Impaired DNA damage response--an Achilles' heel sensitizing cancer to chemotherapy and radiotherapy

Long noncoding RNA TUG1 promotes cisplatin resistance in ovarian cancer via upregulation of DNA polymerase eta

Chemoresistance is a major cause of high mortality and poor survival in patients with ovarian cancer (OVCA). Understanding the mechanisms of chemoresistance is urgently required to develop effective therapeutic approaches to OVCA. Here, we show that expression of the long noncoding RNA, taurine upregulated gene 1 (TUG1), is markedly upregulated in samples from OVCA patients who developed resistance to primary platinum-based therapy. Depletion of TUG1 increased sensitivity to cisplatin in the OVCA cell lines, SKOV3 and KURAMOCHI. Combination therapy of cisplatin with antisense oligonucleotides targeting TUG1 coupled with a drug delivery system effectively relieved the tumor burden in xenograft mouse models. Mechanistically, TUG1 acts as a competing endogenous RNA by downregulating miR-4687-3p and miR-6088, both of which target DNA polymerase eta (POLH), an enzyme required for translesion DNA synthesis. Overexpression of POLH reversed the effect of TUG1 depletion on cisplatin-induced cytotoxicity. Our data suggest that TUG1 upregulation allows OVCA to tolerate DNA damage via upregulation of POLH; this provides a strong rationale for targeting TUG1 to overcome cisplatin resistance in OVCA.

The Efficacy of Three Different Oral Hygiene Regimens in Preventing Chemotherapy-Induced Oral Mucositis in Pediatric Patients Receiving Hematopoietic Stem Cell Transplantation

BACKGROUND

Oral mucositis is one of the side effects developed post-hematopoietic stem cell transplant. This retrospective study aimed to assess the efficacy of a mouthwash mixture (lidocaine, sodium alginate, sucralfate, pheniramine) versus hyaluronic acid and a solution of sodium bicarbonate in terms of healing time and weight gain in the treatment of oral mucositis in pediatric patients undergoing allogeneic hematopoietic stem cell transplantation with hemato-oncological malignancies.

METHODS

A total of 171 patients that received chemotherapy for the hematopoietic stem cell transplant were divided into three groups; group 1, treated with a mixed mouthwash of lidocaine, sodium alginate, sucralfate, and pheniramine; group 2, treated with hyaluronic acid; and group 3, treated with an aqueous solution of 5% sodium bicarbonate. Weight and mucositis scale scores derived from medical records of patients.

RESULTS

There was a statistically significant difference in the mucositis scale scores between the groups on the transplant day and days 5, 10, 15 and 20 after the transplantation. At these measurement points, Group 2 (receiving hyaluronic acid) had a lower score, and Group 3 (who received sodium bicarbonate) had a higher score, especially on days 5 and 10 after the transplantation.

CONCLUSION

The results suggest that hyaluronic acid is a more effective treatment option than the other oral care solutions that are frequently used for prophylaxis and treatment of oral mucositis.

DNA Damage and Its Role in Cancer Therapeutics

DNA damage is a double-edged sword in cancer cells. On the one hand, DNA damage exacerbates gene mutation frequency and cancer risk. Mutations in key DNA repair genes, such as breast cancer 1 (BRCA1) and/or breast cancer 2 (BRCA2), induce genomic instability and promote tumorigenesis. On the other hand, the induction of DNA damage using chemical reagents or radiation kills cancer cells effectively. Cancer-burdening mutations in key DNA repair-related genes imply relatively high sensitivity to chemotherapy or radiotherapy because of reduced DNA repair efficiency. Therefore, designing specific inhibitors targeting key enzymes in the DNA repair pathway is an effective way to induce synthetic lethality with chemotherapy or radiotherapy in cancer therapeutics. This study reviews the general pathways involved in DNA repair in cancer cells and the potential proteins that could be targeted for cancer therapeutics.

Identification and characterization of mercaptopyrimidine-based small molecules as inhibitors of nonhomologous DNA end joining

Mercaptopyrimidine derivatives are heterocyclic compounds with potent biological activities including antiproliferative, antibacterial, and anti-inflammatory properties. The present study describes the synthesis and characterization of several mercaptopyrimidine derivatives through condensation of 5,6-diamino-2-mercaptopyrimidin-4-ol with various heterocyclic and aromatic aldehydes. Previous studies have shown that SCR7, synthesized from 5,6-diamino-2-mercaptopyrimidin-4-ol, induced cytotoxicity by targeting cancer cells by primarily inhibiting DNA Ligase IV involved in nonhomologous end joining, one of the major DNA double-strand break repair pathways. Inhibition of DNA repair pathways is considered as an important strategy for cancer therapy. Due to limitations of SCR7 in terms of IC₅₀ in cancer cells, here we have designed, synthesized, and characterized potent derivatives of SCR7 using 5,6-diamino-2-mercaptopyrimidin-4-ol as the starting material. Several synthesized imine compounds exhibited significant improvement in inhibition of end joining and cytotoxicity up to 27-fold lower concentrations than SCR7. Among these, two compounds, SCR116 and SCR132, showed increased cancer cell death in a Ligase IV-dependent manner. Treatment with the compounds also led to reduction in V(D)J recombination efficiency, cell cycle arrest at G2/M phase, accumulation of double-strand breaks inside cells, and improved anti-cancer potential when combined with γ-radiation and radiomimetic drugs. Thus, we describe novel inhibitors of NHEJ with higher efficacy and potential, which can be developed as cancer therapeutics.

Comparative analysis of chlorambucil-induced DNA lesion formation and repair in a spectrum of different human cell systems

Chlorambucil (CLB) belongs to the class of nitrogen mustards (NMs), which are highly reactive bifunctional alkylating agents and were the first chemotherapeutic agents developed. They form DNA interstrand crosslinks (ICLs), which cause a blockage of DNA strand separation, inhibiting essential processes in DNA metabolism like replication and transcription. In fast replicating cells, e.g., tumor cells, this can induce cell death. The upregulation of ICL repair is thought to be a key factor for the resistance of tumor cells to ICL-inducing cytostatic agents including NMs. To monitor induction and repair of CLB-induced ICLs, we adjusted the automated reversed fluorometric analysis of alkaline DNA unwinding assay (rFADU) for the detection of ICLs in adherent cells. For the detection of monoalkylated DNA bases we established an LC-MS/MS method. We performed a comparative analysis of adduct formation and removal in five human cell lines and in peripheral blood mononuclear cells (PBMCs) after treatment with CLB. Dose-dependent increases in adduct formation were observed, and suitable treatment concentrations were identified for each cell line, which were then used for monitoring the kinetics of adduct formation. We observed significant differences in the repair kinetics of the cell lines tested. For example, in A2780 cells, hTERT immortalized VH10 cells, and in PBMCs a time-dependent repair of the two main monoalkylated DNA-adducts was confirmed. Regarding ICLs, repair was observed in all cell systems except for PBMCs. In conclusion, LC-MS/MS analyses combined with the rFADU technique are powerful tools to study the molecular mechanisms of NM-induced DNA damage and repair. By applying these methods to a spectrum of human cell systems of different origin and transformation status, we obtained insight into the cell-type specific repair of different CLB-induced DNA lesions, which may help identify novel resistance mechanisms of tumors and define molecular targets for therapeutic interventions.

