1. Preparation and characterization of [99TcO] apcitide: a technetium labeled peptide
Lynn C Francesconi, Yongyong Zheng, Judit Bartis, Michael Blumenstein, Catherine Costello, Mark A De Rosch Inorg Chem. 2004 May 3;43(9):2867-75. doi: 10.1021/ic035473w.
[99mTcO] apcitide (99mTcO(P246)), the technetium complex of the 13 amino acid, apcitide, cyclo-(D-Tyr-Apc-Gly-Asp-Cys)-Gly-Gly-Cys(Acm)-Gly-Cys(Acm)-Gly-Gly-Cys-NH2, where Apc is L-[S-(3-aminopropyl)]cysteine (an arginine mimetic) and Acm is the acetamidomethyl protecting group, has high affinity and selectivity for the GPIIb/IIIa receptor that is expressed on the membrane surface of activated platelets and plays an integral role in platelet aggregation and thrombus formation. Bibapcitide, a 26 amino acid, bis-succinimidomethyl ether-linked dimer of the peptide apcitide has been formulated as a single-vial, lyophilized kit having the trade name AcuTect. When sterile, nonpyrogenic sodium pertechnetate (99mTcO4-) in 0.9% sodium chloride is added to the AcuTect radiopharmaceutical kit and the resulting kit is heated, [99mTcO] apcitide forms. This is the first radiopharmaceutical to target acute deep vein thrombosis (DVT) in the lower extremities. We report here the preparation, purification, and isolation of the 99Tc complex of apcitide and its characterization to determine the mode of binding of Tc to apcitide. [99TcO] apcitide was prepared, on the macroscopic level, by reaction of [99TcOCl4]- with apcitide, purified by preparative HPLC and isolated as a trifluoroacetate salt. [99TcO] apcitide can also be formed from the reaction of bibapcitide and 99TcO4- in the presence of Sn(II) and glucoheptonate at 80 degrees C, conditions that mimic the radiopharmaceutical kit preparation. FTIR data show a Tc=O stretch at 961.2 cm(-1), in the range observed for anionic [TcVO]3+ amide thiolate complexes. The mass spectral data is in agreement with the formula, [C51H73O20N17S5Tc]-, consistent with retention of Acm groups and the Tc binding in the Gly11-Gly12-Cys13 region of the peptide. Despite significant spectral overlap due to numerous similar amino acids, all protons of apcitide and [99TcO] apcitide were unambiguously assigned. The observation of two nonequivalent Acm groups and the observation of only 10 NH-CH cross-peaks in the TOCSY and COSY spectra of [99TcO] apcitide (NH-CH cross-peaks were absent for Gly11-Gly12-Cys13), compared to all 13 cross-peaks found in apcitide, provided compelling evidence to support the 99Tc binding to the terminal Gly11-Gly12-Cys13 region of apcitide.
2. Acute thromboscintigraphy with (99m)Tc-apcitide: results of the phase 3 multicenter clinical trial comparing 99mTc-apcitide scintigraphy with contrast venography for imaging acute DVT. Multicenter Trial Investigators
R Taillefer, S Edell, G Innes, J Lister-James J Nucl Med. 2000 Jul;41(7):1214-23.
(99m)Tc-apcitide (formerly known as (99m)Tc-P280) is a radiolabeled peptide that binds with high affinity and specificity to the glycoprotein IIb/IIIa receptors expressed on the activated platelets that are involved in acute thrombosis. The purpose of the phase 3 multicenter clinical trials was to compare (99m)Tc-apcitide scintigraphy with contrast venography for imaging acute deep venous thrombosis (DVT). Methods: A total of 280 patients were enrolled in 2 clinical trials conducted in North America and Europe. Patients were to be within 10 d of onset of signs and symptoms of acute DVT or within 10 d of surgery associated with a high risk of DVT. (99m)Tc-apcitide scintigraphy and contrast venography were to be performed within 36 h. Planar scintigraphic images were obtained at 10, 60, and 120-180 min after injection. (99m)Tc-apcitide scintigrams and contrast venograms were read with masking and also by the institutional investigators. Results: Of a total of 243 patients who were evaluable, 61.7% were receiving heparin at the time of imaging. Masked reading of (99m)Tc-apcitide scintigraphy, compared with masked reading of contrast venography, had a sensitivity, specificity, and agreement of 73.4%, 67.5%, and 69.1%, respectively, which met the prospectively defined target efficacy endpoint in both trials. Institutional reading of (99m)Tc-apcitide scintigraphy, compared with institutional reading of contrast venography, had a sensitivity, specificity, and agreement of 75.5%, 72.8%, and 74.0%, respectively. However, the entire trial population included patients with a history of DVT who may have had old, nonacute venous thrombi that could confound the venography results. Therefore, data from patients having no history of DVT or pulmonary embolism and who presented within 3 d of onset of signs and symptoms (n = 63), i.e., patients for whom a venogram would be expected to be positive only if acute DVT were present, also were analyzed as a subset. In these patients, institutional reading of (99m)Tc-apcitide scintigraphy, compared with institutional reading of contrast venography, had a sensitivity, specificity, and agreement of 90.6%, 83.9%, and 87.3%, respectively. Conclusion: (99m)Tc-apcitide scintigraphy is a new diagnostic modality that is highly sensitive for imaging acute DVT.
3. Imaging characteristics of a novel technetium Tc 99m-labeled platelet glycoprotein IIb/IIIa receptor antagonist in patients With acute deep vein thrombosis or a history of deep vein thrombosis
Shannon M Bates, John Lister-James, Jim A Julian, Raymond Taillefer, Brian R Moyer, Jeffrey S Ginsberg Arch Intern Med. 2003 Feb 24;163(4):452-6. doi: 10.1001/archinte.163.4.452.
Background: The diagnosis of recurrent deep vein thrombosis (DVT) is challenging. Imaging with radiolabeled peptides offers a new approach for detecting acute DVT. Technetium Tc 99m ((99m)Tc)-apcitide binds with high affinity and specificity to the glycoprotein IIb/IIIa receptors expressed on activated platelets and, therefore, (99m)Tc-apcitide scintigraphy should be negative with residual abnormalities caused by old, inactive thrombi and positive with new, active thrombi. Methods: In a prospective multicenter study, (99m)Tc-apcitide imaging was performed on 38 patients with a newly diagnosed first DVT (group 1) and 40 patients with previous DVT, symptoms of postthrombotic syndrome, and chronic intraluminal abnormalities on ultrasonography (group 2). Images were interpreted in a blinded fashion by 2 experts and by newly trained nuclear medicine physicians. The sensitivity and specificity of (99m)Tc-apcitide were determined by calculating the proportion of scans in group 1 patients that were read as "positive for acute DVT" and the proportion of scans in group 2 patients that were read as "negative for acute DVT," respectively. Results: When read by 2 experts, ( 99m)Tc-apcitide had a sensitivity of 92% for both readers and specificities of 82% and 90%. Agreement between the experts was excellent. However, the accuracy and interreader agreement for newly trained nuclear medicine physicians were lower. Conclusions: Technetium Tc 99m-apcitide scintigraphy has potential utility in suspected recurrent DVT because it detects most acute thrombi and has few false-positive results in patients with previous DVT. However, the accuracy appears to depend on the training and experience of the interpreters.
