DNA damage induced by alkylating agents and repair pathways

Evaluation of Hydro-Alcoholic Extract of Trifolium Pratens L. for Its Anti-Cancer Potential on U87MG Cell Line

OBJECTIVE

Glioblastoma multiforme is the most malignant form of brain tumors. Trifolium pratense L. has been suggested for cancer treatment in traditional medicine. Here we have investigated the effects of T. pratense extract on glioblastoma multiforme cell line (U87MG).

MATERIALS AND METHODS

In this experimental study, the effect of T. pratense extract on cell viability was investigated using trypan blue staining, MTT assay, and lactate dehydrogenase activity measurement. Apoptosis and autophagy cell death were detected by fluorescent staining. Nitric oxide (No) production was measured using Griess reaction. Expression levels of some apoptotic and autophagic-related genes were detected using real-time polymerase chain reaction (PCR). The combination effects of T. pratense extract and temozolomide (TMZ) were evaluated by calculating the combination index and dose reduction index values.

RESULTS

After treatment with T. pratense extract, the cell viability was significantly reduced in a time- and dosedependent manner (P<0.05). Apoptosis and autophagy of U87MG cells were significantly increased (P<0.05). Also, T. pratense extract significantly decreased NO production (P<0.05) by U87MG cells. Combination of TMZ and T. pratense extract had a synergistic cytotoxic effect.

CONCLUSION

T. pratense showed anti-cancer properties via induction of apoptosis and autophagy cell death.

Drug resistance in glioblastoma and cytotoxicity of seaweed compounds, alone and in combination with anticancer drugs: A mini review

BACKGROUND

Glioblastomas (GBM) are one of the most aggressive tumor of the central nervous system with an average life expectancy of only 1-2 years after diagnosis, even with the use of advanced treatments with surgery, radiation, and chemotherapy. There are several anticancer drugs with alkylating properties that have been used in the therapy of malignant gliomas. Temozolomide (TMZ) is one of them, widely used even in combination with ionizing radiation. However, the main disadvantage of using these types of drugs in the treatment of GBM is the development of cancer drug resistance. Research of bioactive compounds with anticancer activity has been heavily explored.

PURPOSE

This review focuses on a carotenoid and a phlorotannin present in seaweed, namely fucoxanthin and phloroglucinol, and their anticancer activity against glioblastoma. The combination of natural compounds with conventional drugs is also discussed.

CONCLUSION

Several natural compounds existing in seaweeds, such as fucoxanthin and phoroglucinol, have shown cytotoxic activity in models in vitro and in vivo, acting through different molecular mechanisms, such as antioxidant, antiproliferative, DNA damage/DNA repair, proapoptotic, antiangiogenic and antimetastic. Within the scope of interactions with conventional drugs, there are evidences that some seaweed compounds could be used to potentiate the action of anticancer drugs. However, their effects and mechanisms of action, alone or in combination with anticancer drugs, namely TMZ, in glioblastoma cell, still few explored and require more attention due to the unquestionable high potential of these marine compounds.

Transient Receptor Potential Channel A1 (TRPA1) Regulates Sulfur Mustard-Induced Expression of Heat Shock 70 kDa Protein 6 (HSPA6) In Vitro

The chemosensory transient receptor potential ankyrin 1 (TRPA1) ion channel perceives different sensory stimuli. It also interacts with reactive exogenous compounds including the chemical warfare agent sulfur mustard (SM). Activation of TRPA1 by SM results in elevation of intracellular calcium levels but the cellular consequences are not understood so far. In the present study we analyzed SM-induced and TRPA1-mediated effects in human TRPA1-overexpressing HEK cells (HEKA1) and human lung epithelial cells (A549) that endogenously exhibit TRPA1. The specific TRPA1 inhibitor AP18 was used to distinguish between SM-induced and TRPA1-mediated or TRPA1-independent effects. Cells were exposed to 600 µM SM and proteome changes were investigated 24 h afterwards by 2D gel electrophoresis. Protein spots with differential staining levels were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and nano liquid chromatography electrospray ionization tandem mass spectrometry. Results were verified by RT-qPCR experiments in both HEKA1 or A549 cells. Heat shock 70 kDa protein 6 (HSPA6) was identified as an SM-induced and TRPA1-mediated protein. AP18 pre-treatment diminished the up-regulation. RT-qPCR measurements verified these results and further revealed a time-dependent regulation. Our results demonstrate that SM-mediated activation of TRPA1 influences the protein expression and confirm the important role of TRPA1 ion channels in the molecular toxicology of SM.

Why is there selective subcortical vulnerability in ADHD? Clues from postmortem brain gene expression data

Sub-cortical volumetric differences were associated with attention-deficit/hyperactivity disorder (ADHD) in a recent multi-site, mega-analysis of 1713 ADHD persons and 1529 controls. As there was a wide range of effect sizes among the sub-cortical volumes, it is possible that selective neuronal vulnerability has a role in these volumetric losses. To address this possibility, we used data from Allen Brain Atlas to investigate variability in gene expression profiles between subcortical regions of typically developing brains. We tested the hypothesis that the expression of genes in a set of curated ADHD candidate genes and five a priori selected, biological pathways would be associated with the Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) findings. Across the subcortical regions studied by ENIGMA, gene expression profiles for three pathways were significantly correlated with ADHD-associated volumetric reductions: apoptosis, oxidative stress and autophagy. These correlations were strong and significant for children with ADHD, but not for adults. Although preliminary, these data suggest that variability of structural brain anomalies in ADHD can be explained, in part, by the differential vulnerability of these regions to mechanisms mediating apoptosis, oxidative stress and autophagy.

Effect of Cyclophosphamide Treatment on Central and Effector Memory T Cells in Mice

Immunological memory is a key feature of adaptive immunity. It provides the organism with long-lived and robust protection against infection. The important question is whether cyclophosphamide (CP), as immunosuppressive agent used in cancer therapy and in some autoimmune diseases, may act on the memory T-cell population. We investigated the effect of CP on the percentage of central memory T cells (T_CM) and effector memory T cells (T_EM) in the mouse model of CP-induced immunosuppression (8-10-week-old male C57BL/6 mice CP treated for 7 days at the daily dose of 50 μg/g body weight [bw], manifested the best immunosuppression status, as compared to lower doses of CP: 10 or 20 μg/g bw). The CP induced a significant decrease in the percentage of CD8⁺ (T_CM), compared to nonimmunosuppressed mice. This effect was not observed in the case of CD4⁺ T_CM population. The percentage of gated T_EM with CD4 and CD8 phenotype was significantly decreased in CP-treated mice, as compared to the control ones. Taken together, the above data indicate that CP-induced immunosuppression in mice leads to a reduction in the abundance of central memory cells possessing preferentially CD8⁺ phenotype as well as to a reduction in the percentage of effector memory cells (splenocytes both CD4⁺ and CD8⁺), compared to the cells from nonimmunosuppressed mice. These findings in mice described in this article may contribute to the understanding of the complexity of the immunological responses in humans and extend research on the impact of the CP model of immunosuppression in mice and memory T-cell populations.

Histone H3 lysine 36 methyltransferase mobilizes NER factors to regulate tolerance against alkylation damage in fission yeast

The Set2 methyltransferase and its target, histone H3 lysine 36 (H3K36), affect chromatin architecture during the transcription and repair of DNA double-stranded breaks. Set2 also confers resistance against the alkylating agent, methyl methanesulfonate (MMS), through an unknown mechanism. Here, we show that Schizosaccharomyces pombe (S. pombe) exhibit MMS hypersensitivity when expressing a set2 mutant lacking the catalytic histone methyltransferase domain or a H3K36R mutant (reminiscent of a set2-null mutant). Set2 acts synergistically with base excision repair factors but epistatically with nucleotide excision repair (NER) factors, and determines the timely nuclear accumulation of the NER initiator, Rhp23, in response to MMS. Set2 facilitates Rhp23 recruitment to chromatin at the brc1 locus, presumably to repair alkylating damage and regulate the expression of brc1+ in response to MMS. Set2 also show epistasis with DNA damage checkpoint proteins; regulates the activation of Chk1, a DNA damage response effector kinase; and acts in a similar functional group as proteins involved in homologous recombination. Consistently, Set2 and H3K36 ensure the dynamicity of Rhp54 in DNA repair foci formation after MMS treatment. Overall, our results indicate a novel role for Set2/H3K36me in coordinating the recruitment of DNA repair machineries to timely manage alkylating damage.

