Novel cell-based in vitro screen to identify small-molecule inhibitors against intracellular replication of Cryptococcus neoformans in macrophages

Samantaray, Sweta; Correia, Joao; Garelnabi, Mariam; Voelz, Kerstin; May, Robin C.; Hall, Rebecca

doi:10.1016/j.ijantimicag.2016.04.018

Cited by 22 publications

(21 citation statements)

References 37 publications

(51 reference statements)

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“…These fungi would not need the CD44 interaction to efficiently cross the BBB, consistent with the in vivo observations and supporting the idea of a role for Trojan horse crossing in vivo . These findings highlight the need to consider internalized fungi in assessments of antifungal agents and the potential value of identifying compounds that inhibit intracellular replication of cryptococci, as in a recent screen ( 59 ).…”

Section: Discussionmentioning

confidence: 95%

Trojan Horse Transit Contributes to Blood-Brain Barrier Crossing of a Eukaryotic Pathogen

Santiago-Tirado

Onken

Cooper

et al. 2017

mBio

192

196

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The blood-brain barrier (BBB) protects the central nervous system (CNS) by restricting the passage of molecules and microorganisms. Despite this barrier, however, the fungal pathogen Cryptococcus neoformans invades the brain, causing a meningoencephalitis that is estimated to kill over 600,000 people annually. Cryptococcal infection begins in the lung, and experimental evidence suggests that host phagocytes play a role in subsequent dissemination, although this role remains ill defined. Additionally, the disparate experimental approaches that have been used to probe various potential routes of BBB transit make it impossible to assess their relative contributions, confounding any integrated understanding of cryptococcal brain entry. Here we used an in vitro model BBB to show that a “Trojan horse” mechanism contributes significantly to fungal barrier crossing and that host factors regulate this process independently of free fungal transit. We also, for the first time, directly imaged C. neoformans-containing phagocytes crossing the BBB, showing that they do so via transendothelial pores. Finally, we found that Trojan horse crossing enables CNS entry of fungal mutants that cannot otherwise traverse the BBB, and we demonstrate additional intercellular interactions that may contribute to brain entry. Our work elucidates the mechanism of cryptococcal brain invasion and offers approaches to study other neuropathogens.

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Section: Discussionmentioning

confidence: 95%

Trojan Horse Transit Contributes to Blood-Brain Barrier Crossing of a Eukaryotic Pathogen

Santiago-Tirado

Onken

Cooper

et al. 2017

mBio

192

196

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“…Despite the major health problems caused by cryptococcal infections, there is a lack of new antifungal drugs. Promising, albeit limited, research has demonstrated the potential for repurposing drugs and the implications of this approach for treating cryptococcal infections have been highlighted ( Butts et al, 2013 ; Dehdashti et al, 2013 ; Joffe et al, 2017 ; Rabjohns et al, 2013 ; Rhein et al, 2016 ; Samantaray et al, 2016 ; Spitzer et al, 2011 ). Most studies have screened the Prestwick Chemical Library ( n = 1,120), the Library of Pharmaceutically Active Compounds ( n = 1,280) and the National Institutes of Health clinical collection ( n = 727).…”

Section: Discussionmentioning

confidence: 99%

“…Most studies have screened the Prestwick Chemical Library ( n = 1,120), the Library of Pharmaceutically Active Compounds ( n = 1,280) and the National Institutes of Health clinical collection ( n = 727). Within the last decade, these drug screening studies have led to the discovery of multiple non-antifungal compounds with antifungal activities, which were often novel and fungicidal ( Butts et al, 2013 ; Dehdashti et al, 2013 ; Joffe et al, 2017 ; Rabjohns et al, 2013 ; Samantaray et al, 2016 ; Spitzer et al, 2011 ). Some have demonstrated the ability to target intracellular C. neoformans in macrophages and cryptococcal biofilms and to act synergistically with the widely-used drug fluconazole ( Butts et al, 2013 ; Dehdashti et al, 2013 ; Joffe et al, 2017 ; Rabjohns et al, 2013 ; Samantaray et al, 2016 ; Spitzer et al, 2011 ).…”

Section: Discussionmentioning

confidence: 99%

“…Interestingly, CCBs alone or in combination with fluconazole do not significantly alter the gene expression level of CCH1 and MID1 ( Liu et al, 2016 ) suggesting that either the cell is not sensing a disruption to calcium homeostasis, or CCBs act on targets other than calcium channels. Recently, a screen of the Prestwick Chemical Library® of FDA-approved small molecules identified fendiline hydrochloride, a non-dihydropyridine CCB, as having unique activity to potentiate phagosomal killing of intracellular C. neoformans in host macrophages ( Samantaray et al, 2016 ). Although it has a very different structure to the antifungal CCBs identified here, fendiline is an L-type CCB, suggesting this class of CCBs may be the most promising for antifungal drug development.…”

