Streptonigrin (Bruneomycin), a natural product produced by Streptomyces flocculus, possesses both anti-tumor and anti-bacterial activity. Streptonigrin acts as a pan-PAD inhibitor with IC50s of 48.3±34.2 µM, 26.1±0.3 µM, 0.43±0.03 µM, and 2.5±0.4 µM for PAD1, PAD2, PAD3, and PAD4, respectively.