BD-40, an ellipticine-related DNA intercalative agent induces DNA-protein bridges in vivo

Isoquinolines: Important Cores in Many Marketed and Clinical Drugs

BACKGROUND

Isoquinoline analogs are an important, structurally diverse class of compounds that are extensively used as pharmaceuticals. Derivatives containing the isoquinoline scaffold have become a focus of therapeutic research because of their wide range of biological characteristics. Examples of these drugs, many of which are in clinical application or at the pre-clinical stage, are used to treat a broad swathe of ailments, such as tumors, respiratory diseases, infections, nervous system diseases, cardiovascular and cerebrovascular diseases, endocrine and metabolic diseases.

METHODS

Data were collected from PubMed, Web of Science, and SciFinder, through searches of drug names.

RESULTS

At least 38 isoquinoline-based therapeutic drugs are in clinical application or clinical trials, and their chemical structure and pharmacokinetics are described in detail.

CONCLUSION

The isoquinoline ring is a privileged scaffold which is often preferred as a structural basis for drug design, and plays an important role in drug discovery. This review provides a guide for pharmacologists to find effective preclinical/clinical drugs and examines recent progress in the application of the isoquinoline scaffold.

Spectroscopic study of the interaction of pazelliptine with nucleic acids

The antitumor drug pazelliptine (PZE) binds to natural and synthetic DNA sequences at 100 mM NaCl, pH 7.0, as deduced from the absorption and fluorescence data. Scatchard plots constructed from the results obtained with poly(dG-dC)-poly(dG-dC) give binding constants of base pairs in the range (2-6) x 10(5)M(-1). The modifications in the absorption and fluorescence spectra observed when PZE binds to various polynucleotides, namely poly(dA-dT)-poly(dA-dT), poly(dA)-poly(dT), poly(dG-dC)-poly(dG-dC) and calf thymus DNA, reveal a change in the protonation state of the drug upon binding, increasing the apparent pKa of its 9-N-nitrogen atom. The PZE excited state properties serve as a sensitive probe to distinguish between homo and hetero A-T sites as well as between AT and GC sites. Fluorescence studies reveal that energy transfer occurs from polynucleotide bases to the bound PZE chromophore, a result consistent with an intercalative mode of binding of the drug to DNA. The emission is enhanced when PZE is bound to A-T base pairs (approximately 30% increase of phi(F) whereas it is quenched in the vicinity of G-C base pairs (approximately 90% decrease of phi(F)). Furthermore, the fluorescence spectrum obtained with calf thymus DNA is hardly distinguishable from that obtained with poly(dG-dC)-poly(dG-dC), suggesting a binding of PZE to G-C rich regions.

Topoisomerases, new targets in cancer chemotherapy

The enzymes involved in the regulation of the three-dimensional structure of DNA, topoisomerase I and II, are important for the handling of DNA during vital cellular processes such as translation, transcription and mitosis. The enzymes are currently being studied intensively, they are being biochemically characterized and their mechanism of action is now better understood. Empirically discovered antitumor drugs appear to interfere with these enzymes, especially topoisomerase II. The DNA-topoisomerase II complex, which is an intermediate in the normal enzyme pathway, is stabilized by the drug and forms a 'cleavable complex', which appears to be cytotoxic. The drugs involved are, e.g. anthracyclines, epipodophyllotoxins and acridines. The central role of this enzyme offers the cell an opportunity for the development of resistance by down-regulation of this enzyme or the production of resistant mutants, provided the adaptation does not hamper other vital cell functions. Knowledge of the working mechanism and the cellular regulation of the topoisomerases might lead to the selection of most effective drugs and treatment schedules, and to circumvention of drug resistance.

The in vitro involvement of topoisomerase II in the activity of aza-ellipticine analogues is not correlated with drug activity on isolated nuclei

Aza-ellipticines are DNA intercalative ellipticine analogues with antitumor activity that induce protein-linked DNA breaks in NIH 3T3 cells in culture. The effects of two aza-ellipticine congeners (BD-40 and BR-76) on the activity of purified Calf Thymus type II topoisomerase were studied using pUC13 DNA as substrate. DNA cleavage was stimulated by both molecules at those doses required for inducing lethal effects in cells (DE5O). This effect was reversed by high salt treatment, indicating that it was actually mediated by Topo II. Mapping of cleavage sites on linearized and 3' end-labelled pUC13 DNA showed that ellipticine and aza-ellipticines stimulated the same sites, which differed from those stimulated by m-AMSA. Decatenating activity of Topo II on Trypanosoma cruzi kDNA was both inhibited by ellipticine and BD-40 at concentrations much higher than DE50 concentrations. Activity of aza-ellipticines was also investigated on isolated nuclei. Unlike ellipticine which promoted DNA-breaking activity, BD-40 and BR-76 were repeatedly inactive. Prior treatment of DNA by Proteinase K did not reveal hidden breaks which are formed in intact cells treated with BD-40 (Vilarem et al., 1984, Nucleic Ac. Res. 12, 8653). Concordant with these data, BD-40 did not impair DNA-synthetic activity in isolated nuclei, while Ellipticine largely decreased it. These results indicate that lesions induced in DNA by Aza-ellipticines are mediated by Topo II. The absence of effect of these drugs on isolated nuclei compared to that of Ellipticine may be due to some specific features of the association between Topo II and Aza-ellipticines or reflect a bioactivation step as a prerequisite for in vivo activity.