Novel inhibitors of protein arginine deiminase with potential activity in multiple sclerosis animal model

In multiple sclerosis (MS), myelin basic protein (MBP), critical for the maintenance of myelin compaction and protecting against degradation, is known to contain concentrations of the noncoded amino acid, "citrulline", in abnormal proportions. Peptidyl arginine deiminase (PAD) catalyzes the post-translational citrullination of proteins via the deimination of Arg residues. In the central nervous system, specifically PAD2 and PAD4, are the enzymes responsible for the citrullination. We used in silico screening of commercial libraries to find small molecules that would reversibly inhibit PAD4. An initial set of 10 diverse compounds was selected from the screen, and from these compounds, 3, 4, 6, and 8 showed promising inhibitory activities against PAD4 with Ki in the range of 115-153 μM. Compound 4 was selected to partake in an in vivo MOG EAE mouse model study to evaluate its effect in MS-like conditions. Results from the 24 day pilot mouse study showed an improved clinical outcome for mice being administered compound 4 compared to the control group. In brain, 4 treated mice showed a clear reduction in the CD3 +ve T cells. These results suggest that compound 4 may have potential utility and confirmed that noncovalent inhibitors of PAD enzymes can be developed as potential agents targeting MS pathology.