Comparison between MRI-derived ADC maps and 18FLT-PET in pre-operative glioblastoma.

BACKGROUND AND PURPOSE: Among principal MRI sequences used for a better pre-therapeutic characterization of glioblastoma (GBM), DWI-derived ADC is expected to be a good parameter for the evaluation of cellularity, due to restricted water diffusivity. We aimed here to compare ADC maps to 18FLT-PET, a proliferation tracer, in GBM cases. MATERIALS AND METHODS: Patients underwent 18FLT-PET, followed by multiparametric magnetic resonance imaging (MRI) just prior to surgery. We analysed in this study twenty GBM confirmed patients. The 5th percentile (5p) of the ADC values were thresholded to define the ADCmin ROI, while the 95th percentile (95p) of the SUV FLT values were used to define the FLTmax ROI. The statistical and spatial correlations between these two groups of ROIs were analyzed. RESULTS: We did not observe any significant correlations between ADCmin and FLTmax cut-off values (R2=0.0285), neither between ADCmin and FLTmax ROIs (mean Dice=0.09±0.12). Mean ADC values in the FLTmax defined ROI were significantly higher than the values in the ADCmin ROI (P<0.001). Mean FLT values in the FLTmax ROI were significantly higher than the values in the ADCmin ROI (P<0.001). CONCLUSIONS: When comparing ADC maps to 18FLT uptake, we did not observe significant anatomical overlap nor correlation, between the regions of low ADC and high FLT disabling to clearly link ADC values to cellular proliferation. The exact significance of ADC maps in GBM has yet to be elaborated.

[18F]-FMISO PET study of hypoxia in gliomas before surgery: correlation with molecular markers of hypoxia and angiogenesis.

PURPOSE: Hypoxia in gliomas is associated with tumor resistance to radio- and chemotherapy. However, positron emission tomography (PET) imaging of hypoxia remains challenging, and the validation of biological markers is, therefore, of great importance. We investigated the relationship between uptake of the PET hypoxia tracer [18F]-FMISO and other markers of hypoxia and angiogenesis and with patient survival. PATIENTS AND METHODS: In this prospective single center clinical study, 33 glioma patients (grade IV: n = 24, III: n = 3, and II: n = 6) underwent [18F]-FMISO PET and MRI including relative cerebral blood volume (rCBV) maps before surgery. Maximum standardized uptake values (SUVmax) and hypoxic volume were calculated, defining two groups of patients based on the presence or absence of [18F]-FMISO uptake. After surgery, molecular quantification of CAIX, VEGF, Ang2 (rt-qPCR), and HIF-1α (immunohistochemistry) were performed on tumor specimens. RESULTS: [18F]-FMISO PET uptake was closely linked to tumor grade, with high uptake in glioblastomas (GB, grade IV). Expression of biomarkers of hypoxia (CAIX, HIF-1α), and angiogenesis markers (VEGF, Ang2, rCBV) were significantly higher in the [18F]-FMISO uptake group. We found correlations between the degree of hypoxia (hypoxic volume and SUVmax) and expression of HIF-1α, CAIX, VEGF, Ang2, and rCBV (p < 0.01). Patients without [18F]-FMISO uptake had a longer survival time than uptake positive patients (log-rank, p < 0.005). CONCLUSIONS: Tumor hypoxia as evaluated by [18F]-FMISO PET is associated with the expression of hypoxia markers on a molecular level and is related to angiogenesis. [18F]-FMISO uptake is a mark of an aggressive tumor, almost always a glioblastoma. Our results underline that [18F]-FMISO PET could be useful to guide glioma treatment, and in particular radiotherapy, since hypoxia is a well-known factor of resistance.

Subjective cognitive decline in cognitively normal elders from the community or from a memory clinic: Differential affective and imaging correlates.

