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We evaluated the gain in long-term survival of BDIX rats bearing DHDProB colon cancer developed in the peritoneal cavity after in vivo therapy with the tk gene and GCV. The sensitivity and the bystander effect of DHDProB cells stably transduced with the tk gene evaluated in vitro were low, as one tk+ cell killed two tk- cells. This correlated with the low ability of a fluorescent dye to diffuse through gap junctions. In vivo, more than 75% of tk-transduced cells were required and at least 100 mg/kg/day of GCV had to be injected no later than day 5 after tumor implantation to obtain a curative effect. A partial protection of the cured animals against rechallenge with the parental cells was also observed. Based on these results, a protocol of in vivo gene therapy was designed in which the tk/GCV treatment was combined with IL-2 gene expression. When the tk- and IL-2 encoding plasmids were injected twice i.p. with DOTAP and the animals treated with GCV, three of five rats were cured. This antitumoral activity resulted from the combined toxic effects of DNA/DOTAP and tk/GCV plus a potential immune response mediated by IL-2. [ABSTRACT FROM AUTHOR]

Echinococcus multilocularis protoscolices collected from experimentally infected jirds were incubated for 2 weeks in rat hepatic cell cultures cocultivated with or without feeder cells (BALB/c 3T3 and IAR 20). Scanning and transmission electron microscopy studies were performed during the course of the culture period. Kupffer cells (Kc) were seen adhering to the anterior and posterior ends of the protoscolices. Some protoscolices were fixed to the cell monolayer by a cluster of Kc adhering to the posterior end of the parasite. These cells were phagocytosing the glycocalyx and the electrondense distal end of the microthrix of the protoscolex tegument. An alteration in the superficial tegumental cytoplasm with extensive mitochondrial damage was also noted. The properties expressed by Kc against protoscolices in vitro might also be relevant for proliferation of metacestodes in vivo. [ABSTRACT FROM AUTHOR]

Gene therapy via the herpes simplex virus thymidine kinase (tk) gene and ganciclovir (GCV) treatment eliminates experimental tumors. In this approach, cells expressing the tk gene (tk+) and neighboring tumor cells which do not express the gene are killed. We have demonstrated this bystander effect is enhanced in vitro by gap junctional intercellular communication (GJIC). In order to extend our in vitro results into in vivo situations, we injected into nude mice different ratios of tk+/tk- HeLa cells, either lacking or transfected with connexin43 (Cx43), a gene coding for a gap junction protein. When GCV was administered before tumors were palpable, fewer animals developed tumors, even after a longer period, if the injected cells were mixtures of Cx43+-tk+ and Cx43+-tk- while tumor growth was not prevented with mixtures of HeLa cells not expressing Cx43, ie Cx43--tk+/Cx43--tk-. When GCV was given after the appearance of tumors, the size of the tumors from Cx43- cells was 30% reduced for 3 weeks if 50% of the injected cells were tk+. However, for cells expressing Cx43, the tumor size was 66% reduced if 10% of the cells were tk+. Such a reduction demonstrates a long-term bystander effect which is dependent on Cx43 expression. [ABSTRACT FROM AUTHOR]

In tumors, gap junctional intercellular communication (GJIC) is usually down-regulated and the expression of connexins, membrane proteins constituting gap junction channels, is often low or altered. GJIC, allowing the intercellular diffusion of ganciclovir (GCV) triphosphate, is also one mediator of the ‘bystander effect’, the phenomenon by which herpes simplex virus thymidine kinase (HSVtk)-transduced, neoplastic cells kill surrounding HSVtk-negative cells when treated with GCV. We set up experiments to evaluate the effects of retrovirus-mediated in vivo gene transfer of connexin 43 in malignancies with low GJIC capacity. We found that U-87 human glioblastoma cells transfected in vitro by the human Cx43 cDNA grow signifi- cantly more slowly than control U-87 cells and lose their tumorigenicity when injected subcutaneously in nude mice. When the Cx43 gene was transduced in vitro in U-87 cells by a retroviral producer cell line (N3.2.ii, titer 1.5 × 106 c.f.u./ml) in vivo results were similar. However, only when U-87 cells were co-injected with N3.2.ii cells in nude mice in a 1:5 ratio, a 50% reduction in tumor size was obtained during the first 3 weeks. Moreover the co-injection of U-87 cells with N3.2.ii and SBA cells (a retroviral producer cell line expressing the HSVtk gene), was not able to potentiate the effects of GCV administration, suggesting that Cx43 gene transfer requires more efficient vectors to increase the bystander effect in vivo. [ABSTRACT FROM AUTHOR]