For both host cells the inhibitory effect on the percent infection was in the range of 0.5 to 5.0 μM. Surprisingly, NQ8 and NQ9 caused about a 2.5-fold

decrease of infection. For both host cells, the IC50 values after 48 h of treatment used to calculate the endocytic index are displayed in Table 3. NQ8 was the most active compound. Non-infected macrophages and HMCs treated with the compounds for 2 days were tested with the MTT assay to evaluate their toxicity to mammalian cells. For HMCs, the LC50 values were 8 μM for NQ1 and NQ12 and 10 μM for NQ8; NQ9 was the least toxic quinone with values higher than 10 μM. The LC50 was higher than 10 μM in macrophages for all four compounds. Table 3 IC 50 values (μM) of the naphthoquinones on intracellular Smoothened Agonist cell line BGB324 order amastigotes of T. cruzi Cpd HMC Macrophages NQ1 2.81 ± 0.43a,b 3.65 ± 0.71 NQ8 1.53 ± 0.11 1.49 ± 0.01 NQ9 2.48 ± 0.39 1.63 ± 0.18 NQ12 9.83 ± 2.64 2.51 ± 0.71 aThe IC50 was calculated for the endocytic index (number

of parasites/100 host cells) after two days of treatment. bMean ± standard deviation of at least three independent experiments. Ultrastructural analysis Transmission electron microscopy showed that treatment with the NQs induced important alterations in the mitochondrion of the epimastigotes, leading to swelling and the appearance of membranous structures in the organelle matrix (Figures 2, 3, 4 and 5). Autophagic features, such as atypical cytosolic membranous structures (Figures 3, 4, 5) and the appearance of endoplasmic reticulum surrounding reservosomes (Figures 2 and 5), were detected in treated parasites. The naphthoquinones PI-1840 also led to intense

cytosolic vacuolization (Figures 4 and 5), the formation of blebs in the flagellar region (Figures 2, 3 and 5) and the induction of loss of the electron-density of the cytosol (washed out aspect) (Figures 3 and 5). The scanning electron microscopy technique demonstrated no important morphological alterations in treated epimastigotes (data not shown). Figure 2 Transmission electron microscopy analysis of T. cruzi epimastigotes treated with NQ1. (A) Untreated epimastigote showing normal ultrastructural aspect and presenting typical morphologies of the mitochondrion (M), kinetoplast (K), flagellum (F), nucleus (N), Golgi (G), reservosome (R) and cytostome (Cy). (B-E) The concentration of 0.3 μM NQ1 led to swelling in the mitochondrion (*), the formation of abnormal cytosolic membranous structures (white arrowheads) and the appearance of endoplasmic reticulum surrounding reservosomes (white arrows). Blebs (thick black arrows) was formed in the flagellar membrane of treated parasites. Bars = 500 nm (A, B, E) and 200 nm (C, D). Figure 3 Transmission electron microscopy analysis of T. cruzi epimastigotes treated with NQ8. (A-D) Treatment with 0.