N-terminal selective conjugation method widens the therapeutic window of antibody-drug conjugates by improving tolerability and stability

Spotlight on ideal target antigens and resistance in antibody-drug conjugates: Strategies for competitive advancement

Antibody-drug conjugates (ADCs) represent a novel and promising approach in targeted therapy, uniting the specificity of antibodies that recognize specific antigens with payloads, all connected by the stable linker. These conjugates combine the best targeted and cytotoxic therapies, offering the killing effect of precisely targeting specific antigens and the potent cell-killing power of small molecule drugs. The targeted approach minimizes the off-target toxicities associated with the payloads and broadens the therapeutic window, enhancing the efficacy and safety profile of cancer treatments. Within precision oncology, ADCs have garnered significant attention as a cutting-edge research area and have been approved to treat a range of malignant tumors. Correspondingly, the issue of resistance to ADCs has gradually come to the fore. Any dysfunction in the steps leading to the ADCs' action within tumor cells can lead to the development of resistance. A deeper understanding of resistance mechanisms may be crucial for developing novel ADCs and exploring combination therapy strategies, which could further enhance the clinical efficacy of ADCs in cancer treatment. This review outlines the brief historical development and mechanism of ADCs and discusses the impact of their key components on the activity of ADCs. Furthermore, it provides a detailed account of the application of ADCs with various target antigens in cancer therapy, the categorization of potential resistance mechanisms, and the current state of combination therapies. Looking forward, breakthroughs in overcoming technical barriers, selecting differentiated target antigens, and enhancing resistance management and combination therapy strategies will broaden the therapeutic indications for ADCs. These progresses are anticipated to advance cancer treatment and yield benefits for patients.

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).

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.

Antibody drug conjugates as targeted cancer therapy: past development, present challenges and future opportunities

Antibody drug conjugates (ADCs) are promising cancer therapeutics with minimal toxicity as compared to small cytotoxic molecules alone and have shown the evidence to overcome resistance against tumor and prevent relapse of cancer. The ADC has a potential to change the paradigm of cancer chemotherapeutic treatment. At present, 13 ADCs have been approved by USFDA for the treatment of various types of solid tumor and haematological malignancies. This review covers the three structural components of an ADC-antibody, linker, and cytotoxic payload-along with their respective structure, chemistry, mechanism of action, and influence on the activity of ADCs. It covers comprehensive insight on structural role of linker towards efficacy, stability & toxicity of ADCs, different types of linkers & various conjugation techniques. A brief overview of various analytical techniques used for the qualitative and quantitative analysis of ADC is summarized. The current challenges of ADCs, such as heterogeneity, bystander effect, protein aggregation, inefficient internalization or poor penetration into tumor cells, narrow therapeutic index, emergence of resistance, etc., are outlined along with recent advances and future opportunities for the development of more promising next-generation ADCs.

N-Terminal Modification of Gly-His-Tagged Proteins with Azidogluconolactone

Site-specific protein modifications are vital for biopharmaceutical drug development. Gluconoylation is a non-enzymatic, post-translational modification of N-terminal HisTags. We report high-yield, site-selective in vitro α-aminoacylation of peptides, glycoproteins, antibodies, and virus-like particles (VLPs) with azidogluconolactone at pH 7.5 in 1 h. Conjugates slowly hydrolyse, but diol-masking with borate esters inhibits reversibility. In an example, we multimerise azidogluconoylated SARS-CoV-2 receptor-binding domain (RBD) onto VLPs via click-chemistry, to give a COVID-19 vaccine. Compared to yeast antigen, HEK-derived RBD was immunologically superior, likely due to observed differences in glycosylation. We show the benefits of ordered over randomly oriented multimeric antigen display, by demonstrating single-shot seroconversion and best virus-neutralizing antibodies. Azidogluconoylation is simple, fast and robust chemistry, and should accelerate research and development.