942. Combinatorial Treatment with Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) Gene and a Chemotherapeutic Agent Suppressed Hepatic Metastasis of Colon Carcinoma

As a therapeutic approach to eradicate highly malignant neoplasms including metastatic liver tumors, a powerful, specific and systemically applicable tool that directly destroys tumor cells is required. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various transformed cells, while most normal cells are unsusceptible to the TRAIL-mediated apoptosis induction. In the present study, we evaluated therapeutic efficacy of intravascular TRAIL gene therapy against multiple hepatic metastasis model in mice. A chemotherapeutic agent, actinomycin D, was also administered to assess whether the tumoricidal activity of the TRAIL is further improved by the combination therapy. First, recombinant human TRAIL (rTRAIL) was added to the CT-26 (murine colon carcinoma) in culture in the presence or absence of 10 ng/ml actinomycin D, and cell proliferation and apoptosis were assessed in vitro by means of the tetrazolium and flow cytometric analyses. The treatment with rTRAIL alone failed to affect viability of CT-26 cells, while rTRAIL plus actinomycin D treatment effectively induced apoptosis in a dose dependent fashion. Anti-tumor effect in vivo of the TRAIL plus actinomycin D treatments was then investigated. pGEG.TRAIL was constructed so that the plasmid encoding the 3[variant prime] extracellular domain of human TRAIL fused with a secretory signal sequence. When the vector construct was intravenously transfected into mice, a considerable concentration of TRAIL molecule was detected in the sera of the animals, whereas delivery of a wildtype TRAIL construct did not result in a significant elevation of the genetic product in the murine sera. To establish liver metastasis, CT-26 cells were injected into the spleen of syngenic BALB/c mice (day 0). On days 1 and 8, mice received intravascular transfection with pGEG.TRAIL or pGEG.4 (a control plasmid), while actinomycin D was intraperitoneally injected into some groups of mice. The mice were sacrificed on day 14, when the numbers of metastatic nodules were revealed to be 63.8±31.5 (untreated), 49.4±21.0 (pGEG.4 plus actinomycin D), 52.3±32.7 (pGEG.TRAIL alone) and 14.8±17.3 (pGEG.TRAIL plus actinomycin D). The statistical analyses demonstrated that combination treatment significantly suppressed the liver metastasis in comparison with the untreated and pGEG.4 plus actinomycin D groups (p=0.015 and 0.021, respectively). All of the mice given injections with either the pGEG.sTRAIL or actino