Combination of Radiotherapy and Adenovirus-Mediated p53 Gene Therapy for MDM2-Overexpressing Hepatocellular Carcinoma

The p53 gene plays a determinant role in radiation-induced cell death and its protein product is negatively regulated by MDM2. We investigated whether adenovirus-mediated modified p53 gene transfer, which blocks p53-MDM2 binding, is effective for radiation-induced cell death in hepatocellular carcinoma (HCC) at different MDM2 cellular levels. Human hepatocellular carcinoma cell lines expressing MDM2 at low levels (Huh7) and high levels (SK-Hep1) were used. Ad-p53 and Ad-p53vp are replication-deficient adenoviral vectors containing human wild-type or modified p53, respectively. The anti-tumor effect was highest for Ad-p53 + radiotherapy (RT) in the low-level MDM2 cells, whereas this effect was highest for Ad-p53vp + RT in the MDM2-overexpressing cells. In Huh-7 cells, Ad-p53 + RT decreased cell viability (32%) in vitro and inhibited tumor growth (enhancement factor, 1.86) in vivo. Additionally, p21 expression and apoptosis were increased. In contrast, in SK-Hep1 cells, Ad-p53vp + RT showed decreased cell viability (51%) in vitro and inhibition of tumor growth (enhancement factor, 3.07) in vivo. Caspase-3 expression and apoptosis were also increased. Adenovirus-expressing modified p53, which blocks p53-MDM2 binding, was effective in killing tumor cells overexpressing MDM2. Furthermore, the combination strategy for disruption of the p53-MDM2 interaction with RT demonstrated enhanced anti-tumor effects both in vitro and in vivo.This work was supported by the Ministry of Education, Science and Technology (MEST) and the National Research 210 W. S. Koom et al. Foundation of Korea (NRF) through Nuclear R&D Program, 2010 (Grant number: 2010-0018539), a faculty research grant of Yonsei University College of Medicine for 2009 (6-2009-0102), a research fund (2008) provided from Yonsei Cancer Research Institute, and the Korea Science and Engineering Foundation (R15-2004-024-02001-0, 2009K001644, Dr. C-O.Yun). Il-Kyu Choi is a graduate student sponsored by NRF through National Core Research Center