Kovalente Verknüpfung cyclischer TAT-Peptide mit GFP resultiert in der direkten Aufnahme in lebende Zellen mit sofortiger biologischer Verfügbarkeit

Structure-Uptake Relationship Study of DABCYL Derivatives Linked to Cyclic Cell-Penetrating Peptides for Live-Cell Delivery of Synthetic Proteins

Modifying cyclic cell-penetrating deca-arginine (cR10) peptides with 4-(4-dimethylaminophenylazo)benzoic acid (DABCYL) improves the uptake efficiency of synthetic ubiquitin (Ub) cargoes into living cells. To probe the role of the DABCYL moiety, we performed time-lapse microscopy and fluorescence lifetime imaging microscopy (FLIM) of fluorescent DABCYL-R10 to evaluate the impact on cell entry by the formation of nucleation zones. Furthermore, we performed a structure-uptake relationship study with 13 DABCYL derivatives coupled to CPP to examine their effect on the cell-uptake efficiency when conjugated to mono-Ub through disulfide linkages. Our results show that through structure variations of the DABCYL moiety alone we could reach, at nanomolar concentration, an additional threefold increase in the cytosolic delivery of Ub, which will enable studies on various intracellular processes related to Ub signaling.

Frontiers in Medicinal Chemistry 2022 Goes Virtual

The Frontiers in Medicinal Chemistry (FiMC) meeting, which represents the largest international medicinal chemistry conference in Germany, took place from March 14^th to 16^th 2022 in a fully virtual format. Organized by the Division of Medicinal Chemistry of the German Chemical Society (GDCh) together with the Division of Pharmaceutical & Medicinal Chemistry of the German Pharmaceutical Society (DPhG) and a "local" organization committee from the University of Freiburg headed by Manfred Jung, the meeting brought together 271 participants from around 20 countries. The program included 33 lectures by leading scientists from industry and academia as well as early career investigators. 67 posters were presented in two poster sessions and with over 20.000 poster abstract downloads. The general organization and the time-shift function were very much appreciated as demonstrated by almost 600 on-demand contents retrieved. The online format fitted perfectly to bring together medicinal chemists from academia and industry across the globe.

Spatio-temporal control of cell death by selective delivery of photo-activatable proteins

Protein therapeutics offer exquisite selectivity in targeting cellular processes and behaviors, but are rarely used against non‐cell surface targets due to their poor cellular uptake. While cell‐penetrating peptides can be used to deliver recombinant proteins to the cytosol, it is generally difficult to selectively deliver active proteins to target cells. Here, we report a recombinantly produced, intracellular protein delivery and targeting platform that uses a photocaged intein to regulate the spatio‐temporal activation of protein activity in selected cells upon irradiation with light. The platform was successfully demonstrated for two cytotoxic proteins to selectively kill cancer cells after photoactivation of intein splicing. This platform can generically be applied to any protein whose activity can be disrupted by a fused intein, allowing it to underpin a wide variety of future protein therapeutics.

Enhanced Live-Cell Delivery of Synthetic Proteins Assisted by Cell-Penetrating Peptides Fused to DABCYL

Live-cell delivery of a fully synthetic protein having selectivity towards a particular target is a promising approach with potential applications for basic research and therapeutics. Cell-penetrating peptides (CPPs) allow the cellular delivery of proteins but mostly result in endosomal entrapment, leading to lack of bioavailability. Herein, we report the design and synthesis of a CPP fused to 4-((4-(dimethylamino)phenyl)azo)benzoic acid (DABCYL) to enhance cellular uptake of fluorescently labelled synthetic protein analogues in low micromolar concentration. The attachment of cyclic deca-arginine (cR10) modified with a single lysine linked to DABCYL to synthetic ubiquitin (Ub) and small ubiquitin-like modifier-2 (SUMO-2) scaffolds resulted in a threefold higher uptake efficacy in live cells compared to the unmodified cR10. We could also achieve cR10DABCYL-assisted delivery of Ub and a Ub variant (Ubv) based activity-based probes for functional studies of deubiquitinases in live cells.

An Engineered Escherichia coli Strain with Synthetic Metabolism for in-Cell Production of Translationally Active Methionine Derivatives

In the last decades, it has become clear that the canonical amino acid repertoire codified by the universal genetic code is not up to the needs of emerging biotechnologies. For this reason, extensive genetic code re-engineering is essential to expand the scope of ribosomal protein translation, leading to reprogrammed microbial cells equipped with an alternative biochemical alphabet to be exploited as potential factories for biotechnological purposes. The prerequisite for this to happen is a continuous intracellular supply of noncanonical amino acids through synthetic metabolism from simple and cheap precursors. We have engineered an Escherichia coli bacterial system that fulfills these requirements through reconfiguration of the methionine biosynthetic pathway and the introduction of an exogenous direct trans-sulfuration pathway. Our metabolic scheme operates in vivo, rescuing intermediates from core cell metabolism and combining them with small bio-orthogonal compounds. Our reprogrammed E. coli strain is capable of the in-cell production of l-azidohomoalanine, which is directly incorporated into proteins in response to methionine codons. We thereby constructed a prototype suitable for economic, versatile, green sustainable chemistry, pushing towards enzyme chemistry and biotechnology-based production.

