thioinosine and Carcinoma--Hepatocellular

beta-L-(-)-2',3'-Dideoxy-3'-thiacytidine (3TC) is a cytosine nucleoside analog that potently inhibits the replication of human and duck hepatitis B viruses and human immunodeficiency virus through the activity of its 5'-triphosphate ester metabolite. The present study examined the intracellular decay of 3TC 5'-phosphates and tested strategies for modulating the cellular content of those nucleotides in primary cultures of duck hepatocytes and in human hepatoma 2.2.15 cells and CCRF-CEM T lymphoblasts. Inhibition by deoxycytidine of the 5'-phosphorylation of 3TC in duck hepatocytes confirmed that, as in mammalian cells, deoxycytidine kinase catalyzed 3TC activation. The 5'-mono, 5'-di-, and 5'-triphosphates of 3TC underwent monoexponential elimination from duck hepatocytes and 2.2.15 cells (half-lives, 3.6 to 8.0 h). Thymidine and fludarabine, which are agents that enhance the activity of deoxycytidine kinase, were tested in strategies for increasing the cellular content of 3TC 5'-phosphates. Coordinate treatment of cells with 3TC and thymidine (50 microM) increased the content of 3TC 5'-monophosphate in duck hepatocytes and the content of 3TC 5'-di- and 5'-triphosphates in 2.2.15 cells, but enhancement of 3TC 5'-phosphate levels in CCRF-CEM cells required a higher thymidine concentration (100 microM). Fludarabine (5 microM) did not affect the contents of 3TC 5'-di- and 5'-triphosphates in duck hepatocytes, but modestly increased the contents of those nucleotides in 2.2.15 cells and CCRF-CEM cells. Nitrobenzylthioinosine (NBMPR), an inhibitor of the es facilitated diffusion nucleoside transporter, reduced the level of entry of 3TC into 2.2.15 cells and abolished inward fluxes of thymidine, adenosine, and deoxycytidine. In 2.2.15 cells and CCRF-CEM cells, NBMPR reduced the formation of 3TC 5'-di- and 5'-triphosphates and reversed the thymidine- and fludarabine-induced increases in the formation of those nucleotides. NBMPR protected against the cytotoxicity of 3TC in CCRF-CEM cells, whereas thymidine potentiated that toxicity, apparently by enhancing the formation of 3TC 5'-triphosphate. Taken together, these results indicate that deoxycytidine kinase and the es nucleoside transporter are targets for manipulation of the metabolism and activity of 3TC.

Topics: Affinity Labels; Animals; Anti-HIV Agents; Antineoplastic Agents; Carcinoma, Hepatocellular; Cells, Cultured; Drug Interactions; Ducks; Hepadnaviridae Infections; Hepatitis B Virus, Duck; Humans; Thioinosine; Thymidine; Tumor Cells, Cultured; Vidarabine; Zalcitabine

The cyclic nucleotide forms of 6-mercaptopurine and 6-methylmercaptopurine have been found to be cytotoxic to rat hepatoma cells. Studies with an inhibitor of phosphodiesterase suggest that the cytotoxicity of both cyclic nucleotides results principally from conversion to the 5'-nucleotide. A comparison of the two thiopurine cyclic nucleotides with their nucleoside counterparts has suggested that (a) the thio derivatives act by a common mechanism which is different from that exerted by the methylthio derivatives, and (b) the methylthio cyclic nucleotide acts, at least in part, by a mechanism which differs from that exerted by the methylthio nucleoside.

Topics: Carcinoma, Hepatocellular; Cell Division; Cells, Cultured; Cyclic IMP; Dose-Response Relationship, Drug; Inosine; Inosine Nucleotides; Liver Neoplasms; Methylthioinosine; Neoplasms, Experimental; Phosphodiesterase Inhibitors; Purine Nucleosides; Thioinosine