Recent Developments in ADC Technology: Preclinical Studies Signal Future Clinical Trends

Nanoparticle innovations in targeted cancer therapy: advancements in antibody-drug conjugates

Antibody-drug conjugates (ADCs) have emerged as a promising strategy in targeted cancer therapy, enabling the precise delivery of cytotoxic agents to tumor sites while minimizing systemic toxicity. However, traditional ADCs face significant limitations, including restricted drug loading capacity, where an optimal drug-to-antibody ratio (DAR) is crucial; low DARs may lead to insufficient potency, while high DARs can cause rapid clearance and increased toxicity. Additionally, ADCs often suffer from instability in circulation due to the potential for premature release of cytotoxic agents, resulting in off-target effects and reduced therapeutic efficacy. Furthermore, their large size can impede adequate penetration into solid tumors, particularly in heterogeneous environments with varying antigen expressions. This review explores the innovative use of nanoparticles as carriers for ADCs, which offers a multifaceted approach to enhance therapeutic efficacy. By leveraging the unique properties of nanoparticles, such as their small size and ability to exploit the enhanced permeability and retention (EPR) effect, researchers can improve drug stability, prolong circulation time, and achieve more effective tumor targeting. Recent studies demonstrate that nanoparticle-encapsulated ADCs can significantly enhance treatment outcomes while reducing off-target effects, as evidenced by improved targeting capabilities and reduced toxicity in preclinical models. Despite the promising advancements, challenges remain, including potential nanoparticle toxicity and manufacturing complexities. This review aims to provide a comprehensive overview of the current research on nanoparticle-encapsulated ADCs. It highlights their potential to transform cancer treatment and offers insights into future directions for optimizing these advanced therapeutic strategies.

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.

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.

Preclinical pharmacokinetics, distribution, metabolism and excretion of disitamab vedotin

Background and purpose

Disitamab vedotin is an antibody-drug conjugate (ADC) composed of a humanized IgG1 monoclonal antibody (mAb) targeting HER2 conjugated to monomethyl auristatin E(MMAE) via a cleavable dipeptide linker.

Experimental approach

The pharmacokinetics, distribution, catabolism/metabolism and elimination properties of disitamab vedotin and its payload MMAE were characterized in rats and tumour-bearing mice.

Key results

The configured mAb and total antibody showed linear dynamic characteristics. Moreover, the molecular structure of disitamab vedotin effectively reduces the exposure of MMAE, which has a fast clearance. Two radiolabeled probes were developed to track the fate of different components of the disitamab vedotin, including 125I labelled antibody and 3H labelled MMAE payload of the ADC. Following a single intravenous administration of the radiolabeled probes to the tumour-bearing mice and rats, blood, various tissues, and excreta samples were collected and analyzed for radioactivity and to characterize the metabolites/catabolites. Disitamab vedotin and free MMAE (FM) were majorly distributed in tissues and organs with rich blood flow. Moreover, both disitamab vedotin and MMAE have higher and longer exposure in tumour tissue. Disitamab vedotin was mainly eliminated through renal excretion, while the FM was mainly eliminated through the biliary faecal route (>70 %) and a small fraction (<10 %) was eliminated through renal excretion in the form of catabolites/metabolites, among which, MMAE was identified as the major species, along with 10 other minor species.

Conclusion

These studies provided significant insight into disitamab vedotin pharmacokinetics, distribution, metabolism and elimination properties, which supports the clinical development of disitamab vedotin.

A novel therapeutic strategy utilizing EpCAM aptamer-conjugated gemcitabine for targeting bladder cancer and cancer stem cells

Gemcitabine (GEM) is a first line chemotherapy drug for bladder cancer (BCa). GEM's lack of specificity has led to disadvantages, resulting in low efficiency, especially when combined with the targeted treatment of BCa stem cells (CSCs), which is considered the cause of BCa recurrence and progression. To enhance the anti-cancer effect and reduce the side effects of GEM targeting of BCa cells/CSCs, an aptamer drug conjugate (ApDC) targeted delivery system was used to improve the efficiency of GEM in BCa therapy using EpCAM aptamer-GEM conjugates based on the epithelial cell adhesion molecule (EpCAM), which is highly expressed on the cell membrane of BCa cells/CSCs. We designed and synthesized EpCAM aptamer gemcitabine conjugates (EpCAM-GEMs, one aptamer carried three GEMs). The targeting effect of EpCAM-GEMs was examined in a xenograft model using an in vivo imaging system. To evaluate the antitumor activity and mechanism of EpCAM-GEMs, Cell Counting Kit-8, apoptosis and colony formation assays; BCa CSC xenotransplantation; xenotransplantation of subcutaneous tumors; a lung metastasis model; an in situ model; and biosafety assessment were used in vitro and in vivo. EpCAM is highly expressed on the surface of BCa cells/CSCs. EpCAM-GEMs were automatically synthesized using a DNA synthesizer, were stable in serum, and selectively delivered GEM to kill BCa cells/CSCs. EpCAM-GEMs entered BCa cells via macropinocytosis, released GEM to inhibit DNA synthesis, and degraded all BCa cells under the action of a BCa cell intracellular phosphatase; however, they did not kill normal cells because of their low EpCAM expression. EpCAM-GEMs inhibited BCa growth and metastasis in three bladder tumor models, with good biosafety. These results demonstrated the targeted anti-tumor efficiency and good biosafety of EpCAM-GEMs in BCa treatment, which will provide a new therapeutic strategy in BCa biomarker targeted therapy.

Evaluating the safety of antibody-drug conjugates in lung cancer: A systematic review and meta-analysis

BACKGROUND

Antibody-drug conjugates (ADC) have emerged as a promising treatment for lung cancer. However, their safety profile requires further analysis. This study assessed adverse events (AE) in patients with lung cancer treated with ADCs, with particular focus on differences in pathological types, therapeutic options, and drug components.

METHODS

Prospective trials from various databases up to June 11, 2024, that analyzed treatment-emergent AEs (TEAEs), treatment-related AEs (TRAEs), mortality, and drug discontinuation were identified. Incidence rates were pooled using a random effects model, and their corresponding 95% confidence intervals (CIs) were calculated.

RESULTS

The analysis included 28 studies with 3,127 participants. The pooled incidence of all-grade TEAEs and TRAEs was 98.9 % and 91.4 %, respectively, whereas that of grade ≥ 3 TEAEs and TRAEs was 65.9 % and 41.7 %, respectively. The gastrointestinal system was frequently involved, albeit predominantly in low grades. Hematological system involvement was prevalent in grade ≥ 3 AEs, with respiratory system disorders being more prevalent in severe AEs. Respiratory system disorders were the primary cause of death and drug discontinuation. Subgroup analyses revealed higher incidences of AEs in SCLC than in NSCLC, in combination therapies than in monotherapies, and in ADCs with cleavable linkers. ADCs targeting delta-like protein 3 or carrying pyrrolobenzodiazepine dimer as payloads exhibit higher incidences of grade ≥ 3 TEAEs than those targeting HER2.

CONCLUSION

Effective managing ADC toxicities is crucial in lung cancer treatment, with AE incidence and profiles varying by cancer pathology, treatment regimen, and ADC components. Close monitoring of symptoms associated with gastrointestinal, infection, and respiratory systems is essential. PROSPERO registration number: CRD42024546210.

