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Photosensitizers are catalysts, which can generate singlet oxygen upon their irradiation with light. This reaction has been shown to be suitable for the amplified detection of biomolecules, e.g. nucleic acids. In known nucleic acid-responsive photosensitizers organic quenchers are usually applied. Herein we explored a Cu 2+ -complex of a 5-pyridin-2-yl-1H-pyrazolyl ligand as a quencher of representative photosensitizers of this type. We demonstrated that this complex can efficiently quench fluorescence of the photosensitizers and inhibit the photocatalytic generation of singlet oxygen. The mechanism of quenching was found to be dependent on the nature of the photosensitizer. For example, eosin was found to be quenched by the contact mechanism, whereas In 3+ (pyropheophorbide-a)chloride – by the dynamic mechanism. We concluded that Cu 2+ -based complexes can be considered as cheap and easy to tune alternatives to usually applied organic quenchers. [ABSTRACT FROM AUTHOR]

Hybrid drugs containing ferrocene and phenol residues, whose π systems are not conjugated with each other, exhibit potent anticancer activity as previously reported. Few important open questions are remaining before practical application of these drugs becomes possible. First, their mode of action is not fully clarified. Second, it is not known whether these drugs exhibit cancer cell specificity. Third, due to the presence of the phenol moiety, these drugs can potentially be oxidatively deactivated and eliminated via phase II metabolism when applied in vivo. In this paper we report on synthesis of three prodrugs of aminoferrocene-phenol hybrids, where the phenolic OH group is masked as a boronic acid pinacol ester. We confirmed that the best prodrug in this small series p5 is activated in human ovarian cancer A2780 and Burkitt's lypmphoma BL-2 cells, but remains inactive in representative normal SBLF9 cells. Since p5 does not contain free phenolic OH groups, it will not be metabolized as phenols in vivo. We confirmed that the mechanism of anticancer activity of aminoferrocene-phenol prodrug p5 relies on generation of reactive oxygen species in cells. Prodrugs of ferrocene-phenol hybrid drugs, where π-systems of ferrocene and phenol moieties are not conjugated, were prepared. These prodrugs are activated in cancer cells in the presence of reactive oxygen species inducing oxidative stress, but remain inactive in normal cells. [Display omitted] • We prepared aminoferrocene-phenol (AFP) prodrugs responsive to reactive oxygen species (ROS). • In the presence of ROS the prodrugs generate stable AFP drugs. • AFP prodrugs generate ROS in cancer cells, but not in normal cells. • AFP prodrugs induce cancer cell death via apoptosis and necrosis. • The mechanism of action of AFP prodrugs relies on generation of intracellular ROS. [ABSTRACT FROM AUTHOR]

Known molecular, 'caged' siRNAs are activated by UV light. Since the light of this type is toxic to cells, the uncaging can cause undesired side effects. A modular, molecular system for designing siRNAs is reported, which can be activated by non-toxic light in live cells. For example, siRNAs responsive to green and red light are described. The uncaging is mediated by 1O2 photogenerated on a photosensitizer, which is attached to the 3′-terminus of the lagging strand. The 5′-terminus of the guide strand is alkylated ('caged') with a 9-anthracenyl residue. The latter fragment reacts with the 1O2 with formation of the free (uncaged) 5′-OH terminus. Simultaneously with the uncaging the photosensitizer is bleached and no more 1O2 is generated after this process is completed. The photoactivation of the siRNAs described here is not toxic to cells. [ABSTRACT FROM AUTHOR]

Known molecular, 'caged' siRNAs are activated by UV light. Since the light of this type is toxic to cells, the uncaging can cause undesired side effects. A modular, molecular system for designing siRNAs is reported, which can be activated by non-toxic light in live cells. For example, siRNAs responsive to green and red light are described. The uncaging is mediated by 1O2 photogenerated on a photosensitizer, which is attached to the 3′-terminus of the lagging strand. The 5′-terminus of the guide strand is alkylated ('caged') with a 9-anthracenyl residue. The latter fragment reacts with the 1O2 with formation of the free (uncaged) 5′-OH terminus. Simultaneously with the uncaging the photosensitizer is bleached and no more 1O2 is generated after this process is completed. The photoactivation of the siRNAs described here is not toxic to cells. [ABSTRACT FROM AUTHOR]

Abstract: Common ‘caged’ nucleic acid binders, which can be applied for temporal and spatial control of gene expression, are activated by high energy light (<450nm). The light of this type is damaging to cells and is strongly absorbed by cellular components. Therefore, shifting the triggering light to the visible region (>550nm) is highly desirable. Herein we report on a cyclic peptide nucleic acid (PNA), whose backbone contains a 9,10-dialkoxy-substituted anthracene linker. The sequence of this compound was selected to be complementary to a representative microRNA (miR-92). We demonstrated that the cyclic PNA does not bind complementary nucleic acids and is, correspondingly, ‘caged’. Its uncaging can be conducted by its exposure to red light (635nm) in the presence of pyropheophorbide-a. The latter process is mediated by singlet oxygen (1O2), which cleaves the 9,10-dialcoxyanthracene linker within the PNA with formation of a linear PNA, an efficient binder of the complementary ribonucleic acid. This is the first example of a red light-activated, ‘caged’ peptide nucleic acid. [Copyright &y& Elsevier]

