8-Cl-cAMP induces cell cycle-specific apoptosis in human cancer cells

Abstract

8‐Cl‐cyclic adenosine monophosphate (8‐Cl‐cAMP) has been known to induce growth inhibition and differentiation in a variety of cancer cells by differential modulation of protein kinase A isozymes. To understand the anticancer activity of 8‐Cl‐cAMP further, we investigated the effect of 8‐Cl‐cAMP on apoptosis in human cancer cells. Most of the tested human cancer cells exhibited apoptosis upon treatment with 8‐Cl‐cAMP, albeit with different sensitivity. Among them, SH‐SY5Y neuroblastoma cells and HL60 leukemic cells showed the most extensive apoptosis. The effect of 8‐Cl‐cAMP was not reproduced by other cAMP analogues or cAMP‐elevating agents, showing that the effect of 8‐Cl‐cAMP was not caused by simple activation of protein kinase A (PKA). However, competition experiments showed that the binding of 8‐Cl‐cAMP to the cAMP receptor was essential for the induction of apoptosis. After the treatment of 8‐Cl‐cAMP, cells initially accumulated at the S and G2/M phases of the cell cycle and then apoptosis began to occur among the population of cells at the S/G2/M cell cycle phases, indicating that the 8‐Cl‐cAMP‐induced apoptosis is closely related to cell cycle control. In support of this assumption, 8‐Cl‐cAMP‐induced apoptosis was blocked by concomitant treatment with mimosine, which blocks the cell cycle at early S phase. Interestingly, 8‐Cl‐cAMP did not induce apoptosis in primary cultured normal cells and non‐transformed cell lines, showing that 8‐Cl‐cAMP‐induced apoptosis is specific to transformed cells. Taken together, our results show that the induction of apoptosis is one of the mechanisms through which 8‐Cl‐cAMP exerts anticancer activity.