Abstract 3396: Discovery of BDTX-1535, a novel 4th generation, irreversible, potent, wild type sparing EGFR MasterKey inhibitor that targets oncogenic kinase domain mutations as well as extracellular domain alterations for the treatment of NSCLC and GBM

Abstract Acquired resistance to 3rd generation EGFR inhibitors used in the treatment of NSCLC is common. While the EGFR C797S substitution is a frequently reported post-osimertinib resistance mutation, real world evidence indicates the emergence of additional EGFR alterations that can drive drug resistance: kinase domain mutations (e.g., S768I), extracellular domain alterations (e.g., EGFRvIII, A289X), and EGFR amplification. Moreover, while osimertinib targets the classical EGFR mutations, primary NSCLC tumors are also driven by other oncogenic kinase domain mutations including G719X, S768I, and L861Q, which confer de novo (intrinsic) resistance to 3rd generation EGFR TKIs. A family of extracellular domain alterations occurs in nearly 50% of GBM patients, and these alterations are clinically resistant to all current generation inhibitors. Real world data in GBM demonstrate these EGFR alterations often co-occur and persist throughout treatment with current standard of care therapy. Of critical importance is the observation that the oncogenic isoform of EGFR in GBM is a covalent homo-dimer which can be formed and paradoxically activated by the binding of reversible 1st generation EGFR inhibitors. There is a significant clinical need to develop a potent CNS penetrant EGFR inhibitor that would target both acquired and intrinsic resistance mutations expressed in NSCLC and co-occurring EGFR alterations in GBM. An effective inhibitor should meet four design principles; 1) potent and selective against a broad family of intracellular, extracellular EGFR oncogenic alterations and amplification, 2) wild type EGFR sparing, 3) irreversible to avoid paradoxical activation, and 4) CNS penetrant. BDTX-1535 is a 4th generation irreversible CNS penetrant EGFR MasterKey inhibitor targeting a family of oncogenic EGFR extracellular domain alterations and amplification in GBM patients and EGFR resistance mutations in NSCLC. BDTX-1535 meets all four criteria for a highly effective EGFR inhibitor and was designed using the MAP Discovery Engine to target the activated conformations used by oncogenic EGFR to drive tumorigenesis. BDTX-1535 achieves potent anti-tumor activity against EGFR alterations and amplification across models including NSCLC and GBM PDX and intracranial tumors. BDTX-1535 is currently in a phase I clinical study in patients with NSCLC and GBM harboring sensitive EGFR alterations (NCT05256290). Citation Format: Matthew O'Connor, Matthew Lucas, Sherri Smith, Anthony Trombino, Sudharshan Eathiraj, Elizabeth Buck. Discovery of BDTX-1535, a novel 4th generation, irreversible, potent, wild type sparing EGFR MasterKey inhibitor that targets oncogenic kinase domain mutations as well as extracellular domain alterations for the treatment of NSCLC and GBM [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 3396.