Cascade Mesophase Transitions of Multi-enzyme Responsive Polymeric Formulations

Studying how synthetic polymer assemblies respond to sequential enzymatic stimuli can uncover intricate interactions in biological systems. Using amidase- and esterase-responsive PEG-based diblock (DBA) and triblock amphiphiles (TBAs), we created two distinct formulations: amidase-responsive DBA with esterase-responsive TBA and vice versa. We studied their cascade responses to the two enzymes and the sequence of their introduction. These formulations underwent cascade mesophase transitions upon the addition of the DBA-degrading enzyme, transitioning from (i) coassembled micelles to (ii) triblock-based hydrogel, and ultimately to (iii) dissolved polymers when exposed to the TBA hydrolyzing enzyme. The specific pathway of the two mesophase transitions depended on the compositions of the formulations and the enzyme introduction sequence. The results highlight the potential for designing polymeric formulations with programmable multistep enzymatic responses, mimicking the complex behavior of biological macromolecules.

Molecular Design and Controlled Self-Assembly of Copolymers as Core-Shell-Corona Nanoparticles for Smarter Tumor Treatment

Copolymer-based core-shell-corona nanoparticles have attracted more interest for tumor chemotherapy, owing to their unique multifunctionality benefiting from their unique multilevel topological structure in comparison with the conventional core-shell ones. Here, the recent progress in such core-shell-corona nanoparticle-based drug delivery systems (DDSs) in tumor chemotherapy was reviewed, focusing on additive functionality of the shell layer for controlled drug release performance from the viewpoints of the molecular design and controlled self-assembly, such as stimuli-responsive gatekeepers, independent loading of active substances, and so on. Moreover, future perspectives have been prospected for smarter tumor treatment.

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.

Well-Defined pH-Sensitive Self-Assembled Triblock Copolymer-Based Crosslinked Micelles for Efficient Cancer Chemotherapy

Delivery of chemotherapeutics to cancer cells using polymeric micelles is a promising strategy for cancer treatment. However, limited stability of micelles, premature drug release and off-target effect are the major obstacles that restrict the utilization of polymeric micelles as effective drug delivery systems. In this work, we addressed these issues through the innovative design of targeted pH-sensitive crosslinked polymeric micelles for chemotherapeutic delivery. A well-defined triblock copolymer, poly(ethylene glycol)-b-poly(2-hydroxyethyl methacrylate)-b-poly(butyl acrylate) (PEG-b-PHEMA-b-PBA), was synthesized by living radical polymerization, and then modified by using 4-pentenoic anhydride to incorporate pendant crosslinkable alkene groups in the middle block. The resulting copolymer underwent self-assembly in aqueous solution to form non-crosslinked micelles (NCMs). Subsequently, intramicellar thiol-ene crosslinking was performed by using 1,4-butanediol bis(3-mercaptopropionate) to give crosslinked micelles (CMs) with pH-sensitive crosslinks. The targeted CM (cRGD-DOX₁₀-CM5) was readily prepared by using tumor-targeting ligand cyclo(Arg-Gly-Asp-D-Phe-Cys) (cRGD) together with the 1,4-butanediol bis(3-mercaptopropionate) during the crosslinking step. The study of cumulative DOX release revealed the pH-sensitive feature of drug release from these CMs. An in vitro MTT assay revealed that NCMs and CMs are biocompatible with MCF 10A cells, and the samples exhibited significant therapeutic efficiency as compared to free DOX. Cellular uptake studies confirmed higher uptake of cRGD-DOX₁₀-CM5 by MCF 10A cancer cells via cRGD-receptor-mediated endocytosis as compared to the corresponding analogues without cRGD. These results indicate that such pH-responsive crosslinked PEG-b-PHEMA-b-PBA-based micelles are therapeutically effective against cancer cells and hold remarkable promise to act as smart drug delivery systems for cancer therapy.

