Chlorambucil-taurocholate is transported by bile acid carriers expressed in human hepatocellular carcinomas

Background & Aims: Chemotherapy of hepatocellular carcinomas is hampered by the insufficient accumulation of cytostatic drugs within the tumor cells. The aim of this study was to evaluate the feasibility of therapeutic strategies using antineoplastic agents coupled to bile acids. Methods: Expression of the Na+-taurocholate-cotransporting polypeptide (NTCP) was analyzed in six hepatocellular carcinomas and in nonmalignant liver tissue. Uptake of the cytostatic drug [H-3]chlorambucil-taurocholate (S2676) was measured in Xenopus laevis oocytes injected with total messenger RNA (mRNA) from the carcinomas or peritumor tissue or with complementary RNA encoding the NTCP or the organic anion-transporting polypeptide (OATP) of human liver. Results: Expression of hepatocellular carcinoma mRNA in oocytes resulted in mainly Na+-dependent uptake of chlorambucil-taurocholate. The level of NTCP mRNA in carcinomas amounted to 56% +/- 27% compared with peritumor tissue. Immunofluorescence studies confirmed the expression of NTCP on the surface of hepatocellular carcinoma cells. OATP expression, determined by immunoblotting, was similar in hepatocellular carcinomas and surrounding liver tissue (n = 3). NTCP mediated Na+-dependent uptake of chlorambucil-taurocholate (Michaelis constant, 11 mu mol/L), whereas OATP mediated Na+-independent uptake. Conclusions: Hepatocellular carcinomas express the Na+- dependent bile acid transporter NTCP. Because NTCP mediates high-affinity uptake of chlorambucil-taurocholate, targeting of cytostatic bile acids to hepatocellular carcinomas could become a feasible therapeutic strategy.