Low cost, high temporal resolution optical fiber-based γ-photon sensor for real-time pre-clinical evaluation of cancer-targeting radiopharmaceuticals.

Cancer radiopharmaceutical therapies (RPTs) have demonstrated great promise in the treatment of neuroendocrine and prostate cancer, giving hope to late-stage metastatic cancer patients with currently very few treatment options. These therapies have sparked a large amount of interest in pre-clinical research due to their ability to target metastatic disease, with many research efforts focused towards developing and evaluating targeted RPTs for different cancer types in in vivo models. Here we describe a method for monitoring real-time in vivo binding kinetics for the pre-clinical evaluation of cancer RPTs. Recognizing the significant heterogeneity in biodistribution of RPTs among even genetically identical animal models, this approach offers long-term monitoring of the same in vivo organism without euthanasia in contrast to ex vivo tissue dosimetry, while providing high temporal resolution with a low-cost, easily assembled platform, that is not present in small-animal SPECT/CTs. The method utilizes the developed optical fiber-based γ-photon biosensor, characterized to have a wide linear dynamic range with Lutetium-177 (177Lu) activity (0.5-500 µCi/mL), a common radioisotope used in cancer RPT. The probe's ability to track in vivo uptake relative to SPECT/CT and ex vivo dosimetry techniques was verified by administering 177Lu-PSMA-617 to mouse models bearing human prostate cancer tumors (PC3-PIP, PC3-flu). With this method for monitoring RPT uptake, it is possible to evaluate changes in tissue uptake at temporal resolutions <1 min to determine RPT biodistribution in pre-clinical models and better understand dose relationships with tumor ablation, toxicity, and recurrence when attempting to move therapies towards clinical trial validation.

Design, Synthesis and Preclinical Assessment of 99mTc-iFAP for In Vivo Fibroblast Activation Protein (FAP) Imaging.

Fibroblast activation protein (FAP) is expressed in the microenvironment of most human epithelial tumors. 68Ga-labeled FAP inhibitors based on the cyanopyrrolidine structure (FAPI) are currently used for the detection of the tumor microenvironment by PET imaging. This research aimed to design, synthesize and preclinically evaluate a new FAP inhibitor radiopharmaceutical based on the 99mTc-((R)-1-((6-hydrazinylnicotinoyl)-D-alanyl) pyrrolidin-2-yl) boronic acid (99mTc-iFAP) structure for SPECT imaging. Molecular docking for affinity calculations was performed using the AutoDock software. The chemical synthesis was based on a series of coupling reactions of 6-hidrazinylnicotinic acid (HYNIC) and D-alanine to a boronic acid derivative. The iFAP was prepared as a lyophilized formulation based on EDDA/SnCl2 for labeling with 99mTc. The radiochemical purity (R.P.) was verified via ITLC-SG and reversed-phase radio-HPLC. The stability in human serum was evaluated by size-exclusion HPLC. In vitro cell uptake was assessed using N30 stromal endometrial cells (FAP positive) and human fibroblasts (FAP negative). Biodistribution and tumor uptake were determined in Hep-G2 tumor-bearing nude mice, from which images were acquired using a micro-SPECT/CT. The iFAP ligand (Ki = 0.536 nm, AutoDock affinity), characterized by UV-Vis, FT-IR, 1H-NMR and UPLC-mass spectroscopies, was synthesized with a chemical purity of 92%. The 99mTc-iFAP was obtained with a R.P. >98%. In vitro and in vivo studies indicated high radiotracer stability in human serum (>95% at 24 h), specific recognition for FAP, high tumor uptake (7.05 ± 1.13% ID/g at 30 min) and fast kidney elimination. The results found in this research justify additional dosimetric and clinical studies to establish the sensitivity and specificity of the 99mTc-iFAP.

Preliminary Assessment of the Anti-inflammatory Activity of New Structural Honokiol Analogs with a 4'-O-(2-Fluoroethyl) Moiety and the Potential of Their 18F-Labeled Derivatives for Neuroinflammation Imaging.

