Polymersome-based protein drug delivery - quo vadis?

Protein-based therapeutics are an attractive alternative to established therapeutic approaches and represent one of the fastest growing families of drugs. While many of these proteins can be delivered using established formulations, the intrinsic sensitivity of proteins to denaturation sometimes calls for a protective carrier to allow administration. Historically, lipid-based self-assembled structures, notably liposomes, have performed this function. After the discovery of polymersome-based targeted drug-delivery systems, which offer manifold advantages over lipid-based structures, the scientific community expected that such systems would take the therapeutic world by storm. However, no polymersome formulations have been commercialised. In this review article, we discuss key obstacles for the sluggish translation of polymersome-based protein nanocarriers into approved pharmaceuticals, which include limitations imparted by the use of non-degradable polymers, the intricacies of polymersome production methods, and the complexity of the in vivo journey of polymersomes across various biological barriers. Considering this complex subject from a polymer chemist's point of view, we highlight key areas that are worthy to explore in order to advance polymersomes to a level at which clinical trials become worthwhile and translation into pharmaceutical and nanomedical applications is realistic.

Light-Triggered Cancer Cell Specific Targeting and Liposomal Drug Delivery in a Zebrafish Xenograft Model

Cell-specific drug delivery remains a major unmet challenge for cancer nanomedicines. Here, light-triggered, cell-specific delivery of liposome-encapsulated doxorubicin to xenograft human cancer cells in live zebrafish embryos is demonstrated. This method relies on light-triggered dePEGylation of liposome surfaces to reveal underlying targeting functionality. To demonstrate general applicability of this method, light-triggered, MDA-MB-231 breast cancer cell specific targeting in vivo (embryonic zebrafish) is shown using both clinically relevant, folate-liposomes, as well as an experimental liposome-cell fusion system. In the case of liposome-cell fusion, the delivery of liposomal doxorubicin direct to the cytosol of target cancer cells results in enhanced cytotoxicity, compared to doxorubicin delivery via either folate-liposomes or free doxorubicin, as well as a significant reduction in xenograft cancer cell burden within the embryonic fish.

Strategies for Tumor Hypoxia Imaging Based on Aggregation-Induced Emission Fluorogens

Hypoxia, as a crucial characteristic of cancer, has become an extremely significant direction for researchers to construct fluorescent probes for early diagnosis of tumors. Aggregation-induced emission fluorogens (AIEgens) possess many superior properties to those of conventional fluorophores due to aggregation-induced emission (AIE) features, such as a linear concentration-dependent increase in brightness, remarkable resistance to photobleaching, and the long-term tracking and imaging of cells. Constructing hypoxic response AIEgen-based probes will be very useful for the early diagnosis of tumors. Herein, several hypoxia-responsive probes based on AIEgens reported in the last three years are reported; these examples may lead to the construction of hypoxia-responsive AIE probes used for tumor hypoxia imaging in the future. In addition, typical, conventional hypoxia-responsive bioprobes are presented to further understand hypoxia-responsive fluorescent probes based on AIEgens.

DePEGylation strategies to increase cancer nanomedicine efficacy

To maximize drug targeting to solid tumors, cancer nanomedicines with prolonged circulation times are required. To this end, poly(ethylene glycol) (PEG) has been widely used as a steric shield of nanomedicine surfaces to minimize serum protein absorption (opsonisation) and subsequent recognition and clearance by cells of the mononuclear phagocyte system (MPS). However, PEG also inhibits interactions of nanomedicines with target cancer cells, limiting the effective drug dose that can be reached within the target tumor. To overcome this dilemma, nanomedicines with stimuli-responsive cleavable PEG functionality have been developed. These benefit from both long circulation lifetimes en route to the targeted tumor as well as efficient drug delivery to target cancer cells. In this review, various stimuli-responsive strategies to dePEGylate nanomedicines within the tumor microenvironment will be critically reviewed.

Rapid Self-Assembly of Block Copolymers for Flower-Like Particles with High Throughput

The self-assembly of block copolymers has evolved into a foremost bottom-up approach for building polymeric materials. Historical challenges exist within this lively field, including the scalability and elegant simplicity of self-assembled aggregates with predictable structures. Here, we report a generally applicable strategy for the rapid self-assembly of poly(ethylene glycol)-block-poly(l-lactic acid) with the help of a single oil-in-water emulsion. A kind of flower-like polymer particle with filamentous surface branches is rapidly formed after removing the oil phase from the emulsion system. Moreover, the dimension of the branched filaments and the spherical internal core can be controlled through regulating the block ratio and the emulsification conditions. In particular, we propose an explosion theory as a balance between phase separation and interchain interaction for explaining the formation of the branched structures of the flower-like particles. The particles with high throughput are further functionalized with polypyrrole for their use in enhanced photoelectric-sensing applications.