Source1Group of Human Genetics, Human Cancer Genetics Program, Spanish National Cancer Centre (CNIO). Abstract
Trabectedin is more active in Nucleotide Excision Repair (NER)-efficient and Homologous Recombination Repair (HRR)-deficient cells. Since up to 25% of sporadic breast tumors present somatic inactivation of the HRR pathway (BRCAness-phenotype) we sought to characterize trabectedin effect in BRCA1-proficient and BRCA1-null breast cancer cell lines. We evaluated whether HRR and NER-gene expression correlates with trabectedin sensitivity and explored the response-predictive value of the CUL4A ubiquitin ligase, which ubiquitinates NER pathway members. We characterized trabectedin cytotoxicity, cell cycle effects and BRCA1, BRCA2, XRCC3, XPG, ERCC1 and CUL4A expression in 10 breast cancer cell lines. Gene expression and trabectedin sensitivity association was determined in cell lines. Survival assays after trabectedin treatment were performed in CUL4A-silenced BRCA1-proficient and deficient cells. Due to limited Phase-II clinical trials evaluating trabectedin efficacy in breast cancer patients, we assessed CUL4A immunohistochemical staining in a retrospective series of 118 sarcomas from trabectedin-treated patients to validate in vivo our in vitro observations. In cell lines greater trabectedin sensitivity was associated with higher CUL4A expression and lower BRCA1/ERCC5, BRCA1/CUL4A and XRCC3/CUL4A expression ratios. In agreement, BRCA1-deficient CUL4A-knockdown cells presented higher cell survival after trabectedin exposure than did scramble-control cells. Lack of effect in BRCA1-proficient cells suggests that HRR impairment is key in CUL4A-mediated trabectedin sensitivity. High-CUL4A expression in non-translocation-related sarcoma patients predicted improved PFS (HR=0.37, 95% CI=0.20-0.68, p=0.001) and OS (HR=0.44, 95% CI=0.21-0.93, p=0.026). Our observations support the notion of greater trabectedin activity in tumors exhibiting "BRCAness" and reveal CUL4A as a potential biomarker for definition of trabectedin target patients.