Norditerpene natural products from subterranean fungi with anti-parasitic activity
Cryptosporidium is a common, waterborne gastrointestinal parasite that causes diarrheal disease worldwide. Currently there are no effective therapeutics to treat cryptosporidiosis in at-risk populations. Since natural products are a known source of anti-parasitic compounds, we screened a library of extracts and pure natural product compounds isolated from bacteria and fungi collected from subterranean environments for activity against Cryptosporidium parvum. Eight structurally related norditerpene lactones isolated from the fungus Oidiodendron truncatum collected from the Soudan Iron mine in Minnesota showed potent activity and were further tested to identify the most active compounds. The availability of a diverse suite of natural structural analogs with varying activities allowed us to determine some structure activity relationships for both anti-parasitic activity as well as cytotoxicity. The two most potent compounds, oidiolactones A and B, had EC50s against intracellular Cryptosporidium parvum of 530 and 240 nM respectively without cytotoxicity to confluent HCT-8 host cells. Both compounds also inhibited the related parasite Toxoplasma gondii. Oidiolactone A was active against asexual, but not sexual, stages of C. parvum, and killed 80% of the parasites within 8 hours of treatment. This compound reduced C. parvum infection by 70% in IFN{gamma}-/- mice, with no signs of toxicity. The high potency, low cytotoxicity, and in vivo activity combined with high production, easy isolation from fungi, and synthetic accessibility make oidiolactones A and B attractive scaffolds for the development of new anti-Cryptosporidium therapeutics.