pH-sensitive micelles self-assembled from star-shaped TPGS copolymers with ortho ester linkages for enhanced MDR...

TPGS approved by FDA can be used as a P-gp inhibitor to effectively reverse multi-drug resistance (MDR) and as an anticancer agent for synergistic antitumor effects. However, the comparatively high critical micelle concentration (CMC), low drug loading (DL) and poor tumor target limit its further clinical application. To overcome these drawbacks, the pH-sensitive star-shaped TPGS copolymers were successfully constructed via using pentaerythritol as the initial materials, ortho esters as the pH-triggered linkages and TPGS active-ester as the terminated MDR material. The amphiphilic star-shaped TPGS copolymers could self-assemble into free and doxorubicin (DOX)-loaded micelles at neutral aqueous solutions. The micelles exhibited the lower CMC (8.2 × 10^-5 mg/ml), higher DL (10.8%) and long-term storage and circulation stability, and showed enhanced cellular uptake, apoptosis, cytotoxicity, and growth inhibition for in vitro MCF-7/ADR and/or MCF-7/ADR multicellular spheroids and in vivo MCF-7/ADR tumors via efficiently targeted drug release at tumoral intracellular pH (5.0), MDR reversal of TPGS, and synergistic effect of DOX and TPGS. Therefore, the pH-sensitive micelles self-assembled from star-shaped TPGS copolymers with ortho ester linkages are potentially useful to clinically transform for enhanced MDR cancer treatment.