Neolignans honokiol and 4'-O-methylhonokiol (MH) and their derivatives have pronounced anti-inflammatory activity, as evidenced by numerous pharmacological studies. Literature data suggested that cyclooxygenase type 2 (COX-2) may be a target for these compounds in vitro and in vivo. Recent studies of [11C]MPbP (4'-[11C]methoxy-5-propyl-1,1'-biphenyl-2-ol) biodistribution in LPS (lipopolysaccharide)-treated rats have confirmed the high potential of MH derivatives for imaging neuroinflammation. Here, we report the synthesis of four structural analogs of honokiol, of which 4'-(2-fluoroethoxy)-2-hydroxy-5-propyl-1, 1'-biphenyl (F-IV) was selected for labeling with fluorine-18 (T1/2 = 109.8 min) due to its high anti-inflammatory activity confirmed by enzyme immunoassays (EIA) and neuromorphological studies. The high inhibitory potency of F-IV to COX-2 and its moderate lipophilicity and chemical stability are favorable factors for the preliminary evaluation of the radioligand [18F]F-IV in a rodent model of neuroinflammation. [18F]F-IV was prepared with good radiochemical yield and high molar activity and radiochemical purity by 18F-fluoroethylation of the precursor with Boc-protecting group (15) with [18F]2-fluoro-1-bromoethane ([18F]FEB). Ex vivo biodistribution studies revealed a small to moderate increase in radioligand uptake in the brain and peripheral organs of LPS-induced rats compared to control animals. Pretreatment with celecoxib resulted in significant blocking of radioactivity uptake in the brain (pons and medulla), heart, lungs, and kidneys, indicating that [18F]F-IV is likely to specifically bind to COX-2 in a rat model of neuroinflammation. However, in comparison with [11C]MPbP, the new radioligand showed decreased brain uptake in LPS rats and high retention in the blood pool, which apparently could be explained by its high plasma protein binding. We believe that the structure of [18F]F-IV can be optimized by replacing the substituents in the biphenyl core to eliminate these disadvantages and develop new radioligands for imaging activated microglia.

A benchmarking study of Geant4 for Auger electrons emitted by medical radioisotopes.

Auger emitting radioisotopes are of great interest in targeted radiotherapy because, once internalised in the tumour cells, they can deliver dose locally to the radiation sensitive targets, while not affecting surrounding cells. Geant4 is a Monte Carlo code widely used to characterise the physics mechanism at the basis of targeted radiotherapy. In this work, we benchmarked the modelling of the emission of Auger electrons in Geant4 deriving from the decay of 123I, 124I, 125I radionuclides against existing theoretical approaches. We also compared Geant4 against reference data in the case of 131Cs, which is of interest for brachytherapy. In the case of 125I and 131Cs, the simulation results are compared to experimental measurements as well. Good agreement was found between Geant4 and the reference data. As far as we know, this is the first study aimed to benchmark against experimental measurements the emission of Auger electrons in Geant4 for radiotherapy applications.

PSMA-D4 Radioligand for Targeted Therapy of Prostate Cancer: Synthesis, Characteristics and Preliminary Assessment of Biological Properties.

A new PSMA ligand (PSMA-D4) containing the Glu-CO-Lys pharmacophore connected with a new linker system (L-Trp-4-Amc) and chelator DOTA was developed for radiolabeling with therapeutic radionuclides. Herein we describe the synthesis, radiolabeling, and preliminary biological evaluation of the novel PSMA-D4 ligand. Synthesized PSMA-D4 was characterized using TOF-ESI-MS, NMR, and HPLC methods. The novel compound was subject to molecular modeling with GCP-II to compare its binding mode to analogous reference compounds. The radiolabeling efficiency of PSMA-D4 with 177Lu, 90Y, 47Sc, and 225Ac was chromatographically tested. In vitro studies were carried out in PSMA-positive LNCaP tumor cells membranes. The ex vivo tissue distribution profile of the radioligands and Cerenkov luminescence imaging (CLI) was studied in LNCaP tumor-bearing mice. PSMA-D4 was synthesized in 24% yield and purity >97%. The radio complexes were obtained with high yields (>97%) and molar activity ranging from 0.11 to 17.2 GBq mcmol-1, depending on the radionuclide. In vitro assays confirmed high specific binding and affinity for all radiocomplexes. Biodistribution and imaging studies revealed high accumulation in LNCaP tumor xenografts and rapid clearance of radiocomplexes from blood and non-target tissues. These render PSMA-D4 a promising ligand for targeted therapy of prostate cancer (PCa) metastases.

Preparation and assessment of a new radiotracer technetium-99m-6-hydrazinonicotinic acid-tyrosine as a targeting agent in tumor detecting through single photon emission tomography.

