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 α4ß2-type nicotinic receptors (α4ß2Rs) are trapped in intracellular acidic vesicles containing α4ß2Rs in vitro Nicotine, with lower pKa and α4ß2R 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 α4ß2R-containing GSats. In contrast, [18F]Nifene kinetics were rapid, consistent with its binding to α4ß2Rs but no trapping. Specific [18F]2-FA and [18F]Nifene signals were eliminated in ß2 subunit knock-out (KO) mice or by acute nicotine (AN) injections demonstrating binding to sites on ß2-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 α4ß2R-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 α4ß2R-containing acidic vesicles. Using a fluorescent-labeled high-affinity nicotinic ligand, this study provided evidence that these intracellular acidic vesicles were α4ß2R-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.

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 α4ß2 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.

Efficient Synthesis and HPLC-Based Characterization for Developing Vanadium-48-Labeled Vanadyl Acetylacetonate as a Novel Cancer Radiotracer for PET Imaging.

Bis(acetylacetonato)oxidovanadium(IV) [(VO(acac)2], generally known as vanadyl acetylacetonate, has been shown to be preferentially sequestered in malignant tissue. Vanadium-48 (48V) generated with a compact medical cyclotron has been used to label VO(acac)2 as a potential radiotracer in positron emission tomography (PET) imaging for the detection of cancer, but requires lengthy synthesis. Current literature protocols for the characterization of VO(acac)2 require macroscale quantities of reactants and solvents to identify products by color and to enable crystallization that are not readily adaptable to the needs of radiotracer synthesis. We present an improved method to produce vanadium-48-labeled VO(acac)2, [48V]VO(acac)2, and characterize it using high-performance liquid chromatography (HPLC) with radiation detection in combination with UV detection. The approach is suitable for radiotracer-level quantities of material. These methods are readily applicable for production of [48V]VO(acac)2. Preliminary results of preclinical, small-animal PET studies are presented.

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 α4ß2-type nicotinic receptors (α4ß2Rs) 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 ß2-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.

Accelerator-Based Production of Scandium Radioisotopes for Applications in Prostate Cancer: Toward Building a Pipeline for Rapid Development of Novel Theranostics.

In the field of nuclear medicine, the ß+ -emitting 43Sc and ß- -emitting 47Sc are promising candidates in cancer diagnosis and targeted radionuclide therapy (TRT) due to their favorable decay schema and shared pharmacokinetics as a true theranostic pair. Additionally, scandium is a group-3 transition metal (like 177Lu) and exhibits affinity for DOTA-based chelators, which have been studied in depth, making the barrier to implementation lower for 43/47Sc than for other proposed true theranostics. Before 43/47Sc can see widespread pre-clinical evaluation, however, an accessible production methodology must be established and each isotope's radiolabeling and animal imaging capabilities studied with a widely utilized tracer. As such, a simple means of converting an 18 MeV biomedical cyclotron to support solid targets and produce 43Sc via the 42Ca(d,n)43Sc reaction has been devised, exhibiting reasonable yields. The NatTi(γ,p)47Sc reaction is also investigated along with the successful implementation of chemical separation and purification methods for 43/47Sc. The conjugation of 43/47Sc with PSMA-617 at specific activities of up to 8.94 MBq/nmol and the subsequent imaging of LNCaP-ENZaR tumor xenografts in mouse models with both 43/47Sc-PSMA-617 are also presented.

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.

Assessment of Brain Glucose Metabolism Following Cardiac Arrest by [18F]FDG Positron Emission Tomography.

