Perspectives on the combination of radiotherapy and targeted therapy with DNA repair inhibitors in the treatment of pancreatic cancer

Inhibition of p300 increases cytotoxicity of cisplatin in pancreatic cancer cells

Pancreatic cancer is a notoriously deadly disease with a five-year survival rate around 10 percent. Since early detection of these tumors is difficult, pancreatic cancers are often diagnosed at advanced stages. At this point, genotoxic chemotherapeutics can be used to manage tumor growth. However, side effects of these drugs are severe, limiting the amount of treatment that can be given and resulting in sub-optimal dosing. Thus, there is an urgent need to identify chemo-sensitizing agents that can lower the effective dose of genotoxic agents and as a result reduce the side effects. Here, we use transformed and non-transformed pancreatic cell lines to evaluate DNA repair inhibitors as chemo-sensitizing agents. We used a novel next generation sequencing approach to demonstrate that pancreatic cancer cells have a reduced ability to faithfully repair DNA damage. We then determine the extent that two DNA repair inhibitors (CCS1477, a small molecule inhibitor of p300, and ART558, a small molecule inhibitor of polymerase theta) can exploit this repair deficiency to make pancreatic cancer cells more sensitive to cisplatin, a commonly used genotoxic chemotherapeutic. Immunofluorescence microscopy and cell viability assays show that CCS1477 delayed repair and significantly sensitized pancreatic cancer cells to cisplatin. The increased toxicity was not seen in a non-transformed pancreatic cell line. We also found that while ART558 sensitizes pancreatic cancer cells to cisplatin, it also sensitized non-transformed pancreatic cancer cells.

Parp Inhibitors and Radiotherapy: A New Combination for Prostate Cancer (Systematic Review)

PARPi, in combination with ionizing radiation, has demonstrated the ability to enhance cellular radiosensitivity in different tumors. The rationale is that the exposure to radiation leads to both physical and biochemical damage to DNA, prompting cells to initiate three primary mechanisms for DNA repair. Two double-stranded DNA breaks (DSB) repair pathways: (1) non-homologous end-joining (NHEJ) and (2) homologous recombination (HR); and (3) a single-stranded DNA break (SSB) repair pathway (base excision repair, BER). In this scenario, PARPi can serve as radiosensitizers by leveraging the BER pathway. This mechanism heightens the likelihood of replication forks collapsing, consequently leading to the formation of persistent DSBs. Together, the combination of PARPi and radiotherapy is a potent oncological strategy. This combination has proven its efficacy in different tumors. However, in prostate cancer, there are only preclinical studies to support it and, recently, an ongoing clinical trial. The objective of this paper is to perform a review of the current evidence regarding the use of PARPi and radiotherapy (RT) in PCa and to give future insight on this topic.

Enhancing the anti-tumor response by combining DNA damage repair inhibitors in the treatment of solid tumors

The anti-cancer efficacy of anti-malignancy therapies is related to DNA damage. However, DNA damage-response mechanisms can repair DNA damage, failing anti-tumor therapy. The resistance to chemotherapy, radiotherapy, and immunotherapy remains a clinical challenge. Thus, new strategies to overcome these therapeutic resistance mechanisms are needed. DNA damage repair inhibitors (DDRis) continue to be investigated, with polyadenosine diphosphate ribose polymerase inhibitors being the most studied inhibitors. Evidence of their clinical benefits and therapeutic potential in preclinical studies is growing. In addition to their potential as a monotherapy, DDRis may play an important synergistic role with other anti-cancer therapies or in reversing acquired treatment resistance. Here we review the impact of DDRis on solid tumors and the potential value of combinations of different treatment modalities with DDRis for solid tumors.

Boron Neutron Capture Therapy Eliminates Radioresistant Liver Cancer Cells by Targeting DNA Damage and Repair Responses

Introduction

For advanced hepatocellular carcinoma (HCC), resistance to conservative treatments remains a challenge. In previous studies, the therapeutic effectiveness and DNA damage responses of boric acid-mediated boron neutron capture therapy (BA-BNCT) in HCC have been demonstrated in animal models and HCC cell line. On the other hand, numerous studies have shown that high linear energy transfer (LET) radiation can overcome tumor resistance. Since BNCT yields a mixture of high and low LET radiation, we aimed to explore whether and how BA-BNCT could eliminate radioresistant HCC cells.

