Prodrug-Like, PEGylated Protein Toxin Trichosanthin for Reversal of Chemoresistance

Multidrug resistance (MDR) is a main obstacle in cancer chemotherapy. The MDR mechanisms involve P-glycoprotein (P-gp) overexpression, abnormality of,apoptoiis-related protein, and altered expression of drug-targeting proteihs. Therapeutic proteins ate emerging as candidates for Overcoming cancer MDR because of not only their large molecular size that potentially circumvents the P-gp-mediated drug efflux but also their distinctive bioactivity distinguished from small-molecular drugs. Herein we report trichosanthin, a plant protein toxin, possesses synergistic effect with paditaxeI (PTX) in the PTX-resistance A549/T nonsmall cell lung cancer (NSCLC) cells, by reversing PTX-caused caspase 9 phosphorylation and inducing caspase 3-dependent apopiosis. Moreover, via intein-mediated site-specific protein ligation; a matrix metalloproteinase (MMP)-activatable cell-penetrating trichosanthin delivery system was constructed by modification of a cell-penetrating peptide and MMP-2-sensitive PEGylation to overcome the limitation of in vivo application of trichosanthin, by improving the short half-life and poor tumor targeting, as well as immunogenicity. In a mouse model bearing A549/T tumor, the MMP-activatable trichosanthin was further tested for its application for MDR reversal in combination with PTX liposomes. The delivery system showed synergy effect with PTX-loaded liposome in treating MDR cancer in vivo.