Search

A carcinogen-transformed rat hepatoma cell line (Reuber H-35) was utilized as a model system for investigation of the biochemical factors which may limit the effectiveness of chemotherapy in intrinsically resistant tumors such as hepatocellular carcinoma. Northern blotting demonstrated expression of mRNA coding for the P-170 membrane-glycoprotein associated with the multi-drug resistance phenotype, while Western blotting identified the P-170 glycoprotein in the hepatoma cell membrane. Consistent with these observations, tumor cell sensitivity to the vinca alkaloids, vincristine and vinblastine, to the anthracycline antibiotics, Adriamycin ® and daunorubicin, and to the demethyl-epipodophyllotoxin derivative, VM-26, was enhanced by continuous incubation in the presence of the calcium channel antagonist, verapamil. Verapamil produced a minimal change in cell sensitivity to the demethylepipodophyllotoxin derivative, VP-16, and to the aminoacridine, m -AMSA. Relatively high detoxification potential via the glutathione metabolic pathway was also observed in the hepatoma cell. The capacity of topoisomerase II in nuclear extracts from the hepatoma cell to mediate cleavable complex formation stimulated by VM-26, VP-16 and m -AMSA appeared to be at least comparable to, if not greater than that from drug-sensitive HL-60 cells, suggesting that drug resistance may not occur at the level of this enzyme. Consistent with findings in a number of tumor cell lines resistant to antineoplastic drugs, the antiproliferative activity of the topoisomerase II inhibitors VM-26, VP-16 and m -AMSA appeared to be dissociable from the induction of DNA strand breaks, suggesting that such lesions in DNA may fail to fully account for the antiproliferative activity of these agents in the hepatoma cell.

Metabolism of adriamycin, an anthracycline antibiotic, was characterized in both rat and rabbit hepatocytes under aerobic conditions. Adriamycin was the predominant fluorescent species within the cell in hepatocytes from both the rat and the rabbit. In the rat hepatocyte, the primary intracellular metabolite was deoxyadriamycin aglycone, while significant levels of deoxyadriamycinol aglycone were also synthesized; little adriamycinol was observed in the cells or the incubation medium. In contrast, in the rabbit hepatocyte, significant levels of adriamycinol as well as deoxyadriamycinol aglycone were formed; deoxyadriamycinol aglycone was the primary intracellular metabolite while low levels of deoxyadriamycin aglycone were observed. The relative formation of deoxyadriamycinol aglycone and deoxyadriamycin aglycone suggests that adriamycinol may be metabolized more effectively to the deoxyaglycone derivative than the parent drug. Conjugates of adriamycin were not observed in hepatocytes from either the rat or the rabbit or in the incubation medium.