The anti-cancer transition-state inhibitor MTDIA inhibits human MTAP, inducing autophagy in humanized yeast

Methylthioadenosine-DADMe immucillin-A (MTDIA) is a transition-state analog that potently inhibits the human protein 5'-methylthioadenosine phosphorylase (MTAP) at picomolar concentrations and elicits anti-tumor activity against lung, prostate, colon, cervical, head and neck, and triple-negative breast cancers in cell and animal models. The anti-cancer mechanisms of MTDIA involve elevated methylthioadenosine levels but are not fully understood. The yeast protein MEU1 is functionally equivalent to human MTAP. To gain further understanding, we performed chemical genetic analyses via gene deletion and GFP-tagged protein libraries in yeast that express a member of the human equilibrative nucleoside transporter (ENT) family to permit MTDIA uptake. Genomic and proteomic analyses identified genes and proteins critical to MTDIA bioactivity. Network analysis of these genes and proteins revealed an important link to ribosomal function, which was confirmed by observing reduced levels of ribosomal subunit proteins. Network analysis also implicated autophagy, which was confirmed by analyzing intracellular trafficking of GFP-Atg8 and Phloxine B viability. In yeast, a comparable effect occurred after deletion of MEU1, indicating a single target for MTDIA in yeast. Overall, our yeast model reveals specific components of the ribosome as well as induction of autophagy as integral mechanisms that mediate the bioactivity of MTDIA.