Chimeric adenoviral vector Ad5/F35-mediated APE1 siRNA enhances sensitivity of human colorectal cancer cells to radiotherapy in vitro and in vivo

Abstract

Apurinic/apyrimidinic endonuclease (APE1), a bifunctional AP endonuclease/redox factor, is important in DNA repair and redox signaling, may be associated with radioresistance. Here we investigate whether targeted inhibition of APE1 can sensitize tumor cells to irradiation in vitro and in vivo. We first constructed chimeric adenoviral vector Ad5/F35 carrying human APE1 siRNA (Ad5/ F35-APE1 siRNA). The infectivity of chimeric Ad5/F35 to LOVO colon cancer cells was greater than that of Ad5. APE1 was strongly expressed and nuclear factor kB (NF-kB), a downstream molecule of APE1, known as a radioresistance factor, was constitutively active in LOVO cells. Infection of LOVO cells with Ad5/F35-APE1 siRNA resulted in a dose-dependent decrease of APE1 protein and AP endonuclease activity in vitro. Ad5/F35-APE1 siRNA significantly enhanced sensitivity of LOVO cells to irradiation in clonogenic survival assays, associated with increased cell apoptosis. The APE1 expression in LOVO cells was induced by irradiation in a dose-dependent manner, accompanied with the enhancement of DNA-binding activity of NF-kB and Ad5/F35-APE1 siRNA effectively inhibited constitutive and irradiation-induced APE1 expression and NF-kB activation. In a subcutaneous nude mouse colon cancer model, Ad5/F35-APE1 siRNA (5 Â 10 8 IU, intratumoral injection) inhibited the expression of APE1 protein in LOVO xenografts, and significantly enhanced inhibition of tumor growth by irradiation. In conclusion, APE1 may be involved as one of the radioresistance factors, and targeted inhibition of APE1 shows an effective means of enhancing tumor sensitivity to radiotherapy.

Human Apurinic/Apyrimidinic Endonuclease 1

“…Fishel et al reported that human SKOV-3 ovarian cancer cells treated with APE1 siRNA ex vivo and then implanted into female nude mice exhibit a dramatic reduction in tumor volume and cell proliferation during the period of APE1 depletion (51). Moreover, Xiang et al found that LOVO colon cancer cells injected subcutaneously into nude mice and subsequently treated with APE1-specific siRNA adenoviral particles display reduced tumor growth, particularly when challenged with Xray irradiation, relative to the controls (237). Using this established approach, the Wang group has since shown that in vivo APE1 depletion sensitizes A549 non-small cell lung cancer xenografts to hematoporphyrin derivative-mediated photodynamic therapy (243) and human hepatocellular carcinoma cell lines to radio-therapy (32).…”

“…Hyper-sensitivity of APE1 KD cells has been reported for other clinical DNA-damaging agents, including ionizing radiation (32,150,237), bleomycin (56,170,218), gemcitabine (239), cisplatin (222,246), etoposide (185,221), and photodynamic therapy (236,243). While in some cases it is not obvious what role APE1 would play in repairing the direct DNA damage (e.g., for the crosslinking agent cisplatin), some level of oxidative stress is involved in most genotoxin exposures.…”

Alterations in the expression of the apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE1/Ref-1) in human ovarian cancer and indentification of the therapeutic potential of APE1/Ref-1 inhibitor

“…The APE1 siRNA expression vector, entitled Ad5/F35-APE1 siRNA, constructed by De-Bing Xiang, could inhibit APE1 expression and AP endonuclease activity in a dosedependent manner (13). In this study, APE1 was supressed from 80 to 95% at doses of 20-40 MOI Ad5/F35-APE1 siRNA.…”

“…The APE1 siRNA expression vector named Ad5/F35-APE1 siRNA was constructed by De-Bing Xiang (13). The titer was 1.6x10 10 IU/ml after amplication and purfication.…”

Human Apurinic/Apyrimidinic Endonuclease is a Novel Drug Target in Cancer

“…Double negative APE1 mutation expression is associated with enhanced cytotoxicity to antimetabolites and alkylating agents (McNeill et al 2009). Downregulation of APE1 using an adenoviral vector in a colon cancer mouse model successfully reduced APE1 expression levels and was associated with an increased response to ionising radiation (Xiang et al 2008). This evidence highlights the therapeutic potential of targeting APE1 with small molecular inhibitors to improve radio-and chemotherapeutic efficiency.…”