Synthesis of site-specific antibody-drug conjugates using unnatural amino acids

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.

The synthesis of novel unnatural amino acid by intramolecular aza-Michael addition reaction as multitarget enzyme inhibitors

Synthesis of novel unnatural amino acids (UAAs) from 4-oxo-4-phenylbut-2-enoic acid derivatives with intramolecular aza-Michael addition reaction in the presence of chlorosulfonyl isocyanate (CSI) was reported in soft conditions without any metal catalyst. Acids and base as a catalyst, and solvents effects were investigated for the synthesis of novel UAAs. This novel method provides inexpensive, practicable, and efficient approach to generate UAAs. The use of UAAs has attracted great interest in the development of therapeutic agents and drug discovery to improve their properties. In this context, in addition to the synthesis of new UAAs, their inhibition effects on important metabolic enzymes of acetylcholinesterase (AChE) and carbonic anhydrases I and II (hCA I and II) enzymes were investigated. The compound 2g showed the best inhibition for CA I and AChE enzymes, while compound 2i exhibited the best inhibition profile against CA II isoenzyme. The inhibition values of these compounds were found as 1.85 ± 0.64 for AChE, 0.53 ± 0.07 for hCA I, 0.44 ± 0.15 µM for hCA II, respectively, and they showed a stronger inhibitory property than acetazolamide (standard inhibitor for hCA I and II) and tacrine (standard inhibitor for AChE) molecules. The activity of the studied molecule against different proteins that are hCA I (PDB ID: 2CAB), hCA II (PDB ID: 5AML), and AChE (PDB ID: 1OCE) was examined. Finally, the drug properties of the studied molecule were examined by performing absorption, distribution, metabolism, excretion, and toxicity analysis.

Evolution of Pyrrolysyl-tRNA Synthetase: From Methanogenesis to Genetic Code Expansion

Over 20 years ago, the pyrrolysine encoding translation system was discovered in specific archaea. Our Review provides an overview of how the once obscure pyrrolysyl-tRNA synthetase (PylRS) tRNA pair, originally responsible for accurately translating enzymes crucial in methanogenic metabolic pathways, laid the foundation for the burgeoning field of genetic code expansion. Our primary focus is the discussion of how to successfully engineer the PylRS to recognize new substrates and exhibit higher in vivo activity. We have compiled a comprehensive list of ncAAs incorporable with the PylRS system. Additionally, we also summarize recent successful applications of the PylRS system in creating innovative therapeutic solutions, such as new antibody-drug conjugates, advancements in vaccine modalities, and the potential production of new antimicrobials.

Emerging conjugation strategies and protein engineering technologies aim to improve ADCs in the fight against cancer

Antibody drug conjugates are an exciting therapeutic modality that combines the targeting specificity of antibodies with potent cytotoxins to selectively kill cancer cells. The targeting component improves efficacy and protects non-target cells from the harmful effects of the payload. To date 15 ADCs have been approved by regulatory agencies for commercial use and shown to be valuable tools in the treatment of cancer.The assembly of an ADC requires the chemical ligation of a linker-payload to an antibody. Conventional conjugation methods targeting accessible lysines and cysteines have produced all the ADCs currently on the market. While successful, technologies aiming to improve the homogeneity and stability of ADCs are being developed and tested.Here we provide a review of developing methods for ADC construction. These include enzymatic methods, oligosaccharide remodelling, and technologies using genetic code expansion techniques. The virtues and limitations of each technology are discussed.Emerging conjugation technologies are being applied to produce new formats of ADCs with enhanced functionality including bispecific ADCs, dual-payload ADCs, and nanoparticles for targeted drug delivery. The benefits of these novel formats are highlighted.

Antibody-drug conjugates for non-small cell lung cancer: Advantages and challenges in clinical translation

Lung cancer is the leading cause of cancer death, with non-small cell lung cancer (NSCLC) accounting for approximately 85 % of all lung cancers and having a poor treatment and prognosis. Conventional clinical chemotherapy and immunotherapy are challenged by systemic toxicity and drug resistance, so researchers are increasingly focusing on antibody-drug conjugate (ADC), an innovative concept combining chemotherapy and targeted therapy, in which a drug selectively binds to antigens on the surface of a tumor cell via antibodies, which internalize the ADC, and then transfers the ADC to the lysosome via the endosomes to degrade the drug and kill the tumor cell. Despite the promising nature of ADCs, no ADC product for any indication including NSCLC has been approved for marketing by the FDA to date. In this review, we summarize the main advantages of ADCs and discuss in depth the design of the most desirable ADCs for NSCLC therapy. In addition to preclinical studies, we focus on the current state of clinical research on ADCs as interventions for the treatment of NSCLC by summarizing real-time clinical trial data from ClinicalTrials.gov, and reasonably speculate on the direction of the design of future generations of ADCs.

Precision engineering of antibodies: A review of modification and design in the Fab region

The binding of functional groups to antibodies is crucial for disease treatment, diagnosis, and basic scientific research. Traditionally, antibody modifications have focused on the Fc region to maintain antigen-antibody binding activity. However, such modifications may impact critical antibody functions, including immune cell surface receptor activation, cytokine release, and other immune responses. In recent years, modifications targeting the antigen-binding fragment (Fab) region have garnered increasing attention. Precise modifications of the Fab region not only maximize the retention of antigen-antibody binding capacity but also enhance numerous physicochemical properties of antibodies. This paper reviews the chemical, biological, biochemical, and computer-assisted methods for modifying the Fab region of antibodies, discussing their advantages, limitations, recent advances, and future trends.

Non-canonical amino acids uncover the significant impact of Tyr671 on Taq DNA polymerase catalytic activity

Responsible for synthesizing the complementary strand of the DNA template, DNA polymerase is a crucial enzyme in DNA replication, recombination and repair. A highly conserved tyrosine (Tyr), located at the C-terminus of the O-helix in family A DNA polymerases, plays a critical role in enzyme activity and fidelity. Here, we combined the technology of genetic code extension to incorporate non-canonical amino acids and molecular dynamics (MD) simulations to uncover the mechanisms by which Tyr671 impacts substrate binding and conformation transitions in a DNA polymerase from Thermus aquaticus. Five non-canonical amino acids, namely l-3,4-dihydroxyphenylalanine (l-DOPA), p-aminophenylalanine (pAF), p-acetylphenylalanine (pAcF), p-cyanophenylalanine (pCNF) and p-nitrophenylalanine (pNTF), were individually incorporated at position 671. Strikingly, Y671pAF and Y671DOPA were active, but with lower activity compared to Y671F and wild-type. Y671pAF showed a higher fidelity than the Y671F, despite both possessing lower fidelity than the wild-type. Metadynamics and long-timescale MD simulations were carried out to probe the role of mutations in affecting protein structure, including open conformation, open-to-closed conformation transition, closed conformation, and closed-to-open conformation transition. The MD simulations clearly revealed that the size of the 671 amino acid residue and interactions with substrate or nearby residues were critical for Tyr671 to determine enzyme activity and fidelity.

