Impact of expression system on the function of the C6.5 diabody PET radiotracer

Area of Science:

• Biotechnology
• Oncology
• Radiochemistry

Background:

• Engineered antibodies are suitable for tumor-targeting radioimaging tracers.
• Diabodies offer advantageous molecular size and bivalent structure for diagnostic imaging.
• The anti-HER2 C6.5 diabody (C6.5db) has shown efficacy in preclinical models of HER2-positive cancer.

Purpose of the Study:

• To compare the performance of C6.5db produced in Pichia pastoris (P-C6.5db) versus Escherichia coli (E. C6.5db) as a radioimaging tracer.
• To evaluate the impact of glycosylation on radiotracer characteristics.

Main Methods:

• Production of C6.5db in Pichia pastoris and Escherichia coli.
• Radiolabeling with Iodine-124.
• Evaluation of blood clearance, tumor uptake, and tumor/background ratios in preclinical models.
• Dosimetry measurements.

Main Results:

• Pichia pastoris-produced C6.5db (P-C6.5db) exhibited faster blood clearance and lower overall tumor uptake compared to E. coli-produced C6.5db (E. C6.5db).
• Despite lower uptake, P-C6.5db achieved high tumor/background ratios, essential for effective imaging.
• Dosimetry data indicated that both (124)I-P-C6.5db and (124)I-E-C6.5db are comparable to existing clinical radiotracers.

Conclusions:

• Production system influences radiotracer performance, with Pichia pastoris yielding faster blood clearance.
• High tumor-to-background ratios achieved by P-C6.5db are critical for diagnostic imaging quality.
• Both P-C6.5db and E. C6.5db demonstrate potential as safe and effective HER2-targeting radioimaging agents.