in vitro. Importantly, in preclinical tumor models, DOX@RCMSNs potently suppress MDR tumor growth without eliciting systemic toxicity, demonstrating their potential of clinical translation.

pH/Reduction Dual Stimuli-Triggered Self-Assembly of NIR Theranostic Probes for Enhanced Dual-Modal Imaging and Photothermal Therapy of Tumors

Tumor microenvironment plays a pivotal role in the growth and metastasis of tumors, and has become a promising target for precise diagnosis and treatment of tumors. Herein, a novel smart NIR theranostic probe Cy-1 that can simultaneously respond to low intracellular pH and reductive glutathione (GSH) is reported. This probe has demonstrated to be able to intermolecularly undergo a biologically compatible CBT-Cys condensation reaction to selectively form large nanoaggregates in the tumor microenvironment resulting in its enhanced accumulation and retention in the tumor, which as a consequence significantly improves the sensitivity of NIR/photoacoustic imaging and photothermal therapeutic efficacy of tumors in living mice. We thus believe that this dual stimuli-mediated self-assembly strategy may offer a promising and universal platform for cancer theranostics.

A self-accelerated biocatalyst for glucose-initiated tumor starvation and chemodynamic therapy

A self-accelerated biocatalyst (Bio-Cat) was developed based on BSA and GOx crosslinked nanoproteins for glucose-initiated tumor starvation and chemodynamic therapy. Bio-Cat could catalyze the glucose to elevate the intracellular H₂O₂ level and accelerate the conversion of Fe³⁺/Fe²⁺, resulting in an effective starvation therapy and an accelerated Fenton reaction for chemodynamic therapy.

A pH-activated charge convertible quantum dot as a novel nanocarrier for targeted protein delivery and real-time cancer cell imaging

The rapid developments of nanocarriers based on quantum dots (QDs) have been confirmed to show substantial promise for drug delivery and bioimaging. However, optimal QDs-based nanocarriers still need to have their controlled behavior in vitro and in vivo and decrease heavy metal-associated cytotoxicity. Herein, a pH-activated charge convertible QD-based nanocarrier was fabricated by capping multifunctional polypeptide ligands (mPEG-block-poly(ethylenediamine-dihydrolipoic acid-2,3-dimethylmaleic anhydride)-L-glutamate, PEG-P(ED-DLA-DMA)LG) onto the surface of core/multishell CdSe@ZnS/ZnS QD by means of a ligand exchange strategy, followed by uploading of cytochrome C (CC) (CC-loaded QD-PEG-P(ED-DLA-DMA)LG) via electrostatic interactions, in which QDs that were water-soluble and protein-loading were perfectly integrated. That is, the CC-loaded QD-PEG-P(ED-DLA-DMA)LG inherited excellent fluorescence properties from CdSe@ZnS/ZnS QD for real-time imaging, as well as tumor-microenvironment sensitivities from PEG-P(ED-DLA-DMA)LG for enhanced cellular uptake and CC release. Experimental results verified that the QD-PEG-P(ED-DLA-DMA)LG showed enhanced internalization, rapid endo/lysosomal escape, and supplied legible real-time imaging for lung carcinoma cells. Furthermore, pH-triggered charge-convertible ability enabled the QD-PEG-P(ED-DLA-DMA)LG-CC to effectively kill cancer cells better than did the control groups. Hence, constructing smart nanocomposites by facile ligand-exchange strategy is beneficial to QD-based nanocarrier for tumor-targeting cancer therapy.

Advanced engineered nanoparticulate platforms to address key biological barriers for delivering chemotherapeutic agents to target sites

The widespread development of nanocarriers to deliver chemotherapeutics to specific tumor sites has been motivated by the lack of selective targeting during chemotherapy inducing serious side effects and low therapeutic efficacy. The utmost challenge in targeted cancer therapies is the ineffective drug delivery system, in which the drug-loaded nanocarriers are hindered by multiple complex biological barriers that compromise the therapeutic efficacy. Despite considerable progress engineering novel nanoplatforms for the delivery of chemotherapeutics, there has been limited success in a clinical setting. In this review, we identify and analyze design strategies for improved therapeutic efficacy and unique properties of nanoplatforms, including liposomes, polymeric micelles, nanogels, and dendrimers. We provide a comprehensive and integral description of key biological barriers that nanoplatforms are exposed to during their in vivo journey and discuss associated strategies to overcome these barriers based on the latest research and information available in the field. We expect this review to provide constructive information for the rational design of more effective nanoplatforms to advance precision therapies and accelerate their clinical translation.

