Cancer Letters, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 11 (1981) 339-344 o Elsevier/North-Holland Scientific Publishers Ltd. 339 zyxwvut INHIBITION OF INTERCELLULAR COMMUNICATION BETWEEN LIVER CELLS BY THE LIVER TUMOR PROMOTER l,l,l-TRICHLORO- 2,2-BIS(p-CHLOROPHENYL)ETHANE GARY M. WILLIAMS*, SHYLA TELANG and CHARLES TONG American Heart Foundation, Naylor Dana Institute for Disease Prevention, Valhalla, New York 10595 (U.S.A.) (Received 8 September 1980) (Revised version received 27 October 1980) (Accepted 27 October 1980) SUMMARY A dose dependent inhibition of intercellular communication (metabolic cooperation) between primary cultures of rat liver hepatocytes and an established adult rat liver epithelial cell 6-thioguanine resistant strain by the liver tumor promoter l,l,l-trichloro-2,2-bis (p-chlorophenyl)ethane (DDT) is demonstrated. This in vitro assay is proposed to evaluate the tumor promoting activity of oncogenic agents shown to be non-genotoxic in the liver culture systems. INTRODUCTION Numerous studies have demonstrated the effects of tumor promoters on the surface membranes of cells [ 8,9,14,15]. Such effects are of major interest in the mechanism of action of tumor promotion because they could be the basis for the escape of dormant tumor cells from normal tissue growth regulation. Recently, in vitro systems for studying the effect of tumor promoters on intercellular communication have been described for hamster [ 231 and mouse [ 51 fibroblast cells. Because tumor promotion is both species and organ [ 21 specific, we have adapted the approach of Yotti et al. [ 231 to measure the effect-of liver tumor promoters on intercellular communication between liver cells in culture [ 191. In the present report, we *To whom all correspondence should be addressed. Abbreviations: ARL, adult rat liver epithelial cell; DDT, l,l,l-trichloro-2,2-bis(p-chloro- phenyl)ethane; DMSO, dimethyl sulfoxide; HGPRT, hypoxanthineguanine phosphori- bosyl transferatre; WMES, Williams Medium E with 10% calf serum; TG, 6thioguanine; TGr, 64hioguanine resistant.