Establishment of highly metastatic variants of murine colon adenocarcinoma 26 under serum-free conditions.

Tumor cell variants were established in vitro by treating a metastatic variant of murine colon adenocarcinoma 26 (P-26-select) in serum-free RPMI 1640 medium for 6 to 10 weeks. Five tumor cell lines were established from independent cultures and designated PS-1 to PS-5. The PS cells showed higher growth potential in vitro under serum-free or low-serum conditions than the parental P-26-select. In comparison to P-26-select, the PS cell lines possessed enhanced lung-colonizing ability after i.v. inoculation and metastasized spontaneously to the lung following s.c. inoculation into the flank or the right fore-footpads of BALB/c mice. Metastatic nodules were also observed in the liver. Spleens and livers of the tumor-bearing mice were enlarged mainly as a result of hematopoiesis, suggesting the production of CSF-like substance(s) by the tumor cells. The PS cells secreted increased amounts of putative autocrine growth factor(s) and CSF-like substance(s) in vitro. These characteristics might be related to the in vivo metastatic ability of the PS cells.