Abstract PO-087: Novel high-throughput screen in a breast cancer cell line to identify potent radiosensitizers

There is a need for more broadly applicable radiosensitizers independent of disease state and DNA protein repair status. High throughput screens hold potential for identifying new classes of radiosensitizers from libraries of small molecules. Our group has developed an in vitro high throughput screen identifying radiosensitizers using high content imaging. Due to chromatin condensation, G2/M is acknowledged as the most radiosensitive phase of the cell cycle. We therefore dosed 4T1 breast cancer cells with a library of 1430 FDA approved drugs, then using the high content images, assessed ability to stall in G2/M. We initially eliminated drugs with less than 30% viability from consideration to negate toxicity effects on the CCI. With a CCI cutoff of two standard deviations from the mean, we attained a hit rate of 2.8% with 40 hits. The screen identified both known and novel radiosensitizers belonging to previously unidentified classes. This methodology of cell cycle analysis was confirmed by the more classical flow cytometry assay and a selected hit from the screen was assessed for radiosensitizing ability by clonogenic and γH2AX assays, and in vivo studies. Based on the clonogenic survival fractions, the radiation enhancement ratio was found to be >1 at all doses between 2-6 Gy for the selected drug, with the highest values at 4 and 5 Gy of 4.5. Furthermore, we found two 10 µM doses of the novel radiosensitizer paired with two fractions of 2 Gy was sufficient to significantly decrease 4T1 tumor volume growth in BALB/c mice. Citation Format: Madeleine R. Landry, Allison N. DuRoss, Eunseo Choi, Antony Jozic, Dylan Nelson, Conroy Sun. Novel high-throughput screen in a breast cancer cell line to identify potent radiosensitizers [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-087.