Characterization of two early lead anti-amoebic agents with activity against Naegleria fowleri.

Brain infection by the pathogenic free-living amoebae Naegleria fowleri is a life-threatening illness, with a mortality rate >95% in the US. One of the challenges faced in treating these infections is the lack of efficacious drugs. Here, we further characterize two leads. The first, a N. fowleri enolase inhibitor (HEX ((1-hydroxy-2-oxopiperidin-3-yl) phosphonic acid)), emerged from a target-based approach while the other, BDGR-20191 (rac-(4aR,13bS)-10,11-dichloro-4-(oxetan-3-ylmethyl)-1,2,3,4,4a,5,6,13b-octahydro-8H-[1,6]naphthyridino[5,6-b]quinazolin-8-one), was identified in a phenotypic screen for anti-amoebic agents. Chronic low dose exposure to these agents led to cell lines that were tolerant to each. However, the tolerance phenotypes were reversed in the absence of selection with the agent. Differential gene expression analyses suggest that HEX tolerant cells upregulate cellular components that could impact levels of accumulated glycolytic intermediates, while BDGR-20191 tolerant cells could be targeting membrane biosynthesis. Unbiased metabolomics of the lines supported these possibilities. While HEX and BDGR-20191 are not synergistic with one another or with other standard-of-care drugs, their additive nature suggests they could be a useful addition to current therapeutic cocktails.