Copper-dependent cleavage of DNA by bleomycin

Metal Ions Modify In Vitro DNA Damage Yields with High-LET Radiation

Cu2+ and Co2+ are metals known to increase DNA damage in the presence of hydrogen peroxide through a Fenton-type reaction. We hypothesized that these metals could increase DNA damage following irradiations of increasing LET values as hydrogen peroxide is a product of the radiolysis of water. The reaction mixtures contain either double- or single-stranded DNA in solution with Cu2+ or Co2+ and were irradiated either with X-ray, carbon-ion or iron-ion beams, or they were treated with hydrogen peroxide or bleomycin at increasing radiation dosages or chemical concentrations. DNA damage was then assessed via gel electrophoresis followed with a band intensity analysis. DNA damage was the greatest when DNA in the solution with either metal was treated with only hydrogen peroxide followed by the DNA damage of DNA in the solution with either metal post irradiation of low-LET (X-Ray) or high-LET (carbon-ion and iron-ion), respectively, and demonstrated the least damage after treatment with bleomycin. Cu2+ portrayed greater DNA damage than Co2+ following all experimental conditions. The metals' effect caused more DNA damage and was observed to be LET-dependent for single-strand break formation but inversely dependent for double-strand break formation. These results suggest that Cu2+ is more efficient than Co2+ at inducing both DNA single-strand and double-strand breaks following all irradiations and chemical treatments.

Understanding the Prooxidant Action of Plant Polyphenols in the Cellular Microenvironment of Malignant Cells: Role of Copper and Therapeutic Implications

Plant derived polyphenolic compounds are considered critical components of human nutrition and have shown chemotherapeutic effects against a number of malignancies. Several studies have confirmed the ability of polyphenols to induce apoptosis and regression of tumours in animal models. However, the mechanism through which polyphenols modulate their malignant cell selective anticancer effects has not been clearly established. While it is believed that the antioxidant properties of these molecules may contribute to lowering the risk of cancer induction by causing oxidative damage to DNA, it could not be held responsible for chemotherapeutic properties and apoptosis induction. It is a well known fact that cellular copper increases within the malignant cell and in serum of patients harboring malignancies. This phenomenon is independent of the cellular origin of malignancies. Based on our own observations and those of others; over the last 30 years our laboratory has shown that cellular copper reacts with plant derived polyphenolic compounds, by a Fenton like reaction, which generates reactive oxygen species and leads to genomic DNA damage. This damage then causes an apoptosis like cell death of malignant cells, while sparing normal cells. This communication reviews our work in this area and lays the basis for understanding how plant derived polyphenols can behave as prooxidants (and not antioxidants) within the microenvironment of a malignancy (elevated copper levels) and gives rationale for their preferential cytotoxicity towards malignant cells.

Improvements in Smartphone and Night Vision Imaging Technologies Enable Low Cost, On-Site Assays of Bioluminescent Cells

Technologies enabling on-site environmental detection or medical diagnostics in resource-limited settings have a strong disruptive potential compared to current analytical approaches that require trained personnel in laboratories with immobile, resource intensive instrumentation. Handheld devices, such as smartphones, are now routinely produced with CPUs, RAM, wireless data transfer capabilities, and high-resolution complementary metal oxide semiconductor (CMOS) cameras capable of supporting the capture and processing of bioluminescent signals. In theory, combining the capabilities of these devices with continuously bioluminescent human cell-based bioreporters would allow them to replicate the functionality of more expensive, more complex, and less flexible platforms while supporting human-relevant conclusions. In this work, we compare the performance of smartphone (CMOS) and night vision (image intensifier) devices with in vivo (CCD camera), and in vitro (photomultiplier tube) laboratory instrumentation for monitoring signal dynamics from continuously bioluminescent human cellular models under toxic, stable, and induced expression scenarios. All systems detected bioluminescence from cells at common plating densities. While the in vivo and in vitro systems were more sensitive and detected signal dynamics representing cellular health changes earlier, the night vision and smartphone systems also detected these changes with relatively similar coefficients of variation and linear detection capabilities. The smartphone system did not detect transcriptional induction. The night vision system did detect transcriptional activation, but was less sensitive than the in vivo or in vitro systems and required a stronger induction before the change could be resolved.

