title: Immunohistochemical localization and quantitative expression of somatostatin receptors in normal human spleen and thymus: Implications for the in vivo visualization during somatostatin receptor scintigraphy.
abstract: BACKGROUND
  [111In-DTPA-D-Phe1]-octreotide scintigraphy allows the visualization of SRIF receptor (SSR)-expressing tumors, including thymic tumors, and normal tissues. While the spleen is clearly visualized, the thymus is not depicted, although both contain SSR.
  
  
  OBJECTIVE
  We evaluated whether the heterogeneity, the type, and the amount of SSR might explain this contrasting finding.
  
  
  RESULTS
  By ligand-binding the number of [125I-Tyr11]-SRIF- 14 binding sites resulted comparable between the two tissues, whereas the number of [125I-Tyr3]-octreotide sites was significantly higher in the spleen (p<0.001). Quantitative RTPCR showed a significantly higher expression of sst2A mRNA in the spleen, whereas a significantly higher expression of SRIF and sst3 in the thymus. The highest density of sst2A in the spleen is in line with the in vivo uptake of [111In-DTPA-D-Phe1]- octreotide, which is considered a sst2-preferring ligand. The specificity is confirmed by the evidence that in vivo [111In-DTPA- D-Phe1]-octreotide uptake can be abolished during chronic administration of "cold" octreotide. Immunohistochemistry confirmed a preferential expression of sst2A on microenvironmental cells and of sst3 on lymphoid cells.
  
  
  CONCLUSIONS
  The heterogeneity of SSR expression and the higher SRIF content explain the lack of thymus visualization during scintigraphy, whereas thymic tumors, which do not express SRIF, are visualized. Apart from the affinity of the radioligand, also the efficacy of the internalization is crucial for the in vivo uptake, and both heterogeneity and SRIF content affect this process. These observations might have an important impact when interpretating in vivo visualization of SSR-positive lesions, and when treatment with novel SRIF analogs is considered.
authors.affiliation: Department of Endocrinological and Medical Sciences and Center of Excellence for Biomedical Research, University of Genoa, Viale Benedetto XV, 6-16132-Genoa, Italy. ferone@unige.it
authors.forename: D
authors.initials: D
authors.lastname: Ferone
authors.forename: R
authors.initials: R
authors.lastname: Pivonello
authors.forename: D J
authors.initials: DJ
authors.lastname: Kwekkeboom
authors.forename: F
authors.initials: F
authors.lastname: Gatto
authors.forename: P
authors.initials: P
authors.lastname: Ameri
authors.forename: A
authors.initials: A
authors.lastname: Colao
authors.forename: R R
authors.initials: RR
authors.lastname: de Krijger
authors.forename: F
authors.initials: F
authors.lastname: Minuto
authors.forename: S W J
authors.initials: SW
authors.lastname: Lamberts
authors.forename: P M
authors.initials: PM
authors.lastname: van Hagen
authors.forename: L J
authors.initials: LJ
authors.lastname: Hofland
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D004369:Pentetic Acid / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D012333:RNA, Messenger / Q000235:genetics; D011877:Radionuclide Imaging; D017481:Receptors, Somatostatin / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013154:Spleen / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D013950:Thymus Gland / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D014018:Tissue Distribution; D055815:Young Adult
chemical_list: C442550:(111)indium-DTPA-D-phe octreoide; D012333:RNA, Messenger; D017481:Receptors, Somatostatin; C106140:somatostatin receptor sst2A; C101130:somatostatin receptor type 1; D004369:Pentetic Acid