Onchocerciasis (river blindness), caused by the filarial worm Onchocerca volvulus, is a neglected tropical disease mostly affecting sub-Saharan Africa and is responsible for > 1.3 million years lived with disability. Current control relies almost entirely on ivermectin, which suppresses symptoms caused by the first-stage larvae (microfilariae) but does not kill the long-lived adults. Here, we evaluated emodepside, a semi-synthetic cyclooctadepsipeptide registered for deworming applications in companion animals, for activity against adult filariae (i.e., as a macrofilaricide). We demonstrate the equivalence of emodepside activity on SLO-1 potassium channels in Onchocerca volvulus and Onchocerca ochengi, its sister species from cattle. Evaluation of emodepside in cattle as single or 7-day treatments at two doses (0.15 and 0.75 mg/kg) revealed rapid activity against microfilariae, prolonged suppression of female worm fecundity, and macrofilaricidal effects by 18 months post treatment. The drug was well tolerated, causing only transiently increased blood glucose. Female adult worms were mostly paralyzed; however, some retained metabolic activity even in the multiple high-dose group. These data support ongoing clinical development of emodepside to treat river blindness.

Datasets comprise raw data underpinning graphical plots and charts. Data represent potentials (currents); drug concentrations; parasite counts; semiquantitative scores for parasite motility, fecundity and integrity; host cell counts; and derived data for parasite counts (area-under-the-curve). Full details are provided in the data descriptions.   

Emodepside targets SLO-1 channels of Onchocerca ochengi and induces broad anthelmintic effects in a bovine model of onchocerciasis

DATA DESCRIPTIONS

The following abbreviations are used throughout: EMO1H, emodepside, 0.75 mg/kg, single dose; EMO7H, emodepside, 0.75 mg/kg, daily for 7 days; EMO1L, emodepside, 0.15 mg/kg, single dose; EMO7L, emodepside, 0.15 mg/kg, daily for 7 days; MRSM, melarsomine, 4 mg/kg, every other day for 3 days; PCBO, placebo.

Fig. 1. Emodepside sensitivity of Onchocerca ochengi and Onchocerca volvulus SLO-1 splice variants. Onchocerca spp. SLO-1 splice variants were heterologously expressed in Xenopus laevis oocytes to determine species- and splice variant-specific effects of emodepside. All seven SLO-1 splice variants were able to form functional homomeric ion channels and changes in current could be measured with an electrophysiological two-electrode, voltage-clamp approach with oocytes exposed to increasing concentrations of emodepside (0.3, 1, 3, 10 and 30 µM). For each splice variant at each emodepside concentration, 5–7 oocytes were tested from a single pool of transfected cells to generate biological replicate data; the experiment was performed once.

Fig. 2. Observed plasma PK (concentration vs time curves) for four emodepside dose steps in zebu (Ngaoundéré Gudali) cattle (B. t. indicus).

Dose groups were intravenous emodepside:

A 0.15 mg/kg/day on day 0.

B 0.15 mg/kg/day on days 0–6.

C 0.75 mg/kg/day on day 0.

D 0.75 mg/kg/day on days 0–6.

Emodepside concentration in plasma was determined by tandem mass spectrometry using serial dilutions of single samples per animal (n = 7 per dose group) at each timepoint. Symbols represent observations for individual animals; the lines represent the PK model of emodepside for that dosing regimen. Data are from a single study. No statistical comparisons were made.

Fig. 3. Blood glucose concentrations observed pre- and post-treatment commencement with emodepside by experimental group in zebu (Ngaoundéré Gudali) cattle (B. t. indicus). Glucose concentration in venous blood was determined by test strip assay (MediTouch 2 blood glucose monitor, Medisana, Neuss, Germany). Treatment groups were single dose, or 7 daily doses, of emodepside at 0.15 mg/kg (EMO1L, EMO7L) or 0.75 mg/kg (EMO1H, EMO7H), placebo (PCBO [solketal]) daily for 7 days, and melarsomine (MRSM) 4 mg/kg every other day for 3 days as a positive control.

Fig 4. Mean dermal microfilarial density (n per 100 mg skin) in zebu (Ngaoundéré Gudali) cattle (B. t. indicus) treated with emodepside or melarsomine compared with placebo. Mean dermal microfilarial density was determined by incubation of skin biopsies (in triplicate per animal, per time point) normalised to 100 mg skin. Mean density values are shown at each time point in each treatment group (n = 7 per group).

Fig 5. Histopathology of Onchocerca ochengi nodules treated with emodepside. Parasite sections were scored according to Striebel (1988). Cumulative histopathological scores (across worm tissues and organs) by experimental group and time point. Data points are from a single nodule from different animals at each time point and include scores for male worms where observed in female worm nodules.

Fig 6. Dermal microfilarial load distribution (area under the curve [load*time]) by treatment group in zebu (Ngaoundéré Gudali) cattle (B. t. indicus). Dermal microfilarial density was determined at each time point by incubation of skin biopsies (in triplicate per animal at each time point), normalised to 100 mg skin, then used to estimate total area under the load*time curve.

