Construction of dual-functional polymer nanomaterials with near-infrared fluorescence imaging and polymer prodrug by RAFT-mediated aqueous dispersion polymerization

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.

Stimuli-sensitive polymer prodrug nanocarriers by reversible-deactivation radical polymerization

Polymer prodrugs are based on the covalent linkage of therapeutic molecules to a polymer structure which avoids the problems and limitations commonly encountered with traditional drug-loaded nanocarriers in which drugs are just physically entrapped (e.g., burst release, poor drug loadings). In the past few years, reversible-deactivation radical polymerization (RDRP) techniques have been extensively used to design tailor-made polymer prodrug nanocarriers. This synthesis strategy has received a lot of attention due to the possibility of fine tuning their structural parameters (e.g., polymer nature and macromolecular characteristics, linker nature, physico-chemical properties, functionalization, etc.), to achieve optimized drug delivery and therapeutic efficacy. In particular, adjusting the nature of the drug-polymer linker has enabled the easy synthesis of stimuli-responsive polymer prodrugs for efficient spatiotemporal drug release. In this context, this review article will give an overview of the different stimuli-sensitive polymer prodrug structures designed by RDRP techniques, with a strong focus on the synthesis strategies, the macromolecular architectures and in particular the drug-polymer linker, which governs the drug release kinetics and eventually the therapeutic effect. Their biological evaluations will also be discussed.

RAFT-mediated polymerization-induced self-assembly (RAFT-PISA): current status and future directions

Polymerization-induced self-assembly (PISA) combines polymerization and self-assembly in a single step with distinct efficiency that has set it apart from the conventional solution self-assembly processes. PISA holds great promise for large-scale production, not only because of its efficient process for producing nano/micro-particles with high solid content, but also thanks to the facile control over the particle size and morphology. Since its invention, many research groups around the world have developed new and creative approaches to broaden the scope of PISA initiations, morphologies and applications, etc. The growing interest in PISA is certainly reflected in the increasing number of publications over the past few years, and in this review, we aim to summarize these recent advances in the emerging aspects of RAFT-mediated PISA. These include (1) non-thermal initiation processes, such as photo-, enzyme-, redox- and ultrasound-initiation; the achievements of (2) high-order structures, (3) hybrid materials and (4) stimuli-responsive nano-objects by design and adopting new monomers and new processes; (5) the efforts in the realization of upscale production by utilization of high throughput technologies, and finally the (6) applications of current PISA nano-objects in different fields and (7) its future directions.

Degradable polymeric nanomaterials with a high solid content and multiple morphologies by polymerization-induced self-assembly

The preparation of degradable polymeric nanomaterials with a high solid content and multiple morphologies is highly desirable but still challenging. Here, the RAFT dispersion polymerization of styrene and 5,6-benzo-2-methylene-1,3-dioxepane was demonstrated to achieve various morphologies, including spheres, vesicles, worms, and large compound vesicles, with a high solid content through polymerization-induced self-assembly, which opens up a new avenue for the preparation of degradable polymeric nanomaterials.

Reversible Addition-Fragmentation Chain Transfer Aqueous Dispersion Polymerization of 4-Hydroxybutyl Acrylate Produces Highly Thermoresponsive Diblock Copolymer Nano-Objects

The reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA) using a poly(glycerol monomethacrylate) (PGMA) precursor is an important prototypical example of polymerization-induced self-assembly. 4-Hydroxybutyl acrylate (HBA) is a structural isomer of HPMA, but the former monomer exhibits appreciably higher aqueous solubility. For the two corresponding homopolymers, PHBA is more weakly hydrophobic than PHPMA. Moreover, PHBA has a significantly lower glass transition temperature (T g) so it exhibits much higher chain mobility than PHPMA at around ambient temperature. In view of these striking differences, we have examined the RAFT aqueous dispersion polymerization of HBA using a PGMA precursor with the aim of producing a series of PGMA57-300-PHBA100-1580 diblock copolymer nano-objects by systematic variation of the mean degree of polymerization of each block. A pseudo-phase diagram is constructed using transmission electron microscopy to assign the copolymer morphology after employing glutaraldehyde to cross-link the PHBA chains and hence prevent film formation during grid preparation. The thermoresponsive character of the as-synthesized linear nano-objects is explored using dynamic light scattering and temperature-dependent rheological measurements. Comparison with the analogous PGMA x -PHPMA y formulation is made where appropriate. In particular, we demonstrate that replacing the structure-directing PHPMA block with PHBA leads to significantly greater thermoresponsive behavior over a much wider range of diblock copolymer compositions. Given that PGMA-PHPMA worm gels can induce stasis in human stem cells (see Canton et al., ACS Central Science, 2016, 2, 65-74), our findings are likely to have implications for the design of next-generation PGMA-PHBA worm gels for cell biology applications.

Polymerisation-induced self-assembly (PISA) as a straightforward formulation strategy for stimuli-responsive drug delivery systems and biomaterials: recent advances

Stimuli-responsive amphiphilic block copolymers have emerged as promising nanocarriers for enhancing site-specific and on-demand drug release in response to a range of stimuli such as pH, the presence of redox agents, and temperature. The formulation of amphiphilic block copolymers into polymeric drug-loaded nanoparticles is typically achieved by various methods (e.g. oil-in-water emulsion solvent evaporation, solid dispersion, microphase separation, dialysis or microfluidic separation). Despite much progress that has been made, there remain many challenges to overcome to produce reliable polymeric systems. The main drawbacks of the above methods are that they produce very low solid contents (<1 wt%) and involve multiple-step procedures, thus limiting their scope. Recently, a new self-assembly methodology, polymerisation-induced self-assembly (PISA), has shown great promise in the production of polymer-derived particles using a straightforward one-pot approach, whilst facilitating high yield, scalability, and cost-effectiveness for pharmaceutical industry protocols. We therefore focus this review primarily on the most recent studies involved in the design and preparation of PISA-generated nano-objects which are responsive to specific stimuli, thus providing insight into how PISA may become an effective formulation strategy for the preparation of precisely tailored drug delivery systems and biomaterials, while some of the current challenges and limitations are also critically discussed.

