Partial Suppression of Tumour Production by Dibutyryl Cyclic AMP and Theophylline

ADENOSINE 3′,5′-cyclic monophosphate (cAMP) is the common intracellular mediator of a number of hormones and biogenic amines 1,2 , and cyclic AMP or dibutyryl cyclic AMP (dbc-AMP) also inhibits the growth of various lines of transformed fibroblasts and reverses their abnormal morphological characteristics toward normal without affecting the viability of the cells 5 . But, the effect of cAMP or dbcAMP treatment on the tumorigenicity of the transformed cells is not known. Here we describe an examination of the effect of dbcAMP treatment on the tumour-producing ability in hamsters by chicken–embryo–lethal orphan (CELO) virus-transformed hamster skin cells. The CELO virus is an endogenous adenovirus of chicken eggs, and is oncogenic when inoculated subcutaneously 6 or intracerebrally 7 in hamsters. It is also known to transform hamster embryo fibroblastic cultures 8 , hamster kidney cell cultures 9 and hamster embryo skin cells in vitro (Pendola, R., Yates, V. J., Jasty, V., manuscript in preparation).