Biological properties of 8-methoxypyrimido[4(1),5(1):4,5]thieno(2,3-b)quinoline-4(3H)-one, a new class of DNA intercalating drugs.

BACKGROUND & OBJECTIVES: The compounds containing novel tetracyclic condensed quinoline ring system is of interest because of its close relationship with anticancer drug ellipticine. 8-Methoxypyrimido[4(1),5(1):4,5]thieno(2,3-b)quinoline-4(3H)-one (MPTQ) was investigated to study its effect on in vitro growth inhibition and clonogenic cell survival assay on three tumour cell lines, human promyelocytic leukemia HL-60, melanoma B16F10 and neuro 2a. A systematic study was carried out to evaluate its antitumour efficacy against B16 murine melanoma. Antiinflammatory and analgesic activities of MPTQ were also studied. METHODS: The cytotoxicity of MPTQ on HL-60, B16F10 and neuro 2a cells was estimated by trypan blue exclusion test. The antitumour activity was evaluated using single dose, multiple/daily injections (days 3-6) or intermittent treatments over two weeks against s.c. implanted B16melanoma, both in terms of increased life span and tumour growth inhibition. Antiinflammatory activity was seen on carrageenan induced hind paw oedema. Counting the number of abdominal constrictions after the injection of acetic acid assessed the analgesic response. RESULTS: MPTQ is cytotoxic to all the cell lines tested and ID50 being in the range of 0.08-1.0 microM. MPTQ was studied for anticancer activity in the clonogenic assay. Drug was applied over a wide dose range by 24 h exposure, yielding clear dose-response effects. In vivo antitumour efficacy against B16 melanoma showed evidence of major antitumour activity for MPTQ. Single and multiple i.p. doses of drug proved high level activity against the s.c. grafted B16melanoma, significantly increasing survival (P<0.001) and inhibiting tumour growth (T/C of 3.0%). A reduction (76.48%) in paw volume was noted in 40 mg/kg dose of which was comparable to antiinflammatory activity of 150 mg/kg i.p. of phenylbutazone. Analgesic activity was found to be of peripheral type as there was reduction of 74 per cent in writhing response by MPTQ in dose of 40 mg/kg in mice. INTERPRETATION & CONCLUSION: The results suggested that the compounds containing pyrimidothienoquinoline system particularly 8-methoxy derivative might be potentially useful antitumour agent. We conclude that the correlation of physicochemical properties of the new series of pyrimidothienoquinolines with their pharmacological properties, might help in trying to understand the mechanism of pyrimidothienoquinolines series.

Interaction of the antitumour alkaloid coralyne with duplex deoxyribonucleic acid structures: spectroscopic and viscometric studies.

The interaction of coralyne, an antitumour alkaloid with natural and synthetic duplex DNAs was investigated under conditions where the drug existed fully as a true monomer for the first time using spectrophotometric, spectrofluorimetric, circular dichroic and viscometric techniques. The absorption spectrum of coralyne monomer showed hypochromic and bathochromic effects on binding to duplex DNAs. This effect was used to determine the binding parameters of coralyne. The binding constants for four natural DNAs and four synthetic polynucleotides obtained from spectrophotometric titration, according to an excluded site model, using McGhee-von Hippel analysis, were all in the range of (0.38-9.8) x 10(5) M-1, and showed a relatively high specificity for the GC rich ML DNA and the alternating GC polynucleotide. The binding of coralyne decreased with increasing ionic strength, indicating that the binding affinity has a strong electrostatic component. Coralyne stabilized all the DNAs against thermal strand separation. The intense steady state fluorescence of coralyne was effectively quenched on binding to DNAs and the quantitative data on the Stern-Volmer quenching constant obtained was sequence dependent, being maximum with the GC rich DNA and alternating GC polymer. Circular dichriosm studies further evidenced for a strong perturbation of the B-conformation of DNAs consequent to coralyne binding with the concomitant development of extrinsic circular dichroic bands for the bound drug molecules suggesting their strong intercalated geometry in duplex DNAs. Further tests of intercalation using viscosity measurements on linear and covalently closed plasmid DNA conclusively proved the strong intercalation of coralyne in duplex DNA. Binding of the closely related natural alkaloid, berberine under these conditions showed considerably lower affinity to duplex DNAs in all experiments. Taken together, these results suggest that coralyne binds strongly to duplex DNAs by a mechanism of intercalation with specificity towards alternating GC duplex structure.

1H NMR investigation of the interaction of berberine and sanguinarine with DNA.

Interaction of the alkaloids, berberine and sanguinarine with calf thymus DNA has been studied by 1H NMR. All proton resonances of the two compounds have been assigned using 2D-COSY, NOESY and ROESY spectra. Berberine has been found to partially intercalate into DNA, while sanguinarine shows normal intercalation and also binds more firmly to DNA. The NMR experiments indicate that sanguinarine is more potent than berberine in its activity.