INTRODUCTION: Subjective cognitive decline (SCD) could indicate preclinical Alzheimer's disease, but the existing literature is confounded by heterogeneous approaches to studying SCD. We assessed the differential cognitive, affective, and neuroimaging correlates of two aspects of SCD: reporting high cognitive difficulties on a self-rated questionnaire versus consulting at a memory clinic. METHODS: We compared 28 patients from a memory clinic with isolated SCD, 35 community-recruited elders with similarly high levels of self-reported cognitive difficulties, and 35 community-recruited controls with low self-reported cognitive difficulties. RESULTS: Increased anxiety and amyloid ß deposition were observed in both groups with high self-reported difficulties, whereas subclinical depression and (hippocampal) atrophy were specifically associated with medical help seeking. Cognitive tests showed no group differences. DISCUSSION: These results further validate the concept of SCD in both community- and clinic-based groups. Yet, recruitment methods influence associated biomarkers and affective symptomatology, highlighting the heterogeneous nature of SCD depending on study characteristics.

Cognitive and Brain Profiles Associated with Current Neuroimaging Biomarkers of Preclinical Alzheimer's Disease.

Neuroimaging biomarkers, namely hippocampal volume loss, temporoparietal hypometabolism, and neocortical ß-amyloid (Aß) deposition, are included in the recent research criteria for preclinical Alzheimer's disease (AD). However, how to use these biomarkers is still being debated, especially regarding their sequence. Our aim was to characterize the cognitive and brain profiles of elders classified as positive or negative for each biomarker to further our understanding of their use in the preclinical diagnosis of AD. Fifty-four cognitively normal individuals (age = 65.8 ± 8.3 years) underwent neuropsychological tests (structural MRI, FDG-PET, and Florbetapir-PET) and were dichotomized into positive or negative independently for each neuroimaging biomarker. Demographic, neuropsychological, and neuroimaging data were compared between positive and negative subgroups. The MRI-positive subgroup had lower executive performances and mixed patterns of lower volume and metabolism in AD-characteristic regions and in the prefrontal cortex. The FDG-positive subgroup showed only hypometabolism, predominantly in AD-sensitive areas extending to the whole neocortex, compared with the FDG-negative subgroup. The amyloid-positive subgroup was older and included more APOE ε4 carriers compared with the amyloid-negative subgroup. When considering MRI and/or FDG biomarkers together (i.e., the neurodegeneration-positive), there was a trend for an inverse relationship with Aß deposition such that those with neurodegeneration tended to show less Aß deposition and the reverse was true as well. Our findings suggest that: (1) MRI and FDG biomarkers provide complementary rather than redundant information and (2) relatively young cognitively normal elders tend to have either neurodegeneration or Aß deposition, but not both, suggesting additive rather than sequential/causative links between AD neuroimaging biomarkers at this age. Significance statement: Neuroimaging biomarkers are included in the recent research criteria for preclinical Alzheimer's disease (AD). However, how to use these biomarkers is still being debated, especially regarding their sequence. Our findings suggest that MRI and FDG-PET biomarkers should be used in combination, offering an additive contribution instead of reflecting the same process of neurodegeneration. Moreover, the present study also challenges the hierarchical use of the neuroimaging biomarkers in preclinical AD because it suggests that the neurodegeneration observed in this population is not due to ß-amyloid deposition. Rather, our results suggest that ß-amyloid- and tau-related pathological processes may interact but not necessarily appear in a systematic sequence.

Multimodal imaging based on MRI and PET reveals [(18)F]FLT PET as a specific and early indicator of treatment efficacy in a preclinical model of recurrent glioblastoma.

PURPOSE: The primary objective of this study was to compare the ability of PET and MRI biomarkers to predict treatment efficacy in a preclinical model of recurrent glioblastoma multiforme. METHODS: MRI (anatomical, diffusion, vasculature and oxygenation) and PET ([(18)F]FDG and [(18)F]FLT) parameters were obtained 3 days after the end of treatment and compared with late tumour growth and survival. RESULTS: Early after tumour recurrence, no effect of treatment with temozolomide combined with bevacizumab was observed on tumour volume as assessed by T2-W MRI. At later times, the treatment decreased tumour volume and increased survival. Interestingly, at the earlier time, temozolomide + bevacizumab decreased [(18)F]FLT uptake, cerebral blood volume and oedema. [(18)F]FLT uptake, oedema and cerebral blood volume were correlated with overall survival but [(18)F]FLT uptake had the highest specificity and sensitivity for the early prediction of treatment efficacy. CONCLUSION: The present investigation in a preclinical model of glioblastoma recurrence underscores the importance of multimodal imaging in the assessment of oedema, tumour vascular status and cell proliferation. Finally, [(18)F]FLT holds the greatest promise for the early assessment of treatment efficacy. These findings may translate clinically in that individualized treatment for recurrent glioma could be prescribed for patients selected after PET/MRI examinations.

