Low concentrations of 5-aza-2'-deoxycytidine induce breast cancer stem cell differentiation by triggering tumor suppressor gene expression.

Background: Breast cancer stem cells (BCSCs) are considered the cause of tumor growth, multidrug resistance, metastasis, and recurrence. Therefore, differentiation therapy to reduce self-renewal of BCSCs is a promising approach. We have examined the effects of 5-aza-2 '-deoxycytidine (DAC) on BCSC differentiation. Materials and methods: BCSCs were treated with a range of DAC concentrations from 0.625 to 100 mu M. The differentiation status of DAC-treated BCSCs was graded by changes in cell proliferation, CD44(+)CD24(-) phenotype, expression of tumor suppressor genes, including BRCA1, BRCA2, p15, p16, p53, and PTEN, and antitumor drug resistance. Results: DAC treatment caused significant BCSC differentiation. BCSCs showed a 15%-23% reduction in proliferation capacity, 3.0%-21.3% decrease in the expression of BCSC marker CD44(+)/CD24(-), activation of p53 expression, and increased p15, p16, BRCA1, and BRCA2 expression. Concentrations of DAC ranging from 0.625 to 40 mu M efficiently induce cell cycle arrest in S-phase. ABCG2, highly expressed in BCSCs, also decreased with DAC exposure. Of particular note, drug-sensitivity of BCSCs to doxorubicin, verapamil, and tamoxifen also increased 1.5-, 2.0-, and 3.7-fold, respectively, after pretreatment with DAC. Conclusion: DAC reduced breast cancer cell survival and induced differentiation through reexpression of tumor suppressor genes. These results indicate the potential of DAC in targeting specific chemotherapy-resistant cells within a tumor.