Chlamydomonas POLQ is necessary for CRISPR/Cas9-mediated gene targeting

The use of CRISPR/Cas endonucleases has revolutionized gene editing techniques for research on Chlamydomonas reinhardtii. To better utilize the CRISPR/Cas system, it is essential to develop a more comprehensive understanding of the DNA repair pathways involved in genome editing. In this study, we have analyzed contributions from canonical KU80/KU70-dependent nonhomologous end-joining (cNHEJ) and DNA polymerase theta (POLQ)-mediated end joining on SpCas9-mediated untemplated mutagenesis and homology-directed repair (HDR)/gene inactivation in Chlamydomonas. Using CRISPR/SpCas9 technology, we generated DNA repair-defective mutants ku80, ku70, polQ for gene targeting experiments. Our results show that untemplated repair of SpCas9-induced double strand breaks results in mutation spectra consistent with an involvement of both KU80/KU70 and POLQ. In addition, the inactivation of POLQ was found to negatively affect HDR of the inactivated paromomycin-resistant mut-aphVIII gene when donor single-stranded oligos were used. Nevertheless, mut-aphVIII was still repaired by homologous recombination in these mutants. POLQ inactivation suppressed random integration of transgenes co-transformed with the donor ssDNA. KU80 deficiency did not affect these events but instead was surprisingly found to stimulate HDR/gene inactivation. Our data suggest that in Chlamydomonas, POLQ is the main contributor to CRISPR/Cas-induced HDR and random integration of transgenes, whereas KU80/KU70 potentially plays a secondary role. We expect our results will lead to improvement of genome editing in C. reinhardtii and can be used for future development of algal biotechnology.

Coinage Metal N-Heterocyclic Carbene Complexes: Recent Synthetic Strategies and Medicinal Applications

New weapons are constantly needed in the fight against cancer. The discovery of cisplatin as an anticancer drug prompted the search for new metal complexes. The successful history of cisplatin motivated chemists to develop a plethora of metal-based molecules. Among them, metal-N-heterocyclic carbene (NHC) complexes have gained significant attention because of their suitable qualities for efficient drug design. The enhanced applications of coinage metal-NHC complexes have encouraged a gradually increasing number of studies in the fields of medicinal chemistry that benefit from the fascinating chemical properties of these complexes. This review aims to present recent developments in synthetic strategies and medicinal applications of copper, silver and gold complexes supported by NHC ligands.

HSATII RNA is induced via a noncanonical ATM-regulated DNA damage response pathway and promotes tumor cell proliferation and movement

Pericentromeric human satellite II (HSATII) repeats are normally silent but can be actively transcribed in tumor cells, where increased HSATII copy number is associated with a poor prognosis in colon cancer, and in human cytomegalovirus (HCMV)-infected fibroblasts, where the RNA facilitates viral replication. Here, we report that HCMV infection or treatment of ARPE-19 diploid epithelial cells with DNA-damaging agents, etoposide or zeocin, induces HSATII RNA expression, and a kinase-independent function of ATM is required for the induction. Additionally, various breast cancer cell lines growing in adherent, two-dimensional cell culture express HSATII RNA at different levels, and levels are markedly increased when cells are infected with HCMV or treated with zeocin. High levels of HSATII RNA expression correlate with enhanced migration of breast cancer cells, and knockdown of HSATII RNA reduces cell migration and the rate of cell proliferation. Our investigation links high expression of HSATII RNA to the DNA damage response, centered on a noncanonical function of ATM, and demonstrates a role for the satellite RNA in tumor cell proliferation and movement.

The Glutathione/Metallothionein System Challenges the Design of Efficient O2 -Activating Copper Complexes

Copper complexes are of medicinal and biological interest, including as anticancer drugs designed to cleave intracellular biomolecules by O2 activation. To exhibit such activity, the copper complex must be redox active and resistant to dissociation. Metallothioneins (MTs) and glutathione (GSH) are abundant in the cytosol and nucleus. Because they are thiol-rich reducing molecules with high CuI affinity, they are potential competitors for a copper ion bound in a copper drug. Herein, we report the investigation of a panel of CuI /CuII complexes often used as drugs, with diverse coordination chemistries and redox potentials. We evaluated their catalytic activity in ascorbate oxidation based on redox cycling between CuI and CuII , as well as their resistance to dissociation or inactivation under cytosolically relevant concentrations of GSH and MT. O2 -activating CuI /CuII complexes for cytosolic/nuclear targets are generally not stable against the GSH/MT system, which creates a challenge for their future design.

Assessment of cytotoxic and genotoxic potentials of a mononuclear Fe(II) Schiff base complex with photocatalytic activity in Trigonella

BACKGROUND

In recent times, coordination complexes of iron in various oxidation states along with variety of ligand systems have been designed and developed for effective treatment of cancer cells without adversely affecting the normal cell and tissues of various organs.

METHODS

In this study, we have evaluated the mechanism of action of a Fe(II) Schiff base complex in the crop plant Trigonella foenum-graecum L. (Fenugreek) as the screening system by using morphological, cytological, biochemical and molecular approaches. Further functional characterization was performed using MCF-7 cell line and solid tumour model for the assessment of anti-tumour activity of the complex.

