Fig. 1

Repetitive passaging over the liver resulted in altered colonization of target organs after i.v. injection. A A scheme illustrates the serial injections and the hepatic passaging of WT31 melanoma or its sublines. WT31 was injected i.v.. After 21 days livers were excised and metastases were smashed through a cell strainer to get a single cell suspension. To expand these cells, they were taken back into cell culture. Last, sublines were again injected i.v.. This cycle was repeated five times generating the subline WT31_P5IV. B The ratio of lung to liver metastases of WT31 or WT31_P5IV was calculated and is shown (P = 0.0005, Mann–Whitney test) C, D 0.5 × 10⁶ WT31 and WT31_P5IV melanoma cells were injected i.v. and mice were sacrificed at day 21. C Macroscopic visible lung metastases were quantified. The numbers of macroscopic lung metastases of WT31 or WT31_P5IV melanoma are displayed (P = 0.0077, Mann–Whitney test). A pooled analysis of three different experiments is presented. Representative images of colonized lungs are shown. Scale bars = 1 cm. D Macroscopic visible liver metastases were counted. The number of macroscopic liver metastases of WT31 or WT31_P5IV are presented (P = 0.0531, t-test). Representative images of colonized livers are shown. Scale bars = 1 cm. E The size of liver metastases of WT31 or WT31_P5IV was measured and is presented in mm.² (P = 0.6709, t-test)