Differential tumorigenicity of growth factor-dependent versus -independent CCL39 lung fibroblast lines in nude mice

Several cell lines derived from CCL39 Chinese hamster fibroblasts were characterized so that comparison could be made of their tumorigenic potential and their ability to proliferate in vitro in response to growth factor stimulation. Tumor formation was assessed by implanting single-cell suspensions into the flanks (sc), peritoneal cavity (ip), or tail vein (iv) of BALB/c athymic nude mice, whose ages ranged from 8-10 days (neonatal), to 5-7 weeks (adult), to more than 5 months (old). Serum, insulin (INS), epidermal growth factor (EGF), and alpha-thrombin (THR) were tested for promoting short-term cell proliferation in serum-free medium. CCL39 fibroblasts arrestable in the Go phase required INS and EGF or THR to divide optimally. They formed sc tumors after a long latent period and only in the young and adult mice. Among such tumors, those composed of growth factor-independent variants became lethal ip and iv and grew sc earlier and rapidly in all age groups. These properties were shared by polyomavirus-transformed CCL39 fibroblasts and 1 mutant that divided without growth factors. Mutants that escaped only partially the growth factor requirements had been implanted ip but not iv. They grew at the sc site in newborn and adult mice, with kinetics comparable to that of CCL39 cells. Their expansion in old animals was variable, transient or slow. Neither CCL39 nor 39T10 tumor cells were susceptible to cytotoxic reactions mediated by activated macrophages or natural killer cells. These observations indicate that distinct anatomical regions in nude mice and factors related to their age contribute to present CCL39 heterotransplants with environments that are more or less permissive to their growth. These observations also suggest that cells that achieve growth factor autonomy are more malignant than cells in which growth factor controls of division are less stringent but not abrogated.