Abstract 5422: Dissecting the mechanism of exercise-mediated protection of Dox-induced cardiotoxicity

Doxorubicin (Dox) is one of the most effective drugs for the treatment of childhood cancer patients. However, there is a correlation between Dox dose/intensity and cardiotoxicity. We developed a juvenile mouse cardiotoxicity model and showed that Dox treatment affected the cardiac vessel morphology characterized by punctate vessels with decreased pericytes and endothelial cells. Cardiac blood flow and function (as quantified by echocardiography [Echo]) were also compromised. These abnormalities were not seen in mice treated with exercise (Ex) during Dox. We also demonstrated increased c-kit+ cells in the hearts of mice treated with Dox + Ex. To determine the origin of these c-kit+ cells we performed a bone marrow (BM) transplant using GFP+ BM cells from C57BL/6Tg(UBC-GFP)30Scha/J mice into C57BL/6 WT mice treated with Busulfan and anti-CD4 and anti-DC8 Abs. BM engraftment was documented 4 wks post-transplant. Transplanted mice were treated with Dox twice/wk x 2 wks; Dox + Ex, or control (no treatment). Cardiac function was assessed after treatment by Echo and the heart tissues were evaluated by immunohistochemistry (IHC) for cells expressing GFP (denoting cells derived from the BM); GFP+/NG2+ or GFP+/CD31+ (BM cells differentiated into pericytes or endothelial cells respectively). Echo data confirmed decreased cardiac function in Dox but not Dox + Ex-treated mice. Few GFP+ cells were found in the hearts from control or Dox-treated mice. By contrast, mice treated with Dox + Ex showed a significant increase in GFP+ cells indicating that exercise had induced the migration of BM cells into the heart. Co-localization of GFP/NG2 and GFP/CD31 indicated that these BM stem cells had differentiated into both endothelial cells and pericytes, and that these cells were incorporated into the cardiac vessels. Few GFP+cTnI+ cells were observed in the heart tissues from mice treated with Ex + Dox, indicating that the BM stem cells had not differentiated into cardiomyoctes. These studies suggest that acute Dox-induced cardiac damage may be partially mediated by decreased blood flow secondary to damaged vessels with decreased vascular endothelial cells and pericytes. Ex may inhibit this effect by inducing the migration of BM stem cells to repair the damaged vessels. We also showed that Dox therapy induced phosphorylation of MST1/2, LATS1 and YAP, decreased total YAP, and induced cleavage of caspase-3 and PARP. These changes were not seen in Dox + Ex hearts suggesting that Ex protected cardiomyocytes from Dox-induced apoptosis by suppressing Hippo-YAP signaling. Taken together, our data demonstrated that the protective effect of Ex may be mediated by restoring cardiac blood flow which may in turn inhibit Dox-induced Hippo-YAP signaling-mediated cardiomyocyte apoptosis. These data support the concept that exercise interventions have the potential to decrease Dox-induced cardiac damage and morbidity in childhood cancer patients. Citation Format: Rong-Hua Tao, Masato Kobayashi, Fei Wang, Yuanzheng Yang, Eugenie S. Kleinerman. Dissecting the mechanism of exercise-mediated protection of Dox-induced cardiotoxicity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5422.