siRNA targeting NBS1 or XIAP increases radiation sensitivity of human cancer cells independent of TP53 status

Moving the Needle Forward in Genomically-Guided Precision Radiation Treatment

Radiation treatment (RT) is a mainstay treatment for many types of cancer. Recommendations for RT and the radiation plan are individualized to each patient, taking into consideration the patient's tumor pathology, staging, anatomy, and other clinical characteristics. Information on germline mutations and somatic tumor mutations is at present rarely used to guide specific clinical decisions in RT. Many genes, such as ATM, and BRCA1/2, have been identified in the laboratory to confer radiation sensitivity. However, our understanding of the clinical significance of mutations in these genes remains limited and, as individual mutations in such genes can be rare, their impact on tumor response and toxicity remains unclear. Current guidelines, including those from the National Comprehensive Cancer Network (NCCN), provide limited guidance on how genetic results should be integrated into RT recommendations. With an increasing understanding of the molecular underpinning of radiation response, genomically-guided RT can inform decisions surrounding RT dose, volume, concurrent therapies, and even omission to further improve oncologic outcomes and reduce risks of toxicities. Here, we review existing evidence from laboratory, pre-clinical, and clinical studies with regard to how genetic alterations may affect radiosensitivity. We also summarize recent data from clinical trials and explore potential future directions to utilize genetic data to support clinical decision-making in developing a pathway toward personalized RT.

Application of nano-radiosensitizers in combination cancer therapy

Radiosensitizers are compounds or nanostructures, which can improve the efficiency of ionizing radiation to kill cells. Radiosensitization increases the susceptibility of cancer cells to radiation-induced killing, while simultaneously reducing the potentially damaging effect on the cellular structure and function of the surrounding healthy tissues. Therefore, radiosensitizers are therapeutic agents used to boost the effectiveness of radiation treatment. The complexity and heterogeneity of cancer, and the multifactorial nature of its pathophysiology has led to many approaches to treatment. The effectiveness of each approach has been proven to some extent, but no definitive treatment to eradicate cancer has been discovered. The current review discusses a broad range of nano-radiosensitizers, summarizing possible combinations of radiosensitizing NPs with several other types of cancer therapy options, focusing on the benefits and drawbacks, challenges, and future prospects.

Apoptosis and Pharmacological Therapies for Targeting Thereof for Cancer Therapeutics

Apoptosis is an evolutionarily conserved sequential process of cell death to maintain a homeostatic balance between cell formation and cell death. It is a vital process for normal eukaryotic development as it contributes to the renewal of cells and tissues. Further, it plays a crucial role in the elimination of unnecessary cells through phagocytosis and prevents undesirable immune responses. Apoptosis is regulated by a complex signaling mechanism, which is driven by interactions among several protein families such as caspases, inhibitors of apoptosis proteins, B-cell lymphoma 2 (BCL-2) family proteins, and several other proteases such as perforins and granzyme. The signaling pathway consists of both pro-apoptotic and pro-survival members, which stabilize the selection of cellular survival or death. However, any aberration in this pathway can lead to abnormal cell proliferation, ultimately leading to the development of cancer, autoimmune disorders, etc. This review aims to elaborate on apoptotic signaling pathways and mechanisms, interacting members involved in signaling, and how apoptosis is associated with carcinogenesis, along with insights into targeting apoptosis for disease resolution.

Application of Radiosensitizers in Cancer Radiotherapy

Radiotherapy (RT) is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors. Although great success has been achieved on radiotherapy, there is still an intractable challenge to enhance radiation damage to tumor tissue and reduce side effects to healthy tissue. Radiosensitizers are chemicals or pharmaceutical agents that can enhance the killing effect on tumor cells by accelerating DNA damage and producing free radicals indirectly. In most cases, radiosensitizers have less effect on normal tissues. In recent years, several strategies have been exploited to develop radiosensitizers that are highly effective and have low toxicity. In this review, we first summarized the applications of radiosensitizers including small molecules, macromolecules, and nanomaterials, especially those that have been used in clinical trials. Second, the development states of radiosensitizers and the possible mechanisms to improve radiosensitizers sensibility are reviewed. Third, the challenges and prospects for clinical translation of radiosensitizers in oncotherapy are presented.

Apoptosis Detection Methods in Diagnosis of Cancer and Their Potential Role in Treatment: Advantages and Disadvantages: a Review

INTRODUCTION

Interruption of regulation of apoptosis can play a leading role in cancers where elevated apoptosis causes neurodegeneration, autoimmunity, AIDS, and ischemia. One famous example can be p53's downregulation, which is a tumor suppressor gene, which consequently can cause a decrease in apoptosis rate and intense tumor growth and progression and development and inactivation of 53; it can be extended to many cancers in human. Anyhow, apoptosis is a double-edge sword. There are many trials and studies are going on observation and understanding of different steps involved in apoptosis. Apoptosis has a very major role in carcinogenesis and the treatment of cancer.

AIM

In this updated-cum-comprehensive review, we would like to cover what is apoptosis and cancer and also, will discuss all known methods of apoptosisdetection, their applicability in the treatment of cancer, and their advantages, disadvantages, and limitations.

MATERIAL AND METHODS

Published articles on indexing sources such as PubMed, Scopus from 2000 to date.

RESULT

By considering all above information including each methods pros and cons, these routine methods could be great tool with distinctive qualities in treatmentwhich can be great help from patient perspective and as well from government ad health care system point of view.

CONCLUSION

Accurate diagnosis of cell apoptotic biopathways at different stages assists in evaluating near to exact apoptotic index, which is the perfect sign andindicator for metastasis and also prognosis, thus foreseeing treatment outcome.

