Preparation and evaluation of 99mTc-EDDA/HYNIC-[Lys 3]-bombesin for imaging gastrin-releasing peptide receptor-positive tumours.
BACKGROUND
Bombesin is a peptide that was initially isolated from frog skin and which belongs to a large group of neuropeptides with many biological functions. The human equivalent is gastrin-releasing peptide (GRP), whose receptors are over-expressed in a variety of malignant tumours.


OBJECTIVE
To prepare a HYNIC-[Lys 3]-bombesin analogue that could be easily labelled with 99mTc from lyophilized kit formulations and to evaluate its potential as an imaging agent for GRP receptor-positive tumours.


METHODS
HYNIC was conjugated to the epsilon-amino group of Lys 3 residue at the N-terminal region of bombesin via succinimidyl-N-Boc-HYNIC at pH 9.0. 99mTc labelling was performed by addition of sodium pertechnetate solution and 0.2 M phosphate buffer pH 7.0 to a lyophilized formulation. Stability studies were carried out by reversed phase HPLC and ITLC-SG analyses in serum and cysteine solutions. In-vitro internalization was tested using human prostate cancer PC-3 cells with blocked and non-blocked receptors. Biodistribution and tumour uptake were determined in PC-3 tumour-bearing nude mice.


RESULTS
99mTc-EDDA/HYNIC-[Lys 3]-bombesin was obtained with radiochemical purities >93% and high specific activity ( approximately 0.1 GBq.nmol). Results of in-vitro studies demonstrated a high stability in serum and cysteine solutions, specific cell receptor binding and rapid internalization. Biodistribution data showed a rapid blood clearance, with predominantly renal excretion and specific binding towards GRP receptor-positive tissues such as pancreas and PC-3 tumours.


CONCLUSIONS
99mTc-EDDA/HYNIC-[Lys 3]-bombesin obtained from lyophilized kit formulations has promising characteristics for the diagnosis of malignant tumours that over-express the GRP receptor.
Instituto Nacional de Investigaciones Nucleares, Ocoyoacac, Mexico. gff@nuclear.inin.mx
Guillermina
G
Ferro-Flores
Consuelo
C
Arteaga de Murphy
Jeanette
J
Rodriguez-Cortés
Martha
M
Pedraza-López
María Teresa
MT
Ramírez-Iglesias
D000818:Animals; D001839:Bombesin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D045744:Cell Line, Tumor; D004353:Drug Evaluation, Preclinical; D006801:Humans; D007553:Isotope Labeling; D008297:Male; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009928:Organ Specificity; D015609:Organotechnetium Compounds / Q000737:chemistry / Q000493:pharmacokinetics; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics*; D018004:Receptors, Bombesin / Q000378:metabolism*; D014018:Tissue Distribution
C512311:99mTc-EDDA-HYNIC-(Lys 3)bombesin; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D018004:Receptors, Bombesin; D001839:Bombesin