Thermostability detection and optimization of glycoengineered antibodies and antibody-drug conjugates based on differential scanning flouremitry analysis

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

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

Establishing a Cell-Free Glycoprotein Synthesis System for Enzymatic N-GlcNAcylation

N-linked glycosylation plays a key role in the efficacy of many therapeutic proteins. One limitation to the bacterial glycoengineering of human N-linked glycans is the difficulty of installing a single N-acetylglucosamine (GlcNAc), the reducing end sugar of many human-type glycans, onto asparagine in a single step (N-GlcNAcylation). Here, we develop an in vitro method for N-GlcNAcylating proteins using the oligosaccharyltransferase PglB from Campylobacter jejuni. We use cell-free protein synthesis (CFPS) to test promiscuous PglB variants previously reported in the literature for the ability to produce N-GlcNAc and successfully determine that PglB with an N311V mutation (PglBN311V) exhibits increased GlcNAc transferase activity relative to the wild-type enzyme. We then improve the transfer efficiency by producing CFPS extracts enriched with PglBN311V and further optimize the reaction conditions, achieving a 98.6 ± 0.5% glycosylation efficiency. We anticipate this method will expand the glycoengineering toolbox for therapeutic research and biomanufacturing.

Comparison of "framework Shuffling" and "CDR Grafting" in humanization of a PD-1 murine antibody

Introduction

Humanization is typically adopted to reduce the immunogenicity of murine antibodies generated by hybridoma technology when used in humans.

Methods

Two different strategies of antibody humanization are popularly employed, including "complementarity determining region (CDR) grafting" and "framework (FR) shuffling" to humanize a murine antibody against human programmed death-1 (PD-1), XM PD1. In CDR-grafting humanization, the CDRs of XM PD-1, were grafted into the human FR regions with high homology to the murine FR counterparts, and back mutations of key residues were performed to retain the antigen-binding affinities. While in FR-shuffling humanization, a combinatorial library of the six murine CDRs in-frame of XM PD-1 was constructed to a pool of human germline FRs for high-throughput screening for the most favorable variants. We evaluated many aspects which were important during antibody development of the molecules obtained by the two methods, including antibody purity, thermal stability, binding efficacy, predicted humanness, and immunogenicity, along with T cell epitope prediction for the humanized antibodies.

Results

While the ideal molecule was not achieved through CDR grafting in this particular instance, FR-shuffling proved successful in identifying a suitable candidate. The study highlights FR-shuffling as an effective complementary approach that potentially increases the success rate of antibody humanization. It is particularly noted for its accessibility to those with a biological rather than a computational background.

Discussion

The insights from this comparison are intended to assist other researchers in selecting appropriate humanization strategies for drug development, contributing to broader application and understanding in the field.

Mono-amino acid linkers enable highly potent small molecule-drug conjugates by conditional release

The endosome cleavable linkers have been widely employed by antibody-drug conjugates and small molecule-drug conjugates (SMDCs) to control the accurate release of payloads. An effective linker should provide stability in systemic circulation but efficient payload release at its targeted tumor sites. This conflicting requirement always leads to linker design with increasing structural complexity. Balance of the effectiveness and structural complexity presents a linker design challenge. Here, we explored the possibility of mono-amino acid as so far the simplest cleavable linker (X-linker) for SMDC-based auristatin delivery. Within a diverse set of X-linkers, the SMDCs differed widely in bioactivity, with one (Asn-linker) having significantly improved potency (IC50 = 0.1 nM) and fast response to endosomal cathepsin B cleavage. Notably, this SMDC, once grafted with effector protein fragment crystallizable (Fc), demonstrated a profound in vivo therapeutic effect in aspects of targetability, circulation half-life (t1/2 = 73 h), stability, and anti-tumor efficacy. On the basis of these results, we believe that this mono-amino acid linker, together with the new SMDC-Fc scaffold, has significant potential in targeted delivery application.

