Conditional blockage of TGF-beta signaling using a suicide system HSV-TK in mouse bone marrow cells: an improved gene therapy approach in cancer treatment

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In our previous studies we have utilized a dominant negative TGF-beta type II receptor (TbRIIDN) to block the TGF-beta signaling in mouse bone marrow cells (BMC). When challenged with B16-F10 melanoma cells and TRAMPC-2 mouse prostate cancer cells, TbRIIDN mice were resistant to tumor challenge while control mice were all succumbed to tumor burden. However, TbRIIDN mice developed inflammatory diseases and eventually died from autoimmunity. To utilize TbRIIDN as a powerful tool in cancer treatment and prevent the development of autoimmunity, we used a suicide approach employing a HSV-TK/ganciclovir system. In the present study, we made a fusion protein TbRIIDN-TK that blocks TGF-beta signaling and at the meantime could be regulated through administration of ganciclovir. Using a mouse stem cell virus that harboring TbRIIDN-TK, moue BMC were transduced and TK gene expression was revealed by RT-PCR in infected BMC. When treated with TGF-beta, PAI-1/luciferase assay demonstrated that TbRIIDN-infected BMC had no elevated luciferase activity while control vector Trans-TK infected BMC showed an increased luciferase activity in response to TGF-beta treatment. More importantly, after administration of ganciclovir, TbRIIDN infected BMC showed no proliferation and were non viable while vigorous proliferation was observed in control vector infected BMC. In summary, TbRIIDN-TK/ganciclovir suicide system provides means to regulate TbRIIDN gene expression in treatment of cancer and prevention of autoimmunity.