Targeting Calcium Sensitization Mechanisms In Human Airway Smooth Muscle For Novel Bronchodilator Therapy In Asthma

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Asthma is characterized by airway hyperresponsiveness (AHR) and inflammation. Management of asthma involves controlling airway inflammation with inhaled corticosteroids, and using bronchodilators such as β-2 agonists that inhibit airway smooth muscle (ASM) shortening and prevents or reverses airway narrowing. Despite β-2 agonists’ ability to mitigate asthma exacerbations, they have limitations, especially concerning efficacy and safety. Studies have shown that β-2 agonist use can result in adverse patient outcomes, β-2 adrenergic receptor tachyphylaxis, deterioration of asthma control, and death. New therapeutics are needed to overcome these limitations. Rho kinase (ROCK) inhibitors have generated excitement as potential bronchodilators. Since ROCK activation is necessary to maintain ASM tone by inhibiting MLC phosphatase, ROCK inhibitors allow the constitutively active MLC phosphatase to de-phosphorylate MLC and promote relaxation of ASM. ROCK inhibitors blunt ASM contraction and induce bronchodilation in vitro, ex vivo, and in vivo. Unfortunately, ROCK is ubiquitously expressed and adverse effects such as vasodilation preclude any clinical trials. We present an alternate strategy to induce bronchodilation in human airways by inhibiting the p110δ isoform of phosphoinositide 3-kinase (PI3Kδ) that is not ubiquitously expressed. In primary human ASM cells (HASMCs), we demonstrate that PI3Kδ modulates ROCK activation, and that inhibition of PI3Kδ using a FDA approved drug Cal101 (Idelalisib) attenuates ROCK activation. Cal101 induces relaxation of cultured HASMCs by inhibiting PI3Kδ-mediated activation of ROCK. Using human precision-cut lung slices, we also demonstrate that Cal101 induces bronchodilation of human small airways as effectively as formoterol, an industry standard β-2 agonist. In our model of β-2 agonist tachyphylaxis, the effectiveness of β-2 agonists was significantly attenuated while the effectiveness of Cal101 was not. Thus, our results suggest that PI3Kδ inhibitors represent a novel class of bronchodilators. Furthermore, we demonstrate that Gα12 mediates agonist-induced activation of PI3K and ROCK. These results unveil a novel pathway regulating HASMC signaling that is necessary to elicit shortening. Importantly, our work has uncovered several new targets for bronchodilation and offers new avenues for the treatment of asthma.

Reynold A. Panettieri
Benjamin A. Garcia
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