Differential induction of apoptosis in HER2 and EGFR addicted cancers following PI3K inhibition

Abstract

Non-small cell lung cancers with activating mutations in the epidermal growth factor receptor (EGFR) are highly responsive to EGFR tyrosine kinase inhibitors (TKIs), such as gefitinib and erlotinib. Such cancers are ''addicted'' to EGFR, and treatment with a TKI invariably leads to down-regulation of the PI3K-AKT-mTOR and MEK-ERK signaling pathways, resulting in apoptosis. Using a dual PI3K-mTOR inhibitor, NVP-BEZ235, we evaluated whether PI3K-mTOR inhibition alone induced apoptosis in these cancers. In contrast to HER2-amplified breast cancers, we found that PI3K-mTOR inhibition did not promote substantial apoptosis in the EGFR mutant lung cancers. However, blocking both PI3K-mTOR and MEK simultaneously led to apoptosis to similar levels as the EGFR TKIs, suggesting that downregulation of these pathways may account for much of the apoptosis promoted by EGFR inhibition. In EGFR mutant lung cancers, downregulation of both intracellular pathways converged on the BH3 family of proteins regulating apoptosis. PI3K inhibition led to downregulation of Mcl-1, and MEK inhibition led to up-regulation of BIM. In fact, down-regulation of Mcl-1 by siRNA was sufficient to sensitize these cancers to single-agent MEK inhibitors. Surprisingly, an AKT inhibitor did not decrease Mcl-1 levels, and when combined with MEK inhibitors, failed to induce apoptosis. Importantly, we observed that the combination of PI3K-mTOR and MEK inhibitors effectively shrunk tumors in a transgenic and xenograft model of EGFR T790M-L858R cancers. These data indicate simultaneous inhibition of PI3K-mTOR and MEK signaling is an effective strategy for treating EGFR mutant lung cancers, including those with acquired resistance to EGFR TKIs.ver the past few years, it has become clear that non-small cell lung cancers (NSCLCs) with activating mutations in epidermal growth factor receptor (EGFR) are particularly sensitive to EGFR tyrosine kinase inhibitors (TKIs), and this has emerged as another example of a successful targeted therapy paradigm [reviewed in (1)]. Similarly, breast cancers with amplification of HER2 are often sensitive to HER2 TKIs (lapatinib) and antibodies (trastuzumab) (2, 3).Mounting evidence indicates that both the PI3K-AKT-mTOR and the MEK-ERK pathways are strictly regulated by either EGFR or HER2 in cancers that respond to inhibitors of these RTKs (4). For a cancer to respond to an EGFR TKI, treatment must lead to down-regulation of these intracellular signaling pathways. When most cancers, such as KRAS-mutated cancers, are treated with EGFR TKIs, these intracellular pathways are unaffected, and these cancers are thus de novo resistant (5). In contrast, lung cancers with EGFR mutations have PI3K-AKT-mTOR and MEK-ERK under the sole regulation of EGFR, and when treated with an EGFR TKI, these pathways turn off and the cells undergo substantial apoptosis. However, it remains unknown whether down-regulation of the PI3K-AKT-mTOR, MEK-ERK, or both pathways together is sufficient to recapitulate the apoptotic effects induced by the TKI. Indeed, ...

In Vivo Activity of Combined PI3K/mTOR and MEK Inhibition in a KrasG12D;Pten Deletion Mouse Model of Ovarian Cancer

“…Combined inhibition of both signaling pathways led to improved efficacy because of the enhanced induction of apoptosis, which can be in part attributed to the combined activation of pro-apoptotic BH3-only protein Bim as a result of MEK inhibition and repression of Mcl-1 as a result of PI3K/mTOR inhibition (35,39). Here, the ability of high Bim and low Mcl-1 expression to cooperatively initiate apoptosis in response to PI3K pathway and MEK inhibition is consistent with similar observations in human leukemia cells (40) and human lung cancer cell lines (41). In addition to exploring the effects of combining 2 targeted therapies, it is advantageous to exploit preclinical models to understand the effect of standard chemotherapies in combination with targeted therapeutics, given the established role of standard chemotherapy in ovarian cancer.…”

Constitutive Activation of Epidermal Growth Factor Receptor Promotes Tumorigenesis of Cr(VI)-transformed Cells through Decreased Reactive Oxygen Species and Apoptosis Resistance Development

“…Inhibition of EGFR restored apoptosis in Cr(VI)-transformed cells with commitment to increase of Bax expression and reduction of Bcl-2 expression. This observation is supported by the previous report that treatment the HCC827 cells with EGFR TKIs induced apoptosis via decrease of Mcl-1 expression, an antiapoptotic protein of Bcl-2 family (40).…”

AXL regulates mesothelioma proliferation and invasiveness

“…Interactions between AXL and PI3-K were blocked in a dose-dependent manner by the AXL inhibitor, DP-3975 (Figure 4a), suggesting that AXL regulation of PI3-K/AKT/mTOR signaling requires AXL:PI3-K interaction. AKT is a crucial intermediate in RTK/PI3-K signaling, with contributions to cell proliferation, survival and migration/ invasiveness, depending on cell context (Sordella et al, 2004;Stommel et al, 2007;Harir et al, 2008;Faber et al, 2009). Soft agarose assays confirmed that the PI3-K/AKT/mTOR signaling pathway contributes to AXL-mediated mesothelioma tumorigenic properties (Supplementary Figure 2A and 2C).…”