Synthesis of Carboxy-Dimethylmaleic Amide Linked Polymer Conjugate Based Ultra-pH-sensitive Nanoparticles for Enhanced Antitumor Immunotherapy

Cytotoxic T lymphocytes (CTLs) are an important tool for anticancer immunotherapy. To elicit powerful CTL activities, ultra-pH-sensitive nanoparticles (NPs) based on methoxy poly(ethylene glycol)-b-[poly(diisopropylamino)ethyl methacrylate] have been synthesized as a vaccine delivery platform. A representative CTL epitope, ovalbumin (OVA) peptide antigen, was covalently conjugated to the polymer backbone through an acid responsive carboxy-dimethylmaleic amide linker (CDM) resulting in polymer P-CDM-OVA. Interestingly, while the P-CDM-OVA released OVA peptide slowly in a pH 6.4 buffer, the addition of bovine serum albumin (BSA) mimicking proteins encountered in a cellular and/or in vivo environment significantly accelerated the release process. Successful cell surface presentation of OVA was observed when P-CDM-OVA based ultra-pH-sensitive particles were incubated with antigen presenting cells. These P-CDM-OVA NPs greatly enhanced CTL responses in vivo compared to the free peptide or the previously reported acetalated dextran particles encapsulating OVA. The P-CDM was also investigated for adjuvant conjugation, and the coadministration of P-CDM-OVA and the P-CDM-adjuvant conjugate NPs further improved CTL responses in vivo and effectively reduced tumor growth in mice. Thus, the CDM linked polymer presents a promising platform for anticancer immunotherapy.

100th Anniversary of Macromolecular Science Viewpoint: Biological Stimuli-Sensitive Polymer Prodrugs and Nanoparticles for Tumor-Specific Drug Delivery

The development of smart polymer vehicles to carry and release cytotoxic drugs to tumor tissues and cells while reducing the exposure of drugs in the blood and healthy organs is a highly challenging task with continuously growing interest from multiple fields, including polymer science, pharmaceutical science, nanotechnology, and clinical oncology. Inspired by the unique tumor microenvironment, such as mild acidity and overexpressed enzymes, functional polymer prodrugs and nanoparticles with reversible charge, detachable PEG shell, activatable ligand, and switchable size have been designed to enhance tumor deposition, tumor penetration, tumor cell uptake, and tumoral drug release. Utilizing biological signals inside tumor cells, such as acidic endo/lysosomal pH, elevated glutathione levels, and reactive oxygen species, responsive polymer prodrugs and nanoparticles with good extracellular stability but fast intracellular disintegration have been engineered for specific intracellular drug release. These biological stimuli-sensitive polymer prodrugs and nanoparticles have shown superior specificity and therapeutic efficacy to nonsensitive counterparts and, in certain cases, even clinically approved systems in varying tumor models. In this Viewpoint, design strategies and recent advances of biological stimuli-responsive polymer prodrugs and nanoparticles for tumor-specific drug delivery will be highlighted, and their challenges and future perspectives will be discussed.

Hyaluronic acid-shelled, peptide drug conjugate-cored nanomedicine for the treatment of hepatocellular carcinoma

Peptide-drug conjugate (PDC) is a promising prodrug in drug delivery systems. To fabricate nanostructures with proper molecular design which can self-assemble to spherical morphologies is very important for PDC chemotherapy. In this study, a novel PDC (PDC-DOX₂), in which two doxorubicin (DOX) molecules are conjugated onto a short peptide (KIGLFRWR) with self-assembly function, was designed and synthesized. PDC-DOX₂ with self-assembly properties forms a spherical structure under hydrophobic interaction in water. Hyaluronic acid (HA) was then coated on PDC-DOX₂ micelles to form a HA-shelled, peptide-doxorubicin conjugate-cored nanomedicine (HA@PDC-DOX₂). The amount of HA can regulate the particle size and stabilization of HA@PDC-DOX₂. In addition, HA can actively enhance the targeting effects of PDC-DOX₂ micelles since it can interact with overexpressed receptors in cancer cells. The core-shell structured HA@PDC-DOX₂ nanomedicine showed significantly enhanced potency against hepatocellular carcinoma compared to PDC-DOX₂ micelles as well as free DOX. In this work, a novel PDC which can self-assemble to spherical morphologies and a core-shell structure HA@PDC-DOX₂ nanomedicine are designed and prepared. It provides a convenient strategy for the size control of PDC assemblies and constructs effective PDC-based drug delivery systems for cancer treatment.

