Mercaptan acids modified amphiphilic copolymers for efficient loading and release of doxorubicin

In this paper, four different kinds of mercaptan acids modified amphiphilic copolymers mPEG-b-PATMC-g-SRCOOH (R=CH₂, CH₂CH₂, (CH₂)₁₀ and CH(COOH)CH₂) were successfully synthesized by thiol-ene "click" reaction between pendent carbon-carbon double bonds of PEG-b-PATMC and thiol groups of thioglycolic acid, 3-mercaptopropionic acid, 11-mercaptoundecanoic acid or 2-mercaptosuccinic acid. DLS and TEM measurements showed that all the mPEG-b-PATMC-g-SRCOOH copolymers could self-assemble to form micelles which dispersed in spherical shape with nano-size before and after DOX loading. The positively-charged DOX could effectively load into copolymer micelles via synergistic hydrophobic and electrostatic interactions. All DOX-loaded mPEG-b-PATMC-g-SRCOOH micelles displayed sustained drug release behavior without an initial burst which could be further adjusted by the conditions of ionic strength and pH. Especially in the case of mPEG-b-PATMC-g-S(CH₂)₁₀COOH (P3) micelles, the suitable hydrophobility and charge density were not only beneficial to improve the DOX-loading efficiency, they were also good for obtaining smaller particle size, higher micelle stability and more timely drug delivery. Confocal laser scanning microscopy (CLSM) and MTT assays further demonstrated efficient cellular uptake of DOX delivered by mPEG-b-PATMC-g-SRCOOH micelles and potent cytotoxic activity against cancer cells.