Oxygen extraction fraction is not uniform in human brain: a positron emission tomography study

The regional differences in cerebral oxygen extraction fraction (OEF) in brain were investigated using positron emission tomography (PET) in detail with consideration of systemic errors in PET measurement estimated by simulation studies. The cerebral blood flow (CBF), cerebral blood volume (CBV), OEF, and cerebral metabolic rate of oxygen (CMRO2) were measured on healthy men by PET with 15O-labeled gases. The OEF values in the pons and the parahippocampal gyrus were significantly smaller than in the other brain regions. The OEF value in the lateral side of the occipital cortex was largest among the cerebral cortical regions. Simulation studies have revealed that errors in OEF caused by regional differences in the distribution volume of 15O-labeled water, as well as errors in OEF caused by a mixture of gray and white matter, must be negligible. The regional differences in OEF in brain must exist which might be related to physiological meanings.Article title: Kindly check and confirm the edit made in the article title.I have checked the article title and it is OK as is. Trial registration: The UMIN clinical trial number: UMIN000033382, https://www.umin.ac.jp/ctr/index.htm.

Simultaneous assessment of left ventricular mechanical dyssynchrony using integrated 13N-ammonia PETMR system: direct comparison of PET phase analysis and MR feature tracking

BACKGROUND

To compare phase analysis with positron emission tomography (PA) and magnetic resonance feature tracking derived myocardial strain (FT) for left ventricular (LV) mechanical dyssynchrony using PETMR system in patients with ischemic heart disease.

METHODS AND RESULTS

Patients who underwent rest-pharmacological stress 13N ammonia PETMR were enrolled. Histogram bandwidth (BW) and phase standard deviation (PSD) were compared to global longitudinal, long axis radial, short axis circumferential, and radial strain (GLS, GRS, SA Circ, and SA Rad) obtained from FT. LV dyssynchrony index (SDI) derived from PA and FT were compared. BW and PSD showed significant correlations with FT (a Pearson's coefficient r = 0.64, P < .0001, and r = 0.51, P < .0001 for SA Circ; r = 0.67, P < .0001, and r = 0.74, P < .0001 for GLS; r = - 0.60, P < .0001, r = - 0.61, P < .0001 for SA Rad; r = - 0.62, P < .0001, and r = - 0.68, P < .0001 for GRS, respectively). Bland-Altman plots for SDI showed a preferable agreement (95% limit of agreement - 0.12 to 0.075, - 0.20 to 0.098, - 0.38 to 0.077, and - 0.37 to 0.032; bias 0.0068 ± 0.056, 0.026 ± 0.068, 0.11 ± 0.088, and 0.13 ± 0.079 for SA Circ, SA Rad, GLS, and GRS, respectively).

CONCLUSION

In simultaneous acquisition using PETMR, comparison of PET phase analysis and MR strain showed a good correlation.

[The Questionnaire Survey of Japanese Practice and Environment for Targeted Radionuclide Therapy in 2021]

PURPOSE

Recently, the targeted radionuclide therapy (TRT) was urgently required to adapt the practice and environment because of the implementation of novel therapeutic radiopharmaceuticals such as alpha- and beta- radionuclides therapy. The present study aimed to clarify the questionnaire survey with the current situation (safety controls for workers and patients) at Japanese TRT facilities.

METHODS

The massive questionnaire survey, 2 months from October to November 2021, was conducted among nationwide 251 facilities that have performed TRT in the past two years. The alpha- and beta- therapeutic radiopharmaceuticals were categorized and answered by one representative of the facility under anonymity. We analyzed the actual situation of each facility related to occupational exposure, radiation protection, contamination inspection, patient release criteria, and dosimetry for TRT.

RESULTS

The survey response rate was 69.1% (174 facilities). About 75% of these facilities reported that they either follow the guidelines or take their own measures to reduce occupational exposure. The confirmed means of patient release criteria were 68.0% with the administered radioactivity and 87.2% with the ambient dose rate. The cold run was not performed for the first time at 15.0% and 10.0% of the facilities for β- and α-emitting radionuclides, respectively. The facilities without attachment syringe shields were 39.2% for alpha-radionuclides therapy and 20.3% for beta-radionuclides therapy.