RNA interference (RNAi) using small interfering RNAs (siRNAs) is a powerful tool to target any protein of interest and is becoming more suitable for in vivo applications due to recent developments in RNA delivery systems. To exploit RNAi for cancer treatment, it is desirable to increase its selectivity, e.g., by a prodrug approach to activate the siRNAs upon external triggering, e.g., by using light. Red light is especially well suited for in vivo applications due to its low toxicity and higher tissue penetration. Known molecular (not nanoparticle-based) red-light-activatable siRNA prodrugs rely on singlet oxygen (1O2)-mediated chemistry. 1O2 is highly cytotoxic. Additionally, one of the side products in the activation of the known siRNA prodrugs is anthraquinone, which is also toxic. We herein report on an improved redlight-activatable siRNA prodrug, which does not require 1O2 for its activation. In fact, the 5′ terminus of the antisense strand is protected with an electron-rich azobenzene promoiety. It is reduced and cleaved upon red light exposure in the presence of Sn(IV)(pyropheophorbide a)dichloride acting as a catalyst and ascorbate as a bulk reducing agent. We confirmed the prodrug activation upon red light irradiation both in cell-free settings and in human ovarian cancer A2780 cells. [ABSTRACT FROM AUTHOR]

A concept of fluorescent metal ion sensing with an easily tunable emission wavelength is presented and its principle demonstrated by detection of Cu2+. A fluorescein dye was chemically modified with a metal chelating group and then attached to the terminus of ss-DNA. This was combined with a complementary ss-DNA modified with another fluorescent dye (ATTO 590), emitting at a longer wavelength. In the assembled duplex, fluorescence resonance energy transfer (FRET) between the fluorescein donor (excited at 470 nm) and the ATTO 590 acceptor (emitting at 624 nm) is observed. Proper positioning within the rigid DNA double helix prevents intramolecular contact quenching of the two dyes. Coordination of paramagnetic Cu2+ ions by the chelating unit of the sensor results in direct fluorescence quenching of the fluorescein dye and indirect (by loss of FRET) quenching of the ATTO 590 emission at 624 nm. As a result, emission of the acceptor dye can be used for monitoring of the concentration of Cu2+, with a 20 nM detection limit. The emission wavelength is readily tuned by replacement of ATTO-DNA by other commercially available DNA-acceptor dye conjugates. Fluorescent metal ion sensors emitting at >600 nm are very rare. The possibility of tuning the emission wavelength is important with respect to the optimization of this sensor type for application to biological samples, which usually show broad autofluorescence at <550 nm. [ABSTRACT FROM AUTHOR]

Peptide nucleic acids (PNAs) C- or N-modified with dioxime ligands were prepared by solid-phase synthesis using iron(II)-clathrochelates as protected dioxime building blocks. These PNA bind complementary DNA sequence specifically, though with much reduced affinity in comparison with nonmodified PNA. The dioxime–PNA conjugates bind Cu2+ and Ni2+ at μM concentration. [Copyright &y& Elsevier]

PNAs with terminal modifications of varying structure and charge were synthesized and their binding to DNA was studied. A variation in thermal stability of 19. 8 °C has been observed between the least and the most stable PNA–DNA duplexes. The most stable duplex melts 7.7 °C higher than the duplex of the corresponding non-modified PNA and complementary DNA. It has been shown that sequence fidelity of the PNA conjugate having the highest DNA affinity is significantly better than that of non-modified PNA. The results obtained can be used for the design of PNA probes, whose binding to DNA is sequence independent. [Copyright &y& Elsevier]

Complex formation properties of a novel water soluble thiazolyloxime 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid (H3L1) with Cu2+ and Ni2+ were investigated in solution by potentiometrical and spectral (UV–Vis, EPR, NMR) methods. All Cu2+ and most of Ni2+ complex species detected in solution were found to have square-planar MN4 core with oxime and heterocyclic nitrogen atoms which was rationalized in terms of destabilizing effect of repulsive interaction between oxygen atom of carboxylic group and nitrogen atom of thiazole ring in N,O-coordinated ligand conformation. It has been found that stability of metal complexes in a series of oxime ligands is dependent upon basicity of nitrogen atom of oxime group. The thiazolyloxime forms less stable complexes with Cu2+ but stronger ones with Ni2+ ions when compared to parent 2-(hydroxyimino)propanoic acid. The lower stability obtained for Cu2+ complexes was elucidated in terms of negative inductive effect of the thiazole and nitrile substituents as well as an effect of intramolecular attractive interaction between thiazolyl sulfur and oxime oxygen atoms in thiazolyloxime. In the case of Ni2+ the complexes formed are square-planar and it is why thiazolyl ligand is more effective in metal ion binding than simple 2-(hydroxyimino)propanoic acid forming only octahedral species. The solid state structure of the Co3+ complex K3[Co(HL1)3]·5.5H2O (1) was studied by X-ray analysis. The thiazolyloxime ligand is coordinated to Co3+ via oxime nitrogen and carboxylate oxygen atoms forming five-membered chelate rings. [Copyright &y& Elsevier]

