Radioactivity In Blood Research Articles

(2S, 4R)-4-[18F]Fluoroglutamine for In vivo PET Imaging of Glioma Xenografts in Mice: an Evaluation of Multiple Pharmacokinetic Models

PurposeThe glutamine analogue (2S, 4R)-4-[18F]fluoroglutamine ([18F]FGln) was investigated to further characterize its pharmacokinetics and acquire in vivo positron emission tomography (PET) images of separate orthotopic and subcutaneous glioma xenografts in mice.Procedures[18F]FGln was synthesized at a high radiochemical purity as analyzed by high-performance liquid chromatography. An orthotopic model was created by injecting luciferase-expressing patient-derived BT3 glioma cells into the right hemisphere of BALB/cOlaHsd-Foxn1nu mouse brains (tumor growth monitored via in vivo bioluminescence), the subcutaneous model by injecting rat BT4C glioma cells into the flank and neck regions of Foxn1nu/nu mice. Dynamic PET images were acquired after injecting 10–12 MBq of the tracer into mouse tail veins. Animals were sacrificed 63 min after tracer injection, and ex vivo biodistributions were measured. Tumors and whole brains (with tumors) were cryosectioned, autoradiographed, and stained with hematoxylin-eosin. All images were analyzed with CARIMAS software. Blood sampling of 6 Foxn1nu/nu and 6 C57BL/6J mice was performed after 9–14 MBq of tracer was injected at time points between 5 and 60 min then assayed for erythrocyte uptake, plasma protein binding, and plasma parent-fraction of radioactivity to correct PET image-derived whole-blood radioactivity and apply the data to multiple pharmacokinetic models.ResultsOrthotopic human glioma xenografts displayed PET image tumor-to-healthy brain region ratio of 3.6 and 4.8 while subcutaneously xenografted BT4C gliomas displayed (n = 12) a tumor-to-muscle (flank) ratio of 1.9 ± 0.7 (range 1.3–3.4). Using PET image-derived blood radioactivity corrected by population-based stability analyses, tumor uptake pharmacokinetics fit Logan and Yokoi modeling for reversible uptake.ConclusionsThe results reinforce that [18F]FGln has preferential uptake in glioma tissue versus that of corresponding healthy tissue and fits well with reversible uptake models.

Pharmacokinetic Evaluation of 99mTc-radiolabeled Solid Lipid Nanoparticles and Chitosan Coated Solid Lipid Nanoparticles.

Solid Lipid Nanoparticles (SLNs) possess unique in vivo features such as high resistivity, bioavailability, and habitation at the target site. Coating nanoparticles with polymers such as chitosan greatly affects their pharmacokinetic behavior, stability, tissue uptake, and controlled drug delivery. The aim of this study was to prepare and evaluate the biodistribution of 99mTc-labeled SLNs and chitosan modified SLNs in mice. 99mTc-oxine was prepared and utilized to radiolabel pre-papered SLNs or chitosan coated SLNs. After purification of radiolabeled SLNs (99mTc-SLNs) and radiolabeled chitosan-coated SLNs (99mTc-Chi-SLNs) using Amicon filter, they were injected into BALB/c mice to evaluate their biodistribution patterns. In addition, nanoparticles were characterized using Transmission Electron Microscopy (TEM), Fourier-transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), X-ray Powder Diffraction (XRD) and Dynamic Light Scattering (DLS). 99mTc-oxine with high radiochemical purity (RCP~100%) and stability (RCP > 97% at 24 h) was used to provide 99mTc-SLNs and 99mTc-Chi-SLNs with high initial RCP (100%). TEM image and DLS data suggest 99mTc- SLNs susceptibility to aggregation. To that end, the main portion of 99mTc-SLNs radioactivity accumulates in the liver and intestines, while 99mTc-Chi-SLNs sequesters in the liver, intestines and kidneys. The blood radioactivity of 99mTc-Chi-SLNs was higher than that of 99mTc-SLNs by 7.5, 3.17 and 3.5 folds at 1, 4 and 8 h post-injection. 99mTc- Chi-SLNs uptake in the kidneys in comparison with 99mTc-SLNs was higher by 37.48, 5.84 and 11 folds at 1, 4 and 8h. The chitosan layer on the surface of 99mTc-Chi-SLNs reduces lipophilicity in comparison with 99mTc- SLNs. Therefore, 99mTc-Chi-SLNs are less susceptible to aggregation, which leads to their lower liver uptake and higher kidney uptake and blood concentration.

