Stimulus-responsive self-assembled prodrugs in cancer therapy

Bioorthogonal strategy-triggered In situ co-activation of aggregation-induced emission photosensitizers and chemotherapeutic prodrugs for boosting synergistic chemo-photodynamic-immunotherapy

In situ activation of prodrugs or photosensitizers is a promising strategy for specifically killing tumor cells while avoiding toxic side effects. Herein, we originally develop a bioorthogonally activatable prodrug and pro-photosensitizer system to synchronously yield an aggregation-induced emission (AIE) photosensitizer and a chemotherapeutic drug for synergistic chemo-photodynamic-immunotherapy of tumors. By employing molecular engineering strategy, we rationally design a family of tetrazine-functionalized tetraphenylene-based photosensitizers, one of which (named TzPS5) exhibits a high turn-on ratio, a NIR emission, a typical AIE character, and an excellent ROS generation efficiency upon bioorthogonal-activation. With the aid of integrin- or mitochondria-pretargeting, TzPS5 is successfully applied for highly effective PDT ablation of cancer cells both in vitro and in vivo. On this basis, tumor-targeting TzPS5 (TzPS5-cRGD) is constructed and used jointly with a bioorthogonal prodrug, DOX-TCO, and the two are mutually activated to induce cooperative and tumor-specific PDT and chemotherapy, resulting in amplified therapeutic outcomes and improved biosafeties. Moreover, this combination modality elicits robust immunogenic cell death, stimulates systemic antitumor immunity, thereby suppressing both primary and distant tumors, and blocking the pulmonary tumor metastasis. This work is expected to provide a useful guidance for the rational design of activatable phototheranostic agents, and offer a new strategy for co-activation of prodrugs/pro-photosensitizers to boost synergistic antitumor chemo-photodynamic-immunotherapy.

Self-assembled nanoparticles of rapamycin prodrugs for the treatment of multiple sclerosis

Optimizing the design of nanoparticulate co-delivery systems of antigens and immunomodulators to induce antigen-specific immune tolerance effectively remains a challenge, constrained by low drug loading capacity and premature leakage of active ingredients. Here, we report a prodrug self-assembled nanoparticles (NPs) strategy to synergistically deliver antigen and rapamycin (RAPA) into antigen-presenting cells (APCs) by simply conjugating rapamycin with an aliphatic chain. These prodrug NPs can be efficiently taken up by APCs and then release rapamycin through cleavage of the linker by intracellular esterase. Compared to other nanocarriers, rapamycin prodrug NPs exhibit high drug loading capacity and high stability, providing more rational intracellular synchronous delivery of drugs. The prodrug NPs also demonstrate improved therapeutic efficacy in experimental autoimmune encephalomyelitis (EAE) model mice compared with free antigen and rapamycin. Our findings provide new insights into the design of tolerogenic NPs for treating multiple sclerosis (MS). This delivery platform is also applicable for the alleviation of other autoimmune diseases.

Fine-tuning phenoxy silyl scaffolds for the development of glutathione-responsive prodrugs and antibody-drug conjugates

Silyl ether is particularly attractive for application in drug development for its easy preparation, non-toxicity and remarkable biocompatibility. Earlier studies relied on the use of intracellular acidic conditions to induce the cleavage of alkoxy silyl ethers. However, acidic conditions are not suitable to trigger the release of phenoxy silyl ethers, since they are more stable under acidic conditions compared with neutral conditions. We explored the vulnerability of the phenoxy silyl ether towards biological nucleophilic reagents and found that glutathione (GSH) could effectively and selectively induce the cleavage of phenoxy silyl ether. We also demonstrated that the rate of cleavage was controllable by adjusting the substituents on the phenyl ring. Phenoxy silyl ether-based prodrugs and antibody-drug conjugates (ADCs) were designed and synthesized, which could be effectively activated in cells with high GSH levels and there was an obvious therapeutic window between cells with different GSH levels.

Cell-Active, Arginine-Targeting Irreversible Covalent Inhibitors for Non-Kinases and Kinases

Targeted covalent inhibitors (TCIs) play an essential role in the fields of kinase research and drug discovery. TCI strategies to target more common amino acid side-chains have yet to be demonstrated. Targeting other amino acids would also expand the pharmaceutical industry's toolbox for targeting other tough-to-drug proteins. We report herein a glyoxal-based, arginine-reactive strategy to generate potent and selective small-molecule TCIs of Mcl-1 (an important anti-apoptotic protein) by selectively targeting the conserved arginine (R263) in the protein. We further validated the generality of this strategy by developing glyoxal-based, irreversible covalent inhibitors of AURKA (a cancer-related kinase) that showed exclusive reactivity with a solvent-exposed arginine (R220) of this enzyme. We showed the resulting compounds were potent, selective and cell-active, capable of covalently engaging endogenous AURKA in MV-4-11 cells with long residence time. Finally, we showed the potential application of glyoxal-based TCIs in targeting an acquired drug-resistance mutant of ALK kinase (G1202R).

Recent Advances in Smart Linkage Strategies for Developing Drug Conjugates for Targeted Delivery

Targeted drug delivery systems effectively solve the problem of off-target toxicity of chemotherapeutic drugs by combining chemotherapeutic drugs with antibodies or peptides, thereby promoting drug targeting to the tumor site and bringing further hope for cancer treatment. The development of stimulus-responsive smart linkage technologies has led to the emergence of drug conjugates. Linkage technologies play a crucial role in the design, synthesis, and in vivo circulation of drug conjugates, as they determine the release of cytotoxic drugs from the conjugates and their subsequent therapeutic efficacy. This article reviews some of the smart linkage strategies used in designing drug conjugates, with a focus on the tumor microenvironment and exogenous stimuli as conditions influencing controlled drug release. This review introduces linker classifications and cleavage mechanisms, discusses modular linkers that promote the efficient synthesis of conjugates, and discusses the differences between linkage strategies. Furthermore, this article focuses on the implementation of self-assembly in drug conjugates, which is currently of great interest. Related concepts are introduced and relevant examples of their applications are provided. Furthermore, a comprehensive discourse is presented on the challenges that may arise in the research and clinical implementation of diverse linkage strategies, along with the associated enhancement measures. Finally, the factors that should be considered when designing linkage strategies for drug conjugates are summarized, offering strategies and ideas for scientists involved in drug conjugate research. It is particularly noteworthy that appropriate linkage strategies allow for the intracellular release of drugs after internalization of the conjugates, thereby maximizing their tumor cell-killing effect.

ROS-responsive supramolecular antimicrobial peptides-based nanoprodrugs for cervical cancer therapy

Although antimicrobial peptides (AMPs) as a promising natural drugs can efficiently inhibit cervical cancer, poor bioavailability, low tumor selectivity, and non-selective toxicity still hinder its further application in vivo. In order to effectively address these challenges, we have developed a reactive oxygen species (ROS)-responsive targeting nanoprodrug designed for selective therapy of cervical cancer. Such nanoprodrugs (CEC-OxbCD) are fabricated by the supramolecular self-assembly of the modified β-cyclodextrin (β-CD) and AMPs. Antimicrobial peptide, CecropinXJ (CEC), is a cationic antibacterial peptide isolated from 3rd instar larvae of Bombyx mori from Xinjiang, China. OxbCD is an oxidation-responsive β-cyclodextrin material. CEC-OxbCD were synthesized using the nanoprecipitation/self-assembly method. Subsequently, the particle size distribution, morphology, drug loading efficiency, and release behaviour of CEC-OxbCD were characterised. In vitro and in vivo anti-cancer activities were also evaluated. Nanoprodrugs can be effectively disassembled under stimuli of the tumor- endogenous ROS, resulting in a rapid and on-demand release of antimicrobial peptides (AMPs) with a release rate of 90 %. Furthermore, both in vitro and in vivo experimental results demonstrate that our nanoprodrugs exhibit remarkable therapeutic efficacy against cervical cancer. This work not only provides an effective and promising therapeutic strategy for cervical cancer, but also explores a novel application for AMPs.

