Radiosensitizing effect of Lapatinib in HER2-positive breast cancer cells

Abstract

Introduction: Overexpression of human epidermal growth factor receptor 2 (HER2) is found in about 20% of breast cancer patients. Trastuzumab has been widely used for the treatment of HER2 overexpressing breast cancer, but the incidence of brain metastases has increased due to its inherent limitation of crossing the blood-brain barrier (BBB). Thus, lapatinib, which has a low molecular weight and can cross the BBB, in combination with brain radiotherapy, will be a promising therapeutic strategy in the treatment of brain metastasis from HER2-positive breast cancer. Materials and Methods: To explore the impact of lapatinib on radiation response, we conducted an in vitro experiment using SKBR3 and BT474 breast carcinoma cells exhibiting HER2/neu amplification. Clonogenic assay and western blot was used to investigate the radiosensitivity of lapatinib. Antibody against γH2AX was used to detect DNA damage. Modes of cell death were assessed with V-FITC/propidium iodide double staining, β-galactosidase staining, and LysoTracker Green staining. Results: Pretreatment of Lapatinib led down-regulation of p-HER2, p-EGFR, p-AKT, and p-ERK. Lapatinib increased the radiosensitivity of SKBR3 (SER 1.21 at surviving fraction of 0.5) and BT474 (SER 1.26 at surviving fraction of 0.5) breast carcinoma cells, respectively. Lapatinib hindered repair of DNA damage as suggested by the prolongation of radiation-induced γH2AX foci and down-regulation of p-DNAPKcs. Increased radiation-induced apoptosis and senescence was suggested to be the major mode of cell death induced by lapatinib combined with radiation. Lapatinib didnt increase radiation damage of normal human astrocytes. Conclusions: These findings suggest lapatinib potentiate radiation-induced cell killing in HER2-overexpressing breast cancer cells and could be a useful strategy to increase efficacy of radiotherapy.