Efficient Preparation of Site-Specific Antibody-Drug Conjugates Using Cysteine Insertion.

Area of Science:

• Biopharmaceuticals
• Antibody Engineering
• Drug Discovery

Background:

• Antibody-drug conjugates (ADCs) leverage antibody specificity and potent cytotoxic drugs.
• Site-specific ADCs are typically prepared by engineering cysteine residues via mutagenesis.
• Current methods involve substituting existing amino acids with cysteine for conjugation.

Purpose of the Study:

• To describe a new cysteine insertion engineering approach for site-specific ADC preparation.
• To evaluate the properties and efficacy of ADCs generated using this novel method.
• To explore the potential of cysteine-inserted ADCs in mitigating off-target toxicities.

Main Methods:

• Antibody engineering through cysteine insertion at selected sites.
• Site-specific conjugation of antibodies with a pyrrolobenzodiazepine dimer (SG3249).
• Assessment of ADC biophysical properties, binding affinities, serum stability, cytotoxicity, and in vivo anti-tumor activity.

Main Results:

• Cysteine-inserted antibodies exhibit comparable expression and monomeric content to native antibodies.
• Site-specific conjugation efficiency was similar between cysteine-inserted and cysteine-substituted ADCs.
• Cysteine-inserted ADCs demonstrated potent cytotoxicity, favorable biophysical properties, and significant anti-tumor activity in vivo.
• Certain variants abolished FcγR binding, suggesting reduced innate immune cell uptake and potential mitigation of off-target toxicities.

Conclusions:

• Cysteine insertion is a viable strategy for producing homogeneous, site-specific ADCs.
• This method yields ADCs with potent anti-cancer efficacy and potentially improved safety profiles.
• The ability to abolish FcγR binding offers a promising avenue for reducing ADC-related toxicities.