On the use of DNA as a linker in antibody-drug conjugates: synthesis, stability and in vitro potency

Precision Medicine in Rheumatic Diseases: Unlocking the Potential of Antibody-Drug Conjugates

In the era of precision medicine, antibody-drug conjugates (ADCs) have emerged as a cutting-edge therapeutic strategy. These innovative compounds combine the precision of monoclonal antibodies with the potent cell-killing or immune-modulating abilities of attached drug payloads. This unique strategy not only reduces off-target toxicity but also enhances the therapeutic effectiveness of drugs. Beyond their well established role in oncology, ADCs are now showing promising potential in addressing the unmet needs in the therapeutics of rheumatic diseases. Rheumatic diseases, a diverse group of chronic autoimmune diseases with varying etiologies, clinical presentations, and prognoses, often demand prolonged pharmacological interventions, creating a pressing need for novel, efficient, and low-risk treatment options. ADCs, with their ability to precisely target the immune components, have emerged as a novel therapeutic strategy in this context. This review will provide an overview of the core components and mechanisms behind ADCs, a summary of the latest clinical trials of ADCs for the treatment of rheumatic diseases, and a discussion of the challenges and future prospects faced by the development of next-generation ADCs. SIGNIFICANCE STATEMENT: There is a lack of efficient and low-risk targeted therapeutics for rheumatic diseases. Antibody-drug conjugates, a class of cutting-edge therapeutic drugs, have emerged as a promising targeted therapeutic strategy for rheumatic disease. Although there is limited literature summarizing the progress of antibody-drug conjugates in the field of rheumatic disease, updating the advancements in this area provides novel insights into the development of novel antirheumatic drugs.

Peptide-Directed Attachment of Hydroxylamines to Specific Lysines of IgG Antibodies for Bioconjugations with Acylboronates

The role of monoclonal antibodies as vehicles to deliver payloads has evolved as a powerful tool in cancer therapy in recent years. The clinical development of therapeutic antibody conjugates with precise payloads holds great promise for targeted therapeutic interventions. The use of affinity-peptide mediated functionalization of native off-the-shelf antibodies offers an effective approach to selectively modify IgG antibodies with a drug-antibody ratio (DAR) of 2. Here, we report the traceless, peptide-directed attachment of two hydroxylamines to native IgGs followed by chemoselective potassium acyltrifluoroborate (KAT) ligation with quinolinium acyltrifluoroborates (QATs), which provide enhanced ligation rates with hydroxylamines under physiological conditions. By applying KAT ligation to the modified antibodies, conjugation of small molecules, proteins, and oligonucleotides to off-the-shelf IgGs proceeds efficiently, in good yields, and with simultaneous cleavage of the affinity peptide-directing moiety.

Orthogonal End Labelling of Oligonucleotides through Dual Incorporation of Click-Reactive NTP Analogues

Post-synthetic modification of nucleic acid structures with clickable functionality is a versatile tool that facilitates many emerging applications, including immune evasion, enhancements in stability, fluorescent labelling, chemical 5'-RNA-capping and the development of functional aptamers. While certain chemoenzymatic approaches for 3'-azido and alkynyl labelling are known, equivalent 5'-strategies are either inefficient, complex, or require harsh chemical conditions. Here, we present a modular and facile technology to consecutively modify DNA and RNA strands at both ends with click-modifiable functional groups. Our approach using γ-modified ATP analogues facilitates T4 PNK-catalysed 5'-modification of oligonucleotides, a process that is compatible with TdT-catalysed 3'-elongation using 3'-azido-2',3'-ddGTP. Finally, we demonstrate that our approach is suitable for both oligo-oligo ligations, as well ssDNA circularization. We anticipate that such approaches will pave the way for the synthesis of highly functionalised oligonucleotides, improving the therapeutic and diagnostic applicability of oligonucleotides such as in the realm of next-generation sequencing.

Novel formats of antibody conjugates: recent advances in payload diversity, conjugation, and linker chemistry

INTRODUCTION

In the field of bioconjugates, the focus on antibody - drug conjugates (ADCs) with novel payloads beyond the traditional categories of potent cytotoxic agents is increasing. These innovative ADCs exhibit various molecular formats, ranging from small-molecule payloads, such as immune agonists and proteolytic agents, to macromolecular payloads, such as oligonucleotides and proteins.

AREAS COVERED

This review offers an in-depth exploration of unconventional strategies for designing conjugates with novel mechanisms of action and notable examples of approaches that show promising prospects. Representative examples of novel format payloads and their classification, attributes, and appropriate conjugation techniques are discussed in detail.

EXPERT OPINION

The existing basic technologies used to manufacture ADCs can be directly applied to synthesize novel formatted conjugates. However, a wide variety of new payloads require the creation of customized technologies adapted to the unique characteristics of these payloads. Consequently, fundamental technologies, such as conjugation methods aimed at achieving high drug - antibody ratios and developing stable crosslinkers, are likely to become increasingly important research areas in the future.

