RADIOLABELED SOMATOSTATIN ANALOGS

Somatostatin is a naturally occurring tetradecapeptide that inhibits t he secretion of many hormones. Large numbers of binding sites with hig h affinity for somatostatin have been reported in a variety of tumors. An octapeptide analogue of somatostatin, octreotide (Sandostatin(R)), is currently used in the treatment of patients with somatostatin rece ptor-positive tumors to limit hormonal hypersecretion. In an effort to utilize the high specificity of octreotide for scintigraphic imaging of somatostatin receptor-positive tumors, a tyrosine derivative of oct reotide was prepared and labeled with the radioactive isotope, I-123. While the early clinical results obtained with this radiopharmaceutica l were encouraging, the I-123 labeling procedure proved cumbersome and variable. To circumvent these difficulties, researchers at University Hospital Rotterdam (Holland) and Sandoz Research Institute (Switzerla nd) developed an In-111 labeled analogue of octreotide. This radiophar maceutical is easy to prepare and has proven to be even more effective than the I-123 derivative in the scintigraphic imaging of tumors. The se radiopharmaceutical developments and clinical observations are disc ussed in light of their relevance to the generation of new radiolabele d peptides for the diagnosis and potential radiotherapy of cancer.