Radioresistant cervical cancer shows upregulation of the NHEJ proteins DNA-PKcs, Ku70 and Ku86

DNA-PKcs-Mediated Transcriptional Regulation Drives Prostate Cancer Progression and Metastasis

Emerging evidence demonstrates that the DNA repair kinase DNA-PKcs exerts divergent roles in transcriptional regulation of unsolved consequence. Here, in vitro and in vivo interrogation demonstrate that DNA-PKcs functions as a selective modulator of transcriptional networks that induce cell migration, invasion, and metastasis. Accordingly, suppression of DNA-PKcs inhibits tumor metastases. Clinical assessment revealed that DNA-PKcs is significantly elevated in advanced disease and independently predicts for metastases, recurrence, and reduced overall survival. Further investigation demonstrated that DNA-PKcs in advanced tumors is highly activated, independent of DNA damage indicators. Combined, these findings reveal unexpected DNA-PKcs functions, identify DNA-PKcs as a potent driver of tumor progression and metastases, and nominate DNA-PKcs as a therapeutic target for advanced malignancies.

Cadmium delays non-homologous end joining (NHEJ) repair via inhibition of DNA-PKcs phosphorylation and downregulation of XRCC4 and Ligase IV

Although studies have shown that cadmium (Cd) interfered with DNA damage repair (DDR), whether Cd could affect non-homologous end joining (NHEJ) repair remains elusive. To further understand the effect of Cd on DDR, we used X-ray irradiation of Hela cells as an in vitro model system, along with γH2AX and 53BP1 as markers for DNA damage. Results showed that X-ray significantly increased γH2AX and 53BP1 foci in Hela cells (p < 0.01), all of which are characteristic of accrued DNA damage. The number of foci declined rapidly over time (1-8h postirradiation), indicating an initiation of NHEJ process. However, the disappearance of γH2AX and 53BP1 foci was remarkably slowed by Cd pretreatment (p < 0.01), suggesting that Cd reduced the efficiency of NHEJ. To further elucidate the mechanisms of Cd toxicity, several markers of NHEJ pathway including Ku70, DNA-PKcs, XRCC4 and Ligase IV were examined. Our data showed that Cd altered the phosphorylation of DNA-PKcs, and reduced the expression of both XRCC4 and Ligase IV in irradiated cells. These observations are indicative of the impairment of NHEJ-dependent DNA repair pathways. In addition, zinc (Zn) mitigated the effects of Cd on NHEJ, suggesting that the Cd-induced NHEJ alteration may partly result from the displacement of Zn or from an interference with the normal function of Zn-containing proteins by Cd. Our findings provide a new insight into the toxicity of Cd on NHEJ repair and its underlying mechanisms in human cells.

MiR-20a Induces Cell Radioresistance by Activating the PTEN/PI3K/Akt Signaling Pathway in Hepatocellular Carcinoma

PURPOSE

To investigate the role of miR-20a in hepatocellular carcinoma (HCC) cell radioresistance, which may reveal potential strategies to improve treatment.

METHODS AND MATERIALS

The expression of miR-20a and PTEN were detected in HCC cell lines and paired primary tissues by quantitative real-time polymerase chain reaction. Cell radiation combined with colony formation assays was administrated to discover the effect of miR-20a on radiosensitivity. Bioinformatics prediction and luciferase assay were used to identify the target of miR-20a. The phosphatidylinositol 3-kinase inhibitor LY294002 was used to inhibit phosphorylation of Akt, to verify whether miR-20a affects HCC cell radioresistance through activating the PTEN/PI3K/Akt pathway.

RESULTS

MiR-20a levels were increased in HCC cell lines and tissues, whereas PTEN was inversely correlated with it. Overexpression of miR-20a in Bel-7402 and SMMC-7721 cells enhances their resistance to the effect of ionizing radiation, and the inhibition of miR-20a in HCCLM3 and QGY-7701 cells sensitizes them to it. PTEN was identified as a direct functional target of miR-20a for the induction of radioresistance. Overexpression of miR-20a activated the PTEN/PI3K/Akt signaling pathway. Additionally, the kinase inhibitor LY294002 could reverse the effect of miR-20a-induced radioresistance.

CONCLUSION

MiR-20a induces HCC cell radioresistance by activating the PTEN/PI3K/Akt pathway, which suggests that miR-20a/PTEN/PI3K/Akt might represent a target of investigation for developing effective therapeutic strategies against HCC.

DNA-dependent protein kinase catalytic subunit inhibitor reverses acquired radioresistance in lung adenocarcinoma by suppressing DNA repair

The mechanisms underlying lung cancer radioresistance remain to be fully elucidated. The DNA repair pathway is a predominant target of radiotherapy, which is considered to be involved in the acquired radioresistance of cancer cells. The present study aimed to establish a radioresistant cell model using the A549 human lung cancer cell line, and to further investigate the potential mechanisms underlying the radioresistance. The A549R radioresistant lung cancer cell variant was established by exposing the parental A549 cells to repeated γ-ray irradiation at a total dose of 60 Gy. Colony formation assays were then used to determine cell survival following γ-ray exposure. The established radioresistant cells were subsequently treated with or without the NU7026 DNA-PKcs inhibitor. The levels of DNA damage were determined by counting the number of fluorescent γ-H2AX foci in the cells. The cellular capacity for DNA repair was assessed using antibodies for the detection of various DNA repair pathway proteins. The radioresistant sub-clones exhibited significantly decreased survival following NU7026 treatment, compared with the parental cells, as determined by colony formation assays (P<0.05), and this finding was found to be dose-dependent. Treatment with the DNA-dependent protein kinase (DNA-PK) inhibitor significantly reduced γ-H2AX foci formation (P<0.05) following acute radiation exposure in the radioresistant sub-clones, compared with the parental control cells. The decreased levels of γ-H2AX were accompanied by an increase in the percentage of apoptotic cells in the radioresistant cell line following post-radiation treatment with the DNA-PKcs inhibitor. The expression levels of proteins associated with the DNA repair pathway were altered markedly in the cells treated with NU7026. The results of the present study suggested that radioresistance may be associated with enhanced DNA repair following exposure to radiation, resulting in reduced apoptosis. Therefore, the quantity of γ-H2AX determines the radioresistance of cells. The DNA repair pathway is important in mediating radioresistance, and treatment with the DNA-PKcs inhibitor, NU7026 restored the acquired radiation resistance.

