Correlation of anchorage-independent growth with tumorigenicity of chemically transformed mouse epidermal cells.

The BALB/c mouse primary epidermal cell culture sys tem is currently being developed as a model system for chemical carcinogenesis studies with the immediate aims of achieving a high incidence of chemically induced trans formation and developing rapid assays fortumorigenicity. Primary cultures treated with N-methyl-(V -nitro-N-nitrosoguanidine (1 to 2 /«g/ml) at 0 to 3 days postplating, followed in some cases by phorbol ester treatment, yielded after 3 to 4 months six morphologically altered long-term cell strains of which three were tumorigenic, as determined by injection into syngeneic newborns. One phorbol ester control yielded a tumorigenic strain while two solvent controls gave rise to long-term strains that were nonmalignant. All strains examined showed the presence of intercellular intermediate junctions, an epi thelial marker. No morphological feature distinguished tumorigenic from nontumorigenic strains. Growth rate in monolayer culture and growth in semisolid medium were investigated as potential correlates of tumorigenicity in 16 morphologically altered epidermal cell strains. Al though the tumorigenic cell strains showed a trend toward shorter doubling times, rapid growth in monolayer culture was not a consistent correlate of tumorigenicity. In con trast, colony formation in 0.33% agar medium consistently correlated with tumorigenicity, with all tumorigenic strains positive and all nontumorigenic strains negative. Colonyforming efficiency in soft agar, a parameter that was influenced by initial cell density and serum concentration, did not consistently parallel the degree of tumorigenicity.