DNA Damage Response Alterations in Ovarian Cancer: From Molecular Mechanisms to Therapeutic Opportunities

The DNA damage response (DDR), a set of signaling pathways for DNA damage detection and repair, maintains genomic stability when cells are exposed to endogenous or exogenous DNA-damaging agents. Alterations in these pathways are strongly associated with cancer development, including ovarian cancer (OC), the most lethal gynecologic malignancy. In OC, failures in the DDR have been related not only to the onset but also to progression and chemoresistance. It is known that approximately half of the most frequent subtype, high-grade serous carcinoma (HGSC), exhibit defects in DNA double-strand break (DSB) repair by homologous recombination (HR), and current evidence indicates that probably all HGSCs harbor a defect in at least one DDR pathway. These defects are not restricted to HGSCs; mutations in ARID1A, which are present in 30% of endometrioid OCs and 50% of clear cell (CC) carcinomas, have also been found to confer deficiencies in DNA repair. Moreover, DDR alterations have been described in a variable percentage of the different OC subtypes. Here, we overview the main DNA repair pathways involved in the maintenance of genome stability and their deregulation in OC. We also recapitulate the preclinical and clinical data supporting the potential of targeting the DDR to fight the disease.

Nanotherapeutic Intervention in Photodynamic Therapy for Cancer

The clinical need for photodynamic therapy (PDT) has been growing for several decades. Notably, PDT is often used in oncology to treat a variety of tumors since it is a low-risk therapy with excellent selectivity, does not conflict with other therapies, and may be repeated as necessary. The mechanism of action of PDT is the photoactivation of a particular photosensitizer (PS) in a tumor microenvironment in the presence of oxygen. During PDT, cancer cells produce singlet oxygen (¹O₂) and reactive oxygen species (ROS) upon activation of PSs by irradiation, which efficiently kills the tumor. However, PDT's effectiveness in curing a deep-seated malignancy is constrained by three key reasons: a tumor's inadequate PS accumulation in tumor tissues, a hypoxic core with low oxygen content in solid tumors, and limited depth of light penetration. PDTs are therefore restricted to the management of thin and superficial cancers. With the development of nanotechnology, PDT's ability to penetrate deep tumor tissues and exert desired therapeutic effects has become a reality. However, further advancement in this field of research is necessary to address the challenges with PDT and ameliorate the therapeutic outcome. This review presents an overview of PSs, the mechanism of loading of PSs, nanomedicine-based solutions for enhancing PDT, and their biological applications including chemodynamic therapy, chemo-photodynamic therapy, PDT-electroporation, photodynamic-photothermal (PDT-PTT) therapy, and PDT-immunotherapy. Furthermore, the review discusses the mechanism of ROS generation in PDT advantages and challenges of PSs in PDT.

HPV Enhances HNSCC Chemosensitization by Inhibiting SERPINB3 Expression to Disrupt the Fanconi Anemia Pathway

Head and neck squamous cell carcinoma (HNSCC) is the most common malignant tumor of the head and neck, and the prognosis of patients is poor due to chemotherapeutic resistance. Interestingly, patients with HNSCC induced by human papillomavirus (HPV) infection are more sensitive to chemotherapy and display a better prognosis than HPV-negative patients. The biological relevance of HPV infection and the mechanism underlying chemosensitivity to cisplatin remain unknown. Herein, SERPINB3 is identified as an important target for regulation of cisplatin sensitivity by HPV-E6/E7 in HNSCC. Downregulation of SERPINB3 inhibits cisplatin-induced DNA damage repair and enhances the cytotoxicity of cisplatin. In detail, decreasing SERPINB3 expression reduces the USP1-mediated deubiquitination of FANCD2-FANCI in the Fanconi anemia pathway, thereby interfering with cisplatin-induced DNA interstrand crosslinks repair and further contributing to HNSCC cell apoptosis. To translate this finding, pH-responsive nanoparticles are used to deliver SERPINB3 small interfering RNA in combination with cisplatin, and this treatment successfully reverses cisplatin chemotherapeutic resistance in a patient-derived xenograft model from HPV-negative HNSCC. Taken together, these findings suggest that targeting SERPINB3 based on HPV-positive HNSCC is a potential strategy to overcome cisplatin resistance in HPV-negative HNSCC and improves the prognosis of this disease.

cGAS Regulates the Radioresistance of Human Head and Neck Squamous Cell Carcinoma Cells

Cyclic GMP-AMP synthase (cGAS) plays an important role in biological responses to pathogens. The activation of the cGAS pathway in immune cells is known to induce antitumor effects, but the role of cGAS in cancer cells remains poorly understood. In silico analysis using public databases suggested that high cGAS expression in head and neck squamous cell carcinoma (HNSCC) is indicative of a poor prognosis for HNSCC patients. We therefore investigated the role of cGAS in malignancies and the cellular radiation response of human HNSCC cells (SAS and Ca9-22) in vitro, because radiotherapy is one of the treatments most commonly used for HNSCC. Although cGAS knockdown failed to suppress the proliferation of non-irradiated HNSCC cells, it enhanced the radiosensitivity of HNSCC cells. The administration of the cGAS agonist increased the radioresistance of HNSCC cells. cGAS knockdown increased radiation-induced mitotic catastrophe, apoptosis, or cellular senescence, depending on the cell line, and this cell line-dependent response might be due to different responses of p21 after irradiation. Collectively, our findings indicate that the cGAS pathway regulates the radioresistance of HNSCC cells.

Role of Circulating Biomarkers in Platinum-Resistant Ovarian Cancer

Ovarian cancer (OC) is the second most common cause of death in women with gynecological cancer. Considering the poor prognosis, particularly in the case of platinum-resistant (PtR) disease, a huge effort was made to define new biomarkers able to help physicians in approaching and treating these challenging patients. Currently, most data can be obtained from tumor biopsy samples, but this is not always available and implies a surgical procedure. On the other hand, circulating biomarkers are detected with non-invasive methods, although this might require expensive techniques. Given the fervent hope in their value, here we focused on the most studied circulating biomarkers that could play a role in PtR OC.

