Doxorubicin-induced Cardiotoxicity: the Role of Topoisomerase 2b

 描述(申请人提供)：阿霉素，一种经典的蒽环类药物，尽管有靶向治疗的出现，但在现代癌症治疗中被广泛使用。然而，剂量依赖性的心脏毒性往往限制了它的临床应用。阿霉素的细胞靶点是拓扑异构酶II(TOP2)。阿霉素与DNA和TOP2结合形成TOP2-阿霉素-DNA三元裂解复合体，触发细胞死亡。TOP2有两种酶，Top2a和Top2b。TOP2A是一种已知的细胞增殖标志，在肿瘤中过度表达，但在静止组织中检测不到。因此，Top2a被认为是阿霉素抗肿瘤活性的分子基础。另一方面，阿霉素被认为通过氧化还原循环和产生活性氧(ROS)而引起剂量依赖性的心脏毒性。最近，我们发现心肌细胞特异性的Top2b缺失保护心肌细胞免受阿霉素诱导的DNA双链断裂和转录组的改变，这些都是导致线粒体生物发生和ROS形成缺陷的原因。此外，心肌细胞特异性的Top2b缺失保护小鼠免受阿霉素诱导的进行性心力衰竭的发展，这表明Top2b是阿霉素诱导的心脏毒性的分子基础。在这项提案中，我们将检验阿霉素引起的心脏毒性可以通过从心肌细胞中化学诱导删除Top2b来预防的假设。在初步研究中，我们发现右旋氮杂环己烷通过蛋白酶体依赖的机制诱导Top2b的降解。因此，在给药8小时后，Top2b从心脏中完全消除。值得注意的是，Dexrazoxane不会影响癌细胞中Top2a的稳定性。这一认识促使我们研究了这样一种假设，即右旋氮杂环己烷诱导的Top2b在心脏中的耗竭应该有效地防止阿霉素引起的心脏毒性，同时保留阿霉素的肿瘤杀伤作用。提出了三个目标。具体目的1：确定右旋氮杂环己烷诱导的Top2b在心脏中的降解是否能阻止阿霉素引起的心脏毒性，但仍保留阿霉素的杀瘤活性。具体目的2：确定右旋咪唑氧烷诱导Top2b降解的机制。具体目的3：研究Top2b在心肌细胞中的生理功能。这项提案的成功完成将为设计阿霉素引起的心脏毒性的新预防策略提供重要的见解。

 DESCRIPTION (provided by applicant): Doxorubicin, a classic anthracycline, is widely used in modern cancer treatments, despite the advent of targeted therapy. However, a dose-dependent cardiotoxicity often limits its clinical use. Doxorubicin's cellular target is Topoisomerase II (Top2). Doxorubicin binds both DNA and Top2 to form the ternary Top2-doxorubicin-DNA cleavage complex, which triggers cell death. There are two Top2 enzymes, Top2a and Top2b. Top2a, a known marker of cell proliferation, is over-expressed in tumors but not detectable in quiescent tissues. Thus, Top2a is thought to be the molecular basis of doxorubicin's anti-tumor activity. On the other hand, doxorubicin is believed to cause dose-dependent cardiotoxicity through redox-cycling and generation of reactive oxygen species (ROS). Recently, we showed that cardiomyocyte-specific deletion of Top2b protected cardiomyocytes from doxorubicin-induced DNA double strand breaks and changes in transcriptome that are responsible for defective mitochondrial biogenesis and ROS formation. Furthermore, cardiomyocyte-specific deletion of Top2b protects mice from development of doxorubicin-induced progressive heart failure, suggesting that Top2b is the molecular basis of doxorubicin-induced cardiotoxicity. In this proposal, we will test the hypothesis that doxorubicin-induced cardiotoxicity is preventable by chemical induced-deletion of Top2b from cardiomyocytes. In preliminary studies, we showed that dexrazoxane induced degradation of Top2b through a proteasome- dependent mechanism. Thus, 8 hours after dexrazoxane administration, Top2b is completely eliminated from the heart. Remarkably, dexrazoxane does not affect Top2a stability in cancer cells. This insight prompt us to study the hypothesis that dexrazoxane-induced depletion of Top2b in the heart should be effective in preventing doxorubicin-induced cardiotoxicity, while preserving doxorubicin's tumor killing effect. Three aims are proposed. Specific Aim 1: To determine whether dexrazoxane-induced degradation of Top2b in the heart prevents doxorubicin-induced cardiotoxicity, but preserves doxorubicin's tumoricidal activity. Specific Aim 2: To determine the mechanism of dexrazoxane-induced Top2b degradation. Specific Aim 3: To study the physiologic function of Top2b in cardiomyocytes. Successful completion of this proposal will provide critical insights into designing a new prevention strategy for doxorubicin-induced cardiotoxicity.