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

The Evolution of Anti-CD20 Treatment for Multiple Sclerosis: Optimization of Antibody Characteristics and Function

B-cell depletion with CD20-targeted agents is commonly used for treatment of multiple sclerosis (MS), other autoimmune diseases, and certain hematologic malignancies. Initial apparent success with rituximab in MS and neuromyelitis optica spurred development of the anti-CD20 monoclonal antibody (mAb) therapies ocrelizumab, ofatumumab, and ublituximab as well as the anti-CD19 mAb inebilizumab. While each are effective at targeting and depleting B cells, structural differences translate into different mechanisms of action affecting maintenance of B-cell depletion and safety and tolerability. Although the anti-CD20 mAbs differ in degree of human versus mouse sequences as well as target CD20 epitope, these properties do not appear to substantially affect activity or tolerability. In contrast, an antibody-dependent cell-mediated cytotoxicity (ADCC) versus a complement-dependent cytotoxicity mechanism of action as well as subcutaneous versus intravenous administration may provide improved tolerability. Glycoengineering of the mAbs ublituximab and inebilizumab enhances ADCC and can overcome the reduced responses to mAb-mediated B-cell depletion associated with certain genetic polymorphisms. Other strategies for therapeutic targeting of CD20, including brain shuttle antibodies (e.g., RO7121932), bispecific antibodies, chimeric antigen receptor T-cell therapies, and antibody-drug conjugates, are in active clinical development and may be future treatment approaches in MS and other B-cell-mediated autoimmune diseases.

Elucidating Critical Factors of Internalization and Drug Release of Antibody-Drug Conjugates (ADCs) Using Kinetic Parameters Evaluated by a Novel Tool Named TORCH

During the past decade, antibody-drug conjugates (ADCs) have emerged as new drugs in cancer therapy with 15 ADCs already approved such as Kadcyla, Enhertu, and Adcetris. ADCs contain a cytotoxic drug that is linked to an antibody, allowing for specific delivery of the warhead to tumor cells. Typically, the antibody targets a tumor-specific antigen expressed on the cell surface. After the internalization of ADCs into cells, the linker is often cleaved by enzymes in the lysosomal compartment of the cell, releasing the warhead and thereby allowing for its interaction with, for example, the DNA or the tubulin cytoskeleton, which finally leads to cell death. Consequently, binding, internalization, and drug release are key attributes for the efficacy of ADCs. Here, we describe a novel molecule named TORCH (Turn On after Release by CatHepsins) that contains a fluorescence quencher system that is separated by a cathepsin B-cleavable linker. When conjugated to an antibody, the TORCH molecule allows one to gain valuable insights on the internalization and drug release of ADCs. While we cannot exclude the influence of other factors such as receptor recycling, we have found that the receptor density is directly related to the amount of payload released intracellularly, meaning that the internalization per receptor is very similar for all investigated antibodies and cell lines.

Preparation and anti-tumor ability evaluation of anti-PD-L1 conjugated curcumin in colon cancer

Immune checkpoint inhibitors have been approved for various solid tumor treatments but have shown poor efficacy on colon cancer. Curcumin has been proven as an anti-tumor agent that inhibits cell cycle and tumor cell proliferation. Moreover, curcumin has also been reported to have the ability to inhibit PD-L1 expression, which might benefit the therapeutic efficacy of immune checkpoint inhibitors. Therefore, we proposed using antibody-drug conjugate (ADC) could effectively inhibit tumor proliferation and reverse the immunosuppression in colon cancer. We prepared an anti-PD-L1 conjugated curcumin with a ROS-responsive linker of phenylboronic acid carbamate, which provides chemo-drug active targeting ability and tumor environment-responsive release. Both in vitro and in vivo data confirm the improved cytotoxicity of anti-PD-L1-PBA-Cur and inhibited cell invasion. More importantly, the PD-L1 expression on the tumor surface was significantly reduced after being treated with ADC. The in vivo inhibition of tumor progression and PD-L1 expression was confirmed in both subcutaneous and in-suit mouse models. This study provides an effective colon treatment strategy with the advantages of high tumor targeting efficiency and immunopotentiation potential.

Recent doxorubicin-conjugates in cancer drug delivery: Exploring conjugation strategies for enhanced efficacy and reduced toxicity

Doxorubicin is a first-line treatment of cancer that works on the mechanism of DNA intercalation and topoisomerase II poisoning. Since the 20th century, Doxorubicin has been used as a promising drug to treat several types of cancer, both solid or metastatic, including breast, thyroid, bladder, ovarian, or gastric cancer, etc. Even though it shows promising effects on cancer cells, it also shows its effects on healthy cells with cancerous cells, which leads to several severe side effects, such as cardiomyopathy, phlebitis, congestive heart failure (CHF), etc., which limits its usage in chemotherapy. Several research has focused on the targeted delivery of doxorubicin to cancerous cells to reduce side effects and improve efficacy. To optimize its anticancer potential, scientists have recently been developing nano-formulations and investigating various conjugations. The structure of doxorubicin consists of two primary functional groups that can be employed for conjugation with a variety of biomolecules, The first is the primary amine group in a sugar moiety, and the other one is the primary hydroxyl group in the aliphatic chain ring. In this paper, we have mentioned several conjugations of doxorubicin such as antibodies, nanoparticles, polymers, and phytochemical conjugations. Different studies regarding these conjugations are also mentioned, which represent promising strategies to optimize cancer treatment by minimizing side effects.

Tumor-specific biochemical nanoconversion of self-assembled peptide-conjugated paclitaxel-docetaxel-based nanoparticles

Docetaxel (DTX, 1) and paclitaxel (PTX, 2) are famous cytotoxic agents widely used in cancer therapy, however, their low specificity for tumor cells often results in severe systemic toxicity. Beyond conventional prodrug strategies, this study introduces a novel nanoconversion technology that chemically modifies DTX to form self-assembled nanoparticles (NPs), which subsequently convert into a paclitaxel-mimicking molecule (PTXm, 3). Hydrophilic acetylated Phe-Arg-Arg-Phe peptide ((Ac)FRRF, 4) and hydrophobic docetaxel were conjugated to prepare self-assembled (Ac)FRRF-DTX NPs. The selective cleavage of the Arg-Phe bond by cathepsin B, which is abundant in cancer cells, facilitated the nanoconversion of PTXm (3) from (Ac)FRRF-DTX NPs, demonstrating effective cytotoxic effects. Utilizing the cleavage site of peptide and specific sequences (ex. Arg-Arg-Phe), this approach does not simply act as a prodrug but allows the nanomaterial to transform into another cytotoxic biomolecule within tumors. (Ac)FRRF-DTX NPs exhibited remarkable physicochemical properties, superior anti-cancer efficacy, and low toxicity, showcasing an innovative conversion in peptide-conjugated nanomedicine. Unlike traditional prodrug chemistry, this tumor-specific nanoconversion process involves the biochemical transformation of DTX (1) into PTXm (3) via enzymatic action. Overall, this study provides an outstanding example of chemical drug molecular modification through the concept of nanoconversion.

Expanding horizons of cancer immunotherapy: hopes and hurdles

Background

Tumor displays various forms of tumor heterogeneity including immune heterogeneity that allow cancer cells to survive during conventional anticancer drug interventions. Thus, there is a strong rationale for overcoming anticancer drug resistance by employing the components of immune cells. Using the immune system to target tumor cells has revolutionized treatment. Recently, significant progress has been achieved at preclinical and clinical levels to benefit cancer patients.

