ABSTRACT
INTRODUCTION: The aim of this study was to synthesize and perform a side-by-side comparison of two new tumor-angiogenesis PET tracers (68)Ga-NODAGA-E[c(RGDyK)](2) and (64)Cu-NODAGA-E[c(RGDyK)](2) in vivo using human xenograft tumors in mice. Human radiation burden was estimated to evaluate potential for future use as clinical PET tracers for imaging of neo-angiogenesis. METHODS: A (68)Ge/(68)Ga generator was used for the synthesis of (68)Ga-NODAGA-E[c(RGDyK)](2). (68)Ga and (64)Cu labeled NODAGA-E[c(RGDyK)](2) tracers were administrated in nude mice bearing either human glioblastoma (U87MG) or human neuroendocrine (H727) xenograft tumors. PET/CT scans at 3 time points were used for calculating the tracer uptake in tumors (%ID/g), integrin αVß3 target specificity was shown by blocking with cold NODAGA-E[c(RGDyK)](2), and biodistribution in normal organs were also examined. From biodistribution data in mice human radiation-absorbed doses were estimated using OLINDA/EXM software. RESULTS: (68)Ga-NODAGA-E[c(RGDyK)](2) was synthesized with a radiochemical purity of 89%-99% and a specific activity (SA) of 16-153 MBq/nmol. (64)Cu-NODAGA-E[c(RGDyK)](2) had a purity of 92%-99% and an SA of 64-78 MBq/nmol. Both tracers showed similar uptake in xenograft tumors 1h after injection (U87MG: 2.23 vs. 2.31%ID/g; H727: 1.53 vs. 1.48%ID/g). Both RGD dimers showed similar tracer uptake in non-tumoral tissues and a human radiation burden of less than 10 mSv with an administered dose of 200 MBq was estimated. CONCLUSION: (68)Ga-NODAGA-E[c(RGDyK)](2) and (64)Cu-NODAGA-E[c(RGDyK)](2) can be easily synthesized and are both promising candidates for PET imaging of integrin αVß3 positive tumor cells. (68)Ga-NODAGA-E[c(RGDyK)](2) showed slightly more stable tumor retention. With the advantage of in-house commercially (68)Ge/(68)Ga generators, (68)Ga-NODAGA-E[c(RGDyK)](2) may be the best choice for future clinical PET imaging in humans.
Subject(s)
Acetates/chemistry , Cell Transformation, Neoplastic , Copper Radioisotopes , Glioblastoma/pathology , Heterocyclic Compounds, 1-Ring/chemistry , Oligopeptides/chemistry , Positron-Emission Tomography/methods , Animals , Cell Line, Tumor , Female , Gallium Radioisotopes , Glioblastoma/blood supply , Glioblastoma/diagnostic imaging , Humans , Mice , Mice, Nude , Neovascularization, Pathologic/diagnostic imaging , Oligopeptides/pharmacokinetics , Radiochemistry , Radiometry , Tissue Distribution , Tomography, X-Ray ComputedABSTRACT
Peptide receptor radionuclide therapy (PRRT) is a relatively new mode of internally targeted radiotherapy currently in clinical trials. In PRRT, ionizing radioisotopes conjugated to somatostatin analogues are targeted to neuroendocrine tumors (NETs) via somatostatin receptors. Despite promising clinical results, very little is known about the mechanism of tumor control. By using NCI-H727 cells in an in vivo murine xenograft model of human NETs, we showed that (177)Lu-DOTATATE PRRT led to increased infiltration of CD86+ antigen presenting cells into tumor tissue. We also found that following treatment with PRRT, there was significantly increased tumor infiltration by CD49b+/FasL+ NK cells potentially capable of tumor killing. Further investigation into the immunomodulatory effects of PRRT will be essential in improving treatment efficacy.
ABSTRACT
UNLABELLED: The purpose of this study was to investigate whether a correction for annihilation photon attenuation in small objects such as mice is necessary. The attenuation recovery for specific organs and subcutaneous tumors was investigated. A comparison between different attenuation correction methods was performed. METHODS: Ten NMRI nude mice with subcutaneous implantation of human breast cancer cells (MCF-7) were scanned consecutively in small animal PET and CT scanners (MicroPET(TM) Focus 120 and ImTek's MicroCAT(TM) II). CT-based AC, PET-based AC and uniform AC methods were compared. RESULTS: The activity concentration in the same organ with and without AC revealed an overall attenuation recovery of 9-21% for MAP reconstructed images, i.e., SUV without AC could underestimate the true activity at this level. For subcutaneous tumors, the attenuation was 13 ± 4% (9-17%), for kidneys 20 ± 1% (19-21%), and for bladder 18 ± 3% (15-21%). The FBP reconstructed images showed almost the same attenuation levels as the MAP reconstructed images for all organs. CONCLUSIONS: The annihilation photons are suffering attenuation even in small subjects. Both PET-based and CT-based are adequate as AC methods. The amplitude of the AC recovery could be overestimated using the uniform map. Therefore, application of a global attenuation factor on PET data might not be accurate for attenuation correction.