PAM-OBG: A monoamine oxidase B specific prodrug that inhibits MGMT and generates DNA interstrand crosslinks, potentiating temozolomide and chemoradiation therapy in intracranial glioblastoma

Via extensive analyses of genetic databases, we have characterized the DNA-repair capacity of glioblastoma with respect to patient survival. In addition to elevation of O⁶-methylguanine DNA methyltransferase (MGMT), down-regulation of three DNA repair pathways; canonical mismatch repair (MMR), Non-Homologous End-Joining (NHEJ), and Homologous Recombination (HR) are correlated with poor patient outcome. We have designed and tested both in vitro and in vivo, a monoamine oxidase B (MAOB) specific prodrug, PAM-OBG, that is converted by glioma MAOB into the MGMT inhibitor O⁶-benzylguanine (O⁶BG) and the DNA crosslinking agent acrolein. In cultured glioma cells, we show that PAM-OBG is converted to O⁶BG, inhibiting MGMT and sensitizing cells to DNA alkylating agents such as BCNU, CCNU, and Temozolomide (TMZ). In addition, we demonstrate that the acrolein generated is highly toxic in glioma treated with an inhibitor of Nucleotide Excision Repair (NER). In mouse intracranial models of primary human glioma, we show that PAM-OBG increases survival of mice treated with either BCNU or CCNU by a factor of six and that in a chemoradiation model utilizing six rounds of TMZ/2Gy radiation, pre-treatment with PAM-OBG more than doubled survival time.

Augmentation of diethylnitrosamine-induced early stages of rat hepatocarcinogenesis by 1,2-dimethylhydrazine

Diethylnitrosamine (DEN) and 1,2-dimethylhydrazine (DMH) are classical carcinogens used in experimental rodent carcinogenesis. However, the interaction effects of these carcinogens on biochemical and molecular changes during carcinogenesis have not been investigated. Therefore, the effect of DEN and DMH co-administration on preneoplastic lesion formation and its molecular mechanism in rats were determined. Triple intraperitoneal administrations of DEN were made before, during or after double subcutaneous injections of DMH. At week 8 of the experiment, the preneoplastic hepatic glutathione-S-transferase placental form (GST-P) positive foci and colonic aberrant crypt foci (ACF) were analyzed. The combined treatment of these carcinogens increased toxicity to rats. Administration of DMH alone did not induce hepatic GST-P positive foci, while co-treatment with DMH enhanced hepatic GST-P positive foci formation. However, DEN did not influence the size or number of colonic ACF. The treatment with DMH alone induced CYP2E1 and P450 reductase, demonstrating that DMH enhanced DEN metabolism in DEN- and DMH-treated rats. These findings were related to increases in hepatic O⁶-methylguanine DNA adducts and hepatotoxicity, which are associated with the induction of cell proliferation and liver cancer development. DEN-induced early stages of rat hepatocarcinogenesis were synergistically promoted by DMH via metabolic enzyme induction leading to enhanced DNA mutation and hepatocarcinogenicity.

Double-barreled gun: Combination of PARP inhibitor with conventional chemotherapy

DNA repair pathways are evolutionarily conserved molecular mechanisms that maintain the integrity of genomic DNA. In cancer therapies, the integrity and activity of DNA repair pathways predict therapy resistance and disease outcome. Members of the poly (ADP-ribose) polymerase (PARP) family initiate and organize the biologic process of DNA repair, which counteracts many types of chemotherapies. Since the first development in approximately 3 decades ago, PARP inhibitors have greatly changed the concept of cancer therapy, leading to encouraging improvements in tumor suppression and disease outcomes. Here we summaries both pre-clinical and clinical findings of PARP inhibitors applications, particularly for combination therapies.

IMGN779, a Novel CD33-Targeting Antibody-Drug Conjugate with DNA-Alkylating Activity, Exhibits Potent Antitumor Activity in Models of AML

The myeloid differentiation antigen CD33 has long been exploited as a target for antibody-based therapeutic approaches in acute myeloid leukemia (AML). Validation of this strategy was provided with the approval of the CD33-targeting antibody-drug conjugate (ADC) gemtuzumab ozogamicin in 2000; the clinical utility of this agent, however, has been hampered by safety concerns. Thus, the full potential of CD33-directed therapy in AML remains to be realized, and considerable interest exists in the design and development of more effective ADCs that confer high therapeutic indices and favorable tolerability profiles. Here, we describe the preclinical characterization of a novel CD33-targeting ADC, IMGN779, which utilizes a unique DNA-alkylating payload to achieve potent antitumor effects with good tolerability. The payload, DGN462, is prototypical of a novel class of purpose-created indolinobenzodiazeprine pseudodimers, termed IGNs. With low picomolar potency, IMGN779 reduced viability in a panel of AML cell lines in vitro Mechanistically, the cytotoxic activity of IMGN779 involved DNA damage, cell-cycle arrest, and apoptosis consistent with the mode of action of DGN462. Moreover, IMGN779 was highly active against patient-derived AML cells, including those with adverse molecular abnormalities, and sensitivity correlated to CD33 expression levels. In vivo, IMGN779 displayed robust antitumor efficacy in multiple AML xenograft and disseminated disease models, as evidenced by durable tumor regressions and prolonged survival. Taken together, these findings identify IMGN779 as a promising new candidate for evaluation as a novel therapeutic in AML. Mol Cancer Ther; 17(6); 1271-9. ©2018 AACR.

A network meta-analysis: the overall and progression-free survival of glioma patients treated by different chemotherapeutic interventions combined with radiation therapy (RT)

Different chemotherapy drugs are generally introduced in clinical practices combining with therapy for glioma treatment. However, these chemotherapy drugs have rarely been compared with each other and the optimum drug still remains to be proved. In this research, medical databases were consulted, PubMed, Embase and Cochrane Library included. As primary outcomes, hazard ratio (HR) of overall survival (OS) and progression-free survival (PFS) with their corresponding 95% credential intervals (CrI) were reported. A network meta-analysis was conducted; the surface under the cumulative ranking curve (SUCRA) was utilized for treatment rank and a cluster analysis based on SUCRA values was performed. This research includes 14 trials with 3,681 subjects and eight interventions. In terms of network meta-analysis, placebo was proved to be inferior to the combination of temozolomide (TMZ), nimustine (ACNU) and cisplatin (CDDP). Also, bevacizumab (BEV) in conjunction with TMZ were significantly more effective than placebo with an HR of 0.40. The estimated probabilities from SUCRA verified the above outcomes, confirming that the combination of TMZ, ACNU and CDDP exhibited the highest ranking probability of 0.889 with respect to OS, while BEV in combination with TMZ - with a probability of 0.772 - ranked the first place with respect to PFS. According to the results of this network meta-analysis, the combination of (1) TMZ, ACNU and CDDP; (2) BEV in combination with TMZ and (3) cilengitide in combination with TMZ, are considered as the preferable choices of chemotherapy drugs for glioma treatment.

Temozolomide and Pituitary Tumors: Current Understanding, Unresolved Issues, and Future Directions

Temozolomide, an alkylating agent, initially used in the treatment of gliomas was expanded to include pituitary tumors in 2006. After 12 years of use, temozolomide has shown a notable advancement in pituitary tumor treatment with a remarkable improvement rate in the 5-year overall survival and 5-year progression-free survival in both aggressive pituitary adenomas and pituitary carcinomas. In this paper, we review the mechanism of action of temozolomide as alkylating agent, its interaction with deoxyribonucleic acid repair systems, therapeutic effects in pituitary tumors, unresolved issues, and future directions relating to new possibilities of targeted therapy.

