TABLE 4.

Susceptibility of L. major lines to antimony in the presence of BSO^a

Compound	Mean EC50 (μM) ± SD (RI [EC50 decrease])
	pUCNEO	LABCG2
SbIII	6.50 ± 1.01	37.45 ± 1.50 (5.8)†
SbIII + BSO	4.96 ± 1.23 (1.3)	8.23 ± 0.91 (1.7 [4.5])*

^aParasites were grown in M199 culture medium supplemented with 10% hiFBS for 72 h at 28°C in the presence of increasing concentrations of Sb^III. Cell viability was determined by using an MTT-based assay as described in Materials and Methods. Resistance indexes (RI), indicated in parentheses, were calculated by dividing the EC₅₀ for the Leishmania line overexpressing LABCG2 by that for the Leishmania control line (pUCNEO) with the same treatment. The EC₅₀ decrease, indicated in square brackets, was calculated by dividing the EC₅₀ after Sb^III treatment by that for treatment with Sb^III plus BSO (a γ-glutamylcysteine synthetase inhibitor) in each Leishmania line. A total of 3 mM BSO was added to the culture medium 48 h before the susceptibility experiment was performed. The data are the means ± standard deviations of results from three independent experiments. Significant differences were determined by the Student t test (†, P < 0.01 for pUCNEO versus the LABCG2 line; *, P < 0.01 for the LABCG2 line treated with versus without BSO).