Morphology Regulation in Redox Destructible Amphiphilic Block Copolymers and Impact on Intracellular Drug Delivery.

In two ABA type amphiphilic block copolymers (P1, P2), the hydrophobic B block consists of a bioreducible segmented poly(disulfide) (PDS), while poly-N-isopropylacrylamide (PNIPAM) or poly(triethyleneglycol)methylether-methacrylate (PTEGMA) serve as the hydrophilic A blocks in P1 and P2, respectively, leading to the formation of polymersome and micelle, owing to the difference in the packing parameters. Both exhibit comparable doxorubicin (Dox) encapsulation efficiency, but glutathione (GSH) triggered release appears much faster from the polymersome than micelle owing to the complete degradation of the PDS segment in polymersome morphology unlike in micelle. Dox-loaded polymers (P1-Dox and P2-Dox) exhibit minimum toxicity to normal cells like C2C12. By contrast, P1-Dox shows excellent killing efficiency to the HeLa cells (cancer cell) (in which the GSH concentration is significantly higher). However, P2-Dox reveals a rather poor activity even to HeLa cells. Fluorescence microscopy studies show comparable cellular uptake of P1-Dox and P2-Dox. But the polymersome entrapped dye escapes fast from the cargo and reach the nucleus, while the drug-loaded micelle remains trapped in the perinuclear zone explaining the significant difference in the drug delivery performance of polymersome and micelle.