Abstract 2978: E2F1 regulates cell competition, increase proliferation and inhibits chemotherapy resistance in cancer cells
Authors: Valdivia Andres Felipe , Cowan Matthew , Zhao Guangyuan , Cardenas Horacio , Matei Daniela 
Published: June 2022

Abstract
Introduction: Tumor heterogeneity is a key element during the development of chemo-resistance and tumor relapse. It remains unknown how resistant tumor cells influence sensitive cells during conditions of cohabitation. The goal of our study was to determine driving factors mediating interactions between resistant and sensitive cancer cells and the effects of cohabitation on both phenotypes.
Materials and methods: We used two isogenic ovarian cancer cell lines pairs, sensitive and resistant to platinum: OVCAR5 (IC50 = 2.05 uM) vs. OVCAR5-CisR (IC50 = 7.26 uM) and PEO1 (IC50 = 5.92 uM) vs. PE04 (IC50 = 14.45 uM) labeled with either GFP or RFP. The cell pairs were seeded together in long direct term culture, separated by fluorescence activated cell sorting (FACS), and used for RNAseq analysis, proliferation assays, Cisplatin IC50 determinations, and cell cycle analysis.
Results: Long Term direct co-culture (14 Days) of platinum-sensitive and -resistant cells induced increased proliferation (p &lt; 0.001) and a greater proportions of cells in the S and G2 phases of the cell cycle in sensitive PEO1 and OVCAR5 cells compared with cells cultured by themselves. Resistance to platinum of the sensitive cell lines decreased further by co-culture (IC50 change from 5.92 uM to 2.79 uM in PE01, and from 2.05 uM to 1.51 uM in OVCAR5). No changes in cell proliferation, or resistance to platinum occurred in the platinum resistant cells. Use of conditioned media of resistance cells did not change proliferation, or response to platinum of sensitive cells. RNAseq detected 3840 differentially expressed genes; 1774 upregulated and 2066 downregulated. IPA analysis showed enrichment of the cell cycle pathways (Cell Cycle Control, Cyclins and Cell Cycle Regulation, among others) and upregulation of cell proliferation genes including the E2F1 transcription factor. Western blot and qRT-PCR confirmed upregulation of E2F1 in co-cultured platinum sensitive cells vs cells in monoculture. Furthermore, western blot measurements showed increased levels of other proteins involved in cell cycle regulation such as CDK4 and CDK6. Cell cycle analysis indicated an increase of cells in S and G2 phase in the co-cultured platinum sensitive cells (18.8% up G2 phase; p = 0.031). Treatment with the CDK4/6 inhibitor Palbociclib or with the E2F1 inhibitor HLM006474 reverted the increase in proliferation rate.
Conclusion: Long term cohabitation of platinum-sensitive and -resistant cancer cells drives sensitive cells to a higher proliferative state, which is more responsive to platinum. Direct cell-cell contact modulates cell cycle progression in sensitive cells through a mechanism regulated by E2F1. Our data reveal unexpected effects caused by interactions between cancer cells with different proliferative rates and levels of platinum resistance, modelling competition between cells in heterogeneous tumors.
Citation Format: Andres Felipe Valdivia, Matthew Cowan, Guangyuan Zhao, Horacio Cardenas, Daniela Matei. E2F1 regulates cell competition, increase proliferation and inhibits chemotherapy resistance in cancer cells [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 2978.