Antineoplastic Drug-Free Anticancer Strategy Enabled by Host-Defense-Peptides-Mimicking Synthetic Polypeptides

An antineoplastic drug-free anticancer strategy enabled by host defense peptides (HDPs)-mimicking synthetic polypeptides is reported. The polypeptide exhibits a broad spectrum of anticancer activity in 12 cancer cell lines, including drug-resistant and highly metastatic tumor cells. Detailed mechanistic studies reveal that the cationic anticancer polypeptide (ACPP) can directly induce rapid necrosis of cancer cells within minutes through a membrane-lytic mechanism. Moreover, a pH-sensitive zwitterionic derivative of ACPP (DA-ACPP) is prepared for in vivo application. DA-ACPP shows negligible hemolysis under neutral physiological conditions, and can be converted back to ACPP in slightly acidic tumor environments, resulting in selective killing of cancer cells. Consequently, DA-ACPP shows an effective inhibition of tumor growth in both 4T1 orthotopic breast tumor models and B16-F10 melanoma pulmonary metastatic models. Overall, these findings demonstrate that synthetic HDPs-mimicking polypeptides represent safe and effective antineoplastic agents, which sheds new light on the development of drug-free synthetic polymers for cancer therapy.

Protective Role of IRBIT on Sodium Bicarbonate Cotransporter-n1 for Migratory Cancer Cells

IP₃ receptor-binding protein released with IP₃ (IRBIT) interacts with various ion channels and transporters. An electroneutral type of sodium bicarbonate cotransporter, NBCn1, participates in cell migration, and its enhanced expression is related to cancer metastasis. The effect of IRBIT on NBCn1 and its relation to cancer cell migration remain obscure. We therefore aimed to determine the effect of IRBIT on NBCn1 and the regulation of cancer cell migration due to IRBIT-induced alterations in NBCn1 activity. Overexpression of IRBIT enhanced cancer cell migration and NBC activity. Knockdown of IRBIT or NBCn1 and treatment with an NBC-specific inhibitor, S0859, attenuated cell migration. Stimulation with oncogenic epidermal growth factor enhanced the expression of NBCn1 and migration of cancer cells by recruiting IRBIT. The recruited IRBIT stably maintained the expression of the NBCn1 transporter machinery in the plasma membrane. Combined inhibition of IRBIT and NBCn1 dramatically inhibited the migration of cancer cells. Combined modulation of IRBIT and NBCn1 offers an effective strategy for attenuating cancer metastasis.

Layered double hydroxide nanostructures and nanocomposites for biomedical applications

Layered double hydroxide (LDH) nanostructures and related nanocomposites have attracted significant interest in biomedical applications including cancer therapy, bioimaging and antibacterial treatment. These materials hold great advantages including low cost and facile preparation, convenient drug loading, high drug incorporation capacity, good biocompatibility, efficient intracellular uptake and endosome/lysosome escape, and natural biodegradability in an acidic environment. In this review, we summarize the development of three types of LDH nanostructures including pristine LDH, surface modified LDH, and LDH nanocomposites for a range of biomedical applications. The advantages and disadvantages of LDH nanostructures and insights into the future development are also discussed.

Virus-like nanoparticle as a co-delivery system to enhance efficacy of CRISPR/Cas9-based cancer immunotherapy

The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-associated protein 9 (Cas9) system holds great promise for the cancer gene therapy. However, due to complicated signal networks and various compensatory mechanisms in tumors, adjusting a single molecular pathway has limited effects on cancer treatments. Herein, a virus-like nanoparticle (VLN) was reported as a versatile nanoplatform to co-deliver CRISPR/Cas9 system and small molecule drugs for effective malignant cancer treatment. VLN has a core-shell structure, in which small molecule drugs and CRISPR/Cas9 system are loaded in the mesoporous silica nanoparticle (MSN)-based core, which is further encapsulated with a lipid shell. This structure allows VLN maintaining stable during blood circulation. As reaching tumors, VLN releases the CRISPR/Cas9 system and small molecule drugs in response to the reductive microenvironment, resulting in the synergistic regulation of multiple cancer-associated pathways. By loading a single guide RNA (sgRNA) targeting programmed death-ligand 1 and axitinib, VLN achieved to disrupt multiple immunosuppressive pathways and suppress the growth of melanoma in vivo. More importantly, VLN can co-deliver almost any combination of sgRNAs and small molecule drugs to tumors, suggesting the great potential of VLN as a general platform for the development of advanced combination therapies against malignant tumors.