Targeting DNA Damage Response Pathway in Ovarian Clear Cell Carcinoma

Ovarian clear cell carcinoma (OCCC) is one of the major types of ovarian cancer and is of higher relative prevalence in Asians. It also shows higher possibility of resistance to cisplatin-based chemotherapy leading to poor prognosis. This may be attributed to the relative lack of mutations and aberrations in homologous recombination-associated genes, which are crucial in DNA damage response (DDR), such as BRCA1, BRCA2, p53, RAD51, and genes in the Fanconi anemia pathway. On the other hand, OCCC is characterized by a number of genetic defects rendering it vulnerable to DDR-targeting therapy, which is emerging as a potent treatment strategy for various cancer types. Mutations of ARID1A, PIK3CA, PTEN, and catenin beta 1 (CTNNB1), as well as overexpression of transcription factor hepatocyte nuclear factor-1β (HNF-1β), and microsatellite instability are common in OCCC. Of particular note is the loss-of-function mutations in ARID1A, which is found in approximately 50% of OCCC. ARID1A is crucial for processing of DNA double-strand break (DSB) and for sustaining DNA damage signaling, rendering ARID1A-deficient cells prone to impaired DNA damage checkpoint regulation and hence sensitive to poly ADP ribose polymerase (PARP) inhibitors. However, while preclinical studies have demonstrated the possibility to exploit DDR deficiency in OCCC for therapeutic purpose, progress in clinical application is lagging. In this review, we will recapitulate the preclinical studies supporting the potential of DDR targeting in OCCC treatment, with emphasis on the role of ARID1A in DDR. Companion diagnostic tests (CDx) for predicting susceptibility to PARP inhibitors are rapidly being developed for solid tumors including ovarian cancers and may readily be applicable on OCCC. The potential of various available DDR-targeting drugs for treating OCCC by drawing analogies with other solid tumors sharing similar genetic characteristics with OCCC will also be discussed.

Dysfunctional activity of classical DNA end-joining renders acquired resistance to carboplatin in human ovarian cancer cells

Ovarian cancer is the deadliest gynecological malignancy worldwide. Although chemotherapy is required as the most standard treatment strategy for ovarian cancer, the survival rates are very low, largely because of high incidence of recurrence due to resistance to conventional surgery and genotoxic chemotherapies. Carboplatin-resistant ovarian cancer cells were generated by continuous treatment over six months. Carboplatin-resistance induced morphological alterations and promoted the rates of proliferation and migration of SKOV3 compared to the parental cells. Interestingly, carboplatin-resistant SKOV3 showed the high levels of γH2AX foci formed at the basal level, and the levels of γH2AX foci remained even after the recovery time, suggesting that the DNA damage response and repair machinery were severely attenuated by carboplatin-resistance. Surprisingly, the expression levels of XRCC4, a critical factor in non-homologous end joining (NHEJ) DNA repair, were significantly decreased in carboplatin-resistant SKOV3 compared with those in non-resistant controls. Furthermore, restoration of NHEJ in carboplatin-resistant SKOV3 by suppression of ABCB1 and/or AR re-sensitized carboplatin-resistant cells to genotoxic stress and reduced their proliferation ability. Our findings suggest that attenuation of the NHEJ DNA repair machinery mediated by resistance to genotoxic stress might be a critical cause of chemoresistance in patients with ovarian cancer.

Targeting DNA Damage Response and Repair to Enhance Therapeutic Index in Cisplatin-Based Cancer Treatment

Platinum-based chemotherapies, such as cisplatin, play a large role in cancer treatment. The development of resistance and treatment toxicity creates substantial barriers to disease control, yet. To enhance the therapeutic index of cisplatin-based chemotherapy, it is imperative to circumvent resistance and toxicity while optimizing tumor sensitization. One of the primary mechanisms by which cancer cells develop resistance to cisplatin is through upregulation of DNA repair pathways. In this review, we discuss the DNA damage response in the context of cisplatin-induced DNA damage. We describe the proteins involved in the pathways and their roles in resistance development. Common biomarkers for cisplatin resistance and their utilization to improve patient risk stratification and treatment personalization are addressed. Finally, we discuss some of the current treatments and future strategies to circumvent the development of cisplatin resistance.

The PI3K/mTOR Inhibitor Ompalisib Suppresses Nonhomologous End Joining and Sensitizes Cancer Cells to Radio- and Chemotherapy

As the predominant pathway for the repair of DNA double-strand breaks (DSB), non-homologous end joining (NHEJ) attenuates the efficacy of cancer treatment which relies on the introduction of DSBs, such as radiotherapy and genotoxic drugs. Identifying novel NHEJ inhibitors is of great importance for improving the therapeutic efficiency of radio- or chemotherapy. Here we miniaturized our recently developed NHEJ detecting system into a 96-well plate-based format and interrogated an FDA approved drug library containing 1732 compounds. A collection of novel hits were considered to be potential DSB repair inhibitors at the noncytotoxic concentration. We identified omipalisib as an efficient sensitizer for DNA damage-induced cell death in vitro. Furthermore, in vitro analysis uncovered the repressive effect of omipalisib on the phosphorylation of DNA-dependent protein kinase catalytic subunit induced by ionizing radiation and doxorubicin, which led to the suppression of NHEJ pathway. IMPLICATIONS: In summary, our findings suggested the possibility for repurposing these candidates as radio- or chemosensitizers, which might extend their clinical application in cancer therapy.

Characterization of a hyaluronic acid and folic acid-based hydrogel for cisplatin delivery: Antineoplastic effect in human ovarian cancer cells in vitro

We successfully prepared and characterized a hyaluronic acid- and folic acid-based hydrogel for the delivery of cisplatin (GEL-CIS) with the aim to induce specific and efficient incorporation of CIS into ovarian cancer (OC) cells, improve its antineoplastic effect and avoid CIS-resistance. The slow and controlled release of the drug from the polymeric network and its swelling degree at physiologic pH suggested its suitability for CIS delivery in OC. We compared here the effects of pure CIS to that of GEL-CIS on human OC cell lines, either wild type or CIS-resistant, in basal conditions and in the presence of macrophage-derived conditioned medium, mimicking the action of tumor-associated macrophages in vivo. GEL-CIS inhibited OC cell growth and migration more efficiently than pure CIS and modulated the expression of proteins involved in the Epithelial Mesenchymal Transition, a process playing a key role in OC metastatic spread and resistance to CIS.

