Abstract 2114: Enhancing therapeutic strategies for osimertinib-resistant EGFR-mutant NSCLC: A HER3 dual-payload ADC (dpADC) with topoisomerase I and EGFR tyrosine kinase inhibitor

Abstract Background: EGFR tyrosine kinase inhibitors (TKIs) have significantly improved the survival rate and the quality of life of the NSCLC patients with EGFR mutation in the first line setting. For example, Osimertinib, a potent third-generation EGFR TKI, has demonstrated exceptional efficacy in metastatic NSCLC with specific EGFR mutations. Despite its success, the emergence of drug resistance, often linked to elevated HER3 protein expression, remains a significant challenge. U3-1402 (HER3-Dxd), an HER3 ADC, demonstrates a promising result in managing Osimertinib-resistant NSCLC. It has been reported that combining U3-1402 with Osimertinib has shown enhanced efficacy in resistant cell lines and mouse models. Here, we explore a novel HER3 dual-payload ADC (HER3 dpADC), uniquely combining a Topoisomerase I inhibitor and an EGFR TKI within a single antibody structure using the enzymatic site-specific conjugation platform developed by GeneQuantum (GQ). This innovative approach demonstrates potent and synergistic anti-tumor effects in vitro and in vivo, presenting an alternative therapeutic strategy for EGFR-mutant NSCLC patients. Results: GQ's dpADC platform technology employs two orthogonal enzymatic site-specific conjugations and stable linker technologies to efficiently generate the dual-payload ADC with high homogeneity and quality. For HER3 dpADC, HER3 Ab was conjugated with a novel Topoisomerase I inhibitor, TopoIx, and an EGFR tyrosine kinase inhibitor. In vitro DAR analysis revealed high linker stability, with minimal free payload release even after 96 hours of plasma incubation. Binding affinity assessments confirmed comparable affinity between HER3 dpADC and HER3 mAb in specific EGFR exon 19 deletion cell lines. Using various NSCLC cell lines in a 3D-spheroid culture system, HER3 dpADC demonstrated significant dose-dependent and synergistic anti-tumor activities. A robust bystander killing efficacy was observed in both HER3+/HER3- HEK293T cell coculture assays. Evaluation in CDX mouse models consistently demonstrated heightened in vivo efficacy by HER3 dpADC, aligning with the promising in vitro data. In NSCLC patient-derived xenograft (PDX) mouse models representing EGFR tyrosine kinase inhibitor-sensitive or resistant phenotypes, HER3 dpADC induced tumor regressions with no obvious toxicity, underscoring its potential as the next-generation HER3 targeting agent. Conclusion: The innovative HER3 dpADC, leveraging an efficient dual enzymatic site-specific conjugation, exhibited robust anti-tumor efficacy in both in vitro and in vivo settings, surpassing single-agent treatments. Its synergistic mechanism of action presents a promising possibility for developing a more potent and the front-line therapeutic solutions in NSCLC patients who have progressed on standard therapies. Citation Format: Lina Wang, Meijun Xiong, Xinju Gao, Chengang Zhou, Yu Han, Yanchun Li, Junhao Wang, Lili Shi, Gang Qin, Paul H. Song. Enhancing therapeutic strategies for osimertinib-resistant EGFR-mutant NSCLC: A HER3 dual-payload ADC (dpADC) with topoisomerase I and EGFR tyrosine kinase inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2114.