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.

Investigation of antiproliferative efficacy and apoptosis induction in leukemia cancer cells using irinotecan-loaded liposome-embedded nanofibers constructed from chitosan

Liposomes and nanofibers have been implemented as efficacious vehicles for delivering anticancer drugs. With this view, this study explores the antiproliferative efficacy and apoptosis induction in leukemia cancer cells utilizing irinotecan-loaded liposome-embedded nanofibers fabricated from chitosan, a biological source. Specifically, we investigate the effectiveness of poly(ε-caprolactone) (PCL)/chitosan (CS) (core)/irinotecan (CPT)nanofibers (termed PCL-CS10 CPT), PCL/chitosan/irinotecan (core)/PCL/chitosan (shell) nanofibers (termed CS/CPT/PCL/CS), and irinotecan-coloaded liposome-incorporated PCL/chitosan-chitosan nanofibers (termed CPT@Lipo/CS/PCL/CS) in releasing irinotecan in a controlled manner and treating leukemia cancer. The fabricated formulations were characterized utilizing Fourier transform infrared analysis, transmission electron microscopy, scanning electron microscopy, dynamic light scattering, zeta potential, and polydispersity index. Irinotecan was released in a controlled manner from nanofibers filled with liposomes over 30 days. The cell viability of the fabricated nanofibrous materials toward Human umbilical vein endothelial cells (HUVECs) non-cancerous cells after 168 h was >98 % ± 1 %. The CPT@Lipo/CS/PCL/CS nanofibers achieved maximal cytotoxicity of 85 % ± 2.5 % against K562 leukemia cancer cells. The CPT@Lipo/CS/PCL/CS NFs exhibit a three-stage drug release pattern and demonstrate significant in vitro cytotoxicity. These findings indicate the potential of these liposome-incorporated core-shell nanofibers for future cancer therapy.

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.

Ultrasound-mediated delivery of flexibility-tunable polymer drug conjugates for treating glioblastoma

Effective chemotherapy delivery for glioblastoma multiforme (GBM) is limited by drug transport across the blood-brain barrier and poor efficacy of single agents. Polymer-drug conjugates can be used to deliver drug combinations with a ratiometric dosing. However, the behaviors and effectiveness of this system have never been well investigated in GBM models. Here, we report flexible conjugates of hyaluronic acid (HA) with camptothecin (CPT) and doxorubicin (DOX) delivered into the brain using focused ultrasound (FUS). In vitro toxicity assays reveal that DOX-CPT exhibited synergistic action against GBM in a ratio-dependent manner when delivered as HA conjugates. FUS is employed to improve penetration of DOX-HA-CPT conjugates into the brain in vivo in a murine GBM model. Small-angle x-ray scattering characterizations of the conjugates show that the DOX:CPT ratio affects the polymer chain flexibility. Conjugates with the highest flexibility yield the highest efficacy in treating mouse GBM in vivo. Our results demonstrate the association of FUS-enhanced delivery of combination chemotherapy and the drug-ratio-dependent flexibility of the HA conjugates. Drug ratio in the polymer nanocomplex may thus be employed as a key factor to modulate FUS drug delivery efficiency via controlling the polymer flexibility. Our characterizations also highlight the significance of understanding the flexibility of drug carriers in ultrasound-mediated drug delivery systems.

Galactosylated Core-Shell Nanoparticles with pH/GSH Dual Sensitivity for Targeting Hepatocellular Carcinoma

Galactosylated core-shell nanoparticles (NPs) with diameters of sub-50 nm were fabricated in one pot by reversible addition-fragmentation chain transfer (RAFT) soap-free emulsion polymerization. Their galactosylated shells and acidic cores endow them with high targeting and drug loading efficiencies, respectively. Morever, the physical shrinkage and cleavage of the disulfide cross-linked NPs can realize the rapid release of loaded doxorubicin (DOX) under pH 5.0 and reduced glutathione (GSH) conditions. The combination of these excellent properties resulted in an even lower IC₅₀ of DOX-loaded NPs than free DOX, demonstrating that this platform would be promising in targeting the therapy of hepatocellular carcinoma.