The goal of investigation was to bring up an impressive way to synthesize technetium-99 m-6-hydrazinonicotinic acid-tyrosine (99mTc-HYNIC-Tyr), a newfound radiotracer, and to assess the capacity of being as a tumor scintigraphy agent. The conjugate was prepared by solid phase method using tritely chloride resin. The precursor HYNIC-Tyr was labeled with 99mTc which was accomplished at 100 °C through the coligands tricine and EDDA. Furthermore, the serum albumin binding, cellular attachment, organs uptake and tumor accumulation were measured. C6 glioma cells were used for cellular and tumor uptake studies. 99mTc-HYNIC-Tyr was prepared with labeling yield of >99% (n = 3). Radiotracer showed stability in serum proteins in incubates temperature. Specific cellular attachment of radiotracer was noticeable in C6 glioma cells with dissociation constant in nano molar range (21.03 ± 1.54 nM). The amount of uptake in C6 rat glioma xenograft was 2.61 ± 0.12 percent of injection dose per gram after 30 min. In whole-body scintigraphy, C6 glioma tumor was easy to be traced and interpreted at 1 h after administration of radiotracer. Our data suggest that 99mTc-HYNIC-Tyr, a new radiotracer based on amino acid, efficiently differentiates the tumor cells and goes into them. Our results indicate that this radiotracer has excellent capacity to detect tumor cells in rat and to be included as a radiopharmaceutical for detecting cancer tumors.

Radioiodination and in vivo assessment of the potential of newly synthesized pyrrolizine-5-carboxamides derivative in tumor model.

Recently, pyrrolizine derivatives have been reported to possess numerous anticancer activities. In a previous study, (EZ)-6-((4-chlorobenzylidene)-amino)-7-cyano-N-(p-tolyl)-2,3-dihydro-1H-pyrrolizine carboxamide (EZPCA) compound was synthesized and the cytotoxic activity of EZPCA toward COX-2 enzyme (overexpressed in cancer cells) was reported. In order to assess the suitability of this compound as a promising pilot structure for in vivo applications, EZPCA was radiolabeled with radioiodine-131 (131I) and various factors affecting radiolabeling process were studied. Quality control studies of [131I]iodo-EZPCA were performed using paper chromatography and HPLC was used as a co-chromatographic technique for confirming the radiochemical yield. Biodistribution studies of [131I]iodo-EZPCA were undertaken in normal and tumor bearing mice. The radiochemical yield percentage of [131I]iodo-EZPCA was 94.20 ± 0.12%. The biodistribution results showed evident tumor uptake of [131I]iodo-EZPCA with promising target/non-target (T/NT) ratios. As a conclusion, these data suggest that [131I]iodo-EZPCA had high binding efficiency, high tumor uptake and sufficient stability to be used be used in diagnostic studies.

Single-cell radioluminescence microscopy with two-fold higher sensitivity using dual scintillator configuration.

Radioluminescence microscopy (RLM) is an imaging technique that allows quantitative analysis of clinical radiolabeled drugs and probes in single cells. However, the modality suffers from slow data acquisition (15-30 minutes), thus critically affecting experiments with short-lived radioactive drugs. To overcome this issue, we suggest an approach that significantly accelerates data collection. Instead of using a single scintillator to image the decay of radioactive molecules, we sandwiched the radiolabeled cells between two scintillators. As proof of concept, we imaged cells labeled with [18F]FDG, a radioactive glucose popularly used in oncology to image tumors. Results show that the double scintillator configuration increases the microscope sensitivity by two-fold, thus reducing the image acquisition time by half to achieve the same result as the single scintillator approach. The experimental results were also compared with Geant4 Monte Carlo simulation to confirm the two-fold increase in sensitivity with only minor degradation in spatial resolution. Overall, these findings suggest that the double scintillator configuration can be used to perform time-sensitive studies such as cell pharmacokinetics or cell uptake of short-lived radiotracers.

Accuracy of Oral 67Gallium Citrate Scintigraphy in assessment of inflammatory activity of Crohn's disease.