Enhancement of membrane lipid peroxidation in lung cancer cells irradiated with monoenergetic X-rays at the K-shell resonance absorption peak of phosphorus

The aim of this study was to determine whether membrane lipid peroxidation in mammalian cells is enhanced by X-ray irradiation at the K-shell resonance absorption peak of phosphorus. A549 and wild-type p53-transfected H1299 (H1299/wtp53) cell lines derived from human lung carcinoma were irradiated with monoenergetic X-rays at 2.153 keV, the phosphorus K-shell resonance absorption peak, or those at 2.147 or 2.160 keV, which are off peaks. Immunofluorescence staining for 4-hydroxy-2-nonenal (HNE), a lipid peroxidation product, was used as marker for protein modification. In both cell lines, the HNE production was significantly enhanced after irradiation at 2.153 keV compared to sham-irradiation. The enhancement (E) was calculated as the ratio of the fluorescence intensity of irradiated cells to that of sham-irradiated cells. In both the cell lines, E2.153 was significantly larger than E2.147 and no significant difference between E2.147 and E2.160 was observed. The extra enhancement at 2.153 keV was possibly caused by energy transition within the phosphorus K-shell resonance absorption. Our results indicate that membrane lipid peroxidation in cells is enhanced by the Auger effect after irradiation at the K-shell resonance absorption peak of phosphorus rather than by the photoelectric effect of the constituent atoms in the membrane lipid at 2.147 keV.

Comparison of Radiosensitization by HDAC Inhibitors CUDC-101 and SAHA in Pancreatic Cancer Cells

Pancreatic cancer has a poor prognosis. New treatment options are urgently required to improve patient outcomes. One promising new class of anticancer drugs are synthetic histone deacetylase inhibitors (HDACi) which modulate chromatin structure and gene expression by blocking histone deacetylation. In this study, we aimed at comparing the in vitro capacities of the HDACi SAHA and CUDC-101 to increase radiosensitivity of human pancreatic tumor cell lines. Therefore, three pancreatic cancer cell lines (Su.86.86, MIA Paca-2, T3M-4) were treated with SAHA (1.5–5 µM) or CUDC-101 (0.25–3 µM) and after 24 h irradiated. Cell proliferation, clonogenic survival and apoptosis was determined. Additionally, cell lysates were investigated for the expression of apoptosis-related proteins. CUDC-101 and SAHA increased the radiation sensitivity of pancreatic tumor cell lines in a dose-dependent manner. This was evidenced by cell proliferation and clonogenic survival. Furthermore, enhanced radiation sensitivity after CUDC-101 or SAHA treatment was confirmed for Su.86.86 and T3M-4 cells in a 3-D microtissue approach. Increased amounts of subG1 cells and diminished full length PARP-1 suggest increased radiation-induced apoptosis after SAHA or CUDC-101 treatment. The comparison of both inhibitors in these assays manifested CUDC-101 as more potent radiosensitizer than SAHA. In line, western blot quantification of the apoptosis-inhibitory proteins XIAP and survivin showed a stronger down-regulation in response to CUDC-101 treatment than after SAHA application. These proteins may contribute to the synergy between HDAC inhibition and radiation response. In conclusion, these preclinical results suggest that treatment with the HDAC inhibitors CUDC-101 or SAHA can enhance radiation-induced cytotoxicity in human pancreatic cells. However, comparison of both inhibitors identified the multi target inhibitor CUDC-101 as more potent radiosensitizer than the HDAC inhibitor SAHA.

RNA interference to enhance radiation therapy: Targeting the DNA damage response

RNA interference (RNAi) therapy is an emerging class of biopharmaceutical that has immense potential in cancer medicine. RNAi medicines are based on synthetic oligonucleotides that can suppress a target protein in tumour cells with high specificity. This review explores the attractive prospect of using RNAi as a radiosensitiser by targeting the DNA damage response. There are a multitude of molecular targets involved in the detection and repair of DNA damage that are suitable for this purpose. Recent developments in delivery technologies such nanoparticle carriers and conjugation strategies have allowed RNAi therapeutics to enter clinical trials in the treatment of cancer. With further progress, RNAi targeting of the DNA damage response may hold great promise in guiding radiation oncology into the era of precision medicine.

Down-regulation of XIAP enhances the radiosensitivity of esophageal cancer cells in vivo and in vitro

The study investigated the effects of X-chromosome-linked inhibitor of apoptosis (XIAP) gene silencing on the radiosensitivity of esophageal cancer (EC) cells. Western blotting was used to select EC cell lines with XIAP overexpression. Selected EC9706 and KYSE30 cell lines were both divided into four groups: the blank control group, the negative control (NC) group (transfected with pBSHH1), the siRNA-enhanced group (transfected with pBSHH1-XIAP1-siRNA), and the siRNA-decreased group (transfected with pBSHH1-XIAP2-siRNA). Expressions of XIAP were measured by reverse-transcription quantitative PCR (RT-qPCR) and Western blotting, cell survival and viability by MTT assay and colony formation assay, and cell apoptosis by flow cytometry, respectively. Caspase-3 and caspase-9 activity were detected using caspase-3 and caspase-9 activity detection kits. A nude mice model of EC9706 cell line was established to measure tumorigenesis ability. Compared with the NC group, XIAP mRNA and protein expressions were decreased, caspase-3 and caspase-9 activity and apoptosis were up-regulated, and cell survival rate and colony-forming efficiency were lower in the siRNA-enhanced and siRNA-decreased groups in both the cell lines; while the opposite trends were found in the siRNA-decreased group compared with the siRNA-enhanced group. Tumor weight and volume of nude mice were decreased in the siRNA-enhanced and siRNA-decreased groups than those in the NC group, and were elevated in the siRNA-decreased group compared with the siRNA-enhanced group. These results indicate that XIAP gene silencing would strengthen the radiosensitivity of EC9706 cells, which provides a novel target for the treatment of EC.

