Short report: floxacrine analog WR 243251 inhibits hematin polymerization.

Floxacrine was a promising antimalarial compound that led to the identification of WR 243251. On the basis of their structures, we suspected that these compounds might be good inhibitors of hematin polymerization. Indeed, WR 243251 was as potent and floxacrine was only 2-fold less potent than chloroquine as inhibitors of this process. However, this hematin polymerization inhibition did not completely account for the increased antimalarial potency of WR 243251 versus chloroquine. The WR 243251 ketone hydrolysis product WR 243246 was without activity against hematin polymerization. These data also confirm that hematin polymerization inhibition can be quite sensitive to small changes in inhibitor structure.

Anticancer agents suppressive for adult parasites of filariasis in Mongolian jirds.

Eight chemical structures not previously reported to possess antifilarial activity have been identified. A total of 79 compounds with anticancer properties were evaluated for possible macrofilaricidal activity against Brugia pahangi and Acanthocheilonema viteae transplanted into male Mongolian jirds (Meriones unguiculatus). All eight active compounds were suppressive for the onchocerciasis type (Acanthocheilonema viteae) of the disease. None was macrofilaricidal for the lymphatic form (Brugia pahangi). These new structures may represent a nucleus around which effective drugs can be synthesized.

Antimicrobial activities of mefloquine and a series of related compounds.

Mefloquine was found to have bactericidal activity against methicillin- and fluoroquinolone-susceptible and -resistant strains of Staphylococcus aureus and Staphylococcus epidermidis and gentamicin- and vancomycin-resistant strains of Enterococcus faecalis and Enterococcus faecium. The MICs were 16 microg/ml, and the minimal bactericidal concentrations (MBCs) were 16 to 32 microg/ml. These concentrations cannot be achieved in serum. Mefloquine was active at a more achievable concentration against penicillin-susceptible and -resistant Streptococcus pneumoniae, with MICs of 0.2 to 1.5 microg/ml. Mefloquine was not active against gram-negative bacteria and yeasts. In an attempt to find more active derivatives, 400 mefloquine-related compounds were selected from the chemical inventory of The Walter Reed Army Institute of Research. We identified a series of compounds containing a piperidine methanol group attached to pyridine, quinoline, and benzylquinoline ring systems. These had activities similar to that of mefloquine against S. pneumoniae but were far more active against other gram-positive bacteria (MICs for staphylococci, 0.8 to 6.3 microg/ml). They had activities similar to that of amphotericin B against Candida spp. and Cryptococcus neoformans. Combinations of the compounds with gentamicin and vancomycin were additive against staphylococci and pneumococci. The MIC and MBC of gentamicin were decreased by four- to eightfold when this drug was combined with limiting dilutions of the compounds. There was no antagonism with other antimicrobial drugs. The compounds were rapidly bactericidal. They appear to act by disrupting cell membranes. Combinations of the compounds with aminoglycoside antibiotics may have potential for therapeutic use.

Structural specificity of chloroquine-hematin binding related to inhibition of hematin polymerization and parasite growth.

