2,4-Diaminopteridine-Based Compounds as Precursors for De Novo Synthesis of Antifolates: a Novel Class of Antimalarials

Abstract

We have tested the hypothesis that 2,4-diamino-6-hydroxymethyl-pteridine (DAP), 2,4-diaminopteroic acid (DAPA), and 2,4 diamino-N10-methyl-pteroic acid (DAMPA) could be converted into aminopterin (from DAP and DAPA) and methotrexate (from DAMPA), both of which are potent inhibitors of dihydrofolate reductase, a proven drug target for Plasmodium falciparum. DAP, DAPA, and DAMPA inhibited parasite growth in the micromolar range; DAMPA was the most active, with 50% inhibitory concentrations in vitro of 446 ng/ml against the antifolate-sensitive strain and 812 ng/ml against the highly resistant strain under physiological folate conditions. DAMPA potentiates the activity of the sulfone dapsone, an inhibitor of dihydropteroate synthase, but not that of chlorcycloguanil, a known inhibitor of dihydrofolate reductase (DHFR). Experiments with a Saccharomyces cerevisiae strain dependent upon the P. falciparum DHFR enzyme showed that DHFR is a target of DAMPA in that system. We hypothesize that DAMPA is converted to methotrexate by the parasite dihydrofolate synthase, which explains the synergy of DAMPA with dapsone but not with chlorcycloguanil. This de novo synthesis will not occur in the host, since it lacks the complete folate pathway. If this hypothesis holds true, the de novo synthesis of the toxic compounds could be used as a framework for the search for novel potent antimalarial antifolates.Chemotherapy remains one of the most important tools for the management of falciparum malaria. However, malaria control is hampered by the emergence and spread of parasites resistant to almost all available antimalarial drugs. This situation is critical in Africa as a result of the spread of resistance to the combination sulfadoxine-pyrimethamine, an inexpensive treatment widely used in African countries (9, 16-18, 25, 28). As an alternative, a number of combinations with artemisinins are being recommended and implemented, but questions about the cost and the adequacy of the supply of artemisinins and the intrinsic ability of Plasmodium falciparum to select drug-resistant parasite populations underline the need to identify novel agents.

Replacing Sulfa Drugs with Novel Dhps Inhibitors

“…The generated product goes on to act as an inhibitor and/or replacement product for subsequent enzymes in the folate biosynthetic pathway, which ultimately leads to its inhibition. It is important to note that there have also been previous reports of aminopterin and sulfonamide precursors that are activated by DHPS into larger molecules that, in turn, inhibit different steps in folate biosynthesis [47,48]. These studies demonstrate that catalysis by DHPS can be used as a novel prodrug strategy for drug discovery, and it also demonstrates that sulfonamide antibacterials are prone to intracellular metabolism and/or modification in M. tuberculosis as well as in other microorganisms.…”

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

“…Therefore, we raise the same concern regarding the toxicity of the drug if used to treat Babesia infections in dogs and cattle. Nevertheless, 2,4-diamino-N10-methyl-pteroic acid, a methotrexate precursor which has antimalarial activity (32,34) and is less toxic, might be safely used to treat P. falciparum infection because the parasite can metabolize this inactive precursor to active methotrexate. We hope that the same logic could apply to Babesia infections.…”

Novel molecular targets for antimalarial chemotherapy

“…An alternative strategy could be the combination of an effective TS inhibitor and a nucleoside that can be utilised by the host. N 5 -N 10 -methylene tetrahydrofolate analogues, which inhibit TS without being metabolised into the nucleotide pool, are considered attractive alternatives [39]. Such analogues need to be explored further.…”