Rare codon recoding for efficient noncanonical amino acid incorporation in mammalian cells

The ability to genetically encode noncanonical amino acids (ncAAs) has empowered proteins with improved or previously unknown properties. However, existing strategies in mammalian cells rely on the introduction of a blank codon to incorporate ncAAs, which is inefficient and limits their widespread applications. In this study, we developed a rare codon recoding strategy that takes advantage of the relative rarity of the TCG codon to achieve highly selective and efficient ncAA incorporation through systematic engineering and big data-model predictions. We highlight the broad utility of this strategy for the incorporation of dozens of ncAAs into various functional proteins at the wild-type protein expression levels, as well as the synthesis of proteins with up to six-site ncAAs or four distinct ncAAs in mammalian cells for downstream applications.

Applications of genetic code expansion technology in eukaryotes

Unnatural amino acids (UAAs) have gained significant attention in protein engineering and drug development owing to their ability to introduce new chemical functionalities to proteins. In eukaryotes, genetic code expansion (GCE) enables the incorporation of UAAs and facilitates posttranscriptional modification (PTM), which is not feasible in prokaryotic systems. GCE is also a powerful tool for cell or animal imaging, the monitoring of protein interactions in target cells, drug development, and switch regulation. Therefore, there is keen interest in utilizing GCE in eukaryotic systems. This review provides an overview of the application of GCE in eukaryotic systems and discusses current challenges that need to be addressed.

A Genetically Encoded Photocaged Cysteine for Facile Site-Specific Introduction of Conjugation-Ready Thiol Residues in Antibodies

Antibody-drug conjugates (ADCs) have emerged as a powerful class of anticancer therapeutics that enable the selective delivery of toxic payloads into target cells. There is increasing appreciation for the importance of synthesizing such ADCs in a defined manner where the payload is attached at specific permissive sites on the antibody with a defined drug to antibody ratio. Additionally, the ability to systematically alter the site of attachment is important to fine-tune the therapeutic properties of the ADC. Engineered cysteine residues have been used to achieve such site-specific programmable attachment of drug molecules onto antibodies. However, engineered cysteine residues on antibodies often get "disulfide-capped" during secretion and require reductive regeneration prior to conjugation. This reductive step also reduces structurally important disulfide bonds in the antibody itself, which must be regenerated through oxidation. This multistep, cumbersome process reduces the efficiency of conjugation and presents logistical challenges. Additionally, certain engineered cysteine sites are resistant to reductive regeneration, limiting their utility and the overall scope of this conjugation strategy. In this work, we utilize a genetically encoded photocaged cysteine residue that can be site-specifically installed into the antibody. This photocaged amino acid can be efficiently decaged using light, revealing a free cysteine residue available for conjugation without disrupting the antibody structure. We show that this ncAA can be incorporated at several positions within full-length recombinant trastuzumab and decaged efficiently. We further used this method to generate a functional ADC site-specifically modified with monomethyl auristatin F (MMAF).

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

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

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.

Production and characterization of a camelid single domain anti-CD22 antibody conjugated to DM1

Antibody drug conjugates (ADCs) with twelve FDA approved drugs, known as a novel category of anti-neoplastic treatment created to merge the monoclonal antibody specificity with cytotoxicity effect of chemotherapy. However, despite many undeniable advantages, ADCs face certain problems, including insufficient internalization after binding, complex structures and large size of full antibodies especially in targeting of solid tumors. Camelid single domain antibody fragments (Nanobody®) offer solutions to this challenge by providing nanoscale size, high solubility and excellent stability, recombinant expression in bacteria, in vivo enhanced tissue penetration, and conjugation advantages. Here, an anti-human CD22 Nanobody was expressed in E.coli cells and conjugated to Mertansine (DM1) as a cytotoxic payload. The anti-CD22 Nanobody was expressed and purified by Ni-NTA resin. DM1 conjugated anti-CD22 Nanobody was generated by conjugation of SMCC-DM1 to Nanobody lysine groups. The conjugates were characterized using SDS-PAGE and Capillary electrophoresis (CE-SDS), RP-HPLC, and MALDI-TOF mass spectrometry. Additionally, flow cytometry analysis and a competition ELISA were carried out for binding evaluation. Finally, cytotoxicity of conjugates on Raji and Jurkat cell lines was assessed. The drug-to-antibody ratio (DAR) of conjugates was calculated 2.04 using UV spectrometry. SDS-PAGE, CE-SDS, HPLC, and mass spectrometry confirmed conjugation of DM1 to the Nanobody. The obtained results showed the anti-CD22 Nanobody cytotoxicity was enhanced almost 80% by conjugation with DM1. The binding of conjugates was similar to the non-conjugated anti-CD22 Nanobody in flow cytometry experiments. Concludingly, this study successfully suggest that the DM1 conjugated anti-CD22 Nanobody can be used as a novel tumor specific drug delivery system.

Electrochemical labelling of hydroxyindoles with chemoselectivity for site-specific protein bioconjugation

Electrochemistry has recently emerged as a powerful approach in small-molecule synthesis owing to its numerous attractive features, including precise control over the fundamental reaction parameters, mild reaction conditions and innate scalability. Even though these advantages also make it an attractive strategy for chemoselective modification of complex biomolecules such as proteins, such applications remain poorly developed. Here we report an electrochemically promoted coupling reaction between 5-hydroxytryptophan (5HTP) and simple aromatic amines-electrochemical labelling of hydroxyindoles with chemoselectivity (eCLIC)-that enables site-specific labelling of full-length proteins under mild conditions. Using genetic code expansion technology, the 5HTP residue can be incorporated into predefined sites of a recombinant protein expressed in either prokaryotic or eukaryotic hosts for subsequent eCLIC labelling. We used the eCLIC reaction to site-specifically label various recombinant proteins, including a full-length human antibody. Furthermore, we show that eCLIC is compatible with strain-promoted alkyne-azide and alkene-tetrazine click reactions, enabling site-specific modification of proteins at two different sites with distinct labels.

