Solid phase synthesis, radiolabeling and biological evaluation of a 99mTc-labeled αVβ3 tripeptide (RGD) conjugated to DOTA as a tumor imaging agent

Abstract

Solid phase synthesis of peptides-radiometal chelator can facilitate the creation of radioactive peptide libraries to be utilized in high throughput in in vivo screening of targeted molecular imaging agents. An αVβ3 tripeptide derivative DOTA-NH-Arg-Gly-Asp was synthesized by Fmoc solid phase peptide synthesis and analyzed by spectroscopic techniques. In order to radiolabel this RGD peptide with 99mTc-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was incorporated as a chelator. The DOTA-peptide conjugate binds to 99mTc with high efficiency at ambient temperature. The resulting conjugate is stable under physiological conditions for at least 24 h after radiocomplexation. The receptor binding studies of 99mTc-DOTA- αVβ3-tripeptide in established human tumor cell lines U-87MG and BMG revealed Kd values in the nM and μM range respectively. U-87MG tumors in athymic mice were accumulated in the γ-images and major accumulation of the radiotracer was observed in kidneys followed by liver and lungs. High tumor uptake was shown in the U-87MG tumor bearing athymic mice; tumor to muscle ratios reached 8.13 ± 2.18 and 35.09 ± 4.78 at 1 and 4 h after post injection respectively.