The interaction of nogalamycin and analogs with DNA and other biopolymers

Abstract

The interaction with calf thymus DNA of the anthracycline antibiotics, nogalamycin and its analogs, was studied by electronic absorption, circular dichroism (CD), thermal denaturation, solvent partition and pulse radiolysis techniques. The Scatchard, thermal denaturation (Δ T m ), difference circular dichroism (ΔCD) and solvent partition binding parameters gave the same order of relative binding on a given lot of DNA, but some parameters were DNA-lot-dependent. In general, molecules containing the sugar moiety nogalose at C-7 or those having the natural or ‘dis’ stereochemistry of nogalamycin at C-7 bound more strongly to DNA than did the molecules lacking nogalose or those with the opposite configuration at C-7 (‘con’ stereochemistry). This stereochemical-binding correlation differs from that found for adriamycin which has the ‘con’ stereochemistry, but which binds strongly to DNA. Scatchard binding parameters could not be obtained from the pulse radiolysis or solvent partition techniques because of solubility difficulties. The 7-con- O-alkylnogarol analogs differed in binding behavior from the other analogs. Although active tumor agents, they formed substantially weaker complexes with calf thymus DNA. They exhibited relatively large ΔCD spectra with human albumin (HA), in contrast to nogalamycin and some of the other analogs which formed strong DNA complexes but exhibited very small ΔCD spectra with HA. The HA and DNA binding results correlate with published data which show that 7-con- O-methylnogarol accumulates in the cytoplasm and its uptake is enhanced by fetal serum albumin, while daunomycin, an antitumor drug which binds strongly to DNA, accumulates in the nuclei and its uptake is unaffected by fetal serum albumin. Collectively, the data suggest that DNA may not be the primary target molecule for the antitumor activity of 7-con- O-methylnogarol or the other 7-con- O-alkylnogarol analogs. This conclusion is further supported by L1210 cell growth inhibition experiments with the drugs premixed with calf thymus DNA. The ΔCD, Δ T m and Scatchard binding parameters indicate that the nogalamycin molecules differ from adriamycin in their interaction with calf thymus DNA. Base pair specificity studies by CD indicate that the nogalamycin molecules interact differently with poly(dA-dT) · (dT-dA) as compared to poly(dG-dC) · (dC-dG) or calf thymus DNA.