BACKGROUND: Cardiac arrest (CA) patients who survived by cardiopulmonary resuscitation (CPR) can present different levels of neurological deficits ranging from minor cognitive impairments to persistent vegetative state and brain death. The pathophysiology of the resulting brain injury is poorly understood, and whether changes in post-CA brain metabolism contribute to the injury are unknown. Here we utilized [18F]fluorodeoxyglucose (FDG)-Positron emission tomography (PET) to study in vivo cerebral glucose metabolism 72 h following CA in a murine CA model. METHODS: Anesthetized and ventilated adult C57BL/6 mice underwent 12-min KCl-induced CA followed by CPR. Seventy-two hours following CA, surviving mice were intraperitoneally injected with [18F]FDG (~ 186 µCi/200 µL) and imaged on Molecubes preclinical micro-PET/computed tomography (CT) imaging systems after a 30-min awake uptake period. Brain [18F]FDG uptake was determined by the VivoQuant software on fused PET/CT images with the 3D brain atlas. Upon completion of Positron emission tomography (PET) imaging, remaining [18F]FDG radioactivity in the brain, heart, and liver was determined using a gamma counter. RESULTS: Global increases in brain [18F]FDG uptake in post-CA mice were observed compared to shams and controls. The median standardized uptake value of [18F]FDG for CA animals was 1.79 versus sham 1.25 (p < 0.05) and control animals 0.78 (p < 0.01). This increased uptake was consistent throughout the 60-min imaging period and across all brain regions reaching statistical significance in the midbrain, pons, and medulla. Biodistribution analyses of various key organs yielded similar observations that the median [18F]FDG uptake for brain was 7.04%ID/g tissue for CA mice versus 5.537%ID/g tissue for sham animals, p < 0.05). CONCLUSIONS: This study has successfully applied [18F]FDG-PET/CT to measure changes in brain metabolism in a murine model of asystolic CA. Our results demonstrate increased [18F]FDG uptake in the brain 72 h following CA, suggesting increased metabolic demand in the case of severe neurological injury. Further study is warranted to determine the etiology of these changes.

The Relative Importance of Clinical and Socio-demographic Variables in Prognostic Prediction in Non-Small Cell Lung Cancer: A Variable Importance Approach.

BACKGROUND: Prognostic modeling in health care has been predominantly statistical, despite a rapid growth of literature on machine-learning approaches in biological data analysis. We aim to assess the relative importance of variables in predicting overall survival among patients with non-small cell lung cancer using a Variable Importance (VIMP) approach in a machine-learning Random Survival Forest (RSF) model for posttreatment planning and follow-up. METHODS: A total of 935 non-small cell lung cancer patients were randomly and equally divided into 2 training and testing cohorts in an RFS model. The prognostic variables included age, sex, race, the TNM Classification of Malignant Tumors (TNM) stage, smoking history, Eastern Cooperative Oncology Group performance status, histologic type, treatment category, maximum standard uptake value of whole-body tumor (SUVmaxWB), whole-body metabolic tumor volume (MTVwb), and Charlson Comorbidity Index. The VIMP was calculated using a permutation method in the RSF model. We further compared the VIMP of the RSF model to that of the standard Cox survival model. We examined the order of VIMP with the differential functional forms of the variables. RESULTS: In both the RSF and the standard Cox models, the most important variables are treatment category, TNM stage, and MTVwb. The order of VIMP is more robust in RSF model than in Cox model regarding the differential functional forms of the variables. CONCLUSIONS: The RSF VIMP approach can be applied alongside with the Cox model to further advance the understanding of the roles of prognostic factors, and improve prognostic precision and care efficiency.

In†Vivo Imaging of the Tumor-Associated Enzyme NCEH1 with a Covalent PET Probe.

Herein, we report the development of an 18 F-labeled, activity-based small-molecule probe targeting the cancer-associated serine hydrolase NCEH1. We undertook a focused medicinal chemistry campaign to simultaneously preserve potent and specific NCEH1 labeling in live cells and animals, while permitting facile 18 F radionuclide incorporation required for PET imaging. The resulting molecule, [18 F]JW199, labels active NCEH1 in live cells at nanomolar concentrations and greater than 1000-fold selectivity relative to other serine hydrolases. [18 F]JW199 displays rapid, NCEH1-dependent accumulation in mouse tissues. Finally, we demonstrate that [18 F]JW199 labels aggressive cancer tumor cells in vivo, which uncovered localized NCEH1 activity at the leading edge of triple-negative breast cancer tumors, suggesting roles for NCEH1 in tumor aggressiveness and metastasis.

