Torc1 Inhibition Using A Drug Combination Approach In Saccharomyces Cerevisiae

The yeast vacuole is functionally analogous to the mammalian lysosome, a dynamic organelle responsible for macromolecule degradation, receptor down regulation and stress survival. As with lysosomes, the vacuole also serves as the platform for T arget o f R apamycin C omplex 1 (TORC1) signaling. TORC1 is the master regulator of cell growth and proliferation and its hyperactivity is associated with cancer and metabolic diseases. Inhibition of TORC1 signaling by rapamycin is associated with severe toxicities. Therefore, combination of drugs that can regulate TORC1 at lower, less toxic concentrations can be advantageous in treatments of TORC1 hyperactivity. A yeast genomic deletion strain screen in our lab uncovered deletion strains with h ypersensitivity to hy gromycin B ( hhy mutants), all of which exhibited defects in vacuole trafficking, morphology and/or function. Recent findings in our lab indicate that hhy mutants also have compromised TORC1 signaling, and that intact lysosomal trafficking is a prerequisite for this signaling. Thus, drugs that affect lysosomal trafficking may have potential for use in combination with lower levels of rapamycin in TORC1 inhibition. We are currently testing hygromycin B and other vesicular trafficking inhibitory drugs in combination with sub‐inhibitory levels of rapamycin and assessing cumulative effects on growth. To date, we have established such a cumulative effect for hygromycin B and rapamycin drug combination. Additionally, our prior microscopic studies show that vacuolar Tor1‐GFP is mislocalized in hhy mutants especially in presence of hygromycin B. Biochemical localization assays of native Tor1 following drug treatments in wild type and hhy mutants are in progress.