Potentiality of syringetin for preferential radiosensitization to cancer cells

PURPOSE

To examine the enhancing effects of syringetin on the radiosensitivity of normal and cancer cells, and the related mechanism.

MATERIALS AND METHODS

We used normal human lung and mouse fibroblasts as well as human lung and mouse cancer cells derived from the above normal fibroblasts. Cell radiosensitivity was measured using a colony formation assay. Apoptosis was analyzed with DAPI staining and Western blots. DNA lesions were analyzed with γH2AX immunofluorescent staining.

RESULTS

The colony formation assay showed that syringetin enhanced radiosensitivity more effectively in cancer cells (H1299 and C3H/MCA clone 15) compared with normal cells (HFL-III and C3H/10T1/2). The radiosensitizing effect of syringetin was observed in mutated p53 and wild-type p53-transfected H1299 cells regardless of p53 status. Apoptosis was more frequently observed in X-ray-irradiated H1299 cells combined with syringetin compared with X-ray-only-treated cells. Enhanced apoptosis by syringetin was not observed in HFL-III cells. Western blot analysis showed that X-ray-induced Caspase-3 activation was enhanced by syringetin in H1299 cells. The number of X-ray-induced DNA double-strand breaks (DSB) measured by quantitative analysis of γH2AX foci was the same for H1299 cells treated with X-rays with or without syringetin.

CONCLUSIONS

This study supports the hypothesis that syringetin enhances radiosensitivity more effectively in cancer cells than in normal cells through enhancement of the Caspase-3-mediated apoptosis pathway. Syringetin could be useful in the development of novel efficacious radiosensitizers.

Association between Genetic Variants in DNA Double-Strand Break Repair Pathways and Risk of Radiation Therapy-Induced Pneumonitis and Esophagitis in Non-Small Cell Lung Cancer

Radiation therapy (RT)-induced pneumonitis and esophagitis are commonly developed side effects in non-small cell lung cancer (NSCLC) patients treated with definitive RT. Identifying patients who are at increased risk for these toxicities would help to maximize treatment efficacy while minimizing toxicities. Here, we systematically investigated single nucleotide polymorphisms (SNPs) within double-strand break (DSB) repair pathway as potential predictive markers for radiation-induced esophagitis and pneumonitis. We genotyped 440 SNPs from 45 genes in DSB repair pathways in 250 stage I–III NSCLC patients who received definitive radiation or chemoradiation therapy, followed by internal validation in 170 additional patients. We found that 11 SNPs for esophagitis and 8 SNPs for pneumonitis showed consistent effects between discovery and validation populations (same direction of OR and reached significance in meta-analysis). Among them, rs7165790 in the BLM gene was significantly associated with decreased risk of esophagitis in both discovery (OR = 0.59, 95% CI: 0.37–0.97, p = 0.037) and validation subgroups (OR = 0.45, 95% CI: 0.22–0.94, p = 0.032). A strong cumulative effect was observed for the top SNPs, and gene-based tests revealed 12 genes significantly associated with esophagitis or pneumonitis. Our results support the notion that genetic variations within DSB repair pathway could influence the risk of developing toxicities following definitive RT in NSCLC.

Enhancement of cellular radiation sensitivity through degradation of Chk1 by the XIAP-XAF1 complex

X-linked inhibitor of apoptosis (XIAP) and Chk1 are potential molecular targets in radiotherapy. However, their molecular association in the regulation of radiation sensitivity has been rarely studied. Here, we show that XIAP modulates radiation sensitivity by regulating stability of Chk1 in lung cancer cells. Both Chk1 and XIAP are highly expressed in various lung cancer cells. Overexpression of XIAP increased cell survival following genotoxic treatments by preventing downregulation of Chk1. However, XIAP reversed Chk1-protective activity in the presence of XIAP-associated factor 1 (XAF1) by degrading Chk1 via ubiquitination-dependent proteasomal proteolysis. The XIAP-XAF1 complex-mediated Chk1 degradation also required CUL4A and DDB1. Chk1 or XIAP was associated with DDB1 and CUL4A. Depletion of CUL4A or DDB1 prevented the XIAP-XAF1-mediated Chk1 degradation suggesting involvement of a CUL4A/DDB1-based E3 ubiquitin ligase in the process or its collaboration with XIAP E3 ligase activity. Taken together, our findings show that XIAP plays a dual role in modulation of Chk1 stability and cell viability following IR. In the absence of XAF1, XIAP stabilizes Chk1 under IR with corresponding increase of cell viability. By contrast, when XAF1 is overexpressed, XIAP facilitates Chk1 degradation, which leads to enhancement of radiation sensitivity. This selective regulation of Chk1 stability by XIAP and XAF1 could be harnessed to devise a strategy to modulate radiation sensitivity in lung cancer cells.

Targeting IAP proteins in combination with radiotherapy

The efficacy of radiotherapy critically depends on the activation of intrinsic cell death programs in cancer cells. This implies that evasion of cell death, a hallmark of human cancers, can contribute to radioresistance. Therefore, novel strategies to reactivate cell death programs in cancer cells are required in order to overcome resistance to radiotherapy. Since Inhibitor of Apoptosis (IAP) proteins are expressed at high levels in multiple cancers and block cell death induction at a central point, therapeutic targeting of IAP proteins represents a promising approach to potentiate the efficacy of radiotherapy. The current review discusses the concept of targeting IAP proteins in combination with radiotherapy.