Negatively charged polymer-shielded supramolecular nano-micelles with stimuli-responsive property for anticancer drug delivery

A new kind of negatively charged polymer-shielded supramolecular nano-micelles with dual-responsive property was designed for tumor treatment, which was prepared on the basis of adamantane terminated linear PAsp(DIP) and disulfide-β-cyclodextrin-terminated PAsp(EDA). The supramolecular nano-micelles comprised a 2,3-dimethylmaleic anhydride (DA) protective layer to stabilize the micelles, a pH-responsive core to package hydrophobic model drugs, and a disulfide-crosslinked interlayer to shackle the core against drug leakage under normal physiological conditions. After arriving at the tumor tissue via EPR, the targeting function could be turned on by dislodging DA groups on the surface of micelles, which allowed the drug-loaded nano-micelles to be easily phagocytized by the tumor cells, and then release the drug inside the cells induced by the increased glutathione level and acidic pH. The results indicated that the charge-conversional dual-responsive supramolecular nano-micelles showed excellent antitumor activity.

Interfacial photocrosslinking of polymer particles possessing nucleobase photoreactive groups for hollow/capsule polymer fabrication

Herein, polystyrene-based particles possessing nucleobases in polymer side chains were prepared and nucleobase groups were applied to the interfacial photocrosslinking as photoreactive groups for the first time for fabricating hollow/capsule particles.

Near-Infrared Light-Responsive Shell-Crosslinked Micelles of Poly(d,l-lactide)-b-poly((furfuryl methacrylate)-co-(N-acryloylmorpholine)) Prepared by Diels-Alder Reaction for the Triggered Release of Doxorubicin

In the present study, we developed near-infrared (NIR)-responsive shell-crosslinked (SCL) micelles using the Diels-Alder (DA) click reaction between an amphiphilic copolymer poly(d,l-lactide)20-b-poly((furfuryl methacrylate)10-co-(N-acryloylmorpholine)78) (PLA20-b-P(FMA10-co-NAM78)) and a diselenide-containing crosslinker, bis(maleimidoethyl) 3,3'-diselanediyldipropionoate (BMEDSeDP). The PLA20-b-P(FMA10-co-NAM78) copolymer was synthesized by RAFT polymerization of FMA and NAM using a PLA20-macro-chain transfer agent (PLA20-CTA). The DA reaction between BMEDSeDP and the furfuryl moieties in the copolymeric micelles in water resulted in the formation of SCL micelles. The SCL micelles were analyzed by 1H-NMR, FE-SEM, and DLS. An anticancer drug, doxorubicin (DOX), and an NIR sensitizer, indocyanine green (ICG), were effectively incorporated into the SCL micelles during the crosslinking reaction. The DOX/ICG-loaded SCL micelles showed pH- and NIR-responsive drug release, where burst release was observed under NIR laser irradiation. The in vitro cytotoxicity analysis demonstrated that the SCL was not cytotoxic against normal HFF-1 cells, while DOX/ICG-loaded SCL micelles exhibited significant antitumor activity toward HeLa cells. Thus, the SCL micelles of PLA20-b-P(FMA10-co-NAM78) can be used as a potential delivery vehicle for the controlled drug release in cancer therapy.

Synthesis, classification and properties of hydrogels: their applications in drug delivery and agriculture

Absorbent polymers or hydrogel polymer materials have an enhanced water retention capacity and are widely used in agriculture and medicine. The controlled release of bioactive molecules (especially drug proteins) by hydrogels and the encapsulation of living cells are some of the active areas of drug discovery research. Hydrogel-based delivery systems may result in a therapeutically advantageous outcome for drug delivery. They can provide various sequential therapeutic agents including macromolecular drugs, small molecule drugs, and cells to control the release of molecules. Due to their controllable degradability, ability to protect unstable drugs from degradation and flexible physical properties, hydrogels can be used as a platform in which various chemical and physical interactions with encapsulated drugs for controlled release in the system can be studied. Practically, hydrogels that possess biodegradable properties have aroused greater interest in drug delivery systems. The original three-dimensional structure gets broken down into non-toxic substances, thus confirming the excellent biocompatibility of the gel. Chemical crosslinking is a resource-rich method for forming hydrogels with excellent mechanical strength. But in some cases the crosslinker used in the synthesis of the hydrogels may cause some toxicity. However, the physically cross-linked hydrogel preparative method is an alternative solution to overcome the toxicity of cross-linkers. Hydrogels that are responsive to stimuli formed from various natural and synthetic polymers can show significant changes in their properties under external stimuli such as temperature, pH, light, ion changes, and redox potential. Stimulus-responsive hydrogels have a wider range of applications in biomedicine including drug delivery, gene delivery and tissue regeneration. Stimulus-responsive hydrogels loaded with multiple drugs show controlled and sustained drug release and can act as drug carriers. By integrating stimulus-responsive hydrogels, such as those with improved thermal responsiveness, pH responsiveness and dual responsiveness, into textile materials, advanced functions can be imparted to the textile materials, thereby improving the moisture and water retention performance, environmental responsiveness, aesthetic appeal, display and comfort of textiles. This review explores the stimuli-responsive hydrogels in drug delivery systems and examines super adsorbent hydrogels and their application in the field of agriculture.

