3,3′-Diindolylmethane (DIM): A molecular scaffold for inhibition of WWP1 and WWP2, members of the NEDD4 family HECT E3 ligases

Indole-3-carbinol (I3C) is a metabolic derivative of glucobrassicin found in cruciferous vegetables. Known for its anticarcinogenic properties, I3C has been shown to target the NEDD4 family HECT E3 ligases, NEDD4-1 and WWP1, yet in vitro confirmation for the latter is lacking. Here, we characterize the interactions of I3C and a set of 17 derivatives with WWP1 and its homologue, WWP2. Saturation transfer difference (STD) NMR analysis confirmed strong interaction of I3C with WWP1 but weaker with WWP2. However, while autoubiquitination activity assays revealed weak inhibition of WWP1, the I3C condensation product, 3,3′-diindolylmethane (DIM), was more potent (IC50 111.2 μM; 95% CI = 85.1, 145.8). Molecular modeling of DIM to the ubiquitin exosite of both enzymes suggested the WW2 domain makes hydrophobic interactions with the ligand that may contribute to inhibitory action. Taken together, our results suggest future drug lead development should focus on the SAR between WWP1 and DIM.