Methods

Radioresistant human HCC (HepG2-R) cells were established from HepG2 cells via intermittent irradiation. HepG2 and HepG2-R cells were then irradiated with either γ-ray or neutron radiation of BA-BNCT. Colony formation assays were used to assess cell survival and the relative biological effectiveness (RBE). The expression of phosphorylated H2AX (γH2AX) was also examined by immunocytochemistry and Western blot assays to evaluate the extent of DNA double-strand breaks (DSBs). Finally, the expression levels of DNA damage response-associated proteins were determined, followed by cell cycle analysis and caspase-3 activity analysis.

Results

Our data demonstrated that under the same dose by γ-ray, BNCT effectively eliminated radioresistant HCC by increasing the number of DNA DSBs (p < 0.05) and impeding their repair (p < 0.05), which verified the high RBE of BNCT. We also found that BNCT resulted in delayed homologous recombination (HR) and inhibited the nonhomologous end-joining (NHEJ) pathway during DNA repair. Markedly, BNCT increased cell arrest (p < 0.05) in the G₂/M phase by altering G₂ checkpoint signaling and increased PUMA-mediated apoptosis (p < 0.05).

Conclusion

Our data suggest that DNA damage and repair responses could affect the anticancer efficiency of BNCT in radioresistant HepG2-R cells, which highlights the potential of BNCT as a viable treatment option for recurrent HCC.

Human papillomavirus oncoproteins and post-translational modifications: generating multifunctional hubs for overriding cellular homeostasis

Human papillomaviruses (HPVs) are major human carcinogens, causing around 5% of all human cancers, with cervical cancer being the most important. These tumors are all driven by the two HPV oncoproteins E6 and E7. Whilst their mechanisms of action are becoming increasingly clear through their abilities to target essential cellular tumor suppressor and growth control pathways, the roles that post-translational modifications (PTMs) of E6 and E7 play in the regulation of these activities remain unclear. Here, we discuss the direct consequences of some of the most common PTMs of E6 and E7, and how this impacts upon the multi-functionality of these viral proteins, and thereby contribute to the viral life cycle and to the induction of malignancy. Furthermore, it is becoming increasingly clear that these modifications, may, in some cases, offer novel routes for therapeutic intervention in HPV-induced disease.

Mitochondrial Targeted Peptide (KLAKLAK)2, and its Synergistic Radiotherapy Effects on Apoptosis of Radio Resistant Human Monocytic Leukemia Cell Line

BACKGROUND

Ionizing radiation plays a significant role in cancer treatment. Despite recent advances in radiotherapy approaches, the existence of irradiation-resistant cancer cells is still a noteworthy challenge. Therefore, developing novel therapeutic approaches are still warranted in order to increase the sensitivity of tumor cells to radiation. Many types of research rely on the role of mitochondria in radiation protection.

OBJECTIVE

Here, we aimed to target the mitochondria of monocyticleukemia (THP-1) radio-resistant cell line cells by a mitochondrial disrupting peptide, D (KLAKLAK)2, and investigate the synergistic effect of Gamma-irradiation and KLA for tumor cells inhibition in vitro.

MATERIAL AND METHODS

In this experimental study, KLA was delivered into THP-1 cells using a Cell-Penetrating Peptide (CPP).The cells were then exposed to gamma-ray radiation both in the presence and absence of KLA conjugated with CPP. The impacts of KLA, ionizing radiation or combination of both were then evaluated on the cell proliferation and apoptosis of THP-1 cells using MTT assay and flow cytometry, respectively.

RESULTS

The MTT assay indicated the anti-proliferative effects of combined D (KLAKLAK)₂ peptide with ionizing radiation on THP-1cells. Moreover, synergetic effects of KLA and ionizing radiation reduced cell viability and consequently enhanced cell apoptosis.

CONCLUSION

Using KLA peptide in combination with ionizing irradiation increases the anticancer effects of radio-resistant THP-1 cells. Therefore, the combinational therapy of (KLAKLAK)₂ and radiation is a promising strategy for cancer treatment the in future.

