Species specificity affects the choice of S9 preparations for use in the hamster embryo cell transformation system

Before their use as a source of carcinogen-activating enzymes in the hamster embryo cell transformation assay, liver, kidney, lung, and small intestine S9 fractions from Syrian golden hamsters and Sprague-Dawley rats were evaluated for toxicity to hamster embryo target cells. Sprague-Dawley rat liver and kidney S9 were highly toxic to the hamster embryo cells (90 to 100%). When retested at lower concentrations these tissue fractions were still quite toxic (up to 75%). In contrast, hamster liver and kidney S9 were considerably less toxic (14 to 25%). The S9 preparations were also evaluated for their ability to metabolize N-2-acetylaminofluorene to 2-aminofluorene and N-hydroxy-acetylaminofluorene, products that transform hamster embryo cells. Large amounts of N-hydroxy-acetylaminofluorene were formed in the presence of preparations from hamster liver and small intestine, whereas kidney and lung S9 fractions were considerably less active. No detectable levels of N-hydroxy-acetylaminofluorene were formed after incubation of N-2-acetylaminofluorene with any of the rat S9 preparations. High levels of deacetylase activity were found in hamster liver and small intestine S9 fractions, at least eightfold higher than those obtained from equivalent rat preparations. Hamster kidney and lung S9 fractions showed low levels of deacetylase activity. There was no detectable activity in equivalent preparations from rats. When tested with N-2-acetylaminofluorene in the hamster embryo cell clonal transformation system, transformed colonies were obtained with hamster liver S9, with and without an external NADPH-generating system.