Vancomycin Resistance Is Overcome by Conjugation of Polycationic Peptides

Multidrug-resistant bacteria represent one of the biggest challenges facing modern medicine. The increasing prevalence of glycopeptide resistance compromises the efficacy of vancomycin, for a long time considered as the last resort for the treatment of resistant bacteria. To reestablish its activity, polycationic peptides were conjugated to vancomycin. By site-specific conjugation, derivatives that bear the peptide moiety at four different sites of the antibiotic were synthesized. The most potent compounds exhibited an approximately 1000-fold increased antimicrobial activity and were able to overcome the most important types of vancomycin resistance. Additional blocking experiments using d-Ala-d-Ala revealed a mode of action beyond inhibition of cell-wall formation. The antimicrobial potential of the lead candidate FU002 for bacterial infection treatments could be demonstrated in an in vivo study. Molecular imaging and biodistribution studies revealed that conjugation engenders superior pharmacokinetics.

De Novo Design of Cell-Penetrating Foldamers

Cell-penetrating peptides (CPPs) have gained much attention as carriers of hydrophilic molecules, such as drugs, peptides, and nucleic acids, into cells. CPPs are mainly composed of cationic amino acid residues, which play an important role in their intracellular uptake via interactions with acidic groups on cell surfaces. In addition, the secondary structures of CPPs also affect their cell-membrane permeability. Based on this knowledge, a variety of cell-penetrating foldamers (oligomers that form organized secondary structures) have been developed to date. In this account, we describe recent attempts to develop cell-penetrating foldamers containing various building blocks, and their application as DDS carriers.

Cysteine-Selective Phosphonamidate Electrophiles for Modular Protein Bioconjugations

We describe a new technique in protein synthesis that extends the existing repertoire of methods for protein modification: A chemoselective reaction that induces reactivity for a subsequent bioconjugation. An azide-modified building block reacts first with an ethynylphosphonite through a Staudinger-phosphonite reaction (SPhR) to give an ethynylphosphonamidate. The resulting electron-deficient triple bond subsequently undergoes a cysteine-selective reaction with proteins or antibodies. We demonstrate that ethynylphosphonamidates display excellent cysteine-selective reactivity combined with superior stability of the thiol adducts, when compared to classical maleimide linkages. This turns our technique into a versatile and powerful tool for the facile construction of stable functional protein conjugates.

Efficient Cytoplasmic Delivery of Antisense Probes Assisted by Cyclized-Peptide-Mediated Photoinduced Endosomal Escape

Intracellular delivery and endosomal release of antisense oligonucleotides remain a significant challenge in the development of gene-targeted therapeutics. Previously, noncovalently cyclized TAT peptide (Cyc-TAT), in which the final ring-closing step is accomplished by hybridization of two short complementary γPNA segments, has been proven more efficient than its linear analogues at entering cells. As Cyc-TAT also readily accommodates a binding site, that is, an overhanging γPNA sequence, for codelivery of functional nucleic acid probes into cells, we were able to demonstrate that the overhang-Cyc-TAT penetrated into A549 cells when carrying an anti-telomerase γPNA that specifically reduced telomerase activity by over 97 %. Herein, we report that the cyclized TAT(FAM) can escape endosomes much more efficiently than the linear TAT(FAM) after LED illumination (490 nm). Based on this observation, the endosomal release of overhang-Cyc-TAT(FAM)/anti-telomerase γPNA complex can be greatly enhanced by photoactivation, thus shortening cell treatment time from 60 to 3 h, while keeping the same high efficiency in inhibiting telomerase activity inside A549 cells.

Enhanced Delivery of Synthetic Labelled Ubiquitin into Live Cells by Using Next-Generation Ub-TAT Conjugates

Proteins and other macromolecules can be delivered into live cells by noninvasive techniques using cell-penetrating peptides. These peptides are easily synthesised by solid-phase peptide synthesis and can be conjugated onto cargo molecules to mediate cellular delivery. We designed a TAT-based cell-penetrating ubiquitin (Ub) reagent by conjugating a dimeric disulfide-linked TAT peptide to the C terminus of a rhodamine-labelled Ub (RhoUb) protein. This reagent efficiently enters the cell by endocytosis and escapes from endosomes into the cytoplasm. Once the conjugate is inside the cytoplasm, the delivery vehicle is proteolytically removed by endogenous deubiquitinases (DUBs), at which point the intrinsic ubiquitination machinery is able to incorporate the RhoUb into ubiquitin conjugates. Our approach enables the controlled delivery of labelled or mutant Ub derivatives into cells, increasing our options for studying the ubiquitin system.

