Abstract
The use of radiolabeled peptide ligands as diagnostics and therapeutics in nuclear oncology has increased recently. One of the most frequently used radiopharmaceutical is 99mTc-EDDA/HYNIC-TOC, a somatostatin analog with affinity for certain types of somatostatin receptors, overexpressed in tumors of neuroendocrine origin. The radiopharmaceutical is not readily available; therefore we introduced its “in house” preparation within project activities supported by the International Atomic Energy Agency (IAEA). We optimized the radiolabeling protocol, prepared a small batch of frozen kits, performed ITLC quality control and animal biodistribution during the preclinical evaluation procedures. The co-ligand exchange labeling procedure was carried out at 100°C during 10 min, resulting in radiochemical purity >90%. The biodistribution scintigrams in normal Wistar rats showed rapid blood clearance after 15 min and predominant kidney accumulation after 4 h, in accordance with the data reported by other authors. Storage stability of the formulated small batch frozen kit (-20°C) was evaluated within 6 months, with radiolabeling yield ranging between 94,3% and 96,9%. We conclude that frozen kit can be a safe alternative to the freeze-dried for small batch in house production, and after the satisfactory preclinical evaluation, the “in house” prepared 99mTc-EDDA/ HYNIC-TOC can be introduced in clinical practice as specific targeting agent for somatostatin receptor scintigraphy.
Highlights
The development of Nuclear Medicine towards molecular diagnostic imaging modality in the past two decades was followed by intensive research and applicative work resulting with introduction of wide variety of new generation radiopharmaceuticals
Labeled peptides have proven their potential as targeting agents for receptor scintigraphy, especially the synthetic analogs with preferable biological half-life and in vivo stability
Octreotide, a somatostatin analog, was used to compound 111In-DTPA-octreotide (OctreoScan), the first commercial radiolabeled peptide, regulatory approved in Europe and USA for clinical application
Summary
The development of Nuclear Medicine towards molecular diagnostic imaging modality in the past two decades was followed by intensive research and applicative work resulting with introduction of wide variety of new generation radiopharmaceuticals. Octreotide, a somatostatin analog, was used to compound 111In-DTPA-octreotide (OctreoScan), the first commercial radiolabeled peptide, regulatory approved in Europe and USA for clinical application. It became the imaging agent of choice for detection of Peptide labeling with 99mTc-pertechnetate is a complex task and considering the small size of peptide. One of the earliest efficient labeling methods was reported by Maecke (Maecke and Béhé, 1996) and later developed by Decristoforo (Decristoforo and Mather, 1999). They used Tyr3octreotide (TOC) conjugated with HYNIC (hydrazinonicotic acid) as a bifunctional chelator. To stabilize the 99mTc - HYNICTOC complex, EDDA (ethylendiamine N, N’ diacetic acid) was used as co-ligand, resulting with favorable biodistribution, low blood levels and high renal excretion of the radiopharmaceutical
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