Effect of Conjugation Site and Technique on the Stability and Pharmacokinetics of Antibody-Drug Conjugates

Site-Specific Stability Evaluation of Antibody-Drug Conjugate in Serum Using a Validated Liquid Chromatography-Mass Spectrometry Method

Antibody-drug conjugate (ADC) consists of engineered antibodies and cytotoxic drugs linked via a chemical linker, and the stability of ADC plays a crucial role in ensuring its safety and efficacy. The stability of ADC is closely related to the conjugation site; however, no method has been developed to assess the stability of different conjugation sites due to the low response of conjugated peptides. In this study, an integrated strategy was developed and validated to assess the stability of different conjugation sites on ADC in serum. Initial identification of the conjugated peptides of the model drug ado-trastuzumab emtansine (T-DM1) was achieved by the proteomic method. Subsequently, a semiquantitative method for conjugated peptides was established in liquid chromatography-hybrid linear ion trap triple quadrupole mass spectrometry (LC-QTRAP-MS/MS) based on the qualitative information. The pretreatment method of the serum sample was optimized to reduce matrix interference. The method was then validated and applied to evaluate the stability of the conjugation sites on T-DM1. The results highlighted differences in stability among the different conjugation sites on T-DM1. This is the first study to assess the stability of different conjugation sites on the ADC in serum, which will be helpful for the design and screening of ADCs in the early stages of development.

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.

Technical, preclinical, and clinical developments of Fc-glycan-specific antibody-drug conjugates

Antibody-drug conjugates (ADCs) have emerged as a powerful avenue in the therapeutic treatment of cancer. Site-specific antibody-drug conjugations represent the latest trend in the development of ADCs, addressing the limitations of traditional random conjugation technologies. This article summarizes the innovative development of Fc-glycan-specific ADCs (gsADCs), which utilize the conserved Fc N-glycan as the anchor point for site-specific conjugation. This approach offers significant strengths, including improved ADC homogeneity and overall hydrophilicity, enhanced pharmacokinetics and therapeutic index, and potentially reduced Fc receptor-mediated side effects. Currently dozens of gsADCs are in different preclinical and clinical development stages. Notably, JSKN003 and IBI343 have demonstrated promising results in phase 1 trials and are advancing into phase 3 studies. This review discusses the advantages of Fc-glycan-conjugation, various glycan-specific conjugation techniques, and the preclinical and clinical development of gsADCs. While challenges such as increased manufacturing cost for large-scale production need continuous innovation to overcome and there are different opinions regarding the pros and cons of reduced/diminished affinities to Fc gamma receptors, ongoing research and clinical progress underscore the potential of gsADCs to renovate ADC cancer therapy.

Design and synthesis of novel site-specific antibody-drug conjugates that target TROP2

The approval of Trodelvy® validates TROP2 as a druggable but challenging target for antibody-drug conjugates (ADCs) to treat metastatic triple-negative breast cancer (mTNBC). Here, based on the TROP2-targeted antibody sacituzumab, we designed and developed several site-specific ADC candidates, which employ MMAE (monomethyl auristatin E) as the toxin, via IgG glycoengineering or affinity-directed traceless conjugation. Systematic evaluation of these site-specific ADCs in homogeneity, hydrophilicity, stability, and antitumor efficiency was conducted. The results indicate that the site-specific ADCs gsADC 3b made from one-step glycoengineering exhibit good aggregation stability and in vivo efficacy, providing a new format of ADCs that target TROP2.