Antibody and antibody fragments site-specific conjugation using new Q-tag substrate of bacterial transglutaminase

During the last few years Antibody-Drug Conjugates (ADCs) have become one of the most active and very promising therapeutic weapons. Lessons learned from the traditional chemical conjugations (via lysine or cysteine residues of the antibodies) and the clinical studies of the developed ADCs have recently paved the way to the improvement of the conjugation technologies. Use of site-specific conjugation is considered as the promising path for improving the design and development of homogeneous ADCs with controlled Drug-Antibody ratio (DAR). Moreover, some of these conjugations can be applied to antibody fragments such as Fab, scfv and VHH for which random and chemical conjugation showed significant limitations. In this study, we identified a novel small peptide substrate (Q-tag) with high affinity and specificity of bacterial transglutaminase which can be genetically fused to different formats of antibodies of interest for the development of enzymatic site-specific conjugation we named "CovIsolink" platform. We describe the synthesis of chemically defined drugs conjugation in which the site and stoichiometry of conjugation are controlled using a genetically encoded Q-tag peptide with specific amino acids which serves as a substrate of bacterial transglutaminase. This approach has enabled the generation of homogeneous conjugates with DAR 1,7 for full IgG and 0,8 drug ratio for Fab, scfv and VHH antibody fragments without the presence of significant amounts of unconjugated antibody and fragments. As a proof of concept, Q-tagged anti Her-2 (human IgG1 (Trastuzumab) and the corresponding fragments (Fab, scfv and VHH) were engineered and conjugated with different aminated-payloads. The corresponding Cov-ADCs were evaluated in series of in vitro and in vivo assays, demonstrating similar tumor cell killing potency as Trastuzumab emtansine (Kadcyla®) even with lower drug-to-antibody ratio (DAR).

Targeted drug delivery using nanobodies to deliver effective molecules to breast cancer cells: the most attractive application of nanobodies

Targeted drug delivery is one of the attractive ways in which cancer treatment can significantly reduce side effects. In the last two decades, the use of antibodies as a tool for accurate detection of cancer has been noted. On the other hand, the binding of drugs and carriers containing drugs to the specific antibodies of cancer cells can specifically target only these cells. However, the use of whole antibodies brings challenges, including their large size, the complexity of conjugation, the high cost of production, and the creation of immunogenic reactions in the body. The use of nanobodies, or VHHs, which are a small part of camel heavy chain antibodies, is very popular due to their small size, high craftsmanship, and low production cost. In this article, in addition to a brief overview of the structure and characteristics of nanobodies, the use of this molecule in the targeted drug delivery of breast cancer has been reviewed.

Oxime-Linked Peptide-Daunomycin Conjugates as Good Tools for Selection of Suitable Homing Devices in Targeted Tumor Therapy: An Overview

Chemotherapy is still one of the main therapeutic approaches in cancer therapy. Nevertheless, its poor selectivity causes severe toxic side effects that, together with the development of drug resistance in tumor cells, results in a limitation for its application. Tumor-targeted drug delivery is a possible choice to overcome these drawbacks. As well as monoclonal antibodies, peptides are promising targeting moieties for drug delivery. However, the development of peptide-drug conjugates (PDCs) is still a big challenge. The main reason is that the conjugates have to be stable in circulation, but the drug or its active metabolite should be released efficiently in the tumor cells. For this purpose, suitable linker systems are needed that connect the drug molecule with the homing peptide. The applied linker systems are commonly categorized as cleavable and non-cleavable linkers. Both the groups possess advantages and disadvantages that are summarized briefly in this manuscript. Moreover, in this review paper, we highlight the benefit of oxime-linked anthracycline-peptide conjugates in the development of PDCs. For instance, straightforward synthesis as well as a conjugation reaction proceed in excellent yields, and the autofluorescence of anthracyclines provides a good tool to select the appropriate homing peptides. Furthermore, we demonstrate that these conjugates can be used properly in in vivo studies. The results indicate that the oxime-linked PDCs are potential candidates for targeted tumor therapy.

The target atlas for antibody-drug conjugates across solid cancers

Antibody-Drug Conjugates (ADCs) represent a rapidly advancing category of oncology therapeutics, spanning the targeted therapy for both hematologic malignancies and solid cancers. A crucial aspect of ADC research involves the identification of optimal surface antigens that can effectively differentiate target cells from most mammalian cell types. Herein, we have devised an algorithm and compiled an extensive dataset annotating cell membrane proteins. This dataset is derived from comprehensive transcriptomic, proteomic, and genomic data encompassing 19 types of solid cancer as well as normal tissues. The aim is to uncover potential therapeutic surface antigens for precise ADC targeting. The resulting target landscape comprises 165 combinations of targets and indications, along with 75 candidates of cell surface proteins. Notably, 35 of these candidates possess characteristics suitable for ADC targeting, and have not been previously reported in ADC research and development. Additionally, we have identified a total of 159 ADCs from a pool of 760 clinical trials. Of these, 72 ADCs are presently undergoing interventional evaluation for a variety of solid cancer types, targeting 36 unique antigens. We conducted an analysis of their expression in normal tissues using this comprehensive annotation dataset, revealing a diverse range of profiles for the current ADC targets. Moreover, we emphasize that the biological impacts of target antigens have the potential to enhance their clinical effectiveness. We propose a comprehensive assessment of the drugability of target antigens, considering multiple facets. This study represents a thorough exploration of pan-cancer ADC targets over the past two decades, underscoring the potential of a comprehensive solid cancer target atlas to broaden the scope of ADC therapies.

Click chemistry in the synthesis of antibody-drug conjugates

Antibody-Drug Conjugates (ADC) are a new class of anticancer therapeutics with immense potential. They have been rapidly advancing in the last two decades. This fast speed of development has become possible due to several new technologies and methods. One of them is Click Chemistry, an approach that was created only two decades ago, but already is actively utilized for bioconjugation, material science and drug discovery. In this review, we researched the impact of Click Chemistry reactions on the synthesis and development of ADCs. The information about the most frequently utilized reactions, such as Michael's addition, Copper-catalyzed azide-alkyne [3+2] cycloaddition (CuAAC), Strain-promoted azide-alkyne [3+2] cycloaddition (SPAAC), oxime bond formation, hydrazine-iso-Pictet-Spengler Ligation (HIPS), Diels-Alder reactions have been summarized. The implementation of thiol-maleimide Click Chemistry reaction in the synthesis of numerous FDA-approved Antibody-Drug Conjugates has been reported. The data amassed in the present review provides better understanding of the importance of Click Chemistry in the synthesis, development and improvement of the Antibody-Drug Conjugates and it will be helpful for further researches related to ADCs.