AIM: The main goal in Crohn´s disease (CD) is a sustained suppression of inflammatory activity associated with mucosa healing in endoscopic evaluation. During clinical routine, there are small numbers of good markers to monitor inflammatory activity under treatment. We postulated that Oral 67Gallium Citrate Scintigraphy is able to mark inflammatory disease in mucosa and deep inflammation in CD, when used in oral form. OBJECTIVE: Measure the accuracy of Oral 67Gallium Citrate Scintigraphy in intestinal inflammatory activity of Crohn´s disease. PATIENTS AND METHODS: In a prospective consecutive cross-sectional study from January 2018 to June 2019, the ileocolonic region of 32 patients with CD were studied by dividing into four regions of interest (ROI) from the ileum to the rectum. A total of 128 intestinal segments were analyzed in cluster data. Accuracy values of Oral 67Gallium Scintigraphy and colonoscopy tests were evaluated with the histological reference test. Values of the respective receiver operating characteristic (ROC) curves were obtained  and compared. The reliability between the tests was evaluated by Kappa statistical with the segment-level analyses using variance adjustments. All statistical analyses were performed with a test significance level of 0.05. RESULTS: The study population included 32 patients with CD (10 men, 22 women; average age 39 years). Disease time was five years on average. Anti-TNFs treatment was found in 71%. The most found phenotype of the Montreal classification was L3. Differences in ROC curves for colonoscopy (0.94) and Oral 67Ga Scintigraphy (0.96) did not show significant value (p = 0.32). The sensitivity of scintigraphy to detect intestinal inflammatory activity in CD was 64%, specificity of 96% and accuracy of 84%. A high agreement was found between oral scintigraphy and histological measurements with kappa = 0.64. CONCLUSIONS: Oral 67Ga Scintigraphy had similar accuracy and agreement compared to colonoscopy in the identification of inflammatory activity in Crohn´s Disease. This new approach may be useful and less invasive for long term follow-ups.

Synthesis and Evaluation of Ga-68-Labeled Rhein for Early Assessment of Treatment-Induced Tumor Necrosis.

PURPOSE: This study aimed to synthesize a necrosis-avid agent using rhein as a precursor and labeled with gallium-68 (Ga-68) for positron emission tomography/computed tomography (PET/CT) imaging, to evaluate response to anticancer treatment in a mouse model. PROCEDURES: 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated rhein was radiolabeled with Ga-68 to formulate [68Ga]DOTA-rhein. The in vitro stability of [68Ga]DOTA-rhein was assessed by radio-HPLC. Necrosis avidity was evaluated in a mouse model of muscle necrosis by microPET/CT imaging, biodistribution study, histochemical staining, and autoradiography studies. Murine tumor models with the subcutaneous implantation of S180 cell lines were generated for the evaluation of therapeutic effect. Tumor necrosis was induced by the treatment of combretastatin A4 disodium phosphate (CA4P), and microPET/CT imaging was performed at 1 h post tracer injection. DNA binding studies were conducted to explore the necrosis avidity mechanism of the tracer. RESULTS: [68Ga]DOTA-rhein exhibited a satisfactory yield, a radiochemical purity over 97 %, and a good serum stability. The uptakes of [68Ga]DOTA-rhein in necrotic muscles and tumors were significantly higher than those in normal muscles and tumors (P < 0.05). The results of autoradiography and histochemical staining were consistent with the selective uptake of the radiotracer in necrotic regions. MicroPET/CT images showed a high uptake of the tracer in necrotic muscles and necrotic tumors. DNA binding studies suggested that necrosis avidity correlated with DNA binding to a certain extent. CONCLUSIONS: Our results demonstrated that [68Ga]DOTA-rhein showed a prominent necrosis avidity and could be a useful probe for early assessment of response to anticancer therapy by PET/CT imaging.

Assessment of Chemotherapy-Induced Organ Damage with Ga-68 Labeled Duramycin.

PURPOSE: Evaluation of [68Ga]NODAGA-duramycin as a positron emission tomography (PET) tracer of cell death for whole-body detection of chemotherapy-induced organ toxicity. PROCEDURES: Tracer specificity of Ga-68 labeled NODAGA-duramycin was determined in vitro using competitive binding experiments. Organ uptake was analyzed in untreated and doxorubicin, busulfan, and cisplatin-treated mice 2 h after intravenous injection of [68Ga]NODAGA-duramycin. In vivo data were validated by immunohistology and blood parameters. RESULTS: In vitro experiments confirmed specific binding of [68Ga]NODAGA-duramycin. Organ toxicities were detected successfully using [68Ga]NODAGA-duramycin PET/X-ray computed tomography (CT) and confirmed by immunohistochemistry and blood parameter analysis. Organ toxicities in livers and kidneys showed similar trends in PET/CT and immunohistology. Busulfan and cisplatin-related organ toxicities in heart, liver, and lungs were detected earlier by PET/CT than by blood parameters and immunohistology. CONCLUSION: [68Ga]NODAGA-duramycin PET/CT was successfully applied to non-invasively detect chemotherapy-induced organ toxicity with high sensitivity in mice. It, therefore, represents a promising alternative to standard toxicological analyses with a high translational potential.

