THE INHIBITION OF ATR INCREASES CISPLATIN SENSITIVITY IN MISMATCH REPAIRDEFICIENT COLON TUMOR CELLS

CAYADO-GUTIERREZ, NIUBYS; FANELLI, MARIEL; REDONDO, ANALIA L; CUELLO-CARRIÓN, DARIO; VARGAS ROIG, LAURA M; NADIN, SILVINA B

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 signalingpathway is critical for cPt-induced DNA damage response (DDR). It plays a crucial role in regulating cell cycle progression, promoting DNArepair, 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 cPtresistance. Accordingly, the ATR pathway and Hsp27 have become attractive therapeutic targets. This study aims to investigate ATR/CHK1pathway and Hsp27 roles in cPt-exposed human colon cancer cell lines: HCT116+ch2 (MMR deficient, MMR-) and HCT116+ch3 (MMRproficient, MMR+). ATR was inhibited by VE-821 (VE) and Hsp27 was downregulated with OGX-427 before cPt treatment. Cells weretreated 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