99mTc-labeling of a hydrazinonicotinamide-conjugated vitronectin receptor antagonist useful for imaging tumors

This report describes the (99m)Tc labeling of a HYNIC-conjugated vitronectin receptor antagonist (SQ168 = [2-[[[5-[carboonyl]-2-pyridinyl]hydrazono]methyl]benzenesulfonic acid]-Glu(cyclo[Lys-Arg-Gly-Asp-D-Phe])-cyclo[Lys-Arg-Gly-Asp-D-Phe]). The ternary ligand complex [(99m)Tc(SQ168)(tricine)(TPPTS)] (RP593) was prepared using a non-SnCl(2)-containing formulation. The corresponding (99)Tc analogue, [(99)Tc]RP593, was also prepared and characterized by HPLC and LC-MS. A HPLC concordance experiment using RP593 and [(99)Tc]RP593 showed that the same technetium complex was prepared at both the tracer and macroscopic levels. The LC-MS data is completely consistent with the 1:1:1:1 composition for Tc:SQ168:tricine:TPPTS and provides direct evidence that the two radiometric peaks in the radio-HPLC chromatogram of RP593 are indeed due to the resolution of diastereomers. In an in vitro receptor binding assay, [(99)Tc]RP593 was shown to have comparable binding affinity for the vitronectin receptor to that of SQ168 itself.