RESULTS

Our results indicate efficiency of the Fe(II) Schiff base complex in the induction of double strand breaks in DNA. Complex treatment clearly induced cytotoxic and genotoxic damage in Trigonella seedlings. The Fe-complex treatment caused cell cycle arrest via the activation of ATM-ATR kinase mediated DNA damage response pathway with the compromised expression of CDK1, CDK2 and CyclinB1 protein in Trigonella seedlings. In cultured MCF-7 cells, the complex induces cytotoxicity and DNA fragmentation through intracellular ROS generation. Fe-complex treatment inhibited tumour growth in solid tumour model with no additional side effects.

CONCLUSION

The growth inhibitory and cytotoxic effects of the complex result from activation of DNA damage response along with oxidative stress and cell cycle arrest.

GENERAL SIGNIFICANCE

Overall, our results have provided comprehensive information on the mechanism of action and efficacy of a Fe(II) Schiff base complex in higher eukaryotic genomes and indicated its future implications as potential therapeutic agent.

Response of the Green Alga Chlamydomonas reinhardtii to the DNA Damaging Agent Zeocin

DNA damage is a ubiquitous threat endangering DNA integrity in all living organisms. Responses to DNA damage include, among others, induction of DNA repair and blocking of cell cycle progression in order to prevent transmission of damaged DNA to daughter cells. Here, we tested the effect of the antibiotic zeocin, inducing double stranded DNA breaks, on the cell cycle of synchronized cultures of the green alga Chlamydomonas reinhardtii. After zeocin application, DNA replication partially occurred but nuclear and cellular divisions were completely blocked. Application of zeocin combined with caffeine, known to alleviate DNA checkpoints, decreased cell viability significantly. This was probably caused by a partial overcoming of the cell cycle progression block in such cells, leading to aberrant cell divisions. The cell cycle block was accompanied by high steady state levels of mitotic cyclin-dependent kinase activity. The data indicate that DNA damage response in C. reinhardtii is connected to the cell cycle block, accompanied by increased and stabilized mitotic cyclin-dependent kinase activity.

Iron and Copper Intracellular Chelation as an Anticancer Drug Strategy

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body.

Iron and Copper Intracellular Chelation as an Anticancer Drug Strategy

A very promising direction in the development of anticancer drugs is inhibiting the molecular pathways that keep cancer cells alive and able to metastasize. Copper and iron are two essential metals that play significant roles in the rapid proliferation of cancer cells and several chelators have been studied to suppress the bioavailability of these metals in the cells. This review discusses the major contributions that Cu and Fe play in the progression and spreading of cancer and evaluates select Cu and Fe chelators that demonstrate great promise as anticancer drugs. Efforts to improve the cellular delivery, efficacy, and tumor responsiveness of these chelators are also presented including a transmetallation strategy for dual targeting of Cu and Fe. To elucidate the effectiveness and specificity of Cu and Fe chelators for treating cancer, analytical tools are described for measuring Cu and Fe levels and for tracking the metals in cells, tissue, and the body.

Importance of Metal-Ion Exchange for the Biological Activity of Coordination Complexes of the Biomimetic Ligand N4Py

Metal coordination complexes can display interesting biological activity, as illustrated by the bleomycins (BLMs), a family of natural antibiotics that when coordinated to a redox-active metal ion, show antitumor activity. Yet, which metal ion is required for the activity in cells is still subject to debate. In this study, we described how different metal ions affect the intracellular behavior and activity of the synthetic BLM-mimic N, N-bis(2-pyridylmethyl)- N-bis(2-pyridyl)methylamine (N4Py). Our study shows that a mixture of iron(II), copper(II), and zinc(II) complexes can be generated when N4Py is added to cell cultures but that the metal ion can also be exchanged by other metal ions present in cells. Moreover, the combination of chemical data, together with the performed biological experiments, shows that the active complex causing oxidative damage to cells is the FeII-N4Py complex and not per se the metal complex that was initially added to the cell culture medium. Finally, it is proposed that the high activity observed upon the addition of the free N4Py ligand is the result of a combination of scavenging of biologically relevant metals and oxidative damage caused by the iron(II) complex.

