Metabolism of Eicar (5-Ethynyl-1-β-D- Ribofuranosylimidazole-4-Carboxamide),A Potent Inhibitor of Inosinate Dehydrogenase

Abstract

The cytostatic agent 5-ethynyl-l-β-D-ribofuranosylimidazole-4-carboxamide (EICAR) causes a rapid and marked inhibition of inosinate (IMP) dehydrogenase activity in intact tumor cells. [³H]EICAR is metabolised in L1210 cells to its 5′-mono-, 5′-di- and 5′-triphos-phate in a concentration-dependent manner. The metabolites accumulate proportionally with the initial extracellular EICAR concentrations (ranging from 0.25 to 200 μM). The nicoti-namide adenine dinucleotide (NAD) analogue of EICAR, designated EAD, also accumulates within the cells and becomes the major metabolite after 48 hr incubation with 5 μM [³H]EI-CAR. EAD has a markedly longer intracellular half-life than EICAR 5′-mono-, 5′-di- and 5′-triphosphate. An additional EICAR metabolite elutes on an anion exchange Partisphere SAXHPLC chromatogram between EICAR 5′-di- and 5′-triphosphate. Its intracellular levels are~10-fold lower than those of EAD and the nature of this metabolite has still to be identified. The differential role of EAD and EICAR 5′-monophosphate in the inhibition of IMP dehydrogenase is currently under investigation.