Expanding the Versatility of Microbial Transglutaminase Using α-Effect Nucleophiles as Noncanonical Substrates

Injectable glucose oxidase-immobilized gelatin hydrogel prevents tumor recurrence via oxidation therapy

In clinical practice, surgery is the preferred treatment for breast cancer; however, the high recurrence rate due to residual tumors after surgery remains a major issue. Hydrogels can reduce the side effects of residual tumors and exert strong anticancer effects, thereby showing potential as therapeutic agents for suppressing tumor recurrence after surgery. Glucose oxidase (GOD)-immobilized gelatin hydrogels (GOD-gelatin hydrogel) were prepared by bioorthogonal click chemistry. Then, the anticancer effect, tumor recurrence inhibition, and biodegradability of the resulting hydrogels were evaluated through cell and animal experiments. GOD-gelatin hydrogel showed cytotoxicity and anticancer effect via H2O2 generation. Unlike free GOD, GOD-gelatin hydrogel remained in the surgical site after implant and continued to suppress tumor recurrence over time. The proposed GOD-gelatin hydrogel system can be easily implanted at the surgical site after tumor surgery, representing a novel treatment to suppress tumor recurrence without any systemic toxicity.

The Evolving Landscape of Antibody-Drug Conjugates: In Depth Analysis of Recent Research Progress

Antibody-drug conjugates (ADCs) are targeted immunoconjugate constructs that integrate the potency of cytotoxic drugs with the selectivity of monoclonal antibodies, minimizing damage to healthy cells and reducing systemic toxicity. Their design allows for higher doses of the cytotoxic drug to be administered, potentially increasing efficacy. They are currently among the most promising drug classes in oncology, with efforts to expand their application for nononcological indications and in combination therapies. Here we provide a detailed overview of the recent advances in ADC research and consider future directions and challenges in promoting this promising platform to widespread therapeutic use. We examine data from the CAS Content Collection, the largest human-curated collection of published scientific information, and analyze the publication landscape of recent research to reveal the exploration trends in published documents and to provide insights into the scientific advances in the area. We also discuss the evolution of the key concepts in the field, the major technologies, and their development pipelines with company research focuses, disease targets, development stages, and publication and investment trends. A comprehensive concept map has been created based on the documents in the CAS Content Collection. We hope that this report can serve as a useful resource for understanding the current state of knowledge in the field of ADCs and the remaining challenges to fulfill their potential.

Design and Characterization of Immune-Stimulating Imidazo[4,5-c]quinoline Antibody-Drug Conjugates

Traditional antibody-drug conjugate (ADC) technology has employed tumor-targeting antibodies to selectively deliver ultrapotent cytotoxins to tumor tissue. While this technology has been highly successful, resulting in the FDA approval of over 10 ADCs, the field continues to struggle with modest efficacy and significant off-target toxicity. Concurrent with the struggles of the ADC field, a new generation of immune-activating therapeutics has arisen, most clearly exemplified by the PD-1/PD-L1 inhibitors that are now part of standard-of-care treatment regimens for a variety of cancers. The success of these immuno-oncology therapeutic agents has prompted the investigation of a variety of new immuno-stimulant approaches, including toll-like receptor (TLR) activators. Herein, we describe the optimization of ADC technology for the selective delivery of a potent series of TLR7 agonists. A series of imidazole[4,5-c]quinoline agonists (as exemplified by compound 1) were shown to selectively agonize the human and mouse TLR7 receptor at low nanomolar concentrations, resulting in the release of IFNα from human peripheral blood mononuclear cells (hPBMCs) and the upregulation of CD86 on antigen-presenting cells. Compound 1 was attached to a deglycosylated (Fc-γ null) HER2-targeting antibody via a cleavable linker, resulting in an ADC (anti-HER2_vc-1) that potently and selectively activated the TLR7 pathway in tumor-associated macrophages via a "bystander" mechanism. We demonstrated that this ADC rapidly released the TLR7 agonist into the media when incubated with HER2+ cells. This release was not observed upon incubation with an isotype control ADC and furthermore was suppressed by co-administration of the naked antibody. In co-culture experiments with HER2+ HCC1954 cells, this ADC induced the activation of the NFκB pathway in mouse macrophages and the release of IFNα from hPBMCs, while a corresponding isotype control ADC did not. Finally, we demonstrated that IP administration of anti-HER2_vc-1 induced complete tumor regression in an HCC1954 xenograft study in SCID beige mice. Unlike related ADC technology that has been reported recently, our technology relies on the passive diffusion of the TLR7 agonist into tumor-associated macrophages rather than Fc-γ-mediated uptake. Based on these observations, we believe that this ADC technology holds significant potential for both oncology and infectious disease applications.

