An immunosuppressive antibody-drug conjugate

Advances and challenges in immunosuppressive antibody drug conjugates

Since the approval of Mylotarg™ in 2000 for acute myeloid leukemia, antibody-drug conjugates (ADCs) have significantly advanced precision medicine, particularly for oncology applications. ADCs combine an antibody, a linker, and a payload to result in a targeted therapeutic that minimizes toxicity resulting from systemic drug exposure. This review explores the innovative application of ADC technology towards immunosuppressive therapeutics, primarily focusing on antibody-mediated delivery of glucocorticoids (GCs). Despite their potent anti-inflammatory effects, the clinical use of GCs is limited by adverse systemic effects including osteoporosis, high blood sugar, adrenal insufficiency, weight gain, and glaucoma. Therefore, targeted delivery via ADCs presents a promising strategy to enhance therapeutic efficacy while reducing toxicity. Herein, we review the current status of immune-suppressing ADC technology, starting with early investigations of CD163-targeted dexamethasone and moving to the design of ADCs employing next-generation ultra-potent GCs. Additionally, we will discuss the current status of anti-inflammatory ADCs that employ non-glucocorticoid immune-suppressive medications. Throughout, we will highlight preclinical and clinical data that serves to derisk and drive investment in this new therapeutic class. In parallel, we will focus on ADC design principles that illustrate the importance of careful selection of payload, linker, and conjugation technology in this emerging field.

Innovative payloads for ADCs in cancer treatment: moving beyond the selective delivery of chemotherapy

Antibody-drug conjugates (ADCs) have emerged as a transformative approach in cancer therapy by enhancing tumor targeting and minimizing systemic toxicity compared to traditional chemotherapy. Initially developed with chemotherapy agents as payloads, ADCs have now incorporated alternative payloads, such as immune-stimulating agents, natural toxins, and radionuclides, to improve therapeutic efficacy and specificity. A significant advancement in ADC technology is the integration of Proteolysis Targeting Chimeras (PROTACs), which enable the precise degradation of cellular targets involved in tumorigenesis. This strategy enhances the specificity and precision of cancer therapies, addressing key mechanisms in cancer cell survival. Moreover, incorporating radioactive isotopes into ADCs is an emerging strategy aimed at further improving therapeutic outcomes. By delivering localized radiation, this approach offers the potential to enhance the efficacy of treatment and expand the therapeutic arsenal. Despite these innovations, challenges remain, including dysregulated immune activation, severe adverse effects, and intrinsic immunogenicity of some agents. These emerging issues highlight the ongoing need for optimization in ADC therapy. This review summarizes the latest developments in ADC technology, focusing on novel payloads, PROTAC integration, and the potential for combining ADCs with other therapeutic modalities to refine cancer treatment and improve patient outcomes.

Target protein identification in live cells and organisms with a non-diffusive proximity tagging system

Identifying target proteins for bioactive molecules is essential for understanding their mechanisms, developing improved derivatives, and minimizing off-target effects. Despite advances in target identification (target-ID) technologies, significant challenges remain, impeding drug development. Most target-ID methods use cell lysates, but maintaining an intact cellular context is vital for capturing specific drug-protein interactions, such as those with transient protein complexes and membrane-associated proteins. To address these limitations, we developed POST-IT (Pup-On-target for Small molecule Target Identification Technology), a non-diffusive proximity tagging system for live cells, orthogonal to the eukaryotic system. POST-IT utilizes an engineered fusion of proteasomal accessory factor A and HaloTag to transfer Pup to proximal proteins upon directly binding to the small molecule. After significant optimization to eliminate self-pupylation and polypupylation, minimize depupylation, and optimize chemical linkers, POST-IT successfully identified known targets and discovered a new binder, SEPHS2, for dasatinib, and VPS37C as a new target for hydroxychloroquine, enhancing our understanding these drugs' mechanisms of action. Furthermore, we demonstrated the application of POST-IT in live zebrafish embryos, highlighting its potential for broad biological research and drug development.

Mitochondrial Control of Proteasomal Psmb5 Drives the Differentiation of Tissue-Resident Memory T Cells in Patients with Rheumatoid Arthritis

OBJECTIVE

To explore T cell-intrinsic mechanisms underpinning the mal-differentiation of tissue-resident memory T (Trm) cells in patients with rheumatoid arthritis (RA).

METHODS

Circulating T cells from patient with RA and healthy individuals were used for Trm cell differentiation. The role of Hobit in Trm differentiation was investigated through targeted silencing experiments. Psmb5 expression regulation was explored by identifying BRD2 as a key transcription factor, with the interaction validated through chromatin immunoprecipitation-quantitative polymerase chain reaction. The impact of BRD2 succinylation on Trm differentiation was examined by manipulating succinyl-CoA levels in T cells. Humanized NSG chimeras representing synovitis provided insights into Trm infiltration in RA synovitis and were used for translational experiments.

RESULTS

In patients with RA, a notable predisposition of CD4+ T cells toward differentiation into Trm cells was observed, demonstrating a positive correlation with the disease activity score 28. Remarkably, Hobit was a pivotal facilitator in the formation of RA CD4+ Trm cells. Mechanistic studies unveiled the dysregulation of proteasomal Psmb5 in T cells of patients with RA as the key factor contributing to elevated Hobit protein levels. The deficiency of proteasomal Psmb5 was intricately linked to BRD2, with succinylation exerting a significant impact on Psmb5 transcription and Trm cell differentiation. This heightened BRD2 succinylation was attributed to elevated levels of mitochondrial succinyl-CoA in RA T cells. Consequently, targeting succinyl-CoA within CD4+ T cells controlled the inflammation of synovial tissues in humanized chimeras.

CONCLUSION

Mitochondrial succinyl-CoA fosters the succinylation of BRD2, resulting in compromised transcription of proteasomal Psmb5 and the differentiation of Trm cells in RA.