Pharmacokinetics interaction study of 99mTc-glutathione radiopharmaceutical with doxorubicin in mice (mus musculus)

The use of radiopharmaceuticals for cancer diagnosis and therapy is increasing. The radiopharmaceutical is also used to monitor the progress of a disease and determine the appropriate treatment. However, the use of radiopharmaceuticals needs to pay attention to the alteration in pharmacokinetics, pharmacology, and toxicity that are influenced by the drugs consumed by patients. Interaction between drugs with radiopharmaceuticals will cause alteration in pharmacokinetic effects. Therefore, this study aimed to determine the pharmacokinetic interaction of “-Tc-Glutathione radiopharmaceuticals with doxorubicin cancer drug in mice (Mus musculus). The pharmacokinetic studies were performed using four groups of animal model and each group consists of three rats. The groups were classified to normal mice without treatment of doxorubicin as normal mice control (I), normal mice treated with doxorubicin (II), cancer model mice without treatment of doxorubicin as cancer model mice control (III), and cancer model mice treated with doxorubicin (IV). The radioactivity in blood at a certain interval was then calculated to determine the distribution and elimination half-time. The distribution halftime of group I, II, III, and IV were 0.004±0.001, 0.0037±0.0001, 0.003±0.0001, and 0.0037±0.0001 hours, respectively, while the elimination half-time were 5.310±1.050, 10.7344±0.4692, 72.712±2.427, and 26.9320±7.8152 hours, respectively. The results of the T-test showed that there was a significant difference in elimination half-life of 99mTc-Glutathione between the treated group and the control group. These results indicate that administration of the doxorubicin before administration of 99m-Tc-Glutathione needs to be avoided because it can alter the elimination half-life of »-Tc-Glutathione. The results of this study are expected to provide benefits for clinicians in nuclear medicine to avoid the interpretation of incorrect diagnosis results, to achieve high-quality health service and will have a positive impact on the appropriate treatment for patients.

Spatial heterogeneity of radiolabeled choline positron emission tomography in tumors of patients with non-small cell lung cancer: first-in-patient evaluation of [18F]fluoromethyl-(1,2-2H4)-choline.

Purpose: The spatio-molecular distribution of choline and its metabolites in tumors is highly heterogeneous. Due to regulation of choline metabolism by hypoxic transcriptional signaling and other survival factors, we envisage that detection of such heterogeneity in patient tumors could provide the basis for advanced localized therapy. However, non-invasive methods to assess this phenomenon in patients are limited. We investigated such heterogeneity in Non-Small Cell Lung Cancer (NSCLC) with [18F]fluoromethyl-(1,2-2H4) choline ([18F]D4-FCH) and positron emission tomography/computed tomography (PET/CT).Experimental design: [18F]D4-FCH (300.5±72.9MBq [147.60-363.6MBq]) was administered intravenously to 17 newly diagnosed NSCLC patients. PET/CT scans were acquired concurrently with radioactive blood sampling to permit mathematical modelling of blood-tissue transcellular rate constants. Comparisons were made with biopsy-derived choline kinase-α (CHKα) expression and diagnostic [18F]fluorodeoxyglucose ([18F]FDG) scans.Results: Oxidation of [18F]D4-FCH to [18F]D4-fluorobetaine was suppressed (48.58±0.31% parent at 60 min) likely due to the deuterium isotope effect embodied within the design of the radiotracer. Early (5 min) and late (60 min) images showed specific uptake of tracer in all 51 lesions (tumors, lymph nodes and metastases) from 17 patients analyzed. [18F]D4-FCH-derived uptake (SUV60max) in index primary lesions (n=17) ranged between 2.87-10.13; lower than that of [18F]FDG PET [6.89-22.64]. Mathematical modelling demonstrated net irreversible uptake of [18F]D4-FCH at steady-state, and parametric mapping of the entire tumor showed large intratumorally heterogeneity in radiotracer retention, which is likely to have influenced correlations with biopsy-derived CHKα expression.Conclusions: [18F]D4-FCH is detectable in NSCLC with large intratumorally heterogeneity, which could be exploited in the future for targeting localized therapy.

Evaluation of the total distribution volume of 18F-FBPA in normal tissues of healthy volunteers by non-compartmental kinetic modeling

ObjectiveBoron neutron capture therapy (BNCT) is a noninvasive radiation therapy method for cancer treatment. In BNCT, 4-borono-2-[18F]-fluoro-L-phenylalanine (18F-FBPA) PET has been employed to estimate 10B accumulation in target tumors and normal tissues if 10B borono-L-phenylalanine (10B-BPA) is used as a boron carrier. The purpose of the current study was to evaluate the total distribution volume (Vt) of 18F-FBPA in normal organs of healthy volunteers by kinetic analysis and to estimate boron concentration in normal organs for the therapeutic dose of 10B-BPA using obtained Vt values.MethodsSix healthy volunteers were injected with 18F-FBPA (3–5 MBq/kg), and 7 PET-CT scans were performed subsequently. 18F-FBPA radioactivity in whole blood and plasma was measured before, and eight times after the injection. PET images were analyzed by PMOD software. Twelve volumetric regions of interest including the brain, heart, right lung, spleen, liver, parotid salivary glands, esophagus, stomach, pancreas, intestines, and bone marrow were drawn manually for each subject and analyzed with the Logan plot and two Ichise multilinear analyses (MA1 and MA2). The better model was defined by several goodness-of-fit parameters and residual distribution. After Vt values had been derived, boron concentration was estimated in ppm for the 10B-BPA-fructose (10B-BPA-fr) dose 30 g 1 and 2 h post-injection using Vt and interpolated plasma activity data.ResultsThe Ichise MA2 model showed the best fit among all models. Akaike Information Criterion (AIC) was the lowest for the Ichise’s MA2 in all regions (mean AIC value − 14.0) comparing to the other models (Logan plot mean AIC 31.4; Ichise MA1 model mean AIC − 4.2). Mean Vt values of the Ichise MA2 model ranged from 0.94 ± 0.14 ml/ml in the pancreas to 0.16 ± 0.02 ml/ml in the right lung. Estimated boron concentration for 10B-BPA-fr had the highest value in the pancreas (14.0 ± 1.9 ppm 1 h after, and 5.7 ± 1.7 ppm 2 h after the 18F-FBPA administration) and the lowest value in the right lung (2.4 ± 0.3 ppm 1 h, and 1.0 ± 0.3 ppm 2 h post-injection).ConclusionThe 10B concentration in normal tissues was best estimated using Vt values of 18F-FBPA with the Ichise multilinear analysis 2 (MA2).Trail registryThe UMIN clinical trial number: UMIN000022850.

