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Quantitative imaging of RAD51 expression as a marker of platinum resistance in Ovarian Cancer

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 high-RAD51 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 high-RAD51 EOC. The qIHC approach is generalizable to other proteins with a continuum instead of discrete/bimodal expression.

ORGANISM(S): Homo sapiens

PROVIDER: GSE166539 | GEO | 2021/02/11

REPOSITORIES: GEO

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Project description:Purpose:Triple negative breast cancer (TNBC) commonly metastasizes to the brain and predicts poor prognosis with limited therapeutic options. TNBC frequently harbors BRCA mutations translating to platinum sensitivity; platinum response may be augmented by additional suppression of DNA repair mechanisms through poly(ADP-ribose)polymerase (PARP) inhibition. We evaluated brain penetrance and efficacy of Carboplatin +/- the PARP inhibitor ABT888, and investigated gene expression changes in murine intracranial (IC) TNBC models stratified by BRCA and molecular subtype status. Experimental design:Athymic mice were inoculated intra-cerebrally with BRCA-mutant: SUM149 (basal), MDA-MB-436 (claudin-low), or BRCA-wild-type: MDA-MB-468 (basal), MDA-MB-231BR (claudin-low) TNBC cells and treated with PBS control (IP, weekly), Carboplatin (50mg/kg/week, IP), ABT888 (25mg/kg/day, OG), or their combination. DNA-damage (?-H2AX) and apoptosis (cleaved-Caspase-3(cC3)) were assessed via IHC of IC tumors. Gene expression of BRCA-mutant IC tumors was measured. Results: Carboplatin+/-ABT888 significantly improved survival in BRCA-mutant IC models compared to control, but did not improve survival in BRCA-wild-type IC models. Carboplatin+ABT888 revealed a modest survival advantage versus Carboplatin in BRCA-mutant models. ABT888 yielded a marginal survival benefit in the MDA-MB-436 but not in the SUM149 model. BRCA-mutant SUM149 expression of ?-H2AX and cC3 proteins was elevated in all treatment groups compared to Control, while BRCA-wild-type MDA-MB-468 cC3 expression did not increase with treatment. Carboplatin treatment induced common gene expression changes in BRCA-mutant models.Conclusions: Carboplatin+/-ABT888 improves survival in BRCA-mutant IC TNBC models with corresponding DNA damage and gene expression changes. Combination therapy represents a promising treatment strategy for patients with TNBC brain metastases warranting further clinical investigation. reference x sample

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Quantitative imaging of RAD51 expression as a marker of platinum resistance in Ovarian Cancer

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