Enzymatic multifunctional biodegradable polymers for pH- and ROS-responsive anticancer drug delivery

A new family of multifunctional biodegradable block copolymers, PEG-poly(ω-pentadecalactone-co-N-methyldiethyleneamine sebacate-co-2,2'-thiodiethylene sebacate) (PEG-PMT), were synthesized via lipase-catalyzed copolymerization procedures. Amphiphilic PEG-PMT copolymers can be readily transformed into stable micellar nanoparticles through self-assembling processes in aqueous medium. The particle sizes increase dramatically after exposure of the particles to the acidic pH and high reactive oxygen species (ROS) conditions in tumor microenvironments, due to protonation of thioether groups and oxidation of amino groups in the PMT micelle cores, respectively. For example, docetaxel (DTX)-loaded PEG-PM-19 % TS micelles were triggered synergistically by acidic pH and ROS stimuli to release over 85 % of the anti-cancer drug. In particular, DTX/PEG-PMT-19 % TS and DTX/PEG-PMT-48 % TS micelles performed better than commercial Duopafei formulation in prohibiting growth of CT-26 tumors xenografed in vivo (70 % of tumor-inhibiting efficiency). Biosafety analysis revealed that DTX-loaded PEG-PMT nanoparticles possessed minimal toxicity towards normal organs, such as liver and kidney. These experimental data demonstrated that the pH- and ROS-responsive PEG-PMT micelles are promising vectors for both delivery of anti-tumor drugs and their controlled release at tumor intracellular sites.

Oxidative instability of boronic acid-installed polycarbonate nanoparticles

Oxidative stress, caused by the overproduction of reactive oxygen species (ROS), is often observed in degenerative and/or metabolic diseases, tumors, and inflamed tissues. Boronic acids are emerging as a unique class of responsive biomaterials targeting ROS because of their reactivity toward H2O2. Herein, we examine the oxidative reactivity of nanoparticles from a boronic acid-installed polycarbonate. The extent of oxidation under different concentrations of H2O2 was tracked by the change in fluorescence intensity of an encapsulated solvatochromic reporter dye, demonstrating their sensitivity to biologically-relevant concentrations of hydrogen peroxide. Oxidation-triggered particle destabilization, however, was shown to be highly dependent on the concentration of the final oxidized polymer product, and was only achieved if it fell below polymer critical micelle concentration. Our results indicate that these nanocarriers serve as an excellent dual pH/H2O2 responsive vehicle for drug delivery.

Development and disassembly of single and multiple acid-cleavable block copolymer nanoassemblies for drug delivery

Acid-degradable block copolymer-based nanoassemblies are promising intracellular candidates for tumor-targeting drug delivery as they exhibit the enhanced release of encapsulated drugs through their dissociation.

Supramolecularly cross-linked amphiphilic block copolymer assembly by the dipolar interaction of a merocyanine dye

Dipolar interaction driven dimerization of a merocyanine (MC) dye has been exploited to achieve non-covalently crosslinked stable micelles in water and reverse micelles in toluene with emissive properties from a MC-pendant amphiphilic block copolymer.