Approach

A review of literature from the past ten years across PubMed, Scopus, and Web of Science focused on immunotherapy strategies. These include immune checkpoint inhibitors (ICIs), tumor-infiltrating lymphocyte therapy, antibody-drug conjugates (ADCs), cancer vaccines, CAR T-cell therapy, and the role of the gut microbiome.

Conclusion

While immunotherapy outcomes have improved, particularly for tumor types such as melanoma and non-small cell lung cancer (NSCLC), challenges persist regarding predictive biomarker identification and better management. Ongoing research on modifiers of immune function like gut microbiome-derived metabolites, next-generation ADCs, and new classes of biologics is warranted. Overall, continued investigation toward optimizing synergistic immunotherapeutic combinations through strategic drug delivery systems is imperative for preclinical and clinical success in cancer patients.

Integrated strategy for biotransformation of antibody-drug conjugates and multidimensional interpretation via high-resolution mass spectrometry

The characterization of the release mechanism and stability in circulation for novel antibody-drug conjugates (ADCs) has become essential to address the complex variables (linker or payload selection, antibody, conjugating site). Understanding the integrated biotransformation of released catabolites and intact ADCs is necessary to elucidate the mechanism of action and mitigate the premature payload release and formation of inactive ADCs during circulation, which can lead to pharmacokinetic/pharmacodynamic disconnection. Herein, we present a comprehensive strategy for the biotransformation of ADCs from both small- and large-molecule perspectives. Two ADCs with common cleavable linkers were investigated: ADC-1 (maleimidocaproyl glycine-glycine-phenylalanine-glycine deruxtecan) and ADC-2 (maleimidocaproyl valine-citrulline-p-aminobenzyl carbamate monomethyl auristatin E). First, the payload-related catabolites released from lysosome, S9, and tumor cells were identified by sensitive data mining based on high-resolution mass spectrometry to reveal the pharmacologically active components. Second, we demonstrated the biotransformation occurring in intact ADCs using middle-down and bottom-up approaches, which particularly contributed to their instability in incubation. The combined immune capture with subunit or peptide analysis enables a comprehensive evaluation of the structural integrity of ADCs, whereas solely quantitative payload release is insufficient to determine the ADCs' stability. Although subunit analysis can visualize the deconjugation by mass shift directly, the precise and low percentage of biotransformation tended to be imperceptible in intact mass spectra. Therefore, a bottom-up method was developed to analyze three representative peptides conjugated with linker-payload. These multiple dimensional biotransformation approaches provide overall insights into the ADC development. SIGNIFICANCE STATEMENT: A thorough understanding of the release mechanism and stability is pivotal for advancing antibody drug conjugates (ADCs) therapeutics. However, the inherent complexity of ADCs poses significant challenges in biotransformation analysis. We developed an integrated strategy to systematically evaluate ADC biotransformation, encompassing payload release mechanisms and plasma stability assessments with middle-down and bottom-up approaches. This advancement not only clarifies the mechanism of action but also supports the rational design of ADC candidates, such as linker chemistry, payload selection, and antibody engineering.

Navigating the Landscape of Resistance Mechanisms in Antibody-Drug Conjugates for Cancer Treatment

Antibody-drug conjugates (ADCs) are an innovative approach in cancer therapy, combining the specificity of monoclonal antibodies (mAb) with the cytotoxic effect of chemotherapy agents. Despite the remarkable efficacy demonstrated in clinical studies, primary and secondary resistance to ADCs represent a concern and a significant challenge. Known resistance mechanisms mainly involve the targeted tumor antigen; the internalization, trafficking, and cleavage processes; the cytotoxic payload; and the intrinsic tumor cell dynamics of cell death and cell signaling. Key strategies to overcome these resistance mechanisms include the use of antibodies targeting the same antigen but with different payloads, developing dual-payload ADCs that target multiple cellular pathways, switching from non-cleavable to cleavable linkers, and combining ADCs with other therapies such as immune checkpoint inhibitors and antiangiogenic agents. By improving our understanding of what underlies the mechanisms of resistance to ADCs and implementing and studying systems to overcome these mechanisms, as well as using innovative therapeutic combinations, ADCs have the potential to continue to play a fundamental role in the treatment of tumors, especially refractory ones, providing patients with more effective and long-lasting therapeutic options, as well as better outcomes.

Fundamental properties and principal areas of focus in antibody-drug conjugates formulation development

Antibody-drug conjugates (ADCs) have emerged as a rapidly expanding class of therapeutics driven by their superior specificity and clinical efficacy. 14 out of 16 commercially approved ADCs are formulated as lyophilized forms because ADC is generally considered to be less stable than unmodified antibody. The formulation development for ADCs, particularly liquid formulation, presents unique challenges due to their intricate structural complexity, physicochemical properties, and degradation pathways. This review provides the first comprehensive analysis of formulation strategies employed in commercial ADCs. Furthermore, this review discusses the key areas of focus for ADCs throughout the formulation development workflow, spanning from the initial formulation development to the final stage of drug product manufacturing. In addition, we identify and analyze the distinctive technical challenges in ADC formulation development compared to unconjugated antibody, while proposing potential solutions to these challenges. Finally, we offer strategic perspectives on future directions in ADC formulation development to advance this promising therapeutic modality.

Meta-Analysis of Exposure-Adverse Event Relationships for Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) have become a vital class of therapeutics in oncology because of their ability to selectively deliver potent drug molecules to tumor cells. However, ADC-associated toxicities cause high failure rates in the clinic and hinder their full potential. Due to the complex structure and pharmacokinetics of ADCs, it is challenging to identify the drivers of their toxicities. Here, quantitative analysis was performed to correlate the incidence of clinical adverse events (AEs) with nine different commonly measured exposure parameters collected from study-level summary data. We considered ADC analytes for different classes of ADCs, to identify ADC analytes that are strongly associated with the AEs for ADCs. Published clinical exposure and safety data for any grade and grade ≥3 AEs from 40 publications across six ADCs and three payloads were collected and analyzed. Exposure-AE relationships were quantified using logit models, and the strength of the correlations and rank order were determined. The analysis suggests that deruxtecan ADC-related toxicities correlated most strongly with the exposure of the free payload; monomethyl auristatin E (MMAE) ADC-related toxicities correlated with the free MMAE area under the curve; and pyrrolobenzodiazepine ADC-related toxicities correlated with no specific analyte but the dose. These findings agree with the published literature and support the notion that AE profiles are often shared by ADCs that deliver the same cytotoxic payload. The exposure-AE relationships presented here, together with identification of the most informative ADC analytes, may facilitate more focused mechanistic studies on the drivers of clinical AEs and could support dosing decisions during clinical development of ADCs.

Prostate-Specific Membrane Antigen-Targeted Antibody-Drug Conjugates: A Promising Approach for Metastatic Castration-Resistant Prostate Cancer

Prostate cancer (PCa), especially metastatic castration-resistant prostate cancer (mCRPC), is a significant cancer characterized by its poor prognosis and limited treatment options. Prostate-specific membrane antigen (PSMA) has emerged as a diagnostic and therapeutic target for PCa due to its restricted expression in malignant prostate tissues. In this case, several PSMA-targeting molecules were developed for radiotherapy and immunotherapy. Antibody-drug conjugates (ADCs) are a novel therapeutic approach for various carcinomas that can selectively target PSMA-positive tumor cells and minimize off-target toxicity. ADCs have made great progress in the treatment of breast and bladder cancers, and some have received FDA approval for target therapy. However, studies on PSMA ADCs are limited, and most clinical trials are at stage I or II. Therefore, this study reviewed trials about PSMA-targeting ADCs for the treatment of PCa. Clinical trials have reported a favorable pharmacokinetic profile and antitumor activity. Toxicity studies have revealed manageable adverse effects, with no significant off-target toxicity in PSMA-negative tissues. This study highlights the therapeutic potential of PSMA ADCs for the treatment of mCRPC. However, it also emphasizes the necessity of further clinical investigation to optimize efficacy, safety, and patient outcomes.