A convergent fabrication of pH and redox dual-responsive hybrids of mesoporous silica nanoparticles for the treatment of breast cancer

Mesoporous silica nanoparticle (MSN), sodium hyaluronate (SH), silk fibroin (SS), and oxidized sodium carboxymethyl cellulose (O-CMC) hybrids were used to develop an intelligent drug delivery platform that may be employed for pH and redox-responsive bi-drug administration. The first drug, cytarabine (Cyt), was loaded with amino-functionalized mesoporous silica (MSN-NH₂) encased by the hydrogel of cystamine (Cys) and SH cross-linked by amide bonds. Hydrophobic doxorubicin (DOX) was co-loaded with Cyt/MSN-NH₂/SA in the hydrogel of SS and O-CMC in the Cyt- loaded hydrogel. Dual-responsive drug delivery may be achieved by encapsulating SS and O-CMC in a hydrogel, including Cyt/MSN-NH₂/SA/DOX/SS/O-CMC, which has acyl hydrazone bonds (-HC = N) and disulfide bond (-S-S-) exchange reaction with glutathione (GSH). Compared to hydrogels encapsulating only one drug (Cyt or DOX), cell survival analysis revealed that the newly fabricated hydrogels have significantly greater chemotherapeutic efficacy. The cell proliferation of the fabricated nanoparticles was examined in MCF-7 and MDA-MB-231 cells, which indicates that the nanoparticles effectively kill the cancer cells without affecting non-cancerous cells. Further, we effectively investigated the morphological changes, and various biochemical staining methods examined nuclear fragmentation/condensation. Furthermore, the biosafety of the nanoparticles was investigated by the in vivo animal model, which reveals that they remarkably enhanced the safety profile in various organs. These outcomes demonstrated that this nanoparticle platform was a promising beneficial agent for improving breast cancer treatment.

Progress and challenges of graphene and its congeners for biomedical applications

Nanomaterials by virtue of their small size and enhanced surface area, present unique physicochemical properties that enjoy widespread applications in bioengineering, biomedicine, biotechnology, disease diagnosis, and therapy. In recent years, graphene and its derivatives have attracted a great deal of attention in various applications, including photovoltaics, electronics, energy storage, catalysis, sensing, and biotechnology owing to their exceptional structural, optical, thermal, mechanical, and electrical. Graphene is a two-dimensional sheet of sp2 hybridized carbon atoms of atomic thickness, which are arranged in a honeycomb crystal lattice structure. Graphene derivatives are graphene oxide (GO) and reduced graphene oxide (rGO), which are highly oxidized and less oxidized forms of graphene, respectively. Another form of graphene is graphene quantum dots (GQDs), having a size of less than 20 nm. Contemporary graphene research focuses on using graphene nanomaterials for biomedical purposes as they have a large surface area for loading biomolecules and medicine and offer the potential for the conjugation of fluorescent dyes or quantum dots for bioimaging. The present review begins with the synthesis, purification, structure, and properties of graphene nanomaterials. Then, we focussed on the biomedical application of graphene nanomaterials with special emphasis on drug delivery, bioimaging, biosensing, tissue engineering, gene delivery, and chemotherapy. The implications of graphene nanomaterials on human health and the environment have also been summarized due to their exposure to their biomedical applications. This review is anticipated to offer useful existing understanding and inspire new concepts to advance secure and effective graphene nanomaterials-based biomedical devices.

Prodrug and Glucose Oxidase Coloaded Photodynamic Hydrogels for Combinational Therapy of Melanoma

With the advantages of high safety and selectivity, photodynamic therapy (PDT) has been widely used for cancer treatments, while the anticancer efficacy is often limited because of its relying on oxygen concentrations. Therefore, sole PDT fails to achieve the desired therapeutic effect for hypoxic tumors. To address this issue, we herein report the construction of prodrug and glucose oxidase (GOx) coloaded alginate (ALG) hydrogels for PDT-combined chemotherapy of melanoma. The hydrogels are in situ formed in tumor sites after injection of ALG solution containing semiconducting polymer nanoparticles, hypoxia-responsive prodrug tirapazamine (TPZ), and GOx, which is based on chelation of ALG by endogenous Ca²⁺. Due to the presence of semiconducting polymer nanoparticles acting as photosensitizers, the hydrogels mediate PDT to produce singlet oxygen (¹O₂) for directly killing tumor cells, in which oxygen is consumed to create a more hypoxic tumor microenvironment. Moreover, the loaded GOx within hydrogels can deplete oxygen to further aggravate tumor hypoxia. As such, TPZ is effectively activated by hypoxia to cause cancer cell death via chemotherapy. Thus, the hydrogels with laser irradiation achieve a combinational action of PDT with chemotherapy to almost completely eradicate tumors, leading to a much higher therapeutic efficacy relative to sole PDT. This study will provide a promising injectable hydrogel platform for effective treatments of cancer.

