Rational design of humanized antibody inhibitors for cathepsin S.

Cathepsin S (CTSS) is involved in pathogenesis of many human diseases. Inhibitors blocking its protease activity hold therapeutic potential. In comparison to small-molecule inhibitors, monoclonal antibodies capable of inhibiting CTSS enzymatic activity may possess advantageous pharmacological properties. Here we designed and produced inhibitory antibodies targeting human CTSS by genetically fusing the propeptide of procathepsin S (proCTSS) with antibodies in clinic. The resulting antibody fusions in full-length or fragment antigen-binding format could be stably expressed and potently inhibit CTSS proteolytic activity in high specificity. These fusion antibodies not only demonstrate a new approach for facile synthesis of antibody inhibitors against CTSS, but also represent novel anti-CTSS therapeutic candidates.

Eliciting anti-cancer immunity by genetically engineered multifunctional exosomes.

Exosomes are cell-derived nanovesicles involved in regulating intercellular communications. In contrast to conventional nanomedicines, exosomes are characterized by unique advantages for therapeutic development. Despite their major successes in drug delivery, the full potential of exosomes for immunotherapy remains untapped. Herein we designed genetically engineered exosomes featured with surfaced-displayed antibody targeting groups and immunomodulatory proteins. Through genetic fusions with exosomal membrane proteins, Expi293F cell-derived exosomes were armed with monoclonal antibodies specific for human T-cell CD3 and epidermal growth factor receptor (EGFR) as well as immune checkpoint modulators, programmed death 1 (PD-1) and OX40 ligand (OX40L). The resulting genetically engineered multifunctional immune-modulating exosomes (GEMINI-Exos) can not only redirect and activate T cells toward killing EGFR-positive triple negative breast cancer (TNBC) cells but also elicit robust anti-cancer immunity, giving rise to highly potent inhibition against established TNBC tumors in mice. GEMINI-Exos represent candidate agents for immunotherapy and may offer a general strategy for generating exosome-based immunotherapeutics with desired functions and properties.

Expanding the toolbox of exosome-based modulators of cell functions.

Exosomes are cell-derived extracellular vesicles and play important roles in mediating intercellular communications. Due to their unique advantages in transporting a variety of biomolecules, exosomes have been emerging as a new class of nanocarriers with great potential for therapeutic applications. Despite advancements in loading chemotherapeutics and interfering RNAs into exosomes, active incorporation of protein molecules into exosomes remains challenging owing to their distinctive physicochemical properties and/or a lack of knowledge of cargo sorting during exosome biogenesis. Here we report the generation of a novel type of engineered exosomes with actively incorporated membrane proteins or soluble protein cargos, named genetically infused functionally tailored exosomes (GIFTed-Exos). Through genetic fusion with exosome-associated tetraspanin CD9, transmembrane protein CD70 and glucocorticoid-induced tumor necrosis factor receptor family-related ligand (GITRL) could be displayed on exosome surface, resulting in GIFTed-Exos with excellent T-cell co-stimulatory activities. By genetically linking to a CD9-photocleavable protein fusion, fluorescent protein mCherry, apoptosis-inducing protein apoptin, and antioxidant enzyme catalase could be effectively packed into exosomes for light-controlled release. The generated GIFTed-Exos display notable in vitro and in vivo activities for delivering distinct types of protein cargos to target cells. As a possibly general approach, GIFTed-Exos provide new opportunities to create exosomes with new functions and properties for biomedical research.

A two-trick pony: lysosomal protease cathepsin B possesses surprising ligase activity.

Cathepsin B is an important protease within the lysosome, where it helps recycle proteins to maintain proteostasis. It is also known to degrade proteins elsewhere but has no other known functionality. However, by carefully monitoring peptide digestion with liquid chromatography and mass spectrometry, we observed the synthesis of novel peptides during cathepsin B incubations. This ligation activity was explored further with a variety of peptide substrates to establish mechanistic details and was found to operate through a two-step mechanism with proteolysis and ligation occurring separately. Further explorations using varied sequences indicated increased affinity for some substrates, though all were found to ligate to some extent. Finally, experiments with a proteolytically inactive form of the enzyme yielded no ligation, indicating that the ligation reaction occurs in the same active site but in the reverse direction of proteolysis. These results clearly establish that in its native form cathepsin B can act as both a protease and ligase, although protease action eventually dominates over longer periods of time.

Site-specific antibody-drug conjugates with variable drug-to-antibody-ratios for AML therapy.

Random conjugations of chemotherapeutics to monoclonal antibodies result in heterogeneous antibody-drug conjugates (ADCs) with suboptimal pharmacological properties. We recently developed a new technology for facile generation of homogeneous ADCs by harnessing human CD38 catalytic domain and its dinucleotide-derived covalent inhibitor, termed ADP-ribosyl cyclase-enabled ADCs (ARC-ADCs). Herein we advance this technology by designing and synthesizing ARC-ADCs with customizable drug-to-antibody ratios (DARs). Through varying numbers and locations of CD38 fused to an antibody targeting human C-type lectin-like molecule-1 (hCLL-1), ARC-ADCs featuring DARs of 2 and 4 were rapidly generated via a single step with cytotoxic monomethyl auristatin F (MMAF) as payloads. In contrast to anti-hCLL-1 ARC-ADC carrying 2 drug molecules, anti-hCLL-1 ARC-ADC with a DAR of 4 shows highly potent activity in killing hCLL-1-positive acute myeloid leukemia (AML) cells both in vitro and in vivo. This work provides novel ADC candidates for combating AML and supports ARC-ADC as a general and versatile approach for producing site-specific ADCs with defined DARs.

