Transverse location of anthracyclines in lipid bilayers. Paramagnetic quenching studies.
Quenching of anthracycline fluorescence by a series of spin-labeled fatty acids was used to probe the transverse location of the drug in phosphatidylcholine bilayers in the form of small unilamellar vesicles. Stern-Volmer plots of the quenching data indicate that the fluorophore moiety of the anthracycline is intercalated into the hydrocarbon region of the bilayer, with deeper penetration observed in fluid-phase than in solid-phase vesicles. 31P-NMR parameters (T1 and nuclear Overhauser enhancement (NOE] are unaffected by the presence of drug, consistent with a binding site removed from the interfacial region. Comparison of intensity (F0/F) plots with lifetime (tau 0/tau) data shows that the predominant mechanism of anthracycline quenching by membrane-bound nitroxides is static. Since the membrane-bound drug is also accessible to quenching by I-, the binding site in the membrane must create a channel which is accessible to solvent. Two other fluorescent probes, 12-(9-anthroyloxy)stearate (12-AS) and diphenylhexatriene (DPH), were employed to confirm the results obtained with the anthracyclines, giving quenching data representative of their location in the bilayer.
Constantinides
P P
PP
Lipogen, Inc., Knoxville, TN 37932.
Wang
Y Y
YY
Burke
T G
TG
Tritton
T R
TR
D000903:Antibiotics, Antineoplastic / Q000032:analysis*; D002360:Carubicin / Q000032:analysis; D004317:Doxorubicin / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy; D005453:Fluorescence; D005456:Fluorescent Dyes; D008051:Lipid Bilayers / Q000032:analysis*; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy; D010759:Phosphorus Isotopes; D013113:Spin Labels
D000903:Antibiotics, Antineoplastic; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D010759:Phosphorus Isotopes; D013113:Spin Labels; D004317:Doxorubicin; D002360:Carubicin