Tumor microenvironment-oriented adaptive nanodrugs based on peptide self-assembly

The aberrant metabolism of tumor cells creates an inimitable microenvironment featuring acidic pH, high glutathione (GSH) levels, and overexpression of certain enzymes, which benefits the overwhelming progress of a tumor. Peptide self-assembly, emerging as a biofriendly and versatile fabrication strategy, harnesses multiple noncovalent interactions to obtain a variety of nanostructures tailored on demand. Orchestrating the reversible nature of noncovalent interactions and abnormal physiological parameters in the tumor microenvironment enables peptide-based nanodrugs to be targetable or switchable, thereby improving the drugs' bioavailability and optimizing the treatment outcome. This review will focus on peptide-modulated self-assembly of photosensitizers, chemotherapeutic drugs, immunoactive agents for tumor microenvironment-oriented adaptive phototherapy, chemotherapy, immunotherapy and combinatorial therapy. We will emphasize the building block design, the intermolecular interaction principle, adaptive structural transformation in the tumor microenvironment and corresponding therapeutic efficacy, and aim to elucidate the critical role of peptide-modulated, tumor microenvironment-oriented adaptive assemblies in improving the therapeutic index. Challenges and opportunities will be covered as well to advance the development and clinical application of tumor therapies based on peptide self-assembly materials and techniques.

Aptamer-Functionalized Gold Nanostars for on-Demand Delivery of Anticancer Therapeutics

Gold nanostars (AuNS) are promising carriers for targeted delivery of therapeutic oligonucleotides, but their potential in fabricating an on-demand drug release system in a facile and robust way remains to be explored. In this paper, we used a model aptamer (HApt), acting not only as a target ligand but also as a natural thermal-responsive material, to decorate AuNS. The prepared gold nanoconstruct, HApt@AuNS, displayed stoichiometric loading capacity of the anthracycline drug doxorubicin (Dox). The on-demand drug release was realized by illuminating nanoconstructs with near-infrared (NIR) light. Furthermore, a higher degree of Dox release from the nanoconstructs was achieved in an acidic environment, compared to neutral conditions. The in vitro experiments showed that Dox-intercalation did not affect the cell uptake efficiency of HApt@AuNS, which could enter cells through clathrin-mediated endocytosis and microtubule-dependent active transport to lysosomes. Dox-loaded HApt@AuNS exhibited intracellular on-demand drug release and enhanced toxicity against cancer cells by NIR-irradiation.

ATP Suppression by pH-Activated Mitochondria-Targeted Delivery of Nitric Oxide Nanoplatform for Drug Resistance Reversal and Metastasis Inhibition

Mitochondria, which are important mediators for cancer initiation, growth, metastasis, and drug resistance, have been considered as a major target in cancer therapy. Herein, an acid-activated mitochondria-targeted drug nanocarrier is constructed for precise delivery of nitric oxide (NO) as an adenosine triphosphate (ATP) suppressor to amplify the therapeutic efficacy in cancer treatments. By combining α-cyclodextrin (α-CD) and acid-cleavable dimethylmaleic anhydride modified PEG conjugated mitochondria-targeting peptide, the nanocarrier shows prolonged blood circulation time and enhanced cellular uptake together with selectively restoring mitochondria-targeting capability under tumor extracellular pH (6.5). Such specific mitochondria-targeted delivery of NO proves crucial in inducing mitochondria dysfunction through facilitating mitochondrial membrane permeabilization and downregulating ATP level, which can inhibit P-glycoprotein-related bioactivities and formation of tumor-derived microvesicles to combat drug resistance and cancer metastasis. Therefore, this pioneering acid-activated mitochondria-targeted NO nanocarrier is supposed to be a malignant tumor opponent and may provide insights for diverse NO-relevant cancer treatments.

