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Antibody-drug conjugates (ADCs) are an established modality for the tissue-specific delivery of chemotherapeutics. However, due to the hydrophobic nature of many cytotoxic payloads, challenges remain in developing chemically stable ADCs with high drug loading. In previous studies, payload structure, unique stimuli-responsive chemistries, and PEGylated cross-linkers have been used to decrease ADC hydrophobicity. In this work, we investigate the effect of a new parameter, cross-linker sequence. A support-free synthesis of PEGylated, sequence-defined cross-linkers was developed and applied to the synthesis of three constitutionally isomeric ADCs containing PEG side chains and a monomethyl auristatin E payload. Placement of PEG side chains distally from the payload was found to yield an ADC with altered hydrophilicity, antigen binding, and in vitro potency. This work establishes a versatile method for synthesizing multifunctional cross-linkers and identifies cross-linker sequence as a new handle for modulating the performance of ADCs.

A promising molecular target for aggressive cancers is the urokinase receptor (uPAR). A fully human, recombinant antibody that binds uPAR to form a stable complex that blocks uPA-uPAR interactions (2G10) and is internalized primarily through endocytosis showed efficacy in a mouse xenograft model of highly aggressive, triple negative breast cancer (TNBC). Antibody-drug conjugates (ADCs) of 2G10 were designed and produced bearing tubulin inhibitor payloads ligated through seven different linkers. Aldehyde tag technology was employed for linking, and either one or two tags were inserted into the antibody heavy chain, to produce site-specifically conjugated ADCs with drug-to-antibody ratios of either two or four. Both cleavable and non-cleavable linkers were combined with two different antimitotic toxins—MMAE (monomethylauristatin E) and maytansine. Nine different 2G10 ADCs were produced and tested for their ability to target uPAR in cell-based assays and a mouse model. The anti-uPAR ADC that resulted in tumor regression comprised an MMAE payload with a cathepsin B cleavable linker, 2G10-RED-244-MMAE. This work demonstrates in vitro activity of the 2G10-RED-244-MMAE in TNBC cell lines and validates uPAR as a therapeutic target for TNBC.

Use of the formylglycine generating enzyme (FGE)-a copper-dependent posttranslational protein modifier-represents a particularly elegant method taken directly from nature of introducing a unique amino acid into the larger context of a protein. Formylglycine (fGly) is a crucial component of the active site of sulfatases, where it directly participates in the breakdown of sulfate ester substrates. In the context of bioconjugation this aldehyde containing amino acid can be an invaluable reactive handle for the chemical conjugation of molecules. Here we describe a detailed method for generating formylglycine-containing proteins in a mammalian system developed specifically for the production of antibody-drug conjugates (ADCs) but applicable to a wide range of proteins.

Oncology treatment has been revolutionized by the introduction of immune checkpoint inhibitor drugs, which enable 20–40% of patients to generate anti-tumor immune responses. Combination treatment approaches with chemotherapeutic drugs may enable responses in the remaining patient cohorts. In this regard, a handful of drugs are promising due to their ability to induce immunogenic cell death in target cells. However, these agents are systemically delivered and indiscriminately cytotoxic to proliferating cells. By contrast, antibody-drug conjugates can selectively deliver a cytotoxic payload to a tumor, sparing most healthy cells. The ability of antibody-drug conjugates to induce immunogenic cell death in target cells has not yet been determined, although preclinical in vivo studies suggest this possibility. Here, we describe for the first time production of the in vitro hallmarks of immunogenic cell death – ecto-calreticulin and secreted ATP and HMGB1 protein – by cells in response to treatment with antibody-drug conjugates bearing a maytansine payload.

Background: Aerobic formylglycine-generating enzyme (FGE) converts cysteine to formylglycine in vivo. Results: Purified FGE requires preactivation with copper to convert cysteine to formylglycine in vitro. Conclusion: FGE is a metalloenzyme. It is also a useful biocatalyst for the production of proteins that contain aldehyde tags. Significance: Understanding FGE biochemistry informs research on sulfatases and enables expanded biotechnology applications of the aldehyde tag., To further our aim of synthesizing aldehyde-tagged proteins for research and biotechnology applications, we developed methods for recombinant production of aerobic formylglycine-generating enzyme (FGE) in good yield. We then optimized the FGE biocatalytic reaction conditions for conversion of cysteine to formylglycine in aldehyde tags on intact monoclonal antibodies. During the development of these conditions, we discovered that pretreating FGE with copper(II) is required for high turnover rates and yields. After further investigation, we confirmed that both aerobic prokaryotic (Streptomyces coelicolor) and eukaryotic (Homo sapiens) FGEs contain a copper cofactor. The complete kinetic parameters for both forms of FGE are described, along with a proposed mechanism for FGE catalysis that accounts for the copper-dependent activity.