Poly-isoprenylated ifosfamide analogs: Preactivated antitumor agents as free formulation or nanoassemblies

Oxazaphosphorines including cyclophosphamide, trofosfamide and ifosfamide (IFO) belong to the alkylating agent class and are indicated in the treatment of numerous cancers. However, IFO is subject to limiting side-effects in high-dose protocols. To circumvent IFO drawbacks in clinical practices, preactivated IFO analogs were designed to by-pass the toxic metabolic pathway. Among these IFO analogs, some of them showed the ability to self-assemble due to the use of a poly-isoprenyloxy chain as preactivating moiety. We present here, the in vitro activity of the nanoassembly formulations of preactivated IFO derivatives with a C-4 geranyloxy, farnesyloxy and squalenoxy substituent on a large panel of tumor cell lines. The chemical and colloidal stabilities of the geranyloxy-IFO (G-IFO), farnesyloxy-IFO (F-IFO) and squalenoxy-IFO (SQ-IFO) NAs were further evaluated in comparison to their free formulation. Finally, pharmacokinetic parameters and maximal tolerated dose of the most potent preactivated IFO analog (G-IFO) were determined and compared to IFO, paving the way to in vivo studies.

Molecular Basis of Gut Microbiome-Associated Colorectal Cancer: A Synthetic Perspective

A significant challenge toward studies of the human microbiota involves establishing causal links between bacterial metabolites and human health and disease states. Certain strains of commensal Escherichia coli harbor the 54-kb clb gene cluster which codes for small molecules named precolibactins and colibactins. Several studies suggest colibactins are genotoxins and support a role for clb metabolites in colorectal cancer formation. Significant advances toward elucidating the structures and biosynthesis of the precolibactins and colibactins have been made using genetic approaches, but their full structures remain unknown. In this Perspective we describe recent synthetic efforts that have leveraged biosynthetic advances and shed light on the mechanism of action of clb metabolites. These studies indicate that deletion of the colibactin peptidase ClbP, a modification introduced to promote accumulation of precolibactins, leads to the production of non-genotoxic pyridone-based isolates derived from the diversion of linear biosynthetic intermediates toward alternative cyclization pathways. Furthermore, these studies suggest the active genotoxins (colibactins) are unsaturated imines that are potent DNA damaging agents, thereby confirming an earlier mechanism of action hypothesis. Although these imines have very recently been detected in bacterial extracts, they have to date confounded isolation. As the power of "meta-omics" approaches to natural products discovery further advance, we anticipate that chemical synthetic and biosynthetic studies will become increasingly interdependent.

A curious new role for MRN in Schizosaccharomyces pombe non-homologous end-joining

Chromosomal breaks can be healed by several repair processes, including one called non-homologous end-joining (NHEJ) where the two broken ends are ligated together with a loss of 0-5 bp of DNA. The protein requirements for NHEJ of cut DNA ends in the budding yeast Saccharomyces cerevisiae include its version of the Mre11-Rad50-Nbs1 (MRN) complex. In contrast, the fission yeast Schizosaccharomyces pombe and mammalian cells do not require MRN for this process. Recent work in S. pombe used transposon excision to generate breaks that were capped by DNA hairpins, which must be opened to produce ligatable ends. Repair in S. pombe was through an NHEJ reaction that now requires MRN. Surprisingly, wild type cells and MRN mutants that lack nuclease activity showed the same levels of excision. These genetic results suggest that MRN recruits an unknown hairpin-opening nuclease for this unusual NHEJ reaction.

Sevoflurane and isoflurane genotoxicity in kidney cells of mice

The aim of this study was to evaluate the DNA damage and repair in kidney cells of Swiss albino mice after repeated exposure to sevoflurane and isoflurane and compare their detrimental effects. We used the alkaline comet assay to establish the genetic damage and measured three parameters: tail length, tail moment, and tail intensity of comets. These parameters were measured immediately after exposure to the above mentioned inhalation anaesthetics, two hours, six hours, and 24 hours later and were compared with the control group. Mean values of all three parameters were significantly higher in experimental groups compared to the control group. DNA damage in kidney cells of mice exposed to sevoflurane increased continuously before it reached its peak 24 hours after exposure. Isoflurane induced the highest DNA damage two hours after exposure. Levels of DNA damage recorded 24 h after cessation of exposure to both tested compounds suggest that sevoflurane was slightly more genotoxic than isoflurane to kidney cells of mice. According to these results, the currently used volatile anaesthetics sevoflurane and isoflurane are able to damage DNA in kidney cells of mice. Such findings suggest a possibility for similar outcomes in humans and that fact must be taken into account in everyday clinical practice.

DNA-dependent protein kinase plays a central role in transformation of breast epithelial cells following alkylation damage

DNA alkylating agents form the first line of cancer chemotherapy. They not only kill cells but also behave as potential carcinogens. MNU, a DNA methylating agent, is well known to induce mammary tumours in rodents. However, the mechanism of tumorigenesis is not well understood. Our study reports a novel role played by DNA-dependent protein kinase (DNA-PK) in methylation damage-induced transformation using three-dimensional breast acinar cultures. Here, we report that exposure of breast epithelial cells to MNU inhibited polarisation at the basolateral domain, increased dispersal of the Golgi at the apical domain and induced an epithelial-to-mesenchymal transition (EMT)-like phenotype as well as invasion. This altered Golgi phenotype correlated with impaired intracellular trafficking. Inhibition of DNA-PK resulted in almost complete reversal of the altered Golgi phenotype and partial rescue of the polarity defect and EMT-like phenotype. The results confirm that methylation damage-induced activation of DNA-PK is a major mechanism in mediating cellular transformation.This article has an associated First Person interview with the first author of the paper.

Hybrid of DNA-targeting Chlorambucil with Pt(IV) Species to Reverse Drug Resistance

Two hybrids of Pt(IV) species were designed and prepared by addition of a chlorambucil unit to the axial positions of the Pt(IV) complexes derived from DN603 and DN604. In vitro studies of two hybrids against two pairs of cisplatin sensitive and resistant cancer cell lines indicated that compound 5 had superior antitumor activity to cisplatin and chlorambucil via suppressing DNA damage repair to reverse drug resistance. Mechanistic investigation suggested that the potent antitumor activity of compound 5 arose from its major suppression of CK2-mediated MRE11-RAD50-NBS1(MRN) complex promotion of DNA double-strand break (DSB) repair. In nude mice with A549/CDDP xenografts, compound 5 exhibited higher anticancer efficacy than cisplatin and chlorambucil by reversing drug resistance, displayed improved effectiveness, and had no toxicity effects. Overall, compound 5 is a promising drug candidate, which could promote the anticancer activity and reverse drug resistance by attenuating CK2-induced MRN-dependent DSB repair.

Therapy-related myeloid neoplasms: when genetics and environment collide

Therapy-related myeloid neoplasms (t-MN) arise as a late effect of chemotherapy and/or radiation administered for a primary condition, typically a malignant disease, solid organ transplant or autoimmune disease. Survival is measured in months, not years, making t-MN one of the most aggressive and lethal cancers. In this Review, we discuss recent developments that reframe our understanding of the genetic and environmental aetiology of t-MN. Emerging data are illuminating who is at highest risk of developing t-MN, why t-MN are chemoresistant and how we may use this information to treat and ultimately prevent this lethal disease.

15N-, 13C- and ¹H-NMR Spectroscopy Characterization and Growth Inhibitory Potency of a Combi-Molecule Synthesized by Acetylation of an Unstable Monoalkyltriazene

6-(3-Methyltriaz-1-en-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione referred to as EG22 (8a), is an open-chain 3-alkyl-1,2,3-triazene termed “combi-molecule” designed to inhibit poly(adenosine diphosphate ribose) polymerase (PARP) and damage DNA. To delay its hydrolysis, acetylation of N3 was required. Being a monoalkyl-1,2,3-triazene, EG22 could assume two tautomers in solution or lose nitrogen during the reaction, thereby leading to several acetylated compounds. Instead, one compound was observed and to unequivocally assign its structure, we introduced isotopically labeled reagents in its preparation, with the purpose of incorporating ¹⁵N at N2 and ¹³C in the 3-methyl group. The results showed that the 1,2,3-triazene moiety remained intact, as confirmed by ¹⁵N-NMR, coupling patterns between the ¹⁵N-labeled N2 and the ¹³C-labeled methyl group. Furthermore, we undertook heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) experiments that permitted the detection and assignment of all four nitrogens in 6-(3-acetyl-3-methyltriaz-1-en-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione, referred to as ZSM02 (9a), whose structure was further confirmed by X-ray crystallography. The structure showed a remarkable coplanarity between the N-acetyltriazene and the naphtalimide moiety. Thus, we unequivocally assigned 9a as the product of the reaction and compared its growth inhibitory activity with that of its precursor, EG22. ZSM02 exhibited identical growth inhibitory profile as EG22, suggesting that it may be a prodrug of EG22.

