Arginine-glycine-aspartate (RGD) peptide binds to the integrin αvβ3, which plays a crucial role in tumor angiogenesis and metastasis. Previously developed 68Ga-labeled cyclic RGD peptides are rapidly excreted from the circulatory system. In the present study, we developed a 68Ga-labeled cyclic RGD peptide with a biphenyl group between the chelator and RGD peptide, i.e., 68Ga-NOTA-biphenyl-c(RGDyK). Then, we performed the comparison with the reference compound, i.e., 68Ga-NOTA-c(RGDyK). 68Ga-NOTA-biphenyl-c(RGDyK) was 37% less hydrophilic than 68Ga-NOTA-c(RGDyK). For positron emission tomography imaging, 68Ga-NOTA-biphenyl-c(RGDyK) had a longer retention time and showed a higher signal-to-noise ratio in tumors than 68Ga-NOTA-c(RGDyK). However, the biphenyl-radiopeptide displayed the relatively high non-specific binding. From these perspectives, incorporation of the biphenyl group to the RGD generates pros and cons.
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