Modeling the Interplay Between Tumor Volume Regression and Oxygenation in Uterine Cervical Cancer During Radiotherapy Treatment

This paper describes a patient-specific mathematical model to predict the evolution of uterine cervical tumors at a macroscopic scale, during fractionated external radiotherapy. The model provides estimates of tumor regrowth and dead-cell reabsorption, incorporating the interplay between tumor regression rate and radiosensitivity, as a function of the tumor oxygenation level. Model parameters were estimated by minimizing the difference between predicted and measured tumor volumes, these latter being obtained from a set of 154 serial cone-beam computed tomography scans acquired on 16 patients along the course of the therapy. The model stratified patients according to two different estimated dynamics of dead-cell removal and to the predicted initial value of the tumor oxygenation. The comparison with a simpler model demonstrated an improvement in fitting properties of this approach (fitting error average value <5%, p < 0.01), especially in case of tumor late responses, which can hardly be handled by models entailing a constant radiosensitivity, failing to model changes from initial severe hypoxia to aerobic conditions during the treatment course. The model predictive capabilities suggest the need of clustering patients accounting for cancer cell line, tumor staging, as well as microenvironment conditions (e.g., oxygenation level).

MicroRNAs Used in Combination with Anti-Cancer Treatments Can Enhance Therapy Efficacy

MicroRNAs (miRNAs), a recently discovered class of small non-coding RNAs, constitute a promising approach to anti-cancer treatments when they are used in combination with other agents. MiRNAs are evolutionarily conserved non-coding RNAs that negatively regulate gene expression by binding to the complementary sequence in the 3'-untranslated region (UTR) of target genes. MiRNAs typically suppress gene expression by direct association with target transcripts, thus decreasing the expression levels of target proteins. The delivery to cells of synthetic miRNAs that mimic endogenous miRNA targeting genes involved in the DNA-Damage Response (DDR) can perturb the process, making cells more sensitive to chemotherapy or radiotherapy. This review examines how cells respond to combined therapy and it provides insights into the role of miRNAs in targeting the DDR repair pathway when they are used in combination with chemical compounds or ionizing radiation to enhance cellular sensitivity to treatments.

Rational design of cancer-targeted BSA protein nanoparticles as radiosensitizer to overcome cancer radioresistance

Radiotherapy displays curative potential for cervical cancer management, but radioresistance occurs during long-term therapy. To overcome this limitation, tumor-targeted nanotechnology has been proposed to enhance the radiosensitivity of solid tumors. Herein, we used biocompatible bovine serum albumin nanoparticles (BSANPs) as carriers of organic selenocompound (PSeD) with folate (FA) as the targeting ligand to fabricate a cancer-targeted nanosystem. The combination of PSeD and BSANPs endowed the nanosystem with higher light absorption and reactive oxygen species (ROS) generation owing to their properties of surface plasmon resonance (SPR) effect, heavy metal effect, high refractive index and nanoparticulate interfacial effect. The combined treatment drastically increased the ROS overproduction, VEGF/VEGFR2 inactivation and inhibition of XRCC-1-mediated repair of DNA damage, thus triggering G2/M phase arrest and apoptosis. Taken together, our findings demonstrate the utility of FA-BSANPs as a promising radiosensitizer to improve cancer radiotherapy.

DNA-PKcs deficiency sensitizes the human hepatoma HepG2 cells to cisplatin and 5-fluorouracil through suppression of the PI3K/Akt/NF-κB pathway

The aim of the present study was to investigate the effects of DNA-PKcs deficiency on the chemosensitivity of human hepatoma HepG2 cells to cisplatin (CDDP) and 5-fluorouracil (5-Fu), and to explore the underlying molecular mechanism. After transfection with DNA-PKcs siRNA or control siRNA, HepG2 cells were exposed to combination treatment of CDDP and 5-Fu. The cell viability, DNA damage, cell apoptosis, intracellular reactive oxygen species and glutathione (GSH) level, expression of apoptosis related proteins, activity of phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway, and nuclear factor-κB (NF-κB) pathways were assessed. The combination of CDDP and 5-Fu had a synergistic cytotoxic effect in HepG2 cells in terms of the cell viability, DNA damage, apoptosis, and oxidative stress level. DNA-PKcs siRNA could sensitize the HepG2 cells to the combined treatment. DNA-PKcs suppression further reduced the Akt phosphorylation level and Bcl-2 expression in HepG2 cells exposed to CDDP and 5-Fu, but enhanced the expression of pro-apoptotic proteins p53 and caspase-3. Moreover, CDDP could inhibit the transcriptional activity of NF-κB through degradation of IkB-α, while 5-Fu alone seemed in some extent increases the NF-κB activity. The combined treatment with CDDP and 5-Fu resulted in significantly decrease of the transcriptional activity of NF-κB, which was further aggravated by DNA-PKcs siRNA treatment. In conclusion, DNA-PKcs suppression had complementary effects in combination with CDDP and 5-Fu treatment in HepG2 cells, which was associated with suppression of NF-κB signaling pathway cascade, activation of caspase-3 and p53, as well as down-regulation of Bcl-2 and GSH.