Comparative Analysis between [(18)F]Fludarabine-PET and [(18)F]FDG-PET in a Murine Model of Inflammation.

Lymphoma research has advanced thanks to introduction of [(18)F]fludarabine, a positron-emitting tool. This novel radiotracer has been shown to display a great specificity for lymphoid tissues. However, in a benign process such as inflammation, the uptake of this tracer has not been questioned. Indeed, in inflammatory zones, elevated glucose metabolism rate may result in false-positives with [(18)F]FDG-PET Imaging. In the present investigation, it has been argued that cells, involved in inflammation, might be less avid of [(18)F]fludarabine. To generate inflammation, Swiss mice were intramuscularly injected with 0.1 mL of turpentine oil into the right front paw. Imaging sessions with (18)F-labeled tracers named above were conducted on days 5 and 25 after inoculation. For each animal, volumes of interest (VOI), delineating the muscle of the inflamed (IP) and normal paws (NP), were determined on PET scans. For characterization of inflammation, muscle samples from IP and NP were stained with hematoxylin and eosin (H&E). In early (day 5) inflammation, [(18)F]FDG accumulation was 4.00 ± 1.65 times greater in the IP than in the contralateral NP; for [(18)F]fludarabine, this IP/NP ratio was 1.31 ± 0.28, resulting in a significant difference between radiotracer groups (p < 0.01). In late (day 25) inflammation, the IP/NP ratios were 2.07 ± 0.49 and 1.03 ± 0.07, for [(18)F]FDG and [(18)F]fludarabine, respectively (p < 0.001). [(18)F]Fludarabine showed significantly weaker uptake in inflammation when compared with [(18)F]FDG. This encouraging finding suggests that [(18)F]fludarabine-PET might well be a robust approach for distinguishing tumor from inflammatory tissue, avoiding false-positive PET results and thus enabling an accurate imaging of lymphoma.

Region-specific hierarchy between atrophy, hypometabolism, and ß-amyloid (Aß) load in Alzheimer's disease dementia.

Gray matter atrophy, glucose hypometabolism, and ß-amyloid Aß deposition are well-described hallmarks of Alzheimer's disease, but their relationships are poorly understood. The present study aims to compare the local levels of these three alterations in humans with Alzheimer's disease. Structural magnetic resonance imaging, (18)F-fluorodeoxyglucose positron emission tomography (PET), and (18)F-florbetapir PET data from 34 amyloid-negative healthy controls and 20 demented patients with a high probability of Alzheimer's disease etiology (attested using neuroimaging biomarkers as recently recommended) were analyzed. For each patient and imaging modality, age-adjusted Z-score maps were computed, and direct between-modality voxelwise comparison and correlation analyses were performed. Significant differences in the levels of atrophy, hypometabolism, and Aß deposition were found in most brain areas, but the hierarchy differed across regions. A cluster analysis revealed distinct subsets of regions: (1) in the hippocampus, atrophy exceeded hypometabolism, whereas Aß load was minimal; (2) in posterior association areas, Aß deposition was predominant, together with high hypometabolism and lower but still significant atrophy; and (3) in frontal regions, Aß deposition was maximal, whereas structural and metabolic alterations were low. Atrophy and hypometabolism significantly correlated in the hippocampus and temporo-parietal cortex, whereas Aß load was not significantly related to either atrophy or hypometabolism. These findings provide direct evidence for regional variations in the hierarchy and relationships between Aß load, hypometabolism, and atrophy. Altogether, these variations probably reflect the differential involvement of region-specific pathological or protective mechanisms, such as the presence of neurofibrillary tangles, disconnection, as well as compensation processes.

