Abstract 4515: Tumor suppressor XAF1 inhibits hepatocellular carcinoma growth and angiogenesis

Background and Aims: X-linked inhibitor of apoptosis (XIAP)-associated factor 1(XAF1) is a novel identified XIAP antagonist and a potential tumor suppressor. Our previous study has shown that stable overexpression of XAF1 could induce apoptosis and inhibit tumorigenesis in hepatocellular carcinoma (HCC). However, the therapeutic effect and mechanism of XAF1 on HCC remains unknown. Materials and Methods: Recombinant adenovirus Ad5/F35-XAF1 and control virus Ad5/F35-Null were generated. Cellular proliferation was detected by methyl thiazolyl tetrazolium (MTT). Cell apoptosis was determined by Flow cytometry using Annexin V-FITC/PI double staining and terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL). The expression of genes was detected by RT-PCR, Western Blot and immunohistochemistry (IHC). Tumor growth in vivo was determined in a nude mice xenograft model. Microvessel density (MVD) was measured by CD31 IHC staining. Results: The expression of XAF1 was extremely low or undectable in four HCC cell lines (SMMC7721, Hep3B, HepG2, Bel7404) and 30 human HCC tissues compared with the paired non-cancer liver tissues, while the high expression of XIAP was detected in HCC tissues than in normal live tissues. Infection of Ad5/F35-XAF1 virus increased the expression of XAF1 in all 4 HCC cell lines, significantly inhibited cell proliferation and induced cell apoptosis in a dose- and -time dependent manner, resulting in the cleavage of caspase-3, −8, −9 and PARP, release of cytochrome c, upregulation of pro-apoptotic protein Bax and BNIP3L, and downregulation of XIAP. Furthermore, intra-tumoral injection of Ad5/F35-XAF1 virus significantly induced apoptosis in vivo and inhibited HCC xenograft growth. Notably, Ad5/F35-XAF1 virus treatment significantly upregulated the expression of angiopoietin-2 protein and decreased MVD in tumor xenograft tissues. Furthermore, adeno-XAF1 treatment significantly prolonged the survival time of animals bearing tumor xenografts. No obvious pathological changes in main organs were observed in XAF1 virus-treated mice. Conclusion: Our results show that restoration of XAF1 expression obviously induces cell apoptosis and inhibits the HCC both in vitro and in vivo. Expression of XAF1 could significantly suppressed tumor angiogenesis probably through upregulating angiopoietin-2 expression to remold the newly-born vessels. Our results suggest that XAF1 may have a potential candidate for HCC gene therapy. The project was supported by National Nature Science foundation of China No. 30500221 (Tu SP) and NIH grant R01CA120915 (Yang CS). *Corresponding author: Shui-Ping Tu, E-mail: Tushuiping@yahoo.com. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. 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 4515.