Analysis of the antimalarial activity of a selected series of 17 9-phenanthrenecarbinols against cultured strains of Plasmodium falciparum and against P. berghei in mice following oral administration indicated that the rankings of activities within the series were influenced by substituents on the 9-carbinol and the route of administration. Compounds with alkylamino-alkyl groups were ranked as most active by an in vitro screening system which assayed activity against chloroquine-sensitive and chloroquine-resistant strains of cultured P. falciparum by the inhibition of uptake of radiolabelled hypoxanthine. There were few differences in ranking of activities between the two strains. Although there was a significant difference between activities of an erythro- and a threo-racemate, activities of the four optical isomers of this compound were comparable. Among the series, compounds with a 2-piperidyl substituent on the 9-carbinol were ranked most active by the oral route of administration as assayed by the cure rates of mice infected with P. berghei. Correlation of these observations with previously published data on the activity of these compounds against P. falciparum in Owl monkeys and P. berghei in mice following subcutaneous administration suggested that neither species of host nor strains of parasite significantly influenced the ranking of activities of this class of compound.

The antimalarial activities of amodiaquine, the desethyl metabolite of amodiaquine, chloroquine, and mefloquine were evaluated against 35 field isolates of Plasmodium falciparum collected from eastern Thailand, October-December 1985, to define patterns of cross-resistance among these compounds. The assay system was based on the in vitro inhibition of schizont maturation. The parasites were generally sensitive to mefloquine (mean 50%-inhibitory concentrations = 9.98 nM) and highly resistant to chloroquine (IC50 = 313 nM). The mean in vitro activity of desethylamodiaquine (67.5 nM) was approximately 3.5 times lower than that of amodiaquine (18.2 nM). There was a significant rank-order correlation between the IC50S of desethylamodiaquine and chloroquine, but not between amodiaquine and chloroquine, which suggests that the apparent cross-resistance between chloroquine and amodiaquine observed in clinical studies may be more closely related to the cross-resistance between chloroquine and the metabolite rather than between chloroquine and the parent compound. Isolates with IC50 values of amodiaquine greater than 20 nM demonstrated a high degree of correlation with values of desethylamodiaquine; however, it was not possible to accurately predict the sensitivity to desethylamodiaquine of isolates which had IC50 values of amodiaquine of less than 20 nM.

The individual effects of two putative metabolites of primaquine (5,6-dihydroxyprimaquine and 5,6-dihydroxy-8-aminoquinoline) on the hexose monophosphate shunt (HMS) and on the ATP-dependent proteolytic system which rapidly degrades oxidized erythrocyte protein were measured in intact red blood cells in vitro from two blood donors. In red cells treated with nitrite (1-40 mM) or phenylhydrazine (0.01-10 mM), proteolytic activity was detected only with concentrations (7.5 mM NaNO2 and 0.25 mM phenylhydrazine) causing greater than 15-fold elevation of HMS activity, and glucose-6-phosphate dehydrogenase (G6PD)-deficient (25% of normal activity) red cell suspensions thus treated showed approximately 30% greater proteolysis. G6PD-normal and deficient red cells treated with the primaquine analogs, however, did not experience proteolysis with concentrations (0.25 mM) in excess of those causing 17-fold elevation of HMS activity. Stimulation of the HMS by the primaquine analogs thus appears unrelated to an erythrotoxic oxidative stress. Methylene blue is known to cause an elevation of HMS activity through direct and diaphorase II-dependent oxidation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) which is independent of injurious oxidative stress. It was found that the putative primaquine metabolites also caused direct and diaphorase II-dependent oxidation of NADPH in dilute hemolysate, thus suggesting that the putative primaquine metabolites have a methylene blue-like redox disposition in red blood cells. Results obtained in this study suggest that the hemolytic toxicity of primaquine may be unrelated to processes which lead to oxidative deterioration of red cell protein.

Of 10 000 compounds tested for tissue schizontocidal activity in a Plasmodium gallinaceum-chick model, 157 were also tested in a definitive mouse test (DMT) and 277 in a rhesus monkey test (RMT). The results in the avian model were 78% and 55% in agreement with those of the DMT and RMT, respectively. This result is not as good as that for a tissue schizontocidal mouse screen previously reported, which showed 93% and 80% agreement with DMT and RMT, respectively. More than three-quarters of the compounds tested in DMT and RMT were 8-aminoquinolines, a chemical class known to have tissue schizontocidal activity.