Synthesis and in vitro characterisation of ifenprodil-based fluorescein conjugates as GluN1/GluN2B N-Methyl-D-aspartate receptor antagonists.

GluN2B-containing NMDA receptors are involved in many important physiological functions and play a pivotal role in mediating pain as well as in several neurodegenerative disorders. We aimed to develop fluorescent probes to target the GluN2B subunit selectively in order to allow better understanding of the relationships between receptor localisation and physiological importance. Ifenprodil, known as the GluNR2B antagonist of reference, was chosen as the template for the elaboration of probes. We had previously reported a fluorescein conjugate that was shown (by confocal microscopy imaging of DS-red-labelled cortical neurons) to bind specifically to GluN2B. To elaborate this probe, we explored the influence of both the nature and the attachment point of the spacer between the fluorophore and the parent compound, ifenprodil. We performed chemical modifications of ifenprodil at the benzylic position and on the phenol ring by introducing secondary amine or amide functions and evaluated alkyl chains from two to 20 bonds either including or not including secondary amide functions as spacers. The previously developed probe was found to display the greatest activity in the inhibition of NMDA-induced Ca(2+) influx by calcium imaging experiments on HEK293 cells transfected with the cDNA encoding for GluN1-1A and GluN2B. Further investigations revealed that this probe had a neuroprotective effect equivalent to that of ifenprodil in a standard test for neurotoxicity. Despite effects of lesser amplitude with these probes relative to ifenprodil, we demonstrated that they displaced [(3) H]ifenprodil in mouse brain slices in a similar manner.

Noninvasive assessment of hypoxia with 3-[18F]-fluoro-1-(2-nitro-1-imidazolyl)-2-propanol ([18F]-FMISO): a PET study in two experimental models of human glioma.

Despite multiple advances in cancer therapies, patients with glioblastoma (GBM) still have a poor prognosis. Numerous glioma models are used not only for the development of innovative therapies but also to optimize conventional ones. Given the significance of hypoxia in drug and radiation resistance and that hypoxia is widely observed among GBM, the establishment of a reliable method to map hypoxia in preclinical human models may contribute to the discovery and translation of future and more targeted therapies. The aim of this study was to compare the hypoxic status of two commonly used human orthotopic glioma models (U87 and U251) developed in rats and studied by noninvasive hypoxia imaging with 3-[18F]fluoro-1-(2-nitro-1-imidazolyl)-2-propanol-micro-positron emission tomography ([18F]-FMISO-µPET). In parallel, because of the relationships between angiogenesis and hypoxia, we used magnetic resonance imaging (MRI), histology, and immunohistochemistry to characterize the tumoral vasculature. Although all tumors were detectable in T2-weighted MRI and 2-deoxy-2-[18F]fluoro-d-glucose-µPET, only the U251 model exhibited [18F]-FMISO uptake. Additionally, the U251 tumors were less densely vascularized than U87 tumors. Our study demonstrates the benefits of noninvasive imaging of hypoxia in preclinical models to define the most reliable one for translation of future therapies to clinic based on the importance of intratumoral oxygen tension for the efficacy of chemotherapy and radiotherapy.

Confocal microscopy imaging of NR2B-containing NMDA receptors based on fluorescent ifenprodil-like conjugates.

We describe the synthesis and pharmacological characterization of a first generation of ifenprodil conjugates 4-7 as fluorescent probes for the confocal microscopy imaging of the NR2B-containing NMDA receptor. The fluorescein conjugate 6 displayed a moderate affinity for NMDAR but a high selectivity for the NR2B subunit and its NTD. Fluorescence imaging of DS-red labeled cortical neurons showed an exact colocalization of the probe 6 with small protrusions along the dendrites related to a specific binding on NR2B-containing NMDARs.

Radiolabelling of 1,4-disubstituted 3-[18F]fluoropiperidines and its application to new radiotracers for NR2B NMDA receptor visualization.

