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Immunotherapy, alone or in combination with other therapies, is widely used against cancer. Glycoprotein Mucin 1 (MUC1), which is overexpressed and aberrantly glycosylated in tumor cells, is one of the most promising candidates to engineer new cancer vaccines. In this context, the development of stable antigens that can elicit a robust immune response is mandatory. Here, we describe the design and in vivo biological evaluation of three vaccine candidates based on MUC1 glycopeptides that comprise unnatural elements in their structure. By placing the Tn antigen (GalNAcα-O-Ser/Thr) at the center of the design, the chemical modifications include changes to the peptide backbone, glycosidic linkage, and carbohydrate level. Significantly, the three vaccines elicit robust immune responses in mice and produce antibodies that can be recognized by several human cancer cells. In all cases, a link was established between the conformational changes induced by the new elements in the antigen presentation and the immune response induced in mice. According to our data, the development of effective MUC1-based vaccines should use surrogates that mimic the conformational space of aberrantly glycosylated MUC1 glycopeptides found in tumors.

N-Acetylgalactosamine (GalNAc)-type O-glycosylation is an essential posttranslational modification (PTM) that plays fundamental roles in biology. Malfunction of this PTM is exemplified by the presence of truncated O-glycans in cancer. For instance, the glycoprotein MUC1 is overexpressed in many tumor tissues and tends to carry simple oligosaccharides that allow for the presentation of different tumor-associated antigens, such as the Tn or sTn antigens (GalNAc-α-1-O-Thr/Ser and Neu5Acα2-6GalNAcα1-O-Ser/Thr, respectively). In other cases, such as tumoral calcinosis associated with O-glycosylation of the fibroblast growth factor 23, O-glycans are absent or less abundant. Significant progress has been made in determining the three-dimensional structures of biomolecules that recognize GalNAc, such as antibodies, lectins, mucinases, GalNAc-transferases, and other glycosyltransferases. Analysis of the complexes between these entities and GalNAc-containing glycopeptides, in most cases derived from crystallographic or NMR analysis, provides an understanding of the key structural elements that control molecular recognition of these glycopeptides. Here, we describe and compare the binding sites of these proteins in detail, focusing on how the GalNAc moieties interact selectively with them. We also summarize the differences and similarities in GalNAc recognition. In general, the recognition of GalNAc-containing glycopeptides is determined by hydrogen bonds between hydroxyl groups and the N-acetyl group of GalNAc with proteins, as well as CH-π contacts in which the hydrophobic α-face of the sugar and the methyl group of NHAc can be involved. The latter interaction usually provides the basis for selectivity. It is worth noting that binding of these glycopeptides depends primarily on recognition of the sugar moiety, with some exceptions such as a few anti-MUC1 antibodies that primarily recognize the peptide backbone and use the sugar to facilitate shape complementarity or to establish a limited number of interactions with the protein. Focusing specifically on the GalNAc moiety, we can observe that there is some degeneracy of interactions within the same protein families, likely due to substrate flexibility. However, when all studied proteins are considered together, despite the commonalities within each protein family, no pattern can be discerned between the different families, apart from the presence of common residues such as Tyr, His, or Asp, which are responsible for hydrogen bonds. The lack of a pattern can be anticipated, given the diverse functions of mucinases, glycosyltransferases, antibodies, and lectins. Finally, it is important to point out that the conformational differences observed in solution in glycopeptides bearing GalNAc-α-1-O-Ser or GalNAc-α-1-O-Thr also can be found in the bound state. This unique characteristic is exploited, for instance, by the enzyme C1GalT1 to broadly glycosylate both acceptor substrates. The findings summarized in this review may contribute to the rational structure-guided development of therapeutic vaccines, novel diagnostic tools for early cancer detection, and new cancer treatments for cancer with tailored anti-Tn or anti-STn antibodies or new drugs to inhibit GalNAc-T isoenzymes.

