The anti-hepatitis drug DDB chemosensitizes multidrug resistant cancer cells <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> by inhibiting P-gp and enhancing apoptosis

Summary Purpose: DDB (dimethyl-4,4′-dimethoxy-5,6,5′6′-dimethylene dioxybiphenyl-2,2′-dicarboxylate) is a synthetic hepatoprotectant which has been widely used to treat chronic viral hepatitis B patients in China for more than 20 years. In this study, we evaluated DDB as a multidrug resistance (MDR) chemosensitizing agent. Methods: A panel of sensitive and resistant cancer cell lines were treated with various concentration of DDB, and the effect on chemosensitivity and accumulation of anticancer drugs; promotion of apoptosis and P-glycoprotein (P-gp) expression were determined by MTT (Dimethyl thiazolyl-2,5-diphenyltetrazolium bromide) assay, fluorospectrometry and flow cytometry respectively. Drug resistance reversal activity of DDB was also examined in BALB/c nude mice bearing both acquired MDR human nasopharyngeal carcinoma KBv200 and parental KB xenografts. The effect of DDB on the pharmacokinetics of Dox and hematological toxicity induced by Dox was measured in ICR and C₅₇/BL mice, respectively. Results: DDB at nontoxic concentrations of 12.5, 25 and 50 μM partly reversed the resistance to vincristine, doxorubicin, paclitaxel in acquired MDR breast carcinoma MCF-7/Adr cells, KBv200 and intrinsic MDR human hepatocarcinoma Bel₇₄₀₂ cells, whereas no chemosensitizing effect of DDB was observed in sensitive KB and MCF-7 cells. DDB increased the intracellular accumulation of doxorubicin and inhibited surface P-gp expression in MCF-7/Adr cells. Furthermore, it was found that DDB promoted doxorubicin-induced apoptosis of Bel₇₄₀₂ cells through enhanced caspase-3 activation. Co-administration of DDB at 300 and 500 mg/kg orally to nude mice increased the antitumor activity of vincristine to KBv200 xenografts without a significant increase in toxicity. In contrast, Co-administration of DDB did not inhibit the growth of KB xenografts. DDB also markedly reduced the decrease of leukocytes in doxorubicin-treated C₅₇/BL mice. Co-administration of DDB increased Dox concentration in ICR mice bearing S180 sarcoma, but no pharmacokinetical interaction with Dox was observed. Conclusion: These results indicate that DDB has MDR reversal activity by inhibiting P-gp and when used in combination with anti-cancer drugs, it could potentially be used as a clinical treatment for P-gp-mediated MDR cancers.