Identification of Natural Product Inhibitors against Human Nicotinamide N-Methyltransferase (hNNMT): An In Silico and in vitro Approach

Abstract Human nicotinamide N-methyltransferase (hNNMT) plays a pivotal role in phase-II biotransformation and is classified within the SAM-dependent methyltransferases family. Notably, hNNMT’s overexpression is common in various diseases, including metabolic disorders and various cancer types, which makes it an attractive therapeutic target. The motivation of this research was to examine the potential inhibitory property of flavonoids against hNNMT. A panel of commercially available flavonoids were subjected to molecular docking to assess their binding affinity with hNNMT, followed by in vitro binding assays to validate their inhibitory activity. In-house expression and purification of hNNMT protein were carried out to perform these experiments. The hNNMT activity of these molecules was determined using spectrofluorimetry using quinoline as the substrate. N-methylnicotinamide were used as positive control. Quercetin and morin emerged as potent inhibitors of hNNMT activity by in vitro. Furthermore, comprehensive analyses encompassing physicochemical properties, pharmacokinetics, drug-likeness, and toxicity profiles were conducted for these compounds in silico. A 250 ns molecular dynamics simulation was performed on hNNMT complexes with quercetin and morin to substantiate their inhibitory potential. Morin exhibited the highest potency amidst the polyphenols screened, with an IC50 value of 14.97 ± 0.38 μM followed by Quercetin with 29.95 ± 1.3 μM. This research highlights the significant inhibitory potential of quercetin and morin against hNNMT and warrants further exploration of flavonoids as NNMT inhibitors to improve their potency through structure-based drug design.