| Summary: | 博士 === 國立臺灣大學 === 微生物學研究所 === 100 === Overexpression of HER2 has been frequently detected in many types of human cancer, most notably breast and ovarian cancers. HER2 overexpression is associated with increased angiogenesis, increased metastasis, increased chemoresistance and reduced survival. Inhibition of HER2 in HER2-overexpressing cancers can lead to reduced angiogenesis, reduced chemoresistance and improved survival. Previously, we reported that Simian Virus 40 T/t-common polypeptide can inhibit HER2, suppress the tumorigenic potential of HER2-overexpressing cancer cells and specifically induce apoptosis in HER2-overexpressing human cancer cell lines. In the part I of this thesis, we further explored the effect of T/t-common on tumor angiogenesis. We found that T/t-common could inhibit the ability of HER2-overexpressing cancer cells, but not low HER2-expressing cancer cells, to induce the migration and tube formation of endothelial cells. Reexpression of HER2 could block T/t-common’s activity to inhibit the ability of HER2-overexpressing cancer cells to induce the migration and tube formation of endothelial cells. We further tested whether T/t-common could affect HER2-overexpressing cancer cells to express and secrete angiogenic and anti-angiogenic factors. We found that T/t-common could inhibit the expression of proangiogenic factor VEGF-A, IL-8, bFGF, uPA and MMP-2, and induce the expression of anti-angiogenic factor TSP-1and TIMP-1 in HER2-overexpressing human SK-OV-3 ovarian cancer cells. T/t-common was found to be able to repress the expression of HIF-1α, a transcription factor required for VEGF-A expression, through inhibiting HER2-mediated ERK1/2 activity. Moreover, T/t-common was found to be able to activate p38 pathway, leading to up-regulation of TSP-1. Through regulating HER2-ERK1/2-HIF-1α-VEGF-A and HER2-p38-TSP-1 signaling pathways in HER2-overexpressing cancer cells, T/t-common could inhibit these cancer cells to recruit endothelial cells, leading to inhibition of angiogenesis in HER2-overexpressing tumors. Two experiments described below demonstrated that T/t-common indeed can inhibit tumor angiogenesis. First, in Matrigel plug assays, we demonstrated that conditioned medium from T/t-common-transduced SK-OV-3 cancer cells had lower ability to induce blood vessel formation in Matrigel plugs than that from control SK-OV-3 cells. Second, infection of adenovirus carrying T/t-common gene could lead to inhibition of the growth and microvessel formation of SK-OV-3 tumors in NOD/SCID mice model. Taken together, the above suggest that T/t-common had the potential to be developed as a new antiangiogenic agent specific for treating HER2-overexpressing ovarian cancers.
In the part II of this thesis, we investigated whether T/t-common could enhance the sensitivity of HER2-overexpressing human cancer cells to chemotherapeutic agents such as cisplatin (CDDP) and doxorubicin (DXR). We found that T/t-common could specifically enhance the sensitivity of HER2-overexpressing human cancer cells, but not that of HER2 low-expressing human cancer cells, to CDDP and DXR. T/t-common could specifically enhance CDDP- or DXR-induced apoptosis by activating caspase-3 activity in HER2-overexpressing cancer cells. T/t-common expression led to down-regulation of Bcl-2 and Bcl-XL, inhibition of ERK activity, and activation of JNK activity in CDDP- or DXR-treated HER2-overexpressing BT-474 cancer cells. This modulation of apoptosis regulatory molecules by T/t-common may contribute to its ability to enhance CDDP- or DXR-induced apoptosis in HER2-overexpressing cancer cells. Finally, we showed that T/t-common could enhance the antitumor activity of DXR on HER2-overexpressing SK-OV-3.ip1 tumor in NOD/SCID mice. Together, these data demonstrated that T/t-common could sensitize HER2-overexpressing cancer cells to chemotherapeutic agents CDDP or DXR, and suggest that combination therapy using T/t-common gene and chemotherapeutic agents (such as CDDP or DXR) may overcome tumor chemoresistance and thus provide a new approach for treatment of HER2-overexpressing cancers.
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