Abstract 4852: Induction of HRD by targeting G9a and MTDH in DNA repair proficient endometrial cancer cells

Abstract

Abstract The homologous recombination repair (HRR) pathway is required for high-fidelity repair of double-strand DNA breaks. Cancer cells with HRR deficiency due to somatic BRCA1 or BRCA2 mutations are sensitive to platinum agents and targeted therapy with PARP inhibitors. Endometrial cancer is the most common cancer of the female reproductive system. DNA damage agents are commonly used in treatment but tumors often develop resistance. Metadherin (MTDH) has been shown to be amplified in a wide range of solid tumors as well as in leukemia and lymphoma. Overexpression of MTDH is correlated with angiogenesis, metastasis, and chemoresistance. Histone lysine N-methyl-transferase G9a catalyzes the demethylation of histone H3 at lysine residue 9 (H3K9) resulting in a repressive histone modification. The objective of this study is to validate the function of MTDH and G9a in HRR and test the potential to target MTDH or G9a to increase drug sensitivity. p21 expression was induced when G9a was depleted. DNA damage induced MTDH expression at 4 hours after 8Gy γ-irradiation in the well validated endometrial adenocarcinoma cell line Ishikawa H. However, induction of MTDH protein expression by the same radiation dosage was reduced when G9a was depleted. The G9a inhibitor UNC0642 itself can also induce the expression of MTDH after 24 hours treatment. Ishikawa parental cells and two Ishikawa sub-cell lines in which G9a was depleted by CRISPR were tested for the DNA damage biomarker γH2Ax and Rad51 foci formation at 4 hours following 8Gy irradiation. G9a depletion was shown to decrease Rad51 foci formation and to increase the formation of γH2Ax foci. Two natural products, Celastrol and Pristimerim were found to inhibit MTDH, FANCD2 and FANCI protein levels, which may be used to induce BRCA-ness in homologous recombination repair proficient cancer cells. G9a depletion results in the reduction of irradiation-induced Rad51 foci formation and an increase of irradiation-induced γH2Ax foci formation. We suggest that G9a depletion can increase cancer cell sensitivity to DNA damage agents. MTDH is induced by DNA damage and is a G9a inhibitor. MTDH depletion causes reduction of irradiation-induced Rad51 foci. This study is supported by the University of Iowa Department of Obstetrics and Gynecology Research Development Fund, NIH grant R01CA99908 and R01CA184101. Citation Format: Xiangbing Meng, Shujie Yang, Jianling Bi, Yiyang Li, Yuping Zhang, Sudartip Areecheewaku, Mary Li, Zihan Wang, Aliasger K. Salem, Kimberly K. Leslie. Induction of HRD by targeting G9a and MTDH in DNA repair proficient endometrial cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4852.