RECQ1 expression is upregulated in response to DNA damage and in a p53-dependent manner

Sensitivity of cancer cells to DNA damaging chemotherapeutics is determined by DNA repair processes. Consequently, cancer cells may upregulate the expression of certain DNA repair genes as a mechanism to promote chemoresistance. Here, we report that RECQ1, a breast cancer susceptibility gene that encodes the most abundant RecQ helicase in humans, is a p53-regulated gene, potentially acting as a defense against DNA damaging agents. We show that RECQ1 mRNA and protein levels are upregulated upon treatment of cancer cells with a variety of DNA damaging agents including the DNA-alkylating agent methylmethanesulfonate (MMS). The MMS-induced upregulation of RECQ1 expression is p53-dependent as it was observed in p53-proficient but not in isogenic p53-deficient cells. The RECQ1 promoter is bound by endogenous p53 and is responsive to p53 in luciferase reporter assays suggesting that RECQ1 is a direct target of p53. Treatment with the chemotherapeutic drugs temozolomide and fotemustine also increased RECQ1 mRNA levels whereas depletion of RECQ1 enhanced cellular sensitivity to these agents. These results identify a previously unrecognized p53-mediated upregulation of RECQ1 expression in response to DNA damage and implicate RECQ1 in the repair of DNA lesions including those induced by alkylating and other chemotherapeutic agents.

E. coli mismatch repair enhances AT-to-GC mutagenesis caused by alkylating agents

Alkylating agents are known to induce the formation of O⁶-alkylguanine (O⁶-alkG) and O⁴-alkylthymine (O⁴-alkT) in DNA. These lesions have been widely investigated as major sources of mutations. We previously showed that mismatch repair (MMR) facilitates the suppression of GC-to-AT mutations caused by O⁶-methylguanine more efficiently than the suppression of GC-to-AT mutations caused by O⁶-ethylguanine. However, the manner by which O⁴-alkyT lesions are repaired remains unclear. In the present study, we investigated the repair pathway involved in the repair of O⁴-alkT. The E. coli CC106 strain, which harbors Δprolac in its genomic DNA and carries the F'CC106 episome, can be used to detect AT-to-GC reverse-mutation of the gene encoding β-galactosidase. Such AT-to-GC mutations should be induced through the formation of O⁴-alkT at AT base pairs. As expected, an O⁶-alkylguanine-DNA alkyltransferase (AGT) -deficient CC106 strain, which is defective in both ada and agt genes, exhibited elevated mutant frequencies in the presence of methylating agents and ethylating agents. However, in the UvrA-deficient strain, the methylating agents were less mutagenic than in wild-type, while ethylating agents were more mutagenic than in wild-type, as observed with agents that induce O⁶-alkylguanine modifications. Unexpectedly, the mutant frequencies decreased in a MutS-deficient strain, and a similar tendency was observed in MutL- or MutH-deficient strains. Thus, MMR appears to promote mutation at AT base pairs. Similar results were obtained in experiments employing double-mutant strains harboring defects in both MMR and AGT, or MMR and NER. E. coli MMR enhances AT-to-GC mutagenesis, such as that caused by O⁴-alkylthymine. We hypothesize that the MutS protein recognizes the O⁴-alkT:A base pair more efficiently than O⁴-alkT:G. Such a distinction would result in misincorporation of G at the O⁴-alkT site, followed by higher mutation frequencies in wild-type cells, which have MutS protein, compared to MMR-deficient strains.

DNA Polymerases ImuC and DinB Are Involved in DNA Alkylation Damage Tolerance in Pseudomonas aeruginosa and Pseudomonas putida

Translesion DNA synthesis (TLS), facilitated by low-fidelity polymerases, is an important DNA damage tolerance mechanism. Here, we investigated the role and biological function of TLS polymerase ImuC (former DnaE2), generally present in bacteria lacking DNA polymerase V, and TLS polymerase DinB in response to DNA alkylation damage in Pseudomonas aeruginosa and P. putida. We found that TLS DNA polymerases ImuC and DinB ensured a protective role against N- and O-methylation induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in both P. aeruginosa and P. putida. DinB also appeared to be important for the survival of P. aeruginosa and rapidly growing P. putida cells in the presence of methyl methanesulfonate (MMS). The role of ImuC in protection against MMS-induced damage was uncovered under DinB-deficient conditions. Apart from this, both ImuC and DinB were critical for the survival of bacteria with impaired base excision repair (BER) functions upon alkylation damage, lacking DNA glycosylases AlkA and/or Tag. Here, the increased sensitivity of imuCdinB double deficient strains in comparison to single mutants suggested that the specificity of alkylated DNA lesion bypass of DinB and ImuC might also be different. Moreover, our results demonstrated that mutagenesis induced by MMS in pseudomonads was largely ImuC-dependent. Unexpectedly, we discovered that the growth temperature of bacteria affected the efficiency of DinB and ImuC in ensuring cell survival upon alkylation damage. Taken together, the results of our study disclosed the involvement of ImuC in DNA alkylation damage tolerance, especially at low temperatures, and its possible contribution to the adaptation of pseudomonads upon DNA alkylation damage via increased mutagenesis.

Phase I/II Study of Temozolomide Plus Nimustine Chemotherapy for Recurrent Malignant Gliomas: Kyoto Neuro-oncology Group

The objective of this phase I/II study was to examine the efficacy and toxicity profile of temozolomide (TMZ) plus nimustine (ACNU). Patients who had received a standard radiotherapy with one or two previous chemo-regimens were enrolled. In phase I, the maximum-tolerated dose (MTD) by TMZ (150 mg/m2/day) (Day 1-5) plus various doses of ACNU (30, 35, 40, 45 mg/m2/day) (Day 15) per 4 weeks was defined on a standard 3 + 3 design. In phase II, these therapeutic activity and safety of this regimen were evaluated. Forty-nine eligible patients were enrolled. The median age was 50 years-old. Eighty percent had a KPS of 70-100. Histologies were glioblastoma (73%), anaplastic astrocytoma (22%), anaplastic oligodendroglioma (4%). In phase I, 15 patients were treated at four cohorts by TMZ plus ACNU. MTD was TMZ (150 mg/m2) plus ACNU (40 mg/m2). In phase II, 40 patients were treated at the dose of cohort 3 (MTD). Thirty-five percent of patients experienced grade 3 or 4 toxicities, mainly hematologic. The overall response rate was 11% (4/37). Sixty-eight percent (25/37) had stable disease. Twenty-two percent (8/37) showed progression. Progression-free survival (PFS) rates at 6 and 12 months were 24% (95% CI, 12-35%) and 8% (95% CI, 4-15%). Median PFS was 13 months (95% CI, 9.2-17.2 months). Overall survival (OS) at 6 and 12 were 78% (95% CI, 67-89%) and 49% (95% CI, 33-57%). Median OS was 11.8 months (95% CI, 8.2-14.5 months). This phase I/II study showed a moderate toxicity in hematology and may has a promising efficacy in OS, without inferiority in PFS.

