In vitro flubendazole-induced damage to vital tissues in adult females of the filarial nematode Brugia malayi

Abstract

The use of a microfilaricidal drug for the control of onchocerciasis and lymphatic filariasis necessitates prolonged yearly dosing. Prospects for elimination or eradication of these diseases would be enhanced by availability of a macrofilaricidal drug. Flubendazole (FLBZ), a benzimidazole anthelmintic, is an appealing candidate macrofilaricide. FLBZ has demonstrated profound and potent macrofilaricidal effects in a number of experimental filarial rodent models and one human trial. Unfortunately, FLBZ was deemed unsatisfactory for use in mass drug administration (MDA) campaigns due to its markedly limited oral bioavailability. However, a new formulation that provided sufficient bioavailability following oral administration could render FLBZ an effective treatment for onchocerciasis and LF. This study characterized the effects of FLBZ and its reduced metabolite (FLBZ-R) on filarial nematodes in vitro to determine the exposure profile which results in demonstrable damage. Adult female Brugia malayi were exposed to varying concentrations of FLBZ or FLBZ-R (100 nM–10 μM) for up to five days, after which worms were fixed for histology. Morphological damage following exposure to FLBZ was observed prominently in the hypodermis and developing embryos at concentrations as low as 100 nM following 24 h exposure. The results indicate that damage to tissues required for reproduction and survival can be achieved at pharmacologically relevant concentrations.

Profiling the macrofilaricidal effects of flubendazole on adult female Brugia malayi using RNAseq

“…In the current study, we used the RNAseq approach to identify significant genes and biological processes that were being affected in B. malayi when challenged with FLBZ. Analysis of GO terms highlights the influence FLBZ on filarial embryonic development, consistent with previous findings (O'Neill et al., 2015, O'Neill et al., 2016). Significantly enriched GO terms are commonly associated with RNAi phenotypes of embryo/larval lethality or impairments to overall morphogenesis for C. elegans homologues.…”

“…Hypodermal damage is a common theme among the benzimidazoles including FLBZ (Lacey, 1988, Franz et al., 1990a, Kumar and Lai, 1998, Hanser et al., 2003, Shalaby et al., 2009, Cárdenas et al., 2010, O'Neill et al., 2015). Previous studies have shown that short-term exposure to FLBZ leads to extensive damage to B. malayi hypodermal tissue (O'Neill et al., 2015). Given that components of the nematode cuticle are synthesized and delivered to the surface through the hypodermis (Page and Winter 2003), it is not surprising that hypodermal tissue damage would result in a dampening of cuticle synthesis.…”

“…The evolutionary life-history theory predicts that there is a trade-off between reproduction, growth and survival depending on the availability of resources (Zera and Harshman, 2001). It is conceivable that the insult of drug exposure or resulting damage to tissues involved in nutrient acquisition (O'Neill et al., 2015) could stimulate down-regulation of genes not required for immediate survival, such as those involved in reproduction.…”

“…Exposure to relatively high but pharmacologically relevant concentrations (10 μM) of FLBZ for 24 h was not lethal and worms were able to recover (O'Neill et al., 2015, O'Neill et al., 2016). These studies used histological techniques to assess tissues damage in an effort to determine a concentration range which may be lethal over this time-period.…”

“…Previous data show that exposure to pharmacologically relevant concentrations of FLBZ elicits damage to the hypodermis, developing embryos, and intestine of adult female B. malayi , but this damage is not accompanied by apparent changes in motility or viability (O'Neill et al., 2015). These changes were observed via histology, a method which is challenging for evaluating drug-induced damage.…”