DNA Thermal Denaturation Studies Research Articles

Biological Properties of IRIM, the Iridium(III) Analogue of (Imidazolium (Bisimidazole) Tetrachlororuthenate) (ICR)

Some biological aspects of the new complex imidazolium bisimidazole tetrachloro iridate(III)-IRIM- the iridium(III) analogue of ICR, were considered. More in detail the conformational effects produced by IRIM on DNA and the cytotoxic properties of IRIM on some selected human cell lines were measured. Dialysis experiments and DNA thermal denaturation studies are suggestive of poor binding of IRIM to DNA; formation of interstrand crosslinks is not observed. In any case CD measurements suggest that addition of increasing amounts of IRIM to calf thymus DNA results into significant spectral changes, that are diagnostic of a direct interaction with DNA. A number of experiments carried out on the A2780 human ovarian carcinoma, B16 murine melanoma, MCF7 and TS mammary adenocarcinoma tumor cell lines strongly point out that IRIM does not exhibit significant growth inhibition effects within the concentration range 10-4-10-6 M. It is suggested that the lower biological effects of IRIM compared to ICR are a consequence of the larger kinetic inertness of the iridium(III) center with respect to ruthenium(III).

Preparation and Biological Activity of Heteroaryl-Substituted Bile Steroids

The synthesis, and growth inhibition studies against the L1210 mouse leukaemia, �MCF-7 human breast cancer and SKOV-3 ovarian carcinoma cell lines, of derivatives of lithocholic acid and cholic acid in which quinoline-3-carboxylate and acridine-9-carboxylate are substituted at the 3 and/or the 24 position are reported. The 3α,24-diheteroaryl-substituted steroid systems, lithocholic acid, cholic acid, quinoline and acridine-9-carboxylic acid showed no significant biological activity against any of the cell lines. In contrast, when either a single quinoline-3-carboxylate or acridine-9-carboxylate unit is substituted onto position 24 of the steroid derivatives, significant activity against L1210, and weak activity against the MCF-7 and SKOV-3 lines is exhibited. DNA thermal denaturation studies of these compounds showed no detectable binding to calf thymus DNA.

Cell-killing activity and kinetic analysis of a novel antitumor compound NC-190, a benzo[a]phenazine derivative.

A novel antitumor compound, N‐β‐dimethylaminoethyl 9‐carboxy‐5‐hydroxy‐10‐methoxybenzo[a]‐phenazine‐6‐carboxamide sodium salt (NC‐190), was evaluated for antitumor activity in vitro against cultured tumor cell lines, and the kinetics of cell killing was elucidated. NC‐190 strongly inhibited the growth of all of 3 murine tumor cell lines, 7 human tumor cell lines and 2 normal cell lines. With continuous exposure, the 50% inhibition concentrations were in the range of 0.005–0.06 μg/ml, except for KATO‐III (2.15 μ g/ml). By colony‐forming assay, concentrations of NC‐190 giving 90% cell kill (IC90) at various exposure times were obtained with HeLa S3 cells. The plot of IC90exposure time on a log‐log scale was linear for NC‐190 with a slope of ‐1, which is typical for cell cycle phase‐nonspecific agents. A 2 h treatment with NC‐190 induced a rapid reduction in cell viability at doses of more than 3 μ g/ml. At the dose where colony formation was completely inhibited, cell viability was persistently reduced to below 20% during the cell culture period. NC‐190 cauced a dose‐ and time‐dependent reduction in DNA synthesis. The inhibitions of RNA and protein synthesis were less than that of DNA synthesis. Spectroscopic studies of NC‐190 mixed with calf thymus DNA demonstrated that NC‐190 was capable of interacting with DNA. However, DNA thermal denaturation studies suggested that intercalation of NC‐190 was weak in comparison with those of classical intercalating drugs.

A new pyrrole-amidine antibiotic TAN-868 A.

A new pyrrole-amidine antibiotic TAN-868 A was isolated from the culture broth of Streptomyces idiomorphus sp. nov. Its chemical structure was determined by spectroscopic analyses and degradation studies to be 4-[(2S,4R)-4-hydroxy-5-iminoprolyl]amino- N-(2-amidinoethenyl)-2-pyrrolecarboxamide. The antibiotic is active against bacteria, fungi and a protozoan, and has cytotoxic activity against murine tumor cells. DNA thermal denaturation studies suggest that TAN-868 A preferentially interacts with AT rich regions of double-stranded DNA.

Interactions of histones and histone peptides with DNA Thermal denaturation and solubility studies

The interactions of DNA with the five histone components (H1, H2B, H2A, H3 and H4) and with a number of histone fragments (N-H1 (1–72), C-H1 (73–216), N-H2B (1–59), C-H2B (63–125), N-H2A (1–39), C-H2A (58–129), N-H4 (1–84) and C-H4 (85–102) have been studied by using the techniques of thermal denaturation and solubility behaviour. Complexes in 10 −3 M phosphate buffer, 2 · 10 −5 M Na 2-EDTA, pH 7.0 were prepared by the direct mixing method. For lysine-rich histones (H1 and H2B) it has been found that the main characteristics which governs the interaction with DNA are located in the very lysine-rich part of the molecules, i.e. in the C-H1 and N-H2B segments. These regions are also responsible for a cooperative distribution of the histone along the DNA molecules in the artificial complexes. It appears from our studies that the tertiary structure of the moderately, arginine-rich histone (H2A) is an essential feature for its interaction with DNA. The two arginine-rich histones (H3 and H4) complexed with DNA behave in a similar way, both in thermal denaturation and in DNA precipitation. In the case of C-H4, a marked shift of the melting profile has been observed which is correlated with the presence in the peptide of the hydrophilic cluster Lys-Arg-Gln-Gly-Arg-Thr. Out results suggest that large segments rich in lysine and basic clustering within histones give rise to different modes of electrostatic interaction with DNA.