Interaction of phenosafranine with nucleic acids and model polyphosphates. II. Characterisation of phenosafranine binding to DNA

The in vitro interaction with DNA of several hypoxic radiosensitizers

The five 5-nitroimidazole derivatives and the four glyoxylic compounds tested in this paper for their interaction with DNA with and without irradiation had previously been reported to act as radiosensitizers at a cellular level. Our aim was to find if the radiosensitizing activity of these products could be due to their interaction with DNA. For this purpose the formation of a complex was tested by comparing the spectrophotometrical absorbances of (DNA-product) solutions with those of DNA and of the products, at the absorption maxima of the products. None of the products formed in vitro a complex with DNA. The irradiation of product solutions with and without DNA induced a molecular degradation of the product which was linearly correlated with the radiation dose. The G values characterizing this radiodegradation showed that the presence of DNA did not modify the radiosensitivity of the products, neither in aerobic nor under hypoxic irradiation conditions. These results proved that the radiosensitizing properties of these compounds cannot be attributed to their chemical interaction with DNA.

Intercalative binding to DNA of antitumour drugs derived from 3-nitro-1,8-naphthalic acid

Two new antitumour drugs, imide derivatives of 3-nitro-1,8-naphthalic acid having different basic side chains linked to the imide nitrogen, have been shown to bind to double-helical DNA by intercalation. At ionic strength 0.01 mol/litre, pH 7, their intrinsic association constants are about 1.45 x 10(5) M-1 and each bound ligand molecule occludes about 3.4 nucleotides of the DNA lattice. They remove and reverse the supercoiling of closed circular duplex PM2 DNA with apparent unwinding angles of 11-12 degrees per bound drug molecule, referred to an assumed unwinding angle of 26 degrees for ethidium. They increase the viscosity of sonicated rod-like DNA fragments, each bound drug molecule producing a calculated increment in length of 2.2 - 2.5 A. No important differences between the DNA-binding characteristics of the two drugs were detected, though one appears marginally more active than the other in certain biological tests.

Interaction of phenosafranine with nucleic acids and model polyphosphates. III. Heterogeneity in phenosafranine interactions with DNA base pairs

Fluorescence and circular dichroism spectral measurements, thermal denaturation studies and binding competition experiments with netropsin and actinomycin D were carried out in systems containing phenosafranine bound to DNA's differing in base composition. The investigated properties exhibit a heterogeneity related to the content of A.T and G.C pairs in DNA and to the nature of phenosafranine binding modes. At low level of saturation of binding sites (r less than 0.1) phenosafranine does not show strong preference for any of the DNA base pairs in the overall binding. However, the strong monomer non-cooperative binding outside the helix (mode I1) occurs predominantly, even though not exclusively in G.C rich regions. The strong binding modes involving intercalated dye molecules (mode I2 and eventually mode II1) prevail in A.T rich regions. These binding modes become the principal types of strong phenosafranine interaction with DNA when the level of saturation of binding sites increases, i.e. at r greater than 0.1.20