The Interaction of the Metallo-Glycopeptide Anti-Tumour Drug Bleomycin with DNA

The cancer chemotherapeutic drug, bleomycin, is clinically used to treat several neoplasms including testicular and ovarian cancers. Bleomycin is a metallo-glycopeptide antibiotic that requires a transition metal ion, usually Fe(II), for activity. In this review, the properties of bleomycin are examined, especially the interaction of bleomycin with DNA. A Fe(II)-bleomycin complex is capable of DNA cleavage and this process is thought to be the major determinant for the cytotoxicity of bleomycin. The DNA sequence specificity of bleomycin cleavage is found to at 5′-GT* and 5′-GC* dinucleotides (where * indicates the cleaved nucleotide). Using next-generation DNA sequencing, over 200 million double-strand breaks were analysed, and an expanded bleomycin sequence specificity was found to be 5′-RTGT*AY (where R is G or A and Y is T or C) in cellular DNA and 5′-TGT*AT in purified DNA. The different environment of cellular DNA compared to purified DNA was proposed to be responsible for the difference. A number of bleomycin analogues have been examined and their interaction with DNA is also discussed. In particular, the production of bleomycin analogues via genetic manipulation of the modular non-ribosomal peptide synthetases and polyketide synthases in the bleomycin gene cluster is reviewed. The prospects for the synthesis of bleomycin analogues with increased effectiveness as cancer chemotherapeutic agents is also explored.

Rad5 coordinates translesion DNA synthesis pathway by recognizing specific DNA structures in saccharomyces cerevisiae

DNA repair is essential to maintain genome integrity. In addition to various DNA repair pathways dealing with specific types of DNA lesions, DNA damage tolerance (DDT) promotes the bypass of DNA replication blocks encountered by the replication fork to prevent cell death. Budding yeast Rad5 plays an essential role in the DDT pathway and its structure indicates that Rad5 recognizes damaged DNA or stalled replication forks, suggesting that Rad5 plays an important role in the DDT pathway choice. It has been reported that Rad5 forms subnuclear foci in the presence of methyl methanesulfonate (MMS) during the S phase. By analyzing the formation of Rad5 foci after MMS treatment, we showed that some specific DNA structures rather than mono-ubiquitination of proliferating cell nuclear antigen are required for the recruitment of Rad5 to the damaged site. Moreover, inactivation of the base excision repair (BER) pathway greatly decreased the Rad5 focus formation, suggesting that Rad5 recognizes specific DNA structures generated by BER. We also identified a negative role of overexpressed translesion synthesis polymerase Polη in the formation of Rad5 foci. Based on these data, we propose a modified DDT pathway model in which Rad5 plays a role in activating the DDT pathway.

An intelligent NIR-responsive chelate copper-based anticancer nanoplatform for synergistic tumor targeted chemo-phototherapy

The chelate copper-based anticancer drug bleomycin (BLM) is usually believed to bind metal ions especially Cu(ii) to generate the "activated BLM" for DNA cleavage. Herein, BLM and L-menthol (LM) co-loaded hollow mesoporous Cu_2-xS nanoparticles (HMCu_2-xS NPs) with surface folic acid (FA) modification were formulated to construct an intelligent NIR-responsive nanoplatform for synergistic tumor targeted chemo-phototherapy. With the tumor targeting ability of the folate receptor (FR)-positive, FA-HMCu_2-xS/BLM/LM could pinpoint tumor cells efficiently. Under NIR irradiation, the versatile HMCu_2-xS would be bound to exploit the merits of phototherapy (including PTT and PDT-like effects) for cancer treatment. Meanwhile, benefiting from the controllable "solid-liquid" (S-L) phase transition feature of LM as a gatekeeper, FA-HMCu_2-xS/BLM/LM offered a platform for simultaneous NIR-mediated temperature-responsive BLM and copper ion release, which further initiated the generation of the "activated BLM". As a matter of course, the remarkable synergistic combination of Cu-dependent chemo-phototherapy in vitro and in vivo by such a smart all-in-one drug delivery nanoplatform developed here provided information for advancing nanotherapy in biomedical fields.

Interaction of Zn(II)bleomycin-A2 and Zn(II)peplomycin with a DNA hairpin containing the 5'-GT-3' binding site in comparison with the 5'-GC-3' binding site studied by NMR spectroscopy

Bleomycins are a group of glycopeptide antibiotics synthesized by Streptomyces verticillus that are widely used for the treatment of various neoplastic diseases. These antibiotics have the ability to chelate a metal center, mainly Fe(II), and cause site-specific DNA cleavage. Bleomycins are differentiated by their C-terminal regions. Although this antibiotic family is a successful course of treatment for some types of cancers, it is known to cause pulmonary fibrosis. Previous studies have identified that bleomycin-related pulmonary toxicity is linked to the C-terminal region of these drugs. This region has been shown to closely interact with DNA. We examined the binding of Zn(II)peplomycin and Zn(II)bleomycin-A2 to a DNA hairpin of sequence 5'-CCAGTATTTTTACTGG-3', containing the binding site 5'-GT-3', and compared the results with those obtained from our studies of the same MBLMs bound to a DNA hairpin containing the binding site 5'-GC-3'. We provide evidence that the DNA base sequence has a strong impact in the final structure of the drug-target complex.

