Automated synthesis, characterization and biological evaluation of [68Ga]Ga-AMBA, and the synthesis and characterization of natGa-AMBA and [67Ga]Ga-AMBA

Ga-AMBA (Ga-DO3A-CH2CO-G-[4-aminobenzoyl]-QWAVGHLM-NH2) is a bombesin-like agonist with high affinity for gastrin releasing peptide receptors (GRP-R). Syntheses for natGa-AMBA, [67Ga]Ga-AMBA and [68Ga]Ga-AMBA were developed. The preparation of HPLC-purified and Sep-Pak purified [68Ga]Ga-AMBA were fully automated, using the built-in radiodetector of the Tracerlab FX F-N synthesizer to monitor fractionated 68Ge/68Ga generator elution and purification. The total synthesis time, including the fractional elution of the generator, was 20 min for Sep-Pak purified material and 40 min for HPLC-purified [68Ga]Ga-AMBA. Both [67Ga]Ga-AMBA and [177Lu]Lu-AMBA showed comparable high affinity for GRP-R in the human prostate cancer cell line PC-3 in vitro (kD=0.46±0.07; 0.44±0.08 nM), high internalization (78; 77%) and low efflux from cells at 2 h (2.4±0.7; 2.9±1.8%). Biodistribution results in PC-3 tumor-bearing male nude mice showed comparable uptake for [177Lu]Lu-, [111In]In-, [67Ga]Ga- and [68Ga]Ga-AMBA.