There is good momentum in the discovery and development of drugs active against the blood stage of malaria, but new compounds active against other stages of malaria are sorely needed. As the goal of malaria eradication is now on center stage, new drugs active against the liver stage of malaria, most particularly the dormant hypnozoites of Plasmodium vivax and P. ovale will be required. Our long-term goal is to leverage RC-12 to discover a new orally active single-dose antimalarial drug with high efficacy against hypnozoites and other exoerythrocytic stage parasites. The objective of this proposal, the first step in pursuit of this goal, is to identify the active metabolites of RC-12 that endow tis chemotype with its high efficacy in the 'gold-standard'hypnozoite animal model - P. cynomolgi-infected rhesus monkeys. Our central hypothesis is that species-specific metabolism accounts for the dichotomy between the high efficacy of RC-12 against P. cynomolgi hypnozoites in rhesus monkeys and the lack of efficacy of RC-12 against P. vivax hypnozoites in humans. This hypothesis arose on the basis of preliminary data produced in our laboratories. The rationale that underlies this research is to provide tools to begin to elucidate the pharmacokinetics/pharmacodynamics (PK/PD) of RC-12 and to identify new leads (active metabolites) for drug discovery. To do so, and to test our central hypothesis, we propose the following three specific aims: 1) To synthesize the nine putative human, monkey, and rat RC-12 CYP450 metabolites to confirm their assigned structures;2) To establish a baseline metabolic and pharmacokinetic profile for RC-12;3) To assess RC-12 and its CYP450 metabolites for activity against P. cynomolgi hypnozoites in both rhesus and human hepatocytes. Our approach is innovative because the metabolism and PK of RC-12 have never been studied and our proposed use of both rhesus and human hepatocytes will effectively dissect differences in host metabolism vs. protozoal species compound susceptibility without using P. vivax parasites. The expected outcomes from this work are as follows. First, we will achieve a thorough understanding of the CYP450 metabolism of RC-12. Second, we will identify one or more active metabolites of RC-12. Third, we will have, for the first time, generated PK data for RC-12. We assert that our proposed research is significant because it will provide the basis for the discovery of a new orally active antimalarial drug with high efficacy against P. vivax and P. ovale hypnozoites and other exoerythrocytic stage parasites informed by our knowledge of the PK/PD profile of RC-12.
This proposed research is relevant to NIH's mission because it will generate new knowledge about the metabolism and pharmacokinetics of RC-12, a promising chemotype active against liver-stage malaria. This work will generate the necessary baseline data to initiate a multi-dimensional lead optimization campaign that could lead to the discovery of a new antimalarial drug. The project is relevant to public health because the discovery of such a drug would be important in the chemotherapy and eradication of malaria.
