Neverthe less, MDR1 expression was more robustly till up regulated following exposure to both epigenetic modulating drugs. It might be questioned whether the analyzed region of the MDR1 gene is critical for regulation of expression. None theless, it has been previously demonstrated that the CpG island analyzed in our study was involved in the regulation of MDR1 transcriptional Inhibitors,Modulators,Libraries activity and that it was densely methylated in PCa. Alternatively, the possibility that exposure to DAC and TSA leads to re activation of genes which positively regulate MDR1 can not be dismissed. To further investigate whether histone modification might be involved in MDR1 silencing in PCa, we com pared histone active marks at the MDR1 gene promoter, after exposure to TSA alone or in combination with DAC, compared to untreated cells.

We found an overall en hancement in these active marks following exposure to TSA and/or DAC, in particular the H3K4me2 mark. Im portantly, these findings were correlated, at protein level, with an increase Inhibitors,Modulators,Libraries in P gp expression. Interestingly, enhancement of H3Ac at the MDR1 promoter has been previously correlated with gene activation in sarcoma cell lines. Thus, our results indicate that histone onco modifications are likely to be the most important epigenetic event associated with MDR1 downregulation in PCa, although it is associated with dense Inhibitors,Modulators,Libraries CpG island methylation. There is some controversy regarding which epigenetic alteration arises first and how it relates to effective gene silencing. Remarkably, in PCa, histone onco modifications herald CpG methylation in RASSF1A downregulation whereas the opposite occurs for GSTP1 inactivation.

Although either scenario might fit our observations, the occurrence of promoter methylation early in prostate carcinogenesis and the experimental gene re expression observed following Inhibitors,Modulators,Libraries exposure to epi genetic modulating drugs without significant changes in promoter methylation levels, suggest that CpG methyla tion precedes histone onco modifications. MDR1 has been associated with the multidrug resist ance phenotype. Thus, from a biological standpoint, it is almost counterintuitive that MDR1 gene silencing is as sociated with PCa development and progression as the loss of P gp expression may be interpreted as an unfavorable change for neoplastic Inhibitors,Modulators,Libraries cells. However, even in other tumor models, P pg expression was found to be higher in localized than in metastatic disease also indicating a connection between P gp loss of expression selleckchem AZD9291 and tumor progression. This is also supported by the previous finding that MDR1 downregulation was associated with increased cell prolifera tion and unaltered apoptosis in PCa. Nevertheless, MDR1 silencing may also provide a therapeutic opportunity PCa treatment.