99mTc-NC100692--a tracer for imaging vitronectin receptors associated with angiogenesis: a preclinical investigation.

INTRODUCTION: Technetium 99m (99mTc)-NC100692 is being developed as a marker of vitronectin receptor expression. The purpose of this study was to confirm the binding affinity [dissociation constant (Kd)] of 99mTc-NC100692 for a range of integrin receptors including alphavbeta3 and alphavbeta5 as well as to establish the biodistribution and metabolic stability of 99mTc-NC100692 in Wistar rats. METHODS: The Kd of 99mTc-NC100692 for a range of human integrin receptors was established in an in vitro saturation binding assay. The biodistribution and metabolic stability of 99mTc-NC100692 in normal Wistar rats was investigated. RESULTS: The Kd of 99mTc-NC100692 to alphavbeta3 and alphavbeta5 was less than 1 nM. It was not possible to saturate the binding of 99mTc-NC10092 towards alphaIIbbeta3, alpha5beta1, alpha3beta1 or alpha1beta1, and as a result, accurate Kd values could not be determined. The biodistribution of 99mTc-NC100692 in male and female Wistar rats showed that radioactivity was rapidly excreted, predominantly into the urine, with very little background tissue retention apart from the liver and kidneys. Kidney and liver retention was reduced in the presence of excess NC100692 ligand. In vivo, there was little systemic metabolism of 99mTc-NC100692. CONCLUSIONS: 99mTc-NC100692 has a high affinity for the vitronectin receptors that are associated with angiogenesis. 99mTc-NC100692 is metabolically stable in the systemic circulation of rats with a biodistribution that is favourable for imaging purposes. This evidence suggests that 99mTc-NC100692 might be a useful marker of vitronectin receptor expression in vivo.

(99m)Tc-NC100668, a new tracer for imaging venous thromboemboli: pre-clinical biodistribution and incorporation into plasma clots in vivo and in vitro.

PURPOSE: (99m)Tc-NC100668 is a new radiotracer being developed to aid the diagnosis of thromboembolism. The structure of NC100668 is similar to a region of human alpha(2)-antiplasmin, which is a substrate for factor XIIIa (FXIIIa). The purpose of this study was to confirm the uptake of (99m)Tc-NC100668 into forming plasma clot and to establish the biodistribution of (99m)Tc-NC100668 in Wistar rats. METHODS: The in vitro plasma clot uptake of (99m)Tc-NC100668 and other compounds with known affinities to FXIIIa was measured using a plasma clot assay. The biodistribution and blood clot uptake of radioactivity of (99m)Tc-NC100668 in normal Wistar rats and those bearing experimentally induced deep vein thrombi were investigated. RESULTS: The in vitro uptake of (99m)Tc-NC100668 was greater than that for [(14)C]dansyl cadaverine, a known substrate of FXIIIa in the plasma clot assay. The biodistribution of (99m)Tc-NC100668 in male and female Wistar rats up to 24 h p.i. showed that radioactivity was rapidly excreted, predominantly into the urine, with very little background tissue retention. In vivo the uptake and retention of (99m)Tc-NC100668 into the blood clot was greater than could be accounted for by non-specific accumulation of the radiotracer within the blood clot. CONCLUSION: (99m)Tc-NC100668 was retained by plasma clots in vitro and blood clots in vivo. No significant tissue retention which could interfere with the ability to image thrombi in vivo was observed. This evidence suggests that (99m)Tc-NC100668 might be useful in the detection of thromboembolism.

The in vivo and in vitro metabolic profile of 99mTc-NC100668, a new tracer for imaging venous thromboembolism: identification and biodistribution of the principal radiolabeled metabolite.

(99m)Tc-NC100668 [Acetyl-Asn-Gln-Glu-Gln-Val-Ser-Pro-Tyr(3-iodo)-Thr-Leu-Leu-Lys-Gly-NC100194] is a radiopharmaceutical imaging agent being developed to aid the diagnosis of thromboembolism. The stability profile of (99m)Tc-NC100668 was investigated by high-performance liquid chromatography (HPLC) after in vitro exposure to blood and plasma obtained from rat and human, as well as to urine and bile obtained from rat. The metabolic profile of (99m)Tc-NC100668 exposed to human and rat hepatic S9 (a liver homogenate-rich cytochrome P450) was also studied. The profile of (99m)Tc-labeled species in plasma, urine, and bile was investigated following i.v. administration of (99m)Tc-NC100668 to rat. The major species observed in vitro and in vivo consisted of the (99m)Tc-chelator (NC100194) [N,N-Bis(N-(1,1-dimethyl-2-(hydroxylimino-)propyl)aminoethyl)aminoethylamine] attached to the C-terminal amino acid residue and referred to as (99m)Tc-complex of Gly-NC100194. The identity of the major metabolite was confirmed by cochromatography with an authentic standard and the genuine metabolite using a second HPLC method. The minor metabolites were sodium pertechnetate ((99m)Tc) and (99m)Tc-NC100194. In addition, a small number of other species were transiently observed in vitro; they were not investigated further. The biodistribution of the major metabolite was studied in male Wistar rats. The affinity of the major metabolite toward plasma clot was established using a plasma clot-forming assay. A minor uptake of (99m)Tc-complex of Gly-NC100194 in the plasma clot and a rapid removal from the body were noted. In conclusion, the metabolites of (99m)Tc-NC100668 are not anticipated to have a negative impact on the ability of the test substance to image blood clots.