Systematic Assessment of the Adsorption of 99mTc-Radiopharmaceuticals onto Plastic Syringes.

The phenomenon of adsorption of several 99mTc-radiopharmaceuticals onto disposable syringes is common knowledge and can reach a level of up to 50%, with the result being inadequate dosing. The resulting underdosing has a substantial influence on the quality of imaging, especially in pediatric patients. Therefore, we aimed to establish a standardized in vitro assessment to investigate the adsorption of several 99mTc-radiopharmaceuticals on various brands of syringes. Methods: The 99mTc-radiopharmaceuticals were prepared according to manufacturer instructions. For the assessment, the disposable syringes (n = 3) were filled to one third of capacity with the 99mTc preparation and incubated for 30 min at room temperature. The syringes were emptied into evacuated vials, and the radioactivity of the syringes was measured before and after they were emptied. Furthermore, the dilution effect of 99mTc preparations was studied. We used 2 different brands of syringes and systematically examined 99mTc-pertechnetate, 99mTc-butedronate, 99mTc-oxidronate, 99mTc-medronate, 99mTc-tetrofosmin, 99mTc-sestamibi, 99mTc(V)-dimercaptosuccinic acid, and 99mTc-succimer. Additionally, 99mTc-succimer was retested with 5 brands of syringes. Results: 99mTc-pertechnetate, 99mTc-phosphonates, and 99mTc(V)-dimercaptosuccinic acid showed no significant adsorption. The measured radioactive retention of 2%-5% was equivalent to the determined dead volume. Using 99mTc-tetrofosmin, we found a slight but significant adsorption of 4%-7%. The 99mTc-sestamibi preparation showed a nonsignificant retention of 3%-5%. However, when the 99mTc-sestamibi was diluted 1:10 with saline, the adsorption rate increased to 9%-13%. 99mTc-succimer displayed different adsorption levels depending on the brand of syringe and the preparation technique. The adsorption of 99mTc-succimer, prepared from kits according to the instructions, did not exceed 15%. The 1:10 saline dilution of a 99mTc-succimer kit preparation, as well as an in-house preparation, demonstrated a radioactive syringe adsorption rate of more than 30%. Conclusion: The results revealed the significance of syringe adsorption of radiopharmaceuticals in the prevention of underdosing. Therefore, a quality assurance assessment is recommended before the introduction of new brands of plastic syringes or routine application of diluted or in-house radiopharmaceuticals.

In vitro and In vivo Assessment of Suitable Reference Region and Kinetic Modelling for the mGluR1 Radioligand [11C]ITDM in Mice.

PURPOSE: This study aimed at investigating binding specificity, suitability of reference region-based kinetic modelling, and pharmacokinetics of the metabotropic glutamate receptor 1 (mGluR1) radioligand [11C]ITDM in mice. PROCEDURES: We performed in vivo blocking as well as displacement of [11C]ITDM during positron emission tomography (PET) imaging using the specific mGluR1 antagonist YM-202074. Additionally, we assessed in vitro blocking of [3H]ITDM at two different doses of YM-202074. As an alternative to reference region models, we validated the use of a noninvasive image-derived input function (IDIF) compared to an arterial input function measured with an invasive arteriovenous (AV) shunt using a population-based curve for radiometabolite correction and characterized the pharmacokinetic modelling of [11C]ITDM in the mouse brain. Finally, we also assessed semi-quantitative approaches. RESULTS: In vivo blocking with YM-202074 resulted in a decreased [11C]ITDM binding, ranging from - 35.8 ± 8.0 % in pons to - 65.8 ± 3.0 % in thalamus. Displacement was also markedly observed in all tested regions. In addition, in vitro [3H]ITDM binding could be blocked in a dose-dependent manner. The volume of distribution (VT) based on the noninvasive IDIF (VT (IDIF)) showed excellent agreement with the VT values based on the metabolite-corrected plasma input function regardless of the metabolite correction (r2 > 0.943, p < 0.0001). Two-tissue compartmental model (2TCM) was found to be the preferred model and showed optimal agreement with Logan plot (r2 > 0.960, p < 0.0001). A minimum scan duration of 80 min was required for proper parameter estimation. SUV was not reliable (r2 = 0.379, p = 0.0011), unlike the SUV ratio to the SUV of the input function, which showed to be a valid approach. CONCLUSIONS: No suitable reference region could be identified for [11C]ITDM as strongly supported by in vivo and in vitro evidence of specific binding in all brain regions. However, by applying appropriate kinetic models, [11C]ITDM PET imaging represents a promising tool to visualize mGluR1 in the mouse brain.

