Abstract 4442: TP53 hot spot mutations in ovarian cancer: Selective resistance to microtubule stabilizing agents in monoclonal cells and comparison of clinical outcomes from The Cancer Genome Atlas data

TP53 is mutated in 96% of high grade serous epithelial ovarian carcinomas (HGS EOC) sequenced by The Cancer Genome Atlas (TCGA). Missense mutations at hot spot codons R273, R248, and R175 are the most common oncogenic TP53 mutations among ovarian cancers. To evaluate if TP53 hot spot mutations confer selective resistance to microtubule stabilizing agents (MSAs), the effects of MSAs on hot spot TP53 mutant ovarian carcinoma cell lines were determined. HGS EOCs that expressed one of the three most common TP53 hot spot missense mutations were also identified and studied using TCGA datasets. The human TP53 wild-type ovarian carcinoma cell line A2780 was stably transfected with an empty vector pCMV-neo or a missense TP53 mutation at hot spot codon 175 (m175), 248 (m248), or 273 (m273). Doubling times and inhibitory concentrations of each cell line treated with the MSAs paclitaxel, epoB, and ixabepilone were determined. Effects of epoB on TP53 expression, phosphorylation, and acetylation, as well as TP53-regulated expression of p21 and mdm2, were examined by Western blot analysis. Expression of TP53 target genes p21, GADD45, BAX, PIDD, NF-kB2, PAI-1, and MDR1 was also measured by RT-PCR. Available TCGA genomic and clinical datasets of HGS EOCs were used to identify patients whose tumors expressed one of the three most common TP53 hot spot mutations. Progression free and overall survival outcomes, TP53 expression levels, and available disease and treatment parameters of patients with the hot spot mutations were compared. PARP cleavage, cell growth and cytotoxicity studies demonstrate that the TP53 mutant cell line m248 is resistant to epoB and is not acetylated during epoB treatment. p21 and PAI-1 were induced by epoB in A2780 cells. Expression of p21, GADD45 and PAI-1 in mutant cell lines was generally down regulated. The cell line m273 is 2-3-fold resistant to paclitaxel, possibly due to high expression of MDR1. Patients identified from available TCGA ovarian cancer datasets whose tumors expressed a TP53 missense mutation at codon R273 (n = 15), R248 (n = 11), or R175 (n = 15) demonstrated 10.8, 12.3 and 17.8 months (p = 0.54) median progression free survival and 84.1, 36.1, and 60.6 months (p = 0.23) median overall survival outcomes, respectively. Differences in TP53 expression level, debulking status, disease stage and grade, and age at presentation between cases grouped according to hot spot mutation were not significant. Monoclonal human ovarian cancer cells with different TP53 hot spot mutations were selectively resistant to MSAs paclitaxel and epoB. Patients with HGS EOC and a TP53 hot spot mutation had comparable charactertistics and outcomes. Mutational studies in monoclonal cell lines may offer limited insight regarding clinical disease in HGS EOC considering the established high genetic instability and heterogeneity of HGS EOC. Citation Format: Brandon-Luke L. Seagle, Gerda Hofstteter, Chia-Ping Yang, Kevin Eng, Oluwatosin Odunsi-Akanji, Kunle Odunsi, Shohreh Shahabi. TP53 hot spot mutations in ovarian cancer: Selective resistance to microtubule stabilizing agents in monoclonal cells and comparison of clinical outcomes from The Cancer Genome Atlas data. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4442. doi:10.1158/1538-7445.AM2015-4442