Nanobody-Targeted Conditional Antimicrobial Therapeutics

Conditional therapeutics that rely on disease microenvironment-specific triggers for activation are a promising strategy to improve therapeutic cargos. Among the investigated triggers, protease activity is used most often because of its dysregulation in several diseases. How to optimally fine-tune protease activation for different therapeutic cargos remains a challenge. Here, we designed nanobody-targeted conditional antimicrobial therapeutics to deliver a model therapeutic peptide and protein to the site of bacterial infection. We explored several parameters that influence proteolytic activation. We report the use of targeting nanobodies to enhance the activation of therapeutics that are otherwise activated inefficiently despite extensive optimization of the cleavable linker. Specifically, the pairing of Ly6G/C or ADAM10-targeting nanobodies with ADAM10-cleavable linkers improved activation via proximity-enabled reactivity. This study demonstrates a distinct role of active targeting in conditional therapeutic activation. More broadly, this optimization framework provides a guideline for the development of conditional therapeutics to treat various diseases in which protease activity is dysregulated.

Translational Advances in Oncogene and Tumor-Suppressor Gene Research

Cancer, characterized by the uncontrolled proliferation of cells, is one of the leading causes of death globally, with approximately one in five people developing the disease in their lifetime. While many driver genes were identified decades ago, and most cancers can be classified based on morphology and progression, there is still a significant gap in knowledge about genetic aberrations and nuclear DNA damage. The study of two critical groups of genes-tumor suppressors, which inhibit proliferation and promote apoptosis, and oncogenes, which regulate proliferation and survival-can help to understand the genomic causes behind tumorigenesis, leading to more personalized approaches to diagnosis and treatment. Aberration of tumor suppressors, which undergo two-hit and loss-of-function mutations, and oncogenes, activated forms of proto-oncogenes that experience one-hit and gain-of-function mutations, are responsible for the dysregulation of key signaling pathways that regulate cell division, such as p53, Rb, Ras/Raf/ERK/MAPK, PI3K/AKT, and Wnt/β-catenin. Modern breakthroughs in genomics research, like next-generation sequencing, have provided efficient strategies for mapping unique genomic changes that contribute to tumor heterogeneity. Novel therapeutic approaches have enabled personalized medicine, helping address genetic variability in tumor suppressors and oncogenes. This comprehensive review examines the molecular mechanisms behind tumor-suppressor genes and oncogenes, the key signaling pathways they regulate, epigenetic modifications, tumor heterogeneity, and the drug resistance mechanisms that drive carcinogenesis. Moreover, the review explores the clinical application of sequencing techniques, multiomics, diagnostic procedures, pharmacogenomics, and personalized treatment and prevention options, discussing future directions for emerging technologies.

From tissue-specific to tissue-agnostic: HER2 overexpression and the rise of antibody-drug conjugates

The growing importance of HER2 expression as a biomarker across multiple cancers is largely driven by advances in HER2-directed antibody-drug conjugates. The recent approval of trastuzumab deruxtecan (T-DXd) as a tumor-agnostic therapy has revolutionized treatment strategies for HER2-overexpressed tumors beyond breast, gastric, and colorectal cancers (CRC). This mini-review explores the evolving role of assessing HER2 overexpression in pan-solid tumors, following the recent approval of T-DXd as a tumor-agnostic therapy. It examines how HER2 scoring criteria for pan-tumor indications rely on immunohistochemistry (IHC) assessment, which may be prone to subjective interpretation and interobserver variability, and how these criteria differ from those used in breast, gastric, and CRC tumors. We also address the potential for NGS approaches to identify ERBB2 copy number gain (CNG) and the utility of artificial intelligence (AI) algorithms to enhance the consistency and accuracy of HER2 score interpretation for T-DXd treatment eligibility in solid tumors.

Electrochemical methods for evaluation of therapeutic monoclonal antibodies: A review

Biopharmaceuticals are complex pharmaceutical drug products produced by biotechnology in living systems. Small changes in the production process can induce differences in the structure of the active ingredient, which may have a strong impact on its pharmacological properties. Therefore, quality assurance of biopharmaceuticals results in a high analytical effort. Strict quality and stability monitoring of potentially critical quality attributes (CQAs) is required. Electrochemical methods have been contributing to the expansion of sensors and biosensors due to their advantages, such as cost-effectiveness and easy operation. Here, we discuss the recent developments in sensors and biosensors using electrochemical techniques employed for the determination of biopharmaceuticals, namely monoclonal antibodies (mAb) and fragments of mAbs. In the frame of this information, this review aims to critically address electrochemical sensors and biosensors for the analysis of biopharmaceuticals reported since 2016. Electrochemical bio(sensors) development has been mainly based on gold and aptamers, respectively, as the most used electrode material and biorecognition element. Also, Bevacizumab (BEVA) was the main therapeutic mAb detected and 69% of the works described a (bio)sensor) that can be applied to therapeutic drug monitoring.

Formation of mono- and dual-labelled antibody fragment conjugates via reversible site-selective disulfide modification and proximity induced lysine reactivity

Many protein bioconjugation strategies focus on the modification of lysine residues owing to the nucleophilicity of their amine side-chain, the generally high abundance of lysine residues on a protein's surface and the ability to form robustly stable amide-based bioconjugates. However, the plethora of solvent accessible lysine residues, which often have similar reactivity, is a key inherent issue when searching for regioselectivity and/or controlled loading of an entity. A relevant example is the modification of antibodies and/or antibody fragments, whose conjugates offer potential for a wide variety of applications. Thus, research in this area for the controlled loading of an entity via reaction with lysine residues is of high importance. In this article, we present an approach to achieve this by exploiting the quantitative and reversible site-selective modification of disulfides using pyridazinediones, which facilitates near-quantitative proximity-induced reactions with lysines to enable controlled loading of an entity. The strategy was appraised on several clinically relevant antibody fragments and enabled the formation of mono-labelled lysine-modified antibody fragment conjugates via the formation of stable amide bonds and the use of click chemistry for modular modification. Furthermore, through the use of multiple cycles of this novel strategy, an orthogonally bis-labelled lysine-modified antibody fragment conjugate was also furnished.

Molecular mechanisms for stabilizing biologics in the solid state

Protein drugs exhibit challenges of biophysical and biochemical instability due to their structural complexity and rich dynamics. Solid-state biologics aim to enhance stability by increasing molecular rigidity within the formulation matrix, representing a primary category of drug products alongside sterile liquid formulations. Understanding the molecular mechanisms behind the stabilization and destabilization of protein drugs, influenced by formulation composition and drying processes, provides scientific rationale for drug product design. This review aims to elaborate on the two primary models of water-to-sugar substitution and matrix vitrification, respectively, via thermodynamic and kinetic stabilization. It offers an up-to-date review of experimental investigations into these hypotheses, specifically elucidating protein structure and protein-excipient interactions at the molecular level, molecular dynamics across a broad range of motion regimes, and microscopic attributes such as protein-sugar and protein-salt miscibility and microenvironmental acidity, in relevant liquid, frozen, and solid states, using advanced biophysical techniques for solid-state analysis. Moreover, we discuss how these mechanistic understandings facilitate the investigation and prediction of critical stability behaviors and enables the design of solid biological drug products.

