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.
Asai
Takashi
T
Department of Tropical Medicine and Parasitology, Keio University School of Medicine, Shinjuku-ku, Tokyo 160-8582, Japan.
Takeuchi
Tsutomu
T
Diffenderfer
Jeff
J
Sibley
L David
LD
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