Cancer Letters

Cancer Letters

Volume 364, Issue 1, 1 August 2015, Pages 70-78
Cancer Letters

Original Articles
Enhancing therapeutic efficacy of the MEK inhibitor, MEK162, by blocking autophagy or inhibiting PI3K/Akt signaling in human lung cancer cells

https://doi.org/10.1016/j.canlet.2015.04.028Get rights and content

Highlights

  • MEK162 inhibits the growth of human lung cancer cells with varied potencies.

  • MEK162 induces G1 arrest, autophagy and/or apoptosis.

  • MEK162 activates Akt signaling while effectively suppressing the MEK/ERK signaling.

  • Blocking autophagy enhances MEK162's growth-inhibitory effects.

  • The combination of MEK162 and BKM120, a PI3K inhibitor, significantly augments anticancer efficacy both in vitro and in vivo.

Abstract

Human non-small cell lung cancer (NSCLC) displays activated MEK/ERK signaling due to a high frequency of K-Ras mutation and is thus a potential candidate for MEK-targeted therapy. The current study focuses on demonstrating the activity of MEK162 (binimetinib), a MEK inhibitor under clinical testing, against NSCLC and exploring possible mechanism-driven strategies to enhance its therapeutic efficacy. MEK162 inhibits the growth of human NSCLC cell lines with varied potencies through induction of G1 cell cycle arrest and apoptosis. Moreover, it induces autophagy and accordingly the combination of MEK162 with the autophagy inhibitor, chloroquine, synergistically inhibits the growth of NSCLC cells and enhances apoptosis. MEK162 activates Akt signaling while effectively inhibiting MEK/ERK signaling. Accordingly, the combination of MEK162 and BKM120 (buparlisib), a pan-PI3K inhibitor, abrogates induced Akt activation and significantly augments therapeutic efficacy against the growth of NSCLC cells both in vitro and in vivo. Hence our findings warrant further evaluation of these rational combinations in the clinic.

Introduction

Ras, particularly K-Ras, is frequently mutated in human non-small cell lung cancer (NSCLC), especially in tumors with adenocarcinoma histology. Ras mutations often result in the activation of the RAF/MEK/ERK pathway [1]. Thus, agents that target this signaling pathway may have potential for treatment of this type of cancer and hence have actively been investigated pre-clinically and clinically. A number of MEK inhibitors such as selumetinib (AZD6244) and trametinib (GSK1120212) have progressed into clinical trials [1]. A randomized phase II trial of docetaxel with and without selumetinib revealed that the combination had numerically superior overall survival and a statistically significant improvement in progression-free survival and objective response rate, albeit with some concern regarding increased adverse effects [2]. Despite a strong scientific rationale, the activity of MEK inhibitors appears to be similar in NSCLC patients with and without K-Ras mutations [1].

MEK162 (binimetinib; ARRY-162 or ARRY-438162) is an orally available non-ATP-competitive allosteric inhibitor of MEK1/2. MEK162 has shown effectiveness in inhibiting the in vitro proliferation of patient-derived N-Ras mutnat melanomas [3] and of pancreatic cancer cells [4]. Moreover MEK162 combined with other targeted agents has displayed promising anticancer activity in different preclinical models. For example, the combination of MEK162 with a PKC inhibitor results in sustained inhibition of MEK/ERK signaling and enhances therapeutic efficacy against the growth of uveal melanoma cells both in vitro and in vivo [5]. The combination of MEK162 and imatinib (Gleevec), a BCR-Abl/c-kit/PDGF Rinhibitor, synergistically suppresses the growth of gastrointestinal stromal tumor in vitro and in vivo [6]. The combination of MEK162 and perifosine, an Akt inhibitor, synergistically inhibits the growth of lung cancer cells in vitro and in vivo [7]. In the clinic, MEK162 has shown some activity in patients with N-Ras-mutated melanoma [8].

The preclinical activity of MEK162 against the growth of human NSCLC cells, the modulatory effects of MEK162 on the MEK/ERK and other signaling pathways such as phosphoinositide 3-kinase (PI3K)/Akt and mammalian target of rapamycin (mTOR) pathways, and the potential impact of genetic alterations on cell responses to MEK162 have not been studied and thus were the focus of this study. Moreover, we were interested in developing mechanism-driven combinations to enhance the therapeutic efficacy of MEK162 based on our understanding of the biology of MEK162 in NSCLC cells. Hence we also studied the efficacy of MEK162 combined with autophagy or PI3K inhibition on the growth of NSCLC cells in vitro and in vivo.

Section snippets

Reagents

MEK162 and BKM120 (buparlisib) were supplied by Novartis Pharmaceuticals Corporation (East Hanover, NJ). AZD6244 was purchased from Selleckchem (Houston, TX). Chloroquine and rabbit polyclonal anti-actin antibody were purchased from Sigma Chemical Co. (St. Louis, MO). Antibodies against ERK1/2, p-ERK1/2 (T202/Y204), Akt, p-Akt (S473), p-S6 (S235/S236), p-4EBP1 (T37/46), 4EBP1, p-70S6K (T389), 70S6K, PRAS40, p-PRAS40 (T246), p-GSK3α/β (S21/9), p-90RSK2 (S380), caspase-8 and

MEK162 inhibits the growth of human NSCLC cell lines with varied potencies

To determine whether MEK162 effectively inhibits the growth of human NSCLC cells, we treated a panel of 14 NSCLC cell lines harboring different genetic mutations (Table 1) with varying concentrations (0.04–10 µM) of MEK162 in comparison with another MEK inhibitor AZD6244 for 3 days and then measured changes in cell number. Both MEK162 and AZD6244 reduced cell numbers in a concentration-dependent manner with IC50s ranging from 0.015 µM to >10 µM. Clearly MEK162 and AZD6244 have varying potencies

Discussion

This study examined the growth inhibitory effects of MEK162 against a panel of 14 human NSCLC cell lines with different genetic mutations including Ras (K- and N-Ras), p53, LKB1, PTEN, PIK3CA, EGFR and CDKA2N (Table 1). These cell lines displayed varying degrees of sensitivity to MEK162, and another MEK inhibitor, AZD6244; i.e., some cell lines (e.g., H157 and H522) were intrinsically sensitive to MEK162 treatment, while others (e.g., H596 and EKVX) were intrinsically resistant (Fig. 1).

Conflict of interest

The authors declare that they have no conflict of interest.

Acknowledgements

We are grateful to Dr. A. Hammond in our department for editing the manuscript.

This study was supported by the NIH/NCI R01 CA118450 (SYS) and R01 CA160522 (SYS).

WY is a visiting medical student participated in the Xiangya-Emory Visiting Medical Student Program. TKO, FRK and SYS are Georgia Research Alliance Distinguished Cancer Scientists.

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