Water-Soluble Trityl Radicals for Fluorescence Imaging.

Stable tris(trichlorophenyl)methyl radicals have gained interest as all-organic bioimaging agents combining fluorescent and paramagnetic properties. However, cellular uptake has so far only been reported for nanoparticles, because molecular hydrophobic trityl radicals are not soluble in aqueous media. Here, we report the synthesis and characterization of new water-soluble tris(trichlorophenyl)methyl radical derivatives exhibiting red doublet emission. Solubility in water is achieved through functionalization with oligoethylene glycol (OEG) chains. The emission behavior of OEG functionalized trityl radicals is studied in polar environments. Donor-functionalization with carbazole evokes a charge-transfer excited state that is efficiently quenched in polar solvents. In contrast, click-reaction mediated attachment of OEG-azide and trityl acetylene furnishes a triazole functionalized radical with locally excited states and emission in water. Confocal fluorescence microscopy proves successful uptake of the material by macrophages in cell culture, showing the potential of our water soluble trityl radical for fluorescence bioimaging.

Biodegradable Polyimidazole Particles as Contrast Agents Produced by Direct Arylation Polymerization.

Conjugated polymer particles provide an important platform for the development of theranostic nanoagents. However, the number of biocompatible and foremost biodegradable π-conjugated polymers is limited. Imidazole is a π-conjugated motif that is abundant in biological systems. Oxidative degradation of imidazole is present in nature via enzymatic or free radical processes. In this work, we introduce polymer particles consisting purely of polyimidazole. We employ direct arylation polymerization and adapt it to a dispersion polymerization protocol to yield uniform and narrowly dispersed nanoparticles. We employ this mechanism to produce linear and cross-linked polymer particles to tune the optical properties from fluorescent to photoacoustically active. We show that the particles can be degraded by H2O2 as well as by reactive oxygen species produced by cells and we detect the degradation products. Altogether, our results suggest that polyimidazole particles represent ideal candidates for theranostic applications.

Croconaine-Based Polymer Particles as Contrast Agents for Photoacoustic Imaging.

In the development and optimization of imaging methods, photoacoustic imaging (PAI) has become a powerful tool for preclinical biomedical diagnosis and detection of cancer. PAI probes can improve contrast and help identify pathogenic tissue. Such contrast agents must meet several requirements: they need to be biocompatible, and absorb strongly in the near-infrared (NIR) range, while relaxing the photoexcited state thermally and not radiatively. In this work, polymer nanoparticles are produced with croconaine as a monomer unit. Small molecular croconaine dyes are known to act as efficient pigments, which do not show photoluminescence. Here, for the first time croconaine copolymer nanoparticles are produced from croconic acid and a range of aromatic diamines. Following a dispersion polymerization protocol, this approach yields monodisperse particles of adjustable size. All synthesized polymers exhibit broad absorption within the NIR spectrum and therefore represent suitable candidates as contrast agents for PAI. The optical properties of these polymer particles are discussed with respect to the relation between particle size and outstanding photoacoustic performance. Biocompatibility of the polymer particles is demonstrated in cell viability experiments.

Chemoselective Dual Labeling of Native and Recombinant Proteins.

The attachment of two different functionalities in a site-selective fashion represents a great challenge in protein chemistry. We report site specific dual functionalizations of peptides and proteins capitalizing on reactivity differences of cysteines in their free (thiol) and protected, oxidized (disulfide) forms. The dual functionalization of interleukin 2 and EYFP proceeded with no loss of bioactivity in a stepwise fashion applying maleimide and disulfide rebridging allyl-sulfone groups. In order to ensure broader applicability of the functionalization strategy, a novel, short peptide sequence that introduces a disulfide bridge was designed and site-selective dual labeling in the presence of biogenic groups was successfully demonstrated.

Microwave-Assisted Desulfonylation of Polysulfonamides toward Polypropylenimine.

