Linker technologies for antibody-drug conjugates

Antibody drug conjugates: Design implications for clinicians

OBJECTIVE

There are currently 11 antibody-drug conjugates (ADC) that are FDA approved for use in oncologic disease states, with many more in the pipeline. The authors aim to review the pharmacokinetic profiles of the components of ADCs to engage pharmacist practitioners in practical considerations in the care of patients. This article provides an overview on the use of ADCs in the setting of organ dysfunction, drug-drug interactions, and management of on- and off-target adverse effects.

DATA SOURCES

A systematic search of the literature on ADCs through September 2023 was conducted. Clinical trials as well as articles on ADC design and functional components, adverse effects, and pharmacokinetics were reviewed. Reviewed literature included prescribing information as well as tertiary sources and primary literature.

DATA SUMMARY

A total of 11 ADCs were reviewed for the purpose of this article. A description of the mechanism of action and structure of ADCs is outlined, and a table containing description of each currently FDA-approved ADC is included. Various mechanisms of ADC toxicity are reviewed, including how ADC structure may be implicated.

CONCLUSION

It is imperative that pharmacist clinicians understand the design and function of each component of an ADC to continue to assess new approvals for use in oncology patients. Understanding the design of the ADC can help a pharmacy practitioner compare and contrast adverse effect profiles to support their multidisciplinary teams and to engage patients in education and management of their care.

Progress in the study of antibody-drug conjugates for the treatment of cervical cancer

Cervical cancer is the second most prevalent malignancy affecting women's health globally, and the number of morbidity and mortality from cervical cancer continues to rise worldwide. The 5-year survival rate of patients with recurrent or metastatic cervical cancer is significantly reduced, and existing treatment modalities have low efficacy and high adverse effects, so there is a strong need for new, effective, and well-tolerated therapies. Antibody-drug conjugates (ADCs) are a new targeted therapeutic modality that can efficiently kill tumor cells. This review aims to summarize the composition, research, and development history and mechanism of action of ADCs, to review the research progress of ADCs in the treatment of cervical cancer, and to summarize and prospect the application of ADCs.

Structural and functional analysis of engineered antibodies for cancer immunotherapy: insights into protein compactness and solvent accessibility

Antibodies are crucial tools in various biomedical applications, including immunotherapy. In this study, we focused on designing and engineering antibodies to enhance their structural dynamics and functional properties. By employing advanced computational techniques and experimental validation, we gained crucial insights into the impact of specific mutations on the engineered antibodies. This study investigates the design and engineering of antibodies to improve their structural dynamics and functional properties. Structural attributes, such as protein compactness and solvent accessibility, were assessed, revealing interesting trends in anti-CD3 and anti-HER2 antibodies. Mutations in CD3 antibodies resulted in a more stable conformation, while mutant HER2 antibodies exhibited altered interaction with the target. Analysis of secondary structure assignments demonstrated significant changes in the folding and stability of the mutant antibodies compared to the wild-type counterparts. The conformational landscape of the engineered antibodies was explored, providing insights into folding pathways and binding mechanisms. Overall, the current study highlights the significance of antibody design and engineering in modulating structural dynamics and functional properties. The findings contribute to developing improved immunotherapeutic strategies by optimising antibody-based therapeutics for targeted diseases with enhanced efficacy and precision.Communicated by Ramaswamy H. Sarma.

Antibody-drug conjugates in cancer therapy: innovations, challenges, and future directions

The emergence of antibody-drug conjugates (ADCs) as a potential therapeutic avenue in cancer treatment has garnered significant attention. By combining the selective specificity of monoclonal antibodies with the cytotoxicity of drug molecules, ADCs aim to increase the therapeutic index, selectively targeting cancer cells while minimizing systemic toxicity. Various ADCs have been licensed for clinical usage, with ongoing research paving the way for additional options. However, the manufacture of ADCs faces several challenges. These include identifying suitable target antigens, enhancing antibodies, linkers, and payloads, and managing resistance mechanisms and side effects. This review focuses on the strategies to overcome these hurdles, such as site-specific conjugation techniques, novel antibody formats, and combination therapy. Our focus lies on current advancements in antibody engineering, linker technology, and cytotoxic payloads while addressing the challenges associated with ADC development. Furthermore, we explore the future potential of personalized medicine, leveraging individual patients' molecular profiles, to propel ADC treatments forward. As our understanding of the molecular mechanisms driving cancer progression continues to expand, we anticipate the development of new ADCs that offer more effective and personalized therapeutic options for cancer patients.

Considerations for the design of antibody drug conjugates (ADCs) for clinical development: lessons learned

Antibody-drug conjugates (ADCs) have emerged as a novel therapeutic strategy that has successfully reached patient treatment in different clinical scenarios. ADCs are formed by an antibody against a specific tumor-associated antigen (TAA), a cytotoxic payload, and a chemical linker that binds both. To this regard, most efforts have been focused on target identification, antibody design and linker optimization, but other relevant aspects for clinical development have not received the necessary attention. In this article using data from approved ADCs, we evaluated all characteristics of these agents, including payload physicochemical properties, in vitro potency, drug antibody ratio (DAR), exposure-response relationships, and clinical development strategies. We suggest that compounds with best options for clinical development include those with optimal payload physicochemical properties and cleavable linkers that would lead to a bystander effect. These modalities can facilitate the development of ADCs in indications with low expression of the TAA. Early clinical development strategies including changes in the schedule of administration with more frequent doses are also discussed in the context of an efficient strategy. In conclusion, we highlight relevant aspects that are needed for the optimal development of ADCs in cancer, proposing options for improvement.

