In-111-DTPA-D-Phe(1)-octreotide binding and somatostatin receptor subtypesin thyroid tumors

The purpose of this study was to evaluate the potential for therapy of thyr oid tumors using the radiolabeled somatostatin (SS) analog octreotide. Meth ods: Concentrations of In-111 activity in human thyroid tumors and normal t hyroid tissue and blood samples were determined 1-15 d after intravenous in jection of In-111-diethylenetriaminepentaacetic acid-Phe(1)-octreotide. The results were compared with SS receptor (sstr) subtype profile (by Northern blot analysis) and the relative expression of the second subtype, sstr2 (b y ribonuclease protection assay, RPA). The true tumor volumes in lymph node metastases from 1 patient were estimated. In total, tissues from 68 patien ts were included in the study. Results: The highest tumor-to-blood ratio (T /B) for medullary thyroid carcinoma (MTC) was 360; for follicular adenoma ( FA), 190; for Hurthle cell adenoma (HCA), 140; and for Hurthle cell carcino ma (HCC) and papillary carcinoma (PC), 70. The corresponding value was 7-18 for normal thyroid tissue, with higher values for colloid goiter (8-48) an d thyroiditis (7-120), A high TIE was related to a large fraction of tumor cells in lymph node metastases. T/Bs were higher for the tumor samples with expression of sstr2 at Northern blot analysis than for those without. All thyroid tumor types regularly expressed sstr1, sstr3, sstr4, and sstr5. sst r2 was expressed in most MTC tumors but was not detected in FA or PC and wa s irregularly expressed in HCA and HCC. However, RPA analysis detected sstr 2 in all tumors studied. Conclusion: Despite the lack of sstr2 at Northern blot analysis in most of the thyroid tumors studied, high T/Bs were in gene ral found when compared with corresponding values for normal thyroid tissue . The sometimes extremely high ratios are promising and indicate a possibil ity of using radiolabeled octreotide for radiation therapy of sstr-positive tumors in the future.