Novel Biological and Molecular Characterization in Radiopharmaceutical Preclinical Design

In this study, the potential of a digital autoradiography system equipped with a super resolution screen has been evaluated to investigate the biodistribution of a 18F-PSMA inhibitor in a prostate cancer mouse model. Twelve double xenograft NOD/SCID mice (LNCAP and PC3 tumours) were divided into three groups according to post-injection time points of an 18F-PSMA inhibitor. Groups of 4 mice were used to evaluate the biodistribution of the radiopharmaceutical after 30-, 60- and 120-min post-injection. Data here reported demonstrated that the digital autoradiography system is suitable to analyse the biodistribution of an 18F-PSMA inhibitor in both whole small-animal bodies and in single organs. The exposure of both whole mouse bodies and organs on the super resolution screen surface allowed the radioactivity of the PSMA inhibitor distributed in the tissues to be detected and quantified. Data obtained by using a digital autoradiography system were in line with the values detected by the activity calibrator. In addition, the image obtained from the super resolution screen allowed a perfect overlap with the tumour images achieved under the optical microscope. In conclusion, biodistribution studies performed by the autoradiography system allow the microscopical modifications induced by therapeutic radiopharmaceuticals to be studied by comparing the molecular imaging and histopathological data at the sub-cellular level.

On site production of [18F]PSMA-1007 using different [18F]fluoride activities: practical, technical and economical impact

Background Prostate-specific membrane antigen is overexpressed in prostate cancer and it is considered a good target for positron emission tomography/computed tomography imaging of primary cancer and recurrent/metastatic disease, as well as for radioligand therapy. Different PSMA-analogues labeled with [68Ga]gallium have been investigated, showing excellent imaging properties; however, only small amounts can be produced for each radiolabeling. Recently, a [18F]fluoride labeled PSMA-inhibitor, [18F]PSMA-1007, has been introduced, and it has ensured large-scale productions, overcoming this limitation of [68Ga]PSMAs. In this study, PSMA-1007 has been labeled with low (A), medium (B) and high (C) starting activities of [18F]fluoride, in order to verify if radiochemical yield, radiochemical purity and stability of [18F]PSMA-1007 were affected. These parameters have been measured in sixty-five consecutive batches. In addition, the estimation of [18F]PSMA-1007 production costs is provided. Results The radiochemical yield for low and medium activities of [18F]fluoride was 52%, while for the high one it decreased to 40%. The radiochemical purity was 99% for all three activities. [18F]PSMA-1007 did not show radiolysis up to 8 h after the end of synthesis, confirming that the radiopharmaceutical is stable and suitable to perform diagnostic studies in humans for a long period of time after the end of radiolabeling. Furthermore, radiochemical stability was demonstrated in fetal bovine serum at 4 °C and 37 °C for 120′. Conclusions A starting activity of [18F]fluoride of 90 GBq (B) seems to be the best option enabling a final amount of about of 50 GBq of [18F]PSMA-1007, which is promising as it allows to: (a) perform a large number of scans, and/or (b) supply the radiopharmaceutical to any peripheral diagnostic centers in need.

On Site Production of [18F]-PSMA1007 Using Different [18F]-fluoride Activities. Practical, Technical and Economical Impact.

BackgroundProstate-Specific Membrane Antigen is overexpressed in prostate cancer and it is considered a good target for staging of primary and recurrences as well as for radioligand therapy. Different PSMA-analogues have been investigated, labeled with [68Ga], showing excellent imaging properties; although, only small amounts can be produced for single synthesis. Recently, a fluorinated PSMA-inhibitor, [18F]-PSMA-1007, has been introduced, ensuring large-scale productions. In this study, the radiosynthesis of [18F]-PSMA-1007 using low (A), medium (B) and high (C) starting activities of [18F]-Fluoride, has been fully tested. The following parameters radiochemical yield, radiochemical purity and stability of [18F]-PSMA-1007 have been measured in 65, consecutive batches to verify the effects of the three different conditions. In addition, the analysis of the costs for the production has been performed. ResultsThe radiochemical yield percentage for low and medium range of activities of [18F]-Fluoride was 52%, while for the high range it decreases to 40%. The radiochemical purity was 99% in all three tested starting activities. [18F]-PSMA-1007 did not show radiolysis up to 8 hours after the end of synthesis, confirming that the radiopharmaceutical is stable an suitable for PET studies in humans. Furthermore, stability studies performed in fetal bovine serum demonstrated radiochemical stability at 37°C for 120’. ConclusionsA starting activity of [18F]-Fluoride of 90 GBq (range B) enables a final amount of [18F]-PSMA-1007 of about 50 GBq, which is powerful for different choices: to perform up to 25 PET/CT scans in a referral institution for prostate cancer, and/or to supply the eventual peripheral PET centers.

