Abstract 4725: Engineering a novel serine-degrading enzyme for targeted cancer therapy

Abstract The non-essential amino acid L-serine (serine) is the second most consumed amino acid by cancer cells, supporting their survival and proliferation by contributing to the biosynthesis of nucleotides, lipids, and proteins. Serine-auxotrophic tumors such as luminal breast cancers have compromised serine synthesis pathways, thus rely on extracellular serine, making them vulnerable to serine depletion therapies. While dietary serine restriction, the only current method to reduce serine availability for tumors in vivo, has shown limited success in reducing tumor growth, its application is hindered by poor patient compliance and an inadequate reduction of circulating serine. To overcome these limitations, we developed an engineered human serine/threonine dehydratase (eSDH) enzyme that irreversibly depletes over 95% of circulating serine and threonine without requiring dietary changes. Preclinical studies show that eSDH treatment significantly inhibits the growth of serine-auxotrophic tumors. To enhance the therapeutic potential of eSDH and reduce off-target effects, particularly the depletion of the essential amino acid threonine, we focused on improving the specificity of eSDH for serine. Through iterative structure-based engineering, we developed a new SDH variant with over 20 times higher selectivity for serine toward threonine. Both in vitro and in vivo studies have confirmed that this novel SDH variant depletes serine while preserving threonine in cell culture media and serum. Current efforts are focused on improving the stability of the new SDH variant to extend its half-life in serum and optimize dosing for greater therapeutic efficiency. This advancement allows us to target serine-auxotrophic cancers more precisely while minimizing the impact on normal cells. The broader impact of this work lies in establishing enzymatic serine depletion as a more effective and feasible alternative to dietary restriction for cancer therapy. This approach could provide a new therapeutic strategy for treating various serine-auxotrophic tumors, offering better patient compliance and fewer side effects. Citation Format: Ladan Mashouri, Ebru Cayir, Sarita Bhetawal, Daniel J Diaz, Vipin Rawat, Jonathan Coloff, George Georgiou, Everett Stone. Engineering a novel serine-degrading enzyme for targeted cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4725.