Abstract 7150: Molecular insights into the oncogenic influence between mutant HER3, mutant KRAS, and their synergistic interplay in colorectal cancer pathogenesis

Abstract Colorectal cancer (CRC) is a disease of the colon and rectum that will claim about 52, 550 American lives in 2023. In recent years, more attention has been paid to HER2 and HER3’s roles in colorectal cancers, as they may cause resistance to targeted therapies. We are investigating the role of naturally co-occurring HER3 and KRAS mutations in colorectal cancer, as about 6% of all colorectal cancers contain a HER3 mutation and 41% contain a KRAS mutation. We have observed that there is a statistically significant co-occurrence of HER3 and KRAS mutations in CRCs while there is mutual exclusivity with mutations in EGFR or HER4 and mutant KRAS in CRC examining 6791 samples from 17 studies. There is a tendency for co-occurrence with HER2 and KRAS mutations that is not statistically significant in these CRC tumor samples. We have found that genetic knockdown of both KRAS and HER3 with siRNA targeting KRAS and HER3 in the CRC cell line SNU-407 (HER3V104M, KRASG12D) results in a statistical reduction in cell proliferation in comparison to genetic knockdown with only KRAS or HER3. Using the SW620 CRC cell line (HER3WT, KRASG12V) as a comparison, we have observed that knocking down HER3 using siRNA had no effect on cell proliferation whereas KRAS knockdown reduced proliferation and the combination showed no statistical difference compared to knocking down only KRAS. Additionally, we have found that there is a striking increase in total HER3 levels in SNU-407 cells when treated with the KRASG12D inhibitor MRTX1133. This feedback loop could limit the efficacy of the KRAS inhibitor. We wished to delineate mutant HER3’s binding partner (s) as HER3 is kinase impaired. Strikingly, we have found that EGFR immunoprecipitates with HER3 in SNU-407 cells. We are expanding our studies to CRC patient derived xenografts (PDXs) with co-occurring HER3 and KRAS mutations and have generated patient derived organoids from these PDXs. Ongoing studies are determining if there is a synergistic relationship with KRAS inhibitors and HER family inhibitors including a HER3 antibody-drug conjugate. Our findings may present a new paradigm for targeted combination therapies in colorectal cancer with the eventual goal of increased overall patient survival. Citation Format: Mary K. Kilroy, Briley Park, Rosalin Mishra, Wasim Feroz, Cecilia Wischmeier, Joan T. Garrett. Molecular insights into the oncogenic influence between mutant HER3, mutant KRAS, and their synergistic interplay in colorectal cancer pathogenesis 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 (6Suppl): Abstract nr 7150.