Abstract 679: Inhibition of Notch signaling causes progenitor-to-hepatocyte differentiation and regressions in a subset of hepatocellular carcinoma by controlling C/EBPα expression and HNF4α activity

Abstract ​​Notch signaling regulates cell fate decisions during development and maintenance of many organs. During hepatogenesis, an active NOTCH2 signal is required for specification of the cholangiocyte lineage, while hepatoblasts remaining in a Notch-off state contribute to the default hepatocyte lineage. Notch pathway activation has been reported in liver tumors, although Notch-related liver cancer mutations are rare. We identified a subset of hepatocellular carcinoma that is exceptionally sensitive to the inhibition of a JAG1-NOTCH2 signal in a mouse preclinical trial using 47 liver cancer PDX models. Transcriptional profiling revealed that the sensitive models resemble a progenitor-like state. Highly selective therapeutic antibodies targeting either the JAG1 ligand or the NOTCH2 receptor triggered hepatocyte differentiation programs and tumor regressions.Single cell analyses revealed heterogeneous transcriptional states at baseline, some of which were profoundly perturbed upon Notch inhibition. Topic modeling combined with inference of transcription factor activities suggested the involvement of HNF4α and C/EBPα in treatment induced changes. Through its target HES1, Notch signaling directly represses C/EBPα expression. Notch inhibition derepresses C/EBPα which then binds chromatin in cooperation with HNF4α. We found that this cooperative binding results in expression of genes associated with mature hepatocyte activity, which was incompatible with tumor maintenance. Importantly, we identify hallmarks to aid the identification of this relatively rare tumor type. We suggest that inducing cell states towards differentiated, less aggressive states, especially using targeted single-agent therapeutics, holds great promise for the treatment of certain tumors in the liver and, by extension, possibly in other progenitor-like cancers. Citation Format: Kerstin Seidel, Robert Piskol, Thi Thu Thao Nguyen, Charisa Cottonham, Mark Merchant, Christian Siebel. Inhibition of Notch signaling causes progenitor-to-hepatocyte differentiation and regressions in a subset of hepatocellular carcinoma by controlling C/EBPα expression and HNF4α activity [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 679.