Multi-drug sequential release systems: Construction and application for synergistic tumor treatment

In tumor treatment, the sequence and timing of drug action have a large influence on therapeutic efficacy. Multi-drug sequential release systems (MDSRS) enable the sequential and/or on-demand release of multiple drugs following the single administration of a therapeutic agent. Several researchers have explored MDSRS, providing fresh strategies for synergistic cancer therapy. This review article first introduces the main characteristics of MDSRS. It then elaborates on the design principles of MDSRS. Subsequently, it summarizes the various structures of carriers used for constructing MDSRS, including core-shell structure, Layer-by-layer structure, Janus structure and hydrogel. Next, through specific examples, the article emphasizes the application of MDSRS in cancer treatment, focusing on their role in remodeling the tumor microenvironment (TME) and enhancing therapeutic effects through multiple mechanisms. Finally, the article discusses the current limitations and challenges of these systems and proposes potential future solutions. Overall, this review underscores the importance of the sequence and timing of drug therapy in cancer treatment, providing valuable theoretical and technical guidance for pharmaceutical research.

Esterase-Responsive Self-Immolative Prodrugs for the Sustained Delivery of the Anticancer Drug 5-Fluorouracil with Turn-On Fluorescence

Stimuli-responsive prodrugs of anticancer drugs are advantageous for the selective delivery of drugs to cancer cells with minimized off-target side effects. In the present study, esterase-activatable fluorogenic prodrugs of the chemotherapeutic drug 5-fluorouracil (5-FU) have been rationally designed and synthesized using multi-step organic synthesis. While 5-FU was connected directly with the fluorophore via a C-N bond in the prodrug BJ-50, an additional self-immolative benzylic spacer with a carbonate linker was incorporated in the prodrug BJ-92. Although absorption and emission spectroscopic studies revealed the activation of both the prodrugs by porcine liver esterase (PLE), reverse-phase HPLC studies confirmed the inability of BJ-50 to release the active drug 5-FU. In contrast, a sustained release of 5-FU and Cou-OH was observed from BJ-92 in the presence of PLE. The endogenous esterase-mediated activation of the prodrug BJ-92 was validated by the turn-on fluorescence in A549 cells and the anti-proliferative activities in A549, and HEK-293 cells. Modulation of the expression of a few cancer marker proteins by BJ-92 and 5-FU was studied to evaluate their anticancer activities. As esterases are overexpressed in cancer cells, the prodrug in the present study would be helpful in selectively delivering 5-FU to cancer cells with reduced off-target side-effects.

X-ray-Triggered Activation of Polyprodrugs for Synergistic Radiochemotherapy

X-ray-induced photodynamic therapy (XPDT) can penetrate deeply into the tumor tissues to overcome the disadvantage of conventional PDT. However, the therapeutic efficacy of XPDT in cancer therapy is still restricted due to the insufficient reactive oxygen species (ROS) generation at a relatively low irradiation dosage. Herein, we present the tumor pH and ROS-responsive polyprodrug micelles to load the X-ray photosensitizer verteporfin (VP) as an ROS production enhancer. The block copolymer polyprodrug consisting of hydrophilic poly(ethylene glycol) (PEG) as well as the segments of thioketal-linked camptothecin (CPT) methacrylate (CPTKMA) and 2-(pentamethyleneimino)ethyl methacrylate (PEMA) (PEG-b-P(CPTKMA-co-PEMA)) can self-assemble into micelles in aqueous solution and encapsulate VP with a high loading efficiency of 67%. Inside tumor tissues, the zeta potential of the micelles can transform from neutral to positive for promoted cellular internalization under tumor acidity. Followed by X-ray irradiation at the dose of 4 Gy, efficient ROS generation in the presence of VP triggers CPT release. The VP-loaded polyprodrug micelles can finally ablate tumors efficiently via synergistic radiochemotherapy due to deep penetration of X-ray inside tumor tissues, ROS generation enhancement, and triggered CPT release. Consequently, this promising strategy represents a robust therapeutic modality for the enhanced radiochemotherapy of cancers.

A Self-Assembled Nano-Molecular Glue (Nano-mGlu) Enables GSH/H2O2-Triggered Targeted Protein Degradation in Cancer Therapy

Molecular glues are promising protein-degrading agents that hold great therapeutic potential but face significant challenges in rational design, effective synthesis, and precise targeting of tumor sites. In this study, we first overcame some of these limitations by introducing a fumarate-based molecular glue handle onto specific ligands of therapeutic kinases (TBK1, FGFR, and Bcr-Abl), resulting in the effective degradation of these important cancer targets. Despite the broad applicability of the strategy, we unexpectedly discovered potent and widespread cytotoxicity across various cell lines, including noncancerous ones, rendering it less effective in cancer therapy. To address this critical issue, we next developed a self-assembled nanoparticle-based molecular glue (nano-mGlu) based on one of the newly discovered Bcr-Abl-degrading molecular glues (H1-mGlu). We showed that the resulting nano-mGlu (named Cle-NP) was able to release H1-mGlu in vitro in the presence of a high concentration of GSH or H2O2 (commonly found in the tumor microenvironment). Subsequent in vivo antitumor studies with a K562-xenografted mouse model indicated that Cle-NP was highly effective in tumor-specific degradation of endogenous Bcr-Abl expressed in K562 cells, leading to eventual tumor regression while maintaining good biosafety profiles. With key advantages of generality in molecular glue design, targeted delivery (e.g., H1-mGlu), potent antitumor activity partially induced by target-specific degradation, and minimized collateral damage to healthy tissues, our self-assembled nano-mGlu strategy thus provides a novel approach that might hold a significant promise for effective and personalized cancer therapy.

Molecular Matchmakers: Bioconjugation Techniques Enhance Prodrug Potency for Immunotherapy

Cancer patients suffer greatly from the severe off-target side effects of small molecule drugs, chemotherapy, and radiotherapy─therapies that offer little protection following remission. Engineered immunotherapies─including cytokines, immune checkpoint blockade, monoclonal antibodies, and CAR-T cells─provide better targeting and future tumor growth prevention. Still, issues such as ineffective activation, immunogenicity, and off-target effects remain primary concerns. "Prodrug" therapies─classified as therapies administered as inactive and then selectively activated to control the time and area of release─hold significant promise in overcoming these concerns. Bioconjugation techniques (e.g., natural linker conjugation, bioorthogonal reactions, and noncanonical amino acid incorporation) enable the rapid and homogeneous synthesis of prodrugs and offer selective loading of immunotherapeutic agents to carrier molecules and protecting groups to prevent off-target effects after administration. Several prodrug activation mechanisms have been highlighted for cancer therapeutics, including endogenous activation by hypoxic or acidic conditions common in tumors, exogenous activation by targeted bioorthogonal cleavage, or stimuli-responsive light activation, and dual-stimuli activation, which adds specificity by combining these mechanisms. This review will explore modern prodrug conjugation and activation options, focusing on how these strategies can enhance immunotherapy responses and improve patient outcomes. We will also discuss the implications of computational methodology for therapy design and recommend procedures to determine how and where to conjugate carrier systems and "prodrug" groups onto therapeutic agents to enhance the safety and control of these delivery platforms.

