DNA demethylating antineoplastic strategies: a comparative point of view.

Despite the involvement of genetic alterations in neoplastic cell transformation, it is increasingly evident that abnormal epigenetic patterns, such as those affecting DNA methylation and histone posttranslational modifications (PTMs), play an essential role in the early stages of tumor development. This finding, together with the evidence that epigenetic changes are reversible, enabled the development of new antineoplastic therapeutic approaches known as epigenetic therapies. Epigenetic modifications are involved in the control of gene expression, and their aberrant distribution is thought to participate in neoplastic transformation by causing the deregulation of crucial cellular pathways. Epigenetic drugs are able to revert the defective gene expression profile of cancer cells and, consequently, reestablish normal molecular pathways. Considering the emerging interest in epigenetic therapeutics, this review focuses on the approaches affecting DNA methylation, evaluates novel strategies and those already approved for clinical use, and compares their therapeutic potential

Malten, a new synthetic molecule showing in vitro antiproliferative activity against tumour cells and induction of complex DNA structural alterations

Background: Hydroxypyrones represent several classes of molecules known for their high synthetic versatility. This family of molecules shows several interesting pharmaceutical activities and is considered as a promising source of new anti neoplastic compounds. Methods: In the quest to identify new potential anti cancer agents, a new maltol (3-hydroxy-2-methyl-4-pyrone)-derived molecule, named malten (N,N′-bis((3-hydroxy-4-pyron-2-yl)methyl)-N,N′-dimethylethylendiamine), has been synthesised and analysed at both biological and molecular levels for its antiproliferative activity in eight tumour cell lines. Results: Malten exposure led to a dose-dependent reduction in cell survival in all the neoplastic models studied. Sublethal concentrations of malten induce profound cell cycle changes, particularly affecting the S and/or G2-M phases, whereas exposure to lethal doses causes the induction of programmed cell death (apopotosis). The molecular response to malten was also investigated in two biological models: JURKAT and U937 cells. It showed the modulation of genes having key roles in cell cycle progression and apoptosis. Finally, as part of the effort to clarify the action mechanism, we showed that malten is able to impair DNA electrophoretic mobility and drastically reduce both PCR amplificability and fragmentation susceptibility of DNA. Conclusion: Taken together, these results show that malten may exert its antiproliferative activity through the induction of complex DNA structural modifications. This evidence, together with the high synthetic versatility of maltol-derived compounds, makes malten an interesting molecular scaffold for the future design of new potential anticancer agents

Premature senescence induced by DNA demethylating agent (Decitabine) as therapeutic option for malignant pleural mesothelioma.

The drug-dependent induction of premature senescence in neoplastic cells is considered per se an important tumor suppressive mechanism. DNA demethylating agents recently introduced in clinical trials, such as 5-aza-cytidine (Decitabine) and its derivatives, have been extensively characterized in recent years as antiproliferative compounds that act through multiple mechanisms, which have not yet been fully clarified. We recently analyzed the introduction of Decitabine in therapy for malignant pleural mesothelioma (MPM) observing that, despite the ability to induce profound biological effects in MPM cells, the drug failed to generate a massive apoptotic response. Since one of the most intriguing aspects of DNA demethylating agents is the possibility to accelerate the senescent response of tumor cells, we investigated the hypothesis of Decitabine inducing, in vitro, the premature aging of MPM cells

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\u2032-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

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

THE EXPRESSION OF THE KRAS mRNA ISOFORMS 4A AND 4B IN PLASMA: A COMPARISON BETWEEN LUNG ADENOCARCINOMA PATIENTS AND HEALTHY DONORS THROUGH LIQUID BIOPSY