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.

A comprehensive overview on antibody-drug conjugates: from the conceptualization to cancer therapy

Antibody-Drug Conjugates (ADCs) represent an innovative class of potent anti-cancer compounds that are widely used in the treatment of hematologic malignancies and solid tumors. Unlike conventional chemotherapeutic drug-based therapies, that are mainly associated with modest specificity and therapeutic benefit, the three key components that form an ADC (a monoclonal antibody bound to a cytotoxic drug via a chemical linker moiety) achieve remarkable improvement in terms of targeted killing of cancer cells and, while sparing healthy tissues, a reduction in systemic side effects caused by off-tumor toxicity. Based on their beneficial mechanism of action, 15 ADCs have been approved to date by the market approval by the Food and Drug Administration (FDA), the European Medicines Agency (EMA) and/or other international governmental agencies for use in clinical oncology, and hundreds are undergoing evaluation in the preclinical and clinical phases. Here, our aim is to provide a comprehensive overview of the key features revolving around ADC therapeutic strategy including their structural and targeting properties, mechanism of action, the role of the tumor microenvironment and review the approved ADCs in clinical oncology, providing discussion regarding their toxicity profile, clinical manifestations and use in novel combination therapies. Finally, we briefly review ADCs in other pathological contexts and provide key information regarding ADC manufacturing and analytical characterization.

Antibody-Drug Conjugates: A Review of Approved Drugs and Their Clinical Level of Evidence

Antibody-drug conjugates (ADCs) are an innovative family of agents assembled through linking cytotoxic drugs (payloads) covalently to monoclonal antibodies (mAbs) to be delivered to tumor tissue that express their particular antigen, with the theoretical advantage of an augmented therapeutic ratio. As of June 2023, eleven ADCs have been approved by the Food and Drug Administration (FDA) and are on the market. These drugs have been added to the therapeutic armamentarium of acute myeloblastic and lymphoblastic leukemias, various types of lymphoma, breast, gastric or gastroesophageal junction, lung, urothelial, cervical, and ovarian cancers. They have proven to deliver more potent and effective anti-tumor activities than standard practice in a wide variety of indications. In addition to targeting antigen-expressing tumor cells, bystander effects have been engineered to extend cytotoxic killing to low-antigen-expressing or negative tumor cells in the heterogenous tumor milieu. Inevitably, myelosuppression is a common side effect with most of the ADCs due to the effects of the cytotoxic payload. Also, other unique side effects are specific to the tissue antigen that is targeted for, such as the cardiac toxicity with Her-2 targeting ADCs, and the hemorrhagic side effects with the tissue factor (TF) targeting Tisotumab vedotin. Further exciting developments are centered in the strategies to improve the tolerability and efficacy of the ADCs to improve the therapeutic window; as well as the development of novel payloads including (1) peptide-drug conjugates (PDCs), with the peptide replacing the monoclonal antibody, rendering greater tumor penetration; (2) immune-stimulating antibody conjugates (ISACs), which upon conjugation of the antigen, cause an influx of pro-inflammatory cytokines to activate dendritic cells and harness an anti-tumor T-cell response; and (3) the use of radioactive isotopes as a payload to enhance cytotoxic activity.

Antibody-Drug Conjugates in Lung Cancer: Recent Advances and Implementing Strategies

Antibody-drug conjugates (ADCs) are one of the fastest-growing oncology therapeutics, merging the cytotoxic effect of conjugated payload with the high specific ability and selectivity of monoclonal antibody targeted on a specific cancer cell membrane antigen. The main targets for ADC development are antigens commonly expressed by lung cancer cells, but not in normal tissues. They include human epidermal growth factor receptor 2, human epidermal growth factor receptor 3, trophoblast cell surface antigen 2, c-MET, carcinoembryonic antigen-related cell adhesion molecule 5, and B7-H3, each with one or more specific ADCs that showed encouraging results in the lung cancer field, more in non-small-cell lung cancer than in small-cell lung cancer histology. To date, multiple ADCs are under evaluation, alone or in combination with different molecules (eg, chemotherapy agents or immune checkpoint inhibitors), and the optimal strategy for selecting patients who may benefit from the treatment is evolving, including an improvement of biomarker understanding, involving markers of resistance or response to the payload, besides the antibody target. In this review, we discuss the available evidence and future perspectives on ADCs for lung cancer treatment, including a comprehensive discussion on structure-based drug design, mechanism of action, and resistance concepts. Data were summarized by specific target antigen, biology, efficacy, and safety, differing among ADCs according to the ADC payload and their pharmacokinetics and pharmacodynamics properties.