Investigation into the mechanism of action of the antimicrobial peptides Os and Os-C derived from a tick defensin

Os and Os-C are two novel antimicrobial peptides, derived from a tick defensin, which have been shown to have a larger range of antimicrobial activity than the parent peptide, OsDef2. The aim of this study was to determine whether the peptides Os and Os-C are mainly membrane acting, or if these peptides have possible additional intracellular targets in Escherichia coli and Bacillus subtilis. Transmission electron microscopy revealed that both peptides adversely affected intracellular structure of both bacteria causing different degrees of granulation of the intracellular contents. At the minimum bactericidal concentrations, permeabilization as determined with the SYTOX green assay seemed not to be the principle mode of killing when compared to melittin. However, fluorescent triple staining indicated that the peptides caused permeabilization of stationary phase bacteria and TEM indicated membrane effects. Studies using fluorescently labeled peptides revealed that the membrane penetrating activity of Os and Os-C was similar to buforin II. Os-C was found to associate with the septa of B. subtilis. Plasmid binding studies showed that Os and Os-C binds E. coli plasmid DNA at a similar charge ratio as melittin. These studies suggest membrane activity for Os and Os-C with possible intracellular targets such as DNA. The differences in permeabilization at lower concentrations and binding to DNA between Os and Os-C, suggest that the two peptides have dissimilar modes of action.

Structural features facilitating tumor cell targeting and internalization by bleomycin and its disaccharide

We have shown previously that the bleomycin (BLM) carbohydrate moiety can recapitulate the tumor cell targeting effects of the entire BLM molecule, that BLM itself is modular in nature consisting of a DNA-cleaving aglycone which is delivered selectively to the interior of tumor cells by its carbohydrate moiety, and that there are disaccharides structurally related to the BLM disaccharide which are more efficient than the natural disaccharide at tumor cell targeting/uptake. Because BLM sugars can deliver molecular cargoes selectively to tumor cells, and thus potentially form the basis for a novel antitumor strategy, it seemed important to consider additional structural features capable of affecting the efficiency of tumor cell recognition and delivery. These included the effects of sugar polyvalency and net charge (at physiological pH) on tumor cell recognition, internalization, and trafficking. Since these parameters have been shown to affect cell surface recognition, internalization, and distribution in other contexts, this study has sought to define the effects of these structural features on tumor cell recognition by bleomycin and its disaccharide. We demonstrate that both can have a significant effect on tumor cell binding/internalization, and present data which suggests that the metal ions normally bound by bleomycin following clinical administration may significantly contribute to the efficiency of tumor cell uptake, in addition to their characterized function in DNA cleavage. A BLM disaccharide-Cy5** conjugate incorporating the positively charged dipeptide d-Lys-d-Lys was found to associate with both the mitochondria and the nuclear envelope of DU145 cells, suggesting possible cellular targets for BLM disaccharide-cytotoxin conjugates.

Kanamycin Resistance Cassette for Genetic Manipulation of Treponema denticola

Treponema denticola has been recognized as an important oral pathogen of the "red complex" bacterial consortium that is associated with the pathogenesis of endodontal and periodontal diseases. However, little is known about the virulence of T. denticola due to its recalcitrant genetic system. The difficulty in genetically manipulating oral spirochetes is partially due to the lack of antibiotic resistance cassettes that are useful for gene complementation following allelic replacement mutagenesis. In this study, a kanamycin resistance cassette was identified and developed for the genetic manipulation of T. denticola ATCC 35405. Compared to the widely used ermF-ermAM cassette, the kanamycin cassette used in the transformation experiments gave rise to additional antibiotic-resistant T. denticola colonies. The kanamycin cassette is effective for allelic replacement mutagenesis as demonstrated by inactivation of two open reading frames of T. denticola, TDE1430 and TDE0911. In addition, the cassette is also functional in trans-chromosomal complementation. This was determined by functional rescue of a periplasmic flagellum (PF)-deficient mutant that had the flgE gene coding for PF hook protein inactivated. The integration of the full-length flgE gene into the genome of the flgE mutant rescued all of the defects associated with the flgE mutant that included the lack of PF filament and spirochetal motility. Taken together, we demonstrate that the kanamycin resistance gene is a suitable cassette for the genetic manipulation of T. denticola that will facilitate the characterization of virulence factors attributed to this important oral pathogen.