MNGI-13. DYNAMIC IMAGING OF MENINGIOMA WITH 3’-DEOXY-3’-[18F]-FLUOROTHYMIDINE USING POSITRON EMISSION TOMOGRAPHY: A POSSIBLE PREDICTOR OF TUMOR GROWTH

Abstract BACKGROUND Positron emission tomography (PET) with 3’-deoxy-3’-[18F]-fluorothymidine (18F-FLT) provides a non-invasive assessment of in vivo tumor proliferation that could be useful for predicting growth potential in meningiomas. We aimed to study static and dynamic 18F-FLT PET metrics prospectively to assess metabolic activity of meningioma, and their associations to potential tumor growth on subsequent MRI scans. METHODS Between April 2017 and December 2018, 44 patients harboring MRI-suspected (n = 37) and histologically-verified residual meningiomas (n = 7) underwent a 60-minute dynamic 18F-FLT PET prior to imaging surveillance. Maximum and mean standardized uptake values (SUVmax, SUVmean) with/without normalisation to blood radioactivity obtained from a 40-60-minute static PET image and a 60-minute venous blood sampling were calculated. Total volume of distribution (VT) was estimated by kinetic modeling using a two-tissue reversible compartmental model with a fractional blood volume and metabolite-corrected image-derived input function. Tumor growth rate was calculated by volumetric analysis of subsequent MRI scans. RESULTS At the time of this writing, a total of 53 follow-up MRI scans from 33 patients were available for review, with a median follow-up time of 11 months (range, 4–22.5 months). Tumor growth/progression was observed in 12 cases with a monthly median growth rate of 0.10 cm3 (range, 0.03–3.41 cm3). All 18F-FLT metrics were significantly higher in patients with radiological progression compared to patients with stable findings with maximum tumor-to-blood-ratio (TBRmax) as the most promising imaging biomarker (4.9 ± 1.4 vs. 3.4 ± 1.0, P = .003; Mann-Whitney) and the strongest predictor for tumor progression (hazard ratio, 3.125; 95% confidence interval, 1.390–7.028; P = .006; univariate binary logistic regression). Age, gender, previous residual remnant(s) and initial tumor volume (median, 3.1 cm3; range, 0.2–55.3 cm3) had no influence. CONCLUSION 18F-FLT PET imaging could be a valuable tool in designing a patient-tailored surveillance strategy for patients with asymptomatic meningiomas.

Effect of adding vasopressin on the distribution of lidocaine in tissues, anesthetic action, and circulatory dynamics.

We examined whether vasopressin affects the distribution, anesthesia duration, and circulatory dynamics of lidocaine. Blood flow was measured after injecting 0.003, 0.03, or 0.3U/mL vasopressin and 2% lidocaine (L) to the upper lip of rats. Radioactivity and distribution of 14C-labeled L (CL) in the palate, palatal mucosa, maxilla bone, and blood was measured by autoradiography after injecting CL and CL + 0.03 U/mL vasopressin. To evaluate anesthesia duration, somatosensory-evoked potentials, blood pressure, and pulse rate were measured after L, 0.03 U/mL vasopressin, and L + 0.03 U/mL vasopressin injection to the palatal mucosa. Blood flow from 10 to 60min was significantly lower with 0.03 U/mL vasopressin and L + 0.03 U/mL vasopressin than with L. Radioactivity in the palatal mucosa and maxilla bone was significantly higher at 5-60min and 2-60min with CL + 0.03 U/mL vasopressin than with CL. Blood radioactivity reached the maximum at 0.5 and 50min with CL and CL + 0.03 U/mL vasopressin, respectively. Autoradiogram showed higher distribution with CL + 0.03 U/mL vasopressin than CL. Peak-to-peakamplitude 30-60min was significantly lower with L + 0.03 U/mL vasopressin than with L. Lidocaine did not affect blood pressure and pulse rate with 0.03 U/mL vasopressin-only or combined with 2%-lidocaine. Topical 0.03 U/mL vasopressin injection reduced the tissue blood flow, promoted the localization and retention, and extended the anesthesia duration of lidocaine, leaving circulatory dynamics unaffected.

