Date Published: March 5, 2008
Publisher: Public Library of Science
Author(s): Ernest J. Mui, Guy A. Schiehser, Wilbur K. Milhous, Honghue Hsu, Craig W. Roberts, Michael Kirisits, Stephen Muench, David Rice, J. P. Dubey, Joseph W. Fowble, Pradipsinh K. Rathod, Sherry F. Queener, Susan R. Liu, David P. Jacobus, Rima McLeod, Greg Matlashewski
Abstract: Background and MethodologyToxoplasma gondii causes substantial morbidity, mortality, and costs for healthcare in the developed and developing world. Current medicines are not well tolerated and cause hypersensitivity reactions. The dihydrotriazine JPC-2067-B (4, 6-diamino-1, 2-dihydro-2, 2-dimethyl-1-(3′(2-chloro-, 4-trifluoromethoxyphenoxy)propyloxy)-1, 3, 5-triazine), which inhibits dihydrofolate reductase (DHFR), is highly effective against Plasmodium falciparum, Plasmodium vivax, and apicomplexans related to T. gondii. JPC-2067-B is the primary metabolite of the orally active biguanide JPC-2056 1-(3′-(2-chloro-4-trifluoromethoxyphenyloxy)propyl oxy)- 5-isopropylbiguanide, which is being advanced to clinical trials for malaria. Efficacy of the prodrug JPC-2056 and the active metabolite JPC-2067-B against T. gondii and T. gondii DHFR as well as toxicity toward mammalian cells were tested.Principal Findings and ConclusionsHerein, we found that JPC-2067-B is highly effective against T. gondii. We demonstrate that JPC-2067-B inhibits T. gondii growth in culture (IC50 20 nM), inhibits the purified enzyme (IC50 6.5 nM), is more efficacious than pyrimethamine, and is cidal in vitro. JPC-2067-B administered parenterally and the orally administered pro-drug (JPC-2056) are also effective against T. gondii tachyzoites in vivo. A molecular model of T. gondii DHFR-TS complexed with JPC-2067-B was developed. We found that the three main parasite clonal types and isolates from South and Central America, the United States, Canada, China, and Sri Lanka have the same amino acid sequences preserving key binding sites for the triazine.SignificanceJPC-2056/JPC-2067-B have potential to be more effective and possibly less toxic treatments for toxoplasmosis than currently available medicines.
Partial Text: Toxoplasmosis is a neglected tropical disease as well as a significant illness affecting persons throughout the world and new and improved medicines are greatly needed for this and other apicomplexan infections –. In developing tropical countries, the problems for persons with AIDS can be exacerbated due to lack of both anti-retroviral treatment and anti-Toxoplasma gondii treatment. In this setting, this opportunistic pathogen causes substantial neurologic disease and treatment of this illness can be especially difficult because current gold standard medicines are unobtainable and/or unaffordable and, due to their toxicity, require monitoring which exceeds the capacity of many of the available health care systems. Toxoplasmic eye disease (chorioretinitis) is frequent in certain areas of Brazil and Colombia, areas where the gold standard drugs are particularly problematic, and is caused by atypical parasites that present major recrudescent and recurrent clinical problems. T. gondii is highly pathogenic and lethal in an emerging problem in French Guiana and Suriname ,.
Our studies demonstrate that JPC-2067-B is effective against T. gondii in vitro with an IC50 of 20 nM and in vivo when administered by i.p. injection and the pro-drug JPC-2056 is effective in vivo when administered orally. Each of our results described herein with this novel new class of anti-folate compound, dihydrotriazine, parallels earlier findings with progenitors of this class which were not as suitable for use for humans, e.g. proguanil  and WR99210 . The major and compelling advantages of JPC-2056, which is moving into clinical trials, is in the reduction of toxicity and development of a much more readily bioavailable compound than WR99210. WR99210 will never be a medicine for humans because of difficulties in those areas, also reflected in the effect on the mammalian enzyme, Table 1. The advantages of bioavailability, high potency, specificity, selectivity and potential for elimination of toxicities that occur with pyrimethamine either used alone or in conjunction with sulfadiazine and other medicines and because JPC-2056 will be entering clinical trials for the treatment of malaria, testing of this new class of anti-folates against the related apicomplexan T. gondii , was very important. Our results suggest that the activity against T. gondii is significant and that JPC-2056 has the potential to replace the combination of pyrimethamine plus sulfadiazine or second line drugs in the treatment of toxoplasmosis.