Linker Design Impacts Antibody-Drug Conjugate Pharmacokinetics and Efficacy via Modulating the Stability and Payload Release Efficiency

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.

Comparison of quaternary ammonium-based linkers for antibody-drug conjugates based on camptothecin derivatives

Antibody-drug conjugates (ADCs) with camptothecin derivatives as payloads have been a hot topic of interest and research since the launch of DS-8201a. As an important component of ADCs, the adequate stability of the linker during circulation and its rapid release at the target site are crucial for the efficient efficacy of ADCs. Although traditional quaternary ammonium ADCs based on dipeptide linkers were highly stable and could be released by specific enzymes, their poor in vitro anti-tumor activity had limited their further exploration. We applied a methylsulfonylethylamine-modified MAC self-elimination system to a valine-alanine linker and constructed a quaternary ammonium ADC (HER2-11) that combines both stability and cleavability. The optimization of the linker effectively improved the in vitro cellular activity of conventional quaternary ammonium ADCs, but the complex intracellular cleavage mechanism of HER2-11 resulted in a weaker anti-tumor activity compared to HER2-GGFG-DXd, which provides great reference value for the continued research of this type of linker in the future.

Advances and challenges in immunosuppressive antibody drug conjugates

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

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.

Unlocking the Complexity of Antibody-Drug Conjugates: A Cutting-Edge LC-HRMS Approach to Refine Drug-to-Antibody Ratio Measurements with Highly Reactive Payloads

The complexity of therapeutic proteins like antibody-drug conjugates (ADCs) holds a tremendous analytical challenge. Complementary mass spectrometry approaches such as peptide mapping and intact mass analysis are required for the in-depth characterization of these bioconjugates. Cysteine-linked ADCs have shown a unique challenge for characterization, mainly when the conjugation is carried out on interchain cysteines, because their intact analysis requires native mass spectrometry conditions to preserve non-covalent binding between antibody chains. In this work, two different approaches were proposed. Specifically, a full scan data-independent all ion fragmentation (FS-AIF) and a full scan data-dependent targeted MS2 (FS-ddtMS2) were applied to generate complementary datasets for a cysteine-linked ADC characterization with a highly reactive payload. These two methods were applied to in vitro plasma stability and in vivo PK samples to calculate and refine mean drug-to-antibody ratio over time. Using this approach, we successfully characterized an ADC containing a hydrolysis-sensitive payload and refined the "active" drug-to-antibody ratio on in vitro stability and in vivo samples. These two methods allowed the confirmation of the different ADC species and potential metabolites of conjugated payload attached to the antibody backbone in a single analysis without needing a dedicated method for the conjugated payload metabolite identification.

Engineered IgG Fc-conjugation prolongs the half-life of florfenicol and alleviates pneumonia in mice

Small molecule drugs often exhibit short half-lives, requiring frequent administrations to maintain therapeutic concentrations over an extended period. To address this issue, the fragment crystallizable (Fc) region of IgG, known to prolong the half-life of antibodies via its interaction with the Fc neonatal receptor, was harnessed as a carrier protein to extend the half-life of a small molecule drug, florfenicol. Florfenicol, was chemically coupled to a recombinant Fc protein expressed using the eukaryotic expression system in HEK293 cells. The Fc-florfenicol conjugate exhibited a substantially prolonged half-life of from 3.8 to 9.1 h compared to unconjugated florfenicol and demonstrated excellent therapeutic properties in treating pneumonia in a mouse model. Our results, combined with the literature analysis on Fc-small molecule conjugates, show that Fc can substantially enhance the drug's half-life and suggest the potential for its use as a carrier in novel delivery systems.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

Datopotamab Deruxtecan Versus Chemotherapy in Previously Treated Inoperable/Metastatic Hormone Receptor-Positive Human Epidermal Growth Factor Receptor 2-Negative Breast Cancer: Primary Results From TROPION-Breast01

PURPOSE

The global, phase 3, open-label, randomized TROPION-Breast01 study assessed the trophoblast cell surface antigen 2-directed antibody-drug conjugate datopotamab deruxtecan (Dato-DXd) versus investigator's choice of chemotherapy (ICC) in hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer.

METHODS

Adult patients with inoperable/metastatic HR+/HER2‒ breast cancer, who had disease progression on endocrine therapy, for whom endocrine therapy was unsuitable, and had received one to two previous lines of chemotherapy in the inoperable/metastatic setting, were randomly assigned 1:1 to Dato-DXd (6 mg/kg once every 3 weeks) or ICC (eribulin/vinorelbine/capecitabine/gemcitabine). Dual primary end points were progression-free survival (PFS) by blinded independent central review (BICR) and overall survival (OS).

RESULTS

Patients were randomly assigned to Dato-DXd (n = 365) or ICC (n = 367). Dato-DXd significantly reduced the risk of progression or death versus ICC (PFS by BICR hazard ratio [HR], 0.63 [95% CI, 0.52 to 0.76]; P < .0001). Consistent PFS benefit was observed across subgroups. Although OS data were not mature, a trend favoring Dato-DXd was observed (HR, 0.84 [95% CI, 0.62 to 1.14]). The rate of grade ≥3 treatment-related adverse events (TRAEs) with Dato-DXd was lower than ICC (20.8% v 44.7%). The most common TRAEs (any grade; grade ≥3) were nausea (51.1%; 1.4%) and stomatitis (50%; 6.4%) with Dato-DXd and neutropenia (grouped term, 42.5%; 30.8%) with ICC.

CONCLUSION

Patients receiving Dato-DXd had statistically significant and clinically meaningful improvement in PFS and a favorable and manageable safety profile, compared with ICC. Results support Dato-DXd as a novel treatment option for patients with inoperable/metastatic HR+/HER2‒ breast cancer who have received one to two previous lines of chemotherapy in this setting.

Detailed Structural Elucidation of Antibody-Drug Conjugate Biotransformation Species Using High Resolution Multiple Reaction Monitoring Mass Spectrometry with Orthogonal Dissociation Methods

Antibody-drug conjugates (ADCs) are a promising drug modality substantially expanding in both the discovery space and clinical development. Assessing the biotransformation of ADCs in vitro and in vivo is important in understanding their stability and pharmacokinetic properties. We previously reported biotransformation pathways for the anti-B7H4 topoisomerase I inhibitor ADC, AZD8205, puxitatug samrotecan, that underpin its structural stability in vivo using an intact protein liquid chromatography-high resolution mass spectrometry (LC-HRMS) approach. Herein, we employed a LC-high resolution multiple reaction monitoring (LC-MRMHR) approach using both collision-induced dissociation (CID) and electron-activated dissociation (EAD) methods, confirming our earlier findings. Furthermore, we were able to obtain additional detailed structural information on the biotransformation products expanding on earlier intact analyses. We also highlight the high sensitivity of LC-MRMHR for successfully identifying minor biotransformation products at low concentrations that were not detectable using the intact protein LC-HRMS workflow. Especially, EAD aided in the confirmation of biotransformation species that contain newly formed disulfide bonds due to the preferential dissociation of disulfide bonds using this method. We observed biotransformation reactions that vary between linker-payload (PL) conjugation sites on the antibody. For example, the trend toward constitutional isomerism in thio-succinimide linker hydrolysis, and the resulting positional isomers from thiol adduct formation following linker-PL deconjugation. The reported orthogonal analytical approaches highly complement and fortify the intact protein LC-HRMS data. This study sheds further light on detailed structural characterization of various ADC species and validates the proposed biotransformation pathways explaining the stability of AZD8205 in vivo.

