Identification of small-molecule inhibitors of nucleoside triphosphate hydrolase in Toxoplasma gondii.
Approximately 150,000 small-molecule compounds were tested by a robotic screening assay for their ability to inhibit nucleoside triphosphate hydrolase (NTPase), a novel enzyme of the tachyzoite form of Toxoplasma gondii. Five unrelated species of compounds were found to inhibit the activities of both NTPase isoforms (NTPase isoform I [NTPase-I] and NTPase-II). The 50% inhibitory concentrations (IC(50)s) ranged from 0.1 to 20 microM, and in general, the IC(50)s were similar for both NTPase isoforms. However, the activity of NTPase-I was 20 times more sensitive than the activity of NTPase-II to one of the inhibitors: 9-hydroxy-10-(pentachlorophenoxy)stearic acid. The five compounds identified also prevented tachyzoite replication in vitro, with IC(50)s ranging from approximately 7 to > or =50 microM. The most effective of these initial compounds, 2-phenylthio-indole, was used to identify six additional, structurally related compounds, which were tested for their inhibitory effects on enzyme activities and tachyzoite replication. Surprisingly, these compounds were competitive inhibitors of NTPase-I but noncompetitive inhibitors of NTPase-II. Modifications to the indole and phenol rings resulted in alterations of activity, thus providing insight into the structural features that are important for inhibition of T. gondii NTPases.
Department of Tropical Medicine and Parasitology, Keio University School of Medicine, Shinjuku-ku, Tokyo 160-8582, Japan.
Takashi
T
Asai
Tsutomu
T
Takeuchi
Jeff
J
Diffenderfer
L David
LD
Sibley
D017766:Acid Anhydride Hydrolases / Q000037:antagonists & inhibitors*; D000818:Animals; D004353:Drug Evaluation, Preclinical; D004791:Enzyme Inhibitors / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D006593:Hexokinase / Q000378:metabolism; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D007700:Kinetics; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D043583:Nucleoside-Triphosphatase; D012371:Robotics; D013329:Structure-Activity Relationship; D014122:Toxoplasma / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D006593:Hexokinase; D017766:Acid Anhydride Hydrolases; D043583:Nucleoside-Triphosphatase