Chengyuan Qian

Genetic Polymorphism of DNA Base-excision Repair Genes (APE1, OGG1 and XRCC1) and Their Correlation with Risk of Lung Cancer in a Chinese Population

BACKGROUND AND AIMS Reactive oxygen species (ROS) and numerous carcinogens may cause DNA damage including oxidative base lesions that contribute to the risk of lung cancer. The base excision repair (BER) pathway could effectively remove oxidative lesions in which 8-oxoguanine glycosylase-1 (OGG1), x-ray repair cross-complementing 1 (XRCC1), and apurinic/apyimidinic endonuclease 1 (APE1) play key roles. The aim of this study was to analyze the polymorphisms of DNA BER genes (OOG1, XRCC1 and APE1) and explore their associations, and the combined effects of these variants, with risk of lung cancer. METHODS In a hospital-based, case-control study of 455 lung cancer cases and 443 cancer-free hospital controls, the SNPs of OGG1 (Ser326Cys), XRCC1 (Arg399Gln), APE1 (Asp148Glu and -141T/G) were genotyped and analyzed for their correlation with the risk of lung cancer in multivariate logistic regression models. RESULTS Individuals homozygous for the variants APE1 -141GG showed a protective effect for lung cancer overall (OR=0.62; 95% CI: 0.42-0.91; p=0.02) and for lung adenocarcinoma (OR=0.65; 95% CI, 0.44-0.96; p=0.03). When analyzing the combined effects of variant alleles, 84 patients and controls were identified who were homozygous for two or three of the potential protective alleles (i.e., OGG1 326Cys, XRCC1 399Gln and APE1 -141G). ORs were significantly reduced when all patients were analyzed (OR=0.62; 95% CI: 0.38-0.99; p=0.05). CONCLUSIONS The combined effects of polymorphisms within BER genes may contribute to the tumorigenesis of lung cancer.

Association of DNA base excision repair genes (OGG1, APE1 and XRCC1) polymorphisms with outcome to platinum-based chemotherapy in advanced nonsmall-cell lung cancer patients.

Polymorphism of DNA base excision repair (BER) genes affects DNA repair capacity and may alter sensitivity to platinum‐based chemotherapy regimens. This study investigated polymorphisms of OGG1 Ser326Cys, APE1 Asp148Glu APE1‐141T/G and XRCC1 Arg399Gln for association with clinical outcome in 235 advanced inoperable nonsmall‐cell lung cancer (NSCLC) patients after treatment with platinum‐based chemotherapy. The multivariate analysis showed that OGG1 326 GC was associated with poor PFS [hazard ratio (HR) 1.730, p = 0.005], while XRCC1 399 GA, or GA+AA, was associated with poor OS in short‐term period (HR 1.718, p = 0.003; HR 1.691, p = 0.003, respectively). Patients with OGG1 326/XRCC1 399 variant alleles had a higher risk to die early in short‐term period (HR 1.929, p < 0.001). Furthermore, patients with XRCC1 399 variant allele (GA+AA) had higher risk of hematologic toxicity (p = 0.009), whereas patients carrying the OGG1 326 variant (GG), or the APE1‐141 GG variant, had reduced risk of gastrointestinal toxicity (p = 0.015 and p = 0.023, respectively). The data from the current study provide evidence that OGG1 Ser326Cys, XRCC1 Arg399Gln, APE1 Asp148Glu, and APE1‐141T/G polymorphisms may be useful in predicting clinical outcomes in patients with advanced inoperable NSCLC that will undergo platinum‐based chemotherapy.

Silencing of APE1 enhances sensitivity of human hepatocellular carcinoma cells to radiotherapy in vitro and in a xenograft model.

