Current developments in single photon radiopharmaceuticals for tumor imaging.

Development of peptides and amino acids labeled with single photon gamma emitters has promoted a large number of investigations in nuclear medicine especially for tumor imaging. Radiolabeled peptides have several advantages over antibodies mainly related to immunogenicity and size. Tumor localization and total body clearance of peptides are more rapid compared to antibodies. Recently, several somatostatin analogues labeled with Tc-99m have been studied by several different investigators. In-111 labeled lanreotide (Mauritus) was reported to be highly successful in localization of neuroendocrine tumors. A synthetic amino acid, alpha methyl tyrosine labeled with I-123 was shown to be transported to tumors by a carrier mediated system. Development of a glucose analog labeled with a single photon emitting radionuclide and meeting the structural requirements for hexokinase reaction and phosphorylation have not yet been possible. However, it has been possible to synthesize chemically stable single photon glucose analogues interacting with glut(s), glucose transporters.