Identification of an extracellular vesicle-related gene signature in the prediction of pancreatic cancer clinical prognosis

Although extracellular vesicles (EVs) in body fluid have been considered to be ideal biomarkers for cancer diagnosis and prognosis, it is still difficult to distinguish EVs derived from tumor tissue and normal tissue. Therefore, the prognostic value of tumor-specific EVs was evaluated through related molecules in pancreatic tumor tissue. NA sequencing data of pancreatic adenocarcinoma (PAAD) were acquired from The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC). EV-related genes in pancreatic cancer were obtained from exoRBase. Protein–protein interaction (PPI) network analysis was used to identify modules related to clinical stage. CIBERSORT was used to assess the abundance of immune and non-immune cells in the tumor microenvironment. A total of 12 PPI modules were identified, and the 3-PPI-MOD was identified based on the randomForest package. The genes of this model are involved in DNA damage and repair and cell membrane-related pathways. The independent external verification cohorts showed that the 3-PPI-MOD can significantly classify patient prognosis. Moreover, compared with the model constructed by pure gene expression, the 3-PPI-MOD showed better prognostic value. The expression of genes in the 3-PPI-MOD had a significant positive correlation with immune cells. Genes related to the hypoxia pathway were significantly enriched in the high-risk tumors predicted by the 3-PPI-MOD. External databases were used to verify the gene expression in the 3-PPI-MOD. The 3-PPI-MOD had satisfactory predictive performance and could be used as a prognostic predictive biomarker for pancreatic cancer.

The p.Ser64Leu and p.Pro104Leu missense variants of PALB2 identified in familial pancreatic cancer patients compromise the DNA damage response

PALB2 has been identified as a breast and pancreatic cancer susceptibility gene. Utilizing a targeted sequencing approach, we discovered two novel germline missense PALB2 variants c.191C>T and c.311C>T, encoding p.Ser64Leu and p.Pro104Leu, respectively, in individuals in a pancreatic cancer registry. No missense PALB2 variants from familial pancreatic cancer patients, and few PALB2 variants overall, have been functionally characterized. Given the known role of PALB2, we tested the impact of p.Ser64Leu and p.Pro104Leu variants on DNA damage responses. Neither p.Ser64Leu nor p.Pro104Leu have clear effects on interactions with BRCA1 and KEAP1, which are mediated by adjacent motifs in PALB2. However, both variants are associated with defective recruitment of PALB2, and the RAD51 recombinase downstream, to DNA damage foci. Furthermore, p.Ser64Leu and p.Pro104Leu both largely compromise DNA double-strand break-initiated homologous recombination, and confer increased cellular sensitivity to ionizing radiation (IR) and the poly (ADP-ribose) polymerase (PARP) inhibitor Olaparib. Taken together, our results represent the first demonstration of functionally deleterious PALB2 missense variants associated with familial pancreatic cancer and of deleterious variants in the N-terminus outside of the coiled-coil domain. Furthermore, our results suggest the possibility of personalized treatments, using IR or PARP inhibitor, of pancreatic and other cancers that carry a deleterious PALB2 variant.

The Role of Posttranslational Modifications in DNA Repair

The human body is a complex structure of cells, which are exposed to many types of stress. Cells must utilize various mechanisms to protect their DNA from damage caused by metabolic and external sources to maintain genomic integrity and homeostasis and to prevent the development of cancer. DNA damage inevitably occurs regardless of physiological or abnormal conditions. In response to DNA damage, signaling pathways are activated to repair the damaged DNA or to induce cell apoptosis. During the process, posttranslational modifications (PTMs) can be used to modulate enzymatic activities and regulate protein stability, protein localization, and protein-protein interactions. Thus, PTMs in DNA repair should be studied. In this review, we will focus on the current understanding of the phosphorylation, poly(ADP-ribosyl)ation, ubiquitination, SUMOylation, acetylation, and methylation of six typical PTMs and summarize PTMs of the key proteins in DNA repair, providing important insight into the role of PTMs in the maintenance of genome stability and contributing to reveal new and selective therapeutic approaches to target cancers.

KIF23 enhances cell proliferation in pancreatic ductal adenocarcinoma and is a potent therapeutic target

Background

In recent research, high expression of kinesin family member 23 (KIF23), one of the kinesin motor proteins involved in the regulation of cytokinesis, has been shown to be related to poor prognosis in glioma and paclitaxel-resistant gastric cancer, as a results of the enhancement of proliferation, migration, and invasion. In this study, we analyzed the role of KIF23 in the progression of pancreatic ductal adenocarcinoma.