Investigation of pH-responsive block glycopolymers with different structures for the delivery of doxorubicin

To understand the influence of the construction of pH-responsive glycopolymer carriers on loading and release behaviors of the drug, three types of block glycopolymers with similar compositions but different constructions, PEG-b-P(DEA-co-GAMA), PEG-b-PDEA-b-PGAMA and PEG-b-PGAMA-b-PDEA, were successfully synthesized via atom transfer radical polymerization (ATRP) method. The compositions and structures of the three glycopolymers were characterized using 1H NMR (nuclear magnetic resonance) and GPC (gel permeation chromatography), while the morphology and size of aggregates from pH-sensitive block glycopolymers were measured using TEM (transmission electron microscopy) and DLS (dynamic light scattering). The results indicated that the micelles prepared from PEG-b-PGAMA-b-PDEA had a more compact shell structure. The drug-loaded micelles were prepared using the diafiltration method at pH 10, and the loading content and loading efficiency were analyzed using a UV-visible spectrophotometer. DOX-loaded micelles formed by PEG-b-PGAMA-b-PDEA with the more compact shell construction showed the highest loading content and loading efficiency (12.0 wt% and 58.0%) compared with the other two micelles. Moreover, the DOX release tests of these micelles were carried out under two PBS conditions (pH 7.4 and pH 5.5), and the DOX release amount in a certain time was analyzed using a UV-visible spectrophotometer. The results showed that the more compact shell construction of the three layered micelle obstructed the diffusion of a proton into the PDEA core at pH 5.5 and delayed the drug from releasing under both conditions. Moreover the two-layered micelle with a PDEA and PGAMA mixed core showed a relatively high release amount owing to the porous core permitting unimpeded releasing at pH 7.4 and promoted the protonation of PDEA at pH 5.5. Insights gained from this study show that the structure of block copolymers, leading to different constructions of micelles, could adjust the drug loading and release behavior to certain extent, thus it may contribute to improving the design of desirable drug delivery systems.

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.

Synthesis of crosslinkable diblock terpolymers PDPA-b-P(NMS-co-OEG) and preparation of shell-crosslinked pH/redox-dual responsive micelles as smart nanomaterials

Crosslinked polymer nanomaterials have attracted great attention due to their stability and highly controllable drug delivery; herein, a series of well-defined amphiphilic PDPA-b-P(NMS-co-OEG) diblock terpolymers (P1–P3) were designed and prepared via RAFT polymerization and were self-assembled into non-cross-linked (NCL) nanomicelles, which were further prepared into shell-cross-linked (SCL) micelles via cystamine-based in situ shell cross-linking. Using P3 as an optimized polymer, SCL-P3 micelles were prepared, which demonstrated remarkable pH/redox-dual responsive behaviour. For drug delivery, camptothecin (CPT)-loaded SCL-P3 micelles were prepared and showed much higher CPT-loading capability than their NCL-P3 counterparts. Notably, the SCL-P3 micelles showed good synergistic pH/redox-dual responsive CPT release properties, making them potential “smart” nanocarriers for drug delivery.

A series of well-defined amphiphilic PDPA-b-P(NMS-co-OEG) diblock terpolymers were prepared via RAFT polymerization and self-assembled into non-cross-linked nanomicelles, and then shell-cross-linked micelles via cystamine-based in situ shell cross-linking.

Disassembly and tumor-targeting drug delivery of reduction-responsive degradable block copolymer nanoassemblies

Review on recent strategies to synthesize novel disulfide-containing reductively-degradable block copolymers and their nanoassemblies as being classified with the number, position, and location of the disulfide linkages toward effective tumor-targeting intracellular drug delivery exhibiting enhanced release of encapsulated drugs.

