Inhibition of glutathione synthesis as a chemotherapeutic strategy for trypanosomiasis.

Abstract

With the expectation that trypanosomal glutathione (GSH) plays a major protective role against the endogenous oxidant stress that results form high intracellular levels of H2O2, we sought to deplete Trypanosoma brucei brucei of their GSH through inhibition of its biosynthesis. Administration of buthionine sulfoximine (BSO), a reversible inhibitor of gamma-glutamylcysteine synthetase, to parasitemic mice resulted in a progressive decrease in trypanosome GSH content, such that parasites isolated after 5 h or BSO treatment contained 50% of normal values. When BSO administration was continued for 18 h (intraperitoneal injection of 4 mmol/kg every 1.5 h), parasitemias temporarily cleared. When inhibitory plasma levels of BSO were maintained for about 27 h, two out of six infected mice were cured and the rest had significantly prolonged survival. These findings demonstrate the potential value of GSH depletion for the treatment of trypanosomiasis.

Gene Knockdown of γ-Glutamylcysteine Synthetase by RNAi in the Parasitic Protozoa Trypanosoma brucei Demonstrates That It Is an Essential Enzyme

“…This effect on parasite survival correlated directly to loss of ␥-GCS RNA and protein and to a depletion of the cellular thiol pools. As was observed in prior studies on blood stage parasites (21), the ␥-GCS inhibitor BSO was toxic to the growth of procyclic parasites. GSH was able to rescue the RNA i cell death phenotype, but it did not rescue BSO toxicity.…”

“…Further validation of the target would be obtained by demonstrating that parasite cells can be killed by agents that function by inhibiting the target enzyme. The potent ␥-GCS inhibitor, BSO, had been demonstrated previously to have antitrypanosomal activities in a rodent model; however, the mechanism of action of BSO killing was not clearly established (21).…”

“…In particular an enzyme-activated, potent inhibitor of ␥-GCS, buthionine sulfoximine (BSO), was shown to cure or prolong survival of mice infected with a bloodstream form T. brucei (21). These studies implicated ␥-GCS as a potential drug target, and the observed selectivity of BSO suggested that trypanosomes are more sensitive to GSH depletion than mammalian cells.…”

Insights into the redox biology of Trypanosoma cruzi: Trypanothione metabolism and oxidant detoxification

“…brucei-infected mice [52]. GSH synthesis has not been extensively 259 studied in T. cruzi but BSO has been used as an experimental tool for 260 decreasing GSH and, to a lesser extent, T(SH) 2 and Gsp levels 261 [43,44,53].…”

Escherichia coli γ-Glutamylcysteine Synthetase

“…In all cases examined, ␥-GCS is rate-limiting and is feedback-inhibited by GSH. In protozoa and mammals, potent inhibitors of ␥-GCS such as buthionine sulfoximine (BSO) have been used to block GSH synthesis and promote GSH depletion (21)(22)(23). Cells depleted of GSH are more susceptible to the toxic effects of radiation (16,24), many cancer chemotherapy drugs (25), and internally generated oxidants (22), and the increased vulnerability of cells pharmacologically depleted of GSH has been exploited therapeutically (23,25).…”