Understanding the DNA double-strand break repair and its therapeutic implications

Repair of DNA double-strand breaks (DSBs) and its regulation are tightly integrated inside cells. Homologous recombination, nonhomologous end joining and microhomology mediated end joining are three major DSB repair pathways in mammalian cells. Targeting proteins associated with these repair pathways using small molecule inhibitors can prove effective in tumors, especially those with deregulated repair. Sensitization of cancer to current age therapy including radio and chemotherapy, using small molecule inhibitors is promising and warrant further development. Although several are under clinical trial, till date no repair inhibitor is approved for commercial use in cancer patients, with the exception of PARP inhibitors targeting single-strand break repair. Based on molecular profiling of repair proteins, better prognostic and therapeutic output can be achieved in patients. In the present review, we highlight the different mechanisms of DSB repair, chromatin dynamics to provide repair accessibility and modulation of inhibitors in association with molecular profiling and current gold standard treatment modalities for cancer.

Synthesis of new N,N′-Pd(Pt) complexes based on sulfanyl pyrazoles, and investigation of their in vitro anticancer activity

The synthesis of new N,N′-mononuclear bi-ligand Pd(ii) and tri-ligand Pt(ii)complexes bearing sulfanyl(phenyl, benzyl, cyclohexyl, 4-hydroxyphenyl)3,5-dimethyl-1H-pyrazole ligands has been carried out. The obtained compounds were studied for apoptosis-inducing activity and effect on the cell cycle for Jurkat, K562, and U937 neoplastic cell cultures and conditionally normal human embryonic kidney HEK293 cells. The cells showed the highest sensitivity to platinum and palladium complexes in comparison with ligands and cisplatin. The cytotoxic properties are enhanced for compounds with cyclohexyl substituents at the S-atom in sulfanyl pyrazoles and complexes.

Efficient cytostatics against Jurkat, K562 and U937 neoplastic cell lines were found among the synthesized new Pd(ii) and Pt(ii)complexes (six examples) with sulfanyl-1H-pyrazole ligands using in vitro assay.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Folate-Conjugated and Dual Stimuli-Responsive Mixed Micelles Loading Indocyanine Green for Photothermal and Photodynamic Therapy

A folic acid targeted mixed micelle system based on co-assembly of poly(ε-caprolactone)-b-poly(methoxytri(ethylene glycol) methacrylate-co-N-(2-methacrylamido)ethyl folatic amide) and poly(ε-caprolactone)-b-poly(diethylene glycol monomethyl ether methacrylate) is developed to encapsulate indocyanine green (ICG) for photothermal therapy and photodynamic therapy. In this study, the use of folic acid is not only for specific cancer cell recognition, but also in virtue of the carboxylic acid on folic acid to regulate the pH-dependent thermal phase transition of polymeric micelles for controlled drug release. The prepared ICG-loaded mixed micelles possess several superior properties such as a preferable thermoresponsive behavior, excellent storage stability, and good local hyperthermia and reactive oxygen species generation under near-infrared (NIR) irradiation. The photototoxicity induced by the ICG-loaded micelles has efficiently suppressed the growth of HeLa cells (folate receptor positive cells) under NIR irradiation compared to that of HT-29, which has low folate receptor expression. Hence, this new type of mixed micelles with excellent features could be a promising delivery system for controlled drug release, effective cancer cell targeting, and photoactivated therapy.

Glutathione-mediated antioxidant response and aerobic metabolism: two crucial factors involved in determining the multi-drug resistance of high-risk neuroblastoma

Neuroblastoma, a paediatric malignant tumor, is initially sensitive to etoposide, a drug to which many patients develop chemoresistance. In order to investigate the molecular mechanisms responsible for etoposide chemoresistance, HTLA-230, a human MYCN-amplified neuroblastoma cell line, was chronically treated with etoposide at a concentration that in vitro mimics the clinically-used dose. The selected cells (HTLA-Chr) acquire multi-drug resistance (MDR), becoming less sensitive than parental cells to high doses of etoposide or doxorubicin. MDR is due to several mechanisms that together contribute to maintaining non-toxic levels of H₂O₂. In fact, HTLA-Chr cells, while having an efficient aerobic metabolism, are also characterized by an up-regulation of catalase activity and higher levels of reduced glutathione (GSH), a thiol antioxidant compound. The combination of such mechanisms contributes to prevent membrane lipoperoxidation and cell death. Treatment of HTLA-Chr cells with L-Buthionine-sulfoximine, an inhibitor of GSH biosynthesis, markedly reduces their tumorigenic potential that is instead enhanced by the exposure to N-Acetylcysteine, able to promote GSH synthesis.

Collectively, these results demonstrate that GSH and GSH-related responses play a crucial role in the acquisition of MDR and suggest that GSH level monitoring is an efficient strategy to early identify the onset of drug resistance and to control the patient's response to therapy.

Overcoming hypoxia-induced tumor radioresistance in non-small cell lung cancer by targeting DNA-dependent protein kinase in combination with carbon ion irradiation

Background

Hypoxia-induced radioresistance constitutes a major obstacle for a curative treatment of cancer. The aim of this study was to investigate effects of photon and carbon ion irradiation in combination with inhibitors of DNA-Damage Response (DDR) on tumor cell radiosensitivity under hypoxic conditions.

Methods

Human non-small cell lung cancer (NSCLC) models, A549 and H1437, were irradiated with dose series of photon and carbon ions under hypoxia (1% O₂) vs. normoxic conditions (21% O₂). Clonogenic survival was studied after dual combinations of radiotherapy with inhibitors of DNA-dependent Protein Kinase (DNAPKi, M3814) and ATM serine/threonine kinase (ATMi).

Results

The OER at 30% survival for photon irradiation of A549 cells was 1.4. The maximal oxygen effect measured as survival ratio was 2.34 at 8 Gy photon irradiation of A549 cells. In contrast, no significant oxygen effect was found after carbon ion irradiation. Accordingly, the relative effect of 6 Gy carbon ions was determined as 3.8 under normoxia and. 4.11 under hypoxia. ATM and DNA-PK inhibitors dose dependently sensitized tumor cells for both radiation qualities. For 100 nM DNAPKi the survival ratio at 4 Gy more than doubled from 1.59 under normoxia to 3.3 under hypoxia revealing a strong radiosensitizing effect under hypoxic conditions. In contrast, this ratio only moderately increased after photon irradiation and ATMi under hypoxia. The most effective treatment was combined carbon ion irradiation and DNA damage repair inhibition.