Antibody-Drug Conjugates for Lung Cancer: Payloads and Progress

Antibody Drug Conjugates (ADCs) are a novel class of therapeutic that structurally comprise an antibody directed at a tumor epitope connected via a linker to a cytotoxic payload that have shown significant antitumor activity across a range of malignancies including lung cancer. In this article we review the pharmacology of ADCs, describe results of trials with ADCs directed at targets in lung cancer including Trophoblast cell-surface antigen 2(TROP2), HER3, MET, Carcinoembryonic antigen-related cell adhesion molecular 5(CECAM-5) and HER2. Trastuzumab Deruxtecan (also known as DS-8201a or T-DXd) an ADC directed at HER2 recently became the first ADC to receive FDA approval in lung cancer, on the basis of its activity in tumors with HER2 mutations, demonstrated in the Destiny-Lung01 and Lung02 trials.

AR13 peptide-conjugated liposomes improve the antitumor efficacy of doxorubicin in mice bearing C26 colon carcinoma; in silico, in vitro, and in vivo study

Currently, liposomes have emerged as efficient and safer nano-carriers for targeted therapy in different cancers. This work aimed to employ PEGylated liposomal doxorubicin (Doxil®/PLD), modified with AR13 peptide, to target Muc1 on the surface of colon cancerous cells. We performed molecular docking and simulation studies (using Gromacs package) of AR13 peptide against Muc1 to analyze and visualize the peptide-Muc1 binding combination. For in vitro analysis, the AR13 peptide was post-inserted into Doxil® and verified by TLC, ¹H NMR, and HPLC techniques. The zeta potential, TEM, release, cell uptake, competition assay, and cytotoxicity studies were performed. In vivo antitumor activities and survival analysis on mice bearing C26 colon carcinoma were studied. Results showed that after 100 ns simulation, a stable complex between AR13 and Muc1 formed, and molecular dynamics analysis confirmed this interaction. In vitro analysis demonstrated significant enhancement of cellular binding and cell uptake. The results of in vivo study on BALB/c mice bearing C26 colon carcinoma, revealed an extended survival time to 44 days and higher tumor growth inhibition compared to Doxil®. Thus, the AR13 peptide could be explored as a potent ligand for Muc1, improving therapeutic antitumor efficiency in colon cancer cells.

The most common linkers in bioactive molecules and their bioisosteric replacement network

Structures of the large majority of bioactive molecules are composed of several rings that are decorated by substituents and connected by linkers. While numerous cheminformatics studies focusing on rings and substituents are available, practically nothing has been published about the third important structural constituent of bioactive molecules - the linkers. The current study attempts to fill this gap. The most common linkers present in bioactive molecules are identified, their properties analyzed and a method for linker similarity search introduced. The bioisosteric replacement network of linkers is generated based on a large corpus of structure-activity data from medicinal chemistry literature. The results are presented in a graphical form and the underlying data are also made available for download. This analysis is intended to help medicinal chemists to better understand the role of linkers, particularly heterocyclic rings in bioactive molecules and to select an optimal set of linkers in their future project.

Postulating the possible cellular signalling mechanisms of antibody drug conjugates in Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders in the world. Although the basic pathology of the disease is elucidated, it is difficult to restore or prevent the worsening of neurodegeneration and its symptoms. Antibody and small molecule-based approaches have been studied and are in study individually, but a combined approach like conjugation has not been performed to date. The conjugation between antibodies and drugs which are already used for Alzheimer's treatment or developed specifically for this purpose may have better efficacy and dual action in mitigating Alzheimer's disease. A probable mechanism for antibody-drug conjugates in Alzheimer's disease is discussed in the present review.

Antibody-drug conjugates in lung cancer: dawn of a new era?

Antibody-drug conjugates (ADCs) are one of fastest growing classes of oncology drugs in modern drug development. By harnessing the powers of both cytotoxic chemotherapy and targeted therapy, ADCs are unique in offering the potential to deliver highly potent cytotoxic agents to cancer cells which express a pre-defined cell surface target. In lung cancer, the treatment paradigm has shifted dramatically in recent years, and now ADCs are now joining the list as potential options for lung cancer patients. Since 2020, the first ADC for NSCLC patients has been FDA-approved (trastuzumab deruxtecan) and two ADCs have been granted FDA Breakthrough Therapy Designation, currently under evaluation (patritumab deruxtecan, telisotuzumab vedotin). Furthermore, several early-phase trials are assessing various novel ADCs, either as monotherapy or in combinations with advanced lung cancer, and more selective and potent ADCs are expected to become therapeutic options in clinic soon. In this review, we discuss the structure and mechanism of action of ADCs, including insights from pre-clinical work; we summarize the ADCs' recent progress in lung cancer, describe toxicity profiles of ADCs, and explore strategies designed to enhance ADC potency and overcome resistance. In addition, we discuss novel ADC strategies of interest in lung cancer, including non-cytotoxic payloads, such as immunomodulatory and anti-apoptotic agents.