Functionalized Folic Acid-Conjugated Amphiphilic Alternating Copolymer Actively Targets 3D Multicellular Tumour Spheroids and Delivers the Hydrophobic Drug to the Inner Core

Engineering of a “smart” drug delivery system to specifically target tumour cells has been at the forefront of cancer research, having been engineered for safer, more efficient and effective use of chemotherapy for the treatment of cancer. However, selective targeting and choosing the right cancer surface biomarker are critical for a targeted treatment to work. Currently, the available delivery systems use a two-dimensional monolayer of cancer cells to test the efficacy of the drug delivery system, but designing a “smart” drug delivery system to be specific for a tumour in vivo and to penetrate the inner core remains a major design challenge. These challenges can be overcome by using a study model that integrates the three-dimensional aspect of a tumour in a culture system. Here, we tested the efficacy of a functionalized folic acid-conjugated amphiphilic alternating copolymer poly(styrene-alt-maleic anhydride) (FA-DABA-SMA) via a biodegradable linker 2,4-diaminobutyric acid (DABA) to specifically target and penetrate the inner core of three-dimensional avascular human pancreatic and breast tumour spheroids in culture. The copolymer was quantitatively analyzed for its hydrophobic drug encapsulation efficiency using three different chemical drug structures with different molecular weights. Their release profiles and tumour targeting properties at various concentrations and pH environments were also characterized. Using the anticancer drug curcumin and two standard clinical chemotherapeutic hydrophobic drugs, paclitaxel and 5-fluorouracil, we tested the ability of FA-DABA-SMA nanoparticles to encapsulate the differently sized drugs and deliver them to kill monolayer pancreatic cancer cells using the WST-1 cell proliferation assay. The findings of this study revealed that the functionalized folic acid-conjugated amphiphilic alternating copolymer shows unique properties as an active “smart” tumor-targeting drug delivery system with the ability to internalize hydrophobic drugs and release the chemotherapeutics for effective killing of cancer cells. The novelty of the study is the first to demonstrate a functionalized “smart” drug delivery system encapsulated with a hydrophobic drug effectively targeting and penetrating the inner core of pancreatic and breast cancer spheroids and reducing their volumes in a dose- and time-dependent manner.

Acid-Triggered Polymer Backbone Degradation and Disassembly to Achieve Release of Camptothecin from Functional Polyphosphoramidate Nanoparticles

Camptothecin (CPT) is a promising anticancer drug, yet its therapeutic potential has been limited by poor water solubility and facile hydrolysis of the lactone form into an inactive carboxylate form at neutral pH. In this work, a fundamental synthetic methodology was advanced to allow for the preparation of well-defined functional polyphosphoramidate (PPA)-based block copolymers that coassembled with CPT into nanoparticles, which underwent coincident acid-triggered polymer backbone degradation, nanoparticle disassembly, and CPT release. Encapsulation of CPT by the PPA polymer inhibited premature hydrolysis of CPT at pH 7.4 and enabled accelerated CPT release at pH 5.0 (ca. 4× faster than at pH 7.4). Two degradable oxazaphospholidine monomers, with one carrying an alkyne group, were synthesized to access well-defined block PPAs (dispersity, Đ<1.2) via sequential organobase-catalyzed ring-opening polymerizations (ROP). The resulting amphiphilic block copolymers (PEOMP-b-PBYOMP) were physically loaded with CPT to achieve well-dispersed nanotherapeutics, which allowed the aqueous suspension of CPT at concentrations up to 3.2 mg/mL, significantly exceeding the aqueous solubility of the drug (<2.0 μg/mL at 37 °C). Cytotoxicity studies revealed enhanced efficacy of the CPT-loaded nanoparticles over free CPT in cancer cells and similar toxicity in normal cells.

Synthesis and biological evaluation of redox/NIR dual stimulus-responsive polymeric nanoparticles for targeted delivery of cisplatin

Functional drug delivery systems enabling various favorable characteristics including specific targets, efficient cellular uptake and controllable release. At present work, a folate and cRGD dual modified nanoparticles based on NIR light and glutathione dual stimuli-responsive release system was successfully prepared and which simultaneously deliver cisplatin and ICG to tumor sites to enhance controllability. The prepared nanoparticles showed a stable uniform spherical morphology of 77.59 nm particle size range in PBS (pH = 7.4, 25 °C) and the encapsulated cisplatin were rapidly released in acidic environment especially added glutathione (GSH) and NIR irradiation. Moreover, the prepared nanoparticles can be efficiently internalized by tumor cells through the enhanced dual targeted ligands (folate and cRGD) for ICG imaging. The cytotoxicity assays showed that the cells viability decreased to 1.95% (SGC-7901) when been exposed to NIR light, and which further decreased to 1.25% in MCF-7 cells. Thus, the prepared nanoparticles showed excellent performance for photothermal conversion therapy of tumor cells and especially on human breast tumor cells. Our research highlights the great potential of stimuli-responsive smart nanoparticles in biomaterial and nano-biomedicine.

