A simplified protocol for the automated production of 2-[18 F]fluoro-3-[2-((S)-3-pyrrolinyl)methoxy]pyridine ([18 F]nifene) on an IBA Synthera® module

The α4β2 nicotinic acetylcholine receptor (nAChR) ligand 2-[18 F]fluoro-3-[2-((S)-3-pyrrolinyl)methoxy]pyridine ([18 F]nifene) has been synthesized in 10% decay-corrected radiochemical yield using the IBA Synthera® platform (IBA Cyclotron Solutions, Louvain-la-Neuve, Belgium) with an integrated fluidic processor (IFP). Boc-nitronifene served as the precursor, and 20% trifluoroacetic acid (TFA) was used to deprotect the Boc-group after radiolabeling. By omitting the solvent extraction step after radiolabeling, the process was simplified to a single step with no manual intervention. [18 F]Nifene was obtained in decay-corrected radiochemical yields of 10 ± 2% (n = 20) and radiochemical purity >99%. Typical specific radioactivities of 2700-4865 mCi/μmole (100-180 GBq/μmol) were measured at the end of synthesis; total synthesis times were about 1 h 40 min.

Evaluation of an Image-Derived Input Function for Kinetic Modeling of Nicotinic Acetylcholine Receptor-Binding PET Ligands in Mice

Positron emission tomography (PET) radioligands that bind with high-affinity to α4β2-type nicotinic receptors (α4β2Rs) allow for in vivo investigations of the mechanisms underlying nicotine addiction and smoking cessation. Here, we investigate the use of an image-derived arterial input function and the cerebellum for kinetic analysis of radioligand binding in mice. Two radioligands were explored: 2-[18F]FA85380 (2-FA), displaying similar pKa and binding affinity to the smoking cessation drug varenicline (Chantix), and [18F]Nifene, displaying similar pKa and binding affinity to nicotine. Time-activity curves of the left ventricle of the heart displayed similar distribution across wild type mice, mice lacking the β2-subunit for ligand binding, and acute nicotine-treated mice, whereas reference tissue binding displayed high variation between groups. Binding potential estimated from a two-tissue compartment model fit of the data with the image-derived input function were higher than estimates from reference tissue-based estimations. Rate constants of radioligand dissociation were very slow for 2-FA and very fast for Nifene. We conclude that using an image-derived input function for kinetic modeling of nicotinic PET ligands provides suitable results compared to reference tissue-based methods and that the chemical properties of 2-FA and Nifene are suitable to study receptor response to nicotine addiction and smoking cessation therapies.

Trapping of Nicotinic Acetylcholine Receptor Ligands Assayed by In Vitro Cellular Studies and In Vivo PET Imaging

A question relevant to nicotine addiction is how nicotine and other nicotinic receptor membrane-permeant ligands, such as the anti-smoking drug varenicline (Chantix), distribute in brain. Ligands, like varenicline, with high pKa and high affinity for α4β2-type nicotinic receptors (α4β2Rs) are trapped in intracellular acidic vesicles containing α4β2Rs in vitro Nicotine, with lower pKa and α4β2R affinity, is not trapped. Here, we extend our results by imaging nicotinic PET ligands in vivo in male and female mouse brain and identifying the trapping brain organelle in vitro as Golgi satellites (GSats). Two PET 18F-labeled imaging ligands were chosen: [18F]2-FA85380 (2-FA) with varenicline-like pKa and affinity and [18F]Nifene with nicotine-like pKa and affinity. [18F]2-FA PET-imaging kinetics were very slow consistent with 2-FA trapping in α4β2R-containing GSats. In contrast, [18F]Nifene kinetics were rapid, consistent with its binding to α4β2Rs but no trapping. Specific [18F]2-FA and [18F]Nifene signals were eliminated in β2 subunit knock-out (KO) mice or by acute nicotine (AN) injections demonstrating binding to sites on β2-containing receptors. Chloroquine (CQ), which dissipates GSat pH gradients, reduced [18F]2-FA distributions while having little effect on [18F]Nifene distributions in vivo consistent with only [18F]2-FA trapping in GSats. These results are further supported by in vitro findings where dissipation of GSat pH gradients blocks 2-FA trapping in GSats without affecting Nifene. By combining in vitro and in vivo imaging, we mapped both the brain-wide and subcellular distributions of weak-base nicotinic receptor ligands. We conclude that ligands, such as varenicline, are trapped in neurons in α4β2R-containing GSats, which results in very slow release long after nicotine is gone after smoking.SIGNIFICANCE STATEMENT Mechanisms of nicotine addiction remain poorly understood. An earlier study using in vitro methods found that the anti-smoking nicotinic ligand, varenicline (Chantix) was trapped in α4β2R-containing acidic vesicles. Using a fluorescent-labeled high-affinity nicotinic ligand, this study provided evidence that these intracellular acidic vesicles were α4β2R-containing Golgi satellites (GSats). In vivo PET imaging with F-18-labeled nicotinic ligands provided additional evidence that differences in PET ligand trapping in acidic vesicles were the cause of differences in PET ligand kinetics and subcellular distributions. These findings combining in vitro and in vivo imaging revealed new mechanistic insights into the kinetics of weak base PET imaging ligands and the subcellular mechanisms underlying nicotine addiction.

