Prognostic significance of ataxia-telangiectasia mutated, DNA-dependent protein kinase catalytic subunit, and Ku heterodimeric regulatory complex 86-kD subunit expression in patients with nonsmall cell lung cancer

Role of DNA-dependent protein kinase catalytic subunit in cancer development and treatment

DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a key component of the non-homologous end-joining (NHEJ) pathway, is involved in DNA double-strand break repair, immunocompetence, genomic integrity, and epidermal growth factor receptor signaling. Clinical studies indicate that expression and activity of DNA-PKcs is correlated with cancer progression and response to treatment. Various anti-DNA-PKcs strategies have been developed and tested in preclinical studies to exploit the benefit of DNA-PKcs inhibition in sensitization of radiotherapy and in combined modality therapy with other antitumor agents. In this article, we review the association between DNA-PKcs and cancer development and discuss current approaches and mechanisms for inhibition of DNA-PKcs. The future challenges are to understand how DNA-PKcs activity is correlated with cancer susceptibility and to identify those patients who would most benefit from DNA-PKcs inhibition.

Aberrant expression of proteins involved in signal transduction and DNA repair pathways in lung cancer and their association with clinical parameters

BACKGROUND

Because cell signaling and cell metabolic pathways are executed through proteins, protein signatures in primary tumors are useful for identifying key nodes in signaling networks whose alteration is associated with malignancy and/or clinical outcomes. This study aimed to determine protein signatures in primary lung cancer tissues.

METHODOLOGY/ PRINCIPAL FINDINGS

We analyzed 126 proteins and/or protein phosphorylation sites in case-matched normal and tumor samples from 101 lung cancer patients with reverse-phase protein array (RPPA) assay. The results showed that 18 molecules were significantly different (p<0.05) by at least 30% between normal and tumor tissues. Most of those molecules play roles in cell proliferation, DNA repair, signal transduction and lipid metabolism, or function as cell surface/matrix proteins. We also validated RPPA results by Western blot and/or immunohistochemical analyses for some of those molecules. Statistical analyses showed that Ku80 levels were significantly higher in tumors of nonsmokers than in those of smokers. Cyclin B1 levels were significantly overexpressed in poorly differentiated tumors while Cox2 levels were significantly overexpressed in neuroendocrinal tumors. A high level of Stat5 is associated with favorable survival outcome for patients treated with surgery.

CONCLUSIONS/ SIGNIFICANCE

Our results revealed that some molecules involved in DNA damage/repair, signal transductions, lipid metabolism, and cell proliferation were drastically aberrant in lung cancer tissues, and Stat5 may serve a molecular marker for prognosis of lung cancers.

Molecular markers for cancer prognosis and treatment: have we struck gold?

The last decade has witnessed an emerging role for molecular or biochemical markers indicating a specific cellular mechanism or tissue function, often called 'biomarkers'. Biomarkers such as altered DNA, proteins and inflammatory cytokines are critical in cancer research and strategizing treatment in the clinic. In this review we look at the application of biological indicators to cancer research and highlight their roles in cancer detection and treatment. With technological advances in gene expression, genomic and proteomic analysis, biomarker discovery is expanding fast. We focus on some of the predominantly used markers in different types of malignancies, their advantages, and their limitations. Finally we conclude by looking at the future of biomarkers, their utility in the tumorigenic studies, and the progress towards personalized treatment strategies.

Ku80 is differentially expressed in human lung carcinomas and upregulated in response to irradiation in mice

Based on the role of Ku80 in mediating radiation-induced DNA repair, we investigated Ku80 expression in human lung cancers of different pathological types and evaluated the effect of radiotherapy on Ku80 expression levels in a mouse model. We used immunohistochemistry and real-time PCR to determine Ku80 protein and mRNA levels, respectively. We inoculated nude mice with A549 cells and subjected the tumor-bearing mice to varying doses of irradiation. Lung carcinoma tissue exhibited higher Ku80 mRNA and protein levels when compared with normal tissue. Among the tumor subtypes, lung adenocarcinoma and lung squamous carcinoma showed higher levels of Ku80 protein and mRNA, compared with small-cell lung carcinoma. There was a dose-dependent and time-dependent increase in Ku80 mRNA levels in nude mice that were inoculated with A549 cells and exposed to varying doses of irradiation. Ku80 may play an important role in the DNA damage response pathway. Higher Ku80 levels in lung squamous carcinoma and adenocarcinoma may explain their lower radiosensitivity when compared with small-cell lung carcinoma. Ku80 expression levels could be useful in predicting radiosensitivity of lung tumors and inhibition of Ku80 may be an interesting target to improve radiosensitivity in lung cancer patients.

Radiosensitization and growth inhibition of cancer cells mediated by an scFv antibody gene against DNA-PKcs in vitro and in vivo

BACKGROUND

Overexpression of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is commonly occurred in cancers and causes radioresistance and poor prognosis. In present study, the single-chain variable antibody fragments (scFv) targeting DNA-PKcs was developed for the application of radiosensitization in vitro and in vivo. A humanized semisynthetic scFv library and the phage-display antibodies technology were employed to screen DNA-PKcs scFv antibody.

METHODS

DNA-PKcs epitopes were predicted and cloned. A humanized semisynthetic scFv library and the phage-display antibodies technology were employed to screen DNA-PKcs scFv antibody. DNA damage repair was analyzed by comet assay and immunofluorescence detection of gammaH2AX foci. The radiosensitization in vivo was determined on Balb/c athymic mice transplanted tumours of HeLa cells.

RESULTS

Four epitopes of DNA-PKcs have been predicted and expressed as the antigens, and a specific human anti-DNA-PKcs scFv antibody gene, anti-DPK3-scFv, was obtained by screening the phage antibody library using the DNA-PKcs peptide DPK3. The specificity of anti-DPK3-scFv was verified, in vitro. Transfection of HeLa cells with the anti-DPK3-scFv gene resulted in an increased sensitivity to IR, decreased repair capability of DNA double-strand breaks (DSB) detected by comet assay and immunofluorescence detection of gammaH2AX foci. Moreover, the kinase activity of DNA-PKcs was inhibited by anti-DPK3-scFv, which was displayed by the decreased phosphorylation levels of its target Akt/S473 and the autophosphorylation of DNA-PKcs on S2056 induced by radiation. Measurement of the growth and apoptosis rates showed that anti-DPK3-scFv enhanced the sensitivity of tumours transplanted in Balb/c athymic mice to radiation therapy.

CONCLUSION

The antiproliferation and radiosensitizing effects of anti-DPK3-scFv via targeting DNA-PKcs make it very appealing for the development as a novel biological radiosensitizer for cancer therapeutic potential.