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Bispecific degraders (PROTACs) of ERα are expected to be advantageous over current inhibitors of ERα signaling (aromatase inhibitors/SERMs/SERDs) used to treat ER+ breast cancer. Information from DNA-encoded chemical library screening provides a method to identify novel PROTAC binding features as the linker positioning, and binding elements are determined directly from the screen. After screening ∼120 billion DNA-encoded molecules with ERα WT and 3 gain-of-function mutants, with and without estradiol to identify features that enrich ERα competitively, the off-DNA synthesized small molecule exemplars exhibited nanomolar ERα binding, antagonism, and degradation. Click chemistry synthesis on an alkyne E3 ligase engagers panel and an azide variant that rapidly generated bispecific nanomolar degraders of ERα, with PROTACs inhibiting ER+ MCF7 tumor growth in a mouse xenograft model of breast cancer. This study validates this approach toward identifying novel bispecific degrader leads from DECL screening with minimal optimization. Citation Format: Anthony D. Keefe, Jeremy S. Disch, Jennifer Duffy, Esther C. Lee, Diana Gikunju, Betty Chan, Benjamin D. Levin, Michael I. Monteiro, Sarah A. Talcott, Anthony Lau, Fei Zhou, Anton Kozhushnyan, Neil E. Westlund, Patrick B. Mullins, Yan Yu, Moritz von Rechenberg, Junyi Zhang, Yelena Arnautova, Yanbin Liu, Ying Zhang, Andrew J. McRiner, Anna Kohlmann, Matthew A. Clark, John W. Cuozzo, Christelle Huguet, Shilpi Arora. Discovery of new targeted protein degraders using DNA-encoded chemistry. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5346.

The c-MET receptor tyrosine kinase has received considerable attention as a cancer drug target yet there remains a need for inhibitors which are selective for c-MET and able to target emerging drug-resistant mutants. We report here the discovery, by screening a DNA-encoded chemical library, of a highly selective c-MET inhibitor which was shown by X-ray crystallography to bind to the kinase in an unprecedented manner. These results represent a novel mode of inhibiting c-MET with a small molecule and may provide a route to targeting drug-resistant forms of the kinase whilst avoiding potential toxicity issues associated with broad kinome inhibition.