Sensitivity of malignant mesothelioma lacking Merlin to the FAK inhibitor VS-6063: Evaluation of merlin/NF2 status in clinical samples.

Abstract

e18541 Background: Malignant pleural mesothelioma (MPM) is an aggressive tumor in the pleural lining of the lung often resulting from prior exposure to asbestos. MPM patients are usually diagnosed at an advanced stage of disease and the prognosis is poor. Median survival after diagnosis is 9 to 12 months and standard-of-care agents such as cisplatin and pemetrexed have only a modest impact on median survival time for MPM patients. New therapeutic modalities are urgently needed to improve the prognosis of MPM patients. 40-50% of MPM patients exhibit homozygous disruption of the NF2 tumor suppressor gene by mutation and/or deletion resulting in lack of expression of functional merlin protein. Methods: Proliferation of drug-treated mesothelioma cell lines in 3-dimensional (3D) Matrigel culture was assessed by MTS, and MPM xenograft growth was measured in vehicle- vs. FAK inhibitor-treated SCID mice. Since absence of merlin expression can theoretically result from several mechanisms including NF2 mutation and chromosome 22 abnormalities, we assessed NF2 gene deletion by FISH and merlin protein levels by IHC in the same human mesothelioma tumor samples. Results: Among a panel of mesothelioma cell lines in 3D culture, MPM lines lacking expression of merlin protein were found to be especially sensitive to the selective FAK inhibitor VS-6063. In contrast, MPM cell lines with wildtype merlin were less sensitive with EC50 values greater than 1 μM. Accordingly, oral dosing with a FAK inhibitor induced significant tumor growth inhibition in a merlin-negative mesothelioma model in mice. To enable the planned stratification of MPM patients by merlin status, an immunohistochemistry (IHC) assay has been optimized to quantify merlin protein levels. A merlin IHC H-score below the defined cutoff was associated with loss of at least one copy of chromosome 22, indicating that chromosomal deletion is an important mechanism of merlin loss in mesothelioma patients. Conclusions: These data support the clinical development of VS-6063 for treatment of malignant pleural mesothelioma patients stratified by merlin/NF2 status. A potentially pivotal mesothelioma trial is set to initiate in 2013.