Predictive SNPs for radiation-induced damage in lung cancer patients with radiotherapy: a potential strategy to individualize treatment

In the treatment of lung cancer, radiotherapy has become one of the most important therapies, despite its sometimes unpredictable side effects. As such, identifying lung cancer patients who are at high risk of developing severe radiation-induced damage (mainly radiation pneumonitis and radiation-induced esophageal toxicity) and applying effect intervention or monitoring techniques are important. Although human diversity to a certain amount is explained by clinical and dosimetric factors, the presence of specific genetic determinants also influences the occurrence of radiation-induced damage. Here we summarize the data on mechanisms of radiation pneumonitis and radiation-induced esophageal toxicity supporting the involvement of variances of genes in the evolution of radiation-induced damage. Furthermore, the available evidence from current clinical studies of genetic polymorphisms for the prediction of radiation pneumonitis and radiation-induced esophageal toxicity is discussed. Eventually, this may help to truly individualize radiotherapy, using a personal genetic profile of the most relevant genes for each lung cancer patient.

A novel antagonist to the inhibitors of apoptosis (IAPs) potentiates cell death in EGFR-overexpressing non-small-cell lung cancer cells

In the effort to develop an efficient chemotherapy drug for the treatment of non-small-cell lung cancer (NSCLC), we analyzed the anti-tumorigenic effects of a novel small molecule targeting the inhibitor of apoptosis (IAPs), HM90822B, on NSCLC cells. HM90822B efficiently decreased IAP expression, especially that of XIAP and survivin, in several NSCLC cells. Interestingly, cells overexpressing epidermal growth factor receptor (EGFR) due to the mutations were more sensitive to HM90822B, undergoing cell cycle arrest and apoptosis when treated. In xenograft experiments, inoculated EGFR-overexpressing NSCLC cells showed tumor regression when treated with the inhibitor, demonstrating the chemotherapeutic potential of this agent. Mechanistically, decreased levels of EGFR, Akt and phospho-MAPKs were observed in inhibitor-treated PC-9 cells on phosphorylation array and western blotting analysis, indicating that the reagent inhibited cell growth by preventing critical cell survival signaling pathways. In addition, gene-specific knockdown studies against XIAP and/or EGFR further uncovered the involvement of Akt and MAPK pathways in HM90822B-mediated downregulation of NSCLC cell growth. Together, these results support that HM90822B is a promising candidate to be developed as lung tumor chemotherapeutics by targeting oncogenic activities of IAP together with inhibiting cell survival signaling pathways.

Mutations in the FHA-domain of ectopically expressed NBS1 lead to radiosensitization and to no increase in somatic mutation rates via a partial suppression of homologous recombination

Ionizing radiation induces DNA double-strand breaks (DSBs). Mammalian cells repair DSBs through multiple pathways, and the repair pathway that is utilized may affect cellular radiation sensitivity. In this study, we examined effects on cellular radiosensitivity resulting from functional alterations in homologous recombination (HR). HR was inhibited by overexpression of the forkhead-associated (FHA) domain-mutated NBS1 (G27D/R28D: FHA-2D) protein in HeLa cells or in hamster cells carrying a human X-chromosome. Cells expressing FHA-2D presented partially (but significantly) HR-deficient phenotypes, which were assayed by the reduction of gene conversion frequencies measured with a reporter assay, a decrease in radiation-induced Mre11 foci formation, and hypersensitivity to camptothecin treatments. Interestingly, ectopic expression of FHA-2D did not increase the frequency of radiation-induced somatic mutations at the HPRT locus, suggesting that a partial reduction of HR efficiency has only a slight effect on genomic stability. The expression of FHA-2D rendered the exponentially growing cell population slightly (but significantly) more sensitive to ionizing radiation. This radiosensitization effect due to the expression of FHA-2D was enhanced when the cells were irradiated with split doses delivered at 24-h intervals. Furthermore, enhancement of radiation sensitivity by split dose irradiation was not seen in contact-inhibited G0/G1 populations, even though the cells expressed FHA-2D. These results suggest that the FHA domain of NBS1 might be an effective molecular target that can be used to induce radiosensitization using low molecular weight chemicals, and that partial inhibition of HR might improve the effectiveness of cancer radiotherapy.

Prognostic significance of XIAP and NF-κB expression in esophageal carcinoma with postoperative radiotherapy

BACKGROUND

X-chromosome-linked IAP (XIAP) and nuclear factor-κB (NF-κB) are frequently overexpressed and correlate closely with chemoradiotherapy resistance and poor prognosis in many cancers. However, the significance of XIAP and NF-κB expression in radiotherapy sensitivity and its effect on the prognosis of esophageal squamous cell carcinoma (ESCC) are still unknown. The aim of this study was to examine XIAP and NF-κB status in ESCC patients undergoing postoperative radiotherapy after radical surgery, and to evaluate their clinical significance.

METHODS

A total of 78 ESCC patients treated with postoperative radiotherapy after radical surgery were enrolled in this study. We immunohistochemically investigated the expression of XIAP and NF-κB in tissues from enrolled patients with specific antibodies. Then, the correlations among XIAP, NF-κB expression, clinicopathological features and its prognostic relevance in ESCC were analyzed.

RESULTS

The increased expression of XIAP and NF-κB in ESCC tissues were clearly correlated with the tumor differentiation and p-TNM stage. Significant positive correlations were found between the expression status of XIAP and NF-κB (r = 0.779, P = 0.000). Overexpression of XIAP and NF-κB and metastasis were significantly associated with shorter overall survival times in univariate analysis (P < 0.05). Multivariate analysis also confirmed that XIAP expression was an independent prognostic factor (P = 0.005).