Beyond DNA repair: DNA-PK function in cancer

The DNA-dependent protein kinase (DNA-PK) is a pivotal component of the DNA repair machinery that governs the response to DNA damage, serving to maintain genome integrity. However, the DNA-PK kinase component was initially isolated with transcriptional complexes, and recent findings have illuminated the impact of DNA-PK-mediated transcriptional regulation on tumor progression and therapeutic response. DNA-PK expression has also been correlated with poor outcome in selected tumor types, further underscoring the importance of understanding its role in disease. Herein, the molecular and cellular consequences of DNA-PK are considered, with an eye toward discerning the rationale for therapeutic targeting of DNA-PK.

SIGNIFICANCE

Although DNA-PK is classically considered a component of damage response, recent findings illuminate damage-independent functions of DNA-PK that affect multiple tumor-associated pathways and provide a rationale for the development of novel therapeutic strategies.

Beyond DNA repair: DNA-PK function in cancer

The DNA-dependent protein kinase (DNA-PK) is a pivotal component of the DNA repair machinery that governs the response to DNA damage, serving to maintain genome integrity. However, the DNA-PK kinase component was initially isolated with transcriptional complexes, and recent findings have illuminated the impact of DNA-PK-mediated transcriptional regulation on tumor progression and therapeutic response. DNA-PK expression has also been correlated with poor outcome in selected tumor types, further underscoring the importance of understanding its role in disease. Herein, the molecular and cellular consequences of DNA-PK are considered, with an eye toward discerning the rationale for therapeutic targeting of DNA-PK.

SIGNIFICANCE

Although DNA-PK is classically considered a component of damage response, recent findings illuminate damage-independent functions of DNA-PK that affect multiple tumor-associated pathways and provide a rationale for the development of novel therapeutic strategies.

Genotypic characteristics of resistant tumors to pre-operative ionizing radiation in rectal cancer

Due to a wide range of clinical response in patients undergoing neo-adjuvant chemoradiation for rectal cancer it is essential to understand molecular factors that lead to the broad response observed in patients receiving the same form of treatment. Despite extensive research in this field, the exact mechanisms still remain elusive. Data raging from DNA-repair to specific molecules leading to cell survival as well as resistance to apoptosis have been investigated. Individually, or in combination, there is no single pathway that has become clinically applicable to date. In the following review, we describe the current status of various pathways that might lead to resistance to the therapeutic applications of ionizing radiation in rectal cancer.

Chemotherapeutic compounds targeting the DNA double-strand break repair pathways: the good, the bad, and the promising

The repair of DNA double-strand breaks (DSBs) is a critical cellular mechanism that exists to ensure genomic stability. DNA DSBs are the most deleterious type of insult to a cell's genetic material and can lead to genomic instability, apoptosis, or senescence. Incorrectly repaired DNA DSBs have the potential to produce chromosomal translocations and genomic instability, potentially leading to cancer. The prevalence of DNA DSBs in cancer due to unregulated growth and errors in repair opens up a potential therapeutic window in the treatment of cancers. The cellular response to DNA DSBs is comprised of two pathways to ensure DNA breaks are repaired: homologous recombination and non-homologous end joining. Identifying chemotherapeutic compounds targeting proteins involved in these DNA repair pathways has shown promise as a cancer therapy for patients, either as a monotherapy or in combination with genotoxic drugs. From the beginning, there have been a number of chemotherapeutic compounds that have yielded successful responses in the clinic, a number that have failed (CGK-733 and iniparib), and a number of promising targets for future studies identified. This review looks in detail at how the cell responds to these DNA DSBs and investigates the chemotherapeutic avenues that have been and are currently being explored to target this repair process.

Biological effects of (125)i seeds radiation on A549 lung cancer cells: G2/M arrest and enhanced cell death

External beam radiation (EBRT) and (125)I seeds continuous low dose rate radiation (CLDR) were used to treat patients with lung cancer. We herein investigated the biological effects of EBRT and CLDR on lung cancer cells. A549 human lung cancer cell line was thus exposed to different doses of EBRT and CLDR. CLDR was more efficient to inhibit cell growth than EBRT. CLDR induced increased DNA damage as evidenced by long-lasting p-H2AX activity. The enhanced inhibitory effects of CLDR on lung cancer cell growth may be, at least in part, due to the increased Bax/Bcl2 ratio and cyclin B1-mediated G2/M arrest.

High Expression of SOX2 and OCT4 Indicates Radiation Resistance and an Independent Negative Prognosis in Cervical Squamous Cell Carcinoma

Radiotherapy (RT) as a preoperative or postoperative adjuvant or primary treatment is the most common management modality for locally advanced cervical cancer. Radioresistance of tumor cells remains a major therapeutic problem. Consequently, we aimed to explore if the stem cell biomarkers SOX2 and OCT4 protein could be used to predict radioresistance in patients with locally advanced cervical squamous cell carcinoma (LACSCC). These 132 patients were divided into two groups (radiation-resistant and radiation-sensitive groups) according to progress-free survival (PFS). Using pretreatment paraffin-embedded tissues, we evaluated SOX2 and OCT4 expression using immunohistochemical staining. The percentage of overexpression of SOX2 and OCT4 in the radiation-resistant group was much higher than that in the radiation-sensitive group (p<0.001 and p <0.001, respectively). The patients with high expression of SOX2 and OCT4 showed a shorter PFS than those with low expression. Our study suggests that the expression of SOX2 and OCT4 in tumor cells indicates resistance to radiotherapy and that these two factors were important predictors of poor survival in patients with LACSCC (hazard ratio [95% CI], 2.294 [1.013, 5.195] and 2.300 [1.050, 5.037], respectively; p=0.046 and p=0.037, respectively).

