title: SB-224289 Antagonizes the Antifungal Mechanism of the Marine Depsipeptide Papuamide A.
abstract: 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.
authors.affiliation: Department of Microbiology, University of Tennessee, Knoxville, Tennessee, United States of America.
authors.forename: Chelsi D
authors.initials: CD
authors.lastname: Cassilly
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee, 38105, United States of America.
authors.forename: Marcus M
authors.initials: MM
authors.lastname: Maddox
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee, 38105, United States of America.
authors.forename: Philip T
authors.initials: PT
authors.lastname: Cherian
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee, 38105, United States of America.
authors.forename: John J
authors.initials: JJ
authors.lastname: Bowling
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, College of Pharmacy, Medical University of South Carolina, Medical University of South Carolina, Charleston, South Carolina, United States of America.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Hamann
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee, 38105, United States of America.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Lee
authors.affiliation: Department of Microbiology, University of Tennessee, Knoxville, Tennessee, United States of America.
authors.forename: Todd B
authors.initials: TB
authors.lastname: Reynolds
mesh_terms: D000935:Antifungal Agents / Q000737:chemistry / Q000494:pharmacology*; D010717:CDPdiacylglycerol-Serine O-Phosphatidyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D002176:Candida albicans / Q000187:drug effects; D047630:Depsipeptides / Q000737:chemistry / Q000494:pharmacology*; D004336:Drug Antagonism; D055808:Drug Discovery; D025141:Drug Resistance, Fungal; D057166:High-Throughput Screening Assays; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D010881:Piperidones / Q000737:chemistry / Q000494:pharmacology*; D013141:Spiro Compounds / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000935:Antifungal Agents; D047630:Depsipeptides; D010881:Piperidones; C108518:SB 22489G; D013141:Spiro Compounds; C474170:papuamide A; C516618:theopapuamide; D010717:CDPdiacylglycerol-Serine O-Phosphatidyltransferase