Genes that suppress
tumorigenesis can be silenced by epigenetic events, such as aberrant DNA methylation and modification of
chromatin structure. Inhibitors of
DNA methylase and
histone deacetylase (HDAC) can potentially reverse these events. The aim of this study was to determine the in vitro
antineoplastic activity of
5-aza-2'-deoxycytidine (5-AZA-CdR), a potent inhibitor of
DNA methylase, in combination with
depsipeptide (depsi), an inhibitor of HDAC, on human
breast carcinoma cells. We observed a synergistic
antineoplastic interaction between 5-AZA-CdR and depsi in their capacity to inhibit colony formation of Hs578T and MCF-7
breast carcinoma cells. In order to understand the molecular mechanism of this interaction, we investigated the effect of these drugs on the activation of the 14-3-3sigma,
E-cadherin and
tissue inhibitor of metalloproteinase 3 (TIMP3)
cancer-related genes, which were reported to be silenced by aberrant methylation in many
breast tumor cell lines. 14-3-3sigma was reported to produce G cell cycle arrest following DNA damage.
E-cadherin and TIMP3 function as suppressors of
tumor metastasis. Semi-quantitative RT-PCR was used to determine the effect of the co-administration of 5-AZA-CdR and depsi on four
breast carcinoma cell lines for the reactivation of these genes. We observed a synergistic activation of
E-cadherin by the combination in Hs578T, MDA-MB-231 and MDA-MB-435
tumor cells. For 14-3-3sigma, we demonstrated an additive to synergistic activation by the combination for Hs578T and MDA-MB-435
tumor cells, respectively. In the MCF-7
tumor cells, the
drug combination produced a synergistic activation of TIMP3. The association between the synergistic
antineoplastic activity and the synergistic activation of the target genes in this study suggests that the mechanism of anticancer activity of 5-AZA-CdR, in combination with depsi, is probably related to their enhanced activation of different types of tumor suppressor genes that have been silenced by epigenetic events.(2)