Discovery of short-course antiwolbachial quinazolines for elimination of filarial worm infections

Abstract

Parasitic filarial nematodes cause debilitating infections in people in resource-limited countries. A clinically validated approach to eliminating worms uses a 4- to 6-week course of doxycycline that targets Wolbachia, a bacterial endosymbiont required for worm viability and reproduction. However, the prolonged length of therapy and contraindication in children and pregnant women have slowed adoption of this treatment. Here, we describe discovery and optimization of quinazolines CBR417 and CBR490 that, with a single dose, achieve >99% elimination of Wolbachia in the in vivo Litomosoides sigmodontis filarial infection model. The efficacious quinazoline series was identified by pairing a primary cell-based high-content imaging screen with an orthogonal ex vivo validation assay to rapidly quantify Wolbachia elimination in Brugia pahangi filarial ovaries. We screened 300,368 small molecules in the primary assay and identified 288 potent and selective hits. Of 134 primary hits tested, only 23.9% were active in the worm-based validation assay, 8 of which contained a quinazoline heterocycle core. Medicinal chemistry optimization generated quinazolines with excellent pharmacokinetic profiles in mice. Potent antiwolbachial activity was confirmed in L. sigmodontis, Brugia malayi, and Onchocerca ochengi in vivo preclinical models of filarial disease and in vitro selectivity against Loa loa (a safety concern in endemic areas). The favorable efficacy and in vitro safety profiles of CBR490 and CBR417 further support these as clinical candidates for treatment of filarial infections.

Oxfendazole mediates macrofilaricidal efficacy against the filarial nematode Litomosoides sigmodontis in vivo and inhibits Onchocerca spec. motility in vitro

“…Thus, the L . sigmodontis rodent model was chosen by the Bill & Melinda Gates Foundation for the “Macrofilaricidal Drug Accelerator Program” to identify new compounds with a macrofilaricidal effect [ 17 , 23 – 25 , 54 , 55 ]. Despite this, all filarial rodent models have a shorter filarial life-span in comparison to human pathogenic filariae and differences in the location of the parasites and the associated accessibility of the drug to the filariae (thoracic cavity for L .…”

“…The L . sigmodontis rodent model has been used to validate macrofilaricidal drug candidates by a consortium led by the Bill & Melinda Gates Foundation, Drugs for Neglected Diseases initiative (DND i ), academia, and pharmaceutical companies and has supported the advancement of a few macrofilaricidal compounds through preclinical and clinical development [ 17 , 22 – 28 ]. In this study we demonstrate that oxfendazole exhibits excellent macrofilaricidal efficacy following both oral and sc administrations in the L .…”

The endosymbiont Wolbachia rebounds following antibiotic treatment

“…Wolbachia titers were reduced by >95% in female worms from rifampicin treated animals at the 1-week timepoint compared to those of worms from vehicle animals. The extensive reduction of Wolbachia titers in adult worms has been previously described in other rodent studies with filarial worms, but the studies were terminated 16-18 weeks post-treatment [26,27,29,40,50], and the long-term effects of antibiotic treatment on filarial worms and their Wolbachia were not evaluated in these models.…”

“…Several studies have recently shown that short courses of 7-and 14-days of anti-Wolbachia compounds hold promise as excellent drugs to treat onchocerciasis and LF [25][26][27][28][29]. Studies by Hübner et al however, showed that suboptimal treatment regimens of doxycycline in the Litomosoides sigmodontis infection model did not lead to a sustained reduction in Wolbachia loads in worms 14-18 weeks post-treatment and that longer term studies were needed to assess permanent sterilization of female adult worms [27,29].…”

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

“…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].…”