title: Bisphosphonate inhibitors of Toxoplasma gondi growth: in vitro, QSAR, and in vivo investigations.
abstract: We have investigated the activity of 60 bisphosphonates against the replication of Toxoplasma gondii in vitro and of three of the most active compounds, in vivo. The two most active compounds found were n-alkyl bisphosphonates containing long (n = 9 or 10) hydrocarbon chains, not the nitrogen-containing species used in bone resorption therapy. The target of all of the most active bisphosphonates appears to be the isoprene biosynthesis pathway enzyme farnesyl pyrophosphate synthase (FPPS), as indicated by the correlations between T. gondii growth inhibition and FPPS (human and Leishmania major) enzyme inhibition and by the fact that a T. gondii strain engineered to overexpress FPPS required considerably higher levels of bisphosphonates to achieve 50% growth inhibition, while the IC(50) for atovaquone (which does not inhibit FPPS) remained the same in the overexpressing strain. The phosphonate inhibitor of the non-mevalonate pathway, fosmidomycin, which inhibits the enzyme 1-deoxyxylulose-5-phosphate reductoisomerase, had no effect on T. gondii growth. To investigate structure-activity relationships (SARs) in more detail, we used two three-dimensional quantitative SAR methods: comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA), to investigate all 60 bisphosphonates. Both the CoMFA and CoMSIA models indicated a 60-70% contribution from steric interactions and a 30-40% contribution from electrostatic interactions and using four N = 55 training sets for each method, we found on average between a factor of 2 and 3 error in IC(50) prediction. The three most active compounds found in vitro were tested in vivo in a Smith-Webster mouse model and the two most active bisphosphonates were found to provide up to an 80% protection from death, a considerable improvement over that found previously with nitrogen-containing bisphosphonates. This effect may originate in the much higher therapeutic indices of these alkyl bisphosphonates, as deduced from in vitro assays using LD(50) values for growth inhibition of a human cell line. Overall, these results indicate that alkyl bisphosphonates are promising compounds for further development as agents against Toxoplasma gondii growth, in vivo.
authors.affiliation: Laboratory of Molecular Parasitology, Department of Pathobiology and Center for Zoonoses Research, University of Illinois at Urbana-Champaign, 2001 South Lincoln Avenue, Urbana, Illinois, 61802, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Ling
authors.forename: Gurmukh
authors.initials: G
authors.lastname: Sahota
authors.forename: Sarah
authors.initials: S
authors.lastname: Odeh
authors.forename: Julian M W
authors.initials: JM
authors.lastname: Chan
authors.forename: Fausto G
authors.initials: FG
authors.lastname: Araujo
authors.forename: Silvia N J
authors.initials: SN
authors.lastname: Moreno
authors.forename: Eric
authors.initials: E
authors.lastname: Oldfield
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000037:antagonists & inhibitors; D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors* / Q000235:genetics; D000818:Animals; D000981:Antiprotozoal Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology / Q000633:toxicity; D002460:Cell Line; D004164:Diphosphonates / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology / Q000633:toxicity; D005578:Fosfomycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D051228:Geranyltranstransferase; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors; D010088:Oxidoreductases / Q000037:antagonists & inhibitors; D021281:Quantitative Structure-Activity Relationship; D014122:Toxoplasma / Q000187:drug effects*; D014123:Toxoplasmosis / Q000401:mortality / Q000517:prevention & control
chemical_list: D000981:Antiprotozoal Agents; D004164:Diphosphonates; D009097:Multienzyme Complexes; D005578:Fosfomycin; C024640:fosmidomycin; D010088:Oxidoreductases; C114231:1-deoxy-D-xylulose 5-phosphate reductoisomerase; D019883:Alkyl and Aryl Transferases; D051228:Geranyltranstransferase; D019747:Aldose-Ketose Isomerases