Methods

A bioinformatic method was used to analyze the KIF23 mRNA level in pancreatic tumor tissues compared with normal pancreatic tissues and to analyze the connection between high KIF23 expression and prognosis. We examined the expression of KIF23 using immunohistochemistry and analyzed the connection between the expression of KIF23 and clinicopathological features in pancreatic ductal adenocarcinoma patients. In addition, a colony formation assay, MTT assay, and western blot assay were performed in vitro, along with a mouse xenograft model in vivo, to analyze the effect of KIF23 on proliferation. Further, the correlation between KIF23 and CDCA8 was analyzed by TCGA and immunohistochemical data.

Results

Bioinformatic results showed that KIF23 mRNA expression was higher in pancreatic tumor tissues than in normal pancreatic tissues and a poor prognosis has been linked to the high expression of KIF23. Immunohistochemistry revealed that KIF23 was highly expressed at the protein level and high expression of KIF23 correlated with adverse clinicopathological features. Our experimental results demonstrated that knockdown of KIF23 could inhibit the proliferation of pancreatic cells. Further, a positive correlation between KIF23 and CDCA8 expression existed, and KIF23 might promote pancreatic cancer proliferation by affecting CDCA8 expression.

Conclusions

Our data showed that high expression of KIF23 is associated with a poor prognosis, and KIF23 might be a potential therapeutic target for pancreatic ductal adenocarcinoma.

Epigenetic based synthetic lethal strategies in human cancers

Over the past decades, it is recognized that loss of DNA damage repair (DDR) pathways is an early and frequent event in tumorigenesis, occurring in 40-50% of many cancer types. The basis of synthetic lethality in cancer therapy is DDR deficient cancers dependent on backup DNA repair pathways. In cancer, the concept of synthetic lethality has been extended to pairs of genes, in which inactivation of one by deletion or mutation and pharmacological inhibition of the other leads to death of cancer cells whereas normal cells are spared the effect of the drug. The paradigm study is to induce cell death by inhibiting PARP in BRCA1/2 defective cells. Since the successful application of PARP inhibitor, a growing number of developed DDR inhibitors are ongoing in preclinical and clinical testing, including ATM, ATR, CHK1/2 and WEE1 inhibitors. Combination of PARP inhibitors and other DDR inhibitors, or combination of multiple components of the same pathway may have great potential synthetic lethality efficiency. As epigenetics joins Knudson’s two hit theory, silencing of DDR genes by aberrant epigenetic changes provide new opportunities for synthetic lethal therapy in cancer. Understanding the causative epigenetic changes of loss-of-function has led to the development of novel therapeutic agents in cancer. DDR and related genes were found frequently methylated in human cancers, including BRCA1/2, MGMT, WRN, MLH1, CHFR, P16 and APC. Both genetic and epigenetic alterations may serve as synthetic lethal therapeutic markers.

PP2A and tumor radiotherapy

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase that serves as a key regulator of cellular physiology in the context of apoptosis, mitosis, and DNA damage responses. Canonically, PP2A functions as a tumor suppressor gene. However, recent evidence suggests that inhibiting PP2A activity in tumor cells may represent a viable approach to enhancing tumor sensitivity to chemoradiotherapy as such inhibition can cause cells to enter a disordered mitotic state that renders them more susceptible to cell death. Indeed, there is evidence that inhibiting PP2A can slow tumor growth following radiotherapy in a range of cancer types including ovarian cancer, liver cancer, malignant glioma, pancreatic cancer, and nasopharyngeal carcinoma. In the present review, we discuss current understanding of the role of PP2A in tumor radiotherapy and the potential mechanisms whereby it may influence this process.

Nuclear IGF1R interact with PCNA to preserve DNA replication after DNA-damage in a variety of human cancers

Nuclear IGF1R has been linked to poor outcome in cancer. We recently showed that nuclear IGF1R phosphorylates PCNA and increases DNA damage tolerance. In this paper we aimed to describe this mechanism in cancer tissue as well as in cancer cell lines. In situ proximity ligation assay identified frequent IGF1R and PCNA colocalization in many cancer types. IGF1R/PCNA colocalization was more frequently increased in tumor cells than in adjacent normal, and more prominent in areas with dysplasia and invasion. However, the interaction was often lost in tumors with poor response to neoadjuvant treatment and most metastatic lesions. In two independent cohorts of serous ovarian carcinomas and oropharyngeal squamous cell carcinomas, stronger IGF1R/PCNA colocalization was significantly associated with a higher overall survival. Ex vivo irradiation of ovarian cancer tissue acutely induced IGF1R/PCNA colocalization together with γH2AX-foci formations. In vitro, RAD18 mediated mono-ubiquitination of PCNA during replication stress was dependent on IGF1R kinase activity. DNA fiber analysis revealed that IGF1R activation could rescue stalled DNA replication forks, but only in cancer cells with baseline IGF1R/PCNA interaction. We believe that the IGF1R/PCNA interaction is a basic cellular mechanism to increase DNA stress tolerance during proliferation, but that this mechanism is lost with tumor progression in conjunction with accumulated DNA damage and aberrant strategies to tolerate genomic instability. To exploit this mechanism in IGF1R targeted therapy, IGF1R inhibitors should be explored in the context of concomitant induction of DNA replication stress as well as in earlier clinical stages than previously tried.

