Prodrug Nanotherapy Demonstrates Anticryptosporidial Efficacy in a Mouse Model of Chronic Infection

The gastrointestinal disease cryptosporidiosis, caused by the genus , is a common cause of diarrheal diseases in children, particularly in developing countries and frequently fatal in immunocompromised individuals. ()-specific bifunctional dihydrofolate reductase-thymidylate synthase (DHFR-TS) has been a molecular target for inhibitor design. (.) While nanomolar inhibitors of DHFR-TS have been identified at the biochemical level, effective delivery of these compounds to achieve anticryptosporidial activity in cell culture and models of parasite infection remains a major challenge in developing new therapies. Previous studies, using a nanotherapy approach, have shown a promising DHFR-TS inhibitor, 906, that can successfully target parasites in cell culture with nanomolar anticryptosporidial activity. This formulation utilized poly(lactic--glycolic acid) (PLGA) nanoparticles (NPs) loaded with 906 (NP-906) and conjugated with a monoclonal antibody (MAb) on the nanoparticle surface to specifically target the glycoprotein GP25-200 in excysting oocysts. However, a limitation for use is antibody susceptibility to gastric acidity. To address this gap, a prodrug diethyl ester form of 906 (MAb-NP-Prodrug) was synthesized that allowed higher compound loading in the MAb-coated PLGA nanoparticles. An oral formulation was prepared by loading lyophilized MAb-NP-Prodrug into gelatin capsules with an enteric coating for gastric stability. Proof-of-concept studies with this oral formulation demonstrated antiparasitic activity in a chronic mouse model of infection. Efficacy was observed after a low daily dose of 2 × 8 mg kg for 5 days, when examined 6 and 20 days postinfection, offering a new avenue of drug delivery to be further explored.