title: Mechanisms of thymidine kinase/ganciclovir and cytosine deaminase/ 5-fluorocytosine suicide gene therapy-induced cell death in glioma cells.
abstract: Suicide gene transfer using thymidine kinase (TK) and ganciclovir (GCV) treatment or the cytosine deaminase (CD)/5-fluorocytosine (5-FC) system represents the most widely used approach for gene therapy of cancer. However, molecular pathways and resistance mechanisms remain controversial for GCV-mediated cytotoxicity, and are virtually unknown for the CD/5-FC system. Here, we elucidated some of the cellular pathways in glioma cell lines that were transduced to express the TK or CD gene. In wild-type p53-expressing U87 cells, exposure to GCV and 5-FC resulted in a weak p53 response, although apoptosis was efficiently induced. Cell death triggered by GCV and 5-FC was independent of death receptors, but accompanied by mitochondrial alterations. Whereas expression of Bax remained unaffected, in particular, GCV and also 5-FC caused a decline in the level of Bcl-2. Similar findings were obtained in 9L and T98G glioma cells that express mutant p53, and also underwent mitochondrial apoptosis in both the TK/GCV and CD/5-FC system. Upon treatment of 9L cells with 5-FC, Bcl-xL expression slowly declined, whereas exposure to GCV resulted in the rapid proapoptotic phosphorylation of Bcl-xL. These data suggest that TK/GCV- and CD/5-FC-induced apoptosis does neither require p53 nor death receptors, but converges at a mitochondrial pathway triggered by different mechanisms of modulation of Bcl-2 proteins.
authors.affiliation: Institute of Molecular Medicine, Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Fischer
authors.forename: Sabine
authors.initials: S
authors.lastname: Steffens
authors.forename: Susanne
authors.initials: S
authors.lastname: Frank
authors.forename: Nikolai G
authors.initials: NG
authors.lastname: Rainov
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: Christof M
authors.initials: CM
authors.lastname: Kramm
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D045744:Cell Line, Tumor; D043525:Cytosine Deaminase / Q000235:genetics*; D005437:Flucytosine / Q000494:pharmacology*; D015774:Ganciclovir / Q000494:pharmacology*; D041722:Genes, Transgenic, Suicide / Q000187:drug effects*; D015316:Genetic Therapy / Q000379:methods*; D005910:Glioma / Q000628:therapy*; D006801:Humans; D008928:Mitochondria / Q000502:physiology; D009154:Mutation / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis / Q000378:metabolism; D051381:Rats; D013937:Thymidine Kinase / Q000235:genetics*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D005437:Flucytosine; D013937:Thymidine Kinase; D043525:Cytosine Deaminase; D015774:Ganciclovir