Scalable preparation and differential pharmacologic and toxicologic profiles of primaquine enantiomers.

Hematotoxicity in individuals genetically deficient in glucose-6-phosphate dehydrogenase (G6PD) activity is the major limitation of primaquine (PQ), the only antimalarial drug in clinical use for treatment of relapsing Plasmodium vivax malaria. PQ is currently clinically used in its racemic form. A scalable procedure was developed to resolve racemic PQ, thus providing pure enantiomers for the first time for detailed preclinical evaluation and potentially for clinical use. These enantiomers were compared for antiparasitic activity using several mouse models and also for general and hematological toxicities in mice and dogs. (+)-(S)-PQ showed better suppressive and causal prophylactic activity than (-)-(R)-PQ in mice infected with Plasmodium berghei. Similarly, (+)-(S)-PQ was a more potent suppressive agent than (-)-(R)-PQ in a mouse model of Pneumocystis carinii pneumonia. However, at higher doses, (+)-(S)-PQ also showed more systemic toxicity for mice. In beagle dogs, (+)-(S)-PQ caused more methemoglobinemia and was toxic at 5 mg/kg of body weight/day given orally for 3 days, while (-)-(R)-PQ was well tolerated. In a novel mouse model of hemolytic anemia associated with human G6PD deficiency, it was also demonstrated that (-)-(R)-PQ was less hemolytic than (+)-(S)-PQ for the G6PD-deficient human red cells engrafted in the NOD-SCID mice. All these data suggest that while (+)-(S)-PQ shows greater potency in terms of antiparasitic efficacy in rodents, it is also more hematotoxic than (-)-(R)-PQ in mice and dogs. Activity and toxicity differences of PQ enantiomers in different species can be attributed to their different pharmacokinetic and metabolic profiles. Taken together, these studies suggest that (-)-(R)-PQ may have a better safety margin than the racemate in human.

Antiparasitic activities and toxicities of individual enantiomers of the 8-aminoquinoline 8-[(4-amino-1-methylbutyl)amino]-6-methoxy-4-methyl-5-[3,4-dichlorophenoxy]quinoline succinate.

8-Aminoquinolines are an important class of antiparasitic agents, with broad utility and excellent efficacy, but also limitations due to hematological toxicities, primarily methemoglobinemia and hemolysis. One representative from this class, (+/-)-8-[(4-amino-1-methylbutyl)amino]-6-methoxy-4-methyl-5-[3,4-dichlorophenoxy]quinoline succinate (NPC1161C), proved extremely efficacious in animal models of malaria and pneumocystis pneumonia. This racemic mixture was separated into its component enantiomers by chemical and chromatographic means. The enantiomers were evaluated for antiparasitic activity in murine models of Plasmodium berghei, Pneumocystis carinii, and Leishmania donovani infection, as well as the propensity to elicit hematotoxicity in dogs. The (-)-enantiomer NPC1161B was found to be more active (by severalfold, depending on the dosing regimen) than the (+)-enantiomer NPC1161A in all of these murine models. In addition, the (-) enantiomer showed markedly reduced general toxicity in mice and reduced hematotoxicity in the dog model of methemoglobinemia. It is concluded that the configuration at the asymmetric center in the 8-amino side chain differentially affects efficacy and toxicity profiles and thus may be an important determinant of the "therapeutic window" for compounds in this class.

Correlation of organism burden and alveolar macrophage counts during infection with Pneumocystis carinii and recovery.

Changes in the number of alveolar macrophages were correlated with organism burden during Pneumocystis carinii infection. The lungs of healthy, dexamethasone-treated, and dexamethasone-treated and P. carinii-infected rats were lavaged with phosphate-buffered saline. Counting of alveolar macrophages in the lavage fluids revealed that P. carinii infection caused a 58% decrease in the number of alveolar macrophages and that higher P. carinii organism burdens caused a more rapid decrease in alveolar macrophage number. As a control, healthy rats were challenged with the same number of organisms as that normally used to generate P. carinii infections in dexamethasone-treated rats. Thirteen days after challenge, these rats had a profound (54%) increase in alveolar macrophage number in response to the challenge, while the number of alveolar macrophages in immunosuppressed and P. carinii-infected rats had decreased significantly by this time point. These experiments created the first animal model to mimic human pneumocystis pneumonia in alveolar macrophage number alterations. Reduction of P. carinii organism numbers by treatment of rats with trimethoprim and sulfamethoxazole brought a slow rebound in alveolar macrophage number, while recovery from P. carinii infection by cessation of immunosuppression brought a rapid rebound in alveolar macrophage number. These results suggest that both the immune state of the host and P. carinii burden affect alveolar macrophage number.