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.

Antibody-Vincristine Conjugates as Potent Anticancer Therapeutic Agents

Antibody-drug conjugates (ADCs) are a well-established class of therapeutics primarily used in oncology to selectively deliver highly cytotoxic agents into cancer cells. While ADCs should theoretically spare healthy tissues and diminish side effects in patients, off-target toxicity is still observed, all the more serious, as the drugs are extremely potent. In the quest toward safer payloads, we used the conventional chemotherapeutic drug vincristine to develop antibody-vincristine conjugates. Vincristine was N-alkylated with a cleavable linker and the resulting linker-payload conjugated to free cysteines of antibodies. We show that trastuzumab-vincristine conjugates display subnanomolar potency in vitro on HER2-positive cells, 2 orders of magnitude lower than free vincristine and comparable with marketed ADC. In vivo, trastuzumab-vincristine conjugates led to remarkable efficacy when compared to two standards of care, with complete tumor regression just 9 days after single administration. This highlights the untapped potential of the chemotherapeutic arsenal toward the development of novel ADC.

Targeting Refractory Triple-Negative Breast Cancer with Sacituzumab Govitecan: A New Era in Precision Medicine

Advanced triple-negative breast cancer (TNBC) has poorer outcomes due to its aggressive behavior and restricted therapeutic options. While therapies like checkpoint inhibitors and PARP inhibitors offer some benefits, chemotherapy remains ineffective beyond the first line of treatment. Antibody-drug conjugates (ADCs) like sacituzumab govitecan-hziy (SG) represent a significant advancement. SG combines SN-38, an irinotecan derivative, with a Trop-2-targeting antibody via a pH-sensitive linking moiety, achieving a good drug:antibody ratio. In a phase I-II study involving metastatic TNBC (mTNBC) individuals, SG achieved an overall response rate of 33.3% and a median response period of 7.7 months. The phase III ASCENT trial demonstrated SG's efficacy in relapsed or refractory TNBC, improving median progression-free survival and median overall survival compared to chemotherapy. Common side effects include neutropenia, nausea, and fatigue. This article highlights the clinical potential, pharmacokinetics, safety profile, and resistance mechanisms of SG along with key ongoing clinical trials, emphasizing its role in managing refractory mTNBC, especially in third-line therapy. The review also discusses current strategies for managing adverse reactions and sequencing ADC treatments in clinical practice, along with the predicted basis of resistance. The optimal sequencing of SG relative to other ADCs, such as trastuzumab deruxtecan or T-DXd, remains an evolving question, especially as newer agents with distinct mechanisms of action and safety profiles enter the field. Further research is essential to establish evidence-based strategies for sequencing SG and addressing disease progression post-ADC therapy.

QSP modeling of a transiently inactivating antibody-drug conjugate highlights benefit of short antibody half life

Antibody drug conjugates (ADC) are a promising class of oncology therapeutics consisting of an antibody conjugated to a payload via a linker. DYP688 is a novel ADC comprising of a signaling protein inhibitor payload (FR900359) that undergoes unique on-antibody inactivation in plasma, resulting in complex pharmacology. To assess the impact of FR inactivation on DYP688 pharmacology and clinical developability, we performed translational modeling of preclinical PK and tumor growth inhibition (TGI) data, accompanied by mechanistic Krogh cylinder tumor modeling. Using a PK-TGI model, we identified a composite exposure-above-tumorostatic concentration (AUCTSC) metric as the PK-driver of efficacy. To underpin the mechanisms behind AUCTSC as the driver of efficacy, we performed quantitative systems pharmacology (QSP) modeling of DYP688 intratumoral pharmacokinetics and pharmacodynamics. Through exploratory simulations, we show that by deviating from canonical ADC design dogma, DYP688 has optimal FR900359 activity despite its transient inactivation. Finally, we performed the successful preclinical to clinical translation of DYP688 PK, including the payload inactivation kinetics, evidenced by good agreement of the predicted PK to the observed interim clinical PK. Overall, this work highlights early quantitative pharmacokinetics as a missing link in the ADC design-developability chasm.

The Efficacy and Safety of Folate Receptor α-Targeted Antibody-Drug Conjugate Therapy in Patients With High-Grade Epithelial Ovarian, Primary Peritoneal, or Fallopian Tube Cancers: A Systematic Review and Meta-Analysis

BACKGROUND

Antibody-drug conjugates (ADC) have emerged as a highly promising systemic option in the treatment of recurrent ovarian cancer. The present study aimed to evaluate the treatment efficacy of folate receptor α (FRα)-targeting ADCs, associated treatment-related adverse events (TRAEs), and their impact on treatment safety.

METHODS

We conducted an electronic search to identify prospective trials of single-agent ADCs targeting FRα and those combined with chemotherapy in recurrent ovarian cancer. Information regarding the objective response rate (ORR) and TRAEs was collectively analyzed, and differences in subgroups based on FRα receptor expression levels were investigated. The protocol was registered with PROSPERO (CRD42023491151).

RESULTS

Ten studies with a total of 940 patients (859 treated with Mirvetuximab soravtansine-gynx (MIRV)), 45 with Farletuzumab Ecteribulin (MORAb-202), and 36 with Luveltamab Tazevibulin (STRO-002) were included in this meta-analysis. Based on the pooled data, the ORR of the entire cohort was 37% (95% CI: 0.30-0.43), while that of the high-FRα expression group was 34% (95% CI: 0.26-0.42). The incidence of grade ≥ 3 adverse events was 27% (95% CI: 0.19-0.36).

CONCLUSION

FRα-targeting ADCs, including MIRV, demonstrated definite efficacy and good safety as novel choices for second-line and beyond treatment of advanced or recurrent ovarian cancer. Patients with high FRα expression showed ORR and PFS benefits similar to those in the overall cohort.

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.