Resistance to radiotherapy is a key limitation for the treatment of human hepatocellular carcinoma (HCC). To overcome this problem, we investigated the correlation between radioresistance and the human apurinic/apyrimidinic endonuclease (APE1), a bifunctional protein, which plays an important role in DNA repair and redox regulation activity of transcription factors. In the present study, we examined the radiosensitivity profiles of three human HCC cell lines, HepG2, Hep3B, and MHCC97L, using the adenoviral vector Ad5/F35-mediated APE1 siRNA (Ad5/F35-siAPE1). The p53 mutant cell lines MHCC97L showed radioresistance, compared with HepG2 and Hep3B cells. APE1 was strongly expressed in MHCC97L cells and was induced by irradiation in a dose-dependent manner, and Ad5/F35-siAPE1 effectively inhibited irradiation-induced APE1 and p53 expression. Moreover, silencing of APE1 significantly potentiated the growth inhibition and apoptosis induction by irradiation in all tested human HCC cell lines. In addition, Ad5/F35-siAPE1 significantly enhanced inhibition of tumor growth and potentiated cell apoptosis by irradiation both in HepG2 and MHCC97L xenografts. In conclusion, down regulation of APE1 could enhance sensitivity of human HCC cells to radiotherapy in vitro and in vivo.

CALIFORNIUM-252 BRACHYTHERAPY COMBINED WITH EXTERNAL-BEAM RADIOTHERAPY FOR CERVICAL CANCER: LONG-TERM TREATMENT RESULTS

PURPOSE To observe, by retrospective analysis, the curative effects and complications due to californium-252 (252Cf) neutron intracavitary brachytherapy (ICBT) combined with external-beam radiotherapy (EBRT) in the treatment of cervical cancer. METHODS AND MATERIALS From February 1999 to December 2007, 696 patients with cervical cancer (Stages IB to IIIB) were treated with 252Cf-ICBT in combination of EBRT. Of all, 31 patients were at Stage IB, 104 at IIA, 363 at IIB, 64 at IIIA, and 134 at IIIB. Californium-252 ICBT was delivered at 7-12 Gy per insertion per week, with a total dose of 29-45 Gy to reference point A in three to five insertions. The whole pelvic cavity was treated with 8-MV X-ray external irradiation at 2 Gy per fraction, four times per week. After 16-38 Gy of external irradiation, the center of the whole pelvic field was blocked with a 4-cm-wide lead shield, with a total external irradiation dose of 44-56 Gy. The total treatment course was 5 to 6 weeks. RESULTS Overall survival rate at 3 and 5 years for all patients was 76.0% and 64.9%, respectively. Disease-free 3- and 5-year survival rates of patients were 71.2% and 58.4%, respectively. Late complications included vaginal contracture and adhesion, radiation proctitis, radiation cystitis, and inflammatory bowel, which accounted for 5.8%, 7.1%, 6.2%, and 4.9%, respectively. Univariate analysis results showed significant correlation of stage, age, histopathologic grade, and lymph node status with overall survival. Cox multiple regression analysis showed that the independent variables were stage, histopathologic grade, tumor size, and lymphatic metastasis in all patients. CONCLUSION Results of this series suggest that the combined use of 252Cf-ICBT with EBRT is an effective method for treatment of cervical cancer.

Induction of Apoptosis in Human Multiple Myeloma Cell Lines by Ebselen via Enhancing the Endogenous Reactive Oxygen Species Production

Ebselen a selenoorganic compound showing glutathione peroxidase like activity is an anti-inflammatory and antioxidative agent. Its cytoprotective activity has been investigated in recent years. However, experimental evidence also shows that ebselen causes cell death in several cancer cell types whose mechanism has not yet been elucidated. In this study, we examined the effect of ebselen on multiple myeloma (MM) cell lines in vitro. The results showed that ebselen significantly enhanced the production of reactive oxygen species (ROS) accompanied by cell viability decrease and apoptosis rate increase. Further studies revealed that ebselen can induce Bax redistribution from the cytosol to mitochondria leading to mitochondrial membrane potential ΔΨm changes and cytochrome C release from the mitochondria to cytosol. Furtherly, we found that exogenous addition of N-acetyl cysteine (NAC) completely diminished the cell damage induced by ebselen. This result suggests that relatively high concentration of ebselen can induce MM cells apoptosis in culture by enhancing the production of endogenous ROS and triggering mitochondria mediated apoptotic pathway.

Human apurinic/apyrimidinic endonuclease siRNA inhibits the angiogenesis induced by X-ray irradiation in lung cancer cells.