The use of prosthetic groups for synthesis of addressed RFLP molecules for positron emission tomography

The aim of the research. An intensive research is underway to create new methods for the synthesis of fl uorine-18 labeled radiopharmaceuticals. Th e aim of this work is to select iodoaliphatic carboxylic acids and esters for radiopharmaceuticals labeling. Material and methods. A simple way to obtain z-yodalifi c carbonic acids and complex esters from commercially available cyclic ketones has been developed. Automatic synthesis of 18F-fl uoroproprostatic groups and 18F fl uoride peptide agents is successfully carried out using new original materials and various purifi cation methods with solid phase cartridges Results. In further work, it is planned to use diff erent 18F-fl uoroproproprostatic groups for synthesis with various peptide agents. Conclusion. Based on these compounds 18F-fl uoroproproprostatic groups were synthesized. Octreotid as an analogue of somatostatin, the non-immunoglobulin-specifi c frame proteins (designed ankyrin repeat proteins) for targeted imaging of tumor cells hyperexpressing Her-2/neu, and prostate-specifi c membrane antigen (PSMA) inhibitor are signifi cant peptide agents.

Development of an Albumin-Based PSMA Probe With Prolonged Half-Life

Prostate-specific membrane antigen (PSMA) is an attractive target for the diagnosis and therapy of prostate cancer as it is specifically overexpressed in prostate cancer cells. Improving the circulation of radioligands in the blood is considered as an effective strategy that can improve tumor burden, which benefits detection of small lesions and improves the effect of PSMA radioligand therapy (PRLT). In this study, we introduced maleimidopropionic acid (MPA) to a PSMA-targeted tracer and developed Al18F-PSMA-CM, which targets human serum albumin (HSA) binding and PSMA. Al18F-PSMA-CM is evaluated in vitro and in vivo for stability, PSMA specificity, and biodistribution in 22Rv1 tumor-bearing mice. Al18F-PSMA-CM was prepared with a radiochemical purity of >99% and specific activity of 11.22–18.70 MBq/nmol. Al18F-PSMA-CM was stable in vitro and in vivo and prolonged circulation in blood with a binding ratio of 47 ± 3.2% and Kd value of 3.08 ± 0.45 nM to HSA. The uptake of Al18F-PSMA-CM in PSMA(+) 22Rv1 cells was increased in 2 h, and the uptake was blocked by a PSMA inhibitor, ZJ-43. The Kd value of Al18F-PSMA-CM to PSMA was 8.46 ± 0.24 nM. Al18F-PSMA-CM was accumulated in kidneys and 22Rv1 tumors [74.76 ± 15.42 and 6.16 ± 0.74 ID%/g at 2 h post injection (p.i.)], which were decreased by −80.0 and −84.3% when co-injected with ZJ-43. Al18F-PSMA-CM showed high PSMA specificity and accumulated in 22Rv1 tumors with increasing uptake in 4 h. MPA moiety showed the ability to prolong the half-life of tracers, and the MPA-conjugated tracer showed the potential to improve tumor uptake. MPA may be a choice to develop radiopharmaceuticals for PRLT of prostate cancer.

Preparation and Biological Evaluation of [99mTc]Tc-CNGU as a PSMA-Targeted Radiotracer for the Imaging of Prostate Cancer

Prostate-specific membrane antigen (PSMA) is a well-established biological target that is overexpressed on the surface of prostate cancer lesions. Radionuclide-labeled small-molecule PSMA inhibitors have been shown to be promising PSMA-specific agents for the diagnosis and therapy of prostate cancer. In this study, a glutamate-urea-based PSMA-targeted ligand containing an isonitrile (CNGU) was synthesized and labeled with 99mTc to prepare [99mTc]Tc-CNGU with a high radiochemical purity (RCP). The CNGU ligand showed a high affinity toward PSMA (Ki value is 8.79 nM) in LNCaP cells. The [99mTc]Tc-CNGU exhibited a good stability in vitro and hydrophilicity (log P = −1.97 ± 0.03). In biodistribution studies, BALB/c nude mice bearing LNCaP xenografts showed that the complex had a high tumor uptake with 4.86 ± 1.19% ID/g, which decreased to 1.74 ± 0.90% ID/g after a pre-injection of the selective PSMA inhibitor ZJ-43, suggesting that it was a PSMA-specific agent. Micro-SPECT imaging demonstrated that the [99mTc]Tc-CNGU had a tumor uptake and that the uptake was reduced in the image after blocking with ZJ-43, further confirming its PSMA specificity. All of the results in this work indicated that [99mTc]Tc-CNGU is a promising PSMA-specific tracer for the imaging of prostate cancer.