Genetic fusions of either full enzymes or peptide tags with a protein of interest have enabled the synthesis of protein conjugates with precise control over the site of attachment and number of payloads incorporated. Engineering of protein glycans, depending on the application, can lead to similar control for nonengineered glycoproteins. Recent advances in the field of chemoenzymatic modifications of proteins for site-specific protein conjugation will be reviewed. These techniques have been used in an array of fields for the execution of innovative and valuable experiments. Specific industrial applications of these technologies will be highlighted.

It is becoming increasingly clear that site-specific conjugation offers significant advantages over conventional conjugation chemistries used to make antibody–drug conjugates (ADCs). Site-specific payload placement allows for control over both the drug-to-antibody ratio (DAR) and the conjugation site, both of which play an important role in governing the pharmacokinetics (PK), disposition, and efficacy of the ADC. In addition to the DAR and site of conjugation, linker composition also plays an important role in the properties of an ADC. We have previously reported a novel site-specific conjugation platform comprising linker payloads designed to selectively react with site-specifically engineered aldehyde tags on an antibody backbone. This chemistry results in a stable C–C bond between the antibody and the cytotoxin payload, providing a uniquely stable connection with respect to the other linker chemistries used to generate ADCs. The flexibility and versatility of the aldehyde tag conjugation platform has enabled us to undertake a systematic evaluation of the impact of conjugation site and linker composition on ADC properties. Here, we describe the production and characterization of a panel of ADCs bearing the aldehyde tag at different locations on an IgG1 backbone conjugated using Hydrazino-iso-Pictet-Spengler (HIPS) chemistry. We demonstrate that in a panel of ADCs with aldehyde tags at different locations, the site of conjugation has a dramatic impact on in vivo efficacy and pharmacokinetic behavior in rodents; this advantage translates to an improved safety profile in rats as compared to a conventional lysine conjugate.

Background The ability to site-specifically conjugate a protein to a payload of interest (e.g., a fluorophore, small molecule pharmacophore, oligonucleotide, or other protein) has found widespread application in basic research and drug development. For example, antibody-drug conjugates represent a class of biotherapeutics that couple the targeting specificity of an antibody with the chemotherapeutic potency of a small molecule drug. While first generation antibody-drug conjugates (ADCs) used random conjugation approaches, next-generation ADCs are employing site-specific conjugation. A facile way to generate site-specific protein conjugates is via the aldehyde tag technology, where a five amino acid consensus sequence (CXPXR) is genetically encoded into the protein of interest at the desired location. During protein expression, the Cys residue within this consensus sequence can be recognized by ectopically-expressed formylglycine generating enzyme (FGE), which converts the Cys to a formylglycine (fGly) residue. The latter bears an aldehyde functional group that serves as a chemical handle for subsequent conjugation. Results The yield of Cys conversion to fGly during protein production can be variable and is highly dependent on culture conditions. We set out to achieve consistently high yields by modulating culture conditions to maximize FGE activity within the cell. We recently showed that FGE is a copper-dependent oxidase that binds copper in a stoichiometric fashion and uses it to activate oxygen, driving enzymatic turnover. Building upon that work, here we show that by supplementing cell culture media with copper we can routinely reach high yields of highly converted protein. We demonstrate that cells incorporate copper from the media into FGE, which results in increased specific activity of the enzyme. The amount of copper required is compatible with large scale cell culture, as demonstrated in fed-batch cell cultures with antibody titers of 5 g · L−1, specific cellular production rates of 75 pg · cell−1 · d−1, and fGly conversion yields of 95–98 %. Conclusions We describe a process with a high yield of site-specific formylglycine (fGly) generation during monoclonal antibody production in CHO cells. The conversion of Cys to fGly depends upon the activity of FGE, which can be ensured by supplementing the culture media with 50 uM copper(II) sulfate. Electronic supplementary material The online version of this article (doi:10.1186/s12896-016-0254-0) contains supplementary material, which is available to authorized users.