Fig 7. Distribution of counts for uterine contents at different dose steps. (A) oocytes, (B) all developing embryonic stages, (C) normal, and (D) degenerated intrauterine microfilariae in cattle treated with emodepside or melarsomine compared with placebo. Counts for uterine contents were determined in samples from each animal (n = 7 animals per treatment group), then used to estimate total area under the load*time curve. The boxplot is ordered by dose steps of emodepside (grey shading). The thick bar is the median, the limits of each box are the interquartile range, the whiskers are the smallest/largest value within 1.5x the interquartile range, and the open circles are outliers. The placebo control and melarsomine (positive control) are shown in orange and black, respectively.

Fig 8. Linear model describing the relationship between change in adult female worm (Onchocerca ochengi) motility over time and total emodepside dose. The anterior end of the female worm was removed from the worm mass and incubated alongside intact male worms for 30 min at 37˚C for visual motility assessment on a three-point scale. A linear model of worm motility over time for a given treatment group was estimated and repeated for each group; the slope β for each group is reported. The null hypothesis was β = 0, and t statistics were used to test and reject the null hypothesis and to estimate the P value.

Figure D in S1 Text. PK analysis of emodepside concentration in cattle. (a) Simulated plasma concentration–time profiles of emodepside in cattle over 1 week after repeated daily administration of 0.15 mg/kg or 0.75 mg/kg via 15 min IV infusion based on a PK studies in two Holstein cows (receiving 1 mg/kg and 2.13 mg/kg respectively). (b) Observed plasma concentration of emodepside in zebu cattle (data points) receiving once-daily IV emodepside 0.15 mg/kg, 0.15 mg/kg for 2 days, 0.75 mg/kg, or placebo (data not shown), and predicted concentration–time profiles after model fitting (red lines) of data from PK studies in two Holstein cows. Emodepside concentration in plasma was determined by tandem mass spectrometry; lower limit of quantitation was 1.0 mg/L. All samples in the placebo control were below the lower limit of quantitation. No statistical comparisons were made.

Figure E in S1 Text. Ratio of skin to plasma concentrations of emodepside in zebu (Ngaoundéré Gudali) cattle (B. t. indicus) over time. Drug concentrations are shown as µg/L.

Figure F in S1 Text. Dermal microfilarial density (n per 100 mg skin) in zebu (Ngaoundéré Gudali) cattle (B. t. indicus) treated with emodepside or melarsomine compared with placebo. Dermal microfilarial density was determined by incubation of skin biopsies (in triplicate per animal, per time point) and normalised to 100 mg skin.

Figure G in S1 Text. Mean numbers of (A) oocytes, (B) developing embryonic stages, (C) normal, and (D) degenerated intrauterine microfilariae in cattle treated with emodepside or melarsomine compared with placebo. Uterine counts (including intrauterine microfilariae) were made after homogenizing the posterior part of the female worm and counting the stages in a standardised manner in a Fuchs-Rosenthal chamber.

Figure H in S1 Text. Effects of emodepside on adult female worm motility. Mean worm motility values over time by treatment group. Worm motility score: 0 = none; 1 = intermediate; 2 = normal.

Figure I in S1 Text. Effects of emodepside on adult female worm viability (MTT reduction). Worms were subjected to a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for metabolic activity (Renz et al., 1995), in which the insoluble formazan product was dissolved in dimethyl sulfoxide and quantified colorimetrically at 620 nm in a microplate reader.

Figure J in S1 Text. Effects of emodepside on mean adult female worm fecundity in comparison with melarsomine and placebo. The female worm mass was subjectively scored for fecundity on a four-point scale (0, uteri empty or worm structure degraded; 1, low; 2, intermediate; 3, normal) by examining the uterine contents microscopically in situ.

Figure K in S1 Text. Effects of emodepside on mean adult male worm motility in comparison with melarsomine and placebo. Mean worm motility values over time by treatment group. Worm motility score: 0 = none; 1 = intermediate; 2 = normal.

Figure M in S1 Text. Nodular polymorphonuclear counts per high-power field for each treatment group and time point. Relevant cell counts per high-power field are highlighted.

Figure N in S1 Text. Nodular eosinophil counts as a percentage of total polymorphonuclear cell counts for each treatment group and time point. Relevant cell counts per high-power field are highlighted.

Figure O in S1 Text. Linear model describing the relationship between change in adult male worm motility over time and total emodepside dose. Intact male worms were removed from the worm mass and incubated alongside the anterior end of the female worms for 30 min at 37˚C for visual motility assessment on a three-point scale (Renz et al., 1995). A linear model of worm motility over time for a given treatment group was estimated and repeated for each group; the slope β is reported. The null hypothesis was β = 0, and t statistics were used to reject the null hypothesis and to estimate the P value.

Table I in S1 Text. Fraction of normal adult worm motility (% [n]) by treatment group, sex, and time point. Worm motility score: 0 = none; 1 = intermediate; 2 = normal.