ABSTRACT
Advances in tumor biology research have led to the possibility of early detection of cancers and rational intervention of cancer development using chemopreventive agents. A significant number of potential chemopreventive agents have been identified from epidemiological surveys, independent research efforts, clinical data or based on structural homology with known chemopreventive agents. We have developed a fast, reliable in vitro model for screening potential chemopreventive agents using inhibition of anchorage-independent growth of a human lung tumor cell line, A427.A427 cells were plated in soft agarose containing a known chemopreventive agent, 13-cis-retinoic acid as the test agent and allowed to develop colonies for 28 days. A cytotoxicity test was used concurrently with anchorage independent assay for measuring the relative survival of cells to ensure that any observed inhibition of anchorage independent growth is due to the biological activity of the chemopreventive agent and not due to cellular toxicity. At the end of 28 days of growth, the stained colonies were enumerated, and the inhibition of spontaneous colony formation was measured. 13-cis-Retinoic acid inhibited the growth of A427 colonies in a concentration dependent manner. Data from 25 successive experiments indicate that a concentration of 33 microM consistently inhibited colony formation by 66.2 +/- 16.5 percent, ranging from 27 to 96.1% inhibition. This assay is a useful tool for screening potential chemopreventive agents, as it uses human cells as substrates rendering the efficacy data feasible for direct extrapolation to humans.
