Benzamide riboside induces apoptosis independent of Cdc25A expression in human ovarian carcinoma N.1 cells

One of the mechanisms of action of a new oncolytic agent, benzamide ribosid e (BR) is by inhibiting inosine 5'-monophosphate dehydrogenase (IMPDH) whic h catalyzes the formation of xanthine 5'-monophosphate from inosine 5'-mono phosphate and nicotinamide adenine dinucleotide, thereby restricting the bi osynthesis of guanylates. In the present study BR (10-20 mu M) induced apop tosis in a human ovarian carcinoma N.1 cell line (a monoclonal derivative o f its heterogenous parent line HOC-7). This was ascertained by DNA fragment ation, TUNEL assay, [poly(ADP)ribose polymerase]-cleavage and alteration in cell morphology. Apoptosis was accompanied by sustained c-Myc expression, concurrent down-regulation of cdc25A mRNA and protein, and by inhibition of Cdk2 activity, Both Cdk2 and cdc25A are G(1) phase specific genes and Cdk2 is the target of Cdc25A. These studies demonstrate that BR exhibits dual m echanisms of action, first by inhibiting IMPDH, and second by inducing apop tosis, which is associated with repression of components of the cell cycle that are downstream of constitutive c-Myc expression.