Potential of antibody-drug conjugates (ADCs) for cancer therapy

The primary purpose of ADCs is to increase the efficacy of anticancer medications by minimizing systemic drug distribution and targeting specific cells. Antibody conjugates (ADCs) have changed the way cancer is treated. However, because only a tiny fraction of patients experienced long-term advantages, current cancer preclinical and clinical research has been focused on combination trials. The complex interaction of ADCs with the tumor and its microenvironment appear to be reliant on the efficacy of a certain ADC, all of which have significant therapeutic consequences. Several clinical trials in various tumor types are now underway to examine the potential ADC therapy, based on encouraging preclinical results. This review tackles the potential use of ADCs in cancer therapy, emphasizing the essential processes underlying their positive therapeutic impacts on solid and hematological malignancies. Additionally, opportunities are explored to understand the mechanisms of ADCs action, the mechanism of resistance against ADCs, and how to overcome potential resistance following ADCs administration. Recent clinical findings have aroused interest, leading to a large increase in the number of ADCs in clinical trials. The rationale behind ADCs, as well as their primary features and recent research breakthroughs, will be discussed. We then offer an approach for maximizing the potential value that ADCs can bring to cancer patients by highlighting key ideas and distinct strategies.

Synchronous intracellular delivery of EGFR-targeted antibody-drug conjugates by p38-mediated non-canonical endocytosis

Monoclonal antibodies targeting the epidermal growth factor receptor (EGFR), including cetuximab and panitumumab, have been used in clinic settings to treat cancer. They have also recently been applied to antibody–drug conjugates (ADCs); however, their clinical efficacy is limited by several issues, including lower internalization efficiency. The binding of cetuximab to the extracellular domain of EGFR suppresses ligand-induced events; therefore, we focus on ligand-independent non-canonical EGFR endocytosis for the delivery of ADCs into cells. Tumor necrosis factor-α (TNF-α) strongly induces the endocytosis of the cetuximab-EGFR complex within 15 min via the p38 phosphorylation of EGFR in a tyrosine kinase-independent manner. A secondary antibody conjugated with saporin, a ribosome-inactivating protein, also undergoes internalization with the complex and enhances its anti-proliferative activity. Anti-cancer agents, including cisplatin and temozolomide, also induce the p38-mediated internalization. The results of the present study demonstrate that synchronous non-canonical EGFR endocytosis may be a feasible strategy for promoting the therapeutic efficacy of EGFR-targeting ADCs in clinical settings.

Polymer-drug conjugates: Design principles, emerging synthetic strategies and clinical overview

Adagen, an enzyme replacement treatment for adenosine deaminase deficiency, was the first protein-polymer conjugate to be approved in early 1990s. Post this regulatory approval, numerous polymeric drugs and polymeric nanoparticles have entered the market as advanced or next-generation polymer-based therapeutics, while many others have currently been tested clinically. The polymer conjugation to therapeutic moiety offers several advantages, like enhanced solubilization of drug, controlled release, reduced immunogenicity, and prolonged circulation. The present review intends to highlight considerations in the design of therapeutically effective polymer-drug conjugates (PDCs), including the choice of linker chemistry. The potential synthetic strategies to formulate PDCs have been discussed along with recent advancements in the different types of PDCs, i.e., polymer-small molecular weight drug conjugates, polymer-protein conjugates, and stimuli-responsive PDCs, which are under clinical/preclinical investigation. Current impediments and regulatory hurdles hindering the clinical translation of PDC into effective therapeutic regimens for the amelioration of disease conditions have been addressed.

Antibody drug conjugate: the "biological missile" for targeted cancer therapy

Antibody–drug conjugate (ADC) is typically composed of a monoclonal antibody (mAbs) covalently attached to a cytotoxic drug via a chemical linker. It combines both the advantages of highly specific targeting ability and highly potent killing effect to achieve accurate and efficient elimination of cancer cells, which has become one of the hotspots for the research and development of anticancer drugs. Since the first ADC, Mylotarg^® (gemtuzumab ozogamicin), was approved in 2000 by the US Food and Drug Administration (FDA), there have been 14 ADCs received market approval so far worldwide. Moreover, over 100 ADC candidates have been investigated in clinical stages at present. This kind of new anti-cancer drugs, known as “biological missiles”, is leading a new era of targeted cancer therapy. Herein, we conducted a review of the history and general mechanism of action of ADCs, and then briefly discussed the molecular aspects of key components of ADCs and the mechanisms by which these key factors influence the activities of ADCs. Moreover, we also reviewed the approved ADCs and other promising candidates in phase-3 clinical trials and discuss the current challenges and future perspectives for the development of next generations, which provide insights for the research and development of novel cancer therapeutics using ADCs.

Stepping forward in antibody-drug conjugate development

Antibody-drug conjugates (ADCs) are cancer therapeutic agents comprised of an antibody, a linker and a small-molecule payload. ADCs use the specificity of the antibody to target the toxic payload to tumor cells. After intravenous administration, ADCs enter circulation, distribute to tumor tissues and bind to the tumor surface antigen. The antigen then undergoes endocytosis to internalize the ADC into tumor cells, where it is transported to lysosomes to release the payload. The released toxic payloads can induce apoptosis through DNA damage or microtubule inhibition and can kill surrounding cancer cells through the bystander effect. The first ADC drug was approved by the United States Food and Drug Administration (FDA) in 2000, but the following decade saw no new approved ADC drugs. From 2011 to 2018, four ADC drugs were approved, while in 2019 and 2020 five more ADCs entered the market. This demonstrates an increasing trend for the clinical development of ADCs. This review summarizes the recent clinical research, with a specific focus on how the in vivo processing of ADCs influences their design. We aim to provide comprehensive information about current ADCs to facilitate future development.