The number and stability of lysosomes (LYs) are different in cancer and healthy cells that makes them a possible target for cancer specific therapy. However, no LY‐targeting drug is clinically approved yet. We describe in this paper a new therapeutic approach based on alkylation of lysosomal thiols in cancer cells by reversible thiol binder 11. The treatment with 11 increases the level of lysosomal reactive oxygen species leading to their destabilization, disruption and immunogenic cancer cell death. These effects are not observed in healthy cells. In murine sarcoma Nemeth‐Kellner (NK)/Ly‐RB model, 11 exhibits the spectacular therapeutic effect: it extends the lifespan of the treated mice from 21 to 85 days and cures 40 % of mice. The survived mice develop antibodies against tumor NK/Ly‐RB cells. Their repeated challenge with the NK/Ly‐RB cells results in 100 % mice survival compared to 0 % survival in the control group of naïve mice. Ex vivo data indicate that neutrophils in spleen of the cured animals are also involved in targeting cancer cells and produce neutrophil extracellular traps. In summary, 11 induces the direct antitumor effect supported by humoral immune responses, as well as priming neutrophil's reaction against tumors. [ABSTRACT FROM AUTHOR]

The autocatalytic photochemical reaction, which is potentially controlled by any selected nucleic acid, is highly sequence specific and not inhibited by its products, was developed. This reaction generates colored and fluorescent products, which can be monitored by the naked eye. [ABSTRACT FROM AUTHOR]

A fluorogenic, nucleic acid directed, Cu+-catalyzed chemical reaction was developed that allows sequence-specific detection of nucleic acids at concentrations as low as 20 nM through monitoring of the increase of the fluorescence intensity. A single nucleotide mismatch in the template strand leads to the complete inhibition of this reaction. We observed that a Cu+ ion stabilized with a water-soluble ligand is a significantly more efficient catalyst than free Cu+. [ABSTRACT FROM AUTHOR]

Abstract: Two Cu2+-binding ligands were covalently attached to termini of short DNAs. The optimal compound of this type forms a catalytically inert complex with Cu2+. In the presence of a complementary nucleic acid the complex is decomposed forming products, which may catalyze hydrolysis of carboxylic acid esters. We have demonstrated that this process can be applied for sequence specific detection of nucleic acids. [Copyright &y& Elsevier]

Hydrolysis of activated esters, e.g., picolinic acid and a-amino acid esters, in the presence of Cu2+ salts is a stoichiometric process because products of this reaction bind the catalytic metal ion substantially stronger than starting materials do. Herein we report improved ester substrates, which are cleaved in the presence of catalytic amounts of Cu2+; 55 turnovers of hydrolysis are observed for the best substrate, acetic acid 2-hydroxypyridine ester. We demonstrate that this reaction can be used for sensitive and selective detection of Cu2+ by using both absorption and fluorescence spectroscopy. [ABSTRACT FROM AUTHOR]

• We synthesized a new protected nucleoamino acid based on diaminobutanoic acid (DABA). • Peptide-like solid phase synthesis led to a novel hexathymine DABA-nucleopeptide 3. • 3 bound DNA/RNA in a sequence specific manner altering more or less their structure. • 3 drastically altered the polyrA secondary structure forming a quite stable complex. • 3 bound G-quadruplex DNAs showing a parallel vs antiparallel topology selectivity. Herein we present the synthesis of a l -diaminobutanoic acid (DABA)-based nucleopeptide (3), with an oligocationic backbone, realized by solid phase peptide synthesis using thymine-bearing DABA moieties alternating in the sequence with free ones. CD studies evidenced the ability of this oligothymine nucleopeptide, well soluble in aqueous solution, to alter the secondary structure particularly of complementary RNA (poly rA vs poly rU) and inosine-rich RNAs, like poly rI and poly rIC, and showed its preference in binding double vs single-stranded DNAs. Furthermore, ESI mass spectrometry revealed that 3 bound also G-quadruplex (G4) DNAs, with either parallel or antiparallel topologies (adopted in our experimental conditions by c-myc and tel 22 , respectively). However, it caused detectable changes only in the CD of c-myc (whose parallel G4 structure was also thermally stabilized by ~3 °C), while leaving unaltered the antiparallel structure of tel 22. Interestingly, CD and UV analyses suggested that 3 induced a hybrid mixed parallel/antiparallel G4 DNA structure in a random-coil tel 22 DNA obtained under salt-free buffer conditions. Titration of the random-coil telomeric DNA with 3 gave quantitative information on the stoichiometry of the obtained complex. Overall, the findings of this work suggest that DABA-based nucleopeptides are synthetic nucleic acid analogues potentially useful in antigene and antisense strategies. Nevertheless, the hexathymine DABA-nucleopeptide shows an interesting behaviour as molecular tool per se thanks to its efficacy in provoking G4 induction in random coil G-rich DNA, as well as for the possibility to bind and stabilize c-myc oncogene in a G4 structure. [ABSTRACT FROM AUTHOR]

Reports on the preparation of a series of conjugates of peptide nucleic acids (PNA) and Zr(IV) complexes. Ability of the complexes to hydrolyze DNA; Use of MLDI-TOF mass spectrometry and HPLC; Identification of the most efficient artificial restriction enzyme.

