LOCAL FAS/APO-1 (CD95) LIGAND-MEDIATED TUMOR-CELL KILLING IN-VIVO

Fas/APO-1 (CD95) is a cell surface receptor which mediates apoptosis when ligated by specific antibodies or by its recently cloned natural ligand, FasL. We have studied the cytotoxic potential of Fast in vivo using Fas/APO-1-expressing Yac-1 cells as targets. Supernatant harvested from Neuro-2a cells transfected with the murine Fast cDNA contains Fast and transduces a potent apoptotic signal to Yac-l cells in vitro. Specificity of Fast-mediated cytotoxicity was con firmed by competition assays using soluble Fas or anti-Fas/APO-1 F(ab')(2) fragments which specifically interfere with FasL-Fas/APO-1 interactions. Intraperitoneal injection of Fast-containing supernatant efficiently killed Yac-l target cells which had been implanted in capsules into the peritoneal cavity of mice. Analysis of the target cells revealed DNA fragmentation and nuclear changes typical of apoptosis. As previously shown, intraperitoneal injection of anti-Fas/APO-1 antibodies caused liver failure (Ogasawara, J., Watanabe, F.R., Adachi, M., Matsuzawa, A., Kasugai, T, Kitamura, Y., Itoh, N., Suda, T. and Nagata, S., Nature 1993. 364: 806) and was observed at doses which did not reduce Yac-l cell viability. In contrast, Fast did not induce histopathology in the liver when applied intraperitoneally at doses cytotoxic for Yac-l cells. However, intravenous administration of Fast induced lethal liver hemorrhages and hepatocyte apoptosis. Thus, locally applied Fast kills tumor cells very efficiently without systemic toxicity and may therefore represent a candidate for local tumor treatment.