YY1-mediated PTEN dephosphorylation antagonizes IR-induced DNA repair contributing to tongue squamous cell carcinoma radiosensitization

Ionizing radiation (IR) confers a survival advantage in tongue squamous cell carcinoma (TSCC), however, IR resistance limits its efficacy. Although Yin Yang 1 (YY1) has been reported to play a role in genotoxic drug resistance by accelerating DNA repair, its role in TSCC radioresistance remains unclear. In this study, we examined YY1 mRNA and protein expression in human tongue cancer samples using qRT-PCR and western blotting, respectively. DNA array data identified YY1 mRNA expression in IR sensitivity or resistance cell lines and tissues. Tongue carcinoma primary cells and CAL27 cells with YY1 stably overexpressed or knocked-down were exposed to IR and evaluated for cell proliferation and apoptosis by CCK8-assay and caspase-3 assay, respectively. We also examined DNA damage- or repair-related indicators, such as YY1, p-H2AX, nuclear PTEN, p-PTEN, and Rad51 through Western blot analysis. Additionally, we explored the mechanism of IR-induced PTEN nuclear translocation by introducing a series of PTEN phosphorylation site mutations and co-IP assay. We observed that YY1 mRNA and protein are highly expressed in TSCC tissues, which was correlated with worse overall survival. Moreover, higher expression of YY1 and Rad51 was observed in radioresistant cells and tissues, overexpression of YY1 led to IR resistance in TSCC cells, whereas YY1 knockdown sensitized TSCC cells to IR. The underlying mechanism showed that the overexpression of YY1 upregulated nuclear PTEN and Rad51 expression, which is essential for DNA repair. IR upregulated YY1, nuclear PTEN, and Rad51; thus, knockdown of YY1 completely blocked IR-induced upregulation of nuclear PTEN/Rad51. IR upregulated PTEN phosphorylation, and mutation of the phosphorylation site of Ser380 nearly completely blocked IR-induced PTEN nuclear translocation. Furthermore, the phosphatase PP2A negatively regulated pS380-PTEN, and knockdown of YY1 completely blocked IR-induced pS380-PTEN through PP2A. In conclusion, knockdown of YY1 enhanced TSCC radiosensitivity through PP2A-mediated dephosphorylation of PTEN Ser380; thus, antagonizing the IR-induced nuclear PTEN/Rad51 axis and targeting YY1 may reverse IR resistance in TSCC.

Proton Irradiation Increases the Necessity for Homologous Recombination Repair Along with the Indispensability of Non-Homologous End Joining

Technical improvements in clinical radiotherapy for maximizing cytotoxicity to the tumor while limiting negative impact on co-irradiated healthy tissues include the increasing use of particle therapy (e.g., proton therapy) worldwide. Yet potential differences in the biology of DNA damage induction and repair between irradiation with X-ray photons and protons remain elusive. We compared the differences in DNA double strand break (DSB) repair and survival of cells compromised in non-homologous end joining (NHEJ), homologous recombination repair (HRR) or both, after irradiation with an equal dose of X-ray photons, entrance plateau (EP) protons, and mid spread-out Bragg peak (SOBP) protons. We used super-resolution microscopy to investigate potential differences in spatial distribution of DNA damage foci upon irradiation. While DNA damage foci were equally distributed throughout the nucleus after X-ray photon irradiation, we observed more clustered DNA damage foci upon proton irradiation. Furthermore, deficiency in essential NHEJ proteins delayed DNA repair kinetics and sensitized cells to both, X-ray photon and proton irradiation, whereas deficiency in HRR proteins sensitized cells only to proton irradiation. We assume that NHEJ is indispensable for processing DNA DSB independent of the irradiation source, whereas the importance of HRR rises with increasing energy of applied irradiation.

