Abstract A27: An apoptosis-based screen for targeted agents in rhabdomyosarcoma reveals potential combination therapies

Intensification of therapy for rhabdomyosarcoma (RMS) by combining conventional chemotherapies has not proven effective at improving long-term survival. More selective small molecules may improve outcomes when added to chemotherapeutic backbones, but the optimal actionable targets in RMS are not well defined. An alternative strategy to develop combination therapies is to identify agents with complementary methods of apoptotic induction that can be paired with synergistic results. We first set out to identify classes of drugs that induce apoptosis in representative fusion-positive (FP) and fusion-negative (FN) cell lines. We built a screening assay using high-throughput microscopy to quantify both cell number (Hoechst nuclear staining) and apoptosis (NucView 488 Caspase-3 Enzyme Substrate [Biotium]). Technical controls included DMSO and staurosporine. The assay had a SSMD β score of 6.4, demonstrating excellent quality for screening. We represented FP-RMS with RMS13 cells and represented FN-RMS with RD cells. We screened ~2,000 bioactive compounds spanning a wide variety of biochemical mechanisms and targets. We tested compounds at 5 μM to identify even weakly active agents, since they might synergize with other drugs. We deemed “active” compounds to be those that reduced cell number 4 SD below DMSO-treated wells. Specific drug targets were enriched among the set of active compounds. In RD cells, for example, 16 of 25 (64%) HDAC inhibitors reduced cell number and activated caspase 3, which is greater than the library average of 264/1,921 compounds (14%) (p Citation Format: Amit J. Sabnis, Steven Chen, Carolina Morales, Benjamin S. Braun. An apoptosis-based screen for targeted agents in rhabdomyosarcoma reveals potential combination therapies [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A27.