利用猴病毒四十型 T/t-common合併 GM-CSF治療Neu大量表現的小鼠腫瘤

Abstract

HER2/neu proto-oncogene is a member of epidermal growth factor receptor family. Overexpression and amplification of HER2/neu is found in many types of human cancer, including ovary, breast, lung, bladder, colon and gastrointestinal cancers. Overexpression of HER2/neu in cancers is correlated with enhanced metastasis, angiogenesis, and chemoresistance, and poor prognosis. Therefore treatment of HER2/neu-overexpressing cancers has become an urgent issue in cancer therapy. Previously we reported that simian virus 40 (SV40) T/t-common polypeptide, which contains the N-terminal common domain of SV40 large T and small t antigens, could specifically induce apoptosis in HER2/neu-overexpressing human cancer cell lines but not in non-transformed cell lines and HER2/neu low-expressing human cancer cell lines. In this study, we investigated the anti-tumor effect of combination therapy using T/t-common and granulocyte macrophage colony-stimulating factor (GM-CSF), which can enhance the tumor-antigen presentation capacity of dendritic cells and is one of the most potent cytokines used in cancer immunotherapy. Since T/t-common is known to be able to induce apoptosis of HER2/neu-overexpressing cancer cells, it is possible that GM-CSF may enhance the anti-tumor effect of T/t-common by inducing anti-tumor immunity. To test the anti-tumor effect of T/t-common plus GM-CSF in immuno-competent mice bearing the neu-overexpressing MBT-2 tumors, we first tested whether T/t-common could induce apoptosis in neu-overexpressing MBT-2 bladder cancer cells. Our data indicated that infection of adenovirus carrying the T/t-common gene (rAd-T/t) could specifically induce apoptosis in neu-overexpressing MBT-2 cancer cells but not in neu low-expressing mouse colon CT-26 cancer cells. We next tested whether treatment of established MBT-2 tumors in syngenic C3H mice with both rAd-T/t and adenovirus carrying the GM-CSF gene (rAd-GMCSF) could lead to greater tumor suppression than treatment with adenovirus carrying either gene alone. We did not get a conclusive result for this experiment primarily due to two reasons: (i) heterogeneous tumor size caused by MBT-2 cancer cells; and (ii) suppression of anti-tumor immune response caused by adenovirus infection. To solve the first problem (i.e., heterogeneous tumor size), we have cloned the MBT-2 cells and tested the growth of these MBT-2-derived clones in syngenic C3H mice. We obtained three MBT-2-derived neu-overexpressing clones which gave homogeneous tumor size and grew at a rate similar or faster than parental MBT-2 cells. These clones can be used in the future experiments. To solve the second problem (i.e., suppression of immune response by delivering vector adenovirus), We tested the possibility of using positive-charged liposome to deliver genes into MBT-2 tumors grown in immuno-competent C3H mice. Our preliminary data indicated that positive-charged liposome could introduce the green fluorescence protein gene into established MBT-2 tumors through intratumor injection. Further studies are needed to demonstrate whether positive-charged liposome could introduce T/t-common and GM-CSF genes into established MBT-2 tumors in C3H mice and whether liposome carrying these two genes could be used to treat neu-overexpressing MBT-2 tumors in immuno-competent C3H mice.