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Antimicrobial Agents and Chemotherapy, April 2000, p. 1047-1050, Vol. 44, No. 4
Department of Biology, The Catholic
University of America, Washington, DC 20064
Received 2 September 1999/Returned for modification 19 October
1999/Accepted 30 December 1999
Unlike mammalian cells, malarial parasites are completely dependent
on the de novo pyrimidine pathway and lack the enzymes to salvage
preformed pyrimidines. In the present study, first, it is shown that
1843U89, even without polyglutamylation, is a potent folate-based
inhibitor of purified malarial parasite thymidylate synthase. The
binding was noncompetitive with respect to methylenetetrahydrofolate, and 1843U89 had a Ki of 1 nM. The compound also
had potent antimalarial activity in vitro. Plasmodium
falciparum cells in culture were inhibited by 1843U89, with a
50% inhibitory concentration of about 70 nM. The compound was
effective against drug-sensitive as well as drug-resistant clones of
P. falciparum. As predicted by the biochemistry of the
parasite, the potent inhibition of parasite proliferation by 1843U89
could not be reversed with 10 µM thymidine. In contrast, in the
presence of 10 µM thymidine, mammalian cells were unaffected by
1843U89 even at concentrations as high as 0.1 mM, thus offering a
selectivity window of more than 1,000-fold. On this basis, folate-based
thymidylate synthase inhibitors may represent a powerful additional
tool that can be used to combat drug-resistant malaria.
Malaria is the cause of over 200 million infections and 2 million deaths per year (36). With
the recent acceleration in malarial parasite drug resistance (27,
38), there is a strong need to identify new chemotherapeutic
strategies. Malarial parasites are completely dependent on de novo
pyrimidine biosynthesis and cannot salvage pyrimidines (30,
33). In sharp contrast, mammalian cells readily transport
pyrimidine bases and nucleosides and convert them into nucleotides
(24). Thus, a combination of an effective de novo pyrimidine
biosynthesis inhibitor and a nucleoside (that only the host can use)
should be efficacious (24).
Of all the de novo pyrimidine biosynthesis enzymes, thymidylate
synthase (TS) is particularly attractive as a target for malaria chemotherapy. It is metabolically linked to dihydrofolate reductase (DHFR), a proven target of antimalarial agents such as pyrimethamine (6, 9, 39). DHFR and TS are part of a single bifunctional polypeptide (1, 3, 4). Even partial inhibition of TS leads
to nucleotide imbalances and cell death (15, 16, 19, 40).
The availability of many known nucleotide- and folate-based potent
inhibitors of TS facilitates applications to treatments for malaria
(2, 7, 17, 29). However, TS is one of the most conserved
proteins in the cell. No inhibitors bind to TS from one species more
tightly than they bind to TS from another species.
To inhibit malarial parasite TS selectively, one must exploit distant
differences in metabolism between malarial and mammalian cells
(24, 26, 28). For example, 5-fluoro-2'-deoxyuridylate (5-FdUMP) is a potent TS inhibitor (2, 20, 29), but it is
5-fluoroorotate, a metabolic precursor of 5-FdUMP, that causes inactivation of malarial parasite TS and inhibition of cell
proliferation at nanomolar concentrations (24, 26). It takes
high micromolar concentrations of 5-fluoroorotate to inhibit mammalian
cells significantly (24). Furthermore, combining
5-fluoroorotate with uridine further improves the selective toxicity of
5-fluoroorotate (23, 24).
In an earlier study, the quinazoline folate-based mammalian TS
inhibitor D1694 (Fig. 1) (17)
was tested against malarial parasites in culture (28). As
expected, the toxic effects of D1694 on mammalian cells could be
reversed with 10 µM thymidine, but in a promising outcome, the toxic
effects on malarial parasites remained unaltered (28).