Synthesis and Applications of Porphyrin-Biomacromolecule Conjugates

With potential applications in materials and especially in light-responsive biomedicine that targets cancer tissue selectively, much research has focused on developing covalent conjugation techniques to tether porphyrinoid units to various biomacromolecules. This review details the key synthetic approaches that have been employed in the recent decades to conjugate porphyrinoids with oligonucleotides and peptides/proteins. In addition, we provide succinct discussions on the subsequent applications of such hybrid systems and also give a brief overview of the rapidly progressing field of porphyrin-antibody conjugates. Since nucleic acid and peptide systems vary in structure, connectivity, functional group availability and placement, as well as stability and solubility, tailored synthetic approaches are needed for conjugating to each of these biomacromolecule types. In terms of tethering to ONs, porphyrins are typically attached by employing bioorthogonal chemistry (e.g., using phosphoramidites) that drive solid-phase ON synthesis or by conducting post-synthesis modifications and subsequent reactions (such as amide couplings, hydrazide-carbonyl reactions, and click chemistry). In contrast, peptides and proteins are typically conjugated to porphyrinoids using their native functional groups, especially the thiol and amine side chains. However, bioorthogonal reactions (e.g., Staudinger ligations, and copper or strain promoted alkyne-azide cycloadditions) that utilize de novo introduced functional groups onto peptides/proteins have seen vigorous development, especially for site-specific peptide-porphyrin tethering. While the ON-porphyrin conjugates have largely been explored for programmed nanostructure self-assembly and artificial light-harvesting applications, there are some reports of ON-porphyrin systems targeting clinically translational applications (e.g., antimicrobial biomaterials and site-specific nucleic acid cleavage). Conjugates of porphyrins with proteinaceous moieties, on the other hand, have been predominantly used for therapeutic and diagnostic applications (especially in photodynamic therapy, photodynamic antimicrobial chemotherapy, and photothermal therapy). The advancement of the field of porphyrinoid-bioconjugation chemistry from basic academic research to more clinically targeted applications require continuous fine-tuning in terms of synthetic strategies and hence there will continue to be much exciting work on porphyrinoid-biomacromolecule conjugation.

Introduction to Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are innovative biopharmaceutical products in which a monoclonal antibody is linked to a small molecule drug with a stable linker. Most of the ADCs developed so far are for treating cancer, but there is enormous potential for using ADCs to treat other diseases. Currently, ten ADCs have been approved by the United States Food and Drug Administration (FDA), and more than 90 ADCs are under worldwide clinical development. Monoclonal antibodies have evolved from research tools to powerful therapeutics in the past 30 years. Tremendous strides have been made in antibody discovery, protein bioengineering, formulation, and delivery devices. This manuscript provides an overview of the biology, chemistry, and biophysical properties of each component of ADC design. This review summarizes the advances and challenges in the field to date, with an emphasis on antibody conjugation, linker-payload chemistry, novel payload classes, drug-antibody ratio (DAR), and product development. The review emphasizes the lessons learned in the development of oncology antibody conjugates and look towards future innovations enabling other therapeutic indications. The review discusses resistance mechanisms to ADCs, and give an opinion on future perspectives.

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.

Generation of Antibody-Drug Conjugate Resistant Models

Simple Summary

Antibody-drug conjugates (ADCs) constitute new and effective therapies in cancer. However, resistance is frequently observed in treated patients after a given period of time. That resistance may be present from the beginning of the treatment (primary or de novo resistance) or raise after an initial response to the ADC (secondary resistance). Knowing the causes of those resistances is a necessity in the field as it may help in designing strategies to overcome them. Because of that, it is necessary to develop models that allow the identification of mechanisms of resistance. In this review, we present different approaches that have been used to model ADC resistance in the preclinical setting, and that include the use of established cell lines, patient-derived ex vivo cultures and xenografts primarily or secondarily resistant to the ADC.

Abstract

In the last 20 years, antibody-drug conjugates (ADCs) have been incorporated into the oncology clinic as treatments for several types of cancer. So far, the Food and Drug Administration (FDA) has approved 11 ADCs and other ADCs are in the late stages of clinical development. Despite the efficacy of this type of drug, the tumors of some patients may result in resistance to ADCs. Due to this, it is essential not only to comprehend resistance mechanisms but also to develop strategies to overcome resistance to ADCs. To reach these goals, the generation and use of preclinical models to study those mechanisms of resistance are critical. Some cells or patient tumors may result in primary resistance to the action of an ADC, even if they express the antigen against which the ADC is directed. Isolated primary tumoral cells, cell lines, or patient explants (patient-derived xenografts) with these characteristics can be used to study primary resistance. The most common method to generate models of secondary resistance is to treat cancer cell lines or tumors with an ADC. Two strategies, either continuous treatment with the ADC or intermittent treatment, have successfully been used to develop those resistance models.

A dual-enzyme cleavable linker for antibody-drug conjugates

A novel enzyme cleavable linker for antibody-drug conjugates is reported. The 3-O-sulfo-β-galactose linker is cleaved sequentially by two lysosomal enzymes - arylsulfatase A and β-galactosidase - to release the payload in targeted cells. An α-HER2 antibody-drug conjugate synthesised using this highly hydrophilic dual-cleavable linker exhibited excellent cytotoxicity and selectivity.