Nanoscale characterization illustrates the cisplatin-mediated biomechanical changes of B16-F10 melanoma cells

Cells reorganize their membrane biomechanical dynamics in response to environmental stimuli or inhibitors associated with their physiological/pathological processes, and disease therapeutics. To validate the biophysical dynamics during cell exposure to anti-cancer drugs, we investigate the nanoscale biological characterization in melanoma cells undergoing cisplatin treatment. Using atomic force microscopy, we demonstrate that the cellular morphology and membrane ultrastructure are altered after exposure to cisplatin. In contrast to their normal spindle-like shape, cisplatin causes cell deformation rendering cells flat and enlarged, which increases the cell area by 3-4 fold. Additionally, cisplatin decreases the topography height values for both the cytoplasmic and nuclear regions (by 40-80% and 60%, respectively). Furthermore, cisplatin increases the cytoplasmic root mean square roughness by 110-240% in correlation with the drug concentration and attenuates the nuclear RMS by 60%. Moreover, the cellular adhesion force was enhanced, while the Young's modulus elasticity was attenuated by ∼2 and ∼2.3 fold, respectively. F-actin phalloidin staining revealed that cisplatin enlarges the cell size through enhanced stress fiber formation and promotes cytoskeletal reorganization. Immunoblot analyses further revealed that the activities of focal adhesion proteins, such as FAK and c-Src, are upregulated by cisplatin through phosphorylation at tyrosine 397 and 530, respectively. Collectively, these results show that cisplatin-treated melanoma cells not only exhibit the upregulation of FAK-mediated signaling to enhance the cytoskeleton mechanical stretch, but also promote the cytoskeletal rearrangement resulting in 43% decrease in the cell modulus. These mechanisms thus promote the malignancy and invasiveness of the melanoma cells.

Mirvetuximab Soravtansine (IMGN853), a Folate Receptor Alpha-Targeting Antibody-Drug Conjugate, Potentiates the Activity of Standard of Care Therapeutics in Ovarian Cancer Models

Elevated folate receptor alpha (FRα) expression is characteristic of epithelial ovarian cancer (EOC), thus establishing this receptor as a candidate target for the development of novel therapeutics to treat this disease. Mirvetuximab soravtansine (IMGN853) is an antibody-drug conjugate (ADC) that targets FRα for tumor-directed delivery of the maytansinoid DM4, a potent agent that induces mitotic arrest by suppressing microtubule dynamics. Here, combinations of IMGN853 with approved therapeutics were evaluated in preclinical models of EOC. Combinations of IMGN853 with carboplatin or doxorubicin resulted in synergistic antiproliferative effects in the IGROV-1 ovarian cancer cell line in vitro. IMGN853 potentiated the cytotoxic activity of carboplatin via growth arrest and augmented DNA damage; cell cycle perturbations were also observed in cells treated with the IMGN853/doxorubicin combination. These benefits translated into improved antitumor activity in patient-derived xenograft models in vivo in both the platinum-sensitive (IMGN853/carboplatin) and platinum-resistant (IMGN853/pegylated liposomal doxorubicin) settings. IMGN853 co-treatment also improved the in vivo efficacy of bevacizumab in platinum-resistant EOC models, with combination regimens causing significant regressions and complete responses in the majority of tumor-bearing mice. Histological analysis of OV-90 ovarian xenograft tumors revealed that concurrent administration of IMGN853 and bevacizumab caused rapid disruption of tumor microvasculature and extensive necrosis, underscoring the superior bioactivity profile of the combination regimen. Overall, these demonstrations of combinatorial benefit conferred by the addition of the first FRα-targeting ADC to established therapies provide a compelling framework for the potential application of IMGN853 in the treatment of patients with advanced ovarian cancer.

Preparation of Intrastrand {G}O(6) -Alkylene-O(6) {G} Cross-Linked Oligonucleotides

This unit describes the preparation O(6) -2'-deoxyguanosine-butylene-O(6) -2'-deoxyguanosine dimer phosphoramidites and precursors for incorporation of site-specific intrastrand cross-links (IaCL) into DNA oligonucleotides. Protected 2'-deoxyguanosine dimers are produced using the Mitsunobu reaction. IaCL DNA containing the intradimer phosphodiester are first chemically phosphorylated, followed by a ring-closing reaction using the condensing reagent 1-(2-mesitylenesulfonyl)-3-nitro-1H-1,2,4-triazole. Phosphoramidites are incorporated into oligonucleotides by solid-phase synthesis and standard deprotection and cleavage protocols are employed. This approach allows for the preparation of IaCL DNA substrates in amounts and purity amenable for biophysical characterization, and biochemical studies as substrates to investigate DNA repair and bypass pathways. © 2016 by John Wiley & Sons, Inc.

The survival significance of a measurable enhancing lesion after completing standard treatment for newly diagnosed glioblastoma

The goal of this study was to analyze the survival outcome according to the treatment response after completing standard treatment protocol for newly diagnosed glioblastoma (GBM) and to suggest a patient who should be considered for further treatment. After approving by our Institutional Review Board, 57 patients (38 male, 19 female; median age, 52years; age range, 16-81years) with newly diagnosed GBM who completed standard treatment protocol were examined retrospectively. According to the treatment response using the RANO criteria, there were 20 patients with complete response (CR), five patients with partial response (PR), 13 patients with stable disease (SD) and 19 patients with progressive disease (PD) after the completion of standard treatment. Patients (PR+SD+PD) with a measurable enhancing lesion were categorized the MEL group (n=37). We analyzed the difference of survival outcome between CR group and MEL group. The median progression-free survival (PFS) in the CR group was significantly better than that of the MEL group (18.0months vs. 3.0months, p=0.004). The median overall survival (OS) was also significantly longer in the CR group (25.0months vs. 15.0months, p=0.005). However, there was no significant difference in the survival outcome of the CR group compared with that of the subset of MEL group patients who showed PR or SD. Poor survival outcome was found only in MEL group patients who exhibited progression. Patients with a measurable enhancing lesion showing progression after completion of standard treatment protocol are appropriate candidates for further treatment.

DNA Damage and Pulmonary Hypertension

Pulmonary hypertension (PH) is defined by a mean pulmonary arterial pressure over 25 mmHg at rest and is diagnosed by right heart catheterization. Among the different groups of PH, pulmonary arterial hypertension (PAH) is characterized by a progressive obstruction of distal pulmonary arteries, related to endothelial cell dysfunction and vascular cell proliferation, which leads to an increased pulmonary vascular resistance, right ventricular hypertrophy, and right heart failure. Although the primary trigger of PAH remains unknown, oxidative stress and inflammation have been shown to play a key role in the development and progression of vascular remodeling. These factors are known to increase DNA damage that might favor the emergence of the proliferative and apoptosis-resistant phenotype observed in PAH vascular cells. High levels of DNA damage were reported to occur in PAH lungs and remodeled arteries as well as in animal models of PH. Moreover, recent studies have demonstrated that impaired DNA-response mechanisms may lead to an increased mutagen sensitivity in PAH patients. Finally, PAH was linked with decreased breast cancer 1 protein (BRCA1) and DNA topoisomerase 2-binding protein 1 (TopBP1) expression, both involved in maintaining genome integrity. This review aims to provide an overview of recent evidence of DNA damage and DNA repair deficiency and their implication in PAH pathogenesis.

Deciphering the genomic targets of alkylating polyamide conjugates using high-throughput sequencing

Chemically engineered small molecules targeting specific genomic sequences play an important role in drug development research. Pyrrole-imidazole polyamides (PIPs) are a group of molecules that can bind to the DNA minor-groove and can be engineered to target specific sequences. Their biological effects rely primarily on their selective DNA binding. However, the binding mechanism of PIPs at the chromatinized genome level is poorly understood. Herein, we report a method using high-throughput sequencing to identify the DNA-alkylating sites of PIP-indole-seco-CBI conjugates. High-throughput sequencing analysis of conjugate 2: showed highly similar DNA-alkylating sites on synthetic oligos (histone-free DNA) and on human genomes (chromatinized DNA context). To our knowledge, this is the first report identifying alkylation sites across genomic DNA by alkylating PIP conjugates using high-throughput sequencing.