Unfortunately, D1694 had only modest potency against malarial parasites
(50% inhibitory concentration [IC50], 20 µM). Kinetic
studies revealed that D1694 was a relatively poor inhibitor of malarial
parasite TS (Ki, 2.8 µM), but the
polyglutamate form of D1694 was potent (Ki, 1.5 nM) (14). Thus, the poor activity of D1694 against parasite
cells could be due, at least in part, to the poor polyglutamylation of
D1694 (37).
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Potent and Selective Activity of a Combination of Thymidine
and 1843U89, a Folate-Based Thymidylate Synthase Inhibitor,
against Plasmodium falciparum
ABSTRACT
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
INTRODUCTION
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
View larger version (14K):
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FIG. 1.
Comparison of structures of the substrate
methylenetetrahydrofolate to the folate-based TS inhibitors D1694 and
1843U89.
In the present study, we examined the antimalarial potential of 1843U89 (Fig. 1), a member of a new group of potent folate-based TS inhibitors that do not require polyglutamylation for tight binding to the target TS or for antiproliferative activity (7).
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MATERIALS AND METHODS |
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Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
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Reagents. 1843U89 was kindly provided by Eric Furfine of Glaxo Wellcome, Research Triangle Park, N.C., and D1694 was provided by F. T. Boyle of Zeneca Pharmaceuticals, Cheshire, United Kingdom.
Inhibition of malarial parasite TS. Recombinant malarial parasite DHFR-TS was purified to homogeneity as described previously (14, 32a). A discontinuous tritium release assay was used to measure enzyme activity under initial rate conditions (14, 31).
Cell culture. Plasmodium falciparum clones D6 and W2 were kindly provided by D. Kyle and W. Milhous, Walter Reed Army Institute of Research (27), and FCR3, HB3, and 3D7 were provided by T. Wellems, National Institutes of Health (27). Parasites were propagated in vitro as described previously (35). Mouse lymphocytic leukemia (L1210) cells were obtained from the American Type Culture Collection, Manassas, Va.
Antiproliferation assays. All cytotoxicity assays were performed in 96-well plates (5, 24, 28). P. falciparum-infected erythrocytes were set up with 0.5% initial parasitemia in 2% hematocrit and were exposed to various concentrations of 1843U89 for 48 h and then pulsed with 0.5 µCi of radioactive hypoxanthine for 24 h. Mouse L1210 cells were set up at an initial density of 4,000 cells per well in a 96-well plate with various concentrations of 1843U89. After 48 h, the cells were exposed to 0.5 µCi of hypoxanthine for 24 h. In all cases, incorporation of radioactivity into precipitable nucleic acids again served as a measure of cell proliferation.
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RESULTS |
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Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
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Inhibition of malarial parasite TS by 1843U89.
Exposure of purified malarial parasite TS to various concentrations of
1843U89 in the presence of subsaturating concentrations of substrates
revealed that the compound was effective at nanomolar concentrations
(Fig. 2A). It was not necessary to have
1843U89 in a polyglutamate form in order to see potent inhibition. In contrast, D1694 without polyglutamylation inhibited malarial parasite TS only at concentrations in the micromolar range (Fig. 2A).
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Tightness of 1843U89 binding. A detailed kinetic analysis of the binding interactions between malarial parasite TS and 1843U89 showed that this compound was noncompetitive with respect to methylenetetrahydrofolate (Fig. 2B). From a secondary plot of the slopes of the inhibition lines from Fig. 2B, 1843U89 was found to have a Ki of 1 nM against malarial parasite TS (Fig. 2C).
Antiproliferative activity of 1843U89 against P. falciparum.
As with mammalian L1210 cells, nanomolar
concentrations of 1843U89 were sufficient to inhibit proliferation of
the human malarial parasite P. falciparum (Fig.
3A). Parasite clones that were derived from different parts of the world and that showed large differences in
resistance to traditional antimalarial compounds (27) were approximately equally sensitive to 1843U89. For clones D6, HB3, 3D7,
and W2 the 1843U89 IC50 was 70 nM both with and without 10 µM thymidine (data not shown). The IC50 for clone FCR3
was slightly higher (200 nM).
