Abstract 1080: The effect of germline polymorphisms on somatic hotspot mutations in TP53 for the treatment of high-grade serous ovarian carcinoma

Introduction: Due to frequent recurrences and acquired resistance to platinum-based chemotherapy in high-grade serous ovarian cancer (HGS OvCa), it is important to identify novel targets and pathways to overcome drug resistance and improve the outcome of patients with ovarian cancer. TP53, which encodes the transcription factor p53, is mutated in 96% of HGS OvCa . Majority of the studies that establish the relationship between mutations in TP53 and cancer have focused on hotspot somatic mutations. In addition to somatic mutations, nonsynonymous germline single nucleotide polymorphisms (SNPs) at codon 72 play a role in altering the function of p53 and a cancer susceptibility. However, the effect of codon 72 (P72R) polymorphism on somatic mutations in TP53 is not well characterized with regard to the Epithelial to Mesenchymal phenotype and cancer progression. Objective: -Characterize the effect of somatic mutations in TP53 in the presence of the P72R SNP on cellular morphology and the Epithelial to Mesenchymal transition (EMT) transcriptional network. -Determine the effect of somatic mutations in TP53 in the presence of the P72R SNP on proliferation and the cell cycle checkpoint transcriptional network Experimental Procedures: We generated 8 pairs of hotspot mutations in TP53 in the context of the P72 or R72 SNP into p53-null SKOV3 cells. Cell morphology was recorded by fluorescence microscopy. Using CHIP-seq, RNA-seq and immunoblotting, we studied the effect of the polymorphism + mutation on EMT markers like BMP1, CALD1, CAMK2N1, CDH2 that are up-regulated during EMT and genes like CAV2, CDH1, DSP, FGFBP1, IL1RN, KRT19, MITF that are down-regulated during EMT. We used techniques like chromatin immunoprecipitation ChIP-seq, gene expression profiling, and computational methods to construct blueprints of the transcription factors like Cyclin D1, p21 that play a role in cell cycle checkpoint regulation which help understand compromised pathways due to the presence of somatic mutations in combination with germline polymorphisms. Summary: - Hotspot mutants with the R72 SNP cause changes in cell morphology resembling mesenchymal cells whereas mutants with the P72 SNP resemble epithelial cells. This effect can be accounted for by changes in the EMT network. - The hotspot missense mutants with R72 have a greater growth potential in comparison to their P72 counterpart which could explain the Gain of Function (GOF) effect of the former. Conclusions: Germline polymorphisms at codon 72 in the p53 protein plays a significant role in regulating the Gain-of-Function (GOF) effect of TP53 somatic hotspot mutations. This is significant because it will be useful in designing a treatment plan for patients with specific somatic mutations and germline polymorphisms. Citation Format: Cristabelle Madona N. De Souza. The effect of germline polymorphisms on somatic hotspot mutations in TP53 for the treatment of high-grade serous ovarian carcinoma [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 1080.