In order to develop a novel and useful building block for the development of radiotracers for positron emission tomography (PET), we studied the radiolabelling of 1,4-disubstituted 3-[(18)F]fluoropiperidines. Indeed, 3-fluoropiperidine became a useful building block in medicinal chemistry for the pharmacomodulation of piperidine-containing compounds. The radiofluorination was studied on substituted piperidines with electron-donating and electron-withdrawing N-substituents. In the instance of electron-donating N-substituents such as benzyl or butyl, configuration retention and satisfactory fluoride-18 incorporation yields up to 80% were observed. In the case of electron-withdrawing N-substituents leading to carbamate or amide functions, the incorporation yields depend on the 4-susbtitutent (2 to 63%). The radiolabelling of this building block was applied to the automated radiosynthesis of NR2B NMDA receptor antagonists and effected by a commercially available radiochemistry module. The in vivo evaluation of three radiotracers demonstrated minimal brain uptakes incompatible with the imaging of NR2B NMDA receptors in the living brain. Nevertheless, moderate radiometabolism was observed and, in particular, no radiodefluorination was observed which demonstrates the stability of the 3-position of the fluorine-18 atom. In conclusion, the 1,4-disubstituted 3-[(18)F]fluoropiperidine moiety could be of value in the development of other radiotracers for PET even if the evaluation of the NR2B NMDA receptor antagonists failed to demonstrate satisfactory properties for PET imaging of this receptor.

Multimodal evaluation of hypoxia in brain metastases of lung cancer and interest of hypoxia image-guided radiotherapy.

Lung cancer patients frequently develop brain metastases (BM). Despite aggressive treatment including neurosurgery and external-radiotherapy, overall survival remains poor. There is a pressing need to further characterize factors in the microenvironment of BM that may confer resistance to radiotherapy (RT), such as hypoxia. Here, hypoxia was first evaluated in 28 biopsies from patients with non­small cell lung cancer (NSCLC) BM, using CA-IX immunostaining. Hypoxia characterization (pimonidazole, CA-IX and HIF-1α) was also performed in different preclinical NSCLC BM models induced either by intracerebral injection of tumor cells (H2030-Br3M, H1915) into the cortex and striatum, or intracardial injection of tumor cells (H2030-Br3M). Additionally, [18F]-FMISO-PET and oxygen-saturation-mapping-MRI (SatO2-MRI) were carried out in the intracerebral BM models to further characterize tumor hypoxia and evaluate the potential of Hypoxia-image-guided-RT (HIGRT). The effect of RT on proliferation of BM ([18F]-FLT-PET), tumor volume and overall survival was determined. We showed that hypoxia is a major yet heterogeneous feature of BM from lung cancer both preclinically and clinically. HIGRT, based on hypoxia heterogeneity observed between cortical and striatal metastases in the intracerebrally induced models, showed significant potential for tumor control and animal survival. These results collectively highlight hypoxia as a hallmark of BM from lung cancer and the value of HIGRT in better controlling tumor growth.

Copper-catalyzed amination of (bromophenyl)ethanolamine for a concise synthesis of aniline-containing analogues of NMDA NR2B antagonist ifenprodil.

An operationally simple and concise synthesis of anilinoethanolamines, as NMDA NR2B receptor antagonist ifenprodil analogues, was developed via a copper-catalyzed amination of the corresponding bromoarene. Coupling was achieved with linear primary alkylamines, alpha,omega-diamines, hexanolamine and benzophenone imine, as well as with aqueous ammonia, in good yields using CuI and N,N-diethylsalicylamide, 2,4-pentadione or 2-acetylcyclohexanone as catalytic systems. Amination with ethylene diamine was efficient even in the absence of an additive ligand, whereas no reaction occurred with ethanolamine whatever the conditions used. The anilinoethanolamines were evaluated as NR2B receptor antagonists in a functional inhibition assay. Aminoethylanilines displayed inhibition effects close to that of ifenprodil.

Synthesis, radiosynthesis and biological evaluation of 1,4-dihydroquinoline derivatives as new carriers for specific brain delivery.

