21083 Background: While BRCA1 germline mutations are uncommon, and contribute to fewer than 5% of breast cancer cases, epigenetic alterations in BRCA1 occur more frequently. BRCA1 promoter methylation has been detected in 10–30% of breast tumors. Given the role of BRCA1 in DNA repair and cell cycle regulation, we hypothesize that cells with decreased expression of BRCA1 secondary to promoter methylation will be sensitive to DNA damaging agents and resistant to microtubule inhibitors, as has previously been shown for cells deficient in BRCA1 secondary to mutation. Methods: BRCA1 methylation was determined using methylation specific PCR (MSP) as previously described (Wei et al, Cancer Research 2005). The relative sensitivities of BRCA1 methylated, mutated and competent cells to cisplatin and paclitaxel were determined in five representative breast cancer cell lines using the AlamarBlue cytotoxicity assay. Exponentially growing cells were treated with increasing concentrations of cisplatin and paclitaxel for 96 hours. IC50 values and 95% confidence intervals (CI) were calculated from sigmoidal dose response curves fitted with SAS 9.1 Proc NLIN. Western blot analysis for BRCA1 was performed on each cell line. Results: Conclusions: Only one of the two BRCA1 methylated cell lines studied (UACC3199) was sensitive to cisplatin and resistant to paclitaxel, as hypothesized. While both cell lines are methylated, western blot analysis revealed that both express BRCA1, but to a lesser degree than unmethylated cells. BRCA1 methylation, as assessed by non-quantitative MSP, does not correlate with sensitivity to cisplatin and resistance to paclitaxel. Quantification of BRCA1 promoter methylation may better predict chemosensitivity. Identification of the degree of BRCA1 methylation which does correlates with sensitivity to cisplatin and resistance to paclitaxel could improve treatment selection for patients with breast cancer. This work was supported by the US Army Grant W81XWH-04–1-0545. [Table: see text] No significant financial relationships to disclose.
Association of BRCA1 promoter methylation with sporadic breast cancers: Evidence from 40 studies