Objective: Radiotherapy is an important and effective treatment method for non-small cell lung cancer (NSCLC). Nonetheless, radiotherapy can alter the expression of proangiogenic molecules and induce angiogenesis. Human apurinic/apyrimidinic endonuclease (APE1) is a multifunctional protein, which has DNA repair and redox function. Our previous studies indicated APE1 is also a crucial angiogenic regulator. Thus, we investigated the effect of APE1 on radiation-induced angiogenesis in lung cancer and its underlying mechanism. Methods: Tumor specimens of 136 patients with NSCLC were obtained from 2003 to 2008. The APE1 and vascular endothelial growth factor (VEGF) expression, as well as microvessel density (MVD) were observed with immunohistochemistry in tumor samples. Human lung adenocarcinoma A549 cells were treated with Ad5/F35-APE1 siRNA and/or irradiation, and then the cells were used for APE1 analysis by Western blot and VEGF analysis by RT-PCR and ELISA. To elucidate the underline mechanism of APE1 on VEGF expression, HIF-1α protein level was determined by Western blot, and the DNA binding activity of HIF-1α was detected by EMSA. Transwell migration assay and capillary-like structure assay were used to observe the migration and capillary-like structure formation ability of human umbilical veins endothelial cells (HUVECs) that were co-cultured with Ad5/F35-APE1 siRNA and (or) irradiation treated A549 cells culture medium. Results: The high expression rates of APE1 and VEGF in NSCLC were 77.94% and 66.18%, respectively. The expressions of APE1 was significantly correlated with VEGF and MVD (r=0.369, r=0.387). APE1 and VEGF high expression were significantly associated with reduced disease free survival (DFS) time. The high expressions of APE1 and VEGF on A549 cells were concurrently induced by X-ray irradiation in a dose-dependent manner. Silencing of APE1 by Ad5/F35-APE1 siRNA significantly decreased DNA binding activity of HIF-1α and suppressed the expression of VEGF in A549 cells, moreover, significantly inhibited the endothelial cells immigration and capillary-like structure formation induced by irradiated A549 cells. Conclusion: Our results indicate that APE1 may play a crucial role in angiogenesis induced by irradiation. Administration of Ad5/F35-APE1 siRNA during radiotherapy could be a potent adjuvant therapeutic approach to enhance the radiotherapy response, effectively eliminate metastasis and improve the efficacy of radiotherapy for NSCLC.

Apurinic/apyrimidinic endonuclease 1 induced upregulation of fibroblast growth factor 2 and its receptor 3 induces angiogenesis in human osteosarcoma cells.

Tumor angiogenesis contributes to inferior prognosis in osteosarcoma. Apurinic/apyrimidinic endonuclease 1 (APE1) and fibroblast growth factor 2 (FGF2) and its receptor 3 (FGFR3) signaling pathway plays an important role in the angiogenic process. In this study we observed that high expression of APE1, FGF2 and FGFR3, and microvessel density are positively correlated with poor prognosis of osteosarcoma patients. Furthermore, the Cox model showed that the tumor size, FGF2 and its receptor 3 (FGFR3), and microvessel density were adverse prognostic factors. Based on our clinical data, and the fact that APE1 is involved in tumor angiogenesis, we hypothesize that it is very likely that APE1 may indirectly promote angiogenesis by upregulating fibroblast FGF2 and FGFR3. Our preliminary data show small interfering RNA‐mediated silence of APE1 experiments, which further supports this hypothesis. APE1‐small interfering RNA significantly inhibited tumor angiogenesis by downregulating in vitro expression of FGF2 and FGFR3 in human umbilical vein endothelial cells in Matrigel tube formation assay, and further inhibited tumor growth in vivo in a mouse xenograft model. Thus, the proposed APE1‐FGF2 and FGFR3 pathway may provide a novel mechanism for regulation of FGF2 and FGFR3 by APE1 in tumor angiogenesis.

Small-molecule BH3 mimetic and pan-Bcl-2 inhibitor AT-101 enhances the antitumor efficacy of cisplatin through inhibition of APE1 repair and redox activity in non-small-cell lung cancer.

