Identification of Cryptosporidium parvum Active Chemical Series by Repurposing the Open Access Malaria Box

The apicomplexan parasites Cryptosporidium parvum and Cryptosporidium hominis are major etiologic agents of human cryp-tosporidiosis. The infection is typically self-limited in immunocompetent adults, but it can cause chronic fulminant diarrhea in immunocompromised patients andmalnutrition and stunting in children. Nitazoxanide, the current standard of care for cryp-tosporidiosis, is only partially efficacious for children and is nomore effective than a placebo for AIDS patients. Unfortunately, financial obstacles to drug discovery for diseases that disproportionately affect low-income countries and technical limitations associated with studies of Cryptosporidium biology impede the development of better drugs for treating cryptosporidiosis. Using a cell-based high-throughput screen, we queried theMedicines for Malaria Venture (MMV) Open Access Malaria Box for activity against C. parvum. We identified 3 novel chemical series derived from the quinolin-8-ol, allopurinol-based, and 2,4-diamino-quinazoline chemical scaffolds that exhibited submicromolar potency against C. parvum. Potency was conserved in a subset of compounds from each scaffold with varied physicochemical properties, and two of the scaffolds identified exhibit more rapid inhibition of C. parvum growth than nitazoxanide, making them excellent candidates for further development. The 2,4-di-amino-quinazoline and allopurinol-based compounds were also potent growth inhibitors of the related apicomplexan parasite Toxoplasma gondii, and a good correlation was observed in the relative activities of the compounds in the allopurinol-based series against T. gondii and C. parvum. Taken together, these data illustrate the utility of the Open Access Malaria Box as a source of both potential leads for drug development and chemical probes to elucidate basic biological processes in C. parvu