Bis(vinylsulfonyl)piperazines as efficient linkers for highly homogeneous antibody-drug conjugates

Triptolide-based cleavable antibody-drug conjugates for pancreatic cancer

Antibody-drug conjugates (ADCs) have emerged as a highly promising modality for the treatment of various tumors, including pancreatic cancer. Due to the modular nature of ADCs, their efficacy is heavily influenced by the choice of antibody, payload, and linker. Given the therapeutic potential of triptolide for pancreatic cancer, this study aims to harness triptolide as the cytotoxic payload to construct ADCs targeting pancreatic cancer. Silyl ethers were utilized for the first time as cleavable linkers to connect triptolide with an antibody. This is because silyl ethers can be easily synthesized and the rate of drug release can be regulated by modifying the silyl ether groups. The release profile of the resulting linkers was investigated. And considering the balance between cleavage and stability, one silyl ether-based linker was selected to prepare an ADC, named A10. Meanwhile, a traditional dipeptide linker-based ADC, A9, was synthesized for comparison. The ADC A10 demonstrated superior inhibitory effects compared to ADC A9, both in vitro and in vivo. A10 displayed targeted cytotoxicity against cells with high PD-L1 expression and demonstrated a bystander killing effect on cells with low PD-L1 expression. In vivo imaging studies indicated that fluorescently labeled A10 accumulated in tumor regions. Additionally, significant antitumor activities of A10 were observed against Panc 08.13-derived tumor xenografts.

Exploiting synthetic lethality in PDAC with antibody drug conjugates and ATR inhibition

Pancreatic ductal adenocarcinoma (PDAC) remains a highly lethal malignancy with poor prognosis. Antibody-drug conjugates (ADCs) and their combinations with various anti-tumor drugs have made great progress. Camptothecin, and its derivatives (Dxd, SN-38 or exatecan) targeted TOP1 are effective payloads due to their potent anti-tumor activity. ADCs offer a promising avenue, particularly when integrated with synthetic lethality strategies. In this study, the ADC SA-7-49 is engineered by conjugating exatecan to an anti-TROP2 antibody. The synthetic lethality between camptothecin and the ataxia telangiectasia-mutated and rad3-related (ATR) inhibitors in PDAC cells has been identified through a comprehensive screening of DNA damage response pathways. Drug interactions are quantified using Zero interaction potency (ZIP) scores. RNA sequencing is employed to elucidate the mechanisms driving synergistic effects. ATR inhibitors synergize with camptothecin by inducing apoptosis via ATR-Chk1 pathway inhibition. Knockdown of ATR enhances the sensitivity of PDAC cells to camptothecin and SA-7-49. SA-7-49 selectively targets and eradicates PDAC cells and xenografts without side effects, augmenting anti-tumor activity via synthetic lethality. Our findings reveal a novel therapeutic strategy by integrating ADC technology with synthetic lethality in PDAC.

Site-Selective Antibody Conjugation with Dibromopyrazines

In recent years, antibody conjugates have evolved as state-of-the-art options for diagnostic and therapeutic applications. During site-selective antibody conjugation, incomplete rebridging of antibody chains limits the homogeneity of conjugates and calls for the development of new rebridging agents. Herein, we report a dibromopyrazine derivative optimized to reach highly homogeneous conjugates rapidly and with high conversion on rebridging of trastuzumab, even providing a feasible route for antibody modification in acidic conditions. Furthermore, coupling a fluorescent dye and a cytotoxic drug resulted in effective antibody conjugates with excellent serum stability and in vitro selectivity, demonstrating the utility of the dibromopyrazine rebridging agent to produce on-demand future antibody conjugates for diagnostic or therapeutic applications.

