IN VITRO Volume14, No. 10, 1978 Allrightsreserved 9 EXPLANT CULTURE OF RAT COLON: A MODEL SYSTEM FOR STUDYING METABOLISM OF CHEMICAL CARCINOGENS H. AUTRUP, G. D. STONER, F. JACKSON, C. C. HARRIS, A. K. M. SHAMSUDDIN, L. A. BARRETT, AND B. F. TRUMP Human Tissue Studies Section, Experimental Pathology Branch, CarcinogenesisProgram, Division of Cancer Cause and Prevention, National Cancer Institute. Bethesda, Maryland 20014 (H. A., G. D. S., F. J., C. C. H); and Department of Pathology, University of Maryland, School of Medicine, Baltimore, Maryland21201 (A. K. M., L. A. B., B. F. T.) SUMMARY An explant culture system has been developed for the long-term maintenance of colonic tissue from the rat. Explants of 1 cm 2 in size were placed in tissue-culture dishes to which was added 2 ml of CMRL-1066 medium supplemented with glucose, hydrocortisone,/~- retinyl acetate, and either 2.5% bovine albumin or 5% fetal bovine serum. The dishes were placed in a controlled-atmosphere chamber which was gassed with 95% O2 and 5% CO2. The chamber then was placed on a rocker platform which rocked at 10 cycles per min caus- ing the medium to flow intermittently over the epithelial surface. The explants were incu- bated at 30 ~ C. The viability of the tissue was measured both by incorporation of specific precursors into cellular macromolecules and by monitoring of tissue morphology with light and electron microscopy. Cultured rat colon was able to metabolize benzo[a]pyrene, 7,12- dimethylbenz[a]anthracene, aflatoxin B1, dimethylnitrosamine, 1,2-dimethylhydrazine, and methylazoxymethanol acetate into chemical species that bind to cellular DNA and protein. Key words: colon; explant culture; carcinogen INTRODUCTION Cancer of the colon is one of the most common cancers in the industrialized world. Epidemiologi- cal studies indicate that colonic cancer is related mainly to dietary factors including fat and micro- nutrients (1-3). An animal model system for in- vestigating these factors has been developed (4,5). Intrarectal administration of either N-methyl N'- nitro-N-nitrosguanidine or 1,2-dimethylhydra- zinc to rats caused adenocarcinoma which was histologically quite similar to colonic adenocar- cinoma in man (4-6). Similar results were found when azoxymethane was given by subcutaneous administration (5). The extrapolation of carcinogenesis data from studies utilizing experimental animals to man pre- sents a complex problem. A new approach to pro- vide a link between the experimental animal stud- ies and human is to use in vitro systems that per- mit comparative studies under similar conditions of exposure to carcinogens, e.g. explant cultures of human and rat colon. In our laboratories ex- plant systems have been developed for culturing metabolism. human target tissues; i.e. bronchus (7), pancreatic duct (8) and colon (9), and explants of human colon were able to metabolize procarcinogens of several chemical classes, e.g. benzo[a]pyrene (BP), dimethyinitrosamine (DMN), and 1,2- dimethylhydrazine (1,2-DMH) (10). In the present report, the development of an ex- plant system for rat colonic tissue is described. Three major variables that permitted the long- term culturing of rat colonic tissue were (a) in- creased 02 tension; (b) supplementation of the medium with glucose; and (c) lowering the incu- bation temperature to 30 ~ C. The metabolism of various proeareinogens by rat colonic tissue cul- tured for 4 days was investigated. Recently, methods also have been described for the explant culture of colon from newborn rats, newborn hamsters (11 ), and adult mice (12). MATERIALS AND METHODS Animals. Male Charles River CD rats (Charles River, Wilmington, Mass.), 4- to 5-week-old, 868