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.

Synthesis and Biological Evaluation of a Carbamate-Containing Tubulysin Antibody-Drug Conjugate

Antibody-drug conjugates (ADCs) use antibodies to deliver cytotoxic payloads directly into tumor cells via specifically binding to the target cell surface antigens. ADCs can enhance the anti-tumor effects of antibodies, and increase the delivery of cytotoxic payloads to cancer cells with a better therapeutic index. An ADC was prepared with a potent carbamate-containing tubulysin analogue attached to an anti-mesothelin antibody via a Cit-Val dipeptide linker. An aniline functionality in the tubulysin analogue was created to provide a site of linker attachment via an amide bond that would be stable in systemic circulation. Upon ADC internalization into antigen-positive cancer cells, the Cit-Val dipeptide linker was cleaved by lysosomal proteases, and the drug was released inside the tumor cells. The naturally occurring acetate of tubulysin was modified to a carbamate to reduce acetate hydrolysis of the ADC in circulation and to increase the hydrophilicity of the drug. The ADC bearing the monoclonal anti-mesothelin antibody and the carbamate-containing tubulysin was highly potent and immunologically specific to H226 human lung carcinoma cells in vitro, and efficacious at well-tolerated doses in a mesothelin-positive OVCAR3 ovarian cancer xenograft mouse model.

Artificial Glycoproteins as a Scaffold for Targeted Drug Therapy

Akin to a cellular "fingerprint," the glycocalyx is a glycan-enriched cellular coating that plays a crucial role in mediating cell-to-cell interactions. To gain a better understanding of the factors that govern in vivo recognition, artificial glycoproteins were initially created to probe changes made to the accumulation and biodistribution of specific glycan assemblies through biomimicry. As a result, the organ-specific accumulation for a variety of glycoproteins decorated with simple and/or complex glycans was identified. Additionally, binding trends with regard to cancer cell selectivity were also investigated. To exploit the knowledge gained from these studies, numerous groups thus became engaged in developing targeted drug methodologies based on the use of artificial glycoproteins. This has either been done through adopting the glycoprotein scaffold as a drug carrier, or to directly glycosylate therapeutic proteins/enzymes to localize their biological activity. The principle aim of this Review is to present the foundational research that has driven artificial glycoprotein-based targeting and subsequent adaptations with potential therapeutic applications.

ADCs, as Novel Revolutionary Weapons for Providing a Step Forward in Targeted Therapy of Malignancies

:

Antibody drug conjugates (ADCs), as potent pharmaceutical trojan horses for cancer treatment, provide superior efficacy and specific targeting along with low risk of adverse reactions compared to traditional chemotherapeutics. In fact, the development of these agents combines the selective targeting capability of monoclonal antibody (mAb) with high cytotoxicity of chemotherapeutics for controlling the neoplastic mass growth. Different ADCs (more than 60 ADCs) in preclinical and clinical trials were introduced in this novel pharmaceutical field. Various design-based factors must be taken into account for improving the functionality of ADC technology, including selection of appropriate target antigen and high binding affinity of fragment (miniaturized ADCs) or full mAbs (preferentially use of humanized or fully human antibodies compared to murine and chimeric ones), use of bispecific antibodies for dual targeting effect, linker engineering and conjugation method efficacy to obtain more controlled drug to antibody ratio (DAR). Challenging issues affecting therapeutic efficacy and safety of ADCs, including bystander effect, on- and off-target toxicities, multi drug resistance (MDR) are also addressed. 4 FDA-approved ADCs in the market, including ADCETRIS ®, MYLOTARG®, BESPONSA ®, KADCYLA®. The goal of the current review is to evaluate the key parameters affecting ADCs development.

Novel Silyl Ether-Based Acid-Cleavable Antibody-MMAE Conjugates with Appropriate Stability and Efficacy

Antibody-drug conjugate (ADC) is a novel efficient drug delivery system that has been successfully used in clinical practice, and it has become a research hotspot in the anti-tumor drug field. Acid-cleavable linkers were first used in clinical ADCs, but their structural variety (e.g., hydrazone and carbonate) is still limited, and their stability is usually insufficient. Designing novel acid-cleavable linkers for the conjugation of the popular cytotoxin monomethyl auristatin E (MMAE) has always been a significant topic. In this paper, we generate a novel, silyl ether-based acid-cleavable antibody-MMAE conjugate, which skillfully achieves efficient combination of amino-conjugated MMAE with the acid-triggered silyl ether group by introducing p-hydroxybenzyl alcohol (PHB). The stability, acid-dependence cleavage, effective mechanism, efficacy and safety of the resulting ADC were systematically studied; the results show that it exhibits a significant improvement in stability, while maintaining appropriate efficacy and controlled therapeutic toxicity. This strategy is expected to expand a new type of acid-cleavable linkers for the development of ADCs with highly potent payloads.

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.

