Roles of BIM induction and survivin downregulation in lapatinib-induced apoptosis in breast cancer cells with HER2 amplification

Abstract

Lapatinib, a dual tyrosine kinase inhibitor of the epidermal growth factor receptor and human epidermal growth factor receptor 2 (HER2), is clinically active in patients with breast cancer positive for HER2 amplification. The mechanism of this anti-tumor action has remained unclear, however. We have now investigated the effects of lapatinib in HER2 amplification-positive breast cancer cells with or without an activating PIK3CA mutation. Lapatinib induced apoptosis in association with upregulation of the pro-apoptotic protein Bcl-2 interacting mediator of cell death (BIM) through inhibition of the MEK-ERK signaling pathway in breast cancer cells with HER2 amplification. RNA interference (RNAi)-mediated depletion of BIM inhibited lapatinib-induced apoptosis, implicating BIM induction in this process. The pro-apoptotic effect of lapatinib was less pronounced in cells with a PIK3CA mutation than in those without one. Lapatinib failed to inhibit AKT phosphorylation in PIK3CA mutant cells, likely because of hyperactivation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway by the mutation. Depletion of PIK3CA (a catalytic subunit of PI3K) revealed that survivin expression is regulated by the PI3K pathway in these cells, suggesting that insufficient inhibition of PI3K-survivin signaling is responsible for the limited pro-apoptotic effect of lapatinib in HER2 amplification-positive cells with a PIK3CA mutation. Consistent with this notion, depletion of survivin by RNAi or treatment with a PI3K inhibitor markedly increased the level of apoptosis in PIK3CA mutant cells treated with lapatinib. Our results thus suggest that inhibition of both PI3K-survivin and MEK-ERK-BIM pathways is required for effective induction of apoptosis in breast cancer cells with HER2 amplification.

Antitumor Action of the MET Tyrosine Kinase Inhibitor Crizotinib (PF-02341066) in Gastric Cancer Positive for MET Amplification

“…Furthermore, depletion of BIM by RNAi resulted in inhibition of crizotinib-induced apoptosis in gastric cancer cells with MET amplification, indicating that upregulation of BIM contributes to the induction of apoptosis by the MET-TKI in such cells. These findings are consistent with those of previous studies of lung cancer cells with EGFR mutations and breast cancer cells with HER2 amplification (13)(14)(15)(16)(17). However, our observations revealed that depletion of BIM did not completely abolish crizotinib-induced apoptosis, suggesting that another apoptotic regulator might contribute to MET-TKIinduced apoptotic cell death.…”

“…However, depletion of STAT3 by RNAi had no substantial effect on expression of XIAP and c-IAP1 in such cells (data not shown). Previous studies have shown that XIAP and c-IAP1 were not substantially affected by EGFR-TKIs in EGFR mutationpositive non-small cell lung cancer cells or by HER2-targeting agents in breast cancer cells positive for HER2 amplification (16,17). Given that inhibition of MET results in downregulation of XIAP and c-IAP1 in MET amplification-positive gastric cancer cells, the mechanism by which the expression of such proteins is regulated likely differs between MET and other receptor tyrosine kinases including EGFR and HER2.…”

“…We found that a PI3K inhibitor or RNAimediated depletion of AKT reduced the abundance of survivin, indicating that the expression of survivin is regulated by PI3K-AKT signaling in MET amplification-positive gastric cancer cells. Previous studies have shown that the expression of survivin is dependent on PI3K-AKT signaling that operates downstream of receptor tyrosine kinases and is essential for cell survival in EGFR mutation-positive non-small cell lung cancer cells as well as in breast cancer cells positive for HER2 amplification (16,17). These results suggest that downregulation of survivin via inhibition of the MET-PI3K-AKT pathway likely also contributes to the induction of apoptosis by crizotinib in MET amplification-positive gastric cancer cells.…”

“…Induction of the proapoptotic BH3-only protein BIM has been found to be important for TKI-induced apoptosis in EGF receptor (EGFR) gene mutation-positive lung cancer and HER2 amplification-positive breast cancer (13)(14)(15)(16)(17). To investigate whether the upregulation of BIM is related to the induction of apoptosis by crizotinib, we transfected MET amplification-positive gastric cancer cells with siRNAs specific for BIM mRNAs.…”

The Potential Benefits of BIM in the Further Pursuit of Biomarker Discovery in Cancer Therapeutics

“…Although their previous study suggested that the combination of NVP-BEZ235 and AZD6244 could be an alternative strategy for EGFR -mutant NSCLC cells ( 5 ), this combination failed to increase apoptosis in EGFR -mutant cells with low BIM expression in their current study. Another recent study demonstrated that NVP-BEZ235 combined with lapatinib increased apoptosis compared with each agent alone in PIK3CA -mutant breast cancer cells with high BIM expression ( 6 ). This combination should be assessed Insight into the molecular events underlying oncogenesis has prompted the development of new treatment approaches such as molecularly targeted therapies, which are overcoming the limited overall survival and severe side effects of traditional cytotoxic cancer therapeutics.…”