5-Fluorouracil-methotrexate conjugate enhances the efficacy of 5-fluorouracil in colorectal cancer therapy

To extend the short half-life of fluorouracil (Fu), enhance its tumor targeting, improve efficacy, and reduce side effects, providing a new approach for colorectal cancer treatment. Fluorouracil was hydroxylated and conjugated with methotrexate to form a 5-fluorouracil-methotrexate conjugate (MF). This was complexed with sulfobutyl ether-β-cyclodextrin (MF-SEBCD) using a stirring method to create an injectable formulation. In vitro studies assessed the conversion of MF-SEBCD in plasma and its antitumor activity. In vivo studies examined antitumor activity, preliminary safety, pharmacokinetics, and tissue distribution. MF was synthesized with a 25% yield and purity above 95%. The water solubility of MF increased by 92-fold with MF-SEBCD preparation. In vitro, MF-SEBCD effectively converted into Fu in plasma and showed strong antitumor activity, with IC50 values of 0.51, 1.29, and 1.26 µM for MC38, HT29, and 4T1 cells, respectively. In vivo, MF-SEBCD achieved a tumor inhibition rate of 57.08%. Pharmacokinetic studies showed that MF-SEBCD extended Fu's half-life to 47 min, nearly double that of Fu injection. Tissue distribution analysis confirmed improved tumor targeting. MF-SEBCD effectively prolongs Fu's half-life, enhances tumor targeting, increases antitumor efficacy, and reduces side effects, offering a promising approach for colorectal cancer treatment.

Key considerations based on pharmacokinetic/pharmacodynamic in the design of antibody-drug conjugates

Background

Antibody-drug conjugate (ADC) is an anticancer drug that links toxins to specifically targeted antibodies via linkers, offering the advantages of high target specificity and high cytotoxicity. However, complexity of its structural composition poses a greater difficulty for drug design studies.

Objectives

Pharmacokinetic/pharmacodynamic (PK/PD) based consideration of ADCs has increasingly become a hot research topic for optimal drug design in recent years, providing possible ideas for obtaining ADCs with desirable properties.

Methods

From the assessment of the ADC action process based on PK/PD, we introduce the main research strategies of ADCs. In addition, we investigated the strategies to solve the prominent problems of ADC in the clinic in recent years, and summarized and evaluated the specific ways to optimize various problems of ADC based on the PK/PD model from two perspectives of optimizing the structure and properties of the drugs themselves. Through the selection of target antigen, the optimization of the linker, the optimization of novel small molecule toxins as payload, the optimization of ADC, overcoming the multi-drug resistance of ADC, improving the ADC tumor penetration of ADC, surface modification of ADC and surface bystander effect of ADC provide a more comprehensive and accurate framework for designing new ADCs.

Results

We've expounded comprehensively on applying pharmacokinetics or pharmacodynamics while designing ADC to obtain higher efficacy and fewer side effects. From the ADC's PK/PD property while coming into play in vivo and the PK/PD study strategy, to specific ADC optimization methods and recommendations based on PK/PD, it has been study-approved that the PK/PD properties exert a subtle role in the development of ADC, whether in preclinical trials or clinical promotion.

Conclusion

The study of PK/PD unfolds the detailed mechanism of ADC action, making it easier to control related parameters in the process of designing ADC, limited efficacy and inevitable off-target toxicity remain a challenging bottleneck.

Landscape of clinical drug development of ADCs used for the pharmacotherapy of cancers: an overview of clinical trial registry data from 2002 to 2022

BACKGROUND

To provide reference for clinical development of ADCs in the industry, we analyzed the landscape and characteristics of clinical trials about antibody-drug conjugates (ADCs).

METHOD

Clinical trials to study ADCs used for the pharmacotherapy of cancers initiated by the sponsor were searched in the Cite line Pharma Intelligence (Trialtrove database), and the landscape and characteristics of these clinical trials were analyzed from multiple perspectives, such as the number, phases, status, indications, and targets of the clinical trials.

RESULT

As of December 31, 2022, a total of 431 clinical trials have been initiated to study ADCs used for the pharmacotherapy of cancers, and the number of the last 10 years was 5.5 times as large as the first 11 years. These clinical trials involved 47 indications, including breast cancer, lymphoma (lymphoma, non-Hodgkin's and lymphoma, Hodgkin's), unspecified solid tumor, bladder cancer and lung cancer (lung, non-small cell cancer and lung, small cell cancer). As for each of these five indications, 50 + clinical trials have been carried out, accounting for as high as 48.50% (454/936). ADCs involve 38 targets, which are relatively concentrated. Among them, ERBB2 (HER2) and TNFRSF8 (CD30) involve in 100 + registered clinical trials, and TNFRSF17 (BCMA), NECTIN4 and CD19 in 10 + trials. The clinical trials for these five targets account for 79.02% (354/448) of the total number. Up to 93.97% (405/431) of these clinical trials explored the correlation between biomarkers and efficacy. Up to 45.91% (292/636) of Lots (lines of treatment) applied in the clinical trials were the second line. Until December 31, 2022, 54.52% (235/431) of the clinical trials have been completed or terminated.

CONCLUSION

ADCs are a hotspot of research and development in oncology clinical trials, but the indications, targets, phases, and Lot that have been registered are seemingly relatively concentrated at present. This study provides a comprehensive analysis which can assist researchers/developer quickly grasp relevant knowledge to assess a product and also providing new clues and ideas for future research.

Can we do better with Mylotarg? Model-based assessment of opportunities to improve therapeutic index

Late-stage clinical trial failures increase the overall cost and risk of bringing new drugs to market. Determining the pharmacokinetic (PK) drivers of toxicity and efficacy in preclinical studies and early clinical trials supports quantitative optimization of drug schedule and dose through computational modeling. Additionally, this approach permits prioritization of lead candidates with better PK properties early in development. Mylotarg is an antibody-drug conjugate (ADC) that attained U.S. Food and Drug Administration (FDA) approval under a fractionated dosing schedule after 17 years of clinical trials, including a 10-year period on the market resulting in hundreds of fatal adverse events. Although ADCs are often considered lower risk for toxicity due to their targeted nature, off-target activity and liberated payload can still constrain dosing and drive clinical failure. Under its original schedule, Mylotarg was dosed infrequently at high levels, which is typical for ADCs because of their long half-lives. However, our PK modeling suggests that these regimens increase maximum plasma concentration (Cmax)-related toxicities while producing suboptimal exposures to the target receptor. Our analysis demonstrates that the benefits of dose fractionation for Mylotarg tolerability should have been obvious early in the drug's clinical development and could have curtailed the proliferation of ineffective Phase III studies. We also identify schedules likely to be even more efficacious without compromising on tolerability. Alternatively, a longer-circulating Mylotarg formulation could obviate the need for dose fractionation, allowing superior patient convenience. Early-stage PK optimization through quantitative modeling methods can accelerate clinical development and prevent late-stage failures.

Trastuzumab deruxtecan in breast cancer

Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate (ADC) consisting of a humanised, anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibody covalently linked to a topoisomerase I inhibitor cytotoxic payload (DXd). The high drug-to-antibody ratio (8:1) ensures a high DXd concentration is delivered to target tumour cells, following internalisation of T-DXd and subsequent cleavage of its tetrapeptide-based linker. DXd's membrane-permeable nature enables it to cross cell membranes and potentially exert antitumour activity on surrounding tumour cells regardless of HER2 expression. T-DXd's unique mechanism of action is reflected in its efficacy in clinical trials in patients with HER2-positive advanced breast cancer (in heavily pretreated populations and in those previously treated with a taxane and trastuzumab), as well as HER2-low metastatic breast cancer. Thus, ADCs such as T-DXd have the potential to change the treatment paradigm of targeting HER2 in metastatic breast cancer, including eventually within the adjuvant/neoadjuvant setting.

