Abstract
The ongoing pandemic spread of the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) demands skillful strategies for novel drug development, drug repurposing and cotreatments, in particular focusing on existing candidates of host-directed antivirals (HDAs). The developmental drug IMU-838, currently being investigated in a phase 2b trial in patients suffering from autoimmune diseases, represents an inhibitor of human dihydroorotate dehydrogenase (DHODH) with a recently proven antiviral activity in vitro and in vivo. Here, we established an analysis system for assessing the antiviral potency of IMU-838 and DHODH-directed back-up drugs in cultured cell-based infection models. By the use of SARS-CoV-2-specific immunofluorescence, Western blot, in-cell ELISA, viral yield reduction and RT-qPCR methods, we demonstrated the following: (i) IMU-838 and back-ups show anti-SARS-CoV-2 activity at several levels of viral replication, i.e., protein production, double-strand RNA synthesis, and release of infectious virus; (ii) antiviral efficacy in Vero cells was demonstrated in a micromolar range (IMU-838 half-maximal effective concentration, EC50, of 7.6 ± 5.8 µM); (iii) anti-SARS-CoV-2 activity was distinct from cytotoxic effects (half-cytotoxic concentration, CC50, >100 µM); (iv) the drug in vitro potency was confirmed using several Vero lineages and human cells; (v) combination with remdesivir showed enhanced anti-SARS-CoV-2 activity; (vi) vidofludimus, the active determinant of IMU-838, exerted a broad-spectrum activity against a selection of major human pathogenic viruses. These findings strongly suggest that developmental DHODH inhibitors represent promising candidates for use as anti-SARS-CoV-2 therapeutics.
Highlights
Emerging viruses have repeatedly raised challenging medical problems due to the hurdles in rapidly generating test systems, vaccines and antiviral drugs
Productive infection was monitored by Western blot analysis using a human anti-SARS-CoV-2 convalescent serum (Figure 1A), and viral stocks were quantitated by titration of infectious units using human anti-SARS-CoV-2 convalescent antiserum in an in-house developed in-cell ELISA or a newly produced monoclonal antibody against the viral spike protein for in-cell indirect immunofluorescence (IF) staining (Figure 1B)
The first indication for a SARS-CoV-2-directed activity of IMU-838 was obtained by assessing its inhibitory potential by in-cell IF staining using mAb-S
Summary
Emerging viruses have repeatedly raised challenging medical problems due to the hurdles in rapidly generating test systems, vaccines and antiviral drugs. IMU-838 is a next-generation inhibitor of human dihydroorotate dehydrogenase (DHODH) containing the moiety of vidofludimus as its active determinant. The oral drug formulation is currently in phase 2 clinical development for autoimmune diseases including multiple sclerosis, ulcerative colitis and primary sclerosing cholangitis. More than 650 individuals have already been treated with IMU-838 or its active moiety, and the safety profile is comparable to the placebo cohort [1,2,3]. Data from the EMPhASIS trial have shown activity of IMU-838 in multiple sclerosis patients who have met the primary and secondary endpoints with high statistical significance [3]. DHODH inhibitors are known to inhibit metabolically active cells, such as cancer cells and hyperactivated lymphocytes [4]. A highly relevant improvement in understanding the mechanisms of DHODH inhibitors was the finding that virus-infected cells are metabolically active and, show strict dependence on DHODH for maintaining their high metabolic turnover [5]
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