Repurposing Infectious Disease Hits as Anti-Cryptosporidium Leads

Abstract

New drugs are critically needed to treat Cryptosporidium infections, particularly for malnourished children under 2 years old in the developing world and persons with immunodeficiencies. Bioactive compounds from the Tres-Cantos GSK library that have activity against other pathogens were screened for possible repurposing against Cryptosporidium parvum growth. Nineteen compounds grouped into nine structural clusters were identified using an iterative process to remove excessively toxic compounds and screen related compounds from the Tres-Cantos GSK library. Representatives of four different clusters were advanced to a mouse model of C. parvum infection, but only one compound, an imidazole-pyrimidine, led to significant clearance of infection. This imidazole-pyrimidine compound had a number of favorable safety and pharmacokinetic properties and was maximally active in the mouse model down to 30 mg/kg given daily. Though the mechanism of action against C. parvum was not definitively established, this imidazole-pyrimidine compound inhibits the known C. parvum drug target, calcium-dependent protein kinase 1, with a 50% inhibitory concentration of 2 nM. This compound, and related imidazole-pyrimidine molecules, should be further examined as potential leads for Cryptosporidium therapeutics.

Identification of and Structural Insights into Hit Compounds Targeting N-Myristoyltransferase for Cryptosporidium Drug Development

“…Our previous experience comparing target-based screens to cell-based assays suggests that IC 50 less than 2 μM is necessary to see growth inhibition, thus it is not surprising that the low affinity inhibitors did not show inhibition in this assay. 39 Crystallizable Constructs of CpNMT Provide A Platform for Structure-Guided Inhibitor Development. We performed a screening of CpNMT constructs to identify ones that could be overexpressed and used to generate highresolution co-crystal structures of the enzyme bound to the inhibitors (Supplementary Methods and Tables S1 and S2).…”

“…We found that compound 1 , but not 2 or 9 , inhibits growth of parasite on HCT-8 cells (Figure ). Our previous experience comparing target-based screens to cell-based assays suggests that IC 50 less than 2 μM is necessary to see growth inhibition, thus it is not surprising that the low affinity inhibitors did not show inhibition in this assay …”

Emerging treatment options for cryptosporidiosis

“…Phenotypic screens may identify compounds with novel targets or pathways, with the caveat that target identification and MoA studies are often needed after active compounds are discovered. There have been a number of additional phenotypic screens for Cryptosporidium drug discovery [ 25 , 26 ], though the compounds discussed in this review are the most advanced.…”

Tyrosine Kinase Inhibitors Display Potent Activity against Cryptosporidium parvum

“…Drug repurposing involves the identification of new uses of approved drugs, while target repurposing, for infectious diseases, involves the matching of pathogen targets with their human orthologs in which hits/leads have been described ( 29 , 30 ). Among infectious diseases, other pragmatic approaches to accelerate new drug-discovery efforts include the repurposing of bioactive compounds with activity in similar pathogens ( 26 ). High-throughput screening of kinase libraries such as the publicly available GlaxoSmithKline (GSK) Published Kinase Inhibitor Set (PKIS) and other kinase collections have resulted in identification of hit compounds against other parasites such as Plasmodium falciparum and Trypanosoma brucei and thus provided an excellent starting point for further optimization and validation of compounds using target-based approaches ( 29 , 31 – 33 ).…”