PROGRESSIVE LOSS OF SENSITIVITY TO ENDOTHELIUM-DERIVED GROWTH-INHIBITORS EXPRESSED BY HUMAN-MELANOMA CELLS DURING DISEASE PROGRESSION

Tumor progression is frequently associated with changes in responsiven ess of tumor cells to paracrine growth factors. A potential major sour ce of such paracrine factors in solid tumors are endothelial cells sin ce this type of cell can constitute a sizeable fraction of the cellula r composition of solid tumors. As an initial step to examining the pos sible effects of endothelial cell-associated growth factors on tumor c ell growth, a panel of human melanoma cell lines representative of dif ferent stages of tumor progression was employed for studies utilizing endothelial cell-derived growth modulators. Macrovascular or microvasc ular human endothelial cells from umbilical vein or from skin, respect ively, inhibited melanoma cell growth in direct coculture experiments. The potency of this inhibitory effect diminished as a function of mel anoma progression. Conditioned media from endothelial cell cultures mi micked the effect of the cell coculture experiments, suggesting the in volvement of soluble growth factor(s). Approximately 50-75% of the con ditioned media inhibitory effect was abrogated by addition of the neut ralizing antibody to interleukin-6 (IL-6). Gel filtration chromatograp hy revealed the presence of additional inhibitors in endothelial cell conditioned medium. Two peaks of activity were detected with apparent molecular weights of approximately 100-150 Kd and 20-30 Kd, the latter containing IL-6 activity. Whereas early-stage radial growth phase (RG P) primary tumor-derived melanoma cells were sensitive to at least thr ee different endothelial products of high or low molecular weight (inc luding IL-6), melanoma cells from more advanced metastatic lesions wer e resistant to the latter activities, and retained only partial sensit ivity to the high molecular weight inhibitor. More advanced vertical g rowth phase (VGP) primary melanoma cell lines expressed intermediate i nhibition-sensitive phenotypes. Thus human melanoma development appear s to be associated with progressive loss of sensitivity to the growth inhibitory effects of IL-6 and other factors produced by endothelial c ells. This is likely to be a result of a selection process when tumor cells are confronted with adjacent vasculature during the progress of tu mor angiogenesis. (C) 1994 Wiley-Liss, Inc.