Advanced architectures in the design of responsive polymers for cancer nanomedicine

In recent decades, nanoparticles have shown significant promise as an oncology treatment modality. Responsive polymers represent a promising class of nanoparticles that can trigger delivery through the exploitation of a specific stimuli. Response to a stimulus is one of the most basic processes found in living systems. As such, the desire to engineer dynamic and functional materials is becoming more prevalent in an effort to achieve precise control over our environment. The combination of controlled radical polymerization and high yielding chemistry strategies provide an excellent basis for the development of the next generation of drug delivery systems. The versatility of polymer chemistries available enables the synthesis of increasingly complex architectures with enhanced delivery specificity and control over the desired properties to interface with biological systems. This tutorial review highlights recent developments in polymer-based approaches to internally responsive nanoparticles for oncology. Presented are concise overviews of the current challenges and opportunities in cancer nanomedicine, common polymer-based architectures, and the basis for internally triggered stimuli-response relationships commonly employed in oncology applications. Examples of the chemistry used in the design of environmentally labile nanomaterials are discussed, and we outline recent advances in creating advanced bioresponsive drug delivery architectures.

Responsive Emulsions Stabilized by Amphiphilic Supramolecular Graft Copolymers Formed in Situ at the Oil-Water Interface

Amphiphilic supramolecular graft copolymers which can stabilize oil-in-water (o/w) emulsions and enable responsive demulsification were demonstrated in this study. Linear poly[( N, N-dimethylacrylmide)- stat-(3-acrylamidophenylboronic acid)] (PDMA- stat-PAPBA) copolymers with phenylboronic acid (PBA) groups and linear polystyrene homopolymers with cis-diol terminals (PS(OH)₂) were synthesized by reversible addition-fragmentation chain transfer polymerization. By the homogenization of the biphasic mixtures of an alkaline water solution of PDMA- stat-PAPBA copolymer and a toluene solution of PS(OH)₂ homopolymer, stable o/w emulsions could be generated, although neither PDMA- stat-PAPBA nor PS(OH)₂ alone was able to stabilize the emulsion. It was verified that the dispersed oil droplets in the emulsions were stabilized by the amphiphilic PDMA- stat-PAPBA- g-PS supramolecular graft copolymers, which were formed in situ at the oil-water interface by the complexation between the lateral PBA groups of PDMA- stat-PAPBA and the diol terminals of PS(OH)₂ during homogenization. These emulsions showed pH- and glucose-responsive demulsification because of the reversible B-O bonds between the PDMA- stat-PAPBA backbones and the PS side chains. The effects of polymer concentrations on emulsion formation were also investigated. The current study provides an alternative method for the facile preparation of responsive polymeric emulsifiers, which potentially may be extended to other polymer pairs containing PBA and cis-diol groups.

Co-Delivery of Drugs and Genes Using Polymeric Nanoparticles for Synergistic Cancer Therapeutic Effects

Drug and gene delivery systems based on nanoparticles, microparticles and hydrogels have been widely studied for cancer treatment in the past decade. To achieve an efficient and safe delivery, selection of drug and gene delivery carrier is critical. Biocompatible polymeric nanoparticles are considerably promising carrier candidates in delivery of drugs and genes because of their unique chemical and physical properties. However, delivery of a drug or gene sometimes cannot achieve a satisfactory treatment effect. Therefore, co-delivery of dual drugs or co-delivery of a drug and a gene in a polymeric nanoparticle has attracted attention. Such co-delivery systems can overcome multi-drug resistance of chemical drugs and achieve a synergistic therapeutic effect. In this progress report, we summarize recent progress in the preparation and application of polymeric drug and gene co-delivery nanosystems. The remaining challenges and future trends in this field are also included.