Exploring the Sensitivity of Antibody-Drug Conjugate Efficacy to the Selection of Payload, Antibody, and Cell line

Antibody-drug conjugates (ADCs) make up a growing class of targeted therapeutics with important applications in cancer treatment. ADCs are highly modular in nature and thus can be engineered to target any cancer type, but their efficacy is strongly influenced by the specific choice of payload, antibody, and target cell. Considering the number of possible antibody-payload combinations, ADC development would benefit from an efficient method to narrow the number of ADC compositions to those with the highest and most universal potency prior to assessing pharmacokinetics and pharmacodynamics in animal models. To facilitate the identification of optimal ADC compositions, we describe the use of photoreactive antibody-binding domain-drug conjugates (known commercially as oYo-Link) to enable the site-specific labeling of off-the-shelf antibodies. This approach allows for the rapid generation of ADCs with a drug-to-antibody ratio of ∼2 with no subsequent purification required. As a demonstration of this approach, ADCs were generated with different combinations of tubulin-inhibitor drugs (DM1, DM4, VcMMAE, and VcMMAF) and anti-EGFR antibodies (cetuximab, panitumumab, anti-EGFR clone 425, and anti-EGFR clone 528) and were delivered to three EGFR-expressing cell lines (A431, A549, and MDA-MB-231). Real-time cytolysis assays indicated that the most effective antibody varied based on the choice of cell line: cetuximab was most potent against A431 cells, while 425 and 528 led to the greatest cytotoxicity against A549 and MDA-MB-231 cells. These results did not correlate with differences in measured anti-EGFR binding affinity as cetuximab had the highest affinity across all three cell lines, while 425 and 528 had the lowest affinities for all three cell lines. Panitumumab, which had the second-highest anti-EGFR affinity, exhibited the least effective cytolysis across A431, A549, and MDA-MB-231 cells. By demonstrating that ADC potency toward a given target is dependent on both the antibody and drug chosen, these findings can guide the selection of ADCs for further in vivo analysis.

Unnatural Amino Acid Engineering for Intracellular Delivery of Protein Therapeutics

Protein drugs are a critically important therapeutic modality due to the sophisticated binding recognition, catalytic properties, and disease relevance of proteins. There is a clear need for new strategies able to improve pharmacokinetics, bioavailability, and/or intracellular delivery of therapeutic proteins, as stability limitations have significantly hindered clinical advancement, and most proteins are membrane impermeable. Bioconjugation strategies able to site-specifically modify proteins with cell binding, and other ligands offer a particularly valuable approach to facilitate protein delivery due to the importance of ligand presentation on protein bioactivity and cellular uptake. We explored unnatural amino acid (UAA) incorporation as a novel strategy to tunably incorporate clustered cell-binding ligands in fluorescent proteins and suicide enzymes, resulting in substantial increases in cell-specific uptake and targeted cell-killing activity. These approaches offer a valuable and versatile method to modify a variety of proteins and enable improved clinical potential.

Affinity-Directed Site-Specific Protein Labeling and Its Application to Antibody-Drug Conjugates

Chemically modified proteins have diverse applications; however, conventional chemo-selective methods often yield heterogeneously labeled products. To address this limitation, site-specific protein labeling holds significant potential, driving extensive research in this area. Nevertheless, site-specific modification of native proteins remains challenging owing to the complexity of their functional groups. Therefore, a method for site-selective labeling of intact proteins is aimed to design. In this study, a novel approach to traceless affinity-directed intact protein labeling is established, which leverages small binding proteins and genetic code expansion technology. By applying this method, a site-specific antibody labeling with a drug, which leads to the production of highly effective antibody-drug conjugates specifically targeting breast cancer cell lines is achieved. This approach enables traceless conjugation of intact target proteins, which is a critical advantage in pharmaceutical applications. Furthermore, small helical binding proteins can be easily engineered for various target proteins, thereby expanding their potential applications in diverse fields. This innovative approach represents a significant advancement in site-specific modification of native proteins, including antibodies. It also bears immense potential for facilitating the development of therapeutic agents for various diseases.

Engineering Hepatitis B Virus (HBV) Protein Particles for Therapeutic Delivery

Nature provides an abundance of proteins whose structures and reactivity have been perfected through evolution to perform specific tasks necessary for biological function. The structural and functional properties of many natural proteins are quite valuable for the construction and customization of drug delivery vehicles. Self-assembling protein nanoparticle platforms are particularly useful scaffolds, as their multi-subunit designs allow the attachment of a high density of modifying molecules such as cell-binding ligands that provide avidity for targeting and facilitate encapsulation of large quantities of therapeutic payload. We explored SpyCatcher/SpyTag conjugation as a system to modify hepatitis B virus (HBV)-like particles (HBV VLPs). Using this simple decoration strategy, we demonstrated efficient and cell-selective killing of inflammatory breast cancer cells via delivery of yeast cytosine deaminase suicide enzymes combined with 5-fluoro-cytosine prodrugs.

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.

Production of antibodies and antibody fragments containing non-natural amino acids in Escherichia coli

Therapeutic bioconjugates are emerging as an essential tool to combat human disease. Site-specific conjugation technologies are widely recognized as the optimal approach for producing homogeneous drug products. Non-natural amino acid (nnAA) incorporation allows the introduction of bioconjugation handles at genetically defined locations. Escherichia coli (E. coli) is a facile host for therapeutic nnAA protein synthesis because it can stably replicate plasmids encoding genes for product and nnAA incorporation. Here, we demonstrate that by engineering E. coli to incorporate high levels of nnAAs, it is feasible to produce nnAA-containing antibody fragments and full-length immunoglobulin Gs (IgGs) in the cytoplasm of E. coli. Using high-density fermentation, it was possible to produce both of these types of molecules with site-specifically incorporated nnAAs at titers > 1 g/L. We anticipate this strategy will help simplify the production and manufacture of promising antibody therapeutics.

An overview of site-specific methods for achieving antibody drug conjugates with homogenous drug to antibody ratio

INTRODUCTION

Antibody drug conjugates (ADCs) have emerged as a potent tool in cancer treatment, where cytotoxic drugs are linked to antibodies targeting specific antigens. While conventional ADC synthesis methods have seen success as commercials therapeutics, there is a growing interest in next-generation ADCs, looking at homogeneity of the drug-to-antibody ratio.

AREAS COVERED

The article provides a high-level overview for achieving said homogeneity by site-directed conjugations via encompassing engineered amino acids, enzyme-mediated strategies, peptide sequences, affinity peptides, and beyond. As the field rapidly evolves with multiple ADCs in clinical trials and the advent of biosimilars, the article explores the benefits and challenges in both conventional and non-platform ADC technologies.

EXPERT OPINION

The choice of site selection approach must be based on multiple criteria as discussed in this report. Two ADCs made from conjugation to engineered cysteines have been approved by regulatory agencies which have contributed to the excitement in this space. For the others, though successful as proof-of-concept, the true test of merit will be determined as these technologies advance into the clinic. The promise of improving the therapeutics index and decreasing toxicities will continue to drive progress in this area.