Modelling cyclotron-based production of radioisotopes via TOPAS

Objective. In this work, the irradiation of natural titanium foils in the beam-stop of a compact medical cyclotron, an IBA CYCLONE 18/9, is simulated to assess the efficacy of using a beam-stop as a target holder, and using two different target geometries, in the production of vanadium-48, a positron-emitting radioisotope with potential utility as a cancer imaging agent in positron emission tomography.Approach. TOPAS, the TOol for PArticle Simulation, a Geant4-based Monte Carlo program, was used to model the cyclotron beam parameters, choose an appropriate physics list, and simulate the irradiation of targets made from foils of 12 or 12.5μm thickness. These simulation yields were compared to theoretical yields calculated using cross section data from the literature, as well as assayed yields from experimental irradiations.Main results.We found that most physics lists in TOPAS overestimate the cross section in the desired energy range (16-20 MeV) by at least 136%, with the exception of those using the Bertini Cascade Model. Compared to assayed yields, TOPAS provided a minimum of 0.4% error for cup-shaped targets and at least a 12% overestimation for sphere-shaped targets.Significance.These simulations provide a tool to help explain irregularities in radioisotope production yield and motivate modifications to increase target yield.

The optimal 18F-fluoromisonidazole PET threshold to define tumor hypoxia in preclinical squamous cell carcinomas using pO2 electron paramagnetic resonance imaging as reference truth

PURPOSE

To identify the optimal threshold in 18F-fluoromisonidazole (FMISO) PET images to accurately locate tumor hypoxia by using electron paramagnetic resonance imaging (pO2 EPRI) as ground truth for hypoxia, defined by pO2 [Formula: see text] 10 mmHg.

METHODS

Tumor hypoxia images in mouse models of SCCVII squamous cell carcinoma (n = 16) were acquired in a hybrid PET/EPRI imaging system 2 h post-injection of FMISO. T2-weighted MRI was used to delineate tumor and muscle tissue. Dynamic contrast enhanced (DCE) MRI parametric images of Ktrans and ve were generated to model tumor vascular properties. Images from PET/EPR/MRI were co-registered and resampled to isotropic 0.5 mm voxel resolution for analysis. PET images were converted to standardized uptake value (SUV) and tumor-to-muscle ratio (TMR) units. FMISO uptake thresholds were evaluated using receiver operating characteristic (ROC) curve analysis to find the optimal FMISO threshold and unit with maximum overall hypoxia similarity (OHS) with pO2 EPRI, where OHS = 1 shows perfect overlap and OHS = 0 shows no overlap. The means of dice similarity coefficient, normalized Hausdorff distance, and accuracy were used to define the OHS. Monotonic relationships between EPRI/PET/DCE-MRI were evaluated with the Spearman correlation coefficient ([Formula: see text]) to quantify association of vasculature on hypoxia imaged with both FMISO PET and pO2 EPRI.

RESULTS

FMISO PET thresholds to define hypoxia with maximum OHS (both OHS = 0.728 [Formula: see text] 0.2) were SUV [Formula: see text] 1.4 [Formula: see text] SUVmean and SUV [Formula: see text] 0.6 [Formula: see text] SUVmax. Weak-to-moderate correlations (|[Formula: see text]|< 0.70) were observed between PET/EPRI hypoxia images with vascular permeability (Ktrans) or fractional extracellular-extravascular space (ve) from DCE-MRI.

CONCLUSION

This is the first in vivo comparison of FMISO uptake with pO2 EPRI to identify the optimal FMISO threshold to define tumor hypoxia, which may successfully direct hypoxic tumor boosts in patients, thereby enhancing tumor control.