CONCLUSIONS

XIAP and NF-κB are intensively expressed in ESCC. The level of XIAP is positively correlated to progression and prognosis of ESCC.

Smac mimetic compound LCL161 sensitizes esophageal carcinoma cells to radiotherapy by inhibiting the expression of inhibitor of apoptosis protein

Currently, unresectable esophageal squamous cell carcinoma (ESCC) is primarily treated by chemoradiotherapy. However, the outcome has not improved significantly due to radioresistance of cancer cells. This study aimed to determine the radiosensitizing effect of LCL161, a novel second mitochondrial-derived activator of caspase (Smac) mimetic, in ESCC cells. ESCC cell lines were treated with LCL161 or radiation, alone or in combination. Cell proliferation was detected by MTT assay. Radiosensitization was evaluated by clonogenic survival assay. Cell apoptosis was detected by flow cytometry. The results showed that LCL161 potently sensitized ESCC cells to radiation with a sensitization enhancement ratio of 1.4-2.0. LCL161 increased radiation-induced DNA double-stranded breaks and promoted the apoptosis of ESCC cells, which could be abrogated by a pan-caspase inhibitor z-VAD-FMK. Furthermore, LCL161 decreased the level of cIAP1 in ESCC cells in a dose-dependent manner and synthesized with irradiation to promote the activation of caspase 8 and the upregulation of TNFα expression in ESCC cells. In conclusion, LCL161 acts as a strong radiosensitizer in human esophageal cancer cells by inhibiting the expression of cIAP1 and promoting the activation of caspase 8, leading to enhanced apoptosis.

The effects of antioxidants on gene expression following gamma-radiation (GR) and proton radiation (PR) in mice in vivo

Ionizing radiation (IR) generates free radicals that interact randomly with a range of intracellular biomolecules that can result in lethal cellular injury. Therefore, IR-inflicted damage is a highly complex interplay of vastly different pathophysiological processes, including inflammation, epithelial regeneration, tissue remodeling, and fibrosis. The development of safe and effective radioprotectors that protect normal tissues following IR exposure is highly desirable. It was previously shown that dietary supplementation with an antioxidant (AOX) diet containing SeM (0.06 μg/g diet), α-lipoic acid (85.7 μg/g diet), NAC (171.4 μg/g diet), sodium ascorbate (142.8 μg/g diet), and vitamin E succinate (71.4μg/ g diet) was an effective countermeasure to lethality in mice following γ-radiation (GR) and proton radiation (PR). ( 1) (,) ( 2) Here we are examining the effect of the AOX diet on global gene expression following RBE-weighted doses of GR (7.0 Gy) and PR (6.4 Gy) in an attempt to gain further insight into the molecular mechanism of action of AOX diet in the context of radiation exposure. The AOX diet altered the expression pattern of several pro- and anti-apoptotic genes. Our data suggest that the AOX diet may alter IL6 signaling following GR and completely block the expression of the prokineticin PROK2, the ligand to the G protein-coupled receptors PROKR1 and PROKR2, which are involved in a number of pathophysiological processes.

Current progress of RNA aptamer-based therapeutics

Aptamers are single-stranded nucleic acids that specifically recognize and bind tightly to their cognate targets due to their stable three-dimensional structure. Nucleic acid aptamers have been developed for various applications, including diagnostics, molecular imaging, biomarker discovery, target validation, therapeutics, and drug delivery. Due to their high specificity and binding affinity, aptamers directly block or interrupt the functions of target proteins making them promising therapeutic agents for the treatment of human maladies. Additionally, aptamers that bind to cell surface proteins are well suited for the targeted delivery of other therapeutics, such as conjugated small interfering RNAs (siRNA) that induce RNA interference (RNAi). Thus, aptamer-siRNA chimeras may offer dual-functions, in which the aptamer inhibits a receptor function, while the siRNA internalizes into the cell to target a specific mRNA. This review focuses on the current progress and therapeutic potential of RNA aptamers, including the use of cell-internalizing aptamers as cell-type specific delivery vehicles for targeted RNAi. In particular, we discuss emerging aptamer-based therapeutics that provide unique clinical opportunities for the treatment various cancers and neurological diseases.

DNA repair polymorphisms influence the risk of second neoplasm after treatment of childhood acute lymphoblastic leukemia

PURPOSE

Patients treated for childhood acute lymphoblastic leukemia (ALL) are considered to be at increased risk of developing second neoplasm. The aim of our study was to identify DNA repair polymorphisms contributing to the risk of second neoplasm in clinically well-characterized Slovenian patients treated for childhood ALL.

METHODS

Pediatric patients diagnosed with ALL between 1971 and 2001 were included in the study. According to the identified clinical risk factors for second neoplasm, a matched set of cases with second neoplasm and controls was selected and genotyped for 11 DNA repair polymorphisms.

RESULTS

Among 359 pediatric patients with ALL, 20 second neoplasms were observed. The dose of radiotherapy (P = 0.011), administration of epipodophyllotoxins (P = 0.006), and the dose of anthracyclines (P < 0.001) showed a significant association with the risk of second neoplasm. Among genetic factors, we observed a significant association of NBN 1197G allele with increased risk of second neoplasms (RR = 4.36; 95 % CI: 1.19-15.98; P = 0.026), while the risk was decreased in carriers of XRCC3-316G allele compared with patients with wild-type genotype (RR = 0.20; 95 % CI: 0.04-0.99; P = 0.049).