Unleashing the Potential: Designing Antibody-Targeted Lipid Nanoparticles for Industrial Applications with CMC Considerations and Clinical Outlook

Antibody-targeted lipid nanoparticles (Ab-LNPs) are rapidly gaining traction as multifaceted platforms in precision medicine, adept at delivering a diverse array of therapeutic agents, including nucleic acids and small molecules. This review provides an incisive overview of the latest developments in the field of Ab-LNP technology, with a special emphasis on pivotal design aspects such as antibody engineering, bioconjugation strategies, and advanced formulation techniques. Furthermore, it addresses critical chemistry, manufacturing, and controls (CMC) considerations and thoroughly examines the in vivo dynamics of Ab-LNPs, underscoring their promising potential for clinical application. By seamlessly blending scientific advancements with practical industrial perspectives, this review casts a spotlight on the burgeoning role of Ab-LNPs as an innovative and potent tool in the realm of targeted drug delivery.

Truncation-Free Genetic Code Expansion with Tetrazine Amino Acids for Quantitative Protein Ligations

Quantitative labeling of biomolecules is necessary to advance areas of antibody-drug conjugation, super-resolution microscopy imaging of molecules in live cells, and determination of the stoichiometry of protein complexes. Bio-orthogonal labeling to genetically encodable noncanonical amino acids (ncAAs) offers an elegant solution; however, their suboptimal reactivity and stability hinder the utility of this method. Previously, we showed that encoding stable 1,2,4,5-tetrazine (Tet)-containing ncAAs enables rapid, complete conjugation, yet some expression conditions greatly limited the quantitative reactivity of the Tet-protein. Here, we demonstrate that reduction of on-protein Tet ncAAs impacts their reactivity, while the leading cause of the unreactive protein is near-cognate suppression (NCS) of UAG codons by endogenous aminoacylated tRNAs. To overcome incomplete conjugation due to NCS, we developed a more catalytically efficient tRNA synthetase and developed a series of new machinery plasmids harboring the aminoacyl tRNA synthetase/tRNA pair (aaRS/tRNA pair). These plasmids enable robust production of homogeneously reactive Tet-protein in truncation-free cell lines, eliminating the contamination caused by NCS and protein truncation. Furthermore, these plasmid systems utilize orthogonal synthetic origins, which render these machinery vectors compatible with any common expression system. Through developing these new machinery plasmids, we established that the aaRS/tRNA pair plasmid copy-number greatly affects the yields and quality of the protein produced. We then produced quantitatively reactive soluble Tet-Fabs, demonstrating the utility of this system for rapid, homogeneous conjugations of biomedically relevant proteins.

Introduction of Carbonyl Groups into Antibodies

Antibodies and their derivatives (scFv, Fabs, etc.) represent a unique class of biomolecules that combine selectivity with the ability to target drug delivery. Currently, one of the most promising endeavors in this field is the development of molecular diagnostic tools and antibody-based therapeutic agents, including antibody-drug conjugates (ADCs). To meet this challenge, it is imperative to advance methods for modifying antibodies. A particularly promising strategy involves the introduction of carbonyl groups into the antibody that are amenable to further modification by biorthogonal reactions, namely aliphatic, aromatic, and α-oxo aldehydes, as well as aliphatic and aryl-alkyl ketones. In this review, we summarize the preparation methods and applications of site-specific antibody conjugates that are synthesized using this approach.

Development of Multivalent Conjugates with a Single Non-Canonical Amino Acid

Proteins represent powerful biomacromolecules due to their unique functionality and broad utility both in the cell and in non-biological applications. The genetic encoding of non-canonical amino acids (ncAAs) facilitates functional diversification of these already powerful proteins. Specifically, ncAAs have been demonstrated to provide unique functional handles to bioorthogonally introduce novel functionality via conjugation reactions. Herein we examine the ability of a single ncAA to serve as a handle to generate multivalent bioconjugates to introduce two or more additional components to a protein, yielding a multivalent conjugate. To accomplish this aim, p-bromopropargyloxyphenyalanine (pBrPrF) was genetically encoded into both superfolder green fluorescent protein (sfGFP) and ubiquitin model proteins to serve as a conjugation handle. A sequential bioconjugation sequence involving a copper-assisted cycloaddition reaction coupled with a subsequent Sonogashira cross-coupling was then optimized. The linkage of two additional molecules to the model protein via these reactions yielded the desired multivalent bioconjugate. This domino approach using a single ncAA has a plethora of applications in both therapeutics and diagnostics as multiple unique moieties can be introduced into proteins in a highly controlled fashion.

Use of non-canonical amino acids in genetic code expansion-based therapeutics: Effects on mouse gut microbiota

Vaccines and cell therapeutics based on genetic code expansion are emerging. A crucial step in these therapeutic technologies is the oral administration of non-canonical amino acids (ncAAs) to control pathogen growth and therapeutic protein levels in vivo. Investigating the toxicity effects of ncAAs can help identify more suitable candidates for developing genetic code expansion-based vaccines and cell therapeutics. In this study, we determined the effects of three ncAAs, namely, 4-acetyl-phenylalanine (pAcF), 4-iodo-phenylalanine (pIoF), and 4-methoxy-phenylalanine (pMeoF), commonly used in genetic code expansion-based vaccines and cell therapeutics, on the main organs, serum biochemical parameters, and gut microbiota in mice. We observed that pIoF and pMeoF significantly altered serum biochemical parameters to some extent. Moreover, the alterations in the mouse gut microbial composition were considerably greater after the oral administration of pIoF and pMeoF than after that of pAcF, compared with that in the control mice. These findings suggest that pAcF is more suitable than pIoF and pMeoF for application in genetic code expansion-based vaccines and cell therapeutics as it disturbs the physiological and gut microecological balance in mice to a lesser extent.

Dual stop codon suppression in mammalian cells with genomically integrated genetic code expansion machinery

Stop codon suppression using dedicated tRNA/aminoacyl-tRNA synthetase (aaRS) pairs allows for genetically encoded, site-specific incorporation of non-canonical amino acids (ncAAs) as chemical handles for protein labeling and modification. Here, we demonstrate that piggyBac-mediated genomic integration of archaeal pyrrolysine tRNA (tRNAPyl)/pyrrolysyl-tRNA synthetase (PylRS) or bacterial tRNA/aaRS pairs, using a modular plasmid design with multi-copy tRNA arrays, allows for homogeneous and efficient genetically encoded ncAA incorporation in diverse mammalian cell lines. We assess opportunities and limitations of using ncAAs for fluorescent labeling applications in stable cell lines. We explore suppression of ochre and opal stop codons and finally incorporate two distinct ncAAs with mutually orthogonal click chemistries for site-specific, dual-fluorophore labeling of a cell surface receptor on live mammalian cells.