Noncanonical Amino Acid Incorporation in Animals and Animal Cells

Noncanonical amino acids (ncAAs) are synthetic building blocks that, when incorporated into proteins, confer novel functions and enable precise control over biological processes. These small yet powerful tools offer unprecedented opportunities to investigate and manipulate various complex life forms. In particular, ncAA incorporation technology has garnered significant attention in the study of animals and their constituent cells, which serve as invaluable model organisms for gaining insights into human physiology, genetics, and diseases. This review will provide a comprehensive discussion on the applications of ncAA incorporation technology in animals and animal cells, covering past achievements, current developments, and future perspectives.

The Evolution of Antibody-Drug Conjugates: Toward Accurate DAR and Multi-specificity

Antibody-drug conjugates (ADCs) consist of antibodies, linkers and payloads. They offer targeted delivery of potent cytotoxic drugs to tumor cells, minimizing off-target effects. However, the therapeutic efficacy of ADCs is compromised by heterogeneity in the drug-to-antibody ratio (DAR), which impacts both cytotoxicity and pharmacokinetics (PK). Additionally, the emergence of drug resistance poses significant challenges to the clinical advancement of ADCs. To overcome these limitations, a variety of strategies have been developed, including the design of multi-specific drugs with accurate DAR. This review critically summarizes the current challenges faced by ADCs, categorizing key issues and evaluating various innovative solutions. We provide an in-depth analysis of the latest methodologies for achieving homogeneous DAR and explore design strategies for multi-specific drugs aimed at combating drug resistance. Our discussion offers a current perspective on the advancements made in refining ADC technologies, with an emphasis on enhancing therapeutic outcomes.

Applications of genetic code expansion technology in eukaryotes

Unnatural amino acids (UAAs) have gained significant attention in protein engineering and drug development owing to their ability to introduce new chemical functionalities to proteins. In eukaryotes, genetic code expansion (GCE) enables the incorporation of UAAs and facilitates posttranscriptional modification (PTM), which is not feasible in prokaryotic systems. GCE is also a powerful tool for cell or animal imaging, the monitoring of protein interactions in target cells, drug development, and switch regulation. Therefore, there is keen interest in utilizing GCE in eukaryotic systems. This review provides an overview of the application of GCE in eukaryotic systems and discusses current challenges that need to be addressed.

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.

Antibody drug conjugates beyond cytotoxic payloads

For many years, antibody drug conjugates (ADC) have teased with the promise of targeted payload delivery to diseased cells, embracing the targeting of the antibody to which a cytotoxic payload is conjugated. During the past decade this promise has started to be realised with the approval of more than a dozen ADCs for the treatment of various cancers. Of these ADCs, brentuximab vedotin really laid the foundations of a template for a successful ADC with lysosomal payload release from a cleavable dipeptide linker, measured DAR by conjugation to the Cys-Cys interchain bonds of the antibody and a cytotoxic payload. Using this ADC design model oncology has now expanded their repertoire of payloads to include non-cytotoxic compounds. These new payload classes have their origins in prior medicinal chemistry programmes aiming to design selective oral small molecule drugs. While this may not have been achieved, the resulting compounds provide excellent starting points for ADC programmes with some compounds amenable to immediate linker attachment while for others extensive SAR and structural information offer invaluable design insights. Many of these new oncology payload classes are of interest to other therapeutic areas facilitating rapid access to drug-linkers for exploration as non-oncology ADCs. Other therapeutic areas have also pursued unique payload classes with glucocorticoid receptor modulators (GRM) being the most clinically advanced in immunology. Here, ADC payloads come full circle, as oncology is now investigating GRM payloads for the treatment of cancer. This chapter aims to cover all these new ADC approaches while describing the medicinal chemistry origins of the new non-cytotoxic payloads.

G protein-coupled receptor-targeting antibody-drug conjugates: Current status and future directions

In recent years, antibody-drug conjugates (ADCs) have emerged as promising anti-cancer therapeutic agents with several having already received market approval for the treatment of solid tumor and hematological malignancies. As ADC technology continues to improve and the range of indications treatable by ADCs increases, the repertoire of target antigens has expanded and will undoubtedly continue to grow. G protein-coupled receptors (GPCRs) are well-characterized therapeutic targets implicated in many human pathologies, including cancer, and represent a promising emerging target of ADCs. In this review, we will discuss the past and present therapeutic targeting of GPCRs and describe ADCs as therapeutic modalities. Moreover, we will summarize the status of existing preclinical and clinical GPCR-targeted ADCs and address the potential of GPCRs as novel targets for future ADC development.

An Overview of the Development and Preclinical Evaluation of Antibody-Drug Conjugates for Non-Oncological Applications

Typically, antibody-drug conjugates (ADCs) are made up of a humanized antibody and a small-molecule medication connected by a chemical linker. ADCs' ability to deliver cytotoxic agents to the specific site with reduced side effects showed promising results in oncology. To date, fourteen ADCs have been approved by the US Food and Drug Administration, and approximately 297 ADCs are in pre-clinical/clinical stages in the oncology area. Inspired by these outcomes, a few scientists explored the potential of antibody-drug conjugates in non-oncological conditions such as arthritis, myasthenia gravis, immunological disorders, and kidney failure. However, there are limited data available on the non-oncological applications of antibody-drug conjugates. This current review focuses on the non-oncological applications of antibody-drug conjugates, their developmental studies, testing procedures, in vitro evaluations, and pre-clinical testing. Additionally, a summary of the restrictions, difficulties, and prospects for ADCs in non-oncological applications is provided.

