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Biomedical subjects

W E Gutteridge

Publications and source records attributed to W E Gutteridge.

At least 19 recordsLinked to original sources
PubMed1999

New tools for malaria therapy.

In the absence of vaccines, new chemotherapies are needed urgently to help in the prevention and control of malaria. A number of strategies are being followed world-wide in attempts to discover and develop them: (a) resurrecting 'forgotten' molecules; (b) developing new formulations of existing products; (c) finding ways to bypass known toxicological limitations of existing products; (d) looking for combinations of existing products; (e) discovering molecules which reverse the resistance phenotype; (f) identifying 'old' chemical entities (OCEs) for new, antimalarial, indications; (g) discovering new chemical entities (NCEs) directed towards already exploited biological targets; (h) discovering NCEs directed to novel biological targets. Examples of such strategies are given below, together with an indication of their advantages and limitations.

Drug Design↗
PubMed1997

Designer drugs: pipe-dreams or realities?

New chemotherapies are urgently needed for the parasitic infections of animals and for the tropical diseases of man. Rational molecular design approaches to attempt to discover such products require a massive investment of resources upfront of actual chemical synthesis. However, such investment is justified, since chemical synthesis itself is highly resource-consuming. The fact that few targets have yet been validated to justify a rational approach is an argument only to get on and validate more. Not all the components of molecular design can yet be done totally rationally, but this is not an argument against applying this approach where it is possible. Absence of a successful track record is inevitable for any newly emerging technology. It is too early to draw conclusions about the relative costs of rational design versus empirical synthesis, since the former is only now beginning to become reality and the latter is in the middle of a (combinatorial) revolution. Similarly, it is too soon to predict with certainty which of these two approaches will prevail in the long run. However, they lend themselves to parallel tracks, so both may well continue for the foreseeable future. Current concerns about who would develop successful discoveries are not reasons for stopping discovery research. Indeed, a string of putative products held at the discovery/development interface would be useful ammunition to those trying to develop partnerships such as a Tropical Diseases R & D Alliance aimed at carrying out such work and sharing costs.

Animals↗
PubMed1996

Nitric oxide synthase activity in malaria-infected mice.

Nitric oxide (NO) is implicated in a variety of major cellular functions including defence from invasion by microbical pathogens. Evidence has been presented suggesting that it is an important mediator of protection in the early non-specific responses to malaria in mice infected with Plasmodium chabaudi (Taylor-Robinson et al. 1993). Other data from in vitro studies on the asexual stages of human parasite Plasmodium falciparum indicated that while nitric oxide itself may not be inhibitory to parasite development, its downstream products do have some anti-plasmodial activity (Rockett et al. 1991) and these could be generated by macrophages (Gyan et al. 1994). Similarly, the sexual phases of both rodent (Motard et al. 1993) and human malaria (Naotunne et al. 1993) are reportedly susceptible to the toxic effects mediated by nitric oxide generated by blood leucocytes in the course of transmission to the mosquito vector.

Animals↗
PubMed1995

Characterization of the enhanced transport of L- and D-lactate into human red blood cells infected with Plasmodium falciparum suggests the presence of a novel saturable lactate proton cotransporter.

