Received for publication February 7, 2006.
Revised April 4, 2006.
Accepted for publication April 5, 2006.

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

Abstract

^99mTc NC100668 is a radiopharmaceutical imaging agent being developed to aid the diagnosis of thromboembolism. The stability profile of ^99mTc-NC100668 was investigated by HPLC after in vitro exposure to blood and plasma obtained from rat and man as well as urine and bile obtained from rat. The metabolic profile of ^99mTc-NC100668 exposed to human and rat hepatic S9 was also studied. The profile of ^99mTc-labeled species in plasma, urine and bile was investigated following intravenous administration of ^99mTc-NC100668 to rat. The major species observed in vitro and in vivo consisted of the ^99mTc-chelator (NC100194) attached to the C terminal amino acid residue and referred to as ^99mTc-complex of Gly- NC100194. The identity of the major metabolite was confirmed by co-chromatography with an authentic standard and the genuine metabolite using a second HPLC method. The minor metabolites were sodium pertechnetate (^99mTc) and ^99mTc-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 towards plasma clot was established using a plasma clot forming assay. A minor uptake of ^99mTc-complex of Gly-NC100194 in the plasma clot and a rapid removal from the body were noted. Biodistribution and plasma clot uptake studies showed that ^99mTc-complex of Gly NC100194 will not have a negative effect upon the clinical usefulness of the test substance. In conclusion the metabolites of ^99mTc-NC100668 are not anticipated to have a negative impact on the ability of the test substance to image blood clots.

Key words: HPLC, metabolite identification