Evaluation of absorption, distribution, metabolism, and excretion of [14C]-rucaparib, a poly(ADP-ribose) polymerase inhibitor, in patients with advanced solid tumors

SummaryRucaparib, a poly(ADP-ribose) polymerase inhibitor, is licensed for use in recurrent ovarian, fallopian tube, or primary peritoneal cancer. We characterized the absorption, distribution, metabolism, and elimination of rucaparib in 6 patients with advanced solid tumors following a single oral dose of [14C]-rucaparib 600 mg (≈140 μCi). Total radioactivity (TRA) in blood, plasma, urine, and feces was measured using liquid scintillation counting. Unchanged rucaparib concentrations in plasma were determined using validated liquid chromatography with tandem mass spectrometry. Maximum concentration (Cmax) of TRA and unchanged rucaparib in plasma was 880 ng Eq/mL and 428 ng/mL, respectively, at approximately 4 h post dose; terminal half-life was >25 h for both TRA and rucaparib. The plasma TRA-time profile was parallel to yet higher than that of rucaparib, suggesting the presence of metabolites in plasma. Mean blood:plasma ratio of radioactivity was 1.0 for Cmax and 0.8 for area under the concentration-time curve from time zero to infinity. Mean postdose recovery of TRA was 89.3% over 12 days (71.9% in feces; 17.4% in urine). Unchanged rucaparib and M324 (oxidative metabolite) were the major components in plasma, contributing to 64.0% and 18.6% of plasma radioactivity, respectively. Rucaparib and M324 were the major rucaparib-related components (each ≈7.6% of dose) in urine, whereas rucaparib was the predominant component (63.9% of dose) in feces. The high fecal recovery of unchanged rucaparib could be attributed to hepatic excretion and/or incomplete oral absorption. Overall, these data suggest that rucaparib is eliminated through multiple pathways, including metabolism and renal and biliary excretion.

04:21 PM Abstract No. 334 Prospective study of systemic Yttrium-90 elution during radioembolization of hepatic metastases

Evaluate total blood radioactivity (BR) after SIR-Spheres yttrium-90 (90Y) radioembolization (TARE) and differences in BR based on delivery method and clinical variables. 20 patients (10 men) with hepatic metastases undergoing first TARE were enrolled. Blood samples were drawn at baseline and 0, 10, 20, 30, 60, and 120 minutes after 90Y administration. BR was measured with a gamma counter and scaled by estimated blood volume. Time activity curves were fit to a biexponential model. Percent-instilled radioactivity in the bloodstream was calculated using area under the fitted curve; differences between delivery methods and clinical parameters were examined. Non-parametric statistical tests were utilized. Adverse events were recorded. In 10 patients, SIR-Spheres were instilled using 50% Isovue diluted in saline in the D line, and 10 were treated with D5W in the D line. Mean administered activity was 27.7 mCi and 36.2 mCi, respectively. Fraction of 90Y in the blood was significantly higher for those treated with dilute contrast compared to D5W (median 0.5% of the injected activity vs 0.2%, p = 0.001). Across both groups, maximum activity delivered to a patient was 55.9 mCi; a maximum of 1% of administered radioactivity was measured as free 90Y in the blood. Assuming these highest-case values and complete decay of all free 90Y in bone, we calculated a resulting dose to red marrow of 1.59 cGy using OLINDA/EXM. This represents only a small fraction of the procedure’s cumulative radiation dose. A non-significant decrease in fluoroscopy time was seen with contrast delivery medium (7.5 vs 8.3 minutes). No significant differences were seen in post-treatment leukocytes. There were no immediate complications. Within the first month, 12 patients (60%) experienced adverse events: mild post-embolization syndrome (8), dehydration requiring IV fluids (1), liver failure (1), acute kidney injury (1), and death from sepsis related to UTI. Blood sampling after radioembolization captured time activity curve and estimated BR. Delivery with dilute contrast resulted in a significant increase in BR compared to D5W, though the differences are not thought to be clinically meaningful.

Inhibition of ABCB1 and ABCG2 at the Mouse Blood-Brain Barrier with Marketed Drugs To Improve Brain Delivery of the Model ABCB1/ABCG2 Substrate [11C]erlotinib.

