Abstract 1079: A synthetic lethal strategy using PARP and ATM inhibition for overcoming trastuzumab-resistance in HER2-positive cancers

Abstract

Abstract Background: DNA damage response (DDR) pathway is essential for maintaining genomic stability, cell survival, and tumorigenesis. However, the roles of DDR pathway in HER2-positive tumors remain unclear. This study aims to discover the function of DDR in trastuzumab-resistant (TR) cells to better understand HER2-biology and to suggest novel treatment strategy using DDR-targeting agents in HER2-positive TR tumors. Methods: Four HER2-positive TR cell lines (NCI-N87TR, SNU-216TR, SNU-2670TR, and SNU-2773TR) and their corresponding parental cells (NCI-N87, SNU-216, SNU-2670, and SNU-2773) were subject to immunoblotting to identify expression profiles of DDR proteins. Proteasome inhibitor MG-132 and cycloheximide chase assay were used for understanding PARP1 dynamics in TR cells. MTT assay and colony-forming assay were performed to evaluate antiproliferative effect of PARP inhibitor (PARPi, olaparib), ATM inhibitor (ATMi, AZD0156) and ATR inhibitor (ATRi, Ceralasertib). DNA damage and homologous recombination repair (HRR) efficiency were measured by comet assay and immunofluorescence respectively. Cell cycle analysis using flow cytometry was performed to assess drug-induced apoptosis. Results: Increase of PARP1 expression was observed in all four TR cells. Decreased proteasomal degradation of PARP1 was found in TR cells compared to parental cells. Olaparib showed better anti-proliferative effect in TR cells compared to parental cells. After treating with olaparib, there was a defect in formation of Rad51 foci, instead, there was induction of phosphorylation of ATM and ATR in TR cells, which might attenuate the effects of olaparib in TR cells. Combination of olaparib with AZD0156 showed stronger anti-tumor effect than olaparib monotherapy in TR cells. Moreover, synthetic lethal interaction was observed by olaparib/AZD0156 combination in TR cells. Interestingly, this synthetic lethal interaction was exclusively occurred in TR cells not in parental cells. Even though olaparib and ceralasertib combination showed better anti-tumor effect than each single drug in some TR cells, synthetic lethal interaction was not observed by olaparib/ceralasertib combination in TR cells. Conclusion: Dual inhibition of PARP1 and ATM could be a good strategy to overcome the resistance to trastuzumab in HER2-positive cancers using its synthetic lethal interaction. Citation Format: Kyoung-Seok Oh, Ah-Rong Nam, Ju-Hee Bang, Hye-Rim Seo, Jae-Min Kim, Jeesun Yoon, Tae-Yong Kim, Do-Youn Oh. A synthetic lethal strategy using PARP and ATM inhibition for overcoming trastuzumab-resistance in HER2-positive cancers [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 1079.