β-Seleno-α-amino acids, known as selenocysteine (Sec) derivatives, have emerged as important targets because of their role in chemical biology, not only as part of selenoproteins with important redox properties, but also because of their activity as antivirals or metabolites effective in inhibiting carcinogenesis. In addition, there is demand for this type of compounds due to their use in native chemical ligation to construct large peptides. Therefore, this review summarizes the various synthetic methods that have been published to construct Sec derivatives. Most of them involve the generation of the C–Se bond by nucleophilic substitution reactions, but other reactions such as radical or multicomponent strategies are also reported. Of particular importance is the Se-Michael addition of Se-nucleophiles to chiral bicyclic dehydroalanines, in which the stereogenic center is generated under complete stereocontrol.1 Introduction2 Previously Reviewed Synthesis of Sec3 Retrosynthesis of Sec Derivatives4 Sec Derivatives by Nucleophilic Substitutions5 Sec Derivatives by Radical Processes6 Sec Derivatives by 1,4-Conjugate Additions7 Conclusion

Strained alkenes and alkynes are the predominant dienophiles used in inverse electron demand Diels–Alder (IEDDA) reactions. However, their instability, cross-reactivity, and accessibility are problematic. Unstrained dienophiles, although physiologically stable and synthetically accessible, react with tetrazines significantly slower relative to strained variants. Here we report the development of potassium arylethynyltrifluoroborates as unstrained dienophiles for fast, chemically triggered IEDDA reactions. By varying the substituents on the tetrazine (e.g., pyridyl- to benzyl-substituents), cycloaddition kinetics can vary from fast (k2 = 21 M–1 s–1) to no reaction with an alkyne-BF3 dienophile. The reported system was applied to protein labeling both in the test tube and fixed cells and even enabled mutually orthogonal labeling of two distinct proteins.

10 p.-5 fig.-1 graph. abst., The human macrophage galactose lectin (MGL) is anendocytic type II transmembrane receptor expressed on immaturemonocyte-derived dendritic cells and activated macrophages and playsa role in modulating the immune system in response to infections andcancer. MGL contains an extracellular calcium-dependent (C-type)carbohydrate recognition domain (CRD) that specifically bindsterminalN-acetylgalactosamine glycan residues such as the Tn andsialyl-Tn antigens found on tumor cells, as well as otherN-andO-glycans displayed on certain viruses and parasites. Even though theglycan specificity of MGL is known and several binding glycoproteinshave been identified, the molecular basis for substrate recognition hasremained elusive due to the lack of high-resolution structures. Here wepresent crystal structures of the MGL CRD at near endosomal pH and in several complexes, which reveal details of the interactionswith the natural ligand, GalNAc, the cancer-associated Tn-Ser antigen, and a synthetic GalNAc mimetic ligand. Like theasialoglycoprotein receptor, additional calcium atoms are present and contribute to stabilization of the MGL CRD fold. Thestructure provides the molecular basis for preferential binding ofN-acetylgalactosamine over galactose and prompted the re-evaluation of the binding modes previously proposed in solution. Saturation transfer difference nuclear magnetic resonance dataacquired using the MGL CRD and interpreted using the crystal structure indicate a single binding mode for GalNAc in solution.Models of MGL1 and MGL2, the mouse homologues of MGL, explain how these proteins might recognize LewisXand GalNAc,respectively, This work was supported by funding from Gabrielle’s Angel Foundation for Cancer Research to G.B., grants 12/IA/1398and 16/IA/4419 from Science Foundation Ireland to P.V.M.and GOIPG/2016/858 from the Irish Research Council toA.G. F.M., H.C., and A.D. acknowledge Fundação para a Ciência e a Tecnologia (FCT-Portugal) for funding ProjectsIF/00780/2015 and PTDC/BIA-MIB/31028/2017 and UCI-BIO Project UIDB/04378/2020, as well as the Ph.D. grantattributed to A.D. (PD/BD/142847/2018). The NMRspectrometers are part of the National NMR Network(PTNMR) and are partially supported by InfrastructureProject 22161 (co-financed by FEDER through COMPETE2020, POCI, and PORL and FCT through PIDDAC). F.J.C.acknowledges funding from Agencia Estatal de Investigación(Spain) for Grant RTI2018-094751-B-C22 and CIBERES, aninitiative from the Spanish Institute of Health Carlos III. F.C.thanks Agencia Estatal de Investigación (Spain) for Grant RTI2018-099592-B-C2.

