Specific Inhibition of Orai1-mediated Calcium Signalling Resolves Inflammation and Clears Bacteria in an ARDS Model.

Rationale: Acute Respiratory Distress Syndrome (ARDS) has an unacceptably high mortality rate (35%) and is without effective therapy. Orai1 is a Ca 2+ channel involved in store operated Ca 2+ entry (SOCE), a process that exquisitely regulates inflammation. Orai1 is considered a druggable target, but to date, no Orai1-specific inhibitors exist. Objectives: To evaluate whether ELD607, a first-in-class Orai1 antagonist, can treat ARDS caused by bacterial pneumonia in preclinical models. Methods: ELD607 pharmacology was evaluated in HEK293T cells and freshly-isolated ARDS patient immune cells. A murine acute lung injury model caused by bacterial pneumonia was then used. Mice were infected with P. aeruginosa , S. aureus , methicillin-resistant S. aureus (MRSA) or multidrug-resistant P. aeruginosa (MDR- Pa ) and then treated with ELD607 intranasally. Measurements and Main Results: ELD607 specifically inhibited SOCE in HEK293T cells with an IC 50 of 9 nM. ELD607 was stable in ARDS airway secretions and inhibited SOCE in ARDS immune cells. In vivo , inhaled ELD607 significantly reduced neutrophilia and improved survival. Surprisingly, Orai1 inhibition by ELD607 caused a significant reduction in lung bacteria, including MRSA. ELD607 worked as an immunomodulator that reduced cytokine levels, lowered neutrophilia and promoted both macrophage-mediated resolution of inflammation and clearance of bacteria. Indeed, when alveolar macrophages were depleted with inhaled clodronate, ELD607 was no longer able to resolve inflammation or clear bacteria. Conclusions: These data indicate that specific Orai1 inhibition by ELD607 may be a novel approach to reduce multi-organ inflammation and treat antibiotic-resistant bacteria.