Antibody-Drug Conjugates in the Pipeline for Treatment of Melanoma: Target and Pharmacokinetic Considerations

Melanoma is an aggressive, rapidly developing form of skin cancer that affects about 22 per 100,000 individuals. Treatment options for melanoma patients are limited and typically involve surgical excision of moles and chemotherapy. Survival has been improved in recent years through targeted small molecule inhibitors and antibody-based immunotherapies. However, the long-term side effects that arise from taking chemotherapies can negatively impact the lives of patients because they lack specificity and impact healthy cells along with the cancer cells. Antibody-drug conjugates are a promising new class of drugs for the treatment of melanoma. This review focuses on the development of antibody-drug conjugates for melanoma and discusses the existing clinical trials of antibody-drug conjugates and their use as a melanoma treatment. So far, the antibody-drug conjugates have struggled from efficacy problems, with modest effects at best, leading many to be discontinued for melanoma. At the same time, conjugates such as AMT-253, targeting melanoma cell adhesion molecule, and mecbotamab vedotin  targeting AXL receptor tyrosine kinase, are among the most exciting for melanoma treatment in the future.

Antibody-Antibiotic Conjugates: A Comprehensive Review on Their Therapeutic Potentials Against BacterialInfections

INTRODUCTION

Antibodies are significant agents in the immune system and have proven to be effective in treating bacterial infections. With the advancement of antibody engineering in recent decades, antibody therapy has evolved widely.

AIM

This review aimed to investigate a new method as a therapeutic platform for the treatment of bacterial infections and explore the novel features of this method in conferring pathogen specificity to broad-spectrum antibiotics.

MATERIAL AND METHODS

A literature review was conducted addressing the following topics about antibody-antibiotic conjugates (AACs): (1) structure and mechanism of action; (2) clinical effectiveness; (3) advantages and disadvantages.

RESULT

Antibody conjugates are designed to build upon the progress made in the development of monoclonal antibodies for the treatment of diseases. Despite the growing emergence of antibiotic resistance among pathogenic bacteria worldwide, novel antimicrobials have not been sufficiently expanded to combat the global crisis of antibiotic resistance. A recently developed strategy for the treatment of infectious diseases is the use of AACs, which are specifically activated only in host cells.

CONCLUSION

A novel therapeutic AAC employs an antibody to deliver the antibiotic to the bacteria. The AACs can release potent antibacterial components that unconjugated forms may not exhibit with an appropriate therapeutic index. This review highlights how this science has guided the design principles of an impressive AAC and discusses how the AAC model promises to enhance the antibiotic effect against bacterial infections.

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

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

Incidence of antibody-drug conjugate-related fatigue in patients with breast cancer: A systematic review and meta-analysis

BACKGROUND

Numerous studies have reported the efficacy of antibody-drug conjugates (ADCs) for treating breast cancer. However, during cytotoxic drug treatment, long-term disabling fatigue is common. Moreover, studies in the relevant literature have indicated that fatigue can significantly increase the incidence of depression and sleep disorders. Therefore, this meta-analysis aims to evaluate the incidence of fatigue in breast cancer survivors treated with ADCs.

METHODS

PubMed, EMBASE, Web of Science, and Cochrane Library databases were systematically searched for articles and conference abstracts published before March 16, 2023. Further, two authors independently extracted data from the included studies. The primary outcome of this study was the incidence of all-grade fatigue caused by the use of ADCs in patients with breast cancer. Finally, a random-effects model was used to calculate the incidence and 95% confidence intervals (CIs) of the outcome.

RESULTS

Overall, 7963 patients from 31 studies were included in this meta-analysis to assess the incidence of fatigue caused by the use of approved and marketed ADCs in patients with breast cancer. Notably, the incidence of all-grade fatigue during ADC monotherapy was 39.84% (95% CI, 35.09%-44.69%). In subgroup analyses, among ADCs, the incidence of trastuzumab deruxtecan-induced fatigue was the highest, with an all-grade fatigue incidence of 47.05% (95% CI, 42.38%-51.75%). Meanwhile, the incidence of trastuzumab emtansine (T-DM1)-induced all-grade fatigue was 35.17% (95% CI, 28.87%-41.74%), which was the lowest among ADCs. Further, the incidence of all-grade fatigue due to sacituzumab govitecan was 42.82% (95% CI, 34.54%-51.32%), which was higher than that due to T-DM1. Moreover, the incidence of fatigue was higher with T-DM1 combination therapy than with monotherapy.

CONCLUSIONS

Clinicians have highlighted the high incidence of ADC-related fatigue and its negative impact on patients' physical and mental health, making fatigue an important research variable. The results of this study will further contribute to a comprehensive understanding of ADCs, which have some clinical importance and are of great benefit to patients with breast cancer.

Synthesis of site-specific Fab-drug conjugates using ADP-ribosyl cyclases

Targeted delivery of small-molecule drugs via covalent attachments to monoclonal antibodies has proved successful in clinic. For this purpose, full-length antibodies are mainly used as drug-carrying vehicles. Despite their flexible conjugation sites and versatile biological activities, intact immunoglobulins with conjugated drugs, which feature relatively large molecular weights, tend to have restricted tissue distribution and penetration and low fractions of payloads. Linking small-molecule therapeutics to other formats of antibody may lead to conjugates with optimal properties. Here, we designed and synthesized ADP-ribosyl cyclase-enabled fragment antigen-binding (Fab) drug conjugates (ARC-FDCs) by utilizing CD38 catalytic activity. Through rapidly forming a stable covalent bond with a nicotinamide adenine dinucleotide (NAD+ )-based drug linker at its active site, CD38 genetically fused with Fab mediates robust site-specific drug conjugations via enzymatic reactions. Generated ARC-FDCs with defined drug-to-Fab ratios display potent and antigen-dependent cytotoxicity against breast cancer cells. This work demonstrates a new strategy for developing site-specific FDCs. It may be applicable to different antibody scaffolds for therapeutic conjugations, leading to novel targeted agents.

Antibody-drug conjugates targeting HER2 for the treatment of urothelial carcinoma: potential therapies for HER2-positive urothelial carcinoma

Urothelial carcinoma (UC) is a common cancer characterized by high morbidity and mortality rates. Despite advancements in treatment, challenges such as recurrence and low response rates persist. Antibody-drug conjugates (ADCs) have emerged as a promising therapeutic approach for various cancers, although their application in UC is currently limited. This review focuses on recent research regarding ADCs designed to treat UC by targeting human epidermal growth factor receptor 2 (HER2), a surface antigen expressed on tumor cells. ADCs comprise three main components: an antibody, a linker, and a cytotoxic payload. The antibody selectively binds to tumor cell surface antigens, facilitating targeted delivery of the cytotoxic drug, while linkers play a crucial role in ensuring stability and controlled release of the payload. Cleavable linkers release the drug within tumor cells, while non-cleavable linkers ensure stability during circulation. The cytotoxic payload exerts its antitumor effect by disrupting cellular pathways. HER2 is commonly overexpressed in UCs, making it a potential therapeutic target. Several ADCs targeting HER2 have been approved for cancer treatment, but their use in UC is still being tested. Numerous HER2 ADCs have demonstrated significant growth inhibition and induction of apoptosis in translational models of HER2-overexpressing bladder cancer. Ongoing clinical trials are assessing the efficacy and safety of ADCs targeting HER2 in UC, with the aim of determining tumor response and the potential of ADCs as a treatment option for UC patients. The development of effective therapies with improved response rates and long-term effectiveness is crucial for advanced and metastatic UC. ADCs targeting HER2 show promise in this regard and merit further investigation for UC treatment.