Drug deconjugation-assisted peptide mapping by LC-MS/MS to identify conjugation sites and quantify site occupancy for antibody-drug conjugates

Antibody-drug conjugates (ADCs) are a heterogeneous mixture of conjugated species with varied drug loadings. Depending on conjugation sites, linkers and drugs can exhibit different stability as influenced by the solvent-accessibility and local charge, resulting in different ADC efficacy, pharmacokinetics, and toxicity. Conjugation site analysis is critical for ADC structural characterization to assure product quality and consistency. It enables early conjugation studies at site-specific levels, confirms the absence of unexpected products to support conjugation process development, and aids in ensuring lot-to-lot consistency for comparability studies. Peptide mapping using liquid chromatography-tandem mass spectrometry is the industry standard method for analyzing conjugation sites. However, some concerns remain for this approach as the large and hydrophobic drug moieties often result in poor MS/MS fragmentation quality and impede the identification of conjugation sites. Additionally, the ionization discrepancy between conjugated and unconjugated peptides can lead to a relatively large bias for site occupancy calculation. In this work, we present a simple drug deconjugation-assisted peptide mapping method to identify and quantify the drug conjugation for ADCs with protease-cleavable linkers. Papain-based drug deconjugation was used to remove the highly hydrophobic drug moiety, which significantly improved the quantitation accuracy of conjugation level and the fragmentation quality. Sample preparation conditions were optimized to avoid introducing artificial modifications, allowing the tracking of initial sample status and subsequent changes of quality attributes during process development and stability assessment. This method was applied to analyze thermally-stressed ADC samples to monitor changes of site-specific conjugation levels, DAR, succinimide hydrolysis of the linker, and various PTMs. We believe this is an effective and straightforward tool for conjugation site analysis while simultaneously monitoring multiple quality attributes for ADCs with protease-cleavable linkers.

Potent antitumor activity of anti-HER2 antibody-topoisomerase I inhibitor conjugate based on self-immolative dendritic dimeric-linker

Antibody-drug conjugates (ADCs) are a rapidly expanding class of anticancer therapeutics, with 14 ADCs already approved worldwide. We developed unique linker technologies for the bioconjugation of drug molecules with controlled-release applications. We synthesized cathepsin-cleavable ADCs using a dimeric prodrug system based on a self-immolative dendritic scaffold, resulting in a high drug-antibody ratio (DAR) with the potential to reach 16 payloads due to its dendritic structure, increased stability in the circulation and efficient release profile of a highly cytotoxic payload at the targeted site. Using our novel cleavable linker technologies, we conjugated the anti-human epidermal growth factor receptor 2 (anti-HER2) antibody, trastuzumab, with topoisomerase I inhibitors, exatecan or belotecan. The newly synthesized ADCs were tested in vitro on mammary carcinoma cells overexpressing human HER2, demonstrating a substantial inhibitory effect on the proliferation of HER2-positive cells. Importantly, a single dose of our trastuzumab-based ADCs administered in vivo to mice bearing HER2-positive tumors, showed a dose-dependent inhibition of tumor growth and survival benefit, with the most potent antitumor effects observed at 10 mg/kg, which resulted in complete tumor regression and survival of 100% of the mice. Overall, our novel dendritic technologies using the protease-cleavable Val-Cit linker present an opportunity for the development of highly selective and potent controlled-released therapeutic payloads. This strategy could potentially lead to the development of novel and effective ADC technologies for patients diagnosed with HER2-positive cancers. Moreover, our proposed ADC linker technology can be implemented in additional medical conditions such as other malignancies as well as autoimmune diseases that overexpress targets, other than HER2.

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.

Impact of antibody architecture and paratope valency on effector functions of bispecific NKp30 x EGFR natural killer cell engagers

Natural killer (NK) cells emerged as a promising effector population that can be harnessed for anti-tumor therapy. In this work, we constructed NK cell engagers (NKCEs) based on NKp30-targeting single domain antibodies (sdAbs) that redirect the cytotoxic potential of NK cells toward epidermal growth factor receptor (EGFR)-expressing tumor cells. We investigated the impact of crucial parameters such as sdAb location, binding valencies, the targeted epitope on NKp30, and the overall antibody architecture on the redirection capacity. Our study exploited two NKp30-specific sdAbs, one of which binds a similar epitope on NKp30 as its natural ligand B7-H6, while the other sdAb addresses a non-competing epitope. For EGFR-positive tumor targeting, humanized antigen-binding domains of therapeutic antibody cetuximab were used. We demonstrate that NKCEs bivalently targeting EGFR and bivalently engaging NKp30 are superior to monovalent NKCEs in promoting NK cell-mediated tumor cell lysis and that the architecture of the NKCE can substantially influence killing capacities depending on the NKp30-targeting sdAb utilized. While having a pronounced impact on NK cell killing efficacy, the capabilities of triggering antibody-dependent cellular phagocytosis or complement-dependent cytotoxicity were not significantly affected comparing the bivalent IgG-like NKCEs with cetuximab. However, the fusion of sdAbs can have a slight impact on the NK cell release of immunomodulatory cytokines, as well as on the pharmacokinetic profile of the NKCE due to unfavorable spatial orientation within the molecule architecture. Ultimately, our findings reveal novel insights for the engineering of potent NKCEs triggering the NKp30 axis.

