Environmental modulation of the expression of differentiation and malignancy in six human squamous cell carcinoma...

Cell lines from six human squamous cell carcinomas exhibiting different degrees of differentiation and malignancy were studied under in vitro and in vivo growth conditions. The stability of phenotypic traits of these carcinoma cells and their sensitivity to environmental influences were analyzed to further elucidate the interdependency of differentiation and malignancy expressed under experimental conditions. In conventional (submerged) cultures the cell lines exhibited unique growth patterns with an individual but generally poor expression of differentiation (stratification). In a new organotypical culture assay where the cells grew on lifted collagen gels at the air-medium interface, three-dimensional structures were formed exhibiting organizational features and degrees of differentiation similar to those of the respective tumors. Both in tumors formed after s.c. injection of cells and in transplants (performed with silicone chambers on the dorsal muscle fascia) in nude mice, an enhancement of the individually distinct pattern of differentiation was observed. While anchorage independent growth was an unreliable marker for malignancy, all six lines were tumorigenic after s.c. injection into nude mice. However, the tumor yield (20 to 100%) and latency period (2 to 12 weeks) varied considerably. In contrast all lines exhibited (within 1 to 2 weeks) invasive growth in 100% of animals after transplantation onto the dorsal muscle fascia. All tumors (squamous carcinomas) and invading cells were identified as epithelial and as human by specific antibodies. The two new test systems, the organotypical culture assay in vitro and the transplantation assay in vivo, proved to be reliable and sensitive models also for human squamous carcinoma cells to analyze their differentiative and malignant potential. In comparing the individually maintained degrees of differentiation and malignancy in the different test systems, it was apparent that, opposite to the prevailing opinion, cell lines with the highest differentiation potential were at least as malignant as were the least differentiated ones.