A dynamic covalent polymeric antimicrobial for conquering drug-resistant bacterial infection

Increasing bacterial drug resistance to antibiotics has posed a major threat to contemporary public health, which resulted in a large number of people suffering from serious infections and ending up dying without any effective therapies every year. Here, a dynamic covalent polymeric antimicrobial, based on phenylboronic acid (PBA)-installed micellar nanocarriers incorporating clinical vancomycin and curcumin, is developed to overcome drug-resistant bacterial infections. The formation of this antimicrobial is facilitated by reversible dynamic covalent interactions between PBA moieties in polymeric micelles and diols in vancomycin, which impart favorable stability in blood circulation and excellent acid-responsiveness in the infection microenvironment. Moreover, the structurally similar aromatic vancomycin and curcumin molecules can afford π-π stacking interaction to realize simultaneous delivery and release of payloads. In comparison with monotherapy, this dynamic covalent polymeric antimicrobial demonstrated more significant eradication of drug-resistant bacteria in vitro and in vivo due to the synergism of the two drugs. Furthermore, the achieved combination therapy shows satisfied biocompatibility without unwanted toxicity. Considering various antibiotics contain diol and aromatic structures, this simple and robust strategy can become a universal platform to combat the ever-threatening drug-resistant infectious diseases.

Hyaluronic Acid Nanoparticles for Immunogenic Chemotherapy of Leukemia and T-Cell Lymphoma

Ratiometric delivery of combination chemotherapy can achieve therapeutic efficacy based on synergistic interactions between drugs. It is critical to design such combinations with drugs that complement each other and reduce cancer growth through multiple mechanisms. Using hyaluronic acid (HA) as a carrier, two chemotherapeutic agents-doxorubicin (DOX) and camptothecin (CPT)-were incorporated and tested for their synergistic potency against a broad panel of blood-cancer cell lines. The pair also demonstrated the ability to achieve immunogenic cell death by increasing the surface exposure levels of Calreticulin, thereby highlighting its ability to induce apoptosis via an alternate pathway. Global proteomic profiling of cancer cells treated with HA-DOX-CPT identified pathways that could potentially predict patient sensitivity to HA-DOX-CPT. This lays the foundation for further exploration of integrating drug delivery and proteomics in personalized immunogenic chemotherapy.

A Nanosized Codelivery System Based on Intracellular Stimuli-Triggered Dual-Drug Release for Multilevel Chemotherapy Amplification in Drug-Resistant Breast Cancer

Lacking nano-systems for precisely codelivering the chemotherapeutics paclitaxel (PTX) and the natural P-glycoprotein (P-gp) inhibitor, quercetin (QU), into cancer cells and controlling their intracellular release extremely decreased the anticancer effects in multidrug resistant (MDR) tumors. To overcome this hurdle, we constructed hybrid polymeric nanoparticles (PNPs) which consist of redox-sensitive PTX/polyethyleneimine-tocopherol hydrogen succinate-dithioglycollic acid PNPs and pH-sensitive hyaluronic acid-QU conjugates. The obtained hybrid PNPs can be internalized into drug-resistant breast cancer cells by the hyaluronic acid/CD44-mediated endocytosis pathway and escape from the lysosome through the “proton sponge effect”. Under the trigger of intracellular stimuli, the nanoplatform used the pH/glutathione dual-sensitive disassembly to release QU and PTX. The PTX diffused into microtubules to induce tumor cell apoptosis, while QU promoted PTX retention by down-regulating P-gp expression. Moreover, tocopherol hydrogen succinate and QU disturbed mitochondrial functions by generating excessive reactive oxygen species, decreasing the mitochondrial membrane potential, and releasing cytochrome c into the cytosol which consequently achieved intracellular multilevel chemotherapy amplification in MDR cancers. Importantly, the PNPs substantially suppressed tumors growth with an average volume 2.54-fold lower than that of the control group in the MCF-7/ADR tumor-bearing nude mice model. These presented PNPs would provide a valuable reference for the coadministration of natural compounds and anticarcinogens for satisfactory combination therapy in MDR cancers.

