Abstract 4402: EGFR and LGR5 dual-targeting antibody-drug conjugate-based therapeutic strategies for the improved treatment of colorectal cancer

Abstract Colorectal cancer (CRC) remains the second-leading cause of cancer-associated death in the United States, indicating an urgent need for improved therapies. Antibody-drug conjugates (ADCs) are a promising class of therapeutics that function as “biological missiles,” employing the specificity of monoclonal antibodies to direct highly potent drug payloads to cancer cells while sparing normal tissues. We have developed ADCs targeting leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), a marker of normal adult intestinal stem cells and CRC stem-like cells with roles in CRC tumorigenesis, tumor progression, metastasis, and drug resistance. While LGR5-targeting ADCs incorporating microtubule inhibitors promoted tumor regression in select xenograft models and were well-tolerated, tumors eventually relapse following treatment cessation due to LGR5 downregulation and suboptimal ADC payload selection (Gong et al. 2016, Molecular Cancer Therapeutics). Thus, this work aims to investigate multi-targeting therapeutic strategies with improved LGR5-targeting ADCs to improve CRC care and prevent relapse. Our work showed that therapies targeting the epidermal growth factor receptor (EGFR), including cetuximab (CTX) which is approved for KRASWTmetastatic CRC, increased LGR5 protein levels in CRC cell lines, tumor organoids, and mouse models independent of KRAS mutational status. To evaluate EGFR and LGR5 dual-targeting approaches, we generated a novel LGR5-targeting ADC incorporating a topoisomerase I inhibitor payload via site-specific conjugation that was well-tolerated in immunocompetent mice. Importantly, combination of CTX with LGR5-targeting ADCs significantly enhanced anti-tumor efficacy and extends survival as compared to ADC and CTX monotherapies in RASMUT CRC patient-derived xenografts (High et al. 2025, Cell Reports Medicine). Still, tumors eventually relapsed following combination treatment, warranting investigation into alternative dosing regimens and dual-targeting modalities. We have therefore generated two EGFR:LGR5 bispecific antibodies (bsAbs) that promote lysosome-mediated EGFR degradation. EGFR:LGR5 bsAbs demonstrated minimal cytotoxicity in CRC cells, necessitating drug conjugation to generate highly potent EGFR:LGR5 bispecific ADCs (bsADCs). Importantly, EGFR:LGR5 bsADCs exert 100- to 1000-fold enhanced potency over LGR5 ADCs with identical linker-payloads in LGR5/EGFR-expressing CRC cell lines of varying genetic backgrounds. These promising findings warrant further investigation into the anti-tumor efficacy of EGFR:LGR5 bsADC monotherapy versus combination therapy of CTX and LGR5 ADCs in CRC xenograft models. Taken together, this work strongly rationalizes dual-targeting of EGFR and LGR5 as an effective therapeutic option for CRC and other EGFR- and LGR5-expressing cancers. Citation Format: Peyton C. High, Zhengdong Liang, Maya Cappellino, Tiffani Blackburn, Cara Guernsey-Biddle, Shraddha Subramanian, Yueh-Ming Shyu, Adela Aldana, Yukimatsu Toh, Kendra S. Carmon. EGFR and LGR5 dual-targeting antibody-drug conjugate-based therapeutic strategies for the improved treatment of colorectal cancer [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 4402.