title: Structural requirements for optimized delivery, inhibition of oxidative stress, and antiapoptotic activity of targeted nitroxides.
abstract: Suppression of mitochondrial production of reactive oxygen species is a promising strategy against intrinsic apoptosis typical of degenerative diseases. Stable nitroxide radicals such as 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPOL) and its analogs combine several important features, including recycleability, electron acceptance from respiratory complexes, superoxide dismutase mimicry, and radical scavenging. Although successful in antioxidant protection, their effective concentrations are too high for successful in vivo applications. Recently (J Am Chem Soc 127:12460, 2005), we reported that 4-amino 2,2,6,6-tetramethyl-1-piperidinyloxy, covalently conjugated to a five-residue segment of gramicidin S (GS), was integrated into mitochondria and blocked actinomycin D (ActD)-induced superoxide generation and apoptosis. Using a model of ActD-induced apoptosis in mouse embryonic cells, we screened a library of nitroxides to explore structure-activity relationships between their antioxidant/antiapoptotic properties and chemical composition and three-dimensional (3D) structure. High hydrophobicity and effective mitochondrial integration are necessary but not sufficient for high antiapoptotic/antioxidant activity of a nitroxide conjugate. By designing conformationally preorganized peptidyl nitroxide conjugates and characterizing their 3D structure experimentally (circular dichroism and NMR) and theoretically (molecular dynamics), we established that the presence of the beta-turn/beta-sheet secondary structure is essential for the desired activity. Monte Carlo simulations in model lipid membranes confirmed that the conservation of the d-Phe-Pro reverse turn in hemi-GS analogs ensures the specific positioning of the nitroxide moiety at the mitochondrial membrane interface and maximizes their protective effects. These new insights into the structure-activity relationships of nitroxide-peptide and -peptide isostere conjugates are instrumental for development of new mechanism-based therapeutically effective agents.
authors.affiliation: Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15219, USA.
authors.forename: Jianfei
authors.initials: J
authors.lastname: Jiang
authors.forename: Igor
authors.initials: I
authors.lastname: Kurnikov
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Belikova
authors.forename: Jingbo
authors.initials: J
authors.lastname: Xiao
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhao
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Amoscato
authors.forename: Rebecca
authors.initials: R
authors.lastname: Braslau
authors.forename: Armido
authors.initials: A
authors.lastname: Studer
authors.forename: Mitchell P
authors.initials: MP
authors.lastname: Fink
authors.forename: Joel S
authors.initials: JS
authors.lastname: Greenberger
authors.forename: Peter
authors.initials: P
authors.lastname: Wipf
authors.forename: Valerian E
authors.initials: VE
authors.lastname: Kagan
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D002942:Circular Dichroism; D003497:Cyclic N-Oxides / Q000737:chemistry / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D006096:Gramicidin / Q000031:analogs & derivatives / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D008958:Models, Molecular; D018384:Oxidative Stress / Q000187:drug effects*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship
chemical_list: D000975:Antioxidants; D003497:Cyclic N-Oxides; D006096:Gramicidin; C015527:4-amino-TEMPO; D003609:Dactinomycin