Piper and Vismia species from Colombian Amazonia differentially affect cell proliferation of hepatocarcinoma cells

There is an increasing interest to identify plant-derived natural products with antitumor activities. In this work, we have studied the effects of aqueous leaf extracts from Amazonian Vismia and Piper species on human hepatocarcinoma cell toxicity. Results showed that, depending on the cell type, the plants displayed differential effects; thus, Vismia baccifera induced the selective killing of HepG2, while increasing cell growth of PLC-PRF and SK-HEP-1. In contrast, these two last cell lines were sensitive to the toxicity by Piper krukoffii and Piper putumayoense, while the Piperaceae did not affect HepG2 growth. All the extracts induced cytotoxicity to rat hepatoma McA-RH7777, but were innocuous (V. baccifera at concentrations < 75 µg/mL) or even protected cells from basal death (P. putumayoense) in primary cultures of rat hepatocytes. In every case, cytotoxicity was accompanied by an intracellular accumulation of reactive oxygen species (ROS). These results provide evidence for the anticancer activities of the studied plants on specific cell lines and suggest that cell killing could be mediated by ROS, thus involving mechanisms independent of the plants free radical scavenging activities. Results also support the use of these extracts of the Vismia and Piper genera with opposite effects as a model system to study the mechanisms of the antitumoral activity against different types of hepatocarcinoma.

The functional landscape of Hsp27 reveals new cellular processes such as DNA repair and alternative splicing and proposes novel anticancer targets

Previously, we identified the stress-induced chaperone, Hsp27, as highly overexpressed in castration-resistant prostate cancer and developed an Hsp27 inhibitor (OGX-427) currently tested in phase I/II clinical trials as a chemosensitizing agent in different cancers. To better understand the Hsp27 poorly-defined cytoprotective functions in cancers and increase the OGX-427 pharmacological safety, we established the Hsp27-protein interaction network using a yeast two-hybrid approach and identified 226 interaction partners. As an example, we showed that targeting Hsp27 interaction with TCTP, a partner protein identified in our screen increases therapy sensitivity, opening a new promising field of research for therapeutic approaches that could decrease or abolish toxicity for normal cells. Results of an in-depth bioinformatics network analysis allying the Hsp27 interaction map into the human interactome underlined the multifunctional character of this protein. We identified interactions of Hsp27 with proteins involved in eight well known functions previously related to Hsp27 and uncovered 17 potential new ones, such as DNA repair and RNA splicing. Validation of Hsp27 involvement in both processes in human prostate cancer cells supports our system biology-predicted functions and provides new insights into Hsp27 roles in cancer cells.

A short DNA sequence confers strong bleomycin binding to hairpin DNAs

Bleomycins A₅ and B₂ were used to study the structural features in hairpin DNAs conducive to strong BLM–DNA interaction. Two members of a 10-hairpin DNA library previously found to bind most tightly to these BLMs were subsequently noted to share the sequence 5′-ACGC (complementary strand sequence 5′-GCGT). Each underwent double-strand cleavage at five sites within, or near, an eight base pair region of the DNA duplex which had been randomized to create the original library. A new hairpin DNA library was selected based on affinity for immobilized Fe(III)·BLM A₅. Two of the 30 newly identified DNAs also contained the sequence 5′-ACGC/5′-GCGT. These DNAs bound to the Fe(II)·BLMs more tightly than any DNA characterized previously. Surface plasmon resonance confirmed tight Fe(III)·BLM B₂ binding and gave an excellent fit for a 1:1 binding model, implying the absence of significant secondary binding sites. Fe(II)·BLM A₅ was used to assess sites of double-strand DNA cleavage. Both hairpin DNAs underwent double-strand cleavage at five sites within or near the original randomized eight base region. For DNA 12, four of the five double-strand cleavages involved independent single-strand cleavage reactions; DNA 13 underwent double-strand DNA cleavage by independent single-strand cleavages at all five sites. DNA 14, which bound Fe·BLM poorly, was converted to a strong binder (DNA 15) by insertion of the sequence 5′-ACGC/5′-GCGT. These findings reinforce the idea that tighter DNA binding by Fe·BLM leads to increased double-strand cleavage by a novel mechanism and identify a specific DNA motif conducive to strong BLM binding and cleavage.

Total syntheses of (-)-pyrimidoblamic acid and P-3A

Total syntheses of (-)-pyrimidoblamic acid and P-3A are disclosed. Central to the convergent approach is a powerful inverse electron demand Diels-Alder reaction between substituted electron-deficient 1,2,3-triazines and a highly functionalized and chiral primary amidine, which forms the pyrimidine cores and introduces all necessary stereochemistry in a single step. Intrinsic in the convergent approach is the potential it provides for the late stage divergent synthesis of modified analogs bearing deep-seated changes in either the pyrimidine cores or the highly functionalized C2 side chain common to both natural products. The examination of the key cycloaddition reaction revealed that the inherent 1,2,3-triazine mode of cycloaddition (C4/N1 vs C5/N2) as well as the amidine regioselectivity were unaffected by introduction of two electron-withdrawing groups (-CO2R) at C4 and C6 of the 1,2,3-triazine even if C5 is unsubstituted (Me or H), highlighting the synthetic potential of the powerful pyrimidine synthesis.