Facile Rebridging Conjugation Approach to Attain Monoclonal Antibody-Targeted Nanoparticles with Enhanced Antigen Binding and Payload Delivery

Adopting conventional conjugation approaches to construct antibody-targeted nanoparticles (NPs) has demonstrated suboptimal control over the binding orientation and the structural stability of monoclonal antibodies (mAbs). Hitherto, the developed antibody-targeted NPs have shown proof of concept but lack product homogeneity, batch-to-batch reproducibility, and stability, precluding their advancement toward the clinic. To circumvent these limitations and advance toward clinical application, herein, a refined approach based on site-specific construction of mAb-immobilized NPs will be appraised. Initially, the conjugation of atezolizumab (anti-PDL1 antibody, Amab) with polymeric NPs was developed using bis-haloacetamide (BisHalide) rebridging chemistry, followed by click chemistry (NP-Fab BisHalide Ab and NP-Fc BisHalide Ab). For comparison purposes, mAb-immobilized NPs developed utilizing conventional conjugation methods, namely, N-hydroxysuccinimide (NHS) coupling and maleimide chemistry (NP-NHS Ab and NP-Mal Ab), were included. Next, flow cytometry and confocal microscopy experiments evaluated the actively targeted NPs (loaded with fluorescent dye) for cellular binding and uptake. Our results demonstrated the superior and selective binding and uptake of NP-Fab BisHalide Ab and NP-Fc BisHalide Ab into EMT6 cells by 19-fold and 13-fold, respectively. To evaluate the PDL1-dependent cell uptake and the selectivity of the treatments, a blocking step of the PDL1 receptor with Amab was performed prior to incubation with NP-Fab BisHalide Ab and NP-Fc BisHalide Ab. To our delight, the binding and uptake of fluorescent NPs were reduced significantly by 3-fold for NP-Fab BisHalide Ab, demonstrating the PDL1-mediated uptake. Moreover, NP-Fab BisHalide Ab and NP-Fc BisHalide Ab were entrapped with the paclitaxel payload, and their cytotoxicity was evaluated. They showed significant enhancements compared to free paclitaxel and NP-NHS Ab. Overall, this work will provide a facile conjugation method that could be implemented to actively target NPs with a plethora of therapeutic mAbs approved for various malignancies.

The Evolution of Antibody-Drug Conjugates: Toward Accurate DAR and Multi-specificity

Antibody-drug conjugates (ADCs) consist of antibodies, linkers and payloads. They offer targeted delivery of potent cytotoxic drugs to tumor cells, minimizing off-target effects. However, the therapeutic efficacy of ADCs is compromised by heterogeneity in the drug-to-antibody ratio (DAR), which impacts both cytotoxicity and pharmacokinetics (PK). Additionally, the emergence of drug resistance poses significant challenges to the clinical advancement of ADCs. To overcome these limitations, a variety of strategies have been developed, including the design of multi-specific drugs with accurate DAR. This review critically summarizes the current challenges faced by ADCs, categorizing key issues and evaluating various innovative solutions. We provide an in-depth analysis of the latest methodologies for achieving homogeneous DAR and explore design strategies for multi-specific drugs aimed at combating drug resistance. Our discussion offers a current perspective on the advancements made in refining ADC technologies, with an emphasis on enhancing therapeutic outcomes.

Bispecific Antibodies Produced via Chemical Site-Specific Conjugation Technology: AJICAP Second-Generation

Bispecific antibodies (BisAbs) are biotherapeutics that amalgamate the specificities of two distinct antibodies into one molecule, however, their engineering requires genetic modification and remains time-consuming. Therefore, we used AJICAP second-generation technology, which drives the production of site-specific conjugation without genetic modification requirements, to generate BisAbs. Using haloketone chemistry as an alternative to maleimide chemistry, we successfully produced site-specific antibody conjugates. Pharmacokinetic studies revealed that the haloketone-based antibody conjugate was stable in the rat plasma. The resultant BisAbs were rigorously evaluated, and surface plasmon resonance measurements and flow cytometry analyses confirmed that the antigen binding remained intact. Additionally, the affinity for the neonatal Fc receptor (FcRn) was retained after conjugation. Further cytotoxicity evaluation emphasized the pronounced activity of the generated BisAbs. This novel approach introduces a fully chemical, site-specific strategy capable of producing BisAbs, heralding a new era in the field of biotherapeutics.