CONCLUSION

We clarified the Japanese problem for TRT practice and environment by the questionnaire survey. Our findings indicated that the Japanese guidelines and manuals for TRT were not partly followed in the nationwide facilities.

Activation cross sections of proton-induced reactions on natural platinum up to 30 MeV

Activation cross sections of proton-induced reactions on natural platinum were measured. The stacked-foil activation technique and high-resolution gamma-ray spectrometry were used. The production cross sections of ^{198, 196, 196m2, 195, 194, 193, 192, 191}Au, ¹⁹¹Pt, and ^{192, 190}Ir were determined up to 30 MeV. The experimental results were compared with previous experimental data and theoretical calculations in the TENDL-2019 library.

Manual on the proper use of meta-[211At] astato-benzylguanidine ([211At] MABG) injections in clinical trials for targeted alpha therapy (1st edition)

In this manuscript, we present the guideline for use of meta-[²¹¹At] astatobenzylguanidine ([²¹¹At] MABG), a newly introduced alpha emitting radiopharmaceutical to the up-coming World’s first clinical trial for targeted alpha therapy (TAT) at Fukushima Medical University in Japan, focusing on radiation safety issues in Japan. This guideline was prepared based on a study supported by the Ministry of Health, Labour, and Welfare, and approved by the Japanese Society of Nuclear Medicine on Oct. 5th, 2021. The study showed that patients receiving [²¹¹At] MABG do not need to be admitted to a radiotherapy room and that TAT using [²¹¹At] MABG is possible on an outpatient basis. The radiation exposure from the patient is within the safety standards of the ICRP and IAEA recommendations for the general public and caregivers or patient’s family members. In this guideline, the following contents are also included: precautions for patients and their families, safety management associated with the use of [²¹¹At] MABG, education and training, and disposal of medical radioactive contaminants. TAT using [²¹¹At] MABG in Japan should be carried out according to this guideline. Although this guideline is based on the medical environment and laws and regulations in Japan, the issues for radiation protection and evaluation methodology presented in this guideline are useful and internationally acceptable as well.

Nonclinical study and applicability of the absorbed dose conversion method with a single biodistribution measurement for targeted alpha-nuclide therapy

Background

We recently reported a new absorbed dose conversion method, RAP (RAtio of Pharmacokinetics), for ²¹¹At-meta-astatobenzylguanidine (²¹¹At-MABG) using a single biodistribution measurement, the percent injected dose/g. However, there were some mathematical ambiguities in determining the optimal timing of a single measurement of the percent injected dose/g. Thus, we aimed to mathematically reconstruct the RAP method and to examine the optimal timing of a single measurement.

Methods

We derived a new formalism of the RAP dose conversion method at time t. In addition, we acquired a formula to determine the optimal timing of a single measurement of the percent injected dose/g, assuming the one-compartment model for biological clearance.

Results

We investigated the new formalism’s performance using a representative RAP coefficient with radioactive decay weighting. Dose conversions by representative RAP coefficients predicted the true [²¹¹At]MABG absorbed doses with an error of 10% or less. The inverses of the representative RAP coefficients plotted at 4 h post-injection, which was the optimal timing reported in the previous work, were very close to the new inverses of the RAP coefficients 4 h post-injection. Next, the behavior of the optimal timing was analyzed by radiolabeled compounds with physical half-lives of 7.2 h and 10 d on various biological clearance half-lives. Behavior maps of optimal timing showed a tendency to converge to a constant value as the biological clearance half-life of a target increased. The areas of optimal timing for both compounds within a 5% or 10% prediction error were distributed around the optimal timing when the biological clearance half-life of a target was equal to that of the reference. Finally, an example of RAP dose conversion was demonstrated for [²¹¹At]MABG.

Conclusions

The RAP dose conversion method renovated by the new formalism was able to estimate the [²¹¹At]MABG absorbed dose using a similar pharmacokinetics, such as [¹³¹I]MIBG. The present formalism revealed optimizing imaging time points on absorbed dose conversion between two radiopharmaceuticals. Further analysis and clinical data will be needed to elucidate the validity of a behavior map of the optimal timing of a single measurement for targeted alpha-nuclide therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00425-z.

