A study for cancer gene therapy through Fas-mediated apoptosis

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We examined the antitumor activity of anti-Fas Ab (Jo2) and soluble recombinant FasL (rFasL) against MH134 cells transfected with Fas cDNA (F6B). Original MH134 cells do not express Fas and are refractory to Fas-mediated apoptosis. In vitro, rFasL and Jo2 (200ng/ml) induced complete cell death of F6b when determined with MTT assay. This cell death was proved to be through apoptosis by Hoechist staining. On the other hand, in vivo, we investigated antitumor effects of rFasL and Jo2 on F6b using double-mutant mice (C3H-gld/gld ・ Ipr/Ipr). Both therapeutic agents induced temporary antitumor effects but did not produce complete cure of tumors in any mice. Recently, it has been reported that many tumors express Fas antigen on their cell surface. Therefore, we established C8h line by transfecting Fas cDNA to MM2 cells which constitutively express Fas at a low level but are resistent to Fas-mediated apoptosis. In vitro, C8h cells were killed through apoptosis completely with rFasL but partially with Jo2. The result suggests that rFasL and Jo2 may bind to different epitopes on Fas antigen and induce apoptosis through different signal pathways. In addition, rFasL appears to be superior to Jo2, because tumor cells developed the resistance to Fas-mediated apoptosis more easily when treated with rFasL than Jo2.