The Existing Drug Vorinostat as a New Lead Against Cryptosporidiosis by Targeting the Parasite Histone Deacetylases.

Background: Cryptosporidiosis affects all human populations, but can be much more severe or life-threatening in children and individuals with weak or weakened immune systems. However, current options to treat cryptosporidiosis are limited.

Methods: An in vitro phenotypic screening assay was employed to screen 1200 existing drugs for their anticryptosporidial activity and to determine the inhibitory kinetics of top hits. Selected top hits were further evaluated in mice. The action of the lead compound vorinostat on the parasite histone deacetylase (HDAC) was biochemically validated.

Results: Fifteen compounds exhibited anticryptosporidial activity at nanomolar level in vitro. Among them, the histone deacetylase (HDAC) inhibitor vorinostat retained outstanding efficacy in vitro (half maximal effective concentration, EC50 = 203 nM) and in an interleukin 12 knockout mouse model (50% inhibition dose = 7.5 mg/kg). Vorinostat was effective on various parasite developmental stages and could irreversibly kill the parasite. Vorinostat was highly effective against the parasite native HDAC enzymes (half maximal inhibitory concentration, IC50 = 90.0 nM) and a recombinant Cryptosporidium parvum HDAC (the inhibitor constant, Ki = 123.0 nM).

Conclusions: These findings suggest the potential for repurposing of vorinostat to treat cryptosporidiosis, and imply that the parasite HDAC can be explored for developing more selective anticryptosporidial therapeutics.