Structural analysis of nanobody interactions with their prostate-specific membrane antigen binding epitopes

Area of Science:

• Structural biology
• Immunology
• Oncology

Background:

• Prostate-specific membrane antigen (PSMA) is a key target in prostate cancer diagnostics and therapy.
• Current monoclonal antibodies for PSMA targeting have limitations in tissue penetration and clearance.
• Nanobodies (NBs) present a promising alternative due to their small size, unique binding capabilities, and rapid clearance.

Purpose of the Study:

• To map the binding epitopes of nanobodies (NBs) to Prostate-specific membrane antigen (PSMA).
• To understand the structural basis of NB-PSMA interactions at atomic resolution.
• To explore the potential for developing novel theranostic agents for prostate cancer.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine high-resolution structures of NB-PSMA complexes.
• Structural analysis focused on interactions between PSMA and three specific nanobodies: NB7, NB8, and NB37.
• Binding affinities and epitope mapping were investigated.

Main Results:

• Nanobody 7 (NB7) exhibited the highest affinity for PSMA, attributed to a larger binding interface and stabilizing interactions.
• NB7 and NB8 can bind simultaneously to distinct PSMA epitopes without functional interference, enabling heterovalent strategies.
• NB7 demonstrates specific binding to human PSMA, not murine PSMA, due to key amino acid differences.

Conclusions:

• Structural insights into NB-PSMA interactions facilitate the design of advanced diagnostic and therapeutic agents.
• Simultaneous binding of NB7 and NB8 opens avenues for novel theranostic applications in prostate cancer.
• The species specificity of NB7 is defined by critical amino acid variations in PSMA.