"Bottom-up" Construction of Multi-Polyprodrug-Arm Hyperbranched Amphiphiles for Cancer Therapy

Despite the great advantages of polymer-drug conjugates (PDC) in cancer therapy, control of the drug loading site and degree via a facile approach remains a great challenge. Herein, by combining the controllability of the "bottom-up" strategy and the stability of multiarm hyperbranched amphiphiles, we have developed novel multi-polyprodrug-arm hyperbranched amphiphiles (H40-star-(PHCPTMA-b-PMPC), hPCM) via reversible addition-fragmentation chain transfer (RAFT) polymerization for cancer therapy. The hPCM was constructed via two-step polymerization of an acid-labile prodrug monomer and a zwitterionic monomer, respectively. By using an H40 macroRAFT agent, 10-hydroxycamptothecine (HCPT) prodrug monomers were directly polymerized via the "bottom-up" strategy as a polyprodrug-arm inner-shell of hPCM with homogeneous drug distribution. The drug loading content can be facilely tuned through variation of the feed ratio of HCPTMA/H40 macroRAFT agent. Finally, the poly-zwitterionic hydrophilic outer-shell of hPCM was formed by RAFT polymerization of zwitterionic monomer to ensure preferable biocompatibility. By dissolving in dilute solution, unimolecular micelles of hPCM can be obtained, which endow desirable stability for the micelles. The effective cellular internalization, extended blood retention time, considerable accumulation in tumor tissue, and excellent anticancer activity of the hPCM micelles have been evaluated both in vitro and in vivo. This novel multi-polyprodrug-arm hyperbranched amphiphile constructed via the "bottom-up" strategy may open up new horizons for exploring next-generation PDC-based drug delivery systems.

Strategies for improving the payload of small molecular drugs in polymeric micelles

In the past few years, substantial efforts have been made in the design and preparation of polymeric micelles as novel drug delivery vehicles. Typically, polymeric micelles possess a spherical core-shell structure, with a hydrophobic core and a hydrophilic shell. Consequently, poorly water-soluble drugs can be effectively solubilized within the hydrophobic core, which can significantly boost their drug loading in aqueous media. This leads to new opportunities for some bioactive compounds that have previously been abandoned due to their low aqueous solubility. Even so, the payload of small molecular drugs is still not often satisfactory due to low drug loading and premature release, which makes it difficult to meet the requirements of in vivo studies. This problem has been a major focus in recent years. Following an analysis of the published literature in this field, several strategies towards achieving polymeric micelles with high drug loading and stability are presented in this review, in order to ensure adequate drug levels reach target sites.

The application of blocked isocyanate chemistry in the development of tunable thermoresponsive crosslinkers

The synthesis of a novel monomer, methacryloyl pyrazole, and its subsequent reaction with diisocyanates to produce thermoresponsive crosslinkers is reported.

PAA-g-PLA amphiphilic graft copolymer: synthesis, self-assembly, and drug loading ability

This article reports the synthesis of a PAA-g-PLA amphiphilic polymer by the combination of RAFT polymerization and organocatalytic ROP, which could self-assemble into spheres in aqueous media for sustained release of doxorubicin.

Dual-sensitive and biodegradable core-crosslinked HPMA copolymer–doxorubicin conjugate-based nanoparticles for cancer therapy

The nanoplatform of biosafe crosslinked copolymer-NPs efficiently delivers anticancer drugs to tumor cellsviablood circulation.

New Insight into a Cancer Theranostic Probe: Efficient Cell-Specific Delivery of SN-38 Guided by Biotinylated Poly(vinyl alcohol)

