Inhibitors of Histone Deacetylases; evaluation and target identification of a cardioprotective combination therapy for cancer

心肌收缩功能的恶化是成功的癌症治疗的主要限制。此外，心脏功能与癌症相关的发病率和死亡率密切相关。蒽环类药物是公认的抗癌药物，也是许多经典治疗方案的一部分，具有严重的心脏副作用。尽管其具有临床相关性，但对于所涉及的下游靶点和联合治疗的潜在心脏保护机制的了解非常有限。组蛋白去乙酰化酶（HDAC）作为表观遗传阻遏物起作用。最近的研究表明，HDAC抑制剂（HDACi）不仅在各种癌症实体中成功地作为治疗剂，而且在心力衰竭的临床前模型中对心脏有益。尽管HDACi的有益潜力已被证实，但其心脏保护作用的具体下游机制迄今尚未阐明。在我们正在进行的工作中，我们鉴定了伴侣蛋白14-3-3在用伏立诺他（第一种FDA批准的HDACi）治疗后在心肌细胞中被过度乙酰化。我们可以证明，14-3-3的超乙酰化导致与II类HDAC（即HDAC 4和5）的结合减少。核HDAC 4/5作为转录因子（TF）肌细胞增强因子2（MEF 2）的阻遏物，MEF 2是上调导致病理性心脏重塑和功能障碍的基因所必需的。此外，我们发现伏立诺他抑制HDAC 4/5的核输出。相反，伏立诺他导致新生大鼠心室心肌细胞（NRMV）中MEF 2的显著抑制，而HDAC 4和HDAC 5的敲低减弱了伏立诺他依赖性MEF 2抑制。这些结果表明，伏立诺他的保护作用部分由HDAC 4/5传递。因此，我们发现HDAC 4的心肌细胞特异性缺失增加了用蒽环类药物“阿霉素”治疗时对心功能障碍的易感性，并上调了MEF 2靶基因myh 7。myh 7-启动子被进一步确定为以阿霉素依赖性方式与拓扑异构酶IIb结合。基于我们未发表的工作，我们提出HDAC依赖性MEF 2抑制在阿霉素诱导的心脏毒性中的关键作用。这种效果可以通过与HDACi伏立诺他共同治疗来放大。尽管如此，由伏立诺他和独立于TF MEF 2的其他潜在下游靶点引起的表观遗传变化仍然是未知的，这就是为什么它们需要进一步研究的原因。具体目标是：一曰：（a）鉴定心脏中的整体HDACi依赖性表观遗传变化和（B）测定心肌细胞中HDACi靶向的基因组区域。2：确定MEF 2在阿霉素治疗后病理基因调控控制中的作用。第三章：确定伏立诺他在体内与蒽环类药物联合治疗时的潜在心脏保护作用，并通过体外功能获得和丧失实验阐明下游机制。

Deterioration of myocardial contractile function is a major limitation for successful cancer therapies. Moreover, cardiac function is strongly associated with cancer-related morbidity and mortality. Anthracyclines, which are well-established anti-cancer drugs and part of many classical therapeutic regimes share profound cardiac side effects. Despite its clinical relevance, there is only very limited knowledge about the downstream targets involved and potential cardioprotective mechanisms of co-therapies. Histone deacetylases (HDACs) work as epigenetic repressors. Recent work has shown that HDAC inhibitors (HDACi) not only successful as therapeutics in various cancer entities but also beneficial for the heart in preclinical models of heart failure. Even though its beneficial potential has been shown, the specific downstream mechanisms of the cardioprotective effects of HDACi are not clarified so far. In our ongoing work, we identified the chaperone 14-3-3 to be hyperacetylated in cardiomyocytes upon treatment with vorinostat, the first FDA approved HDACi. We could show, that hyperacetylation of 14-3-3 leads to reduced binding to class II HDACs, namely HDAC4 and 5. Nuclear HDAC4/5 act as repressors of the transcription factor (TF) myocyte enhancer factor 2 (MEF2), which is required for upregulation of genes that are causative for pathological cardiac remodeling and dysfunction. In addition, we found that vorinostat inhibits the nuclear export of HDAC4/5. Conversely, vorinostat resulted in remarkable suppression of MEF2 in neonatal rat ventricular cardiomyocytes (NRMVs) while knockdown of HDAC4 and HDAC5 attenuated the vorinostat-dependent MEF2 inhibition. These results suggest that the protective effects of vorinostat are partially transmitted by HDAC4/5. Accordingly, we found that cardiomyocyte-specific deletion of HDAC4 increases the susceptibility for cardiac dysfunction upon treatment with the anthracycline ‘doxorubicin’ and upregulates the MEF2 target gene myh7. The myh7-promotor was further identified to be bound to topoisomerase IIb in a doxorubicin-dependent manner. Based on our unpublished work, we propose a crucial role of HDAC-dependent MEF2 inhibition in doxorubicin-induced cardiotoxicity. This effect can be amplified by co-treatment with the HDACi vorinostat. Still, the epigenetic changes caused by vorinostat and potential other downstream targets independent of the TF MEF2 are widely unknown, which is why they require further investigations. The specific aims are: 1: (a) Identification of global HDACi-dependent epigenetic changes in the heart and (b) determination of HDACi-targeted genomic regions in cardiomyocytes. 2: To determine the role of MEF2 in the control of pathological gene regulation upon doxorubicin treatment. 3: To determine potential cardioprotective effects of vorinostat upon co-treatment with anthracyclines in vivo and to elucidate of the downstream mechanism via gain and loss of function experiments in vitro.