Elucidating the anti-cancer mechanisms for transition-state structure inhibitors of nucleoside phosphorylases methylthioadenosine-DADMe-immucillin A and forodesine

Transition-state structure analogues are among the most powerful chemical inhibitors discovered to date with picomolar efficacy for enzymes. The nucleoside analogue methylthioadenosine-DADMe-immucillin A (MTDIA) is an inhibitor of the enzyme methylthioadenosine phosphorylase (MTAP) in polyamine biosynthesis. The recently approved forodesine (Mundesine®) is an inhibitor of purine nucleoside phosphorylase (PNP) and purine synthesis. Although the targets of these drugs were known at the time of drug design, it is important to know the compendium of cellular perturbations resulting from use of these inhibitors. Several suspected mechanisms of MTDIA and forodesine in progression of apoptotic cell death have been identified but the underlying mechanisms initiating apoptosis remain elusive. We hypothesize that numerous cellular processes are affected in MTDIA and forodesine treatments given the importance of polyamine and purine synthesis in cancer cells. To elucidate the unsuspected mechanisms mediating anti-cancer activity, unbiased genomic analyses were employed using Saccharomyces cerevisiae. First, gene-gene interactions with MEU1 (the MTAP orthologue in yeast) were determined using Synthetic Genetic Array methodology followed by assessment of drug-gene interactions with MTDIA treatment under a MEU1 essential condition with MTA as the sole source of sulphur. Disruptions to suspected mechanisms of amino acid metabolism, carbohydrate metabolism, response to starvation, vesicle-mediated transport, vacuole fusion, lipid homeostasis, chromatin organisation, transcription, and translation were implicated well as unsuspected mechanisms of NAD+ dependent cellular processes, multi-vesicular body formation, endosomal transport, ion homeostasis, mitochondrion organisation, and cell cycle progression. Induction of autophagy was subsequently confirmed with MTDIA to validate the disruptions to vesicle-mediated transport, response to starvation, multi-vesicular body formation and va