Abstract
The therapy of Pneumocystis carinii (PC) pneumonia is often unsuccessful, particularly in patients with acquired immune deficiency syndrome (AIDS). Because of difficulties in growing the organism in vitro or obtaining purified organisms, current treatment choices have been made with little information on the metabolic effects of therapeutic agents on PC. This report quantitates the effects of the commonly used antifolates as well as the classic antineoplastic antifolate methotrexate and a lipid-soluble analogue, trimetrexate, on the target enzyme, dihydrofolate reductase (DHFR), in the PC organisms. Trimethoprim and pyrimethamine were found to be weak inhibitors (ID50 = 39,600 and 2,800 nM, respectively), while methotrexate and trimetrexate were potent reductase inhibitors (ID50 = 1.4 and 26.1 nM, respectively). transport studies with radiolabeled compounds showed that compounds with the classic folate structure (methotrexate and leucovorin) were not taken up by the intact PC organisms. In contrast, trimetrexate exhibited rapid uptake. These results suggest a major therapeutic advantage may be gained by combining a potent, readily transported PC DHFR inhibitor such as trimetrexate with the reduced folate leucovorin to achieve a highly potent antiprotozoan effect while preventing toxicity to mammalian cells.
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- BERTINO J. R., FISCHER G. A. TECHNIQUES FOR STUDY OF RESISTANCE TO FOLIC ACID ANTAGONISTS. Methods Med Res. 1964;10:297–307. [PubMed] [Google Scholar]
- Burchall J. J., Hitchings G. H. Inhibitor binding analysis of dihydrofolate reductases from various species. Mol Pharmacol. 1965 Sep;1(2):126–136. [PubMed] [Google Scholar]
- Cushion M. T., Stanforth D., Linke M. J., Walzer P. D. Method of testing the susceptibility of Pneumocystis carinii to antimicrobial agents in vitro. Antimicrob Agents Chemother. 1985 Dec;28(6):796–801. doi: 10.1128/aac.28.6.796. [DOI] [PMC free article] [PubMed] [Google Scholar]
- DeLean A., Munson P. J., Rodbard D. Simultaneous analysis of families of sigmoidal curves: application to bioassay, radioligand assay, and physiological dose-response curves. Am J Physiol. 1978 Aug;235(2):E97–102. doi: 10.1152/ajpendo.1978.235.2.E97. [DOI] [PubMed] [Google Scholar]
- Drake J. C., Allegra C. J., Chabner B. A. A re-evaluation of the competitive protein binding assay for methotrexate binding to dihydrofolate reductase. Biochem Pharmacol. 1986 Apr 1;35(7):1212–1214. doi: 10.1016/0006-2952(86)90166-8. [DOI] [PubMed] [Google Scholar]
- Henderson G. B., Zevely E. M. Transport routes utilized by L1210 cells for the influx and efflux of methotrexate. J Biol Chem. 1984 Feb 10;259(3):1526–1531. [PubMed] [Google Scholar]
- Horwich A. L., Kalousek F., Mellman I., Rosenberg L. E. A leader peptide is sufficient to direct mitochondrial import of a chimeric protein. EMBO J. 1985 May;4(5):1129–1135. doi: 10.1002/j.1460-2075.1985.tb03750.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hughes W. T., Smith B. L. Efficacy of diaminodiphenylsulfone and other drugs in murine Pneumocystis carinii pneumonitis. Antimicrob Agents Chemother. 1984 Oct;26(4):436–440. doi: 10.1128/aac.26.4.436. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kamen B. A., Eibl B., Cashmore A., Bertino J. Uptake and efficacy of trimetrexate (TMQ, 2,4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl] quinazoline), a non-classical antifolate in methotrexate-resistant leukemia cells in vitro. Biochem Pharmacol. 1984 May 15;33(10):1697–1699. doi: 10.1016/0006-2952(84)90298-3. [DOI] [PubMed] [Google Scholar]
- Kovacs J. A., Hiemenz J. W., Macher A. M., Stover D., Murray H. W., Shelhamer J., Lane H. C., Urmacher C., Honig C., Longo D. L. Pneumocystis carinii pneumonia: a comparison between patients with the acquired immunodeficiency syndrome and patients with other immunodeficiencies. Ann Intern Med. 1984 May;100(5):663–671. doi: 10.7326/0003-4819-100-5-663. [DOI] [PubMed] [Google Scholar]
- Leoung G. S., Mills J., Hopewell P. C., Hughes W., Wofsy C. Dapsone-trimethoprim for Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome. Ann Intern Med. 1986 Jul;105(1):45–48. doi: 10.7326/0003-4819-105-1-45. [DOI] [PubMed] [Google Scholar]
- McCutchan T. F., Welsh J. A., Dame J. B., Quakyi I. A., Graves P. M., Drake J. C., Allegra C. J. Mechanism of pyrimethamine resistance in recent isolates of Plasmodium falciparum. Antimicrob Agents Chemother. 1984 Nov;26(5):656–659. doi: 10.1128/aac.26.5.656. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Moran R. G., Colman P. D. A simple procedure for the synthesis of high specific activity tritiated (6S)-5-formyltetrahydrofolate. Anal Biochem. 1982 May 1;122(1):70–78. doi: 10.1016/0003-2697(82)90252-4. [DOI] [PubMed] [Google Scholar]
- Myers C. E., Lippman M. E., Elliot H. M., Chabner B. A. Competitive protein binding assay for methotrexate. Proc Natl Acad Sci U S A. 1975 Sep;72(9):3683–3686. doi: 10.1073/pnas.72.9.3683. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Walzer P. D., Powell R. D., Jr, Yoneda K. Experimental Pneumocystis carinii pneumonia in different strains of cortisonized mice. Infect Immun. 1979 Jun;24(3):939–947. doi: 10.1128/iai.24.3.939-947.1979. [DOI] [PMC free article] [PubMed] [Google Scholar]