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

Recent Technological and Intellectual Property Trends in Antibody-Drug Conjugate Research

Antibody-drug conjugate (ADC) therapy, an advanced therapeutic technology comprising antibodies, chemical linkers, and cytotoxic payloads, addresses the limitations of traditional chemotherapy. This study explores key elements of ADC therapy, focusing on antibody development, linker design, and cytotoxic payload delivery. The global rise in cancer incidence has driven increased investment in anticancer agents, resulting in significant growth in the ADC therapy market. Over the past two decades, notable progress has been made, with approvals for 14 ADC treatments targeting various cancers by 2022. Diverse ADC therapies for hematologic malignancies and solid tumors have emerged, with numerous candidates currently undergoing clinical trials. Recent years have seen a noteworthy increase in ADC therapy clinical trials, marked by the initiation of numerous new therapies in 2022. Research and development, coupled with patent applications, have intensified, notably from major companies like Pfizer Inc. (New York, NY, USA), AbbVie Pharmaceuticals Inc. (USA), Regeneron Pharmaceuticals Inc. (Tarrytown, NY, USA), and Seagen Inc. (Bothell, WA, USA). While ADC therapy holds great promise in anticancer treatment, challenges persist, including premature payload release and immune-related side effects. Ongoing research and innovation are crucial for advancing ADC therapy. Future developments may include novel conjugation methods, stable linker designs, efficient payload delivery technologies, and integration with nanotechnology, driving the evolution of ADC therapy in anticancer treatment.

The ever-expanding landscape of antibody-drug conjugates (ADCs) in solid tumors: A systematic review

BACKGROUND

The advent of targeted therapies signaled novel avenues for more optimal oncological outcomes. Antibody-drug conjugates (ADCs) have risen as a cornerstone of the ever-expanding targeted therapy era. The purpose of this systematic review is to delineate the rapidly evolving clinical landscape of ADCs for solid tumors.

METHODS

A literature search was performed in Medline, Embase and Cochrane databases for phase II and III clinical trials. Outcomes of interest were the objective response rate, overall survival, progression-free survival and adverse events.

RESULTS

A total of 92 clinical trials (76 phase II and 16 phase III) evaluated the efficacy and safety of ADCs for a plethora of solid tumors. Out of the 30 investigated ADCs, 8 have received approval by regulatory organizations for solid tumors. Currently, 52 phase III clinical trials for ADCs are ongoing.

CONCLUSION

ADCs have shown promising results for several solid tumors and various cancer settings.

Antibody drug conjugates beyond cytotoxic payloads

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

Trends in the Development of Antibody-Drug Conjugates for Cancer Therapy

In cancer treatment, the first-generation, cytotoxic drugs, though effective against cancer cells, also harmed healthy ones. The second-generation targeted cancer cells precisely to inhibit their growth. Enter the third-generation, consisting of immuno-oncology drugs, designed to combat drug resistance and bolster the immune system's defenses. These advanced therapies operate by obstructing the uncontrolled growth and spread of cancer cells through the body, ultimately eliminating them effectively. Within the arsenal of cancer treatment, monoclonal antibodies offer several advantages, including inducing cancer cell apoptosis, precise targeting, prolonged presence in the body, and minimal side effects. A recent development in cancer therapy is Antibody-Drug Conjugates (ADCs), initially developed in the mid-20th century. The second generation of ADCs addressed this issue through innovative antibody modification techniques, such as DAR regulation, amino acid substitutions, incorporation of non-natural amino acids, and enzymatic drug attachment. Currently, a third generation of ADCs is in development. This study presents an overview of 12 available ADCs, reviews 71 recent research papers, and analyzes 128 clinical trial reports. The overarching objective is to gain insights into the prevailing trends in ADC research and development, with a particular focus on emerging frontiers like potential targets, linkers, and drug payloads within the realm of cancer treatment.

Antibody-drug conjugates: the paradigm shifts in the targeted cancer therapy

Cancer is one of the deadliest diseases, causing million of deaths each year globally. Conventional anti-cancer therapies are non-targeted and have systemic toxicities limiting their versatile applications in many cancers. So, there is an unmet need for more specific therapeutic options that will be effective as well as free from toxicities. Antibody-drug conjugates (ADCs) are suitable alternatives with the right potential and improved therapeutic index for cancer therapy. The ADCs are highly precise new class of biopharmaceutical products that covalently linked a monoclonal antibody (mAb) (binds explicitly to a tumor-associated surface antigen) with a customized cytotoxic drug (kills cancer cells) and tied via a chemical linker (releases the drug). Due to its precise design, it brings about the target cell killing sparing the normal counterpart and free from the toxicities of conventional chemotherapy. It has never been so easy to develop potential ADCs for successful therapeutic usage. With relentless efforts, it took almost a century for scientists to advance the formula and design ADCs for its current clinical applications. Until now, several ADCs have passed successfully through preclinical and clinical trials and because of proven efficacy, a few are approved by the FDA to treat various cancer types. Even though ADCs posed some shortcomings like adverse effects and resistance at various stages of development, with continuous efforts most of these limitations are addressed and overcome to improve their efficacy. In this review, the basics of ADCs, physical and chemical properties, the evolution of design, limitations, and future potentials are discussed.

Transglutaminase in Foods and Biotechnology

Stabilization and reusability of enzyme transglutaminase (TGM) are important goals for the enzymatic process since immobilizing TGM plays an important role in different technologies and industries. TGM can be used in many applications. In the food industry, it plays a role as a protein-modifying enzyme, while, in biotechnology and pharmaceutical applications, it is used in mediated bioconjugation due to its extraordinary crosslinking ability. TGMs (EC 2.3.2.13) are enzymes that catalyze the formation of a covalent bond between a free amino group of protein-bound or peptide-bound lysine, which acts as an acyl acceptor, and the γ-carboxamide group of protein-bound or peptide-bound glutamine, which acts as an acyl donor. This results in the modification of proteins through either intramolecular or intermolecular crosslinking, which improves the use of the respective proteins significantly.

Dual function of protein phosphatase 5 (PPP5C): An emerging therapeutic target for drug discovery

Phosphorylation of proteins is reversibly controlled by the kinases and phosphatases in many posttranslational regulation patterns. Protein phosphatase 5 (PPP5C) is a serine/threonine protein phosphatase showing dual function by simultaneously exerting dephosphorylation and co-chaperone functions. Due to this special role, PPP5C was found to participate in many signal transductions related to various diseases. Abnormal expression of PPP5C results in cancers, obesity, and Alzheimer's disease, making it a potential drug target. However, the design of small molecules targeting PPP5C is struggling due to its special monomeric enzyme form and low basal activity by a self-inhibition mechanism. Through realizing the PPP5C's dual function as phosphatase and co-chaperone, more and more small molecules were found to regulate PPP5C with a different mechanism. This review aims to provide insights into PPP5C's dual function from structure to function, which could provide efficient design strategies for small molecules targeting PPP5C as therapeutic candidates.