Immuno-PET imaging for non-invasive assessment of cetuximab accumulation in non-small cell lung cancer.

BACKGROUNDS: Overexpression of epidermal growth factor receptor (EGFR) has been established as a valid therapeutic target of non-small cell lung cancer (NSCLC). However, the clinical benefit of cetuximab as an EGFR-targeting drug is still controversial, partially due to the lack of effective means to identify suitable patients. This study aimed to investigate the potential of radiolabeled cetuximab as a non-invasive tool to predict cetuximab accumulation in NSCLC tumor xenografts with varying EGFR expression levels. METHODS: The NSCLC tumors in model mice were subjected to in vivo biodistribution study and positron emission tomography (PET) imaging 48 h after injection of either 111In- or 64Cu-labeled cetuximab. The EGFR expression levels of NSCLC tumors were determined by ex vivo immunoblotting. RESULTS: We found that tumors with high EGFR expression had significantly higher [111In]In-DOTA-cetuximab accumulation than tumors with moderate to low EGFR expression (P < 0.05). Strong correlations were found between [111In]In-DOTA-cetuximab tumor uptake and EGFR expression level (r = 0.893), and between [64Cu]Cu-DOTA-cetuximab tumor uptake with EGFR expression level (r = 0.915). PET imaging with [64Cu]Cu-DOTA-cetuximab allowed clear visualization of tumors. CONCLUSION: Our findings suggest that this immuno-PET imaging can be clinically translated as a tool to predict cetuximab accumulation in NSCLC cancer patients prior to cetuximab therapy.

Quality of radiochemical purity in multiple samples of various fractionated cold kits: Testing a cost & time effective technique.

OBJECTIVE: This study was aimed to assess technical aspects of fractionation of commonly used cold kits in Nuclear Medicine. MATERIALS AND METHODS: A total of 90 samples (30 samples each) of technetium-99m methylene diphosphonate (99mTc-MDP), 99mTc-diethylenetriaminepentaacetic acid (DTPA) and 99mTc-dimercaptosuccinic acid (DMSA III) were taken on various days. The radiochemical purity was calculated of each fraction of these cold kits by using paper chromatography. RESULTS: The mean value of radiochemical purity of 99mTc -MDP, 99mTc -DTPA and 99mTc-DMSA(III) were calculated as ~ 95.12%, 91.43% and 95.68% and standard deviation (SD) were ~ 5.43, 8.36 and 3.88, respectively. Maximum time in which fractionation procedure completed i.e. time required for preparing the fraction or thawing was 10 minutes. All fractionated aliquots were between 1 and 15 days. Radiopharmaceutical bio-distribution was found to be appropriate during imaging in all samples. CONCLUSION: Fractionation of cold kits using standardised technique is a time and cost-effective method and does not deteriorate the quality of labelling in commonly used pharmaceuticals in our study. We have used fractionated aliquots up to 3 days of preparation in patients with clinically usable radiochemical purity. Deep frozen fractions can be used up to 15 days in our experience.

Assessment of 213Bi-anti-EGFR MAb treatment efficacy in malignant cancer cells with [1-13C]pyruvate and [18F]FDG.

Evaluation of response to therapy is among the key objectives of oncology. A new method to evaluate this response includes magnetic resonance spectroscopy (MRS) with hyperpolarized 13C-labelled metabolites, which holds promise to provide new insights in terms of both therapeutic efficacy and tumor cell metabolism. Human EJ28Luc urothelial carcinoma and LN18 glioma cells were treated with lethal activity concentrations of a 213Bi-anti-EGFR immunoconjugate. Treatment efficacy was controlled via analysis of DNA double-strand breaks (immunofluorescence γH2AX staining) and clonogenic survival of cells. To investigate changes in metabolism of treated cells vs controls we analyzed conversion of hyperpolarized [1-13C]pyruvate to [1-13C]lactate via MRS as well as viability of cells, lactate formation and lactate dehydrogenase activity in the cellular supernatants and [18F]FDG uptake in treated cells vs controls, respectively. Treatment of malignant cancer cells with 213Bi-anti-EGFR-MAb induced intense DNA double-strand breaks, resulting in cell death as monitored via clonogenic survival. Moreover, treatment of EJ28Luc bladder cancer cells resulted in decreased cell viability, [18F]FDG-uptake and an increased lactate export. In both EJ28Luc and LN18 carcinoma cells treatment with 213Bi-anti-EGFR-MAb triggered a significant increase in lactate/pyruvate ratios, as measured with hyperpolarized [1-13C]pyruvate. Treatment with 213Bi-anti-EGFR-MAb resulted in an effective induction of cell death in EJ28Luc and LN18 cells. Lactate/pyruvate ratios of hyperpolarized [1-13C]pyruvate proved to detect early treatment response effects, holding promise for future clinical applications in early therapy monitoring.

