Comparison of The Novel K Ca 3.1 Inhibitor SAN903 with Nintedanib and Pirfenidone In A Model of Idiopathic Pulmonary Fibrosis

Abstract

Hypothesis Idiopathic pulmonary fibrosis (IPF) is a chronic and debilitating disease characterized by progressive lung fibrosis and declined function. IPF is a fatal condition with an expected survival time of 3-4 years, despite two medicines, nintedanib and pirfenidone, having been registered by the FDA/EMA. There is a clear need for more effective treatment options. KCa3.1 is a Ca2+-activated K+- channel expressed in fibroblasts/myofibroblasts, immune cells, and many epithelia/endothelia. The KCa3.1 channel is reported to control proliferation, migration, as well as cytokine release and collagen deposition in fibrosis models and inhibition of the KCa3.1 channel is hypothesized to ameliorate this inflammatory/fibrotic cascade. This study reports the testing of a novel KCa3.1 inhibitor, SAN903, compared to nintedanib and pirfenidone in a mouse model of IPF. Method C57BL/6J mice were given a single lung instillation of bleomycin (1.5 IU/kg) or saline (sham) and followed for 21 days. Groups of 2 × 8 animals (experiment lines 1 and 2) were dosed with SAN903 (30mg/kg, bid, po), nintedanib (60mg/kg, qd, po), pirfenidone (200mg/kg, bid, po), or vehicle (bid, po). Dose selection for nintedanib and pirfenidone were taken from the literature and adjusted to approach calculated human equivalent doses. Physical examination and body weights were recorded daily. At day 22, line 1 mice were sacrificed, and the lungs prepared for histochemical evaluation (H&E and MT staining). Line 2 mice were anesthetized and bronchoalveolar lavage fluid (BALF) collected for analysis. Statistical testing consisted of one-way/repeated measures ANOVA followed by Fisher´s LSD test with significance set at alpha P<0.05. Result Increase in histopathological score, biochemical parameters and cellular infiltration indicated robust and statistically significant inflammation/fibrosis in the vehicle group (p<0.0001 vs sham). No mortalities were reported during the study. SAN903 significantly (N=16) counteracted body weight decline caused by bleomycin, whereas nintedanib showed a trend towards improved outcomes and pirfenidone significantly worsened the decline. Histology revealed significant reductions of both inflammation and fibrosis in the SAN903 treated group (P=0.03), whereas nintedanib showed a numerical effect and pirfenidone trended towards impaired outcomes. The difference in effect between SAN903 and pirfenidone on fibrosis score was statistically significant (p=0.002). Analysis of BALF showed no significant effects on total or differential cell counts by any compound, whereas nintedanib significantly reduced TGF-1β (p=0.003) and SAN903 showed trend of inhibition (p=0.15). None of the compounds significantly decreased lung hydroxyproline contents. Conclusion: SAN903 reduced lung inflammation and fibrosis in the mouse bleomycin-model of lung fibrosis. The effects of SAN903 on lung pathology seem superior to the two standard-of-care medicines for IPF.