Gianfranco Chiarelotto

Synthesis and antiproliferative activity of some variously substituted acridineand azacridine derivatives

A group of 9-substituted acridine and azacridine derivatives (m-AMSA analogues) were synthesised following classical procedures as potential antitumour agents with inhibitory effects on DNA topoisomerase II. Some were found to have noticeable cytotoxicity against human HL-60 and HeLa cells grown in culture. Their non-covalent interactions with calf thymus DNA have been studied using fluorescence quenching. We evaluated DNA damage produced by the tested compounds by means of DNA filter elution and protein precipitation techniques. Catalytic studies carried out with purified topoisomerase confirmed these agents as antitopoisomerase inhibitors. Chemotherapy of solid-tumour-bearing mice with tested compounds allowed an aza-analogue (compound IIIb), as potent as m-AMSA but less toxic towards the host, to be recognised.

Pyrrolo-quinoline derivatives as potential antineoplastic drugs

Some novel pyrrolo-quinoline derivatives have been synthesized as potential antineoplastic agents. They contain an angular aromatic tricyclic or tetracyclic system, to which the methanesulfon-anisidide side chain typical of amsacrine as such, or lacking the m-methoxy substituent, is connected. A methyl group can be present at position 7 of the pyrrolo-quinoline ring. The novel compounds exhibit interesting cell growth inhibitory properties when tested against the NCI panel of cell lines, in particular those obtained from solid tumors like CNS-, melanoma- and prostate-derived cells. The mechanism of cytotoxic action does not seem to be related to topoisomerase II poisoning ability. Most active proved to be compound 4a, which lacks both methyl and methoxy substituents, followed by 5a, having the methoxy group only. Biological activity is less pronounced in the tetracyclic family of derivatives 6 and 7.

Mannich bases of 3H-pyrrolo[3,2-f]quinoline having vasorelaxing activity

Mannich bases obtained by aminoalkylation of 3H-pyrrolo[3,2-f]quinoline were designed and prepared as potential vasorelaxing agents. Compounds Ia-Va were characterised by IR, 1H-NMR, mass spectral data and elemental analysis; IIb,c-Vb,c were also confirmed by 1H-NMR spectra of reaction mixtures. To estimate their vascular activity, prototypes 1-(N,N-dimethylaminomethyl)- (Ia) and 1-(4-phenyl-piperazin-1-ylmethyl)- (IVa) 3H-pyrrolo[3,2-f]quinoline derivatives were studied in rat-tail arteries. In tissues precontracted with 0.5 microM 5-hydroxytryptamine (5-HT), 3 microM phenylephrine or 80 mM KCl, Ia and IVa showed endothelium-independent relaxing action. In a preliminary study on the cellular mechanisms of Ia, the influence of propranolol, a beta-receptor antagonist, and ketanserin, a 5-HT(2A)-receptor antagonist, was checked. In the presence of phenylephrine, the vasorelaxing effect of Ia was not affected by these inhibitors.

Novel pyrrolo[3,2-f]quinolines: synthesis and antiproliferative activity.

Novel pyrrolo[3,2,f]quinoline derivatives have been synthesized and tested as antiproliferative agents. They are characterized by an angular aromatic tricyclic system, to which a methyl group can be bound at position 7, and by a methanesulfon-anisidide side chain as such, or lacking the m-methoxy substituent at position 1. The novel compounds were shown to exhibit cell growth inhibitory properties when tested against the NCI panel of cell lines, in particular those obtained from leukemias. Although the compounds are able to stimulate topoisomerase II poisoning at high concentration, the cell growth inhibition properties do not appear to rest principally on this mechanism of action. Overall, the most active proved to be compound 9, having the m-methoxy substituent typical of amsacrine, followed by the 7-methyl derivative 10 and by the unsubstituted compound 8. Comparison with previously investigated regioisomers shows modulation of activity dictated by the position and conformational freedom of side-chain groups.

DNA-targeting pyrroloquinoline-linked butenone and chalcones: synthesis and biological evaluation.

A series of conjugates of alpha,beta-unsaturated ketone systems, phenyl-butenone and diaryl-propenones (chalcones), with the tricyclic planar pyrroloquinoline nucleus were synthesised and evaluated for their anticancer properties. The aim was to target DNA by butenone and chalcones, and determine the occurrence of interactions with the macromolecule or related functional enzymes. The ability to inhibit cell growth was assayed on three human tumor cell lines, and the capacity to form molecular complexes with DNA was studied by linear flow dichroism (LD). The effect on the activity of the nuclear enzyme DNA topoisomerase II was also investigated. A noticeable cytotoxic effect was observed for all pyrroloquinoline-conjugated compounds 5 and 7a-c, particularly against human melanoma cell line JR8 (IC(50) 1.2-3.3 microM); the unconjugated chalcones (8a-c) and butenone had a lower or no effect at the tested concentrations. LD experiments confirmed the pyrroloquinoline nucleus as an efficacious carrier for intercalative complexation with DNA. The ability of pyrroloquinoline derivatives to intercalate between base pairs appears to inhibit the relaxation of supercoiled DNA by topoisomerase II, while they induce no significant DNA cleavage. Since the concentrations inhibiting the enzyme appear relatively high with respect to cytotoxicity, the effective intercalation could affect the activity of more DNA processing enzymes and these overall nuclear effects may induce cell death.

Synthesis and biological properties of a new series of N-pyrido substituted tetrahydrocarbazoles.

A series of methyl and ethyl quaternary pyridiniumtetrahydrocarbazoles was synthesized and studied in comparison with ellipticine, chosen as a reference. In general, their antiproliferative activity, tested in different biological substrates, appeared to be higher than that of the corresponding non-quaternarized compounds. This fact could be attributed to the introduction of a positive charge in the molecule, which can stabilize the molecular complex they form with DNA. In a prokaryotic system, the T2 bacteriophage, both quaternarized and non-quaternarized compounds inhibited its infectivity moderately, in a similar way to ellipticine. This effect seemed to be connected to a direct activity on the virions rather than on the indicator bacteria. In mammalian cells, the pyridiniumtetrahydrocarbazoles were more effective. In particular, they appeared to be very active in inhibiting DNA synthesis in Ehrlich ascites cells; some of them were as effective as ellipticine. However, pyridiniumtetrahydrocarbazoles were less active in comparison with ellipticine when their capacity for inhibiting the clonal growth in Chinese hamster ovary (CHO) cells was tested. A similar picture was obtained studying the formation of chromosome aberrations and of sister chromatid exchanges in the same cells. These different responses can be explained considering that the data on DNA synthesis reflect effects only on DNA replication within a short time, without considering any later consequences; on the contrary, in the long-term tests, other events, which lead to cell killing or genotoxicity, can take place. Pyridiniumtetrahydrocarbazoles damage DNA, inducing double-strand breaks efficiently. These observations, together with the data already obtained on unsubstituted derivatives, suggest the pyridiniumtetrahydrocarbazoles induce antiproliferative and genotoxic effects, very probably by inhibiting topoisomerase II.