Effect of phorbol myristate acetate on cultured tumor cells derived from different stages of avian sarcoma virus (ASV)-induced neoplastic growth.

We have investigated the action of the tumor promoter phorbol 12-myristate-13-acetate (PMA) on avian sarcoma cells cultured from avian sarcoma virus (ASV)-induced tumors at various stages of growth and on normal chicken embryo fibroblasts (CEF). We found that exposure to PMA (30 ng/ml) led to decreased expression of the malignant phenotype of avian sarcoma cells which had been derived from progressively-growing or regressing neoplasms. For example, treatment with PMA caused inhibition of growth of cultured avian tumor cells as well as decreased synthesis of DNA and protein. In addition, such treatment resulted in reduced expression of pp60src kinase activity. Direct inoculation of PMA into growing avian sarcomas led to an enhancement of the tumor regression which occurs in this system as a consequence of a strong cell-mediated, anti-tumor immune response.