Implantation of human colorectal carcinoma cells in the liver studied by in vivo fluorescence videomicroscopy

In vivo fluorescence videomicroscopy (IVFM) was used to analyse the behavior of weakly and highly metastatic human colorectal carcinoma (CRC) cells during implantation in the liver. A highly metastatic human CRC cell line, CX-1, and a weakly metastatic line, Clone A, were double-labeled with rhodamine B isothiocyanate-dextran (Rd-Dx) to locate cells and with calcein AM to assess cell metabolic activity in an experimental metastasis model. Double-labeled CRC cells (2.0 x 10⁶) were injected into the spleens of groups of nude mice and the livers observed by IVFM over the next 72 h. CRC cells were implanted within 30 s after injection into either portal venules or the proximal third of hepatic sinusoids. Approximately 0.5% of CRC cells traversed the liver through portal-central venous shunts and implanted in the lung. The number of CX-1 cells in the liver was similar to that of Clone A cells during the first 12 h. However, more CX-1 cells than Clone A cells remained in the liver at 24 h and were in groups of and 12 cells whereas only a few, single Clone A cells were detected in the liver at 72 h. Not all Clone A cells are committed to die within 4 h of implantation because cells harvested 4 h after hepatic implantation proliferated normally in vitro when removed from the hepatic microenvironment. Since the stress of mechanical deformation during implantation may cause differences in cell survival, CX-1 and Clone A cells were passed through filters with 8 μm pores in vitro at 10-15 cm of water pressure to recreate the trauma of hepatic implantation. Approximately 50% of both CX-1 and Clone A cells were lysed. Furthermore, both CRC lines remained metabolically active when co-cultivated with liver cells for at least 24 h in vitro. Thus, the difference in metastatic potential between the two CRC lines may reside in their response to the combination of mechanical implantation and subsequent growth in the liver parenchyma.