Elucidation of the DNA sequence preferences of daunomycin.

The sequence specificity of daunomycin was assessed using competition equilibrium dialysis, DNAse I footprinting and an E. coli RNA polymerase transcription inhibition assay; similar studies were performed on adriamycin and a new bis-intercalating daunomycin dimer. The results clearly demonstrate that the highest affinity sites are CA for daunomycin and adriamycin, and CACA for the bis-daunomycin. Other modest affinity (GC, CG, CT, TC, CC, AC) and poor affinity binding sites (AA, AT, TA) were also observed. Our results are in agreement with (a) the observed 5'-pyrimidine-purine-3' sequence preference of intercalating drugs, (b) the reported role played by OH(9) of daunomycin in the stabilization of the drug/DNA intercalation complex, and (c) the thermodynamics of nearest neighbour base-pair unstacking at the intercalation site. The CA specificity of daunomycin and adriamycin suggests that their biological activity may arise from association with the CA containing sequences which are thought to be associated with genetic regulatory elements in eukaryotes. The implications for future anthracycline drug design are presented in this context.

The DNA-association and biological activity of a new bis(14-thiadaunomycin).

A new bis-daunomycin has been synthesized and characterized by 13C-n.m.r. and reversed-phase h.p.l.c. The compound was found to be highly self-associated in aqueous solution and to bis-intercalate into DNA with a residence time about 200-fold greater than the parent compound daunomycin. Although the bis-daunomycin and its parent congener were taken up by V79 Chinese hamster ovarian leukaemia cells to similar extents, the cytotoxicity of the former was considerably lower. The possible in vivo relationship between DNA binding affinity and cytotoxicity is discussed.

The 5'-CA DNA-sequence preference of daunomycin.

The DNA-sequence specificity of daunomycin was investigated by DNase I footprinting and an E. coli RNA polymerase transcription-inhibition assay. The 5'-CA sequence was identified as being the highest affinity binding site, although other modest affinity (5'-GC, CG, CT, TC, AC) and poor affinity sites (5'-AA, AT, TA) were also observed. The preference of daunomycin for 5'-CA nucleotide sequence suggests that its biological activity may arise from association with the 5'-CA-containing sequences thought to be associated with genetic regulatory elements in eukaryotes.

DNA binding specificity of a series of cationic metalloporphyrin complexes.

The sequence specificities of a series of cationic metalloporphyrins toward a 139 base pair restriction fragment of pBR-322 DNA have been studied by DNase I footprinting methodology. Analysis using controlled digests and quantitative autoradiography/microdensitometry revealed that the 5- and 6-coordinate complexes of meso-tetrakis(N-methyl-4-pyridiniumyl)porphine, MT4MPyP, where M is Mn, Fe, Co, and Zn, were found to bind to AT regions of DNA. Footprinting analysis involving the radiolabel on the opposing strand of restriction fragment showed site skewing in the direction of the 3' end of the fragment, indicating that the porphyrins bind in the minor groove of DNA. The significant increase in DNase I catalyzed hydrolysis observed in various regions of the fragment appeared to be primarily due to a decrease in available substrate DNA upon porphyrin binding with possible contributions from structural changes in DNA caused by ligand binding. The complexes NiT4MPyP and CuT4MPyP were found to bind to both AT and GC regions of the fragment, producing different degrees of inhibition in the two regions. Since the outside-binding porphyrins can neither intercalate or effectively hydrogen bond to DNA, they appear to read sequence by responding to steric and/or electrostatic potential effects located in the minor groove of DNA.

DNA cleavage specificity of a group of cationic metalloporphyrins.

The ability of a group of water-soluble metalloporphyrins to cleave DNA has been investigated. Incubation of Mn3+, Fe3+, or Co3+ complexes of meso-tetrakis(N-methyl-4-pyridiniumyl)porphine (H2T4MPyP) with DNA in the presence of ascorbate, superoxide ion, or iodosobenzene results in DNA breakage. Comparisons between the rates of porphyrin autodestruction with the rates of strand scission of covalently closed circular PM2 DNA indicate that the porphyrins remain intact during the cleavage process. Analysis of the porphyrin-mediated strand scissions on a 139-base-pair restriction fragment of pBR322 DNA using gel electrophoresis/autoradiography/microdensitometry reveals that the minimum porphyrin cleavage site is (A X T)3. The cleavage pattern within a given site was found to be asymmetric, indicating that porphyrin binding and the strand scission process are highly directional in nature. In addition to an analysis of the mechanism of porphyrin-mediated strand breakage in terms of the DNA cleavage mechanism of methidium-propyl-iron-EDTA and Fe-bleomycin, the potential of the cationic metalloporphyrins as footprinting probes and as new "reporter ligands" for DNA is presented and discussed.