Size and Charge Adaptive Clustered Nanoparticles Targeting the Biofilm Microenvironment for Chronic Lung Infection Management

Chronic lung infection caused by bacterial biofilms is an extremely serious clinical problem, which can lead to the failure of antibiotic therapy. Although nanoparticles have shown great potential in the treatment of biofilms, the efficient penetration and retention of nanoparticles in biofilms is still a big challenge. To address this issue, we herein fabricate size and charge adaptive azithromycin (AZM)-conjugated clustered nanoparticles (denoted as AZM-DA NPs) as therapeutic agents for treating biofilms. The AZM-DA NPs are prepared by electrostatic complexation between AZM conjugated amino-ended poly(amidoamine) dendrimer (PAMAM) and 2,3-dimethyl maleic anhydride (DA) modified poly(ethylene glycol)-block-polylysine (PEG-b-PLys). It is noteworthy that the AZM-DA NPs can disassemble in an acidic biofilm microenvironment (pH 6.0), leading to the release of secondary AZM-conjugated PAMAM nanoparticles (PAMAM-AZM NPs). PAMAM-AZM NPs with small size and positive charge are beneficial for improved penetration and retention inside biofilms, enhanced permeabilization of the bacterial membrane, and increased internalization of AZM, thus exhibiting excellent antibiofilm activities. AZM-DA NPs are also favorable as long-term antibacterial agents due to the reduced occurrence of drug resistance. In vivo therapeutic performance is confirmed by the reduced bacterial burden and the alleviated inflammation in the chronic lung infection model. This research not only develops an innovative strategy for antibiotic delivery in vivo but also provides an effective way for the management of biofilm-associated infections, including chronic lung infection.

Zwitterionic-to-cationic charge conversion polyprodrug nanomedicine for enhanced drug delivery

Zwitterionic surface modification is a promising strategy for nanomedicines to achieve prolonged circulation time and thus effective tumor accumulation. However, zwitterion modified nanoparticles suffer from reduced cellular internalization efficiency.

Methods: A polyprodrug-based nanomedicine with zwitterionic-to-cationic charge conversion ability (denoted as ZTC-NMs) was developed for enhanced chemotherapeutic drug delivery. The polyprodrug consists of pH-responsive poly(carboxybetaine)-like zwitterionic segment and glutathione-responsive camptothecin prodrug segment.

Results: The ZTC-NMs combine the advantages of zwitterionic surface and polyprodrug. Compared with conventional zwitterionic surface, the ZTC-NMs can respond to tumor microenvironment and realize ZTC surface charge conversion, thus improve cellular internalization efficiency of the nanomedicines.

Conclusions: This ZTC method offers a strategy to promote the drug delivery efficiency and therapeutic efficacy, which is promising for the development of cancer nanomedicines.

Stimuli-Responsive Polysaccharide Enveloped Liposome for Targeting and Penetrating Delivery of survivin-shRNA into Breast Tumor

Silencing the inhibitor of apoptosis (IAP) by RNAi is a promising method for tumor therapy. One of the major challenges lies in how to sequentially overcome the system barriers in the course of the tumor targeting delivery, especially in the tumor accumulation and penetration. Herein we developed a novel stimuli-responsive polysaccharide enveloped liposome carrier, which was constructed by layer-by-layer depositing redox-sensitive amphiphilic chitosan (CS) and hyaluronic acid (HA) onto the liposome and then loading IAP inhibitor survivin-shRNA gene and permeation promoter hyaluronidase (HAase) sequentially. The as-prepared HA/HAase/CS/liposome/shRNA (HCLR) nanocarrier was verified to be stable in blood circulation due to the negative charged HA shield. The tumor targeting recognition and the enhanced tumor accumulation of HCLR were visualized by fluorescence resonance energy transfer (FRET) and in vivo fluorescence biodistribution. The deshielding of HA and the protonizing of CS in slightly acidic tumor extracellular pH environment (pH_e, 6.8-6.5) were demonstrated by ζ potential change from -23.1 to 29.9 mV. The pH_e-responsive HAase release was confirmed in the tumor extracellular mimicking environments, and the intratumoral biodistribution showed that the tumor penetration of HCLR was improved. The cell uptake of HCLR in pH_e environment was significantly enhanced compared with that in physiological pH environment. The increased shRNA release of HCLR was approved in 10 mM glutathione (GSH) and tumor cells. Surprisingly, HCLR suppressed the tumor growth markedly through survivin silencing and meanwhile maintained low toxicity to mice. This study indicates that the novel polysaccharide enveloped HCLR is promising in clinical translation, thanks to the stimuli-triggered tumor accumulation, tumor penetration, cell uptake, and intracellular gene release.