The formation of catalytically competent enzyme-substrate complex is not a bottleneck in lesion excision by human alkyladenine DNA glycosylase

Human alkyladenine DNA glycosylase (AAG) protects DNA from alkylated and deaminated purine lesions. AAG flips out the damaged nucleotide from the double helix of DNA and catalyzes the hydrolysis of the N-glycosidic bond to release the damaged base. To understand better, how the step of nucleotide eversion influences the overall catalytic process, we performed a pre-steady-state kinetic analysis of AAG interaction with specific DNA-substrates, 13-base pair duplexes containing in the 7th position 1-N6-ethenoadenine (εA), hypoxanthine (Hx), and the stable product analogue tetrahydrofuran (F). The combination of the fluorescence of tryptophan, 2-aminopurine, and 1-N6-ethenoadenine was used to record conformational changes of the enzyme and DNA during the processes of DNA lesion recognition, damaged base eversion, excision of the N-glycosidic bond, and product release. The thermal stability of the duplexes characterized by the temperature of melting, T_m, and the rates of spontaneous opening of individual nucleotide base pairs were determined by NMR spectroscopy. The data show that the relative thermal stability of duplexes containing a particular base pair in position 7, (T_m(F/T) < T_m(εA/T) < T_m(Hx/T) < T_m(A/T)) correlates with the rate of reversible spontaneous opening of the base pair. However, in contrast to that, the catalytic lesion excision rate is two orders of magnitude higher for Hx-containing substrates than for substrates containing εA, proving that catalytic activity is not correlated with the stability of the damaged base pair. Our study reveals that the formation of the catalytically competent enzyme-substrate complex is not the bottleneck controlling the catalytic activity of AAG.

DNA damage regulation and its role in drug-related phenotypes in the malaria parasites

DNA of malaria parasites, Plasmodium falciparum, is subjected to extraordinary high levels of genotoxic insults during its complex life cycle within both the mosquito and human host. Accordingly, most of the components of DNA repair machinery are conserved in the parasite genome. Here, we investigated the genome-wide responses of P. falciparum to DNA damaging agents and provided transcriptional evidence of the existence of the double strand break and excision repair system. We also showed that acetylation at H3K9, H4K8, and H3K56 play a role in the direct and indirect response to DNA damage induced by an alkylating agent, methyl methanesulphonate (MMS). Artemisinin, the first line antimalarial chemotherapeutics elicits a similar response compared to MMS which suggests its activity as a DNA damaging agent. Moreover, in contrast to the wild-type P. falciparum, two strains (Dd2 and W2) previously shown to exhibit a mutator phenotype, fail to induce their DNA repair upon MMS-induced DNA damage. Genome sequencing of the two mutator strains identified point mutations in 18 DNA repair genes which may contribute to this phenomenon.

Immunomodulatory activity of mefenamic acid in mice models of cell-mediated and humoral immunity

OBJECTIVES

Previously, different nonsteroidal anti-inflammatory drugs (NSAIDs) have been evaluated for their potential immunomodulatory activities. Mefenamic acid is a well-known NSAID and is used in the treatment of musculoskeletal disorders, inflammation, fever, and pain. To the best of our knowledge, promising data regarding the immunomodulatory activity of mefenamic acid is scarce. Current study investigates the immunomodulatory activity of mefenamic acid in different models of cell-mediated and humoral immunity.

MATERIALS AND METHODS

Immunomodulatory effects on cell-mediated immunity were evaluated using dinitrochlorobenzene-induced delayed type hypersensitivity (DTH) and cyclophosphamide-induce myelosuppression assays. While effects on humoral immunity were evaluated using hemagglutination assay and mice lethality test.

RESULTS

Hematological analysis showed that mefenamic acid significantly reduced white blood cell count, red blood cell (RBC) count, hemoglobin content, lymphocytes levels, and neutrophils levels in healthy mice as compared with control, suggesting the immunosuppressive activity of mefenamic acid. Treatment with mefenamic acid also significantly reduced all the hematological parameters in cyclophosphamide-induced neutropenic mice, as compared with positive control group. We found that treatment with mefenamic acid significantly suppressed DTH after 24 h, 48 h, and 72 h, as compared with positive control group. Mefenamic acid treated groups showed a significant reduction in antibody titer against sheep RBCs as compared to control group, similar to the effect of cyclophosphamide. We also found increased mice lethality rate in mefenamic acid treated groups, as compared with positive control group.

CONCLUSIONS

The results provided basic information of immunosuppression of mefenamic acid on both cell-mediated and humoral immunity.

Homeostatic responses of colonic LGR5+ stem cells following acute in vivo exposure to a genotoxic carcinogen

Perturbations in DNA damage, DNA repair, apoptosis and cell proliferation in the base of the crypt where stem cells reside are associated with colorectal cancer (CRC) initiation and progression. Although the transformation of leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5)(+) cells is an extremely efficient route towards initiating small intestinal adenomas, the role of Lgr5(+) cells in CRC pathogenesis has not been well investigated. Therefore, we further characterized the properties of colonic Lgr5(+) cells compared to differentiated cells in Lgr5-EGFP-IRES-creER(T2) knock-in mice at the initiation stage of carcinogen azoxymethane (AOM)-induced tumorigenesis using a quantitative immunofluorescence microscopy approach. At 12 and 24h post-AOM treatment, colonic Lgr5(+) stem cells (GFP(high)) were preferentially damaged by carcinogen, exhibiting a 4.7-fold induction of apoptosis compared to differentiated (GFP(neg)) cells. Furthermore, with respect to DNA repair, O(6)-methylguanine DNA methyltransferase (MGMT) expression was preferentially induced (by 18.5-fold) in GFP(high) cells at 24h post-AOM treatment compared to GFP(neg) differentiated cells. This corresponded with a 4.3-fold increase in cell proliferation in GFP(high) cells. These data suggest that Lgr5(+) stem cells uniquely respond to alkylation-induced DNA damage by upregulating DNA damage repair, apoptosis and cell proliferation compared to differentiated cells in order to maintain genomic integrity. These findings highlight the mechanisms by which colonic Lgr5(+) stem cells respond to cancer-causing environmental factors.

DNA Alkylating Agent Protects Against Spontaneous Hepatocellular Carcinoma Regardless of O6-Methylguanine-DNA Methyltransferase Status

Hepatocellular carcinoma is increasingly important in the United States as the incidence rate rose over the last 30 years. C3HeB/FeJ mice serve as a unique model to study hepatocellular carcinoma tumorigenesis because they mimic human hepatocellular carcinoma with delayed onset, male gender bias, approximately 50% incidence, and susceptibility to tumorigenesis is mediated through multiple genetic loci. Because a human O(6)-methylguanine-DNA methyltransferase (hMGMT) transgene reduces spontaneous tumorigenesis in this model, we hypothesized that hMGMT would also protect from methylation-induced hepatocarcinogenesis. To test this hypothesis, wild-type and hMGMT transgenic C3HeB/FeJ male mice were treated with two monofunctional alkylating agents: diethylnitrosamine (DEN; 0.025 μmol/g body weight) on day 12 of life with evaluation for glucose-6-phosphatase-deficient (G6PD) foci at 16, 24, and 32 weeks or N-methyl-N-nitrosurea (MNU; 25 mg MNU/kg body weight) once monthly for 7 months starting at 3 months of age with evaluation for liver tumors at 12 to 15 months of age. No difference in abundance or size of G6PD foci was measured with DEN treatment. In contrast, it was unexpectedly found that MNU reduces liver tumor prevalence in wild-type and hMGMT transgenic mice despite increased tumor prevalence in other tissues. hMGMT and MNU protections were additive, suggesting that MNU protects through a different mechanism, perhaps through the cytotoxic N7-alkylguanine and N3-alkyladenine lesions which have low mutagenic potential compared with O(6)-alkylguanine lesions. Together, these results suggest that targeting the repair of cytotoxic lesions may be a good preventative for patients at high risk of developing hepatocellular carcinoma.