RAD51 is a potential marker for prognosis and regulates cell proliferation in pancreatic cancer

BACKGROUND

The DNA damage and repair pathway is considered a promising target for developing strategies against cancer. RAD51, also known as RECA, is a recombinase that performs the critical step in homologous recombination. RAD51 has recently received considerable attention due to its function in tumor progression and its decisive role in tumor resistance to chemotherapy. However, its role in pancreatic cancer has seldom been investigated. In this report, we provide evidence that RAD51, regulated by KRAS, promotes pancreatic cancer cell proliferation. Furthermore, RAD51 regulated aerobic glycolysis by targeting hypoxia inducible factor 1α (HIF1α).

METHODS

TCGA (The Cancer Genome Atlas) dataset analysis was used to examine the impact of RAD51 expression on overall survival of pancreatic cancer patients. Lentivirus-mediated transduction was used to silence RAD51 and KRAS expression. Quantitative real-time PCR and western blot analysis validated the efficacy of the knockdown effect. Analysis of the glycolysis process in pancreatic cancer cells was also performed. Cell proliferation was determined using a CCK-8 (Cell Counting Kit-8) proliferation assay.

RESULTS

Pancreatic cancer patients with higher levels of RAD51 exhibited worse survival. In pancreatic cancer cells, RAD51 positively regulated cell proliferation, decreased intracellular reactive oxygen species (ROS) production and increased the HIF1α protein level. KRAS/MEK/ERK activation increased RAD51 expression. In addition, RAD51 was a positive regulator of aerobic glycolysis.

CONCLUSION

The present study reveals novel roles for RAD51 in pancreatic cancer that are associated with overall survival prediction, possibly through a mechanism involving regulation of aerobic glycolysis. These findings may provide new predictive and treatment targets for pancreatic cancer.

Antineoplastic Effect of a Combined Mitotane Treatment/Ionizing Radiation in Adrenocortical Carcinoma: A Preclinical Study

Mitotane (MTT) is an adrenolytic drug used in adjuvant and advanced treatments of adrenocortical carcinoma (ACC). Ionizing radiation (IR) is also used in adrenal cancer treatment, even though its biological action remains unknown. To provide a reliable in vivo preclinical model of ACC, we used mouse xenografts bearing human ACC to test the effects of MTT and IR alone and in combination. We evaluated tumor growth inhibition by the RECIST criteria and analyzed the cell cycle by flow cytometry (FCM). In the xenograft ACC model treated with MTT/IR in combination, we observed a marked inhibition of tumor growth, with strong tumor regression (p < 0.0001) compared to MTT and IR given alone (p < 0.05). The MTT results confirm its antisteroidogenic activity (p < 0.05) in the xenograft ACC model, revealing its ability to render cancer cells more prone to radiotherapy treatment. In addition, to explain the biological effect of these treatments on the Mismatch Repair System (MMR), we interfered with the MSH2 gene expression in untreated and MTT/IR-treated H295R and SW13 cell lines. Moreover, we observed that upon treatment with MTT/IR to induce DNA damage, MSH2 gene inhibition in both the H295R and SW13 cell lines did not allow DNA damage repair, thus inducing cell death. In conclusion, MTT seems to have a radiosensitizing property and, when given in combination with IR, is able to promote neoplastic growth inhibition, leading to a significant reduction in tumor size due to cell death.

Optical and x-ray technology synergies enabling diagnostic and therapeutic applications in medicine

X-ray and optical technologies are the two central pillars for human imaging and therapy. The strengths of x-rays are deep tissue penetration, effective cytotoxicity, and the ability to image with robust projection and computed-tomography methods. The major limitations of x-ray use are the lack of molecular specificity and the carcinogenic risk. In comparison, optical interactions with tissue are strongly scatter dominated, leading to limited tissue penetration, making imaging and therapy largely restricted to superficial or endoscopically directed tissues. However, optical photon energies are comparable with molecular energy levels, thereby providing the strength of intrinsic molecular specificity. Additionally, optical technologies are highly advanced and diversified, being ubiquitously used throughout medicine as the single largest technology sector. Both have dominant spatial localization value, achieved with optical surface scanning or x-ray internal visualization, where one often is used with the other. Therapeutic delivery can also be enhanced by their synergy, where radio-optical and optical-radio interactions can inform about dose or amplify the clinical therapeutic value. An emerging trend is the integration of nanoparticles to serve as molecular intermediates or energy transducers for imaging and therapy, requiring careful design for the interaction either by scintillation or Cherenkov light, and the nanoscale design is impacted by the choices of optical interaction mechanism. The enhancement of optical molecular sensing or sensitization of tissue using x-rays as the energy source is an important emerging field combining x-ray tissue penetration in radiation oncology with the molecular specificity and packaging of optical probes or molecular localization. The ways in which x-rays can enable optical procedures, or optics can enable x-ray procedures, provide a range of new opportunities in both diagnostic and therapeutic medicine. Taken together, these two technologies form the basis for the vast majority of diagnostics and therapeutics in use in clinical medicine.

