title: Plasma Protein Binding Structure-Activity Relationships Related to the N-Terminus of Daptomycin.
abstract: Daptomycin is a lipopeptide antibiotic that is highly bound to plasma proteins. To date, the plasma components and structure-activity relationships responsible for the plasma protein binding profile of daptomycin remain uncharacterized. In the present study we have employed a surface plasmon resonance assay together with molecular docking techniques to investigate the plasma protein binding structure-activity relationships related to the N-terminal fatty acyl of daptomycin. Three compounds were investigated: (1) native daptomycin, which displays an N-terminal n-decanoyl fatty acid side chain, and two analogues with modifications to the N-terminal fatty acyl chain; (2) des-acyl daptomycin; and (3) acetyl-daptomycin. The surface plasmon resonance (SPR) data showed that the binding profile of native daptomycin was in the rank order human serum albumin (HSA) ≫ α-1-antitrypsin > low-density lipoprotein ≥ hemoglobin > sex hormone binding globulin > α-1-acid-glycoprotein (AGP) > hemopexin > fibrinogen > α-2-macroglobulin > β2-microglobulin > high-density lipoprotein > fibronectin > haptoglobulin > transferrin > immunoglobulin G. Notably, binding to fatty acid free HSA was greater than binding to nondelipidated HSA. SPR and ultrafiltration studies also indicated that physiological concentrations of calcium increase binding of daptomycin and acetyl-daptomycin to HSA and AGP. A molecular model of the daptomycin-human serum albumin A complex is presented that illustrates the pivotal role of the N-terminal fatty acyl chain of daptomycin for binding to drug site 1 of HSA. In proof-of-concept, the capacity of physiological cocktails of the identified plasma proteins to inhibit the antibacterial activity of daptomycin was assessed with in vitro microbiological assays. We show that HSA, α-1-antitrypsin, low-density lipoprotein, sex hormone binding globulin, α-1-acid-glycoprotein, and hemopexin are responsible for the majority of the sequestering activity in human plasma. The findings are relevant to medicinal chemistry programs focused on the development of next-generation daptomycin lipopeptides. Tailored modifications to the N-terminal fatty acyl domain of the daptomycin molecule should yield novel daptomycin lipopeptides with more ideal plasma protein binding profiles to increase the levels of active (free) drug in plasma and improved in vivo activity.
authors.affiliation: Drug Development and Innovation, Drug Delivery, Disposition and Dynamics. Monash Institute of Pharmaceutical Sciences, Monash University , 381 Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: Elena K
authors.initials: EK
authors.lastname: Schneider
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland 306 Carmody Road St. Lucia QLD 4072, Australia.
authors.forename: Johnny X
authors.initials: JX
authors.lastname: Huang
authors.affiliation: Animal Nutrition and Health, Grasslands Research Centre, Ag Research Limited , Tennent Drive, Private Bag 11008, Palmerston North 4442, New Zealand.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Carbone
authors.affiliation: Drug Development and Innovation, Drug Delivery, Disposition and Dynamics. Monash Institute of Pharmaceutical Sciences, Monash University , 381 Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: Meiling
authors.initials: M
authors.lastname: Han
authors.affiliation: Monash Biomedicine Discovery Institute, Department of Microbiology, Monash University , Clayton, VIC 3800, Australia.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Monash Biomedicine Discovery Institute, Department of Microbiology, Monash University , Clayton, VIC 3800, Australia.
authors.forename: Sue
authors.initials: S
authors.lastname: Nang
authors.affiliation: School of Medicine, Deakin University , Geelong, VIC 3216, Australia.
authors.forename: Keith K
authors.initials: KK
authors.lastname: Khoo
authors.affiliation: School of Medicine, Deakin University , Geelong, VIC 3216, Australia.
authors.forename: Johnson
authors.initials: J
authors.lastname: Mak
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland 306 Carmody Road St. Lucia QLD 4072, Australia.
authors.forename: Matthew A
authors.identifier: 0000-0003-3147-3460
authors.initials: MA
authors.lastname: Cooper
authors.affiliation: Monash Biomedicine Discovery Institute, Department of Microbiology, Monash University , Clayton, VIC 3800, Australia.
authors.forename: Jian
authors.initials: J
authors.lastname: Li
authors.affiliation: Drug Development and Innovation, Drug Delivery, Disposition and Dynamics. Monash Institute of Pharmaceutical Sciences, Monash University , 381 Royal Parade, Parkville, Victoria 3052, Australia.
authors.forename: Tony
authors.identifier: 0000-0002-0017-7952
authors.initials: T
authors.lastname: Velkov
mesh_terms: D001665:Binding Sites; D001798:Blood Proteins / Q000737:chemistry* / Q000378:metabolism*; D017576:Daptomycin / Q000737:chemistry* / Q000494:pharmacology*; D006801:Humans; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D011485:Protein Binding; D000075462:Serum Albumin, Human / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship; D020349:Surface Plasmon Resonance; D000515:alpha 1-Antitrypsin / Q000737:chemistry / Q000378:metabolism
chemical_list: D001798:Blood Proteins; C043392:SERPINA1 protein, human; D000515:alpha 1-Antitrypsin; D017576:Daptomycin; D000075462:Serum Albumin, Human
keywords: N-terminus; daptomycin; plasma protein binding