Role of glutathione S-transferase P1, P-glycoprotein and multidrug resistance-associated protein 1 in acquired doxorubicin resistance

While P-glycoprotein (Pgp) and multidrug resistance-associated protein 1 (M RP1) are known to be important in acquired doxorubicin resistance, the role of glutathione S-transferases (GST) remains unclear. Our study assessed ro les of these 3 factors in a human drug-sensitive carcinoma cell line (HEp2) , a subclone made resistant by prolonged incubation in doxorubicin (HEp2A), and HEp2 cells stably transfected with human GSTP1, Drug-resistant HEp2A c ells showed greater total GST activity, GSTP class enzyme expression, Pgp e xpression, MRP1 transcript expression, drug efflux and at least 13-fold gre ater resistance to doxorubicin than the parent HEp2 cell line. GSTM class e nzyme expression was similar in both cell types, while GSTA class enzymes w ere not detected, In the resistant HEp2A cells, cytotoxicity was markedly e nhanced by the Pgp/MRP inhibitor verapamil at low doxorubicin concentration s. The GST inhibitor curcumin also enhanced cytotoxicity in HEp2A cells whe n the Pgp/MRP efflux barrier had been reversed by verapamil or overcome by high doxorubicin concentrations. In addition, curcumin had a chemosensitisi ng effect at low doxorubicin concentrations in HEp2 cells. Stable transfect ion of HEp2 cells with human GSTP1 increases doxorubicin resistance 3-fold over control cells. Our study indicates involvement of GSTP enzymes as well as efflux mechanisms in the acquired doxorubicin-resistance phenotype. (C) 2001 Wiley-Liss, Inc.