Multifunctional carbon quantum dots as a theranostic nanomedicine for fluorescence imaging-guided glutathione depletion to improve chemodynamic therapy

To minimize unwanted reactions with high concentrations of reduced glutathione (GSH) in the tumor microenvironment (TME) during chemodynamic therapy (CDT), a simple and effective strategy was developed to fabricate a TME stimuli-responsive theranostic nanomedicine (Fe-CD) for fluorescence imaging-guided GSH depletion and cancer therapy by combining fluorescent imaging carbon dots (CD) and Fe(III). Introducing Fe(III) into Fe-CD not only quenched the fluorescence of CD while reacting with and consuming intracellular GSH for fluorescence imaging of the depletion of GSH but also provided a source of metal ions to generate more abundant hydroxyl radicals (•OH) with hydrogen peroxide (H₂O₂) through the Fenton reaction to improve CDT. Fe-CD showed promising •OH generation under H₂O₂ to effectively degrade methylene blue in vitro and obviously activate the green fluorescence of the reactive oxygen species (ROS) probe in cells. Benefiting from the fluorescence enhancement in response to TME stimulation, Fe-CD greatly enhanced CDT cytotoxicity while monitoring successful GSH depletion by fluorescence imaging. Fe-CD has the potential to act as a theranostic nanomedicine for fluorescence imaging-guided GSH depletion to amplify CDT.

The effect of spacers in dual drug-polymer conjugates toward combination therapeutic efficacy

Recently, a great effort has been made to perfect the therapeutic effect of solid tumor, from single-agent therapy to combined therapy and many other polymer-drug conjugations with dual or more anticancer agents due to their promising synergistic effect and higher drug level accumulation towards tumor tissues. Different polymer-drug spacers present diverse therapeutic efficacy, therefore, finding an appropriate spacer is desirable. In this study, dual drugs that are doxorubicin (DOX) and mitomycin C (MMC) were conjugated onto a polymer carrier (xyloglucan) via various peptide or amide bonds, and a series of polymers drug conjugates were synthesized with different spacers and their effect on tumor treatment efficacy was studied both in vitro and in vivo. The result shows that the synergistic effect is better when using different linker to conjugate different drugs rather than using the same spacer to conjugate different drugs on the carrier. Particularly, the finding of this works suggested that, using peptide bond for MMC and amide bond for DOX to conjugate dual drugs onto single XG carrier could improve therapeutic effect and synergy effect. Therefore, in polymer-pharmaceutical formulations, the use of different spacers to optimize the design of existing drugs to enhance therapeutic effects is a promising strategy.

Recent advances in polymeric core-shell nanocarriers for targeted delivery of chemotherapeutic drugs

The treatment effect of chemotherapeutics is often impeded by nonspecific biodistribution and limited biocompatibility. Polymeric core-shell nanocarriers (PCS NCs) composed of a polymer core and at least one shell have been widely applied for cancer therapy and have shown great potential in selectively delivering chemotherapeutic drugs to tumor sites. These PCS NCs can effectively ameliorate the delivery efficiency and therapeutic index of anticarcinogens by prolonging drug residence in the bloodstream, enhancing tumor tissue drug penetration, facilitating cellular drug uptake, controlling the spatiotemporal release of payloads, or codelivering two or more bioactive agents. This review summarizes recently published literature on using PCS NCs to transport chemotherapeutic drugs with poor aqueous solubility and discusses their design principles, structural features, functional properties, and potential limitations.

Engineering glutathione-responsive near-infrared polymeric prodrug system for fluorescence imaging in tumor therapy

The release and biodistribution of drugs in the body have an important impact on tumor diagnosis and treatment. Near-infrared (NIR) fluorescent active fluorophores with good photostability are used to detect drug release and perform in vivo imaging. Here, we developed a glutathione-responsive NIR prodrug POEGMA-b-P(CPT-CyOH) (PCC) for effective cancer diagnosis and treatment, whereby the camptothecin (CPT) and NIR fluorophore CyOH in PCC are connected by disulfide bonds. In vitro experiments confirmed that PCC was quickly taken up by cells. The high concentration of tumor intracellular glutathione caused the cleavage of the PCC disulfide bonds, leading to the release of the chemotherapeutic drug CPT, indicating that PCC can promote apoptosis. Moreover, owing to the fluorescent properties of CyOH, PCC was successfully used for in vivo imaging to observe the drug penetration and enrichment capabilities in tumors. Finally, PCC successfully inhibited tumor growth, indicating that the prodrug has a good anti-tumor effect. This work provides new strategies for chemical drug delivery and precise cancer treatment.