CONCLUSIONS

Our results suggest an important role of NBN 1197A>G and XRCC3-316A>G polymorphisms in the development of second neoplasm in patients treated for childhood ALL.

Inhibitor of Apoptosis (IAP) proteins as therapeutic targets for radiosensitization of human cancers

Radiotherapy initiates a variety of signaling events in cancer cells that eventually lead to cell death in case the DNA damage cannot be repaired. However, the signal transduction pathways that mediate cell death in response to radiation-inflicted DNA damage are frequently disturbed in human cancers, contributing to radioresistance. For example, aberrant activation of antiapoptotic programs such as high expression of Inhibitor of Apoptosis (IAP) proteins has been shown to interfere with the efficacy of radiotherapy. Since IAP proteins have been linked to radioresistance in several malignancies, therapeutic targeting of IAP proteins may open new perspectives to overcome radioresistance. Therefore, molecular targeting of IAP proteins may provide novel opportunities to reactivate cell death pathways that mediate radiation-induced cytotoxicity. A number of strategies have been developed in recent years to antagonize IAP proteins for the treatment of cancers. Some of these approaches have already been translated into a clinical application. While IAP protein-targeting agents are currently being evaluated in early clinical trials alone or in combination with conventional chemotherapy, they have not yet been tested in combination with radiation therapy. Therefore, it is a timely subject to discuss the opportunities of antagonizing IAP proteins for radiosensitization. Preclinical studies demonstrating the potential of this concept in relevant in vitro and in vivo models underscore that this combination approach warrants further clinical investigation. Thus, combination protocols using IAP antagonists together with radiotherapy may pave the avenue to more effective radiation-based treatment options for cancer patients.

Therapeutic strategies for head and neck cancer based on p53 status

Squamous cell carcinomas of the head and neck (HNSCC) are one of the most common types of cancers worldwide, and despite advances in treatment, they still represent a clinical challenge. Inactivation of one or more components in the p53 signaling pathway is an extremely common event in human neoplasia, including HNSCC. The loss of p53 function is responsible for increased aggressiveness in cancers, while tumor chemoresistance and radioresistance can depend on deleted p53 expression, or on the expression of mutated-p53 proteins. Thus, consideration and manipulation of the p53 status during HNSCC cancer therapy should be considered. This review discusses the p53 signaling pathways activated by various cellular stresses, including exposure to cancer therapies. The recognition of the p53 status in cancer cells is a significant factor and could provide valuable assistance during the selection of an effective therapeutic approach.

Apoptosis in cancer: from pathogenesis to treatment

Apoptosis is an ordered and orchestrated cellular process that occurs in physiological and pathological conditions. It is also one of the most studied topics among cell biologists. An understanding of the underlying mechanism of apoptosis is important as it plays a pivotal role in the pathogenesis of many diseases. In some, the problem is due to too much apoptosis, such as in the case of degenerative diseases while in others, too little apoptosis is the culprit. Cancer is one of the scenarios where too little apoptosis occurs, resulting in malignant cells that will not die. The mechanism of apoptosis is complex and involves many pathways. Defects can occur at any point along these pathways, leading to malignant transformation of the affected cells, tumour metastasis and resistance to anticancer drugs. Despite being the cause of problem, apoptosis plays an important role in the treatment of cancer as it is a popular target of many treatment strategies. The abundance of literature suggests that targeting apoptosis in cancer is feasible. However, many troubling questions arise with the use of new drugs or treatment strategies that are designed to enhance apoptosis and critical tests must be passed before they can be used safely in human subjects.

Polymorphisms of homologous recombination genes and clinical outcomes of non-small cell lung cancer patients treated with definitive radiotherapy

The repair of DNA double-strand breaks (DSBs) is the major mechanism to maintain genomic stability in response to irradiation. We hypothesized that genetic polymorphisms in DSB repair genes may affect clinical outcomes among non-small cell lung cancer (NSCLC) patients treated with definitive radio(chemo)therapy. We genotyped six potentially functional single nucleotide polymorphisms (SNPs) (i.e., RAD51 −135G>C/rs1801320 and −172G>T/rs1801321, XRCC2 4234G>C/rs3218384 and R188H/rs3218536 G>A, XRCC3 T241M/rs861539 and NBN E185Q/rs1805794) and estimated their associations with overall survival (OS) and radiation pneumonitis (RP) in 228 NSCLC patients. We found a predictive role of RAD51 −135G>C SNP in RP development (adjusted hazard ratio [HR] = 0.52, 95% confidence interval [CI], 0.31–0.86, P = 0.010 for CG/CC vs. GG). We also found that RAD51 −135G>C and XRCC2 R188H SNPs were independent prognostic factors for overall survival (adjusted HR = 1.70, 95% CI, 1.14–2.62, P = 0.009 for CG/CC vs. GG; and adjusted HR = 1.70; 95% CI, 1.02–2.85, P = 0.043 for AG vs. GG, respectively) and that the SNP-survival association was most pronounced in the presence of RP. Our study suggests that HR genetic polymorphisms, particularly RAD51 −135G>C, may influence overall survival and radiation pneumonitis in NSCLC patients treated with definitive radio(chemo)therapy. Large studies are needed to confirm our findings.

