Establishment of a new strategy for colorectal cancer gene therapy by controlling Wnt-signal molecules

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Recent studies indicate that the activation of Wnt-signal pathway, which is composed of the sequential reactions including loss of APC function, resulting accumulation of beta-Catenin and the activation of the down-stream target gene such as c-Myc via transcriptional factors, is deeply involved in the colorectal carcinogenesis. It might be possible to suppress the tumor growth by controlling theses Wnt-signal molecules.For this purpose, two strategies are planned. One is to construct some vector systems, which enable to decrease the level of beta-Catenin in colon cancer cells. The other is to set up the toxic gene therapy, where the up-regulated signal pathway toward c-Myc is connected to express some toxic genes such as DT-A.Strategy 1. Construction of the beta-Catenin down-regulation vector and its application of gene therapyThe entire length of APC gene is very huge and disadvantageous for gene transfer. On the other hand, the central one third portion of APC gene (1260-2056 a.a.) i … More s essential for beta-Catenin degradation. This smaller portion (it is called, APC-Core) functions like a scaffold protein. The APC-Core was put under the control of the various promoters including CMV and MT promoter. These vectors have some potential to induce the apoptosis, when introduced into the colorectal cancer cell lines. Then, in vivo utility of theses vectors were examined. One colorectal cancer cell line, DLD-1 was inoculated in the nude mice to analyze the in vivo gene transfer efficiency. Adenoviral gene transfer and electroporation were adapted. It was indicated that the adenovial method was much more efficient than the electroporation. In the view point of the curability, even by the adenovial method, cancer cell could not be driven away completely from the host. Repetitious use of the adenovirus is thought to diminish its effectiveness mainly due to its immunogenisity. The APC-Core has some potential to induce the apoptosis in the colorectal cancer, but some efficient gene transfer methods into colorectal cancer must be established.Strategy 2. Construction of the colorectal cancer specific toxic gene therapyThe signal to c-Myc activation was utilized to this strategy. The 5' promoter region of c-Myc was connected to the minimum promoter and DT-A gene. This regulation is not so tight and specific toxicicity in the colorectal cancer cell lines could not be achieved. Less