Human erythrocytes parasitized with the malarial protozoan Plasmodium falciparum showed rates of L-lactate, D-lactate, and pyruvate uptake many fold greater than control cells. Thus it was necessary to work at 0 degrees C to resolve true initial rates of transport. Studies on the dependence of the rate of transport on substrate concentration implied the presence in parasitized cells of both a saturable mechanism blocked by alpha-cyano-4-hydroxycinnamate (CHC) and a nonsaturable mechanism insensitive to CHC. The former was dominant at physiological substrate concentrations with Km values for pyruvate and D-lactate of 2.3 and 5.2 mM, respectively, with no stereoselectivity for L- over D-lactate. CHC was significantly less effective as an inhibitor of lactate transport in parasitized erythrocytes than in uninfected cells, whereas p-chloromercuribenzenesulfonate, a potent inhibitor in control cells, gave little or no inhibition of lactate transport into parasitized erythrocytes. Inhibition of transport into infected cells was also observed with phloretin, furosemide, niflumic acid, stilbenedisulfonate derivatives, and 5-nitro-2-(3-phenylpropylamino)benzoic acid at concentrations similar to those that inhibit the lactate carrier of control erythrocytes. These compounds were more effective inhibitors of the rapid transport of chloride into infected cells than of lactate transport, whereas CHC was more effective against lactate transport. This implies that different pathways are involved in the parasite-induced transport pathways for lactate and chloride. The transport of L-lactate into infected erythrocytes was also inhibited by D-lactate, pyruvate, 2-oxobutyrate, and 2-hydroxybutyrate. The intracellular accumulation of L-lactate at equilibrium was dependent on the transmembrane pH gradient, suggesting a protogenic transport mechanism. Our data are consistent with lactate and pyruvate having direct access to the malarial parasite, perhaps via the proposed parasitophorous duct or some close contact between the host cell and parasite plasma membranes, with transport across the latter by both a proton-linked carrier (CHC-sensitive, saturable, and the major route) and free diffusion of the undissociated acid (CHC-insensitive, unsaturable, and a minor route).

Animals↗
PubMed1995

Interactions of atovaquone with other antimalarial drugs against Plasmodium falciparum in vitro.

A series of Plasmodium falciparum in vitro drug sensitivity studies were conducted in order to evaluate atovaquone in combination with other antimalarial drugs and thus to identify a potential partner for a fixed combination. The derived isobolograms indicated that drug interactions ranged from antagonism through addition to synergy. Of particular note were the quinolines and artemisinin analogues, which were all antagonistic, and the biguanides and tetracycline, which showed synergy. Proguanil emerged as the most promising of the current antimalarials as a partner for atovaquone in a fixed combination, with tetracycline as back-up.

Animals↗
PubMed1992

The activity of hydroxynaphthoquinones against Leishmania donovani.

The hydroxynaphthoquinones, buparvaquone, 250C80 and 56W82, showed high activity in vitro against Leishmania donovani amastigotes in mouse peritoneal macrophages, with ED50 values of 0.05, 2.95 and 13.82 microM, respectively. Fourteen other hydroxynaphthoquinones were tested, of which only 566C80 and 608C86 showed significant activity against amastigotes. Buparvaquone, 250C80 and 56W82 were also highly-active against cultured promastigotes. In a BALB/c mouse model, treatment with 100 mg/kg/day for five days with buparvaquone, 250C80 and 566C80 (atovaquone) reduced liver amastigote numbers by 60%, 22% and 30.5%, respectively.

Animals↗
PubMed1992

In vitro and in vivo activities of the hydroxynaphthoquinone 566C80 against the cyst form of Toxoplasma gondii.

The in vitro and in vivo activities of the hydroxynaphthoquinone 566C80 against the cyst form of Toxoplasma gondii were evaluated. In vitro treatment (100 micrograms of 566C80 per ml for 3 days) of cysts isolated from brains of mice infected for 1, 2, 3, 4, or 9 months resulted in loss of viability of the cysts and did not reveal any influence of the duration of in vivo infection on sensitivity to the drug. In vivo experiments to determine the effect of prolonged treatment with 200 mg of 566C80 per kg of body weight per day on cysts in brains of CBA/Ca mice infected with strain ME49 revealed a steady and significant decline in the numbers of cysts compared with the numbers in untreated controls. Histopathology of brains from control mice revealed inflammatory infiltrates around capillaries and in the parenchymas and meninges which were consistently less evident in the brains of treated mice. In addition, cysts were rarely observed in treated mice, whereas extensive inflammation and large numbers of cysts were found throughout the entire brain in control mice infected for the same period. The reduction in the numbers of cysts was evident as early as day 5 of treatment but was more marked at 8 weeks of treatment. The numbers of cysts in the brains of Swiss Webster mice infected for 3 or 6 months also significantly decreased following treatment for 15 or 30 days with the same dose of 566C80. Our results indicate that 566C80 has excellent activity against cysts of T. gondii both in vivo and in vitro and that sensitivity of the cysts to 566C80 is not affected by the duration of the infection in vivo.

