5-aza-2'-Deoxycytidine enhances the radiosensitivity of breast cancer cells.
OBJECTIVE
To investigate the effect of the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (DAC), on radiosensitivity in breast cancer cells.


METHODS
Two breast cancer cell lines, MDA-MB-231 and MDA-MB-435, were evaluated. The methylation status and the mRNA expression of three genes (ER, PR, and HIC-1) that were frequently hypermethylated in these cell lines were determined as a function of DAC exposure. 3-(4,5)-dimethylthiahiazo-(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) absorbance and a colony-forming assay were used to estimate cell viability and radiosensitivity. Using cell-cycle analysis, γ-histone H2A (γ-H2AX) formation assays and methylation-specific polymerase chain reaction (MSP) analysis of three genes correlated with radiosensitivity (BRCA1, 14-3-3σ, and E-cadherin), the mechanism of DAC enhancement of radiosensitivity was explored.


RESULTS
DAC induced the demethylation and reactivation of silent genes in both cell lines. The combination of DAC and irradiation induced growth suppression in vitro. DAC, 5 μM, enhanced sensitivity to ionizing radiation. DAC followed by irradiation correlated with G2/M arrest and the retardation of repair of radiation-induced double strand breaks. DAC reversed the methylation status of genes connected with radiosensitization. The different radiosensitization effects observed with different breast cancers cells may correlate with the primary methylation status of radiosensitizing genes.


CONCLUSIONS
Treatment strategies that include DAC present promising options for sensitizing breast cancer cells to irradiation.
Department of Pathology, Kunming General Hospital, Kunming, Yunnan, China.
Li
L
Wang
Yong
Y
Zhang
RongQing
R
Li
Yue
Y
Chen
XinYan
X
Pan
GuiYun
G
Li
Fang
F
Dai
JuLun
J
Yang
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D003114:Colony-Forming Units Assay; D019175:DNA Methylation / Q000187:drug effects; D000077209:Decitabine; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects* / Q000528:radiation effects; D006801:Humans; D012333:RNA, Messenger / Q000235:genetics; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
D000964:Antimetabolites, Antineoplastic; D012333:RNA, Messenger; D011838:Radiation-Sensitizing Agents; D000077209:Decitabine; D001374:Azacitidine