A novel mouse model of sporadic colon cancer induced by combination of conditional Apc genes and chemical carcinogen in the absence of Cre recombinase.

Although valuable insights into colon cancer biology have been garnered from human colon cancer cell lines and primary colonic tissues, and animal studies using human colon cancer xenografts, immunocompetent mouse models of spontaneous or chemically induced colon cancer better phenocopy human disease. As most sporadic human colon tumors present adenomatous polyposis coli (APC) gene mutations, considerable effort has gone into developing mice that express mutant Apc alleles that mimic human colon cancer pathogenesis. A serious limitation of many of these Apc-mutant murine models, however, is that these mice develop numerous tumors in the small intestine but few, if any, in the colon. In this work, we examined three spontaneous mouse models of colon tumorigenesis based upon the widely used multiple intestinal neoplasia (Min) mouse: mice with either constitutive or conditional Apc mutations alone or in combination with caudal-related homeobox transcription factor CDX2P-Cre transgene - either with or without exposure to the potent colon carcinogen azoxymethane. Using the CDX2 promoter to drive Cre recombinase transgene expression effectively inactivated Apc in colonocytes, creating a model with earlier tumor onset and increased tumor incidence/burden, but without the Min mouse model's small intestine tumorigenesis and susceptibility to intestinal perforation/ulceration/hemorrhage. Most significantly, azoxymethane-treated mice with conditional Apc expression, but absent the Cre recombinase gene, demonstrated nearly 50% tumor incidence with two or more large colon tumors per mouse of human-like histology, but no small intestine tumors - unlike the azoxymethane-resistant C57BL/6J-background Min mouse model. As such this model provides a robust platform for chemoprevention studies.

Lectin-functionalized mesoporous silica nanoparticles for endoscopic detection of premalignant colonic lesions.

Colorectal cancer (CRC) is one of the leading causes of cancer-deaths worldwide. Methods for the early in situ detection of colorectal adenomatous polyps and their precursors - prior to their malignancy transformation into CRC - are urgently needed. Unfortunately at present, the primary diagnostic method, colonoscopy, can only detect polyps and carcinomas by shape/morphology; with sessile polyps more likely to go unnoticed than polypoid lesions. Here we describe our development of polyp-targeting, fluorescently-labeled mesoporous silica nanoparticles (MSNs) that serve as targeted endoscopic contrast agents for the early detection of colorectal polyps and cancer. In vitro cell studies, ex vivo histopathological analysis, and in vivo colonoscopy and endoscopy of murine colorectal cancer models, demonstrate significant binding specificity of our nanoconstructs to pathological lesions via targeting aberrant α-L-fucose expression. Our findings strongly suggest that lectin-functionalized fluorescent MSNs could serve as a promising endoscopic contrast agent for in situ diagnostic imaging of premalignant colonic lesions.

PGC1α-mediated mitofusin-2 deficiency in female rats and humans with pulmonary arterial hypertension.