Self-Boosting Programmable Release of Multiple Therapeutic Agents by Activatable Heterodimeric Prodrug-Enzyme Assembly for Antitumor Therapy

Endogenous stimuli-responsive prodrugs, due to their disease lesion specificity and reduced systemic toxicity, have been widely explored for antitumor therapy. However, reactive oxygen species (ROS) as classical endogenous stimuli in the tumor microenvironment (TME) are not enough to achieve the expected drug release. Herein, a ROS-activatable heterodimeric prodrug-loaded enzyme assembly is developed for self-boosting programmable release of multiple therapeutic agents. The heterodimeric prodrug NBS-TK-PTX (namely NTP) is composed of 5-(ethylamino)-9-diethylaminobenzo[a]phenothiazinium chloride analog (NBS), paclitaxel (PTX) and ROS-responsive thioketal (TK) linker, which shows a strong binding affinity with glucose oxidase (GOx), thus obtaining NTP@GOx assembly. Notably, the enzymatic activity of GOx in NTP@GOx is inhibited by NTP. The programmable release is achieved by following steps: i) NTP@GOx is partially dissociated in acidic TME, thus releasing a small segment of NTP and GOx. Thereupon, the enzymatic activity of GOx is recovered; ii) GOx-triggered pH reduction further facilitates the dissociation of NTP@GOx, thus accelerating a large amount of NTP and GOx release; iii) The TK linker of prodrug NTP is cleaved by hydrogen peroxide generated by GOx catalysis, thus expediting the release of NBS for Type-I photodynamic therapy and PTX for chemotherapy, respectively. The NTP@GOx shows great potential for multimodal synergistic cancer therapy.

Stimuli-responsive prodrugs with self-immolative linker for improved cancer therapy

Self-immolative prodrugs have gained significant attention as an innovative approach for targeted cancer therapy. These prodrugs are engineered to release the active anticancer agents in response to specific triggers within the tumor microenvironment, thereby improving therapeutic precision while reducing systemic toxicity. This review focuses on the molecular architecture and design principles of self-immolative prodrugs, emphasizing the role of stimuli-responsive linkers and activation mechanisms that enable controlled drug release. Recent advancements in this field include the development of prodrugs that incorporate targeting moieties for enhanced site-specificity. Moreover, the review discusses the incorporation of targeting moieties to achieve site-specific drug delivery, thereby improving the selectivity of treatment. By summarizing key research from the past five years, this review highlights the potential of self-immolative prodrugs to revolutionize cancer treatment strategies and pave the way for their integration into clinical practice.

Dual stimuli-responsive biotinylated polymer-drug conjugate for dual drug delivery

Stimuli-responsive nanoscale polymer-drug conjugates are one of the most promising alternatives in the realm of advanced therapeutics, rendering several characteristics such as spatio-temporal control over drug release, reduced off-target toxicity, enhanced bioavailability, and longer blood circulation time of the drug. Fostered by the aforementioned conceptualization, our quest to develop an ideal polymer-drug conjugate has originated the present investigation of developing a reactive oxygen species (ROS) and esterase-responsive self-assembled polymer-drug (chlorambucil, CBL) conjugate with biotin pendants (DP2) for cancer cell targeting, surrogating another antineoplastic drug, doxorubicin (DOX) via physical encapsulation (DP2@DOX). The ROS and esterase trigger not only released the covalently stitched CBL but also resulted in DOX release by dismantling the amphiphilic balance of the nanoaggregates. Biotinylation-mediated enhancement of cellular uptake of DP2@DOX was reflected in the synergistic anticancer activity of both the drugs (CBL and DOX) in HeLa cells (biotin receptor-positive cells) compared to HEK 293T cells (biotin receptor-negative cells). Furthermore, the selective internalization of the fluorophore-tagged DOX-loaded polymer (DP4@DOX) in HeLa cells compared to HEK 293T cells was confirmed by confocal microscopy and flow cytometry. In summary, the present investigation demonstrates a state-of-the-art self-assembled polymer-drug conjugate as a next-generation dual stimuli-responsive drug delivery vehicle.

Nanoscale Mixed-Ligand Metal-Organic Framework for X-ray Stimulated Cancer Therapy

Concurrent localized radiotherapy and systemic chemotherapy are standards of care for many cancers, but these treatment regimens cause severe adverse effects in many patients. Herein, we report the design of a mixed-ligand nanoscale metal-organic framework (nMOF) with the ability to simultaneously enhance radiotherapeutic effects and trigger the release of a potent chemotherapeutic under X-ray irradiation. We synthesized a new functional quaterphenyl dicarboxylate ligand conjugated with SN38 (H2QP-SN) via a hydroxyl radical-responsive covalent linkage. Because of the similar length of QP-SN and bis(p-benzoato)porphyrin (DBP) ligands, QP-SN was incorporated into Hf-DBP nMOF to afford a novel multifunctional mixed-ligand Hf-DBP-QP-SN nMOF with good biocompatibility. Hf-DBP-QP-SN not only enhances radiation damage to tumors via a unique radiotherapy-radiodynamic therapy (RT-RDT) process but also increases ·OH generation from radiolysis with electron-dense Hf12 secondary building units (SBUs) to release SN38 from Hf-DBP-QP-SN for chemotherapy. Elevated levels of hydrogen peroxide in the tumor microenvironment further stimulate the release of SN38 by enhancing ·OH generation under X-ray irradiation. With low doses of X-ray irradiation, Hf-DBP-QP-SN suppressed the growth of CT26 colon and 4T1 breast tumors by 93.5% and 95.2%, respectively, without any sign of general toxicity. Our study highlights the potential of using ionizing radiation-mediated chemistry for on-demand activation of nanotherapeutics for synergistic radiotherapy and chemotherapy without causing severe adverse effects.

Bioorthogonal chemistry-based prodrug strategies for enhanced biosafety in tumor treatments: current progress and challenges

Cancer is a significant global health challenge, and while chemotherapy remains a widely used treatment, its non-specific toxicity and broad distribution can lead to systemic side effects and limit its effectiveness against tumors. Therefore, the development of safer chemotherapy alternatives is crucial. Prodrugs hold great promise, as they remain inactive until they reach the cancer site, where they are selectively activated by enzymes or specific factors, thereby reducing side effects and improving targeting. However, subtle differences in the microenvironments between tumors and normal tissue may still result in unintended cytotoxicity. Bioorthogonal reactions, known for their selectivity and precision without interfering with natural biochemical processes, are gaining attention. When combined with prodrug strategies, these reactions offer the potential to create highly effective chemotherapy drugs. This review examines the safety and efficacy of prodrug strategies utilizing various bioorthogonal reactions in cancer treatment.