Conclusions

Carbon ions efficiently eradicate hypoxic tumor cells. Both, ATMi and DNAPKi elicit radiosensitizing effects. DNAPKi preferentially sensitizes hypoxic cells to radiotherapy.

Electronic supplementary material

The online version of this article (10.1186/s13014-017-0939-0) contains supplementary material, which is available to authorized users.

Novel tetrahydroacridine and cyclopentaquinoline derivatives with fluorobenzoic acid moiety induce cell cycle arrest and apoptosis in lung cancer cells by activation of DNA damage signaling

Lung cancer is still the leading cause of cancer-related death worldwide, indicating a necessity to develop more effective therapy. Acridine derivatives are potential anticancer agents due to their ability to intercalate DNA as well as inhibit enzymes involved in replication and transcription. Recently, we have evaluated anticancer activity of 32 novel acridine-based compounds. We found that the most effective were tetrahydroacridine and cyclopentaquinoline derivatives with fluorobenzoic acid containing eight and nine carbon atoms in the aliphatic chain. The aim of this study was to determine the molecular mechanisms of compounds-induced cell cycle arrest and apoptosis in human lung adenocarcinoma cells. All compounds activated Ataxia telangiectasia mutated kinase and phosphorylated histone H2A.X at Ser139 indicating DNA damage. Treatment of cells with the compounds increased phosphorylation and accumulation of p53 that regulate cell cycle as well as apoptosis. All compounds induced G0/1 cell cycle arrest by phosphorylation of cyclin-dependent kinase 2 at Tyr15 resulting in attenuation of the kinase activity. In addition, cyclopentaquinoline derivatives induced expression of cyclin-dependent kinase 2 inhibitor, p21; however, tetrahydroacridine derivatives had no significant effect on p21. Moreover, all compounds decreased the mitochondrial membrane potential accompanied by increased expression of Bax and down-regulation of Bcl-2, suggesting activation of the mitochondrial pathway. All compounds also significantly attenuated the migration rates of lung cancer cells. Collectively, our findings suggest a central role of activation of DNA damage signaling in response to new acridine derivatives treatment to induce cell cycle arrest and apoptosis in cancer cells and provide support for their further development as potential drug candidates.

Sensitization strategies in lung cancer

The commonly used treatment avenues employed by cancer physicians include surgery, radiotherapy (RT) and chemotherapy in addition to rapid developmental and confirmatory studies on the efficacy of targeted therapies. However, the success rate in these commonly used treatments remains relatively low due to associated side effects, such as normal cell targeting/toxicity and resistance. In addition, investigators are continuing their efforts to enhance the efficacy of RT and chemotherapy to prevent associated side effects and improve the survival rate of the affected patient in order to increase patient survival. In the present study, we have reviewed the sensitization approaches used to improve chemotherapy and RT sensitivity in tumors.

Chemical Reactivity Window Determines Prodrug Efficiency toward Glutathione Transferase Overexpressing Cancer Cells

Glutathione transferases (GSTs) are often overexpressed in tumors and frequently correlated to bad prognosis and resistance against a number of different anticancer drugs. To selectively target these cells and to overcome this resistance we previously have developed prodrugs that are derivatives of existing anticancer drugs (e.g., doxorubicin) incorporating a sulfonamide moiety. When cleaved by GSTs, the prodrug releases the cytostatic moiety predominantly in GST overexpressing cells, thus sparing normal cells with moderate enzyme levels. By modifying the sulfonamide it is possible to control the rate of drug release and specifically target different GSTs. Here we show that the newly synthesized compounds, 4-acetyl-2-nitro-benzenesulfonyl etoposide (ANS-etoposide) and 4-acetyl-2-nitro-benzenesulfonyl doxorubicin (ANS-DOX), function as prodrugs for GSTA1 and MGST1 overexpressing cell lines. ANS-DOX, in particular, showed a desirable cytotoxic profile by inducing toxicity and DNA damage in a GST-dependent manner compared to control cells. Its moderate conversion of 500 nmol/min/mg, as catalyzed by GSTA1, seems hereby essential since the more reactive 2,4-dinitrobenzenesulfonyl doxorubicin (DNS-DOX) (14000 nmol/min/mg) did not display a preference for GSTA1 overexpressing cells. DNS-DOX, however, effectively killed GSTP1 (20 nmol/min/mg) and MGST1 (450 nmol/min/mg) overexpressing cells as did the less reactive 4-mononitrobenzenesulfonyl doxorubicin (MNS-DOX) in a MGST1-dependent manner (1.5 nmol/min/mg) as shown previously. Furthermore, we show that the mechanism of these prodrugs involves a reduction in GSH levels as well as inhibition of the redox regulatory enzyme thioredoxin reductase 1 (TrxR1) by virtue of their electrophilic sulfonamide moiety. TrxR1 is upregulated in many tumors and associated with resistance to chemotherapy and poor patient prognosis. Additionally, the prodrugs potentially acted as a general shuttle system for DOX, by overcoming resistance mechanisms in cells. Here we propose that GST-dependent prodrugs require a conversion rate "window" in order to selectively target GST overexpressing cells, while limiting their effects on normal cells. Prodrugs are furthermore a suitable system to specifically target GSTs and to overcome various drug resistance mechanisms that apply to the parental drug.

NRAGE is involved in homologous recombination repair to resist the DNA-damaging chemotherapy and composes a ternary complex with RNF8-BARD1 to promote cell survival in squamous esophageal tumorigenesis

NRAGE, a neurotrophin receptor-interacting melanoma antigen-encoding gene homolog, is significantly increased in the nucleus of radioresistant esophageal tumor cell lines and is highly upregulated to promote cell proliferation in esophageal carcinomas (ECs). However, whether the overexpressed NRAGE promotes cell growth by participating in DNA-damage response (DDR) is still unclear. Here we show that NRAGE is required for efficient double-strand breaks (DSBs) repair via homologous recombination repair (HRR) and downregulation of NRAGE greatly sensitizes EC cells to DNA-damaging agents both in vitro and in vivo. Moreover, NRAGE not only regulates the stability of DDR factors, RNF8 and BARD1, in a ubiquitin-proteolytic pathway, but also chaperons the interaction between BARD1 and RNF8 via their RING domains to form a novel ternary complex. Additionally, the expression of NRAGE is closely correlated with RNF8 and BARD1 in esophageal tumor tissues. In summary, our findings reveal a novel function of NRAGE that will help to guide personalized esophageal cancer treatments by targeting NRAGE to increase cell sensitivity to DNA-damaging therapeutics in the long run.