Applications of synthetic biology in medical and pharmaceutical fields

Synthetic biology aims to design or assemble existing bioparts or bio-components for useful bioproperties. During the past decades, progresses have been made to build delicate biocircuits, standardized biological building blocks and to develop various genomic/metabolic engineering tools and approaches. Medical and pharmaceutical demands have also pushed the development of synthetic biology, including integration of heterologous pathways into designer cells to efficiently produce medical agents, enhanced yields of natural products in cell growth media to equal or higher than that of the extracts from plants or fungi, constructions of novel genetic circuits for tumor targeting, controllable releases of therapeutic agents in response to specific biomarkers to fight diseases such as diabetes and cancers. Besides, new strategies are developed to treat complex immune diseases, infectious diseases and metabolic disorders that are hard to cure via traditional approaches. In general, synthetic biology brings new capabilities to medical and pharmaceutical researches. This review summarizes the timeline of synthetic biology developments, the past and present of synthetic biology for microbial productions of pharmaceutics, engineered cells equipped with synthetic DNA circuits for diagnosis and therapies, live and auto-assemblied biomaterials for medical treatments, cell-free synthetic biology in medical and pharmaceutical fields, and DNA engineering approaches with potentials for biomedical applications.

Payload diversification: a key step in the development of antibody-drug conjugates

Antibody-drug conjugates (ADCs) is a fast moving class of targeted biotherapeutics that currently combines the selectivity of monoclonal antibodies with the potency of a payload consisting of cytotoxic agents. For many years microtubule targeting and DNA-intercalating agents were at the forefront of ADC development. The recent approval and clinical success of trastuzumab deruxtecan (Enhertu^®) and sacituzumab govitecan (Trodelvy^®), two topoisomerase 1 inhibitor-based ADCs, has shown the potential of conjugating unconventional payloads with differentiated mechanisms of action. Among future developments in the ADC field, payload diversification is expected to play a key role as illustrated by a growing number of preclinical and clinical stage unconventional payload-conjugated ADCs. This review presents a comprehensive overview of validated, forgotten and newly developed payloads with different mechanisms of action.

Identification of proteomic landscape of drug-binding proteins in live cells by proximity-dependent target ID

Direct identification of the proteins targeted by small molecules can provide clues for disease diagnosis, prevention, and drug development. Despite concentrated attempts, there are still technical limitations associated with the elucidation of direct interactors. Herein, we report a target-ID system called proximity-based compound-binding protein identification (PROCID), which combines our direct analysis workflow of proximity-labeled proteins (Spot-ID) with the HaloTag system to efficiently identify the dynamic proteomic landscape of drug-binding proteins. We successfully identified well-known dasatinib-binding proteins (ABL1, ABL2) and confirmed the unapproved dasatinib-binding kinases (e.g., BTK and CSK) in a live chronic myeloid leukemia cell line. PROCID also identified the DNA helicase protein SMARCA2 as a dasatinib-binding protein, and the ATPase domain was confirmed to be the binding site of dasatinib using a proximity ligation assay (PLA) and in cellulo biotinylation assay. PROCID thus provides a robust method to identify unknown drug-interacting proteins in live cells that expedites the mode of action of the drug.

An Enzymatically Cleavable Tripeptide Linker for Maximizing the Therapeutic Index of Antibody-Drug Conjugates

Valine-citrulline is a protease-cleavable linker commonly used in many drug delivery systems, including antibody-drug conjugates (ADC) for cancer therapy. However, its suboptimal in vivo stability can cause various adverse effects such as neutropenia and hepatotoxicity, leading to dose delays or treatment discontinuation. Here, we report that glutamic acid-glycine-citrulline (EGCit) linkers have the potential to solve this clinical issue without compromising the ability of traceless drug release and ADC therapeutic efficacy. We demonstrate that our EGCit ADC resists neutrophil protease-mediated degradation and spares differentiating human neutrophils. Notably, our anti-HER2 ADC shows almost no sign of blood and liver toxicity in healthy mice at 80 mg kg-1. In contrast, at the same dose level, the FDA-approved anti-HER2 ADCs Kadcyla and Enhertu show increased levels of serum alanine aminotransferase and aspartate aminotransferase and morphologic changes in liver tissues. Our EGCit conjugates also exert greater antitumor efficacy in multiple xenograft tumor models compared with Kadcyla and Enhertu. This linker technology could substantially broaden the therapeutic windows of ADCs and other drug delivery agents, providing clinical options with improved efficacy and safety.

Bioanalytical Methods and Strategic Perspectives Addressing the Rising Complexity of Novel Bioconjugates and Delivery Routes for Biotherapeutics

In recent years, an increase in the discovery and development of biotherapeutics employing new modalities, such as bioconjugates or novel routes of delivery, has created bioanalytical challenges. The inherent complexity of conjugated molecular structures means that quantification of the bioconjugate and its multiple components is critical for preclinical/clinical studies to inform drug discovery and development. Moreover, bioconjugates involve additional multifactorial complexity because of the potential for in vivo catabolism and biotransformation, which may require thorough investigations in multiple biological matrices. Furthermore, excipients that enhance absorption are frequently evaluated and employed for the development of oral and inhaled biotherapeutics. Risk-benefit assessments are required for novel or existing excipients that utilize dosages above previously approved levels. Bioanalytical methods that can measure both excipients and potential drug metabolites in biological matrices are highly relevant to these emerging bioanalysis challenges. We discuss the bioanalytical strategies for analyzing bioconjugates such as antibody-drug conjugates and antibody-oligonucleotide conjugates and review recent advances in bioanalytical methods for the quantification and characterization of novel bioconjugates. We also discuss bioanalytical considerations for both biotherapeutics and excipients through novel administration routes and review analyses in various biological matrices, from the extensively studied serum or plasma to tissue biopsy in the context of preclinical and clinical studies from both technical and regulatory perspectives.

