Comparison of 111In-DOTA-NOC and 111In-DOTA-TATE Distribution in the Target and Dose-limiting Tissues: Conflicting Results In Vitro and In Vivo

Background: In this study, some important biological characteristics of two radiolabelled somatostatin analogues 111 In-DOTA-1-Nal 3 -octreotide (DOTA-NOC) and 111 In-DOTA-Tyr 3 -octreotate (DOTA-TATE) were compared. Materials and Methods: Rats were used for in vivo biodistribution experiments and in vitro cell models (OK and AR42J cell lines) were used for simulating the internalization in the kidney and in subtype 2 somatostatin receptor (SSTR2)-positive tissues, respectively. Results: Significantly higher radioactivity concentrations in rat organs with high density of somatostatin receptors after 111 In-DOTA-NOC administration in comparison with 111 In-DOTA-TATE were observed. The predominant urine excretion was associated with accumulation of the radioactivity in the kidney, where higher retention of 111 In-DOTA-TATE compared to 111 In-DOTA-NOC was detected. In the OK cell line the opposite results were found. No significant differences in the in vitro internalization and externalization of radioactivity to AR42J cell line were found for either peptide suggesting their same affinity for SSTR2. Conclusion: Preclinical experiments indicated that 111 In-DOTA-NOC is a very promising peptide for somatostatin receptor-positive tumour visualization. The conflict between the in vitro and in vivo kidney handling showed that the transfer of results from in vitro to in vivo conditions and their interpretation should be performed very carefully because both types of experiments can be affected by different factors, making their simple comparison difficult.