Improving Tumor Hypoxia Location in 18F-Misonidazole PET with Dynamic Contrast-enhanced MRI Using Quantitative Electron Paramagnetic Resonance Partial Oxygen Pressure Images

Purpose

To enhance the spatial accuracy of fluorine 18 (18F) misonidazole (MISO) PET imaging of hypoxia by using dynamic contrast-enhanced (DCE) MR images as a basis for modifying PET images and by using electron paramagnetic resonance (EPR) partial oxygen pressure (pO2) as the reference standard.

Materials and Methods

Mice (n = 10) with leg-borne MCa4 mammary carcinomas underwent EPR imaging, T2-weighted and DCE MRI, and 18F-MISO PET/CT. Images were registered to the same space for analysis. The thresholds of hypoxia for PET and EPR images were tumor-to-muscle ratios greater than or equal to 2.2 mm Hg and less than or equal to 14 mm Hg, respectively. The Dice similarity coefficient (DSC) and Hausdorff distance (d H ) were used to quantify the three-dimensional overlap of hypoxia between pO2 EPR and 18F-MISO PET images. A training subset (n = 6) was used to calculate optimal DCE MRI weighting coefficients to relate EPR to the PET signal; the group average weights were then applied to all tumors (from six training mice and four test mice). The DSC and d H were calculated before and after DCE MRI-corrected PET images were obtained to quantify the improvement in overlap with EPR pO2 images for measuring tumor hypoxia.

Results

The means and standard deviations of the DSC and d H between hypoxic regions in original PET and EPR images were 0.35 mm ± 0.23 and 5.70 mm ± 1.7, respectively, for images of all 10 mice. After implementing a preliminary DCE MRI correction to PET data, the DSC increased to 0.86 mm ± 0.18 and the d H decreased to 2.29 mm ± 0.70, showing significant improvement (P < .001) for images of all 10 mice. Specifically, for images of the four independent test mice, the DSC improved with correction from 0.19 ± 0.28 to 0.80 ± 0.29 (P = .02), and the d H improved from 6.40 mm ± 2.5 to 1.95 mm ± 0.63 (P = .01).

Conclusion

Using EPR information as a reference standard, DCE MRI information can be used to correct 18F-MISO PET information to more accurately reflect areas of hypoxia.Keywords: Animal Studies, Molecular Imaging, Molecular Imaging-Cancer, PET/CT, MR-Dynamic Contrast Enhanced, MR-Imaging, PET/MR, Breast, Oncology, Tumor Mircoenvironment, Electron Paramagnetic ResonanceSupplemental material is available for this article.© RSNA, 2021.

Abstract 1648: Multimodal imaging of tumor hypoxia with 18F-misonidazole PET, EPR, and MRI

Introduction: In tumor mouse models, electron paramagnetic resonance (EPR) imaging has been used to quantify pO2 in-vivo for oxygen-guided radiation therapy. Irradiating the hypoxic tumor sub-regions with a boost of radiation significantly increased survival probability when compared to the boosted radiation of normoxic tumor sub-regions. These results indicate 1) the importance of accurate oxygen imaging in-vivo and 2) an advantage to dose-painting hypoxic tumor sub-regions to improve radiation therapy outcomes of hypoxic tumor treatment. The purpose of this study is to evaluate the accuracy of hypoxia imaging using 18F-misonidazole (FMISO) with PET imaging while using EPR imaging as the reference standard for true hypoxia. We include T2-weighted MRI to define tumor anatomy and dynamic contrast enhanced (DCE)-MRI imaging to model vasculature properties to make FMISO PET more accurate in its measurement of hypoxia.

Methods: We used six SCC7 tumor mouse models in C3H mice, grown in the leg in the range of 200-500 mm3. Under minimal anesthesia, each mouse leg was set in a soft vinylpolysiloxane cast with embedded fiducials for registered images. A custom-built PET insert was inserted into a 720 MHz EPR imager for near-simultaneous imaging with PET and EPR, acquired two hours post-injection of FMISO to allow the radiotracer to bind to hypoxic tumor cells. Then, T2-weighted and gadodiamide DCE-MRI images were acquired and Ktrans and ve parameters were fitted to model tumor vasculature properties using the Tofts model. Data from all modalities were registered using fiducials, and resampled to isotropic (0.5 mm)3 voxels. The thresholds for hypoxia were defined as tumor to muscle ratio (TMR) ≥ 2 and pO2 ≤ 10 torr for PET and EPR, respectively. To correct the PET image using DCE-MRI parameters, we first modeled FMISO retention as a logistic function of pO2 to map the EPR image to PET TMR image, so that its sigmoidal point of inflection was at the threshold of retention. Then we estimated optimal weighting coefficients of DCE-MRI parameters to add or subtract voxel by voxel to the PET data so that its definition of hypoxia is more similar to the EPR image's hypoxia definition. The quality of overlap between hypoxic tumor regions as defined by PET and EPR was assessed using the Dice Similarity Coefficient (DSC) and the Hausdorff Distance (HD), before and after applying a correction to the PET data.

