Protein synthesis but not DNA synthesis is required for tumor cell invasion in vitro

The effects of protein and DNA synthesis inhibitors on in vitro tumor cell invasion was studied in a quantitative invasion system using human amnion. Highly invasive M5076 tumor cells were incubated on the basement membrane (BM) of the amnion in the presence of cycloheximide, aphidicolin or sodium butyrate. Tumor cell penetration through the entire thickness of the amnion was measured after 24 h. Protein synthesis in the M5076 cells was inhibited 95% within 1 h by 10(-6)M cycloheximide while DNA synthesis was unaffected. Treatment with cycloheximide reduced the number of spontaneously invading cells by 82% and by 66% in the presence of the chemoattractant, formylmethyl leucine-phenylalanine (FMLP), known to stimulate invasiveness. DNA synthesis in the M5076 tumor cells was selectively inhibited with aphidicolin (10 micrograms/ml). Although the DNA synthesis was greatly reduced, no significant effect on invasiveness with or without FMLP was observed. A less specific inhibitor of DNA synthesis, sodium butyrate (1 mM), arrested cell proliferation in the G1 phase of the cell cycle. When the butyrate-treated M5076 cells were tested in the invasion assay, a 50% increase in the number of invasive cells was observed. All three inhibitors were used in concentrations that did not affect cell viability or cell attachment to the amnion. These data indicate that protein synthesis but not DNA synthesis and not cell proliferation are required for tumor cells to invade native connective tissue barriers in vitro.