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Antimalarial activity of 1843U89 in the presence of thymidine. P. falciparum-infected erythrocytes as well as mouse L1210 cells were tested for their sensitivities to 1843U89 in the presence of 10 µM thymidine. Unlike mammalian cells, all malarial parasite clones remained completely sensitive to 1843U89 in the presence of thymidine (Fig. 3B).
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DISCUSSION |
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Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
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Given the absence of pyrimidine salvage pathways in P. falciparum, the whole de novo pyrimidine biosynthesis pathway can be considered a potential target for selective chemotherapy. Yet, with one exception (24), most inhibitors of de novo pyrimidine biosynthesis enzymes have unimpressive antiproliferative activity against intact malarial parasites (18, 22, 32). Atovaquone, which was originally thought to act by blocking the biosynthesis of orotate, inhibits parasite proliferation primarily by disrupting mitochondrial membrane potential (34).
The compound with a truly potent and selective antimalarial activity directed at pyrimidine metabolism is 5-fluoroorotate. This compound inhibits parasites with an IC50 of about 5 nM (24), is equally effective against drug-sensitive as well as drug-resistant P. falciparum (24), and can cure malaria in mice and is orally available (12, 23). However, in order to use this compound as a single agent without the possibility of drug resistance (11, 25, 27), it is necessary to achieve concentrations in the serum of the treated animal that approach 1 to 10 µM (23). Such concentrations are dangerously close to what is tolerated in mammalian cells (23).
The primary mechanism by which 5-fluoroorotate causes parasite death is probably quite different from the mechanism by which high doses of 5-fluoroorotate cause toxicity in the host. It is known that nanomolar levels of 5-fluoroorotate inhibit TS in malarial parasites (26). The toxicity of high levels of 5-fluoroorotate, in contrast, probably arises from incorporation of 5-fluoropyrimidine nucleotides into RNA and possibly DNA (8, 13, 20). This complicates the strategy of using nucleosides to rescue mammalian cells. Thymidine or uridine alone decreases the toxic effects of very high doses of 5-fluoroorotate but does not completely eliminate them (24).
In contrast to 5-fluoropyrimidine-based strategies, folate-based strategies have some distinct advantages. Folate analogs are not metabolically degraded and they cannot be incorporated into nucleic acids. If a folate analog inhibits TS with potency, selectivity will arise automatically if TS is the only target of the antifolate.
In the present study, we demonstrate that 1843U89 inhibits malarial parasites at midnanomolar concentrations. This is an approximately 1,000 times greater potency than that of the previous folate-based TS inhibitor tried against malarial parasites. Unlike folate-based DHFR inhibitors, which show as much as 1,000-fold differences in their antiproliferative activities against different clones of P. falciparum (6, 9, 10, 21, 39), 1843U89 was approximately equally effective against all parasite clones tested. 1843U89 seems to act through a mechanism which is independent of all currently used antimalarial drugs and which is independent of the common drug resistance mechanisms used by malarial parasites. The mechanism that underlies the slight resistance of clone FCR3 to 1843U89 is not yet clear. Consistent with the inability of malarial parasites to salvage pyrimidines, inhibition of parasite proliferation by 1843U89 persisted even in the presence of thymidine. In sharp contrast, in the presence of 10 µM thymidine, mouse L1210 cells were not susceptible to 1843U89, even when the limits of solubility of this compound were approached.
It is expected that small variation in the structure of 1843U89 might result in even more potent activity against malarial parasites, either because the compound binds to malarial parasite TS better or because it is a better substrate for transport or polyglutamylation in the parasite.
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ACKNOWLEDGMENTS |
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P.K.R. thanks Eric Furfine and John Reardon of Glaxo Welcome and F. T. Boyle of Zeneca Pharmaceuticals for taking interest in malaria chemotherapy, for providing us with TS inhibitors, and for helpful discussions.
This work was supported by Public Health Service grants from the National Institute of Allergy and Infectious Diseases (grants AI26912 and AI40956). P.K.R. is a recipient of a Burroughs Wellcome Fund New Initiatives in Malaria Research Award.
