Samenvatting
Multiple Myeloma (MM) is a still incurable clonal neoplasia of mature plasma cells in the bone marrow (BM), resulting in an excess production of monoclonal antibodies. Studies indicate that next to genetic defects, changes in the epigenetic regulation also play a major role in MM pathogenesis. The best studied epigenetic modifications are DNA methylation and post-translational histone modifications (PTMs, e.g. acetylation and methylation). These epigenetic modifications co-operate intensively to control chromatin compactness and thus gene expression. In cancer, the epigenetic landscape is completely disturbed. Intergenic regions are often hypomethylated leading to genomic instability, while promoter-associated CpG islands of tumor suppressor genes are instead hypermethylated and/or deacetylated leading to a loss-of-function. Of interest, these epigenetic aberrations are reversible and thus present interesting new targets for therapeutic intervention. Two main classes of anti-cancer agents that target the epigenetic regulation of gene expression are the histone deacetylase (HDAC) and DNA methyltransferase (DNMT) inhibitors. Both classes have extensively been validated to have anti-cancer activity. In addition, HDACi were also found to have potent anti-MM effects. However, little is known about the anti-MM effects of the DNMTi decitabine (DAC), especially about its direct cytotoxic properties.Here, we first investigated the direct anti-MM effect of DAC and the underlying mechanisms of action using a panel of different human cell lines and the murine 5T33MM model. Based on DAC sensitivity we could divide the cells into 1) a DAC-sensitive group, showing a G2/M phase arrest and rapid DAC-induced cell death and 2) a more DAC-resistant group, presenting a delayed G0/G1 arrest followed by apoptosis. In both groups, however, apoptosis is caspase-mediated. In both groups, DAC was also shown to induce DNA damage as evidenced by an increase in ?-H2AX. However, in contrast to the DAC-resistant group, the first group was not able to cope with the DAC-induced DNA damage, as evidenced by massive accumulation of ?-H2AX and intensive chromatin remodeling. The anti-MM activity of DAC was also confirmed in vivo. In the 5T33MM model, DAC induced a significant decrease in tumor load and increase in survival rates. Since epigenetic regulation is based on the intensive cooperation between DNA methylation and PTMs, we hypothized that combination of DAC with a HDACi might further augment the sensitivity towards DAC. In the past, the host lab already demonstrated potent anti-MM effects of the HDACi JNJ-26484585 (JNJ). Therefore, we used this agent to investigate the potential synergistic anti-MM effects of DAC in combination with JNJ. Co-treatment was found to synergistically induce MM apoptosis and enhance cleavage of caspases and PARP compared to either agents alone. Moreover, in vivo we observed a significant decrease in tumor load and increase in survival probability compared to treatment with either agents.
In short, we demonstrated preclinical anti-MM effects of DAC in vitro and in vivo. Mechanistically, DAC induced DNA damage followed by either a rapid G2-phase or a delayed G1-phase arrest and subsequent caspase-mediated apoptosis. In addition, JNJ further potentiates the anti-MM activity of DAC.
| Datum prijs | 14 jun 2013 |
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| Originele taal | English |
| Begeleider | Elke De Bruyne (Promotor) |