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

Fas/APO-1 (CD95) is a cell surface receptor which mediates apoptosis w hen ligated by specific antibodies or by its recently cloned natural l igand, FasL. We have studied the cytotoxic potential of Fast in vivo u sing Fas/APO-1-expressing Yac-1 cells as targets. Supernatant harveste d from Neuro-2a cells transfected with the murine Fast cDNA contains F ast and transduces a potent apoptotic signal to Yac-l cells in vitro. Specificity of Fast-mediated cytotoxicity was con firmed by competitio n assays using soluble Fas or anti-Fas/APO-1 F(ab')(2) fragments which specifically interfere with FasL-Fas/APO-1 interactions. Intraperiton eal 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 fragmentatio n and nuclear changes typical of apoptosis. As previously shown, intra peritoneal 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: 8 06) and was observed at doses which did not reduce Yac-l cell viabilit y. In contrast, Fast did not induce histopathology in the liver when a pplied intraperitoneally at doses cytotoxic for Yac-l cells. However, intravenous administration of Fast induced lethal liver hemorrhages an d hepatocyte apoptosis. Thus, locally applied Fast kills tumor cells v ery efficiently without systemic toxicity and may therefore represent a candidate for local tumor treatment.