Parameters of blood-induced infections of the Vietnam Oak Knoll, Vietnam Smith, and Uganda Palo Alto strains of Plasmodium falciparum studied in 395 Panamanian owl monkeys in this laboratory between 1976-1984 were compared with those reported from another laboratory for 665 Colombian owl monkeys, studied between 1968-1975, and, at the time, designated Aotus trivirgatus griseimembra. The virulence of these strains was less in Panamanian than in Colombian owl monkeys, as indicated by lower mortality rates of the Panamanian monkeys during the first 30 days of patency. Maximum parasitemias of the Vietnam Smith and Uganda Palo Alto strain, in Panamanian owl monkeys dying during the first 15 days of patent infection, were significantly higher than in Colombian owl monkeys. Panamanian owl monkeys that survived the primary attack had significantly higher maximum parasitemias than the surviving Colombian owl monkeys. Peak parasitemias were attained significantly earlier after patency in Panamanian than in Colombian owl monkeys, irrespective of the strain of P. falciparum. More Panamanian than Colombian owl monkeys evidenced self-limited infection after the primary attack of either the Vietnam Smith or Uganda Palo Alto strain. The duration of the primary attacks and recrudescences were significantly shorter in Panamanian than in Colombian owl monkeys. Mean peak parasitemias during recrudescence were usually higher in Panamanian owl monkeys than in Colombian monkeys. Differences of infection parameters were probably attributable, in part, to geographical origin of the two monkey hosts and parasite strains.

Treatment of mouse tail skins with hexachlorophene (1.25% w/v) in absolute methanol or 70% isopropanol suppressed Schistosoma mansoni infections by more than 95% even when the application was performed up to three days prior to exposure to cercarial suspensions by tail immersion. Treatment with concentrations of 0.313% or higher one day prior to exposure provided at least 98% protection when the treated surface was not subjected to water washes of greater duration than 1/2 hour. Tail immersion application of 1.25% hexachlorophene one day prior to exposure still provided 87-92% protection after 3 hours water wash. Wipe application of 1.25% hexachlorophene three days prior to exposure still provided 93% protection following 3 hours water wash. High cercarial recoveries from exposure tubes at the end of exposure periods indicated high antipenetrant activity for hexachlorophene. Sufficient hexachlorophene leached from treated tail skins into the surrounding water to affect subsequently added cercariae so that they were no longer infective to untreated mice.

Existing primary screens for radical curative antimalarial drugs fail to adequately detect many compounds which affect the latent, exoerythrocytic hypnozoite, the stage of the parasite responsible for relapse. At the same time, these screens falsely identify a wide range of compounds with no radical curative activity. The avian malaria, Plasmodium gallinaceum, and Aedes aegypti mosquitos were used in a screen which measures the effects of candidate compounds on gametocytes and their development within the mosquito. Sporontocidal and gametocytocidal effects could be differentiated by this screen. In a blind study, those compounds shown to be exclusively gametocytocidal were those same drugs which had previously been shown to have radical curative effects against true relapsing malarias. The chicken malaria gametocyte screen was more sensitive than the rodent screens in detecting useful compounds, with a minimum of false positive identifications.

The antitrypanosomal activity of 2,5-bis(4-guanylphenyl)furan dihydrochloride was evaluated with Trypanosoma rhodesiense in a primate model and its toxicological profile determined. The new antitrypanosomal agent failed to show chemotherapeutic advantages over pentamidine and investigation of the compound was halted.

A series of 2-acylpyridine thiosemicarbazones was evaluated in vitro against a chloroquine-resistant Plasmodium falciparum strain. Antimalarial activity was assessed by the inhibition of uptake of [G-3H]hypoxanthine by the parasites. Among the mono- and disubstituted derivatives tested, 13 of 17 had 50% inhibitory doses of less than 10 ng/ml. Increasing the size of the ring at N4 from four to five, six, and seven members produced concomitant decreases in activity. Similarly, increasing the size of the aliphatic substituent on the azomethine carbon reduced activity. Selected compounds were also tested against a chloroquine-susceptible strain. The results suggested that the activities of these agents were not modified significantly by resistance to chloroquine. In general, in vitro activities correlate poorly with the in vivo activities in mice infected with Plasmodium berghei.

The dihydrofolate reductase inhibitor 2,4-diamino-6-(2-naphthyl-sulfonyl)-quinazoline and its tetrahydro analog 2,4-diamino-6-(2-naphthyl-sulfonyl)-5,6,7,8-tetrahydroquinazoline were evaluated for possible synergism in treating trophozoite-induced Plasmodium cynomolgi var. bastianellii malaria of rhesus monkeys. The degree of synergism, if it exists, was found to be not nearly as great as observed previously with this combination of drugs against Plasmodium berghei infections of mice.

An antimalarial drug testing system is described which utilizes trophozoite induced Plasmodium cynomolgi malaria in rhesus monkeys. The schizonticidal activity of standard antimalarial drugs in this system is reported. The system accurately predicted anti-malarial activity in man of 8 of 9 compounds selected for clinical trials.

1.1. The production of CO2 from selected carbohydrates by male and female Schistosoma mansoni and S. japonicum was studied.2.2. The largest amounts of CO2 were produced from glucose, fructose and mannose while lesser amounts were provided from galactose, maltose, lactose, glucosamine and mannitol.3.3. Both sex- and species-related differences were found.4.4. The differences observed in CO2 production from individually labeled carbons of the glucose molecule and quantitative differences in this incorporation of the glucose carbons into glycogen also suggested quantitative differences in the metabolic pathways between species and sexes.