Novel trastuzumab-DM1 conjugate: Synthesis and bio-evaluation

Antibody-drug conjugates are now of considerable interest and are recommended for the treatment of cancers. Linkers are having a crucial role in potency and efficacy of these drugs. Herein, for the first time, we have used a water-soluble poly-ethylene glycol based linker (succinimidyl-[(N-maleimido propionamido)-diethyleneglycol] [SM(PEG)2]) for lysine amide coupling of DM1 drug to trastuzumab considering evaluation of the effect of using a hydrophilic linker on physicochemical and biological properties of the resulting conjugate in comparison to the conjugate containing succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC) linker, which has a relative hydrophobic nature. The physicochemical properties of synthesized conjugates were investigated in terms of drug to antibody ratio, size variants and free drug quantities. In vitro biological activity of trastuzumab-DM1 conjugates was assessed on breast cancer cell lines expressing different levels of HER2 using binding affinity, antiproliferative, apoptosis, and antibody-dependent cell-mediated cytotoxicity (ADCC) assays. Synthesized conjugate containing hydrophilic linker, showed higher drug to antibody ratio, no aggregated form and higher cellular toxicity in comparison to SMCC bearing conjugate. Binding affinity and ADCC potential of conjugates was not affected upon the usage of hydrophilic linker. In conclusion, application of SM(PEG)2 for coupling of DM1 to trastuzumab enhance desirable characteristics of the resulting conjugate.

Antibody-drug conjugates (ADCs) for cancer therapy: Strategies, challenges, and successes

Targeted delivery of therapeutic molecules into cancer cells is considered as a promising strategy to tackle cancer. Antibody-drug conjugates (ADCs), in which a monoclonal antibody (mAb) is conjugated to biologically active drugs through chemical linkers, have emerged as a promising class of anticancer treatment agents, being one of the fastest growing fields in cancer therapy. The failure of early ADCs led researchers to explore strategies to develop more effective and improved ADCs with lower levels of unconjugated mAbs and more-stable linkers between the drug and the antibody, which show improved pharmacokinetic properties, therapeutic indexes, and safety profiles. Such improvements resulted in the US Food and Drug Administration approvals of brentuximab vedotin, trastuzumab emtansine, and, more recently, inotuzumab ozogamicin. In addition, recent clinical outcomes have sparked additional interest, which leads to the dramatically increased number of ADCs in clinical development. The present review explores ADCs, their main characteristics, and new research developments, as well as discusses strategies for the selection of the most appropriate target antigens, mAbs, cytotoxic drugs, linkers, and conjugation chemistries.

Resistance to Antibody-Drug Conjugates

Antibody-drug conjugates (ADC) are multicomponent molecules constituted by an antibody covalently linked to a potent cytotoxic agent. ADCs combine high target specificity provided by the antibody together with strong antitumoral properties provided by the attached cytotoxic agent. At present, four ADCs have been approved and over 60 are being explored in clinical trials. Despite their effectiveness, resistance to these drugs unfortunately occurs. Efforts to understand the bases underlying such resistance are being carried out with the final purpose of counteracting them. In this review, we report described mechanisms of resistance to ADCs used in the clinic along with other potential ones that may contribute to resistance acquisition. We also discuss strategies to overcome resistance to ADCs. Cancer Res; 78(9); 2159-65. ©2018 AACR.

Development and Properties of Valine-Alanine based Antibody-Drug Conjugates with Monomethyl Auristatin E as the Potent Payload

Antibody-drug conjugates (ADCs), designed to selectively deliver cytotoxic agents to antigen-bearing cells, are poised to become an important class of cancer therapeutics. Human epithelial growth factor receptor (HER2) is considered an effective target for cancer treatment, and a HER2-targeting ADC has shown promising results. Most ADCs undergoing clinical evaluation contain linkers that have a lysosomal protease-cleavable dipeptide, of which the most common is valine-citrulline (VC). However, valine-alanine (VA), another dipeptide comprising two human essential amino acids, has been used in next generation ADCs loading new toxins, but the druggable properties of ADCs loaded the most popular monomethyl auristatin E (MMAE) remain to be further explored. In this study, we generated VA-based ADCs that connected MMAE to an anti-HER2 antibody. We studied the differences in the preparation process, in vitro stability, cathepsin B activity and in vitro cytotoxicity of VA-based ADC compared to the ADC of VC. VA had comparable performance to VC, which preliminarily displays its practicability. Additional efficacy and safety studies in a xenograft model indicate this novel ADC exerted potent anti-tumor activity and negligible toxicity. The results of this study show the application potential of VA-based ADC with MMAE as the payload.

Intracellular trafficking of new anticancer therapeutics: antibody-drug conjugates

Antibody-drug conjugate (ADC) is a milestone in targeted cancer therapy that comprises of monoclonal antibodies chemically linked to cytotoxic drugs. Internalization of ADC takes place via clathrin-mediated endocytosis, caveolae-mediated endocytosis, and pinocytosis. Conjugation strategies, endocytosis and intracellular trafficking optimization, linkers, and drugs chemistry present a great challenge for researchers to eradicate tumor cells successfully. This inventiveness of endocytosis and intracellular trafficking has given considerable momentum recently to develop specific antibodies and ADCs to treat cancer cells. It is significantly advantageous to emphasize the endocytosis and intracellular trafficking pathways efficiently and to design potent engineered conjugates and biological entities to boost efficient therapies enormously for cancer treatment. Current studies illustrate endocytosis and intracellular trafficking of ADC, protein, and linker strategies in unloading and also concisely evaluate practically applicable ADCs.