Simulation of the distribution of astatine-211 solution dispersion in a lab room

OBJECTIVE

This study aimed to evaluate the distribution of Astatine-211 (211At) solution dispersion in a small animal cage using autoradiography imaging to simulate the dispersion of 211At in a lab room to eventually prevent user's risk of internal exposure in terms of radiation safety.

METHODS

211At radiation sources with two chemical properties (Na211At and Free 211At) were prepared. The solutions of 211At were placed onto a dish with paper, and then, it was placed in a small animal cage for 3 h. After removing the dish, an imaging plate with attaching reference sources was placed at four walls of the cage for 15 h in a lead box. Imaging plates were read, and all pixel data were calculated using Microsoft Excel 2016 to obtain three-dimensional (3D) distribution. Calculated results were depicted using a 3D sphere model.

RESULTS

The mean activity of Free 211At was 2.3 times higher than that of Na211At on all autoradiography images. In the cage, the shape of the dispersion of Na211At was almost homogeneous, whereas that of Free 211At was more heterogeneous.

CONCLUSION

We found that the solution of 211At vaporized naturally and was distributed heterogeneously in the cage, and the chemical properties of 211At influenced their behaviors. These results must be considered to minimize the risks of radiation safety.

Activation cross section measurement of alpha-particle induced reactions on natural neodymium

Excitation functions of alpha-particle induced reactions on ^natNd up to 50 MeV were measured at the RIKEN AVF cyclotron. To derive cross sections activation method, stacked target technique and gamma-ray spectrometry were adopted. Formations of ^153,145Sm, ^{151,150,149,148m,148g,144,143}Pm, and ^149,147Nd were investigated. The results were compared with the previous experimental data and the TENDL-2019 data. Discrepancies among most of them were found.

Evaluation of Effect of Ninjin'yoeito on Regional Brain Glucose Metabolism by 18F-FDG Autoradiography With Insulin Loading in Aged Mice

Introduction: A recent clinical study revealed that Ninjin'yoeito (NYT) may potentially improve cognitive outcome. However, the mechanism by which NYT exerts its effect on elderly patients remains unclear. The aim of this study is to evaluate the effect of Ninjin'yoeito on regional brain glucose metabolism by ¹⁸F-FDG autoradiography with insulin loading in aged wild-type mice.

Materials and Methods: After 12 weeks of feeding NYT, mice were assigned to the control and insulin-loaded groups and received an intraperitoneal injection of human insulin (2 U/kg body weight) 30 min prior to ¹⁸F-FDG injection. Ninety minutes after the injection, brain autoradiography was performed.

Results: After insulin loading, the ¹⁸F-FDG accumulation showed negative changes in the cortex, striatum, thalamus, and hippocampus in the control group, whereas positive changes were observed in the NYT-treated group.

Conclusions: Ninjin'yoeito may potentially reduce insulin resistance in the brain regions in aged mice, thereby preventing age-related brain diseases.

Evaluation of organ glucose metabolism by 18F-FDG accumulation with insulin loading in aged mice compared with young normal mice

It is important to determine the functional changes of organs that occur as a result of aging, the understanding of which may lead to the maintenance of a healthy life. Glucose metabolism in healthy bodies is one of the potential markers used to evaluate the changes of organ function. Thus, information about normal organ glucose metabolism may help to understand the functional changes of organs. [¹⁸F]-Fluoro-2-deoxy-2-d-glucose (¹⁸F-FDG), a glucose analog, has been used to measure glucose metabolism in various fields, such as basic medical research and drug discovery. However, glucose metabolism changes in aged animals have not yet been fully clarified. The aim of this study is to evaluate changes in glucose metabolism in organs and brain regions by measuring ¹⁸F-FDG accumulation and ¹⁸F-FDG autoradiography with insulin loading in aged and young wild-type mice. In the untreated groups, the levels of ¹⁸F-FDG accumulation in the blood, plasma, muscle, lungs, spleen, pancreas, testes, stomach, small intestine, kidneys, liver, brain, and brain regions, namely, the cortex, striatum, thalamus, and hippocampus, were all significantly higher in the aged mice. The treated group showed lower ¹⁸F-FDG accumulation levels in the pancreas and kidneys, as well as in the cortex, striatum, thalamus, and hippocampus in the aged mice than the untreated groups, whereas higher ¹⁸F-FDG accumulation levels were observed in those in the young mice. These results demonstrate that insulin loading decreases effect on ¹⁸F-FDG accumulation levels in some organs of the aged mice. Therefore, aging can increase insulin resistance and lead to systemic glucose metabolism dysfunction.