An optically modulated "turn-on" theranostic prodrug TP1 has been explored and formulated with biotinylated poly(vinyl alcohol) (biotinPVA) to obtain desired pharmacokinetics. TP1, consisting of the antineoplastic camptothecin analogue SN-38, and the fluorescent dye rhodol green have been covalently conjugated through a disulfide bond. Glutathione triggering the release of drug and fluorophore has been well established by UV-vis measurements through mass spectral analysis in physiological conditions. The biocompatible biotinPVA formulated prodrug (PTP1) showed remarkably higher stability against blood serum and cell-specific activation in contrast to that of TP1. Significantly, PTP1 permits monitoring of the delivery and release of well-known topoisomerase I inhibitor SN-38 by modulating fluorescence signal at λ_em 550 nm within intracellular milieus. Moreover, theranostic probe PTP1 exhibited dose-dependent antiproliferative activity against receptor-positive HeLa cells, whereas it did not show such an effect against receptor-negative NIH3T3 cells. Finally, the cell-specific antiproliferative activity of PTP1 via the apoptotic pathway is an efficient approach in cancer theranostics. Thus, futuristic PTP1 could be a promising agent in which diagnostic and prognostic data will be monitored synergistically.

Zwitterionic Phosphorylcholine-TPE Conjugate for pH-Responsive Drug Delivery and AIE Active Imaging

Polymeric micelles have emerged as a promising nanoplatform for cancer theranostics. Herein, we developed doxorubicin (DOX) encapsulated pH-responsive polymeric micelles for combined aggregation induced emission (AIE) imaging and chemotherapy. The novel zwitterionic copolymer poly(2-methacryloyloxyethylphosphorylcholine-co-2-(4-formylphenoxy)ethyl methacrylate) (poly(MPC-co-FPEMA)) was synthesized via RAFT polymerization and further converted to PMPC-hyd-TPE after conjugation of tetraphenylethene (TPE, a typical AIE chromophore) via acid-cleavable hydrazone bonds. The AIE activatable copolymer PMPC-hyd-TPE could self-assemble into spherical PC-hyd-TPE micelles, and DOX could be loaded through hydrophobic interactions. The zwitterionic micelles exhibited excellent physiological stability and low protein adsorption due to the stealthy phosphorylcholine (PC) shell. In addition, the cleavage of hydrophobic TPE molecules under acidic conditions could induce swelling of micelles, which was verified by size changes with time at pH 5.0. The in vitro DOX release profile also exhibited accelerated release rate with pH value decreasing from 7.4 to 5.0. Fluorescent microscopy and flow cytometry studies further demonstrated fast internalization and accumulation of drug loaded PC-hyd-TPE-DOX micelles in HepG2 cells, resulting in considerable time/dose-dependent cytotoxicity. Meanwhile, high-quality AIE imaging of PC-hyd-TPE micelles was confirmed in HepG2 cells. Notably, ex vivo imaging study exhibited efficient accumulation and drug release of PC-hyd-TPE-DOX micelles in the tumor tissue. Consequently, the multifunctional micelles with combined nonfouling surface, AIE active imaging, and pH-responsive drug delivery showed great potential as novel nanoplatforms for a new generation of cancer theranostics.

An Enzyme-Responsive Nanogel Carrier Based on PAMAM Dendrimers for Drug Delivery

G4 PAMAM dendrimer molecules were modified via covalently conjugating RGDC, RAADyC, and PEG chains on the periphery (Mac-1), by which a nanogel drug carrier with enzyme-sensitivity (NG-1) was constructed through an oxidation reaction by using NaIO4 to initiate the chemical cross-link of the functional groups on the periphery of dendrimers. Mac-1 and NG-1 both had a spherelike shape with a relatively uniform size of 20 nm for Mac-1 and 50 nm for NG-1 as evidenced by TEM, SEM, and DLS measurements. NG-1 showed much higher drug loading capacity as compared with that of Mac-1 although the cavities in the dendritic structure were used to encapsulate drug molecules as reported in many literatures. In addition, the size of NG-1 with embedded doxorubicin hydrochloride (DOX) decreased significantly to 15 nm in the presence of elastase, which indicated the decomposition of the nanogel triggered by enzyme, leading to drug release in a sustained manner in vitro. The NG-1 carrier was noncytotoxic and biocompatible, and it achieved the same cytotoxicity as free DOX when the drug molecules were loaded inside. From confocal images, the penetrative process of DOX from nanogel could be clearly observed in 8 h. Such a dendrimer-based nanogel may be a potential nanocarrier for drug delivery in cancer therapy.