Conjugates of peptide nucleic acids (PNA) and metal binding ligands were prepared using solid-phase synthesis. Stability of duplexes of bis-picolylamine–PNA conjugates and DNA was found to be modulated by equimolar concentrations of bioavailable metal ions: Ni2+, Zn2+>Cu2+. Sequence specificity of PNA was not compromised in the presence of these metal ions. [Copyright &y& Elsevier]

Red fluorescent dyes are usually charged, lipophilic molecules with relatively high molecular weight, which tend to localize in specific intracellular locations, e. g., a cyanine dye Cy5 is biased towards mitochondria. They are often used as markers of biomolecules including nucleic acids and proteins. Since the molecular weight of the dyes is much smaller than that of the biomolecules, the labelling has a negligible effect on the properties of the biomolecules. In contrast, conjugation of the dyes to low molecular weight (pro)drugs can dramatically alter their properties. For example, conjugates of Cy5 with lysosome‐targeting aminoferrocenes accumulate in mitochondria and exhibit no intracellular effects characteristic for the parent (pro)drugs. Herein we tested several neutral and negatively charged dyes for labelling lysosome‐targeting aminoferrocenes 7 and 8 as well as a non‐targeted control 3. We found that a BODIPY derivative BDP‐TR exhibits the desired unbiased properties: the conjugation does not disturb the intracellular localization of the (pro)drugs, their mode of action, and cancer cell specificity. We used the conjugates to clarify the mechanism of action of the aminoferrocenes. In particular, we identified new intermediates, explained why lysosome‐targeting aminoferrocenes are more potent than their non‐targeted counterparts, and evaluated their distribution in vivo. [ABSTRACT FROM AUTHOR]

Pro-drugs, which ideally release their active compound only at the site of action, i.e., in a cancer cell, are a promising approach towards an increased specificity and hence reduced side effects in chemotherapy. A popular form of pro-drugs is esters, which are activated upon their hydrolysis. Since carboxylesterases that catalyse such a hydrolysis reaction are also abundant in normal tissue, it is of great interest whether a putative pro-drug is a probable substrate of such an enzyme and hence bears the danger of being activated not just in the target environment, i.e., in cancer cells. In this work, we study the binding mode of carboxylesters of the drug molecule camptothecin, which is an inhibitor of topoisomerase I, of varying size to human carboxylesterase 2 (HCE2) by molecular docking and molecular dynamics simulations. A comparison to irinotecan, known to be a substrate of HCE2, shows that all three pro-drugs analysed in this work can bind to the HCE2 protein, but not in a pose that is well suited for subsequent hydrolysis. Our data suggest, moreover, that for the irinotecan substrate, a reactant-competent pose is stabilised once the initial proton transfer from the putative nucleophile Ser202 to the His431 of the catalytic triad has already occurred. Our simulation work also shows that it is important to go beyond the static models obtained from molecular docking and include the flexibility of enzyme–ligand complexes in solvents and at a finite temperature. Under such conditions, the pro-drugs studied in this work are unlikely to be hydrolysed by the HCE2 enzyme, indicating a low risk of undesired drug release in normal tissue. [ABSTRACT FROM AUTHOR]

Peptide nucleic acid (PNA) is a mimic of DNA which has excellent binding affinity and sequence specificity toward oligonucleotides. Researchers have synthesized PNA in which a Zn2+ chelating ligand is conjugated via an aromatic linker. Intercalation of the aromatic linker is regulated by the metal coordination to the ligand. It has been recently shown that unsymmetrically modified naphthalene diimide intercalates within PNA:DNA duplex and strongly stabilizes it. Therefore, this aromatic fragment was chosen as a linker between PNA and the ligand. As ligands, strong Zn2+ binders were selected: bis(picolyl)amine and 1,4,8,11-tetraazacyclotetradecane.

Presents information on metal catalysis in which a DNA-templated cleavage reaction in which a metal complex is attached to an oligonucleotide analogue is the catalytic component. Catalytic cycle proposed in which metal complex and substrate are attached to short sequences of peptide nucleic acids (PNA); Advantages of using PNA over DNA; Kinetic experiments to support the reduction of high background rate by variation of N-terminal PNA modifications.

Despite their long history and their synthetic potential underlined by various recent advances, radical thiol‐yne coupling reactions have so far only rarely been exploited for the functionalization of biomolecules, and no examples yet exist for their application in live cells ‐ although natural thiols show widespread occurrence therein. By taking advantage of the particular cellular conditions of mitochondria in cancer cells, we have demonstrated that radical thiol‐yne coupling represents a powerful reaction principle for the selective targeting of these organelles. Within our studies, fluorescently labeled reactive alkyne probes were investigated, for which the fluorescent moiety was chosen to enable both mitochondria accumulation as well as highly sensitive detection. After preliminary studies under cell‐free conditions, the most promising alkyne‐dye conjugates were evaluated in various cellular experiments comprising analysis by flow cytometry and microscopy. All in all, these results pave the way for improved future therapeutic strategies relying on live‐cell compatibility and selectivity among cellular compartments. [ABSTRACT FROM AUTHOR]

Because cellular uptake of anticancer PtII and PtIV drugs occurs by different mechanisms, the latter ones can exhibit substantial activity towards cells, which have either intrinsic or acquired resistance towards PtII drugs. However, this positive effect is diminished due to reductive activation of PtIV drugs in extracellular space that can be one of the reasons why they have not yet been approved for clinical use despite over 60 clinical trials conducted worldwide. Herein, we suggest a solution to this problem by achieving highly specific intracellular versus extracellular prodrug reduction. In particular, we prepared a hybrid PtIV prodrug containing two pro-reductants. This hybrid was uptaken by cells, the pro-reductants were activated in the cancer-specific microenvironment (high H2O2), and reduced PtIV by two one-electron transfers. The drug formed in this way induced cell death both in cisplatin-sensitive and resistant cell lines, but remained nontoxic to normal cells. [ABSTRACT FROM AUTHOR]

