Effectiveness of THB001, A Selective KIT Inhibitor, in Uncovering Mast Cell Function in Asthma

Abstract Introduction: THB001 is a selective inhibitor of KIT, a receptor that is vital for many aspects of mast cell biology, including differentiation and survival. In patients with allergic asthma, mast cells are significantly elevated in the lungs, and they are profoundly involved in both early and late allergic reactions by releasing contractile mediators (histamine, leukotrienes), cytokines (e.g. IL-4, IL-5) and chemokines (e.g. CCL5, CCL7). Reducing mast cells in the airways of asthmatic patients is, therefore, a potential treatment strategy for asthma. This study aims to evaluate the effectiveness of THB001 in inhibiting mast cell responses and to further investigate how mast cells contribute to initiation and progression of asthma. Method: Isolated tracheal segments from house dust mite (HDM)-sensitized guinea pigs were incubated with THB001 at concentrations of 1, 3 and 10 µM for 4, 8, or 13 days. After incubation, the responses of each segment to potassium chloride and HDM using myography. An HDM-induced guinea pig asthma model was established over 25 days through two sensitizations and four challenges. Starting on day 8, guinea pigs were fed either a control diet or a 1% THB001 diet. Breathing patterns were recorded using whole-body plethysmography for one hour after each challenge. On the final day, airway responsiveness was evaluated using FlexiVent, followed by collection of lung tissue. Results:In vitro, THB001 markedly reduced HDM responses in tracheal segments after 4, 8 and 13 days of culture, with a significant decrease in mast cell numbers (Vehicle: 59.1±6.3/nm2vs. 1 µM: 40.4±7.3/nm2 and vs. 10 µM: 39.8±4.0/nm2; p<0.05) observed by day 13. In vivo, THB001 effectively inhibited bronchoconstriction after HDM challenges. Additionally, treatment with THB001 reduced the increased central and peripheral airway resistance and elastance caused by HDM exposure. Histological analysis of lung tissue showed that THB001 completely reversed HDM-induced increases in mast cell numbers (Control+Vehicle 4.6±0.4/100 µm vs. HDM+Vehicle 10.2±0.6/100 µm; HDM+Vehicle vs. HDM+THB 1.7±0.3/100 µm; p<0.0001), airway smooth muscle layer thickness, and collagen deposition, while partially reducing elevated airway inflammation and mucus cell counts. Conclusion:In vitro, THB001 effectively suppressed the contractions in guinea pig trachea to HDM. In vivo, THB001 markedly inhibited the HDM-induced asthmatic features such as early allergic reaction, airway inflammation, airway hyperresponsiveness, and remodeling. These results indicate that allergic asthma is caused by activation of mast cells and that inhibiting this action is a promising treatment of asthma.