8-methoxycaffeine-induced protein-associated DNA breaks in isolated L1210 cell nuclei.

8-methoxycaffeine (8-MOC) is a caffeine derivative more potent than its parental compound in inducing chromosomal aberrations. 8-MOC has been postulated to produce chromosomal aberrations by DNA topoisomerase II inhibition. The effect of 8-MOC on nuclear DNA were studied by alkaline elution experiments and compared with those of Ellipticine and Adriamycin (ADR). Like Ellipticine and ADR, 8-MOC induced single strand breaks (SSBs), double strand breaks (DSBs), and DNA-protein cross-links (DPCs) in a bell-shaped manner with respect to drug concentration. As in the case of ADR and Ellipticine, 8-MOC induced equal SSB and DPC frequencies. These results could suggest that 8-MOC induces DNA breaks by interacting with DNA topoisomerase II or with a similar DNA metabolism enzyme.

Biochemical and enzymatic aspects of caffeine and caffeine derivatives induced DNA strand breaks.

The results presented here point to the difficulties that exist in connection with the identification of the molecular target of caffeine. Our data support the evidence that caffeine and caffeine derivatives cause DNA-protein cross-links (DPC) in whole mammalian cells or in isolated nuclei. These DPC have the same properties (saturability, reversibility and temperature-dependence) as those produced by an enzymatic inhibition. The experiments performed in reconstituted systems, in the presence of purified DNA topoisomerase II, do not support the original hypothesis that this enzyme might be a possible target for this class of drugs. We suggest the possibility that other DNA metabolism enzymes are involved in the biological effects of caffeine and caffeine derivatives. Further biochemical and molecular data are necessary to identify which of these enzymes is in fact affected.