Inhibition of Bcl-2/Bcl-xL and c-MET causes synthetic lethality in model systems of glioblastoma

Yiru Zhang,Georg Karpel-Massler,Chang Shu,Giulio Kleiner,Catarina M Quinzii,Chiaki Tsuge Ishida,Markus D Siegelin,Elena Bianchetti,Mike-Andrew Westhoff,Maria J Sanchez-Quintero

doi:10.1038/s41598-018-25802-0

Yiru Zhang, Georg Karpel-Massler + Show 8 more

Open Access

https://doi.org/10.1038/s41598-018-25802-0

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Abstract

Recent data suggest that glioblastomas (GBM) activate the c-MET signaling pathway and display increased levels in anti-apoptotic Bcl-2 family members. Therefore, targeting these two deregulated pathways for therapy might yield synergistic treatment responses. We applied extracellular flux analysis to assess tumor metabolism. We found that combined treatment with ABT263 and Crizotinib synergistically reduces the proliferation of glioblastoma cells, which was dependent on dual inhibition of Bcl-2 and Bcl-xL. The combination treatment led to enhanced apoptosis with loss of mitochondrial membrane potential and activation of caspases. On the molecular level, c-MET-inhibition results in significant energy deprivation with a reduction in oxidative phosphorylation, respiratory capacity and a suppression of intracellular energy production (ATP). In turn, loss of energy levels suppresses protein synthesis, causing a decline in anti-apoptotic Mcl-1 levels. Silencing of Mcl-1 enhanced ABT263 and MET-inhibitor mediated apoptosis, but marginally the combination treatment, indicating that Mcl-1 is the central factor for the induction of cell death induced by the combination treatment. Finally, combined treatment with BH3-mimetics and c-MET inhibitors results in significantly smaller tumors than each treatment alone in a PDX model system of glioblastoma. These results suggest that c-MET inhibition causes a selective vulnerability of GBM cells to Bcl-2/Bcl-xL inhibition.

Highlights

Malignant glial brain tumors remain to be incurable
We validated that Crizotinib acts on-target by confirming in whole cell protein lysates of NCH644 GBM stem-like cells and U87 cells that Crizotinib elicits a reduction in phosphorylation of c-MET (Supplementary Figure 1C), confirming that this compound is active in our model systems
We found that in all model systems tested, Crizotinib and ABT263 reduced the proliferation of GBM cells in a synergistic manner, revealing CI values of less than 1.0 (Fig. 1B–D)

Summary

Introduction

Malignant glial brain tumors remain to be incurable. Out of this group, the most common primary malignant brain tumor is glioblastoma[1]. There have been recent advances in the molecular diagnosis and characterization of these tumors, they still remain therapeutically resistant. In part, this can be linked to heterogeneity, which is exemplified by the simultaneous activation of multiple different pathways that are often times related to kinase signaling. C-MET appears to be important for the growth and maintenance of stem-like GBM cells, a population of tumor cells within glial brain tumors that is responsible for therapeutic resistance and progression[2,3]. The anti-apoptotic Bcl-2 family members are a cornerstone in cell death regulation in glioblastoma cells They can be inhibited by selective compounds, called BH3-mimetics that elicit on-target efficacy in the nanomolar range. Targeting kinase signaling will interfere with energy production in cancer cells and inevitably exacerbate metabolic vulnerabilities that are therapeutically targetable

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