Genetic Code Expansion: Recent Developments and Emerging Applications

The concept of genetic code expansion (GCE) has revolutionized the field of chemical and synthetic biology, enabling the site-specific incorporation of noncanonical amino acids (ncAAs) into proteins, thus opening new avenues in research and applications across biology and medicine. In this review, we cover the principles of GCE, including the optimization of the aminoacyl-tRNA synthetase (aaRS)/tRNA system and the advancements in translation system engineering. Notable developments include the refinement of aaRS/tRNA pairs, enhancements in screening methods, and the biosynthesis of noncanonical amino acids. The applications of GCE technology span from synthetic biology, where it facilitates gene expression regulation and protein engineering, to medicine, with promising approaches in drug development, vaccine production, and gene editing. The review concludes with a perspective on the future of GCE, underscoring its potential to further expand the toolkit of biology and medicine. Through this comprehensive review, we aim to provide a detailed overview of the current state of GCE technology, its challenges, opportunities, and the frontier it represents in the expansion of the genetic code for novel biological research and therapeutic applications.

New insights into the mechanisms of the immune microenvironment and immunotherapy in osteosarcoma

Osteosarcoma, a malignant bone tumor primarily affecting adolescents, is highly invasive with a poor prognosis. While surgery and chemotherapy have improved survival for localized cases, pulmonary metastasis significantly reduces survival to approximately 20%, highlighting the need for novel treatments. Immunotherapy, which leverages the immune system to target osteosarcoma cells, shows promise. This review summarizes the biological characteristics of osteosarcoma, mechanisms of pulmonary metastasis, and the tumor immune microenvironment (TME). It involves recent immunotherapy advances, including monoclonal antibodies, tumor vaccines, immune cell therapies, checkpoint inhibitors, and oncolytic viruses, and discusses combining these with standard treatments.

The journey of antibody-drug conjugates for revolutionizing cancer therapy: A review

Antibody-drug conjugates (ADCs) represent a powerful class of targeted cancer therapies that harness the specificity of monoclonal antibodies to deliver cytotoxic payloads directly to tumor cells, minimizing off-target effects. This review explores the advancements in ADC technologies, focusing on advancing next-generation ADCs with novel payloads, conjugation strategies, and enhanced pharmacokinetic profiles. In particular, we highlight innovative payloads, including microtubule inhibitors, spliceosome modulators, and RNA polymerase inhibitors, that offer new mechanisms of cytotoxicity beyond traditional apoptosis induction. Additionally, the introduction of sophisticated conjugation techniques, such as site-specific conjugation using engineered cysteines, enzymatic methods, and integration of non-natural amino acids, has greatly improved the homogeneity, efficacy, and safety of ADCs. Furthermore, the review delves into the mechanistic insights into ADC action, detailing the intracellular pathways that facilitate drug release and cell death, and discussing the significance of bioconjugation methods in optimizing drug-antibody ratios (DARs). The establishment of comprehensive databases like ADCdb, which catalog vital pharmacological and biological data for ADCs, is also explored as a critical resource for advancing ADC research and clinical application. Finally, the clinical landscape of ADCs is examined, with a focus on the evolution of FDA-approved ADCs, such as Gemtuzumab Ozogamicin and Trastuzumab Emtansine, as well as emerging candidates in ongoing trials. As ADCs continue to evolve, their potential to revolutionize cancer therapy remains immense, offering new hope for more effective and personalized treatment options. ADCs also offer a significant advancement in targeted cancer therapy by merging the specificity of monoclonal antibodies with cytotoxic potency of chemotherapeutic agents. Hence, this dual mechanism intensifies tumor selectivity while minimizing systemic toxicity, paving the way for more effective and safer cancer treatments.

Exploring immunotherapy with antibody-drug conjugates in solid tumor oncology

Immunotherapy has emerged as a hallmark of hope in the formidable battle against solid tumors such as breast cancer, colorectal cancer, etc., with antibody-drug conjugates (ADCs) starting a new era of precision medicine. This chapter delves into the dynamic landscape of immunotherapeutic strategies, focusing on the transformative potential of ADCs. ADCs represent a combination of chemotherapy and immunotherapy, more innovative chemotherapy. We emphasize the intricate interplay between tumor biology and therapeutic intervention, uncovering the mechanisms underlying ADC efficacy and the hurdles they must overcome. Each facet of ADC development is carefully examined, from the delicate balance between payload potency and safety to the quest for enhanced tumor penetration. We also elucidate the synergistic potential of combining ADCs with existing modalities, including chemotherapy and radiation therapy, to amplify therapeutic outcomes while mitigating adverse effects. As we navigate the complexities of solid tumor oncology, a profound understanding of the immunotherapeutic potential of ADCs is gained, offering hope for a cure for patients and clinicians alike. Henceforth, we delve into this transformative journey as we advance in solid tumor treatment regimens using immunotherapy with ADCs, poised at the forefront of oncological innovation.

αFAP-specific nanobodies mediate a highly precise retargeting of modified AAV2 capsids thereby enabling specific transduction of tumor tissues

Due to the refractiveness of tumor tissues to adeno-associated virus (AAV) transduction, AAV vectors are poorly explored for cancer therapy delivery. Here, we aimed to engineer AAVs to target tumors by enabling the specific engagement of fibroblast activation protein (FAP). FAP is a cell surface receptor distinctly upregulated in the reactive tumor stroma, but rarely expressed in healthy tissues. Thus, targeting FAP presents an opportunity to selectively transduce tumor tissues. To achieve this, we modified the capsid surface of AAV2 with an αFAP nanobody to retarget the capsid to engage FAP receptor. Following transduction, we observed a 23- to 80-fold increase in the selective transduction of FAP+ tumor cells in vitro, and greater than 5-fold transduction of FAP+ tumor tissues in vivo. Subsequent optimization of the VP1-nanobody expression cassette further enhanced the transduction efficiency of the modified capsids. Due to the limited αFAP nanobodies repertoires, we broadened the versatility of this high-fidelity platform by screening a naive VHH yeast display library, leading to the identification of several novel αFAP nanobody candidates (KD = 0.1 to >100 nM). Hence, our study offers new opportunity for the application of AAV vectors for highly selective delivery of therapeutics to the tumor stroma.

Enhancing Anti-Cancer Immune Response by Acidosis-Sensitive Nanobody Display

One of the main challenges with many cancer immunotherapies is that biomarkers are needed for targeting. These biomarkers are often associated with tumors but are not specific to a particular tumor and can lead to damage in healthy tissues, resistance to treatment, or the need for customization for different types of cancer due to variations in targets. A promising alternative approach is to target the acidic microenvironment found in most solid tumor types. This can be achieved using the pH (Low) Insertion Peptide (pHLIP), which inserts selectively into cell membranes under acidic conditions, sparing healthy tissues. pHLIP has shown potential for imaging, drug delivery, and surface display. For instance, we previously used pHLIP to display epitopes on the surfaces of cancer cells, enabling antibody-mediated immune cell recruitment and selective killing of cancer cells. In this study, we further explored this concept by directly fusing an anti-CD16 nanobody, which activates natural killer (NK) cells, to pHLIP, eliminating the need for antibody recruitment. Our results demonstrated the insertion of pH-sensitive agents into cancer cells, activation of the CD16 receptor on effector cells, and successful targeting and destruction of cancer cells by high-affinity CD16+ NK cells in two cancer cell lines.

