In vitro/in vivo assessment of the targeting ability of [Tc] Tc-labeled an aptide specific to the extra domain B of fibronectin (APT) for colorectal cancer.

OBJECTIVE

The APT is an aptide specific to the extra domain B (EDB) of fibronectin with high affinity for EDB, which is expressed in malignant tumors including brain cancer (U87MG) and colorectal cancer (HT-29). Aim of this study was to evaluate the [Tc] Tc-APT potential as an imaging probe for colorectal cancer.

METHODS

Radiochemical purity was evaluated by HPLC and radio-isotope TLC scanner. Blocking study for specific binding assay and affinity calculation (K) on HT-29 cell lines were also carried out. Planar imaging and bio-distribution studies were performed in HT-29 tumor-bearing mice.

RESULTS

The APT was efficiently labeled with technetium-99m in high radiochemical yield (up to 97%). Cellular binding study demonstrated specific binding of the [Tc] Tc-APT in cultured HT-29 cells. The K value was found to be 40.46 ± 13.39 nM. The tumor-to-muscle ratio was ~ 1.5 in ex vivo bio-distribution study at 1 h after injection. Planar imaging study showed higher activity accumulation in EDB expressing HT-29 tumor relative to muscle (used as control) (~ 1.7) at 1 h.

CONCLUSIONS

Although more studies are required to find out the full potential of this radio-ligand as an imaging probe, the present results nevertheless provide useful information about [Tc] Tc-APT, which might be beneficial in design and development of new [Tc] Tc-APT for efficient targeting of tumor in vivo.