Considerable data now support the hypothesis that chloroquine (CQ)-hematin binding in the parasite food vacuole leads to inhibition of hematin polymerization and parasite death by hematin poisoning. To better understand the structural specificity of CQ-hematin binding, 13 CQ analogues were chosen and their hematin binding affinity, inhibition of hematin polymerization, and inhibition of parasite growth were measured. As determined by isothermal titration calorimetry (ITC), the stoichiometry data and exothermic binding enthalpies indicated that, like CQ, these analogues bind to two or more hematin mu-oxo dimers in a cofacial pi-pi sandwich-type complex. Association constants (K(a)'s) ranged from 0.46 to 2.9 x 10(5) M(-1) compared to 4.0 x 10(5) M(-1) for CQ. Remarkably, we were not able to measure any significant interaction between hematin mu-oxo dimer and 11, the 6-chloro analogue of CQ. This result indicates that the 7-chloro substituent in CQ is a critical structural determinant in its binding affinity to hematin mu-oxo dimer. Molecular modeling experiments reinforce the view that the enthalpically favorable pi-pi interaction observed in the CQ-hematin mu-oxo dimer complex derives from a favorable alignment of the out-of-plane pi-electron density in CQ and hematin mu-oxo dimer at the points of intermolecular contact. For 4-aminoquinolines related to CQ, our data suggest that electron-withdrawing functional groups at the 7-position of the quinoline ring are required for activity against both hematin polymerization and parasite growth and that chlorine substitution at position 7 is optimal. Our results also confirm that the CQ diaminoalkyl side chain, especially the aliphatic tertiary nitrogen atom, is an important structural determinant in CQ drug resistance. For CQ analogues 1-13, the lack of correlation between K(a) and hematin polymerization IC(50) values suggests that other properties of the CQ-hematin mu-oxo dimer complex, rather than its association constant alone, play a role in the inhibition of hematin polymerization. However, there was a modest correlation between inhibition of hematin polymerization and inhibition of parasite growth when hematin polymerization IC(50) values were normalized for hematin mu-oxo dimer binding affinities, adding further evidence that antimalarial 4-aminoquinolines act by this mechanism.

Successful topical treatment of murine cutaneous leishmaniasis with a combination of paromomycin (Aminosidine) and gentamicin.

Cutaneous leishmaniasis is presently treated with 20 days of parenteral therapy with a frequently toxic drug (antimony). Topical formulations of paromomycin (15%) plus methylbenzethonium chloride (MBCL, 12%) or plus urea (10%) in soft white paraffin have been tested for Old and New World disease in humans. We compared the efficacy of a new topical formulation, WR 279,396 (paromomycin [15%] plus gentamicin [0.5%]) to the clinical formulations in the treatment of cutaneous disease in BALB/c mice. Sixty-day-old lesions were treated twice a day for 10 days, and the response to therapy was determined over a further 70 days. For ulcers due to Leishmania major or to Leishmania mexicana, 100% of lesions in the WR 279,396 group healed by day 20 after therapy and did not relapse by day 70; 83% of lesions healed without relapse in the paromomycin-MBCL group. In the paromomycin-urea group, 100% of L. major lesions healed by day 30 but 30% relapsed. For ulcers due to Leishmania panamensis or Leishmania amazonensis, all lesions treated with WR 279,396 healed and did not relapse; < 50% of lesions treated with paromomycin-MBCL healed by day 30, and all lesions relapsed by day 70. In addition to being active, WR 279,396 was not toxic in this model and appears to have a cosmetic effect (promoting hair growth, healing, and limiting the size of the scar).

8-Aminoquinolines active against blood stage Plasmodium falciparum in vitro inhibit hematin polymerization.

From the Walter Reed Army Institute of Research (WRAIR) inventory, thirteen 8-aminoquinoline analogs of primaquine were selected for screening against a panel of seven Plasmodium falciparum clones and isolates. Six of the 13 8-aminoquinolines had average 50% inhibitory concentrations between 50 and 100 nM against these P. falciparum clones and were thus an order of magnitude more potent than primaquine. However, excluding chloroquine-resistant clones and isolates, these 8-aminoquinolines were all an order of magnitude less potent than chloroquine. None of the 8-aminoquinolines was cross resistant with either chloroquine or mefloquine. In contrast to the inactive primaquine prototype, 8 of the 13 8-aminoquinolines inhibited hematin polymerization more efficiently than did chloroquine. Although alkoxy or aryloxy substituents at position 5 uniquely endowed these 13 8-aminoquinolines with impressive schizontocidal activity, the structural specificity of inhibition of both parasite growth and hematin polymerization was low.

Polyamines: agents with macrofilaricidal activity.