Generation of binder-format-payload conjugate-matrices by antibody chain-exchange

The generation of antibody-drug conjugates with optimal functionality depends on many parameters. These include binder epitope, antibody format, linker composition, conjugation site(s), drug-to-antibody ratio, and conjugation method. The production of matrices that cover all possible parameters is a major challenge in identifying optimal antibody-drug conjugates. To address this bottleneck, we adapted our Format Chain Exchange technology (FORCE), originally established for bispecific antibodies, toward the generation of binder-format-payload matrices (pair-FORCE). Antibody derivatives with exchange-enabled Fc-heterodimers are combined with payload-conjugated Fc donors, and subsequent chain-exchange transfers payloads to antibody derivatives in different formats. The resulting binder-format-conjugate matrices can be generated with cytotoxic payloads, dyes, haptens, and large molecules, resulting in versatile tools for ADC screening campaigns. We show the relevance of pair-FORCE for identifying optimal HER2-targeting antibody-drug conjugates. Analysis of this matrix reveals that the notion of format-defines-function applies not only to bispecific antibodies, but also to antibody-drug conjugates.

Extensive Biotransformation Profiling of AZD8205, an Anti-B7-H4 Antibody-Drug Conjugate, Elucidates Pathways Underlying Its Stability In Vivo

What happens to macromolecules in vivo? What drives the structure-activity relationship and in vivo stability for antibody-drug conjugates (ADCs)? These interrelated questions are increasingly relevant due to the re-emerging importance of ADCs as an impactful therapeutic modality and the gaps that exist in our understanding of ADC structural determinants that underlie ADC in vivo stability. Complex macromolecules, such as ADCs, may undergo changes in vivo due to their intricate structure as biotransformations may occur on the linker, the payload, and/or at the modified conjugation site. Furthermore, the dissection of ADC metabolism presents a substantial analytical challenge due to the difficulty in the identification or quantification of minor changes on a large macromolecule. We employed immunocapture-LCMS methods to evaluate in vivo changes in the drug-antibody ratio (DAR) profile in four different lead ADCs. This comprehensive characterization revealed that a critical structural determinant contributing to the ADC design was the linker, and competition of the thio-succinimide hydrolysis reaction over retro-Michael deconjugation can result in superb conjugation stability in vivo. These data, in conjunction with additional factors, informed the selection of AZD8205, puxitatug samrotecan, a B7-H4-directed cysteine-conjugated ADC bearing a novel topoisomerase I inhibitor payload, with durable DAR, currently being studied in the clinic for the potential treatment of solid malignancies (NCT05123482). These results highlight the relevance of studying macromolecule biotransformation and elucidating the ADC structure-in vivo stability relationship. The comprehensive nature of this work increases our confidence in the understanding of these processes. We hope this analytical approach can inform future development of bioconjugate drug candidates.

Monoclonal antibodies: From magic bullet to precision weapon

Monoclonal antibodies (mAbs) are used to prevent, detect, and treat a broad spectrum of non-communicable and communicable diseases. Over the past few years, the market for mAbs has grown exponentially with an expected compound annual growth rate (CAGR) of 11.07% from 2024 (237.64 billion USD estimated at the end of 2023) to 2033 (679.03 billion USD expected by the end of 2033). Ever since the advent of hybridoma technology introduced in 1975, antibody-based therapeutics were realized using murine antibodies which further progressed into humanized and fully human antibodies, reducing the risk of immunogenicity. Some benefits of using mAbs over conventional drugs include a drastic reduction in the chances of adverse reactions, interactions between drugs, and targeting specific proteins. While antibodies are very efficient, their higher production costs impede the process of commercialization. However, their cost factor has been improved by developing biosimilar antibodies as affordable versions of therapeutic antibodies. Along with the recent advancements and innovations in antibody engineering have helped and will furtherly help to design bio-better antibodies with improved efficacy than the conventional ones. These novel mAb-based therapeutics are set to revolutionize existing drug therapies targeting a wide spectrum of diseases, thereby meeting several unmet medical needs. This review provides comprehensive insights into the current fundamental landscape of mAbs development and applications and the key factors influencing the future projections, advancement, and incorporation of such promising immunotherapeutic candidates as a confrontation approach against a wide list of diseases, with a rationalistic mentioning of any limitations facing this field.

Linker and Conjugation Site Synergy in Antibody-Drug Conjugates: Impacts on Biological Activity

Antibody-drug conjugates (ADCs) produced using general conjugation methods yield heterogeneous products containing mixtures of species with different numbers of payloads per antibody (drug-antibody ratios) conjugated at multiple sites. This heterogeneity affects the stability, efficacy, and safety of ADCs. Thus, various site-specific conjugation methods have been developed to achieve homogeneity in ADCs. It was reported that linker structures and conjugation sites generally affected the characteristics of site-specific ADCs such as stability, efficacy, and safety. However, the combined effects of conjugation sites and linker structures on the physicochemical and biological characteristics of site-specific ADCs have remained unclear. In this study, we generated 30 homogeneous site-specific ADCs with a combination of six conjugation sites and five linker structures using THIOMAB technology and evaluated the characteristics of these homogeneous ADCs. We found that both conjugation sites and linker structures affected characteristics unique to ADCs (linker stability as well as target-dependent and target-independent cytotoxicity) in site-specific ADCs. Especially, conjugation to the constant regions of the light chain and the presence of polyethylene glycol structures in the linker are important for those ADC-specific characteristics. Interestingly, we also found that the effects of linker structures on the target-independent cytotoxicity of homogeneous ADCs at certain conjugation sites differed from those seen in conventional heterogeneous ADCs. Our results suggest that optimizing linker structures based on the conjugation site may be necessary for site-specific ADCs.

Anti-Claudin-2 Antibody-Drug Conjugates for the Treatment of Colorectal Cancer Liver Metastasis

We have previously demonstrated that Claudin-2 is required for colorectal cancer (CRC) liver metastasis. The expression of Claudin-2 in primary CRC is associated with poor survival and highly expressed in liver metastases. Claudin-2 also promotes breast cancer liver metastasis by enabling seeding and cancer cell survival. These observations support Claudin-2 as a potential therapeutic target for managing patients with liver metastases. Antibody-drug conjugates (ADC) are promising antitumor therapeutics, which combine the specific targeting ability of monoclonal antibodies with the potent cell killing activity of cytotoxic drugs. Herein, we report the generation of 28 anti-Claudin-2 antibodies for which the binding specificities, cross-reactivity with claudin family members, and cross-species reactivity were assessed by flow cytometry analysis. Multiple drug conjugates were tested, and PNU was selected for conjugation with anti-Claudin-2 antibodies binding either extracellular loop 1 or 2. Anti-Claudin-2 ADCs were efficiently internalized and were effective at killing Claudin-2-expressing CRC cancer cells in vitro. Importantly, PNU-conjugated-anti-Claudin-2 ADCs impaired the development of replacement-type CRC liver metastases in vivo, using established CRC cell lines and patient-derived xenograft (PDX) models of CRC liver metastases. Results suggest that the development of ADCs targeting Claudin-2 is a promising therapeutic strategy for managing patients with CRC liver-metastatic disease who present replacement-type liver metastases.