Integrated PET/MRI scanner with oxygen-15 labeled gases for quantification of cerebral blood flow, cerebral blood volume, cerebral oxygen extraction fraction and cerebral metabolic rate of oxygen

OBJECTIVES

Measurement of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO₂) by PET with oxygen-15 labeled gases is useful for diagnosis and treatment planning in cases of chronic occlusive cerebrovascular disease. In the present study, CBF, CBV, OEF and CMRO₂ were measured using the integrated design of PET/MRI scanner system. This is a first attempt to measure cerebral perfusion and oxygen metabolism using PET/MRI with oxygen-15 labeled gases.

METHODS

PET/MRI measurements with the steady-state method of oxygen-15 labeled gases, carbon monoxide (C¹⁵O), oxygen (¹⁵O₂), and carbon dioxide (C¹⁵O₂) were performed on nine healthy men. Two kinds of attenuation correction for PET were performed using MRI with Dixon sequence (DIXON) and Dixon sequence with model-based bone segmentation (DIXONbone). A real-time motion correction of PET images was also performed using simultaneously measured MR images to detect head motion.

RESULTS

Mean and SD values of CBF, CBV, OEF, and CMRO₂ in the cerebral cortices with attenuation correction by DIXON were 31 ± 4 mL/100 mL/min, 2.7 ± 0.2 mL/mL, 0.40 ± 0.07, and 2.5 ± 0.3 mL/100 mL/min without real-time motion correction, and 33 ± 4 mL/100 mL/min, 2.7 ± 0.2 mL/mL, 0.40 ± 0.07, and 2.6 ± 0.3 mL/100 mL/min with real-time motion correction, respectively. Values with of CBF, CBV, OEF, and CMRO₂ with attenuation correction by DIXONbone were 35 ± 5 mL/100 mL/min, 2.8 ± 0.2 mL/mL, 0.40 ± 0.07, and 2.8 ± 0.3 mL/100 mL/min without real-time motion correction, and 38 ± 5 mL/100 mL/min, 2.8 ± 0.2 mL/mL, 0.40 ± 0.07, and 3.0 ± 0.4 mL/100 mL/min with real-time motion correction, respectively.

CONCLUSIONS

Using PET/MRI with oxygen-15 labeled gases, CBF, CBV, OEF, and CMRO₂ could be measured. Values of CBF, CBV, and CMRO₂ measured with attenuation correction by DIXON were significantly lower than those measured with correction by DIXONbone. One of the reasons for this is that attenuation correction of DIXON does not take into consideration of the photon absorption by bone. OEF values, corresponding to ratios of CMRO₂ to CBF, were not affected by attenuation correction methods. Values of CBF and CMRO₂ with a real-time motion correction were significantly higher than those without correction. Using PET/MRI with adequate corrections, similar values of CBF, CBV, OEF, and CMRO₂ as PET alone scanner system reported previously were obtained.

TRAIL REGISTRATION

The UMIN clinical trial number: UMIN000033382.

