A repurposing strategy for Hsp90 inhibitors demonstrates their potency against filarial nematodes

Novel drugs are required for the elimination of infections caused by filarial worms, as most commonly used drugs largely target the microfilariae or first stage larvae of these infections. Previous studies, conducted in vitro, have shown that inhibition of Hsp90 kills adult Brugia pahangi. As numerous small molecule inhibitors of Hsp90 have been developed for use in cancer chemotherapy, we tested the activity of several novel Hsp90 inhibitors in a fluorescence polarization assay and against microfilariae and adult worms of Brugia in vitro. The results from all three assays correlated reasonably well and one particular compound, NVP-AUY922, was shown to be particularly active, inhibiting Mf output from female worms at concentrations as low as 5.0 nanomolar after 6 days exposure to drug. NVP-AUY922 was also active on adult worms after a short 24 h exposure to drug. Based on these in vitro data, NVP-AUY922 was tested in vivo in a mouse model and was shown to significantly reduce the recovery of both adult worms and microfilariae. These studies provide proof of principle that the repurposing of currently available Hsp90 inhibitors may have potential for the development of novel agents with macrofilaricidal properties

Recovery of adult worms and Mf from mice post-NVP-AUY922 treatment.

**<p>not every animal received the full complement of 10 female worms.</p><p>Recoveries from individual drug-treated mice: 3/10; 1/10; 2/9; 1/9; 1/10.</p><p>Only 2 of the 8 worms recovered were normal, all others were coated in cells and largely immobile</p><p>Recoveries from individual control animals: 8/9; 3/10; 4/10; 6/10; 5/10. All worms recovered from control animals showed normal motility and had no adherent cells with the exception of a single worm, in each of two mice.</p

Structures of Hsp90 inhibitors used in the <i>in vitro</i> experiments.

<p>Figure shows chemical structures of Geldanamycin (GA), NVP-AUY0922, NVP-BEP800, SNX-9203 and SNX-2112.</p

Binding affinity of various Hsp90 inhibitors versus human Hsp90α, <i>B. pahangi</i> and <i>B. malay</i>i Hsp90 in the FP assay.

a<p>Best fit (95% confidence intervals).</p><p>nd = not determined.</p

A 24-AUY922 reduces Mf output from female worms.

<p>Graph shows the mean (± SD) Mf output from groups of six female <i>B. pahangi</i> worms exposed to 250 nM, 25 nM or 10 nM NVP-AUY922 for a period of 24 h only (time 0). Worms were washed free of drug and cultures continued in medium alone for a further 24 h or 48 h and Mf output quantified. P<0.05 for 250 nM and 25 nM compared to control at all time points; for 10 nM drug, P<0.05 for 48 h only. <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002699#s3" target="_blank">Results</a> shown are representative of two experiments.</p

Minimal effective doses of various compounds on Mf viability.

<p>Mf were cultured in 24-well plates in 2.0 ml medium containing drug at doubling dilutions from 4.0 µM to 0.976 nM. Plates were scored daily by microscopy and the percentage of worms alive estimated at each time point. <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002699#s3" target="_blank">Results</a> are representative of three separate experiments.</p

NVP-AUY922 significantly reduces Mf output from female worms at 10 nM.

<p>Graph shows mean (± SD) Mf output from groups of six female <i>B. pahangi</i> worms after 72 h exposure to NVP-AUY922 at 500, 100, 50, 25 10, 5 and 1 nM compared to DMSO control. Mf output is significantly different from control at all concentrations to 10 nM NVP-AUY922 (P≤0.0087). <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002699#s3" target="_blank">Results</a> shown are representative of three experiments. In this experiment, cultures were continued for a further 3 days and Mf counted again. At this time point (a total of 6 days exposure to drug), Mf output was significantly different from controls at 5 nM NVP-AUY922 (P = 0.0043) but not at 1 nM.</p