Research ArticleInfectious Disease

Metal-captured inhibition of pre-mRNA processing activity by CPSF3 controls Cryptosporidium infection

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Science Translational Medicine  06 Nov 2019:
Vol. 11, Issue 517, eaax7161
DOI: 10.1126/scitranslmed.aax7161

Controlling Cryptosporidium

The apicomplexan parasite Cryptosporidium causes potentially life-threatening gastrointestinal symptoms, and treatment can be ineffective in vulnerable patient groups. Swale et al. show that a benzoxabarole, previously found to be effective against other apicomplexans, controlled cryptosporidiosis better than the standard of care in both neonatal and immunocompromised mouse models of infection. Biochemical assays and a cocrystal structure of the benzoxabarole bound to the active site of parasitic cleavage and polyadenylation specificity factor 3 (CPSF3) suggested that the selective targeting of Cryptosporidium by the benzoxabarole resulted from inhibition of parasitic pre-mRNA processing. This study proposes a potential treatment against cryptosporidiosis and provides insight into how oxabaroles inhibit apicomplexan parasites.


Cryptosporidium is an intestinal pathogen that causes severe but self-limiting diarrhea in healthy humans, yet it can turn into a life-threatening, unrelenting infection in immunocompromised patients and young children. Severe diarrhea is recognized as the leading cause of mortality for children below 5 years of age in developing countries. The only approved treatment against cryptosporidiosis, nitazoxanide, has limited efficacy in the most vulnerable patient populations, including malnourished children, and is ineffective in immunocompromised individuals. Here, we investigate inhibition of the parasitic cleavage and polyadenylation specificity factor 3 (CPSF3) as a strategy to control Cryptosporidium infection. We show that the oxaborole AN3661 selectively blocked Cryptosporidium growth in human HCT-8 cells, and oral treatment with AN3661 reduced intestinal parasite burden in both immunocompromised and neonatal mouse models of infection with greater efficacy than nitazoxanide. Furthermore, we present crystal structures of recombinantly produced Cryptosporidium CPSF3, revealing a mechanism of action whereby the mRNA processing activity of this enzyme is efficiently blocked by the binding of the oxaborole group at the metal-dependent catalytic center. Our data provide insights that may help accelerate the development of next-generation anti-Cryptosporidium therapeutics.

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