Linear polyethylenimine (L-PEI) has been the gold standard for gene delivery and is typically prepared by hydrolysis from poly(2-oxazoline)s. Recently, also the anionic polymerization of activated aziridines was reported as a potential pathway toward linear and well-defined polyamines. However, only sulfonamide-activated aziridines so far undergo the living anionic polymerization and their desulfonylation was only reported scarcely. This is mainly due to the relatively high stability of the sulfonamides and the drastic change in solubility during the desulfonylation. Herein, we investigated the desulfonylation of such poly(aziridine)s prepared from tosylated or mesylated propyleneimine to afford linear polypropylenimine (L-PPI) as an alternative to L-PEI. Different desulfonylation strategies for tosylated (Ts) and mesylated (Ms) PPI were studied. The reductive cleavage of the sulfonamide with sodium bis(2-methoxy ethoxy) aluminum hydride yielded 80% of deprotected amine groups. Quantitative conversion to L-PPI was obtained, when the tosylated PPI was hydrolyzed under acidic conditions with pTsOH under microwave (MW) irradiation. The same treatment removed 90% of the mesyl groups from the mesylated PPI analog. The MW-assisted acidic hydrolysis represents a fast, inexpensive and easy approach in comparison to other methods, where complex reaction conditions and tedious purifications are major drawbacks, however some chain scission may occur. The high purity of the obtained products, in combination with the versatility of the activated aziridine chemistry, demonstrate many advantages of our strategy, especially for future biomedical implementations.

Generation and Characterization of Virus-Enhancing Peptide Nanofibrils Functionalized with Fluorescent Labels.

Retroviral gene transfer is the method of choice for the stable introduction of genetic material into the cellular genome. However, efficient gene transfer is often limited by low transduction rates of the viral vectors. We have recently described a 12-mer peptide, termed EF-C, that forms amyloid-like peptide nanofibrils (PNF), strongly increasing viral transduction efficiencies. These nanofibrils are polycationic and bind negatively charged membranes of virions and cells, thereby overcoming charge repulsions and resulting in increased rates of virion attachment and gene transfer. EF-C PNF enhance vector transduction more efficiently than other soluble additives and offer prospects for clinical applications. However, while the transduction-enhancing activity of PNF has been well-characterized, the exact mechanism and the kinetics underlying infection enhancement as well as the cellular fate of the fibrils are hardly explored. This is partially due to the fact that current labeling techniques for PNF rely on amyloid probes that cause high background staining or lose signal intensities after cellular uptake. Here, we sought to generate EF-C PNF covalently coupled with fluorescent labels. To achieve such covalent bioconjugates, the free amino groups of the EF-C peptide were coupled to the ATTO 495 or 647N NHS ester dyes. When small amounts of the labeled peptides were mixed with a 100- to 10 000-fold excess of the native peptide, PNF formed that were morphologically indistinguishable from those derived from the unlabeled peptide. The fluorescence of the fibrils could be readily detected using fluorescence spectroscopy, microscopy, and flow cytometry. In addition, labeled and nonlabeled fibrils captured viral particles and increased retroviral transduction with similar efficacy. These covalently fluorescence-labeled PNF are valuable tools with which to elucidate the mechanism(s) underlying transduction attachment and the fate of the fibrils in cells, tissues, and animal models.

Water-soluble allyl sulfones for dual site-specific labelling of proteins and cyclic peptides.

Water-soluble allyl sulfones provide convenient site-specific disulfide rebridging of native proteins and cyclic peptides. The site-selective functionalization of (a) the peptide hormone somatostatin, (b) the interchain disulfide of bovine insulin and (c) functionalization of the proteins GFP and lysozyme with allyl sulfones proceeds in aqueous solution. Allyl sulfones offer three functionalizable sites that react with thiol containing molecules in a step-wise fashion. Dual labeling of proteins and cyclic peptides is achieved i.e. the attachment of a chromophore and an affinity tag in a single reaction step, which is of great significance for the construction of precise multifunctional peptide and protein conjugates.

Receptor selective ruthenium-somatostatin photosensitizer for cancer targeted photodynamic applications.

The efficient conjugation of a ruthenium complex and the peptide hormone somatostatin is presented. The resultant biohybrid offers valuable features for photodynamic therapy such as remarkable cellular selectivity, rapid cell uptake by receptor-mediated endocytosis, efficient generation of (1)O2 upon irradiation, potent phototoxicity as well as low cytotoxicity in the "off"-state.

Discovery and characterization of an endogenous CXCR4 antagonist.

