Reversion of P‑gp-Mediated Drug Resistance in Ovarian Carcinoma Cells with PHPMA-Zosuquidar Conjugates

Inhibition of P-glycoprotein (P-gp) transporter is an attractive approach for the reversion of cancer-associated multidrug resistance (MDR). Poly­(N-(2-hydroxypropyl) methacrylamide) (PHPMA)-based carriers that are able to release the anticancer drug doxorubicin in the lysosomes have shown promise to reduce P-gp mediated resistance. This is attributed to the release of the drug in close proximity to the nucleus and distant from the P-gp transporter. This work presents a strategy to maximize P-gp inhibition and enhance doxorubicin cytotoxicity in cancer cells by using a dual functional PHPMA conjugate carrying both the anticancer drug doxorubicin and the P-glycoprotein inhibitor zosuquidar (Zos). While doxorubicin was connected to the polymer backbone via a lysosomally cleavable spacer, the P-gp inhibitor Zos was attached by a hydrazone linker in order to promote release in the early stage of the endocytic process and maximize its cytosolic concentration in proximity of the P-gp transporter. Following Zos modification and determination of its ability to inhibit P-gp, conjugation to the PHPMA polymer backbone resulted in enhanced doxorubicin cytotoxicity in resistant A2780ADR ovarian carcinoma cells. Finally, the incorporation of both Dox and Zos in a single polymer carrier enhanced P-gp inhibition as compared to a control PHPMA conjugate containing only Dox.