Background: Human fibronectin extra-domain B (EDB) is particularly expressed during angiogenesis
progression. It is, thus, a promising marker of tumour growth. Aptides are a novel class of peptides with
high-affinity binding to specific protein targets. APTEDB is an antagonist-like ligand that especially interacts with
human fibronectin EDB.
Objective: This study was the first attempt in which the hydrazinonicotinamide (HYNIC)-conjugated APTEDB
was labelled with technetium-99m (99mTc) as an appropriate radiotracer and tricine/EDDA exchange labeling.
Methods: Radiochemical purity, normal saline, and serum stability were evaluated by HPLC and radio-isotope
TLC scanner. Other examinations, such as protein-binding calculation, dissociation radioligand binding assay,
and partition coefficient constant determination, were also carried out. The cellular-specific binding of 99mTc-
HYNIC-conjugated APTEDB was assessed in two EDB-positive (U87MG) and EDB-negative (U373MG) cell
lines. Bio-distribution was investigated in normal mice as well as in U87MG and U373MG tumour-bearing
mice. Eventually, the radiolabelled APTEDB was used for tumour imaging using planar SPECT.
Results: Radiolabelling was achieved with high purity (up to 97%) and accompanied by high solution (over
90% after overnight) and serum (80% after 2 hours) stability. The obtained cellular-specific binding ratio was
greater than nine-fold. In-vivo experiments showed rapid blood clearance with mainly renal excretion and tumour
uptake specificity (0.48±0.03% ID/g after 1h). The results of the imaging also confirmed considerable
tumour uptake for EDB-positive cell line compared with the EDB-negative one.
Conclusion: Aptides are considered to be a potent candidate for biopharmaceutical applications. They can be
modified with imaging or therapeutic agents. This report shows the capability of 99mTc-HYNIC-APTEDB for
human EDB-expressing tumours detection.