Pathophysiological and pharmacological considerations to improve the design and application of antibody-drug conjugates

Antibody-drug conjugates (ADC) have emerged as one of the pillars of clinical disease management in oncology. The biggest hurdle to widespread development and application of ADCs has been a narrow therapeutic index. Advances in antibody technologies and formats as well as novel linker and payload chemistries have begun to facilitate structural improvements to ADCs. However, the interplay of structural characteristics with physiologic and pharmacologic factors determining therapeutic success has garnered less attention. This review elaborates on the pharmacology of ADCs, the pathophysiology of cancerous tissues, and the reciprocal consequences on ADC properties and functions. While most currently approved ADCs utilize either microtubule inhibition or DNA damage as primary mechanisms of action, we present arguments to expand this repertoire and highlight the need for payload mechanisms that exploit disease-specific vulnerabilities. We promote the idea that the choice of antibody format, targeting antigen, linker properties, and payload of an ADC should be deliberately fit for purpose by taking the pathophysiology of disease and the specific pharmacology of the drug entity into account, thus allowing a higher probability of clinical success.

Design and Development of Glucocorticoid Receptor Modulators as Immunology Antibody-Drug Conjugate Payloads

Glucocorticoid receptor modulators (GRM) are the first-line treatment for many immune diseases, but unwanted side effects restrict chronic dosing. However, targeted delivery of a GRM payload via an immunology antibody-drug conjugate (iADC) may deliver significant efficacy at doses that do not lead to unwanted side effects. We initiated our α-TNF-GRM ADC project focusing on identifying the optimal payload and a linker that afforded stable attachment to both the payload and antibody, resulting in the identification of the synthetically accessible maleimide-Gly-Ala-Ala linker. DAR 4 purified ADCs were shown to be more efficacious in a mouse contact hypersensitivity model than the parent α-TNF antibody. Analysis of P1NP and corticosterone biomarkers showed there was a sufficient therapeutic window between efficacy and unwanted effects. In a chronic mouse arthritis model, α-TNF-GRM ADCs were more efficacious than both the parent α-TNF mAb and an isotype control bearing the same GRM payload.

Making Sense of "Nonsense" and More: Challenges and Opportunities in the Genetic Code Expansion, in the World of tRNA Modifications

The evolutional development of the RNA translation process that leads to protein synthesis based on naturally occurring amino acids has its continuation via synthetic biology, the so-called rational bioengineering. Genetic code expansion (GCE) explores beyond the natural translational processes to further enhance the structural properties and augment the functionality of a wide range of proteins. Prokaryotic and eukaryotic ribosomal machinery have been proven to accept engineered tRNAs from orthogonal organisms to efficiently incorporate noncanonical amino acids (ncAAs) with rationally designed side chains. These side chains can be reactive or functional groups, which can be extensively utilized in biochemical, biophysical, and cellular studies. Genetic code extension offers the contingency of introducing more than one ncAA into protein through frameshift suppression, multi-site-specific incorporation of ncAAs, thereby increasing the vast number of possible applications. However, different mediating factors reduce the yield and efficiency of ncAA incorporation into synthetic proteins. In this review, we comment on the recent advancements in genetic code expansion to signify the relevance of systems biology in improving ncAA incorporation efficiency. We discuss the emerging impact of tRNA modifications and metabolism in protein design. We also provide examples of the latest successful accomplishments in synthetic protein therapeutics and show how codon expansion has been employed in various scientific and biotechnological applications.

A Strategy for Selective Deletion of Autoimmunity-Related T Cells by pMHC-Targeted Delivery

Autoimmune diseases such as rheumatoid arthritis are caused by immune system recognition of self-proteins and subsequent production of effector T cells that recognize and attack healthy tissue. Therapies for these diseases typically utilize broad immune suppression, which can be effective, but which also come with an elevated risk of susceptibility to infection and cancer. T cell recognition of antigens is driven by binding of T cell receptors to peptides displayed on major histocompatibility complex proteins (MHCs) on the cell surface of antigen-presenting cells. Technology for recombinant production of the extracellular domains of MHC proteins and loading with peptides to produce pMHCs has provided reagents for detection of T cell populations, and with the potential for therapeutic intervention. However, production of pMHCs in large quantities remains a challenge and a translational path needs to be established. Here, we demonstrate a fusion protein strategy enabling large-scale production of pMHCs. A peptide corresponding to amino acids 259-273 of collagen II was fused to the N-terminus of the MHC_II beta chain, and the alpha and beta chains were each fused to human IgG4 Fc domains and co-expressed. A tag was incorporated to enable site-specific conjugation. The cytotoxic drug payload, MMAF, was conjugated to the pMHC and potent, peptide-specific killing of T cells that recognize the collagen pMHC was demonstrated with tetramerized pMHC-MMAF conjugates. Finally, these pMHCs were incorporated into MMAF-loaded 3DNA nanomaterials in order to provide a biocompatible platform. Loading and pMHC density were optimized, and peptide-specific T cell killing was demonstrated. These experiments highlight the potential of a pMHC fusion protein-targeted, drug-loaded nanomaterial approach for selective delivery of therapeutics to disease-relevant T cells and new treatment options for autoimmune disease.

Antibody-Drug Conjugates: Functional Principles and Applications in Oncology and Beyond

In the era of precision medicine, antibody-based therapeutics are rapidly enriched with emerging advances and new proof-of-concept formats. In this context, antibody-drug conjugates (ADCs) have evolved to merge the high selectivity and specificity of monoclonal antibodies (mAbs) with the cytotoxic potency of attached payloads. So far, ten ADCs have been approved by FDA for oncological indications and many others are currently being tested in clinical and preclinical level. This paper summarizes the essential components of ADCs, from their functional principles and structure up to their limitations and resistance mechanisms, focusing on all latest bioengineering breakthroughs such as bispecific mAbs, dual-drug platforms as well as novel linkers and conjugation chemistries. In continuation of our recent review on anticancer implication of ADC's technology, further insights regarding their potential usage outside of the oncological spectrum are also presented. Better understanding of immunoconjugates could maximize their efficacy and optimize their safety, extending their use in everyday clinical practice.

