TOXOPLASMA RIBONUCLEOTIDE REDUCTASE AS A DRUG TARGET

Toxoplasma gondii, the causative agent of toxoplasmosis, results in
severe disease in neonates and the immunocompromised, including AIDS
patients. Currently there are few effective chemotherapeutic options,
and those that are available are frequently associated with adverse side
effects. Ribonucleotide reductase is an enzyme which catalyzes the
conversion of ribonucleotides to deoxyribonucleotides and therefore is
essential for DNA synthesis. Ribonucleotide reductase (RNR) has proven
to be a promising target for chemotherapy of herpes virus infections.
The primary goal of this project is to characterize ribonucleotide
reductase of Toxoplasma gondii and evaluate the enzyme as a potential
target for chemotherapy of toxoplasmosis. As part of this effort we plan
to clone the RNR genes and express biologically active enzyme. This
recombinant enzyme will be fully biochemically characterized. In vitro
RNR assays, in conjunction with parasite tissue culture will be used to
screen candidate inhibitors. Effective agents and currently available
anti-Toxoplasma agents will be tested for synergistic action against
parasites. Any agents which appear to have promise as specific anti-
Toxoplasma agents will also be tested in in vivo models of toxoplasmosis.
In addition, peptides corresponding to the C-terminal sequences of the
small subunit of RNR will be tested for their ability to inhibit RNR.
Mutant parasites resistant to candidate drugs will be generated and
analyzed in order to more fully understand the basis of drug-enzyme
interaction. Our hope is that these studies will form the basis for
design of new novel agents for treatment of toxoplasmosis.