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FOOTNOTES |
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* Corresponding author. Mailing address: Department of Biology, The Catholic University of America, 620 Michigan Ave. NE, Washington, DC 20064. Phone: (202) 319-5278. Fax: (202) 319-5721. E-mail: rathod{at}cua.edu.
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REFERENCES |
|---|
|
Top
Abstract
Introduction
Materials and Methods
Results
Discussion
References
|
|---|
| 1. |
Bzik, D. J.,
W. B. Li,
T. Horii, and J. Inselburg.
1987.
Molecular cloning and sequence analysis of the Plasmodium falciparum dihydrofolate reductase-thymidylate synthase gene.
Proc. Natl. Acad. Sci. USA
84:8360-8364 |
| 2. | Carreras, C. W., and D. V. Santi. 1995. The catalytic mechanism and structure of thymidylate synthase. Annu. Rev. Biochem. 64:721-762[CrossRef][Medline]. |
| 3. | Chen, G. X., and J. W. Zolg. 1987. Purification of the bifunctional thymidylate synthase-dihydrofolate reductase complex from the human malaria parasite Plasmodium falciparum. Mol. Pharmacol. 32:723-730[Abstract]. |
| 4. |
Coderre, J. A.,
S. M. Beverley,
R. T. Schimke, and D. V. Santi.
1983.
Overproduction of a bifunctional thymidylate synthetase-dihydrofolate reductase and DNA amplification in methotrexate-resistant Leishmania tropica.
Proc. Natl. Acad. Sci. USA
80:2132-2136 |
| 5. |
Desjardins, R. E.,
C. J. Canfield,
J. D. Haynes, and J. D. Chulay.
1979.
Quantitative assessment of antimalarial activity in vitro by a semiautomated microdilution technique.
Antimicrob. Agents Chemother.
16:710-718 |
| 6. | Diggens, S. M., W. E. Gutteridge, and P. I. Trigg. 1970. Altered dihydrofolate reductase associated with a pyrimethamine-resistant Plasmodium berghei berghei produced in a single step. Nature 228:579-580[CrossRef][Medline]. |
| 7. |
Duch, D. S.,
S. Banks,
I. K. Dev,
S. H. Dickerson,
R. Ferone,
L. S. Heath,
J. Humphreys,
V. Knick,
W. Pendergast,
S. Singer, et al.
1993.
Biochemical and cellular pharmacology of 1843U89, a novel benzoquinazoline inhibitor of thymidylate synthase.
Cancer Res.
53:810-818 |
| 8. |
Evans, R. M.,
J. D. Laskin, and M. T. Hakala.
1980.
Assessment of growth-limiting events caused by 5-fluorouracil in mouse cells and in human cells.
Cancer Res.
40:4113-4122 |
| 9. |
Ferone, R.
1970.
Dihydrofolate reductase from pyrimethamine-resistant Plasmodium berghei.
J. Biol. Chem.
245:850-854 |
| 10. |
Foote, S. J.,
D. Galatis, and A. F. Cowman.
1990.
Amino acids in the dihydrofolate reductase-thymidylate synthase gene of Plasmodium falciparum involved in cycloguanil resistance differ from those involved in pyrimethamine resistance.
Proc. Natl. Acad. Sci. USA
87:3014-3017 |
| 11. | Gassis, S., and P. K. Rathod. 1996. Frequency of drug resistance in Plasmodium falciparum: a nonsynergistic combination of 5-fluoroorotate and atovaquone suppresses in vitro resistance. Antimicrob. Agents Chemother. 40:914-919[Abstract]. |
| 12. |
Gomez, Z. M., and P. K. Rathod.
1990.
Antimalarial activity of a combination of 5-fluoroorotate and uridine in mice.
Antimicrob. Agents Chemother.