Novel amphiphilic fluorine-containing nanocarriers for oxygen self-sufficiency "AND" GSH depletion sequentially to enhance photodynamic therapy

In order to maximize the retention of the photodynamic therapy (PDT) efficacy, while avoiding the dilemma of hypoxia and high reducing substances in tumor tissue, fluoropolymers were synthesized in a simple and effective methods. Fluorous effect with good oxygen carrying capacity was endowed by the fluorine-containing section in fluoropolymers and the perfluorodecalin (PFD) together, the reaction site with GSH was provided by the disulfide bond, which enhanced PDT efficiency through the sequential "AND" logic gate design. Two kind of fluorine-containing nanocarriers (M-Ce6 and E-Ce6) were obtained by solvent evaporation or ultrasound emulsification with PFD, respectively. In vitro, both of them showed promising high ROS generation under photoirradiation. Benefiting by cavitation effects, E-Ce6 had a more significant statistical difference in cellular uptake. Furthermore, the cells incubating with E-Ce6 hardly were noticed that the hypoxia signal appeared under hypoxia, while reducing the intracellular GSH content by more than 15%. Through the sequential "AND" logic gate design, ROS production even under hypoxia and GSH conditions of E-Ce6 was also almost 1.5 times that of Ce6 under normoxia. Enhancing effect of E-Ce6 was 13.47 times and 6.85 times, while selectivity ratio reached 5.13 times and 4.81 times compared with Ce6 and M-Ce6. The two-pronged strategy showed a high potential for delivering the Ce6 to deep inside of cancer cells and killing it in the simulated tumor by PDT. These above results demonstrated the potential of E-Ce6, as oxygen self-sufficiency and GSH depletion nanocarriers for combined enhancement of photodynamic therapy.

Endogenous reactive oxygen species burst induced and spatiotemporally controlled multiple drug release by traceable nanoparticles for enhancing antitumor efficacy

Reactive oxygen species (ROS) are not only used as a therapeutic reagent in chemodynamic therapy (CDT), to stimulate the release of antineoplastic drugs, they can also be used to achieve a combined effect of CDT and chemotherapy to enhance anticancer effects. Herein, we synthesized a pH-responsive prodrug (PEG2k-NH-N-DOX), ROS-responsive prodrug (PEG2k-S-S-CPT-ROS), organic CDT agents (TPP-PEG2k-LND, TPP-PEG2k-TOS), and T1-enhanced magnetic resonance imaging contrast agents (Gd-DTPA-N16-16), and used them to encapsulate combrestatinA4 (CA4) to prepare traceable pH/ROS dual-responsive multifunctional nanoparticles (TLDCAG NPs) with endogenous ROS burst and spatiotemporally controlled multiple drug release ability. Firstly, TLDCAG NPs were accumulated in the tumor cell microenvironment via an enhanced permeability and retention (EPR) effect. Secondly, CA4 was released and specifically destroyed angiogenesis to facilitate the interaction between the tumor and the remaining TLDCG NPs. After accumulating in tumor cells, the TLDCG NPs could be destroyed under acidic conditions to quickly release doxorubicin (DOX), TPP-PEG2k-LND, and TPP-PEG2k-TOS. Thirdly, TPP-PEG2k-LND and TPP-PEG2k-TOS quickly targeted mitochondria, induced endogenous ROS bursts, reduced the mitochondrial membrane potential, and induced tumor cell apoptosis. Endogenous ROS can not only be used as a therapeutic reagent for CDT, but also can cut off the thioketal bond in PEG2k-S-S-CPT-ROS and release camptothecin (CPT). Finally, TLDCAG NPs were traced by magnetic resonance imaging (MRI). Furthermore, in vitro and vivo results indicate that the TLDCAG NPs have vigorous antitumor activity and negligible systemic toxicity. Therefore, the TLDCAG NPs provide an efficient strategy for enhancing antitumor efficacy.

Hyaluronic acid conjugates for topical treatment of skin cancer lesions

Skin cancer is one of the most common types of cancer in the United States and worldwide. Topical products are effective for treating cancerous skin lesions when surgery is not feasible. However, current topical products induce severe irritation, light-sensitivity, burning, scaling, and inflammation. Using hyaluronic acid (HA), we engineered clinically translatable polymer-drug conjugates of doxorubicin and camptothecin termed, DOxorubicin and Camptothecin Tailored at Optimal Ratios (DOCTOR) for topical treatment of skin cancers. When compared to the clinical standard, Efudex, DOCTOR exhibited high cancer-cell killing specificity with superior safety to healthy skin cells. In vivo studies confirmed its efficacy in treating cancerous lesions without irritation or systemic absorption. When tested on patient-derived primary cells and live-skin explants, DOCTOR killed the cancer with a selectivity as high as 21-fold over healthy skin tissue from the same donor. Collectively, DOCTOR provides a safe and potent option for treating skin cancer in the clinic.

