PREPARATION OF LYOPHILIZED KIT OF HYNIC-[Tyr3]-OCTREOTATE AND LABELING STUDIES WITH 99m-TECHNETIUM / Preparo do reagente liofilizado HYNIC-[Tyr3]-Octreotato e estudo de marcação com Tecnécio-99m

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The development of radiolabeled molecules with high specificity for an organ or tumor has been contributed to the precise diagnostic in nuclear medicine. Somatostatin labeled derivatives constitutes a particular example of labeled peptide applied in the localization of neuroendocrine tumors. Nowadays, the 111In-DTPA-octreotideo is the radiopharmaceutical applied in diagnostic procedures for the visualization of tumors with high expression of somatostatin receptors. However, the 111-indium is a radionuclide that presents some limitations related to availability (cyclotron production), half-life (67 hours) and the emission of medium energy photons (171 keV e 245 keV), not favorable to the acquisition of images in SPECT (Single Photon Emission Computed Tomography). The favorable physical properties of the 99m-technetium (99mTc) make this radionuclide the more favorable to substitute the 111-indium on peptide labeling procedures. This work studied the preparation and labeling of a lyophilized kit of HYNIC-Tyr3-octreotate (HYNIC-octreotate) with 99mTc, base on previously described procedures and using tricine and EDDA (ethylendiaminediacetic acid) as coligands. It was studied the labeling parameters (incubation time, temperature, volume and perthecnetate activity) and the stability of the lyophilized preparation. Additionally, it was studied the influence of the pre-freezing using liquid nitrogen in the stability of the lyophilized preparation, as well as the influence of manitol in the labeling yield and biological distribution of the complex. The stability studies showed that the lyophilization using liquid nitrogen pre-freezing resulted in a lyophilized preparation with stability over 4 month when stored under refrigeration. The stability of the lyophilized preparation obtained without liquid nitrogen pre-freezing was similar.The labeling studies determined the best labeling conditions, resulting in a radiochemical yield superior than 90%. The use of manitol in the formulation did not influence the formation of the complex 99mTc-HYNIC-Octreotate, as evidenced in HPLC and in the scintigraphic studies of the complex biodistribution in rabbits. Invasive biodistribution studies using xenographed Nude mice (pancreatic tumor cells AR42J) and healthy Swiss mice, and scintigraphic studies in rabbits showed the fast kinetic distribution, renal uptake and significative tumoral uptake of the labeled peptide. The results of labeling studies with 99mTc, the production of the lyophilized kit and the biodistribution studies suggest that the 99mTc-HYNIC-Octreotate is a potential radiopharmaceutical to be applied in the diagnostic of neuroendocrine tumors in nuclear medicine.

ASSUNTO(S)

radiofármacos somatostatin hynic-octreotate hynic-octreotato radiopharmaceutical somatostatina tumor neuroendócrino neuroendocrine tumors

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