Abstract B073: C-terminal Binding Protein (CtBP): a critical regulator of ErbB2/3 signaling in PDAC

Abstract Pancreatic ductal adenocarcinoma (PDAC) remains among the most lethal of human cancers with a 5-year survival of ~10%, underscoring the need to identify new therapeutic vulnerabilities. Previously, we reported high expression of transcriptional co-regulators C-terminal binding proteins (CtBP) 1 and 2 in human PDAC, however their precise role in PDAC formation or progression remains unclear. Here we have studied PDAC tumor dependency on CtBPs for growth and metastasis, using an orthotopic syngeneic pancreatic tumor mouse model employing a mouse PDAC cell line (CKP) derived from a pancreatic tumor that formed in a mouse expressing mutated K-Ras in the setting of p53 deletion. CRISPR-based homozygous deletion of Ctbp2 in the parental mouse PDAC cell line (CKP CtBP2 KO) dramatically decreased orthotopic PDAC tumor growth, drastically reduced metastatic potential, and significantly prolonged survival. Interrogating differential gene expression of the orthotopic PDAC tumors from Ctbp2 WT vs Ctbp2 KO cohorts, we identified significant downregulation of the EGFR-superfamily receptor ErbB3 in Ctbp2 KO tumors, and further determined that CtBP2 regulates expression of both the ErbB2 and 3 EGFR superfamily genes in PDAC cells. We therefore hypothesized that CtBP regulation of physiologic ErbB2/3 signaling contributes, in part, to PDAC growth and metastasis. Indeed, we observed that Ctbp2 KO cells exhibited near complete loss of ErbB2/3 expression and exhibited severely attenuated activation of phospho-Akt after neuregulin stimulation of ErbB2/3, and furthermore, human PDAC cells also demonstrated CtBP dependence of ErbB3 expression. Our results suggest that a subset of PDAC tumors are dependent on physiologic ErbB2/3 signaling and could be targeted by pharmacologic inhibitors of ErbB2 and/or ErbB3. Providing proof of concept, the ErbB2-targeted multikinase inhibitor lapatinib effectively killed the ErbB3 expressing CKP PDAC cells, while CKP CtBP2 KO cells, where ErbB3 expression was extinguished, were resistant to lapatinib. Taken together, our data suggests that ErB2/3 targeted therapeutics can effectively target a critical PDAC dependency on physiologic ErbB2/3 signaling which is the result of CtBP’s oncogenic transcriptional program that drives PDAC tumor progression. Citation Format: Kranthi Kumar Chougoni, Haemin Park, Priyadarshan K. Damle, Martin Michael Dcona, Barbara Szomju, Mikhail G. Dozmorov, Michael Idowu, Steven R. Grossman. C-terminal Binding Protein (CtBP): a critical regulator of ErbB2/3 signaling in PDAC [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B073.