Assessment of Targeted Nanoparticle Assemblies for Atherosclerosis Imaging with Positron Emission Tomography and Potential for Clinical Translation.

Nanoparticles have been assessed in preclinical models of atherosclerosis for detection of plaque complexity and treatment. However, their successful clinical translation has been hampered by less than satisfactory plaque detection and lack of a general strategy for assessing the translational potential of nanoparticles. Herein, nanoparticles based on comb-co-polymer assemblies were synthesized through a modular construction approach with precise control over the conjugation of multiple functional building blocks for in vivo evaluation. This high level of design control also allows physicochemical properties to be varied in a controllable fashion. Through conjugation of c-atrial natriuretic factor (CANF) peptide and radiolabeling with 64Cu, the 64Cu-CANF-comb nanoparticle was assessed for plaque imaging by targeting natriuretic peptide clearance receptor (NPRC) in a double-injury atherosclerosis model in rabbits. The prolonged blood circulation and enhanced binding capacity of 64Cu-CANF-comb nanoparticles provided sensitive and specific imaging of NPRC overexpressed in atherosclerotic lesions by positron emission tomography at intervals during the progression of the disease. Ex vivo tissue validation using autoradiography and immunostaining on human carotid endarterectomy specimens demonstrated specific binding of 64Cu-CANF-comb to human NPRC receptors. Taken together, this study not only shows the potential of NPRC-targeted 64Cu-CANF-comb nanoparticles for increased sensitivity to an epitope that increases during atherosclerosis plaque development but also provides a useful strategy for the general design and assessment of the translational potential of nanoparticles in cardiovascular imaging.

Internal radiation dose assessment of radiopharmaceuticals prepared with cyclotron-produced 99m Tc.

PURPOSE: Technetium-99m (99m Tc) is the radioisotope most widely used in diagnostic nuclear medicine. It is readily available from 99 Mo/99m Tc generators as the ß- decay product of the 99 Mo (T½  = 66 h) parent nuclide. This latter is obtained as a fission product in nuclear reactors by neutron-induced reactions on highly enriched uranium. Alternative production routes, such as direct reactions using proton beams on specific target materials [100 Mo(p,2n)99m Tc], have the potential to be both reliable and relatively cost-effective. However, results showed that the 99m Tc extracted from proton-bombarded 100 Mo-enriched targets contains small quantities of several Tc radioisotopes (93m Tc, 93 Tc, 94 Tc, 94m Tc, 95 Tc, 95m Tc, 96 Tc, and 97m Tc). The aim of this work was to estimate the dose increase (DI) due to the contribution of Tc radioisotopes generated as impurities, after the intravenous injection of four radiopharmaceuticals prepared with cyclotron-produced 99m Tc (CP-99m Tc) using 99.05% 100 Mo-enriched metallic targets. METHODS: Four 99m Tc radiopharmaceuticals (pertechnetate, sestamibi (MIBI), hexamethylpropylene-amine oxime (HMPAO) and disodium etidronate (HEDP)) were considered in this study. The biokinetic models reported by the International Commission on Radiological Protection (ICRP) for each radiopharmaceutical were used to define the main source organs and to calculate the number of disintegrations per MBq that occurred in each source organ (Nsource ) for each Tc radioisotope present in the CP-99m Tc solution. Then, target organ equivalent doses and effective dose were calculated for each Tc radioisotope with the OLINDA/EXM software versions 1.1 and 2.0, using the calculated Nsource values and the adult male phantom as program inputs. Total effective dose produced by all Tc isotopes impurities present in the CP-99m Tc solution was calculated using the fraction of total activity corresponding to each radioisotope and compared with the effective dose delivered by the generator-produced 99m Tc. RESULTS: In all cases, the total effective DI of CP-99m Tc radiopharmaceuticals calculated with either versions of the OLINDA software was less than 10% from 6 up to 12 h after EOB. 94m Tc and 93m Tc are the Tc radioisotopes with the highest concentration in the CP-99m Tc solution at EOB. However, their contribution to DI 6 h after EOB is minimal, due to their short half-lives. The radioisotopes with the largest contribution to the effective DI are 96 Tc, followed by 95 Tc and 94 Tc. This is due to the types of their emissions and relatively long half-lives, although their concentration in the CP-99m Tc solution is five times lower than that of 94m Tc and 93m Tc at the EOB. CONCLUSIONS: The increase in the radiation dose caused by other Tc radioisotopes contained in CP-99m Tc produced as described here is quite low. Even though the concentrations of the 94 Tc and 95 Tc radioisotopes in the CP-99m Tc solution exceed the limits established by the European Pharmacopoeia, CP-99m Tc radiopharmaceuticals could be used in routine nuclear medicine diagnostic studies if administered from 6 to 12 h after the EOB, thus maintaining the effective DI within the 10% limit.