RATIONALE: Pulmonary arterial hypertension (PAH) is a lethal, female-predominant, vascular disease. Pathologic changes in PA smooth muscle cells (PASMC) include excessive proliferation, apoptosis-resistance, and mitochondrial fragmentation. Activation of dynamin-related protein increases mitotic fission and promotes this proliferation-apoptosis imbalance. The contribution of decreased fusion and reduced mitofusin-2 (MFN2) expression to PAH is unknown. OBJECTIVES: We hypothesize that decreased MFN2 expression promotes mitochondrial fragmentation, increases proliferation, and impairs apoptosis. The role of MFN2's transcriptional coactivator, peroxisome proliferator-activated receptor γ coactivator 1-α (PGC1α), was assessed. MFN2 therapy was tested in PAH PASMC and in models of PAH. METHODS: Fusion and fission mediators were measured in lungs and PASMC from patients with PAH and female rats with monocrotaline or chronic hypoxia+Sugen-5416 (CH+SU) PAH. The effects of adenoviral mitofusin-2 (Ad-MFN2) overexpression were measured in vitro and in vivo. MEASUREMENTS AND MAIN RESULTS: In normal PASMC, siMFN2 reduced expression of MFN2 and PGC1α; conversely, siPGC1α reduced PGC1α and MFN2 expression. Both interventions caused mitochondrial fragmentation. siMFN2 increased proliferation. In rodent and human PAH PASMC, MFN2 and PGC1α were decreased and mitochondria were fragmented. Ad-MFN2 increased fusion, reduced proliferation, and increased apoptosis in human PAH and CH+SU. In CH+SU, Ad-MFN2 improved walking distance (381 ± 35 vs. 245 ± 39 m; P < 0.05); decreased pulmonary vascular resistance (0.18 ± 0.02 vs. 0.38 ± 0.14 mm Hg/ml/min; P < 0.05); and decreased PA medial thickness (14.5 ± 0.8 vs. 19 ± 1.7%; P < 0.05). Lung vascularity was increased by MFN2. CONCLUSIONS: Decreased expression of MFN2 and PGC1α contribute to mitochondrial fragmentation and a proliferation-apoptosis imbalance in human and experimental PAH. Augmenting MFN2 has therapeutic benefit in human and experimental PAH.

Validation of the design of a high-sensitivity and high-resolution PET system for a preclinical PET/EPR hybrid scanner.

We report the development of a high-sensitivity and high-resolution PET subsystem for a next-generation preclinical PET/EPR hybrid scanner for investigating and improving hypoxia imaging with PET. The PET subsystem consists of 14 detector modules (DM) installed within a cylindrical supporting frame whose outer and inner diameters are 115mm and 60mm, respectively. Each DM contains eight detector units (DU) in a row and each DU is made of a 12×12 array of 1×1×10mm3 LYSO crystals (with a 1.05mm pitch) coupled to a 4×4 silicon photomultiplier (SiPM) array that has a 3.2mm pitch (Hamamatsu multi-pixel photon counter (MPPC) array 14161-3050HS-04). The PET subsystem has a 104mm axial field-of-view (AFOV) that is sufficient for full-body mouse imaging, therefore enabling temporal and spatial correlation studies of tumor hypoxia between PET and EPR. It employs 1mm-width crystals to support sub-millimeter image resolution that is desired for mouse imaging. Al-though a DM contains 1,152 LYSO crystals, by use of a newly devised signal readout method only six outputs are produced. Recently a partial prototype of this subsystem consisting of four DMs is built. In this paper, we present performance measurement results obtained for the developed DMs and initial imaging results obtained by the prototype. The developed DMs show uniformly superior performance in identifying the hit crystal and detector unit, in energy resolution, and in coincidence time resolution. The images obtained for a 22Na point source and a 18F-filled U-shaped tube source show an image resolution of about 1.1mm and 1.2mm FWHM in the transverse and axial directions respectively, and demonstrate successful imaging over the entire 104mm AFOV of the prototype. This estimated image resolution however includes the contribution by the source size.

Flexible peritoneal windows for quantitative fluorescence and bioluminescence preclinical imaging.