Glyco-optimization (OPopS TM ) of aminoglycosides has been performed by replacing the existing sugar moiety with a variety of sugar derivatives. Glycosylation of the 6-position of nebramine provided a library of novel 4,6-linked aminoglycosides (AMGs). Among them, compounds 8b , g , i , l , and 8u with 2″-amino, 2″,3″-diamino, 2″,4″-diamino, 3″,4″-diamino, 3″-amino groups, respectively, showed significant antimicrobial activity against Gram-(+) and -(−) bacteria. Several were particularly potent against Pseudomonus aeruginosa with MICs in the 1–2 μg/mL range.

Heterobifunctional protein fusions are gaining interest as next-generation biopharmaceuticals.1–5 Combining proteins with disparate functions can enable multidrug therapy with a single chemical entity,6, 7 add a targeting element to an otherwise nonspecific therapeutic,8, 9 or improve the pharmacokinetic profile of a rapidly cleared molecule.10, 11 Indeed, heterobifunctional proteins, such as immunoglobulin G (IgG) Fc domain fusions, are among the top-selling biotherapeutics on the market today.12 These biomolecules are primarily generated as genetic fusions. The DNA sequences that encode the individual protein components are fused in tandem to direct the expression of a single polypeptide that comprises the two proteins joined together at their N and C termini, respectively. However, this limited topology is not ideal for every protein combination, as some polypeptides require unmodified termini for optimal bioactivity13 or can suffer from expression difficulties as a result of folding and processing issues.3, 14, 15

Click to view: Glycopolymers can be used to display glycans on microarrays in native-like architectures. The structurally uniform alkyne-terminated mucin mimetic glycopolymers (see picture; TR = fluorophore) were printed on azide-functionalized chips by microcontact printing in the presence of a copper catalyst. The surface-bound glycopolymers bind lectins in a ligand-specific manner.

The properties of therapeutic proteins can be enhanced by chemical modification. Methods for site-specific protein conjugation are critical to such efforts. Here, we demonstrate that recombinant proteins expressed in mammalian cells can be site-specifically modified by using a genetically encoded aldehyde tag. We introduced the peptide sequence recognized by the endoplasmic reticulum (ER)-resident formylglycine generating enzyme (FGE), which can be as short as 6 residues, into heterologous proteins expressed in mammalian cells. Cotranslational modification of the proteins by FGE produced products bearing a unique aldehyde group. Proteins bearing this “aldehyde tag” were chemically modified by selective reaction with hydrazide- or aminooxy-functionalized reagents. We applied the technique to site-specific modification of monoclonal antibodies, the fastest growing class of biopharmaceuticals, as well as membrane-associated and cytosolic proteins expressed in mammalian cells.

The controlled addition of structurally defined components to live cell membranes can facilitate the molecular level analysis of cell surface phenomena. Here we demonstrate that cell surfaces can be engineered to display synthetic bioactive polymers at defined densities by exogenous membrane insertion. The polymers were designed to mimic native cell-surface mucin glycoproteins, which are defined by their dense glycosylation patterns and rod-like structures. End-functionalization with a hydrophobic anchor permitted incorporation into the membranes of live cultured cells. We probed the dynamic behavior of cell-bound glycopolymers bearing various hydrophobic anchors and glycan structures using fluorescence correlation spectroscopy (FCS). Their diffusion properties mirrored those of many natural membrane-associated biomolecules. Furthermore, the membrane-bound glycopolymers were internalized into early endosomes similarly to endogenous membrane components and were capable of specific interactions with protein receptors. This system provides a platform to study cell-surface phenomena with a degree of chemical control that cannot be achieved using conventional biological tools.

Mycobacteria, including persistent pathogens like Mycobacterium tuberculosis, have an unusual membrane structure in which, outside the plasma membrane, a nonfluid hydrophobic fatty acid layer supports a fluid monolayer rich in glycolipids such as trehalose 6,6′-dimycolate (TDM; cord factor). Given the abilities of mycobacteria to survive desiccation and trehalose in solution to protect biomolecules and whole organisms during freezing, drying, and other stresses, we hypothesized that TDM alone may suffice to confer dehydration resistance to the membranes of which it is a constituent. We devised an experimental model that mimics the structure of mycobacterial envelopes in which an immobile hydrophobic layer supports a TDM-rich, two-dimensionally fluid leaflet. We have found that TDM monolayers, in stark contrast to phospholipid membranes, can be dehydrated and rehydrated without loss of integrity, as assessed by fluidity and protein binding. Strikingly, this protection from dehydration extends to TDM-phospholipid mixtures with as little as 25mol % TDM. The dependence of the recovery of membrane mobility upon rehydration on TDM fraction shows a functional form indicative of spatial percolation, implying that the connectivity of TDM plays a crucial role in membrane preservation. Our observations are the first reported instance of dehydration resistance provided by a membrane glycolipid.

