Tunable pH-Responsive Polymeric Micelle for Cancer Treatment

The development of bioresponsive polymers is important in drug delivery systems. Herein, we reported the construction of a series of pH-sensitive micelles by conjugating the hydrophilic polyethylene glycol (PEG) segment to a hydrophobic farnesylthiosalicylate derivative, FTS-hydrazide (FTS-H), with a hydrazone linker, whose cleavability can be conveniently modulated by choosing various lengths of the carbon chain or appropriate electron-withdrawing groups with different steric environment around the hydrazone linker. We examined the hydrolysis rates of these pH-sensitive micelles in both neutral and acidic conditions. One of the pH-sensitive micelles (PHF-2) was found to be highly sensitive to acidic conditions while being fairly stable in neutral conditions. Furthermore, PHF-2 micelles well retained the antitumor activity of free FTS-H. We further evaluated the use of PHF-2 micelles as a carrier for delivering paclitaxel (PTX) and the triggered release of PTX under the acidic environment. PTX-loaded PHF-2 micelles showed enhanced antitumor activity compared with free PTX, likely because of the combinational effect between PHF-2 micelles and loaded PTX.