Cryptosporidiosis, a diarrheal disease usually caused by Cryptosporidium parvum or Cryptosporidium hominis in humans, can result in fulminant
diarrhea and death in
AIDS patients and
chronic infection and
stunting in children.
Nitazoxanide, the current standard of care, has limited efficacy in children and is no more effective than placebo in patients with advanced
AIDS. Unfortunately, the lack of financial incentives and the technical difficulties associated with working with Cryptosporidium parasites have crippled efforts to develop effective treatments. In order to address these obstacles, we developed and validated (Z' score = 0.21 to 0.47) a cell-based high-throughput assay and screened a library of
drug repurposing candidates (the NIH Clinical Collections), with the hopes of identifying safe, FDA-approved drugs to treat
cryptosporidiosis. Our screen yielded 21 compounds with confirmed activity against C. parvum growth at concentrations of <10 μM, many of which had well-defined mechanisms of action, making them useful tools to study basic biology in addition to being potential
therapeutics. Additional work, including structure-activity relationship studies, identified the human 3-hydroxy-3-methyl-glutaryl-coenzyme A (
HMG-CoA) reductase inhibitor itavastatin as a potent inhibitor of C. parvum growth (50% inhibitory concentration [IC(50)] = 0.62 μM). Bioinformatic analysis of the Cryptosporidium genomes indicated that the parasites lack all known
enzymes required for the synthesis of
isoprenoid precursors. Additionally,
itavastatin-induced growth inhibition of C. parvum was partially reversed by the addition of exogenous
isopentenyl pyrophosphate, suggesting that
itavastatin reduces Cryptosporidium growth via on-target inhibition of host
HMG-CoA reductase and that the parasite is dependent on the host cell for synthesis of
isoprenoid precursors.