Chemoselective Methionine Labelling of Recombinant Trastuzumab Shows High In Vitro and In Vivo Tumour Targeting

A highly effective 2-step system for site-specific antibody modification and conjugation of the monoclonal antibody Herceptin (commercially available under Trastuzumab) in a cysteine-independent manner was used to generate labelled antibodies for in vivo imaging. The first step contains redox-activated chemical tagging (ReACT) of thioethers via engineered methionine residues to introduce specific alkyne moieties, thereby offering a novel easy way to fundamentally change the process of antibody bioconjugation. The second step involves modification of the introduced alkyne via azide-alkyne cycloaddition 'click' conjugation. The versatility of this 2-step approach is demonstrated here by the selective incorporation of a fluorescent dye but can also be applied to a wide variety of different conjugation partners depending on the desired application in a facile manner. Methionine-modified antibodies were characterised in vitro, and the diagnostic potential of the most promising variant was further analysed in an in vivo xenograft animal model using a fluorescence imaging modality. This study demonstrates how methionine-mediated antibody conjugation offers an orthogonal and versatile route to the generation of tailored antibody conjugates with in vivo applicability.

Hiding Payload Inside the IgG Fc Cavity Significantly Enhances the Therapeutic Index of Antibody-Drug Conjugates

The inadequate understanding of the structure-activity relationship (SAR) of glycosite-specific antibody-drug conjugates (ADCs) hinders its design and development. Herein, we revealed the systemic SAR and structure-toxicity relationship (STR) of gsADCs by constructing 50 gsADC structures bearing three glycan subtypes and diverse linker-drug combinations. According to the results, extra hydrophilic linkers are indispensable for the intact glycan-based gsADCs to achieve better in vivo efficacy. Meanwhile, the gsADCs that conjugate linker-drug complexes onto the terminal sialic acid are more stable and potent than the ones conjugated onto the terminal galactose in vivo. Notably, the LacNAc-based gsADCs, which shortened the spacer and located the linker-drug more inside the immunoglobulin class G (IgG) Fc cavity, showed excellent hydrophilicity, in vivo activity, pharmacokinetics, and safety. Conclusively, we found that hiding the linker-toxin into the Fc cavity can significantly enhance the therapeutic index of LacNAc-based gsADCs, which will benefit the further design of ADCs with optimal druggability.

Site-Specific Conjugation of Metal-Chelating Polymers to Anti-Frizzled-2 Antibodies via Microbial Transglutaminase

Metal-chelating polymer-based radioimmunoconjugates (RICs) are effective agents for radioimmunotherapy but are currently limited by nonspecific binding and off-target organ uptake. Nonspecific binding appears after conjugation of the polymer to the antibody and may be related to random lysine conjugation since the polymers themselves do not bind to cells. To investigate the role of conjugation sites on nonspecific binding of polymer RICs, we developed a microbial transglutaminase reaction to prepare site-specific antibody-polymer conjugates. The reaction was enabled by introducing a Q-tag (i.e., 7M48) into antibody (i.e., Fab) fragments and synthesizing a polyglutamide-based metal-chelating polymer with a PEG amine block to yield substrates. Mass spectrometric analyses confirmed that the microbial transglutaminase conjugation reaction was site-specific. For comparison, random lysine conjugation analogs with an average of one polymer per Fab were prepared by bis-aryl hydrazone conjugation. Conjugates were prepared from an anti-frizzled-2 Fab to target the Wnt pathway, along with a nonbinding specificity control, anti-Luciferase Fab. Fabs were engineered from a trastuzumab-based IgG1 framework and lack lysines in the antigen-binding site. Conjugates were analyzed for thermal conformational stability by differential scanning fluorimetry, which showed that the site-specific conjugate had a similar melting temperature to the parent Fab. Binding assays by biolayer interferometry showed that the site-specific anti-frizzled-2 conjugate maintained high affinity to the antigen, while the random conjugate showed a 10-fold decrease in affinity, which was largely due to changes in association rates. Radioligand cell-binding assays on frizzled-2+ PANC-1 cells and frizzled-2- CHO cells showed that the site-specific anti-frizzled-2 conjugate had ca. 4-fold lower nonspecific binding compared to the random conjugate. Site-specific conjugation appeared to reduce nonspecific binding associated with random conjugation of the polymer in polymer RICs.