Self-targeted polymersomal co-formulation of doxorubicin, camptothecin and FOXM1 aptamer for efficient treatment of non-small cell lung cancer

In spite of huge developments in cancer treatment, versatile combinational formulations of different chemotherapeutic agents to enhance anticancer activity while reducing systemic toxicity still remains a challenge. In this regard, in the current study, an amphiphilic hyaluronic acid-b-polycaprolactone diblock copolymer was synthesized using "click chemistry". The synthesized copolymer was self-assembled to form polymersomal structures for co-encapsulation of hydrophilic doxorubicin (DOX) and hydrophobic camptothecin (CPT) in their interior aqueous compartment and their bilayer, respectively with 1:10 and 1:1 ratios. The prepared polymersomal combinational formulation surrounded by hyaluronic acid brush as hydrophilic segment, could provide active targeting of the system against CD44 marker expressed on the surface of cancerous cells. The hyaluronic acid shell could also provide flexible chemistry for the conjugation of therapeutic FOXM1-specific DNA aptamer (Forkhead Box M1; against transcription factor FOXM1) on the surface of polymersomes in order to further suppress cancerous cell proliferation. The obtained results demonstrated that the prepared co-formulation provided sustained, controlled release of the entrapped drugs during 200 h. In vitro cytotoxicity experiments on non-small cell lung cancer, A549 and SK-MES-1 cell lines, demonstrated that the co-formulation of DOX and CPT provided synergistic effect and significantly higher cytotoxicity in comparison with free drugs. The cytotoxicity experiment also indicated that the aptamer conjugation on the co-formulations surface could significantly increase the cytotoxicity and induce apoptosis in combination therapy on both A549 and SK-MES-1 cell lines while aptamer-conjugated blank NPs did not show any cytotoxicity which emphasizes on the sensitization capability of the FOXM1 DNA aptamer against non-small cell lung cancer. Furthermore, it was shown that the co-formulation with or without aptamer renders the formulation specific tumor accumulation in vivo 24 h post-administration, assisting the combination synergy observed in vitro to be translated to in vivo antitumor efficacy. This combinatorial delivery platform strongly offers a novel approach for the synergistic controlled transportation of several chemotherapeutics for the treatment of non-small cell lung cancer.

A traceable, GSH/pH dual-responsive nanoparticles with spatiotemporally controlled multiple drugs release ability to enhance antitumor efficacy

Constructing highly efficient and multifunctional nanoparticles to overcome the multiple challenges of targeted drug delivery is a new strategy urgently needed in tumor therapy. Here, we synthesized pH-responsive prodrug (PEG_2K-NH-N-DOX), GSH-responsive prodrug (PEG_2K-S-S-CPT), folate-receptor targeting polymers (FA-PEG_2K-L8, FA-PEG_2K-TOS) and T1-enhanced magnetic resonance imaging contrast agents (Gd-DTPA-N16-16), used to encapsulate combrestatinA4 (CA4) to prepare multifunctional nanoparticles (FTDCAG NPs). Unlike other nanoparticles, FTDCAG NPs contains three drugs with the ability to control the release in time and space, which can maximize the effectiveness of precise cancer chemotherapy. We first confirmed that specific binding between FTDCAG NPs and overexpressed folate-receptor cells by flow cytometry and confocal laser scanning microscopy. We then investigated the spatiotemporally controlled release ability of FTDCAG NPs loaded with doxorubicin (DOX), CA4 and camptothecin (CPT). Relative to pH = 7.4, the release efficiency of CA4 in the pH = 6.5 increased by 63.4 %. The first released CA4 is able to destroy the angiogenesis and help tumor cells to be exposed to the remaining FTDCG NPs. After being internalized into the tumor cells, FTDCG NPs is disassembled and the CPT and DOX were released due to the increase of intracellular GSH concentration and the decrease of pH value. Besides, the relaxation time of FTDCAG NPs is 3.86 times that of clinical Gd-DTPA, and the in vitro and vivo T1-weighted imaging is brighter, which can be used to trace the nanoparticles by MRI. Therefore, FTDCAG NPs provide an efficient strategy for the design of multifunctional drug delivery systems for enhancing antitumor efficacy.