Design and evaluation of glutathione responsive glycosylated camptothecin nanosupramolecular prodrug

A novel tumor-targeted glutathione responsive Glycosylated-Camptothecin nanosupramolecular prodrug (CPT-GL NSp) was designed and fabricated via a disulfide bond. The effects of glycoligand with different polarities on solubility, self-assembly, stability, cellular uptake, and glutathione responsive cleaving were explored, and an optimal glycosylated ligand was selected for nanosupramolecular prodrug. It has been found that CPT-GL NSp exhibited higher drug loading than traditional nanoparticles. Among of which maltose modified NSp had the strongest anti-tumor effects than that of glucose and maltotriose. CPT-SS-Maltose had a similar anti-tumor ability to Irinotecan (IR), but the superior performance in solubility, hemolysis, and uptake of HepG2 cells.

Preparation and in vitro evaluation of amphiphilic paclitaxel small molecule prodrugs and enhancement of oral absorption

A series of novel amphiphilic paclitaxel (PTX) small molecule prodrugs, PTX-succinic anhydride-cystamine (PTX-Cys), PTX-dithiodipropionic anhydride (PTX-SS-COOH) and PTX-succinic anhydride-cystamine-valine (PTX-SS-Val) were designed, synthesized and evaluated against cancer cell lines. Compared with paclitaxel, these prodrugs contained water-soluble groups such as amino, carboxyl and amino acid, which improved the aqueous solubility of the prodrugs. More importantly, the valine was introduced in PTX-SS-Val molecule and made the molecule conform to the structural characteristics of intestinal oligopeptide transporter PEPT1 substrate. Thus the oral bioavailability of prodrug could be improved because of the mediation of PEPT1 transporter. These small molecule paclitaxel prodrugs could self-assemble into nanoparticles in aqueous solution, which effectively improved the solubility of paclitaxel, and had certain stability in pH 6.5, pH 7.4 buffer solutions and simulated gastrointestinal fluids. Some of these prodrugs, especially for PTX-Cys and PTX-SS-Val, exhibited nearly equal or slightly better anticancer activity when compared to paclitaxel. Further studies on PTX-Cys and PTX-SS-Val showed that both had good intestinal absorption in the rat single-pass intestinal perfusion (SPIP) experiments. Oral pharmacokinetic experiments showed that PTX-SS-Val could effectively improve the oral bioavailability of PTX.

Analytical Methods for the Detection and Quantification of ADCs in Biological Matrices

Understanding pharmacokinetics and biodistribution of antibody–drug conjugates (ADCs) is a one of the critical steps enabling their successful development and optimization. Their complex structure combining large and small molecule characteristics brought out multiple bioanalytical methods to decipher the behavior and fate of both components in vivo. In this respect, these methods must provide insights into different key elements including half-life and blood stability of the construct, premature release of the drug, whole-body biodistribution, and amount of the drug accumulated within the targeted pathological tissues, all of them being directly related to efficacy and safety of the ADC. In this review, we will focus on the main strategies enabling to quantify and characterize ADCs in biological matrices and discuss their associated technical challenges and current limitations.

Antibody-Drug Conjugates: The Last Decade

An armed antibody (antibody–drug conjugate or ADC) is a vectorized chemotherapy, which results from the grafting of a cytotoxic agent onto a monoclonal antibody via a judiciously constructed spacer arm. ADCs have made considerable progress in 10 years. While in 2009 only gemtuzumab ozogamicin (Mylotarg^®) was used clinically, in 2020, 9 Food and Drug Administration (FDA)-approved ADCs are available, and more than 80 others are in active clinical studies. This review will focus on FDA-approved and late-stage ADCs, their limitations including their toxicity and associated resistance mechanisms, as well as new emerging strategies to address these issues and attempt to widen their therapeutic window. Finally, we will discuss their combination with conventional chemotherapy or checkpoint inhibitors, and their design for applications beyond oncology, to make ADCs the magic bullet that Paul Ehrlich dreamed of.

Capturing the Magic Bullet: Pharmacokinetic Principles and Modeling of Antibody-Drug Conjugates

Over the past two decades, antibody-drug conjugates (ADCs) have emerged as a promising class of drugs for cancer therapy and have expanded to nononcology fields such as inflammatory diseases, atherosclerosis, and bacteremia. Eight ADCs are currently approved by FDA for clinical applications, with more novel ADCs under clinical development. Compared with traditional chemotherapy, ADCs combine the target specificity of antibodies with chemotherapeutic capabilities of cytotoxic drugs. The benefits include reduced systemic toxicity and enhanced therapeutic index for patients. However, the heterogeneous structures of ADCs and their dynamic changes following administration create challenges in their development. The understanding of ADC pharmacokinetics (PK) is crucial for the optimization of clinical dosing regimens when translating from animal to human. In addition, it contributes to the optimization of dose selection and clinical monitoring with regard to safety and efficacy. This manuscript reviews the PK characteristics of ADCs and summarizes the diverse approaches for PK modeling that can be used to evaluate an ADC at the preclinical and clinical stages to support their successful development. Despite the numerous available options, fit-for-purpose modeling approaches for the PK and PD of ADCs should be critically planned and well-thought-out to adequately support the development of an ADC.