Development of a MMAE-based antibody-drug conjugate targeting B7-H3 for glioblastoma

B7-H3 (immunoregulatory protein B7-homologue 3) is overexpressed in many cancer cells with limited expression in normal tissues, considered to be a promising target for tumor therapeutics. Clinical trials of antibody-drug conjugates (ADCs) against different targets for glioblastoma have been investigated and showed potent efficacies. In this study, we developed a homogeneous ADC 401-4 with a drug-to-antibody ratio (DAR) of 4, which was prepared by conjugation of Monomethyl auristatin E (MMAE) to a humanized anti-B7-H3 mAb 401, through a divinylsulfonamide-mediated disulfide re-bridging approach. In vitro studies, 401-4 displayed specific killing against B7-H3-expressing tumors and was more effective in cells with higher levels of B7-H3 for different glioblastoma cells. 401-4 was furthered labeled with Cy5.5 to yield a fluorescent conjugate 401-4-Cy5.5. The in vivo imaging studies showed that the conjugate accumulated in tumor regions and exhibited the ability to target-specific delivery. In addition, significant antitumor activities for 401-4 was observed against U87-derived tumor xenografts in a dose dependent manner.

Phenyldivinylsulfonamides for the construction of antibody-drug conjugates with controlled four payloads

Phenyldivinylsulfonamides emerged from a series of divinylsulfonamides, demonstrating their ability to effectively re-bridge disulfide bonds. This kind of linkers was attached to monomethyl auristatin E (MMAE) and further conjugated with a model antibody, trastuzumab. After optimization, the linker 20 can deliver stable and highly homogenous DAR (Drug-to-Antibody Ratio) four antibody-drug conjugates (ADCs). The method was also applicable for other IgG1 antibodies to obtain ADCs with controlled four payloads. Moreover, the MMAE-bearing ADC is potent, selective and efficacious against target cell lines.

Chemical modification of proteins - challenges and trends at the start of the 2020s

Ribosomally expressed proteins perform multiple, versatile, and specialized tasks throughout Nature. In modern times, chemically modified proteins, including improved hormones, enzymes, and antibody-drug-conjugates have become available and have found advanced industrial and pharmaceutical applications. Chemical modification of proteins is used to introduce new functionalities, improve stability or drugability. Undertaking chemical reactions with proteins without compromising their native function is still a core challenge as proteins are large conformation dependent multifunctional molecules. Methods for functionalization ideally should be chemo-selective, site-selective, and undertaken under biocompatible conditions in aqueous buffer to prevent denaturation of the protein. Here the present challenges in the field are discussed and methods for modification of the 20 encoded amino acids as well as the N-/C-termini and protein backbone are presented. For each amino acid, common and traditional modification methods are presented first, followed by more recent ones.

Site-specific construction of triptolide-based antibody-drug conjugates

Antibody-drug conjugates (ADCs) have emerging as efficient agents to target deliver cytotoxic drugs and reduce their off-target side effects. Triptolide has attracted attention to be used in ADC development. Herein, three rationally designed triptolide drug-linkers have been synthesized for use in site-specific construction of ADCs. Carbamates that were supposed to be more stable than carbonates were introduced to attach triptolide to the linkers. PEG and discrete PEG chains were incorporated to improve the hydrophilicity of drug-linkers. The ADCs were finally site-specifically prepared by conjugation of the drug-linkers to trastuzumab through disulfide re-bridging approach. The preliminary anti-tumor activities of these ADCs were evaluated and they displayed high potencies against HER2-targeted cancer in vitro and in vivo.

Antibody-drug conjugates: Recent advances in linker chemistry

Antibody–drug conjugates (ADCs) are gradually revolutionizing clinical cancer therapy. The antibody–drug conjugate linker molecule determines both the efficacy and the adverse effects, and so has a major influence on the fate of ADCs. An ideal linker should be stable in the circulatory system and release the cytotoxic payload specifically in the tumor. However, existing linkers often release payloads nonspecifically and inevitably lead to off-target toxicity. This defect is becoming an increasingly important factor that restricts the development of ADCs. The pursuit of ADCs with optimal therapeutic windows has resulted in remarkable progress in the discovery and development of novel linkers. The present review summarizes the advance of the chemical trigger, linker‒antibody attachment and linker‒payload attachment over the last 5 years, and describes the ADMET properties of ADCs. This work also helps clarify future developmental directions for the linkers.

