Automated synthesis, characterization and biological evaluation of [(68)Ga]Ga-AMBA, and the synthesis and characterization of (nat)Ga-AMBA and [(67)Ga]Ga-AMBA.

Ga-AMBA (Ga-DO3A-CH(2)CO-G-[4-aminobenzoyl]-QWAVGHLM-NH(2)) is a bombesin-like agonist with high affinity for gastrin releasing peptide receptors (GRP-R). Syntheses for (nat)Ga-AMBA, [(67)Ga]Ga-AMBA and [(68)Ga]Ga-AMBA were developed. The preparation of HPLC-purified and Sep-Pak purified [(68)Ga]Ga-AMBA were fully automated, using the built-in radiodetector of the Tracerlab FX F-N synthesizer to monitor fractionated (68)Ge/(68)Ga 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 [(68)Ga]Ga-AMBA. Both [(67)Ga]Ga-AMBA and [(177)Lu]Lu-AMBA showed comparable high affinity for GRP-R in the human prostate cancer cell line PC-3 in vitro (k(D)=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 [(177)Lu]Lu-, [(111)In]In-, [(67)Ga]Ga- and [(68)Ga]Ga-AMBA.