Straightforward approach to efficient oxidative DNA cleaving agents based on Cu(II) complexes of heterosubstituted cyclens

The Cu(II) complexes of cyclen and two of its heterosubstituted analogues were shown to be efficient oxidative DNA cleavers. The reactivity strongly depends on the heteroatom inserted into the macrocycle (O > S > N)

Significantly enhanced proteolytic activity of cyclen complexes by monoalkylation

A simple approach towards efficient artificial proteases based on the cyclen ligand is presented. We thus achieved an increase of the proteolytic activity of two orders of magnitude when compared to the unsubstituted cyclen complex. Amphiphilic Cu(II) and Co(III) complexes cut BSA and myoglobin as model substrates at μM concentrations. MALDI-ToF MS is used to identify the cleavage fragments

Experimental and computational investigation of heteroatom substitution in nucleolytic Cu(ii) cyclen complexes for balancing stability and redox activity

Cu(II) complexes of cyclen-based ligands CuL1–CuL6 were synthesized and characterized. The corresponding ligands L1–L6 comprise different donor sets including S and O atoms. Whereas cyclen (L1) is commercially available, L2–L6 were synthesized according to protocols available in the literature. Cleavage activity of the complexes towards plasmid DNA was tested in the presence and absence of ascorbate as a reducing agent (oxidative vs. hydrolytic cleavage). As previously shown, the substitution of N donor atoms with hard donor O atoms leads to efficient oxidative nucleases, but dissociation of the complex upon reduction. We thus opted for S substitution (soft donors) to stabilize the reduced Cu(I) species. Increasing the S content, however, leads to species that are difficult to reoxidize in order to ensure efficient oxidative DNA cleavage. We are showing by experimental (cyclic voltammetry) and computational means (DFT) that the rational combination of O and S atoms next to two nitrogen donors within the macrocycle (oxathiacyclen complex CuL6) leads to the stabilization of both redox states. The complex thus exhibits the highest oxidative DNA cleavage activity within this family of cyclen-based Cu(II) complexes – without leaching of the metal ion during reduction

