Novel Plasmodial Surface Anion Channel Inhibitors as Antimalarial Drugs

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DESCRIPTION (provided by applicant): The overall objective of this project is to generate new, potent, selective antimalarials that act through a novel mechanism of blocking the plasmodial surface anion channel (PSAC), a previously unexploited and highly conserved plasmodial target. Human malaria is caused by five species of protozoan parasites in the genus Plasmodium. It is estimated that there are more than 200 million clinical cases of P. falciparum malaria and over 600,000 deaths annually, with ninety percent of the deaths occurring in sub-Saharan Africa. The malaria parasites, most importantly P. falciparum, require two hosts, which are humans and female Anopheles mosquitoes. Disease is transmitted to humans from the bite of an infected mosquito. There are no effective vaccines available to prevent malaria, but several small molecule treatment options exist, such as chloroquine (CQ) and artemisinin. CQ, once the mainstay of malaria treatment, has lost much of its efficacy because of mutations that confer resistance. Resistance to artemisinin-based therapy is now appearing in Southeast Asia. New small molecule drugs, especially those working on new targets that may be less susceptible to acquired resistance, are desperately needed. PSAC is a newly discovered essential antimalarial target which was recently validated by gene identification experiments. The channel is produced by the parasite and inserts into the infected erythrocyte membrane. It was demonstrated by Dr. Sanjay Desai, NIH, that PSAC inhibitors, discovered by high-throughput screening, kill parasites by direct action on this channel. In preliminary studies, Dr. Desai, developed and applied a screen for PSAC inhibitors using a sorbitol transport assay, which resulted in the identification of several chemotypes that displayed inhibitory potencies (K0.5 PSAC block) in the nanomolar range. Compounds also inhibited plasmodial growth with low nanomolar potencies (IC50). Two of the "hit compound" chemical scaffolds were chosen for medicinal chemistry optimization on the basis of their potency, low cytotoxicity, tractability of synthesis and overall favorable in vitro "drug-like" ADME results. The first, MBX 2366, was subjected to SAR evaluation in a Phase I SBIR project. Compounds in this series demonstrated efficacy, low toxicity and excellent in vitro ADME properties. The Phase II project proposed here will focus on lead optimizing and scale-up chemistry, further mechanism of action studies and then in vivo pharmacokinetics and toxicology studies in preparation for efficacy testing. We will test the efficacy of prioritized compounds in the humanized SCID mouse model, to be conducted by Medicines for Malaria Venture (MMV). In Phase III, we will conduct IND-enabling preclinical studies to advance several of the most potent and least toxic compounds from the MBX 2366 scaffold. The interdisciplinary approach, which will merge the antimalarial expertise of Dr. Desai and Dr. Jeremy Burrows of MMV with the anti-infective research and development capabilities of Microbiotix, will produce inhibitors for a newly discovered, essential and conserved malarial target and provide new treatment options for resistant infections.