Modulation of human tumor colony growth in soft agar by serum

The factors controlling the growth of human tumor cells in soft agar are poorly understood. However, it has been demonstrated that serum provides factors which promote anchorage-independent growth. We tested 58 tumor specimens, which were obtained from patients with adenocarcinoma of the lung, colon, ovary or squamous cell carcinoma, for their ability to form colonies in soft agar in serum-free or serum-supplemented media. The cells were unable to replicate, and none of the hormones or growth factors tested: insulin (I), transferrin (T), selenium (S), estradiol (E), hydrocortisone (H) or epidermal growth factor (EGF) could substitute for serum. Examination of the serum dose-response curves indicated that growth factors reduced the serum concentrations needed to support anchorage-independent growth. The addition of the supplements and the lowering of serum concentrations increased cloning efficiencies (C.E.) in 38/51 trials, when cells were able to grow initially. The addition of ITS increased C.E. in 18/21 cases, HITES in 15/17 cases and EGF in 12/18 cases as compared to controls. ITS and HITES increased the number of colonies only when serum was the limiting factor. EGF, however, increased the number of colonies even when serum was not the limiting factor. The ability of the supplements to enhance growth could not be correlated to tumor type or initial cloning efficiencies. However, in only 1/25 cases were cells that were unable to form colonies under standard conditions induced to form colonies in the presence of the growth factors. Normal and tumor-derived human fibroblasts did not form colonies in soft agar in the presence of these growth factors. The results suggest that human tumor cells may require the presence of serum-derived factors for growth in soft agar.