Review of dose justifications for antibody-drug conjugate approvals from clinical pharmacology perspective: A focus on exposure-response analyses

Antibody-drug conjugates (ADCs) are revolutionizing cancer treatment by specific targeting of the cancer cells thereby improving the therapeutic window of the drugs. Nevertheless, they are not free from unwanted toxicities mainly resulting from non-specific targeting and release of the payload. Therefore, the dosing regimen must be optimized through integrated analysis of the risk-benefit profile, to maximize the therapeutic potential. Exposure-response (E-R) analysis is one of the most widely used tools for risk-benefit assessment and it plays a pivotal role in dose optimization of ADCs. However, compared to conventional E-R analysis, ADCs pose unique challenges since they feature properties of both small molecules and antibodies. In this article, we review the E-R analyses that have formed the key basis of dose justification for each of the 12 ADCs approved in the USA. We discuss the multiple analytes and exposure metrics that can be utilized for such analysis and their relevance for safety and efficacy of the treatment. For the endpoints used for the E-R analysis, we were able to uncover commonalities across different ADCs for both safety and efficacy. Additionally, we discuss dose optimization strategies for ADCs which are now a critical component in clinical development of oncology drugs.

An Underlying Cause and Solution to the Poor Size Exclusion Chromatography Performance of Antibody-Drug Conjugates

PURPOSES

Antibody-drug conjugate (ADC) size variants are frequently assessed by size exclusion chromatography (SEC). However, poor chromatography performance is often observed during SEC analysis. Existing studies have primarily focused on qualitatively describing non-specific interactions between ADCs and the column matrix. The purposes of the current study are to introduce an underlying cause from a novel perspective on the protein-protein interaction (PPI) mechanism, characterized by quantifying diffusion interaction parameter (kD) values, and to provide several strategies to reduce PPI and improve column performance during SEC analysis.

METHODS

Two kinds of ADCs with varying hydrophobicity properties and their corresponding monoclonal antibodies are used as models. The hydrophobicity of these products was verified using the relative calculated logarithm of the partition coefficient of a substance in n-octanol (oil) and water (rCLogP) and reversed-phase high performance liquid chromatography (RP-HPLC), and the size variants were analyzed using SEC. Finally, the PPI was characterized by kD values of these four products.

RESULTS

The results of rCLogP and RP-HPLC indicated that ADC-1 is relatively hydrophobic, whereas ADC-2 is relatively hydrophilic. In the SEC analysis of the ADC-1, substituting sodium chloride with L-arginine hydrochloride or adding a specific concentration of acetonitrile as an organic solvent to the mobile phase resulted in reduced PPI and enhanced column performance. Conversely, the impact on ADC-2 was negligible.

CONCLUSIONS

This study provides insights into improving the performance of SEC analysis for ADCs through strategies involving alterations in mobile phase composition. The changes in column performance can be quantitatively explained by the PPI mechanism.

Imaged Capillary Isoelectric Focusing Coupled to High-Resolution Mass Spectrometry (icIEF-MS) for Cysteine-Linked Antibody-Drug Conjugate (ADC) Heterogeneity Characterization Under Native Condition

Native mass spectrometry (nMS) is a cutting-edge technique that leverages electrospray ionization MS (ESI-MS) to investigate large biomolecules and their complexes in solution. The goal of nMS is to retain the native structural features and interactions of the analytes during the transition to the gas phase, providing insights into their natural conformations. In biopharmaceutical development, nMS serves as a powerful tool for analyzing complex protein heterogeneity, allowing for the examination of non-covalently bonded assemblies in a state that closely resembles their natural folded form. Herein, we present an imaged capillary isoelectric focusing-MS (icIEF-MS) workflow to characterize cysteine-linked antibody-drug conjugate (ADC) under native conditions. Two ADCs were analyzed: a latest generation cysteine-linked ADC polatuzumab vedotin and the first FDA-approved cysteine-linked ADC brentuximab vedotin. This workflow benefits from a recently developed icIEF system that is MS-friendly and capable of directly coupling to a high-sensitivity MS instrument. Results show that the icIEF separation is influenced by both drug payloads and the post-translational modifications (PTMs), which are then promptly identified by MS. Overall, this native icIEF-MS method demonstrates the potential to understand and control the critical quality attributes (CQAs) that are essential for the safe and effective use of ADCs.

Engineering peptide drug therapeutics through chemical conjugation and implication in clinics

The development of peptide drugs has made tremendous progress in the past few decades because of the advancements in modification chemistry and analytical technologies. The novel-designed peptide drugs have been modified through various biochemical methods with improved diagnostic, therapeutic, and drug-delivery strategies. Researchers found it a helping hand to overcome the inherent limitations of peptides and bring continued advancements in their applications. Furthermore, the emergence of peptide-drug conjugates (PDCs)-utilizes target-oriented peptide moieties as a vehicle for cytotoxic payloads via conjugation with cleavable chemical agents, resulting in the key foundation of the new era of targeted peptide drugs. This review summarizes the various classifications of peptide drugs, suitable chemical modification strategies to improve the ADME (adsorption, distribution, metabolism, and excretion) features of peptide drugs, and recent (2015-early 2024) progress/achievements in peptide-based drug delivery systems as well as their fruitful implication in preclinical and clinical studies. Furthermore, we also summarized the brief description of other types of PDCs, including peptide-MOF conjugates and peptide-UCNP conjugates. The principal aim is to provide scattered and diversified knowledge in one place and to help researchers understand the pinching knots in the science of PDC development and progress toward a bright future of novel peptide drugs.

Antitumor activities of anti‑CD44 monoclonal antibodies in mouse xenograft models of esophageal cancer

CD44 is a type I transmembrane glycoprotein associated with poor prognosis in various solid tumors. Since CD44 plays a critical role in tumor development by regulating cell adhesion, survival, proliferation and stemness, it has been considered a target for tumor therapy. Anti‑CD44 monoclonal antibodies (mAbs) have been developed and applied to antibody‑drug conjugates and chimeric antigen receptor‑T cell therapy. Anti-pan‑CD44 mAbs, C44Mab‑5 and C44Mab‑46, which recognize both CD44 standard (CD44s) and variant isoforms were previously developed. The present study generated a mouse IgG2a version of the anti‑pan‑CD44 mAbs (5‑mG2a and C44Mab‑46‑mG2a) to evaluate the antitumor activities against CD44‑positive cells. Both 5‑mG2a and C44Mab‑46‑mG2a recognized CD44s‑overexpressed CHO‑K1 (CHO/CD44s) cells and esophageal tumor cell line (KYSE770) in flow cytometry. Furthermore, both 5‑mG2a and C44Mab‑46‑mG2a could activate effector cells in the presence of CHO/CD44s cells and exhibited complement-dependent cytotoxicity against both CHO/CD44s and KYSE770 cells. Furthermore, the administration of 5‑mG2a and C44Mab‑46‑mG2a significantly suppressed CHO/CD44s and KYSE770 xenograft tumor development compared with the control mouse IgG2a. These results indicate that 5‑mG2a and C44Mab‑46‑mG2a could exert antitumor activities against CD44‑positive cancers and be a promising therapeutic regimen for tumors.