P-Glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) are two efflux transporters at the blood-brain barrier (BBB), which effectively restrict brain distribution of diverse drugs, such as tyrosine kinase inhibitors. There is a crucial need for pharmacological ABCB1 and ABCG2 inhibition protocols for a more effective treatment of brain diseases. In the present study, seven marketed drugs (osimertinib, erlotinib, nilotinib, imatinib, lapatinib, pazopanib, and cyclosporine A) and one nonmarketed drug (tariquidar), with known in vitro ABCB1/ABCG2 inhibitory properties, were screened for their inhibitory potency at the BBB in vivo. Positron emission tomography (PET) using the model ABCB1/ABCG2 substrate [11C]erlotinib was performed in mice. Tested inhibitors were administered as i.v. bolus injections at 30 min before the start of the PET scan, followed by a continuous i.v. infusion for the duration of the PET scan. Five of the tested drugs increased total distribution volume of [11C]erlotinib in the brain ( VT,brain) compared to vehicle-treated animals (tariquidar, + 69%; erlotinib, + 19% and +23% for the 21.5 mg/kg and the 43 mg/kg dose, respectively; imatinib, + 22%; lapatinib, + 25%; and cyclosporine A, + 49%). For all drugs, increases in [11C]erlotinib brain distribution were lower than in Abcb1a/b(-/-)Abcg2(-/-) mice (+149%), which suggested that only partial ABCB1/ABCG2 inhibition was reached at the mouse BBB. The plasma concentrations of the tested drugs at the time of the PET scan were higher than clinically achievable plasma concentrations. Some of the tested drugs led to significant increases in blood radioactivity concentrations measured at the end of the PET scan (erlotinib, + 103% and +113% for the 21.5 mg/kg and the 43 mg/kg dose, respectively; imatinib, + 125%; and cyclosporine A, + 101%), which was most likely caused by decreased hepatobiliary excretion of radioactivity. Taken together, our data suggest that some marketed tyrosine kinase inhibitors may be repurposed to inhibit ABCB1 and ABCG2 at the BBB. From a clinical perspective, moderate increases in brain delivery despite the administration of high i.v. doses as well as peripheral drug-drug interactions due to transporter inhibition in clearance organs question the translatability of this concept.

Improved Immuno-PET Imaging of HER2-Positive Tumors in Mice: Urokinase Injection-Triggered Clearance Enhancement of 64Cu-Trastuzumab.

Immuno-positron emission tomography (immuno-PET) is expected to improve the specificity of small chemical tracers such as 18F-fluorodeoxyglucose. Whole antibodies significantly accumulate in target molecule-expressing tumors but frequently persist too long in the blood circulation for imaging purposes. We investigated the utility of whole antibodies, 64Cu-labeled via a urokinase-substrate linker, and their exogenous urokinase-responsive cleavage to enhance clearance of immuno-PET probes from the blood and shorten the time required to develop adequate imaging contrast. Specifically, we used 64Cu-labeled trastuzumab in human epidermal growth factor receptor 2 (HER2)-positive tumor-bearing mice. 64Cu-labeled trastuzumab with a urokinase-cleavage site (64Cu-CB-TE1A1P-USL-trastuzumab) was synthesized using a bifunctional chelator incorporating an urokinase substrate peptide. Urokinase cleavage was analyzed in vitro by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and radio-gel permeation-high-performance liquid chromatography. Improvements in radioisotope clearance and HER2-imaging by urokinase injection were evaluated by PET imaging and ex vivo biodistribution studies in A431 tumor-bearing mice. 64Cu-CB-TE1A1P-USL-trastuzumab was cleaved into smaller radioactive fragments by 20 000 IU/mL urokinase treatment in vitro at an efficacy of ∼95%. The probe targeted HER2 in A431 tumors in mice within 24 h post-injection, and approximately two-thirds of the probe in the blood circulation was eliminated via renal clearance of radioactive fragments after three urokinase injections. Therefore, the tumor/blood ratio increased 3.0-fold. Without urokinase injection, the tumor accumulation of 64Cu-CB-TE1A1P-USL-trastuzumab slowly increased, and the blood radioactivity decreased over 72 h. However, the tumor/blood ratios in mice after three urokinase injections were higher at 24 h than those in mice without injections at 72 h. The results indicate that our approach shortened the time required to develop adequate imaging contrast of immuno-PET by >2 days. Therefore, this approach can benefit high-sensitivity imaging under lower radioactive decay conditions and can decrease patient radiation exposure. In addition, it could reduce other adverse effects of radioimmunotherapy.

Practical Clinical Measurement of Radiotracer Concentration in Blood: Initial Device Concept and Feasibility Testing.

Kinetic analysis of PET data requires continuous measurement of radioactivity in the arterial blood throughout the acquisition time, termed the arterial input function. The arterial input function is used as an input to compartmental modeling, which can be a better predictor of disease progression than SUV measurements from static PET images. Current common methods of measuring blood concentrations include image-derived, population-based, and manual sampling. These all have challenges due to logistical and technologic issues, as well as patient burden. The aim of this study was to design, develop, and assess a device that is practical and effective for the routine measurement of β-emitting radiotracer concentration in blood without the drawbacks of current methods and for which metabolite analysis is not required. Methods: Designs that integrated a scintillating fiber and a silicon photomultiplier with a general-purpose venous access catheter for in vivo measurement were considered. Other design requirements included miniaturization, high sampling rates, and stopping power for β-particles. Preliminary prototypes were designed to test the feasibility of the concept. Phantom tests were developed to mimic human vasculature. Tests of linearity, sensitivity, signal-to-noise ratios, the impact of vein diameter, and the influence of γ-radiation were conducted. Results: Prototype sensors were constructed using 2 different diameters of polystyrene-based scintillating fibers. Fibers were custom-polished and fixed to a silicon photomultiplier. Sensor output was linear, with R 2 = 0.999 over the range from 0.037 to 9.25 MBq/mL. Absolute sensitivity was approximately 450 counts per second per MBq/mL. Measured signal-to-noise ratios ranged from 1.2:1 to 3.2:1 using a blood-to-tissue concentration ratio of 1:1. Sensor output increased with vein diameter and showed no sensitivity to γ-radiation. Conclusion: In experiments with phantom models, the prototype provided accurate measurements of β-emitting radiotracer concentration. The design will be refined for in vivo testing. The ability to routinely gather blood input function data would facilitate the adoption of kinetic modeling of PET data.

