Thrombus imaging using technetium-99m-labeled high-potency GPIIb/IIIa receptor antagonists. Chemistry and initial biological studies
Platelet-specific compounds which are radiolabeled with γ-emitting radionuclides may be particularly useful for the noninvasive in vivo detection of thrombi. The synthesis of peptides which are potent inhibitors of platelet aggregation and which contain a chelator for the radionuclide technetium-99m are described. The target compounds were designed such that stable, oxotechnetium(V) species could be prepared where the site of metal coordination was well defined. A strategy was employed where the pharmacophore -Arg-Gly-Asp-(RGD), or RGD mimetic, was constrained in a ring which was formed by the S-alkylation of a cysteine residue with an N-terminal chloroacetyl group. Binding affinities were enhanced by the replacement of arginine with the arginine mimetics S-(3-aminopropyl)cysteine and 4- amidinophenylalanine. Further enhancements could be obtained by the synthesis of oligomers which contained two or more rings containing receptor binding regions. The increase in binding affinity seen was more than that expected from a simple stoichiometric increase of pharmacophore. The most potent compounds described had IC50s of approximately 0.03 μM for the inhibition of human platelet aggregation. Two of the more potent peptides (P280 and P748) were labeled with technetium-99m and assessed in a canine thrombosis model. The 99mTc complexes of the peptides prepared in this work hold promise as thrombus imaging agents due to their high receptor binding affinity, ease of preparation, and expected rapid pharmacokinetics.
Pearson, Daniel A.,Lister-James, John,McBride, William J.,Wilson, David M.,Martel, Lawrence J.,Civitello, Edgar R.,Dean, Richard T.
Fluorobenzamidrazone thrombin inhibitors: Influence of fluorine on enhancing oral absorption
LB30057 (1) is a selective and efficacious oral thrombin inhibitor. Fluorine-substitution on the phenylene ring of the benzamidrazone portion in both compound 1 and its derivatives gave, in many cases, enhanced oral absorption in rats while maintaining the intrinsic potency and selectivity. Compound 2 demonstrated a 3-fold increase in absorption.
Thrombin inhibitors with functionalized benzamidines as surrogates for arginine were designed, synthesized, and characterized. Amino acid sequence difference in the position 190 between thrombin and trypsin was exploited in the design to enhance selectivity over trypsin. A representative compound 6 showed high potency (Ki of 45.5 nM) and extremely high specificity over trypsin (over 10,000 fold).
Kim, Sangsoo,Hwang, Sang Yeul,Kim, Young Kwan,Yun, Mikyung,Oh, Yeong Soo
p. 769 - 774
(2007/10/03)
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