Activities of Endochin-Like Quinolones Against in vitro Cultured Besnoitia besnoiti Tachyzoites

Abstract

Endochin-like quinolones (ELQs) potently inhibit the proliferation of Plasmodium, Toxoplasma, Neospora, and Babesia by targeting the cytochrome b Qo and Qi sites and interfering with oxidative phosphorylation and pyrimidine biosynthesis. The activities of 14 different ELQs were assessed against B. besnoiti tachyzoites grown in human foreskin fibroblasts (HFF) by quantitative real time PCR. The values for 50% proliferation inhibition (IC50) of five ELQs were determined in a 3-days growth assay after an initial screen of 12 ELQs at 0.01, 0.1, and 1 µM. The IC50s of ELQ-121,-136, and-316 were 0.49, 2.36, and 7.97 nM, respectively. The IC50s of ELQs tested against B. besnoiti were higher than IC50s previously observed for P. falciparum and T. gondii. However, the B. besnoiti cytochrome b sequence and the predicted Qo and Qi ELQ binding sites in the Toxoplasma, Neospora, and Besnoitia cytochrome b are virtually identical, suggesting that the differences in ELQ susceptibility are not due to variations in the substrate binding sites. TEM of ELQ-treated parasites primarily demonstrated alterations within the parasite mitochondrion, profound thickening of the nuclear membrane, as well as increased vacuolization within the tachyzoite cytoplasm. Long-term treatment assays of intracellular B. besnoiti with ELQs for up to 20 days followed by the release of drug pressure caused a substantial delay in parasite growth and proliferation while ELQs were present, but parasite proliferation resumed days after ELQs were removed. Interestingly, structural alterations persisted after ELQ removal and parasite proliferation was slowed. These findings provide a basis for further in vivo studies of ELQs as therapeutic options against B. besnoiti infection.

Endochin-like quinolone-300 and ELQ-316 inhibit Babesia bovis, B. bigemina, B. caballi and Theileria equi

“…Interestingly, our calculated values of IC 50 for ELQ-300 and ELQ-316 are in the same range or lower than values estimated for other related apicomplexans in previous studies. ELQ-316 IC 50 values of 7.97, 0.66 and 0.35 nM were established for Besnoitia besnoiti and Toxoplasma gondii tachyzoites, respectively [ 28 , 29 ]. In addition, a previous study demonstrated ELQ-300 IC 50 values of 15.4 and 23.1 nM for Plasmodium knowlsei and P. falciparum , respectively [ 15 ].…”

Neospora caninum: Structure and Fate of Multinucleated Complexes Induced by the Bumped Kinase Inhibitor BKI-1294

“…Specimens were polymerized at 65 • C overnight, ultrathin sections were cut on a Reichert and Jung ultramicrotome (Reichert and Jung, Vienna) and were placed on 300 mesh formvar-carbon coated nickel grids (Plano GmbH, Marburg, Germany). They were stained in Uranyless ™ and lead citrate (EMS, Hatfield, PA, USA) as described [30], and specimens were inspected on a CM12 TEM operating at 80 kV.…”

Endochin-like quinolone-300 and ELQ-316 inhibit Babesia bovis, B. bigemina, B. caballi and Theileria equi 

“…Interestingly, our calculated values of IC 50 for ELQ-300 and ELQ-316 are in the same range or lower than values estimated for other related apicomplexans in previous studies. ELQ-316 IC 50 values of 7.97, 0.66 and 0.35 nM were established for Besnoitia besnoiti and Toxoplasma gondii tachyzoites, respectively [28,29]. In addition, a previous study demonstrated ELQ-300 IC 50 values of 15.4 and 23.1 nM for P. knowlsei and P. falciparum, respectively [15].…”