Treatment Of Primary Amebic Meningoencephalitis Research Articles

Brain-eating amoeba: Recognition and treatment of primary amebic meningoencephalitis.

Brain-eating amoeba: Recognition and treatment of primary amebic meningoencephalitis.

Drug discovery for primary amebic meningoencephalitis: from screen to identification of leads

ABSTRACT Introduction: Naegleria fowleri is responsible for primary amebic meningoencephalitis (PAM) which has a fatality rate of >97%. Because of the rarity of the disease, pharmaceutical companies do not pursue new drug discovery for PAM. Yet, it is possible that the infection is underreported and finding a better drug would have an impact on people suffering from this deadly infection. Areas covered: This paper reports the efforts undertaken by different academic groups over the last 20 years to test different compounds against N. fowleri. The drug discovery research encompassed synthesis of new compounds, development and use of high-throughput screening methods and attempts to repurpose clinically developed or FDA-approved compounds for the treatment of PAM. Expert opinion: In absence of economic investment to develop new drugs for PAM, repurposing the FDA-approved drugs has been the best strategy so far to identify new leads against N. fowleri. Increasing use of high-throughput phenotypic screening has the potential to accelerate the identification of new leads, either in monotherapy or in combination treatment. Since phase II clinical trial is not possible for PAM, it is critical to demonstrate in vivo efficacy of a clinically safe compound to translate the discovery from lab to the clinic.

HMG-CoA Reductase Inhibitors as Drug Leads against Naegleria fowleri

Primary amebic meningoencephalitis (PAM), caused by the free-living ameba Naegleria fowleri, has a fatality rate of over 97%. Treatment of PAM relies on amphotericin B in combination with other drugs, but few patients have survived with the existing drug treatment regimens. Therefore, development of effective drugs is a critical unmet need to avert deaths from PAM. Since ergosterol is one of the major sterols in the membrane of N. fowleri, disruption of isoprenoid and sterol biosynthesis by small-molecule inhibitors may be an effective intervention strategy against N. fowleri. The genome of N. fowleri contains a gene encoding HMG-CoA reductase (HMGR); the catalytic domains of human and N. fowleri HMGR share <60% sequence identity with only two amino acid substitutions in the active site of the enzyme. Considering the similarity of human and N. fowleri HMGR, we tested well-tolerated and widely used HMGR inhibitors, known as cholesterol-lowering statins, against N. fowleri. We identified blood-brain-barrier-permeable pitavastatin as a potent amebicidal agent against the U.S., Australian, and European strains of N. fowleri. Pitavastatin was equipotent to amphotericin B against the European strain of N. fowleri; it killed about 80% of trophozoites within 16 h of drug exposure. Pretreatment of trophozoites with mevalonate, the product of HMGR, rescued N. fowleri from inhibitory effects of statins, demonstrating that HMGR of N. fowleri is the target of statins. Because of the good safety profile and availability for both adult and pediatric uses, consideration should be given to repurposing the fast-acting pitavastatin for the treatment of PAM.

In Vitro Evaluation of Farnesyltransferase Inhibitor and its Effect in Combination with 3-Hydroxy-3-Methyl-Glutaryl-CoA Reductase Inhibitor against Naegleria fowleri

Free-living amoeba Naegleria fowleri causes a rapidly fatal infection primary amebic meningoencephalitis (PAM) in children. The drug of choice in treating PAM is amphotericin B, but very few patients treated with amphotericin B have survived PAM. Therefore, development of efficient drugs is a critical unmet need. We identified that the FDA-approved pitavastatin, an inhibitor of HMG Co-A reductase involved in the mevalonate pathway, was equipotent to amphotericin B against N. fowleri trophozoites. The genome of N. fowleri contains a gene encoding protein farnesyltransferase (FT), the last common enzyme for products derived from the mevalonate pathway. Here, we show that a clinically advanced FT inhibitor lonafarnib is active against different strains of N. fowleri with EC50 ranging from 1.5 to 9.2 µM. A combination of lonafarnib and pitavastatin at different ratios led to 95% growth inhibition of trophozoites and the combination achieved a dose reduction of about 2- to 28-fold for lonafarnib and 5- to 30-fold for pitavastatin. No trophozoite with normal morphology was found when trophozoites were treated for 48 h with a combination of 1.7 µM each of lonafarnib and pitavastatin. Combination of lonafarnib and pitavastatin may contribute to the development of a new drug regimen for the treatment of PAM.

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

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.

Synergistic Activities of Azithromycin and Amphotericin B against Naegleria fowleri In Vitro and in a Mouse Model of Primary Amebic Meningoencephalitis

Naegleria fowleri is responsible for producing a rapidly fatal central nervous system infection known as primary amebic meningoencephalitis (PAM). To date, amphotericin B, an antifungal agent, is the only agent with established clinical efficacy in the treatment of PAM. However, amphotericin B is not always successful in treating PAM and is associated with severe adverse effects. We previously found azithromycin to be more effective than amphotericin B in a mouse model of PAM. We therefore investigated the combination of amphotericin B and azithromycin in vitro and in a mouse model of PAM. For the in vitro studies, 50% inhibitory concentrations were calculated for each drug alone and for the drugs in fixed combination ratios of 1:1, 3:1, and 1:3. We found amphotericin B and azithromycin to be synergistic at all three of the fixed combination ratios. In our mouse model of PAM, a combination of amphotericin B (2.5 mg/kg of body weight) and azithromycin (25 mg/kg) protected 100% of the mice, whereas amphotericin B alone (2.5 mg/kg) protected only 27% of mice and azithromycin alone (25 mg/kg) protected 40% of mice. This study indicates that amphotericin B and azithromycin are synergistic against the Lee strain of N. fowleri, suggesting that the combined use of these agents may be beneficial in treating PAM.

