Trastuzumab aggravates radiation induced cardiotoxicity in mice

Some breast cancer patients with overexpression of human epidermal growth factor receptor 2 need both chest radiotherapy and targeted therapy with trastuzumab (TRZ). The cardiotoxicity associated with combined treatment potentially restricts the clinical benefits of antitumor therapy. There is no consensus on whether and how chest radiotherapy can be given in concurrent with TRZ at present, considering the cardiotoxicity. This study intends to establish an in vitro and in vivo heart injury model by irradiation and TRZ, analyze whether there is a synergistic effect in heart, and to explore the molecular changes. First, an in vitro irradiation model of H9C2 cardiomyocytes was established. The effects of TRZ and radiation on cardiomyocyte injury were observed by cell flow cytometry, CCK-8 test, Western blot, γ-H2AX fluorescence focus formation and cell Reactive Oxygen Species (ROS) content test. Second, the mouse heart injury model was set up by X-ray cardiac irradiation combined with TRZ. Six months later, the cardiac function was analyzed by small animal ultrasound and ¹⁸FDG-micro PET/CT. The morphological changes of heart tissue were assessed by histological section. We found that concurrent TRZ aggravates the injury effect of irradiation on cardiomyocytes in vitro. The influence of TRZ might be consequence of inhibiting Akt phosphorylation, promoting the excessive accumulation of ROS in cells and promoting intracellular DNA damage. In animal experiments, the dysfunction of diastolic and myocardial ischemia of mouse heart was observed by echocardiography and ¹⁸FDG-micro PET/CT, respectively; myocardial fibrosis and cardiomyocyte apoptosis were also observed. Therefore, our in vitro and in vivo experiments have revealed that TRZ combined irradiation caused more cardiotoxicity than irradiation or TRZ alone. These results suggested that the concurrent management of TRZ and radiotherapy should be carefully made in clinical practice, and more attention is needed on cardiac safety.