Overexpression of BLM promotes DNA damage and increased sensitivity to platinum salts in triple-negative breast and serous ovarian cancers

Background

Platinum-based therapy is an effective treatment for a subset of triple-negative breast cancer and ovarian cancer patients. In order to increase response rate and decrease unnecessary use, robust biomarkers that predict response to therapy are needed.

Patients and methods

We performed an integrated genomic approach combining differential analysis of gene expression and DNA copy number in sensitive compared with resistant triple-negative breast cancers in two independent neoadjuvant cisplatin-treated cohorts. Functional relevance of significant hits was investigated in vitro by overexpression, knockdown and targeted inhibitor treatment.

Results

We identified two genes, the Bloom helicase (BLM) and Fanconi anemia complementation group I (FANCI), that have both increased DNA copy number and gene expression in the platinum-sensitive cases. Increased level of expression of these two genes was also associated with platinum but not with taxane response in ovarian cancer. As a functional validation, we found that overexpression of BLM promotes DNA damage and induces sensitivity to cisplatin but has no effect on paclitaxel sensitivity.

Conclusions

A biomarker based on the expression levels of the BLM and FANCI genes is a potential predictor of platinum sensitivity in triple-negative breast cancer and ovarian cancer.

Abstract P3-04-08: A proteo-probe for nucleotide excision repair in breast cancers

The response of tumor cells to DNA damaging agents is often compromised, a weakness readily exploited for therapeutic purposes. Despite the general use of genotoxic treatments, the nature and extent of DNA damage in tumor cells is generally under-investigated, or remains unknown. We postulate DNA repair deficient breast tumor cells exhibit significantly more DNA damage after genotoxic treatments, compared to repair proficient cells.

We present a technology to detect specific DNA damage and monitor repair as a basis to categorize cancers into homogenous groups of malignancies. We rely on the use of biochemically purified DNA damage recognition complexes as ready-to-use reagents, or “proteo-probes” for DNA damage.

We developed a proteo-probe based on a purified DDB2 protein complex. DDB2 is a DNA damage recognition protein part of the nucleotide excision repair (NER) that recognizes and repairs bulky DNA adducts caused for example by UV irradiation or cisplatin. We show the DDB2 proteo-probe binds to nuclei of UV-irradiated cells. We followed the DDB2 proteo-probe signal over time, and observed a decrease concordant with the completion of NER. We then successfully distinguished repair proficient cells from genetically characterized NER-deficient cells obtained from patients. We conclude the DDB2 proteo-probe can be used to detect activation of NER by UV-induced DNA damage, and subsequent repair in situ.

It has been proposed that some breast cancers carry NER deficiencies. We screened a panel of cancer cell lines using the DDB2 proteo-probe and discovered obvious NER deficient (NER-D) cell lines. In addition, we correlated NER activity with cisplatin sensitivity. We further determined whether NER deficiency in breast cancer cell lines was caused by loss-of-function of NER genes through complementation.

The classification of breast cancer cell lines based on NER activity presented here suggests more investigation is needed about NER in breast cancers. Ultimately, we envision NER deficiencies could be used to select breast cancer patients for DNA-repair targeted therapy.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-04-08.