The Dawn of a New Era: Targeting the "Undruggables" with Antibody-Based Therapeutics

The high selectivity and affinity of antibodies toward their antigens have made them a highly valuable tool in disease therapy, diagnosis, and basic research. A plethora of chemical and genetic approaches have been devised to make antibodies accessible to more "undruggable" targets and equipped with new functions of illustrating or regulating biological processes more precisely. In this Review, in addition to introducing how naked antibodies and various antibody conjugates (such as antibody-drug conjugates, antibody-oligonucleotide conjugates, antibody-enzyme conjugates, etc.) work in therapeutic applications, special attention has been paid to how chemistry tools have helped to optimize the therapeutic outcome (i.e., with enhanced efficacy and reduced side effects) or facilitate the multifunctionalization of antibodies, with a focus on emerging fields such as targeted protein degradation, real-time live-cell imaging, catalytic labeling or decaging with spatiotemporal control as well as the engagement of antibodies inside cells. With advances in modern chemistry and biotechnology, well-designed antibodies and their derivatives via size miniaturization or multifunctionalization together with efficient delivery systems have emerged, which have gradually improved our understanding of important biological processes and paved the way to pursue novel targets for potential treatments of various diseases.

A comprehensive review of key factors affecting the efficacy of antibody drug conjugate

Antibody Drug Conjugate (ADC) is an emerging technology to overcome the limitations of chemotherapy by selectively targeting the cancer cells. ADC binds with an antigen, specifically over expressed on the surface of cancer cells, results decrease in bystander effect and increase in therapeutic index. The potency of an ideal ADC is entirely depending on several physicochemical factors such as site of conjugation, molecular weight, linker length, Steric hinderance, half-life, conjugation method, binding energy and so on. Inspite of the fact that there is more than 100 of ADCs are in clinical trial only 14 ADCs are approved by FDA for clinical use. However, to design an ideal ADC is still challenging and there is much more to be done. Here in this review, we have discussed the key components along with their significant role or contribution towards the efficacy of an ADC. Moreover, we also explained about the recent advancement in the conjugation method. Additionally, we spotlit the mode of action of an ADC, recent challenges, and future perspective regarding ADC. The profound knowledge regarding key components and their properties will help in the synthesis or production of different engineered ADCs. Therefore, contributes to develop an ADC with low safety concern and high therapeutic index. We hope this review will improve the understanding and encourage the practicing of research in anticancer ADCs development.

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.

Antibody-Drug Conjugates Containing Payloads from Marine Origin

Antibody-drug conjugates (ADCs) are an important class of therapeutics for the treatment of cancer. Structurally, an ADC comprises an antibody, which serves as the delivery system, a payload drug that is a potent cytotoxin that kills cancer cells, and a chemical linker that connects the payload with the antibody. Unlike conventional chemotherapy methods, an ADC couples the selective targeting and pharmacokinetic characteristics related to the antibody with the potent cytotoxicity of the payload. This results in high specificity and potency by reducing off-target toxicities in patients by limiting the exposure of healthy tissues to the cytotoxic drug. As a consequence of these outstanding features, significant research efforts have been devoted to the design, synthesis, and development of ADCs, and several ADCs have been approved for clinical use. The ADC field not only relies upon biology and biochemistry (antibody) but also upon organic chemistry (linker and payload). In the latter, total synthesis of natural and designed cytotoxic compounds, together with the development of novel synthetic strategies, have been key aspects of the consecution of clinical ADCs. In the case of payloads from marine origin, impressive structural architectures and biological properties are observed, thus making them prime targets for chemical synthesis and the development of ADCs. In this review, we explore the molecular and biological diversity of ADCs, with particular emphasis on those containing marine cytotoxic drugs as the payload.

New Technologies Bloom Together for Bettering Cancer Drug Conjugates

Drug conjugates, including antibody-drug conjugates, are a step toward realizing Paul Ehrlich's idea from over 100 years ago of a "magic bullet" for cancer treatment. Through balancing selective targeting molecules with highly potent payloads, drug conjugates can target specific tumor microenvironments and kill tumor cells. A drug conjugate consists of three parts: a targeting agent, a linker, and a payload. In some conjugates, monoclonal antibodies act as the targeting agent, but new strategies for targeting include antibody derivatives, peptides, and even small molecules. Linkers are responsible for connecting the payload to the targeting agent. Payloads impact vital cellular processes to kill tumor cells. At present, there are 12 antibody-drug conjugates on the market for different types of cancers. Research on drug conjugates is increasing year by year to solve problems encountered in conjugate design, such as tumor heterogeneity, poor circulation, low drug loading, low tumor uptake, and heterogenous expression of target antigens. This review highlights some important preclinical research on drug conjugates in recent years. We focus on three significant areas: improvement of antibody-drug conjugates, identification of new conjugate targets, and development of new types of drug conjugates, including nanotechnology. We close by highlighting the critical barriers to clinical translation and the open questions going forward. SIGNIFICANCE STATEMENT: The development of anticancer drug conjugates is now focused in three broad areas: improvements to existing antibody drug conjugates, identification of new targets, and development of new conjugate forms. This article focuses on the exciting preclinical studies in these three areas and advances in the technology that improves preclinical development.

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.