Applying Antibodies Inside Cells: Principles and Recent Advances in Neurobiology, Virology and Oncology

To interfere with cell function, many scientists rely on methods that target DNA or RNA due to the ease with which they can be applied. Proteins are usually the final executors of function but are targeted only indirectly by these methods. Recent advances in targeted degradation of proteins based on proteolysis-targeting chimaeras (PROTACs), ubiquibodies, deGradFP (degrade Green Fluorescent Protein) and other approaches have demonstrated the potential of interfering directly at the protein level for research and therapy. Proteins can be targeted directly and very specifically by antibodies, but using antibodies inside cells has so far been considered to be challenging. However, it is possible to deliver antibodies or other proteins into the cytosol using standard laboratory equipment. Physical methods such as electroporation have been demonstrated to be efficient and validated thoroughly over time. The expression of intracellular antibodies (intrabodies) inside cells is another way to interfere with intracellular targets at the protein level. Methodological strategies to target the inside of cells with antibodies, including delivered antibodies and expressed antibodies, as well as applications in the research areas of neurobiology, viral infections and oncology, are reviewed here. Antibodies have already been used to interfere with a wide range of intracellular targets. Disease-related targets included proteins associated with neurodegenerative diseases such as Parkinson's disease (α-synuclein), Alzheimer's disease (amyloid-β) or Huntington's disease (mutant huntingtin [mHtt]). The applications of intrabodies in the context of viral infections include targeting proteins associated with HIV (e.g. HIV1-TAT, Rev, Vif, gp41, gp120, gp160) and different oncoviruses such as human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV) and Epstein-Barr virus, and they have been used to interfere with various targets related to different processes in cancer, including oncogenic pathways, proliferation, cell cycle, apoptosis, metastasis, angiogenesis or neo-antigens (e.g. p53, human epidermal growth factor receptor-2 [HER2], signal transducer and activator of transcription 3 [STAT3], RAS-related RHO-GTPase B (RHOB), cortactin, vascular endothelial growth factor receptor 2 [VEGFR2], Ras, Bcr-Abl). Interfering at the protein level allows questions to be addressed that may remain unanswered using alternative methods. This review addresses why direct targeting of proteins allows unique insights, what is currently feasible in vitro, and how this relates to potential therapeutic applications.

Site-specific antibody fragment conjugates for targeted imaging

This work details the use of amber suppression-mediated genetic incorporation of unnatural amino acids (UAAs), specifically p-azido-l-phenylalanine (pAzF) and p-acetyl-l-phenylalanine (pAcF), to develop site-specifically labeled antibody Fab fragments. These antibody fragment conjugates represent a novel class of imaging agents with optimal stability, efficacy, and pharmacological properties, which have demonstrated promising potential for probing and understanding the in vivo bio-distributions of protein targets of interest. This chapter provides general guidelines for preparing these Fab conjugates, and details of follow-up bioassays such as single-agent based positron emission tomography (PET) imaging of immune-checkpoint protein PD-L1, and the use of GCN4-mediated switchable antibody conjugates for near-infrared fluorescent imaging of cancer-related biomarkers.

Designing Chimeric Molecules for Drug Discovery by Leveraging Chemical Biology

After the first seed concept introduced in the 18th century, different disciplines have attributed different names to dual-functional molecules depending on their application, including bioconjugates, bifunctional compounds, multitargeting molecules, chimeras, hybrids, engineered compounds. However, these engineered constructs share a general structure: a first component that targets a specific cell and a second component that exerts the pharmacological activity. A stable or cleavable linker connects the two modules of a chimera. Herein, we discuss the recent advances in the rapidly expanding field of chimeric molecules leveraging chemical biology concepts. This Perspective is focused on bifunctional compounds in which one component is a lead compound or a drug. In detail, we discuss chemical features of chimeric molecules and their use for targeted delivery and for target engagement studies.

Advances in antibody engineering for rheumatic diseases

The advent of biologic therapies, particularly antibody therapeutics, has revolutionized the pharmacological treatment of many rheumatic diseases. Antibody discovery began with the immunization of mice for the production of rodent immunoglobulins, but advances in protein and genetic engineering have now made it possible to generate fully human antibodies, which are better tolerated by patients. For most clinical applications in rheumatology, antibodies have been used as blocking agents capable of neutralizing the function of pro-inflammatory proteins, such as TNF. The latest strategies involve antibody products armed with effector moieties, such as anti-inflammatory drugs or cytokines, or antibody products that are specific for multiple targets for the selective inhibition of inflammation at sites of disease. Antibodies are some of the best-selling drugs in the world, and with further advances in antibody development, engineering of armed antibodies and bispecific products will have an important role in the treatment of rheumatic diseases.

Antibody Conjugates-Recent Advances and Future Innovations

Monoclonal antibodies have evolved from research tools to powerful therapeutics in the past 30 years. Clinical success rates of antibodies have exceeded expectations, resulting in heavy investment in biologics discovery and development in addition to traditional small molecules across the industry. However, protein therapeutics cannot drug targets intracellularly and are limited to soluble and cell-surface antigens. Tremendous strides have been made in antibody discovery, protein engineering, formulation, and delivery devices. These advances continue to push the boundaries of biologics to enable antibody conjugates to take advantage of the target specificity and long half-life from an antibody, while delivering highly potent small molecule drugs. While the "magic bullet" concept produced the first wave of antibody conjugates, these entities were met with limited clinical success. This review summarizes the advances and challenges in the field to date with emphasis on antibody conjugation, linker-payload chemistry, novel payload classes, absorption, distribution, metabolism, and excretion (ADME), and product developability. We discuss lessons learned in the development of oncology antibody conjugates and look towards future innovations enabling other therapeutic indications.

Pushing the Envelope: Advancement of ADCs Outside of Oncology

The majority of ADCs in preclinical and clinical development are for oncology indications where cytotoxic payloads are targeted to antigen-expressing cancer cells. However, the modulation of pathogenic cellular activity via ADC-mediated delivery of bioactive small molecules is also an attractive concept for non-oncology indications leading to an expanded application of the technology. Here we summarize those ADCs that have been described so far for non-oncology applications and which cover a variety of payload mechanisms beyond cell killing, from early in vitro proof-of-concept experiments to clinical trials. As our understanding of ADC technology continues to grow, it is anticipated that the development of ADCs as therapeutics for disease areas outside of oncology will also increase.

