BACKGROUND: Contemporary cardiovascular practice relies increasingly on thrombolysis as a therapeutic modality. Its optimal use requires prompt, noninvasive delineation of thrombotic occlusion in arterial beds and rapid detection of reocclusion after initially successful thrombolysis. METHODS AND RESULTS: We have been developing an approach to noninvasively image thrombi in which plasminogen-activating properties of tissue-type plasminogen activator (t-PA) are attenuated by treatment with D-Phe-L-Pro-L-Arg-chloromethyl ketone (PPACK) and have shown that the inactive t-PA avidly and promptly binds to clots in vitro. In the present study, we conjugated this material to a residualizing label, radioiodinated dilactitol tyramine (*I-DLT), and characterized the potential use of the inactivated, conjugated t-PA as a radiopharmaceutical for imaging thrombi in vivo. The approach developed requires not only avid binding of the tracer to thrombi but also rapid clearance from plasma and a lack of prompt release of radiolabeled degradation products from the liver. The rapid clearance of unaltered or PPACK-treated t-PA was not influenced by conjugation to *I-DLT, but the release of radioiodinated degradation products into plasma after injection of *I-DLT-conjugated t-PA was markedly less than release of degradation products of directly radioiodinated t-PA. When 131I-DLT-PPACK-t-PA was infused for 15 minutes intravenously after a bolus injection of 20% in dogs with coronary, pulmonary, or carotid artery thrombi, clearance was rapid. Mean +/- SEM thrombus-to-blood ratios of radioactivity were high, ranging from 37 +/- 9:1 and 2.8 +/- 0.6:1 with carotid thrombi formed concomitantly or approximately 30 minutes before infusion of tracer, respectively, to 35:1 for concomitantly formed coronary thrombi, 42 +/- 7:1 and 8.1 +/- 0.8:1 for concomitantly formed and preformed pulmonary thrombi, respectively, and 18:1 for a preformed femoral artery thrombus. Thrombi were detectable by planar gamma scintigraphy even though image quality was affected adversely by low concentrations of radioactivity that in aggregate composed a relatively large amount of radioactivity in underlying and overlying tissues. This limitation was overcome by tomographic imaging, which was used to detect both femoral and pulmonary thrombi. CONCLUSIONS: Use of enzymatically inactivated t-PA coupled to a residualizing label permits rapid detection and localization of thrombi in vivo.
BACKGROUND: Contemporary cardiovascular practice relies increasingly on thrombolysis as a therapeutic modality. Its optimal use requires prompt, noninvasive delineation of thrombotic occlusion in arterial beds and rapid detection of reocclusion after initially successful thrombolysis. METHODS AND RESULTS: We have been developing an approach to noninvasively image thrombi in which plasminogen-activating properties of tissue-type plasminogen activator (t-PA) are attenuated by treatment with D-Phe-L-Pro-L-Arg-chloromethyl ketone (PPACK) and have shown that the inactive t-PA avidly and promptly binds to clots in vitro. In the present study, we conjugated this material to a residualizing label, radioiodinated dilactitol tyramine (*I-DLT), and characterized the potential use of the inactivated, conjugated t-PA as a radiopharmaceutical for imaging thrombi in vivo. The approach developed requires not only avid binding of the tracer to thrombi but also rapid clearance from plasma and a lack of prompt release of radiolabeled degradation products from the liver. The rapid clearance of unaltered or PPACK-treated t-PA was not influenced by conjugation to *I-DLT, but the release of radioiodinated degradation products into plasma after injection of *I-DLT-conjugated t-PA was markedly less than release of degradation products of directly radioiodinated t-PA. When 131I-DLT-PPACK-t-PA was infused for 15 minutes intravenously after a bolus injection of 20% in dogs with coronary, pulmonary, or carotid artery thrombi, clearance was rapid. Mean +/- SEM thrombus-to-blood ratios of radioactivity were high, ranging from 37 +/- 9:1 and 2.8 +/- 0.6:1 with carotid thrombi formed concomitantly or approximately 30 minutes before infusion of tracer, respectively, to 35:1 for concomitantly formed coronary thrombi, 42 +/- 7:1 and 8.1 +/- 0.8:1 for concomitantly formed and preformed pulmonary thrombi, respectively, and 18:1 for a preformed femoral artery thrombus. Thrombi were detectable by planar gamma scintigraphy even though image quality was affected adversely by low concentrations of radioactivity that in aggregate composed a relatively large amount of radioactivity in underlying and overlying tissues. This limitation was overcome by tomographic imaging, which was used to detect both femoral and pulmonary thrombi. CONCLUSIONS: Use of enzymatically inactivated t-PA coupled to a residualizing label permits rapid detection and localization of thrombi in vivo.
Authors: D R Elmaleh; A J Fischman; A Tawakol; A Zhu; T M Shoup; U Hoffmann; A-L Brownell; P C Zamecnik Journal: Proc Natl Acad Sci U S A Date: 2006-10-12 Impact factor: 11.205
Authors: D R Elmaleh; J Narula; J W Babich; A Petrov; A J Fischman; B A Khaw; E Rapaport; P C Zamecnik Journal: Proc Natl Acad Sci U S A Date: 1998-01-20 Impact factor: 11.205
Authors: Marius C Wick; Christina Mayerl; Aleksandar Backovic; Ruurd van der Zee; Werner Jaschke; Hermann Dietrich; Georg Wick Journal: Cell Stress Chaperones Date: 2008-05-09 Impact factor: 3.667