In spite of numerous reports dealing with the use of 1,4-dihydropyridines as carriers to deliver biological active compounds to the brain, this chemical delivery system (CDS) suffers from poor stability of the 1,4-dihydropyridine derivatives towards oxidation and hydration reactions seriously limiting further investigations in vivo. In an attempt to overcome these limitations, we report herein the first biological evaluation of more stable annellated NADH models in the quinoline series as relevant neuroactive drug-carrier candidates. The radiolabeled 1,4-dihydroquinoline [(11)C] was prepared to be subsequently peripherally injected in rats. The injected animals were sacrificed and brains were collected. The radioactivity measured in rat brain indicated a rapid penetration of the carrier [(11)C] into the CNS. HPLC analysis of brain homogenates showed that oxidation of [(11)C] into the corresponding quinolinium salt [(11)C] was completed in less than 5 min. An in vivo evaluation in mice is also reported to illustrate the potential of such 1,4-dihydroquinoline derivatives to transport a neuroactive drug in the CNS. For this purpose, gamma-aminobutyric acid (GABA), well known to poorly cross the brain blood barrier (BBB) was connected to this 1,4-dihydroquinoline-type carrier. After i.p. injection of 1,4-dihydroquinoline-GABA derivative in mice, a significant alteration of locomotor activity (LMA) was observed presumably resulting from an enhancement of central GABAergic activity. These encouraging results give strong evidence for the capacity of carrier-GABA derivative to cross the BBB and exert a pharmacological effect on the CNS. This study paves the way for further progress in designing new redox chemical delivery systems.

[18F]-Fludarabine for Hematological Malignancies.

With the emergence of PET/CT using 18F-FDG, molecular imaging has become the reference for lymphoma lesion detection, tumor staging, and response assessment. According to the response in some lymphoma subtypes it has also been utilized for prognostication of disease. Although 18F-FDG has proved useful in the management of patients with lymphoma, the specificity of 18F-FDG uptake has been critically questioned, and is not without flaws. Its dependence on glucose metabolism, which may indiscriminately increase in benign conditions, can affect the 18F-FDG uptake in tumors and may explain the causes of false-positive imaging data. Considering these drawbacks, 18F-fludarabine, an adenine nucleoside analog, was developed as a novel PET imaging probe. An efficient and fully automated radiosynthesis has been implemented and, subsequently preclinical studies in xenograft murine models of hematological maligancies (follicular lymphoma, CNS lymphoma, multiple myeloma) were conducted with this novel PET probe in parallel with 18F-FDG. The results demonstrated several crucial points: tumor-specific targeting, weaker uptake in inflammatory processes, stronger correlation between quantitative values extracted from [18]F-fludarabine and histology when compared to 18F-FDG-PET, robustness during immunotherapy with rituximab, divergent responses between CNS lymphoma and glioblastoma (GBM). All these favorable findings permitted to establish a "first in man" study where 10 patients were enrolled. In DLBCL patients, increased uptake was observed in sites considered abnormal by CT and [18F]FDG; in two patients discrepancies were observed in comparison with 18F-FDG. In CLL patients, the uptake coincided with sites expected to be involved and displayed a significant uptake in hematopoietic bone marrow. No uptake was observed, whatever the disease group, in the cardiac muscle and brain. Moreover, its mean effective dose was below the effective dose reported for 18F-FDG. These preclinical and clinical findings revealed a marked specificity of 18F-fludarabine for lymphoma tissues. Furthermore, it might well be a robust tool for correctly quantifying the disease, in the presence of confounding inflammatory processes, thus avoiding false-positive results, and an innovative approach for imaging hematological malignancies.

64Cu-ATSM/64Cu-Cl2 and their relationship to hypoxia in glioblastoma: a preclinical study.