Background: Liquid biopsy represents an innovative tool in precision oncology to overcome current limitations associated with tissue biopsies. Circulating DNA, but also mRNA could be a useful source of cancer biomarkers. The KRAS gene encodes two splice variants, 4A and 4B. Studies established that the two isoforms are both expressed, the ratio can be altered in tumors, and mutationally activated 4A and 4B both mediate lung carcinogenesis[1]. No data are available about their expression in plasma. We have recently started to collect plasma for a prospective analysis in metastatic lung adenocarcinoma (LA) patients (pts) that are candidate for immunotherapy and chemotherapy. We also started collecting plasma from healthy donors (HD). Herewith we present very preliminary results of a comparison of the KRAS mRNA isoforms (4A and 4B) expression levels between LA pts and HD. Materials and methods: The KRAS isoforms mRNA (4A and 4B) expression levels in plasma were analyzed in 16 LA pts and 5 HD. The plasma from pts was collected at the beginning of the treatment and used to extract the RNA. The RNA was then transcribed in cDNA and 7ng were used to perform the quantitative real-time PCR (RT-qPCR) to detect the KRAS isoforms expression. The RT-qPCR Ct values (the higher value corresponds to a lower mRNA expression level) were converted in Cy0 by a tool for accurate and precise quantification of template and used to compare mRNA expression levels between pts and HD[2]. Data were analyzed with the Mann-Whitney test. Results: The RNA concentration in LA pts and HD was significantly different (p=0.0318): the median concentration value in plasma was 32.3 ng/ml versus 23.5 ng/ml, respectively. A significant difference was also found for the median values of the KRAS isoforms mRNA expression levels between LA pts and HD: Cy0=31.7 versus Cy0=34.6 (p=0.0034), respectively, for KRAS 4A; Cy0=31.5 versus Cy0=34.5 (p=0.0013), respectively, for KRAS 4B. Conclusions: Although in a small size group, these data are very promising. They show a higher concentration of circulating RNA and a higher expression of both the KRAS isoforms in LA pts compared to HD. Patients enrollment is ongoing, and if the data here reported will be still confirmed, circulating KRAS mRNA could be a promising biomarker

Clinical Relevance of ABCB1, ABCG2, and ABCC2 Gene Polymorphisms in Chronic Myeloid Leukemia Patients Treated With Nilotinib

Tyrosine kinase inhibitors (TKIs) have radically changed the outcome of chronic myeloid leukemia (CML) patients in the last 20 years. Moreover, the advent of second generation TKIs, namely nilotinib and dasatinib, have largely increased the number of CML patients achieving deep and sustained molecular responses. However, the possible mechanisms capable of influencing the maintenance of the long-term molecular response are not yet fully known and understood. In this light, polymorphisms in MDR-ABC transporters may influence the efficacy and safety of TKIs. In this study, we examined seven single nucleotide polymorphisms (SNPs) in four ABC transporter genes: ABCC1 rs212090 (5463T>A), ABCC2 rs3740066 (3972C>T), ABCC2 rs4148386 G>A, ABCC2 rs1885301 (1549G>A), ABCG2 rs2231137 (34G>A), ABCG2 rs2231142 G>C, ABCB1 rs1045642 (3435C>T), to determine their effect on the achievement and/or loss of molecular response in 90 CML patients treated with nilotinib. We found that ABCC2 rs3740066 CC and CT as well as the ABCB1 rs1045642 TT genotypes correlated with a higher probability to achieve MR3 in a shorter time (p=0.02, p=0.004, and p=0.01), whereas ABCG2 rs2231137 GG was associated with lower probability of MR3 achievement (p=0.005). Moreover, ABCC2 rs3740066 CC genotype, the ABCB1 rs1045642 CC and TT genotypes were positively correlated with MR4 achievement (p=0.02, p=0.007, and p=0.003). We then generated a predictive model incorporating the information of four genotypes, to evaluate the combined effect of the SNPs. The combination of SNPs present in the model affected the probability and the time to molecular response. This model had a high prognostic significance for both MR3 and MR4 (p=0.005 and p=0.008, respectively). Finally, we found ABCG2 rs2231142 GG genotype to be associated with a decrease risk of MR3 loss. In conclusion, MDR-transporters SNPs may significantly affect the achievement and loss of molecular response in CML patients treated with nilotinib