Abstract 1556: A novel tripeptide, tyroserleutide, inhibits irradiation-induced invasiveness and metastasis of hepatocellular carcinoma

Abstract Background: In preliminary studies, we have shown increased intrahepatic and pulmonary metastases of hepatocellular carcinoma (HCC) long-time after radiotherapy using a metastatic human HCC orthotopic nude mice model. Tyroserleutide (YSL), which was authorized by Food and Drug Administration of USA as an orphan drug in September 2004, is a novel small molecule antitumor tripeptide. Previous studies have demonstrated YSL inhibited tumor growth of HCC in animal model. However, its effects on HCC metastasis are still unknown. We investigated YSL effects on the irradiation-induced invasiveness and metastatic potential of HCC and its related mechanism. Methods: The invasiveness of MHCC97L cells in vitro was detected using transwell invasion assay. A metastatic human HCC orthotopic nude mice model of MHCC97L was applied. YSL was administered directly to the model and further to the model postradiotherapy. Effects on tumor growth and pulmonary metastasis were evaluated. Pimonidazole and hypoxia-inducible factor 1α (HIF-1α) were used as hypoxia markers. Hypoxia, matrix metalloproteinase-2 (MMP-2), transmembrane protease serine 4 (TMPRSS4), and epithelial mesenchymal transition (EMT) related proteins (E-cadherin, SIP1, Vimentin, and N-cadherin) were determined by immunohistochemistry, quantitative real-time PCR, and Western blot. Results: YSL inhibited MHCC97L cells proliferation and invasion in vitro with or without irradiation. YSL did not significantly prohibit tumor growth but decreased pulmonary metastasis and prolonged life-span, which correlated with down-regulation of MMP-2. Radiotherapy inhibited tumor growth in early stage and promoted tumor hypoxia. Considering the limited life-span of mice, as well as discharging the effects of tumor load on mice, we adopted “tumor re-inoculation”. Although the replanted tumor volume in radiotherapy group had no significance in statistics as compared to its control, the incidence of lung metastasis increased postradiotherapy (6/6 versus 3/6, P = 0.046). YSL inhibited the growth of replanted tumor with radiotherapy. Furthermore, YSL almost completely inhibited lung metastasis induced by irradiation. YSL at 160 or 320 μg/kg/day significantly reduced lung metastases (1/6 versus 6/6, P = 0.002 for both groups, compared with the radiotherapy group). YSL down-regulated HIF-1α and TMPRSS4, and eventually inhibited EMT (up-regulation of E-cadherin and down-regulation of SIP1, Vimentin and N-cadherin) were associated with its anti-metastasis capability. Conclusions: YSL inhibits the enhanced invasiveness and metastatic potential of HCC induced by irradiation through down-regulation of HIF-1α and TMPRSS4 and inhibition of EMT. YSL may act as a new anti-metastasis agent for the clinical use of combination with radiotherapy. [Supported by China Postdoctoral Science Foundation-funded project (No. 20080440077)] Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1556.