LRP11 activates β-catenin to induce PD-L1 expression in prostate cancer

Prostate cancer (PRAD) is associated with abnormal cholesterol metabolism and low-density lipoprotein (LDL) receptor-related protein (LRP) family is essential for the homeostasis of cholesterol. Immune check points like PD-L1 are vital for tumour cells to evade immune attack. However, the potential cross-talk between these two pathways has not been explored before in PRAD. Insight from the regulation mechanism of PD-L1 in PRAD may help to optimise PD-L1 based immunotherapy. In this study, we investigated a regulation network of LRP11/β-catenin/PD-L1 in PRAD. We showed that the expression of LRP11 and PD-L1 was up-regulated in PRAD compared to paired normal tissues. LRP11 expression was positively correlated to PD-L1 expression in PRAD tissues. Further experiments in two PRAD cell lines with LRP11 over-expression and knockdown showed that LRP11 induced PD-L1 expression through β-catenin signalling. In addition, LRP11 over-expression in PRAD cell line induced immunosuppression of Jurkat cell in in-vitro co-culture system. The effects of LRP11 could be blocked by neutralising LRP11 or PD-L1 antibody. Our results provide evidence for a novel regulation mechanism of PD-L1 expression in PRAD and LRP11 may be a potential therapeutic target in PRAD.

Antibody therapeutics and immunoregulation in cancer and autoimmune disease

Cancer and autoimmune disease are closely related, and many therapeutic antibodies are widely used in clinics for the treatment of both diseases. Among them, the anti-CD20 antibody has proven to be effective against both lymphoid malignancy and autoimmune disease. Moreover, immune checkpoint blockade using the anti-PD1/PD-L1/CTLA4 antibody has improved the prognosis of patients with refractory solid tumors. At the same time, however, over-enhancement of immunoreaction can induce autoimmune reaction. Although anti-TNF antibody therapies represent a breakthrough in the treatment of autoimmune diseases, optimal management is required to control the serious associated issues, including development and progression of cancer, and it is becoming more and more important to control the immunoreaction. In addition, next-generation antibody therapeutics such as antibody-drug conjugates and bispecific antibodies, are anticipated to treat uncontrolled cancer and autoimmune disease. IL-7R signaling plays an important role in the development and progression of both lymphoid malignancy and autoimmune disease. In addition, abnormal homing activity and steroid resistance caused by IL-7R signaling may worsen prognosis. Therefore, anti-IL-7R targeting antibody therapies that enable suppression of such pathophysiological status have the potential to be beneficial for the treatment of both diseases. In this review, we discuss current antibody therapeutics in cancer and autoimmune disease, and describe a new therapeutic strategy for immunoregulation including IL-7R targeting antibodies.

Real-Time, in Vivo Correlation of Molecular Structure with Drug Distribution in the Brain Striatum Following Convection Enhanced Delivery

The blood-brain barrier (BBB) represents a major obstacle in delivering therapeutics to brain lesions. Convection-enhanced delivery (CED), a method that bypasses the BBB through direct, cannula-mediated drug delivery, is one solution to maintaining increased, effective drug concentration at these lesions. CED was recently proven safe in a phase I clinical trial against diffuse intrinsic pontine glioma (DIPG), a childhood cancer. Unfortunately, the exact relationship between drug size, charge, and pharmacokinetic behavior in the brain parenchyma are difficult to observe in vivo. PET imaging of CED-delivered agents allows us to determine these relationships. In this study, we label different modifications of the PDGFRA inhibitor dasatinib with fluorine-18 or via a nanofiber-zirconium-89 system so that the effect of drug structure on post-CED behavior can accurately be tracked in vivo, via PET. Relatively unchanged bioactivity is confirmed in patient- and animal-model-derived cell lines of DIPG. In naïve mice, significant individual variability in CED drug clearance is observed, highlighting a need to accurately understand drug behavior during clinical translation. Generally, the half-life for a drug to clear from a CED site is short for low molecular weight dasatinib analogs that bare different charge; 1-3 (1, 32.2 min (95% CI: 27.7-37.8), 2, 44.8 min (27.3-80.8), and 3, 71.7 min (48.6-127.6) minutes) and is much longer for a dasatinib-nanofiber conjugate, 5, (42.8-57.0 days). Positron emission tomography allows us to accurately measure the effect of drug size and charge in monitoring real-time drug behavior in the brain parenchyma of live specimens.

Catalyst free hydrazone ligation for protein labeling and modification using electron-deficient benzaldehyde reagents

Bioorthogonal reactions have emerged as valuable tools for site-specific protein labeling and modification in vitro and in vivo. Hydrazone and oxime ligation has recently attracted considerable attention for wide applications in the conjugation of biomolecules. However, this kind of reaction has suffered from slow kinetics under physiological conditions and toxicity or complications of the reaction system due to catalysts. In this work we have developed an electron-deficient benzaldehyde reagent, which can be easily equipped with various types of bio-functional molecules for catalyst-free hydrazone ligation. The reagent can be equipped with not only small molecules such as fluorescence dyes or drugs, but also macromolecules like PEG. These can be precisely ligated to the C-terminus of proteins by an efficient hydrazone reaction at neutral pH and room temperature. The new reagent based catalyst-free hydrazone ligation provides a practical approach for the site specific modification of proteins.