Preliminary Evaluation of Astatine-211-Labeled Bombesin Derivatives for Targeted Alpha Therapy

There are various diagnostic and therapeutic agents for prostate cancer using bombesin (BBN) derivatives, but astatine-211 (²¹¹At)-labeled BBN derivatives have yet to be studied. This study presented a preliminary evaluation of ²¹¹At-labeled BBN derivative. Several nonradioactive iodine-introduced BBN derivatives (IB-BBNs) with different linkers were synthesized and their binding affinities measured. Because IB-3 exhibited a comparable affinity to native BBN, [²¹¹At]AB-3 was synthesized and the radiochemical yields of [²¹¹At]AB-3 was 28.2 ± 2.4%, with a radiochemical purity of >90%. The stability studies and cell internalization/externalization experiments were performed. [²¹¹At]AB-3 was taken up by cells and internalized; however, radioactivity effluxed from cells over time. In addition, the biodistribution of [²¹¹At]AB-3, with and without excess amounts of BBN, were evaluated in PC-3 tumor-bearing mice. Despite poor stability in murine plasma, [²¹¹At]AB-3 accumulated in tumor tissue (4.05 ± 0.73%ID/g) in PC-3 tumor-bearing mice, which was inhibited by excess native BBN (2.56 ± 0.24%ID/g). Accumulated radioactivity in various organs is probably due to free ²¹¹At. Peptide degradation in murine plasma and radioactivity efflux from cells are areas of improvement. The development of ²¹¹At-labeled BBN derivatives requires modifying the BBN sequence and preventing deastatination.

Evaluation of a model-based attenuation correction method on whole-body 18F-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging

The bone cannot be evaluated using magnetic resonance attenuation correction (MRAC) with the Dixon sequence. To solve this issue, the present study aimed to evaluate model-based AC for whole-body 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) positron emission tomography (PET)/magnetic resonance imaging (MRI) by creating bone segmentation. We analyzed and evaluated the data of 31 consecutive patients. The Biograph mMR (Siemens Healthcare) was used for clinical whole-body ¹⁸F-FDG PET/MRI with the conventional MRAC method, and OSIRIX MD software was used to analyze the images. After the examination, the new model-based post-processing MRAC was applied to create μ-maps with bone segmentation, and retrospective PET reconstruction was performed using this μ-map. The bone structures of all patients created using model-based MRAC were visually evaluated. Standard uptake values (SUVs) at 11 anatomical positions in PET images, corrected using the μ-map with and without bone segmentation, were measured and compared. The model-based post-processing MRAC was run for all patients, without errors. Visual evaluation revealed that the model-based post-processing MRAC exhibited poor results for six patients. Furthermore, it exhibited an increasing trend of SUV in the brain compared to the conventional method. Locations other than the brain indicated a similar or decreasing trend. The two methods showed a good linear correlation for all patients. However, patients aged < 20 years exhibited a different trend from those aged ≥ 20 years. We should exercise caution when applying this model-based MRAC for younger patients.

Absorbed dose simulation of meta-211At-astato-benzylguanidine using pharmacokinetics of 131I-MIBG and a novel dose conversion method, RAP

OBJECTIVE

We aimed to estimate in vivo ²¹¹At-labeled meta-benzylguanidine (²¹¹At-MABG) absorbed doses by the two dose conversion methods, using ¹³¹I-MIBG biodistribution data from a previously reported neuroblastoma xenograft model. In addition, we examined the effects of different cell lines and time limitations using data from two other works.

METHODS

We used the framework of the Monte Carlo method to create 3200 virtual experimental data sets of activity concentrations (kBq/g) to get the statistical information. Time activity concentration curves were produced using the fitting method of a genetic algorithm. The basic method was that absorbed doses of ²¹¹At-MABG were calculated based on the medical internal radiation dose formalism with the conversion of the physical half-life time of ¹³¹I to that of ²¹¹At. We have further improved the basic method; that is, a novel dose conversion method, RAP (Ratio of Pharmacokinetics), using percent injected dose/g.

RESULTS

Virtual experiments showed that ²¹¹At-MABG and ¹³¹I-MIBG had similar properties of initial activity concentrations and biological components, but the basic method did not simulate the ²¹¹At-MABG dose. Simulated ²¹¹At-MABG doses from ¹³¹I-MIBG using the RAP method were in agreement with those from ²¹¹At-MABG, so that their boxes overlapped in the box plots. The RAP method showed applicability to the different cell lines, but it was difficult to predict long-term doses from short-term experimental data.

