Pyrimethamin-resistantPlasmodium falciparum lack cross-resistance to methotrexate and 2,4-diamino-5-(substituted benzyl) pyrimidines

Walter, Rolf D.; Bergmann, Bärbel; Kansy, Manfred; Wiese, M. V.; Seydel, Joachim K.

doi:10.1007/bf00930913

Cited by 16 publications

(11 citation statements)

References 20 publications

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“…Methotrexate, pyrimethamine, and trimethoprim inhibit the growth of P. falciparum (44), B. bovis (33), B. caballi, and B. equi in vitro (31) similarly to the inhibition of the growth of B. gibsoni observed in our study. Thus, we provide some evidence that the Babesia DHFR-TS enzyme activity is essential for the parasite's survival, possibly by playing a role in the synthesis of thymidine nucleotides required for DNA biosynthesis and cell replication.…”

Section: Discussionsupporting

confidence: 82%

Cloning, Expression, and Characterization of Babesia gibsoni Dihydrofolate Reductase-Thymidylate Synthase: Inhibitory Effect of Antifolates on Its Catalytic Activity and Parasite Proliferation

Aboge

Jia

Terkawi

et al. 2008

Antimicrob Agents Chemother

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Dihydrofolate reductase-thymidylate synthase (DHFR-TS) is a well-validated antifolate drug target in certain pathogenic apicomplexans, but not in the genusBabesia gibsoni, the causative agent of canine babesiosis, is an important protozoan parasite that poses a major clinical health problem in dogs worldwide (19,29,43). Due to the emergence of resistance and failure of antibabesia agents to eliminate the parasite (5), novel chemotherapeutics with better potency and acceptable safety margins are required to treat the infection. To develop novel chemotherapeutics for apicomplexans related to Babesia, such as the Plasmodium parasites, many studies have focused on well-validated molecular targets, including the dihydrofolate reductase (DHFR) enzyme (10,22,30,39), and to a lesser extent the thymidylate synthase (TS) enzyme (20,25). The DHFR and TS domains are expressed as individual monofunctional enzymes in mammals and bacteria (21,36,41); however, in protozoans (and some plants), DHFR and TS exist as a bifunctional enzyme in which they are expressed on a single polypeptide chain (11,23,35). The DHFR domain is a validated target for chemotherapy of infectious diseases (42) and cancer (17) because it is important for the proliferation of cells due to its function in DNA biosynthesis and cell replication.The DHFR enzyme catalyzes the NADPH-dependent reduction of dihydrofolic acid (DHF) to tetrahydrofolate (4), an essential cofactor in the de novo biosynthesis of nucleotidic bases of DNA, while the TS domain catalyzes the reductive methylation of dUMP to dTMP with concomitant conversion of 5,10-methylenetetrahydrofolate to DHF (8). Therefore, the disruption of DHFR activity by antifolates depletes the reduced folate pool, thus blocking de novo dTMP biosynthesis by the TS enzyme and eventually inhibiting cell multiplication, leading to parasite death. Although antifolates inhibit the activities of bifunctional DHFR-TS enzymes of some pathogenic apicomplexan protozoans and disrupt folate metabolism (42), it has not been shown whether these drugs could also inhibit the activity of the corresponding enzyme in the genus Babesia, which includes the pathogen B. gibsoni.Furthermore, the results of earlier studies of the inhibition of the growth of Babesia bovis in vitro by various antifolates (33) and the inhibition of Babesia equi, as well as Babesia caballi, by pyrimethamine (31) suggested disruption of DHFR-TS activity only. Even in a case where the B. bovis dhfr-ts gene had been isolated and the resistance mechanism to pyrimethamine elucidated (16),

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Section: Discussionsupporting

confidence: 82%

Cloning, Expression, and Characterization of Babesia gibsoni Dihydrofolate Reductase-Thymidylate Synthase: Inhibitory Effect of Antifolates on Its Catalytic Activity and Parasite Proliferation

Aboge

Jia

Terkawi

et al. 2008

Antimicrob Agents Chemother

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“…Studies have demonstrated that both the oxidized and reduced folate (folic and folinic acid, respectively) can cross the membranes of the red blood cells parasitized with P. falciparum, because they can both negate the effects of antifolate drugs (12,42). Methotrexate, an analog of folic acid, uses the RFC receptor to gain intracellular access and has been shown to inhibit P. falciparum at IC 50 s similar to those that inhibit human cells (nanomolar range) (10,39). Taken together, these data suggest the existence of functional folate salvage in P. falciparum.…”