Results: The DSC between hypoxic regions as defined by PET and EPR, before and after applying a correction to PET data, was 0.53 ± 0.2 and 0.80 ± 0.2, respectively. The HD was respectively 3.8 ± 0.5 and 2.1 ± 0.5 mm.

Conclusion: These results indicate that there is poor agreement between FMISO PET hypoxia measurements when compared to hypoxia as defined by EPR pO2 images. Applying our correction method significantly improved the overlap between PET and EPR hypoxic tumor regions.

Citation Format: Inna Gertsenshteyn, Boris Epel, Lara Leoni, Xiaobing Fan, Richard Friefelder, Eugene Barth, Heejong Kim, Marta Zamora, Erica Markiewicz, Darwin Bodero, Mohammed Bhuiyan, Anna Kucharski, Hsiu-Ming Tsai, Mellissa Grana, Subramanian V. Sundramoorthy, Gregory S. Karczmar, Chien-Min Kao, Chin-Tu Chen, Howard Halpern. Multimodal imaging of tumor hypoxia with 18F-misonidazole PET, EPR, and MRI [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1648.

A33 Using serological and surveillance data to infer the introduction date and unobserved transmission dynamics of Zika virus in Fiji 2013–7

Zika virus (ZIKV) has been circulating in the South Pacific since 2007, and transmission in Fiji was first confirmed in 2015. To better understand the history and transmission dynamics of ZIKV in Fiji, we combined a transmission dynamic model with serological and surveillance data from Central Division, Fiji. A longitudinal population representative of seroepidemiological data were available from participants sampled in 2013, 2015, and 2017. In addition, ZIKV case reports were available from 2015 and 2016. Using a Bayesian approach, we fitted a transmission dynamic model with a seasonally varying transmission to these data. We also estimated the virus introduction date, given the effect this has on transmission dynamics as it interacts with the observed seasonal pattern of transmission. We found evidence that the virus was introduced in October 2013 (95% credible interval: April 2013–April 2014) and that the strong seasonal transmission pattern meant the virus persisted for several years with multiple waves of infection in consecutive years. It is important to corroborate this evidence against other work done in the same area. A phylogenetic analysis was performed on 5 ZIKV strains obtained from Fiji in 2015 and 2016, which were aligned with 33 E gene sequences from the Pacific, Americas, and Africa. This analysis showed evidence of virus persistence over multiple years in Central Division, Fiji. The estimated most recent common ancestor of the group isolated from Central Division was November 2013 (95% credible interval: March 2013–July 2015). Our modeling estimate is consistent with these results despite the very different methods being used. The availability of detailed case and serology data in an island outbreak setting, combined with mathematical models, presented a unique opportunity to gain crucial insights into these infections. Our analysis provides evidence that seasonal variation in transmission, combined with other co-circulating flaviviruses, means the timing of ZIKV introduction can have a major impact on outbreak transmission dynamics.

Bistacrines as potential antitrypanosomal agents

Human African Trypanosomiasis (HAT) is caused by two subspecies of the genus Trypanosoma, namely Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense. The disease is fatal if left untreated and therapy is limited due to only five non-adequate drugs currently available. In preliminary studies, dimeric tacrine derivatives were found to inhibit parasite growth with IC₅₀-values in the nanomolar concentration range. This prompted the synthesis of a small, but smart library of monomeric and dimeric tacrine-type compounds and their evaluation of antiprotozoal activity. Rhodesain, a lysosomal cathepsin-L like cysteine protease of T. brucei rhodesiense is essential for parasite survival and likely target of the tacrine derivatives. In addition, the inhibition of trypanothione reductase by bistacrines was found. This flavoprotein oxidoreductase is the main defense against oxidative stress in the thiol redox system unique for protozoa.

