Cyclophilin Inhibitors Restrict Middle East Respiratory Syndrome Coronavirus Via Interferon λ In Vitro And In Mice

While severe coronavirus infections, including Middle East respiratory syndrome coronavirus (MERS-CoV) cause lung injury with high mortality rates, protective treatment strategies are not approved for clinical use. OBJECTIVES: We elucidated the molecular mechanisms by which the cyclophilin inhibitors Cyclosporin A (CsA) and Alisporivir (ALV) restrict MERS-CoV to validate their suitability as readily-available therapy in MERS-CoV infection. METHODS: Calu-3 cells and primary human alveolar epithelial cells (hAEC) were infected with MERS-CoV and treated with CsA or ALV or inhibitors targeting cyclophilin inhibitor-regulated molecules including Calcineurin, NFAT, or MAP kinases. Novel CsA-induced pathways were identified by RNA sequencing and manipulated by gene knockdown or neutralising antibodies. Viral replication was quantified by qRT-PCR and TCID50. Data were validated in a murine MERS-CoV infection model. RESULTS: CsA and ALV both reduced MERS-CoV titers and viral RNA replication in Calu-3 and hAEC improving epithelial integrity. While neither Calcineurin nor NFAT inhibition reduced MERS-CoV propagation, blockade of c-Jun N-terminal kinase diminished infectious viral particle release but not RNA accumulation. Importantly, CsA induced interferon regulatory factor 1 (IRF1), a pronounced type-III-interferon (IFNlambda) response and expression of antiviral genes. Down-regulation of IRF1 or IFNlambda increased MERS-CoV propagation in presence of CsA. Importantly, oral application of CsA reduced MERS-CoV replication in vivo, correlating with elevated lung IFNlambda levels and improved outcome. CONCLUSIONS: We provide evidence that cyclophilin inhibitors efficiently decrease MERS-CoV replication in vitro and in vivo via upregulation of inflammatory, antiviral cell responses, in particular IFNlambda. CsA might therefore represent a promising candidate to treat MERS-CoV infection.