Combinations of registered drugs reduce treatment times required to deplete Wolbachia in the Litomosoides sigmodontis mouse model

Abstract

Filarial parasites can be targeted by antibiotic treatment due to their unique endosymbiotic relationship with Wolbachia bacteria. This finding has led to successful treatment strategies in both, human onchocerciasis and lymphatic filariasis. A 4–6 week treatment course using doxycycline results in long-term sterility and safe macrofilaricidal activity in humans. However, current treatment times and doxycycline contraindications in children and pregnant women preclude widespread administration of doxycycline in public health control programs; therefore, the search for shorter anti-wolbachial regimens is a focus of ongoing research. We have established an in vivo model for compound screening, using mice infected with Litomosoides sigmodontis. We could show that gold standard doxycycline treatment did not only deplete Wolbachia, it also resulted in a larval arrest. In this model, combinations of registered antibiotics were tested for their anti-wolbachial activity. Administration of rifamycins in combination with doxycycline for 7 days successfully depleted Wolbachia by > 2 log (>99% reduction) and thus resulted in a significant reduction of the treatment duration. Using a triple combination of a tetracycline (doxycycline or minocycline), a rifamycin and a fluoroquinolone (moxifloxacin) led to an even greater shortening of the treatment time. Testing all double combinations that could be derived from the triple combinations revealed that the combination of rifapentine (15mg/kg) and moxifloxacin (2 x 200mg/kg) showed the strongest reduction of treatment time in intraperitoneal and also oral administration routes. The rifapentine plus moxifloxacin combination was equivalent to the triple combination with additional doxycycline (>99% Wolbachia reduction). These investigations suggest that it is possible to shorten anti-wolbachial treatment times with combination treatments in order to achieve the target product profile (TPP) requirements for macrofilaricidal drugs of no more than 7–10 days of treatment.

Preclinical development of an oral anti- Wolbachia macrolide drug for the treatment of lymphatic filariasis and onchocerciasis

“…In the first model, interleukin-4 receptor alphadeficient (IL-4R −/− ) BALB/c immunodeficient mice were infected with third-stage larvae (L3) of B. malayi, a human lymphatic filarial pathogen (9). In the second model, BALB/c mice were infected with L3 larvae of Litomosoides sigmodontis, which naturally infects cotton rats (10). In the B. malayi model, infectious stage larvae were isolated from mosquitoes and, after inoculation into the immunodeficient mice, were allowed to develop into adults that produced microfilarial stages contained within the peritoneal cavity of the host animals.…”

In vivo efficacy of the boron-pleuromutilin AN11251 against Wolbachia of the rodent filarial nematode Litomosoides sigmodontis

“…Oral vehicle administrations (1% carboxymethyl cellulose (CMC)/0.1% Tween80) or untreated animals served as negative controls (S1 Table, S2 Table). Since a combination of rifamycins and moxifloxacin was recently shown to allow shortened drug regimens [24], a combination therapy of AN11251 and doxycycline was tested. Therefore, for the combination therapy 40 mg/kg doxycycline and different AN11251 doses were used in a formulation of 10% DMSO in PBS/1% CMC/0.1% Tween80.…”

“…Thus, 10-day BID treatment with 200 mg/kg AN11251 resulted in a Wolbachia depletion that was comparable with high-dose rifampicin treatment for 10 days in the L. sigmodontis mouse model. As combinations of rifamycins and moxifloxacin were recently shown to improve the clearance of Wolbachia in the L. sigmodontis mouse model and combinations of 2 weeks of doxycycline and rifampicin treatment resulted in a moderate macrofilaricidal effect in human W. bancrofti patients [15,24], combinations of AN11251 and doxycycline were investigated in the present study. However, a combination of 100 mg/kg AN11251 with 40 mg/kg doxycycline did not significantly improve the Wolbachia depletion, achieving a Wolbachia depletion of 97% after 7 days of treatment.…”

“…Furthermore, an impact of anti-Wolbachia drug candidates on adult worm burden and microfilariae counts is often not observed due to the slow macrofilaricidal efficacy of anti-Wolbachia compounds and the fact that only~50% of mice develop microfilaremia [35], which is also seen in human lymphatic filariasis [36]. Nevertheless, the L. sigmodontis mouse model is very sensitive to short-course treatments and has repeatedly proven valuable for the screening of potential drug candidates against Wolbachia endosymbionts [24,[37][38][39] and provided the basis for the successful human clinical trials with doxycycline. Even though no macrofilaricidal effect was observed for the tested drugs, human clinical studies demonstrated that doxycycline provides a macrofilaricidal effect in human onchocerciasis patients only after 21-27 months following treatment [40].…”

“…Data from clinical trials with other anti-Wolbachia agents showed that such a Wolbachia reduction greater than 99% lead to a permanent sterilization of the female adult worms. Furthermore, the potential synergism of a combination therapy of doxycycline and AN11251 was evaluated to assess if it was possible to further reduce the treatment time required for Wolbachia depletion [24].…”