Inhibition of DNA‑PK activity sensitizes A549 cells to X‑ray irradiation by inducing the ATM‑dependent DNA damage response

Non‑small cell lung cancer (NSCLC) is radioresistant to X‑rays due to powerful cellular DNA damage repair mechanisms. DNA‑dependent protein kinase (DNA‑PK) is a key enzyme involved in DNA damage repair and the phenomenon and molecular mechanism of NSCLC radionsensitivity were investigated following inhibition of DNA‑PK activity. In the present study A549 cells were treated with the DNA‑PK inhibitor NU7026 and/or siRNA directed against ataxia telangiectasia mutated (ATM), followed by exposure to 4 Gy X‑ray irradiation. Radiosensitivity, DNA damage, apoptosis and protein expression were measured by colony formation assay, γH2AX foci immunofluorescence, Annexin V/PI staining and western blotting, respectively. A Balb/c‑nu/nu xenograft mouse model was established by subcutaneous injection of A549 cells and was used to examine the effect of administering NU7026 via intraperitoneal injection prior to 4 Gy X‑ray exposure. The xenograft tumors were weighed and observed by hematoxylin and eosin staining after irradiation. NU7026 treatment followed by X‑ray irradiation significantly decreased the colony formation ratio of A549 cells, and increased γH2AX foci and cell apoptosis. Furthermore, the combined treatment of NU7026 and X‑rays resulted in growth inhibition and cell apoptosis in A549 xenograft tumors. Consequently, apoptosis regulators full‑length transactivating (TA) p73 and an N‑terminally truncated (DN) p73 were upregulated and downregulated respectively, leading to activation of glucosyltransferases and Rab‑like GTPase activators and myotubularins domain‑containing 4 (GRAMD4) protein to reduce the Bcl‑2/Bax protein ratio. In addition, ATM siRNA efficiently prevented γH2AX foci formation, and enhanced NU7026‑induced inhibition of survival and promoted apoptosis. In conclusion, inhibition of DNA‑PK activity increased the radiosensitivity of A549 cells to X‑ray irradiation. NU7026 treatment activated the ATM‑dependent DNA damage response and induced p73 apoptosis pathway. DNA‑PK inhibitor may be an effective constituent of radiosensitization products. DNA damage repair pathway could be a potential target for radiosensitization.

Inhibition of PI3K/AKT Signaling Pathway Radiosensitizes Pancreatic Cancer Cells with ARID1A Deficiency in Vitro

Pancreatic cancer is among the most aggressive human cancers, and is resistant to regular chemotherapy and radiotherapy. The AT-rich interactive domain containing protein 1A (ARID1A) gene, a crucial chromatin remodeling gene, mutates frequently in a broad spectrum of cancers, including pancreatic cancer. Recent evidence suggests that ARID1A acts as tumor suppressor and plays an important role in DNA damage repair (DDR). However, the effect of ARID1A on the radiosensitivity of pancreatic cancer remains unclear. Herein, we investigated the involvement of ARID1A depletion in the radioresistance of pancreatic cancer cells, and explored the underlying mechanisms. The results reveal that knockdown of ARID1A enhances the radioresistance of pancreatic cancer cells through suppressing apoptosis, impairing G2-M checkpoint arrest, strengthening DDR, and accompanying activation of PI3K/AKT signaling pathway. Moreover, upon inhibition of PI3K/AKT pathway by PI3K-inhibitor LY294002 or AKT-inhibitor mk2206, the radiosensitivity of ARID1A-deficient pancreatic cancer cells is improved in vitro via increased apoptosis and weakened DDR. Taken together, these data suggest that loss of ARID1A expression enhances radioresistance of pancreatic cancer through activation of PI3K/AKT pathway, which maybe a promising target for radiosensitization of ARID1A-deficient pancreatic cancer.