CONCLUSIONS

The present RAP dose conversion method could estimate ²¹¹At-MABG absorbed doses from the pharmacokinetics of ¹³¹I-MIBG with some limitations. The RAP method would be applicable to a large number of subjects for targeted nuclide therapy.

OR03-01 Effects Of Alpha-emitting Meta-211At-astato-benzylguanidine (211At-MABG) Compared To 131I-meta-iodobenzylguanidine (131I-MIBG) on Tumor Growth Suppression in a Pheochromocytoma Mouse Model

Objectives: Given the limited treatment approaches currently available for patients with metastatic pheochromocytoma and paraganglioma (PPGL), new effective approaches are being sought. The radioisotope approach using ¹³¹I-meta-iodobenzylguanidine (¹³¹I-MIBG) has limited survival benefits in metastatic PPGL but is currently considered one of the standard therapeutic approaches. In theory, the alpha-emitting radiopharmaceutical meta-²¹¹At-astato-benzylguanidine (²¹¹At-MABG) could be a very effective targeted treatment for metastatic PPGL. However, this possibility has not been evaluated. Therefore, the purpose of this study was to evaluate the tumor growth suppression effects of ²¹¹At-MABG compared to ¹³¹I-MIBG using a PC-12 mouse pheochromocytoma model.

Methods: Rat pheochromocytoma (PC-12) cells were subcutaneously inoculated into male BALB/c nu/nu nude mice. When tumor volumes reached approximately 300 mm³, mice bearing PC-12 tumors received intravenously either 1.11 MBq of ²¹¹At-MABG (n=6), 31 MBq of ¹³¹I-MIBG (n=3) or vehicle solvent (n = 6). The tumor volume was measured 3 times per week for 2 weeks. The tumor volume was compared among the three groups.

Results: At 14 days, the tumor volumes significantly increased in the control group (328.82±83.65 to 3568.83±693.23 mm³, P<0.001). In contrast, there were no significant changes in tumor volumes in the ²¹¹At-MABG group (284.65±56.77 to 274.3±87.95 mm³, P=0.616) and ¹³¹I-MIBG group (484.40±46.25 to 323.93±127.27 mm³, P=0.084). The ²¹¹At-MABG group showed significantly lower percentage change in tumor volume than did the control group (-5.0±15.99 vs. 1043.83±320.79%, P<0.001), and ¹³¹I-MIBG group also showed significant volume reduction rate compared to that of the control group (-34.33±21.39 vs. 1043.82±320.79%, P<0.001). There was no significant difference in percentage tumor volume changes between the ²¹¹At-MABG and ¹³¹I-MIBG groups (P=0.052). Conclusion: At 14 days after radiopharmaceutical administration, ²¹¹At-MABG produced significant tumor volume reduction as compared to that in the control group and to that associated with ¹³¹I-MIBG, which is considered one of the current treatment options. Therefore, ²¹¹At-MABG may have future clinical applications for the treatment of metastatic pheochromocytoma and paraganglioma.

Possibility of cancer-stem-cell-targeted radioimmunotherapy for acute myelogenous leukemia using 211At-CXCR4 monoclonal antibody

To explore stem-cell-targeted radioimmunotherapy with α-particles in acute myelogenous leukemia (AML), pharmacokinetics and dosimetry of the ²¹¹At-labeled anti-C-X-C chemokine receptor type 4 monoclonal antibody (²¹¹At-CXCR4 mAb) were conducted using tumor xenografted mice. The biological half-life of ²¹¹At-CXCR4 mAb in blood was 15.0 h. The highest tumor uptake of 5.05%ID/g with the highest tumor-to-muscle ratio of 8.51 ± 6.14 was obtained at 6 h. Radiation dosimetry estimated with a human phantom showed absorbed doses of 0.512 mGy/MBq in the bone marrow, 0.287 mGy/MBq in the kidney, and <1 mGy/MBq in other major organs except bone. Sphere model analysis revealed 22.8 mGy/MBq in a tumor of 10 g; in this case, the tumor-to-bone marrow and tumor-to-kidney ratios were 44.5 and 79.4, respectively. The stem-cell-targeted α-particle therapy using ²¹¹At-CXCR4 mAb for AML appears possible and requires further therapeutic studies.

