Apoptosis-inducing anti-HER2 agents operate through oligomerization-induced receptor immobilization

Area of Science:

• Oncology
• Molecular Biology
• Biochemistry

Background:

• Overexpression of Human Epidermal growth factor Receptor 2 (HER2) is crucial in various cancers, particularly HER2-addicted breast cancer.
• Targeting HER2 is a key strategy in cancer therapy, but understanding receptor modulation is vital.

Purpose of the Study:

• To investigate how biparatopic designed ankyrin repeat proteins (bipDARPins) modulate the cell surface organization of HER2.
• To differentiate HER2 modulation by bipDARPins from that induced by conventional antibodies.

Main Methods:

• Dual-color single-molecule tracking to analyze receptor mobility and organization.
• Investigating the spatiotemporal organization of HER2 at the cell surface upon bipDARPin and antibody binding.

Main Results:

• Conventional antibodies moderately reduce HER2 mobility, consistent with bivalent IgG-mediated dimerization.
• Potent apoptosis-inducing bipDARPins cause a dramatic HER2 arrest, forming HER2-DARPin oligomer chains trapped in membrane domains.
• This HER2 "lockdown" by bipDARPins effectively neutralizes receptor tyrosine kinase signaling.

Conclusions:

• Intermolecular bipDARPin crosslinking alone can efficiently neutralize HER2 tyrosine kinase signaling.
• BipDARPin-induced HER2 lockdown via oligomer chain formation represents a novel mechanism for inhibiting cancer cell growth.