Abstract B41: Studying the effect of germline polymorphisms on somatic hotspot mutations in TP53 for the treatment of high-grade serous ovarian carcinoma
Authors: Souza Cristabelle Madona N. de , Chien Jeremy , Madden Jill 
Published: August 2018

Introduction: High-grade serous ovarian carcinomas (HGSOCs) are the most aggressive and histologically important subtype of ovarian cancer. Although over 70% of patients show a complete response to first line of therapy, disease occurrence is observed within 3-5 years and often the subsequent recurrent disease is resistant to platinum-based chemotherapy. Hence it is of importance to identify novel targets and pathways to overcome drug resistance and improve the quality of life of the patient. The gene TP53 encodes the protein p53, a transcription factor that is induced in response to cellular stress and regulates cell cycle arrest, DNA damage repair, and apoptosis, thus inducing an antiproliferative effect on the cell and earning it the title of guardian of the genome. TP53 is found to be mutated in 96.7 % of HGSOC cases, which makes it especially relevant to our study. Most of the somatic mutations found in TP53 are missense mutations that result in amino acid changes at different positions called the hotspot regions and the majority of the studies that understand the relationship of p53 mutations and cancer have focused on hotspot somatic mutations. In addition to somatic mutations, nonsynonymous germline polymorphisms (single-nucleotide polymorphisms) (SNPs) P/R at codon 72 in exon 4 of TP53 play a role in altered p53 function and could pose a risk to cancer susceptibility. Thus, studying the combinatorial role of germline polymorphisms and somatic mutations on cancer progression and recurrence is extremely important to understand HGSOCs and design novel diagnostic and therapeutic tools with a precision medicine approach to overcome the impediments associated with treating HGSOCs.

Experimental Procedures and Aim: To characterize the effect of the P72R germline SNP on sensitivity to cancer therapeutics in cells that have hotspot mutations in TP53: We hypothesize that the P72R SNP regulates sensitivity to common chemotherapeutics like paclitaxel and carboplatin and experimental therapeutics. Moreover, we expect the R72 SNP to be more sensitive to cancer therapeutics in comparison to its P72 counterpart in the cell line having the same hotspot mutation. We will use an isogenic p53 null cell line (SKOV3) with exogenous transduction of mutant TP53 in the context of the P72 or R72 SNP and determine the germline effect by using the same genetic background by: A) testing the effect of common cancer therapeutics mentioned above by using cell viability assays like the SRB assay and Cell Titer Glo assay; B) validating cell death observed by using Annexin V staining, caspase activity assays, and immunoblotting for cleaved PARP and caspase 8; and C) studying the differences in cell cycle arrest induced by chemotherapeutic agents by using cell cycle analysis and immunoblotting for cyclins.

Summary: In summary, the proposed study indicates that the P72R SNP alters the phenotypic behavior of TP53 somatic mutations with the 72R having a greater proliferation rate, sensitivity to therapy, and cell death with the P72 undergoing a negative selection in the population.

Conclusions:

1. Germline polymorphisms at codon 72 in the p53 protein play a significant role in regulating the gain-of-function effect of TP53 somatic hotspot mutations.

2. This regulation encompasses differences in cellular morphology, protein stability, drug resistance, growth potential, cell death, and cell cycle arrest.

3. We aim to further our understanding in elucidating the mechanisms responsible for the relationship between somatic mutations and germline polymorphisms that will ultimately alter the treatment strategies adopted for the patient.

Citation Format: Cristabelle Madona N. de Souza, Jeremy Chien, Jill Madden. Studying 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 AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr B41.