FZ-AD005, a Novel DLL3-Targeted Antibody-Drug Conjugate with Topoisomerase I Inhibitor, Shows Potent Antitumor Activity in Preclinical Models

Delta-like ligand 3 (DLL3) is overexpressed in small cell lung cancer (SCLC) and has been considered an attractive target for SCLC therapy. Rovalpituzumab tesirine was the first DLL3-targeted antibody-drug conjugate (ADC) to enter clinical studies. However, serious adverse events limited progress in the treatment of SCLC with rovalpituzumab tesirine. In this study, we developed a novel DLL3-targeted ADC, FZ-AD005, by using DXd with potent cytotoxicity and a relatively better safety profile to maximize the therapeutic index. FZ-AD005 was generated by a novel anti-DLL3 antibody, FZ-A038, and a valine-alanine (Val-Ala) dipeptide linker to conjugate DXd. Moreover, Fc-silencing technology was introduced in FZ-AD005 to avoid off-target toxicity mediated by FcγRs and showed negligible Fc-mediated effector functions in vitro. In preclinical evaluation, FZ-AD005 exhibited DLL3-specific binding and demonstrated efficient internalization, bystander killing, and excellent in vivo antitumor activities in cell line-derived xenograft and patient-derived xenograft models. FZ-AD005 was stable in circulation with acceptable pharmacokinetic profiles in cynomolgus monkeys. FZ-AD005 was well tolerated in rats and monkeys. The safety profile of FZ-AD005 was favorable, and the highest nonseverely toxic dose was 30 mg/kg in cynomolgus monkeys. In conclusion, FZ-AD005 has the potential to be a superior DLL3-targeted ADC with a wide therapeutic window and is expected to provide clinical benefits for the treatment of patients with SCLC.

Structure-Activity Relationship of Antibody-Oligonucleotide Conjugates: Evaluating Bioconjugation Strategies for Antibody-Phosphorodiamidate Morpholino Oligomer Conjugates for Drug Development

Antibody-oligonucleotide conjugates (AOCs) are promising treatments for Duchenne muscular dystrophy (DMD). They work via induction of exon skipping and restoration of dystrophin protein in skeletal and heart muscles. The structure-activity relationships (SARs) of AOCs comprising antibody-phosphorodiamidate morpholino oligomers (PMOs) depend on several aspects of their component parts. We evaluate the SAR of antimouse transferrin receptor 1 antibody (αmTfR1)-PMO conjugates: cleavable and noncleavable linkers, linker location on the PMO, and the impact of drug-to-antibody ratios (DARs) on plasma pharmacokinetics (PK), oligonucleotide delivery to tissues, and exon skipping. AOCs containing a stable linker with a DAR9.7 were the most effective PMO delivery vehicles in preclinical studies. We demonstrate that αmTfR1-PMO conjugates induce dystrophin protein restoration in the skeletal and heart muscles of mdx mice. Our results show that αmTfR1-PMO conjugates are a potentially effective approach for the treatment of DMD.

Structure-Activity Relationship of Antibody-Oligonucleotide Conjugates: Evaluating Bioconjugation Strategies for Antibody-siRNA Conjugates for Drug Development

Antibody-oligonucleotide conjugates are a promising class of therapeutics for extrahepatic delivery of small interfering ribonucleic acids (siRNAs). These conjugates can be optimized for improved delivery and mRNA knockdown (KD) through understanding of structure-activity relationships. In this study, we systematically examined factors including antibody isotype, siRNA chemistry, linkers, conjugation chemistry, PEGylation, and drug-to-antibody ratios (DARs) for their impact on bioconjugation, pharmacokinetics (PK), siRNA delivery, and bioactivity. Conjugation site (cysteine, lysine, and Asn297 glycan) and DAR proved critical for optimal conjugate PK and siRNA delivery. SiRNA chemistry including 2' sugar modifications and positioning of phosphorothioates were found to be critical for delivery and duration of action. By utilizing cleavable and noncleavable linkers, we demonstrated the impact of linkers on PK and mRNA KD. To achieve optimal properties of antibody-siRNA conjugates, a careful selection of siRNA chemistry, DAR, conjugation sites, linkers, and antibody isotype is necessary.

Synthesis and evaluation of antibody-drug conjugates with high drug-to-antibody ratio using dimaleimide-DM1 as a linker- payload

The notable characteristics of recently emerged Antibody-Drug Conjugates (ADCs) encompass the targeting of Human Epidermal growth factor Receptor 2 (HER2) through monoclonal antibodies (mAbs) and a high ratio of drug to antibody (DAR). The achievements of Kadcyla® (T-DM1) and Enhertu® (T-Dxd) have demonstrated that HER2-targeting antibodies, such as trastuzumab, have shown to be competitive in terms of efficacy and price for development. Furthermore, with the arrival of T-Dxd and Trodelvy®, high-DAR (7-8) ADCs, which differ from the moderate DAR (3-4) ADCs that were formerly regarded as conventional, are being acknowledged for their worth. Following this trend of drug development, we endeavored to develop a high-DAR ADC using a straightforward approach involving the utilization of DM1, a highly potent substance, in combination with the widely recognized trastuzumab. To achieve a high DAR, DM1 was conjugated to reduced cysteine through the simple design and synthesis of various dimaleimide linkers with differing lengths. Using LC and MS analysis, we have demonstrated that our synthesis methodology is uncomplicated and efficacious, yielding trastuzumab-based ADCs that exhibit a remarkable degree of uniformity. These ADCs have been experimentally substantiated to exert an inhibitory effect on cancer cells in vitro, thus affirming their value as noteworthy additions to the realm of ADCs.

Antibody-drug conjugates in cancer therapy: mechanisms and clinical studies

Antibody-drug conjugates (ADCs) consist of monoclonal antibodies that target tumor cells and cytotoxic drugs linked through linkers. By leveraging antibodies' targeting properties, ADCs deliver cytotoxic drugs into tumor cells via endocytosis after identifying the tumor antigen. This precise method aims to kill tumor cells selectively while minimizing harm to normal cells, offering safe and effective therapeutic benefits. Recent years have seen significant progress in antitumor treatment with ADC development, providing patients with new and potent treatment options. With over 300 ADCs explored for various tumor indications and some already approved for clinical use, challenges such as resistance due to factors like antigen expression, ADC processing, and payload have emerged. This review aims to outline the history of ADC development, their structure, mechanism of action, recent composition advancements, target selection, completed and ongoing clinical trials, resistance mechanisms, and intervention strategies. Additionally, it will delve into the potential of ADCs with novel markers, linkers, payloads, and innovative action mechanisms to enhance cancer treatment options. The evolution of ADCs has also led to the emergence of combination therapy as a new therapeutic approach to improve drug efficacy.