BACKGROUND: Diacetyl-bis(N4-methylthiosemicarbazone), labeled with 64Cu (64Cu-ATSM) has been suggested as a promising tracer for imaging hypoxia. However, various controversial studies highlighted potential pitfalls that may disable its use as a selective hypoxic marker. They also highlighted that the results may be tumor location dependent. Here, we first analyzed uptake of Cu-ATSM and its less lipophilic counterpart Cu-Cl2 in the tumor over time in an orthotopic glioblastoma model. An in vitro study was also conducted to investigate the hypoxia-dependent copper uptake in tumor cells. We then further performed a comprehensive ex vivo study to compare 64Cu uptake to hypoxic markers, specific cellular reactions, and also transporter expression. METHODS: µPET was performed 14 days (18F-FMISO), 15 days (64Cu-ATSM and 64Cu-Cl2), and 16 days (64Cu-ATSM and 64Cu-Cl2) after C6 cell inoculation. Thereafter, the brains were withdrawn for further autoradiography and immunohistochemistry. C6 cells were also grown in hypoxic workstation to analyze cellular uptake of Cu complexes in different oxygen levels. RESULTS: In vivo results showed that Cu-ASTM and Cu-Cl2 accumulated in hypoxic areas of the tumors. Cu-ATSM also stained, to a lesser extent, non-hypoxic regions, such as regions of astrogliosis, with high expression of copper transporters and in particular DMT-1 and CTR1, and also characterized by the expression of elevated astrogliosis. In vitro results show that 64Cu-ATSM showed an increase in the uptake only in severe hypoxia at 0.5 and 0.2% of oxygen while for 64Cu-Cl2, the cell retention was significantly increased at 5% and 1% of oxygen with no significant rise at lower oxygen percentages. CONCLUSION: In the present study, we show that Cu-complexes undoubtedly accumulate in hypoxic areas of the tumors. This uptake may be the reflection of a direct dependency to a redox metabolism and also a reflection of hypoxic-induced overexpression of transporters. We also show that Cu-ATSM also stained non-hypoxic regions such as astrogliosis.

Chemical Delivery System of MIBG to the Central Nervous System: Synthesis, 11C-Radiosynthesis, and in Vivo Evaluation.

The norepinephrine transporter (NET) plays an important role in neurotransmission and is involved in a multitude of psychiatric and neurodegenerative diseases. [123I/131I]meta-iodobenzylguanidine (MIBG) is a widely used radiotracer in the diagnosis and follow-up of peripheral neuroendocrine tumors overexpressing the norepinephrine transporter. MIBG does not cross the blood-brain barrier (BBB), and we have demonstrated the "proof-of-concept" that 1,4-dihydroquinoline/quinolinium salt as chemical delivery system (CDS) is a promising tool to deliver MIBG to the brain. To improve BBB passage, various substituents on the 1,4-dihydroquinoline moiety and a linker between CDS and MIBG were added. A series of CDS-MIBG 1a-d was synthesized, labeled with carbon-11, and evaluated in vivo into rats. The in vivo results demonstrated that, although adding substituents on CDS in 1a-c is of no benefit for brain delivery of MIBG, the presence of a linker in CDS-MIBG 1d greatly improved both brain penetration and the release rate of MIBG in the central nervous system.

Interest of Pet Imaging in Multiple Myeloma.

The interest of 18Fluoro-deoxyglucose (FDG) positron emission tomography (PET) imaging in the management of patients with multiple myeloma (MM) for the workup at diagnosis and for therapeutic evaluation has recently been demonstrated. FDG-PET is a powerful imaging tool for bone lesions detection at initial diagnosis with high sensitivity and specificity values. The independent pejorative prognostic value on progression-free survival (PFS) and overall survival (OS) of baseline PET-derived parameters (presence of extra-medullary disease (EMD), number of focal bone lesions (FLs), and maximum standardized uptake values [SUVmax]) has been reported in several large independent prospective studies. During therapeutic evaluation, FDG-PET is considered as the reference imaging technique, because it can be performed much earlier than MRI which lacks specificity. Persistence of significant FDG uptake after treatment, notably before maintenance therapy, is an independent pejorative prognostic factor, especially for patients with a complete biological response. So FDG-PET and medullary flow cytometry are complementary tools for detection of minimal residual disease before maintenance therapy. However, the definition of PET metabolic complete response should be standardized. In patients with smoldering multiple myeloma, the presence of at least one hyper-metabolic lytic lesions on FDG-PET may be considered as a criterion for initiating therapy. FDG-PET is also indicated for initial staging of a solitary plasmacytoma so as to not disregard other bone or extra-medullary localizations. Development of nuclear medicine offer new perspectives for MM imaging. Recent PET tracers are willing to overcome limitations of FDG. (11)C-Methionine, which uptake reflects the increased protein synthesis of malignant cells seems to correlate well with bone marrow infiltration. Lipid tracers, such as Choline or acetate, and some peptide tracers, such as (68) Ga-Pentixafor, that targets CXCR4 (chemokine receptor-4, which is often expressed with high density by myeloma cells), are other promising PET ligands. 18F-fludarabine and immuno-PET targeting CD138 and CD38 also showed promising results in preclinical models.

