Abstract 5366: Hotspot mutations of TP53 sensitize APC-mutated colorectal cancer cells to cetuximab in vitro

Abstract EGFR inhibitor (EGFRi) therapies (cetuximab and panitumumab) have been approved for metastatic CRC patients who harbor wild-type KRAS/NRAS. Unfortunately, only ~50% of treated patients will respond to therapy. While FDA approved for first-line therapy, these agents are seldom used, significantly limiting their utility. Thus, there is an unmet need to develop additional biomarkers to identify EGFRi sensitive patients. Using an innovative hybrid approach fusing gene expression and DNA sequencing, we recently reported that combined mutations in APC and TP53, two major tumor suppressor genes, were strongly correlated with a validated gene expression signature measuring cetuximab sensitivity (CTX-S) in 468 CRC human tumors (Yang et al. Cancer Epidemiol Biomarkers Prev. 2019). Further analysis reported that APC and TP53 mutations predict cetuximab sensitivity across consensus molecular subtypes (CMS1-4) (Thota et al. Cancers. 2021). While APC truncated mutations are known to mediate WNT pathway activation, one of key features of CMS2 CRCs reported to be associated with cetuximab response, little is known about TP53 mutations with cetuximab sensitivity. To investigate a contributive role of mutant TP53 in vitro, we stably transfected expression plasmids of three hotspot mutations (R175H, R248W, R273H) of TP53 in APC-mutated CRC cells such as SW48 cells harboring WT KRAS/NRAS. Multiple stable clones for each of three TP53 mutations (empty vector as a control) were selected for biochemical and RNASeq analyses. We found that the three oncogenic mutations of TP53 enhanced cetuximab-mediated apoptosis under low serum culture conditions (2% FBS). Interestingly, the enhanced drug effect was associated with altered p53 pathway signatures as assessed by RNASeq. In support of the role of TP53 mutations, siRNA-knockdown of TP53 in SW48 cells also demonstrated an increased sensitivity to cetuximab treatments. Collectively, these in vitro analysis supports TP53 mutations, in combination with APC mutations, as predictive mutation biomarkers of cetuximab sensitivity in CRC. Citation Format: Mingli Yang, Heiman Wang, Thomas B. Davis, Lance Pflieger, Ramya Thota, W. Jack Pledger, Timothy J. Yeatman. Hotspot mutations of TP53 sensitize APC-mutated colorectal cancer cells to cetuximab in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5366.