Aberrant intracellular metabolism of T-DM1 confers T-DM1 resistance in human epidermal growth factor receptor 2-positive gastric cancer cells

Trastuzumab emtansine (T-DM1), an antibody-drug conjugate (ADC) consisting of human epidermal growth factor receptor 2 (HER2)-targeted mAb trastuzumab linked to antimicrotubule agent mertansine (DM1), has been approved for the treatment of HER2-positive metastatic breast cancer. Acquired resistance has been a major obstacle to T-DM1 treatment, and mechanisms remain incompletely understood. In the present study, we established a T-DM1-resistant N87-KR cell line from HER2-positive N87 gastric cancer cells to investigate mechanisms of acquired resistance and develop strategies for overcoming it. Although the kinetics of binding, internalization, and externalization of T-DM1 were the same in N87-KR cells and N87 cells, N87-KR was strongly resistant to T-DM1, but remained sensitive to both trastuzumab and DM1. T-DM1 failed to inhibit microtubule polymerization in N87-KR cells. Consistently, lysine-MCC-DM1, the active T-DM1 metabolite that inhibits microtubule polymerization, accumulated much less in N87-KR cells than in N87 cells. Furthermore, lysosome acidification, achieved by vacuolar H+ -ATPase (V-ATPase), was much diminished in N87-KR cells. Notably, treatment of sensitive N87 cells with the V-ATPase selective inhibitor bafilomycin A1 induced T-DM1 resistance, suggesting that aberrant V-ATPase activity decreases T-DM1 metabolism, leading to T-DM1 resistance in N87-KR cells. Interestingly, HER2-targeted ADCs containing a protease-cleavable linker, such as hertuzumab-vc-monomethyl auristatin E, were capable of efficiently overcoming this resistance. Our results show for the first time that a decrease in T-DM1 metabolites induced by aberrant V-ATPase activity contributes to T-DM1 resistance, which could be overcome by HER2-targeted ADCs containing different linkers, including a protease-cleavable linker. Accordingly, we propose that V-ATPase activity in lysosomes is a novel biomarker for predicting T-DM1 resistance.

Advances in antibody-drug conjugates: A new era of targeted cancer therapy

Antibody-drug conjugates (ADCs), a potent class of anticancer therapeutics, comprise a high-affinity antibody (Ab) and cytotoxic payload coupled via a suitable linker for selective tumor cell killing. In the initial phase of their development, two ADCs, Mylotarg^®, and Adcetris^® were approved by the US Food and Drug Administration (FDA) for treating hematological cancer, but the real breakthrough came with the discovery of the breast cancer-targeting ADC, Kadcyla^®. With advances in bioengineering, linker chemistry, and potent cytotoxic payload, ADC technology has become a more powerful tool for targeted cancer therapy. In addition, ADCs with improved safety using humanized Abs with a unified 'drug:antibody ratio' (DAR) have been achieved. Concomitantly, there has been a significant increase in the number of clinical trials with anticancer ADCs with high translation potential.

Modulating Therapeutic Activity and Toxicity of Pyrrolobenzodiazepine Antibody-Drug Conjugates with Self-Immolative Disulfide Linkers

A novel disulfide linker was designed to enable a direct connection between cytotoxic pyrrolobenzodiazepine (PBD) drugs and the cysteine on a targeting antibody for use in antibody-drug conjugates (ADCs). ADCs composed of a cysteine-engineered antibody were armed with a PBD using a self-immolative disulfide linker. Both the chemical linker and the antibody site were optimized for this new bioconjugation strategy to provide a highly stable and efficacious ADC. This novel disulfide ADC was compared with a conjugate containing the same PBD drug, but attached to the antibody via a peptide linker. Both ADCs had similar efficacy in mice bearing human tumor xenografts. Safety studies in rats revealed that the disulfide-linked ADC had a higher MTD than the peptide-linked ADC. Overall, these data suggest that the novel self-immolative disulfide linker represents a valuable way to construct ADCs with equivalent efficacy and improved safety. Mol Cancer Ther; 16(5); 871-8. ©2017 AACR.

Marine Antibody-Drug Conjugates: Design Strategies and Research Progress

Antibody-drug conjugates (ADCs), constructed with monoclonal antibodies (mAbs), linkers, and natural cytotoxins, are innovative drugs developed for oncotherapy. Owing to the distinctive advantages of both chemotherapy drugs and antibody drugs, ADCs have obtained enormous success during the past several years. The development of highly specific antibodies, novel marine toxins' applications, and innovative linker technologies all accelerate the rapid R&D of ADCs. Meanwhile, some challenges remain to be solved for future ADCs. For instance, varieties of site-specific conjugation have been proposed for solving the inhomogeneity of DARs (Drug Antibody Ratios). In this review, the usages of various natural toxins, especially marine cytotoxins, and the development strategies for ADCs in the past decade are summarized. Representative ADCs with marine cytotoxins in the pipeline are introduced and characterized with their new features, while perspective comments for future ADCs are proposed.