How to train glioma cells to die: molecular challenges in cell death

The five-year survival rate for patients with malignant glioma is less than 10%. Despite aggressive chemo/radiotherapy these tumors have remained resistant to almost every interventional strategy evaluated in patients. Resistance to these agents is attributed to extrinsic mechanisms such as the tumor microenvironment, poor drug penetration, and tumoral heterogeneity. In addition, genetic and molecular examination of these tumors has revealed defective apoptotic regulation, enhanced pro-survival autophagy signaling, and a propensity for necrosis that aids in the adaptation to environmental stress and resistance to treatment. The combination of extrinsic and intrinsic hallmarks in glioma contributes to the multifaceted resistance to traditional anti-tumor agents. Here we describe the biology of the disease relevant to therapeutic resistance, with a specific focus on molecular deregulation of cell death pathways. Emerging studies investigating the targeting of these pathways including BH3 mimetics and autophagy inhibitors that are being evaluated in both the preclinical and clinical settings are discussed. This review highlights the pathways exploited by glioblastoma cells that drive their hallmark pro-survival predisposition and makes therapy development such a challenge.

Recurrent Glioblastomas Reveal Molecular Subtypes Associated with Mechanistic Implications of Drug-Resistance

Previously, transcriptomic profiling studies have shown distinct molecular subtypes of glioblastomas. It has also been suggested that the recurrence of glioblastomas could be achieved by transcriptomic reprograming of tumors, however, their characteristics are not yet fully understood. Here, to gain the mechanistic insights on the molecular phenotypes of recurrent glioblastomas, gene expression profiling was performed on the 43 cases of glioblastomas including 15 paired primary and recurrent cases. Unsupervised clustering analyses revealed two subtypes of G1 and G2, which were characterized by proliferation and neuron-like gene expression traits, respectively. While the primary tumors were classified as G1 subtype, the recurrent glioblastomas showed two distinct expression types. Compared to paired primary tumors, the recurrent tumors in G1 subtype did not show expression alteration. By contrast, the recurrent tumors in G2 subtype showed expression changes from proliferation type to neuron-like one. We also observed the expression of stemness-related genes in G1 recurrent tumors and the altered expression of DNA-repair genes (i.e., AURK, HOX, MGMT, and MSH6) in the G2 recurrent tumors, which might be responsible for the acquisition of drug resistance mechanism during tumor recurrence in a subtype-specific manner. We suggest that recurrent glioblastomas may choose two different strategies for transcriptomic reprograming to escape the chemotherapeutic treatment during tumor recurrence. Our results might be helpful to determine personalized therapeutic strategy against heterogeneous glioma recurrence.

Downregulation of BRCA1-BRCA2-containing complex subunit 3 sensitizes glioma cells to temozolomide

We previously found that BRCA1-BRCA2-containing complex subunit 3 (BRCC3) was highly expressed in tumorigenic rat glioma cells. However, the functional role of BRCC3 in human glioma cells remains to be characterized. This study indicated that the upregulation of BRCC3 expression was induced in two human malignant glioblastoma U251 and A172 cell lines following exposure to the alkylating agent, temozolomide (TMZ). Homologous recombination (HR)-dependent DNA repair-associated genes (i.e. BRCA1, BRCA2, RAD51 and FANCD2) were also increased in U251 and A172 cells after treatment with TMZ. BRCC3 gene knockdown through lentivirus-mediated gene knockdown approach not only significantly reduced the clonogenic and migratory abilities of U251 and A172 cells, but also enhanced their sensitization to TMZ. The increase in phosphorylated H2AX foci (γH2AX) formation, an indicator of DNA damage, persisted in TMZ-treated glioma cells with stable knockdown BRCC3 expression, suggesting that BRCC3 gene deficiency is associated with DNA repair impairment. In summary, we demonstrate that by inducing DNA repair, BRCC3 renders glioma cells resistant to TMZ. The findings point to BRCC3 as a potential target for treatment of alkylating drug-resistant glioma.

Effects of hyperthermia on DNA repair pathways: one treatment to inhibit them all

The currently available arsenal of anticancer modalities includes many DNA damaging agents that can kill malignant cells. However, efficient DNA repair mechanisms protect both healthy and cancer cells against the effects of treatment and contribute to the development of drug resistance. Therefore, anti-cancer treatments based on inflicting DNA damage can benefit from inhibition of DNA repair. Hyperthermia – treatment at elevated temperature – considerably affects DNA repair, among other cellular processes, and can thus sensitize (cancer) cells to DNA damaging agents. This effect has been known and clinically applied for many decades, but how heat inhibits DNA repair and which pathways are targeted has not been fully elucidated. In this review we attempt to summarize the known effects of hyperthermia on DNA repair pathways relevant in clinical treatment of cancer. Furthermore, we outline the relationships between the effects of heat on DNA repair and sensitization of cells to various DNA damaging agents.

Increased N7-methyldeoxyguanosine DNA adducts after occupational exposure to pesticides and influence of genetic polymorphisms of paraoxonase-1 and glutathione S-transferase M1 and T1

There are concerns about genetic risks associated with long-term exposure to pesticides as these compounds may damage DNA, resulting in mutations that eventually lead to cancer, neurological, and reproductive adverse health effects. This study assessed DNA damage in intensive agricultural workers exposed to pesticides by determining the levels of N7-methyldeoxyguanosine (N7-MedG), an adduct known to be a robust biomarker of recent exposure to chemical methylating agents. A cohort of 39 plastic greenhouse workers was assessed for changes in lymphocyte DNA N7-MedG levels between low level and high level exposures during the course of a spraying season. The contributions of genetic polymorphisms of the pesticide-metabolizing enzymes paraoxonase-1 (PON1) and the glutathione S-transferases, GSTM1 and GSTT1, on N7-MedG levels and other potential confounders were also assessed. N7-MedG increased in the period of high pesticide exposure as compared to the low exposure period (0.23 and 0.18 µmol N7-MedG/mol dG for the unadjusted and adjusted linear mixed models, P = 0.02 and 0.08, respectively). Significant decreased levels of erythrocyte acetylcholinesterase and plasma cholinesterase were observed in the high versus low exposure period in both the unadjusted (2.85 U/g hemoglobin and 213.13 U/L, respectively) and adjusted linear mixed models (2.99 U/g hemoglobin and 230.77 U/L, respectively), indicating pesticide intake. In intensive agriculture workers, higher pesticide exposure increased DNA alkylation levels, further demonstrating the genotoxicity of pesticides in man. In addition, pesticide-exposed individuals with inherited susceptible metabolic genotypes (particularly, null genotype for GSTM1 and the PON1 192R allele) appear to have an increased risk of genotoxic DNA damage. Environ. Mol. Mutagen. 56:437-445, 2015. © 2014 Wiley Periodicals, Inc.

DNA repair mechanisms in cancer development and therapy

DNA damage has been long recognized as causal factor for cancer development. When erroneous DNA repair leads to mutations or chromosomal aberrations affecting oncogenes and tumor suppressor genes, cells undergo malignant transformation resulting in cancerous growth. Genetic defects can predispose to cancer: mutations in distinct DNA repair systems elevate the susceptibility to various cancer types. However, DNA damage not only comprises a root cause for cancer development but also continues to provide an important avenue for chemo- and radiotherapy. Since the beginning of cancer therapy, genotoxic agents that trigger DNA damage checkpoints have been applied to halt the growth and trigger the apoptotic demise of cancer cells. We provide an overview about the involvement of DNA repair systems in cancer prevention and the classes of genotoxins that are commonly used for the treatment of cancer. A better understanding of the roles and interactions of the highly complex DNA repair machineries will lead to important improvements in cancer therapy.

ZRBA1, a Mixed EGFR/DNA Targeting Molecule, Potentiates Radiation Response Through Delayed DNA Damage Repair Process in a Triple Negative Breast Cancer Model

PURPOSE

ZRBA1 is a combi-molecule designed to induce DNA alkylating lesions and to block epidermal growth factor receptor (EGFR) TK domain. Inasmuch as ZRBA1 downregulates the EGFR TK-mediated antisurvival signaling and induces DNA damage, we postulated that it might be a radiosensitizer. The aim of this study was to further investigate the potentiating effect of ZRBA1 in combination with radiation and to elucidate the possible mechanisms of interaction between these 2 treatment modalities.

METHODS AND MATERIALS

The triple negative human breast MDA-MB-468 cancer cell line and mouse mammary cancer 4T1 cell line were used in this study. Clonogenic assay, Western blot analysis, and DNA damage analysis were performed at multiple time points after treatment. To confirm our in vitro findings, in vivo tumor growth delay assay was performed.

