Molecular SPECT Imaging: An Overview

Table 3

Tc99m- and In-111-labeled peptides.

Compound	Description	Uses	Remarks
In-111 labeled compounds
In-111 pentetreotide (OctreoScan)	^111In has been conjugated to octreotide as DTPA chelated compound to form the labeled somatostatin tracer (^111In-DTPA-octeriotide).	Octreoscan is an agent designed for the scintigraphic localization of primary and metastatic somatostatin receptor positive neuroendocrine tumors, such as carcinoids, gastrinoma, neuroblastomas, pituitary adenomas, and medullary thyroid carcinomas [44].	Pentetreotide only binds with high affinity to the somatostatin receptor subtype SSTR2 with moderate affinity to SSTR3 and SSTR5 and not to SSTR1 and SSTR4 [30].
In-111 lanreotide (Somatuline)	This peptide is modified with DOTA and labeled with ^111In in a similar way as octreotide [45, 46].	The high binding affinity of lanreotide to SSTR3 and SSTR4 makes it suitable to be used as a proper agent for visualization of certain tumors, such as intestinal adenocarcinomas which is not visualized by ^111In-pentetreotide scintigraphy [47].
^99mTc-labeled peptides
Depreotide (NeoSpect)	Depreotide is a synthetic peptide that binds with high affinity to somatostatin receptors (SSTR) in normal as well as abnormal tissues it has been shown that. It accumulate in pulmonary nodules 1.5–2 hours following the i.v injection [48].	This agent is used to detect SSTR-bearing pulmonary masses in patients proven or suspected to have pulmonary lesions by CT and/or chest X-ray. Negative results with ^99mTc-Depreotide can exclude regional lymph node metastasis with a high degree of probability [49].	Labeling of the depreotide (cyclic decapeptide) with ^99mTc is performed by ligand exchange of intermediary ^99mTc-glucoheptonate [50].
Apcitide (AcuTect)	The kit vial contains a lyophilized mixture of depreotide, sodium glucoheptonate, stannous chloride, and sodium EDTA.	^99mTc-apticide binds to the GP IIb/IIIa receptors on activated platelets that are responsible for aggregation in forming the thrombi and, therefore, is used for the detection of acute deep vein thrombosis (DVT) in lower extremities [28].