Solid-phase synthesis of peptide radiopharmaceuticals using Fmoc-N-epsilon-(hynic-Boc)-lysine, a technetium-binding amino acid: application to Tc-99m-labeled salmon calcitonin.
Labeling of proteins with metallic radionuclides for use in radiopharmaceuticals involves covalently attaching a bifunctional chelator. In principle, use of smaller peptides allows this chelator to be incorporated during solid-phase peptide synthesis (SPPS) with total site specificity. To realize the advantages of this approach, a lysine-hynic conjugate Fmoc-N-epsilon-(Hynic-Boc)-Lys was synthesized for incorporating the well-known technetium-99m-binding hydrazinonicotinamide ligand into peptides during SPPS. It was used to synthesize a technetium-99m-labeled salmon calcitonin with the hynic-linked amino acid in place of lysine-18. A trifluoroacetate group protected the hynic during alkaline oxidation to the cyclic disulfide and was readily removed by mild acid treatment. The peptide was efficiently labeled (91-98% radiochemical yield) with Tc-99m in the presence of tricine and SnCl(2) with high specific activity (>100 MBq/microg). The product showed good serum stability and specific affinity for human calcitonin receptors. Fmoc-N-epsilon-(Hynic-Boc)-Lys is a highly versatile technetium-binding amino acid for incorporation into peptides during SPPS. This allows total flexibility and control in the site of attachment and is suitable for a combinatorial approach to peptide radiopharmaceuticals.
Greenland
William E P
WE
Research School of Biosciences, University of Kent, Canterbury CT2 7NJ, UK.
Howland
Kevin
K
Hardy
Judith
J
Fogelman
Ignac
I
Blower
Philip J
PJ
D002116:Calcitonin / Q000737:chemistry*; D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D006834:Hydrazines / Q000737:chemistry; D007553:Isotope Labeling; D008239:Lysine / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D009539:Nicotinic Acids / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D018003:Receptors, Calcitonin / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D013667:Technetium; D014407:Tumor Cells, Cultured
C120392:6-hydrazinopyridine-3-carboxylic acid; D002614:Chelating Agents; C474156:Fmoc-N-epsilon-(Hynic-Boc)-lysine; D006834:Hydrazines; D009539:Nicotinic Acids; D019275:Radiopharmaceuticals; D018003:Receptors, Calcitonin; D013667:Technetium; C028815:salmon calcitonin; D002116:Calcitonin; D008239:Lysine