Use of stable isotope labeled (SIL) antibodies in cassette dosing to improve pharmacokinetics screening efficiency of ADCs with novel cytotoxic payloads

Stable isotope labelling by amino acids in cell culture (SILAC) is an established technique used in quantitative mass spectrometry (MS)-based proteomics. SILAC is also used to generate stable isotope labelled (SIL) antibodies for internal standards (IS) used in LC-MS/MS bioassays to improve quantitative robustness.Total antibody (TAb) is measured to evaluate pharmacokinetics (PK) of antibody drug conjugate (ADC) candidates measured by either ligand binding (LBA) or LC-MS/MS. Herein, we describe an application of SILAC, where multiple SIL combinations of an antibody are used for cassette dosing and PK evaluation.Our preclinical studies demonstrate SILAC-labelled ADC therapeutics did not alter antibody PK. Furthermore, with cassette dosing SIL antibodies exhibited comparable exposure to discretely administered unlabelled test articles in rats.In addition, SIL antibodies were conjugated to cytotoxic payloads to create SIL ADCs and cassette dosed in a cynomolgus monkey PK study and SIL ADCs yielded comparable PK results to discrete dosed unlabelled ADCs.In conclusion, SIL antibodies used with a cassette dosing strategy increases PK screening throughput of ADC candidates in preclinical species. Additionally, cassette dosing strategy further facilitates the responsible use of laboratory animals to achieve the three-Rs (Replacement, Reduction, and Refinement).

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.

Colorimetric sensing for translational applications: from colorants to mechanisms

Colorimetric sensing offers instant reporting via visible signals. Versus labor-intensive and instrument-dependent detection methods, colorimetric sensors present advantages including short acquisition time, high throughput screening, low cost, portability, and a user-friendly approach. These advantages have driven substantial growth in colorimetric sensors, particularly in point-of-care (POC) diagnostics. Rapid progress in nanotechnology, materials science, microfluidics technology, biomarker discovery, digital technology, and signal pattern analysis has led to a variety of colorimetric reagents and detection mechanisms, which are fundamental to advance colorimetric sensing applications. This review first summarizes the basic components (e.g., color reagents, recognition interactions, and sampling procedures) in the design of a colorimetric sensing system. It then presents the rationale design and typical examples of POC devices, e.g., lateral flow devices, microfluidic paper-based analytical devices, and wearable sensing devices. Two highlighted colorimetric formats are discussed: combinational and activatable systems based on the sensor-array and lock-and-key mechanisms, respectively. Case discussions in colorimetric assays are organized by the analyte identities. Finally, the review presents challenges and perspectives for the design and development of colorimetric detection schemes as well as applications. The goal of this review is to provide a foundational resource for developing colorimetric systems and underscoring the colorants and mechanisms that facilitate the continuing evolution of POC sensors.

Small molecule- and peptide-drug conjugates addressing integrins: A story of targeted cancer treatment

Targeted cancer treatment should avoid side effects and damage to healthy cells commonly encountered during traditional chemotherapy. By combining small molecule or peptidic ligands as homing devices with cytotoxic drugs connected by a cleavable or non-cleavable linker in peptide-drug conjugates (PDCs) or small molecule-drug conjugates (SMDCs), cancer cells and tumours can be selectively targeted. The development of highly affine, selective peptides and small molecules in recent years has allowed PDCs and SMDCs to increasingly compete with antibody-drug conjugates (ADCs). Integrins represent an excellent target for conjugates because they are overexpressed by most cancer cells and because of the broad knowledge about native binding partners as well as the multitude of small-molecule and peptidic ligands that have been developed over the last 30 years. In particular, integrin αVβ3 has been addressed using a variety of different PDCs and SMDCs over the last two decades, following various strategies. This review summarises and describes integrin-addressing PDCs and SMDCs while highlighting points of great interest.

Impact of drug-linker on method selection for analytical characterization and purification of antibody-drug conjugates

In addition to traditional characterisation methods of hydrophobic interaction (HIC) and reverse phase (RP) chromatography, an anion exchange chromatography (AIEX) was developed to analyse and purify antibody drug conjugates (ADCs). Since different drug antibody ratio (DAR) species may impact biological activity, therapeutic index, PK parameters or even potential immunogenicity, homogenous ADC DAR demands have been significantly increasing. To accelerate linker designs, drug screening and ADC DAR purification for in vitro and in vivo studies, we built the analytical toolbox including HIC, RP, AIEX, icIEF, SEC, and MS for downstream ADC DAR purification using HIC and AIEX. The established analytical methods can quickly assess the quality of ADC DAR profiles and provide important information to select the proper ADC DAR purification method. Since drug-linker structures can significantly affect ADC physicochemical properties, and highly impact on selections of analytical methods, we applied both HIC and AIEX characterisation and purification platforms to achieve ADC DAR homogenous. Our experiments also implied that unlike HIC, AIEX could be used to separate DAR4 positional isomers.

Homogeneous multi-payload antibody-drug conjugates

Many systemic cancer chemotherapies comprise a combination of drugs, yet all clinically used antibody-drug conjugates (ADCs) contain a single-drug payload. These combination regimens improve treatment outcomes by producing synergistic anticancer effects and slowing the development of drug-resistant cell populations. In an attempt to replicate these regimens and improve the efficacy of targeted therapy, the field of ADCs has moved towards developing techniques that allow for multiple unique payloads to be attached to a single antibody molecule with high homogeneity. However, the methods for generating such constructs-homogeneous multi-payload ADCs-are both numerous and complex owing to the plethora of reactive functional groups that make up the surface of an antibody. Here, by summarizing and comparing the methods of both single- and multi-payload ADC generation and their key preclinical and clinical results, we provide a timely overview of this relatively new area of research. The methods discussed range from branched linker installation to the incorporation of unnatural amino acids, with a generalized comparison tool of the most promising modification strategies also provided. Finally, the successes and challenges of this rapidly growing field are critically evaluated, and from this, future areas of research and development are proposed.

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.

Antibody-Drug Conjugates in the Treatment of Genitourinary Cancers: An Updated Review of Data

The treatment landscape of genitourinary cancers has significantly evolved over the past few years. Renal cell carcinoma, bladder cancer, and prostate cancer are the most common genitourinary malignancies. Recent advancements have produced new targeted therapies, particularly antibody-drug conjugates (ADCs), due to a better understanding of the underlying oncogenic factors and molecular mechanisms involved. ADCs function as a 'drug delivery into the tumor' system. They are composed of an antigen-directed antibody linked to a cytotoxic drug that releases cytotoxic components after binding to the tumor cell's surface antigen. ADCs have been proven to be extremely promising in the treatment of several cancer types. For GU cancers, this novel treatment has only benefited patients with metastatic urothelial cancer (mUC). The rest of the GU cancer paradigm does not have any FDA-approved ADC treatment options available yet. In this study, we have thoroughly completed a narrative review of the current literature and summarized preclinical studies and clinical trials that evaluated the utility, activity, and toxicity of ADCs in GU cancers, the prospects of ADC development, and the ongoing clinical trials. Prospective clinical trials, retrospective studies, case reports, and scoping reviews were included.