At present, there is considerable interest in the use of in vivo fluorescence and bioluminescence imaging to track the onset and progression of pathologic processes in preclinical models of human disease. Optical quantitation of such phenomena, however, is often problematic, frequently complicated by the overlying tissue's scattering and absorption of light, as well as the presence of endogenous cutaneous and subcutaneous fluorophores. To partially circumvent this information loss, we report here the development of flexible, surgically implanted, transparent windows that enhance quantitative in vivo fluorescence and bioluminescence imaging of optical reporters. These windows are metal and glass free and thus compatible with computed tomography, magnetic resonance imaging, positron emission tomography, and single-photon emission computed tomography; they also permit visualization of much larger areas with fewer impediments to animal locomotion and grooming than those previously described. To evaluate their utility in preclinical imaging, we surgically implanted these windows in the abdominal walls of female athymic nude mice and subsequently inoculated each animal with 1 × 10(4) to 1 × 10(6) bioluminescent human ovarian cancer cells (SKOV3ip.1-luc). Longitudinal imaging studies of fenestrated animals revealed up to 48-fold gains in imaging sensitivity relative to nonfenestrated animals, with relatively few complications, allowing wide-field in vivo visualization of nascent metastatic ovarian cancer colonization.

Nanoparticle-programmed self-destructive neural stem cells for glioblastoma targeting and therapy.

A 3-step glioblastoma-tropic delivery and therapy method using nanoparticle programmed self-destructive neural stem cells (NSCs) is demonstrated in vivo: 1) FDA-approved NSCs for clinical trials are loaded with pH-sensitive MSN-Dox; 2) the nanoparticle conjugates provide a delayed drug-releasing mechanism and allow for NSC migration towards a distant tumor site; 3) NSCs eventually undergo cell death and release impregnated MSN-Dox, which subsequently induces toxicity towards surrounding glioma cells.

Lung ¹8F-fluorodeoxyglucose positron emission tomography for diagnosis and monitoring of pulmonary arterial hypertension.

RATIONALE: Pulmonary arterial hypertension (PAH) is a proliferative arteriopathy associated with glucose transporter-1 (Glut1) up-regulation and a glycolytic shift in lung metabolism. Glycolytic metabolism can be detected with the positron emission tomography (PET) tracer (18)F-fluorodeoxyglucose (FDG). OBJECTIVES: The precise cell type in which glycolytic abnormalities occur in PAH is unknown. Moreover, whether FDG-PET is sufficiently sensitive to monitor PAH progression and detect therapeutic regression is untested. We hypothesized that increased lung FDG-PET reflects enhanced glycolysis in vascular cells and is reversible in response to effective therapies. METHODS: PAH was induced in Sprague-Dawley rats by monocrotaline or chronic hypoxia (10% oxygen) in combination with Sugen 5416. Monocrotaline rats were treated with oral dichloroacetate or daily imatinib injections. FDG-PET scans and pulmonary artery acceleration times were obtained weekly. The origin of the PET signal was assessed by laser capture microdissection of airway versus vascular tissue. Metabolism was measured in pulmonary artery smooth muscle cell (PASMC) cultures, using a Seahorse extracellular flux analyzer. MEASUREMENTS AND MAIN RESULTS: Lung FDG increases 1-2 weeks after monocrotaline (when PAH is mild) and is normalized by dichloroacetate and imatinib, which both also regress medial hypertrophy. Glut1 mRNA is up-regulated in both endothelium and PASMCs, but not airway cells or macrophages. PASMCs from monocrotaline rats are hyperproliferative and display normoxic activation of hypoxia-inducible factor-1α (HIF-1α), which underlies their glycolytic phenotype. CONCLUSIONS: HIF-1α-mediated Glut1 up-regulation in proliferating vascular cells in PAH accounts for increased lung FDG-PET uptake. FDG-PET is sensitive to mild PAH and can monitor therapeutic changes in the vasculature.

A Preclinical Positron Emission Tomography (PET) and Electron-Paramagnetic-Resonance-Imaging (EPRI) Hybrid System: PET Detector Module.

