Selection of B16 melanoma cells with increased metastatic potential and low intercellular cohesion using Nuclepore filters.

A method was developed to isolate tumor cell variants which penetrate filter pores 10 X smaller than their cell diameter. Variants with very high penetration ability in a standard filter assay showed increased metastatic capacity compared to non-selected cells when assayed in vivo with intramuscular injection and removal of the primary tumor, or in a subcutaneous injection assay with the primary tumor left intact. The parent cell line, as well as randomly chosen clones displayed less metastatic capacity, which correlated with correspondingly reduced filter penetration rates. A characterization of the cells so far analyzed in vitro showed that selection through Nuclepore filters led to increased invasive spread, reduced intercellular cohesion and a somewhat higher motility. The B16 melanoma cells tested so far which showed this in vitro behavior had increased metastatic capacity, suggesting that such traits may be involved in metastatic behavior of the B16 melanoma. The procedure described for the isolation of variant tumor strains should provide cells which will help to analyze penetration phenomena in metastasis.