MiR-124 Radiosensitizes human colorectal cancer cells by targeting PRRX1

One of the challenges in the treatment of colorectal cancer patients is that these tumors show resistance to radiation. MicroRNAs (miRNAs) are involved in essential biological activities, including chemoresistance and radioresistance. Several research studies have indicated that miRNA played an important role in sensitizing cellular response to ionizing radiation (IR). In this study, we found that miR-124 was significantly down-regulated both in CRC-derived cell lines and clinical CRC samples compared with adjacent non-tumor colorectal tissues, MiR-124 could sensitize human colorectal cancer cells to IR in vitro and in vivo. We identified PRRX1, a new EMT inducer and stemness regulator as a novel direct target of miR-124 by using target prediction algorithms and luciferase assay. PRRX1 knockdown could sensitize CRC cells to IR similar to the effects caused by miR-124. Overexpression of PRRX1 in stably overexpressed-miR-124 cell lines could rescue the effects of radiosensitivity enhancement brought by miR-124. Taking these observations into consideration, we illustrated that miR-124 could increase the radiosensitivity of CRC cells by blocking the expression of PRRX1, which indicated miR-124 could act as a great therapeutic target for CRC patients.

Predictive factors for the sensitivity of radiotherapy and prognosis of esophageal squamous cell carcinoma

PURPOSE

To identify predictive biomarkers for radiosensitization and prognosis of esophageal squamous cell carcinoma (ESCC).

MATERIALS AND METHODS

A total of 150 advanced stage ESCC patients were treated with preoperative radiotherapy. The protein levels of Dicer 1, DNA methyltransferase 1 (Dnmt1), and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and the mRNA levels of Dicer 1, Dnmt1, and let-7b microRNA (miRNA) were measured in ESCC tumor tissues before and after radiotherapy. Global DNA methylation was measured and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was performed.

RESULTS

Negative Dicer 1, Dnmt1, and DNA-PKcs protein expression were observed in 72%, 67.3%, and 50.7% of ESCC patients, respectively. Primary Dicer 1 and Dnmt1 expression positively correlated with radiation sensitization and longer survival of ESCC patients, while increased Dicer 1 and Dnmt1 expression after radiation correlated with increased apoptosis in residual tumor tissues. Dicer 1 and Dnmt1 expression correlated with let-7b miRNA expression and global DNA methylation levels, respectively. In contrast, positive DNA-PKcs expression negatively correlated with radiation-induced pathological reactions, and increased DNA-PKcs expression correlated with increased apoptosis after radiation.

CONCLUSION

Global DNA hypomethylation and low miRNA expression are involved in the sensitization of ESCC to radiotherapy and prognosis of patients with ESCC.

Co-expression of CD147 and GLUT-1 indicates radiation resistance and poor prognosis in cervical squamous cell carcinoma

The aim of this study was to investigate the association of CD147 and GLUT-1, which play important roles in glycolysis in response to radiotherapy and clinical outcomes in patients with locally advanced cervical squamous cell carcinoma (LACSCC). The records of 132 female patients who received primary radiation therapy to treat LACSCC at FIGO stages IB-IVA were retrospectively reviewed. Forty-seven patients with PFS (progression-free survival) of less than 36 months were regarded as radiation-resistant. Eighty-five patients with PFS longer than 36 months were regarded as radiation-sensitive. Using pretreatment paraffin-embedded tissues, we evaluated CD147 and GLUT-1 expression by immunohistochemistry. Overexpression of CD147, GLUT-1, and CD147 and GLUT-1 combined were 44.7%, 52.9% and 36.5%, respectively, in the radiation-sensitive group, and 91.5%, 89.4% and 83.0%, respectively, in the radiation-resistant group. The 5-year progress free survival (PFS) rates in the CD147-low, CD147-high, GLUT-1-low, GLUT-1-high, CD147- and/or GLUT-1-low and CD147- and GLUT-1- dual high expression groups were 66.79%, 87.10%, 52.78%, 85.82%, 55.94%, 82.90% and 50.82%, respectively. CD147 and GLUT-1 co-expression, FIGO stage and tumor diameter were independent poor prognostic factors for patients with LACSCC in multivariate Cox regression analysis. Patients with high expression of CD147 alone, GLUT-1 alone or co-expression of CD147 and GLUT-1 showed greater resistance to radiotherapy and a shorter PFS than those with low expression. In particular, co-expression of CD147 and GLUT-1 can be considered as a negative independent prognostic factor.

Phosphorylated Sp1 is the regulator of DNA-PKcs and DNA ligase IV transcription of daunorubicin-resistant leukemia cell lines

Multidrug resistance (MDR) is a serious problem faced in the treatment of malignant tumors. In this study, we characterized the expression of non-homologous DNA end joining (NHEJ) components, a major DNA double strand break (DSB) repair mechanism in mammals, in K562 cell and its daunorubicin (DNR)-resistant subclone (K562/DNR). K562/DNR overexpressed major enzymes of NHEJ, DNA-PKcs and DNA ligase IV, and K562/DNR repaired DSB more rapidly than K562 after DNA damage by neocarzinostatin (MDR1-independent radiation-mimetic). Overexpressed DNA-PKcs and DNA ligase IV were also observed in DNR-resistant HL60 (HL60/DNR) cells as compared with parental HL60 cells. Expression level of DNA-PKcs mRNA paralleled its protein level, and the promoter activity of DNA-PKcs of K562/DNR was higher than that of K562, and the 5'-region between -49bp and the first exon was important for its activity. Because this region is GC-rich, we tried to suppress Sp1 family transcription factor using mithramycin A (MMA), a specific Sp1 family inhibitor, and siRNAs for Sp1 and Sp3. Both MMA and siRNAs suppressed DNA-PKcs expression. Higher serine-phosphorylated Sp1 but not total Sp1 of both K562/DNR and HL60/DNR was observed compared with their parental K562 and HL60 cells. DNA ligase IV expression of K562/DNR was also suppressed significantly with Sp1 family protein inhibition. EMSA and ChIP assay confirmed higher binding of Sp1 and Sp3 with DNA-PKcs 5'-promoter region of DNA-PKcs of K562/DNR than that of K562. Thus, the Sp1 family transcription factor affects important NHEJ component expressions in anti-cancer drug-resistant malignant cells, leading to the more aggressive MDR phenotype.

