PHENOTYPIC PROPERTIES OF CULTURED TUMOR-CELLS - INTEGRIN ALPHA-IIB-BETA-3 EXPRESSION, TUMOR-CELL-INDUCED PLATELET-AGGREGATION, AND TUMOR-CELL ADHESION TO ENDOTHELIUM AS IMPORTANT PARAMETERS OF EXPERIMENTAL METASTASIS

The present study was undertaken to investigate the factors involved i n determining the metastatic potential of cultured cells derived from solid tumors. We first investigated the effects of cell source and cul ture conditions on lung colony formation by i.v. injected B16a (B16 am elanotic melanoma) cells and inhibition of tumor colony formation by t he thromboxane A2 synthase inhibitor, CGS14854. Prolonged culture resu lted in a 10-fold decrease in the incidence of B 16a lung colonies, wh ereas passage in vivo for 150 days did not affect lung colony formatio n by tumor cells isolated from enzymatic dispersates by centrifugal el utriation. Cultured B16a cells maintained at low density (LD) and harv ested at low passage (LP) formed significantly more lung colonies than B 16a cells harvested at high densities (HD) or high passage (HP). Ov er-confluent tumor cells produced even lower number of lung colonies. Lung colony formation by elutriated B16a cells (i.e., cells freshly is olated from tumor tissue) was consistently inhibited by CGS 14854, whe reas inhibition of lung colony formation by cultured B16a cells was de pendent upon culture conditions. CGS 14854 was ineffective or less eff ective against HD/HP B16a cells. The differences in lung colony format ion between LD, HD and elutriated B16a cells were not due to different ial cell-cycle distribution. Mechanistic studies indicated that LD/LP tumor cells induced aggregation of homologous platelets, whereas HD/HP B 1 6a cells failed to induce significant platelet aggregation. Aggre gation of homologous platelets correlated positively with lung-coloniz ing ability. Additionally, LD/LP cells demonstrated higher adhesion to endothelium than HD/HP B16a cells. Finally, LD/LP B16a cells expresse d higher levels of alpha(IIb)beta3 integrins than HD/HP tumor cells, a s determined by flow cytometry and immunofluorescence.