Project Summary Filariases are a group of neglected tropical diseases produced by infection with microfilaria of Clade III parasitic nematodes that are transmitted by biting insects. One example is the lymphatic filariasis produced by Brugia malayi. Lymphatic filariasis is a debilitating and disfiguring disease which occurs in 120 million people worldwide. Other filarial diseases are River Blindness produced by Onchocerca volvulus and loiasis produced by Loa loa. Prevention and treatment of these nematode parasite diseases relies on the use of anthelmintic drugs because no effective vaccines are available. Prophylaxis using Mass Drug Administration [MDA] programs are limited by the efficacy of existing anthelmintics. Diethylcarbamazine is a mainstay for the treatment of lymphatic filariasis and loiasis in most parts of the world, except in areas where onchocerciasis is present because it is contra-indicated by risks of blindness. Diethylcarbamazine produces rapid clearance of microfilaria and causes ~40% mortality of adult parasites (macrofilaricide). A number of studies have suggested that diethylcarbamazine has an indirect host- mediated mode of action and that diethylcarbamazine acts by changing host arachidonic acid pathways. We have observed that diethylcarbamazine has direct effects on filarial nematodes. We present preliminary observations that show that diethylcarbamazine increases the opening of TRP-2 channels in Brugia malayi, and opening of calcium-activated SLO-1 K channels. The effect is a rapid, transient inhibition of motility followed by recovery: the response accommodates. Emodepside is an emerging and important cyclooctadepsipeptide class of anthelmintic that also has effects on microfilaria and adult filaria. Emodepside treatments could allow a major advance over existing mass drug administration (MDA) programs which require regular treatments to kill adult parasites. One of the sites of action of emodepside is on nematode SLO-1 K channels where opening of the channels inhibits motility, but it is not effective against all filaria. Here we propose to compare effects on filarial SLO- 1 K channels from Brugia, Onchocerca and Loa and to examine actions and interactions of these two drugs to explore their mode of action. We have 3 aims: Aim #1: Characterize, in vitro, the concentration motility-inhibition-response relationships of diethylcarbamazine and emodepside and their combination on: A) Brugia microfilaria; B) Brugia adult females; C) Brugia adult males. We will test the hypothesis that effects of diethylcarbamazine and emodepside are additive, synergistic or antagonistic and dependent of life-cycle stage and sex. Aim #2 Characterize the SLO-1 K channel current responses to diethylcarbamazine and emodepside in isolated Brugia malayi muscle flaps under patch-clamp We will test the hypotheses: a) that the effects of emodepside and diethylcarbamazine interact; b) that the interactions of diethylcarbamazine and emodepside are de...