pH/GSH-Dual-Sensitive Hollow Mesoporous Silica Nanoparticle-Based Drug Delivery System for Targeted Cancer Therapy

The purpose of developing novel anticancer drug delivery systems (DDSs) is to efficiently carry and release drugs into cancer cells and minimize side effects. In this work, based on hollow mesoporous silica nanoparticle (HMSN) and the charge-reversal property, a pH/GSH-dual-sensitive DDS named DOX@HMSN-SS-PLL(cit) was reported. HMSN encapsulated DOX with high efficacy and was then covered by the "gatekeeper" β-cyclodextrin (β-CD) through the glutathione (GSH)-sensitive disulfide bond. Thereafter, adamantine-blocked citraconic-anhydride-functionalized poly-l-lysine (PLL(cit)-Ad) was decorated on the surface of the particles via host-guest interaction. The negatively charged carriers were stable in the neutral environment in vivo and could be effectively transported to the tumor site. The surface charge of the nanoparticles could be reversed in the weakly acidic environment, which increased the cellular uptake ability of the carriers by the cancer cells. After cellular internalization, β-CD can be removed by breakage of the disulfide bond in the presence of a high concentration of GSH, leading to DOX release. The preparation process of the carriers was monitored. The charge-reversal capability and the controlled drug-release behavior of the carriers were also investigated. In vitro and in vivo experiments demonstrated the excellent cancer therapy effect with low side effects of the carriers. It is expected that dual-sensitive DOX@HMSN-SS-PLL(cit) could play an important role in cancer therapy.

Overcoming the biological barriers in the tumor microenvironment for improving drug delivery and efficacy

The delivery of drugs to tumors by nanoparticles is a rapidly growing field. However, the complex tumor microenvironment (TME) barriers greatly hinder drug delivery to tumors. In this study, we first summarized the barriers in TME, including anomalous vasculature, rigid extracellular matrix, hypoxia, acidic pH, irregular enzyme level, altered metabolism pathway and immunosuppressive conditions. To overcome these barriers, many strategies have been developed, such as modulating TME, active targeting by ligand modification and biomimetic strategies, and TME-responsive drug delivery strategies to improve nanoparticle penetration, cellular uptake and drug release. Although extensive progress has been achieved, there are still many challenges, which are discussed in the last section. Overall, we carefully discuss the landscape of TME, development for improving drug delivery, and challenges that need to be further addressed.

Protein-drug conjugate programmed by pH-reversible linker for tumor hypoxia relief and enhanced cancer combination therapy

Combining functional proteins with small molecular drugs into one entity may endow distinct synergistic advantages. However, on account of completely different physicochemical properties of such payloads, co-delivery through systemic administration for therapeutic purpose is challenging. Herein, we designed the protein-drug conjugate HSAP-DC-CAT (human serum albumin/Pt (IV)-dibenzocyclooctyne/chlorin e6-catalase) by modification of CAT and cisplatin pro-drug loaded HSA with pH-sensitive azide linker 3-(azidomethyl)-4-methyl-2,5-furandione (AzMMMan) followed by click chemistry assembly with DC. The dynamic covalent bonds between linker and proteins, on the one hand, can bridge proteins and small molecular drugs in the intermediate state for systemic delivery in the harsh in vivo environment; on the other hand, it can trigger traceless cleavage and release of drugs and proteins with full bioactivity in acidic microenvironment of tumor. The multifunctional HSAP-DC-CAT provides efficient cytosolic transduction in vitro, excellent blood half-lives after systemic administration, and significant antitumor outcome via integrated cisplatin-based chemotherapy and Ce6-based photodynamic therapy enhanced by catalase-induced manipulation of tumor hypoxia microenvironment. This study describes a universal formulation strategy for protein and small molecular drug by a bifunctional linker through amide reaction and click chemistry, with traceless in vivo release of therapeutic units.

