UP-REGULATION OF THE CAMP PKA PATHWAY INHIBITS PROLIFERATION, INDUCESDIFFERENTIATION, AND LEADS TO APOPTOSIS IN MALIGNANT GLIOMAS/

Manipulation of signal transduction pathways has been increasingly use d to modulate tumor growth. We have investigated the effects of up-reg ulation of the cAMP/protein kinase A (PKA) pathway in cell lines and p rimary cultures of malignant gliomas. The malignant glioma cell fine A -172 was treated with agonistic cAMP analogs dibutyryl cyclic AMP (dcA MP) and 8-bromo-cyclic AMP (8-Br-cAMP), an adenylate cyclase activator (forskolin), and a phosphodiesterase inhibitor (3-isobutyl-1-methyl-x anthene [IBMX]). Proliferation was determined by H-3-thymidine assay. Differentiation was measured by morphologic changes, glial fibrillary acidic protein (GFAP) content, and invasion potential. Apoptosis was m easured quantitatively by the TUNEL method, which labels DNA fragments using terminal transferase. Agonistic cAMP analogs, forskolin, and IB MX were found to decrease proliferation in A-172 cells after 24 hours. Treatment with 8-Br-cAMP for 24 hours caused an increase in GFAP and decrease in invasion. Apoptosis was induced after 48 hours in the pres ence of synergistic cAMP analogs for the Type II PKA isozyme, but not Type I PKA isozyme. Activation of PKA by increasing cAMP levels (forsk olin, IBMX) or directly by cAMP analogs correlated with decreased prol iferation, increased differentiation, and induction of apoptosis in A- 172 cells. Modulation of the cAMP/PKA pathway may thus represent a pos sible target site for treating malignant gliomas.