Stabilized, ROS-sensitive β-cyclodextrin-grafted hyaluronic supramolecular nanocontainers for CD44-targeted anticancer drug delivery

Hyaluronic acid (HA)-based tumor microenvironment-responsive nanocontainers are attractive candidates for anticancer drug delivery due to HA's excellent biocompatibility, biodegradability, and CD44-targeting properties. Nevertheless, the consecutive synthesis of stabilized, stealthy, responsive HA-based multicomponent nanomedicines generally requires multi-step preparation and purification procedures, leading to batch-to-batch variation and scale-up difficulties. To develop a facile yet robust strategy for promoted translations, a silica monomer containing a cross-linkable diethoxysilyl unit was prepared to enable in situ crosslinking without any additives. Further combined with the host-guest inclusion complexation between β-cyclodextrin-grafted HA (HA-CD) and ferrocene-functionalized polymers, ferrocene-terminated poly(oligo(ethylene glycol) methyl ether methacrylate (Fc-POEGMA) and Fc-terminated poly(ε-caprolactone)-b-poly(3-(diethoxymethylsilyl)propyl(2-(methacryloyloxy)ethyl) carbamate) (Fc-PCL-b-PDESPMA), a reactive oxygen species (ROS)-sensitive supramolecular polymer construct, Fc-POEGMA/Fc-PCL-b-PDESPMA@HA-CD was readily fabricated to integrate stealthy POEGMA, tumor active targeting HA, and an in situ cross-linkable PDESPMA sequence. Supramolecular amphiphilic copolymers with two different POEGMA contents of 25 wt% (P1) and 20 wt% (P2) were prepared via a simple physical mixing process, affording two core-crosslinked (CCL) micelles via an in situ sol-gel process of ethoxysilyl groups. The P1-based CCL micelles show not only desired colloidal stability against high dilution, but also an intracellular ROS-mimicking environment-induced particulate aggregation that is beneficial for promoted intracellular release of the loaded cargoes. Most importantly, P1-based nanomedicines exhibited greater cytotoxicity in CD44 receptor-positive HeLa cells than that in CD44 receptor-negative MCF-7 cells. Overall, this work developed HA-based nanomedicines with sufficient extracellular colloidal stability and efficient intracellular destabilization properties for enhanced anticancer drug delivery via smart integration of in situ crosslinking and supramolecular complexation.

Stability of a Multiresponsive Sulfonium Vinyl Sulfide Linker toward Nucleophilic/Radical Thiols, Reactive Nitrogen Species, and in Cells under Pro-inflammatory Stimulation

Chemical linkages that respond to biological stimuli are important for many pharmaceutical and biotechnological applications, making it relevant to explore new variants with different responsivity profiles. This work explores the responsiveness of a TAT peptide-based sulfonium vinyl sulfide probe that responds to nucleophilic thiols, radical thiol species (RTS), and reactive nitrogen species (RNS). Under model conditions, response to nucleophilic thiols was very slow (hours/days), though fast with down to molar equivalents of either RTS or RNS (minutes). These reactions led to the traceless release of a methionine-containing peptide in the first two cases and to a hydroxy nitration adduct in the third case. Despite the sensitive nature of the probe, it remained stable for at least ∼2 h in the presence of cells during TAT-mediated trafficking, even under pro-inflammatory stimulation. The thiol-responsiveness is intermediate to that observed for disulfide linkers and conventional cysteine-maleimide linkers, presenting opportunities for biotechnological applications.

Rationally designed BCR-ABL kinase inhibitors for improved leukemia treatment via covalent and pro-/dual-drug targeting strategies

BACKGROUND

Chronic Myeloid Leukemia (CML) is a blood cancer that remains challenging to cure due to drug resistance and side effects from current BCR-ABL inhibitors. There is an urgent need for novel and more effective BCR-ABL targeting inhibitors and therapeutic strategies to combat this deadly disease.

METHOD

We disclose an "OH-implant" strategy to improve a noncovalent BCR-ABL inhibitor, PPY-A, by adding a hydroxyl group to its scaffold. By taking advantage of this OH "hot spot", we designed a panel of irreversible covalent kinase inhibitors and hypoxia-responsive pro-/dual-drugs, and their biological activities were studied in vitro, in cellulo and in vivo.

RESULT

The resulting compound B1 showed enhanced solubility and biological activity. B4 achieved sustained BCR-ABL inhibition by forming a stable covalent bond with ABL kinase. Hypoxia-responsive prodrug P1 and dual-drugs D1/D2/D3 demonstrated significant anti-tumor effects under hypoxic conditions. The in vivo studies using K562-xenografted mice showed that B1 displayed superior antitumor activity than PPY-A, while P1 and D3 offered better safety profiles alongside significant tumor control.

CONCLUSION

We have successfully developed a chemical biology approach to convert a known noncovalent BCR-ABL inhibitor into more potent and safer inhibitors through covalent and pro-/dual-drug targeting strategies. Our "OH-implant" approach and the resulting drug design strategies have general applicability and hold promise for improvement the performance of various other reported drugs/drug candidates, thereby providing advanced medicines for disease treatment.

Stimuli-Responsive Aptamer-Drug Conjugates for Targeted Drug Delivery and Controlled Drug Release

Chemotherapy is widely used for cancer therapy but with unsatisfied efficacy, mainly due to the inefficient delivery of anticancer agents. Among the critical "five steps" drug delivery process, internalization into tumor cells and intracellular drug release are two important steps for the overall therapeutic efficiency. Strategy based on active targeting or TME-responsive is developed individually to improve therapeutic efficiency, but with limited improvement. However, the combination of these two strategies could potentially augment the drug delivery efficiency and therapeutic efficiency, consequently. Therefore, this work constructs a library of stimuli-responsive aptamer-drug conjugates (srApDCs), as "dual-targeted" strategy for cancer treatment that enables targeted drug delivery and controlled drug release. Specifically, this work uses different stimuli-responsive linkers to conjugate a tumor-targeting aptamer (i.e., AS1411) with drugs, forming the library of srApDCs for targeted cancer treatment. This design hypothesis is validated by the experimental data, which indicated that the aptamer could selectively enhance uptake of the srApDCs and the linkers could be cleaved by pathological cues in the TME to release the drug payload, leading to a significant enhancement of therapeutic efficacy. These results underscore the potential of the approach, providing a promising methodology for cancer therapy.

Reactive oxygen species driven prodrug-based nanoscale carriers for transformative therapies

Reactive oxygen species (ROS) drive processes in various pathological conditions serving as an attractive target for therapeutic strategies. This review highlights the development and use of ROS-dependent prodrug-based nanoscale carriers that has transformed many biomedical applications. Incorporating prodrugs into nanoscale carriers not only improves their stability and solubility but also enables site-specific drug delivery ultimately enhancing the therapeutic effectiveness of the nanoscale carriers. We critically examine recent advances in ROS-responsive nanoparticulate platforms, encompassing liposomes, polymeric nanoparticles, and inorganic nanocarriers. These platforms facilitate precise control over drug release upon encountering elevated ROS levels at disease sites, thereby minimizing off-target effects and maximizing therapeutic efficiency. Furthermore, we investigate the potential of combination therapies in which ROS-activated prodrugs are combined with other therapeutic agents and underscore their synergistic potential for treating multifaceted diseases. This comprehensive review highlights the immense potential of ROS-dependent prodrug-based nanoparticulate systems in revolutionizing biomedical applications; such nanoparticulate systems can facilitate selective and controlled drug delivery, reduce toxicity, and improve therapeutic outcomes for ROS-associated diseases.

Organelle-based immunotherapy strategies for fighting against cancer

Destruction of subcellular organelles can cause dysfunction and even death of cells to elicit immune responses. In this review, the characteristics and functions of important organelles are mainly summarized. Then, the intelligent immunotherapeutic strategies and suggestions based on influencing the organelles are further highlighted. This review will provide ideas for developing novel and effective immunotherapy strategies and advance the development of cancer immunotherapy.

