8-CHLORO-CAMP INDUCES APOPTOTIC CELL-DEATH IN A HUMAN MAMMARY-CARCINOMA CELL (MCF-7) LINE

8-Cl-cAMP and 8-NH2-cAMP induced MCF-7 cell death. The type(s) of cell death were studied in more detail and compared with the cell death ty pe (apoptosis) induced by okadaic acid, an inhibitor of serine/threoni ne phosphatases. By morphological criteria dying cells showed loss of cell-cell interactions and microvilli, condensation of nuclear chromat in and segregation of cytoplasmic organelles. By in situ nick end-labe lling, using digoxigenin-conjugated dUTP as probe, a large fraction of 8-Cl-cAMP, 8-NH2-cAMP and 8-Cl-adenqsine-exposed cells stained positi vely in the advanced stages of death. In the early phase of chromatin condensation the cells stained negatively. Specific (internucleosomal) DNA fragmentation was not observed. The MCF-7 cell death induced by 8 -Cl-cAMP and 8-NH2-cAMP was not mediated by activation of the cAMP kin ase since more stable cAMP analogues (8-CPT-cAMP and N-6-benzoyl-cAMP) or forskolin failed to induce death. Furthermore, 8-Cl-cAMP action wa s counteracted by adenosine deaminase and 3-isobutyl-1-methylxanthine, and mimicked by 8-Cl-adenosine, a major metabolite of 8-Cl-cAMP. It i s concluded that 8-Cl- and 8-NH2-cAMP can induce morphological and bio chemical effects resembling apoptotic cell death in MCF-7 cells throug h their conversion into potent cytotoxic metabolite(s).