Influence of Donor Atom Exchange and Intercalator Substitution

Krebserkrankungen sind weltweit die zweithäufigste Todesursache. Während sie durch Mutationen der DNA ausgelöst werden, kann die gezielte Veränderung oder Zerstörung von DNA dazu führen, dass die Krebszelle abstirbt. So wurden Krebserkrankungen seit 1978 unter anderem sehr erfolgreich mit DNA-bindenden Medikamenten wie Cisplatin behandelt. Immer häufiger auftretende Resistenzen und Nebenwirkungen altgedienter Krebsmedikamente verlangen die Entwicklung neuer Wirkstoffe. Kandidaten für neue Medikamente gegen Krebs sind künstliche Nukleasen, die reaktive Sauerstoffspezies generieren und DNA oxidativ spalten können. Im Rahmen der vorliegenden Arbeit wurden zwei Strategien genutzt, um ausgehend vom Kupfer(II)cyclen-Komplex neue effektive Metallonukleasen herzustellen. Zunächst wurde untersucht, inwiefern der sukzessive Heteroatomaustausch der Cyclenstickstoffatome die Nukleaseaktivität des Komplexes beeinflusst. Es wurden zehn verschiedene makrozyklische Kupfer(II)-Komplexe mit [NAXB]-Donorsystem dargestellt, bei denen vom Kupfer(II)cyclen-Komplex (A = 4; B = 0) bis hin zum kompletten Sauerstoffanalogon (X = O; A = 0; B = 4) und Schwefelanalogon (X = S; A = 0; B = 4) alle Komplexe charakterisiert und über Agarose-Gelelektrophorese auf ihre Nukleaseaktivität hin untersucht wurden. Die Untersuchung der Sauerstoffanaloga des Cyclens brachte hervor, dass die Nukleaseaktivität gegenüber dem Kupfer(II)cyclen-Komplex erhöht ist und vom Sauerstoffanteil und der Komplexgeometrie abhängt. Durch elektrochemische Untersuchungen konnte der Grund für dieses Verhalten festgestellt werden: Keiner der Kupfer(II )oxacyclen-Komplexe zeigte eine elektrochemisch reversible Reduktion, vielmehr führt die Reduktion zur Freisetzung von Kupfer(I). Es wird vermutet, dass dieses „freie Kupfer“ zur DNA-Spaltung beiträgt. Im Gegensatz dazu bilden die Schwelfelanaloga sowohl stabile Kupfer(II)- als auch Kupfer(I)-Komplexe. Sie können elektrochemisch reversibel reduziert werden und weisen im Vergleich mit der Ausgangsverbindung Kupfer(II)cyclen eine verbesserte DNA-Spaltaktivität auf. Die DNA-Affinität des Kupfer(II)cyclen-Komplexes und seine photochemische und oxidative DNA-Spaltaktivität konnte zudem durch die Substitution mit der DNA-Targetingfunktion Anthrachinon erhöht werden. Hierbei konnte durch die Untersuchung von Komplexen mit verschiedenen Linkerlängen zwischen Cyclenkomplex und Anthrachinongruppe gezeigt werden, dass die Substitution mit der Targetinggruppe die DNA-Spaltaktivität erhöht, jedoch keine direkte Korrelation zwischen DNA-Affinität und DNA-Spaltaktivität besteht. So führt die Substitution mit mehreren Anthrachinongruppen zum Beispiel zu einer Erhöhung der DNA-Affinität, jedoch konnte über Rasterkraftmikroskopie gezeigt werden, dass anstatt einer erhöhten DNA-Spaltaktivität die Vernetzung verschiedener DNA-Stränge erreicht wird. Die mit der DNA-Vernetzung einhergehende Veränderung der DNA-Struktur führt zusätzlich dazu, dass einige der mehrfachsubstituierten Anthrachinonkomplexe die DNA-Synthese bereits in nM-Konzentrationen zum Erliegen bringen können. Zytotoxizitätsuntersuchungen konnten die biologische Aktivität dieser Komplexe auch in Krebszellen bestätigen.Cancer is among the two leading causes of death worldwide. While mutations of DNA are causing cancer, wilful modification of the DNA structure and its damage can cause death of cancer cells. In this fashion the DNA alkylating agent cisplatin has been used for the treatment of cancer since 1978. Dose- limiting side effects and the increasing resistance of some cancer types against certain drugs call for the development of novel treatments. Among the candidates of such new drugs are metallonucleases, which generate reactive oxygen species and thus promote the oxidative cleavage of DNA. In the line of the present thesis two approaches for the development of new artificial nucleases starting from copper(II) cyclen have been employed: First the effect of the gradual exchange of the macrocyclic heteroatoms on the nuclease activity of the respective complexes was investigated. Ten different copper(II) complexes with [NAXB] donor sets were synthesized and characterized, resulting in a series of complexes ranging from copper(II) cyclen (A = 4; B = 0) over the all oxygen complex (X = O; A = 0; B = 4) to the all sulphur complex (X = S; A = 0; B = 4). These complexes were subjected to DNA cleavage experiments under reducing conditions. After incubation the samples were analysed by agarose gel electrophoresis. Opposite to the copper(II) cyclen complex the oxygen containing complexes showed an increasing DNA cleavage activity that is dependent on both the geometry and the oxygen content of the respective complex. The assessment of the complexes by electrochemical measurements revealed that the reduction of the copper(II) complexes to the corresponding copper(I) species is electrochemically irreversible and leads to the release of free copper(I) ions. Complexes with higher oxygen content have a lower affinity to the copper(I) species and are more prone to release copper. Assumedly it is the free copper species that is catalytically active and causes the DNA cleavage. In contrast to the complexes of oxygen-containing ligands the sulphur containing complexes show electrochemically reversible reduction and are more efficient nucleases than the copper(II) cyclen complex. Secondly the DNA affinity of the copper(II) cyclen complex along with its photochemical and oxidative cleavage activity was improved by substituting it with the DNA targeting function anthraquinone. While the substitution with this targeting group increases the DNA cleavage activity of the copper(II) cyclen complex substantially, the linker length has only impact on DNA affinity, but not on cleavage activity. While substitution of the cyclen moiety with several targeting groups increases DNA affinity, in place of an increase of DNA cleavage activity these complexes are crosslinking different DNA strands as could be shown by atomic force microscopy. Along with this alteration of the DNA structure the DNA synthesis is inhibited at even nanomolar complex concentrations. Cytotoxicity experiments prove that this activity is retained even in cancer cells

Ability of Azathiacyclen Ligands to Stop Cu(Aβ)‐Induced Production of Reactive Oxygen Species: [3N1S] is the Right Donor Set

International audienceAlzheimer’s disease (AD) is an incurable neurodegenerative disease that leads to the progressive and irreversible loss of mental functions. The amyloid beta (Aβ) peptide involved in the disease is responsible for the production of damaging reactive oxygen species (ROS) when bound to Cu ions. A therapeutic approach, which consists in removing Cu ions from Aβ to alter this deleterious interaction, is currently developed. In this context, we report the ability of 5 different 12-membered thiaazacyclen ligands to capture Cu from Aβ and to redox silence it. We propose that the presence of a sole sulfur atom in the ligand increases the rate of Cu capture and removal from Aβ, while the kinetic aspect of the chelation was an issue encountered with the 4N parent ligand. The best ligand in removing Cu from Aβ and inhibiting the associated ROS production is the 1-thia-4,7,10-triazacyclododecane [3N1S]. Indeed the replacement of more N by S atoms makes the corresponding Cu complexes easier to reduce and thus able to produce ROS on their own. In addition, the ligand with three sulfur atoms has a weaker affinity for Cu(II) than Aβ, and is thus unable to remove Cu from CuAβ

Wolkenschauen 23 Kunstler betrachten den Himmel

Publication and exhibition 23 artists looking up at the sky. contribution to the publication and presentation of two photographs from the series "Scaffolders can't fly" in Kunstverein Passau and Grosse Rathausgalerie der Stadt Landschut & Neue Galerie im Gotischen Stadel auf der Muhleninsel, Austria. Curated by Michael Jan