Abstract 1082: Regorafenib resistance is associated with senescence-like phenotype and EMT in colorectal cancer (CRC)

The introduction of the multi-targeted tyrosine kinase inhibitor (TKI) regorafenib in clinical routine improve patients' survival with metastatic CRC who failed to respond to standard therapies, however at the cost of significant toxicities. Moreover, patients' tumor exhibit heterogeneous responses and become resistant. Its mechanism of action remains largely unknown, challenging the selection of patients through the identification of clinically useful predictive biomarkers. This study aimed to explore the effects on human CRC cell lines of short- and long-term exposure to regorafenib and investigate resistance-related mechanisms. Two representative CRC cell lines were used, HCT-116 and SW480. Short-term (3 days) and long-term exposure to IC50 values (HCT-116, 3µM and 6µM; SW480, 5µM and 6µM respectively) were intended to explore intrinsic and acquired resistance. The observation of early morphological changes (increased cell volume) in SW480 cells after regorafenib exposure led us to investigate a drug-initiated senescence-like phenotype commonly associated with resistance to treatment allowing cell death escape. These cells acquired stable senescent-like properties (slow-cycling cells, high β-galactosidase activity) and the majority of them were arrested in the G2/M cell cycle phase after long treatment exposure. A specific senescence-associated secretome (high sIL6Rα in cell supernatants) was also observed. In contrast, HCT-116 cells exposed to regorafenib presented early senescent features (high β-galactosidase activity) but developed over time an acquired resistance triggering EMT (high migration activity, upregulation of EMT-related factors) also known to contribute to TKI resistance. Moreover, the investigation of MAPK and PI3K/AKT pathways pointed to the latter as a significant player in acquired resistance of HCT-116 cells (increase of AKT phosphorylation) possibly related to the presence of a PI3KCA mutation in this cell line. Our findings provide new insights into the phenotypic plasticity of CRC cells under treatment pressure able to (1) either acquire stable senescent-like properties or (2) use early senescence state to undergo EMT. Our findings need further investigations of the major determinants involved in regorafenib-induced phenotype-switching and may help to develop new therapeutic strategies to overcome related resistances. Citation Format: Pashalina Kehagias, Mohammad Krayem, Nadège Kindt, Ahmad Najem, Caroline Vandeputte, Fabrice Journé, Ahmad Awada, Ghanem E. Ghanem, Alain Hendlisz. Regorafenib resistance is associated with senescence-like phenotype and EMT in colorectal cancer (CRC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1082.