Determination of Gamma Camera's Calibration Factors for Quantitation of Diagnostic Radionuclides in Simultaneous Scattering and Attenuation Correction.

OBJECTIVE: The characterization of cancerous tissue and bone metastasis can be distinguished by accurate assessment of accumulated uptake and activity from different radioisotopes. The various parameters and phenomena such as calibration factor, Compton scattering, attenuation and penetration intrinsicallyinfluence calibration equation, and the qualification of images as well. METHODS: The camera calibration factor (CF) translates reconstructed count map into absolute activity map, which is determined by both planar and tomographic scans using different phantom geometries. In this study, the CF for radionuclides of Tc-99m and Sm-153 in soft tissue and bone was simulated by the Monte Carlo method, and experimental results were obtained in equivalent tissue and bone phantoms. It may be employed for the simultaneous correction of the scattering and attenuation rays interacted with the camera, leading to corrected counts. Also, the target depth (d) may be estimated by a combination of scattering and photoelectric functions, which we have published before. RESULTS: The calibrated equations for soft tissue phantom for the radionuclides were obtained by RTc = - 10d+ 300 and RSm = -8d + 100, and the relative errors between the simulated and experimental results were 4.5% and 3.1%, respectively. The equations for bone phantom were RTc = -30d + 300 and RSm = - 10d + 100, and the relative errors were 5.4% and 5.6%. The R and d are in terms of cpm/mCi and cm. Besides, the collimators' impact was evaluated on the camera response, and the relevant equations were obtained by the Monte Carlo method. The calibrated equations as a function of various radiation angles on the center of camera's cells without using collimator indicated that both sources have the same quadratic coefficient by -2E-08 and same vertical width from the origin by 8E-05. CONCLUSION: The presented procedure may help determine the absorbed dose in the target and likewise optimize treatment planning.

Assessment of S values for I131 and Y90 based on the Digimouse voxel phantom.

INTRODUCTION: Most preclinical studies using radiopharmaceuticals have been carried out on mice. In nuclear medicine and radioimmunotherapy procedures, I131 and Y90 have been widely used. For better estimation of doses from these procedures, S value plays a vital role. In this study, we have evaluated S values for major source and target combinations of Digimouse voxel phantom. MATERIALS AND METHODS: We have used the Digimouse voxel phantom which was incorporated in Monte Carlo code FLUKA. Simulation studies were performed using Monte Carlo simulation code FLUKA. Latest publication of International Commission on Radiological Protection (ICRP) report 110 was used for assigning the values of organ compositions and densities. Photon and electron spectra for I131 and Y90 have been taken from the ICRP publication 107. For Digimouse voxel phantom, we have simulated 9 source regions with an assumed uniform distribution of I131 and Y90. RESULTS AND DISCUSSION: S values have been evaluated for I131 and Y90 for different source and target combinations of Digimouse voxel phantom and presented in tabular form. The S values can be applied prospectively or retrospectively to the calculation of radiation doses internally exposed to I131 and Y90, including nuclear medicine and radioimmunotherapy procedures. These S values have been very important for the calculation of absorbed doses for various organs similar in size to present study for mice. CONCLUSION: In this study S value for I131 and Y90 were evaluated for major organs of digimouse voxel phantom. These S values are very important for absorbed dose calculation for various organs of a mouse.