Diverse protein manipulations with genetically encoded glutamic acid benzyl ester

Site-specific modification of proteins has significantly advanced the use of proteins in biological research and therapeutics development. Among various strategies aimed at this end, genetic code expansion (GCE) allows structurally and functionally distinct non-canonical amino acids (ncAAs) to be incorporated into specific sites of a protein. Herein, we genetically encode an esterified glutamic acid analogue (BnE) into proteins, and demonstrate that BnE can be applied in different types of site-specific protein modifications, including N-terminal pyroglutamation, caging Glu in the active site of a toxic protein, and endowing proteins with metal chelator hydroxamic acid and versatile reactive handle acyl hydrazide. Importantly, novel epigenetic mark Gln methylation is generated on histones via the derived acyl hydrazide handle. This work provides useful and unique tools to modify proteins at specific Glu or Gln residues, and complements the toolbox of GCE.

Enzymatic Methods for the Site-Specific Radiolabeling of Targeting Proteins

Site-specific conjugation of proteins is currently required to produce homogenous derivatives for medicine applications. Proteins derivatized at specific positions of the polypeptide chain can actually show higher stability, superior pharmacokinetics, and activity in vivo, as compared with conjugates modified at heterogeneous sites. Moreover, they can be better characterized regarding the composition of the derivatization sites as well as the conformational and activity properties. To this aim, several site-specific derivatization approaches have been developed. Among these, enzymes are powerful tools that efficiently allow the generation of homogenous protein-drug conjugates under physiological conditions, thus preserving their native structure and activity. This review will summarize the progress made over the last decade on the use of enzymatic-based methodologies for the production of site-specific labeled immunoconjugates of interest for nuclear medicine. Enzymes used in this field, including microbial transglutaminase, sortase, galactosyltransferase, and lipoic acid ligase, will be overviewed and their recent applications in the radiopharmaceutical field will be described. Since nuclear medicine can benefit greatly from the production of homogenous derivatives, we hope that this review will aid the use of enzymes for the development of better radio-conjugates for diagnostic and therapeutic purposes.

Enzyme-Agnostic Lysosomal Screen Identifies New Legumain-Cleavable ADC Linkers

Over the past two decades, antibody drug conjugates (ADCs) and small molecule drug conjugates (SMDCs) have widely employed valine-citruline and related cathepsin-cleavable linkers due to their stability in plasma and their rapid cleavage by lysosomal cathepsins. However, a number of recent studies have illustrated that these linkers are subject to cleavage by exogenous enzymes such as Ces1C and neutrophil elastase, thus resulting in off-target release of drug. As such, there is a need to diversify the portfolio of ADC linkers in order to overcome nonspecific drug release. Rather than targeting cathepsins, we began with an "enzyme agnostic" screen in which a panel of 75 peptide FRET pairs were screened for cleavage in lysosomal extracts and in plasma. Unexpectedly, a series of Asn-containing peptides emerged from this screen as being cleaved far more quickly than traditional ValCit-type linkers while retaining excellent stability in plasma. Catabolism studies demonstrated that these linkers were cleaved by legumain, an asparaginyl endopeptidase that is overexpressed in a variety of cancers and is known to be present in the lysosome. MMAE-containing ADCs that incorporated these new linkers were shown to exhibit highly potent and selective cytotoxicity, comparable to analogous ValCit ADCs. Importantly, the Asn-containing linkers were shown to be completely stable to human neutrophil elastase, an enzyme thought to be responsible for the neutropenia and thrombocytopenia associated with ValCitPABC-MMAE ADCs. The legumain-cleavable ADCs were shown to have excellent stability in both mouse and human serum, retaining >85% of the drug after 1 week of incubation. Moreover, the corresponding small molecule FRET pairs exhibited <10% cleavage after 18 h in mouse and human serum. On the basis of these results, we believe that these new linkers (AsnAsn in particular) have significant potential in both ADC and SMDC drug delivery applications.