Spatiotemporal Concurrent Liberation of Cytotoxins from Dual-Prodrug Nanomedicine for Synergistic Antitumor Therapy

Nanomedicine developed to date by means of directly encapsulating cytotoxins suffers from crucial drawbacks, including premature release and detoxification prior to arrival at pharmaceutics targets. To these respects, redox-responsive polymeric prodrugs of platinum (Pt) and camptothecin (CPT), selectively and concomitantly activated in the cytoplasm, were elaborated in manufacture of dual prodrug nanomedicine. Herein, multiple CPTs were conjugated to poly(lysine) (PLys) segments of block copolymeric poly(ethylene glycol) (PEG)-PLys through the redox responsive disulfide linkage [PEG-PLys(ss-CPT)] followed by reversible conversion of amino groups from PLys into carboxyl groups based on their reaction with cis-aconitic anhydride [PEG-PLys(ss-CPT&CAA)]. On the other hand, Pt(IV) in conjugation with dendritic polyamindoamine [(G3-PAMAM-Pt(IV)] was synthesized for electrostatic complexation with PEG-PLys(ss-CPT&CAA) into dual prodrug nanomedicine. Subsequent investigations proved that the elaborated nanomedicine could sequentially respond to intracellular chemical potentials to overcome a string of predefined biological barriers and facilitate intracellular trafficking. Notably, PEG-PLys(ss-CPT&CAA) capable of responding to the acidic endosomal microenvironment for transformation into endosome-disruptive PEG-PLys(ss-CPT), as well as release of G3-PAMAM-Pt(IV) from nanomedicine, prompted transclocation of therapeutic payloads from endosomes into cytosols. Moreover, concurrent activation and liberation of cytotoxic CPT and Pt(II) owing to their facile responsiveness to the cytoplasmic reducing microenvironment have demonstrated overwhelming cytotoxic potencies. Eventually, systemic administration of the dual prodrug construct exerted potent tumor suppression efficacy in treatment of intractable solid breast adenocarcinoma, as well as an appreciable safety profile. The present study illustrated the first example of nanomedicine with a dual prodrug motif, precisely and concomitantly activated by the same subcellular stimuli before approaching pharmaceutic action targets, thus shedding important implication in development of advanced nanomedicine to seek maximized pharmaceutic outcomes.

Preparation of ROS-responsive core crosslinked polycarbonate micelles with thioketal linkage

Herein, we prepared novel reactive oxygen species (ROS) responsive core crosslinked (CCL/TK) polycarbonate micelles conveniently by click reaction between amphiphilic diblock copolymer poly(ethylene glycol)-poly(5-methyl-5-propargylxycar-bonyl-1,3-dioxane-2-one) (PEG-PMPC) with pendant alkynyl group and thioketal containing azide derivative bis (2-azidoethyl) 3, 3'- (propane-2, 2-diylbis (sulfanediyl)) dipropanoate (TK-N₃). The CCL/TK micelles were obtained with small size of 146.4 nm, showing excellent stability against dilution and high doxorubicin (DOX) loading. In vitro toxicity tests demonstrated that the obtained CCL/TK micelles have good biocompatibility and low toxicity with cell viability above 95 %. Furthermore, DOX-loaded CCL/TK micelles showed significantly superior toxicity with IC₅₀ values for HeLa and MCF-7 cells about 3.74 μg/mL and 3.91 μg/mL, respectively. Confocal laser scanning microscope (CLSM) and flow cytometry showed excellent internalization efficiency and intracellular drug release of DOX-loaded CCL/TK micelles. The obtained ROS-responsive CCL/TK micelles showed great potential for anticancer drug delivery.

Rational Construction of a Mitochondrial Targeting, Fluorescent Self-Reporting Drug-Delivery Platform for Combined Enhancement of Endogenous ROS Responsiveness

