Activity of Auranofin against Multiple Genotypes of Naegleria fowleri and Its Synergistic Effect with Amphotericin B In Vitro

Abstract

Primary amebic meningoencephalitis, caused by brain infection with a free-living ameba, Naegleria fowleri, leads to extensive inflammation of the brain and death within 3–7 days after symptoms begin. Treatment of primary amebic meningoencephalitis relies on amphotericin B in combination with other drugs, but use of amphotericin B is associated with severe adverse effects. Despite a fatality rate of over 97%, economic incentive to invest in development of antiamebic drugs by the pharmaceutical industry is lacking. Development of safe and rapidly acting drugs remains a critical unmet need to avert future deaths. Since FDA-approved anti-inflammatory and antiarthritic drug auranofin is a known inhibitor of selenoprotein synthesis and thioredoxin reductase and the genome of N. fowleri encodes genes for both selenocysteine biosynthesis and thioredoxin reductases, we tested the effect of auranofin against N. fowleri strains of different genotypes from the USA, Europe, and Australia. Auranofin was equipotent against all tested strains with an EC50 of 1–2 μM. Our growth inhibition study at different time points demonstrated that auranofin is fast-acting, and ∼90% growth inhibition was achieved within 16 h of drug exposure. A short exposure of N. fowleri to auranofin led to the accumulation of intracellular reactive oxygen species. This is consistent with auranofin’s role in inhibiting antioxidant pathways. Further, combination of auranofin and amphotericin B led to 95% of growth inhibition with 2–9-fold dose reduction for amphotericin B and 3–20-fold dose reduction for auranofin. Auranofin has the potential to be repurposed for the treatment of primary amebic meningoencephalitis.

Primary Amoebic Meningoencephalitis by Naegleria fowleri: Pathogenesis and Treatments

“…PAM is characterized by a mortality rate of 98% and, to date, no more than a dozen people have survived the infection [ 20 , 21 ]. This high mortality has been attributed to delays in diagnosis, a lack of safe and effective treatments, and the difficulty of delivering drugs to the brain [ 22 ]. Despite the fact that PAM presents a low morbidity rate, it has been postulated that climate change and increased temperatures could result in a higher frequency of N. fowleri infections [ 10 , 17 ].…”

“…The concentration of 12.5 µM of AF inhibited the growth of the trophozoites by 97% after 24 h, and the drug showed no cytotoxicity to human astrocytes at concentrations lower than 5 µM. AF is a potential new drug to treat PAM due to its anti-inflammatory properties, its capacity to penetrate the BBB, and synergistic activity with AmB [ 22 ].…”

Differential growth rates and in vitro drug susceptibility to currently used drugs for multiple isolates of Naegleria fowleri

“…There are numerous studies that report the susceptibility of 1 to 3 clinical isolates of N. fowleri to a variety of drugs (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28) and only 4 studies that use 5 or more different isolates (29)(30)(31)(32). As such, we selected amphotericin B, fluconazole, ketoconazole, miconazole, posaconazole, azithromycin, rifampin, and miltefosine to assess their efficacy and determine the consistency in the response among N. fowleri clinical isolates of various genotypes, geographical locales, and temporal origins.…”

Joining forces: Leveraging novel combination therapies to combat infections with eukaryotic pathogens

“…Several repurposed drugs may increase the delivery of conventional drugs to target tissues. Auranofin, an anti-arthritic drug, synergized with conventional amphotericin B to inhibit growth of Naegleria fowleri [ 53 ]. Auranofin impairs the N .…”

“…It also may improve drug delivery of amphotericin B across the blood–brain barrier, which might be advantageous for treating neuroinvasive N . fowleri infections [ 53 ]. Conventional treatment of T .…”