Activities of therapeutic agents against Naegleria fowleri in vitro and in a mouse model of primary amebic meningoencephalitis.

Inhalation of water contaminated with Naegleria fowleri may lead to a potentially fatal infection of the central nervous system known as primary amebic meningoencephalitis (PAM). Amphotericin B (AMB), an antifungal drug, is the only agent with established clinical efficacy in the treatment of PAM, though therapy with this drug is not always effective and has been associated with adverse effects on the kidneys and other organs. We investigated the activity of various therapeutic agents against N. fowleri in an attempt to identify other useful agents for treating PAM. Several of these agents exhibited in vitro activity against the Lee (M67) strain of N. fowleri. The minimum inhibitory concentrations of these agents were 0.1 microg/ml (ketoconazole), 1 microg/ml (liposomal AMB), and 10 microg/ml (minocycline, quinupristin-dalfopristin, and trifluoperazine). Other agents had a minimum inhibitory concentration > 10 microg/ml (linezolid) or > 100 microg/ml (rifampin). In a mouse model of PAM, none of the untreated control mice survived, whereas the survival of treated animals was 50% (quinupristin-dalfopristin), 30% (ketoconazole and liposomal AMB), 20% (trifluoperazine), and 10% (linezolid and minocycline). Further studies are needed to ascertain whether these agents have synergistic activity with AMB in vitro and in vivo.

Activities of azithromycin and amphotericin B against Naegleria fowleri in vitro and in a mouse model of primary amebic meningoencephalitis.

Inhalation of fresh water containing the free-living ameba Naegleria fowleri may lead to a potentially fatal infection known as primary amebic meningoencephalitis. Amphotericin B is the only agent with established clinical efficacy in the treatment of primary amebic meningoencephalitis in humans, but therapy with this drug is often associated with adverse effects on the kidneys and other organs, and not all persons treated with amphotericin B have survived. We investigated the in vitro activity and in vivo efficacy of newer therapeutic agents in an attempt to identify other useful agents for treating primary amebic meningoencephalitis. Azithromycin has shown in vitro activity against Acanthamoeba spp. and in vivo activity against experimental toxoplasmosis. In our study, the MIC of azithromycin against N. fowleri was 13.4 micro M (10 micro g/ml), which was 123 times greater than the MIC of amphotericin B, which was 0.108 micro M (0.1 micro g/ml). Azithromycin protected 100% of mice infected with N. fowleri at a dose of 75 mg/kg/day for 5 days, whereas amphotericin B protected only 50% of mice at a dose of 7.5 mg/kg/day for 5 days, and all control mice died during the 28-day observation period. We conclude that azithromycin has both in vitro and in vivo activity versus N. fowleri and may be a useful addition to therapy for primary amebic meningoencephalitis.

Primary amebic meningoencephalitis: A review of the clinical literature

Primary amebic meningoencephalitis (PAM) is a rapidly progressive and potentially fatal infection frequently contracted by swimming in bodies of warm fresh water. The etiological agent in most reported cases of PAM is the ameboflagellate Naegleria fowleri. Infection with this organism closely mimics and is often mistaken for a bacterial or a viral pyogenic meningitis. Recovery is rare and depends on rapid diagnosis and treatment. Physicians treating individuals who present with an acute pyogenic meningitis should consider the diagnosis of PAM, particularly if the patient has a recent history of swimming in warm fresh water. We review the recent literature for cases of PAM and the discuss ecology of N. fowleri and the clinical presentation, diagnosis, and treatment of PAM.

Amebic Encephalitis Unlikely

To the Editor. — A successful treatment of primary amebic meningoencephalitis (PAM) was described by Brown 1 in the June 1991 issue of theARCHIVES. Brown stated that a previously healthy 32-year-old summer-camp swimming instructor was admitted to the hospital with severe headache, fever (37.9°C), and meningeal signs that rapidly progressed to coma. The computed tomographic scan of the head was normal, and a lumbar puncture yielded cloudy cerebrospinal fluid (CSF) with 5356 × 10 6 /L white blood cells (0.98 neutrophils), a glucose level of 5.55 mmol/L, and a protein level of 6.10 g/L. Gram's staining of the CSF was negative for bacteria, and three motile amebas were seen on wet mount by a pathologist experienced with freeliving amebas. The patient also had been waterskiing in a small, relatively stagnant, freshwater lake several days prior to the onset of symptoms. The patient was treated with amphotericin B and rifampin,

Successful treatment of primary amebic meningoencephalitis

Successful treatment of primary amebic meningoencephalitis

Successful Treatment of Primary Amebic Meningoencephalitis

The fourth documented survivor of primary amebic meningoencephalitis, a young man with a history of waterskiing in a stagnant freshwater lake in northeastern Pennsylvania, is presented. Early consideration of this unusual diagnosis, based on historical factors (recent contact with warm fresh water), coupled with prompt aggressive therapy with high-dose amphotericin B is emphasized in achieving a successful outcome.