Nanoformulations for delivering nucleotides into cells as vaccinations as well as treatment of various diseases have recently gained great attention. Applying such formulations for a local treatment strategy, e.g., for cancer therapy, is still a challenge, for which improved delivery concepts are needed. Hence, this work focuses on the synthesis of superparamagnetic iron oxide nanoparticles (SPIONs) for a prospective "magnetofection" application. By functionalizing SPIONs with an active catechol ester (CafPFP), polyethyleneimine (PEI) was covalently bound to their surface while preserving the desired nanosized particle properties with a hydrodynamic size of 86 nm. When complexed with plasmid-DNA (pDNA) up to a weight ratio of 2.5% pDNA/Fe, no significant changes in particle properties were observed, while 95% of the added pDNA was strongly bound to the SPION surface. The transfection in A375-M cells for 48 h with low amounts (10 ng) of pDNA, which carried a green fluorescent protein (GFP) sequence, resulted in a transfection efficiency of 3.5%. This value was found to be almost 3× higher compared to Lipofectamine (1.2%) for such low pDNA amounts. The pDNA-SPION system did not show cytotoxic effects on cells for the tested particle concentrations and incubation times. Through the possibility of additional covalent functionalization of the SPION surface as well as the PEI layer, Caf-PEI-SPIONs might be a promising candidate as a magnetofection agent in future. [ABSTRACT FROM AUTHOR]

We developed a simple protocol for high-yielding synthesis of conjugates of a deuterated dihydro- N, N, N′, N′-tetramethylrhodamine (F*) with oligodeoxyribonucleotides and a 2′-OMe RNA (a representative nuclease-resistant, chemically modified oligonucleotide) using easily accessible starting materials including NaBD and conjugates of oligonucleotides with N, N, N′, N′-tetramethylrhodamine (F). These compounds were found to be stable in air and insensitive to light at 525, 635 and 650 nm, whereas slow activation occurs upon their exposure to 470 nm light. However, at the conditions of the templated reaction, in the presence of a target nucleic acid and a photocatalyst based on the eosin structure, the F* is oxidized forming fluorescent F. This reaction is >30-fold faster than the background reaction in the absence of the template. Moreover, the presence of a single mismatch in the target nucleic acid slows down the templated reaction by eightfold. These activatable dyes can potentially find applications as nucleic acid-specific probes for super-resolution imaging in live cells. [ABSTRACT FROM AUTHOR]

• Low stability of aminoferrocenes limits the anticancer activity of their prodrugs. • 4-Ferrocenylaniline is more chemically stable than aminoferrocene. • 4-Ferrocenylaniline is an efficient catalyst of generation of ROS. • 4-Ferrocenylaniline prodrugs exhibit excellent anticancer activity. Ferrocene derivatives often exhibit anticancer activity. For example, our group has developed aminoferrocene-based (AF) prodrugs, which are activated in the presence of reactive oxygen species (ROS), present in large quantities in cancer cells. The activation reaction leads to formation of AF's, whose redox potential is shifted by 300–400 mV to negative values as compared to the parent AF prodrugs. Correspondingly, these drugs are very electron rich and can, therefore, act as catalysts of generation of highly toxic hydroxyl radicals (HO●) from H 2 O 2. That contributes to the cytotoxicity of AF prodrugs. Unfortunately, AF's are chemically very unstable. Therefore, their lifetime in cells is < 1 h that limits the anticancer activity of the AF prodrugs. In this paper we report on new 4-ferrocenylaniline-based (4-FcAn) prodrugs. These are activated in the presence of ROS thereby releasing 4-FcAn. We confirmed that 4-FcAn is more electron rich than the corresponding prodrug (ΔE 1/2 = 86 mV) and can generate HO● from H 2 O 2 analogously to AF. Furthermore, we observed that (a) 4-ferrocenylanilines are substantially more stable (>6 h) than AF's and (b) the corresponding prodrugs are substantially more active than the structurally related AF prodrugs. We found that, analogously to AF prodrugs, the new prodrugs exhibit their anticancer activity via generation of ROS in cancer cells. [Display omitted] [ABSTRACT FROM AUTHOR]

Elevated levels of reactive oxygen species (ROS) and deficient mitochondria are two weak points of cancer cells. Their simultaneous targeting is a valid therapeutic strategy to design highly potent anticancer drugs. The remaining challenge is to limit the drug effects to cancer cells without affecting normal ones. We have previously developed three aminoferrocene (AF)‐based derivatives, which are activated in the presence of elevated levels of ROS present in cancer cells with formation of electron‐rich compounds able to generate ROS and reduce mitochondrial membrane potential (MMP). All of them exhibit important drawbacks including either low efficacy or high unspecific toxicity that prevents their application in vivo up to date. Herein we describe unusual AF‐derivatives lacking these drawbacks. These compounds act via an alternative mechanism: they are chemically stable in the presence of ROS, generate mitochondrial ROS in cancer cells, but not normal cells and exhibit anticancer effect in vivo. [ABSTRACT FROM AUTHOR]