Drug-to-Antibody Ratio Estimation via Proteoform Peak Integration in the Analysis of Antibody-Oligonucleotide Conjugates with Orbitrap Fourier Transform Mass Spectrometry

The therapeutic efficacy and pharmacokinetics of antibody-drug conjugates (ADCs) in general, and antibody-oligonucleotide conjugates (AOCs) in particular, depend on the drug-to-antibody ratio (DAR) distribution and average value. The DAR is considered a critical quality attribute, and information pertaining to it needs to be gathered during ADC/AOC development, production, and storage. However, because of the high structural complexity of ADC/AOC samples, particularly in the initial drug-development stages, the application of the current state-of-the-art mass spectrometric approaches can be limited for DAR analysis. Here, we demonstrate a novel approach for the analysis of complex ADC/AOC samples, following native size-exclusion chromatography Orbitrap Fourier transform mass spectrometry (FTMS). The approach is based on the integration of the proteoform-level mass spectral peaks in order to provide an estimate of the DAR distribution and its average value with less than 10% error. The peak integration is performed via a truncation of the Orbitrap's unreduced time-domain ion signals (transients) before mass spectra generation via FT processing. Transient recording and processing are undertaken using an external data acquisition system, FTMS Booster X2, coupled to a Q Exactive HF Orbitrap FTMS instrument. This approach has been applied to the analysis of whole and subunit-level trastuzumab conjugates with oligonucleotides. The obtained results indicate that ADC/AOC sample purification or simplification procedures, for example, deglycosylation, could be omitted or minimized prior to the DAR analysis, streamlining the drug-development process.

A Platform for Site-Specific DNA-Antibody Bioconjugation by Using Benzoylacrylic-Labelled Oligonucleotides

Many bioconjugation strategies for DNA oligonucleotides and antibodies suffer limitations, such as site-specificity, stoichiometry and hydrolytic instability of the conjugates, which makes them unsuitable for biological applications. Here, we report a new platform for the preparation of DNA-antibody bioconjugates with a simple benzoylacrylic acid pentafluorophenyl ester reagent. Benzoylacrylic-labelled oligonucleotides prepared with this reagent can be site-specifically conjugated to a range of proteins and antibodies through accessible cysteine residues. The homogeneity of the prepared DNA-antibody bioconjugates was confirmed by a new LC-MS protocol and the bioconjugate probes were used in fluorescence or super-resolution microscopy cell imaging experiments. This work demonstrates the versatility and robustness of our bioconjugation protocol that gives site-specific, well-defined and plasma-stable DNA-antibody bioconjugates for biological applications.

Leucine-rich alpha-2-glycoprotein 1 (LRG1) as a novel ADC target

Leucine-rich alpha-2-glycoprotein 1 (LRG1) is present abundantly in the microenvironment of many tumours where it contributes to vascular dysfunction, which impedes the delivery of therapeutics. In this work we demonstrate that LRG1 is predominantly a non-internalising protein. We report the development of a novel antibody-drug conjugate (ADC) comprising the anti-LRG1 hinge-stabilised IgG4 monoclonal antibody Magacizumab coupled to the anti-mitotic payload monomethyl auristatin E (MMAE) via a cleavable dipeptide linker using the site-selective disulfide rebridging dibromopyridazinedione (diBrPD) scaffold. It is demonstrated that this ADC retains binding post-modification, is stable in serum and effective in in vitro cell studies. We show that the extracellular LRG1-targeting ADC provides an increase in survival in vivo when compared against antibody alone and similar anti-tumour activity when compared against standard chemotherapy, but without undesired side-effects. LRG1 targeting through this ADC presents a novel and effective proof-of-concept en route to improving the efficacy of cancer therapeutics.

Non-specific interactions of antibody-oligonucleotide conjugates with living cells

Antibody-Oligonucleotide Conjugates (AOCs) represent an emerging class of functionalized antibodies that have already been used in a wide variety of applications. While the impact of dye and drug conjugation on antibodies' ability to bind their target has been extensively studied, little is known about the effect caused by the conjugation of hydrophilic and charged payloads such as oligonucleotides on the functions of an antibody. Previous observations of non-specific interactions of nucleic acids with untargeted cells prompted us to further investigate their impact on AOC binding abilities and cell selectivity. We synthesized a series of single- and double-stranded AOCs, as well as a human serum albumin-oligonucleotide conjugate, and studied their interactions with both targeted and non-targeted living cells using a time-resolved analysis of ligand binding assay. Our results indicate that conjugation of single strand oligonucleotides to proteins induce consistent non-specific interactions with cell surfaces while double strand oligonucleotides have little or no effect, depending on the preparation method.

Antibody-Oligonucleotide Conjugates: A Twist to Antibody-Drug Conjugates

A summary of the key technological advancements in the preparation of antibody-oligonucleotide conjugates (AOCs) and the distinct advantages and disadvantages of AOCs as novel therapeutics are presented. The merits and demerits of the different approaches to conjugating oligonucleotides to antibodies, antibody fragments or other proteins, mainly from the perspective of AOC purification and analytical characterizations, are assessed. The lessons learned from in vitro and in vivo studies, especially the findings related to silencing, trafficking, and cytotoxicity of the conjugates, are also summarized.