Site-Specific Modification of Native IgGs with Flexible Drug-Load

Area of Science:

• Bioconjugation Chemistry
• Antibody Engineering
• Pharmacology

Background:

• Site-specific conjugation of antibodies yields antibody-drug conjugates (ADCs) with enhanced efficacy and tolerability over stochastic methods.
• Challenges remain in precisely controlling drug load and attaching multiple payloads to antibodies.

Purpose of the Study:

• To demonstrate a simple, direct method for modifying native IgG antibodies at glutamine 295 (Q295) without protein engineering.
• To achieve flexible drug-to-antibody ratios (DARs) with one or multiple payloads.

Main Methods:

• Utilized short, lysine-containing peptides and microbial transglutaminase for conjugation to native IgG antibodies at Q295.
• Generated HER2-targeting ADCs using trastuzumab with DARs of 2 and 4, employing orthogonal conjugation for varied payloads.
• Conducted quantitative biodistribution studies using ¹¹¹In-radiolabeled conjugates.

Main Results:

• Successfully conjugated antibodies with flexible DARs (2 and 4) using diverse payloads.
• Demonstrated high tumor uptake and minimal off-target tissue accumulation of radiolabeled conjugates.
• A single dose of trastuzumab conjugated to α-Amanitin resulted in complete, durable tumor remission and was well-tolerated.

Conclusions:

• The Q295 conjugation method offers a straightforward approach for creating homogeneous ADCs with controlled DARs.
• This technique facilitates the development of potent ADCs with improved therapeutic profiles.
• The demonstrated efficacy and tolerability highlight the potential of this method for novel cancer therapeutics.