Repair of radiation damage of U2OS osteosarcoma cells is related to DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity

The present study was to investigate the effects of DNA-PKcs deficiencies on radiation sensitivity of human osteosarcoma U2OS cells to γ-ray and to explore the underlying molecular mechanism. In vitro, U2OS cells were transfected with different DNA-PKcs siRNAs or control siRNAs to establish stably siRNA-transfected cell lines U2OS-Si and U2OS-Sc, respectively. Cell viability and apoptosis after irradiation were analyzed using cell counting kit (CCK-8) and flow cytometric assay, respectively. Expressions of apoptosis-related and oxidative stress-responded proteins were assessed using Western blot. The tumorigenesis activity was examined in nude mice xenograft osteosarcoma mode. Results showed that DNA-PKcs siRNA significantly could inhibit U2OS viability and cell proliferation after exposure to irradiation. Compared with the U2OS and U2OS-Sc cells, the U2OS-Si cells induced higher apoptosis rate and loss of mitochondrial membrane potentials, accompanying with more reactive oxygen species (ROS) and malondialdehyde (MDA) production, increased DNA double-strand breaks (DSBs) induced by irradiation. Protein levels of the anti-apoptotic Bcl-2 were downregulated most obviously in U2OS-Si cells after irradiation, while pro-apoptotic factor Bax and caspase-3 upregulated. Moreover, the antioxidants protein expression levels of Nuclear factor-erythroid 2-related factor 2 (Nrf2) and its target heme oxygenase-1 (HO-1) were also significantly reduced in parallel to DNA-PKcs inhibition in U2OS-Si cells. In nude mice xenograft model, DNA-PKcs siRNA remarkably inhibited tumor growth and dissemination. In conclusion, DNA-PKcs siRNA might have a potential for osteosarcoma treatment by sensitizing osteosarcoma cells to γ-ray through modulation on oxidative stress-mediated DNA DSBs repair and mitochondrial pathway apoptosis.

Selenium substitution endows cystine with radiosensitization activity against cervical cancer cells

Selenium substitution could endow cystine the radiosensitization activity against cervical cancer HeLa cells through overproduction of ROS and activation of downstream signaling, which suggests this could be a novel strategy for design of cancer radiosensitizers.

A hormone-DNA repair circuit governs the response to genotoxic insult

Alterations in DNA repair promote tumor development, but the impact on tumor progression is poorly understood. Here, discovery of a biochemical circuit linking hormone signaling to DNA repair and therapeutic resistance is reported. Findings show that androgen receptor (AR) activity is induced by DNA damage and promotes expression and activation of a gene expression program governing DNA repair. Subsequent investigation revealed that activated AR promotes resolution of double-strand breaks and resistance to DNA damage both in vitro and in vivo. Mechanistically, DNA-dependent protein kinase catalytic subunit (DNAPKcs) was identified as a key target of AR after damage, controlling AR-mediated DNA repair and cell survival after genotoxic insult. Finally, DNAPKcs was shown to potentiate AR function, consistent with a dual role in both DNA repair and transcriptional regulation. Combined, these studies identify the AR-DNAPKcs circuit as a major effector of DNA repair and therapeutic resistance and establish a new node for therapeutic intervention in advanced disease.

SIGNIFICANCE

The present study identifies for the fi rst time a positive feedback circuit linking hormone action to the DNA damage response and shows the significant impact of this process on tumor progression and therapeutic response. These provocative findings provide the foundation for development of novel nodes of therapeutic intervention for advanced disease.

Nuclear survivin and its relationship to DNA damage repair genes in non-small cell lung cancer investigated using tissue array

PURPOSE

To investigate the predictive role and association of nuclear survivin and the DNA double-strand breaks repair genes in non-small cell lung cancer (NSCLC): DNA-dependent protein kinase catalytic subunit (DNA-PKcs), Ku heterodimeric regulatory complex 70-KD subunit (Ku70) and ataxia-telangiectasia mutated (ATM).

METHODS

The protein expression of nuclear survivin, DNA-PKcs, Ku70 and ATM were investigated using immunohistochemistry in tumors from 256 patients with surgically resected NSCLC. Furthermore, we analyzed the correlation between the expression of nuclear survivin, DNA-PKcs, Ku70 and ATM. Univariate and multivariate analyses were performed to determine the prognostic factors that inuenced the overall survival and disease-free survival of NSCLC.

RESULTS

The expression of nuclear survivin, DNA-PKcs, Ku70 and ATM was significantly higher in tumor tissues than in normal tissues. By dichotomizing the specimens as expressing low or high levels of nuclear survivin, nuclear survivin correlated significantly with the pathologic stage (P = 0.009) and lymph node status (P = 0.004). The nuclear survivin levels were an independent prognostic factor for both the overall survival and the disease-free survival in univariate and multivariate analyses. Patients with low Ku70 and DNA-PKcs expression had a greater benefit from radiotherapy than patients with high expression of Ku70 (P = 0.012) and DNA-PKcs (P = 0.02). Nuclear survivin expression positively correlated with DNA-PKcs (P<0.001) and Ku70 expression (P<0.001).

