Interaction of the C14-OH group of adriamycin with DNA phosphate as spectroscopically evidenced

Remote loading of doxorubicin into liposomes driven by a transmembrane phosphate gradient

This study examines a new method for the remote loading of doxorubicin into liposomes. It was shown that doxorubicin can be loaded to a level of up to 98% into large unilamellar vesicles composed of egg phosphatidylcholine/cholesterol (7/3 mol/mol) with a transmembrane phosphate gradient. The different encapsulation efficiencies which were achieved with ammonium salts (citrate 100%, phosphate 98%, sulfate 95%, acetate 77%) were significantly higher as compared to the loading via sodium salts (citrate 54%, phosphate 52%, sulfate 44%, acetate 16%). Various factors, including pH-value, buffer capacity, solubility of doxorubicin in different salt solutions and base counter-flow, which likely has an influence on drug accumulation in the intraliposomal interior are taken into account. In contrast to other methods, the newly developed remote loading method exhibits a pH-dependent drug release property which may be effective in tumor tissues. At physiological pH-value doxorubicin is retained in the liposomes, whereas drug release is achieved by lowering the pH to 5.5 (approximately 25% release at 25 degrees C or 30% at 37 degrees C within two h). The DXR release of liposomes which were loaded via a sulfate gradient showed a maximum of 3% at pH 5.5.

NaDNA-bipyridyl-(ethylenediamine)platinum (II) complex: structure in oriented wet-spun films and fibers

Complexes of NaDNA with bipyridyl-(ethylenediamine)platinum(II) (abbreviated [(bipy)Pt(en)](2+)) in solid, oriented films, prepared with a wet-spinning method, have been studied using x-ray diffraction, elastic neutron scattering, two-dimensional magic-angle-spinning nuclear magnetic resonance (NMR), infrared (IR) linear dichroism, and IR absorption. All of these experiments indicate that the DNA in this complex is in the B conformation. The neutron diffraction experiments reveal that the rise per residue is 3.31 A, indicating that the [(bipy)Pt(en)](2+) molecular ion causes a small distortion of the B conformation. The neutron data in the direction perpendicular to the helical axis are consistent with a centered orthorhombic unit cell with a=22.65 A and b=32.2 A. The NMR and IR experiments show that the orientation of phosphate groups in the DNA small middle dot[(bipy)Pt(en)](2+) complex is the same as that observed for pure DNA in the B conformation. The IR experiments also show that the [(bipy)Pt(en)](2+) molecular ion stabilizes the B conformation of DNA down to 59% relative humidity, a low water activity. Mechanochemical experiments on wet-spun NaDNA fibers in 68% ethanol with and without [(bipy)Pt(en)](2+) reveal a 9% elongation of the DNA fibers as the complex is formed.

DNA-helix bending, stiffening and elongation on ligand binding; analysis for several DNA-drug systems, general viscometric DNA response and stereochemical implications

For several DNA-ligand systems the DNA helix bending, stiffening and elongation behaviour is treated quantitatively. The experimental basis are viscosity data from literature as a function of r, the ratio of drug molecules bound per DNA monomer unit. If the relative viscosity changes delta y1(r) and delta yh(r) for DNA of low and high molar mass, respectively, are known, the relative changes of contour length, delta L/L degrees, and of persistence length, delta a/a degrees, can be evaluated as a function of r, as repeatedly demonstrated. For random sequence-independent interactions, helix-bending is reflected by a helix-typical increment of delta a/a degrees (r), being zero at r = 0 and also at DNA saturation by bound ligand molecules [Reinert, Biophysical Chemistry 13, 1-14 (1981)]. This characteristic DNA behaviour often enables us to separate the bending and the stiffening increment of delta a/a degrees. The theoretical treatment of this problem (Schütz and Reinert, J. Biomolec. Struct. & Dynam. 9, 315-329, 1991) now permits a more detailed study of the ligand-induced DNA bending. The ligand-DNA systems treated here concern the following drugs (in parentheses DNA bending angle at low r-values): proflavin (8 degrees), daunomycin (11 degrees), aclacinomycin A (9.7 degrees, on cooperative interaction), actinomycin D (16 degrees), mitomycin C (16 degrees), a double intercalating bisphenantridine (12 degrees), 9-deacetyl-daunomycin (8 degrees) and 9-epi-deacetyl-daunomycin (12-18 degrees). We also demonstrate that the consideration of the DNA flexibility and its change on interaction of short DNA molecules with intercalating drugs delivers helix elongation values in better accord with the theoretical value. In the Appendix, a catalogue of simulated delta y(r)-dependences is given for both short and long DNA molecules. It systematically describes the DNA viscosity response upon typical DNA stiffening, elongation, and helix-bending effects.

Subsidiary hydrogen bonding of intercalated anthraquinonic anticancer drugs to DNA phosphate

Several anthraquinone derivatives are active against different kinds of human cancer. The cancerostatic activity has been mainly attributed to their ability to bind strongly to DNA by intercalation. Here, infrared spectroscopy was used to detect further, more specific DNA interactions with the prominent anticancer drugs daunomycin, adriamycin, aclacinomycin A and mitoxantrone as well as with the cytotoxic violamycin BI. The most striking result was a significant decrease in wave number of the band arising from antisymmetric stretching vibration of the PO2- groups of DNA upon complexation with adriamycin, aclacinomycin A, violamycin BI and mitoxantrone. This became evident after separation of the contributions from conformational changes of DNA to the influence on the wave number of that band. The drug-induced shift was interpreted in terms of the formation of a hydrogen bond between the intercalated drug molecules and the PO2- moiety of DNA via the following terminal hydroxyl groups: C14-OH for adriamycin, C4-OH for both aclacinomycin A and violamycin BI and, more tentatively, the external side-chain OH of mitoxantrone. Theoretical considerations, consisting of semi-empirical CNDO/2 calculations as well as normal coordinate analyses performed with molecular model fragments, provided results confirming and rationalising the experimental findings. The capacities of the anthracyclines for restriction of the conformational flexibility of DNA differ, presumably due to variations in the spatial dimensions of the sugar moieties of the drugs. The compatibility of the present results with data obtained from current geometrical models, especially those for the DNA-daunomycin and DNA-adriamycin complexes, is discussed in detail.