99mTc-HYNIC-Gastrin Peptides: Assisted Coordination of 99mTc by Amino Acid Side Chains Results in Improved Performance Both In Vitro and In Vivo.
The aim of this study was to determine the effects of assisted coordination by amino acids such as histidine and glutamic acid on the function of (99m)Tc-labeled gastrin peptide-hydrazinonicotinamide (HYNIC) conjugates and their ability to target cholecystokinin-R in small-animal models.


METHODS
Three peptide-HYNIC conjugates containing the -AYGWMDF-NH2 C-terminal sequence and combinations of histidine, glutamic acid, and glycine were synthesized, radiolabeled with (99m)Tc/(99)Tc using either tricine or ethylenediaminediacetic acid as a coligand, and analyzed by the high-performance liquid chromatography and liquid chromatography-mass spectrometric techniques. Stability, receptor binding, and internalization and in vivo targeting in AR42J-bearing mice were assessed.


RESULTS
When radiolabeling was performed using tricine as a coligand, the insertion of a histidine residue near the HYNIC residue resulted in the displacement of one molecule of tricine from the coordination sphere, a reduction in the number of radiolabeled species formed, an improvement in the in vitro stability, an increase in the rate of radiopeptide internalization, and a significant improvement in tumor uptake in vivo. When radiolabeling was performed using ethylenediaminediacetic acid as a coligand, no effect on coligand binding, homogeneity, or in vitro stability was observed but a significant improvement in the internalization in vitro and tumor uptake in vivo was again found. All of the complexes formed showed similar receptor affinity in competitive radioligand binding assays.


CONCLUSIONS
The insertion of histidine into the sequence of peptide-HYNIC conjugates can result in more stable, more homogeneous complexes that show improvements in tumor-targeting performance both in vitro and in vivo.
King
Robert
R
Centre for Molecular Oncology and Imaging, Barts and the London School of Medicine, John Vane Science Centre, London, United Kingdom.
Surfraz
M Bashir-Uddin
MB
Finucane
Ciara
C
Biagini
Stefano C G
SC
Blower
Philip J
PJ
Mather
Stephen J
SJ
D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D007089:Image Enhancement / Q000379:methods*; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009842:Oligopeptides / Q000138:chemical synthesis / Q000493:pharmacokinetics; D009928:Organ Specificity; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000493:pharmacokinetics; D015609:Organotechnetium Compounds / Q000138:chemical synthesis / Q000493:pharmacokinetics; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D014018:Tissue Distribution
D000596:Amino Acids; D009842:Oligopeptides; D009942:Organometallic Compounds; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C541348:technetium 99m HYNIC (lysyl)-glutamyl-alanyl-tyrosyl-glycyl-tryptophyl-methionyl-aspartyl-phenylalaninamide; C541350:technetium 99m HYNIC (lysyl)-glycyl-alanyl-tyrosyl-glycyl-tryptophyl-methionyl-aspartyl-phenylalaninamide; C541349:technetium 99m HYNIC (lysyl)-glycyl-histidyl-glutamyl-alanyl-tyrosyl-glycyl-tryptophyl-methionyl-aspartyl-phenylalaninamide