DNA damage responses in cancer stem cells: Implications for cancer therapeutic strategies

The identification of cancer stem cells (CSCs) that are responsible for tumor initiation, growth, metastasis, and therapeutic resistance might lead to a new thinking on cancer treatments. Similar to stem cells, CSCs also display high resistance to radiotherapy and chemotherapy with genotoxic agents. Thus, conventional therapy may shrink the tumor volume but cannot eliminate cancer. Eradiation of CSCs represents a novel therapeutic strategy. CSCs possess a highly efficient DNA damage response (DDR) system, which is considered as a contributor to the resistance of these cells from exposures to DNA damaging agents. Targeting of enhanced DDR in CSCs is thus proposed to facilitate the eradication of CSCs by conventional therapeutics. To achieve this aim, a better understanding of the cellular responses to DNA damage in CSCs is needed. In addition to the protein kinases and enzymes that are involved in DDR, other processes that affect the DDR including chromatin remodeling should also be explored.

A high-throughput yeast assay identifies synergistic drug combinations

Drug combinations are commonly used in the treatment of a range of diseases such as cancer, AIDS, and bacterial infections. Such combinations are less likely to be thwarted by resistance, and they have the desirable potential to be synergistic. Synergistic combinations can have decreased toxicity if lower doses of the constituent agents can be used. Conversely, antagonistic combinations can lead to lower efficacy of a treatment. Unfortunately, practical limitations, including the large number of possible combinations to be tested and the importance of optimizing concentrations and order of addition, discourage systematic studies of compound combinations. To address these limitations, we present a platform to screen drug combinations at multiple concentrations with varying orders of addition in Saccharomyces cerevisiae, at high throughput. In a proof of principle, we screened all possible pairwise combinations of 11 DNA damaging agents and found that of the 66 combinations tested, six were synergistic and three were antagonistic. The strength of two-thirds of these combinations was dependent on the order in which the drugs were added to the cells. We further tested the synergistic and antagonistic combinations in two cancer cell lines and found the combination of mitomycin C and irinotecan to be synergistic in both cell lines. This pilot study demonstrates the utility of using yeast for screening large matrices of drug combinations, and it provides a means to prioritize drug combination tests in human cells. Finally, we underscore the importance of testing the order of addition for assessing drug combinations.

A novel ruthenium(II)-polypyridyl complex inhibits cell proliferation and induces cell apoptosis by impairing DNA damage repair

Ruthenium complexes are widely recognized as one of the most promising DNA damaging chemotherapeutic drugs. The main goal of this study was to explore the anticancer activity and underlying mechanisms of [Ru(phen)(2)(p-BrPIP)](ClO(4))(2), a novel chemically synthesized ruthenium (Ru) complex. To this end, we employed MTT assays to determine the anticancer activity of the complex, and performed single-cell gel electrophoresis (SCGE) and Western blotting to evaluate DNA damage. Our results showed that the Ru(II)-poly complex caused severe DNA damage, possibly by downregulating key factors involved in DNA repair pathways, such as proliferating cell nuclear antigen (PCNA) and ring finger protein 8 (RNF8). In addition, this complex induced cell apoptosis by upregulating both p21 and p53. Taken together, our findings demonstrate that the Ru(II)-poly complex exhibits antitumour activity by inducing cell apoptosis, which results from the accumulation of large amounts of unrepaired DNA damage.

Photodynamic nanomedicine in the treatment of solid tumors: perspectives and challenges

Photodynamic therapy (PDT) is a promising treatment strategy where activation of photosensitizer drugs with specific wavelengths of light results in energy transfer cascades that ultimately yield cytotoxic reactive oxygen species which can render apoptotic and necrotic cell death. Without light the photosensitizer drugs are minimally toxic and the photoactivating light itself is non-ionizing. Therefore, harnessing this mechanism in tumors provides a safe and novel way to selectively eradicate tumor with reduced systemic toxicity and side effects on healthy tissues. For successful PDT of solid tumors, it is necessary to ensure tumor-selective delivery of the photosensitizers, as well as, the photoactivating light and to establish dosimetric correlation of light and drug parameters to PDT-induced tumor response. To this end, the nanomedicine approach provides a promising way towards enhanced control of photosensitizer biodistribution and tumor-selective delivery. In addition, refinement of nanoparticle designs can also allow incorporation of imaging agents, light delivery components and dosimetric components. This review aims at describing the current state-of-the-art regarding nanomedicine strategies in PDT, with a comprehensive narrative of the research that has been carried out in vitro and in vivo, with a discussion of the nanoformulation design aspects and a perspective on the promise and challenges of PDT regarding successful translation into clinical application.

Functional DNA repair signature of cancer cell lines exposed to a set of cytotoxic anticancer drugs using a multiplexed enzymatic repair assay on biochip

The development of resistances to conventional anticancer drugs compromises the efficacy of cancer treatments. In the case of DNA-targeting chemotherapeutic agents, cancer cells may display tolerance to the drug-induced DNA lesions and/or enhanced DNA repair. However, the role of DNA damage response (DDR) and DNA repair in this chemoresistance has yet to be defined. To provide insights in this challenging area, we analyzed the DNA repair signature of 7 cancer cell lines treated by 5 cytotoxic drugs using a recently developed multiplexed functional DNA repair assay. This comprehensive approach considered the complexity and redundancy of the different DNA repair pathways. Data was analyzed using clustering methods and statistical tests. This DNA repair profiling method defined relevant groups based on similarities between different drugs, thus providing information relating to their dominant mechanism of action at the DNA level. Similarly, similarities between different cell lines presumably identified identical functional DDR despite a high level of genetic heterogeneity between cell lines. Our strategy has shed new light on the contribution of specific repair sub-pathways to drug-induced cytotoxicity. Although further molecular characterisations are needed to fully unravel the mechanisms underlying our findings, our approach proved to be very promising to interrogate the complexity of the DNA repair response. Indeed, it could be used to predict the efficacy of a given drug and the chemosensitivity of individual patients, and thus to choose the right treatment for individualised cancer care.