Boron dipyrromethene (BODIPY) in polymer chemistry

The present review provides both a summary and outlook on the exciting field of BODIPYs in polymer chemistry.

Stimuli-responsive phospholipid-drug conjugates (PDCs)-based nanovesicles for drug delivery and theranostics

Liposomes represent one of the most successful nano-drug delivery systems among enormous nano-carriers. Although great progress has been made in conventional liposomes, the emerging shortcomings still impair the therapeutic index. The proposal of stimuli-responsive phospholipid-drug conjugates (PDCs)-based nanovesicles solves the challenges that conventional liposomes are faced with, showing great potential for cancer diagnosis and therapy. Herein, we intend to overview the current progress and unique advantages of stimuli-responsive PDCs-based nanovesicles. First, the challenges of conventional liposomes and the development of PDCs-based nanovesicles are summarized. Next, the stimuli-responsive elements used in current stimuli-responsive PDCs-based nanovesicles are outlined. Then, the unique superiorities of stimuli-responsive PDCs-based nanovesicles for drug delivery and theranostics are highlighted in detail. Finally, the future opportunities and challenges of stimuli-responsive PDCs-based nanovesicles for clinical translation are put forward.

Inhibiting Radiative Transition-Mediated Multifunctional Polymeric Nanoplatforms for Highly Efficient Tumor Phototherapeutics

It is highly desired to explore ideal phototherapeutic nanoplatforms, especially containing satisfactory phototherapeutic agents (PTAs), for potential cancer therapies. Herein, we proposed an effective strategy for designing a highly efficient PTA through inhibiting radiative transition (IRT). Specifically, we developed an ultralow radiative BODIPY derivative (TPA-IBDP) by simply conjugating two triphenylamine units to iodine-substituted BODIPY, which could simultaneously facilitate the nonradiative decay channels of singlet-to-triplet intersystem crossing and intramolecular charge transfer. In comparison to the normal BODIPY compound, TPA-IBDP exhibited an outstanding singlet oxygen yield (31.8-fold) and a higher photothermal conversion efficiency (PCE; over 3-fold), respectively, benefiting from the extended π-conjugated donor-to-accepter (D-A) structure and the heavy atom effect. For tumor phototherapy using TPA-IBDP, TPA-IBDP was conjugated with a H₂O₂-responsive amphiphilic copolymer POEGMA₁₀-b-[PBMA₅-co-(PS-N₃)₂] to construct a multifunctional phototherapeutic BODIPY-based nanoplatform (PB). PB produced abundant singlet oxygen (¹O₂) and heat along with negligible fluorescence emission under near-infrared laser irradiation. Additionally, PB could generate a GSH-depletion scavenger (quinone methide, QM) after reacting with the abundant intracellular H₂O₂ in tumor for the cooperative enhancement of IRT-mediated phototherapy. We envision that this highly efficient multifunctional phototherapeutic nanoplatform cooperated by GSH-depletion could be a valuable paradigm for tumor treatments.

Azoreductase-triggered fluorescent nanoprobe synthesized by RAFT-mediated polymerization-induced self-assembly for drug release

Herein, micelles loaded with doxorubicin (DOX) in situ were synthesized by polymerization-induced self-assembly. Furthermore, the DOX-loaded micelles showed release and fluorescence change, owing to azoreductase-triggered azo bond cleavage.

Real-time near-infrared fluorescence reporting the azoreductase-triggered drug release

Herein, real-time near-infrared fluorescence reporting drug release was demonstrated by the azoreductase-induced cleavage of azo bonds and the subsequent disassembly of aggregates, which caused an enhancement in fluorescence intensity.

pH Driven self-assembly of aza-BODIPY J-aggregates

A pH-driven self-assembly of a simple aza-BODIPY was discovered in PBS solution, whereby ion-specific J-aggregated nanostructures were generated at very low dye concentration (2.5–20 [Formula: see text]M). The aggregation process was investigated in different conditions (pH, temperature and time) by monitoring absorption spectral shifts and associated nanostructure morphological changes. The pH-driven self-assembly process demonstrated an instantaneous thermodynamic phenomenon associated with three characteristic structures, each with distinctive optical properties. When the sample was first formulated within a short time window, a thermodynamically less stable intermediate with an unusual morphology of triangular nanoplates and broad absorption was observed. The formation of these structures was independent of the ions in PBS solution (Na[Formula: see text], K[Formula: see text], thus indicating that the triangular structure was inherent to the anisotropic structure of aza-BODIPY scaffolds. The second structure associated with a metastable pathway generated a uniform population of spherical nanovesicles, while the third structure, generated through a more thermodynamically stable pathway consisted of fibers. The absorption spectra suggested that both spherical and fiber structures contributed to the J-aggregation band at 735 nm in the near infrared optical spectrum and their population in each formulation was concentration dependent. The results highlighted the significance of ion effects in self-assembly of aza-BODIPY and the mechanistic structural changes of the morphology. Furthermore, this fundamental discovery offers a versatile method for the self-assembly of aza-BODIPY J-aggregates as a new nanoplatform with potential photonic applications.