34:1371-1375 |
| 13. | Heidelberger, C., P. V. Danenberg, and R. G. Moran. 1983. Fluorinated pyrimidines and their nucleosides. Adv. Enzymol. Relat. Areas Mol. Biol. 54:58-119[Medline]. |
| 14. | Hekmat-Nejad, M., and P. K. Rathod. 1996. Kinetics of Plasmodium falciparum thymidylate synthase: interactions with high-affinity metabolites of 5-fluoroorotate and D1694. Antimicrob. Agents Chemother. 40:1628-1632[Abstract]. |
| 15. |
Houghton, P. J.,
G. S. Germain,
B. J. Hazelton,
J. W. Pennington, and J. A. Houghton.
1989.
Mutants of human colon adenocarcinoma, selected for thymidylate synthase deficiency.
Proc. Natl. Acad. Sci. USA
86:1377-1381 |
| 16. | Ingraham, H. A., L. Dickey, and M. Goulian. 1986. DNA fragmentation and cytotoxicity from increased cellular deoxyuridylate. Biochemistry 25:3225-3230[CrossRef][Medline]. |
| 17. |
Jackman, A. L.,
G. A. Taylor,
W. Gibson,
R. Kimbell,
M. Brown,
A. H. Calvert,
I. R. Judson, and L. R. Hughes.
1991.
ICI D1694, a quinazoline antifolate thymidylate synthase inhibitor that is a potent inhibitor of L1210 tumor cell growth in vitro and in vivo: a new agent for clinical study.
Cancer Res.
51:5579-5586 |
| 18. | Krungkrai, J., S. R. Krungkrai, and K. Phakanont. 1992. Antimalarial activity of orotate analogs that inhibit dihydroorotase and dihydroorotate dehydrogenase. Biochem. Pharmacol. 43:1295-1301[CrossRef][Medline]. |
| 19. | Kunz, B. A., S. E. Kohalmi, T. A. Kunkel, C. K. Mathews, E. M. McIntosh, and J. A. Reidy. 1994. International Commission for Protection Against Environmental Mutagens and Carcinogens. Deoxyribonucleoside triphosphate levels: a critical factor in the maintenance of genetic stability. Mutat. Res. 318:1-64[Medline]. |
| 20. | Parker, W. B., and Y. C. Cheng. 1990. Metabolism and mechanism of action of 5-fluorouracil. Pharmacol. Ther. 48:381-395[CrossRef][Medline]. |
| 21. |
Peterson, D. S.,
W. K. Milhous, and T. E. Wellems.
1990.
Molecular basis of differential resistance to cycloguanil and pyrimethamine in Plasmodium falciparum malaria.
Proc. Natl. Acad. Sci. USA
87:3018-3022 |
| 22. |
Queen, S. A.,
D. L. VanderJagt, and P. Reyes.
1990.
In vitro susceptibilities of Plasmodium falciparum to compounds which inhibit nucleotide metabolism.
Antimicrob. Agents Chemother.
34:1393-1398 |
| 23. | Rathod, P. K., and Z. M. Gomez. 1991. Plasmodium yoelii: oral delivery of 5-fluoroorotate to treat malaria in mice. Exp. Parasitol. 73:512-514[CrossRef][Medline]. |
| 24. |
Rathod, P. K.,
A. Khatri,
T. Hubbert, and W. K. Milhous.
1989.
Selective activity of 5-fluoroorotic acid against Plasmodium falciparum in vitro.
Antimicrob. Agents Chemother.
33:1090-1094 |
| 25. |
Rathod, P. K.,
M. Khosla,
S. Gassis,
R. D. Young, and C. Lutz.
1994.
Selection and characterization of 5-fluoroorotate-resistant Plasmodium falciparum.
Antimicrob. Agents Chemother.
38:2871-2876 |
| 26. |
Rathod, P. K.,
N. P. Leffers, and R. D. Young.
1992.
Molecular targets of 5-fluoroorotate in the human malaria parasite, Plasmodium falciparum.
Antimicrob. Agents Chemother.
36:704-711 |
| 27. |
Rathod, P. K.,
T. McErlean, and P. C. Lee.
1997.
Variations in frequencies of drug resistance in Plasmodium falciparum.