The Evolving Landscape of Antibody-Drug Conjugates: In Depth Analysis of Recent Research Progress

Antibody-drug conjugates (ADCs) are targeted immunoconjugate constructs that integrate the potency of cytotoxic drugs with the selectivity of monoclonal antibodies, minimizing damage to healthy cells and reducing systemic toxicity. Their design allows for higher doses of the cytotoxic drug to be administered, potentially increasing efficacy. They are currently among the most promising drug classes in oncology, with efforts to expand their application for nononcological indications and in combination therapies. Here we provide a detailed overview of the recent advances in ADC research and consider future directions and challenges in promoting this promising platform to widespread therapeutic use. We examine data from the CAS Content Collection, the largest human-curated collection of published scientific information, and analyze the publication landscape of recent research to reveal the exploration trends in published documents and to provide insights into the scientific advances in the area. We also discuss the evolution of the key concepts in the field, the major technologies, and their development pipelines with company research focuses, disease targets, development stages, and publication and investment trends. A comprehensive concept map has been created based on the documents in the CAS Content Collection. We hope that this report can serve as a useful resource for understanding the current state of knowledge in the field of ADCs and the remaining challenges to fulfill their potential.

Site-specific protein conjugates incorporating Para-Azido-L-Phenylalanine for cellular and in vivo imaging

This work features the use of amber suppression-mediated unnatural amino acid (UAA) incorporation into proteins for various imaging purposes. The site-specific incorporation of the UAA, p-azido-L-phenylalanine (pAzF), provides an azide handle that can be used to complete the strain promoted azide-alkyne click cycloaddition (SPAAC) reaction to introduce an imaging modality such as a fluorophore or a positron emission tomography (PET) tracer on the protein of interest (POI). Such methodology can be pursued directly in mammalian cell lines or on proteins expressed in vitro, thereby conferring a homogeneous pool of protein conjugates. A general procedure for UAA incorporation to use with a site-specific protein labeling method is provided allowing for in vitro and in vivo imaging applications based on the representative proteins PTEN and PD-L1. This approach would help elucidate the cellular or in vivo biological activities of the POI.

Organic-Solvent-Free "Lego-Like" Modular Preparation of Fab-Nondestructive Antibody-Drug Conjugates with Ultrahigh Drug-to-Antibody Ratio

Antibody-drug conjugates (ADCs) have exciting possibilities in targeted tumor therapy. However, in the existing ADC preparation processes, the random attachment of the payloads to the antigen-binding fragments (Fab) greatly increases the risk of disrupting its antigen recognition ability, while the drug-antibody ratio (DAR) is low, leading to a cumbersome preparation process and low drug delivery efficiency. Herein, poly(glutamic acid) is used to expand the number of drug binding sites, based on the "click chemistry" of azide and DBCO, and the high affinity of Fc-III-4C peptide to the crystalline fragment (Fc) of the monoclonal antibodies. Various antibody-polymer-drug conjugates are obtained with ultrahigh DAR using this organic-solvent-free "Lego-like" modular construction. Among them, aHER2-P-MMAE with DAR of 41.6 achieves tumor growth inhibition (TGI) of 99.7% for both medium-sized and large SKOV-3 ovarian tumors, and aPDL1-P-MMAE (DAR = 40.7) achieves TGI of 98.5% for MC38 colon tumors. In summary, a universal platform is created to prepare Fab-nondestructive ADCs with ultrahigh DAR, which can be used to develop precision medicine for personalized anticancer therapy.

Remodeling the cellular stress response for enhanced genetic code expansion in mammalian cells

Genetic code expansion (GCE) reprograms the translational machinery to site-specifically incorporate noncanonical amino acids (ncAAs) into a selected protein. The efficiency of GCE in mammalian cells might be compromised by cellular stress responses, among which, the protein kinase R(PKR)-dependent eIF2α phosphorylation pathway can reduce translation rates. Here we test several strategies to engineer the eIF2α pathway and boost the rate of translation and show that such interventions increase GCE efficiency in mammalian cells. In particular, addition of the N-terminal PKR fragment (1-174) provides a substantial enhancement in cytoplasmic GCE and also in GCE realized by OTOs (orthogonally translating designer organelles), which built on the principle of 2D phase separation to enable mRNA-selective ncAA incorporation. Our study demonstrates an approach for improving the efficiency of GCE and provides a means by which the power of designer organelles can be further optimized to tune protein translation.

A disruptive clickable antibody design for the generation of antibody-drug conjugates

Background

Antibody-drug conjugates are cancer therapeutics that combine specificity and toxicity. A highly cytotoxic drug is covalently attached to an antibody that directs it to cancer cells. The conjugation of the drug-linker to the antibody is a key point in research and development as well as in industrial production. The consensus is to conjugate the drug to a surface-exposed part of the antibody to ensure maximum conjugation efficiency. However, the hydrophobic nature of the majority of drugs used in antibody-drug conjugates leads to an increased hydrophobicity of the generated antibody-drug conjugates, resulting in higher liver clearance and decreased stability.

Methods

In contrast, we describe a non-conventional approach in which the drug is conjugated in a buried part of the antibody. To achieve this, a ready-to-click antibody design was created in which an azido-based non-canonical amino acid is introduced within the Fab cavity during antibody synthesis using nonsense suppression technology. The Fab cavity was preferred over the Fc cavity to circumvent issues related to cleavage of the IgG1 lower hinge region in the tumor microenvironment.

Results

This antibody design significantly increased the hydrophilicity of the generated antibody-drug conjugates compared to the current best-in-class designs based on non-canonical amino acids, while conjugation efficiency and functionality were maintained. The robustness of this native shielding effect and the versatility of this approach were also investigated.

Conclusions

This pioneer design may become a starting point for the improvement of antibody-drug conjugates and an option to consider for protecting drugs and linkers from unspecific interactions.

Investigation of High Molecular Weight Size Variant Formation in Antibody-Drug Conjugates: Microbial Transglutaminase-Mediated Crosslinking

Microbial transglutaminase (mTG) has become a powerful tool for manufacturing antibody-drug conjugates (ADCs). It enables site-specific conjugation by catalyzing formation of stable isopeptide bond between glutamine (Q) side chain and primary amine. However, the downstream impact of mTG-mediated conjugation on ADC product quality, especially on high molecular weight (HMW) size variant formation has not been studied in a systematic manner. This study investigates the mechanisms underlying the formation of HMW size variants in mTG-mediated ADCs using size exclusion chromatography (SEC) and liquid chromatography-mass spectrometry (LC-MS). Our findings revealed that the mTG-mediated glutamine and lysine (K) crosslinking is the primary source of the increased level of HMW size variants in the ADCs. In the study, two monoclonal antibodies (mAbs) with glutamine engineered for site-specific conjugation were used as model systems. Based on the LC-MS analysis, a single lysine (K56) in the heavy chain (HC) was identified as the major Q-K crosslinking site in one of the two mAbs. The HC C-terminal K was observed to crosslink to the target Q in both mAbs. Quantitative correlation was established between the percentage of HMW size variants determined by SEC and the percentage of crosslinked peptides quantified by MS peptide mapping. Importantly, it was demonstrated that the level of HMW size variants in the second ADC was substantially reduced by the complete removal of HC C-terminal K before conjugation. The current work demonstrates that crosslinking and other side reactions during mTG-mediated conjugation needs to be carefully monitored and controlled to ensure process consistency and high product quality of the final ADC drug product.

