Data from Combination Therapy for <i>KIT</i>-Mutant Mast Cells: Targeting Constitutive NFAT and KIT Activity

Abstract

<div>Abstract<p>Resistant KIT mutations have hindered the development of KIT kinase inhibitors for treatment of patients with systemic mastocytosis. The goal of this research was to characterize the synergistic effects of a novel combination therapy involving inhibition of KIT and calcineurin phosphatase, a nuclear factor of activated T cells (NFAT) regulator, using a panel of <i>KIT</i>-mutant mast cell lines. The effects of monotherapy or combination therapy on the cellular viability/survival of <i>KIT</i>-mutant mast cells were evaluated. In addition, NFAT-dependent transcriptional activity was monitored in a representative cell line to evaluate the mechanisms responsible for the efficacy of combination therapy. Finally, shRNA was used to stably knockdown calcineurin expression to confirm the role of calcineurin in the observed synergy. The combination of a KIT inhibitor and a calcineurin phosphatase inhibitor (CNPI) synergized to reduce cell viability and induce apoptosis in six distinct <i>KIT</i>-mutant mast cell lines. Both KIT inhibitors and CNPIs were found to decrease NFAT-dependent transcriptional activity. NFAT-specific inhibitors induced similar synergistic apoptosis induction as CNPIs when combined with a KIT inhibitor. Notably, NFAT was constitutively active in each <i>KIT</i>-mutant cell line tested. Knockdown of calcineurin subunit PPP3R1 sensitized cells to KIT inhibition and increased NFAT phosphorylation and cytoplasmic localization. Constitutive activation of NFAT appears to represent a novel and targetable characteristic of <i>KIT</i>-mutant mast cell disease. Our studies suggest that combining KIT inhibition with NFAT inhibition might represent a new treatment strategy for mast cell disease. <i>Mol Cancer Ther; 13(12); 2840–51. ©2014 AACR</i>.</p></div>