Purpose: To investigate the clinical benefit of additional radiotherapy to patients with unresectable hepatocellular carcinoma treated with transcatheter arterial chemoembolization (TACE) and the molecular effects of radiation on gene expression in hepatoma cells. Experimental Design: Between August 1996 and August 2003, 276 and 64 patients with American Joint Committee on Cancer stage T 3 N 0 M 0 hepatocellular carcinoma receiving TACE alone andTACE followed by three-dimensional conformal radiotherapy, respectively, at our institution were studied. Clinical outcome and pattern of failure were analyzed for the association of survival benefit with radiotherapy. The molecular effects of radiotherapy were studied in vitro and in vivo using human hepatoma cells with different p53 mutation and hepatitis B virus infection status. Results: Median follow-up and survival time in theTACE alone and TACE + radiotherapy groups were 39 and 19 months, and 51and 17 months, respectively. Additional radiotherapy toTACE did not improve overall survival (P = 0.65). However, different failure patterns were noted afterTACE and after radiotherapy. Although all irradiated tumors regressed substantially, radiotherapy rapidly enhanced both intrahepatic and extrahepatic tumor progression outside the radiotherapy treatment field in a significant portion of patients, which offset the benefit of radiotherapy on overall survival. In molecular analysis of the radiation effects on human hepatoma cells, radiotherapy rapidly induced p53-independent transcriptional up-regulation of vascular endothelial growth factor (VEGF), increased VEGF secretion in a dose-, time-, and cell type^dependent manner, and promoted hepatoma cell growth in vivo with enhanced intratumor angiogenesis, which correlated well with elevated levels of serumVEGF. Conclusions: Radiotherapy to eradicate a primary hepatocellular carcinoma might result in the outgrowth of previously dormant microtumors not included in the radiotherapy treatment field. Radiotherapy-inducedVEGF could be a paracrine proliferative stimulus.Therapeutic implications of the study justify the combination of three-dimensional conformal radiotherapy with anti-VEGF angiogenic modalities for the treatment of unresectable hepatocellular carcinoma to reduce relapses.
In addition to genetic changes, epigenetic aberrations also play important roles in radiation- and chemical-induced disorders and carcinogenesis. The present study investigated whether epigenetic therapy with a histone deacetylase (HDAC) inhibitor has dual benefits for radiation-induced oral mucositis and chemical-induced oral carcinogenesis, which should be treated at the same time. The HDAC inhibitor phenylbutyrate was first tested to determine if it influences DNA damage repair and survival in irradiated normal cells in vitro by investigating the patterns and dynamics of phospho-gammaH2AX foci, Rad51 foci and phospho-gammaH2AX/Rad51 colocalization and using the comet and clonogenic assays. Oral mucositis or carcinogenesis was induced in hamsters using radiation or 7,12-dimethylbenz[a]anthracene (DMBA) irritation to the cheek pouch. The ability of phenylbutyrate formed in proper carriers to prevent radiation-induced oral mucositis and inhibit chemical-induced oral carcinogenesis was assessed. The treated or untreated irradiated or DMBA-irritated oral tissues or mucosal epithelia were subjected to the studies of histology, immunohistochemistry, gene expression, comet assay, HDAC activity or oxidative stress. We found that phenylbutyrate promoted DNA repair and survival in normal cells after radiation. Compared with blank or vehicle-treated hamsters, the irradiated mucosa treated with phenylbutyrate had significantly lower oxidative stress and tumor necrosis factor-alpha expression and less severe oral mucositis of a shorter duration. A reduction of the oral tumor incidence, burden and progression by phenylbutyrate correlated with the suppression of oncomiRs and Rad51 overexpression, the upregulation of differentiation markers and the decrease of intracellular HDAC activity and oxidative stress during DMBA-induced oral carcinogenesis. Thus, epigenetic therapy using the HDAC inhibitor as an adjuvant to radiotherapy for chemical-induced oral cancer may provide a promising strategy combining the prevention of radiation-induced oral mucositis and the inhibition of oral carcinogenesis.
The mechanism responsible for hepatitis B virus (HBV) exacerbation during chemotherapy and radiotherapy remains unknown. We investigated whether the activation of DNA repair pathways influences HBV replication. The upregulation of the promyelocytic leukemia (PML) protein and its associated PML nuclear body (PML-NB) by chemotherapy and irradiation-induced DNA repair signaling correlated with the upregulation of HBV pregenomic transcription, HBV-core expression, and HBV DNA replication. The HBV-core protein and HBV DNA localized to PML-NBs, where they associated with PML and histone deacetylase 1 (HDAC1). Chemotherapy and radiotherapy affected the interactions between PML, HBV-core, and HDAC1. The enhanced protein-protein interaction between PML and HBV-core inhibited PML-mediated apoptosis and decreased PML-associated HDAC activity. The reversal of HDAC-mediated repression on the HBV covalently closed circular DNA basal core promoter resulted in the amplification of HBV-core and pregenomic expression. These results suggest that PML in PML-NBs links the DNA damage response with HBV replication and may cooperate with HBV-core and HDAC1 on the HBV covalently closed circular DNA basal core promoter to form a positive feedback loop for HBV exacerbation during chemotherapy and radiotherapy. (Mol Cancer Res 2009;7(10):1672-85)
Hepatitis B virus (HBV) is implicated in liver cancer. The aim of this study was to find out whether HBV or its components [HBV surface antigen (HBsAg), HBV core protein (HBc), and HBV X protein (HBx)] could interfere with the host DNA damage response and repair pathway. The full HBV genome or individual HBV open-reading frame (ORF) was introduced into HepG2 cells to examine the effect on host genomic stability, DNA repair efficacy in response to double-strand DNA damage, and DNA damage-induced cell death. Responses to apoptosis induction in the HBV ORF-transfected HepG2 cells were also compared with those in HBV-positive and HBV-negative human hepatocellular carcinoma (HCC) cells. In the absence of HBV replication, accumulation of HBsAg in liver cells without other HBV proteins enhanced DNA repair protein and tumor suppressor promyelocytic leukemia (PML) degradation, which resulted in resistance to apoptosis induction and deficient double-strand DNA repair. However, HBsAg-positive cells exhibited increased cell death with exposure to the poly(ADP-ribose) polymerase inhibitor that blocks single-strand DNA repair. These results indicate that suppression of PML by HBsAg disrupts cellular mechanisms that respond to double-strand DNA damage for DNA repair or apoptosis induction, which may facilitate hepatocarcinogenesis and open up a synthetic lethality strategy for HBsAg-positive HCC treatment.
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