Recent Advances in the Synthesis of Peptoid Macrocycles

Over the past two decades, developing medical applications for peptides has, and continues to be a highly active area of research. At present there are over 60 peptide-based drugs on the market and more than 140 in various stages of clinical trials. The interest in peptide-based therapeutics arises from their biocompatibility and their ability to form defined secondary and tertiary structures, resulting in a high selectivity for complex targets. However, there are significant challenges associated with the development of peptide-based therapeutics, namely peptides are readily metabolised in vivo. Peptoids are an emerging class of peptidomimetic and they offer an alternative to peptides. Peptoids are comprised of N-substituted glycines where side-chains are located on the nitrogen atom of the amide backbone rather than the α-carbon as is the case in peptides. This change in structure confers a high degree of resistance to proteolytic degradation but the absence of any backbone hydrogen bonding means that peptoids exhibit a high degree of conformational flexibility. Cyclisation has been explored as one possible route to rigidify peptoid structures, making them more selective, and, therefore more desirable as potential therapeutics. This review outlines the various strategies that have been developed over the last decade to access new types of macrocyclic peptoids.

Nanobodies: Chemical Functionalization Strategies and Intracellular Applications

Nanobodies can be seen as next-generation tools for the recognition and modulation of antigens that are inaccessible to conventional antibodies. Due to their compact structure and high stability, nanobodies see frequent usage in basic research, and their chemical functionalization opens the way towards promising diagnostic and therapeutic applications. In this Review, central aspects of nanobody functionalization are presented, together with selected applications. While early conjugation strategies relied on the random modification of natural amino acids, more recent studies have focused on the site-specific attachment of functional moieties. Such techniques include chemoenzymatic approaches, expressed protein ligation, and amber suppression in combination with bioorthogonal modification strategies. Recent applications range from sophisticated imaging and mass spectrometry to the delivery of nanobodies into living cells for the visualization and manipulation of intracellular antigens.

Building Peptide Bonds in Haifa: The Seventh Chemical Protein Synthesis (CPS) Meeting

The power of CPS, live! More than 90 attendees from around the world came together in Haifa to present and hear about cutting-edge science in protein chemistry, from advances in synthetic methods to applications in biology and medicine. The meeting was a powerful demonstration that chemical protein synthesis can provide otherwise unattainable insights into protein structure and function.

Dodging Endosomes: Effective Cytosolic Antibody Delivery

On the inside: New methodologies for delivering antibodies right into the cytosol of cells either directly across the plasma membrane or by allowing the antibody to escape from endosomes have been proposed recently by the Cardoso/Hackenberger and Futaki groups, respectively.

Effect of Preorganized Charge-Display on the Cell-Penetrating Properties of Cationic Peptides

The effect of preorganized versus undefined charge display on the cellular uptake of cationic cell-penetrating peptides (CPPs) was investigated by comparing conformationally well-defined guanidinylated oligoprolines with flexible oligoarginines. Flow cytometry and confocal microscopy studies with different cancer cell lines (HeLa, MCF-7, and HT-29) showed that preorganization of cationic charges in lateral distances of ≈9 Å enhanced the cellular uptake of CPPs. Binding affinity measurements revealed tighter binding of analogues of cell-surface glycans to the guanidinylated octaproline with localized charges compared to flexible octaarginine, a finding that was further correlated to the cellular uptake by studies with CHO cells deficient in glycans on the outer plasma membrane.

ECBS & ICBS 2015 Joint Meeting: Bringing Chemistry to Life

The European Chemical Biology Society (ECBS) and the International Chemical Biology Society (ICBS) recently organized a joint meeting in Berlin. This meeting had more than 250 participants. Four keynote lectures were given by Timothy Mitchison, David Tirrell, Carolyn Bertozzi and Jason Chin; in addition there were 13 invited speakers, 20 selected oral talks and 30 talks selected from 90 posters. The meeting was divided into six topics: chemoproteomics, epigenetics, conjugates for target delivering, anti-infectives, molecular imaging and probing the structure, and function of post-translational modifications. The highlights of the meeting are presented in this report.

An Intrinsically Disordered Peptide Facilitates Non-Endosomal Cell Entry

Many cell-penetrating peptides (CPPs) fold at cell surfaces, adopting α- or β-structure that enable their intracellular transport. However, the same structural folds that facilitate cellular entry can also elicit potent membrane-lytic activity, limiting their use in delivery applications. Further, a distinct CPP can enter cells through many mechanisms, often leading to endosomal entrapment. Herein, we describe an intrinsically disordered peptide (CLIP6) that exclusively employs non-endosomal mechanisms to cross cellular membranes, while being remarkably biocompatible and serum-stable. We show that a single anionic glutamate residue is responsible for maintaining the disordered bioactive state of the peptide, defines its mechanism of cellular entry, and is central to its biocompatibility. CLIP6 can deliver membrane-impermeable cargo directly to the cytoplasm of cells, suggesting its broad utility for delivery of drug candidates limited by poor cell permeability and endosomal degradation.