Persistent DNA damage caused by low levels of mitomycin C induces irreversible cell senescence

Mutations of oncogenes and tumor suppressor genes which activate mTOR through several downstream signaling pathways are common to cancer. Activation of mTOR when combined with inhibition of cell cycle progression or DNA replication stress has previously been shown to promote cell senescence. In the present study, we examined the conditions under which human non-small cell lung carcinoma A549 cells can undergo senescence when treated with the DNA alkylating agent mitomycin C (MMC). While exposure of A549 cells to 0.1 or 0.5 µg/ml of MMC led to their arrest in S phase of the cell cycle and subsequent apoptosis, exposure to 0.01 or 0.02 µg/ml for 6 d resulted in induction of cell senescence and near total (0.01 µg/ml) or total (0.02 µg/ml) elimination of their reproductive potential. During exposure to these low concentrations of MMC, the cells demonstrated evidence of DNA replication stress manifested by expression of γH2AX, p21 (WAF1) and a very low level of EdU incorporation into DNA. The data are consistent with the notion that enduring DNA replication stress in cells known to have activated oncogenes leads to their senescence. It is reasonable to expect that tumors having constitutive activation of oncogenes triggering mTOR signaling may be particularly predisposed to undergoing senescence following prolonged treatment with low doses of DNA damaging drugs.

Oxidative stress in apoptosis and cancer: an update

The oxygen paradox tells us that oxygen is both necessary for aerobic life and toxic to all life forms. Reactive oxygen species (ROS) touch every biological and medical discipline, especially those involving proliferative status, supporting the idea that active oxygen may be increased in tumor cells. In fact, metabolism of oxygen and the resulting toxic byproducts can cause cancer and death. Efforts to counteract the damage caused by ROS are gaining acceptance as a basis for novel therapeutic approaches, and the field of prevention of cancer is experiencing an upsurge of interest in medically useful antioxidants. Apoptosis is an important means of regulating cell numbers in the developing cell system, but it is so important that it must be controlled. Normal cell death in homeostasis of multicellular organisms is mediated through tightly regulated apoptotic pathways that involve oxidative stress regulation. Defective signaling through these pathways can contribute to both unbalance in apoptosis and development of cancer. Finally, in this review, we discuss new knowledge about recent tools that provide powerful antioxidant strategies, and designing methods to deliver to target cells, in the prevention and treatment of cancer.

Curaxins: anticancer compounds that simultaneously suppress NF-κB and activate p53 by targeting FACT

Effective eradication of cancer requires treatment directed against multiple targets. The p53 and nuclear factor κB (NF-κB) pathways are dysregulated in nearly all tumors, making them attractive targets for therapeutic activation and inhibition, respectively. We have isolated and structurally optimized small molecules, curaxins, that simultaneously activate p53 and inhibit NF-κB without causing detectable genotoxicity. Curaxins demonstrated anticancer activity against all tested human tumor xenografts grown in mice. We report here that the effects of curaxins on p53 and NF-κB, as well as their toxicity to cancer cells, result from "chromatin trapping" of the FACT (facilitates chromatin transcription) complex. This FACT inaccessibility leads to phosphorylation of the p53 Ser(392) by casein kinase 2 and inhibition of NF-κB-dependent transcription, which requires FACT activity at the elongation stage. These results identify FACT as a prospective anticancer target enabling simultaneous modulation of several pathways frequently dysregulated in cancer without induction of DNA damage. Curaxins have the potential to be developed into effective and safe anticancer drugs.

Differential proteomics in the search for biomarkers of radiotherapy resistance

The individualization of radiotherapy treatment would be beneficial for cancer patients; however, there are no predictive biomarkers of radiotherapy resistance in routine clinical use. This article describes the body of work in this field where comparative proteomics methods have been used for the discovery of putative biomarkers associated with radiotherapy resistance. A large number of differentially expressed proteins have been reported, mostly from the study of novel radiotherapy-resistant cell lines. Here, we have assessed these putative biomarkers through the discovery, confirmation and validation phases of the biomarker pipeline, and inform the reader on the current status of proteomics-based findings. Suggested avenues for future work are discussed.

Oncolytic viruses in radiation oncology

Oncolytic viruses are investigational cancer treatments. They are currently being assessed as single agents or in combination with standard therapies such as external beam radiotherapy - a DNA damaging agent that is a standard of care for many tumour types. Preclinical data indicate that combinations of oncolytic viruses and radiation therapy are promising, showing additional or synergistic antitumour effects in in vitro and in vivo studies. This interaction has the potential to be multifaceted: viruses may act as radiosensitizing agents, but radiation may also enhance viral oncolysis by increasing viral uptake, replication, gene expression and cell death (apoptosis, autophagy or necrosis) in irradiated cells. Phase I and II clinical trials investigating combinations of viruses and radiation therapy have been completed, paving the way for ongoing phase III studies. The aim of this review is to focus on the therapeutic potential of these combinations and to highlight their mechanistic bases, with particular emphasis on the role of the DNA damage response.

Global gene profiling of spontaneous hepatocellular carcinoma in B6C3F1 mice: similarities in the molecular landscape with human liver cancer

Hepatocellular carcinoma (HCC) is an important cause of morbidity and mortality worldwide. Although the risk factors of human HCC are well known, the molecular pathogenesis of this disease is complex, and in general, treatment options remain poor. The use of rodent models to study human cancer has been extensively pursued, both through genetically engineered rodents and rodent models used in carcinogenicity and toxicology studies. In particular, the B6C3F1 mouse used in the National Toxicology Program (NTP) two-year bioassay has been used to evaluate the carcinogenic effects of environmental and occupational chemicals, and other compounds. The high incidence of spontaneous HCC in the B6C3F1 mouse has challenged its use as a model for chemically induced HCC in terms of relevance to the human disease. Using global gene expression profiling, we identify the dysregulation of several mediators similarly altered in human HCC, including re-expression of fetal oncogenes, upregulation of protooncogenes, downregulation of tumor suppressor genes, and abnormal expression of cell cycle mediators, growth factors, apoptosis regulators, and angiogenesis and extracellular matrix remodeling factors. Although major differences in etiology and pathogenesis remain between human and mouse HCC, there are important similarities in global gene expression and molecular pathways dysregulated in mouse and human HCC. These data provide further support for the use of this model in hazard identification of compounds with potential human carcinogenicity risk, and may help in better understanding the mechanisms of tumorigenesis resulting from chemical exposure in the NTP two-year carcinogenicity bioassay.

The DNA damage response: Balancing the scale between cancer and ageing

Defects in the DNA damage response often lead to an increased susceptibility to cancer, and so the DDR presents an interesting set of novel therapeutic targets. The maintenance of genomic integrity by the DDR has also been found to be involved in the process of organismal ageing. While the removal of cells containing damaged DNA can be beneficial in the prevention of cancer, it may contribute to both normal and pathological ageing.