Decreased chronic-stage cortical 11C-flumazenil binding after focal ischemia-reperfusion in baboons: a marker of selective neuronal loss?

BACKGROUND AND PURPOSE: Although the penumbra can be saved by early reperfusion, in the rat it is consistently affected by selective neuronal loss. Mapping selective neuronal loss in the living primate would be desirable. METHODS: Five young adult baboons underwent (15)O positron emission tomography for cerebral blood flow, cerebral oxygen consumption, and oxygen extraction fraction mapping at baseline and serially during and after 20-hour temporary middle cerebral artery occlusion. At approximately day 30, (11)C-flumazenil (FMZ), a potential positron emission tomography marker of selective neuronal loss, and structural magnetic resonance-based infarct mapping were obtained, and the brain was perfused-fixed. Reduced FMZ binding in noninfarcted cortical middle cerebral artery areas was searched voxel-wise, and specific binding was assessed using compartmental modeling of FMZ time-activity curves. RESULTS: Visual inspection revealed reduced late FMZ uptake in the affected cortical territory, extending well beyond the infarct. Accordingly, the incidence of selected voxels was greater than chance, documenting mildly but significantly reduced FMZ uptake and specific binding. Serial (15)O positron emission tomography revealed moderately severe acute ischemia followed by reperfusion. Histopathology documented only mild neuronal changes in or near the affected areas. CONCLUSIONS: We document moderate but definite late FMZ binding decrements in noninfarcted cortical areas in the baboon, consistent with previous rat and human studies. These were acutely characterized by moderate ischemia followed by reperfusion, consistent with neuronal damage from ischemic or reperfusion injury in the salvaged at-risk tissue. Only mild histopathological changes subtended these FMZ alterations suggesting subtle processes such as isolated dendrite or synapse loss. Whether these changes impact on clinical outcome deserves studying because they may be targeted by specific neuroprotection.

Radiosynthesis and ex vivo evaluation of [11C]-SIB-1553A as a PET radiotracer for beta4 selective subtype nicotinic acetylcholine receptor.

[11C]-SIB-1553A ((+/-)-4-[2-((N-[11C]-methyl)-2-pyrrolidinyl)ethyl]thiophenol) was labelled with carbon-11 (t1/2=20.4 min) and evaluated in vivo as potential radiotracer for noninvasive assessment of the beta4 subunit nicotinic acetylcholine neurotransmission system with positron emission tomography (PET). The labelling precursor was obtained within five steps from N-Boc-prolinal in 45-56% overall yields. The radiosynthesis of [11C]-SIB-1553A was achieved by a selective N-[11C]-methylation in 32 min with a radiochemical purity greater than 97%, 7.5-30 GBq/micromol of specific radioactivity and 55-65% radiochemical yield (decay corrected, based on [11C]methyl iodide). The ex vivo pharmacological profile of [11C]-SIB-1553A was evaluated in rats with biodistribution studies in organs and in brain structures by autoradiography. The radiotracer uptake in the brain reached 0.49 %ID/g at 10 min and no brain radiometabolite was detected 40 min after intravenous injection. The quantification of radioactivity in various cerebral structures indicated a significantly higher radioactivity level at 15 min than at 30 min. Among the beta4 nAChR subunit-rich structures studied in the rat brain, only the thalamus at 15 and 30 min and the hippocampus at 30 min showed significantly higher uptake. Moreover, competition studies performed with SIB-1553A (15 min before the radiotracer injection) revealed only a low specific binding estimated to 7% of the total binding at 15 min and 13% at 30 min.