Doxorubicin-induced Cardiotoxicity: the Role of Topoisomerase 2b

 描述（由申请人提供）：阿霉素是一种经典的蒽环类药物，尽管靶向治疗已经出现，但仍广泛用于现代癌症治疗。然而，剂量依赖性心脏毒性往往限制了其临床应用。阿霉素的细胞靶点是拓扑异构酶II（Top2）。多柔比星结合DNA和Top2以形成三元Top2-多柔比星-DNA切割复合物，其触发细胞死亡。有两种Top2酶，Top 2a和Top 2b。Top 2a是一种已知的细胞增殖标志物，在肿瘤中过表达，但在静止组织中检测不到。因此，Top 2a被认为是阿霉素抗肿瘤活性的分子基础。另一方面，多柔比星被认为通过氧化还原循环和活性氧（ROS）的产生引起剂量依赖性心脏毒性。最近，我们发现心肌细胞特异性缺失Top 2b保护心肌细胞免受阿霉素诱导的DNA双链断裂和转录组变化的影响，这些变化是线粒体生物合成缺陷和ROS形成的原因。此外，心肌细胞特异性缺失Top 2b保护小鼠免受多柔比星诱导的进行性心力衰竭的发展，表明Top 2b是多柔比星诱导的心脏毒性的分子基础。在这项提议中，我们将测试的假设，阿霉素诱导的心脏毒性是可以预防的化学诱导的Top 2b从心肌细胞中删除。在初步研究中，我们表明右雷佐生通过蛋白酶体依赖性机制诱导Top 2b降解。因此，右雷佐生给药后8小时，Top 2b从心脏中完全消除。值得注意的是，右雷佐生不影响癌细胞中的Top 2a稳定性。这一认识促使我们研究以下假设，即右雷佐生诱导的心脏Top 2b耗竭应能有效预防多柔比星诱导的心脏毒性，同时保留多柔比星的肿瘤杀伤作用。提出了三个目标。具体目标1：确定右雷佐烷诱导的Top 2b在心脏中的降解是否可预防多柔比星诱导的心脏毒性，但保留多柔比星的杀肿瘤活性。具体目的2：确定右雷佐烷诱导Top 2b降解的机制。具体目的3：研究Top 2b在心肌细胞中的生理功能。该提案的成功完成将为设计多柔比星诱导的心脏毒性的新预防策略提供重要见解。

 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.