Emerging formats for next-generation antibody drug conjugates

Development of Solid-Phase Site-Specific Conjugation and Its Application toward Generation of Dual Labeled Antibody and Fab Drug Conjugates

The focus of the antibody-drug conjugate (ADC) field is shifting toward development of site-specific, next-generation ADCs to address the issue of heterogeneity, metabolic instability, conjugatability, and less than ideal therapeutic index associated with the conventional (heterogeneous) ADCs. It is evident from the recent literature that the site of conjugation, the structure of the linker, and the physicochemical properties of the linker-payload all have a significant impact on the safety and efficacy of the resulting ADCs. Screening multiple linker-payloads on multiple sites of an antibody presents a combinatorial problem that necessitates high-throughput conjugation and purification methodology to identify ADCs with the best combination of site and payload. Toward this end, we developed a protein A/L-based solid-phase, site-specific conjugation and purification method that can be used to generate site-specific ADCs in a 96-well plate format. This solid-phase method has been shown to be versatile because of its compatibility with various conjugation functional handles such as maleimides, haloacetamides, copper free click substrates, and transglutaminase substrates. The application of this methodology was further expanded to generate dual labeled, site-specific antibody and Fab conjugates.

Editing of mouse and human immunoglobulin genes by CRISPR-Cas9 system

Applications of the CRISPR-Cas9 system to edit the genome have widely expanded to include DNA gene knock-out, deletions, chromosomal rearrangements, RNA editing and genome-wide screenings. Here we show the application of CRISPR-Cas9 technology to edit the mouse and human immunoglobulin (Ig) genes. By delivering Cas9 and guide-RNA (gRNA) with retro- or lenti-virus to IgM(+) mouse B cells and hybridomas, we induce class-switch recombination (CSR) of the IgH chain to the desired subclass. Similarly, we induce CSR in all human B cell lines tested with high efficiency to targeted IgH subclass. Finally, we engineer mouse hybridomas to secrete Fab' fragments instead of the whole Ig. Our results indicate that Ig genes in mouse and human cells can be edited to obtain any desired IgH switching helpful to study the biology of normal and lymphoma B cells. We also propose applications that could transform the technology of antibody production.

Use of a charge reducing agent to enable intact mass analysis of cysteine-linked antibody-drug-conjugates by native mass spectrometry

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The use of nESI-MS to examine intact Antibody Drug Conjugates (ADC).

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Use of TEAA as charge reducing agent improves cysteine-linked ADC characterization.

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TEAA preserves the intact mAb and facilitate easy drug load determination by native MS.

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This method is particularly beneficial for users of low resolution mass spectrometers.

Antibody-drug-conjugates (ADC) are a growing class of anticancer biopharmaceuticals. Conjugation of cysteine linked ADCs, requires initial reduction of mAb inter-chain disulfide bonds, as the drugs are attached via thiol chemistry. This results in the active mAb moiety being transformed from a covalently linked tetramer to non-covalently linked complexes, which hinders precise determination of drug load with LC–MS. Here, we show how the addition of the charge reducing agent triethylammonium acetate (TEAA) preserves the intact mAb structure, is well suited to the study of cysteine linked conjugates and facilitates easy drug load determination by direct infusion native MS.

Antibody-Drug Conjugates for Tumor Targeting-Novel Conjugation Chemistries and the Promise of non-IgG Binding Proteins

Antibody-drug conjugates (ADCs) have emerged as a promising class of anticancer agents, combining the specificity of antibodies for tumor targeting and the destructive potential of highly potent drugs as payload. An essential component of these immunoconjugates is a bifunctional linker capable of reacting with the antibody and the payload to assemble a functional entity. Linker design is fundamental, as it must provide high stability in the circulation to prevent premature drug release, but be capable of releasing the active drug inside the target cell upon receptor-mediated endocytosis. Although ADCs have demonstrated an increased therapeutic window, compared to conventional chemotherapy in recent clinical trials, therapeutic success rates are still far from optimal. To explore other regimes of half-life variation and drug conjugation stoichiometries, it is necessary to investigate additional binding proteins which offer access to a wide range of formats, all with molecularly defined drug conjugation. Here, we delineate recent progress with site-specific and biorthogonal conjugation chemistries, and discuss alternative, biophysically more stable protein scaffolds like Designed Ankyrin Repeat Proteins (DARPins), which may provide such additional engineering opportunities for drug conjugates with improved pharmacological performance.