Contact Inhibition of Transformed Cells Incompletely Restored by Dibutyryl Cyclic AMP

INCREASED levels of cyclic AMP have been found in normal cells as compared with malignant cells^1,2. Several types of malignant cells become morphologically similar to untransformed cells when incubated in media containing cyclic AMP or its derivative dibutyryl adenosine 3′:5′-cyclic monophosphate (dibutyryl cyclic AMP)^3,4. Sheppard reported that 3T3 mouse fibroblasts, transformed by polyoma virus, grew to low saturation density and became less agglutinable with wheat germ agglutinin if theophylline and dibutyryl cyclic AMP were added to the medium⁵.