CXCL12-CXCR4 signaling controls multiple physiological processes and its dysregulation is associated with cancers and inflammatory diseases. To discover as-yet-unknown endogenous ligands of CXCR4, we screened a blood-derived peptide library for inhibitors of CXCR4-tropic HIV-1 strains. This approach identified a 16 amino acid fragment of serum albumin as an effective and highly specific CXCR4 antagonist. The endogenous peptide, termed EPI-X4, is evolutionarily conserved and generated from the highly abundant albumin precursor by pH-regulated proteases. EPI-X4 forms an unusual lasso-like structure and antagonizes CXCL12-induced tumor cell migration, mobilizes stem cells, and suppresses inflammatory responses in mice. Furthermore, the peptide is abundant in the urine of patients with inflammatory kidney diseases and may serve as a biomarker. Our results identify EPI-X4 as a key regulator of CXCR4 signaling and introduce proteolysis of an abundant precursor protein as an alternative concept for chemokine receptor regulation.

Programming Bioactive Architectures with Cyclic Peptide Amphiphiles.

We present a versatile approach for the synthesis of cyclic peptide amphiphiles of the hormone somatostatin (SST) with tunable lipophilic tails to program bioactive nanoarchitectures. A novel bis-alkylation reagent is synthesized that facilitates the functionalization of SST with a thiol anchor. Different hydrophobic moieties are introduced inspired by a biomimetic palmitoylation approach which opens access to cyclic peptide amphiphiles that display rich self-organization and cell membrane interactions.

A disulfide intercalator toolbox for the site-directed modification of polypeptides.

A disulfide intercalator toolbox was developed for site-specific attachment of a broad variety of functional groups to proteins or peptides under mild, physiological conditions. The peptide hormone somatostatin (SST) served as model compound for intercalation into the available disulfide functionalization schemes starting from the intercalator or the reactive SST precursor before or after bioconjugation. A tetrazole-SST derivative was obtained that undergoes photoinduced cycloaddition in mammalian cells, which was monitored by live-cell imaging.

Constructing hybrid protein zymogens through protective dendritic assembly.

The modulation of protein uptake and activity in response to physiological changes forms an integral part of smart protein therapeutics. We describe herein the self-assembly of a pH-responsive dendrimer shell onto the surface of active enzymes (trypsin, papain, DNase I) as a supramolecular protecting group to form a hybrid dendrimer-enzyme complex. The attachment is based on the interaction between boronic acid and salicyl hydroxamate, thus allowing the macromolecular assembly to respond to changes in pH between 5.0 and 7.4 in a highly reversible fashion. Catalytic activity is efficiently blocked in the presence of the dendrimer shell but is quantitatively restored upon shell degradation under acidic conditions. Unlike the native proteases, the hybrid constructs are shown to be efficiently taken up by A549 cells and colocalized in the acidic compartments. The programmed intracellular release of the proteases induced cytotoxicity, thereby uncovering a new avenue for precision biotherapeutics.

A core-shell albumin copolymer nanotransporter for high capacity loading and two-step release of doxorubicin with enhanced anti-leukemia activity.

The native transportation protein serum albumin represents an attractive nano-sized transporter for drug delivery applications due to its beneficial safety profile. Existing albumin-based drug delivery systems are often limited by their low drug loading capacity as well as noticeable drug leakage into the blood circulation. Therefore, a unique albumin-derived core-shell doxorubicin (DOX) delivery system based on the protein denaturing-backfolding strategy was developed. 28 DOX molecules were covalently conjugated to the albumin polypeptide backbone via an acid sensitive hydrazone linker. Polycationic and pegylated human serum albumin formed two non-toxic and enzymatically degradable protection shells around the encapsulated DOX molecules. This core-shell delivery system possesses notable advantages, including a high drug loading capacity critical for low administration doses, a two-step drug release mechanism based on pH and the presence of proteases, an attractive biocompatibility and narrow size distribution inherited from the albumin backbone, as well as fast cellular uptake and masking of epitopes due to a high degree of pegylation. The IC50 of these nanoscopic onion-type micelles was found in the low nanomolar range for Hela cells as well as leukemia cell lines. In vivo data indicate its attractive potential as anti-leukemia treatment suggesting its promising profile as nanomedicine drug delivery system.

Enhancing endosomal escape of transduced proteins by photochemical internalisation.