Proc. Natl. Acad. Sci. USA
94:9389-9393 |
| 28. |
Rathod, P. K., and S. Reshmi.
1994.
Susceptibility of Plasmodium falciparum to a combination of thymidine and ICI D1694, a quinazoline antifolate directed at thymidylate synthase.
Antimicrob. Agents Chemother.
38:476-480 |
| 29. |
Reyes, P., and C. Heidelberger.
1965.
Fluorinated pyrimidines. XXVI. Mammalian thymidylate synthetase: its mechanism of action and inhibition by fluorinated nucleotides.
Mol. Pharmacol.
1:14-30 |
| 30. | Reyes, P., P. K. Rathod, D. J. Sanchez, J. E. Mrema, K. H. Rieckmann, and H. G. Heidrich. 1982. Enzymes of purine and pyrimidine metabolism from the human malaria parasite, Plasmodium falciparum. Mol. Biochem. Parasitol. 5:275-290[CrossRef][Medline]. |
| 31. | Roberts, D. 1966. An isotopic assay for thymidylate synthetase. Biochemistry 5:3546-3548[CrossRef][Medline]. |
| 32. | Seymour, K. K., S. D. Lyons, L. Phillips, K. H. Rieckmann, and R. I. Christopherson. 1994. Cytotoxic effects of inhibitors of de novo pyrimidine biosynthesis upon Plasmodium falciparum. Biochemistry 33:5268-5274[CrossRef][Medline]. |
| 32a. |
Shallom, S. L.,
K. Zhang,
L. Jiang, and P. K. Rathod.
1999.
Essential protein-protein interactions between Plasmodium falciparum thymidylate synthase and dihydrofolate reductase domains.
J. Biol. Chem.
274:37781-37786 |
| 33. | Sherman, I. W. 1998. Purine and pyrimidine metabolism of asexual stages, p. 177-184. In I. W. Sherman (ed.), Malaria: parasite biology, pathogenesis, and protection. ASM Press, Washington, D.C. |
| 34. |
Srivastava, I. K., and A. B. Vaidya.
1999.
A mechanism for the synergistic antimalarial action of atovaquone and proguanil.
Antimicrob. Agents Chemother.
43:1334-1339 |
| 35. |
Trager, W., and J. B. Jensen.
1976.
Human malaria parasites in continuous culture.
Science
193:673-675 |
| 36. | Trigg, P. I., and A. V. Kondrachine. 1998. The current global malaria situation, p. 11-22. In I. W. Sherman (ed.), Malaria: parasite biology, pathogenesis, and protection. ASM Press, Washington, D.C. |
| 37. | Ward, W. H., R. Kimbell, and A. L. Jackman. 1992. Kinetic characteristics of ICI D1694: a quinazoline antifolate which inhibits thymidylate synthase. Biochem. Pharmacol. 43:2029-2031[CrossRef][Medline]. |
| 38. |
White, N. J.
1992.
Antimalarial drug resistance: the pace quickens.
J. Antimicrob. Chemother.
30:571-585 |
| 39. |
Wu, Y.,
L. A. Kirkman, and T. E. Wellems.
1996.
Transformation of Plasmodium falciparum malaria parasites by homologous integration of plasmids that confer resistance to pyrimethamine.
Proc. Natl. Acad. Sci. USA
93:1130-1134 |
| 40. |
Yoshioka, A.,
S. Tanaka,
O. Hiraoka,
Y. Koyama,
Y. Hirota,
D. Ayusawa,
T. Seno,
C. Garrett, and Y. Wataya.
1987.
Deoxyribonucleoside triphosphate imbalance. 5-Fluorodeoxyuridine-induced DNA double strand breaks in mouse FM3A cells and the mechanism of cell death.
J. Biol. Chem.
262:8235-8241 |
Antimicrobial Agents and Chemotherapy, April 2000, p. 1047-1050, Vol. 44, No. 4
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Copyright © 2000, American Society for Microbiology. All rights reserved.
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