SB-224289 Antagonizes the Antifungal Mechanism of the Marine Depsipeptide Papuamide A

• Published in: PloS one 2016-05, Vol.11 (5), p.e0154932-e0154932
• Main Authors: Cassilly, Chelsi D, Maddox, Marcus M, Cherian, Philip T, Bowling, John J, Hamann, Mark T, Lee, Richard E, Reynolds, Todd B
• Format: Article
• Language: English
• Subjects: Antagonists (Biochemistry); Antifungal agents; Antifungal Agents - chemistry; Antifungal Agents - pharmacology; Bacillus cereus; Biology; Biology and Life Sciences; Candida; Candida albicans; Candida albicans - drug effects; CDPdiacylglycerol-Serine O-Phosphatidyltransferase - antagonists & inhibitors; CDPdiacylglycerol-Serine O-Phosphatidyltransferase - metabolism; Cell death; Chemical properties; CHO1 gene; Clonal deletion; Cytotoxicity; Depsipeptides - chemistry; Depsipeptides - pharmacology; Drug Antagonism; Drug Discovery; Drug resistance; Drug Resistance, Fungal; Drug screening; Environmental effects; Fungicides; Gene deletion; High-Throughput Screening Assays; Libraries; Medical screening; Medicine and Health Sciences; Microbial Sensitivity Tests; Molecular Structure; Nosocomial infections; Phenotypes; Phosphatidylserine; Physical Sciences; Piperidones - chemistry; Piperidones - pharmacology; Research and Analysis Methods; Serotonin S1 receptors; Spiro Compounds - chemistry; Spiro Compounds - pharmacology; Theonella; Theonella swinhoei; Toxins
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0154932

In order to expand the repertoire of antifungal compounds a novel, high-throughput phenotypic drug screen targeting fungal phosphatidylserine (PS) synthase (Cho1p) was developed based on antagonism of the toxin papuamide A (Pap-A). Pap-A is a cyclic depsipeptide that binds to PS in the membrane of wild-type Candida albicans, and permeabilizes its plasma membrane, ultimately causing cell death. Organisms with a homozygous deletion of the CHO1 gene (cho1ΔΔ) do not produce PS and are able to survive in the presence of Pap-A. Using this phenotype (i.e. resistance to Pap-A) as an indicator of Cho1p inhibition, we screened over 5,600 small molecules for Pap-A resistance and identified SB-224289 as a positive hit. SB-224289, previously reported as a selective human 5-HT1B receptor antagonist, also confers resistance to the similar toxin theopapuamide (TPap-A), but not to other cytotoxic depsipeptides tested. Structurally similar molecules and truncated variants of SB-224289 do not confer resistance to Pap-A, suggesting that the toxin-blocking ability of SB-224289 is very specific. Further biochemical characterization revealed that SB-224289 does not inhibit Cho1p, indicating that Pap-A resistance is conferred by another undetermined mechanism. Although the mode of resistance is unclear, interaction between SB-224289 and Pap-A or TPap-A suggests this screening assay could be adapted for discovering other compounds which could antagonize the effects of other environmentally- or medically-relevant depsipeptide toxins.