Payload-Binding Fab Fragments Increase the Therapeutic Index of MMAE Antibody-Drug Conjugates

Monomethyl auristatin E (MMAE) is a potent tubulin inhibitor that is used as the payload for four FDA-approved antibody-drug conjugates (ADC). Deconjugated MMAE readily diffuses into untargeted cells, resulting in off-target toxicity. Here, we report the development and evaluation of a humanized Fab fragment (ABC3315) that enhances the therapeutic selectivity of MMAE ADCs. ABC3315 increased the IC50 of MMAE against human cancer cell lines by > 500-fold with no impact on the cytotoxicity of MMAE ADCs, including polatuzumab vedotin (PV) and trastuzumab-vc-MMAE (TvcMMAE). Coadministration of ABC3315 did not reduce the efficacy of PV or TvcMMAE in xenograft tumor models. Coadministration of ABC3315 with 80 mg/kg TvcMMAE significantly (P < 0.0001) increased the cumulative amount of MMAE that was excreted in urine 0 to 4 days after administration from 789.4±19.0 nanograms (TvcMMAE alone) to 2625±206.8 nanograms (for mice receiving TvcMMAE with coadministration of ABC3315). Mice receiving 80 mg/kg TvcMMAE and PBS exhibited a significant drop in white blood cell counts (P = 0.025) and red blood cell counts (P = 0.0083) in comparison with control mice. No significant differences, relative to control mice, were found for white blood cell counts (P = 0.15) or for red blood cell counts (P = 0.23) for mice treated with 80 mg/kg TvcMMAE and ABC3315. Coadministration of ABC3315 with 120 mg/kg PV significantly (P = 0.045) decreased the percentage body weight loss at nadir for treated mice from 11.9%±7.0% to 4.1%±2.1%. Our results demonstrate that ABC3315, an anti-MMAE Fab fragment, decreases off-target toxicity while not decreasing antitumor efficacy, increasing the therapeutic window of MMAE ADCs.

The evolving therapeutic landscape of trastuzumab-drug conjugates: Future perspectives beyond HER2-positive breast cancer

A novel class of drugs, antibody-drug conjugates (ADCs), are now rapidly emerging as highly effective treatments for solid tumours. ADCs conjugate conventional chemotherapeutics with highly selective targeted monoclonal antibodies. Anti-HER2 therapies selectively target cancer cells expressing human epidermal growth factor receptor 2 (HER2), among them trastuzumab has been the first HER2-targeting monoclonal antibody to achieve successful results that made it the backbone of anti-HER2 therapies. Trastuzumab drug conjugates (T-DCs), use trastuzumab as a selective antibody to lead cytotoxic drugs inside cancer cells. Trastuzumab-emtansine (T-DM1) and trastuzumab-deruxtecan (T-Dxd) are the two approved T-DCs. T-Dxd along with other five T-DCs represents "second generation ADCs" that has been firstly tested in HER2 positive breast cancer (BC) and then in HER2-low BC and other cancers showing promising results thanks to extraordinary and innovative pharmacokinetic and pharmacodynamic characteristics. The evidence generated so far are establishing them as a completely new class of agents effective in solid cancer treatments but also warrants physicians against unconventional toxicity profiles. The role of T-DCs in HER2-positive BC has been largely reviewed, while in this review, we provided for the first time in literature an overview of trastuzumab drug conjugates (T-DCs) approved and/or in clinical development with a specific focus on their efficacy and safety profile in HER2-low BC and other solid tumours different from BC. We started by analysing T-DCs biological characteristics that underly the differences in T-DCs pharmacodynamics and safety profile, then presented the main evidence on the activity and efficacy of these emerging T-DCs in HER2-low BC and other HER2 overexpressing and/or mutated solid tumours and lastly, we provided an overview of the complex and still evolving scenario in which these compounds should be allocated. A specific focus on possible combination strategies with other drugs such as immunotherapy, chemotherapy and target therapy, to increase T-DCs activity and eventually overcome future upcoming resistance mechanisms, are here also critically reviewed.

Mechanisms of ADC Toxicity and Strategies to Increase ADC Tolerability

Anti-cancer antibody-drug conjugates (ADCs) aim to expand the therapeutic index of traditional chemotherapy by employing the targeting specificity of monoclonal antibodies (mAbs) to increase the efficiency of the delivery of potent cytotoxic agents to malignant cells. In the past three years, the number of ADCs approved by the Food and Drug Administration (FDA) has tripled. Although several ADCs have demonstrated sufficient efficacy and safety to warrant FDA approval, the clinical use of all ADCs leads to substantial toxicity in treated patients, and many ADCs have failed during clinical development due to their unacceptable toxicity profiles. Analysis of the clinical data has demonstrated that dose-limiting toxicities (DLTs) are often shared by different ADCs that deliver the same cytotoxic payload, independent of the antigen that is targeted and/or the type of cancer that is treated. DLTs are commonly associated with cells and tissues that do not express the targeted antigen (i.e., off-target toxicity), and often limit ADC dosage to levels below those required for optimal anti-cancer effects. In this manuscript, we review the fundamental mechanisms contributing to ADC toxicity, we summarize common ADC treatment-related adverse events, and we discuss several approaches to mitigating ADC toxicity.

A HER2-targeted antibody-novel DNA topoisomerase I inhibitor conjugate induces durable adaptive antitumor immunity by activating dendritic cells

We designed and developed a novel DNA topoisomerase I inhibitor MF-6, which was a more potent cytotoxin and a more potent inducer of immunogenic cell death compared with DXd. To utilize MF-6's ability to induce antitumor immunity, a human epidermal growth factor receptor 2 (HER2)-targeted antibody-drug conjugate (ADC) trastuzumab-L6 that included a cleavable linker and MF-6 was developed. Different from traditional cytotoxic ADC, the antitumor activity of trastuzumab-L6 was assessed by inducing tumor cell immunogenic cell death, activating dendritic cells and cytotoxic CD8+ T cells to acquire durable adaptive immune memory. Tumor cells treated with trastuzumab-L6 were committed to immunogenic cell death, with upregulation of damage-associated molecular patterns and antigen presentation molecules. In a syngeneic tumor model with a mouse cell line that expressed human HER2, immunocompetent mice showed greater antitumor efficacy compared with nude mice. The trastuzumab-L6-cured immunocompetent mice acquired adaptive antitumor memory and rejected subsequent tumor cell challenge. The trastuzumab-L6 efficacy was abrogated when cytotoxic CD8+ T cells were depleted and enhanced when regulatory CD4+ T cells were depleted. The combination of trastuzumab-L6 with immune checkpoint inhibitors significantly increased antitumor efficacy. Enhanced T cell infiltration, dendritic cell activation, and decreased type M2 macrophages in tumor post trastuzumab-L6 administration confirmed the immune-activating responses. In conclusion, trastuzumab-L6 was considered to be an immunostimulatory agent, rather than a traditional cytotoxic ADC, and its antitumor efficacy was enhanced when combined with an anti-PD-L1 and anti-CTLA-4 antibody, which suggested a potential therapeutic strategy.

A magnetic antibody-conjugated nano-system for selective delivery of Ca(OH)2 and taxotere in ovarian cancer cells

An efficient strategy for cancer therapy is presented, in which a tumor mass is initially pretreated with calcium hydroxide, then treated with Taxotere (TXT). In this regard, an advanced delivery system based on iron oxide nanoparticles has been designed. The surface of nanoparticles was functionalized with sortilin (SORT-1, a human IgG1 monoclonal antibody) that specifically encodes caov-4 ovarian cancerous cells. Plasmonic heating of the incorporated gold nanoparticles in polyvinyl alcohol (PVA) has been exploited to control the release process of TXT. The in vitro, ex vivo and in vivo experiments have exhibited high efficacy of a seven-day pretreatment by Ca(OH)₂ plus 14 days treatment program by Ca(OH)₂@Fe₃O₄/PVA/Au-SORT nano-therapeutics, where more penetration ratio resulted in tumor growth inhibition by ca. 78.3%. As a result, due to showing high values of the anti-tumor properties and biosafety, the presented pretreatment strategy is suggested for more effective treatment on the aged tumors.

