Nc100668, a New Tracer for Imaging of Venous Thromboembolism: Disposition and Metabolism in Rats

Abstract

ABSTRACT:The NC100668 consists of a 13-amino acid peptide, N-terminally blocked with an acetyl group containing an iodinated tyrosine and coupled to a Tc-chelator (NC100194) via the C-terminal glycine. Using the common three-letter abbreviations for amino acids, the structure of NC100668 is Acetyl-Asn-Gln-Glu-Gln-Val-Ser-ProTyr(3-iodo)-Thr-Leu-Leu-Lys-Gly-NC100194, where NC100194 is represented by the chemical formula -NH-CH 2 -CH 2 -N(CH 2 -CH 2 -NH-C(CH 3 ) 2 -C(CH 3 )ϭN-OH) 2 . The detailed structure is shown in Fig. 1.99m Tc-NC100668 is being developed as a diagnostic radiopharmaceutical for imaging of venous thromboembolism, which is a major health problem with an estimated average annual incidence in the United States exceeding 1 per 1000 (Silverstein et al., 1998). The peptide moiety of NC100668 is similar to part of the N-terminal sequence in ␣ 2 -antiplasmin (Moroi and Aoki, 1976;Lijnen et al., 1987). The mechanism of action is by covalent linking between a glutamine in ␣ 2 -antiplasmin (corresponding to Gln-2 in NC100668) and a lysine in fibrin mediated by enzymatic action of blood coagulation factor XIIIa (Ichinose et al., 1983;Lee et al., 2001;Jaffer et al., 2004).Diagnostic radiopharmaceuticals are radioactive substances that are administered to patients. Many of these agents are labeled with the ␥-emitter 99m Tc, which has a half-life of 6.02 h (Liu et al., 1997). Due to the short half-life, the 99m Tc-based agents are distributed to hospitals in a Tc-free form as a freeze-dried product ready for labeling with technetium. On the day of the imaging procedure, the 99m Tc is added to the product as the pertechnetate anion TcO 4 Ϫ eluted from a 99 Mo/ 99m Tc generator with saline. The freeze-dried substances are then solubilized in saline in the presence of a reducing agent, which converts the pertechnetate to a lower oxidation state, facilitating coordination to the chelate component of the agent. There is a vast excess of the agent compared with the added Tc as typically less than 1% of the injected agent is in the form of the Tc complex. Hence, the unlabeled agent makes up almost the entire amount of the chemical entity injected, whereas there is only the very small amount of the 99m Tc-labeled agent, which is visualized during the diagnostic imaging procedure. The Tc-free substance is therefore in focus when Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.doi:10.1124/dmd.105.006239.ABBREVIATIONS: NC100668, Acetyl-Asn-Gln-Glu-Gln-Val-Ser-Pro-Tyr(3-iodo)-Thr-Leu-Leu-Lys-Gly-NC100194; NC100194, -NH-CH 2 -CH 2 -N(CH 2 -CH 2 -NH-C(CH 3 ) 2 -C(CH 3 )ϭN-OH) 2 ; Fmoc, 9-fluorenyloxycarbonyl; Boc, butyl oxy carbonyl; PyBOP, benzotriazole-1-yl-oxy-tris-pyrrolidinophosphonium hexafluorophosphate; DMF, dimethylformamide; TFA, trifluoroacetic acid; MS, mass spectrometry; HPLC, high-performance liquid chromatography; QWBA, quantitative whole-body autoradiography; SAC, self-absorption coefficient; % ID, percentage of injected dose; LC-MS, liquid chromatography-mass...

NC100668, a New Tracer Tested for Imaging of Venous Thromboembolism: Pharmacokinetics and Metabolism in Humans

“…All the chemicals and substances used were as previously described in the rat metabolism study (Skotland et al, 2006).…”

“…Analysis of chromatographic and mass spectrometry data was performed as previously described in the rat metabolism study (Skotland et al, 2006). Model-independent pharmacokinetic analyses were performed using PK Solutions 2.0 software (Summit Research Services, Montrose, CO).…”

“…Finally, the samples were evaporated under nitrogen and dissolved in 100 l of sample solvent, mixed, and transferred to plastic micro high-performance liquid chromatography vials. Metabolite identification was performed using the LC/MS system previously described in the rat metabolism study (Skotland et al, 2006).…”

“…We have earlier described a rapid clearance from blood of NC100668 following injection in rats, and that two metabolites and no parent compound were identified in rat urine (Skotland et al, 2006). The present data were obtained using samples collected in a Phase I study performed as a placebo-controlled, observer-blinded, randomized, single ascending dose study with five i.v.…”

“…Using the common three-letter abbreviations for amino acids, the structure of NC100668 is Acetyl-Asn-GlnGlu-Gln-Val-Ser-Pro-Tyr(3-iodo)-Thr-Leu-Leu-Lys-Gly-NC100194 where NC100194 is represented by the chemical formula -NH-CH 2 -CH 2 -N(CH 2 -CH 2 -NH-C(CH 3 ) 2 -C(CH 3 )ϭN-OH) 2 . The mechanism of action and the complete molecular structure of this compound can be found at Skotland et al (2006). Diagnostic radiopharmaceuticals are radioactive substances used for medical imaging of a variety of diseases.…”