A 52-year-old Indian woman with newly diagnosed HER2-positive metastatic breast cancer presents to the oncology clinic. She has bony metastases and hepatic involvement. Her baseline LVEF is 55% (normal). She is started on trastuzumab (Herceptin) as part of her chemotherapy regimen. After 3 months of therapy, she develops progressive dyspnea and orthopnea. Echocardiography reveals LVEF of 42% with global hypokinesis. Which of the following best explains the mechanism of this adverse effect?