Toxoplasmic encephalitis is a common opportunistic infection in AIDS patients. The currently available chemotherapy with pyrimethamine plus a sulfa drug does not always prevent death. Thus new drugs are needed to treat toxoplasmosis in immunosuppressed patients. These new drugs will be sought among the many anticoccidial agents that have been designed to treat infections of chickens with Eimeria species. Two of these anticoccidials, arprinocid and emimycin, have already shown potent activity in animal experiments. Mutants of Toxoplasma gondii resistant to both these drugs have been isolated. One mutant has been used to prove that the form of arprinocid that is active in vivo is the N-oxide. The mechanism of action of emimycin and of arprinocid-N-oxide will be determined. Emimycin is likely to affect pyrimidine metabolism in the parasite while arprinocid-N-oxide may affect purine metabolism. The actions of both drugs will be studied initially by analyses of their effects on the nucleotide pool of T. gondii. Among the additional biochemical aspects to be examined will be permeability to the drug, effects of the drug on various purine and pyrimidine salvage enzymes, and incorporation of the drug into nucleic acids. The mechanisms of action of other antitoxoplasma drugs that will be identified by screening a large catalogue of anticoccidials will also be studied. A key component in analyzing these mechanisms will be the use of multi- and single-step drug resistant mutants of T. gondii. In addition, already isolated mutants of the parasite resistant to pyrimethamine will be studied by comparing the wide type and mutant dihydrofolate reductases. Similarly, already isolated mutants, of T gondii resistant to sulfadiazine will be examined by comparing the wild type and mutant guanosine triphosphate cyclophydrolases. Understanding the mechanisms of action of these various drugs should provide valuable insights into the basic biology and biochemistry of this parasite.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI025817-02
Application #
3139459
Study Section
(SRC)
Project Start
1987-09-30
Project End
1992-04-30
Budget Start
1989-05-01
Budget End
1990-04-30
Support Year
2
Fiscal Year
1989
Total Cost
Indirect Cost
Name
Dartmouth College
Department
Type
Schools of Medicine
DUNS #
041027822
City
Hanover
State
NH
Country
United States
Zip Code
03755
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Pfefferkorn, E R; Borotz, S E; Nothnagel, R F (1993) Mutants of Toxoplasma gondii resistant to atovaquone (566C80) or decoquinate. J Parasitol 79:559-64
Ricketts, A P; Pfefferkorn, E R (1993) Toxoplasma gondii: susceptibility and development of resistance to anticoccidial drugs in vitro. Antimicrob Agents Chemother 37:2358-63
Sibley, L D; LeBlanc, A J; Pfefferkorn, E R et al. (1992) Generation of a restriction fragment length polymorphism linkage map for Toxoplasma gondii. Genetics 132:1003-15
Pfefferkorn, E R; Borotz, S E; Nothnagel, R F (1992) Toxoplasma gondii: characterization of a mutant resistant to sulfonamides. Exp Parasitol 74:261-70
Erbe, D V; Pfefferkorn, E R; Fanger, M W (1991) Functions of the various IgG Fc receptors in mediating killing of Toxoplasma gondii. J Immunol 146:3145-51
Pfefferkorn, E R; Eckel, M E; McAdams, E (1989) Toxoplasma gondii: the biochemical basis of resistance to emimycin. Exp Parasitol 69:129-39
Pfefferkorn, E R; Eckel, M E; McAdams, E (1988) Toxoplasma gondii: in vivo and in vitro studies of a mutant resistant to arprinocid-N-oxide. Exp Parasitol 65:282-9