[Effects of forskolin on cultured glioma cells].

Forskolin is one of the factors that activate adenylate cyclase, which increases the intracellular level of cyclic adenosine monophosphate (AMP). The growth inhibitory effect of forskolin on human glioma (KY) cells was examined both in vitro and in vivo. The cytotoxic effect was evaluated by colony formation assay, and the cytokinetic effect by deoxyribonucleic acid (DNA) histograms using flow cytometry as well as by immunohistochemical study with anti-bromodeoxyuridine (BrdU)-monoclonal antibody. Morphological changes of forskolin-treated KY cells were observed under both light and electron microscopy. The change in the water-soluble protein fraction of KY cells after forskolin treatment was analyzed by two-dimensional polyacrylamide gel electrophoresis. It was found that the growth inhibitory effect of forskolin on KY cells in vitro was dose-dependent up to a concentration of 10 μM. However, cytotoxicity was not observed even at 100 μM. DNA histograms of KY cells treated with 10 μM forskolin did not reveal abolition of any specific phase of the cell cycle, although the both DNA histograms and immunohistochemical study with anti-BrdUmonoclonal antibody demonstrated a reduced number of cells in the S phase. Thus, in KY cells forskolin appears to accumulate in the non-proliferating cell pool. KY cells treated with forskolin showed not only morphological differentiation but also a change in the protein fraction. Certain acidic proteins, including S-100 protein, were markedly increased in these cells. When KY tumors were transplanted into nude mice, intraperitoneal injection of 1 mg/kg/day of forskolin for 10 days resulted in suppression of tumor growth by 47% (wet weight) and a significant decrease in the pro portion of cells in the S phase. These results indicate that forskolin may be useful as an anti-glioma agent.