Probing Estrogen Sulfotransferase-Mediated Inflammation with [11C]-PiB in the Living Human Brain.

BACKGROUND: 2-(4'- [11C]Methylaminophenyl)-6-hydroxybenzothiazole ([11C]-PiB), purportedly a specific imaging agent for cerebral amyloid-ß plaques, is a specific, high affinity substrate for estrogen sulfotransferase (SULT1E1), an enzyme that regulates estrogen homeostasis. OBJECTIVE: In this work, we use positron emission tomography (PET) imaging with [11C]-PiB to assess the functional activity of SULT1E1 in the brain of moyamoya disease patients. METHODS: Ten moyamoya subjects and five control patients were evaluated with [11C]-PiB PET and structural MRI scans. Additionally, a patient with relapsing-remitting multiple sclerosis (RRMS) received [11C]-PiB PET scans before and after steroidal and immunomodulatory therapy. Parametric PET images were established to assess SULT1E1 distribution in the inflamed brain tissue. RESULTS: Increased [11C]-PiB SRTM DVR in the thalamus, pons, corona radiata, and internal capsule of moyamoya cohort subjects was observed in comparison with controls (p ≤ 0.01). This was observed in patients without treatment, with collateralization, and also after radiation. The post-treatment [11C]-PiB PET scan in one RRMS patient also revealed substantially reduced subcortical brain inflammation. In validation studies, [11C]-PiB autoradiography signal in the peri-infarct area of the rat middle cerebral arterial occlusion stroke model was shown to correlate with SULT1E1 immunohistochemistry. CONCLUSION: Strong [11C]-PiB PET signal associated with intracranial inflammation in the moyamoya syndrome cohort and a single RRMS patient appears consistent with functional imaging of SULT1E1 activity in the human brain. This preliminary work offers substantial and direct evidence that significant [11C]-PiB PET focal signals can be obtained from the living human brain with intracranial inflammation, signals not attributable to amyloid-ß plaques.

The Value of In Vitro Binding as Predictor of In Vivo Results: A Case for [18F]FDDNP PET.

PURPOSE: Caution is warranted when in vitro results of biomarkers labeled with tritium were perfunctorily used to criticize in vivo data and conclusions derived with the same tracers labeled with positron emitters and positron emission tomography (PET). This concept is illustrated herein with the PET utilization of [18F]FDDNP, a biomarker used for in vivo visualization of ß-amyloid and tau protein neuroaggregates in humans, later contradicted by in vitro data reported with [3H]FDDNP. In this investigation, we analyze the multiple factors involved in the experimental design of the [3H]FDDNP in vitro study that led to the erroneous interpretation of results. PROCEDURE: The present work describes full details on the synthesis, characterization, purity, and kinetics of radiolytic stability of [3H]FDDNP. The optimal in vitro conditions for detecting tau and ß-amyloid protein aggregates using macroscopic and microscopic autoradiography with both [18F]FDDNP and [3H]FDDNP are also presented. Macroscopic autoradiography determinations were performed with [3H]FDDNP of verified purity using established methods described previously in the literature. RESULTS: The autoradiographic results using phosphate buffered saline (PBS) with less than 1 % EtOH and pure, freshly prepared [3H]FDDNP compared with the earlier reported data using [3H]FDDNP of undetermined purity and PBS in 10 % EtOH demonstrate the critical importance of rigorous experimental design for meaningful in vitro determinations. [18F]FDDNP binding to both amyloid plaques and neurofibrillary tangles was confirmed by amyloid and tau immunohistochemical stains of adjacent tissues. CONCLUSIONS: This work illustrates the sensitivity of in vitro techniques to various experimental conditions and underscores that conclusions obtained from translational in vitro to in vivo determinations must always be performed with extreme care to avoid wrong interpretations that can be perpetuated and assumed without further analysis.

[F-18]FDDNP microPET imaging correlates with brain Aß burden in a transgenic rat model of Alzheimer disease: effects of aging, in vivo blockade, and anti-Aß antibody treatment.

In vivo detection of Alzheimer's disease (AD) neuropathology in living patients using positron emission tomography (PET) in conjunction with high affinity molecular imaging probes for ß-amyloid (Aß) and tau has the potential to assist with early diagnosis, evaluation of disease progression, and assessment of therapeutic interventions. Animal models of AD are valuable for exploring the in vivo binding of these probes, particularly their selectivity for specific neuropathologies, but prior PET experiments in transgenic mice have yielded conflicting results. In this work, we utilized microPET imaging in a transgenic rat model of brain Aß deposition to assess [F-18]FDDNP binding profiles in relation to age-associated accumulation of neuropathology. Cross-sectional and longitudinal imaging demonstrated that [F-18]FDDNP binding in the hippocampus and frontal cortex progressively increases from 9 to 18months of age and parallels age-associated Aß accumulation. Specificity of in vivo [F-18]FDDNP binding was assessed by naproxen pretreatment, which reversibly blocked [F-18]FDDNP binding to Aß aggregrates. Both [F-18]FDDNP microPET imaging and neuropathological analyses revealed decreased Aß burden after intracranial anti-Aß antibody administration. The combination of this non-invasive imaging method and robust animal model of brain Aß accumulation allows for future longitudinal in vivo assessments of potential therapeutics for AD that target Aß production, aggregation, and/or clearance. These results corroborate previous analyses of [F-18]FDDNP PET imaging in clinical populations.

Specific estrogen sulfotransferase (SULT1E1) substrates and molecular imaging probe candidates.

This work focuses on the development of specific substrates for estrogen sulfotransferase (SULT1E1) to produce molecular imaging probes for this enzyme. SULT1E1 is a key enzyme in estrogen homeostasis, playing a central role in the prevention and development of human disease. In vitro sulfation assays showed alkyl and aryl substitutions to a fused heterocyclic system modeled after beta-naphthol (betaN), based on compounds that interact with the estrogen receptor, rendered several molecules with enhanced specificity for SULT1E1 over SULT1A1*1, SULT1A1*2, SULT1A3, and SULT2A1. Several 6-hydroxy-2-arylbenzothiazoles tested demonstrated excellent affinity--V(max)/K(m) ratios-and specificity for SULT1E1. K(m) values ranged from 0.12-2.36 microM. A strong correlation was observed between polarity of the 4'-sustituent on the 2-aryl moiety (Hammett sigma(p)) and the log(V(max)/K(m)) (r = 0.964). Substrate sensitivity is influenced by the acidity of the 6-phenolic group demonstrated by correlating its (1)H NMR chemical shift (delta(OH)) with the log(V(max)/K(m)) (r = 0.963). Acidity is mediated by the electron withdrawing capacity of the 4'-substituent outlined by the correlation of the C-2 (13)C NMR chemical shift (delta(C2)) with the log(V(max)/K(m)) (r = 0.987). 2-[4-(Methylamino)phenyl]-6-hydroxybenzothiazole (2b) was radiolabeled with carbon-11 ((11)C-(2b)) and used in vivo for microPET scanning and tissue metabolite identification. High PET signal was paralleled with the presence of radiolabeled (11)C-(2b)-6-O-sulfate and the SULT1E1 protein detected by western blot. Because this and other members of this family presenting specificity for SULT1E1 can be labeled with carbon-11 or fluorine-18, in vivo assays of SULT1E1 functional activity are now feasible in humans.