A rapid and sensitive bioassay involving cultured rat glioma cells to screen for substances capable of elevating intracellular cyclic AMP concentration.

Cultured rat glioma (ASK) cells are morphologically converted from a spindle to an astrocyte form when treated with dibutyryl cAMP. This morphologic transformation is discernible by light microscopy and can be visually quantitated. As described herein, dose-dependent astrocyte generation was demonstrated by treatment of confluent monolayers with forskolin [1], a compound known to activate adenylate cyclase, and the potency of four forskolin derivatives was found to correlate with previously established biologic potential. Neither a crude ginseng extract nor purified ginsenosides were active in the process, but supplementation of the otherwise inactive ginseng extract with 1 demonstrated 50% of the cells were morphologically converted to the astrocyte form at a concentration of approximately 0.0008%. Retinoic acid was also active in this test system; the morphologic transformation was reversed on treatment with colchicine, and intracellular cAMP concentration was elevated approximately 10-fold. Evaluation of 15 retinoids established a general correlation between the activity in this system and other systems reported in the literature. Thus, the astrocyte formation assay appears to provide several advantages that make it attractive as a screen for the detection or evaluation of substances capable of elevating intracellular cAMP concentration. In addition to technical ease, the procedure is rapid, sensitive, and relatively inexpensive.