ABSTRACT
This chapter examines specific examples of the problems that have occurred in the development of peptides for specific target cell receptors. There has been explosive growth in the interest and development of radiolabeled peptides for both diagnostic and therapeutic applications. To develop a peptide for diagnostic applications, tumor physiology usually plays a secondary role. Somatostatin, 14 amino acid peptide hormone, plays a variety of roles in the human body. Most importantly, it inhibits the release of a wide variety of other hormones including: growth hormone, insulin, glucagon, and gastrin. The peptide sequence of Bombesin contains no Cys residues that could be cross-linked to constrain the secondary structure. Peptides have many advantages including fast clearance, rapid tissue penetration, and low antigenicity, and can be produced easily and inexpensively. In contrast, peptides have problems with in vivo catabolism, unwanted physiological effects, and chelate attachment.