Chiral bicyclic

Protein conjugates are valuable tools for studying biological processes or producing therapeutics, such as antibody-drug conjugates. Despite the development of several protein conjugation strategies in recent years, the ability to modify one specific amino acid residue on a protein in the presence of other reactive side chains remains a challenge. We show that monosubstituted cyclopropenone (CPO) reagents react selectively with the 1,2-aminothiol groups of N-terminal cysteine residues to give a stable 1,4-thiazepan-5-one linkage under mild, biocompatible conditions. The CPO-based reagents, all accessible from a common activated ester CPO-pentafluorophenol (

Boronic acids (BAs) are a promising bioconjugation function to design dynamic materials as they can establish reversible covalent bonds with oxygen/nitrogen nucleophiles that respond to different pH, ROS, carbohydrates and glutathione levels. However, the dynamic nature of these bonds also limits the control over the stability and site-selectivity of the bioconjugation, which ultimately leads to heterogeneous conjugates with poor stability under physiological conditions. Here we disclose a new strategy to install BAs on peptide chains. In this study, a "boron hot spot" based on the 3-hydroxyquinolin-2(1H)-one scaffold was developed and upon installation on a peptide N-terminal cysteine, enables the site-selective formation of iminoboronates with 2-formyl-phenyl boronic acids (Ka of 58128±2 m-1 ). The reaction is selective in the presence of competing lysine ϵ-amino groups, and the resulting iminoboronates, displayed improved stability in buffers solutions and a cleavable profile in the presence of glutathione. Once developed, the methodology was used to prepare cleavable fluorescent conjugates with a laminin fragment, which enabled the validation of the 67LR receptor as a target to deliver cargo to cancer HT29 cells.

Glycosylations promoted by triflate-generating reagents are widespread synthetic methods for the construction of glycosidic scaffolds and glycoconjugates of biological and chemical interest. These processes are thought to proceed with the participation of a plethora of activated high energy intermediates such as the α- and β-glycosyl triflates, or even increasingly unstable glycosyl oxocarbenium-like species, among which only α-glycosyl triflates have been well characterized under representative reaction conditions. Interestingly, the remaining less accessible intermediates, yet to be experimentally described, seem to be particularly relevant in α-selective processes, involving weak acceptors. Herein, we report a detailed analysis of several paradigmatic and illustrative examples of such reactions, employing a combination of chemical, NMR, kinetic and theoretical approaches, culminating in the unprecedented detection and quantification of the true β-glycosyl triflate intermediates within activated donor mixtures. This achievement was further employed as a stepping-stone for the characterization of the triflate anomerization dynamics, which along with the acceptor substitutions, govern the stereochemical outcome of the reaction. The obtained data conclusively show that, even for highly dissociative reactions involving β-close ion pair (β-CIP) species, the formation of the α-glycoside is necessarily preceded by a bimolecular α → β triflate interconversion, which under certain circumstances becomes the rate-limiting step. Overall, our results rule out the prevalence of the Curtin-Hammett fast-exchange assumption for most glycosylations and highlight the distinct reactivity properties of α- and β-glycosyl triflates against neutral and anionic acceptors., A.G.S. would like to thank the EU commission for a MSCA-IF postdoctoral fellowship. L.M.-J and L.D.-C thank the Ministerio de Economía , Industria y Competitividad and the Ministerio de Ciencia, Innovación y Universidades the for their FPI fellowships (BES-2014-070232 and BES-2017-080618). This investigation was supported by research grants from the Spanish Ministry of Science and Innovation (CTQ2016−79255-P, PID2019−107476GB-I00, BFU2017−89707-P, RTI2018−094862-B-100, RTI2018−099592−B-C21, PID2019−104090RB-100, RTI2018−094751−B-C22, and RTI2018−099592−B-C22), the Mizutani Foundation forGlycoscience (200077 and 170045), the Aragon Government (Groups 17R-34) and the computational resources from BIFI-ZCAM (Universidad de Zaragoza, Spain).

