CAY10727 is an inhibitor of protein arginine deiminase (PAD) and is more than 10-fold more selective for PAD3 than PAD 1, 2, and 4. The IC50 values of CAY10727 for PAD 1, 2, 3, and 4 are 120, 27.5, 4.5, and 30.5 μM, respectively. And PAD3 is a PAD isoform associated with neurodegenerative responses to spinal cord injury, and PAD3-IN-1 could be used to study PAD-related neurological diseases.