[reaction: see text] The neuraminic acid derivative 5 is readily converted in several steps to the neuraminic acid dimer 12, linked through the hydroxyl of a 5-N-glycolyl group in an alpha-2,5 glycosidic linkage. The sequence is shown to proceed through a spirocyclic intermediate 9 by in situ NMR experiments. Similar derivatives of N-glycolylneuraminic acid (Neu5Gc), including polymers, have been identified from marine sources, including starfish and sea urchins, often as sulfated derivatives and are thought to mediate sperm-egg recognition.

The covalent binding of an aldehyde side-chain containing protein to a lipid with an aminooxy -modified head group opens a versatile avenue to bio-functionalize lipid membranes without compromising function and dynamic properties of both the protein and the lipid membrane. It was recently found that the site-specific insertion of a 6 amino acid consensus sequence into a protein is sufficient to target it for post-translational modification by formylglycine-generating enzyme (FGE). FGE will enzymatically turn the cysteine in the consensus motif into a formylglycine, thus leading to the site-specific introduction of an aldehyde side chain for further chemical modification. We have engineered the consensus sequence to the C-terminus of an Enhanced Green Fluorescence Protein (EGFP) which was co-expressed with FGE in E. Coli. Lipids were chemically modified to bear a reactive aminooxy group and then conjugated with the aldehyde tagged EGFP. The resulting EGFP-lipid constructs were successfully incorporated into solid supported lipid bilayer as verified by fluorescence microscopy. Membrane integrity as well as protein and lipid motilities were investigated using both fluorescence recovery after photo-bleaching and fluorescence correlation spectroscopy. In order to determine integration efficiency, the surface concentration of EGFP-lipid constructs was monitored as a function of their solution concentration and incubation time. This site specific lipidation strategy promises to allow for the use of a variety of possible lipid anchors as well as to provide unprecedented freedom in the choice of the lipidation site on the protein.

L-selectin mediates lymphocyte homing by facilitating lymphocyte adhesion to addressins expressed in the high endothelial venules (HEV) of secondary lymphoid organs. Peripheral node addressin recognized by the MECA-79 antibody is apparently part of the L-selectin ligand, but its chemical nature has been undefined. We now identify a sulfated extended core1 mucin-type O-glycan, Gal beta 1-->4(sulfo-->6)GlcNAc beta 1-->3Gal beta 1-->3GalNAc, as the MECA-79 epitope. Molecular cloning of a HEV-expressed core1-beta 1,3-N-acetylglucosaminyltransferase (Core1-beta 3GlcNAcT) enabled the construction of the 6-sulfo sialyl Lewis x on extended core1 O-glycans, recapitulating the potent L-selectin-mediated, shear-dependent adhesion observed with novel L-selectin ligands derived from core2 beta1,6-N-acetylglucosaminyltransferase-I null mice. These results identify Core1-beta 3GlcNAcT and its cognate extended core1 O-glycans as essential participants in the expression of the MECA-79-positive, HEV-specific L-selectin ligands required for lymphocyte homing.

We have recently demonstrated that the glycolipid trehalose dimycolate (TDM), a major outer membrane component of dehydration resistant Mycobacterium tuberculosis (MTb), can impart significant dehydration resistance to supported phospholipid membranes. We now report studies of other, related glycolipids both natural and synthetic that exhibit behavior similar to TDM, conferring protection from desiccation to membranes of which they are constituents. We examined solid-supported lipid monolayers, characterizing membrane integrity and two-dimensional fluidity before and after de- and re-hydration with fluorescence imaging and fluorescence recovery after photobleaching (FRAP). As with TDM, the degree of protection is dependent on the fraction of synthetic lipid in the monolayer and there is a distinct minimum fraction needed for protection by each glycolipid. We can control the synthetic lipid fluidity and minimum protecting fraction by designing and synthesizing lipids with particular hydrophobic chain lengths, saturation, and branching, thereby illuminating the role of molecular structure in biophysical function. The advent of these synthetic, protective glycolipids opens the door to the creation of lipid bilayers and liposomes since the relevant hydrophobic and hydrophilic domain sizes can be controlled. These new structures allow investigations of the physical origins of well-known mycobacaterial properties beyond dehydration resistance in controlled experimental contexts, such as the inhibition of membrane fusion.