Tumor microenvironment-responsive multifunctional peptide coated ultrasmall gold nanoparticles and their application in cancer radiotherapy

Two important features are required for promising radiosensitizers: one is selective tumor cell targeting to enhance the therapeutic outcome via lethal DNA damage and the other is rapid clearance to enable excellent biocompatibility for potential clinical application. Herein, ultrasmall gold nanoparticles (Au NPs) with diameter smaller than 5 nm were prepared and covered with a multifunctional peptide to endow them with selective tumor cell uptake capability. Combined with X-ray irradiation, the responsive Au NPs demonstrated superior radio-sensitizing toxicity and rapid renal clearance in vivo. Methods: A responsive peptide (Tat-R-EK) consists of three build blocks were used: a cell and even nuclear penetrating block derived from human immunodeficiency virus-1 transactivator of transcription protein (Tat), an cathepsin B cleavable linker, and a zwitterionic antifouling block. Ultrasmall Au NPs were prepared and then covered by the peptide via the Au-S bonds between gold and thiol groups from cysteine. The morphology, colloidal stability and the responsiveness of obtained Au@Tat-R-EK NPs were studied using transmittance electron microscopy and dynamic laser scattering. The selective cancer cell uptake and accumulation of Au@Tat-R-EK NPs in cancer tissue were studied via ICP-MS in vitro and in vivo, respectively. The cytotoxicity of Au@Tat-R-EK NPs on HepG2 cancer cells was evaluated in terms of cell viability, DNA damage, intracellular reactive oxygen species generation, and apoptosis analysis. Finally, the biocompatibility and tumor destruction ability against orthotopic LM3 liver cancers were verified in vivo. Results: Multifunctional peptide modified ultrasmall Au NPs were successfully prepared. The Au NPs exhibited enough colloidal stability and cathepsin B-responsive surface change, leading to selectively uptake by cancer cells in vitro and accumulation to tumor sites in vivo. Combined with X-ray irradiation, the responsive Au NPs demonstrated superior radio-sensitizing cytotoxicity in vitro and therapeutic outcome on mouse liver cancer in vivo. The ultrasmall size enables rapid clearance of the Au NPs, guarantees the biocompatibility in vivo for potential clinical applications. Conclusion: Some obstacles faced by the Au NPs-based radiotherapy, such as short circulation half-life, non-specific distribution, slow clearance and low radio-sensitizing effect, were effective solved through rational design of the smart nanomedicine. This work provides new insight in designing tumor microenvironment-responsive nanomedicine in cancer radiotherapy.

Nanotherapeutics for Immuno-Oncology: A Crossroad for New Paradigms

With the rapid increase in the use of nanotechnology and immunotherapy for cancer management in the recent past, there are great implications for using nanotechnology in immuno-oncology. However, to deliver clinical success, the scientific and clinical rationale must be critically evaluated when applying nanotechnology to immuno-oncology challenges. This opinion article distinguishes between designing nanotherapeutics for immunotherapy and the past focus on the placement of chemotherapy agents in nanoparticles. We believe the integration of nanotechnology with cancer immunotherapy for nano-immunotherapeutics provides unique opportunities for both fields, paving the way for entirely new therapeutic paradigms. As a particular focus in our article, we envision the necessities and challenges of nanotechnology in the development of in situ cancer vaccines, immune checkpoint inhibitors, adoptive cell transfer, and bispecific antibody therapy.

A General Strategy for Macrotheranostic Prodrug Activation: Synergy between the Acidic Tumor Microenvironment and Bioorthogonal Chemistry

Prodrugs activated by endogenous stimuli face the problem of tumor heterogeneity. Bioorthogonal prodrug activation that utilizes an exogenous click reaction has the potential to solve this problem, but most of the strategies currently used rely on the presence of endogenous receptors or overexpressed enzymes. We herein integrate the acidic, extracellular microenvironment of a tumor and a click reaction as a general strategy for prodrug activation. This was achieved by using a tumor pH-responsive polymer containing tetrazine groups, which formed unreactive micelles in the blood but disassembled in response to tumor pH. The vinyl ether group on the macrotheranostic prodrug (CyPVE) is activated by the tetrazine groups, which was confirmed by tumor-specific fluorescence activation and phototoxicity restoration. Therefore, the bioorthogonal reactions in the context of the ubiquitous acidic tumor microenvironment can provide a general strategy for bioorthogonal prodrug activation.