Abstract

Cancer is amongst the leading causes of death in the world and has plagued humanity for far longer than some would expect. We have come a long way in understanding the physiological changes that correlate with cancer progression, but treatment options remain limited. In this thesis, I developed a high-throughput pipeline to screen thienoisoquinoline derivatives synthesized by Dr. Forgione’s laboratory for their efficacy in reducing cancer cell viability. These derivatives were strategically designed to share a common ¬scaffold and have three functional groups amenable to modifications. From >40 derivatives, we identified our lead compound C75. We characterized the mechanism of action of C75 at a molecular and cellular level to develop a better understanding of its efficacy and selectivity for some cell types over others. Through in vitro assays, we found that C75 prevents microtubule polymerization, destabilizes microtubules, and binds to tubulin at the same site as colchicine (another microtubule-targeting drug). In line with its effects on microtubules, C75 causes mitotic arrest and spindle phenotypes in multiple cancer cell lines in the nanomolar range. However, through comparative studies with colchicine, we found that while colchicine causes a gradual decrease in microtubules and spindle pole collapse in cells, similar concentrations of C75 cause a rapid loss of microtubules and spindle pole fragmentation followed by microtubule re-growth to form multipolar spindles. In addition, C75 and colchicine synergize for reduced viability and spindle phenotypes. Importantly, the phenotypes caused by C75 are similar to those caused by the depletion of ch-TOG, a microtubule polymerase, and tubulin and ch-TOG are displaced and oscillate in C75-treated cells. This suggests that C75 directly causes microtubule depolymerization in cells, or indirectly causes this via inhibiting ch-TOG. We also discovered that C75 has higher efficacy in triple negative breast cancer (TNBC) cells compared to other cell types, suggesting that this could be an ideal group of cancers to explore a potential use for. It will be important to determine if C75 retains its efficacy in TNBCs that are resistant to Taxol, which arises in patients after repeated Taxol use leaving them with few alternative treatment options. We also identified a new derivative that has an even higher efficacy in TNBCs compared to C75, and we are determining if this will be a new lead compound. With a strong understanding of how these compounds work at the molecular and cellular level, we are positioned to carry out in vivo studies to determine their potential for use for treating TNBCs.