CONCLUSIONS

Nuclear survivin may be a prognostic factor for overall survival in patients with resected stage I-IIIA NSCLC. DNA-PKcs and Ku70 could predict the effect of radiotherapy in patients with NSCLC. Nuclear survivin may also stimulates DNA double-strand breaks repair by its interaction with DNA-PKcs and Ku70.

Identification of HLA ligands and T-cell epitopes for immunotherapy of lung cancer

INTRODUCTION

Lung cancer is the most common cancer worldwide. Every year, as many people die of lung cancer as of breast, colon and rectum cancers combined. Because most patients are being diagnosed in advanced, not resectable stages and therefore have a poor prognosis, there is an urgent need for alternative therapies. Since it has been demonstrated that a high number of tumor- and stromal-infiltrating cytotoxic T cells (CTLs) is associated with an increased disease-specific survival in lung cancer patients, it can be assumed that immunotherapy, e.g. peptide vaccines that are able to induce a CTL response against the tumor, might be a promising approach.

METHODS

We analyzed surgically resected lung cancer tissues with respect to HLA class I- and II-presented peptides and gene expression profiles, aiming at the identification of (novel) tumor antigens. In addition, we tested the ability of HLA ligands derived from such antigens to generate a CTL response in healthy donors.

RESULTS

Among 170 HLA ligands characterized, we were able to identify several potential targets for specific CTL recognition and to generate CD8+ T cells which were specific for peptides derived from cyclin D1 or protein-kinase, DNA-activated, catalytic polypeptide and lysed tumor cells loaded with peptide.

CONCLUSIONS

This is the first molecular analysis of HLA class I and II ligands ex vivo from human lung cancer tissues which reveals known and novel tumor antigens able to elicit a CTL response.

DAB2IP regulates autophagy in prostate cancer in response to combined treatment of radiation and a DNA-PKcs inhibitor

Radiation therapy (RT) is an effective strategy for the treatment of localized prostate cancer (PCa) as well as local invasion. However, some locally advanced cancers develop radiation resistance and recur after therapy; therefore, the development of radiation-sensitizing compounds is essential for treatment of these tumors. DOC-2/DAB2 interactive protein (DAB2IP), which is a novel member of the Ras-GTPase activating protein family and a regulator of phosphatidylinositol 3-kinase-Akt activity, is often downregulated in aggressive PCa. Our previous studies have shown that loss of DAB2IP results in radioresistance in PCa cells primarily because of accelerated DNA double-strand break (DSB) repair kinetics, robust G(2)/M checkpoint control, and evasion of apoptosis. A novel DNA-PKcs inhibitor NU7441 can significantly enhance the effect of radiation in DAB2IP-deficient PCa cells. This enhanced radiation sensitivity after NU7441 treatment is primarily due to delayed DNA DSB repair. More significantly, we found that DAB2IP-deficient PCa cells show dramatic induction of autophagy after treatment with radiation and NU7441. However, restoring DAB2IP expression in PCa cells resulted in decreased autophagy-associated proteins, such as LC3B and Beclin 1, as well as decreased phosphorylation of S6K and mammalian target of rapamycin (mTOR). Furthermore, the presence of DAB2IP in PCa cells can lead to more apoptosis in response to combined treatment of NU7441 and ionizing radiation. Taken together, NU7441 is a potent radiosensitizer in aggressive PCa cells and DAB2IP plays a critical role in enhancing PCa cell death after combined treatment with NU7441 and radiation.

MicroRNA-324-3p regulates nasopharyngeal carcinoma radioresistance by directly targeting WNT2B

PURPOSE

Radioresistance severely restricts the clinical treatment of nasopharyngeal carcinoma (NPC). Accumulating evidence demonstrates that aberrant expression of microRNAs (miRNAs) contributes to cancer progression and sensitivity to radiation. Therefore, we aimed to identify miRNAs associated with radioresistance in NPC.

METHODS

Aberrant miRNA-324-3p expression in NPC CNE-2 cells with radioresistance (CNE-2-Rs), compared to its parental cells, was screened by high-throughput sequencing technology and determined by quantitative reverse transcription-polymerase chain reaction analysis (qRT-PCR) analysis. Bioinformatic analysis was used to predict the downstream target genes of miRNA-324-3p. Then, functional and mechanical analyses of miRNA-324-3p in NPC radioresistance were performed by overexpression and down-regulation of miRNA-324-3p in CNE-2-Rs cells and its parental cells. Finally, the clinical significance of miRNA-324-3p and WNT2B was investigated in NPC tissues.

RESULTS

Our data reveal that the expression of miRNA-324-3p is significantly decreased in CNE-2-Rs cells compared to its parental cells, and WNT2B is predicted to be the downstream target of miRNA-324-3p. Both overexpression and down-regulation of miRNA-324-3p following irradiation result in radiosensitivity alterations and protein changes of WNT2B signalling pathway in CNE-2-Rs cells and its parental cells. Importantly, down-regulation of miRNA-324-3p and up-regulation of WNT2B are significantly correlated with advanced clinical stages of NPC and this inverse expression pattern is also observed in NPC tissues before and after irradiation.

CONCLUSIONS

The present study reveals that miRNA-324-3p contributes to the radioresistance of NPC by regulating the WNT2B signalling pathway. Both miRNA-324-3p and WNT2B are potential biomarkers for radioresistance in NPC, which may serve as valuable targets for reversing radioresistance in the management of NPC.

