Abstract A003: Adaptor sequestration and drug-induced potentiation of EGFR are widespread features of oncogenic RTK fusions

Abstract Regulation of cancer cells by their environment contributes to tumorigenesis and drug response, though the extent to which the oncogenic state can alter a cell’s perception of its environment is not clear. EML4-ALK is a receptor tyrosine kinase (RTK) fusion oncoprotein that suppresses transmembrane EGFR signaling in cancer cells. ALK inhibition restores signaling through EGFR, thereby promoting survival and drug tolerance. Here we tested whether such modulation of EGFR activity was common among other RTK fusions, which collectively are found in ∼5% of all cancers. Using live- and fixed-cell microscopy in isogenic and patient-derived cell lines, we found that a wide variety of RTK-fusions suppress transmembrane EGFR and sequester essential adaptor proteins in the cytoplasm, as evidenced by the localization of endogenous Grb2. Targeted therapies rapidly released Grb2 from sequestration and potently reactivated EGFR. Engineered optogenetic analogs of RTK fusions confirmed that cytoplasmic sequestration of Grb2 was sufficient to suppress perception of extracellular EGF and could do so independent of driving signaling from the optogenetic fusion itself, demonstrating that fusion signaling and suppression of EGFR could be functionally decoupled. Our study uncovers that a large number of RTK fusions simultaneously act as both activators and suppressors of signaling, the mechanisms of which could be exploited for new biomimetic therapies that enhance cell killing and suppress drug tolerance. Citation Format: Yuzhi Gao, David Gonzalez-Martinez, Sofia Wissert, Hana Bader, Nidhi Sahni, Anh Le, Robert Doebele, Lukasz Bugaj. Adaptor sequestration and drug-induced potentiation of EGFR are widespread features of oncogenic RTK fusions [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Fusion-Positive Cancer: From Discovery to Therapy; 2026 Jan 13-15; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(1_Suppl):Abstract nr A003.