Stimulus-Responsive Nano-Prodrug Strategies for Cancer Therapy: A Focus on Camptothecin Delivery

Camptothecin (CPT) is a highly cytotoxic molecule with excellent antitumor activity against various cancers. However, its clinical application is severely limited by poor water solubility, easy inactivation, and severe toxicity. Structural modifications and nanoformulations represent two crucial avenues for camptothecin's development. However, the potential for further structural modifications is limited, and camptothecin nanoparticles fabricated via physical loading have the drawbacks of low drug loading and leakage. Prodrug-based CPT nanoformulations have shown unique advantages, including increased drug loading, reduced burst release, improved bioavailability, and minimal toxic side effects. Stimulus-responsive CPT nano-prodrugs that respond to various endogenous or exogenous stimuli by introducing various activatable linkers to achieve spatiotemporally responsive drug release at the tumor site. This review comprehensively summarizes the latest research advances in stimulus-responsive CPT nano-prodrugs, including preparation strategies, responsive release mechanisms, and their applications in cancer therapy. Special focus is placed on the release mechanisms and characteristics of various stimulus-responsive CPT nano-prodrugs and their application in cancer treatment. Furthermore, clinical applications of CPT prodrugs are discussed. Finally, challenges and future research directions for CPT nano-prodrugs are discussed. This review to be valuable to readers engaged in prodrug research is expected.

pH-responsive self-assembled nanoparticles for tumor-targeted drug delivery

Recent advances in the field of drug delivery have opened new avenues for the development of novel nanodrug delivery systems (NDDS) in cancer therapy. Self-assembled nanoparticles (SANPs) based on tumour microenvironment have great advantages in improving antitumor effect, and pH-responsive SANPs prepared by the combination of pH-responsive nanomaterials and self-assembly technology can effectively improve the efficacy and reduce the systemic toxicity of antitumor drugs. In this review, we describe the characteristics of self-assembly and its driving force, the mechanism of pH-responsive NDDS, and the nanomaterials for pH-responsive SANPs type. A series of pH-responsive SANPs for tumour-targeted drug delivery are discussed, with an emphasis on the relation between structural features and theranostic performance.

Single Molecular Nanomedicines Based on Macrocyclic Carrier-Drug Conjugates for Concentration-Independent Encapsulation and Precise Activation of Drugs

Nanomedicines often rely on noncovalent self-assembly and encapsulation for drug loading and delivery. However, challenges such as reproducibility issues due to the multicomponent nature, off-target activation caused by premature drug release, and complex pharmacokinetics arising from assembly dissociation have hindered their clinical translation. In this study, we introduce an innovative design concept termed single molecular nanomedicine (SMNM) based on macrocyclic carrier-drug conjugates. Through the covalent linkage of two chemotherapy drugs to a hypoxia-cleavable macrocyclic carrier, azocalix[4]arene, we obtained two self-included complexes to serve as SMNMs. The intramolecular inclusion feature of the SMNMs has not only demonstrated comprehensive shielding and protection for the drugs but also effectively prevented off-target drug leakage, thereby significantly reducing their side effects and enhancing their antitumor therapeutic efficacy. Additionally, the attributes of being a single component and molecularly dispersed confer advantages such as ease of preparation and good reproducibility for SMNMs, which is desirable for clinical applications.

Targeted pH-Activated Peptide-Based Nanomaterials for Combined Photodynamic Therapy with Immunotherapy

Photodynamic therapy (PDT) has demonstrated efficacy in eliminating local tumors, yet its effectiveness against metastasis is constrained. While immunotherapy has exhibited promise in a clinical context, its capacity to elicit significant systemic antitumor responses across diverse cancers is often limited by the insufficient activation of the host immune system. Consequently, the combination of PDT and immunotherapy has garnered considerable attention. In this study, we developed pH-responsive porphyrin-peptide nanosheets with tumor-targeting capabilities (PRGD) that were loaded with the IDO inhibitor NLG919 for a dual application involving PDT and immunotherapy (PRGD/NLG919). In vitro experiments revealed the heightened cellular uptake of PRGD/NLG919 nanosheets in tumor cells overexpressing αvβ3 integrins. The pH-responsive PRGD/NLG919 nanosheets demonstrated remarkable singlet oxygen generation and photocytotoxicity in HeLa cells in an acidic tumor microenvironment. When treating HeLa cells with PRGD/NLG919 nanosheets followed by laser irradiation, a more robust adaptive immune response occurred, leading to a substantial proliferation of CD3+CD8+ T cells and CD3+CD4+ T cells compared to control groups. Our pH-responsive targeted PRGD/NLG919 nanosheets therefore represent a promising nanosystem for combination therapy, offering effective PDT and an enhanced host immune response.

Package delivered: folate receptor-mediated transporters in cancer therapy and diagnosis

Neoplasias pose a significant threat to aging society, underscoring the urgent need to overcome the limitations of traditional chemotherapy through pioneering strategies. Targeted drug delivery is an evolving frontier in cancer therapy, aiming to enhance treatment efficacy while mitigating undesirable side effects. One promising avenue utilizes cell membrane receptors like the folate receptor to guide drug transporters precisely to malignant cells. Based on the cellular folate receptor as a cancer cell hallmark, targeted nanocarriers and small molecule-drug conjugates have been developed that comprise different (bio) chemistries and/or mechanical properties with individual advantages and challenges. Such modern folic acid-conjugated stimuli-responsive drug transporters provide systemic drug delivery and controlled release, enabling reduced dosages, circumvention of drug resistance, and diminished adverse effects. Since the drug transporters' structure-based de novo design is increasingly relevant for precision cancer remediation and diagnosis, this review seeks to collect and debate the recent approaches to deliver therapeutics or diagnostics based on folic acid conjugated Trojan Horses and to facilitate the understanding of the relevant chemistry and biochemical pathways. Focusing exemplarily on brain and breast cancer, recent advances spanning 2017 to 2023 in conjugated nanocarriers and small molecule drug conjugates were considered, evaluating the chemical and biological aspects in order to improve accessibility to the field and to bridge chemical and biomedical points of view ultimately guiding future research in FR-targeted cancer therapy and diagnosis.

Satellite-Type Sulfur Atom Distribution in Trithiocarbonate Bond-Bridged Dimeric Prodrug Nanoassemblies: Achieving Both Stability and Activatability

Homodimeric prodrug nanoassemblies (HDPNs) hold promise for improving the delivery efficiency of chemo-drugs. However, the key challenge lies in designing rational chemical linkers that can simultaneously ensure the chemical stability, self-assembly stability, and site-specific activation of prodrugs. The "in series" increase in sulfur atoms, such as trisulfide bond, can improve the assembly stability of HDPNs to a certain extent, but limits the chemical stability of prodrugs. Herein, trithiocarbonate bond (─SC(S)S─), with a stable "satellite-type" distribution of sulfur atoms, is developed via the insertion of a central carbon atom in trisulfide bonds. ─SC(S)S─ bond effectively addresses the existing predicament of HDPNs by improving the chemical and self-assembly stability of homodimeric prodrugs while maintaining the on-demand bioactivation. Furthermore, ─SC(S)S─ bond inhibits antioxidant defense system, leading to up-regulation of the cellular ROS and apoptosis of tumor cells. These improvements of ─SC(S)S─ bond endow the HDPNs with in vivo longevity and tumor specificity, ultimately enhancing the therapeutic outcomes. ─SC(S)S─ bond is, therefore, promising for overcoming the bottleneck of HDPNs for efficient oncological therapy.

