SYNTHESIS AND CHARACTERIZATION OF RHENIUM-COMPLEXED ALPHA-MELANOTROPIN ANALOGS

Receptor binding peptides labeled with medically important radionuclid es such as technetium and rhenium are an important tool for the imagin g and treatment of many forms of cancer. This paper describes a method of labeling peptides with rhenium using a natural amino acid chelatin g moiety. The structural characteristics of this chelate moiety, N-ace tyl-cysteine-glycine-cysteine-glycine (NAc-CGCG) complexed with nonrad ioactive rhenium, have been investigated. The stability of this peptid e-metal complex has been evaluated on the tracer level using radioacti ve rhenium-186. The rhenium-bound peptide has been appended to the N t ermini of receptor binding a-melanocyte stimulating hormone (alpha-MSH , r-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2) fragments via sol id phase peptide synthesis. Bioassays and receptor binding studies of the resulting complexes demonstrate that the fragments retained biolog ical activity and exhibited receptor binding constants ranging from 0. 3 to 1.1 nM. This method could provide a general means of labeling bio active peptide fragments that would simplify product purification and characterization.