Synthesis of site-specific antibody-drug conjugates by ADP-ribosyl cyclases.

Most of the current antibody-drug conjugates (ADCs) in clinic are heterogeneous mixtures. To produce homogeneous ADCs, established procedures often require multiple steps or long reaction times. The introduced mutations or foreign sequences may cause high immunogenicity. Here, we explore a new concept of transforming CD38 enzymatic activity into a facile approach for generating site-specific ADCs. This was achieved through coupling bifunctional antibody-CD38 fusion proteins with designer dinucleotide-based covalent inhibitors with stably attached payloads. The resulting adenosine diphosphate-ribosyl cyclase-enabled ADC (ARC-ADC) with a drug-to-antibody ratio of 2 could be rapidly generated through single-step conjugation. The generated ARC-ADC targeting human epidermal growth factor receptor 2 (HER2) displays excellent stability and potency against HER2-positive breast cancer both in vitro and in vivo. This proof-of-concept study demonstrates a new strategy for production of site-specific ADCs. It may provide a general approach for the development of a novel class of ADCs with potentially enhanced properties.

Rational Design of a Humanized Antibody Inhibitor of Cathepsin B.

Cathepsin B (CTSB) is an abundant cysteine protease that functions in both endolysosomal compartments and extracellular regions. A considerable number of preclinical and clinical studies indicate that CTSB is implicated in many human diseases. Expression levels and activity of CTSB significantly correlate with disease progression and severity. Current inhibitors of CTSB are lack of adequate specificity and pharmacological activities. Through structure-guided rational design, we hereby designed and generated a humanized antibody inhibitor targeting human CTSB. This was achieved by genetically fusing the propeptide of procathepsin B, a naturally occurring inhibitor of CTSB, into heavy chain complementarity-determining region 3 (CDR3H) of Herceptin that is used in the clinic for the treatment of breast cancer. The resulting antibody-propeptide fusion displayed high specificity for inhibiting CTSB proteolytic activity at nanomolar levels. Pharmacokinetic studies in mice revealed a plasma half-life of approximately 42 h for this anti-CTSB antibody inhibitor, comparable to that of the parental Herceptin scaffold. This study demonstrates a new approach for the efficient generation of humanized antibody inhibitors with high potency and specificity for human CTSB, which may be extended to develop antibody inhibitors against other disease relevant cathepsin proteases.

A ribose-functionalized NAD+ with unexpected high activity and selectivity for protein poly-ADP-ribosylation.

Nicotinamide adenine dinucleotide (NAD+)-dependent ADP-ribosylation plays important roles in physiology and pathophysiology. It has been challenging to study this key type of enzymatic post-translational modification in particular for protein poly-ADP-ribosylation (PARylation). Here we explore chemical and chemoenzymatic synthesis of NAD+ analogues with ribose functionalized by terminal alkyne and azido groups. Our results demonstrate that azido substitution at 3'-OH of nicotinamide riboside enables enzymatic synthesis of an NAD+ analogue with high efficiency and yields. Notably, the generated 3'-azido NAD+ exhibits unexpected high activity and specificity for protein PARylation catalyzed by human poly-ADP-ribose polymerase 1 (PARP1) and PARP2. And its derived poly-ADP-ribose polymers show increased resistance to human poly(ADP-ribose) glycohydrolase-mediated degradation. These unique properties lead to enhanced labeling of protein PARylation by 3'-azido NAD+ in the cellular contexts and facilitate direct visualization and labeling of mitochondrial protein PARylation. The 3'-azido NAD+ provides an important tool for studying cellular PARylation.

Chemoenzymatic Preparation of 4'-Thioribose NAD.

This chemoenzymatic procedure describes a strategy for the preparation of 4'-thioribose nicotinamide adenine dinucleotide (S-NAD+ ), including chemical synthesis of nicotinamide 4'-riboside (S-NR), recombinant expression and purification of two NAD+ biosynthesis enzymes nicotinamide riboside kinase (NRK) and nicotinamide mononucleotide adenylyltransferase (NMNAT), and enzymatic synthesis of S-NAD+ . The first basic protocol describes the procedures for introduction of nicotinamide onto 4'-thioribose and subsequent deprotection to generate S-NR as the key intermediate for enzymatically synthesizing S-NAD+ . In the second basic protocol, experimental methods are detailed for the production of recombinant human NRK1 and NMNAT1 to catalyze conversion of S-NR to S-NAD+ . The third basic protocol presents the enzymatic approach for the generation of S-NAD+ from S-NR precursor. © 2019 by John Wiley & Sons, Inc.

Facile chemoenzymatic synthesis of a novel stable mimic of NAD.

Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor participating in a variety of important enzyme-catalyzed physiological and pathophysiological processes. Analogues of NAD+ provide key and valuable agents for investigating NAD+-dependent enzymes. In this study, we report the preparation of a novel stable NAD+ mimic, 4'-thioribose NAD+ (S-NAD+), using a facile and efficient chemoenzymatic approach. Substrate activity assays indicated the resulting S-NAD+ is chemically inert to human CD38 and sirtuin 2 enzymes, but capable of participating in redox reactions in a manner similar to NAD+. X-ray crystallographic analysis revealed binding of S-NAD+ to the active site of human CD38 and critical residues involved in leaving group activation and catalysis. By more closely mimicking NAD+ in geometry and electrostatics, the generated S-NAD+ offers a unique and important tool that can be extended to study enzymes utilizing NAD+.