Production cross sections of ytterbium and thulium radioisotopes in alpha-induced nuclear reactions on natural erbium

Activation cross sections of alpha-induced reactions on natural erbium were measured using a 50.9-MeV alpha-beam at the RIKEN AVF cyclotron. Well-established methods for the measurements, the stacked-foil activation technique and gamma-ray spectrometry, were used. Production cross sections of ^166,169Yb and ^{165,166,167,168,170,173}Tm were determined. This is the first measurement of the cross sections of ^166,170Tm. The integral yield of the medical radionuclide ¹⁶⁹Yb was derived from the measured excitation function.

Elimination of tumor hypoxia by eribulin demonstrated by 18F-FMISO hypoxia imaging in human tumor xenograft models

BACKGROUND

Eribulin, an inhibitor of microtubule dynamics, shows antitumor potency against a variety of solid cancers through its antivascular activity and remodeling of tumor vasculature. ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO) is the most widely used PET probe for imaging tumor hypoxia. In this study, we utilized ¹⁸F-FMISO to clarify the effects of eribulin on the tumor hypoxic condition in comparison with histological findings.

MATERIAL AND METHODS

Mice bearing a human cancer cell xenograft were intraperitoneally administered a single dose of eribulin (0.3 or 1.0 mg/kg) or saline. Three days after the treatment, mice were injected with ¹⁸F-FMISO and pimonidazole (hypoxia marker for immunohistochemistry), and intertumoral ¹⁸F-FMISO accumulation levels and histological characteristics were determined. PET/CT was performed pre- and post-treatment with eribulin (0.3 mg/kg, i.p.).

RESULTS

The ¹⁸F-FMISO accumulation levels and percent pimonidazole-positive hypoxic area were significantly lower, whereas the number of microvessels was higher in the tumors treated with eribulin. The PET/CT confirmed that ¹⁸F-FMISO distribution in the tumor was decreased after the eribulin treatment.

CONCLUSIONS

Using ¹⁸F-FMISO, we demonstrated the elimination of the tumor hypoxic condition by eribulin treatment, concomitantly with the increase in microvessel density. These findings indicate that PET imaging using ¹⁸F-FMISO may provide the possibility to detect the early treatment response in clinical patients undergoing eribulin treatment.

Production cross sections of Mo, Nb and Zr radioisotopes from α-induced reaction on natZr

Cross sections of α-induced reactions on natural zirconium were measured up to 50 MeV using the stacked-foil technique, activation method and high resolution γ-ray spectrometry. The production cross sections of ^93m,99Mo, ^{90g,92m,95g,95m,96}Nb and ^88,89g,95Zr were determined and compared with other experimental data measured earlier and result of theoretical calculations. The integral thick target yield of ⁹⁹Mo was deduced from the measured cross section data.

[18F]DPA-714 PET imaging shows immunomodulatory effect of intravenous administration of bone marrow stromal cells after transient focal ischemia

Background

The potential application of bone marrow stromal cell (BMSC) therapy in stroke has been anticipated due to its immunomodulatory effects. Recently, positron emission tomography (PET) with [¹⁸F]DPA-714, a translocator protein (TSPO) ligand, has become available for use as a neural inflammatory indicator. We aimed to evaluate the effects of BMSC administration after transient middle cerebral artery occlusion (MCAO) using [¹⁸F]DPA-714 PET.

The BMSCs or vehicle were administered intravenously to rat MCAO models at 3 h after the insult. Neurological deficits, body weight, infarct volume, and histology were analyzed. [¹⁸F]DPA-714 PET was performed 3 and 10 days after MCAO.

Results

Rats had severe neurological deficits and body weight loss after MCAO. Cell administration ameliorated these effects as well as the infarct volume. Although weight loss occurred in the spleen and thymus, cell administration suppressed it. In both vehicle and BMSC groups, [¹⁸F]DPA-714 PET showed a high standardized uptake value (SUV) around the ischemic area 3 days after MCAO. Although SUV was increased further 10 days after MCAO in both groups, the increase was inhibited in the BMSC group, significantly. Histological analysis showed that an inflammatory reaction occurred in the lymphoid organs and brain after MCAO, which was suppressed in the BMSC group.

