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New approaches to Leishmania chemotherapy: pteridine reductase 1 (PTR1) as a target and modulator of antifolate
1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
Abstract:
Leishmania and other trypanosomatid protozoa require reduced pteridines (pterins and folates) for growth, suggesting that inhibition of these pathways could be targeted for effective chemotherapy. This goal has not yet been realized, indicating that pteridine metabolism may be unusual in this lower eukaryote. We have investigated this possibility using both wild type and laboratory-selected antifolate-resistant strains, and with defined genetic knockouts of several pteridine metabolic genes. In Leishmania, resistance to the antifolate methotrexate is mediated through several mechanisms singly or in combination, including alterations in transport leading to reduced drug influx, overproduction (R-region amplification) or point mutation of dihydrofolate reductase-thymidylate synthase (DHFR-TS), and amplification of a novel pteridine reductase (PTR1, encoded by the H-region). All of the proteins involved are potential targets for antifolate chemotherapy. Notably, parasites in which the gene encoding dihydrofolate reductase (DHFR) has been deleted (dhfr-ts- knockouts) do not survive in animal models, validating this enzyme as a target for effective chemotherapy. However, the properties of pteridine reductase 1 (PTR1) suggest a reason why antifolate chemotherapy has so far not been successful in trypanosomatids. PTR1, by its ability to provide reduced pterins and folates, has the potential to act as a by-pass and/or modulator of DHFR inhibition under physiological conditions. Moreover, PTR1 is less sensitive to many antifolates targeted primarily against DHFR. These findings suggest that successful antifolate chemotherapy in Leishmania will have to target simultaneously both DHFR and PTR1.
Insights
Targeting pteridine metabolism in Leishmania is key for chemotherapy. Inhibiting both dihydrofolate reductase (DHFR) and pteridine reductase 1 (PTR1) is crucial for effective treatment against these protozoan parasites.
Area of Science:
- Parasitology
- Molecular Biology
- Drug Discovery
Background:
- Leishmania and other trypanosomatids rely on pteridines for growth, making their metabolic pathways potential targets for chemotherapy.
- Previous attempts at antifolate chemotherapy have been unsuccessful, suggesting unusual pteridine metabolism in these organisms.
Purpose of the Study:
- To investigate pteridine metabolism in Leishmania and identify effective targets for antifolate chemotherapy.
- To understand the mechanisms of antifolate resistance in Leishmania.
Main Methods:
- Analysis of wild-type and laboratory-selected antifolate-resistant Leishmania strains.
- Genetic knockouts of key pteridine metabolic genes.
- Characterization of drug resistance mechanisms, including transport, enzyme mutations, and gene amplification.
Main Results:
- Antifolate resistance in Leishmania involves altered drug transport, dihydrofolate reductase-thymidylate synthase (DHFR-TS) alterations, and amplification of pteridine reductase 1 (PTR1).
- Deletion of the DHFR gene renders parasites non-viable in animal models, confirming DHFR as a validated therapeutic target.
- PTR1 can bypass or modulate DHFR inhibition and is less sensitive to antifolates, potentially explaining chemotherapy failures.
Conclusions:
- Successful antifolate chemotherapy in Leishmania requires simultaneous targeting of both DHFR and PTR1.
- PTR1's unique role in pteridine metabolism presents a significant challenge and opportunity for drug development against trypanosomatid infections.