Radiation Treatment in Women with Ovarian Cancer: Past, Present, and Future

Ovarian cancer is the most lethal of the gynecologic cancers, with 5-year survival rates less than 50%. Most women present with advanced stage disease as the pattern of spread is typically with dissemination of malignancy throughout the peritoneal cavity prior to development of any symptoms. Prior to the advent of platinum-based chemotherapy, radiotherapy was used as adjuvant therapy to sterilize micrometastatic disease. The evolution of radiotherapy is detailed in this review, which establishes radiotherapy as an effective therapy for women with micrometastatic disease in the peritoneal cavity after surgery, ovarian clear cell carcinoma, focal metastatic disease, and for palliation of advanced disease. However, with older techniques, the toxicity of whole abdominal radiotherapy and the advancement of systemic therapies have limited the use of radiotherapy in this disease. With newer radiotherapy techniques, including intensity-modulated radiotherapy (IMRT), stereotactic body radiotherapy (SBRT), and low-dose hyperfractionation in combination with targeted agents, radiotherapy could be reconsidered as part of the standard management for this deadly disease.

Role of Protein Phosphatase 2A in Osteoblast Differentiation and Function

The reversible phosphorylation of proteins plays hugely important roles in a variety of cellular processes, such as differentiation, proliferation, and apoptosis. These processes are strictly controlled by protein kinases (phosphorylation) and phosphatases (de-phosphorylation). Here we provide a brief history of the study of protein phosphorylation, including a summary of different types of protein kinases and phosphatases. One of the most physiologically important serine/threonine phosphatases is PP2A. This review provides a description of the phenotypes of various PP2A transgenic mice and further focuses on the known functions of PP2A in bone formation, including its role in osteoblast differentiation and function. A reduction in PP2A promotes bone formation and osteoblast differentiation through the regulation of bone-related transcription factors such as Osterix. Interestingly, downregulation of PP2A also stimulates adipocyte differentiation from undifferentiated mesenchymal cells under the appropriate adipogenic differentiation conditions. In osteoblasts, PP2A is also involved in the ability to control osteoclastogenesis as well as in the proliferation and metastasis of osteosarcoma cells. Thus, PP2A is considered to be a comprehensive factor in controlling the differentiation and function of cells derived from mesenchymal cells such as osteoblasts and adipocytes.

MicroRNA-19b-3p regulates nasopharyngeal carcinoma radiosensitivity by targeting TNFAIP3/NF-κB axis

Background

Nasopharyngeal carcinoma (NPC) is among the most common squamous cell carcinoma in South China and Southeast Asia. Radiotherapy is the primary treatment for NPC. However, radioresistance acts as a significant factor that limits the efficacy of radiotherapy for NPC patients. Growing evidence supports that microRNAs (miRNAs) play an important role in radiation response.

Methods

Real-time quantitative PCR was used to analyze the expression of miR-19b-3p in NPC cell lines and NP69. miR-19b-3p expression profiles in NPC tissues were obtained from the Gene Expression Omnibus database. The effect of miR-19b-3p on radiosensitivity was evaluated by cell viability assays, colony formation assays and in vivo experiment. Apoptosis and cell cycle were examined by flow cytometry. Luciferase reporter assay was used to assess the target genes of miR-19b-3p. Expression of target proteins and downstream molecules were analyzed by Western blot.

Results

miR-19b-3p was upregulated in NPC and served as an independent predictor for reduced patient survival. Radioresponse assays showed that miR-19b-3p overexpression resulted in decreased sensitivity to irradiation, whereas miR-19b-3p downregulation resulted in increased sensitivity to irradiation in vitro. Moreover, miR-19b-3p decreased the sensitivity of NPC cells to irradiation in vivo. Luciferase reporter assay confirmed that TNFAIP3 was a direct target gene of miR-19b-3p. Knockdown of TNFAIP3 reduced sensitivity to irradiation, whereas upregulation of TNFAIP3 expression reversed the inhibitory effects of miR-19b-3p on NPC cell radiosensitivity. Mechanistically, we found that miR-19b-3p increased NPC cell radioresistance by activating the TNFAIP3/ NF-κB axis.

Conclusions

miR-19b-3p contributes to the radioresistance of NPC by activating the TNFAIP3/ NF-κB axis. miR-19b-3p is a determinant of NPC radioresponse and may serve as a potential therapeutic target in NPC treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0465-1) contains supplementary material, which is available to authorized users.