AT-101 is a BH3 mimetic and pan-Bcl-2 inhibitor that has shown potent anticancer activity in non-small-cell lung cancer (NSCLC) in murine models, but failed to show clinical efficacy when used in combination with docetaxel in NSCLC patients. Our recent study has demonstrated that AT-101 enhanced the antitumor effect of cisplatin (CDDP) in a murine model of NSCLC via inhibition of the interleukin-6/signal transducer and activator of transcription 3 (STAT3) pathway. This study explored the underlying mechanisms for the enhanced anticancer activity of CDDP by AT-101. Our results show that, when compared with monotherapy, AT-101 significantly enhanced the inhibitory effects of CDDP on proliferation and migration of A549 cells and on tube formation and migration in human umbilical vein endothelial cells. AT-101 promoted the proapoptotic activity of CDDP in A549 cells. AT-101 also enhanced the inhibitory effect of CDDP on DNA repair and redox activities of apurinic/apyrimidinic endonuclease 1 (APE1) in A549 cells. In tumor tissues from nude mice treated with AT-101 plus CDDP or monotherapy, the combination therapy resulted in greater inhibition of angiogenesis and tumor cell proliferation than the monotherapy. These results suggest that AT-101 can enhance the antitumor activity of CDDP in NSCLC via inhibition of APE1 DNA repair and redox activities and by angiogenesis and induction of apoptosis, but other mechanisms cannot be excluded. We are now conducting a Phase II trial to examine the clinical efficacy and safety profile of combined use of AT-101 plus CDDP in advanced NSCLC patients.

Identification of a novel potential antitumor activity of gossypol as an APE1/Ref-1 inhibitor

The human apurinic/apyrimidinic endonuclease 1/redox enhancing factor-1 (APE1/Ref-1), an essential multifunctional protein involved in the repair of oxidative deoxyribonucleic acid (DNA) damage and transcriptional regulation, is often overexpressed in tumor tissues and cancer cells. Moreover, APE1/Ref-1 (APE1) overexpression has been linked to chemoresistance in human tumors. Thus, inhibiting APE1 function in cancer cells is considered a promising strategy to overcome resistance to therapeutic agents. Gossypol is a Bcl-2 homology 3 (BH3)-mimetic agent and is able to bind to the BH3 domain of B-cell lymphoma 2 (Bcl-2) family members. Other studies demonstrated that Bcl-2 directly interacted with APE1 via its BH domains. Using apurinic/apyrimidinic (AP) endonuclease assays, we found that gossypol inhibits the repair activity of APE1. Electrophoretic mobility shift assays and dual luciferase assays showed that gossypol could also inhibit the redox function of APE1. Using dual polarization interferometry technology, we show that gossypol can directly interact with APE1. Furthermore, addition of gossypol, in conjunction with APE1 overexpression, leads to cancer cell death. The addition of gossypol also enhances the cell killing effect of the laboratory alkylating agent methyl methanesulfonate and the clinical agent cisplatin (DDP). Administration of gossypol significantly inhibited the growth of xenografts. Furthermore, the combined treatment of gossypol and DDP resulted in a statistically higher antitumor activity compared with DDP alone in vivo. In conclusion, we have demonstrated that gossypol effectively inhibits the repair and redox activity of APE1 through a direct interaction.

APE1/Ref-1 enhances DNA binding activity of mutant p53 in a redox-dependent manner.

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is a dual function protein; in addition to its DNA repair activity, it can stimulate DNA binding activity of numerous transcription factors as a reduction-oxidation (redox) factor. APE1/Ref-1 has been found to be a potent activator of wild-type p53 (wtp53) DNA binding in vitro and in vivo. Although p53 is mutated in most types of human cancer including hepatocellular carcinoma (HCC), little is known about whether APE1/Ref-1 can regulate mutant p53 (mutp53). Herein, we reported the increased APE1/Ref-1 protein and accumulation of mutp53 in HCC by immunohistochemistry. Of note, it was observed that APE1/Ref-1 high-expression and mutp53 expression were associated with carcinogenesis and progression of HCC. To determine whether APE1/Ref-1 regulates DNA binding of mutp53, we performed electromobility shift assays (EMSAs) and quantitative chromatin immunoprecipitation (ChIP) assays in HCC cell lines. In contrast to sequence-specific and DNA structure-dependent binding of wtp53, reduced mutp53 efficiently bound to nonlinear DNA, but not to linear DNA. Notably, overexpression of APE1/Ref-1 resulted in increased DNA binding activity of mutp53, while downregulation of APE1/Ref-1 caused a marked decrease of mutp53 DNA binding. In addition, APE1/Ref-1 could not potentiate the accumulation of p21 mRNA and protein in mutp53 cells. These data indicate that APE1/Ref-1 can stimulate mutp53 DNA binding in a redox-dependent manner.