Animals↗
PubMed1991

Control of parasitic diseases: a complementary role for vaccines and drugs.

This paper seeks to substantiate its title by discussion of three key questions: why are we attempting to develop parasite vaccines? Will we be successful? If we are, will there still be a need for chemotherapy? It concludes that: parasite vaccines are likely to be safer, cheaper and more efficacious as prophylactics than antiparasite drugs; in time vaccines will be developed for some but not all human parasitic diseases; at least in the short and medium term, drugs will be needed for those already infected and for those for whom, for whatever reason, a vaccination strategy fails.

Animals↗
PubMed1991

566C80: a potent broad spectrum anti-infective agent with activity against malaria and opportunistic infections in AIDS patients.

566C80 is a novel hydroxynaphthoquinone with broad-spectrum anti-parasitic properties. In vitro the compound was more potent against Plasmodium falciparum than any of the established anti-malarial drugs. It had good activity against the pathogen in Aotus monkeys and was also effective in rodents infected with various drug-resistant strains of P. yoelii and P. berghei. In mice the compound showed significant activity against Toxoplasma gondii. Evaluation of the metabolic stability of 566C80 to NADPH-mediated oxidative metabolism was made using microsome preparations from a number of species including man. Unlike other quinones examined, 566C80 was shown to be inert in these assays. In Phase 1 clinical studies up to 750mg of compound were given as a single oral dose to fasted healthy male adults. This was well tolerated and the plasma drug elimination half-life was approximately 70h. In these subjects a 450mg dose gave plasma concentrations of 0.1-0.3 micrograms/ml which were achieved 1 h post-dosing and remained so for at least 7 days. Volunteers ingesting food prior to drug administration had quinone plasma levels which were significantly higher. Phase II trials are now underway to assess 566C80 for use against malaria and opportunistic infections in AIDS patients.

4-Quinolones↗
PubMed1990

Efficacy of a hydroxynaphthoquinone, 566C80, in experimental Pneumocystis carinii pneumonitis.

The efficacy of a new class of drugs for Pneumocystis carinii pneumonitis was demonstrated. 566C80, a hydroxynaphthoquinone, administered orally in a dose of greater than or equal to 100 mg/kg of body weight per day prophylactically prevented P. carinii pneumonitis in 90% or more of rats, while all untreated control animals developed pneumonitis. When 566C80 (100 mg/kg per day) was administered for 3 weeks after P. carinii pneumonitis was established, therapy was totally effective and all of the untreated controls had progressive P. carinii pneumonitis. A dose of 566C80 of between 25 and 50 mg/kg per day protected 50% of the rats from P. carinii pneumonitis, and a dose of between 50 and 100 mg/kg per day cured 50% of those treated for P. carinii pneumonitis. Both prophylaxis and treatment with 566C80 were at least as effective as with trimethoprim-sulfamethoxazole. Animals maintained on immunosuppression after completion of treatment remained free of P. carinii, suggesting a killing effect. Clearance of P. carinii was associated with levels of 60 micrograms or more of 566C80 per ml of plasma. This hydroxynaphthoquinone offers promise as an anti-P. carinii drug.

Animals↗
PubMed1990

An RNA-dependent UMP-incorporating activity is associated with the small subunit of cytoplasmic ribosomes in bloodstream forms of Trypanosoma brucei.

Trypanosoma brucei cytoplasm contained a UMP-incorporating activity which was dependent upon the presence of endogenous RNA, stimulated by exogenous RNA and precipitable by ammonium sulphate. The activity cosedimented with ribosomes, and after ribosome dissociation using EDTA was mainly associated with the small (31S) subunit. Ribosome-associated activity was selective for UTP as a substrate and greatly stimulated by the presence of at least one other nucleoside triphosphate.

Animals↗
PubMed1990

The Wellcome Foundation/World Health Organisation Onchocerciasis Chemotherapy Project Joint Programme to discover and develop a macrofilaricide for onchocerciasis.