Fine-tuning the activation behaviors of ternary modular cabazitaxel prodrugs for efficient and on-target oral anti-cancer therapy

The disulfide bond plays a crucial role in the design of anti-tumor prodrugs due to its exceptional tumor-specific redox responsiveness. However, premature breaking of disulfide bonds is triggered by small amounts of reducing substances (e.g., ascorbic acid, glutathione, uric acid and tea polyphenols) in the systemic circulation. This may lead to toxicity, particularly in oral prodrugs that require more frequent and high-dose treatments. Fine-tuning the activation kinetics of these prodrugs is a promising prospect for more efficient on-target cancer therapies. In this study, disulfide, steric disulfide, and ester bonds were used to bridge cabazitaxel (CTX) to an intestinal lymph vessel-directed triglyceride (TG) module. Then, synthetic prodrugs were efficiently incorporated into self-nanoemulsifying drug delivery system (corn oil and Maisine CC were used as the oil phase and Cremophor EL as the surfactant). All three prodrugs had excellent gastric stability and intestinal permeability. The oral bioavailability of the disulfide bond-based prodrugs (CTX-(C)S-(C)S-TG and CTX-S-S-TG) was 11.5- and 19.1-fold higher than that of the CTX solution, respectively, demonstrating good oral delivery efficiency. However, the excessive reduction sensitivity of the disulfide bond resulted in lower plasma stability and safety of CTX-S-S-TG than that of CTX-(C)S-(C)S-TG. Moreover, introducing steric hindrance into disulfide bonds could also modulate drug release and cytotoxicity, significantly improving the anti-tumor activity even compared to that of intravenous CTX solution at half dosage while minimizing off-target adverse effects. Our findings provide insights into the design and fine-tuning of different disulfide bond-based linkers, which may help identify oral prodrugs with more potent therapeutic efficacy and safety for cancer therapy.

Bending the Rules: Amplifying PD-L1 Immunoregulatory Function Through Flexible Polyethylene Glycol Synthetic Linkers

Immune checkpoint signaling, such as programmed cell death protein-1 (PD-1), is a key target for immunotherapy due to its role in dampening immune responses. PD-1 signaling in T cells is regulated by complex physicochemical and mechanical cues. However, how these mechanical forces are integrated with biochemical responses remains poorly understood. Our previous work demonstrated that the use of an immobilizing polyethylene glycol (PEG) linker on synthetic microgels for the presentation of a chimeric form of PD-L1, SA-PD-L1, lead to local regulatory responses capable of abrogating allograft rejection in a model of cell-based transplantation. We herein provide evidence that enhanced immune regulating function can be obtained when presentation of SA-PD-L1 is achieved through a longer more flexible PEG chain. Presentation of SA-PD-L1 through a linker of high molecular weight, and thus longer length (10 kDa, 60 nm in length), led to enhance conversion of naive T cells into T regulatory cells (Tregs) in vitro. In addition, using a subcutaneous implant model and protein tethered through three different linker sizes (6, 30, and 60 nm) to the surface of PEG hydrogels, we demonstrated that longer linkers promoted PD-1 immunomodulatory role in vivo through three main functions: (1) augmenting immune cell recruitment at the transplant site; (2) promoting the accumulation of naive Tregs expressing migratory markers; and (3) dampening CD8+ cytolytic molecule production while augmenting expression of exhaustion phenotypes locally. Notably, accumulation of Treg cells at the implant site persisted for over 30 days postimplantation, an effect not observed when protein was presented with the shorter version of the linkers (6 and 30 nm). Collectively, these studies reveal a facile approach by which PD-L1 function can be modulated through external tuning of synthetic presenting linkers. Impact statement Recently, there has been a growing interest in immune checkpoint molecules as potential targets for tolerance induction, including programmed cell death protein-1 (PD-1). However, how the mechanics of ligand binding to PD-1 receptor affect downstream activation signaling pathways remains unresolved. By taking advantage of the effect of polyethylene glycol chain length on molecule kinetics in an aqueous solution, we herein show that PD-L1 function can be amplified by adjusting the length of the grafting linker. Our results uncover a potential facile mechanism that can be exploited to advance the role of immune checkpoint ligands, in particular PD-L1, in tolerance induction for immunosuppression-free cell-based therapies.

Exploring the next generation of antibody-drug conjugates

Antibody-drug conjugates (ADCs) are a promising cancer treatment modality that enables the selective delivery of highly cytotoxic payloads to tumours. However, realizing the full potential of this platform necessitates innovative molecular designs to tackle several clinical challenges such as drug resistance, tumour heterogeneity and treatment-related adverse effects. Several emerging ADC formats exist, including bispecific ADCs, conditionally active ADCs (also known as probody-drug conjugates), immune-stimulating ADCs, protein-degrader ADCs and dual-drug ADCs, and each offers unique capabilities for tackling these various challenges. For example, probody-drug conjugates can enhance tumour specificity, whereas bispecific ADCs and dual-drug ADCs can address resistance and heterogeneity with enhanced activity. The incorporation of immune-stimulating and protein-degrader ADCs, which have distinct mechanisms of action, into existing treatment strategies could enable multimodal cancer treatment. Despite the promising outlook, the importance of patient stratification and biomarker identification cannot be overstated for these emerging ADCs, as these factors are crucial to identify patients who are most likely to derive benefit. As we continue to deepen our understanding of tumour biology and refine ADC design, we will edge closer to developing truly effective and safe ADCs for patients with treatment-refractory cancers. In this Review, we highlight advances in each ADC component (the monoclonal antibody, payload, linker and conjugation chemistry) and provide more-detailed discussions on selected examples of emerging novel ADCs of each format, enabled by engineering of one or more of these components.

TROPION-Breast01: Datopotamab deruxtecan vs chemotherapy in pre-treated inoperable or metastatic HR+/HER2- breast cancer

Improving the prognosis for patients with metastatic HR+/HER2- breast cancer remains an unmet need. Patients with tumors that have progressed on endocrine therapy and/or are not eligible for endocrine therapy had limited treatment options beyond chemotherapy. Antibody-drug conjugates are a novel and promising treatment class in this setting. Datopotamab deruxtecan (Dato-DXd) consists of a TROP2-directed humanized IgG1 monoclonal antibody attached via a serum-stable cleavable linker to a topoisomerase I inhibitor payload. TROPION-Breast01 is an ongoing phase III study that is evaluating the efficacy and safety of Dato-DXd compared with investigator's choice of standard-of-care chemotherapy in patients with inoperable or metastatic HR+/HER2- breast cancer who have received one or two prior lines of systemic chemotherapy in the inoperable or metastatic setting. Clinical Trial Registration: NCT05104866 (ClinicalTrials.gov).