Synthesis and evaluation of an N-[18F]fluorodeoxyglycosyl amino acid for PET imaging of tumor metabolism

IntroductionThe limitations of [18F]fluorodeoxyglucose ([18F]FDG), including producing false-positive or -negative results, low image contrast in brain tumor diagnosis and poor differentiation of tumor and inflammatory, necessitate the development of new radiopharmaceuticals. In the present study, a novel [18F]fluoroglycoconjugate tracer, [18F]FDGly-NH-Phe, for tumor metabolism imaging was prepared and evaluated. Methods[18F]FDGly-NH-Phe was prepared by condensing [18F]FDG with L-4-aminophenylalanine in an acidic condition, and purified with semi-preparative-high performance liquid chromatography (HPLC). The in vitro stability study was conducted in phosphate-buffered saline (PBS, pH 4.0–9.18) at room temperature (RT) and in fetal bovine serum (FBS) at 37 °C. The preliminary cellular uptake studies were performed using Hep-2 cell. The bio-distribution studies, PET/CT imaging and metabolism studies were performed and compared with [18F]FDG on ICR or BALB/c nude model mice. Results[18F]FDGly-NH-Phe was derived from a direct condensation of [18F]FDG with L-4-aminophenylalanine with high stability in FBS and PBS (pH of 6.5–9.18). In vitro cell experiments showed that [18F]FDGly-NH-Phe uptake in Hep-2 cells was primarily transported through amino acid transporters including Na+-dependent A system, ASC system, and system B0,+ system. The bio-distribution of [18F]FDGly-NH-Phe in normal ICR mice showed faster blood radioactivity clearance, and lower uptake in brain and heart than [18F]FDG. The performance of PET/CT imaging for [18F]FDGly-NH-Phe in the mice model manifested excellent tumor visualization, high tumor-to-background ratios, and low accumulation in inflammatory lesions. Metabolism studies for [18F]FDGly-NH-Phe indicated high in vivo stability in plasma and urine and decomposition into [18F]FDG in the tumor microenvironment. ConclusionThe results demonstrated that [18F]FDGly-NH-Phe as a novel amino acid PET tracer showed the capability to differentiate tumor from inflammation, and the potentials for future clinical applications.

One-pot enzymatic synthesis of l-[3-11C]lactate for pharmacokinetic analysis of lactate metabolism in rat brain

IntroductionLactate could serve as an energy source and signaling molecule in the brain, although there is insufficient in vivo evidence to support this possibility. Here we aimed to use a one-pot enzymatic synthetic procedure to synthesize l-[3-11C]lactate that can be used to evaluate chemical forms in the blood after intravenous administration, and as a probe for pharmacokinetic analysis of lactate metabolism in in vivo positron emission tomography (PET) scans with normal and fasted rats. MethodsRacemic [3-11C]alanine obtained from 11C-methylation of a precursor and deprotection was reacted with an enzyme mixture consisting of alanine racemase, d-amino acid oxidase, catalase, and lactate dehydrogenase to yield l-[3-11C]lactate via [3-11C]pyruvate. The optical purity was measured by HPLC. Radioactive chemical forms in the arterial blood of Sprague Dawley rats with or without insulin pretreatment were evaluated by HPLC 10 min after bolus intravenous injection of l-[3-11C]lactate. PET scans were performed on normal and fasted rats administered with l-[3-11C]lactate. Resultsl-[3-11C]Lactate was synthesized within 50 min and had decay corrected radiochemical yield, radiochemical purity, and optical purity of 13.4%, >95%, and >99%, respectively. The blood radioactivity peaked immediately after l-[3-11C]lactate injection, rapidly decreased to the minimum value within 90 s, and slowly cleared thereafter. HPLC analysis of blood samples revealed the presence of [11C]glucose (78.9%) and l-[3-11C]lactate (12.1%) 10 min after administration of l-[3-11C]lactate. Insulin pretreatment partly inhibited glyconeogenesis conversion leading to 55.4% as [11C]glucose and 38.9% as l-[3-11C]lactate simultaneously. PET analysis showed a higher SUV in the brain tissue of fasted rats relative to non-fasted rats. ConclusionsWe successfully synthesized l-[3-11C]lactate in a one-pot enzymatic synthetic procedure and showed rapid metabolic conversion of l-[3-11C]lactate to [11C]glucose in the blood. PET analysis of l-[3-11C]lactate indicated the possible presence of active lactate usage in rat brains in vivo.

Impact of dexmedetomidine on the tissue distribution, anesthetic action, and hemodynamic effects of mepivacaine.