A magnetic drug delivery system containing polyvinyl alcohol, gold nanoparticles, and sortilin antibody followed by the plasmonic photothermal heating strategy for the controlled drug release is proposed, with use in ovarian cancer demonstrated.

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.

Linkers: An Assurance for Controlled Delivery of Antibody-Drug Conjugate

As one of the major therapeutic options for cancer treatment, chemotherapy has limited selectivity against cancer cells. Consequently, this therapeutic strategy offers a small therapeutic window with potentially high toxicity and thus limited efficacy of doses that can be tolerated by patients. Antibody-drug conjugates (ADCs) are an emerging class of anti-cancer therapeutic drugs that can deliver highly cytotoxic molecules directly to cancer cells. To date, twelve ADCs have received market approval, with several others in clinical stages. ADCs have become a powerful class of therapeutic agents in oncology and hematology. ADCs consist of recombinant monoclonal antibodies that are covalently bound to cytotoxic chemicals via synthetic linkers. The linker has a key role in ADC outcomes because its characteristics substantially impact the therapeutic index efficacy and pharmacokinetics of these drugs. Stable linkers and ADCs can maintain antibody concentration in blood circulation, and they do not release the cytotoxic drug before it reaches its target, thus resulting in minimum off-target effects. The linkers used in ADC development can be classified as cleavable and non-cleavable. The former, in turn, can be grouped into three types: hydrazone, disulfide, or peptide linkers. In this review, we highlight the various linkers used in ADC development and their design strategy, release mechanisms, and future perspectives.

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

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

Antibody-drug conjugate and free geldanamycin combination therapy enhances anti-cancer efficacy

Antibody drug-conjugates (ADCs) targeting human epidermal growth factor (HER2) are a rapidly expanding class of cancer therapeutics. Such ADCs are known to suffer from inefficient trafficking to the lysosome due to HER2 endosomal recycling, leaving most bound ADCs at the cell surface or in early endosomes. This study aims to increase the maximum cytotoxicity of ADC treatment by co-delivering a small molecule inhibitor targeting the primary chaperone of HER2, heat shock protein 90 (HSP90). We hypothesized that inhibiting HSP90 could aid ADC cytotoxicity by overcoming HER2 endosomal recycling. Flow cytometric studies tracking HER2 surface expression revealed ∼ 10 nM geldanamycin (GA) as the threshold for inhibiting HSP90 mediated HER2 recycling. Cytotoxicity studies in HER2 overexpressing cancer cell lines NCI-N87, MDA-MB-453, and SKOV3 demonstrated that co-administration of ADC alongside 100 nM GA significantly increased cytotoxicity compared to ADC alone. In all cases, baseline cytotoxicity was observed even in low HER2 expressing line MDA-MB-231 cells, indicating possible off-target effects. To mitigate this baseline cytotoxicity, a "pulse treatment" regime was adopted where cells are pre-loaded with T-DM1 or T-MMAE ADCs for 4 h, followed by a 4-hour pulse treatment with ADC and 100 nM GA to initiate trafficking of HER2 bound ADC to the lysosome. Afterwards, GA is removed, and ADC treatment is continued. GA pulse co-treatment decreased the amount of ADC required to achieve maximum cytotoxicity while minimizing baseline cytotoxicity. No such co-treatment regime featuring a pulse sequence has been explored before. Such co-treatments could offer a viable solution to increase ADC efficacy in hard to treat or resistant HER2-positive cancers.

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.

Implementing antibody-drug conjugates (ADCs) in HER2-positive breast cancer: state of the art and future directions

The development of anti-HER2 agents has been one of the most meaningful advancements in the management of metastatic breast cancer, significantly improving survival outcomes. Despite the efficacy of anti-HER2 monoclonal antibodies, concurrent chemotherapy is still needed to maximize response. Antibody-drug conjugates (ADCs) are a class of therapeutics that combines an antigen-specific antibody backbone with a potent cytotoxic payload, resulting in an improved therapeutic index. Two anti-HER2 ADCs have been approved by the FDA with different indications in HER2-positive breast cancer. Ado-trastuzumab emtansine (T-DM1) was the first-in-class HER2-targeting ADC, initially approved in 2013 for metastatic patients who previously received trastuzumab and a taxane, and the label was expanded in 2019 to include adjuvant treatment of high-risk patients with residual disease after neoadjuvant taxane and trastuzumab-based therapy. In 2020, trastuzumab deruxtecan (T-DXd) was the second approved ADC for patients who had received at least 2 lines of anti-HER2-based therapy in the metastatic setting. The success of these two agents has transformed the treatment of HER2-positive breast cancer and has re-energized the field of ADC development. Given their advanced pharmaceutical properties, next-generation HER2-targeted ADCs have the potential to be active beyond traditional HER2-positive breast cancer and may be effective in cells with low expression of HER2 or ERBB2 mutations, opening a spectrum of new possible clinical applications. Ongoing challenges include improving target-specificity, optimizing the toxicity profile, and identifying biomarkers for patient selection. The aim of this review is to summarize the principal molecular, clinical, and safety characteristics of approved and experimental anti-HER2 ADCs, contextualizing the current and future landscape of drug development.

Quantitation of Conjugation-related Residual Solvents in Antibody Drug Conjugates using Headspace Gas Chromatography

Background:

Antibody Drug Conjugates (ADCs) are complex hybrid molecules comprised of a monoclonal antibody (mAb) connected to a small molecule drug through a linker. The key step in the production of ADCs is bringing together the protein in an aqueous buffer with a hydrophobic small molecule in order to achieve conjugation of the molecules. This step involves dissolving the small molecule portion of the compound in an aqueous miscible organic solvent. These solvents and unconjugated small molecules are ideally cleared by downstream processing in order to achieve the desired product quality. As part of the control system to ensure product quality, the determination of residual solvents in pharmaceuticals is of significant importance in order to protect patient safety and ensure an efficacious drug.

Objective:

Headspace gas chromatography (HS-GC) is the most widely used tool for quantification of residual solvents for small molecule active pharmaceutical ingredients (APIs) but is not widely used for the analysis of protein-containing samples. In this study, the detection of residual solvents in headspace injections was explored using various conditions in order to detect commonly used conjugation solvents including N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), Ethylene Glycol (EG), and Propylene Glycol (PG) in an ADC drug product sample.

Methods:

Various organic solvents were explored to enhance the response observed with complex protein and residual solvent matrixes. As EG and PG do not partition into the headspace efficiently in the ADC drug product samples that contain large amounts of water, ionic liquids and other ionic compounds were screened with the ADC samples to see if they could improve the partitioning of the key solvents EG and PG.

Results:

Following headspace and chromatographic optimization, we have developed an approach for the detection and quantification of several conjugation reaction solvents in ADC samples.

Conclusion:

This new approach is an HS-GC method that simplifies Gas Chromatography (GC) analysis and sample preparation and can be readily implemented in quality control testing for bioconjugated products.

Therapeutic roles of antibody drug conjugates (ADCs) in relapsed/refractory lymphomas

Relapsed or refractory lymphoma is commonly treated with combination chemoimmunotherapy and cellular immunotherapy. Modest response rates and associated toxicities are obstacles to achieving durable remission using traditional cytotoxic chemotherapy, especially in frail patients with advanced disease. Antibody drug conjugates represent a new class of novel targeted agents with significant improvement in therapeutic efficacy in the treatment of lymphomas. Several of these agents, which offer improved targeting, greater potency, and better therapeutic index over traditional chemotherapy, are changing the treatment landscape for lymphomas and other hematological malignancies. Despite the therapeutic potential of these agents, the delivery and release of cytotoxic agents to malignant cells through the combination of a monoclonal antibody, payload, and linker represents a complex design challenge. This article reviews the clinical data on currently available antibody drug conjugates and the ongoing development of novel antibody drug conjugates. Antibody drug conjugates constitute an important armamentarium for treatment of lymphomas and their evolving roles in the treatment spectrum are discussed.

