<p> The membrane-bounded lysosome is a dynamic organelle responsible for macromolecule degradation, receptor down regulation, stress survival and pH balance. Intact lysosomal function is critical for proper cell function, as defects in lysosomal trafficking have been associated with neurodegenerative diseases such as Alzheimer&rsquo;s disease. <i>Saccharomyces cerevisiae </i>, budding yeast, is an ideal model organism for studying lysosomal protein trafficking because its vacuole is functionally analogous to the mammalian lysosome and both share conserved trafficking machinery components. </p><p> A previous yeast genomic deletion strain screen in our lab uncovered fourteen deletion strains with h&barbelow;ypersensitivity to <u>hy </u>gromycin B (<i>hhy</i> mutants), all of which exhibited defective vacuolar trafficking, morphology and/or function. Additionally, recent microscopic findings in our lab support that the late-endosome dependent pathway is the affected pathway and that <i>hhy</i>s have compromised T&barbelow;arget of R&barbelow;apamycin C&barbelow;omplex 1&barbelow; signaling. TORC1 regulates cell growth and cell proliferation and its hyperactivity is associated with cancer and metabolic diseases. As with lysosomes, the vacuole also serves as the platform for TORC1 signaling. </p><p> To further assess if the late-endosome dependent pathway is affected by hygromycin B treatment in <i>hhy</i> mutants, vacuolar delivery of two vacuolar markers was assessed. Alkaline phosphatase (ALP) delivery was assessed as a late-endosome independent pathway marker and carboxypeptidase Y (CPY) delivery was assessed as a late-endosome dependent pathway marker. To date, we have observed that hygromycin B treatment disrupts CPY trafficking via the late-endosome dependent pathway while ALP trafficking via the late-endosome independent pathway is unaffected by hygromycin B treatment. </p><p> Rapamycin is the direct inhibitor of TORC1. Rapamycin and its analogs (rapalogs) are currently administered in the treatment of TORC1 hyperactivity. However, therapeutic inhibition of TORC1 signaling by rapamycin is associated with severe toxicities. Since our recent results implicate compromised vacuolar trafficking of Tor1 kinase in <i>hhy</i> mutants, we tested vesicular trafficking inhibiting drugs in combination with rapamycin in order to explore a cumulative effect on TORC1 inhibition assessed by growth of wild type cells. Additionally, we explored the effects of combining two vesicular trafficking drugs on wild type cell growth. </p><p> We established a cumulative effect on wild type growth upon using low concentrations of rapamycin in combination with vesicular trafficking inhibitory drugs. Thus, rapamycin and vesicular trafficking inhibitory drugs have potential for drug combination therapy against TORC1 hyperactivity at lower drug concentrations. Drug combination treatment may be a new and effective way to regulate TORC1 function at sub-toxic levels of rapamycin.</p>