Induced internalisation of functional proteins into cultured cells has become an important aspect in a rising number of in vitro and in vivo assays. The endo-lysosomal entrapment of the transduced proteins remains the major problem in all transduction protocols. In this study we compared the efficiency, cytotoxicity and protein targeting of different commercially available transduction reagents by transducing a well-studied fluorescently labelled protein (Atto488-bovine serum albumin) into cultured human sarcoma cells. The amount of internalised protein and toxicity differed between the different reagents, but the percentage of transduced cells was consistently high. Furthermore, in all protocols the signals of the transduced Atto488-BSA were predominantly punctual consistent with an endosomal localisation. To overcome the endosomal entrapment, the transduction protocols were combined with a photochemical internalisation (PCI) treatment. Using this combination revealed that an endosomal disruption is highly effective in cell penetrating peptide (CPP) mediated transduction, whereas lipid-mediated transductions lead to a lower signal spreading throughout the cytosol. No change in the signal distribution could be achieved in treatments using non-lipid polymers as a transduction reagent. Therefore, the combination of protein transduction protocols based on CPPs with the endosomolytic treatment PCI can facilitate protein transduction experiments in vitro.

Cyclic stretch increases splicing noise rate in cultured human fibroblasts.

BACKGROUND: Mechanical forces are known to alter the expression of genes, but it has so far not been reported whether they may influence the fidelity of nucleus-based processes. One experimental approach permitting to address this question is the application of cyclic stretch to cultured human fibroblasts. As a marker for the precision of nucleus-based processes, the number of errors that occur during co-transcriptional splicing can then be measured. This so-called splicing noise is found at low frequency in pre-mRNA splicing. FINDINGS: The amount of splicing noise was measured by RT-qPCR of seven exon skips from the test genes AATF, MAP3K11, NF1, PCGF2, POLR2A and RABAC1. In cells treated by altered uniaxial cyclic stretching for 18 h, a uniform and significant increase of splicing noise was found for all detectable exon skips. CONCLUSION: Our data demonstrate that application of cyclic stretch to cultured fibroblasts correlates with a reduced transcriptional fidelity caused by increasing splicing noise.

Aberrant Single Exon Skipping is not Altered by Age in Exons of NF1, RABAC1, AATF or PCGF2 in Human Blood Cells and Fibroblasts.

In human pre-mRNA splicing, infrequent errors occur resulting in erroneous splice products as shown in a genome-wide approach. One characteristic subgroup consists of products lacking one cassette exon. The noise in the splicing process, represented by those misspliced products, can be increased by cold shock treatment or by inhibiting the nonsense mediated decay. Here, we investigated whether the splicing noise frequency increases with age in vivo in peripheral bloods cells or in vitro in cultured and aged fibroblasts from healthy donors. Splicing noise frequency was measured for four erroneously skipped NF1 exons and one exon of RABAC1, AATF and PCGF2 by RT-qPCR. Measurements were validated in cultured fibroblasts treated with cold shock or puromycin. Intragenic but not interpersonal differences were detected in splicing noise frequencies in vivo in peripheral blood cells of 11 healthy donors (15 y-85 y) and in in vitro senescent fibroblasts from three further donors. No correlation to the age of the donors was found in the splicing noise frequencies. Our data demonstrates that splicing error frequencies are not altered by age in peripheral blood cells or in vitro aged fibroblasts in the tested exons of the four investigated genes, indicating a high importance of correct splicing in these proliferating aged cells.

Differences in uptake, localization, and processing of PNAs modified by COX VIII pre-sequence peptide and by triphenylphoshonium cation into mitochondria of tumor cells.

Two approaches to target PNAs (peptide nucleic acids) into mitochondria of HeLa cells were compared. In the first, PNA was modified with the lipophilic cation TPP. TPP-PNA accumulated rapidly within mitochondria driven by the membrane potential. It was found to be associated mainly with the mitochondrial membranes. In the second approach the COX VIII pre-sequence peptide was added to the PNA resulting in slow uptake of the peptide-PNA into the mitochondrial matrix. Whereas the amount of the uptake was lower, peptide-PNA was processed intramitochondrially in contrast to the TPP-PNA. Using the Chariot system to cross the cell membrane of HeLa cells, the uptake of peptide-PNA into the mitochondria was demonstrated. If a matrix localization of the free PNA is a pre-requisite for the PNA interaction with mitochondrial DNA, the coupling PNA with an appropriate peptide seems to be the better strategy.