The present study investigated the regional blood flow, tissue distribution, local anesthetic action, and hemodynamic effects of mepivacaine containing dexmedetomidine hydrochloride (DEX) in rats. Blood flow was measured after injection of 0.5% mepivacaine (M group), 12.5µg/ml DEX (D group), or 0.5% mepivacaine containing 12.5µg/ml DEX (DM group) into the upper lip. Mepivacaine distribution was autoradiographically observed in maxillary bone resected after injection of 0.5% 3H-mepivacaine (HM group) or 0.5% 3H-mepivacaine containing 12.5µg/ml DEX (DHM group) into the palatal mucosa adjacent to the right maxillary first molar. Radioactivity was also measured using a liquid scintillation counter. SEP were measured to analyze anesthetic action. Blood pressure and heart rate were measured to compare hemodynamic effect. The addition of DEX significantly decreased blood flow compared to M group from 10 to 60min after injection. The addition of DEX significantly increased the amount of radioactivity compared to HM group in the palatal mucosa from 5 to 60min after injection and in the body of the maxilla from 2 to 60min after injection. Maximum blood radioactivity was measured at 5min after injection in HM group and 50min after injection in DHM group. The addition of DEX significantly decreased peak-to-peak amplitudes compared to M group until 60min after injection. No significant hemodynamic differences were observed. DEX enhances the action of mepivacaine in reducing regional blood flow prolongs its tissue retention, and increases the local anesthetic action without affecting hemodynamics on local administration.

Development of 64Cu-NOTA-Trastuzumab for HER2 Targeting: A Radiopharmaceutical with Improved Pharmacokinetics for Human Studies.

The purpose of this study was to develop 64Cu-labeled trastuzumab with improved pharmacokinetics for human epidermal growth factor receptor 2 (HER2). Methods: Trastuzumab was conjugated with SCN-Bn-NOTA and radiolabeled with 64Cu. Serum stability and immunoreactivity of 64Cu-NOTA-trastuzumab were tested. Small-animal PET imaging and biodistribution studies were performed in a HER2-positive breast cancer xenograft model (BT-474). The internal dosimetry for experimental animals was determined using the image-based approach with the Monte Carlo N-particle code. Results:64Cu-NOTA-trastuzumab was prepared with high radiolabeling yield and radiochemical purity (>98%) and showed high stability in serum and good immunoreactivity. Uptake of 64Cu-NOTA-trastuzumab was highest at 48 h after injection as determined by PET imaging and biodistribution results in BT-474 tumors. The blood radioactivity concentrations of 64Cu-NOTA-trastuzumab decreased biexponentially with time in both mice with and mice without BT-474 tumor xenografts. The calculated absorbed dose of 64Cu-NOTA-trastuzumab was 0.048 mGy/MBq for the heart, 0.079 mGy/MBq for the liver, and 0.047 mGy/MBq for the spleen. Conclusion:64Cu-NOTA-trastuzumab was effectively targeted to the HER2-expressing tumor in vitro and in vivo, and it exhibited a relatively low absorbed dose due to a short residence time. Therefore, 64Cu-NOTA-trastuzumab could be applied to select the right patients and right timing for HER2 therapy, to monitor the treatment response after HER2-targeted therapy, and to detect distal or metastatic spread.

Metabolism and Disposition of Siponimod, a Novel Selective S1P1/S1P5 Agonist, in Healthy Volunteers and In Vitro Identification of Human Cytochrome P450 Enzymes Involved in Its Oxidative Metabolism.

Siponimod, a next-generation selective sphingosine-1-phosphate receptor modulator, is currently being investigated for the treatment of secondary progressive multiple sclerosis. We investigated the absorption, distribution, metabolism, and excretion (ADME) of a single 10-mg oral dose of [14C]siponimod in four healthy men. Mass balance, blood and plasma radioactivity, and plasma siponimod concentrations were measured. Metabolite profiles were determined in plasma, urine, and feces. Metabolite structures were elucidated using mass spectrometry and comparison with reference compounds. Unchanged siponimod accounted for 57% of the total plasma radioactivity (area under the concentration-time curve), indicating substantial exposure to metabolites. Siponimod showed medium to slow absorption (median Tmax: 4 hours) and moderate distribution (Vz/F: 291 l). Siponimod was mainly cleared through biotransformation, predominantly by oxidative metabolism. The mean apparent elimination half-life of siponimod in plasma was 56.6 hours. Siponimod was excreted mostly in feces in the form of oxidative metabolites. The excretion of radioactivity was close to complete after 13 days. Based on the metabolite patterns, a phase II metabolite (M3) formed by glucuronidation of hydroxylated siponimod was the main circulating metabolite in plasma. However, in subsequent mouse ADME and clinical pharmacokinetic studies, a long-lived nonpolar metabolite (M17, cholesterol ester of siponimod) was identified as the most prominent systemic metabolite. We further conducted in vitro experiments to investigate the enzymes responsible for the oxidative metabolism of siponimod. The selective inhibitor and recombinant enzyme results identified cytochrome P450 2C9 (CYP2C9) as the predominant contributor to the human liver microsomal biotransformation of siponimod, with minor contributions from CYP3A4 and other cytochrome P450 enzymes.

Novel Approach for 99mTc-Labeling of Red Blood Cells: Evaluation of 99mTc-4SAboroxime as a Blood Pool Imaging Agent.