Due to oxidative instability, arylboronic acids are not compatible with the solid-phase synthesis of nucleic acids. We solved this problem and, based on these findings, developed siRNA prodrugs activated in the presence of reactive oxygen species (ROS) in vivo. These prodrugs can be used for specific targeting of ROS-rich cancer cells. [ABSTRACT FROM AUTHOR]

Photocatalytic activity of a photosensitizer (PS) in an oligodeoxyribonucleotide duplex 5′-PS∼ODN1/ODN2∼Q-3′ is inhibited because of close proximity of a quencher Q. The ODN2 in this duplex is selected to be longer than the ODN1. Therefore, in the presence of a nucleic acid (analyte), which is fully complementary to the ODN2 strand, the duplex is decomposed with formation of an analyte/ODN2 Q duplex and a catalytically active, single stranded PS ODN1. In this way the catalytic activity of the PS can be controlled by the specific nucleic acids. We applied this reaction earlier for the amplified detection of ribonucleic acids in live cells (Arian, D.; Cló, E.; Gothelf, K.; Mokhir, A. Chem.-Eur. J.2010, 16(1), 288). As a photosensitizer (PS) we used In3+(pyropheophorbide-a)chloride and as a quencher (Q) - Black-Hole-Quencher-3 (BHQ-3). The In3+ complex is a highly active photocatalyst in aqueous solution. However, it can coordinate additional ligands containing thiols (e.g., proteins, peptides, and aminoacids), that modulate properties of the complex itself and of the corresponding bio- molecules. These possible interactions can lead to undesired side effects of nucleic acid controlled photocatalysts (PS∼ODN1/ODN2∼Q) in live cells. In this work we explored the possibility to substitute the In3+ complex for those ones of divalent metal ions, Zn2+ and Pd2+, which exhibit lower or no tendency to coordinate the fifth ligand. We found that one of the compounds tested (Pd(pyropheophorbide-a) is as potent and as stable photosensitizer as its In3+ analogue, but does not coordinate additional ligands that makes it more suitable for cellular applications. When the Pd complex was introduced in the duplex PS∼ODN1/ODN2∼Q as a PS, its photocatalytic activity could be controlled by nucleic acids as efficiently as that of the corresponding In3+ complex. [ABSTRACT FROM AUTHOR]

We developed a 1O2-sensitive linker based on a 9,10-dialkoxyanthracene structure. Its cleavage in the presence of 1O2 is quick and high-yielding. A phosphoramidite containing this fragment was prepared and coupled to a variety of molecular fragments, including nucleosides, fluorescent dyes, and a cholesteryl derivative. On the basis of this building block we prepared a fluorogenic probe for monitoring 1O2 in live mammalian cells and visible-light-activated "caged" oligodeoxyribonucleotides. In particular, the fluorogenic 1O2 probe is a conjugate of 4,7,4′,7′-tetrachlorofluorescein and N,N,N′,N′-tetramethylrhodamine coupled to each other via the 1O2-sensitive linker. Fluorescence of the dyes in this probe is quenched. In the presence of 1O2, the linker is cleaved with formation of 9,10-anthraquinone and two strongly fluorescent dyes: 4,7,4′,7′-tetrachlorofluorescein and N,N,N′,N′-tetramethylrhodamine derivatives. We observed that the fluorescence of the probe correlates with the amount of 1O2 present in solution. The red-light-activated "caged" oligodeoxyribonucleotides are stable duplexes, which consist of an unmodified strand and a blocker strand. The 1O2-sensitive linker is introduced in the interior of the blocker strand. Upon exposure of the duplex to red light in the presence of In3+(pyropheophorbide-a) chloride, the linker is cleaved with formation of the unstable duplex structure. This product decomposes spontaneously, releasing the unmodified strand, which can bind to the complementary target nucleic acid. This uncaging reaction is high-yielding. In contrast, previously reported visible-light-activated reagents are uncaged inefficiently due to competing reactions of sulfoxide and disulfide formation. [ABSTRACT FROM AUTHOR]

We have prepared cyclic peptide nucleic acids (PNA5). These compounds do not bind complementary nucleic acids. One carboxylic ester group was introduced in the backbone of the cyclic PNAs. This group is cleaved in the presence of Cu2+ or coordinatively unsaturated Cu2+ complexes. The cleavage products are linear PNAs. In contrast to the cyclic PNAs, they are efficient nucleic acid binders. The rate of formation of the linear PNAs is proportional to the concentration of the cleaving agents. Therefore, one may apply highly sensitive methods of detection of linear PNAs for determination of Cu2+ concentration. In particular, we have demonstrated that both fluorescent spectroscopy in combination with molecular beacons and MALDI-TOF mass spectrometry are suitable for the detection of Cu2+. A range of related divalent metal ions and Eu3+, Ln3+, Ce3+, and Zr4+ do not interfere with Cu2+ detection. [ABSTRACT FROM AUTHOR]