Strategies and Applications of Antigen-Binding Fragment (Fab) Production in Escherichia coli

With the advancement of genetic engineering, monoclonal antibodies (mAbs) have made far-reaching progress in the treatment of various human diseases. However, due to the high cost of production, the increasing demands for antibody-based therapies have not been fully met. Currently, mAb-derived alternatives, such as antigen-binding fragments (Fab), single-chain variable fragments, bispecifics, nanobodies, and conjugated mAbs have emerged as promising new therapeutic modalities. They can be readily prepared in bacterial systems with well-established fermentation technology and ease of manipulation, leading to the reduction of overall cost. This review aims to shed light on the strategies to improve the expression, purification, and yield of Fab fragments in Escherichia coli expression systems, as well as current advances in the applications of Fab fragments.

Stimulus-cleavable chemistry in the field of controlled drug delivery

Stimulus-cleavable nanoscale drug delivery systems are receiving significant attention owing to their capability of achieving exquisite control over drug release via the exposure to specific stimuli. Central to the construction of such systems is the integration of cleavable linkers showing susceptibility to one stimulus or several stimuli with drugs, prodrugs or fluorogenic probes on the one hand, and nanocarriers on the other hand. This review summarises recent advances in stimulus-cleavable linkers from various research areas and the corresponding mechanisms of linker cleavage and biological applications. The feasibility of extending their applications to the majority of nanoscale drug carriers including nanomaterials, polymers and antibodies are further highlighted and discussed. This review also provides general design guidelines to incorporate stimulus-cleavable linkers into nanocarrier-based drug delivery systems, which will hopefully spark new ideas and applications.

Combretastatin A4-derived payloads for antibody-drug conjugates

We describe the use of natural product combretastatin A4 (CA4) as a versatile new payload for the construction of antibody-drug conjugates (ADCs). Cetuximab conjugates consisting of CA4 derivatives were site-specially prepared by disulfide re-bridging approach using cleavable and non-cleavable linkers. These ADCs retained antigen binding and internalization efficiency and exhibited high potencies against cancer cell lines in vitro. The conjugates also demonstrated significant antitumor activities in EGFR-positive xenograft models without observed toxicities. CA4 appears to be a viable payload option for ADCs research and development.

An overview of process development for antibody-drug conjugates produced by chemical conjugation technology

Introduction: We discuss chemical conjugation strategies for antibody-drug conjugates (ADCs) from an industrial perspective and compare three promising chemical conjugation technologies to produce site-specific ADCs.Areas covered: Currently, nine ADCs are commercially approved and all are produced by chemical conjugation technology. However, seven of these ADCs contain a relatively broad drug distribution, potentially limiting their therapeutic indices. In 2019, the first site-specific ADC was launched on the market by Daiichi-Sankyo. This achievement, and an analysis of clinical trials over the last decade, indicates that current industrial interest in the ADC field is shifting toward site-specific conjugation technologies. From an industrial point of view, we aim to provide guidance regarding established conjugation methodologies that have already been applied to scale-up stages. With an emphasis on highly productive, scalable, and synthetic process robustness, conjugation methodologies for ADC production is discussed herein.Expert opinion: All three chemical conjugation technologies described in this review have various advantages and disadvantages, therefore drug developers can utilize these depending on their biological and/or protein targets. The future landscape of the ADC field is also discussed.

Divinylsulfonamides enable the construction of homogeneous antibody-drug conjugates

Methods that site-specifically attach payloads to an antibody with controlled DAR (Drug-Antibody Ratio) are highly desirable for the generation of homogeneous antibody-drug conjugates (ADCs). We describe the use of N-phenyl-divinylsulfonamide scaffold as a linker platform to site-specifically construct homogeneous DAR four ADCs through a disulfide re-bridging approach. Several monomethyl auristatin E (MMAE)-linkers were synthesized and the drug-linkers that contain electron-donating groups on the phenyl of the linker showed high stability. Her2-targeted MMAE-linker-herceptin and EGFR targeted MMAE-linker-cetuximab conjugates were prepared. The conjugates demonstrated high efficacy and selectivity for killing target-positive cancer cells in vitro. The EGFR-targeted conjugates also showed significant antitumor activities in vivo.