There is a need for effective macrofilaricidal drugs. The polyamine metabolism of filarial worms has been recognized as a possible target for effective drug action. In an attempt to identify agents that might provide leads in developing an effective macrofilaricide, 78 polyamine compounds were selected from among > 250,000 structures that have been amassed by the Walter Reed Army Institute of Research, in the U.S.A. These thousands of agents have been chosen principally for drug-development programmes for other parasitic diseases. The 78 prospective drugs selected were evaluated for their macrofilaricidal activity against Brugia pahangi and Acanthocheilonema viteae, in male Mongolian jirds (Meriones unguiculatus). The animal models using these two parasites were designed to mimic, in so far as possible, human lymphatic filariasis and onchocerciasis, respectively. Thirteen of the compounds were found to be active although none of these has been previously reported to be macrofilaricidal. Two were suppressive for B. pahangi and 11 for A. viteae. These active agents may represent a nucleus around which highly effective drugs can be synthesised.

Development and validation of a method to extract and quantitate paromomycin and gentamicin from an Aquaphilic cream formulation.

Butanol and dilute sulfuric acid were used to extract paromomycin and gentamicin from Aquaphilic-based formulated creams. The extraction procedure was validated over different antibiotic concentration ranges for linearity, precision, accuracy, limited specificity, sensitivity and solution stability.

Dispiro-1,2,4,5-tetraoxanes: a new class of antimalarial peroxides.

Dispiro-1,2,4,5-tetraoxanes 2-4 were synthesized as potential peroxide antimalarial drugs. They had curative activity against Plasmodium berghei in vivo at single doses of 320 and 640 mg/kg which confirms earlier unpublished data. Moreover, artemisinin (1) and 4 had equivalent ED50's against P. berghei in vivo in the multiple-dose Thompson test; neither showed any evidence of acute toxicity at total doses of more than 12 g/kg. Dispiro-1,2,4,5-tetraoxane 4 had IC50's comparable to those of 1 against Plasmodium falciparum clones in vitro. These results confirm the potential of dispiro-1,2,4,5-tetraoxanes as a new class of inexpensive peroxide antimalarial drugs.

Bisquinolines. 1. N,N-bis(7-chloroquinolin-4-yl)alkanediamines with potential against chloroquine-resistant malaria.

On the basis of observations that several bisquinolines such as piperaquine possess notable activity against chloroquine-resistant malaria, 13 N,N-bis-(7-chloroquinolin-4-yl)alkanediamines were synthesized and screened against Plasmodium falciparum in vitro and Plasmodium berghei in vivo. Twelve of the thirteen bisquinolines had a significantly lower resistance index than did chloroquine; the resistance index was apparently unrelated to either in vitro or in vivo activity. Except for two compounds, there was a reasonable correlation between in vitro and in vivo activities. Seven of the thirteen bisquinolines had IC50's of less than 6 nM against both chloroquine-sensitive (D-6) and -resistant (W-2) clones of P. falciparum and were curative against P. berghei at doses of 640 mg/kg. In contrast to chloroquine, these bisquinolines did not show any toxic deaths at curative dose levels. Four bisquinolines, however, caused skin lesions at the site of injection. Maximum activity was seen in bisquinolines with a connecting bridge of two carbon atoms where decreased conformational mobility seemed to increase activity. Bisquinoline 3 (+/-)-trans-N1,N2-bis(7-chloroquinolin-4-yl)cyclohexane-1,2-diamin e was not only the most potent bisquinoline in vitro, but was clearly unique in its in vivo activity--80% and 100% cure rates were achieved at doses of 160 and 320 mg/kg, respectively. In summary, these preliminary results support the premise that bisquinolines may be useful agents against chloroquine-resistant malaria.

Efficacy of intermittent dosage of 8-aminoquinolines for therapy or prophylaxis of Pneumocystis pneumonia in rats.

Experimental 8-aminoquinolines from Walter Reed Army Institute for Research are effective for prophylaxis or therapy of Pneumocystis carinii pneumonia in rat models. In the present study, primaquine, WR6026, and WR238605 were tested in prophylaxis and treatment models of P. carinii pneumonia to compare the effectiveness of continuous versus intermittent dosing. For treatment of P. carinii pneumonia, the drugs showed detectable effects when given once every 4 days (primaquine and WR6026 at doses greater than 8 mg/kg; WR238605 at doses greater than 2 mg/kg). For prophylaxis, WR6026 and WR238605 were effective given alone daily (WR6026 at doses greater than 0.25 mg/kg; WR238605 at doses greater than 0.57 mg/kg). WR6026 and WR238605 at 4 mg/kg given once every 4 days for prophylaxis were as effective as daily trimethoprim-sulfamethoxazole. These studies suggest that higher doses of 8-aminoquinolines administered at appropriate intervals may be as effective as continuous dosing for prophylaxis of P. carinii pneumonia.