N‐alkylaminoferrocene‐based (NAAF) prodrugs are activated in the presence of reactive oxygen species (ROS), based on which these prodrugs target cancer cells (high ROS) and do not affect normal cells (low ROS). To gain some insights into their mode of action in vivo, we have investigated the biodistribution of 18F‐labelled NAAF prodrugs in tumor‐bearing mice by positron emission tomography (PET). Due to the short half‐life of 18F, the experimental time frame was restricted to 60 min. To extend the observation window, a more stable marker is required. In this paper, we report on conjugates of NAAF prodrugs with two cyanine dyes Cy5 and Cy7 including details of their synthesis, characterization and basic properties in cell free settings and their cellular uptake in representative human cancer cells. Finally, the Cy5 conjugate was subjected to in vivo fluorescence imaging studies to determine the prodrug biodistribution over 24 h. [ABSTRACT FROM AUTHOR]

Mn cage complexes are rare, and the ones successfully isolated in the solid state are not stable in water and organic solvents. Herein, we present the first report of mononuclear Mn clathrochelates, in which the encapsulated metal exists in the oxidation state +4. The complexes are extremely stable in the crystalline state and in solutions and show rich redox chemistry. [ABSTRACT FROM AUTHOR]

[Display omitted] Reactions for drug synthesis under cell-like conditions or even inside living cells can potentially be used e.g. , to minimize toxic side effects, to maximize bioactive compound efficacy and/or to address drug delivery problems. Those reactions should be bioorthogonal to enable the generation of drug-like compounds with sufficiently good yields. In the known bioorthogonal Michael reactions, using thiols and phosphines as nucleophiles (e.g. , in C S and C P bond formation reactions) is very common. No bioorthogonal Michael addition with a carbon nucleophile is known yet. Therefore, the development of such a reaction might be interesting for future drug discovery research. In this work, the metal-free Michael addition between cyclohexanone and various trans-β- nitrostyrenes (C C bond formation reaction), catalysed by a dipeptide salt H-Pro-Phe-O-Na+, was investigated for the first time in the presence of glutathione (GSH) and in phosphate-buffered saline (PBS). We demonstrated that with electron-withdrawing substituents on the aromatic ring and in β -position of the trans-β- nitrostyrene yields up to 64% can be obtained under physiological conditions, indicating a potential bioorthogonality of the studied Michael reaction. In addition, the selected Michael products demonstrated activity against human ovarian cancer cells A2780. This study opens up a new vista for forming bioactive compounds via C C bond formation Michael reactions under physiological (cell-like) conditions. [ABSTRACT FROM AUTHOR]

The folding and export of proteins and hydrolysis of unfolded proteins are disbalanced in the endoplasmic reticulum (ER) of cancer cells, leading to so‐called ER stress. Agents further augmenting this effect are used as anticancer drugs including clinically approved proteasome inhibitors bortezomib and carfilzomib. However, these drugs can affect normal cells, which also rely strongly on ER functions, leading, for example, to accumulation of reactive oxygen species (ROS). To address this problem, we have developed ER‐targeted prodrugs activated only in cancer cells in the presence of elevated ROS amounts. These compounds are conjugates of cholic acid with N‐alkylaminoferrocene‐based prodrugs. We confirmed their accumulation in the ER of cancer cells, their anticancer efficacy, and cancer cell specificity. These prodrugs induce ER stress, attenuate mitochondrial membrane potential, and generate mitochondrial ROS leading to cell death via necrosis. We also demonstrated that the new prodrugs are activated in vivo in Nemeth‐Kellner lymphoma (NK/Ly) murine model. [ABSTRACT FROM AUTHOR]

The folding and export of proteins and hydrolysis of unfolded proteins are disbalanced in the endoplasmic reticulum (ER) of cancer cells, leading to so‐called ER stress. Agents further augmenting this effect are used as anticancer drugs including clinically approved proteasome inhibitors bortezomib and carfilzomib. However, these drugs can affect normal cells, which also rely strongly on ER functions, leading, for example, to accumulation of reactive oxygen species (ROS). To address this problem, we have developed ER‐targeted prodrugs activated only in cancer cells in the presence of elevated ROS amounts. These compounds are conjugates of cholic acid with N‐alkylaminoferrocene‐based prodrugs. We confirmed their accumulation in the ER of cancer cells, their anticancer efficacy, and cancer cell specificity. These prodrugs induce ER stress, attenuate mitochondrial membrane potential, and generate mitochondrial ROS leading to cell death via necrosis. We also demonstrated that the new prodrugs are activated in vivo in Nemeth‐Kellner lymphoma (NK/Ly) murine model. [ABSTRACT FROM AUTHOR]

Abstract: Hairpin-structured phosphorothioate oligodeoxyribonucleotides containing a singlet oxygen-sensitive linker in the loop were prepared. These compounds do not bind complementary nucleic acids in the dark. Upon irradiation with red light in the presence of chlorine e6 the linker within these compounds is cleaved and a single-stranded oligodeoxyribonucleotide is produced. The latter compound is an efficient binder of complementary nucleic acids. This is the first example of ‘caged’ phosphorothioate oligodeoxyribonucleotides, whose nucleic acid binding ability is triggered by red light. [Copyright &y& Elsevier]

Conjugate Sn(IV)(pyropheophorbide a)dichloride–(peptide nucleic acid) catalyzes reduction of azobenzene derivatives in the presence of complementary nucleic acid (NA) upon irridiation with red light (660 nm). This is the first red light-induced NA-templated photoreduction. It is highly sensitive to single mismatches in the NA-template and can detect down to 5 nM NAs. [ABSTRACT FROM AUTHOR]

