AJICAP Second Generation: Improved Chemical Site-Specific Conjugation Technology for Antibody-Drug Conjugate Production

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.

AJICAP-M: Traceless Affinity Peptide Mediated Conjugation Technology for Site-Selective Antibody-Drug Conjugate Synthesis

A traceless site-selective conjugation method, "AJICAP-M", was developed for native antibodies at sites using Fc-affinity peptides, focusing on Lys248 or Lys288. It produces antibody-drug conjugates (ADCs) with consistent drug-to-antibody ratios, enhanced stability, and simplified manufacturing. Comparative in vivo assessment demonstrated AJICAP-M's superior stability over traditional ADCs. This technology has been successfully applied to continuous-flow manufacturing, marking the first achievement in site-selective ADC production. This manuscript outlines AJICAP-M's methodology and its effectiveness in ADC production.

Tag-free protein modification by lipoate ligase A: exploring substrate tolerance

This study delves into the functional intricacies of lipoate ligase A (LplA), an enzyme showing great promise in bioconjugation due to its unique capacity for introducing azido groups into proteins without requiring a genetic tag. We aimed to enhance the understanding of LplA's functionality, particularly its substrate tolerance and the reliability of various analytical techniques. A pivotal aspect of our approach was incorporating azido groups into a range of proteins, followed by the addition of the fluorescent molecule Cy3 via click chemistry. Analysis of fluorescent intensity in the altered proteins indicated varying degrees of conjugation. Additionally, phenyl resin-based RP-HPLC facilitated effective separation of modified proteins, unmodified proteins, and remaining fluorescent tags post-separation. SASA analysis provided insights into conjugation trends, guiding the identification of proteins amenable to LplA's tag-free modification. Our findings demonstrate LplA's broad substrate tolerability for protein modification.

Site-selective template-directed synthesis of antibody Fc conjugates with concomitant ligand release

Template-directed methods are emerging as some of the most effective means to conjugate payloads at selective sites of monoclonal antibodies (mAbs). We have previously reported a method based on an engineered Fc-III reactive peptide to conjugate a radionuclide chelator to K317 of antibodies with the concomitant release of the Fc-III peptide ligand. Here, our method was redesigned to target two lysines proximal to the Fc-III binding site, K248 and K439. Using energy minimization predictions and a semi-combinatorial synthesis approach, we sampled multiple Fc-III amino acid substituents of A3, H5, L6 and E8, which were then converted into Fc-III reactive conjugates. Middle-down MS/MS subunit analysis of the resulting trastuzumab conjugates revealed that K248 and K439 can be selectively targeted using the Fc-III reactive variants L6Dap, L6Orn, L6Y and A3K or A3hK, respectively. Across all variants tested, L6Orn-carbonate appeared to be the best candidate, yielding a degree and yield of conjugation of almost 2 and 100% for a broad array of payloads including radionuclide chelators, fluorescent dyes, click-chemistry reagents, pre-targeted imaging reagents, and some cytotoxic small molecules. Furthermore, L6Orn carbonate appeared to yield similar conjugation results across multiple IgG subtypes. In vivo proof of concept was achieved by conjugation of NODAGA to the PD1/PD-L1 immune checkpoint inhibitor antibody atezolizumab, followed by PET imaging of PD-L1 expression in mice bearing PD-L1 expressing tumor xenograft using radiolabeled [64Cu]Cu-atezolizumab.

Antibody-drug conjugates in cancer therapy: innovations, challenges, and future directions

The emergence of antibody-drug conjugates (ADCs) as a potential therapeutic avenue in cancer treatment has garnered significant attention. By combining the selective specificity of monoclonal antibodies with the cytotoxicity of drug molecules, ADCs aim to increase the therapeutic index, selectively targeting cancer cells while minimizing systemic toxicity. Various ADCs have been licensed for clinical usage, with ongoing research paving the way for additional options. However, the manufacture of ADCs faces several challenges. These include identifying suitable target antigens, enhancing antibodies, linkers, and payloads, and managing resistance mechanisms and side effects. This review focuses on the strategies to overcome these hurdles, such as site-specific conjugation techniques, novel antibody formats, and combination therapy. Our focus lies on current advancements in antibody engineering, linker technology, and cytotoxic payloads while addressing the challenges associated with ADC development. Furthermore, we explore the future potential of personalized medicine, leveraging individual patients' molecular profiles, to propel ADC treatments forward. As our understanding of the molecular mechanisms driving cancer progression continues to expand, we anticipate the development of new ADCs that offer more effective and personalized therapeutic options for cancer patients.

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.

Analytical studies on the conjugation site specificity of trastuzumab modified by Escherichia coli lipoate ligase A: multiple-enzyme digestion approach for peptide mapping

Tag-free protein modification has received considerable attention in the field of chemical biology owing to the versatility and simplicity of the reaction sequence. In 2021, a novel tag-free enzymatic modification of antibodies utilizing lipoate ligase A (LplA) was reported to reveal its potential in the production of site-specific antibody conjugates. Primary peptide mapping analysis revealed the biased site specificity of antibodies modified by LplA; however, quantitative analysis remains challenging because of the complicated heterogeneity derived from biased selective modification. In an effort to further understand the site occupancy of LplA-modified antibodies, this study employed numerous unconventional techniques and strategies. Optimization of HPLC conditions and utilization of enzymes such as trypsin, Glu-C, and chymotrypsin significantly increased sequence data coverage. The transition from traditional spectral counting to a more accurate peak area-based label-free quantification helped better analyze peptide modification levels. The results obtained indicate that LplA-induced modifications are specific lysines, particularly the light chain Lys188/190 site, which have an increased modification rate compared to chemically induced modifications. This study not only contributes to the understanding of peptide modification, but also presents an improved methodology that promises to stimulate further research in this field.