Airway hyperresponsiveness (AHR) and airway inflammation are hallmarks of asthma. Refractory asthma manifests with persistent symptoms despite use of high-dose oral corticosteroids and long-acting β2-agonist bronchodilators and poses a major healthcare challenge. Understanding the mechanisms and developing strategies to overcome therapeutic resistance poses a significant unmet need. Airway smooth muscle (ASM) hypercontraction is a key factor of AHR, and T-helper 17 (Th17) cells promote steroid-insensitive neutrophilic airway inflammation (NAI). We found p63RhoGEF, a RhoA activator, plays crucial roles in refractory asthma. We also developed CXN-8, a small molecule inhibitor of p63RhoGEF. Objective: To determine the importance and mechanisms by which p63RhoGEF modulates the asthma diathesis and if CXN-8 inhibits p63RhoGEF to ameliorate AHR and NAI. Long-term goal: To develop new therapies for refractory asthma. Findings: 1) p63- RhoGEF is selectively upregulated in asthmatics and plays a critical role in RhoA activation that controls ASM hypercontraction and Th17 cell differentiation. 2) CXN-8 inhibits ASM contraction and induces relaxation of airway. 3) CXN-8 ameliorates AHR and NAI in murine asthma models. 4) CXN-8 interacts with p63RhoGEF to block RhoA activation. Hypothesis: Targeting p63RhoGEF-stimulated ASM hypercontractility and Th17 cell differentiation with CXN-8 ameliorates AHR and NAI and that CXN-8 therapy represents a novel strategy for refractory asthma. We will test this hypothesis in vitro and in vivo. Aim 1. To define the mechanism underlying p63RhoGEF and CXN-8 regulation of AHR. We will use RNAi and inhibitors to determine the pivotal role and mechanism of p63RhoGEF in hypercontractility of asthmatic human ASM (HASM) cells. We will analyze CXN- 8 regulation of RhoA activity, Ca2+ signaling, contraction/relaxation of β2-agonist-sensitive/insensitive HASM cells. We will combine RNAi, mutagenesis, and surface plasmon resonance to elucidate the specificity and mechanism for CXN-8 regulation of p63RhoGEF. Whether p63RhoGEF loss ameliorates AHR and reduces the effects of CXN-8 will be examined in a house dust mite (HDM)-driven murine model of asthma. Aim 2. To elucidate the mechanism underlying p63RhoGEF and CXN-8 regulation of NAI. We will examine the effects of CXN-8 on Th17 cell differentiation. We will silence RhoA or express an active RhoA mutant to establish its importance in CXN-8 inhibition of Th17 cell differentiation. We will also determine if loss of p63RhoGEF attenuates RhoA activation and Th17 differentiation in cells and HDM-induced NAI in mice and reduces CXN-8 inhibitory effects in vitro and in vivo. Aim 3. To examine the therapeutic potential of CXN-8 in murine models of refractory asthma. We will determine if inhaled CXN-8 is an acute and effective bronchodilator in a murine model of β2-agonist insensitive AHR. We will test lung targeted, long-acting CXN-8 microparticles to alleviate AHR/NAI with limited systemic sid...