Inhibition of non-homologous end joining repair impairs pancreatic cancer growth and enhances radiation response

Pancreatic ductal adenocarcinoma (PDAC) is amongst the deadliest of human cancers, due to its late diagnosis as well as its intense resistance to currently available therapeutics. To identify mechanisms as to why PDAC are refractory to DNA damaging cytoxic chemotherapy and radiation, we performed a global interrogation of the DNA damage response of PDAC. We find that PDAC cells generally harbor high levels of spontaneous DNA damage. Inhibition of Non-Homologous End Joining (NHEJ) repair either pharmacologically or by RNAi resulted in a further accumulation of DNA damage, inhibition of growth, and ultimately apoptosis even in the absence of exogenous DNA damaging agents. In response to radiation, PDAC cells rely on the NHEJ pathway to rapidly repair DNA double strand breaks. Mechanistically, when NHEJ is inhibited there is a compensatory increase in Homologous Recombination (HR). Despite this upregulation of HR, DNA damage persists and cells are significantly more sensitive to radiation. Together, these findings support the incorporation of NHEJ inhibition into PDAC therapeutic approaches, either alone, or in combination with DNA damaging therapies such as radiation.

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.

DNA-PKcs expression predicts response to radiotherapy in prostate cancer

PURPOSE

Double-strand breaks, the most lethal DNA lesions induced by ionizing radiation, are mainly repaired by the nonhomologous end-joining system. The expression of the nonhomologous end-joining pathway has never been studied in prostate cancer, and its prognostic value for patients undergoing radiotherapy remains unknown.

METHODS

Pretreatment biopsies from 238 patients treated with exclusive external beam radiotherapy for localized prostate cancer with ≥ 2 years of follow-up were reviewed to reassess the Gleason score. Of these 238 cases, 179 were suitable for in situ analysis and were included in the tissue microarrays. Expression of the nonhomologous end-joining proteins Ku70, Ku80, DNA-dependent protein kinase, catalytic subunits (DNA-PKcs), and X-ray repair cross complementing 4-like factor was studied by immunohistochemistry, together with the proliferation marker Ki67.

RESULTS

The predictive value of the Gleason score for biochemical relapse (using the Phoenix criteria) was markedly improved after review (P<.0001) compared with the initial score (P=.003). The clinical stage, pretreatment prostate-specific antigen level, and perineural invasion status were also associated with progression-free survival (P=.005, P<.0001, and P=.03, respectively). High proliferation (>4%) tends to be associated with biochemical recurrence; however, the difference did not reach statistical significance (P=.06). Although the expression of Ku70, Ku80, and X-ray repair cross complementing 4-like factor was not predictive of relapse, positive DNA-PKcs nuclear staining was closely associated with biochemical recurrence (P=.0002). On multivariate analysis, only the Gleason score, prostate-specific antigen level, and DNA-PKcs status remained predictive of recurrence (P=.003, P=.002, and P=.01, respectively).

CONCLUSIONS

The results of the present study highly suggest that DNA-PKcs could be a predictive marker of recurrence after radiotherapy, independently of the classic prognostic markers, including the Gleason score modified after review.

Detection of early Abl kinase activation after ionizing radiation by using a peptide biosensor

The ubiquitously expressed Abl protein is a non-receptor tyrosine kinase that undergoes nuclear-cytoplasmic shuttling and is involved in many signaling pathways in the cell. Nuclear Abl is activated by DNA damage to regulate DNA repair, cell-cycle checkpoints and apoptosis. Previous studies have established that ataxia telangiectasia mutated (ATM) activates nuclear Abl by phosphorylating serine 465 (S465) in the kinase domain in response to ionizing radiation (IR). Using a peptide biosensor that specifically reports on the Abl kinase activity, we found that an Abl-S465A mutant, which is not capable of being activated by ATM through the canonical site, was still activated rapidly after IR. We established that DNA-dependent protein kinase (DNAPK) is likely to be responsible for a second pathway to activate Abl early on in the response to IR through phosphorylation at a site other than S465. Our findings show that nuclear and cytoplasmic Abl kinase is activated early on (within 5 min) in response to IR by both ATM and DNAPK, and that although one or the other of these kinases is required, either one is sufficient to activate Abl. These results support the concept of early Abl recruitment by both the ATM and the DNAPK pathways to regulate nuclear events triggered by DNA damage and potentially communicate them to proteins in the cytoplasm.

Inhibition of DNA-dependent protein kinase induces accelerated senescence in irradiated human cancer cells

DNA-dependent protein kinase (DNA-PK) plays a pivotal role in the repair of DNA double-strand breaks (DSB) and is centrally involved in regulating cellular radiosensitivity. Here, we identify DNA-PK as a key therapeutic target for augmenting accelerated senescence in irradiated human cancer cells. We find that BEZ235, a novel inhibitor of DNA-PK and phosphoinositide 3-kinase (PI3K)/mTOR, abrogates radiation-induced DSB repair resulting in cellular radiosensitization and growth delay of irradiated tumor xenografts. Importantly, radiation enhancement by BEZ235 coincides with a prominent p53-dependent accelerated senescence phenotype characterized by positive β-galactosidase staining, G(2)-M cell-cycle arrest, enlarged and flattened cellular morphology, and increased p21 expression and senescence-associated cytokine secretion. Because this senescence response to BEZ235 is accompanied by unrepaired DNA DSBs, we examined whether selective targeting of DNA-PK also induces accelerated senescence in irradiated cells. Significantly, we show that specific pharmacologic inhibition of DNA-PK, but not PI3K or mTORC1, delays DSB repair leading to accelerated senescence after radiation. We additionally show that PRKDC knockdown using siRNA promotes a striking accelerated senescence phenotype in irradiated cells comparable with that of BEZ235. Thus, in the context of radiation treatment, our data indicate that inhibition of DNA-PK is sufficient for the induction of accelerated senescence. These results validate DNA-PK as an important therapeutic target in irradiated cancer cells and establish accelerated senescence as a novel mechanism of radiosensitization induced by DNA-PK blockade.

