Michal M Hoppe ¹, Patrick Jaynes ¹, Joanna D Wardyn ¹, Sai Srinivas Upadhyayula ¹, Tuan Zea Tan ¹, Stefanus Lie ¹, Diana G Z Lim ², Brendan N K Pang ^1 2, Sherlly Lim ¹, Joe P S Yeong ¹, Anthony Karnezis ³, Derek S Chiu ³, Samuel Leung ³, David G Huntsman ³, Anna S Sedukhina ⁴, Ko Sato ⁴, Monique D Topp ⁵, Clare L Scott ⁵, Hyungwon Choi ⁶, Naina R Patel ⁷, Robert Brown ⁷, Stan B Kaye ⁸, Jason J Pitt ¹, David S P Tan ^1 8, Anand D Jeyasekharan ^1 8

¹Cancer Science Institute of Singapore, National University of Singapore, Singapore.
²Department of Pathology, National University Hospital, Singapore.
³British Columbia Cancer Agency, Vancouver, BC, Canada.
⁴Department of Pharmacogenomics, St. Marianna University, Kawasaki, Japan.
⁵The Walter and Eliza Hall Institute of Medical Research, Parkville, Vic., Australia.
⁶Saw Swee Hock School of Public Health, National University of Singapore, Singapore.
⁷Division of Cancer, Imperial College London, London, UK.
⁸Department of Haematology-Oncology, National University Hospital, Singapore.

Abstract

Early relapse after platinum chemotherapy in epithelial ovarian cancer (EOC) portends poor survival. A-priori identification of platinum resistance is therefore crucial to improve on standard first-line carboplatin-paclitaxel treatment. The DNA repair pathway homologous recombination (HR) repairs platinum-induced damage, and the HR recombinase RAD51 is overexpressed in cancer. We therefore designed a REMARK-compliant study of pre-treatment RAD51 expression in EOC, using fluorescent quantitative immunohistochemistry (qIHC) to overcome challenges in quantitation of protein expression in situ. In a discovery cohort (n = 284), RAD51-High tumours had shorter progression-free and overall survival compared to RAD51-Low cases in univariate and multivariate analyses. The association of RAD51 with relapse/survival was validated in a carboplatin monotherapy SCOTROC4 clinical trial cohort (n = 264) and was predominantly noted in HR-proficient cancers (Myriad HRDscore < 42). Interestingly, overexpression of RAD51 modified expression of immune-regulatory pathways in vitro, while RAD51-High tumours showed exclusion of cytotoxic T cells in situ. Our findings highlight RAD51 expression as a determinant of platinum resistance and suggest possible roles for therapy to overcome immune exclusion in RAD51-High EOC. The qIHC approach is generalizable to other proteins with a continuum instead of discrete/bimodal expression.

Keywords: HRD; RAD51; immune exclusion; multiplexed IHC; ovarian cancer.

© 2021 The Authors. Published under the terms of the CC BY 4.0 license.

PMID: 33709473 DOI: 10.15252/emmm.202013366