β-eye: A benchtop system for in vivo molecular screening of labeled compounds

Preclinical nuclear molecular imaging speeds up the mean time from synthesis to market, in drug development process. Commercial imaging systems have in general high cost, require high-cost service contracts, special facilities and trained staff. In the current work, we present β-eye, a benchtop system for in vivo molecular screening of labeled compounds with Positron Emission Tomography (PET) isotopes. The developed system is based on a dual-head geometry, offering simplicity and decreased cost. The goal of the design is to provide 2D, real-time radionuclide images of mice, allowing the recording of fast frames and thus perform fast kinetic studies, with spatial resolution of ∼2 mm. Performance evaluation demonstrates the ability of β-eye to provide quantitative results for injected activities lower than 1.5 MBq, which is adequate for pharmacodynamic studies in small mice.

The Impact of Positron Range on PET Resolution, Evaluated with Phantoms and PHITS Monte Carlo Simulations for Conventional and Non-conventional Radionuclides

PURPOSE

The increasing interest and availability of non-standard positron-emitting radionuclides has heightened the relevance of radionuclide choice in the development and optimization of new positron emission tomography (PET) imaging procedures, both in preclinical research and clinical practice. Differences in achievable resolution arising from positron range can largely influence application suitability of each radionuclide, especially in small-ring preclinical PET where system blurring factors due to annihilation photon acollinearity and detector geometry are less significant. Some resolution degradation can be mitigated with appropriate range corrections implemented during image reconstruction, the quality of which is contingent on an accurate characterization of positron range.

PROCEDURES

To address this need, we have characterized the positron range of several standard and non-standard PET radionuclides (As-72, F-18, Ga-68, Mn-52, Y-86, and Zr-89) through imaging of small-animal quality control phantoms on a benchmark preclinical PET scanner. Further, the Particle and Heavy Ion Transport code System (PHITS v3.02) code was utilized for Monte Carlo modeling of positron range-dependent blurring effects.

RESULTS

Positron range kernels for each radionuclide were derived from simulation of point sources in ICRP reference tissues. PET resolution and quantitative accuracy afforded by various radionuclides in practicable imaging scenarios were characterized using a convolution-based method based on positron annihilation distributions obtained from PHITS. Our imaging and simulation results demonstrate the degradation of small animal PET resolution, and quantitative accuracy correlates with increasing positron energy; however, for a specific "benchmark" preclinical PET scanner and reconstruction workflow, these differences were observed to be minimal given radionuclides with average positron energies below ~ 400 keV.

CONCLUSION

Our measurements and simulations of the influence of positron range on PET resolution compare well with previous efforts documented in the literature and provide new data for several radionuclides in increasing clinical and preclinical use. The results will support current and future improvements in methods for positron range corrections in PET imaging.

Preparation of [In-111]-labeled-DTPA-bombesin conjugates at high specific activity and stability: evaluation of labeling parameters and potential stabilizers

The aim of the present work was to obtain stabilized high specific activity (HSA) (111)In-labeled bombesin conjugates for preclinical evaluations. Parameters influencing the kinetics of labeling were investigated and the effect of stabilizers on HSA radiopeptides stability at room temperature were systematically categorized applying chromatography techniques. A SA of 174 GBq/μmol was achieved with high radiochemical purity, but the labeled compounds exhibited low stability. The addition of stabilizers avoided their radiolysis and significantly increased their stability.

Development of a new bombesin analog radiolabeled with lutetium-177: in vivo evaluation of the biological properties in Balb-C mice

In this work we describe the first results of radiolabeling with lutetium-177 ((177)Lu) and in vivo biodistribution and pharmacokinetics studies in normal Balb-c mice of a new bombesin analog (BEFG2)--DOTA-Phe-X-BBN(6-14), where X is a spacer of two aminoacids. Bombesin (BBN) is an amphibian analog of human gastrin releasing peptide (GRP). Development of radiolabeled BBN derivatives as agents for diagnostic imaging and systemic radiotherapy has increased considerable because of the observation that GRP receptors (GRPr) are over-expressed in a variety of human tumor cells, such as prostate tumor cells. (177)Lu-labeled peptides are attractive due to the excellent radiophysical properties and commercial availability of the radiometal. BEFG2 was successfully labeled with high yield and kept stable for more than 96 hours at 2-8 degrees C and 1 hour in human plasma. Data analysis obtained from the in vivo studies showed that the amount of BEFG2 present in plasma decreased rapidly and became almost undetectable at 60 min p.i., indicating rapid peptide excretion, which is performed mainly by renal pathway. In addition, biodistribution and single photon emission tomography showed low abdominal accumulation of (177)Lu-DOTA- Phe-X-BBN(6-14), indicating that this analog is a potential candidate for tumors target therapy.