Decitabine, differently from DNMT1 silencing, exerts its antiproliferative activity through p21 upregulation in malignant pleural mesothelioma (MPM) cells.

Malignant pleural mesothelioma (MPM) is a locally aggressive neoplasm, principally linked to asbestos fibres exposure. Strong evidences associate this pollutant with induction of DNA breaks, aberrant chromosomes segregation and important chromosomal rearrangements, considered crucial events in malignant transformation. A considerable contribution to cellular transformation in MPM is also given by the presence of high genomic instability, as well as by the increased DNA methylation, and consequent decreased expression, of tumor-suppressor genes. In this study we first demonstrated that MPM cells are characterized by a decreased methylation level of pericentromeric DNA sequences which can justify, at least in part, the genomic instability observed in this neoplasia. Concomitantly, we found a paradoxical increased expression of DNMT1, the most expressed DNA methyltransferases in MPM cells, DNMT3a and all five isoforms of DNMT3b. Thus, we compared two experimental strategies, DNMT1 silencing and usage of a demethylating agent (5-aza-2'-deoxycytidine or Decitabine), both theoretically able to revert the locally hypermethylated phenotype and considered potential future therapeutic approaches for MPM. Interestingly, both strategies substantially decrease cell survival of MPM cells but the antitumor activity of Decitabine, differently from DNMT1 silencing, is mediated, at least in part, by a p53-independent p21 upregulation, and is characterized by the arrest of MPM cells at the G2/M phase of the cell cycle. These results indicate that the two approaches act probably through different mechanisms and, thus, that DNMT1 silencing can be considered an effective alternative to Decitabine for cancer treatment.

Imiquimod and S-27609 as adjuvants of DNA vaccination in a transgenic murine model of HER2/neu-positive mammary carcinoma.

DNA vaccination against HER-2/neu is an effective way to induce an immune response able to oppose the spontaneous development of mammary tumours occurring in HER-2/neu transgenic mice. In this study, we have evaluated the potential of Imiquimod and the analogue S-27609 as adjuvants of DNA vaccination against HER-2/neu in transgenic mice. The association of a DNA vaccine encoding a portion of rat HER2/neu with either Imiquimod or S-27609 was found to delay the development of spontaneous mammary tumours and to reduce their incidence, in comparison with DNA vaccination alone. Almost 80 or 40% of tumour-free mice were found at the end of measurement time in mice vaccinated and supplemented with Imiquimod or S-27609, respectively. The antitumour preventive effect was associated with increased antibody and cell-mediated immune responsiveness against HER-2/neu. In mice vaccinated and supplemented with Imiquimod, a small but significant increase of rat p185neu-specific cytotoxicity and of IFN-gamma and IL-2-producing CD8T cells, together with a reduction of IL-4-producing CD4T cells, and a switch from an IgG1 towards a IgG2a phenotype of anti-p185neu antibodies, suggested a TH1 polarization of the immune response. The immunoregulatory efficacy of S-27609 was lower than that observed for Imiquimod. These data highlight the potential of Imiquimod, and, to a lower extent, of S-27609, as immunological adjuvants of therapeutic DNA vaccines.