THE INHIBITION OF ATR INCREASES CISPLATIN SENSITIVITY IN MISMATCH REPAIR-DEFICIENT COLON TUMOR CELLS

CAYADO GUTIERREZ N; ANALÍA REDONDO; CUELLO-CARRIÓN F.D.; FANELLI M.A*; VARGAS-ROIG L; NADIN S

Congreso; XLI Reunión científica anual de la Sociedad de Biología de Cuyo; 2023

Hereditary Nonpolyposis Colorectal Cancer is characterized by Mismatch repair (MMR) deficiency which is associated with cisplatin (cPt) resistance. cPt is a chemotherapeutic drug widely used to treat several types of human tumors. The activation of the ATR/CHK1 signaling pathway is critical for cPt-induced DNA damage response (DDR). It plays a crucial role in regulating cell cycle progression, promoting DNA repair, and triggering apoptosis. Previously we demonstrated that Hsp27 interacts with DNA MMR proteins in human colon cancer cells. Hsp27 is a molecular chaperone overexpressed in many tumor types, plays a crucial antiapoptotic role, and has been associated with cPt resistance. Accordingly, the ATR pathway and Hsp27 have become attractive therapeutic targets. This study aims to investigate ATR/CHK1 pathway and Hsp27 roles in cPt-exposed human colon cancer cell lines: HCT116+ch2 (MMR deficient, MMR-) and HCT116+ch3 (MMR proficient, MMR+). ATR was inhibited by VE-821 (VE) and Hsp27 was downregulated with OGX-427 before cPt treatment. Cells were treated with 10 μM cPt for 24 h and collected at time 0 (immediately after cPt treatment, T0), 3 (T3), 9 (T9) and 24 (T24) h post-treatment. Cellular viability was determined by CCK8 and the expression of pCHK1 (Ser345), γH2AX (Ser139, marker of DNA double-strand breaks), and Hsp27 was analyzed by Western blot. Combined therapy with cPt+VE significantly reduced cell viability, especially in MMR- cells (p