The primary objective of the Wellcome Foundation/World Health Organisation Onchocerciasis Chemotherapy Project, which began in July 1982, was the discovery and development of a safe and effective macrofilaricide for the treatment of onchocerciasis in man. A multidisciplinary Team of biologists, biochemists and medicinal chemists was assembled. They investigated a variety of potential targets in filariae and carried out in-depth lead optimisation studies on a number of different chemical series. A valuable contribution was made to our understanding of filarial biology and biochemistry and the susceptibility of filariae to various metabolic inhibitors. However, the ultimate goal of identification of a compound worthy of evaluation in man was not achieved and the programme was closed at the end of June 1989. Factors that contributed to this situation and some overall conclusions are discussed.

Animals↗
PubMed1988

Screening of drugs for rapid activity against Trypanosoma cruzi trypomastigotes in vitro.

Previous studies to find drugs with an existing product licence which were active at 4 degrees C within 24 hours and which would be suitable to prevent the transmission of Chagas' disease during blood transfusion were unsuccessful. As part of an alternative approach to identify drugs active at 37 degrees C or 25 degrees C within 2 hours, over 280 compounds were screened against bloodstream trypomastigotes of Trypanosoma cruzi Sonya strain in a microslide test in vitro. Although compounds from a wide range of chemical groups were tested only three polyene antibiotics showed outstanding trypanocidal activity. Amphotericin B, candicidin and trichomycin lysed all trypomastigotes at 8 X 10(-6) as determined by microscopical techniques. However, these compounds also showed toxicity to mammalian erythrocytes at the same concentration after a 24 hours incubation period. It seems unlikely that this approach will yield a candidate replacement for gentian violet.

Amphotericin B↗
PubMed1987

Demonstration of RNA polymerase multiplicity in Trypanosoma brucei. Characterization and purification of alpha-amanitin-resistant and -sensitive enzymes.

We have isolated, characterized and substantially purified two distinct RNA polymerase activities from the flagellate protozoan parasite Trypanosoma brucei. RNA polymerases from this organism were resolved poorly on DEAE-Sephadex, but could be separated with CM-Sephadex. One form was totally resistant to alpha-amanitin, whereas the second was 50% inhibited by 10-20 micrograms of the drug/ml. The enzymes had different salt optima, but both were of high Mr (greater than 480,000) and demonstrated the template preference: poly[d(A-T)] greater than denatured DNA greater than native DNA, and both were more active with Mn2+ than with Mg2+. The amanitin-resistant enzyme, polymerase R, was partially purified by chromatography on CM-Sephadex, DEAE-Sephadex and heparin-Sepharose. This enzyme was very labile, and activity yields were around 9%; after purification, one or two protein bands could be discerned after electrophoresis under non-denaturing conditions, but about 20 polypeptides were resolved on denaturing gels, including a major component (not thought to be part of the enzyme) of Mr 65,000. Polymerase S, sensitive to low alpha-amanitin concentrations, was more extensively purified, with an 18% recovery, and yielded a single major band with two minor ones after native gel electrophoresis. Analysis under denaturing conditions permitted a possible subunit structure for this enzyme to be ascribed.

Amanitins↗
PubMed1987

Trypanosoma cruzi: subcellular distribution of glycolytic and some related enzymes of epimastigotes.

The first six glycolytic enzymes in epimastigote Trypanosoma cruzi were shown to behave similarly during differential centrifugation, when maximum relative specific activity was found in the small granule fraction, and by isopycnic centrifugation, when the bulk of each activity coequilibrated on sucrose gradients with a modal density of 1.23 g/ml. All six showed substantial detergent latency in whole cell homogenates. Electron microscopic examination of fractions from a sucrose gradient with modal density 1.23 g/ml showed the presence of single membrane bound vesicles of diameter 0.2-0.8 micron. It was concluded that these six enzymes were contained in a microbodylike organelle, termed the "glycosome." Phosphoglucose isomerase (EC 5.3.1.9) also possessed substantial soluble activity. No microbody marker enzyme described in other sources could be detected. Peroxidase (EC 1.11.1.7) had an insignificant glycosomal component. Enzymes of amino acid and fatty acid metabolism were not detected in microbody fractions. Marker enzymes for the flagellar pocket and plasma membrane were suggested.

Amino Acids↗