Abstract A153: Novel synergistic drug combinations of PARP, bromodomain, and spindle assembly checkpoint kinase inhibitors by large-scale screen of 150 anticancer agents

Abstract

Abstract The aim of combination drug treatment in cancer therapy is to improve response rate and decrease the probability of the development of drug resistance. The discovery of new effective drug combinations is constrained by the cost and effort of carrying out large unbiased screens. Moreover, results of large synergy screen frequently suffer from poor reproducibility, because deviations in single-agent effects multiply as they are combined. We have previously shown (1) that curve shift analysis by the approach developed by Straetemans et al. (2) is a more robust method of determining synergy than combination matrix screening using Bliss-scoring. In addition we have shown that our workflow for single agent cellular IC50 determination is highly reproducible compared to other workflows (3). To bring these advantages to bear, and to increase the throughput of identifying new synergistic drug combinations, we developed a two-step approach consisting of screening and confirmation. First the influence is tested of a fixed concentration of a compound of interest, on the dose-response curves of a library of more than 150 anticancer agents. This library includes many standard-of-care chemotherapeutic agents, approved and preclinical kinase inhibitors, epigenetic modulators, and compounds acting by other mechanisms (3). Drug combinations resulting in curve-shifts in this initial SynergyScreen™ are then reexamined and confirmed by curve shift analysis using mixtures in various fixed ratios, followed by Chou-Talalay analysis and calculation of Combination Index (CI). By distinguishing separate synergy screening and synergy confirmation stages, our SynergyScreen™ setup capitalizes on insights from high-throughput screening for single agents to discover robust and reproducible synergistic combinations. Results will be presented of a SynergyScreen™ with the poly-ADP ribose polymerase (PARP) inhibitor niraparib, the BET bromodomain inhibitor JQ1, and inhibitors of the spindle assembly checkpoint kinases TTK and Bub1. Screens were performed in one to three different cancer cell lines in which the investigated compounds showed full efficacy in a three-day or five-day cell proliferation assay. New, mechanistically distinct synergies for niraparib were identified that were validated in primary tumor cell samples from ovarian cancer patients and previously reported synergies with DNA-damaging agents and topoisomerase inhibitors were confirmed. TTK inhibitors were found to synergize with Bcl2 inhibitors in cancer cell lines and also in blood cell samples from T cell acute lymphoblastic leukemia patients. Bub1 inhibitors show relatively low antiproliferative activity when tested as single compounds but strongly synergize with taxanes. In conclusion, an efficient screening work flow was developed that can reproducibly identify new synergistic drug combinations.