Two granulysin (GRNLY) based immunotoxins were generated, one containing the scFv of the SM3 mAb (SM3GRNLY) and the other the scFv of the AR20.5 mAb (AR20.5GRNLY). These mAb recognize different amino acid sequences of aberrantly O-glycosilated MUC1, also known as the Tn antigen, expressed in a variety of tumor cell types. We first demonstrated the affinity of these immunotoxins for their antigen using surface plasmon resonance for the purified antigen and flow cytometry for the antigen expressed on the surface of living tumor cells. The induction of cell death of tumor cell lines of different origin positive for Tn antigen expression was stronger in the cases of the immunotoxins than that induced by GRNLY alone. The mechanism of cell death induced by the immunotoxins was studied, showing that the apoptotic component demonstrated previously for GRNLY was also present, but that cell death induced by the immunotoxins included also necroptotic and necrotic components. Finally, we demonstrated the in vivo tumor targeting by the immunotoxins after systemic injection using a xenograft model of the human pancreatic adenocarcinoma CAPAN-2 in athymic mice. While GRNLY alone did not have a therapeutic effect, SM3GRNLY and AR20.5GRNLY reduced tumor volume by 42 and 60%, respectively, compared with untreated tumor-bearing mice, although the results were not statistically significant in the case of AR20.5GRNLY. Histological studies of tumors obtained from treated mice demonstrated reduced cellularity, nuclear morphology compatible with apoptosis induction and active caspase-3 detection by immunohistochemistry. Overall, our results exemplify that these immunotoxins are potential drugs to treat Tn-expressing cancers.

We have designed and synthesized a new self-immolative bioorthogonal cleavable linkerbased on the Grob fragmentation reaction that allows the controlled release of sulfonate-containing compounds such as a dansyl group under physiological conditions. We have alsotuned conveniently the pKa of the pushing group (amino group) using different substituents,leading to more efficient conversions at physiological pH and in some cases even at acidicpH, which is normally found in tumour environments. In addition, the Grob fragmentationtakes place under physiological conditions in living cells, demonstrating the potentialbioorthogonal applicability of the reaction. Based on these promising results, research iscurrently underway to incorporate this type of linker into antibodydrug conjugates for thetargeted delivery of cytotoxic drugs and fluorophores

Selenium plays a crucial role in different biological processes, being necessary for theproper functioning of the human body. Therefore, selenium compounds have becomemolecules of great interest due to their antiviral and anticancer activities and their use as naturalfood supplements.Selenocysteine (Sec) is the 21st genetically encoded amino acid and plays an importantrole in protein folding and stability, conferring interesting redox properties. In addition, protectedselenocysteine derivatives are used as precursors of dehydroalanine, which allows theintroduction of various post-translational modifications. On the other hand, some aryl derivativesof Se serve as chemical models for the inhibition of selenoenzymes, which has implications forcancer therapy. Beyond applications in bioconjugation, selenoamino acids are especiallyrelevant in Native Chemical Ligation (NCL).[1]Although the nucleophilic substitution reaction has been widely employed for thesynthesis of these Sec derivatives, 1,4-conjugate addition has been less explored, especiallythe stereoselective 1,4-conjugate addition of Se-nucleophiles to chiral Michael acceptors.Therefore, in this work, we aim to extend the methodology established by our research group[2]to the synthesis of enantiomerically pure selenoamino acids. The key step of such synthesis isthe attack of different Se-nucleophiles to a chiral dehydroalanine, to obtain a singlediastereoisomer. The methodology is simple and does not require the use of any catalyst,providing excellent yields at room temperature. Subsequent facile acid hydrolysis of the abovediastereoisomers leads to the corresponding selenoamino acids