To maximize the utilization and response to the high oxidative stress environment of tumor sites while avoiding the dilemma of enhancing reactive oxygen species (ROS) response in a single way, mitochondrial targeting combined with fluorescent self-reporting polymeric nanocarriers (1K-TPP and 2K-TPP) with grafted structures were synthesized via a chemoenzymatic method in a high yield to simultaneously enhance the drug delivery of endogenous ROS responses. 1K-TPP and 2K-TPP loaded doxorubicin (DOX) at a high content over 12% and formed homogeneous spherical micelles. In vitro, both of them showed promising high sensitivity (detection limit below 200 nM H₂O₂), fast response, and ratiometric fluorescent self-reporting properties (fluorescent enhancement more than 200 times) to ROS and excellent stability under physiological conditions, while achieving a rapid release of the DOX in response to 1 mM H₂O₂. Cell co-localization experiments exhibited that they had favorable mitochondrial targeting, and mitochondrial isolation experiments also confirmed that the TPP-modified 1K-TPP selectively accumulated nearly three times in mitochondria than that in total cells. The internalization of 1K-TPP and 2K-TPP into cancer cells was greatly improved by nearly 200% compared to that of unmodified control (1K-OH and 2K-OH) and also explored a unique energy-dependent endocytosis. Furthermore, stimulation of endogenous ROS enhanced the green fluorescence intensity (up to 51.4%) of the linked probe so as to destroy the internal structure of the nanocarriers, achieving self-reporting of the drug's intracellular release and tracking of the intracellular location of nanocarriers. The cytotoxicity of DOX-loaded 1K-TPP and 2K-TPP in tumor cells with a higher ROS content showed statistical superiority to that of 1K-OH and 2K-OH, benefiting from the extremely good endogenous ROS response sensitivity leading to the differential selective release of drugs. These results demonstrate the potential of 1K-TPP and 2K-TPP, especially for 1K-TPP, as mitochondria-targeted, fluorescent self-reporting nanocarriers for combined enhancement of endogenous ROS responsiveness.

Sulfur dioxide signaling molecule-responsive polymeric nanoparticles

Stimuli-responsive polymer nano-capsules toward a specific signaling molecule show great potential in the fabrication of smart and efficient controlled/targeted drug vehicles. Herein, we design and synthesize a PEG45-b-PVPOP14 diblock copolymer (PEG = poly(ethylene glycol) and PVPOP = poly(4-vinylphenyl 4-oxopentanoate), the subscripts representing the number of repeat units of each block) with levulinate-protected phenol side groups. The PEG45-b-PVPOP14 diblock copolymer could self-assemble to form large compound micelles in aqueous media. Since the core of the large compound micelles formed contains both hydrophilic PEG and hydrophobic PVPOP domains, this kind of micelle is able to load both hydrophobic and hydrophilic species within the core. The ester moiety of levulinate-protected phenol can be selectively cleaved upon incubation with a sulfite, a derivative of SO2 in aqueous media, to give phenol groups. Thus, the sulfite exhibits the ability to alter the amphiphilicity and further the self-assembled behavior of PEG45-b-PVPOP14. The release of payloads in the core of micelles can be accelerated by triggering of the sulfite. Significantly, the nano-capsule of PEG45-b-PVPOP14 shows specific response to the sulfite (SO2) with slight interference of other bio-species, such as Cys, GSH and Hcy. As far as we are aware, this is the first example of a nano-capsule with sulfite (SO2) specific responsiveness. We envisage that this polymer model could broaden the scope of biological signaling molecule responsive macromolecular systems and provide a new platform to fabricate SO2-responsive biomedicine materials.

Intracellular GSH-responsive camptothecin delivery systems

Smart GSH-responsive camptothecin delivery systems for treatment of tumors and real-time monitoring in vivo and in vitro were described.

Therapeutic polymeric nanomedicine: GSH-responsive release promotes drug release for cancer synergistic chemotherapy

To obtain an efficient dual-drug release and enhance therapeutic efficiency for combination chemotherapy, a glutathione (GSH)-responsive therapeutic amphiphilic polyprodrug copolymer (mPEG-b-PCPT) is synthesized to load doxorubicin (DOX) via hydrophobic and π–π stacking interaction. In this nanomedicine system (mPEG-b-PCPT/DOX), the ratio of the two drugs can be easily modulated by changing the loading content of DOX. The in vitro drug release curves and laser confocal images suggested that the release of CPT and DOX is induced through a “release promotes release strategy”: after internalization into tumor cells, the disulfide bonds in the nanomedicine are cleaved by glutathione (GSH) in the cytoplasm and then lead to the release of CPT. Meanwhile, the disassembly of nanomedicine immediately promotes the co-release of DOX. The optimum dose ratio of CPT and DOX is evaluated via the combination index (CI) value using HepG-2 cells. The results of cell apoptosis and cell viability prove the better synergistic efficiency of the nanomedicine than free drugs at the optimum dose ratio of 1. Consequently, this stimuli-responsive synergistic chemotherapy system provides a direction for the fabrication of nanomedicines possessing promising potential in clinical trials.

In the GSH-responsive doxorubicin loading camptothecin prodrug nanomedicine, easy modulation of the dose ratio and controlled co-release were achieved, and the synergistic effect was significantly improved.