Studying Intermolecular Interactions in an Antibody-Drug Conjugate Through Chemical Screening and Computational Modeling

Antibody-drug conjugates (ADCs) combine the selectivity of antibodies with the cytotoxicity of drug payloads to yield highly targeted and potent therapeutics. Owing to the need to chemically modify residues for attachment of the payload and their more complex structure compared to either component alone, ADCs can present additional challenges related to stability of the final drug product. Here, we report for the first time the use of high-throughput experimental screens and computational techniques to tune the conformational and colloidal behavior of a monomethyl auristatin F-based ADC. The ADC, which exhibits high opalescence with strongly attractive protein-protein interactions, is transformed into a more stable structure by experimentally traversing a library of more than ∼100 formulations. A significant reduction in turbidity and increase in diffusion interaction parameter is observed by varying properties such as pH and ionic strength. Computational modeling rationalized these changes and pointed to the presence of attractive electrostatic interactions between ADC molecules facilitated by the drug payload and histidine residues. Taken together, the experimental and computational work presented provides a general roadmap of studies to perform during ADC development to find stable formulations, while the mechanistic learnings can be applied towards the design and stabilization of other IgG1-based ADCs.

Probing the Internalization and Efficacy of Antibody-Drug Conjugate via Site-Specific Fc-Glycan Labelling of a Homogeneous Antibody Targeting SSEA-4 Bearing Tumors

Antibody drug conjugates (ADC) are an emerging class of pharmaceuticals consisting of cytotoxic agents covalently attached to an antibody designed to target a specific cancer cell surface molecule followed by internalization and intracellular release of payload to exhibit its anticancer activity. Targeted delivery of cytotoxic payload to a variety of specific cells has been demonstrated to have significant enhancement in clinical efficacy and dramatic reduction in off-target toxicity. Site-specific conjugation of payload to the antibody is highly desirable for development of ADC with well-defined antibody-to-drug ratio, enhanced internalization, reduced toxicity, improved stability, desired pharmacological profile and optimal therapeutic index. Here, we reported a site-specific conjugation strategy for evaluation of antibody internalization and efficacy of ADC designed to target SSEA4 on solid tumors. This strategy stems from the azido-fucose tag of a homogeneous antibody Fc-glycan generated via in vitro glycoengineering approach for site-specific conjugation and optimization of antibody-drug ratio to exhibit optimal efficacy. The ADC consisting of a chimeric anti-SSEA4 antibody chMC813-70, conjugated to the antineo-plastic agent monomethyl auristatin E via both cleavable and non-cleavable linkers showed excellent cytotoxicity profile towards SSEA4-bearing cancer cells. A clear distinction in cytotoxicity was observed among cancer cells with different SSEA4 expression levels.

Engineering protein-based therapeutics through structural and chemical design

Protein-based therapeutics have led to new paradigms in disease treatment. Projected to be half of the top ten selling drugs in 2023, proteins have emerged as rivaling and, in some cases, superior alternatives to historically used small molecule-based medicines. This review chronicles both well-established and emerging design strategies that have enabled this paradigm shift by transforming protein-based structures that are often prone to denaturation, degradation, and aggregation in vitro and in vivo into highly effective therapeutics. In particular, we discuss strategies for creating structures with increased affinity and targetability, enhanced in vivo stability and pharmacokinetics, improved cell permeability, and reduced amounts of undesired immunogenicity.

Genetic Code Expansion for Site-Specific Labeling of Antibodies with Radioisotopes

Due to their target specificity, antibody-drug conjugates─monoclonal antibodies conjugated to a cytotoxic moiety─are efficient therapeutics that can kill malignant cells overexpressing a target gene. Linking an antibody with radioisotopes (radioimmunoconjugates) enables powerful diagnostics and/or closely related therapeutic applications, depending on the isotope. To generate site-specific radioimmunoconjugates, we utilized genetic code expansion and subsequent conjugation by inverse electron-demand Diels-Alder cycloaddition reactions. We show that, using this approach, site-specific labeling of trastuzumab with either zirconium-89 (89Zr) for diagnostics or lutetium-177 (177Lu) for therapeutics yields efficient radioimmunoconjugates. Positron emission tomography imaging revealed a high accumulation of site-specifically 89Zr-labeled trastuzumab in tumors after 24 h and low accumulation in other organs. The corresponding 177Lu-trastuzumab radioimmunoconjugates were comparably distributed in vivo.

Aminooxy Click Modification of a Periodate-Oxidized Immunoglobulin G: A General Approach to Antibody-Drug Conjugates with Dye-Mediated Expeditious Stoichiometry Control

A universal approach to the construction of antibody-drug conjugates (ADCs) has been developed. It relies on periodate oxidation of naturally present glycans of immunoglobulin G, followed by oxime ligation and, optionally, copper(I)-catalyzed alkyne-azide cycloaddition for conjugation with a toxic payload. The introduction of highly absorbing cyanine dyes into the linker allows for facile determination of the drug-antibody ratio. We applied this methodology to the synthesis of cytotoxic conjugates of an antibody against the tumor-associated antigen PRAME with doxorubicin and monomethyl auristatin E (MMAE). The resultant conjugates retained their affinity to a large extent, yet their cytotoxicity in vitro varied dramatically: while the doxorubicin-based conjugate did not produce any effect on cells, the MMAE-based one demonstrated specific activity against PRAME-expressing cancer cell lines. Importantly, the latter conjugate constitutes the first reported example of a PRAME-targeting ADC.

Monoclonal antibodies in breast cancer: A critical appraisal

In breast cancer, mAbs can play multifunctional roles like targeting cancer cells, sometimes directly attacking them, helping in locating and delivering therapeutic drugs to targets, inhibiting cell growth and blocking immune system inhibitors, etc. Monoclonal antibodies are also one of the important successful treatment strategies especially against HER2 but they have not been explored much for other types of breast cancers especially in triple negative breast cancers. Monoclonal antibodies impact the feasibility of antigen specificity, bispecific and trispecific mAbs have opened new doors for more targeted specific efficacy. Monoclonal antibodies can be used diversly and with efficacy as compared to other methods of treatment thus maining it a suitable candidate for breast cancer treatment. However, mAbs treatment also causes various side effects such as fever, trembling, fatigue, headache and muscle pain, nausea/vomiting, difficulty in breathing, rashes and bleeding. Understanding the pros and cons of this strategy, we have explored in this review, the current and future potential capabilities of monoclonal antibodies with respect to diagnosis and treatment of breast cancer. DATA AVAILABILITY: Not applicable.