Molecular recognition between oligopeptides and nucleic acids: novel imidazole-containing oligopeptides related to netropsin that exhibit altered DNA sequence specificity.

Oligopeptides have been synthesized that are structurally related to the antiviral antitumor antibiotic netropsin, but in which each of the pyrrole units is successively replaced by an imidazole moiety, as well as their di- and triimidazole-containing counterparts. These compounds bind to duplex DNA with constants in the range (1.06-1.98) X 10(6) M-1 but not to single-stranded DNA. Since they bind to T4 DNA, it is inferred that, like the parent antibiotic netropsin, they are also minor groove selective. This series of compounds exhibits a progressively decreasing preference for AT sites in binding studies with both native DNAs and synthetic oligonucleotides and a corresponding increasing acceptance of GC base pairs. Footprinting experiments utilizing a 139 base pair HindIII/NciI restriction fragment from pBR 322 DNA revealed that these lexitropsins, or information-reading oligopeptides, recognize more sites than the parent netropsin. In addition, some regions of enhanced nuclease action as the result of drug binding to the fragment were identified. The diimidazole compound in particular recognizes GC-rich sites, implying the formation of new hydrogen bonds between G-C(2)NH2 in the minor groove and the additional N3 imidazole nitrogens. It is clear however that, since the lexitropsins appear to tolerate the original (AT)4 site, an N-methylimidazole group on the ligand will permit either a GC or AT base pair in the binding sequence. Another factor that may be significant in molecular recognition is the high negative electrostatic potential of A X T regions of the minor groove, which is likely to strongly influence binding of these cationic species to DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Deoxyribonucleic acid cleavage specificity of a series of acridine- and acodazole-iron porphyrins as functional bleomycin models.

A series of metalloporphyrins linked through basic chains to certain DNA interactive groups has been synthesized. Several of these agents reproduce the characteristic properties of the antitumor glycopeptide bleomycin, including the oxygen-mediated scission of DNA in the presence of thiols, antibiobic activity under aerobic conditions, and activity against human and animal tumor models. Initial screening by scission of PM2-CCC-DNA identified six of the compounds, including those bearing acridine and acodazole intercalating groups, as the most active. The specificity of the oxygen-mediated scission of a 139 base pair HindIII/NciI restriction fragment of pBR322 by these six selected agents was then determined and compared with the action of pancreatic DNase by densitometric scans. All six of these compounds produce uniform base and sequence neutral cleavage of the restriction fragment at each base site. The six active compounds bear either of two types of intercalators, 6-chloro-2-methoxyacridine or acodazole, and with linkages to the ferric binding domain of -NH(CH2)2-, -NH(CH2)3-, -NH(CH2)4-, or -NH(CH2)3NH(CH2)3- and either porphyrin or deuteroporphyrin moieties. Comparison of the Kassoc values for binding to calf thymus DNA suggests that the enhanced binding observed with the linker -NH(CH2)3NH(CH2)3- contributes to the efficiency of sequence neutral DNA scission and may be a factor in the relative anticancer activities of these agents. The iron porphyrins give no evidence of the production of base propenals in DNA degradation, and the autoradiograms clearly indicate that a phosphate group is attached to the 5' end of the oligomer. The scission is partially suppressible by catalase and superoxide dismutase.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer assisted microdensitometric analysis of footprinting autoradiographic DATA.

A system comprised of a linear scanning microdensitometer interfaced to a personal computer has been developed to facilitate analysis of ligand-DNA footprinting autoradiograms. The system, which can be used to record density and sequence information from autoradiographic films, enables the user to relate the area under an autoradiographic band to the concentration of radiolabeled molecules present in the electrophoresis gel. This report describes the computer program which performs the calculations and discusses the ability of the system to accurately determine oligonucleotide concentration, as a function of band separation, photographic response, and the computational algorithm used to calculate band areas.