Tirofiban as potential radiopharmaceutic for detection of thromboembolic disoreders: animal model

Vaskularna oboljenja spadaju među vodeće uzročnike povećanog morbiditeta i mortaliteta kod ljudi koji žive u razvijenim zemljama. Duboka venska tromboza (DVT) i plućna embolija su ozbiljne komplikacije, pa je zato detekcija akutne i rane DVT-e veoma bitna, pre svega, zbog posledica koje one nosi sa sobom (rizik od plućne embolije, hronična venska insuficijencija). Kod ovih patoloških stanja uloga trombocita je suštinska, zbog njihove sposobnosti da formiraju agregate, koji nastaju kao posledica oštećenja krvnog suda. Trobocitni glikoproteinski IIb/IIIa (GPIIb/IIIa) receptor je ključna komponenta u procesu trombocitne agregacije, a samim tim i ciljno mesto za terapijsku intervenciju. Tirofiban (N-(butilsulfonil)-4-O-(4-(4-piperidil)-L-tirozin) je nepeptidni tirozinski derivat, visoko selektivni, kratkodelujući inhibitor fibrinogenskog vezivanja za trombocitni glikoproteinski receptor IIb/IIIa. Kao molekul sa malom molarnom masom tirofiban ima veliku prednost, kako u postupku za njegovo obeležavanje radioaktivnim izotopima, tako i pri njegovoj aplikaciji u organizam, bez opasnosti od pojave imunoloških reakcija nakon primene. Takođe, bitan parametar je i njegova brza eliminacija iz organizma. Tirofiban se vezuje za GPIIb/IIIa receptore na isti način kao što se vezuje i fibrinogen, a može se naći samo u aktivnom ugrušku. Ovaj fenomen pokazuje razliku između akutnog i hroničnog ugruška, pri upotrebi radiofarmaceutika. Obeležavanjem tirofibana radioaktivnim izotopom tehnecijuma (99mTc), kao optimalnim gama emiterom podobnim za dijagnostičku upotrebu, pokazali smo da možemo detektovati patološke promene krvnih sudova, identifikovati lokalizaciju tromba i odrediti morfološke karakteristike tromba. Vizuelizacione studije, rađene na eksperimentalnom animalnom modelu duboke venske tromboze, jasno su nam pokazale akumulaciju tirofibana u femoralnoj veni testiranih životinja. Praćenjem koncentracija neradioaktivnog i radioaktivno obeleženog tirofibana u plazmi, 5, 15, 30, 45 i 60 min. nakon i.v. bolus injekcije, utvrdili smo da 99mTc-tirofiban-a ima identično ponašanje kao i neradioaktivni tirofiban. Uvođenjem tehnecijuma i promenom strukture molekula ne menja se, već poznati, farmakokinetički profil leka...Vascular diseases are one of the leading reasons for increased morbidity and mortality in people living in high-income countries. Deep venous thrombosis (DVT) and pulmonary embolism (PE) are very serious complications and initial detection of them is always very important. In these pathological conditions the role of platelets is very important, their ability to generate aggregates, which occur as a result of damaged blood vessels. The platelet glycoprotein IIb/IIIa (GP IIb / IIIa) receptor is a key component in the process of platelet aggregation, and thus the target site for therapeutic action. Tirofiban (N-(methylsulfonyl)-4-O-(4-(4-piperidinyl)-L-tyrosine) is a non-peptide, derivative of tyrosine, highly selective, short-acting inhibitor of fibrinogen binding to the platelet glycoprotein IIb/IIIa receptor. As a molecule with a small molecular weight and simple chemical structure, tirofiban provide possibility to be used as radiolabeled potential radiopharmaceutical, to inject in the patient without the risk of the occurrence of immune reactions after administration. The size and structure also is an important parameter for its fast elimination from the body. Tirofiban binds GPIIb/IIIa receptors in the same way as fibrinogen, and can be seen only in the active clot. This phenomenon indicates the difference between acute and chronic blood clot, and can be used as advantage for vizualization. The idea to formulate radioactive Tirofiban using Technetium-99m as a radioisotope for labeling and use for diagnostic purpose, was following the demand to detect primary pathological deviations in the blood vessels, to identify the localization of the new fresh thromb and to define its morphological characteristics. Imaging studies performed using experimental animal model of deep vein thrombosis, clearly showed the pathological accumulation of tirofiban in the femoral vein of the animal. The concentration of non-radioactive and radiolabelled tirofiban in plasma 5, 15, 30, 45 and 60 min. observed after i.v. bolus injection, confirmed that 99mTc-Tirofiban has identical behavior as non-radioactive. The introduction of Technetium-99m iside of the structure of molecule of Tirofiban, does not change the regular pharmacokinetic profile of the drug..