A red light-triggered reaction based on cyclic oligonucleotide substrates that is accelerated over 30-fold by specific nucleic acid templates and generates a bright fluorescent probe was developed. We confirmed that this reaction is compatible with fluorescence correlation spectroscopy (FCS) thereby allowing detection of nucleic acids down to 1 nM. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • 16-mer peptides from binding motives of agglutinating salivary proteins act as specific pathogen scavengers. • A reliable orthogonal binding strategy of peptides to stable SPIONs was developed. • Specific pathogen binding capacity of peptide-functionalized SPIONs is clearly dependent on the peptide sequence. • The results could support the development of new treatment options for acute systemic infectious diseases. Abstract Systemic inflammation such as sepsis represents an acute life-threatening condition, to which often no timely remedy can be found. A promising strategy may be to functionalize magnetic nanoparticles with specific peptides, derived from the binding motives of agglutinating salivary proteins, that allow immobilization of pathogens. In this work, superparamagnetic iron oxide nanoparticles with stable polycondensed aminoalkylsilane layer were developed, to which the heterobifunctional linkers N-succinimidyl 3-(2-pyridyldithio)-propanoate (SDPD) and N-succinimidyl bromoacetate (SBA) were bound. These linkers were further chemoselectively reacted with the thiol group of singularly present cysteines of selected peptides. The resulting functional nanoparticles underwent a detailed physicochemical characterization. The biocompatibility of the primarily coated aminoalkylsilane particles was also investigated. To test the pathogen-binding efficacy of the particles, the lipopolysaccharide-immobilization capacity of the peptide-coated particles was compared with free peptides. Here, one particle-bound peptide species succeeded in capturing 90% of the toxin, whereas the degree of immobilization of the toxin with a system that varied in the sequence of the peptide dropped to 35%. With these promising results, we hope to develop extracorporeal magnetic clearance systems for removing pathogens from the human body in order to accelerate diagnosis and alleviate acute disease conditions such as sepsis. [ABSTRACT FROM AUTHOR]

The imaging of reactive oxygen species (ROS) at the molecular level with high sensitivity and specificity by positron emission tomography (PET) could be of enormous interest to increase our knowledge about ROS activity and signalling, especially in tumours. The aim of this research was to optimise the click chemistry‐based radiosynthesis of an 18F‐labelled aminoferrocene glycoconjugate that was derived from an N‐alkylaminoferrocene lead structure known to have anticancer activity in vitro. Applying the solvent system phosphate buffer/THF (12/5), Cu(OAc)2 and sodium ascorbate as reducing agent at 60°C, the alkyne 1 reacted with the 18F‐labelled glycosyl azide [18F]2 in the presence of carrier 3 (47μM) to obtain carrier‐added [18F]4 in a radiochemical yield of 85%. Interestingly, the addition of carrier was essential for sufficient radiochemical yield, because it suppressed the oxidation of no‐carrier‐added (n.c.a.) [18F]4. Future work will include the formulation of c.a. [18F]4 for studying its biodistribution in tumour‐bearing mice. In vivo imaging of reactive oxygen species (ROS) represents a promising strategy for diagnosis and therapy of several types of cancer. In this study, the 18F‐fluoroglycosylation of an aminoferrocene derivative as a potential positron emission tomography (PET) tracer with ROS‐dependent cell uptake mechanism was optimised, providing a radiochemical yield of 85%. Further studies on its biodistribution and in vivo suitability as a ROS‐specific PET tracer are ongoing. [ABSTRACT FROM AUTHOR]

Abstract: Mitochondrial membrane potential is more negative in cancer cells than in normal cells, allowing cancer targeting by delocalized lipophilic cations (DLCs). However, as the difference is rather small, these drugs affect also normal cells. Now a concept of pro‐DLCs is proposed based on an N‐alkylaminoferrocene structure. These prodrugs are activated by the reaction with reactive oxygen species (ROS) forming ferrocenium‐based DLCs. Since ROS are overproduced in cancer, the high‐efficiency cancer‐cell‐specific targeting of mitochondria could be achieved as demonstrated by fluorescence microscopy in combination with two fluorogenic pro‐DLCs in vitro and in vivo. We prepared a conjugate of another pro‐DLC with a clinically approved drug carboplatin and confirmed that its accumulation in mitochondria was higher than that of the free drug. This was reflected in the substantially higher anticancer effect of the conjugate. [ABSTRACT FROM AUTHOR]

Abstract: Mitochondrial membrane potential is more negative in cancer cells than in normal cells, allowing cancer targeting by delocalized lipophilic cations (DLCs). However, as the difference is rather small, these drugs affect also normal cells. Now a concept of pro‐DLCs is proposed based on an N‐alkylaminoferrocene structure. These prodrugs are activated by the reaction with reactive oxygen species (ROS) forming ferrocenium‐based DLCs. Since ROS are overproduced in cancer, the high‐efficiency cancer‐cell‐specific targeting of mitochondria could be achieved as demonstrated by fluorescence microscopy in combination with two fluorogenic pro‐DLCs in vitro and in vivo. We prepared a conjugate of another pro‐DLC with a clinically approved drug carboplatin and confirmed that its accumulation in mitochondria was higher than that of the free drug. This was reflected in the substantially higher anticancer effect of the conjugate. [ABSTRACT FROM AUTHOR]