KIT Inhibition by Imatinib in Patients with Severe Refractory Asthma

Abstract

BACKGROUND: Mast cells are present in the airways of patients who have severe asthma despite glucocorticoid treatment; these cells are associated with disease characteristics including poor quality of life and inadequate asthma control. Stem cell factor and its receptor, KIT, are central to mast-cell homeostasis. We conducted a proof-of- principle trial to evaluate the effect of imatinib, a KIT inhibitor, on airway hyper- responsiveness, a physiological marker of severe asthma, as well as on airway mast-cell numbers and activation in patients with severe asthma. METHODS: We conducted a randomized, double-blind, placebo-controlled, 24-week trial of ima- tinib in patients with poorly controlled severe asthma who had airway hyperrespon- siveness despite receiving maximal medical therapy. The primary end point was the change in airway hyperresponsiveness, measured as the concentration of metha- choline required to decrease the forced expiratory volume in 1 second by 20% (PC20 ). Patients also underwent bronchoscopy. RESULTS: Among the 62 patients who underwent randomization, imatinib treatment reduced airway hyperresponsiveness to a greater extent than did placebo. At 6 months, the methacholine PC20 increased by a mean (±SD) of 1.73±0.60 doubling doses in the imatinib group, as compared with 1.07±0.60 doubling doses in the placebo group (P=0.048). Imatinib also reduced levels of serum tryptase, a marker of mast-cell activa- tion, to a greater extent than did placebo (decrease of 2.02±2.32 vs. 0.56±1.39 ng per milliliter, P=0.02). Airway mast-cell counts declined in both groups. Muscle cramps and hypophosphatemia were more common in the imatinib group than in the placebo group. CONCLUSIONS: In patients with severe asthma, imatinib decreased airway hyperresponsiveness, mast- cell counts, and tryptase release. These results suggest that KIT-dependent processes and mast cells contribute to the pathobiologic basis of severe asthma. (Funded by the National Institutes of Health and others; ClinicalTrials.gov number, NCT01097694.)