Design, Synthesis and in Vitro Biological Evaluation of Reference Compounds of ¹²³I and ⁹⁹Tc^m Labeled Indole Radiotracers for

Novel indole radiotracers for ¹²³I and ⁹⁹Tc^m labeling were designed. The corresponding reference compounds (Indole-I and Indole-MAMA-Re) and the precursor (Indole-MAMA) for ⁹⁹Tc^m labeling were synthesized. Competition binding assays in vitro show that the K_i values of Indole-I for σ₁ and σ₂ receptors are (0.574±0.355) μmol/L and (0.162±0.030) μmol/L( n =3), respectively. The K_i values of Indole-MAMA-Re for σ₁ and σ₂ receptors are (3.75±2.22) μmol/L and (7.83±4.87) μmol/L(n=3), respectively. Furthermore, ⁹⁹Tc^m Indole-MAMA was successfully prepared. The radiochemical purity (RCP) of ⁹⁹Tc^m-Indole-MAMA after purification was higher than 90% by HPLC analysis. The compounds reported in this paper may be used as lead compounds for further structural modification to develop indole SPECT tumor imaging agents with high affinity and selectivity for σ₂ receptors.