Antibody-Drug Conjugate Overview: a State-of-the-art Manufacturing Process and Control Strategy

Antibody-drug conjugates (ADCs) comprise an antibody, linker, and drug, which direct their highly potent small molecule drugs to target tumor cells via specific binding between the antibody and surface antigens. The antibody, linker, and drug should be properly designed or selected to achieve the desired efficacy while minimizing off-target toxicity. With a unique and complex structure, there is inherent heterogeneity introduced by product-related variations and the manufacturing process. Here this review primarily covers recent key advances in ADC history, clinical development status, molecule design, manufacturing processes, and quality control. The manufacturing process, especially the conjugation process, should be carefully developed, characterized, validated, and controlled throughout its lifecycle. Quality control is another key element to ensure product quality and patient safety. A patient-centric strategy has been well recognized and adopted by the pharmaceutical industry for therapeutic proteins, and has been successfully implemented for ADCs as well, to ensure that ADC products maintain their quality until the end of their shelf life. Deep product understanding and process knowledge defines attribute testing strategies (ATS). Quality by design (QbD) is a powerful approach for process and product development, and for defining an overall control strategy. Finally, we summarize the current challenges on ADC development and provide some perspectives that may help to give related directions and trigger more cross-functional research to surmount those challenges.

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.

Therapeutic synthetic and natural materials for immunoengineering

Immunoengineering is a rapidly evolving field that has been driving innovations in manipulating immune system for new treatment tools and methods. The need for materials for immunoengineering applications has gained significant attention in recent years due to the growing demand for effective therapies that can target and regulate the immune system. Biologics and biomaterials are emerging as promising tools for controlling immune responses, and a wide variety of materials, including proteins, polymers, nanoparticles, and hydrogels, are being developed for this purpose. In this review article, we explore the different types of materials used in immunoengineering applications, their properties and design principles, and highlight the latest therapeutic materials advancements. Recent works in adjuvants, vaccines, immune tolerance, immunotherapy, and tissue models for immunoengineering studies are discussed.

Design and Evaluation of Phosphonamidate-Linked Exatecan Constructs for Highly Loaded, Stable, and Efficacious Antibody-Drug Conjugates

Topoisomerase I (TOP1) Inhibitors constitute an emerging payload class to engineer antibody-drug conjugates (ADC) as next-generation biopharmaceutical for cancer treatment. Existing ADCs are using camptothecin payloads with lower potency and suffer from limited stability in circulation. With this study, we introduce a novel camptothecin-based linker-payload platform based on the highly potent camptothecin derivative exatecan. First, we describe general challenges that arise from the hydrophobic combination of exatecan and established dipeptidyl p-aminobenzyl-carbamate (PAB) cleavage sites such as reduced antibody conjugation yields and ADC aggregation. After evaluating several linker-payload structures, we identified ethynyl-phosphonamidates in combination with a discrete PEG24 chain to compensate for the hydrophobic PAB-exatecan moiety. Furthermore, we demonstrate that the identified linker-payload structure enables the construction of highly loaded DAR8 ADCs with excellent solubility properties. Head-to-head comparison with Enhertu, an approved camptothecin-based ADC, revealed improved target-mediated killing of tumor cells, excellent bystander killing, drastically improved linker stability in vitro and in vivo and superior in vivo efficacy over four tested dose levels in a xenograft model. Moreover, we show that ADCs based on the novel exatecan linker-payload platform exhibit antibody-like pharmacokinetic properties, even when the ADCs are highly loaded with eight drug molecules per antibody. This ADC platform constitutes a new and general solution to deliver TOP1 inhibitors with highest efficiency to the site of the tumor, independent of the antibody and its target, and is thereby broadly applicable to various cancer indications.

Impact of dipeptide on ADC physicochemical properties and efficacy identifies Ala-Ala as the optimal dipeptide

Side chains of natural occurring amino acids vary greatly in terms of charge state, polarity, size and hydrophobicity. Using a linear synthetic route, two amino acids were sequentially coupled to a potent glucocorticoid receptor modulator (GRM) to afford a library of dipeptide-GRM linker payloads with a range of in silico properties. The linker payloads were conjugated to a mouse anti-TNF antibody through interchain disulfide Cys. Impact of various dipeptide linkers on ADC physical properties, including solubility, hydrophobicity, and aggregation were evaluated and the in silico properties pI, Log P and tPSA of the linker drugs used to correlate with these properties. ADCs were screened in a GRE luciferase reporter assay to compare their in vitro efficacy. Data identified Ala-Ala as a superior dipeptide linker that allowed a maximum drug load of 10 while affording ADCs with low aggregation.

Polymer Conjugate as the New Promising Drug Delivery System for Combination Therapy against Cancer

This review highlights the advantages of combination therapy using polymer conjugates as drug delivery systems for cancer treatment. In this review, the specific structures and materials of polymer conjugates, as well as the different types of combination chemotherapy strategies, are discussed. Specific targeting strategies, such as monoclonal antibody therapy and small molecule ligands, are also explored. Additionally, self-assembled polymer micelles and overcoming multidrug resistance are described as potential strategies for combination therapy. The assessment of combinational therapeutic efficacy and the challenges associated with polymer conjugates are also addressed. The future outlook aims to overcome these challenges and improve the effectiveness of drug delivery systems for combination therapy. The conclusion emphasizes the potential of polymer conjugates in combination therapy while acknowledging the need for further research and development in this field.

Generation and Characterization of Iduronidase-Cleavable ADCs

A crucial design feature for the therapeutic success of antibody-drug conjugates (ADCs) is the linker that connects the antibody with the drug. Linkers must be stable in circulation and efficiently release the drug inside the target cell, thereby having a fundamental impact on ADC pharmacokinetics and efficacy. The variety of enzymatically cleavable linkers applied in ADCs is limited, and some are believed to be associated with unwanted side effects due to the expression of cleavage-mediating enzymes in nonmalignant cells. Based on a bioinformatic screen of lysosomal enzymes, we identified α-l-iduronidase (IduA) as an interesting candidate for ADC linker cleavage because of its low expression in normal tissues and its overexpression in several tumor types. In the present study, we report a novel IduA-cleavable ADC linker using exatecan and duocarmycin as payloads. We showed the functionality of our linker system in cleavage assays using recombinant IduA or cell lysates and compared it to established ADC linkers. Subsequently, we coupled iduronide-exatecan via interchain cysteines or iduronide-duocarmycin via microbial transglutaminase (mTG) to an anti-CEACAM5 (aCEA5) antibody. The generated iduronide-exatecan ADC showed high serum stability and similar target-dependent tumor cell killing in the subnanomolar range but reduced toxicity on nonmalignant cells compared to an analogous cathepsin B-activatable valine-citrulline-exatecan ADC. Finally, in vivo antitumor activity could be demonstrated for an IduA-cleavable duocarmycin ADC. The presented results emphasize the potential of iduronide linkers for ADC development and represent a tool for further balancing out tumor selectivity and safety.

Improving the efficacy of anti-EGFR drugs in GBM: Where we are going?