Prostate-targeted radiosensitization via aptamer-shRNA chimeras in human tumor xenografts

Dose-escalated radiation therapy for localized prostate cancer (PCa) has a clear therapeutic benefit; however, escalated doses may also increase injury to noncancerous tissues. Radiosensitizing agents can improve ionizing radiation (IR) potency, but without targeted delivery, these agents will also sensitize surrounding normal tissues. Here we describe the development of prostate-targeted RNAi agents that selectively sensitized prostate-specific membrane antigen-positive (PSMA-positive) cells to IR. siRNA library screens identified DNA-activated protein kinase, catalytic polypeptide (DNAPK) as an ideal radiosensitization target. DNAPK shRNAs, delivered by PSMA-targeting RNA aptamers, selectively reduced DNAPK in PCa cells, xenografts, and human prostate tissues. Aptamer-targeted DNAPK shRNAs, combined with IR, dramatically and specifically enhanced PSMA-positive tumor response to IR. These findings support aptamer-shRNA chimeras as selective sensitizing agents for the improved treatment of high-risk localized PCa.

Distinct signaling pathways after higher or lower doses of radiation in three closely related human lymphoblast cell lines

PURPOSE

The tumor suppressor p53 plays an essential role in cellular responses to DNA damage caused by ionizing radiation; therefore, this study aims to further explore the role that p53 plays at different doses of radiation.

MATERIALS AND METHODS

The global cellular responses to higher-dose (10 Gy) and lower dose (iso-survival dose, i.e., the respective D0 levels) radiation were analyzed using microarrays in three human lymphoblast cell lines with different p53 status: TK6 (wild-type p53), NH32 (p53-null), and WTK1 (mutant p53). Total RNAs were extracted from cells harvested at 0, 1, 3, 6, 9, and 24 h after higher and lower dose radiation exposures. Template-based clustering, hierarchical clustering, and principle component analysis were applied to examine the transcriptional profiles.

RESULTS

Differential expression profiles between 10 Gy and iso-survival radiation in cells with different p53 status were observed. Moreover, distinct gene expression patterns were exhibited among these three cells after 10 Gy radiation treatment, but similar transcriptional responses were observed in TK6 and NH32 cells treated with iso-survival radiation.

CONCLUSIONS

After 10 Gy radiation exposure, the p53 signaling pathway played an important role in TK6, whereas the NFkB signaling pathway appeared to replace the role of p53 in WTK1. In contrast, after iso-survival radiation treatment, E2F4 seemed to play a dominant role independent of p53 status. This study dissected the impacts of p53, NFkB and E2F4 in response to higher or lower doses of gamma-irradiation.

Molecularly targeted radiosensitization of human prostate cancer by modulating inhibitor of apoptosis

PURPOSE

The inhibitor of apoptosis proteins (IAP) are overexpressed in hormone-refractory prostate cancer, rendering the cancer cells resistant to radiation. This study aims to investigate the radiosensitizing effect of small-molecule IAP inhibitor both in vitro and in vivo in androgen-independent prostate cancer and the possible mechanism of radiosensitization.

EXPERIMENTAL DESIGN

Radiosensitization of SH-130 in human prostate cancer DU-145 cells was determined by clonogenic survival assay. Combination effect of SH-130 and ionizing radiation was evaluated by apoptosis assays. Pull-down and immunoprecipitation assays were employed to investigate the interaction between SH-130 and IAPs. DU-145 xenografts in nude mice were treated with SH-130, radiation, or combination, and tumor suppression effect was determined by caliper measurement or bioluminescence imaging. Nuclear factor-kappaB activation was detected by luciferase reporter assay and quantitative real-time PCR.

RESULTS

SH-130 potently enhanced radiation-induced caspase activation and apoptosis in DU-145 cells. Both X-linked IAP and cIAP-1 can be pulled down by SH-130 but not by inactive SH-123. Moreover, SH-130 interrupted interaction between X-linked IAP/cIAP-1 and Smac. In a nude mouse xenograft model, SH-130 potently sensitized the DU-145 tumors to X-ray radiation without increasing systemic toxicity. The combination therapy suppressed tumor growth more significantly than either treatment alone, with over 80% of complete tumor regression. Furthermore, SH-130 partially blocked tumor necrosis factor-alpha- and radiation-induced nuclear factor-kappaB activation in DU-145 cells.

CONCLUSIONS

Our results show that small-molecule inhibitors of IAPs can overcome apoptosis resistance and radiosensitize human prostate cancer with high levels of IAPs. Molecular modulation of IAPs may improve the outcome of prostate cancer radiotherapy.

RNA interference-mediated validation of genes involved in telomere maintenance and evasion of apoptosis as cancer therapeutic targets

The discovery of new cancer-related therapeutic targets is mainly based on the identification of genes involved in pathways selectively exploited in cancer cells, including those leading to unlimited replicative potential, evasion of apoptosis, angiogenesis, tissue invasion and metastatic spread. Potentially, a gene--or a gene product--is recognized as a cancer target whether its modulation in experimental models can specifically modify or revert the cancer phenotype. As soon as RNA interference (RNAi)--a natural gene silencing mechanism--was demonstrated in mammalian cells, it rapidly became an essential means for gene knockdown in preclinical models, making it possible to define the role of several human genes and to identify those specifically involved in the onset and progression of cancer. Owing to its powerful gene-silencing properties, RNAi has been proposed as a useful tool to validate new therapeutic targets and to develop innovative anticancer therapies. This chapter summarizes the findings from recent studies relying on the use of RNAi-based approaches to functionally validate therapeutic targets related to two tumor hallmarks: the unlimited replicative potential (i.e., activation of telomere maintenance mechanisms) and evasion of apoptosis (i.e., up-regulation of anti-apoptotic factors).