Section: Discussionmentioning

confidence: 99%

Chemosensitization of Plasmodium falciparum by Probenecid In Vitro

Nzila

Mberu

Bray

et al. 2003

Antimicrob Agents Chemother

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Resistance to drugs can result from changes in drug transport, and this resistance can sometimes be overcome by a second drug that modifies the transport mechanisms of the cell. This strategy has been exploited to partly reverse resistance to chloroquine in Plasmodium falciparum. Studies with human tumor cells have shown that probenecid can reverse resistance to the antifolate methotrexate, but the potential for reversal of antifolate resistance has not been studied in P. falciparum. In the present study we tested the ability of probenecid to reverse antifolate resistance in P. falciparum in vitro. Probenecid, at concentrations that had no effect on parasite viability alone (50 M), was shown to increase the sensitivity of a highly resistant parasite isolate to the antifolates pyrimethamine, sulfadoxine, chlorcycloguanil, and dapsone by seven-, five-, three-, and threefold, respectively. The equivalent effects against an antifolate-sensitive isolate were activity enhancements of approximately 3-, 6-, 1.2-, and 19-fold, respectively. Probenecid decreased the level of uptake of radiolabeled folic acid, suggesting a transport-based mechanism linked to folate salvage. When probenecid was tested with chloroquine, it chemosensitized the resistant isolate to chloroquine (i.e., enhanced the activity of chloroquine). This enhancement of activity was associated with increased levels of chloroquine accumulation. In conclusion, we have shown that probenecid can chemosensitize malaria parasites to antifolate compounds via a mechanism linked to reduced folate uptake. Notably, this effect is observed in both folate-sensitive and -resistant parasites. In contrast to the activities of antifolate compounds, the effect of probenecid on chloroquine sensitivity was selective for chloroquine-resistant parasites (patent P407595GB [W. P. Thompson & Co., Liverpool, United Kingdom] has been filed to protect this intellectual property).

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“…Several investigators have demonstrated that the anti-cancer methotrexate (MTX) and trimetrexate (TMX), which are inhibitors of dihydrofolate reductase (DHFR), are potent against both pyrimethamine (PM) sensitive and PM-resistant P. falciparum strains (parasites harboring wild type or mutant dhfr respectively), including those carrying the Ileu-164-Leu dhfr codon, with IC 50 < 85 nM (inhibitory concentration that kill 50% of parasitaemia) [6-10]. …”

Section: Introductionmentioning

confidence: 99%

A phase I trial to evaluate the safety and pharmacokinetics of low-dose methotrexate as an anti-malarial drug in Kenyan adult healthy volunteers

Chilengi

Rashid

Abdallah

et al. 2011

Malar J

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BackgroundPrevious investigations indicate that methotrexate, an old anticancer drug, could be used at low doses to treat malaria. A phase I evaluation was conducted to assess the safety and pharmacokinetic profile of this drug in healthy adult male Kenyan volunteers.MethodsTwenty five healthy adult volunteers were recruited and admitted to receive a 5 mg dose of methotrexate/day/5 days. Pharmacokinetics blood sampling was carried out at 2, 4, 6, 12 and 24 hours following each dose. Nausea, vomiting, oral ulcers and other adverse events were solicited during follow up of 42 days.ResultsThe mean age of participants was 23.9 ± 3.3 years. Adherence to protocol was 100%. No grade 3 solicited adverse events were observed. However, one case of transiently elevated liver enzymes, and one serious adverse event (not related to the product) were reported. The maximum concentration (Cmax) was 160-200 nM and after 6 hours, the effective concentration (Ceff) was <150 nM.ConclusionLow-dose methotraxate had an acceptable safety profile. However, methotrexate blood levels did not reach the desirable Ceff of 250-400-nM required to clear malaria infection in vivo. Further dose finding and safety studies are necessary to confirm suitability of this drug as an anti-malarial agent.

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Pyrimethamin-resistantPlasmodium falciparum lack cross-resistance to methotrexate and 2,4-diamino-5-(substituted benzyl) pyrimidines

Cited by 16 publications

References 20 publications

Cloning, Expression, and Characterization of Babesia gibsoni Dihydrofolate Reductase-Thymidylate Synthase: Inhibitory Effect of Antifolates on Its Catalytic Activity and Parasite Proliferation

Cloning, Expression, and Characterization of Babesia gibsoni Dihydrofolate Reductase-Thymidylate Synthase: Inhibitory Effect of Antifolates on Its Catalytic Activity and Parasite Proliferation

Chemosensitization of Plasmodium falciparum by Probenecid In Vitro

A phase I trial to evaluate the safety and pharmacokinetics of low-dose methotrexate as an anti-malarial drug in Kenyan adult healthy volunteers

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