title: Inhibition of Calcium-Dependent Protein Kinase 1 (CDPK1) In Vitro by Pyrazolopyrimidine Derivatives Does Not Correlate with Sensitivity of Cryptosporidium parvum Growth in Cell Culture.
abstract: Cryptosporidiosis is a serious diarrheal disease in immunocompromised patients and malnourished children, and treatment is complicated by a lack of adequate drugs. Recent studies suggest that the natural occurrence of a small gatekeeper residue in serine threonine calcium-dependent protein kinase 1 (CDPK1) of Cryptosporidium parvum might be exploited to target this enzyme and block parasite growth. Here were explored the potency with which a series of pyrazolopyrimidine analogs, which are selective for small gatekeeper kinases, inhibit C. parvum CDPK1 and block C. parvum growth in tissue culture in vitro. Although these compounds potently inhibited kinase activity in vitro, most had no effect on parasite growth. Moreover, among those that were active against parasite growth, there was a very poor correlation with their 50% inhibitory concentrations against the enzyme. Active compounds also had no effect on cell invasion, unlike the situation in Toxoplasma gondii, where these compounds block CDPK1, prevent microneme secretion, and disrupt cell invasion. These findings suggest that CPDK1 is not essential for C. parvum host cell invasion or growth and therefore that it is not the optimal target for therapeutic intervention. Nonetheless, several inhibitors with low micromolar 50% effective concentrations were identified, and these may affect other essential targets in C. parvum that are worthy of further exploration.
authors.affiliation: Department of Pathobiology, University of Illinois College of Veterinary Medicine, Urbana, Illinois, USA.
authors.forename: Theresa B
authors.initials: TB
authors.lastname: Kuhlenschmidt
authors.affiliation: Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Florentine U
authors.initials: FU
authors.lastname: Rutaganira
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: Shaojun
authors.initials: S
authors.lastname: Long
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: Keliang
authors.initials: K
authors.lastname: Tang
authors.affiliation: Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Kevan M
authors.initials: KM
authors.lastname: Shokat
authors.affiliation: Department of Pathobiology, University of Illinois College of Veterinary Medicine, Urbana, Illinois, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Kuhlenschmidt
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA sibley@wustl.edu.
authors.forename: L David
authors.initials: LD
authors.lastname: Sibley
mesh_terms: D000818:Animals; D000981:Antiprotozoal Agents / Q000138:chemical synthesis / Q000494:pharmacology*; D002417:Cattle; D002460:Cell Line; D016785:Cryptosporidium parvum / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D004847:Epithelial Cells / Q000187:drug effects / Q000469:parasitology; D005243:Feces / Q000469:parasitology; D015870:Gene Expression; D006801:Humans; D020128:Inhibitory Concentration 50; D008297:Male; D021261:Parasitic Sensitivity Tests; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011720:Pyrazoles / Q000138:chemical synthesis / Q000494:pharmacology*; D011743:Pyrimidines / Q000138:chemical synthesis / Q000494:pharmacology*; D034101:Sporozoites / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development; D013329:Structure-Activity Relationship; D017871:Calcium-Calmodulin-Dependent Protein Kinases
chemical_list: D000981:Antiprotozoal Agents; D011494:Protein Kinases; D015800:Protozoan Proteins; D011720:Pyrazoles; D011743:Pyrimidines; D017871:Calcium-Calmodulin-Dependent Protein Kinases