A potential link between alternative splicing of the NBS1 gene and DNA damage/environmental stress

NBS1 forms a multimetric complex with MRE11/RAD50, which acts as the sensor of DNA double-strand breaks (DSBs). The mechanisms controlling the expression of NBS1 remain largely unknown. Here we show that NBS1 is transcribed as both a wild-type and an alternatively spliced form exhibiting a premature stop codon in an alternative 50-bp exon in intron 2. Although the wild-type transcript predominates in most tissues, the spliced transcript is abundant in resting peripheral blood mononuclear cells (PBMCs). Levels of the spliced form of NBS1 decreased rapidly after irradiation as levels of the wild-type NBS1 transcript increased, resulting in increased levels of NBS1 protein. Both mitogenic stimulation and methyl methanesulfonate treatment also altered the splicing pattern of NBS1. Resting PBMCs, which predominantly express spliced NBS1, were more susceptible to radiation than mitogen-stimulated cells, which showed predominant expression of the wild-type transcript. Since the alternatively spliced NBS1 gene likely did not produce protein, this alternative splicing seems to be associated with the control of NBS1 protein. Thus alternative splicing of the NBS1 gene may be associated with the regulation of NBS1 in response to DSBs, DNA alkylation damage, and mitogenic response.

The eIF4E RNA regulon promotes the Akt signaling pathway

Eukaryotic initiation factor 4E (eIF4E) promotes cellular proliferation and can rescue cells from apoptotic stimuli such as serum starvation. However, the mechanisms underlying apoptotic rescue are not well understood. In this study, we demonstrate that eIF4E overexpression leads to enhanced survival signaling through Akt and that eIF4E requires Akt1 to rescue serum-deprived fibroblasts. Furthermore, a mutant form of eIF4E (W73A), which is messenger RNA (mRNA) export competent but does not promote translation, rescues cells as readily as wild-type eIF4E. We show that eIF4E mediates Akt activation via up-regulation of Nijmegen breakage syndrome 1 (NBS1), a phosphoinositide-3 kinase–Akt pathway upstream activator. Additionally, eIF4E coordinately up-regulates the expression of downstream effectors of the Akt pathway, thereby amplifying Akt signaling effects. A negative regulator of eIF4E, the promyelocytic leukemia protein (PML), suppresses Akt activation and apoptotic rescue. These PML activities likely arise, at least in part, through its inhibition of eIF4E-mediated NBS1 mRNA export. In summary, eIF4E coordinately regulates gene expression to potentiate Akt activation, an activity required for apoptotic rescue.

Double inhibition of XIAP and Bcl-2 axis is beneficial for retrieving sensitivity of renal cell cancer to apoptosis

Renal cell carcinoma (RCC) is known to be resistant to chemo- and radiotherapy due to a high apoptotic threshold. Smac and XIAP (X-linked inhibitor of apoptosis protein) proteins were detected in all RCC cell lines and tissue samples examined. We modulated the function of XIAP, either through its constitutional downregulation with an shRNA vector or by applying a Smac-mimicking peptide. Among RCC cell lines, Caki1 expresses the highest levels of XIAP. We transfected Caki1 with XIAP-targeting shRNA vector and generated stable clones. XIAP was knocked down by RNA interference in clone no. 14 by 81.6% and in clone no. 19 by 85.3%. Compared to the parental and mock-transfected cells, neither clone was more sensitive to conventional chemotherapeutic agents, but both clones were more susceptible to Fas stimulation (P<0.0001) and to pharmacological Bcl-2 inhibition (P<0.0001), as well as to a combination of the two (P<0.0001). Mature Smac binds to XIAP via the N-terminal residues, disrupting its interaction with caspases and promoting their activity. We determined that exposure of Caki1 cells to Smac-N7 peptide (AVPIAQK) resulted in a slight but significant decrease in viability (P=0.0031) and potentiated cisplatin's effect (P=0.0027). In contrast with point targeting of XIAP by shRNA, Smac-N7 peptide is active against several IAP (inhibitor of apoptosis protein) family members, which can explain its role in sensitising cells to cisplatin. Our results suggest that multiple targeting of both Bcl-2 and XIAP or, alternatively, of several IAP family members by the Smac-N7 peptide is a potent way to overcome resistance of RCC to apoptosis-triggering treatment modalities, and might be a new tool for molecular targeted therapy.

Enhanced phosphorylation of Nbs1, a member of DNA repair/checkpoint complex Mre11-RAD50-Nbs1, can be targeted to increase the efficacy of imatinib mesylate against BCR/ABL-positive leukemia cells

Nbs1, a member of the Mre11-RAD50-Nbs1 complex, is phosphorylated by ATM, the product of the ataxia-telangiectasia mutated gene and a member of the phosphatidylinositol 3-kinase-related family of serine-threonine kinases, in response to DNA double-strand breaks (DSBs) to regulate DNA damage checkpoints. Here we show that BCR/ABL stimulated Nbs1 expression by induction of c-Myc-dependent transactivation and protection from caspase-dependent degradation. BCR/ABL-related fusion tyrosine kinases (FTKs) such as TEL/JAK2, TEL/PDGFbetaR, TEL/ABL, TEL/TRKC, BCR/FGFR1, and NPM/ALK as well as interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF) also stimulated Nbs1 expression. Enhanced ATM kinase-dependent phosphorylation of Nbs1 on serine 343 (S343) in response to genotoxic treatment was detected in leukemia cells expressing BCR/ABL and other FTKs in comparison to normal counterparts stimulated with IL-3, GM-CSF, and SCF. Expression of Nbs1-S343A mutant disrupted the intra-S-phase checkpoint, decreased homologous recombinational repair (HRR) activity, down-regulated XIAP expression, and sensitized BCR/ABL-positive cells to cytotoxic drugs. Interestingly, inhibition of Nbs1 phosphorylation by S343A mutant enhanced the antileukemia effect of the combination of imatinib and genotoxic agent.