Design, Synthesis, and DNA Binding Properties of Photoisomerizable Azobenzene−Distamycin Conjugates: An Experimental and Computational Study

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

Azobenzenes are photoswitchable molecules capable of generating significant structural changes upon E-to-Z photoisomerization in peptides or small molecules, thereby controlling geometry and functionality. E-to-Z photoisomerization usually is achieved upon irradiation at 350 nm (π–π* transition), while the Z-to-E isomerization proceeds photochemically upon irradiation at >400 nm (n–π* transition) or thermally. Photoswitchable compounds have frequently been employed as modules, e.g., to control protein–DNA interactions. However, their use in conjunction with minor groove-binding imidazole/pyrrole (Im/Py) polyamides is yet unprecedented. Dervan-type Im/Py polyamides were equipped with an azobenzene unit, i.e., 3-(3-(aminomethyl)phenyl)azophenylacetic acid, as the linker between two Im/Py polyamide strands. Only the (Z)-azobenzene-containing polyamides bound to the minor groove of double-stranded DNA hairpins. Photoisomerization was exemplarily evaluated by ¹H NMR experiments, while minor groove binding of the (Z)-azobenzene derivatives was proven by CD titration experiments. The resulting induced circular dichroism (ICD) bands of the bound ligands, together with the photometric determination of the dsDNA melting temperature, revealed a significant stabilization of the DNA upon association with the ligand. The (Z)-azobenzene acted as a building block inducing a reverse turn, which favored hydrogen bonds between the pyrrole/imidazole amide and the DNA bases. In contrast, the E-configured polyamides did not induce any ICD characteristic for minor groove binding. The incorporation of the photoswitchable azobenzene unit is a promising strategy to obtain photoswitchable Im/Py hairpin polyamides capable of interacting with the dsDNA minor groove only in the Z-configuration.

Modulation of Electronic Mobility of a One-Dimensional Coordination Polymeric Molecular Wire with Light

Metal ions often influence the photoswitching efficiency of a photochromic system. This article reports a one-dimensional polymer having cyclic azobenzenes coordinated to silver ions that are bridged by nitrates. The coordination polymer (CP-2) displays a photoresponsive behavior. The switching ability in the polymer form was faster compared to the parent azobenzene ligand without the metal ions. Azobenzenes are reported to be poorly conducting. Here, although the azobenzene ligand does not show significant electronic mobility, the coordination polymer (CP-2) displays a modest conductivity. The conductance in the cis form of the polymer is significantly higher compared to the trans form. Upon exposure to visible light, the cis form undergoes photoisomerization to the trans form with a drastic drop in the electronic mobility. The trans form can be reverted to the cis form thermally or by using UV light. Thus, this system offers a reversible control of the conductivity using light.

ortho-Fluoroazobenzene derivatives as DNA intercalators for photocontrol of DNA and nucleosome binding by visible light

We report a high-affinity photoswitchable DNA binder, which displays different nucleosome-binding capacities upon visible-light irradiation. Both photochemical and DNA-recognition properties were examined by UV-Vis, HPLC, CD spectroscopy, NMR, FID assays, EMSA and DLS. Our probe sets the basis for developing new optoepigenetic tools for conditional modulation of nucleosomal DNA accessibility.

Reversible photoresponsive activity of a carbonic anhydrase mimic

The carbonic anhydrase (CA) enzyme reversibly transforms carbon dioxide and water to a carbonate ion and a proton. Photoresponsive enzyme mimics, where the CA-activity can be turned on and off reversibly with light, have not been reported so far. We have designed an active site mimic that offers reversible control of the catalytic activity using light. Moreover, in the presence of a cationic polymer, we have demonstrated that the CA-activity was further enhanced by stabilizing the transition state with the cis-form of the enzyme mimic which can catalyze the hydration of gaseous CO2.

Enhanced Release of Molecules upon Ultraviolet (UV) Light Irradiation from Photoresponsive Hydrogels Prepared from Bifunctional Azobenzene and Four-Arm Poly(ethylene glycol)

Advances in biosensors and drug delivery are dependent on hydrogels that respond to external stimuli. In this work, we describe the preparation and characterization of photoresponsive hydrogels prepared by cross-linking of di-NHS ester of azobenzoic acid and four-armed, amine-terminated poly(ethylene glycol). The porous structure and composition of the hydrogels were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The reversible photoisomerization of the azobenzene-containing hydrogel cross-linkers in the gels was confirmed by absorption spectroscopy. Specifically, the photoisomerization of the cross-linkers between their trans and cis configurations was observed by monitoring the absorbance of the hydrogels at the two characteristic peaks of azobenzene (π-π* at 330 nm and n-π* at 435 nm). The effect of photoisomerization on the hydrogel structure was investigated by microscopy. Ultraviolet (UV) irradiation-induced reduction in hydrogel size was observed, which may be a result of the inherently smaller footprint of the cis azobenzene conformation, as well as dipole-dipole interactions between the polar cis azobenzene and the polymer network. The UV-triggered reduction in hydrogel size was accompanied by enhanced release of the near-infrared fluorescent dye Alexa Fluor 750 (AF₇₅₀). Enhanced release of AF₇₅₀ was observed in samples irradiated with UV versus dark control. Together, these data demonstrate the potential of these systems as reversible photoresponsive biomaterials.