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.

Lysosomal-Cleavable Peptide Linkers in Antibody-Drug Conjugates

Antibody-drug Conjugates (ADCs) are a powerful therapeutic modality for cancer treatment. ADCs are multi-functional biologics in which a disease-targeting antibody is conjugated to an effector payload molecule via a linker. The success of currently used ADCs has been largely attributed to the development of linker systems, which allow for the targeted release of cytocidal payload drugs inside cancer cells. Many lysosomal proteases are over expressed in human cancers. They can effectively cleave a variety of peptide sequences, which can be exploited for the design of ADC linker systems. As a well-established linker, valine-citrulline-p-aminobenzyl carbamate (ValCitPABC) is used in many ADCs that are already approved or under preclinical and clinical development. Although ValCitPABC and related linkers are readily cleaved by cathepsins in the lysosome while remaining reasonably stable in human plasma, many studies have shown that they are susceptible to carboxylesterase 1C (Ces1C) in mouse and rat plasma, which hinders the preclinical evaluation of ADCs. Furthermore, neutropenia and thrombocytopenia, two of the most commonly observed dose-limiting adverse effects of ADCs, are believed to result from the premature hydrolysis of ValCitPABC by human neutrophil elastase. In addition to ValCitPABC, the GGFG tetrapeptidyl-aminomethoxy linker is also cathepsin-cleavable and is used in the highly successful ADC drug, DS8201a. In addition to cathepsin-cleavable linkers, there is also growing interest in legumain-sensitive linkers for ADC development. Increasing plasma stability while maintaining lysosomal cleavability of ADC linkers is an objective of intensive current research. This review reports recent advances in the design and structure-activity relationship studies of various peptide/peptidomimetic linkers in this field.

Evaluation of Two Chemoenzymatic Glycan Remodeling Approaches to Generate Site-Specific Antibody-Drug Conjugates

Fc-glycosite-specific antibody-drug conjugation represents a promising direction for the preparation of site-specific antibody-drug conjugates (ADCs). In the present research, we conducted a systemic evaluation of two endoglycosidase-catalyzed chemoenzymatic glycoengineering technologies to prepare glycosite-specific ADCs. In the first two-step approach, the antibody was deglycosylated and then reglycosylated with a modified intact N-glycan oxazoline. In the second one-pot approach, antibodies were deglycosylated and simultaneously glycosylated with a functionalized disaccharide oxazoline. For the comprehensive evaluation, we first optimized and scaled-up the preparation of azido glycan oxazolines. Afterwards, we proved that the one-pot glycan-remodeling approach was efficient for all IgG subclasses. Subsequently, we assembled respective ADCS using two technology routes, with two different linker-payloads combinations, and performed systemic in vitro and in vivo evaluations. All the prepared ADCs achieved high homogeneity and illustrated excellent stability in buffers with minimum aggregates, and exceptional stability in rat serum. All ADCs displayed a potent killing of BT-474 breast cancer cells. Moving to the mouse study, the ADCs prepared from two technology routes displayed potent and similar efficacy in a BT-474 xenograft model, which was comparable to an FDA-approved ADC generated from random conjugation. These ADCs also demonstrated excellent safety and did not cause body weight loss at the tested dosages.

