Objectives: Receptor scintigraphy gains more interest for diagnosis and treatment of tumors, in particular for neuroendocrine tumors (NET). We used a pan-Bombesin analog, the peptide DOTA-PEG2-[D-tyr(6), beta-Ala(11), Thi(13), Nle(14)] BN(6-14) amide (BZH3). BZH3 binds to at least three receptor subtypes: the BB1 (Neuromedin B), BB2 (Gastrin-releasing peptide, GRP), and BB3. Imaging of alpha nu beta 3 integrin expression playing an important role in angiogenesis and metastasis was accomplished with a Ga-68-RGD tetramer. The purpose of this study was to investigate the kinetics and to compare both tracers in an experimental NET cell line. Methods: This study comprised nine nude rats inoculated with the pancreatic tumor cell line AR42J. Dynamic positron emission tomography (PET) scans using Ga-68-BZH3 and Ga-68-RGD tetramer were performed (Ga-68-RGD tetramer: n = 4, Ga-68-BZH3: n = 5). Standardized uptake values (SUVs) were calculated, and a two-tissue compartmental learning-machine model (calculation of K1 - k4 vessel density (VB) and receptor binding potential (RBP)) as well as a non-compartmental model based on the fractal dimension was used for quantitative analysis of both tracers. Multivariate analysis was used to evaluate the kinetic data. Results: The PET kinetic parameters showed significant differences when individual parameters were compared between groups. Significant differences were found in FD, VB, K1, and RBP (p = 0.0275, 0.05, 0.05, and 0.0275 respectively). The 56- to 60-min SUV for Ga-68-BZH3, with a range of 0.86 to 1.29 (median, 1.19) was higher than the corresponding value for the Ga-68-RGD tetramer, with a range of 0.78 to 1.31 (median, 0.99). Furthermore, FD, VB, K1, and RBP for Ga-68-BZH3 were generally higher than the corresponding values for the Ga-68-RGD tetramer, whereas k3 was slightly higher for Ga-68-RGD tetramer. Conclusions: As a parameter that reflects receptor binding, the increase of K1 for Ga-68-BZH3 indicated higher expression of bombesin receptors than that of the alpha nu beta 3 integrin in neuroendocrine tumors. Ga-68-BZH3 seems better suited for diagnosis of NETs owing to higher global tracer uptake.
