Preparation of 99mTc labeled substance P (SP)

Substance P (SP) is an ll-amino acid neuropeptide of the tachykinin family. This study investigated the preparation of an SP analog labeled with 99mTc for imaging SP receptor positive tissue (inflammatory diseases and neoplasms with increased expression of SP receptors). High specific activity 99mTc-SP was prepared using the 1-imino-4-mercaptobutyl (IMB) group as a bifunctional chelator. Biological distribution in mice showed increased 99mTc-SP uptake in the salivary glands (which have a high concentration of SP receptors), but this activity was displaced in animals pre-treated with excess non-radioactive SP. These data show that the uptake of 99mTc-SP is receptor specific. IMB derivatization at the N-terminal location is suitable for labeling of SP analogues with 99mTc. Synthetic analogues of SP labeled with 99mTc may be an attractive alternative to 111In labeled molecules and merit further investigation.