Antibody drug conjugates in the clinic

Antibody-drug conjugates (ADCs), chemotherapeutic agents conjugated to an antibody to enhance their targeted delivery to tumors, represent a significant advancement in cancer therapy. ADCs combine the precise targeting capabilities of antibodies and the potent cell-killing effects of chemotherapy, allowing for enhanced cytotoxicity to tumors while minimizing damage to healthy tissues. Here, we provide an overview of the current clinical landscape of ADCs, highlighting 11 U.S. Food and Drug Administration (FDA)-approved products and discussing over 500 active clinical trials investigating newer ADCs. We also discuss some key challenges associated with the clinical translation of ADCs and highlight emerging strategies to overcome these hurdles. Our discussions will provide useful guidelines for the future development of safer and more effective ADCs for a broader range of indications.

Understanding the chemistry & pharmacology of antibody-drug conjugates in triple-negative breast cancer with special reference to exatecan derivatives

In the spectrum of breast malignancies, triple-negative breast cancer is the most widely spreading subtype of breast cancer due to a low availability of therapeutic remedies. Recently, antibody-drug conjugates dramatically resolved the landscape for the treatment of triple-negative breast cancer. This review mainly focuses on the chemistry, structure, mechanism of action, and role of antibody-drug conjugates in triple-negative breast cancer. Datopotecan Deruxtecan (Dato-DXd) is a new-generation ADC showing encouraging results for TNBC. In this review, we have also emphasized TROP-2-directed Datopotamab deruxtecan ADCs to treat triple-negative breast cancer, its synthesis, mechanism of action, pharmacokinetics, pharmacodynamics, adverse events, and their ongoing clinical trials.

Antibody-Drug Conjugates for the Treatment of Non-Small Cell Lung Cancer with Central Nervous System Metastases

Antibody-drug conjugates (ADCs) represent an emerging class of targeted anticancer agents that have demonstrated impressive efficacy in numerous cancer types. In non-small cell lung cancer (NSCLC), ADCs have become a component of the treatment armamentarium for a subset of patients with metastatic disease. Emerging data suggest that some ADCs exhibit impressive activity even in central nervous system (CNS) metastases, a disease site that is difficult to treat and associated with poor prognosis. Herein, we describe and summarize the existing evidence surrounding ADCs in NSCLC with a focus on CNS activity.

Development of CD33-Targeted Dual Drug-Loaded Nanoparticles for the Treatment of Pediatric Acute Myeloid Leukemia

Paediatric acute myeloid leukemia (AML) is a heterogeneous hematological malignancy still heavily reliant on traditional chemotherapeutic approaches. Combination treatments have shown to be a superior approach, but their success is often hindered by side effects and different drugs' pharmacokinetics. Here, we investigated ABT-737 and Purvalanol A as a potential drug pairing for pediatric AML and described the development of CD33-targeted polymeric nanoparticles (NPs) to enable their simultaneous targeted codelivery. Separate drug encapsulation within poly(lactic-co-glycolic acid) (PLGA) NPs was optimized prior to coencapsulation of both drugs at a synergistic ratio in PEGylated PLGA NPs. The therapeutic effects of formulations were evaluated in a panel of pediatric AML cells, and dual drug-loaded NPs (dual NPs) demonstrated significantly enhanced apoptotic cell death. Moreover, conjugation to gemtuzumab resulted in improved NP binding and internalization in CD33-positive cells. Finally, CD33-targeted dual-loaded NPs showed enhanced cytotoxicity to CD33-positive AML cells via CD33-mediated targeted drug delivery.

Assessment of mirvetuximab soravtansine immunogenicity in patients with folate receptor alpha-positive ovarian cancer

Aim: The aim of this research was to evaluate the immunogenicity of mirvetuximab soravtansine (MIRV), an antibody-drug conjugate in patients with folate receptor alpha-positive ovarian cancer across four clinical studies.Materials & methods: An assay was developed and validated for the detection of antidrug antibodies (ADAs) against MIRV. A cell-based method was also developed and validated for the detection of neutralizing anti-MIRV antibodies (NAbs). Both ADAs and NAbs were assessed across four clinical studies in 734 patients.Results: Across studies, MIRV demonstrated low immunogenicity with 7.8% of patients with treatment-emergent ADAs, 7.2% with treatment-unaffected ADAs, and 0.5% with treatment-enhanced ADAs. MIRV trough concentrations were comparable in ADA-negative and ADA-positive individuals. Limited data suggest that MIRV ADAs may be associated with decreased efficacy. Due to the very limited number of NAb-positive individuals, no conclusions could be drawn on the effect of NAb on efficacy.Conclusion: Both the validation tests and the data from the MIRV clinical studies demonstrated that these assays were suitable and reliable for the detection of MIRV ADAs and NAbs. These validated assays will continue to be used to monitor MIRV immunogenicity in future clinical trials.

Cardiac toxicity of HER-2 targeting antibody-drug conjugates: overview and clinical implications

Antibody-drug conjugates (ADCs) have recently emerged as a promising therapeutic option that combine the specificity of monoclonal antibodies and the cytotoxic effect of chemotherapy. With numerous ADCs approved and on the market, a particular concern of ADCs that target HER-2 has been their cardiac side effects, in view of the crucial role of HER-2 in cardiac development and physiology. While rarely toxic and generally safe, numerous publications have outlined the consistent association of trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd) with the development of cardiac toxicity. Despite not being clinically relevant in most cases, cardiac baseline evaluation, monitoring and early detection of cardiac adverse events remain pivotal with HER-2 targeting ADCs. This review aims to summarize and better characterize the complete cardiac toxicity profile of HER-2 ADCs, with the goal of improving clinical understanding of this adverse event, leading to better recognition, monitoring and management.

Surface-engineered bacteria in drug development

Bacterial surface display in combination with fluorescence-activated cell sorting is a versatile and robust system and an interesting alternative approach to phage display for the generation of therapeutic affinity proteins. The system enables real-time monitoring and sorting of cell populations, which presents unique possibilities for drug development. It has been used to develop several affibody molecules currently being evaluated preclinically for the treatment and diagnosis of, for example, cancer and neurodegenerative diseases. Additionally, it can be implemented in other areas of drug design, such as for mapping epitopes and evolving enzyme specificities.

Advancements in mammalian display technology for therapeutic antibody development and beyond: current landscape, challenges, and future prospects

The evolving development landscape of biotherapeutics and their growing complexity from simple antibodies into bi- and multi-specific molecules necessitates sophisticated discovery and engineering platforms. This review focuses on mammalian display technology as a potential solution to the pressing challenges in biotherapeutic development. We provide a comparative analysis with established methodologies, highlighting key aspects of mammalian display technology, including genetic engineering, construction of display libraries, and its pivotal role in hit selection and/or developability engineering. The review delves into the mechanisms underpinning developability-driven selection via mammalian display and their broader implications. Applications beyond antibody discovery are also explored, alongside advancements towards function-first screening technologies, precision genome engineering and AI/ML-enhanced libraries, situating them in the context of mammalian display. Overall, the review provides a comprehensive overview of the current mammalian display technology landscape, underscores the expansive potential of the technology for biotherapeutic development, addresses the critical challenges for the full realisation of this potential, and examines advances in related disciplines that might impact the future application of mammalian display technologies.