Automated Radiochemical Synthesis of [18F]3F4AP: A Novel PET Tracer for Imaging Demyelinating Diseases

3-[¹⁸F]fluoro-4-aminopyridine, [¹⁸F]3F4AP, is a radiofluorinated analog of the FDA-approved drug for multiple sclerosis 4-aminopyridine (4AP). This compound is currently under investigation as a PET tracer for demyelination. We recently described a novel chemical reaction to produce metafluorinated pyridines consisting of direct fluorination of a pyridine N-oxide and the utilization of this reaction for the radiochemical synthesis of [¹⁸F]3F4AP. In this article, we demonstrate how to produce this tracer using an automated synthesizer and an in-house made flow hydrogenation reactor. We also show the standard quality control procedures performed before releasing the radiotracer for preclinical animal imaging studies. This semi-automated procedure may serve as the basis for future production of [¹⁸F]3F4AP for clinical studies.

Bistacrine derivatives as new potent antimalarials

Linking two tacrine molecules results in a tremendous increase of activity against Plasmodia in comparison to the monomer. This finding prompted the synthesis of a library of monomeric and dimeric tacrine derivatives in order to derive structure-activity relationships. The most active compounds towards chloroquine sensitive Plasmodium strain 3D7 and chloroquine resistant strain Dd2 show IC50 values in the nanomolar range of concentration, low cytotoxicity and target the cysteine protease falcipain-2, which is essential for parasite growth.

[Limited radical approach in differentiated thyroid gland cancers. A prospective study of 107 patients]

From 1979 until 1987 a prospective study about limited radical therapy of 107 patients with differentiated cancer of the thyroid was performed. Nearly all of the tumors were occult papillary or encapsulated papillary and follicular carcinomas. The thyroid was not completely resected. Postoperative therapy consisted in TSH-suppression. After a follow-up of 7.5 (5-12) years one patient had died because of the tumor disease. Four patients had to be reoperated for lymph node metastases and then stayed free of disease as all other patients.

[Lymphangiosarcoma of the leg following radiotherapy for cervical carcinoma]

A case of lymphangiosarcoma of lower extremity was observed in a female aged 68 years who had had radiotherapy for cervical carcinoma. The late therapeutic result was bad, and this indicates the necessity of radical management, that is amputation in hip joint already in an early stage of the disease, although this decision is extremely difficult for the physician.

History of frontal lobotomy in the United States, 1935-1955

The history of frontal lobotomy is a dramatic chapter in the development of medical treatment. Based on experimentally induced lesions in primates, lobotomies were introduced as procedures designed to modify the affect and behavior of hospitalized mental patients. Within 10 years, variations in surgical techniques were numerous, and the treatment was an accepted alternative in many hospitals in the United States. Patients on whom the operation was performed had a variety of diagnoses, including schizophrenia, obsessive-compulsive disorder, and affective illness. With the introduction of neuroleptic medication and behavior and milieu therapies, this surgical treatment for the emotional component of psychiatric illness fell into disuse. As its legacy to medicine, frontal lobotomy provided neuroanatomical information from which contemporary biological theories of behavior developed.

Psychologic stress in myocardial infarction

During the acute phase of myocardial infarction, patients may experience anxiety, depression, denial and decompensation. Their ability to master the painful aspects associated with the stress of this severe illness and to convert defenses to beneficial coping directions depends on their character traits and effective psychiatric intervention. Sequelae to myocardial infarction include invalidism and prolonged disruption of the patient's family life and development.

The so-called "inappropriate" psychiatric consultation request on a medical or surgical ward

Seven cases of psychiatric consultations on medical and surgical wards are reviewed to show how intrapsychic conflicts in the staff may make the consultation request appear inappropriate. On deeper examination, such requests may signify staff dysfunction caused by arousal of conflictual feelings about the behavior of illness of the patient. Mutilated, mute patients appear to arouse fear of agression in their caregivers, who in turn reject such patients, see them as alien and violent, and become illogical in their management. Patients who publicly display sexual behaviors appear to arouse shame over exhibitionism, voyeurism, and masturbation; their caregivers become too passive to effect common-sense measures appropriate to the situation. Very sick and dying patients and ungrateful, demanding patients can arouse anger and despair. Their caregivers may become depressed about failure, feeling helpless and out of control; using projection, they can see such patients as evil or suicidal, and may eventually turn against themselves. The psychiatric consultant, recognizing the conflicts that make the requests seem inappropriate, seeks to substitute higher-level cognitive operations and coping behaviors in the staff (distancing, rationalization, intellectualization, undoing, and altruism) for distortion projection, over-identification, reaction formation, and turning against the self.