Changes in Mitochondrial Function and Cell Death Patterns in Peripheral Blood Mononuclear Cells during Trastuzumab Treatment Following Doxorubicin Chemotherapy

Trastuzumab, a monoclonal antibody which works against human epidermal growth factor receptor 2 (HER2), possibly causes cardiotoxicity through mitochondrial dysfunction. The usefulness of isolated peripheral blood mononuclear cells (PBMCs) in the assessment of trastuzumab-induced cardiotoxicity remains uncertain. This study aimed to determine the temporal changes in mitochondrial function, oxidative stress, and cell death in the isolated PBMCs of HER2-positive breast cancer patients during breast cancer treatment and to compare the changes with HER2-negative breast cancer patients who did not receive trastuzumab therapy. Eighteen newly diagnosed HER2-positive breast cancer women who received sequential doxorubicin and trastuzumab were consecutively recruited. Age- and gender-matched controls with HER2-negative breast cancer were selected. Echocardiography was carried out, and blood samples for the study of cardiac biomarkers and PBMCs were collected periodically during treatment. Only one patient in our cohort developed asymptomatic left ventricular dysfunction during trastuzumab treatment. However, trastuzumab following doxorubicin aggravated subclinical cardiac injury, determined by cardiac troponin and echocardiography. Cellular and mitochondrial oxidative stress in isolated PBMCs remained unchanged throughout breast cancer treatment. Regarding mitochondrial respiration, the maximal respiration and spare respiration capacity was significantly increased in controls after doxorubicin treatment but not in patients who received trastuzumab therapy. Moreover, the percentage of apoptosis and necroptosis in isolated PBMCs was dramatically decreased in the control, compared to patients with trastuzumab treatment. In conclusion, trastuzumab caused subtle myocardial injury and impaired mitochondrial respiration and cell viability in isolated PBMCs.