Enhancing Anti-Cancer Immune Response by Acidosis-sensitive Nanobody Display

One of the main challenges with many cancer immuno-therapies is that they depend on biomarkers for targeting. These biomarkers are often associated with tumors but are not specific to a particular tumor, which can lead to damage in healthy tissues, resistance to treatment, and the need for customization for different types of cancer due to the variations in targets. A promising alternative approach is to target the acidic microenvironment found in most solid tumor types. This can be achieved using the pH (Low) Insertion Peptide (pHLIP), which inserts selectively into cell membranes in acidic conditions, sparing healthy tissues. pHLIP has shown potential for imaging, drug delivery, and surface display. For instance, we previously used pHLIP to display epitopes on the surfaces of cancer cells, enabling antibody-mediated immune cell recruitment and selective killing of cancer cells. In this study, we further this concept by directly fusing an anti-CD16 nanobody, which activates Natural Killer (NK) cells, to pHLIP, eliminating the need for antibody recruitment. Our results demonstrate pH-sensitive insertion into cancer cells, activation of the CD16 receptor on effector cells, and successful targeting and destruction of cancer cells by high-affinity CD16 + NK cells in two cancer cell lines.

Antibody-drug conjugates for non-small cell lung cancer: Advantages and challenges in clinical translation

Lung cancer is the leading cause of cancer death, with non-small cell lung cancer (NSCLC) accounting for approximately 85 % of all lung cancers and having a poor treatment and prognosis. Conventional clinical chemotherapy and immunotherapy are challenged by systemic toxicity and drug resistance, so researchers are increasingly focusing on antibody-drug conjugate (ADC), an innovative concept combining chemotherapy and targeted therapy, in which a drug selectively binds to antigens on the surface of a tumor cell via antibodies, which internalize the ADC, and then transfers the ADC to the lysosome via the endosomes to degrade the drug and kill the tumor cell. Despite the promising nature of ADCs, no ADC product for any indication including NSCLC has been approved for marketing by the FDA to date. In this review, we summarize the main advantages of ADCs and discuss in depth the design of the most desirable ADCs for NSCLC therapy. In addition to preclinical studies, we focus on the current state of clinical research on ADCs as interventions for the treatment of NSCLC by summarizing real-time clinical trial data from ClinicalTrials.gov, and reasonably speculate on the direction of the design of future generations of ADCs.

Current Landscape of Antibody-Drug Conjugate Development in Head and Neck Cancer

Antibody-drug conjugates (ADCs) are fusions of therapeutic drugs and antibodies conjugated by a linker, designed to deliver a therapeutic payload to cells expressing the target antigen. By delivering the highly cytotoxic agent directly to cancer cells, ADCs are designed to enhance safety and broaden the therapeutic window. Recently, ADCs have demonstrated promising efficacy in various solid tumors and are rapidly expanding their indications. The prognosis of patients with advanced head and neck squamous cell carcinoma (HNSCC) remains poor, with no new therapeutics since the advent of anti-PD-1 antibodies in 2016, highlighting a critical need for innovative therapies. Recent preliminary results suggest that ADCs could be promising treatment options for HNSCC as they explore a variety of target antigens, payloads, and linkers. However, for successful adaptation of ADCs in the treatment of HNSCC, addressing key challenges such as payload toxicities, antigen heterogeneity, and adaptive resistance will be essential. Current research focused on new ADC structures, including multispecific antibodies and noncytotoxic payloads, and diverse combination approaches, show promise for future advancements.

Approaches to improve the translation of safety, pharmacokinetics and therapeutic index of ADCs

1. Antibody-drug conjugates (ADCs) are an important class of cancer therapies. They are complex molecules, comprising an antibody, a cytotoxic payload, and a linker. ADCs intend to confer high specificity by targeting a unique antigen expressed predominately on the surface of the tumour cells than on the normal cells and by releasing the potent cytotoxic drug inside the tumour causing cytotoxic cell death. Despite high specificity to tumour antigens, many ADCs are associated with off-target and on-target off-tumour toxicities, often leading to safety concerns before achieving the desirable clinical efficacy. Therefore, it is crucial to improve the therapeutic index (TI) of ADCs to enable the full potential of this important therapeutic modality. 2. The review summarises current approaches to improve the translation of safety, pharmacokinetics, and TI of ADCs. Common safety findings of ADCs resulting from off-target and on-target toxicities and nonclinical approaches to de-risk ADC safety will be discussed; multiple approaches of using preclinical and clinical dose and exposure data to calculate TI to guide clinical dosing will be elaborated; different approaches to improve TI of ADCs, including selecting the right target, right payload-linker and patients, optimising physicochemical properties, and using fractionation dosing, will also be discussed.

Single-Domain Antibodies as Antibody-Drug Conjugates: From Promise to Practice-A Systematic Review

BACKGROUND

Antibody-drug conjugates (ADCs) represent potent cancer therapies that deliver highly toxic drugs to tumor cells precisely, thus allowing for targeted treatment and significantly reducing off-target effects. Despite their effectiveness, ADCs can face limitations due to acquired resistance and potential side effects.

OBJECTIVES

This study focuses on advances in various ADC components to improve both the efficacy and safety of these agents, and includes the analysis of several novel ADC formats. This work assesses whether the unique features of VHHs-such as their small size, enhanced tissue penetration, stability, and cost-effectiveness-make them a viable alternative to conventional antibodies for ADCs and reviews their current status in ADC development.

METHODS

Following PRISMA guidelines, this study focused on VHHs as components of ADCs, examining advancements and prospects from 1 January 2014 to 30 June 2024. Searches were conducted in PubMed, Cochrane Library, ScienceDirect and LILACS using specific terms related to ADCs and single-domain antibodies. Retrieved articles were rigorously evaluated, excluding duplicates and non-qualifying studies. The selected peer-reviewed articles were analyzed for quality and synthesized to highlight advancements, methods, payloads, and future directions in ADC research.

RESULTS

VHHs offer significant advantages for drug conjugation over conventional antibodies due to their smaller size and structure, which enhance tissue penetration and enable access to previously inaccessible epitopes. Their superior stability, solubility, and manufacturability facilitate cost-effective production and expand the range of targetable antigens. Additionally, some VHHs can naturally cross the blood-brain barrier or be easily modified to favor their penetration, making them promising for targeting brain tumors and metastases. Although no VHH-drug conjugates (nADC or nanoADC) are currently in the clinical arena, preclinical studies have explored various conjugation methods and linkers.

CONCLUSIONS

While ADCs are transforming cancer treatment, their unique mechanisms and associated toxicities challenge traditional views on bioavailability and vary with different tumor types. Severe toxicities, often linked to compound instability, off-target effects, and nonspecific blood cell interactions, highlight the need for better understanding. Conversely, the rapid distribution, tumor penetration, and clearance of VHHs could be advantageous, potentially reducing toxicity by minimizing prolonged exposure. These attributes make single-domain antibodies strong candidates for the next generation of ADCs, potentially enhancing both efficacy and safety.

Antibody-Drug Conjugates-Evolution and Perspectives

Antineoplastic therapy is one of the main research themes of this century. Modern approaches have been implemented to target and heighten the effect of cytostatic drugs on tumors and diminish their general/unspecific toxicity. In this context, antibody-drug conjugates (ADCs) represent a promising and successful strategy. The aim of this review was to assess different aspects regarding ADCs. They were presented from a chemical and a pharmacological perspective and aspects like structure, conjugation and development particularities alongside effects, clinical trials, safety issues and perspectives and challenges for future use of these drugs were discussed. Representative examples include but are not limited to the following main structural components of ADCs: monoclonal antibodies (trastuzumab, brentuximab), linkers (pH-sensitive, reduction-sensitive, peptide-based, phosphate-based, and others), and payloads (doxorubicin, emtansine, ravtansine, calicheamicin). Regarding pharmacotherapy success, the high effectiveness expectation associated with ADC treatment is supported by the large number of ongoing clinical trials. Major aspects such as development strategies are first discussed, advantages and disadvantages, safety and efficacy, offering a retrospective insight on the subject. The second part of the review is prospective, focusing on various plans to overcome the previously identified difficulties.

