In the present study, researchers radiolabeled FROP-1 peptide through practicing HYNIC as a chelating moiety (at the C-terminus) and Lys residue as a spacer in order to develop a 99mTc-HYNIC-(tricine-EDDA)-Lys-FROP for the targeting of the MCF-7 breast cancer cells.

Breast cancer is the most common malignancy among women in the world. Development of novel tumor-specific radiopharmaceuticals for early breast tumor diagnosis is highly desirable. In this study, researchers developed 99mTc-HYNIC-(tricine/EDDA)-Lys-FROP peptide with the ability of specific binding to MCF-7 breast tumor.

The FROP-1 peptide was conjugated with the bifunctional chelator hydrazino nicotinamide (HYNIC) and labeled with 99mTc using tricine/EDDA co-ligand. The cellular specific binding of 99mTc-HYNIC-FROP was evaluated on different cell lines as well as with blocking experiment on MCF-7 (human breast adenocarcinoma). The tumor targeting and imaging of this labeled peptide were performed on MCF-7 tumor-bearing mice.

Radiochemical purity for 99mTc-HYNIC-(tricine/EDDA)-FROP was 99% which was determined with ITLC method. This radiolabeled peptide showed high stability in normal saline and serum about 98% which was monitored with HPLC method. In saturation binding experiments, the binding constant (Kd) to MCF-7 cells was determined to be 158 nM.

Biodistribution results revealed that the 99mTc-HYNIC-FROP was mainly exerted from the urinary route. The maximum tumor uptake was found after 30 min post injection (p.i.); however maximum tumor/muscle ratio was seen at 15 min p.i. The tumor uptake of this labeled peptide was specific and blocked by co-injection of excess FROP.

According to the planar gamma imaging result, the tumor was clearly visible due to the tumor uptake of99mTc-HYNIC-(tricine/EDDA)-FROP in the mouse after 15 min p.i. Thus, the 99mTc-HYNIC-(tricine/EDDA)-FROP is considered a promising probe with high specific binding to MCF-7 breast cancer cells.