8-Aminoquinolines from Walter Reed Army Institute for Research for treatment and prophylaxis of Pneumocystis pneumonia in rat models.

Three 8-aminoquinolines from the Walter Reed Army Institute for Research (WRAIR), WR6026, WR238605, and WR242511, strongly inhibited Pneumocystis carinii growth in vitro at 1 microgram/ml. This activity was similar to that of primaquine. In rat therapy models, the WRAIR compounds affected Pneumocystis pneumonia at doses as low as 0.25 mg/kg (WR242511) or 0.5 mg/kg (WR6026 and WR238605). At these doses, primaquine alone was ineffective as therapy. In a rat prophylaxis model, all three WRAIR 8-aminoquinolines were extremely effective at daily doses of 0.57 mg/kg, showing activity greater than that of primaquine at this dosage and comparable to that of trimethoprim-sulfamethoxazole at 50/250 mg/kg.

Quantitative in vitro drug potency and drug susceptibility evaluation of Leishmania ssp. from patients unresponsive to pentavalent antimony therapy.

Quantitative in vitro drug sensitivity of 32 Leishmania isolates (16 from patients failing pentavalent antimony [SbV] therapy) was determined using a radiorespirometric microtechnique (RAM). Of 30 isolates with histories, 22 (73%) RAM tests agreed with patient history; the remaining 8 (27%) did not. There was no difference in RAM drug sensitivity: clinical correlation between 15 isolates tested blindly and 15 with known clinical history (4 did not agree with clinical history in both). Test sensitivity appeared to be limited only by the sensitivity of the Leishmania to SbV and could be detected at 2 micrograms/ml Sb (about 10% of serum drug level). An isolate from a patient with untreated self-healing cutaneous disease was drug resistant. Using RAM, parasite drug sensitivity can be quantified apart from patient physiologic and immunologic variables intrinsic to clinical data. Potency differed a maximum of 100% (weight% Sb:weight% Sb) among drug lots and also between Glucantime and Pentostam. Potency changes between drug lots were not explainable based on Sb content or test-to-test variability. This microtest offers a rapid method for evaluating the drug sensitivity of patient isolates and for determining of the activity of pentavalent antimonials and other candidate anti-leishmanials prior to the initiation of therapy.

Inhibitory effects of histidine analogues on growth and protein synthesis by Plasmodium falciparum in vitro.

The human malaria parasite Plasmodium falciparum synthesizes several proteins that are unusually rich in histidine. We therefore screened histidine analogues for their capacity to inhibit in vitro parasite growth. Analogues were added to cultures of ring-stage parasites, and parasite morphological development was assessed by light microscopy after a 22-hr culture. Inhibition of morphological development was identified as the appearance of condensed or pycnotic parasites rather than mature trophozoites. Inhibition of parasite protein synthesis was assessed by radioactivity counting of [3H] isoleucine incorporated into acid-insoluble products and by sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography of [3H]histidine-labeled malarial proteins. 2-F-L-Histidine and 2-I-D, L-histidine exerted the most pronounced inhibitory effects, the fluoro-analogue being the more effective of the two. At a 0.125 mM concentration, both compounds inhibited parasite growth and 2-F-L-histidine also inhibited protein synthesis. At a 1.0 mM concentration, 2-azido-L-histidine, alpha-methyl-L-histidine and WR 177589A also inhibited P. falciparum growth and protein synthesis. Twenty other histidine analogues, including 5-F-L-histidine and 5-I-L-histidine, showed little or no effect under these conditions. The inhibitory histidine analogues may be of interest for antimalarial chemotherapy if they should prove to have greater effect on P. falciparum protein synthesis than on host protein synthesis.