Pharmacologic modulation of serine/threonine phosphorylation highly sensitizes PHEO in a MPC cell and mouse model to conventional chemotherapy

Background

The failure of cytotoxic cancer regimens to cure the most drug-resistant, well-differentiated solid tumors has been attributed to the heterogeneity of cell types that differ in their capacities for growth, differentiation, and metastases. We investigated the effect of LB1, a small molecule inhibitor of serine/threonine protein phosphatase 2A (PP2A), on its ability to inhibit a low growth fraction and highly drug-resistant solid neuroendocrine tumor, such as metastatic pheochromocytoma (PHEO). Subsequently, we evaluated the increased efficacy of chemotherapy combined with LB1.

Methodology/Principal Findings

The effect of LB1 and temozolomide (TMZ), a standard chemotherapeutic agent that alone only transiently suppressed the growth and regression of metastatic PHEO, was evaluated in vitro on a single PHEO cell line and in vivo on mouse model of metastatic PHEO. In the present study, we show that metastatic PHEO, for which there is currently no cure, can be eliminated by combining LB1, thereby inhibiting PP2A, with TMZ. This new treatment approach resulted in long term, disease-free survival of up to 40% of animals bearing multiple intrahepatic metastases, a disease state that the majority of patients die from. Inhibition of PP2A was associated with prevention of G1/S phase arrest by p53 and of mitotic arrest mediated by polo-like kinase 1 (Plk-1).

Conclusions/Significance

The elimination of DNA damage-induced defense mechanisms, through transient pharmacologic inhibition of PP2A, is proposed as a new approach for enhancing the efficacy of non-specific cancer chemotherapy regimens against a broad spectrum of low growth fraction tumors very commonly resistant to cytotoxic drugs.

Positioning effects of KillerRed inside of cells correlate with DNA strand breaks after activation with visible light

Fluorescent proteins (FPs) are established tools for new applications, not-restricted to the cell biological research. They could also be ideal in surgery enhancing the precision to differentiate between the target tissue and the surrounding healthy tissue. FPs like the KillerRed (KRED), used here, can be activated by excitation with visible day-light for emitting active electrons which produce reactive oxygen species (ROS) resulting in photokilling processes. It is a given that the extent of the KRED's cell toxicity depends on its subcellular localization. Evidences are documented that the nuclear lamina as well as especially the chromatin are critical targets for KRED-mediated ROS-based DNA damaging. Here we investigated the damaging effects of the KRED protein fused to the nuclear lamina and to the histone H2A DNA-binding protein. We detected a frequency of DNA strand breaks, dependent first on the illumination time, and second on the spatial distance between the localization at the chromatin and the site of ROS production. As a consequence we could identify defined DNA bands with 200, 400 and (600) bps as most prominent degradation products, presumably representing an internucleosomal DNA cleavage induced by KRED. These findings are not restricted to the detection of programmed cell death processes in the therapeutic field like PDT, but they can also contribute to a better understanding of the structure-function relations in the epigenomic world.

Genotoxicity of metal nanoparticles

Nanotechnology is currently used in industry, medicine, and military applications, as well as in more than 300 commercial products. Yet, the same properties that make these particles exciting for technology also make them daunting public health concerns because their toxicity is unknown and relatively unexplored. Increased attention is being placed on the study of metal particle genotoxicity; however, a lot of unknowns remain about their effects and the mechanisms. In this article, we highlight some metal and metal oxide nanoparticles of interest and discuss the current in vivo and in vitro studies of genotoxic effects. Many metal nanoparticles were found to cause chromosomal aberrations, DNA strand breaks, oxidative DNA damage, and mutations. Inconsistencies are found in the literature, however, thus drawing conclusions is difficult due to a variety of factors. Therefore, the areas requiring further attention are highlighted and recommendations to improve our understanding of the genotoxic potential are addressed.

Analysis of individual molecular events of DNA damage response by flow- and image-assisted cytometry

This chapter describes molecular mechanisms of DNA damage response (DDR) and presents flow- and image-assisted cytometric approaches to assess these mechanisms and measure the extent of DDR in individual cells. DNA damage was induced by cell treatment with oxidizing agents, UV light, DNA topoisomerase I or II inhibitors, cisplatin, tobacco smoke, and by exogenous and endogenous oxidants. Chromatin relaxation (decondensation) is an early event of DDR chromatin that involves modification of high mobility group proteins (HMGs) and histone H1 and was detected by cytometry by analysis of the susceptibility of DNA in situ to denaturation using the metachromatic fluorochrome acridine orange. Translocation of the MRN complex consisting of Meiotic Recombination 11 Homolog A (Mre11), Rad50 homolog, and Nijmegen Breakage Syndrome 1 (NMR1) into DNA damage sites was assessed by laser scanning cytometry as the increase in the intensity of maximal pixel as well as integral value of Mre11 immunofluorescence. Examples of cytometric detection of activation of Ataxia telangiectasia mutated (ATM), and Check 2 (Chk2) protein kinases using phospho-specific Abs targeting Ser1981 and Thr68 of these proteins, respectively are also presented. We also discuss approaches to correlate activation of ATM and Chk2 with phosphorylation of p53 on Ser15 and histone H2AX on Ser139 as well as with cell cycle position and DNA replication. The capability of laser scanning cytometry to quantify individual foci of phosphorylated H2AX and/or ATM that provides more dependable assessment of the presence of DNA double-strand breaks is outlined. The new microfluidic Lab-on-a-Chip platforms for interrogation of individual cells offer a novel approach for DDR cytometric analysis.

Molecular mechanism of base pairing infidelity during DNA duplication upon one-electron oxidation

The guanine radical cation (G^•+) is formed by one-electron oxidation from its parent guanine (G). G^•+ is rapidly deprotonated in the aqueous phase resulting in the formation of the neutral guanine radical [G(-H)^•]. The loss of proton occurs at the N1 nitrogen, which is involved in the classical Watson-Crick base pairing with cytosine (C). Employing the density functional theory (DFT), it has been observed that a new shifted base pairing configuration is formed between G(-H)^• and C constituting only two hydrogen bonds after deprotonation occurs. Using the DFT method, G(-H)^• was paired with thymine (T), adenine (A) and G revealing substantial binding energies comparable to those of classical G-C and A-T base pairs. Hence, G(-H)^• does not display any particular specificity for C compared to the other bases. Taking into account the long lifetime of the G(-H)^• radical in the DNA helix (5 s) and the rapid duplication rate of DNA during mitosis/meiosis (5-500 bases per s), G(-H)^• can pair promiscuously leading to errors in the duplication process. This scenario constitutes a new mechanism which explains how one-electron oxidation of the DNA double helix can lead to mutations.