Antibody drug conjugates: Progress, pitfalls, and promises

Antibody drug conjugates (ADCs) represent a promising and an efficient strategy for targeted cancer therapy. Comprised of a monoclonal antibody, a cytotoxic drug, and a linker, ADCs offer tumor selectively, reduced toxicity, and improved stability in systemic circulation. Recent approvals of two ADCs have led to a resurgence in ADC research, with more than 60 ADCs under various stages of clinical development. The therapeutic success of future ADCs is dependent on adherence to key requirements of their design and careful selection of the target antigen on cancer cells. Here we review the main components in the design of antibody drug conjugates, improvements made, and lessons learned over two decades of research, as well as the future of third generation ADCs.

Site-Specific Immuno-PET Tracer to Image PD-L1

The rapid ascension of immune checkpoint blockade treatments has placed an emphasis on the need for viable, robust, and noninvasive imaging methods for immune checkpoint proteins, which could be of diagnostic value. Immunoconjugate-based positron emission tomography (immuno-PET) allows for sensitive and quantitative imaging of target levels and has promising potential for the noninvasive evaluation of immune checkpoint proteins. However, the advancement of immuno-PET is currently limited by available imaging tools, which heavily rely on full-length IgGs with Fc-mediated effects and are heterogeneous mixtures upon random conjugation with chelators for imaging. Herein, we have developed a site-specific αPD-L1 Fab conjugate with the chelator 1,4,7-triazacyclononane- N, N', N″-triacetic acid (NOTA), enabling radiolabeling for PET imaging, using the amber suppression-mediated genetic incorporation of unnatural amino acid (UAA), p-azidophenylalanine. This Fab conjugate is homogeneous and demonstrated tight binding toward the PD-L1 antigen in vitro. The radiolabeled version, ⁶⁴Cu-NOTA-αPD-L1, has been employed in PET imaging to allow for effective visualization and mapping of the biodistribution of PD-L1 in two normal mouse models, including the capturing of different PD-L1 expression levels in the spleens of the different mouse types. Follow-up in vivo blocking studies and ex vivo fluorescent staining further validated specific tissue uptakes of the imaging agent. This approach illustrates the utility of UAA-based site-specific Fab conjugation as a general strategy for making sensitive PET imaging probes, which could facilitate the elucidation of the roles of a wide variety of immune checkpoint proteins in immunotherapy.

Developing an Antibody-Drug Conjugate Approach to Selective Inhibition of an Extracellular Protein

Antibody-drug conjugates (ADCs) are a growing class of therapeutics that harness the specificity of antibodies and the cell-killing potency of small-molecule drugs. Beyond cytotoxics, there are few examples of the application of an ADC approach to difficult drug discovery targets. Here, we present the initial development of a non-internalising ADC, with a view to selectively inhibiting an extracellular protein. Employing the wellinvestigated matrix metalloproteinase-9 (MMP-9) as our model, we adapted a broad-spectrum, nonselective MMP inhibitor for conjugation and linked this to a MMP-9-targeting antibody. The resulting ADC fully inhibits MMP-9, and ELISA results suggest antibody targeting can direct a nonselective inhibitor.

Application of Immuno-PET in Antibody-Drug Conjugate Development

Targeted therapies hold great promise for cancer treatment and may exhibit even greater efficacy when combined with patient selection tools. The clinical impact of identifying likely responders includes reducing the number of unnecessary and ineffective therapies as well as more accurately determining drug effects. Positron emission tomography (PET) imaging using zirconium-89 radiolabeled monoclonal antibodies (mAbs), also referred to as zirconium-89 (⁸⁹Zr)-immuno-PET, provides a potential biomarker to measure target expression and verify optimal delivery of targeted agents to tumors. Antibody-drug conjugates (ADCs) combine the high affinity and specificity of mAbs with the potency of cytotoxic drugs to target tumor-expressing antigen and destroy cancer cells. Thus, ⁸⁹Zr-immuno-PET of whole-body biodistribution, pharmacokinetics, and tumor targeting of antibodies and ADCs to predict toxicity and efficacy could help guide individualized treatment. Here, we review how ⁸⁹Zr-immuno-PET is being used as a companion diagnostic with the development of ADCs. Furthermore, we discuss how ⁸⁹Zr-immuno-PET may be utilized in future clinical trials as an adjunct tool with novel ADCs to select cancer patients who have the greatest potential to benefit from treatment and improve ADC dosing regimens.

Starburst Diblock Polyprodrugs: Reduction-Responsive Unimolecular Micelles with High Drug Loading and Robust Micellar Stability for Programmed Delivery of Anticancer Drugs

Polymeric prodrug based on therapeutic nanomedicine has demonstrated great promise for effective tumor growth inhibition, however, the drawbacks of low drug-loading and weak micellar stability limit its application for clinical cancer therapy. Herein, a reduction-responsive starburst block copolymer prodrug CCP [β-cyclodextrin (β-CD)-PCPT_XX-POEGMA, XX: SS or CC] has been developed for cancer therapy. And CCP is composed of β-CD-Br core with multiple reactive sites, as well as a diblock copolymer containing hydrophobic polymerized camptothecin (PCPT) prodrug chain and hydrophilic poly[(ethylene glycol) methyl ether methacrylate] (OEGMA) chain. A family of CCP polymeric prodrugs with different drug loading contents (up to 25%) and various sizes of unimolecular micelles (UMs) (around 30 nm) were obtained by adjusting the block ratio of PCPT_XX and POEGMA. On account of the amphiphilic structure feature, CPP could take shape water-soluble UMs in aqueous medium with excellent micellar stability. Under imitatively reductive tumor microenvironment, anticancer drug CPT could rapidly escape from CCP UMs in terms of disulfide bond breakage. However, this behavior is strongly refrained in the physiological environment. In vitro and in vivo outcome confirmed that CCP UMs showed excellent performance of sufficient tumor accumulation, high-efficiency tumor growth inhibition and low-toxicity for healthy tissues. Based on these gratifying therapeutic efficacy, it is believed that as-present starburst prodrug strategy can offer a brand-new insight for high-efficiency therapeutic nanoplatforms for chemotherapy application.