Polyethylene glycol-based linkers as hydrophilicity reservoir for antibody-drug conjugates

Antibody-drug conjugates (ADCs) are an established therapeutic entity in which potent cytotoxic drugs are conjugated to a monoclonal antibody. In parallel with the great emphasis put on novel site-specific bioconjugation technologies, future advancements in this field also rely on exploring novel linker-drug architectures that improve the efficacy and stability of ADCs. In this context, the use of hydrophilic linkers represents a valid strategy to mask or reduce the inherent hydrophobicity of the most used cytotoxic drugs and positively impact the physical stability and in vivo performance of ADCs. Here, we describe the use of linkers containing monodisperse poly(ethylene glycol) (PEG) moieties for the construction of highly-loaded lysine-conjugated ADCs. The studied ADCs differ in the positioning of PEG (linear or pendant), the bonding type with the antibody (amide or carbamate), and the drug-to-antibody ratio (DAR). These ADCs were first evaluated for their stability in solution under thermal stress, showing that both the drug-linker-polymer design and the nature of the antibody-linker bonding are of great importance for their physical and chemical stability. Amide-coupled ADCs bearing two pendant 12-unit poly(ethylene glycol) chains within the drug-linker structure were the best performing conjugates, distancing themselves from the ADCs obtained with a conventional linear 24-unit PEG oligomer or the linker of Kadcyla®. The pharmacokinetic profiles of amide-linked ADCs, with a linear or pendant configuration of the PEG, were tested in mice in comparison to Kadcyla®. Total antibody pharmacokinetics paralleled the trends in aggregation tendency, with slower clearance rates for the ADCs based on the pendant drug-linker format. The above-mentioned findings have provided important clues on the drug-linker design and revealed that the positioning and configuration of a PEG unit have to be carefully tuned to achieve ADCs with improved stability and pharmacokinetics.

Importance and Considerations of Antibody Engineering in Antibody-Drug Conjugates Development from a Clinical Pharmacologist's Perspective

Antibody-drug conjugates (ADCs) appear to be in a developmental boom, with five FDA approvals in the last two years and a projected market value of over $4 billion by 2024. Major advancements in the engineering of these novel cytotoxic drug carriers have provided a few early success stories. Although the use of these immunoconjugate agents are still in their infancy, valuable lessons in the engineering of these agents have been learned from both preclinical and clinical failures. It is essential to appreciate how the various mechanisms used to engineer changes in ADCs can alter the complex pharmacology of these agents and allow the ADCs to navigate the modern-day therapeutic challenges within oncology. This review provides a global overview of ADC characteristics which can be engineered to alter the interaction with the immune system, pharmacokinetic and pharmacodynamic profiles, and therapeutic index of ADCs. In addition, this review will highlight some of the engineering approaches being explored in the creation of the next generation of ADCs.

Targeted Mass Spectrometry-Based Approach for the Determination of Intrinsic Internalization Kinetics of Cell-Surface Membrane Protein Targets

Successful development of targeted therapeutics aimed at the elimination of diseased cells relies on the target properties and the therapeutics that target them. Currently, target properties have been evaluated through antibody-dependent semiquantitative approaches such as flow cytometry, Western blotting, or microscopy. Since antibodies can alter target properties following binding, antibody-dependent approaches provide at best skewed measurements for target intrinsic properties. To circumvent, here we attempted to develop an antibody-free targeted mass spectrometry-based (ATM) strategy to measure the surface densities and the intrinsic rates (K_int) of CD38 internalization in multiple myeloma cell lines. Using cell-surface biotinylation in conjunction with differential mass tagging to separate inward CD38 molecules from the outbound and nascent ones, the ATM approach revealed diversities in measured CD38 K_int values of 0.239 min^-1 S.E. ± 0.076, 0.109 min^-1 S.E. ± 0.032, and 0.058 min^-1 S.E. ± 0.001 for LP1, NCIH929, and MOLP8 cell lines, respectively. Together with CD38 surface densities, intrinsic K_int values aligned well with the tumor penetration model and supported the outcomes for tumor regression in mouse xenografts upon drug treatment. Additionally, the ATM approach can evaluate molecules with fast K_int as we determined for CTLA4 protein. We believe that the ATM approach has the potential to evaluate diverse cell-surface targets as part of the pharmacological assessment in drug discovery.

Targeting tumor lineage plasticity in hepatocellular carcinoma using an anti-CLDN6 antibody-drug conjugate

Tumor lineage plasticity is emerging as a critical mechanism of therapeutic resistance and tumor relapse. Highly plastic tumor cells can undergo phenotypic switching to a drug-tolerant state to avoid drug toxicity. Here, we investigate the transmembrane tight junction protein Claudin6 (CLDN6) as a therapeutic target related to lineage plasticity for hepatocellular carcinoma (HCC). CLDN6 was highly expressed in embryonic stem cells but markedly decreased in normal tissues. Reactivation of CLDN6 was frequently observed in HCC tumor tissues as well as in premalignant lesions. Functional assays indicated that CLDN6 is not only a tumor-associated antigen but also conferred strong oncogenic effects in HCC. Overexpression of CLDN6 induced phenotypic shift of HCC cells from hepatic lineage to biliary lineage, which was more refractory to sorafenib treatment. The enhanced tumor lineage plasticity and cellular identity change were potentially induced by the CLDN6/TJP2 (tight junction protein 2)/YAP1 (Yes-associated protein 1) interacting axis and further activation of the Hippo signaling pathway. A de novo anti-CLDN6 monoclonal antibody conjugated with cytotoxic agent (Mertansine) DM1 (CLDN6-DM1) was developed. Preclinical data on both HCC cell lines and primary tumors showed the potent antitumor efficiency of CLDN6-DM1 as a single agent or in combination with sorafenib in HCC treatment.

Unlocking the potential of antibody-drug conjugates for cancer therapy

Nine different antibody-drug conjugates (ADCs) are currently approved as cancer treatments, with dozens more in preclinical and clinical development. The primary goal of ADCs is to improve the therapeutic index of antineoplastic agents by restricting their systemic delivery to cells that express the target antigen of interest. Advances in synthetic biochemistry have ushered in a new generation of ADCs, which promise to improve upon the tissue specificity and cytotoxicity of their predecessors. Many of these drugs have impressive activity against treatment-refractory cancers, although hurdles impeding their broader use remain, including systemic toxicity, inadequate biomarkers for patient selection, acquired resistance and unknown benefit in combination with other cancer therapies. Emerging evidence indicates that the efficacy of a given ADC depends on the intricacies of how the antibody, linker and payload components interact with the tumour and its microenvironment, all of which have important clinical implications. In this Review, we discuss the current state of knowledge regarding the design, mechanism of action and clinical efficacy of ADCs as well as the apparent limitations of this treatment class. We then propose a path forward by highlighting several hypotheses and novel strategies to maximize the potential benefit that ADCs can provide to patients with cancer.

