THE INTRACELLULAR FORMATION OF A MONONUCLEOTIDE OF THE ANTIINFLUENZA AGENT 1,3,4-THIADIAZOL-2-YLCYANAMIDE (LY217896)

LY217896 is a substituted thiadiazole compound with anti-influenza activity in vitro and in the mouse model of infection. LY297336 is a ribosylated (N-4) derivative of LY217896, A highly polar intracellular metabolite of LY217896 was isolated by HPLC, and mass spectral analysis and treatment of the metabolite with alkaline phosphatase showed that it was a monophosphate (LY307987) derived from LY217896. The formation of LY307987 was inhibited by 43 and 63% when 10 mu M of LY217896 was incubated with 100 mu M of 8-aminoguanosine (8AGuo) and guanine (Gua), respectively, whereas inosine (Ino) and hypoxanthine (Hx) had no effect on the formation of LY307987. LY217896 inhibited the incorporation of [(14)c]-Hx into nucleic acids in cells which metabolize LY217896; however, LY217896 did not inhibit the formation of inosine 5'-monophosphate (IMP) from Hx in a cell-free HGPRT (hypoxanthine-guanine phosphoribosyltransferase)-catalysed reaction. Incubation of MDCK cells with 10 mu M of LY217896 resulted in an 8-fold increase in the level of intracellular IMP, At 100 mu M, neither LY217896 nor LY297336 inhibited inosine 5'-monophosphate dehydrogenase (IMPDH) and only cellular extracts which contained intracellular metabolites of LY217896 inhibited IMPDH. Quantification of the 5-phosphorylribose pyrophosphate (PRPP) levels in BS-C-1, MDCK, and MCN cells showed a positive correlation between PRPP concentration and cellular