New Fe(iii) and Co(ii) salen complexes with pendant distamycins: selective targeting of cancer cells by DNA damage and mitochondrial pathways

Minor groove binding distamycin like moieties were conjugated with core salens and the corresponding Fe(iii) and Co(ii) complexes were synthesized. Herein, we have shown efficient DNA minor groove binding specificities along with excellent DNA cleavage capacities with metallosalen conjugates. The metal complexes showed toxicity toward various cancer cells over normal cells with high specificity. Interestingly, the Co(ii) complexes exhibited greater activity than the Fe(iii) complexes in accordance with the stronger affinity of the former in the biophysical studies. Active DNA damage, and prominent nuclear condensation along with the release of cytochrome-c from the mitochondria unanimously showed that the metal complexes followed apoptotic pathways to induce cell death.

Strain, switching and fluorescence behavior of a nine-membered cyclic azobenzene

This work defines the smallest ring size for obtaining the trans form of cyclic azobenzene as the thermally stable form.

Selective photoregulation of the activity of glycogen synthase and glycogen phosphorylase, two key enzymes in glycogen metabolism

Glycogen is a polymer of α-1,4- and α-1,6-linked glucose units that provides a readily available source of energy in living organisms. Glycogen synthase (GS) and glycogen phosphorylase (GP) are the two enzymes that control, respectively, the synthesis and degradation of this polysaccharide and constitute adequate pharmacological targets to modulate cellular glycogen levels, by means of inhibition of their catalytic activity. Here we report on the synthesis and biological evaluation of a selective inhibitor that consists of an azobenzene moiety glycosidically linked to the anomeric carbon of a glucose molecule. In the ground state, the more stable (E)-isomer of the azobenzene glucoside had a slight inhibitory effect on rat muscle GP (RMGP, IC50 = 4.9 mM) and Escherichia coli GS (EcGS, IC50 = 1.6 mM). After irradiation and subsequent conversion to the (Z)-form, the inhibitory potency of the azobenzene glucoside did not significantly change for RMGP (IC50 = 2.4 mM), while its effect on EcGS increased 50-fold (IC50 = 32 μM). Sucrose synthase 4 from potatoes, a glycosyltransferase that does not operate on glycogen, was only slightly inhibited by the (E)-isomer (IC50 = 0.73 mM). These findings could be rationalized on the basis of kinetic and computer-aided docking analysis, which indicated that both isomers of the azobenzene glucoside mimic the EcGS acceptor substrate and exert their inhibitory effect by binding to the glycogen subsite in the active center of the enzyme. The ability to selectively photoregulate the catalytic activity of key enzymes of glycogen metabolism may represent a new approach for the treatment of glycogen metabolism disorders.

Advances in the molecular design of potential anticancer agents via targeting of human telomeric DNA

Telomerase is an attractive drug target to develop new generation drugs against cancer.

Unusual viscoelasticity behaviour in aqueous solutions containing a photoresponsive amphiphile

Here, we report unusual behaviour of the viscoelasticity of surfactant aqueous solutions consisting of cationic cetyltrimethylammonium bromide (CTAB) and an anionic photoresponsive amphiphile, sodium [4-(4-butylphenylazo)phenoxy]acetate (C4AzoNa). When C4AzoNa molecules are trans-isomers, spheroidal micelles are formed in the surfactant solution, the viscosity of which is low. Irradiation of this solution by ultraviolet (UV) light yields an aqueous solution of CTAB/cis-C4AzoNa (cis-isomers of C4AzoNa), which is a highly viscous gel consisting of wormlike micelles. The drastic change in the surfactant solution viscosity is attributed to the formation and disruption of wormlike micelles. The geometrical structural transformation of the azobenzene groups in the C4AzoNa molecules of the CTAB/C4AzoNa mixture would lead to a change in the critical packing parameter of the mixture, thereby inducing the morphological transformation of the aggregates (spheroidal micelles to wormlike micelles). To our knowledge, this is the first report of a drastic increase in surfactant solution viscosity by UV light irradiation.

Light-driven conformational regulation of human telomeric G-quadruplex DNA in physiological conditions

Human telomeric G-quadruplexes have raised broad interest not just due to their involvement in the regulation of gene expressions and telomerase activities but also because of their application in nanoarchitectures. Herein, three azobenzene derivatives 1-3 were synthesized with different substituent groups and their photo-isomerization properties were investigated by UV/Vis spectroscopy. Then circular dichroism spectroscopy (CD), fluorescence experiments and native-gel electrophoresis were performed to evaluate their capabilities of conformational photo-regulation both in the absence and presence of metal ions. The results suggested that the compounds synthesized can successfully regulate the conformation of human telomeric G-quadruplex DNA in K(+) conditions to some extent. This work will initiate the possibility for the design and intriguing application of light-induced switching to photoregulate the conformation of G-quadruplex DNA under physiological conditions, providing a possible pathway to control G-quadruplex conformation in biological applications and also expanding the potential use of G-quadruplexes in nanomachines.

New solid phase synthesis of distamycin analogues

A novel and straightforward solid phase synthesis of distamycin analogues containing benzene units has been developed.

Electrospray ionization tandem mass spectrometric characteristics of d4T H-phosphonate and distamycin conjugates

The study of the dissociation of the protonated molecular species [M+H](+) and selected fragment ions allowed proposals for the main fragmentation pathways of the title compounds. The main fragments are formed by expelling a molecule of thymine, thymidine (d4T) or isopropyl. The most striking feature of the tandem mass (MS/MS) spectra is the cleavage of C-CO bonds between N-methylpyrrole and carbonyl groups in the presence of the amidine. Electrospray ionization is proven to be a good method for the structural characterization and identification of these kinds of compounds.