Effects of phytochemicals on ionization radiation-mediated carcinogenesis and cancer therapy

Ionizing radiation (IR)-induced cellular damage is implicated in carcinogenesis as well as therapy of cancer. Advances in radiation therapy have led to the decrease in dosage and localizing the effects to the tumor; however, the development of radioresistance in cancer cells and radiation toxicity to normal tissues are still the major concerns. The development of radioresistance involves several mechanisms, including the activation of mitogenic and survival signaling, induction of DNA repair, and changes in redox signaling and epigenetic regulation. The current strategy of combining radiation with standard cytotoxic chemotherapeutic agents can potentially lead to unwanted side effects due to both agents. Thus agents are needed that could improve the efficacy of radiation killing of cancer cells and prevent the damage to normal cells and tissues caused by the direct and bystander effects of radiation, without have its own systemic toxicity. Chemopreventive phytochemicals, usually non-toxic agents with both cancer preventive and therapeutic activities, could rightly fit in this approach. In this regard, naturally occurring compounds, including curcumin, parthenolide, genistein, gossypol, ellagic acid, withaferin, plumbagin and resveratrol, have shown considerable potential. These agents suppress the radiation-induced activation of receptor tyrosine kinases and nuclear factor-κB signaling, can modify cell survival and DNA repair efficacy, and may potentiate ceramide signaling. These radiosensitizing and counter radioresistance mechanisms of phytochemicals in cancer cells are also associated with changes in epigenetic gene regulation. Because radioresistance involves multiple mechanisms, more studies are needed to discover novel phytochemicals having multiple mechanisms of radiosensitization and to overcome radioresistance of cancer cells. Pre-clinical studies are needed to address the appropriate dosage, timing, and duration of the application of phytochemicals with radiation to justify clinical trials. Nonetheless, some phytochemicals in combination with IR may play a significant role in enhancing the therapeutic index of cancer treatment.

Interrogation of nucleotide excision repair capacity: impact on platinum-based cancer therapy

DNA repair is essential for routine monitoring and repair of damage imparted to our genetic material by exposure to endogenous and exogenous carcinogens, including reactive oxygen species, UV light, and chemicals such as those found in cigarette smoke. Without DNA repair pathways, the continual assault on our DNA would be highly mutagenic and the risk of cancer increased. Paradoxically, the same pathways that help prevent cancer development are detrimental to the efficacy of DNA-damaging cancer therapeutics such as cisplatin. Recent studies demonstrate the inverse relationship between DNA repair capacity and efficacy of platinum-based chemotherapeutics: increased DNA repair capacity leads to resistance, while decreased capacity leads to increased sensitivities. Cisplatin's cytotoxic effects are mediated by formation of intrastrand DNA crosslinks, which are predominantly repaired via the nucleotide excision repair (NER) pathway. In an effort to personalize the treatment of cancers based on DNA repair capacity, we developed an ELISA-based assay to measure NER activity accurately and reproducibly as a prognostic for platinum-based treatments. Here we present an overview of DNA repair and its link to cancer and therapeutics. We also present data demonstrating the ability to detect the proteins of the pre-incision complex within the NER pathway from cell and tissue extracts.

The relationship between p27(kip1) expression and the change of radiosensitivity of esophageal carcinoma cells

OBJECTIVE

Radioresistance is considered the main reason for therapeutic failure in radiotherapy of esophageal carcinoma. However, the underlying mechanisms of radioresistance remain elusive. The purpose of this study was to investigate the relationship between p27(kip1) expression and the change of radiosensitivity of esophageal carcinoma cells.

MATERIAL AND METHODS

Radioresistant cells were gradually isolated by means of repeated gamma-ray irradiation upon esophageal carcinoma cells. The radiosensitivity of established radioresistant cells and parental cells was measured by standard colony-forming assay. Cell cycle was detected by flow cytometry. Western blot method was performed to identify the expression of p27(kip1).

RESULTS

Colony-forming assay showed that the radioresistant cells had obvious radioresistance. Percentage of the radioresistant cells at G(0)/G(1) and G(2)/M phase was significantly decreased, and the percentage of S phase cells was significantly increased compared with the parent cells (p < 0.05). Western blotting revealed that p27(kip1) expression of the radioresistant cells was lower than that of parent cells.

CONCLUSIONS

Our results suggest that cell phase change due to the decrease of p27(kip1) expression is one of the mechanisms of radioresistance in esophageal carcinoma cells.

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.

Molecular characterization of early adenocarcinoma of the uterine cervix by oligonucleotide microarray

PURPOSE

In an attempt to understand the molecular characterization for the early adenocarcinoma of the uterine cervix, an analysis of gene expression profiles obtained from early adenocarcinoma of the uterine cervix was performed to find those genes most aberrantly expressed.

METHODS AND MATERIALS

Total RNA was prepared from 32 samples of early adenocarcinoma of the uterine cervix and 32 paired normal cervix tissues, and hybridized to cancer-associated oligonucleotide microarrays with probe sets complementary to about 1,426 transcripts.

RESULTS

Supervised analysis of gene expression data identified 13 genes that exhibited >2-fold upregulation and 27 genes >2-fold downregulation, respectively, in early adenocarcinoma of the uterine cervix compared to normal cervix. Unsupervised hierarchical clustering of the expression data readily distinguished early adenocarcinoma of the uterine cervix from normal cervix. Two genes (karyopherin alpha 2 and proliferating cell nuclear antigen) were selected randomly for real-time reverse transcription polymerase chain reaction analysis. Both genes were expressed significantly higher in early adenocarcinoma of the uterine cervix than in normal cervix, with p = 0.0003 and <0.0001, respectively. These results were compatible with the microarray data.

CONCLUSIONS

This study has revealed several genes that may be highly attractive candidate molecular markers/targets for early adenocarcinoma of the uterine cervix.