Synthesis and characterization of rhenium and technetium-99m labeled insulin

A (99m)Tc-labeled insulin analogue was synthesized through a direct labeling method in which the [(99m)Tc(CO)(3)](+) core was combined with a protected insulin derivative (9) bearing a M(I) chelate linked to the first amino acid of the B-chain (B1). Regioselective labeling was achieved by careful control over the pH and the reaction time. Following a TFA-anisole mediated deprotection step (decay-corrected yield of 30 +/- 11%, n = 4), the identity of the final (99m)Tc-labeled product was confirmed by HPLC. Displacement of (125)I-insulin from the insulin receptor (IR) by the Re analogue 6 was similar to that of native insulin (17.8 nM vs 11.7 nM, respectively). The extent of autophosphorylation and Akt activation, as indicated by production of phospho-Akt (pAkt), showed no statistical difference between 6 and native insulin in both assays. These results support the use of the reported (99m)Tc-insulin derivative as a tracer for studying insulin biochemistry in vivo.