Development of a Cytotoxic Antibody-Drug Conjugate Targeting Membrane Immunoglobulin E-Positive Cells

High numbers of membrane immunoglobulin E (IgE)-positive cells are characteristic of allergic conditions, atopic dermatitis, or IgE myeloma. Antibodies targeting the extracellular membrane-proximal domain of the membranous IgE-B-cell receptor (BCR) fragment can be used for specific depletion of IgE-BCR-positive cells. In this study, we derivatized such an antibody with a toxin and developed an antibody-drug conjugate (ADC) that showed strong cytotoxicity for an IgE-positive target cell line. Site-specific conjugation with maleimidocaproyl-valine-citrulline-p-aminobenzoyloxycarbonyl-monomethyl-auristatin E via a newly introduced single cysteine residue was used to prepare a compound with a drug-antibody ratio of 2 and favorable biophysical properties. The antibody was rapidly taken up by the target cells, showing almost complete internalization after 4 h of treatment. Its cytotoxic effect was potentiated upon cross-linking mediated by an anti-human IgG F(ab')2 fragment. Because of its fast internalization and strict target specificity, this antibody-drug conjugate presents a valuable starting point for the further development of an anti-IgE cell-depleting agent, operating by the combined action of receptor cross-linking and toxin-mediated cytotoxicity.

Penetration of Nanobody-Dextran Polymer Conjugates through Tumor Spheroids

Here we report the generation of nanobody dextran polymer conjugates (dextraknobs) that are loaded with small molecules, i.e., fluorophores or photosensitizers, for potential applications in cancer diagnostics and therapy. To this end, the molecules are conjugated to the dextran polymer which is coupled to the C-terminus of an EGFR-specific nanobody using chemoenzymatic approaches. A monovalent EGFR-targeted nanobody and biparatopic version modified with different dextran average molecular weights (1000, 5000, and 10,000) were probed for their ability to penetrate tumor spheroids. For monovalent Cy5-labeled dextraknobs, the utilization of smaller sized dextran (MW 5000 vs. 10,000) was found to be beneficial for more homogeneous penetration into A431 tumor spheroids over time. For the biparatopic dual nanobody comprising MW 1000, 5000, and 10,000 dextran labeled with photosensitizer IRDye700DX, penetration behavior was comparable to that of a direct nanobody-photosensitizer conjugate lacking a dextran scaffold. Additionally, dextraknobs labeled with IRDye700DX incubated with cells in 2D and 3D showed potent cell killing upon illumination, thus inducing photodynamic therapy (PDT). In line with previous results, monovalent nanobody conjugates displayed deeper and more homogenous penetration through spheroids than the bivalent conjugates. Importantly, the smaller size dextrans did not affect the distribution of the conjugates, thus encouraging further development of dextraknobs.

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.

Understanding the activity of antibody-drug conjugates in primary and secondary brain tumours

Antibody-drug conjugates (ADCs), a class of targeted cancer therapeutics combining monoclonal antibodies with a cytotoxic payload via a chemical linker, have already been approved for the treatment of several cancer types, with extensive clinical development of novel constructs ongoing. Primary and secondary brain tumours are associated with high mortality and morbidity, necessitating novel treatment approaches. Pharmacotherapy of brain tumours can be limited by restricted drug delivery across the blood-brain or blood-tumour barrier, although data from phase II studies of the HER2-targeted ADC trastuzumab deruxtecan indicate clinically relevant intracranial activity in patients with brain metastases from HER2⁺ breast cancer. However, depatuxizumab mafodotin, an ADC targeting wild-type EGFR and EGFR variant III, did not provide a definitive overall survival benefit in patients with newly diagnosed or recurrent EGFR-amplified glioblastoma in phase II and III trials, despite objective radiological responses in some patients. In this Review, we summarize the available data on the central nervous system activity of ADCs from trials involving patients with primary and secondary brain tumours and discuss their clinical implications. Furthermore, we explore pharmacological determinants of intracranial activity and discuss the optimal design of clinical trials to facilitate development of ADCs for the treatment of gliomas and brain metastases.