Antibody-Drug Conjugates: A promising breakthrough in cancer therapy

Antibody-drug conjugates (ADCs) provide effective cancer treatment through the selective delivery of cytotoxic payloads to the cancer cells. They offer unparalleled precision and specificity in directing drugs to cancer cells while minimizing off-target effects. Despite several advantages, there is a requirement for innovations in the molecular design of ADC owing to drug resistance, cancer heterogeneity along the adverse effects of treatment. The review critically analyses ADC function mechanisms, unraveling the intricate interplay between antibodies, linkers, and payloads in facilitating targeted drug delivery to cancer cells. The article also highlights notable advancements in antibody engineering, which aid in creating highly selective and potent ADCs. Additionally, the review details significant progress in clinical ADC development with an in-depth examination of pivotal trials and approved formulations. Antibody Drug Conjugates (ADCs) are a ground-breaking approach to targeted drug delivery, especially in cancer treatment. They offer unparalleled precision and specificity in directing drugs to cancer cells while minimizing off-target effects. This review provides a comprehensive examination of the current state of ADC development, covering their design, mechanisms of action, and clinical applications. The article emphasizes the need for greater precision in drug delivery and explains why ADCs are necessary.

Chemo- and regio-selective differential modification of native cysteines on an antibody via the use of dehydroalanine forming reagents

Protein modification has garnered increasing interest over the past few decades and has become an important tool in many aspects of chemical biology. In recent years, much effort has focused on site-selective modification strategies that generate more homogenous bioconjugates, and this is particularly so in the antibody modification space. Modifying native antibodies by targeting solvent-accessible cysteines liberated by interchain disulfide reduction is, perhaps, the predominant strategy for achieving more site-selectivity on an antibody scaffold. This is evidenced by numerous approved antibody therapeutics that have utilised cysteine-directed conjugation reagents and the plethora of methods/strategies focused on antibody cysteine modification. However, all of these methods have a common feature in that after the reduction of native solvent-accessible cystines, the liberated cysteines are all reacted in the same manner. Herein, we report the discovery and application of dehydroalanine forming reagents (including novel reagents) capable of regio- and chemo-selectively modifying these cysteines (differentially) on a clinically relevant antibody fragment and a full antibody. We discovered that these reagents could enable differential reactivity between light chain C-terminal cysteines, heavy chain hinge region cysteines (cysteines with an adjacent proline residue, Cys-Pro), and other heavy chain internal cysteines. This differential reactivity was also showcased on small molecules and on the peptide somatostatin. The application of these dehydroalanine forming reagents was exemplified in the preparation of a dually modified antibody fragment and full antibody. Additionally, we discovered that readily available amide coupling agents can be repurposed as dehydroalanine forming reagents, which could be of interest to the broader field of chemical biology.

Incidence and Mitigation of Corneal Pseudomicrocysts Induced by Antibody-Drug Conjugates (ADCs)

Purpose of Review

This study is to highlight the incidence of corneal pseudomicrocysts in FDA-approved antibody-drug conjugates (ADCs), and success of preventive therapies for pseudomicrocysts and related ocular surface adverse events (AEs).

Recent Findings

ADCs are an emerging class of selective cancer therapies that consist of a potent cytotoxin connected to a monoclonal antibody (mAb) that targets antigens expressed on malignant cells. Currently, there are 11 FDA-approved ADCs with over 164 in clinical trials. Various AEs have been attributed to ADCs, including ocular surface AEs (keratitis/keratopathy, dry eye, conjunctivitis, blurred vision, corneal pseudomicrocysts). While the severity and prevalence of ADC-induced ocular surface AEs are well reported, the reporting of corneal pseudomicrocysts is limited, complicating the development of therapies to prevent or treat ADC-related ocular surface toxicity.

Summary

Three of 11 FDA-approved ADCs have been implicated with corneal pseudomicrocysts, with incidence ranging from 41 to 100% of patients. Of the six ADCs that reported ocular surface AEs, only three had ocular substudies to investigate the benefit of preventive therapies including topical steroids, vasoconstrictors, and preservative-free lubricants. Current preventive therapies demonstrate limited efficacy at mitigating pseudomicrocysts and other ocular surface AEs.

Cisplatin in the era of PARP inhibitors and immunotherapy

Platinum compounds such as cisplatin, carboplatin and oxaliplatin are widely used in chemotherapy. Cisplatin induces cytotoxic DNA damage that blocks DNA replication and gene transcription, leading to arrest of cell proliferation. Although platinum therapy alone is effective against many tumors, cancer cells can adapt to the treatment and gain resistance. The mechanisms for cisplatin resistance are complex, including low DNA damage formation, high DNA repair capacity, changes in apoptosis signaling pathways, rewired cell metabolisms, and others. Drug resistance compromises the clinical efficacy and calls for new strategies by combining cisplatin with other therapies. Exciting progress in cancer treatment, particularly development of poly (ADP-ribose) polymerase (PARP) inhibitors and immune checkpoint inhibitors, opened a new chapter to combine cisplatin with these new cancer therapies. In this Review, we discuss how platinum synergizes with PARP inhibitors and immunotherapy to bring new hope to cancer patients.

An insight into the pharmacology of cysteine/methionine containing peptide drugs

Since last century, peptides have emerged as potential drugs with >90 FDA approvals for various targets with several in the pipeline. Sulphur, in peptides is present either as thiol (-SH) from Cys or thioether from Met. In this review, all the peptides approved by FDA since 2000 containing sulphur have been included. Among them ∼50 % contains disulphide bridges. This clearly demonstrates the significance of disulphide bonds in peptide drugs. This can be achieved synthetically by using orthogonal protecting groups (PGs) for -SH. These PGs are compatible with Solid Phase Peptide Synthesis (SPPS), which is still the method of choice for peptide synthesis. The orthogonal PGs used for Cys thiol side chain protecting for disulphide bond formation have been included which are currently in use both by academia and industry from small scale to large scale synthesis. In addition, the details of the FDA approved drugs containing Cys and Met (or both) have also been discussed.

Current Landscape of Cancer Immunotherapy: Harnessing the Immune Arsenal to Overcome Immune Evasion

Cancer immune evasion represents a leading hallmark of cancer, posing a significant obstacle to the development of successful anticancer therapies. However, the landscape of cancer treatment has significantly evolved, transitioning into the era of immunotherapy from conventional methods such as surgical resection, radiotherapy, chemotherapy, and targeted drug therapy. Immunotherapy has emerged as a pivotal component in cancer treatment, harnessing the body's immune system to combat cancer and offering improved prognostic outcomes for numerous patients. The remarkable success of immunotherapy has spurred significant efforts to enhance the clinical efficacy of existing agents and strategies. Several immunotherapeutic approaches have received approval for targeted cancer treatments, while others are currently in preclinical and clinical trials. This review explores recent progress in unraveling the mechanisms of cancer immune evasion and evaluates the clinical effectiveness of diverse immunotherapy strategies, including cancer vaccines, adoptive cell therapy, and antibody-based treatments. It encompasses both established treatments and those currently under investigation, providing a comprehensive overview of efforts to combat cancer through immunological approaches. Additionally, the article emphasizes the current developments, limitations, and challenges in cancer immunotherapy. Furthermore, by integrating analyses of cancer immunotherapy resistance mechanisms and exploring combination strategies and personalized approaches, it offers valuable insights crucial for the development of novel anticancer immunotherapeutic strategies.