The therapeutic antibody sacituzumab induces trophoblast cell-surface antigen-2 conformational rearrangement

Area of Science:

• Structural biology
• Cancer therapeutics
• Molecular interactions

Background:

• Sacituzumab govitecan is an antibody-drug conjugate approved for breast cancer treatment.
• It targets the trophoblast cell-surface antigen-2 (Trop2) to deliver the cytotoxic agent SN-38.
• Understanding the binding mechanism is crucial for optimizing cancer therapy.

Purpose of the Study:

• To determine the X-ray crystal structure of the human Trop2 ectodomain in complex with sacituzumab Fab fragment.
• To elucidate the stoichiometry of sacituzumab binding to Trop2 using various biochemical and biophysical methods.
• To provide structural insights into the interaction between sacituzumab govitecan and its target Trop2.

Main Methods:

• X-ray crystallography at 1.56-Å resolution.
• Cryo-electron microscopy (cryoEM).
• Size-exclusion chromatography with multi-angle light scattering (SEC-MALS).

Main Results:

• The crystal structure revealed a 2:2 stoichiometry of sacituzumab Fab fragments binding to the Trop2 ectodomain dimer.
• This binding induces a conformational change in Trop2.
• Analysis of the intact antibody showed a 2:4 stoichiometry, with sacituzumab engaging two Trop2 dimers.

Conclusions:

• The structural and stoichiometric data provide a detailed molecular understanding of sacituzumab-Trop2 interaction.
• This knowledge can inform the development of improved antibody-drug conjugates targeting Trop2.
• The findings highlight the complex binding mode of sacituzumab to its target antigen.