Highway to Success—Developing Advanced Polymer Therapeutics

Polymer therapeutics are advancing as an important class of drugs. Polymers have already demonstrated their value in extending the half‐life of proteins. They show great potential as delivery systems for improving the therapeutic index of drugs, via biophysical targeting and more recently with more precision targeting. They are also important for intracellular delivery of nucleic acid based drugs. The same frameworks that have been successfully applied to improve the small molecule drug development can be adopted. This approach together with improved pathophysiological disease knowledge and critical developability considerations, imperative given the size and complexity of polymer therapeutics, provides a structured framework that should improve their clinical translation and exploit their functionality and potential. Progress in understanding the right target, gaining the right tissue and cell exposure, ensuring the right safety, selecting the right patient population is discussed. The right commercial considerations are outlined and the need for a multi‐disciplinary approach is emphasized. Crucial developability factors together with scientific and technical advancements to enable pharmaceutical development of a quality robust product are addressed. It is argued that by applying this structured approach to their design and development, polymer therapeutics will continue to grow and develop as important next generation medicines.

Synthesis and Comparative In Vivo Evaluation of Site-Specifically Labeled Radioimmunoconjugates for DLL3-Targeted ImmunoPET

Delta-like ligand 3 (DLL3) is a therapeutic target for the treatment of small cell lung cancer, neuroendocrine prostate cancer, and isocitrate dehydrogenase mutant glioma. In the clinic, DLL3-targeted ⁸⁹Zr-immunoPET has the potential to aid in the assessment of disease burden and facilitate the selection of patients suitable for therapies that target the antigen. The overwhelming majority of ⁸⁹Zr-labeled radioimmunoconjugates are synthesized via the random conjugation of desferrioxamine (DFO) to lysine residues within the immunoglobulin. While this approach is admittedly facile, it can produce heterogeneous constructs with suboptimal in vitro and in vivo behavior. In an effort to circumvent these issues, we report the development and preclinical evaluation of site-specifically labeled radioimmunoconjugates for DLL3-targeted immunoPET. To this end, we modified a cysteine-engineered variant of the DLL3-targeting antibody SC16-MB1 with two thiol-reactive variants of DFO: one bearing a maleimide moiety (Mal-DFO) and the other containing a phenyloxadiazolyl methyl sulfone group (PODS-DFO). In an effort to obtain immunoconjugates with a DFO-to-antibody ratio (DAR) of 2, we explored both the reduction of the antibody with tris(2-carboxyethyl) phosphine (TCEP) as well as the use of a combination of glutathione and arginine as reducing and stabilizing agents, respectively. While exerting control over the DAR of the immunoconjugate proved cumbersome using TCEP, the use of glutathione and arginine enabled the selective reduction of the engineered cysteines and thus the formation of homogeneous immunoconjugates. A head-to-head comparison of the resulting ⁸⁹Zr-radioimmunoconjugates in mice bearing DLL3-expressing H82 xenografts revealed no significant differences in tumoral uptake and showed comparable radioactivity concentrations in most healthy nontarget organs. However, ⁸⁹Zr-DFO_PODS-^DAR2SC16-MB1 produced 30% lower uptake (3.3 ± 0.5 %ID/g) in the kidneys compared to ⁸⁹Zr-DFO_Mal-^DAR2SC16-MB1 (4.7 ± 0.5 %ID/g). In addition, H82-bearing mice injected with a ⁸⁹Zr-labeled isotype-control radioimmunoconjugate synthesized using PODS exhibited ∼40% lower radioactivity in the kidneys compared to mice administered its maleimide-based counterpart. Taken together, these results demonstrate the improved in vivo performance of the PODS-based radioimmunoconjugate and suggest that a stable, well-defined DAR2 radiopharmaceutical may be suitable for the clinical immunoPET of DLL3-expressing cancers.

Immunotherapy with Immunocytokines and PD-1 Blockade Enhances the Anticancer Activity of Small Molecule-Drug Conjugates Targeting Carbonic Anhydrase IX

Small molecule-drug conjugates (SMDCs) represent an alternative to conventional antitumor chemotherapeutic agents, with the potential to improve the therapeutic window of cytotoxic payloads through active delivery at the site of the disease. In this article, we describe novel combination therapies consisting of anti-carbonic anhydrase IX SMDCs combined with different immunomodulatory products. The therapeutic effect of the SMDCs was potentiated by combination with PD-1 blockade and with tumor-homing antibody-cytokine fusions in mouse models of renal cell carcinoma and colorectal cancer. The combination with L19-IL12, a fusion protein specific to the alternatively spliced EDB domain of fibronectin containing the murine IL12 moiety, was also active against large established tumors. Analysis of the microscopic structures of healthy organs performed 3 months after tumor eradication confirmed absence of pathologic abnormalities in the healthy kidney, liver, lung, stomach, and intestine. Our findings may be of clinical significance as they provide motivation for the development of combinations based on SMDCs and immunotherapy for the treatment of renal cell carcinoma and hypoxic tumors.

Antibody-drug conjugates: an evolving approach for melanoma treatment

Melanoma continues to be an aggressive and deadly form of skin cancer while therapeutic options are continuously developing in an effort to provide long-term solutions for patients. Immunotherapeutic strategies incorporating antibody-drug conjugates (ADCs) have seen varied levels of success across tumor types and represent a promising approach for melanoma. This review will explore the successes of FDA-approved ADCs to date compared to the ongoing efforts of melanoma-targeting ADCs. The challenges and opportunities for future therapeutic development are also examined to distinguish how ADCs may better impact individuals with malignancies such as melanoma.

Synergistic therapeutic benefit by combining the antibody drug conjugate, depatux-m with temozolomide in pre-clinical models of glioblastoma with overexpression of EGFR

PURPOSE

Depatux-m is an antibody drug conjugate (ADC) that targets and inhibits growth of cancer cells overexpressing the epidermal growth factor receptor (EGFR) or the 2-7 deletion mutant (EGFRvIII) in tumor models in vitro and in vivo. Treatment of patients suffering from relapsed/refractory glioblastoma (GBM) with a combination of depatux-m and temozolomide (TMZ) tended to increase overall survival. As a first step to understand the nature of the interaction between the two drugs, we investigated whether the interaction was synergistic, additive or antagonistic.

METHODS

The efficacy of ADCs, antibodies, TMZ and radiation was tested in xenograft models of GBM, U-87MG and U-87MG EGFRvIII. Both models express EGFR. U-87MG EGFRvIII was transduced to express EGFRvIII. Changes in tumor volume, biomarkers of cell death and apoptosis after treatment were used to measure efficacy of the various treatments. Synergism of depatux-m and TMZ was verified in three-dimensional cultures of U-87MG and U-87MG EGFRvIII by the method of Chou and Talalay.

RESULTS

Combined with TMZ and radiotherapy (RT), depatux-m inhibited xenograft growth of U-87MG and U-87MG EGFRvIII more than either treatment with depatux-m or TMZ + RT. Durability of the response to depatux-m + TMZ + RT or depatux-m + TMZ was more pronounced in U-87MG EGFRvIII than in U-87MG. Efficacy of depatux-m + TMZ was synergistic in U-87MG EGFRvIII and additive in U-87MG.

CONCLUSION

Adding depatux-m enhances the efficacy of standard of care therapy in preclinical models of GBM. Durability of response to depatux-m + TMZ in vivo and synergy of the drug-drug interaction correlates with the amount of antigen expressed by the tumor cells.

Small molecule drug conjugates (SMDCs): an emerging strategy for anticancer drug design and discovery

Mechanisms of how SMDCs work. Small molecule drugs are conjugated with the targeted ligand using pH sensitive linkers which allow the drug molecule to get released at lower lysosomal pH. It helps to accumulate the chemotherapeutic agents to be localized in the tumor environment upon cleaving of the pH-labile bonds.