A comprehensive review of key factors affecting the efficacy of antibody drug conjugate

Antibody Drug Conjugate (ADC) is an emerging technology to overcome the limitations of chemotherapy by selectively targeting the cancer cells. ADC binds with an antigen, specifically over expressed on the surface of cancer cells, results decrease in bystander effect and increase in therapeutic index. The potency of an ideal ADC is entirely depending on several physicochemical factors such as site of conjugation, molecular weight, linker length, Steric hinderance, half-life, conjugation method, binding energy and so on. Inspite of the fact that there is more than 100 of ADCs are in clinical trial only 14 ADCs are approved by FDA for clinical use. However, to design an ideal ADC is still challenging and there is much more to be done. Here in this review, we have discussed the key components along with their significant role or contribution towards the efficacy of an ADC. Moreover, we also explained about the recent advancement in the conjugation method. Additionally, we spotlit the mode of action of an ADC, recent challenges, and future perspective regarding ADC. The profound knowledge regarding key components and their properties will help in the synthesis or production of different engineered ADCs. Therefore, contributes to develop an ADC with low safety concern and high therapeutic index. We hope this review will improve the understanding and encourage the practicing of research in anticancer ADCs development.

Noncanonical amino acids as doubly bio-orthogonal handles for one-pot preparation of protein multiconjugates

Genetic encoding of noncanonical amino acid (ncAA) for site-specific protein modification has been widely applied for many biological and therapeutic applications. To efficiently prepare homogeneous protein multiconjugates, we design two encodable noncanonical amino acids (ncAAs), 4-(6-(3-azidopropyl)-s-tetrazin-3-yl) phenylalanine (pTAF) and 3-(6-(3-azidopropyl)-s-tetrazin-3-yl) phenylalanine (mTAF), containing mutually orthogonal and bioorthogonal azide and tetrazine reaction handles. Recombinant proteins and antibody fragments containing the TAFs can easily be functionalized in one-pot reactions with combinations of commercially available fluorophores, radioisotopes, PEGs, and drugs in a plug-and-play manner to afford protein dual conjugates to assess combinations of tumor diagnosis, image-guided surgery, and targeted therapy in mouse models. Furthermore, we demonstrate that simultaneously incorporating mTAF and a ketone-containing ncAA into one protein via two non-sense codons allows preparation of a site-specific protein triconjugate. Our results demonstrate that TAFs are doubly bio-orthogonal handles for efficient and scalable preparation of homogeneous protein multiconjugates.

Ferritin-based nanomedicine for disease treatment

Ferritin is an endogenous protein which is self-assembled by 24 subunits into a highly uniform nanocage structure. Due to the drug-encapsulating ability in the hollow inner cavity and abundant modification sites on the outer surface, ferritin nanocage has been demonstrated great potential to become a multi-functional nanomedicine platform. Its good biocompatibility, low toxicity and immunogenicity, intrinsic tumor-targeting ability, high stability, low cost and massive production, together make ferritin nanocage stand out from other nanocarriers. In this review, we summarized ferritin-based nanomedicine in field of disease diagnosis, treatment and prevention. The different types of drugs to be loaded in ferritin, as well as drug-loading methods were classified. The strategies for site-specific and non-specific functional modification of ferritin were investigated, then the application of ferritin for disease imaging, drug delivery and vaccine development were discussed. Finally, the challenges restricting the clinical translation of ferritin-based nanomedicines were analyzed.

Engineered, Scalable Production of Optically Pure l-Phenylalanines Using Phenylalanine Ammonia-Lyase from Arabidopsis thaliana

An efficient preparative-scale synthetic procedure of l-phenylalanine derivatives has been developed using mutant variants of phenylalanine ammonia-lyase from Arabidopsis thaliana (AtPAL). After rigorous reaction engineering, the AtPAL-catalyzed hydroamination reaction of cinnamic acids provided several unnatural amino acids of high synthetic value, such as (S)-m- and (S)-p-methoxyphenylalanine; (S)-o- and (S)-m-methylphenylalanine; and (S)-o- and (S)-p-bromophenylalanine at preparative scale, significantly surpassing the catalytic efficiency in terms of conversions and yields of the previously reported PcPAL-based biotransformations. The AtPAL variants tolerated high substrate and product concentrations, representing an important extension of the PAL-toolbox, while the engineered biocatalytic procedures of improved E-factor and space-time yields fulfill the requirements of sustainable and green chemistry, providing facile access to valuable amino acid building blocks.

Site-Specific Antibody Conjugation with Payloads beyond Cytotoxins

As antibody-drug conjugates have become a very important modality for cancer therapy, many site-specific conjugation approaches have been developed for generating homogenous molecules. The selective antibody coupling is achieved through antibody engineering by introducing specific amino acid or unnatural amino acid residues, peptides, and glycans. In addition to the use of synthetic cytotoxins, these novel methods have been applied for the conjugation of other payloads, including non-cytotoxic compounds, proteins/peptides, glycans, lipids, and nucleic acids. The non-cytotoxic compounds include polyethylene glycol, antibiotics, protein degraders (PROTAC and LYTAC), immunomodulating agents, enzyme inhibitors and protein ligands. Different small proteins or peptides have been selectively conjugated through unnatural amino acid using click chemistry, engineered C-terminal formylglycine for oxime or click chemistry, or specific ligation or transpeptidation with or without enzymes. Although the antibody protamine peptide fusions have been extensively used for siRNA coupling during early studies, direct conjugations through engineered cysteine or lysine residues have been demonstrated later. These site-specific antibody conjugates containing these payloads other than cytotoxic compounds can be used in proof-of-concept studies and in developing new therapeutics for unmet medical needs.

A New Unnatural Amino Acid Derived from the Modification of 4′-(p-tolyl)-2,2′:6′,2″-terpyridine and Its Mixed-Ligand Complexes with Ruthenium: Synthesis, Characterization, and Photophysical Properties

The modification of the methyl group of 4′-(p-tolyl)-2,2′:6′,2″-terpyridine produced the novel unnatural amino acid 3-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)-2-aminopropanoic acid (phet). Mononuclear heteroleptic ruthenium complexes of the general formulae [Ru(L1)(L2)](PF6)2 (L1 = 2-acetylamino-2-(4-[2,2′:6′,2″]terpyridine-4′-yl-benzyl)-malonic acid diethyl ester, (phem), 3-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)-2-aminopropanoic acid, (phet), and L2 = 2,2′:6′,2″-terpyridine (tpy), 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy), 4′-(p-tolyl)-2,2′:6′,2″-terpyridine (mptpy)), as well as the homoleptic [Ru(phem)2](PF6)2 and [Ru(phet)2](PF6)2, were synthesized and characterized by means of NMR spectroscopic techniques, elemental analysis, and high-resolution mass spectrometry. The photophysical properties of the synthesized complexes were also studied.