Antileishmanial activity of the chalcone derivative LQFM064 associated with reduced fluidity in the parasite membrane as assessed by EPR spectroscopy.

A novel chalcone derivative, LQFM064, demonstrated antileishmanial activity against Leishmania (L.) amazonensis, with an IC value of ~10 μM for the promastigote form. Electron paramagnetic resonance (EPR) spectroscopy of a spin-labeled stearic acid incorporated in the plasma membrane of L. amazonensis promastigotes revealed that after 2 h of treatment with LQFM064, the parasite showed remarkable reductions in membrane fluidity. The features of the altered EPR spectra were similar to those reported for the erythrocyte membrane, which was suggested to be due to the cross-linking of oxidized hemoglobin with the cytoskeleton spectrin. In comparison to miltefosine (MIL), LQFM064 demonstrated a much lower hemolytic potential against both erythrocytes in PBS and whole blood, less cytotoxicity in J774.A1 macrophages and equivalent ability to kill parasites internalized in J774.A1 macrophages. Measurements of the IC values for assays with different cell concentrations enabled the estimation of the membrane-water partition coefficient (K), as well as the concentrations of LQFM064 in membrane (c) and aqueous phase (c) that reduces the cell population by 50%. From the K and c values it was deduced that LQFM064 has a greater affinity than MIL for the parasite membrane, but the antiproliferative activity of both substances is exerted at a similar concentration in the plasma membrane.