RESULTS

Our results show that a combination of ZRBA1 and radiation increases the radiation sensitivity of both cell lines significantly with a dose enhancement factor of 1.56, induces significant numbers of DNA strand breaks, prolongs higher DNA damage up to 24 hours after treatment, and significantly increases tumor growth delay in a syngeneic mouse model.

CONCLUSIONS

Our data suggest that the higher efficacy of this combination could be partially due to increased DNA damage and delayed DNA repair process and to the inhibition of EGFR. The encouraging results of this combination demonstrated a significant improvement in treatment efficiency and therefore could be applicable in early clinical trial settings.

Role of p53 in the progression from ochratoxin A-induced DNA damage to gene mutations in the kidneys of mice

Carcinogenic doses of ochratoxin A (OTA) cause increases of mutant frequencies (MFs) of the red/gam gene (Spi(-)) in the kidneys of p53-deficient gpt delta mice, but not in p53-proficient mice. Here, we investigated the role of p53 in the progression from OTA-induced DNA damage to gene mutations. To this end, p53-proficient and -deficient mice were administered 5 mg/kg OTA for 3 days or 4 weeks by gavage. After 3 days of administration, comet assays were performed and there were no differences in the degrees of OTA-induced DNA damage between p53-proficient and -deficient mice. However, the frequencies of γ-H2AX-positive tubular epithelial cells in p53-deficient mice were significantly higher than those in p53-proficient mice, implying that p53 inhibited the progression from DNA damage to DNA double-strand breaks (DSBs). Evaluation of global gene expression and relevant mRNA/protein expression levels demonstrated that OTA increased the expression of Cdkn1a, which encodes the p21 protein, in p53-proficient mice, but not in p53-deficient mice. Moreover, in p53-deficient mice, mRNA levels of cell cycle progression and DSB repair (homologous recombination repair [HR])-related genes were significantly increased. Thus, G1/S arrest due to activation of the p53/p21 pathway may contribute to the prevention of DSBs in p53-proficient mice. In addition, single base deletions/insertions/substitutions were predominant, possibly due to HR. Overall, these results suggested that OTA induced DSBs at the carcinogenic target site in mice and that p53/p21-mediated cell cycle control prevented an increase in the formation of DSBs, leading to gene mutations.

p53 upregulated modulator of apoptosis sensitizes drug-resistant U251 glioblastoma stem cells to temozolomide through enhanced apoptosis

Malignant glioma is a highly aggressive brain tumor with a poor prognosis. Chemotherapy has been observed to prolong overall survival rate and temozolomide (TMZ), a promising chemotherapeutic agent for treating glioblastoma (GBM), possesses the most effective clinical activity at present, although drug resistance limits its clinical outcome. Growing evidence supports the concept that initial and recurrent GBM may derive from glioblastoma stem cells, which may be responsible for drug resistance. However, the molecular mechanisms underlying this resistance remain to be elucidated. In the present study, a TMZ‑resistant GBM cell line, U251R, was developed and subsequently divided into two subpopulations according to the CD133 immunophenotype. No significant difference was identified in the expression of O6‑methylguanine‑DNA‑methyltransferase (MGMT) between CD133+ U251R cells and CD133‑ U251R cells, whereas the CD133+ cell population was more resistant to TMZ‑induced growth inhibition and cell death. TMZ achieves its cytotoxic effect by inducing DNA lesions and p53 upregulated modulator of apoptosis (PUMA) is an essential mediator of DNA damage‑induced apoptosis independently of p53 status. Therefore, whether PUMA effectively enhances growth suppression and induces apoptosis when combined with TMZ was investigated. Consequently, it was found that adenoviruses expressing wild‑type‑PUMA not only lead to the apoptosis of CD133+ U251R cells alone, but also significantly increase their sensitivity toward TMZ by elevating the Bcl‑2‑associated X protein/B‑cell lymphoma‑2 ratio without alterations in MGMT expression. Therefore, PUMA may be a suitable target for intervention to improve the therapeutic efficacy of TMZ.

Increased FOXM1 expression can stimulate DNA repair in normal hepatocytes in vivo but also increases nuclear foci associated with senescence

OBJECTIVES

FOXM1 is a transcription factor that has been shown to promote cell proliferation in many tissues during early development and high cell turnover tissues in adults. In a number of tumour cell lines, enrichment of FOXM1 has been shown to reduce the DNA damage response (DDR) and induction of senescence by a range of DNA-damaging agents, suggesting a role for the protein in DNA repair. Endogenous FOXM1 is expressed at detectable levels in hepatocytes of mice up to 2 weeks of age, but not in older mice. The aim of this investigation has been to better understand the role of the protein in DDR in normal cells in vivo.

MATERIALS AND METHODS

Mice with artificially prolonged elevated FOXM1 expression in hepatocytes, were exposed to alkylating diethylnitrosamine.

RESULTS

FOXM1-enriched mice had dampened DDR after treatment with this alkylating agent, which was consistent with observed increase in expression of genes involved in DNA repair. Paradoxically, mice with FOXM1 expression, within weeks after exposure to the DNA-damaging agent, had increased levels of potentially senescent hepatocytes with large nuclear foci, containing 53BP1. Similarly, spontaneous accumulation of these cells seen with normal ageing in mice was increased with FOXM1 enrichment.

CONCLUSION

Despite its known abilities to promote proliferation and DNA repair, and to reduce ROS, enrichment of FOXM1, as with other oncoproteins, may cause increased persistent DNA lesions and/or senescence in normal murine hepatocytes.

The allure and peril of hematopoietic stem cell transplantation: overcoming immune challenges to improve success

Since its inception in the mid-twentieth century, the complication limiting the application and utility of allogeneic hematopoietic stem cell transplantation (allo-HSCT) to treat patients with hematopoietic cancer is the development of graft-versus-host disease (GVHD). Ironically, GVHD is induced by the cells (T lymphocytes) transplanted for the purpose of eliminating the malignancy. Damage ensuing to multiple tissues, e.g., skin, GI, liver, and others including the eye, provides the challenge of regulating systemic and organ-specific GVH responses. Because the immune system is also targeted by GVHD, this both: (a) impairs reconstitution of immunity post-transplant resulting in patient susceptibility to lethal infection and (b) markedly diminishes the individual's capacity to generate anti-cancer immunity--the raison d'etre for undergoing allo-HSCT. We hypothesize that deleting alloreactive T cells ex vivo using a new strategy involving antigen stimulation and alkylation will prevent systemic GVHD thereby providing a platform for the generation of anti-tumor immunity. Relapse also remains the major complication following autologous HSCT (auto-HSCT). While GVHD does not complicate auto-HSCT, its absence removes significant grant anti-tumor responses (GVL) and raises the challenge of generating rapid and effective anti-tumor immunity early post-transplant prior to immune reconstitution. We hypothesize that effective vaccine usage to stimulate tumor-specific T cells followed by their amplification using targeted IL-2 can be effective in both the autologous and allogeneic HSCT setting. Lastly, our findings support the notion that the ocular compartment can be locally targeted to regulate visual complications of GVHD which may involve both alloreactive and self-reactive (i.e., autoimmune) responses.

Inducible Protective Processes in Animal Systems XIII: Comparative Analysis of Induction of Adaptive Response by EMS and MMS in Ehrlich Ascites Carcinoma Cells

In order to investigate the presence of adaptive response in cancerous cells, two monofunctional alkylating agents, namely, ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS), were employed to treat Ehrlich ascites carcinoma (EAC) cells in vivo. Conditioning dose of 80 mg/kg body weight of EMS or 50 mg/kg body weight of MMS and challenging dose of 240 mg/kg body weight of EMS or 150 mg/kg body weight of MMS were selected by pilot toxicity studies. Conditioned EAC cells when challenged after 8 h time lag resulted in significant reduction in chromosomal aberrations compared to challenging dose of respective agents. As has been proved in earlier studies with normal organisms, even in cancerous cells (EAC), there is presence of adaptive response to methylating and ethylating agents. Furthermore, it is also interesting to note in the present studies that the methylating agent, MMS, is a stronger inducer of the adaptive response than the ethylating agent, EMS.