We report the design and experimental validation of a compact positron emission tomography (PET) detector module (DM) intended for building a preclinical PET and electron-paramagnetic-resonance-imaging hybrid system that supports sub-millimeter image resolution and high-sensitivity, whole-body animal imaging. The DM is eight detector units (DU) in a row. Each DU contains 12×12 lutetium-yttrium oxyorthosilicate (LYSO) crystals having a 1.05 mm pitch read by 4×4 silicon photomultipliers (SiPM) having a 3.2 mm pitch. A small-footprint, highly-multiplexing readout employing only passive electronics is devised to produce six outputs for the DM, including two outputs derived from SiPM cathodes for determining event time and active DU and four outputs derived from SiPM anodes for determining energy and active crystal. Presently, we have developed two DMs that are 1.28×10.24 cm2 in extent and approximately 1.8 cm in thickness, with their outputs sampled at 0.7 GS/s and analyzed offline. For both DMs, our results show successfully discriminated DUs and crystals. With no correction for SiPM nonlinearity, the average energy resolution for crystals in a DU ranges from 14% to 16%. While not needed for preclinical imaging, the DM may support 300-400 ps time-of-flight resolution.

X-ray Activated Nanoplatforms for Deep Tissue Photodynamic Therapy.

Photodynamic therapy (PDT), the use of light to excite photosensitive molecules whose electronic relaxation drives the production of highly cytotoxic reactive oxygen species (ROS), has proven an effective means of oncotherapy. However, its application has been severely constrained to superficial tissues and those readily accessed either endoscopically or laparoscopically, due to the intrinsic scattering and absorption of photons by intervening tissues. Recent advances in the design of nanoparticle-based X-ray scintillators and photosensitizers have enabled hybridization of these moieties into single nanocomposite particles. These nanoplatforms, when irradiated with diagnostic doses and energies of X-rays, produce large quantities of ROS and permit, for the first time, non-invasive deep tissue PDT of tumors with few of the therapeutic limitations or side effects of conventional PDT. In this review we examine the underlying principles and evolution of PDT: from its initial and still dominant use of light-activated, small molecule photosensitizers that passively accumulate in tumors, to its latest development of X-ray-activated, scintillator-photosensitizer hybrid nanoplatforms that actively target cancer biomarkers. Challenges and potential remedies for the clinical translation of these hybrid nanoplatforms and X-ray PDT are also presented.

Illuminating and Radiosensitizing Tumors with 2DG-Bound Gold-Based Nanomedicine for Targeted CT Imaging and Therapy.

Although radiotherapy is one of the most important curative treatments for cancer, its clinical application is associated with undesired therapeutic effects on normal or healthy tissues. The use of targeted agents that can simultaneously achieve therapeutic and imaging functions could constitute a potential solution. Herein, we developed 2-deoxy-d-glucose (2DG)-labeled poly(ethylene glycol) (PEG) gold nanodots (2DG-PEG-AuD) as a tumor-targeted computed tomography (CT) contrast agent and radiosensitizer. The key advantages of the design are its biocompatibility and targeted AuD with excellent sensitivity in tumor detection via avid glucose metabolism. As a consequence, CT imaging with enhanced sensitivity and remarkable radiotherapeutic efficacy could be attained. Our synthesized AuD displayed linear enhancement of CT contrast as a function of its concentration. In addition, 2DG-PEG-AuD successfully demonstrated significant augmentation of CT contrast in both in vitro cell studies and in vivo tumor-bearing mouse models. In tumor-bearing mice, 2DG-PEG-AuD showed excellent radiosensitizing functions after intravenous injection. Results from this work indicate that 2DG-PEG-AuD could greatly potentiate theranostic capabilities by providing high-resolution anatomical and functional images in a single CT scan and therapeutic capability.

Prognostic value of metabolic tumor burden on 18F-FDG PET in nonsurgical patients with non-small cell lung cancer.

