Autophagy stimulates apoptosis in HER2‐overexpressing breast cancers treated by lapatinib

Abstract

HER2-overexpressing breast cancers often show hyperactivation of the HER2/AKT/mTOR signaling pathway. Lapatinib is an oral dual tyrosine kinase inhibitor (TKI) that targets both EGFR and HER2 to inhibit the proliferation of breast cancer cells. However, it is obscure whether and how lapatinib could induce autophagy in breast cancer cells, an important cell response with drug treatment. In this study, we investigated the apoptosis and the autophagy in the HER2-overexpressing breast cancer cells BT474 and AU565 treated with lapatinib, and further examined their relationship. Lapatinib inhibited the proliferation and the rate of DNA synthesis in HER2-positive cells, as observed by MTT, colony formation and EDU assays. Lapatinib not only induced apoptosis accompanied by an increased expression of cleaved Caspase-3 and cleaved PARP, but it also induced autophagy in vitro, as confirmed by electron microscopy (EM), acridine orange (AO) staining and LC3-II expression. Meanwhile, lapatinib inhibited the phosphorylation of HER2, AKT, mTOR, and p70S6K, whereas that of AMPK was activated. When the cells were pre-incubated with 3-Methyladenine (3-MA), the specific autophagy inhibitor, the growth inhibitory ratio and apoptosis rate were frustrated, whereas colony formation and DNA synthesis ability were encouraged. In addition, 3-MA application could up-regulate Caspase-3 and PARP expression, compared with the treatment with lapatinib alone. The addition of 3-MA could attenuate the inhibitory role on HER2/AKT/mTOR pathway and the active role on AMPK that was raised by lapatinib. Therefore, lapatinib simultaneously induced both apoptosis and autophagy in the BT474 and AU565 cells, and in these settings, autophagy facilitates apoptosis.

Small Molecule Inhibition of MDM2–p53 Interaction Augments Radiation Response in Human Tumors

“…Detection of acidic vesicular organelles with acridine orange staining Acidic vesicular organelles (AVO), as marker of autophagy, were detected by acridine orange (AO) flow cytometry as described previously (14). To quantify the development of AVOs, cells were stained with 1 mg/mL of AO for 15 minutes and were then removed from the plate with trypsin-EDTA and collected for flow cytometric analysis.…”

Cardiomyocyte autophagy and cancer chemotherapy

“…First, AMPK, activated by lapatinib, is a robust regulator of autophagy. Consistent, lapatinib activates autophagy in breast cancer cells [67] and leukemic cells [68], whereas this has not been reported for trastuzumab. Second, recent work has revealed that HER-2 physically interacts with Beclin 1 in breast cancer cells, although the biological significance of this interaction is unclear [69].…”

Radiosensitizing effect of lapatinib in human epidermal growth factor receptor 2-positive breast cancer cells

“…An autophagy inhibitor, 3-Methyladenine, attenuated autophagy induced by lapatinib in a study using BT474 cells [32]. Other studies have shown that autophagy was an important mode of cell death following lapatinib treatment [33, 34].…”