Abstract Background: EGFR extracellular domain (ECD) mutations—including EGFRvIII, A289 substitutions, R108 variants, and related structural alterations—drive ligand-independent EGFR activation and highly aggressive tumor biology. These mutations are enriched in glioblastoma (GBM) and also occur in head and neck, lung, and gastrointestinal cancers, where they are associated with therapeutic resistance and poorer patient outcomes. EGFR-ECD mutations are intrinsically resistant to approved EGFR TKIs, including osimertinib, erlotinib, gefitinib, and afatinib, because the structural alterations lie outside the ATP-binding pocket and preserve receptor signaling despite drug engagement. EO1001 is an orally bioavailable, irreversible pan-ErbB inhibitor designed to target both wild-type and structurally altered ErbB receptors. Early signals of clinical benefit in EGFR-ECD mutant GBM patients have been observed in an ongoing Phase 1-2a study (ANZCTR: ACTRN12620000583943), underscoring the need for mechanistic validation. To address this, we initiated a focused preclinical program assessing EO1001 activity in patient derived (PDX) cell culture models harboring clinically relevant EGFR-ECD variants. Methods: PDX GBM cell culture models were selected to evaluate EO1001 across representative EGFR mutation states. EO1001 is tested using a 9-point dose-response curve, run in triplicate at two timepoints. Cell viability and proliferation are quantified using CellTiter-Glo assays. Each plate includes a vehicle control, a DMSO cytotoxicity control, and an FDA-approved EGFR TKI as a positive control to benchmark EO1001 against a clinically used inhibitor known to be ineffective in ECD mutations. Primary endpoints include IC50 values and maximal inhibitory activity to determine whether EO1001 demonstrates direct antiproliferative effects in EGFR-ECD mutant GBM models. Results: Study is ongoing, data will be presented at the AACR annual meeting. Planned analyses will define whether EO1001 demonstrates meaningful activity against EGFR-ECD variants, which represent a therapeutically intractable subgroup characterized by resistance to existing EGFR inhibitors and poor clinical outcomes. Conclusions: This preclinical program will further explore mechanisms of EO1001’s activity in EGFR-ECD mutant cancers, providing support for biomarker-guided clinical development. Citation Format: Jeffrey Bacha, Sophia Frentzas, Malaka Ameratunga, Sarath Kanekal, Ian Nisbet, Neil Sankar, Denni M. Brown, Jasmine Borroel, Rowan Prendergast. Preclinical evaluation of EO1001 in EGFR-ECD mutant solid tumor models: Toward biomarker-directed therapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 5889.
Bacha et al. (Fri,) studied this question.