Preparation and tumor affinity testing of the radioiodinated tetrahydroisoquinoline derivative [123I]TIC(OH) for targeting prostate cancer

This work describes the synthesis and tumor affinity testing of 8-[123I]iodo-L-1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid [ITIC(OH)], a cyclic non-naturally occurring amino acid as an imaging probe for prostate cancer. Parameters for labelling were optimized with regard to the amount of precursor, the temperature and time. Thereafter, ITIC(OH) was evaluated in terms of its uptake in primary human PC-3 and DU-145 prostate cancer cells, followed by analysis of the underlying mechanisms of the radioactivity accumulation in tumor cells. No-carrier-added ITIC(OH) was obtained in 80±15% radiochemical yield and >98% radiochemical purity by a one-step radioiodination, using IODO-GEN as oxidant. The total synthesis time was less than 30 min, and compatible with a clinical routine production. ITIC(OH) accumulated intensively in primary human prostate cancer cells. The radioactivity incorporation in tumor following a 10-min incubation at 37 oC/pH 7.4 varied from 35% to 58% of the total loaded activity per 106 tumor cells (355-540 cpm/1000 cells). Inhibition experiments revealed that ITIC(OH) was taken up into tumor by an active transport different from the common amino acid carrier systems, including the sodium-dependent system A and B+,, and the sodium-independent L- and ASC-type transporter. In contrast, the cellular incorporation was dependent on the membrane potential and correlated with the activity of the mitochondria. In conclusion, the specific and high-level accumulation of ITIC(OH) in human prostate carcinoma cells, indicates that the new radiopharmaceutical is a good candidate for further in vivo investigations to ascertain its potential as an imaging probe for prostate cancer by SPET