Section: Discussionmentioning

confidence: 99%

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Repurposing drugs to fast-track therapeutic agents for the treatment of cryptococcosis

Truong

Monahan

Carter

et al. 2018

PeerJ

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Many infectious diseases disproportionately affect people in the developing world. Cryptococcal meningitis is one of the most common mycoses in HIV-AIDS patients, with the highest burden of disease in sub-Saharan Africa. Current best treatment regimens still result in unacceptably high mortality rates, and more effective antifungal agents are needed urgently. Drug development is hampered by the difficulty of developing effective antifungal agents that are not also toxic to human cells, and by a reluctance among pharmaceutical companies to invest in drugs that cannot guarantee a high financial return. Drug repurposing, where existing drugs are screened for alternative activities, is becoming an attractive approach in antimicrobial discovery programs, and various compound libraries are now commercially available. As these drugs have already undergone extensive optimisation and passed regulatory hurdles this can fast-track their progress to market for new uses. This study screened the Screen-Well Enzo library of 640 compounds for candidates that phenotypically inhibited the growth of Cryptococcus deuterogattii. The anthelminthic agent flubendazole, and L-type calcium channel blockers nifedipine, nisoldipine and felodipine, appeared particularly promising and were tested in additional strains and species. Flubendazole was very active against all pathogenic Cryptococcus species, with minimum inhibitory concentrations of 0.039–0.156 μg/mL, and was equally effective against isolates that were resistant to fluconazole. While nifedipine, nisoldipine and felodipine all inhibited Cryptococcus, nisoldipine was also effective against Candida, Saccharomyces and Aspergillus. This study validates repurposing as a rapid approach for finding new agents to treat neglected infectious diseases.

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“…It is being tested as an adjunct antifungal in a phase III clinical trial (NCT01802385; https://clinicaltrials.gov/). Recent preclinical studies have also identified several additional compounds or molecular scaffolds with anticryptococcal activities (8)(9)(10)(11)(12). There are several antifungal small molecules in preclinical development, but only two of these show efficacies against C. neoformans (13).…”

mentioning

confidence: 99%

Troponoids Can Inhibit Growth of the Human Fungal Pathogen Cryptococcus neoformans

Donlin

Zunica

Lipnicky

et al. 2017

Antimicrob Agents Chemother

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Cryptococcus neoformans is a pathogen that is common in immunosuppressed patients. It can be treated with amphotericin B and fluconazole, but the mortality rate remains 15 to 30%. Thus, novel and more effective anticryptococcal therapies are needed. The troponoids are based on natural products isolated from western red cedar, and have a broad range of antimicrobial activities. Extracts of western red cedar inhibit the growth of several fungal species, but neither western red cedar extracts nor troponoid derivatives have been tested against C. neoformans. We screened 56 troponoids for their ability to inhibit C. neoformans growth and to assess whether they may be attractive candidates for development into anticryptococcal drugs. We determined MICs at which the compounds inhibited 80% of cryptococcal growth relative to vehicle-treated controls and identified 12 compounds with MICs ranging from 0.2 to 15 M. We screened compounds with MICs of Յ20 M for cytotoxicity in liver hepatoma cells. Fifty percent cytotoxicity values (CC 50 s) ranged from 4 to Ͼ100 M. The therapeutic indexes (TI, CC 50 /MIC) for most of the troponoids were fairly low, with most being Ͻ8. However, two compounds had TI values that were Ͼ8, including a tropone with a TI of Ͼ300. These tropones are fungicidal and are not antagonistic when used in combination with fluconazole or amphotericin B. Inhibition by these two tropones remains unchanged under conditions favoring cryptococcal capsule formation. These data support the hypothesis that troponoids may be a productive scaffold for the development of novel anticryptococcal therapies.

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Novel cell-based in vitro screen to identify small-molecule inhibitors against intracellular replication of Cryptococcus neoformans in macrophages

Cited by 22 publications

References 37 publications

Trojan Horse Transit Contributes to Blood-Brain Barrier Crossing of a Eukaryotic Pathogen

Trojan Horse Transit Contributes to Blood-Brain Barrier Crossing of a Eukaryotic Pathogen

Repurposing drugs to fast-track therapeutic agents for the treatment of cryptococcosis

Troponoids Can Inhibit Growth of the Human Fungal Pathogen Cryptococcus neoformans

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