PURPOSE: The objective of this study was to assess the prognostic value of metabolic tumor burden on 2-deoxy-2-[(18)F]fluoro-D-glucose ((18)F-FDG) positron emission tomography (PET)/CT measured with metabolic tumor volume (MTV) and total lesion glycolysis (TLG), independent of Union Internationale Contra la Cancrum (UICC)/American Joint Committee on Cancer (AJCC) tumor, node, and metastasis (TNM) stage, in comparison with that of standardized uptake value (SUV) in nonsurgical patients with non-small cell lung cancer (NSCLC). METHODS: This study retrospectively reviewed 169 consecutive nonsurgical patients (78 men, 91 women, median age of 68 years) with newly diagnosed NSCLC who had pretreatment (18)F-FDG PET/CT scans. The (18)F-FDG PET/CT scans were performed in accordance with National Cancer Institute guidelines. The MTV of whole-body tumor (MTV(WB)), of primary tumor (MTV(T)), of nodal metastases (MTV(N)), and of distant metastases (MTV(M)); the TLG of whole-body tumor (TLG(WB)), of primary tumor (TLG(T)), of nodal metastases (TLG(N)), and of distant metastases (TLG(M)); the SUV(max) of whole-body tumor (SUV(maxWB)), of primary tumor (SUV(maxT)), of nodal metastases (SUV(maxN)), and of distant metastases (SUV(maxM)) as well as the SUV(mean) of whole-body tumor (SUV(meanWB)), of primary tumor (SUV(meanT)), of nodal metastases (SUV(meanN)), and of distant metastases (SUV(meanM)) were measured with the PETedge tool on a MIMvista workstation with manual adjustment. The median follow-up among survivors was 35 months from the PET/CT (range 2-82 months). Statistical methods included Kaplan-Meier curves, Cox regression, and C-statistics. RESULTS: There were a total of 139 deaths during follow-up. Median overall survival (OS) was 10.9 months [95% confidence interval (CI) 9.0-13.2 months]. The MTV was statistically associated with OS. The hazard ratios (HR) for 1 unit increase of ln(MTV(WB)), √(MTV(T)), √(MTV(N)), and √(MTV(M)) before/after adjusting for stage were: 1.47/1.43 (p < 0.001/<0.001), 1.06/1.05 (p < 0.001/<0.001), 1.11/1.10 (p < 0.001/<0.001), and 1.04/1.03 (p = 0.007/0.043), respectively. TLG had statistically significant associations with OS with the HRs for 1 unit increase in ln(TLG(WB)), √(TLG(T)), √(TLG(N)), and √(TLG(M)) before/after adjusting for stage being 1.36/1.33 (p < 0.001/<0.001), 1.02/1.02 (p = 0.001/0.002), 1.05/1.04 (p < 0.001/<0.001), and 1.02/1.02 (p = 0.003/0.024), respectively. The ln(SUV(maxWB)) and √(SUV(maxN)) were statistically associated with OS with the corresponding HRs for a 1 unit increase before/after adjusting for stage being 1.46/1.43 (p = 0.013/0.024) and 1.22/1.16 (p = 0.002/0.040). The √(SUV(meanN)) was statistically associated with OS before and after adjusting for stage with HRs for a 1 unit increase of 1.32 (p < 0.001) and 1.24 (p = 0.015), respectively. The √(SUV(meanM)) and √(SUV(maxM)) were statistically associated with OS before adjusting for stage with HRs for a 1 unit increase of 1.26 (p = 0.017) and 1.18 (p = 0.007), respectively, but not after adjusting for stage (p = 0.127 and 0.056). There was no statistically significant association between OS and √(SUV(maxT)), ln(SUV(meanWB)), or √(SUV(meanT)). There was low interobserver variability among three radiologists with intraclass correlation coefficients (ICC) greater than 0.94 for SUV(maxWB), ln(MTV(WB)), and ln(TLG(WB)). Interobserver variability was higher for SUV(meanWB) with an ICC of 0.806. CONCLUSION: Baseline metabolic tumor burdens at the level of whole-body tumor, primary tumor, nodal metastasis, and distant metastasis as measured with MTV and TLG on FDG PET are prognostic measures independent of clinical stage with low inter-observer variability and may be used to further stratify nonsurgical patients with NSCLC. This study also suggests MTV and TLG are better prognostic measures than SUV(max) and SUV(mean). These results will need to be validated in larger cohorts in a prospective study.