Comparison of Growth Requirements of Two Human Intratumoral Colon Carcinoma Cell Lines in Monolayer and Soft Agarose

The human colon, intratumoral subpopulations HCT 116 and HCT 116a were established in chemically defined medium supplemented with transferrin, insulin, epidermal growth factor (EGF), triiodothyronine, hydrocortisone, and sodium selenite. The responsiveness of the adapted cell lines to these growth factors was compared in anchorage-dependent and -independent assays. HCT 116 cells maintained in serum-free conditions were further adapted to growth factor deprivation, and the effects of these polypeptides were determined in anchorage-independent assays. In monolayer, HCT 116 cells adapted to grow in serum-free medium responded to transferrin but not to EGF or insulin. Similarly adapted HCT 116a cells were, however, insensitive to transferrin addition but manifested a 300 and 500% increase in growth rates with EGF and insulin, respectively. Optimal growth of HCT 116 cells was seen in the presence of insulin and transferrin, while maximum proliferation of HCT 116a cells depended on combined insulin, transferrin, and EGF. In soft agarose, both HCT 116 and HCT 116a subpopulations showed a stringent requirement for transferrin. No combination of growth factors without transferrin supported colony formation. These data suggest that (a) these colon tumor subpopulations may be subject to separate growth controls, and (b) there may be an important role for transferrin in anchorage-independent growth and possibly in the maintenance of malignant characteristics.