Co-targeting KRASG12D and the HER family is efficacious in colorectal cancer.

Colorectal cancer (CRC) is the second leading cause of cancer deaths worldwide, with roughly 41% of CRC cases harboring a KRAS mutation. Acquired resistance to KRAS-targeted treatments has occurred with mechanisms including increased HER family expression among other receptor tyrosine kinases. HER3, a member of the HER family that is kinase impaired, has been shown to be a resistance mechanism upon inhibition of the HER family and downstream targets, including RAS/MEK/ERK and PI3K/AKT. We find that KRAS mutations tend to co-occur with HER3 alterations in a large panel of cancers and in CRCs. Our results show that both total and activated HER3 levels increase in CRC patient-derived organoids and cell lines after treatment with KRASG12D targeted agents, indicating that HER3 could be a potential adaptive response mechanism to KRAS-targeted therapy. Further, we found that genetic knock-down of KRAS and HER3 resulted in a reduction in the growth of CRC cells compared to a single knockdown of either KRAS or HER3. We observed that kinase-impaired HER3 binding partners, as assessed by immunoprecipitation, is cell dependent with EGFR binding HER3 in one cell line. After co-treating CRC cells with pan-HER inhibitors in combination with MRTX1133, a KRASG12D inhibitor, synergistic and additive effects in the reduction in cell growth were observed. Finally, we found that co-targeting KRASG12D mutant cells with a KRASG12D inhibitor and a HER3 antibody-drug conjugate further reduced cell viability. We posit that co-targeting both KRASG12D and HER3, whether directly or indirectly, is a potential therapeutic strategy in CRC patients.