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

Abstract

The apicomplexan parasites Cryptosporidium parvum and Cryptosporidium hominis are major etiologic agents of human cryptosporidiosis. The infection is typically self-limited in immunocompetent adults, but it can cause chronic fulminant diarrhea in immunocompromised patients and malnutrition and stunting in children. Nitazoxanide, the current standard of care for cryptosporidiosis, is only partially efficacious for children and is no more 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 the Medicines 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-diaminoquinazoline 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-diamino-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. parvum and other apicomplexan parasites.

Extensive Shared Chemosensitivity between Malaria and Babesiosis Blood-Stage Parasites

“…Imidocarb exhibited IC 50 values of 230 to 690 nM against the Babesia parasite species, and we observed IC 50 (13). The breadth of babesiacidal Malaria Box inhibitors is striking in relation to the comparatively few Malaria Box inhibitors reportedly active against nonerythrocyte apicomplexans, such as T. gondii, C. parvum, and T. annulata (14)(15)(16). We speculate that this difference may reflect the existence of conserved targets required for proliferation within a similar erythrocytic niche for diverse apicomplexan hemoprotozoan parasites and/or the close phylogenetic relatedness of Plasmodium and Babesia spp.…”

“…In 2011, the nonprofit group Medicines for Malaria Venture (MMV) made available to the research community the Malaria Box, a collection of 400 chemically diverse, previously uncharacterized blood-stage antimalarials (13). Researchers have screened the antiparasitic activities of the Malaria Box compounds in nonerythrocytic host cells for the apicomplexans T. gondii, Cryptosporidium parvum, and Theileria annulata and identified a limited number of inhibitors (Ͻ3% of the library) active against each of these species (14)(15)(16). Here, we measured the susceptibilities of multiple blood-stage Plasmodium and Babesia parasite species to the Malaria Box compounds and found that erythrocyte-specific apicomplexans share considerable chemical sensitivities during the clinically relevant stages of parasitic infection.…”

Repurposing the Open Access Malaria Box To Discover Potent Inhibitors of Toxoplasma gondii and Entamoeba histolytica

“…In a very recent study, a strategy similar to ours was adopted to repurpose the open access Malaria Box to identify chemical series active against Cryptosporidium parvum (42). The authors showed in a subsidiary objective that the 2,4-diamino-quinazoline-based compounds were also potent growth inhibitors of the related apicomplexan parasite T. gondii of the RH strain from which the TS-4 strain used in our study was derived.…”

Inhibition of Calcium-Dependent Protein Kinase 1 (CDPK1) In Vitro by Pyrazolopyrimidine Derivatives Does Not Correlate with Sensitivity of Cryptosporidium parvum Growth in Cell Culture

“…Therefore, there is a need to define new targets and to identify compounds that effectively inhibit parasite growth. An added challenge in working with Cryptosporidium is that it does not undergo continuous propagation in vitro, although short-term tissue culture assays have been used to screen for small-molecule inhibitors of C. parvum replication (9,10).…”