The combination of decitabine and JNJ-26481585 has synergistic anti-myeloma activity.

Beside genetic defects, epigenetic changes are playing a major role in multiple myeloma (MM). DNA methylation and histone acetylation are the best known epigenetic changes and act together to regulate gene expression. Thus, the combination of epigenetic modulating drugs targeting multiple components of the epigenetic machinery, may have synergistic anti-tumor effects. Here, we investigated the therapeutic potential of the combination of a DNMTi decitabine (DAC) with a HDACi JNJ-26481585. We used the human MM cell line OPM2 and the murine cell line 5T33MMvt for in vitro examination of viability, apoptosis and cell cycle effects. Treatment of the cell lines with either DAC or JNJ-26481585 alone decreased proliferation and cell viability. However, combination of both agents significantly decreased viability compared to single agent treatment. Next, we assessed cell cycle phase distribution and apoptosis following treatment with DAC and/or JNJ-26481585. For OPM-2 cells, JNJ-26481585 alone or in combination with DAC resulted in a G1 phase arrest. For 5T33MMvt cells, a temporal G1 phase arrest was observed accompanied by an increase in subG1 phase in the combination groups compared to single agent groups. Moreover, the combination resulted in an increase of apoptotic MM cells compared to each agent alone. For in vivo testing, we used the murine 5T33MM model to evaluate the prophylactic treatment with DAC and/or JNJ-26481585. Combinatory treatment significantly decreased BM tumor burden and microvessel-density compared to single agent treatment. We can conclude that combinations of HDACi and DNMTi show increased anti-tumor effects, compared to single agents. In the future, we will plan an in vivo survival experiment and investigate the underlying working mechanisms of these drugs in vivo.