8-chloro-cyclic adenosine monophosphate, a novel cyclic AMP analog that inhibits human glioma cell growth in concentrations that do not induce differentiation

Cyclic AMP is supposed to play a role in cell growth and differentiation via activation of protein kinase A. The cAMP signal transduction pathway may therefore be used as a target for the development of anticancer drugs. We compared the effects of 8ClcAMP, a newly developed cAMP analog, to the effects of more commonly used cAMP analogs on the morphology and the proliferation of three human glioma cell lines. 8ClcAMP was the most potent growth inhibitor, exhibiting an IC 50 of approximately 10 μ M and inducing growth arrest in all three glioma cell lines at a concentration of 100 μ M. The cAMP analogs 8CPTcAMP, dibutyryl cAMP, and 8BrcAMP were much less potent. If used in concentrations that induce growth arrest, both 8CPTcAMP and IBMX, but not 8ClcAMP, induced morphological differentiation of the glioma cells. Apparently, the growth-inhibiting effect of 8ClcAMP is not paralleled by its ability to induce morphological differentiation. The explanation for this phenomenon may be that 8ClcAMP does not exert its growth-inhibiting effect via activation of cAMP-dependent protein kinase. Two alternative mechanisms of action are discussed. Since 100 μ M 8ClcAMP retarded the growth of normal rat astrocytes only to a marginal extent, without cytotoxic effects, it is concluded that 8ClcAMP may offer interesting perspectives in the treatment of malignant glioma.