111In-labelled octreotide binding by the somatostatin receptor subtype 2 in neuroendocrine tumours.

Background: The aim of this study was to investigate the importance of somatostatin receptor subtype 2 (SSTR2) expression for ¹¹¹In-labelled diethylenetriamine-pentaacetic acid (DTPA)-D-Phe¹-octreotide binding and uptake of ¹¹¹In in neuroendocrine tumours. Methods: ¹¹¹In activity concentrations in surgical biopsies from neuroendocrine tumours (midgut carcinoid and medullary thyroid carcinoma), breast carcinoma and blood were determined 1-8 days after intravenous injection of ¹¹¹In-labelled DTPA-D-Phe¹-octreotide (140-350 MBq). The ratio of ¹¹¹In activity concentrations between tumour tissue and blood (T/B value) was calculated. The expression of SSTR2 messenger RNA (mRNA) in tumour biopsies was quantitated by ribonuclease protection assay and SSTR2 protein was localized by immunocytochemistry. Results: T/B values were highest for tumour biopsies from midgut carcinoids (mean 160 (range 4⁕1200); n = 65) followed by medullary thyroid carcinoma (mean 38 (range 2⁕350); n = 88) and breast carcinoma (mean 18 (range 4⁕41); n = 4). The expression of SSTR2 mRNA (relative to the NCI⁕H69 cell line) was highest in tumour biopsies from midgut carcinoids (mean 2·5 (range 0·83⁕6·0); n = 40) followed by medullary thyroid carcinoma (mean 1·3 (range 0·20⁕6·0); n = 7) and breast carcinoma (mean 0·66 (range 0·29⁕1·0); n = 9). In tumour biopsies SSTR2 protein was localized exclusively to tumour cells. Conclusion: Midgut carcinoid tumours showed a much higher level of SSTR2 expression than medullary thyroid carcinoma in accordance with superior tumour imaging by octreotide scintigraphy. The high SSTR2 mRNA values and T/B values observed in midgut carcinoid tumours were positively correlated. Copyright © 2003 British Journal of Surgery Society Ltd. Published by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]