A tailored phosphoaspartate probe unravels CprR as a response regulator in Pseudomonas aeruginosa interkingdom signaling

Pseudomonas aeruginosa is a difficult-to-treat Gram-negative bacterial pathogen causing life-threatening infections. Adaptive resistance (AR) to cationic peptide antibiotics such as polymyxin B impairs the therapeutic success. This self-protection is mediated by two component systems (TCSs) consisting of a membrane-bound histidine kinase and an intracellular response regulator (RR). As phosphorylation of the key RR aspartate residue is transient during signaling and hydrolytically unstable, the study of these systems is challenging. Here, we apply a tailored reverse polarity chemical proteomic strategy to capture this transient modification and read-out RR phosphorylation in complex proteomes using a nucleophilic probe. In-depth mechanistic insights into an ideal trapping strategy were performed with a recombinant RR demonstrating the importance of fine-tuned acidic pH values to facilitate the attack on the aspartate carbonyl C-atom and prevent unproductive hydrolysis. Analysis of Bacillus subtilis and P. aeruginosa proteomes revealed the detection of multiple annotated phosphoaspartate (pAsp) sites of known RRs in addition to many new potential pAsp sites. With this validated strategy we dissected the signaling of dynorphin A, a human peptide stress hormone, which is sensed by P. aeruginosa to prepare AR. Intriguingly, our methodology identified CprR as an unprecedented RR in dynorphin A interkingdom signaling.

Site-selective modification strategies in antibody-drug conjugates

Antibody-drug conjugates (ADCs) harness the highly specific targeting capabilities of an antibody to deliver a cytotoxic payload to specific cell types. They have garnered widespread interest in drug discovery, particularly in oncology, as discrimination between healthy and malignant tissues or cells can be achieved. Nine ADCs have received approval from the US Food and Drug Administration and more than 80 others are currently undergoing clinical investigations for a range of solid tumours and haematological malignancies. Extensive research over the past decade has highlighted the critical nature of the linkage strategy adopted to attach the payload to the antibody. Whilst early generation ADCs were primarily synthesised as heterogeneous mixtures, these were found to have sub-optimal pharmacokinetics, stability, tolerability and/or efficacy. Efforts have now shifted towards generating homogeneous constructs with precise drug loading and predetermined, controlled sites of attachment. Homogeneous ADCs have repeatedly demonstrated superior overall pharmacological profiles compared to their heterogeneous counterparts. A wide range of methods have been developed in the pursuit of homogeneity, comprising chemical or enzymatic methods or a combination thereof to afford precise modification of specific amino acid or sugar residues. In this review, we discuss advances in chemical and enzymatic methods for site-specific antibody modification that result in the generation of homogeneous ADCs.

Site-specific conjugation of native antibody

Traditionally, non-specific chemical conjugations, such as acylation of amines on lysine or alkylation of thiols on cysteines, are widely used; however, they have several shortcomings. First, the lack of site-specificity results in heterogeneous products and irreproducible processes. Second, potential modifications near the complementarity-determining region may reduce binding affinity and specificity. Conversely, site-specific methods produce well-defined and more homogenous antibody conjugates, ensuring developability and clinical applications. Moreover, several recent side-by-side comparisons of site-specific and stochastic methods have demonstrated that site-specific approaches are more likely to achieve their desired properties and functions, such as increased plasma stability, less variability in dose-dependent studies (particularly at low concentrations), enhanced binding efficiency, as well as increased tumor uptake. Herein, we review several standard and practical site-specific bioconjugation methods for native antibodies, i.e., those without recombinant engineering. First, chemo-enzymatic techniques, namely transglutaminase (TGase)-mediated transamidation of a conserved glutamine residue and glycan remodeling of a conserved asparagine N-glycan (GlyCLICK), both in the Fc region. Second, chemical approaches such as selective reduction of disulfides (ThioBridge) and N-terminal amine modifications. Furthermore, we list site-specific antibody–drug conjugates in clinical trials along with the future perspectives of these site-specific methods.