Induction of some features of glial differentiation in primary cultures of human gliomas by treatment with dibutyrl cyclic AMP.

Explants from 18 gliomas were cultured for periods up to 7 weeks and studied by light microscopy scanning and transmission electron microscopy. Well-differentiated tumor tissue gave rise to early outgrowths of stellate cells showing process orientation. Poorly-differentiated tissue produced a more haphazard out-growth of pleomorphic cells with few processes and flattened pseudopodia. Mean circadian cell displacement was several times greater in poorly-differentiated cells, but was significantly and reversibly reduced by treatment and dibutyryl cAMP (5 X 10(-4)M) for 48 h. Reduction in motility was directly correlated with a change in cell morphology to a more stellate form. Well-differentiated cells had a smooth surface with ruffling restricted to the ends of processes and highly orientated glial filament and microfilament bundles. The poorly-differentiated cell surface had a microvillous, blebbed appearance and ruffling regularly occurred around the edge of the cytoplasm. Glial filaments and microfilaments were fewer and less well orientated in the poorly-differentiated cells; sites of adhesion to the substratum were fewer than in well-differentiated cells. Treatment of malignant cultures with dibutyryl cAMP resulted in smoothing of the cell surface, retraction of processes into thin pseudopodia and the appearance of microfilament bundles within the cells. These features marked the apparent cyto-differentiation. However, there was a loss of attachment, disappearance of microtubules and loss of glial filaments in the cytoplasm which was not compatible with differentiation. Intracellular recordings of membrane potentials gave a significantly higher mean value for well-differentiated cells. The mean membrane potential and input resistance of poorly-differentiated cells was unchanged by the addition of dibutyryl cAMP. The results of this study suggest that some, but not all, features of mature glia are restored in malignant tumour cells by cAMP treatment.