Bioorthogonal Bond Cleavage Chemistry for On-demand Prodrug Activation: Opportunities and Challenges

Time- and space-resolved drug delivery is highly demanded for cancer treatment, which, however, can barely be achieved with a traditional prodrug strategy. In recent years, the prodrug strategy based on a bioorthogonal bond cleavage chemistry has emerged with the advantages of high temporospatial resolution over drug activation and homogeneous activation irrespective of individual heterogeneity. In the past five years, tremendous progress has been witnessed in this field with one such bioorthogonal prodrug entering Phase II clinical trials. This Perspective aims to highlight these new advances (2019-2023) and critically discuss their pros and cons. In addition, the remaining challenges and potential strategic directions for future progress will also be included.

An SS31-rapamycin conjugate via RBC hitchhiking for reversing acute kidney injury

Mitochondrial dysfunction plays a major role in driving acute kidney injury (AKI) via alteration in energy and oxygen supply, which creates further ROS and inflammatory responses. However, mitochondrial targeting medicine in recovering AKI is challenging. Herein, we conjugated SS31, a mitochondria-targeted antioxidant tetrapeptide connecting a cleavable linker to rapamycin (Rapa), which provided specific interaction with FK506-binding protein (FKBP) in the RBCs. Once entering the bloodstream, SS31-Rapa could be directed to the intracellular space of RBCs, allowing the slow diffusion of the conjugate to tissues via the concentration gradient. The new RBC hitchhiking strategy enables the encapsulation of conjugate into RBC via a less traumatic and more natural and permissive manner, resulting in prolonging the t1/2 of SS31 by 6.9 folds. SS31-Rapa underwent the direct cellular uptake, instead of the lysosomal pathway, released SS31 in response to activated caspase-3 stimulation in apoptotic cells, favoring the mitochondrial accumulation of SS31. Combined with autophagy induction associated with Rapa, a single dose of SS31-Rapa can effectively reverse cisplatin and ischemia reperfusion-induced AKI. This work thus highlights a simple and effective RBC hitchhiking strategy and a clinically translatable platform technology to improve the outcome of other mitochondrial dysfunctional related diseases.

Multistage Self-Assembled Nanomaterials for Cancer Immunotherapy

Advances in nanotechnology have brought innovations to cancer therapy. Nanoparticle-based anticancer drugs have achieved great success from bench to bedside. However, insufficient therapy efficacy due to various physiological barriers in the body remains a key challenge. To overcome these biological barriers and improve the therapeutic efficacy of cancers, multistage self-assembled nanomaterials with advantages of stimuli-responsiveness, programmable delivery, and immune modulations provide great opportunities. In this review, we describe the typical biological barriers for nanomedicines, discuss the recent achievements of multistage self-assembled nanomaterials for stimuli-responsive drug delivery, highlighting the programmable delivery nanomaterials, in situ transformable self-assembled nanomaterials, and immune-reprogramming nanomaterials. Ultimately, we perspective the future opportunities and challenges of multistage self-assembled nanomaterials for cancer immunotherapy.

Camptothecin-based prodrug nanomedicines for cancer therapy

Camptothecin (CPT) is a cytotoxic alkaloid that attenuates the replication of cancer cells via blocking DNA topoisomerase 1. Despite its encouraging and wide-spectrum antitumour activity, its application is significantly restricted owing to its instability, low solubility, significant toxicity, and acquired tumour cell resistance. This has resulted in the development of many CPT-based therapeutic agents, especially CPT-based nanomedicines, with improved pharmacokinetic and pharmacodynamic profiles. Specifically, smart CPT-based prodrug nanomedicines with stimuli-responsive release capacity have been extensively explored owing to the advantages such as high drug loading, improved stability, and decreased potential toxicity caused by the carrier materials in comparison with normal nanodrugs and traditional delivery systems. In this review, the potential strategies and applications of CPT-based nanoprodrugs for enhanced CPT delivery toward cancer cells are summarized. We appraise in detail the chemical structures and release mechanisms of these nanoprodrugs and guide materials chemists to develop more powerful nanomedicines that have real clinical therapeutic capacities.

Cell-Specific Degradation of Histone Deacetylase Using Warhead-Caged Proteolysis Targeting Chimeras

Proteolysis targeting chimeras (PROTACs) have shifted the paradigm for drug development via target protein degradation. However, PROTACs may exhibit systemic toxicity to normal cells due to indiscriminate degradation and the utility of inhibitors as a warhead for protein targeting. Here, we propose a new strategy for developing activatable PROTACs for cell-specific degradation of histone deacetylase (HDAC) with minimal side effects via caging of the warhead. Molecular docking reveals that the hydroxyl group of the HDAC inhibitor is crucial for targeting. An enzyme-activatable PROTAC is designed by caging the hydroxyl group with the substrate for NAD(P)H: quinone oxidoreductase 1 (NQO1) overexpressed in cancer cells. We demonstrate that the caged PROTAC can be converted to its active form in response to NQO1. The enzyme-activatable PROTAC allows the efficient and specific degradation of HDAC6 and exerts antiproliferative activity in NQO1-positive cells. The generalizability of the design is further demonstrated by engineering a H2O2-responsive PROTAC for specific degradation of HDAC6 in cells with elevated H2O2. The strategy of caging the ligand for target proteins would afford a new dimension for developing activatable PROTACs with high specificity and minimal side effects.

Dextran-based micelles for combinational chemo-photodynamic therapy of tumors via in vivo chemiluminescence

Natural polysaccharides, represented by dextran, chitosan, and hyaluronic acid, are widely approved for use as pharmaceutical excipients and are important carrier materials for the design of advanced drug delivery systems, particularly in the field of anticancer drug delivery. The combination of stimuli-activable prodrug based chemotherapy and photodynamic therapy (PDT) has attracted increasing attention. Recent studies have verified the effectiveness of this strategy in the treatment of multiple aggressive cancers. However, in such combination, the stimuli-responsive chemotherapy and PDT have their own problems that need to be overcome. The uneven distribution of endogenous stimuli within tumor tissues makes it difficult for prodrug to be completely activated. And the inadequate tissue penetration depth of external light results in low efficiency of PDT. Aiming at these two bottlenecks, we designed a biocompatible dextran based - multi-component nanomedicine (PCL-NPs) that integrate a chemiluminescence agent luminol, a photosensitizer chlorine e6 (Ce6), and a reactive oxygen species (ROS)-activable thioketal-based paclitaxel (PTX) prodrug. The presence of overexpressed hydrogen peroxide (H2O2) inside tumor oxidizes the luminol moiety to generate in-situ light for PDT through chemiluminescence resonance energy transfer (CRET). The singlet oxygen (1O2) produced in this process not only directly kills tumor cells but also amplifies oxidative stress to accelerate the activation of PTX prodrug. We propose that the PCL-NPs have great therapeutic potential by simultaneously enhancing chemotherapy and PDT in a combination therapy.

Tumor Metabolism-Rewriting Nanomedicines for Cancer Immunotherapy

Cancer immunotherapy has become an established therapeutic paradigm in oncologic therapy, but its therapeutic efficacy remains unsatisfactory in the majority of cancer patients. Accumulating evidence demonstrates that the metabolically hostile tumor microenvironment (TME), characterized by acidity, deprivation of oxygen and nutrients, and accumulation of immunosuppressive metabolites, promotes the dysfunction of tumor-infiltrating immune cells (TIICs) and thereby compromises the effectiveness of immunotherapy. This indicates the potential role of tumor metabolic intervention in the reinvigoration of antitumor immunity. With the merits of multiple drug codelivery, cell and organelle-specific targeting, controlled drug release, and multimodal therapy, tumor metabolism-rewriting nanomedicines have recently emerged as an attractive strategy to strengthen antitumor immune responses. This review summarizes the current progress in the development of multifunctional tumor metabolism-rewriting nanomedicines for evoking antitumor immunity. A special focus is placed on how these nanomedicines reinvigorate innate or adaptive antitumor immunity by regulating glucose metabolism, amino acid metabolism, lipid metabolism, and nucleotide metabolism at the tumor site. Finally, the prospects and challenges in this emerging field are discussed.

