title: Schedule-dependent synergistic action of tiazofurin and dipyridamole on hepatoma 3924A cells.
abstract: Tiazofurin is an oncolytic nucleoside analog that has shown therapeutic activity in end-stage acute non-lymphocytic leukemia and in chronic granulocytic leukemia in blast crisis. Tiazofurin is anabolized to the active metabolite, TAD, which inhibits IMP dehydrogenase activity, leading to a reduction in guanylate pools and to the cessation of neoplastic cell proliferation. The drug exhibits potent cytostatic and cytotoxic activity against hepatoma 3924A cells in culture. In growth-inhibition and clonogenic assays, the 50% inhibitory concentration of tiazofurin was 3.8 and 4.2 microM, respectively. Dipyridamole, an inhibitor of nucleoside transport, curtails the salvage of nucleosides and bases for nucleotide biosynthesis. Dipyridamole exhibited cytotoxicity against hepatoma 3924A cells, with an LC50 of 24 microM and an IC50 of 29 microM being recorded. A combination of tiazofurin and dipyridamole provided synergistic cytotoxicity in hepatoma 3924A cells in culture. This synergistic activity was dependent on the order of addition of the drugs. Simultaneous addition of the two drugs produced antagonism, whereas preincubation of cells with tiazofurin or dipyridamole followed by addition of the second drug resulted in synergy. TAD concentrations were significantly higher (129% and 135%) in cells that had been pretreated with tiazofurin or dipyridamole before the addition of the second agent as compared with cells that had been treated simultaneously (113%). These studies indicate the importance of the order of the addition of drugs to obtain a synergistic response in combination chemotherapy and suggest the need for a careful selection of drug modulation in clinical trials of tiazofurin and dipyridamole.
authors.affiliation: Laboratory for Experimental Oncology, Indiana University School of Medicine, Indianapolis 46202-5200.
authors.forename: H N
authors.initials: HN
authors.lastname: Jayaram
authors.forename: K
authors.initials: K
authors.lastname: Murayama
authors.forename: K
authors.initials: K
authors.lastname: Pillwein
authors.forename: W
authors.initials: W
authors.lastname: Zhen
authors.forename: G
authors.initials: G
authors.lastname: Weber
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage* / Q000378:metabolism; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004176:Dipyridamole / Q000008:administration & dosage* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D008114:Liver Neoplasms, Experimental / Q000188:drug therapy* / Q000378:metabolism; D012254:Ribavirin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
chemical_list: D000964:Antimetabolites, Antineoplastic; D000970:Antineoplastic Agents; D012254:Ribavirin; D004176:Dipyridamole; C033706:tiazofurin