Contributions of NMR to the understanding of the coordination chemistry and DNA interactions of metallo-bleomycins

Bleomycins are a family of glycopeptide antibiotics that have the ability to bind and degrade DNA when bound to key metal ions, which is believed to be responsible for their antitumor activity. Knowledge of the structures of metallo-bleomycins is vital to further characterize their mechanism of action. To this end, numerous structural studies on metallo-bleomycins have been conducted. NMR spectroscopy has had a key role in most of these studies, and has led to very important findings involving the coordination chemistry of metallo-bleomycins, and the details of many metallo-bleomycin-DNA spatial correlations for this important drug. This paper reviews the most important contributions of NMR to the bleomycin field.

DNA damage during G2 phase does not affect cell cycle progression of the green alga Scenedesmus quadricauda

DNA damage is a threat to genomic integrity in all living organisms. Plants and green algae are particularly susceptible to DNA damage especially that caused by UV light, due to their light dependency for photosynthesis. For survival of a plant, and other eukaryotic cells, it is essential for an organism to continuously check the integrity of its genetic material and, when damaged, to repair it immediately. Cells therefore utilize a DNA damage response pathway that is responsible for sensing, reacting to and repairing damaged DNA. We have studied the effect of 5-fluorodeoxyuridine, zeocin, caffeine and combinations of these on the cell cycle of the green alga Scenedesmus quadricauda. The cells delayed S phase and underwent a permanent G2 phase block if DNA metabolism was affected prior to S phase; the G2 phase block imposed by zeocin was partially abolished by caffeine. No cell cycle block was observed if the treatment with zeocin occurred in G2 phase and the cells divided normally. CDKA and CDKB kinases regulate mitosis in S. quadricauda; their kinase activities were inhibited by Wee1. CDKA, CDKB protein levels were stabilized in the presence of zeocin. In contrast, the protein level of Wee1 was unaffected by DNA perturbing treatments. Wee1 therefore does not appear to be involved in the DNA damage response in S. quadricauda. Our results imply a specific reaction to DNA damage in S. quadricauda, with no cell cycle arrest, after experiencing DNA damage during G2 phase.

Human AlkB homolog ABH8 Is a tRNA methyltransferase required for wobble uridine modification and DNA damage survival

tRNA nucleosides are extensively modified to ensure their proper function in translation. However, many of the enzymes responsible for tRNA modifications in mammals await identification. Here, we show that human AlkB homolog 8 (ABH8) catalyzes tRNA methylation to generate 5-methylcarboxymethyl uridine (mcm(5)U) at the wobble position of certain tRNAs, a critical anticodon loop modification linked to DNA damage survival. We find that ABH8 interacts specifically with tRNAs containing mcm(5)U and that purified ABH8 complexes methylate RNA in vitro. Significantly, ABH8 depletion in human cells reduces endogenous levels of mcm(5)U in RNA and increases cellular sensitivity to DNA-damaging agents. Moreover, DNA-damaging agents induce ABH8 expression in an ATM-dependent manner. These results expand the role of mammalian AlkB proteins beyond that of direct DNA repair and support a regulatory mechanism in the DNA damage response pathway involving modulation of tRNA modification.

Metal-NHC complexes: a survey of anti-cancer properties

New weapons to fight cancer are constantly needed. Among chemotherapeutics, anti-cancer metal-drugs have enjoyed a long and successful history since the discovery of the benchmark cisplatin. Advances in metal-drug discovery have motivated chemists to build plethora of complex structures. Among them, a novel area is emerging. This article presents a survey of the metal-N-Heterocyclic Carbenes (Ag(I), Au(I), Pd(II) and Cu(I)-NHCs) as potential anti-cancer agents. Most of the metal-NHCs considered display higher cytotoxicities than the reference metallo-drug cisplatin. Some of them are even selective for particular cell lines. Their mechanisms of action at the cellular level are further discussed, showing that the nature of the metal is of great importance. All these promising results demonstrate that this approach deserves more attention and work.

