IDENTIFICATION OF NOVEL POTENTIAL CANCER THERAPIES BY SYNTHETIC LETHAL SCREENING

There is an urgent need for novel effective drug regimens for the treatment of cancer. Current chemotherapy suffers from a slim therapeutic index, with significant toxicity from effective drug doses or tumor recurrence at low drug doses. Identifying synergistic interactions between drugs is a difficult process. To accelerate the discovery of potential drug combinations, I have developed a druggable genome siRNA synthetic lethal screen capable of rapidly identifying novel drug targets that would sensitize cancer cells to sublethal concentrations of microtubule destabilizing agents. I employed a high-throughput cell-based 16,560-siRNA screen to isolate a high-confidence list of genes that, when silenced, enhanced glioblastoma multiforme cancer cell chemosensitivity. Two gene products that were the major focus of my work were midline2 and the neurokinin receptor NK1R. Silencing of midline2, a PP2A-microtubule tether, sensitized cells to two microtubule destabilizing agents, vinblastine and disorazole C1, suggesting a mechanistic dependency of the phosphatidylinositol 3-kinase pathway on microtubule functionality. Combinations of phosphatidylinositol 3-kinase inhibitors with disorazole C1 and several vinca alkaloids confirmed this hypothesis. To verify microtubule destabilizing agent sensitization by NK1R silencing, I demonstrated a significant collaboration of neurokinin receptor NK1R antagonists with low concentrations of vinca alkaloids. These assay results and subsequent novel combination strategies demonstrate the tremendous ability of this synthetic lethal screen to predict potent collaborations between different classes of drugs, as well as identifying molecular constituents mediating those interactions