Assessing mutant p53 in primary high-grade serous ovarian cancer using immunohistochemistry and massively parallel sequencing.

Alexander J Cole,Jayne Maidens,Adele Clarkson,Roderick Clifton-Bligh,Anthony J Gill,Trisha Dwight,Gregory B Gard,Kristie-Ann Dickson,Susan Valmadre,Ying Zhu,Deborah J Marsh

doi:10.1038/srep26191

Abstract

The tumour suppressor p53 is mutated in cancer, including over 96% of high-grade serous ovarian cancer (HGSOC). Mutations cause loss of wild-type p53 function due to either gain of abnormal function of mutant p53 (mutp53), or absent to low mutp53. Massively parallel sequencing (MPS) enables increased accuracy of detection of somatic variants in heterogeneous tumours. We used MPS and immunohistochemistry (IHC) to characterise HGSOCs for TP53 mutation and p53 expression. TP53 mutation was identified in 94% (68/72) of HGSOCs, 62% of which were missense. Missense mutations demonstrated high p53 by IHC, as did 35% (9/26) of non-missense mutations. Low p53 was seen by IHC in 62% of HGSOC associated with non-missense mutations. Most wild-type TP53 tumours (75%, 6/8) displayed intermediate p53 levels. The overall sensitivity of detecting a TP53 mutation based on classification as ‘Low’, ‘Intermediate’ or ‘High’ for p53 IHC was 99%, with a specificity of 75%. We suggest p53 IHC can be used as a surrogate marker of TP53 mutation in HGSOC; however, this will result in misclassification of a proportion of TP53 wild-type and mutant tumours. Therapeutic targeting of mutp53 will require knowledge of both TP53 mutations and mutp53 expression.

Highlights

The tumour suppressor p53 is mutated in cancer, including over 96% of high-grade serous ovarian cancer (HGSOC)
All missense mutations had been previously reported in The Cancer Genome Atlas ovarian study[18] and/or the International Agency for Research on Cancer (IARC) TP53 database (Supplementary Table S1)
Using Massively parallel sequencing (MPS), we identified 94% (68/72) of HGSOC with TP53 mutation and 100% (4/4) of low-grade serous ovarian cancer (LGSOC) were wild-type for TP53, similar to recent studies[18,19,24]

Summary

Introduction

The tumour suppressor p53 is mutated in cancer, including over 96% of high-grade serous ovarian cancer (HGSOC). Pathogenic mutations result in loss or abrogation of wild-type p53 activity, a major mechanism likely being the inability of mutp[53] to bind to response elements in DNA, preventing its function as a transcription factor. Along with the loss of wild-type function, many TP53 mutations result in gain of an oncogenic function for the mutp[53] protein These ‘gain-of-function’ (GOF) TP53 mutations cause mutp[53] to accumulate at high levels in cells, contributing to tumorigenesis and the development of drug resistance[1]. Strategies include restoring normal transcriptional activity of mutp[53] by restoration of wild-type protein folding using drugs such as APR-246 that are currently recruiting for Phase Ib/II clinical trials for recurrent high-grade serous ovarian cancer (HGSOC)[12] or zinc metallochaperones[13]. It is clear that success of these different approaches will be influenced by the type of TP53 mutation present, and whether it results in accumulation of mutp[53] in the cell, severe truncation of the p53 protein, or low to absent levels of p53

Methods

Results

Conclusion