Conclusions

The present results suggest that BMSC therapy could be effective in ischemic stroke due to modulation of systemic inflammatory responses. The [¹⁸F]DPA-714 PET/CT system can accurately demonstrate brain inflammation and evaluate the BMSC therapeutic effect in an imaging context. It has great potential for clinical application.

Dynamic PET evaluation of elevated FLT level after sorafenib treatment in mice bearing human renal cell carcinoma xenograft

Background

Sorafenib, an oral multikinase inhibitor, has anti-proliferative and anti-angiogenic activities and is therapeutically effective against renal cell carcinoma (RCC). Recently, we have evaluated the tumor responses to sorafenib treatment in a RCC xenograft using [Methyl-³H(N)]-3′-fluoro-3′-deoxythythymidine ([³H]FLT). Contrary to our expectation, the FLT level in the tumor significantly increased after the treatment. In this study, to clarify the reason for the elevated FLT level, dynamic 3′-[¹⁸F]fluoro-3′-deoxythymidine ([¹⁸F]FLT) positron emission tomography (PET) and kinetic studies were performed in mice bearing a RCC xenograft (A498).

The A498 xenograft was established in nude mice, and the mice were assigned to the control (n = 5) and treatment (n = 5) groups. The mice in the treatment group were orally given sorafenib (20 mg/kg/day p.o.) once daily for 3 days. Twenty-four hours after the treatment, dynamic [¹⁸F]FLT PET was performed by small-animal PET. Three-dimensional regions of interest (ROIs) were manually defined for the tumors. A three-compartment model fitting was carried out to estimate four rate constants using the time activity curve (TAC) in the tumor and the blood clearance rate of [¹⁸F]FLT.

Results

The dynamic pattern of [¹⁸F]FLT levels in the tumor significantly changed after the treatment. The rate constant of [¹⁸F]FLT phosphorylation (k₃) was significantly higher in the treatment group (0.111 ± 0.027 [1/min]) than in the control group (0.082 ± 0.009 [1/min]). No significant changes were observed in the distribution volume, the ratio of [¹⁸F]FLT forward transport (K₁) to reverse transport (k₂), between the two groups (0.556 ± 0.073 and 0.641 ± 0.052 [mL/g] in the control group).

Conclusions

Our dynamic PET studies indicated that the increase in FLT level may be caused by the phosphorylation of FLT in the tumor after the sorafenib treatment in the mice bearing a RCC xenograft. Dynamic PET studies with kinetic modeling could provide improved understanding of the biochemical processes involved in tumor responses to therapy.

Irbesartan attenuates atherosclerosis in Watanabe heritable hyperlipidemic rabbits: noninvasive imaging of inflammation by 18F-fluorodeoxyglucose positron emission tomography

The purpose of this study was to assess the usefulness of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) in evaluating the antiatherogenic effects of irbesartan, an angiotensin II type 1 receptor blocker. Watanabe heritable hyperlipidemic rabbits were divided into the irbesartan-treated group (75 mg/kg/d; n  =  14) and the control group (n  =  14). After a 9-month treatment, rabbits underwent 18F-FDG PET. Using the aortic lesions, autoradiography and histologic examinations were performed. PET imaging clearly visualized the thoracic lesions of control rabbits and showed a significant decrease in the 18F-FDG uptake level of irbesartan-treated rabbits (78.8% of controls; p < .05). Irbesartan treatment significantly reduced the plaque size (43.1% of controls) and intraplaque macrophage infiltration level (48.1% of controls). The 18F-FDG uptake level in plaques positively correlated with the plaque size (r  =  .65, p < .05) and macrophage infiltration level (r  =  .57, p < .05). Noninvasive imaging by 18F-FDG PET is useful for evaluating the therapeutic effects of irbesartan and reflects inflammation, a key factor involved in the therapeutic effects.