Angiography with radiolabeled red blood cells (RBCs) plays an important role in diagnosis and prognosis in vascular diseases. Both in vitro and in vivo methods have been developed for 99mTc-labeling of RBCs. However, these methods are complicated and lack reproducibility. Therefore, it is highly desirable to develop an alternative method for routine 99mTc-labeling of RBCs. In this report, we present a novel approach for 99mTc-labeling of RBCs. We prepared a new 99mTc(III) radiotracer [99mTcCl(CDO)(CDOH)2B-4AS] (99mTc-4ASboroxime: 4AS-B(OH)2 = 4-aminosulfonylphenyl)boronic acid, and CDOH2 = cyclohexanedione dioxime) in >95% radiochemical purity. Imaging and biodistribution studies were performed in Sprague-Dawley (SD) rats. It was found that the blood radioactivity was ∼6.0%ID/g (∼90% injected dose for 200-225 g SD rats) for 99mTc-4ASboroxime with low uptake in the myocardium, kidneys, liver, lungs, and muscle, most likely due to lack of leakage of 99mTc-labeled RBCs from the intravascular space. The blood radioactivity was almost unchanged over the 2 h period, suggesting that the binding of 99mTc-4ASboroxime to blood components (cells, proteins, and plasma) is stable. The results from γ-counting of the isolated blood components showed that 99mTc-4ASboroxime had >95% of blood radioactivity binding to RBCs, ∼1% to albumin, and ∼3% remaining free in blood plasma, demonstrating its RBC-specificity. The results from imaging studies in SD rats indicated that 99mTc-4ASboroxime is predominantly distributed in the blood pool. Main blood vessels were well delineated in the head/neck and abdominal regions. This statement was further substantiated by the results from imaging studies in pigs. 99mTc-4ASboroxime is an excellent blood pool agent with the potential for diagnosis and prognosis of vascular diseases.

Metabolism of metofluthrin in rats: II. Excretion, distribution and amount of metabolites

1. 14 C-Labelled E/Z isomers of a synthetic pyrethroid metofluthrin ((E/Z)-(1 R,3 R)-2,3,5,6-tetrafluoro-4-(methoxymethyl)benzyl 2,2-dimethyl-3-(1-propenyl)-cyclopropanecarboxylate, abbreviated as RTE/RTZ, respectively) were used for rat metabolism studies. 14 C-RTE or RTZ labelled at the carbonyl-carbon [acid-14C] or the methoxymethylbenzyl-α-carbon [alcohol-14 C] was administered orally to rats at 1 and 20 mg/kg.2. Dosed compounds were mostly absorbed, metabolised, and rapidly excreted. Dose-related increase in blood AUC suggested no saturation of absorption at the high dose. Blood 14 C was maximal at 3–8 h and decreased with a half-life of 52–163 h. Radioactivity in tissues, blood and plasma decreased basically at the same rate and the sum fell below 0.2% of the dose at 168 h.3. Although the major metabolic pathways of the isomers, that is, ester cleavage, O-demethylation and ω-oxidation, were similar, there was a notable difference. The RTZ double bond commonly undergoes epoxidation while RTE double bond mainly undergoes glutathione conjugation, which causes faster elimination from plasma and greater excretion into faeces on RTE. Faster urinary excretion and elimination from blood were observed for the alcohol moiety than the acid moiety.4. In conclusion, this study described the overall metabolic profiles of metofluthrin and identified the differences in metabolic breakdown between the isomers. No marked sex-/dose-related differences were observed.

TBBPA disposition and kinetics in pregnant and nursing Wistar Han IGS rats

Tetrabromobisphenol-A (TBBPA) is a brominated flame retardant (BFR) commonly used in electronics to meet fire safety standards and has the largest worldwide production of any BFR. TBBPA has been detected in human breast milk and maternal/cord serum, indicating exposure to mothers, fetuses, and breastfeeding newborns although exposure to fetuses and newborns is poorly understood. Pregnant or nursing Wistar Han IGS rats were administered [14C]-TBBPA in a single dose (25 mg/kg, 2.5 μCi/kg) and euthanized between 0.5&24 h post dose to determine disposition in pregnant and nursing rats and their pups. Systemic exposure was largely unchanged between 1&8 h post dose in pregnant rats; [14C]-radioactivity in blood varied only slightly between 0.5&8 h (2.6 ± 0.6 → 2.6 ± 0.8 nmol-eq/mL) but was below the limit of detection at 24 h with an absorption half-life of 16min and elimination half-life of 17 h. Cmax was observed at 30min in lactating rats and concentrations fell steadily through 8 h. Plasma from pregnant rats contained a mixture of TBBPA and TBBPA-conjugates at 30min but only metabolites in subsequent samples. TBBPA was not detected in lactating dam plasma in this study. Placental concentrations increased through 8 h while whole-fetus Cmax occurred at 2 h post dose. In lactating animals, liver, uterus, and mammary time-concentration curves lagged slightly behind blood-concentration curves. It was clear from these studies that TBBPA is available to both the developing fetus and nursing pup following maternal exposure, and nursing pups are continuously exposed via contaminated milk produced by their mother. This research was supported in part by the Intramural Research Program of NIH/NCI.