Tumor targeting using affibody molecules: interplay of affinity, target expression level, and binding site...

Area of Science:

• Molecular imaging
• Biotechnology
• Oncology

Background:

• Scaffold proteins like Affibody molecules show promise for radionuclide imaging of cancer.
• Targeting molecular alterations aids patient stratification for therapies.

Purpose of the Study:

• To investigate how human epidermal growth factor receptor 2 (HER2) affinity and binding site composition of Affibody molecules affect tumor targeting in vivo.
• To determine the impact of HER2 receptor density on tumor uptake and imaging contrast.

Main Methods:

• Compared Affibody molecules with moderate (10(-9) M) and high (10(-10) M) affinity for HER2.
• Evaluated tumor xenografts with high (SKOV-3) and low (LS174T) HER2 expression in mice.
• Assessed tumor uptake, retention, and tumor-to-organ ratios at 4 and 24 hours post-injection.

Main Results:

• High-affinity binders showed 2-fold higher retention at 24h in high HER2-expressing tumors (SKOV-3).
• In low HER2-expressing tumors (LS174T), high-affinity probes demonstrated severalfold higher uptake at 4h, increasing by 24h.
• Binding site composition influenced tracer clearance and tumor-to-organ ratios.

Conclusions:

• Optimal HER2-binding Affibody affinity is target expression-dependent: low-nanomolar for high expression, subnanomolar for moderate expression.
• Binding site composition impacts imaging contrast.
• Findings inform the development of novel scaffold affinity protein-based imaging agents.