The large family of polypeptide GalNAc-transferases (GalNAc-Ts) controls with precision how GalNAc

© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited., We describe maleic-acid derivatives as robust cysteine-selective reagents for protein labelling with comparable kinetics and superior stability relative to maleimides. Diamide and amido-ester derivatives proved to be efficient protein-labelling species with a common mechanism in which a spontaneous cyclization occurs upon addition to cysteine. Introduction of chlorine atoms in their structures triggers ring hydrolysis or further conjugation with adjacent residues, which results in conjugates that are completely resistant to retro-Michael reactions in the presence of biological thiols and human plasma. By controlling the microenvironment of the reactive site, we can control selectivity towards the hydrolytic pathway, forming homogeneous conjugates. The method is applicable to several scaffolds and enables conjugation of different payloads. The synthetic accessibility of these reagents and the mild conditions required for fast and complete conjugation together with the superior stability of the conjugates make this strategy an important alternative to maleimides in bioconjugation., This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement N° 836698 and under grant agreement N° 852985. Funding from the Scripps Research Institute (A.A.), FCT Portugal (PhD scholarship PD/BD/135512/2018 to C.F.A. and FCT Stimulus CEECIND/00453/2018 to G.J.L.B.) and Agencia Estatal Investigación of Spain (AEI; Grant RTI2018-099592-B-C21 to F.C.) is also acknowledged.

Glycolipids are prominent components of bacterial membranes that play critical roles not only in maintaining the structural integrity of the cell but also in modulating host-pathogen interactions. PatA is an essential acyltransferase involved in the biosynthesis of phosphatidyl-myo-inositol mannosides (PIMs), key structural elements and virulence factors of Mycobacterium tuberculosis. We demonstrate by electron spin resonance spectroscopy and surface plasmon resonance that PatA is an integral membrane acyltransferase tightly anchored to anionic lipid bilayers, using a two-helix structural motif and electrostatic interactions. PatA dictates the acyl chain composition of the glycolipid by using an acyl chain selectivity “ruler.” We established this by a combination of structural biology, enzymatic activity, and binding measurements on chemically synthesized nonhydrolyzable acyl–coenzyme A (CoA) derivatives. We propose an interfacial catalytic mechanism that allows PatA to acylate hydrophobic PIMs anchored in the inner membrane of mycobacteria, through the use of water-soluble acyl-CoA donors., This work was supported by the MINECO/FEDER EU contracts BFU2016-77427-C2-2-R, BFU2017-92223-EXP, PID2019-105649RB-I00, Severo Ochoa Excellence Accreditation SEV-2016-0644; the Basque Government contract KK-2019/00076; NIH R01AI149297 (to M.E.G.); the MINECO/FEDER EU contract BFU-2015-68981-P and the Basque Government (IT1264-19) (to F.-X.C.); MINECO/FEDER EU contract RTI2018-099592-B-C21 (to F.C.); the Canadian Glycomics Network Grant SD-1 (to T.L.L.). European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 844905 (to B.T.); the Basque Government (to I.A.); CONACyT fellowship no. 291276 (to E.D.P.-P.).

Funder: Frances and Augustus Newman Foundation, Funder: Emmanuel College, University of Cambridge, Funder: Biotechnology and Biological Sciences Research Council, Funder: Centre for Misfolding Diseases, University of Cambridge, Funder: Wellcome Trust, Biomimetics is a design principle within chemistry, biology, and engineering, but chemistry biomimetic approaches have been generally limited to emulating nature's chemical toolkit while emulation of nature's physical toolkit has remained largely unexplored. To begin to explore this, we designed biophysically mimetic microfluidic reactors with characteristic length scales and shear stresses observed within capillaries. We modeled the effect of shear with molecular dynamics studies and showed that this induces specific normally buried residues to become solvent accessible. We then showed using kinetics experiments that rates of reaction of these specific residues in fact increase in a shear-dependent fashion. We applied our results in the creation of a new microfluidic approach for the multidimensional study of cysteine biomarkers. Finally, we used our approach to establish dissociation of the therapeutic antibody trastuzumab in a reducing environment. Our results have implications for the efficacy of existing therapeutic antibodies in blood plasma as well as suggesting in general that biophysically mimetic chemistry is exploited in biology and should be explored as a research area.

