Analysis of DNA Repair–Related Genes in Breast Cancer Reveals CUL4A Ubiquitin Ligase as a Novel Biomarker of Trabectedin Response

Abstract

Trabectedin is more active in nucleotide excision repair (NER)-efficient and homologous recombination repair (HRR)-deficient cells. As 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 were determined in cell lines. Survival assays after trabectedin treatment were conducted in CUL4A-silenced BRCA1-proficient and -deficient cells. Because of limited phase II clinical trials evaluating trabectedin efficacy in patients with breast cancer, 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 nontranslocation-related patients with sarcoma predicted improved progression-free survival [PFS; HR, 0.37; 95% confidence interval (CI), 0.20-0.68, P ¼ 0.001] and overall survival (OS; HR, 0.44; 95% CI, 0.21-0.93, P ¼ 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. Mol Cancer Ther; 12(4); 530-41. Ó2013 AACR.

CUL4A contributes to the biology of basal-like breast tumors through modulation of cell growth and antitumor immune response

“…In this regard our data suggest that the 13q34 amplification could be a robust biomarker for identification of up to 20% basal-like breast cancer patients [12, 13] that might eventually benefit from CUL4A -targeted therapy. Interestingly, in previous studies we observed increased sensitivity to trabectedin in breast cancer cell lines exhibiting high levels of CUL4A in combination with a “BRCAness” status [28]. The potential therapeutic option of CUL4A- targeting in certain subtypes of breast cancer has also been discussed in a recent study reporting a fundamental role of CUL4A in regulating the metastatic behavior of breast cancer cells [11].…”

CUL4A ubiquitin ligase: a promising drug target for cancer and other human diseases

“…It was shown that high CUL4A expression levels confer prostate and breast cancer cell sensitivity to thalidomide and trabectedin, respectively [99,133]. Thus, screening for CUL4A levels in cancer patients may help in achieving better drug response with minimal unwanted side effects.…”

Knockdown of CUL4A inhibits invasion and induces apoptosis in osteosarcoma cells

“…17 But, few studies show that high expression of CUL4A predicts improved progression-free survival and overall survival of breast cancer. 18 In the present study, we further evaluated the expression of CUL4A in OS tissues and found that upregulation of CUL4A, mainly localized in the nucleus, was positively correlated with distant metastases in OS patients but was negatively associated with p27 expression, 10 suggesting that nuclear accumulation of CUL4A might promote the tumorigenesis of OS.…”