Identification of Potent and Selective Human Ecto-Nucleotide Pyrophos- phatase/Phosphodiesterase-3 (hNPP3) Inhibitors

NPP3 inhibitors are promising therapeutic agents due to their potential as anti-cancer, anti-metastatic and anti-neurodegenerative drugs. We have identified the first potent and selective inhibitors of human NPP3. We have also estimated the biochemical properties of the main NPP family members that can hydrolyse nucleotides using p-nitrophenyl-5'-thymidine monophosphate as substrate. Km values were found to be 20 ± 4 and 15 ± 6 M for human NPP1 and NPP3, respectively. Maximum velocity (Vmax) values calculated for NPP1 and NPP3 were 12 ± 2 and 5 ± 1 nmol p-nitrophenol released/min/mg of crude protein, respectively. A series of benzothiazole derivatives and a series of 1,3,4-oxadiazole-2-thiones was tested on hNPP1 and hNPP3. Benzothiazoles were the most potent non competitive inhibitors of hNPP3 described to date. 1,3,4-oxadiazole-2-thiones were also identified as compounds which inhibited specifically NPP3 over NPP1. The most potent compound was further characterized and found to exhibit a non competitive mechanism of inhibition.