There is mounting evidence that normal cells can either inhibit the growth of carcinogen-altered cells and/or affect progression to a neoplastic phenotype. This effect(s) has been observed both in vivo in intact rat tracheal tissues and in rat tracheal epithelial cell cultures. The inhibition of carcinogen-altered cells in culture appears to be associated with the production of an acid and heat stable, dithiothreitol sensitive, nondialyzable protein produced by normal tracheal epithelial cells or esophageal epithelial cells in primary culture. It was found to be optimally produced by 3-4-week-old cultures of normal epithelial cells. In the presence of a 1:4 dilution of normal cell conditioned medium, the colony forming efficiency of a sensitive cell line is decreased 5-fold. Biochemical properties of the inhibitor are similar to those associated with type β transforming growth factor.

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Research was sponsored by the USPHS under Interagency Agreement 40-1268-82, Grant 5R01 CA34695 awarded by the National Cancer Institute, Department of Health and Human Services, and the Office of Health and Environmental Research, U. S. Department of Energy, under contract DE-AC05-840R21400 with the Martin Marietta Energy Systems, Inc.

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