An azanorbornadiene bromovinyl sulfone reagent for cysteine-selective bioconjugation has been developed. Subsequent reaction with dipyridyl tetrazine leads to bond cleavage and formation of a pyrrole-linked conjugate. The latter involves ligation of the tetrazine to the azanorbornadiene-tagged protein through inverse electron demand Diels-Alder cycloaddition with subsequent double retro-Diels-Alder reactions to form a stable pyrrole linkage. The sequence of site-selective bioconjugation followed by bioorthogonal bond cleavage was efficiently employed for the labelling of three different proteins. This method benefits from easy preparation of these reagents, selectivity for cysteine, and stability after reaction with a commercial tetrazine, which has potential for the routine preparation of protein conjugates for chemical biology studies.

An azanorbornadiene bromovinyl sulfone reagent for cysteine‐selective bioconjugation has been developed. Subsequent reaction with dipyridyl tetrazine leads to bond cleavage and formation of a pyrrole‐linked conjugate. The latter involves ligation of the tetrazine to the azanorbornadiene‐tagged protein through inverse electron demand Diels–Alder cycloaddition with subsequent double retro‐Diels–Alder reactions to form a stable pyrrole linkage. The sequence of site‐selective bioconjugation followed by bioorthogonal bond cleavage was efficiently employed for the labelling of three different proteins. This method benefits from easy preparation of these reagents, selectivity for cysteine, and stability after reaction with a commercial tetrazine, which has potential for the routine preparation of protein conjugates for chemical biology studies.

The highly diastereoselective 1,4-conjugate additions of several nitrogen nucleophiles to chiral bicyclic dehydroalanines have been assessed effectively at room temperature in good to excellent yields without needing any catalyst or additional base. This methodology is general, simple, oxygen and moisture tolerant, high-yielding, totally chemo- and stereoselective. This procedure offers an efficient and practical approach for the synthesis of Nβ-substituted α,β-diamino acids, such as 1-isohistidine, τ-histidinoalanine, β-benzylaminoalanine, β-(piperidin-1-yl)alanine, β-(azepan-1-yl)alanine, and fluorescent and ciprofloxacin-containing amino acid derivatives.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological cancer for which treatment options often result in incomplete therapeutic efficacy and long-term side-effects. Interleukin 7 (IL-7) and its receptor IL-7Rα promote T-ALL development and mutational activation of IL-7Rα associates with very high risk in relapsed disease. Using combinatorial phage-display libraries and antibody reformatting, we generated a fully human IgG1 monoclonal antibody (named B12) against both wild-type and mutant human IL-7Rα, predicted to form a stable complex with IL-7Rα at a different site from IL-7. B12 impairs IL-7/IL-7R-mediated signaling, sensitizes T-ALL cells to treatment with dexamethasone and can induce cell death per se. The antibody also promotes antibody-dependent natural killer-mediated leukemia cytotoxicity in vitro and delays T-cell leukemia development in vivo, reducing tumor burden and promoting mouse survival. B12 is rapidly internalized and traffics to the lysosome, rendering it an attractive vehicle for targeted intracellular delivery of cytotoxic cargo. Consequently, we engineered a B12–MMAE antibody–drug conjugate and provide proof-of-concept evidence that it has increased leukemia cell killing abilities as compared with the naked antibody. Our studies serve as a stepping stone for the development of novel targeted therapies in T-ALL and other diseases where IL-7Rα has a pathological role. ISSN:1476-5551 ISSN:0887-6924