The therapies targeting mutations of driver genes in cancer have advanced into clinical trials for a variety of tumors. In glioblastoma (GBM), epidermal growth factor receptor (EGFR) is the most commonly mutated oncogene, and targeting EGFR has been widely investigated as a promising direction. However, the results of EGFR pathway inhibitors have not been satisfactory. Limited blood-brain barrier (BBB) permeability, drug resistance, and pathway compensation mechanisms contribute to the failure of anti-EGFR therapies. This review summarizes recent research advances in EGFR-targeted therapy for GBM and provides insight into the reasons for the unsatisfactory results of EGFR-targeted therapy. By combining the results of preclinical studies with those of clinical trials, we discuss that improved drug penetration across the BBB, the use of multi-target combinations, and the development of peptidomimetic drugs under the premise of precision medicine may be promising strategies to overcome drug resistance in GBM.

Multivalent protein-drug conjugates - An emerging strategy for the upgraded precision and efficiency of drug delivery to cancer cells

With almost 20 million new cases per year, cancer constitutes one of the most important challenges for public health systems. Unlike traditional chemotherapy, targeted anti-cancer strategies employ sophisticated therapeutics to precisely identify and attack cancer cells, limiting the impact of drugs on healthy cells and thereby minimizing the unwanted side effects of therapy. Protein drug conjugates (PDCs) are a rapidly growing group of targeted therapeutics, composed of a cancer-recognition factor covalently coupled to a cytotoxic drug. Several PDCs, mainly in the form of antibody-drug conjugates (ADCs) that employ monoclonal antibodies as cancer-recognition molecules, are used in the clinic and many PDCs are currently in clinical trials. Highly selective, strong and stable interaction of the PDC with the tumor marker, combined with efficient, rapid endocytosis of the receptor/PDC complex and its subsequent effective delivery to lysosomes, is critical for the efficacy of targeted cancer therapy with PDCs. However, the bivalent architecture of contemporary clinical PDCs is not optimal for tumor receptor recognition or PDCs internalization. In this review, we focus on multivalent PDCs, which represent a rapidly evolving and highly promising therapeutics that overcome most of the limitations of current bivalent PDCs, enhancing the precision and efficiency of drug delivery to cancer cells. We present an expanding set of protein scaffolds used to generate multivalent PDCs that, in addition to folding into well-defined multivalent molecular structures, enable site-specific conjugation of the cytotoxic drug to ensure PDC homogeneity. We provide an overview of the architectures of multivalent PDCs developed to date, emphasizing their efficacy in the targeted treatment of various cancers.

Synthesis of Site-Specific Antibody-[60]Fullerene-Oligonucleotide Conjugates for Cellular Targeting

An ideal therapeutic antibody-oligonucleotide conjugate (AOC) would be a uniform construct, contain a maximal oligonucleotide (ON) payload, and retain the antibody (Ab)-mediated binding properties, which leads to an efficient delivery of the ON cargo to the site of therapeutic action. Herein, [60]fullerene-based molecular spherical nucleic acids (MSNAs) have been site-specifically conjugated to antibodies (Abs), and the Ab-mediated cellular targeting of the MSNA-Ab conjugates has been studied. A well-established glycan engineering technology and robust orthogonal click chemistries yielded the desired uniform MSNA-Ab conjugates (MW ∼ 270 kDa), with an oligonucleotide (ON):Ab ratio of 24:1, in 20-26% isolated yields. These AOCs retained the antigen binding properties (Trastuzumab's binding to human epidermal growth factor receptor 2, HER2), studied by biolayer interferometry. In addition, Ab-mediated endocytosis was demonstrated with live-cell fluorescence and phase-contrast microscopy on BT-474 breast carcinoma cells, overexpressing HER2. The effect on cell proliferation was analyzed by label-free live-cell time-lapse imaging.

Antibody-Drug Conjugates: Ushering in a New Era of Cancer Therapy

Antibody-drug conjugates (ADCs) have provided new therapeutic options and significant promise for patients with cancer, particularly where existing treatments are limited. Substantial effort in ADC development is underway globally, with 13 ADCs currently approved and many more in development. The therapeutic benefits of ADCs leverage the ability to selectively target cancer cells through antibody binding, resultant relative sparing of non-malignant tissues, and the targeted delivery of a cytotoxic payload. Consequently, this drug class has demonstrated activity in multiple malignancies refractory to standard therapeutic options. Despite this, limitations exist, including narrow therapeutic windows, unique toxicity profiles, development of therapeutic resistance, and appropriate biomarker selection. This review will describe the development of ADCs, their mechanisms of action, pivotal trials, and approved indications and identify common themes. Current challenges and opportunities will be discussed for this drug class in cancer therapeutics at a time when significant developments in antibody therapies, immunotherapy, and targeted agents are occurring.

Non-traditional approaches for control of antibiotic resistance

INTRODUCTION

The drying up of antibiotic pipeline has necessitated the development of alternative therapeutic strategies to control the problem of antimicrobial resistance (AMR) that is expected to kill 10-million people annually by 2050. Newer therapeutic approaches address the shortcomings of traditional small-molecule antibiotics - the lack of specificity, evolvability, and susceptibility to mutation-based resistance. These 'non-traditional' molecules are biologicals having a complex structure and mode(s) of action that makes them resilient to resistance.

AREAS COVERED

This review aims to provide information about the non-traditional drug development approaches to tackle the problem of antimicrobial resistance, from the pre-antibiotic era to the latest developments. We have covered the molecules under development in the clinic with literature sourced from reviewed scholarly articles, official company websites involved in innovation of concerned therapeutics, press releases from the regulatory bodies, and clinical trial databases.

EXPERT OPINION

Formal introduction of non-traditional therapies in general practice can be quick and feasible only if supported with companion diagnostics and used in conjunction with established therapies. Owing to relatively higher development costs, non-traditional therapeutics require more funding as well as well as clarity in regulatory and clinical path. We are hopeful these issues are adequately addressed before AMR develops into a pandemic.

A beginner's guide to current synthetic linker strategies towards VHL-recruiting PROTACs

Over the last two decades, proteolysis targeting chimeras (PROTACs) have been revolutionary in drug development rendering targeted protein degradation (TPD) as an emerging therapeutic modality. These heterobifunctional molecules are comprised of three units: a ligand for the protein of interest (POI), a ligand for an E3 ubiquitin ligase, and a linker that tethers the two motifs together. Von Hippel-Lindau (VHL) is one of the most widely employed E3 ligases in PROTACs development due to its prevalent expression across tissue types and well-characterised ligands. Linker composition and length has proven to play an important role in determining the physicochemical properties and spatial orientation of the POI-PROTAC-E3 ternary complex, thus influencing the bioactivity of degraders. Numerous articles and reports have been published showcasing the medicinal chemistry aspects of the linker design, but few have focused on the chemistry around tethering linkers to E3 ligase ligands. In this review, we focus on the current synthetic linker strategies employed in the assembly of VHL-recruiting PROTACs. We aim to cover a range of fundamental chemistries used to incorporate linkers of varying length, composition and functionality.