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

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

Advance Progress in Assembly Mechanisms of Carrier-Free Nanodrugs for Cancer Treatment

Nanocarriers have been widely studied and applied in the field of cancer treatment. However, conventional nanocarriers still suffer from complicated preparation processes, low drug loading, and potential toxicity of carriers themselves. To tackle the hindrance, carrier-free nanodrugs with biological activity have received increasing attention in cancer therapy. Extensive efforts have been made to exploit new self-assembly methods and mechanisms to expand the scope of carrier-free nanodrugs with enhanced therapeutic performance. In this review, we summarize the advanced progress and applications of carrier-free nanodrugs based on different types of assembly mechanisms and strategies, which involved noncovalent interactions, a combination of covalent bonds and noncovalent interactions, and metal ions-coordinated self-assembly. These carrier-free nanodrugs are introduced in detail according to their assembly and antitumor applications. Finally, the prospects and existing challenges of carrier-free nanodrugs in future development and clinical application are discussed. We hope that this comprehensive review will provide new insights into the rational design of more effective carrier-free nanodrug systems and advancing clinical cancer and other diseases (e.g., bacterial infections) infection treatment.

Stimuli-Responsive Prodrug Chemistries for Cancer Therapy

Prodrugs are pharmacologically inactive, chemically modified derivatives of active drugs, which, following in vivo administration, are converted to the parent drugs through chemical or enzymatic cleavage. The prodrug approach holds tremendous potential to create the enhanced version of an existing pharmacological agent and leverage those improvements to augment the drug molecules' bioavailability, targeting ability, therapeutic efficacy, safety, and marketability. Especially in cancer therapy, prodrug application has received substantial attention. A prodrug can effectively broaden the therapeutic window of its parent drug by enhancing its release at targeted tumor sites while reducing its access to healthy cells. The spatiotemporally controlled release can be achieved by manipulating the chemical, physical, or biological stimuli present at the targeted tumor site. The critical strategy comprises drug-carrier linkages that respond to physiological or biochemical stimuli in the tumor milieu to yield the active drug form. This review will focus on the recent advancements in the development of various fluorophore-drug conjugates that are widely used for real-time monitoring of drug delivery. The use of different stimuli-cleavable linkers and the mechanisms of linker cleavage will be discussed. Finally, the review will conclude with a critical discussion of the prospects and challenges that might impede the future development of such prodrugs.

Single Functional Group Platform for Multistimuli Responsivities: Tertiary Amine for CO2/pH/ROS-Triggered Cargo Release in Nanocarriers

The design of multistimuli-responsive soft nanoparticles (NPs) often presents synthetic complexities and limited breadth in exploiting changes surrounding physiological environments. Nanocarriers that could collectively take advantage of several endogenous stimuli can offer a powerful tool in nanomedicine. Herein, we have capitalized on the chemical versatility of a single tertiary amine to construct miktoarm polymer-based nanocarriers that respond to dissolved CO2, varied pH, reactive oxygen species (ROS), and ROS + CO2. Curcumin (Cur), an anti-inflammatory phytopharmaceutic, was loaded into micelles, and we validated the sensitivity of the tertiary amine in tuning Cur release. An in vitro evaluation indicated that Cur encapsulation strongly suppressed its toxicity at high concentrations, significantly inhibited nigericin-induced secretion of interleukin-1β by THP-1 macrophages, and the proportion of M2/M1 (anti-inflammatory/pro-inflammatory macrophages) was higher for Cur-loaded NPs than for free Cur. Our approach highlights the potential of a simple-by-design strategy in expanding the scope of polymeric NPs in drug delivery.

Self-assembled nanoformulations of paclitaxel for enhanced cancer theranostics

Chemotherapy has occupied the critical position in cancer therapy, especially towards the post-operative, advanced, recurrent, and metastatic tumors. Paclitaxel (PTX)-based formulations have been widely used in clinical practice, while the therapeutic effect is far from satisfied due to off-target toxicity and drug resistance. The caseless multi-components make the preparation technology complicated and aggravate the concerns with the excipients-associated toxicity. The self-assembled PTX nanoparticles possess a high drug content and could incorporate various functional molecules for enhancing the therapeutic index. In this work, we summarize the self-assembly strategy for diverse nanodrugs of PTX. Then, the advancement of nanodrugs for tumor therapy, especially emphasis on mono-chemotherapy, combinational therapy, and theranostics, have been outlined. Finally, the challenges and potential improvements have been briefly spotlighted.

Doxorubicin prodrug-based nanomedicines for the treatment of cancer

The chemotherapeutic drug of doxorubicin (DOX) has witnessed widespread applications for treating various cancers. DOX-treated dying cells bear cellular modifications which allow enhanced presentation of tumor antigen and neighboring dendritic cell activation. Furthermore, DOX also facilitate the immune-mediated clearance of tumor cells. However, disadvantages such as severe off-target toxicity, and prominent hydrophobicity have resulted in unsatisfactory clinical therapeutic outcomes. The effective delivery of DOX drug molecules is still challenging despite the rapid advances in nanotechnology and biomaterials. Huge progress has been witnessed in DOX nanoprodrugs owing to their brilliant benefits such as tumor stimuli-responsive drug release capacity, high drug loading efficiency and so on. This review summarized recent progresses of DOX prodrug-based nanomedicines to provide deep insights into future development and inspire researchers to explore DOX nanoprodrugs with real clinical applications.

Switching between DNA binding modes with a photo- and redox-active DNA-targeting ligand, part II: the influence of the substitution pattern

A disulfide-functionalized photoactive DNA ligand is presented that enables the control of its DNA-binding properties by a combination of a photocycloaddition reaction and the redox reactivity of the sulfide/disulfide functionalities. In particular, the initially applied ligand binds to DNA by a combination of intercalation and groove-binding of separate benzo[b]quinolizinium units. The association to DNA is interrupted by an intramolecular [4 + 4] photocycloaddition to the non-binding head-to-head cyclomers. In turn, the subsequent cleavage of these cyclomers with dithiothreitol (DTT) regains temporarily a DNA-intercalating benzoquinolizinium ligand that is eventually converted into a non-binding benzothiophene. As a special feature, this sequence of controlled deactivation, recovery and internal shut-off of DNA-binding properties can be performed directly in the presence of DNA.

Smart Delivery Systems Responsive to Cathepsin B Activity for Cancer Treatment

Cathepsin B is a lysosomal cysteine protease, contributing to vital cellular homeostatic processes including protein turnover, macroautophagy of damaged organelles, antigen presentation, and in the extracellular space, it takes part in tissue remodeling, prohormone processing, and activation. However, aberrant overexpression of cathepsin B and its enzymatic activity is associated with different pathological conditions, including cancer. Cathepsin B overexpression in tumor tissues makes this enzyme an important target for smart delivery systems, responsive to the activity of this enzyme. The generation of technologies which therapeutic effect is activated as a result of cathepsin B cleavage provides an opportunity for tumor-targeted therapy and controlled drug release. In this review, we summarized different technologies designed to improve current cancer treatments responsive to the activity of this enzyme that were shown to play a key role in disease progression and response to the treatment.