Copper-Carbon Bonds in Mechanistic and Structural Probing of Proteins as well as in Situations where Copper is a Catalytic or Receptor Site

While copper-carbon bonds are well appreciated in organometallic synthetic chemistry, such occurrences are less known in biological settings. By far, the greatest incidence of copper-carbon moieties is in bioinorganic research aimed at probing copper protein active site structure and mechanism; for example, carbon monoxide (CO) binding as a surrogate for O2. Using infrared (IR) spectroscopy, CO coordination to cuprous sites has proven to be an extremely useful tool for determining active site copper ligation (e.g., donor atom number and type). The coupled (hemocyanin, tyrosinase, catechol oxidase) and non-coupled (peptidylglycine α-hydroxylating monooxygenase, dopamine β-monooxygenase) binuclear copper proteins as well as the heme-copper oxidases (HCOs) have been studied extensively via this method. In addition, environmental changes within the vicinity of the active site have been determined based on shifts in the CO stretching frequencies, such as for copper amine oxidases, nitrite reductases and again in the binuclear proteins and HCOs. In many situations, spectroscopic monitoring has provided kinetic and thermodynamic data on CuI-CO formation and CO dissociation from copper(I); recently, processes occurring on a femtosecond timescale have been reported. Copper-cyano moieties have also been useful for obtaining insights into the active site structure and mechanisms of copper-zinc superoxide dismutase, azurin, nitrous oxide reductase, and multi-copper oxidases. Cyanide is a good ligand for both copper(I) and copper(II), therefore multiple physical-spectroscopic techniques can be applied. A more obvious occurrence of a “Cu-C” moiety was recently described for a CO dehydrogenase which contains a novel molybdenum-copper catalytic site. A bacterial copper chaperone (CusF) was recently established to have a novel d-π interaction comprised of copper(I) with the arene containing side-chain of a tryptophan amino acid residue. Meanwhile, good evidence exists that a plant receptor site (ETR1) utilizes copper(I) to sense ethylene, a growth hormone. A copper olfactory receptor has also been suggested. All of the above mentioned occurrences or uses of carbon-containing substrates and/or probes are reviewed and discussed within the framework of copper proteins and other relevant systems.

In vivo manipulation of the bleomycin biosynthetic gene cluster in Streptomyces verticillus ATCC15003 revealing new insights into its biosynthetic pathway

Bleomycin (BLM), an important clinically used antitumor compound, and its analogs are challenging to prepare by chemical synthesis. Genetic engineering of the biosynthetic pathway in the producer strain would provide an efficient and convenient method of generating new derivatives of this complex molecule in vivo. However, the BLM producing Streptomyces verticillus ATCC15003 has been refractory to all means of introducing plasmid DNA into its cells for nearly two decades. Several years after cloning and identification of the bleomycin biosynthetic gene cluster, this study demonstrates, for the first time, genetic accessibility of this pharmaceutically relevant producer strain by intergeneric Escherichia coli-Streptomyces conjugation. Gene replacement and in-frame deletion mutants were created by lambdaRED-mediated PCR targeting mutagenesis, and the secondary metabolite profile of the resultant mutants confirmed the identity of the BLM biosynthetic gene cluster and established its boundaries. Ultimately, the in-frame blmD deletion mutant strain S. verticillus SB5 resulted in the production of a bleomycin intermediate. The structure of this compound, decarbamoyl-BLM, was elucidated, and its DNA cleavage activity was compared with the parent compounds.

Crystal structure of DNA-bound Co(III) bleomycin B2: Insights on intercalation and minor groove binding

Bleomycins constitute a widely studied class of complex DNA cleaving natural products that are used to treat various cancers. Since their first isolation, the bleomycins have provided a paradigm for the development and discovery of additional DNA-cleaving chemotherapeutic agents. The bleomycins consist of a disaccharide-modified metal-binding domain connected to a bithiazole/C-terminal tail via a methylvalerate-Thr linker and induce DNA damage after oxygen activation through site-selective cleavage of duplex DNA at 5'-GT/C sites. Here, we present crystal structures of two different 5'-GT containing oligonucleotides in both the presence and absence of bound Co(III).bleomycin B(2). Several findings from our studies impact the current view of bleomycin binding to DNA. First, we report that the bithiazole intercalates in two distinct modes and can do so independently of well ordered minor groove binding of the metal binding/disaccharide domains. Second, the Co(III)-coordinating equatorial ligands in our structure include the imidazole, histidine amide, pyrimidine N1, and the secondary amine of the beta aminoalanine, whereas the primary amine acts as an axial ligand. Third, minor groove binding of Co(III).bleomycin involves direct hydrogen bonding interactions of the metal binding domain and disaccharide with the DNA. Finally, modeling of a hydroperoxide ligand coordinated to Co(III) suggests that it is ideally positioned for initiation of C4'-H abstraction.