Dextran-doxorubicin prodrug nanoparticles conjugated with CD147 monoclonal antibody for targeted drug delivery in hepatoma therapy

Antibody-drug conjugates (ADCs) are a class of tumor cell-targeting drugs that have developed rapidly in recent years. From the perspective of further improving ADC targeting and developing natural macromolecules as drug carriers, it is still challenging and necessary to try new targeted drug delivery modalities. In this study, we have developed an antibody-modified prodrug nanoparticle based on biomacromolecule dextran (DEX) to delivery antitumour drug doxorubicin (DOX). Firstly, oxidized dextran (ODEX) and DOX were bonded to yield ODEX-DOX via Schiff base reaction, which can self-assemble into nanoparticles (NPs) carrying some aldehyde groups. Subsequently, the amino groups of CD147 monoclonal antibody were bound to the aldehyde groups on the surface of ODEX-DOX NPs, resulting in acid-responsive and antibody-modified CD147-ODEX-DOX NPs with relatively small particle size and high DOX loading. FT-IR, UV-Vis, HPLC, and ¹H NMR were used to demonstrate the successful synthesis of polymer prodrug ODEX-DOX NPs and antibody-modified nanomedicine CD147-ODEX-DOX NPs. Dynamic light scattering (DLS) was used to evaluate the stability and the pH responsiveness of ODEX-DOX NPs in different media and tumour microenvironment. The in vitro total release content of DOX reached approximately 70% in PB 5.0 buffer solution after 103 h. Furthermore, the in vivo antitumour efficacy and biodistribution experiments confirmed that CD147-ODEX-DOX NPs could significantly inhibit the growth of HepG2 tumour. All of the results indicate that this acid-sensitive nanomedicine has higher safety and targeting effects. It promises to be an ideal strategy for future targeted drug delivery systems and anticancer therapies.

Stimuli-responsive heparin-drug conjugates co-assembled into stable nanomedicines for cancer therapy

The combination of chemotherapy and photodynamic therapy (PDT) has the potential to complement single-drug therapies, but chemotherapeutic agents and photosensitizers often have compromised therapeutic efficacies and strong toxic effects. In this study, we exploited nanotechnology to address this challenge by utilizing heparin as a carrier for co-delivery of chemotherapeutic drugs and photosensitizers for synergistic cancer therapy. Specifically, heparin-paclitaxel (HP-PTX) and heparin-pyropheophorbide-a (HP-Ppa) were synthesized by attaching paclitaxel (PTX), a small molecular chemotherapeutic drug, through a reactive oxygen species (ROS)-responsive linker and Ppa, a photosensitizer, to heparin, respectively. Two conjugates co-assembled into a nanomedicine, HP-PP nanoparticles (NPs), for controllable co-delivery of Ppa and PTX into tumor cells. HP-PP NPs significantly enhanced the in vitro stability of HP-Ppa and the photostability of Ppa, and the synergistic actions of chemotherapy and PDT were confirmed from both in vitro and in vivo antitumor studies. Notably, HP-PP NPs enhanced tumor accumulation of Ppa up to 11-fold and the treatment of 4T1 tumor-bearing mice with HP-PP NPs resulted in a tumor growth inhibition of 98.1% without systemic toxicity. The strategy of co-assembly of heparin conjugates may offer great potential in enhancing the efficacy of combination therapy. STATEMENT OF SIGNIFICANCE: : We proposed a nano-delivery system, HP-PP NPs, which was constructed by co-assembly of heparin-paclitaxel (HP-PTX) and heparin-pyropheophorbide-a (HP-Ppa), to co-deliver PTX and Ppa for synergistic cancer therapy. HP-PP NPs enhanced the photostability and the in vitro stability of Ppa and HP-Ppa, and induced greater cytotoxicity than HP-PTX NPs or HP-Ppa NPs. This co-delivery system displays enhanced tumor accumulation and has a remarkable synergistic antitumor effect with a tumor growth inhibition of 98.1%.

Dual stimulus-triggered bioorthogonal nanosystem for spatiotemporally controlled prodrug activation and near-infrared fluorescence imaging

In this study, we combined low pH and cathepsin B dual-stimulus-triggered delivery carriers with a bioorthogonal reaction-activated prodrug to achieve regulated activation of the prodrug. A workable method for precise tumor therapy and imaging is provided by the bioorthogonal reaction, which activates the prodrug and fluorescent probe.

Carboxylated paclitaxel prodrug nanofibers for enhanced chemotherapy

The facile availability of nanoformulations with enhanced antitumor performance remains a big challenge. Herein, we synthesize paclitaxel prodrugs with amphiphilic structures and robust assembling ability. Carboxylated paclitaxel prodrugs (PSCB) containing disulfide bonds prefer to form exquisite nanofibers, while phenylcarbinol end capped paclitaxel prodrugs (PSP) assemble into spherical nanoparticles. The transformation of morphology from nanofibers to nanorods can be realized via tuning the content of paclitaxel. Hydrophilic domains of PSCB nanofibers accelerate the cleavage of disulfide bond for rapid drug release in tumor cells, thus exhibiting the enhanced cytotoxicity and antitumor activity. This study provides a crucial insight into the functional design of hydrophobic drugs to improve chemotherapy.

Switching between DNA binding modes with a photo- and redox-active DNA-targeting ligand

A disulfide-functionalized bis-benzo[b]quinolizinium is presented that is transformed quantitatively into its cyclomers in a fast intramolecular [4 + 4] photocycloaddition. Both the bis-quinolizinium and the photocyclomers react with glutathione (GSH) or dithiothreitol (DTT) to give 9-(sulfanylmethyl)benzo[b]quinolizinium as the only product. As all components of this reaction sequence have different DNA-binding properties, it enables the external control and switching of DNA association. Hence, the bis-benzo[b]quinolizinium binds strongly to DNA and is deactivated upon photocycloaddition to the non-binding cyclomers. In turn, the subsequent cleavage of the cyclomers with DTT regains a DNA-intercalating benzoquinolizinium ligand. Notably, this sequence of controlled deactivation and recovery of DNA-binding properties can be performed directly in the presence of DNA.

pH-Responsive nanofiber buttresses as local drug delivery devices

Electrospun nanofibers are a 3D scaffold of choice for many drug delivery devices due to their high surface area, significant capacity for drug payload, ease of in situ placement, and scalable manufacture. Herein, we report the synthesis of polymeric, pH-responsive nanofiber buttresses via electrospinning. The homopolymer is comprised of an acrylic backbone with acid-sensitive, hydrolyzable, trimethoxybenzaldehyde-protected side chains that lead to buttress transformation from a hydrophobic to a hydrophilic state under physiologically relevant pH conditions (e.g., extracellular tumor environment with pH = 6.5). Hydrolysis of the side chains leads to an increase in fiber diameter from approximately 350 to 900 nm and the release of the encapsulated drug cargo. In vitro drug release profiles demonstrate that significantly more drug is released at pH 5.5 compared to pH 7.4, thereby limiting the release to the target site, with docetaxel releasing over 20 days and doxorubicin over 7 days. Drug burst release, defined as >50% within 24 hours, does not occur at either pH or with either drug. Drug-loaded buttresses preserve drug activity and are cytotoxic to multiple human cancer lines, including breast and lung. Important to their potential application in surgical applications, the tensile strength of the buttresses is 6.3 kPa and, though weaker than commercially available buttresses, they provide sufficient flexibility and mechanical integrity to serve as buttressing materials via the application with a conventional surgical cutting stapler.