Astatine.

This educational review describes and summarizes the historic discovery of element 85, the experiments leading to its physical and chemical characterization and comparison with its lighter homologue iodine. The half-lives of its longest living isotopes 210 At and 211 At with 8.3 and 7.22 hours respectively together with their alpha decay characteristics made these isotopes interesting for radiation biological research. However, the lack of stable isotopes of astatine presents a strong challenge for all characterizations. Nevertheless, the decay characteristics especially of 211 At stimulated several research groups to develop labelling strategies for the preparation of astatinated radiopharmaceuticals for targeted alpha radiation therapy. Because of the distinct differences in the chemical behaviour of astatine, when compared with iodine, these approaches are quite challenging. Accordingly, quite different labelling strategies have been tested, namely nucleophilic and electrophilic substitution reactions as well as complex forming strategies. Classic and new developments for the preparation of these compounds are reviewed.

Positron Emission Tomography Imaging Reveals Auditory and Frontal Cortical Regions Involved with Speech Perception and Loudness Adaptation.

Considerable progress has been made in the treatment of hearing loss with auditory implants. However, there are still many implanted patients that experience hearing deficiencies, such as limited speech understanding or vanishing perception with continuous stimulation (i.e., abnormal loudness adaptation). The present study aims to identify specific patterns of cerebral cortex activity involved with such deficiencies. We performed O-15-water positron emission tomography (PET) in patients implanted with electrodes within the cochlea, brainstem, or midbrain to investigate the pattern of cortical activation in response to speech or continuous multi-tone stimuli directly inputted into the implant processor that then delivered electrical patterns through those electrodes. Statistical parametric mapping was performed on a single subject basis. Better speech understanding was correlated with a larger extent of bilateral auditory cortex activation. In contrast to speech, the continuous multi-tone stimulus elicited mainly unilateral auditory cortical activity in which greater loudness adaptation corresponded to weaker activation and even deactivation. Interestingly, greater loudness adaptation was correlated with stronger activity within the ventral prefrontal cortex, which could be up-regulated to suppress the irrelevant or aberrant signals into the auditory cortex. The ability to detect these specific cortical patterns and differences across patients and stimuli demonstrates the potential for using PET to diagnose auditory function or dysfunction in implant patients, which in turn could guide the development of appropriate stimulation strategies for improving hearing rehabilitation. Beyond hearing restoration, our study also reveals a potential role of the frontal cortex in suppressing irrelevant or aberrant activity within the auditory cortex, and thus may be relevant for understanding and treating tinnitus.

Synthesis and analysis of 2-[211At]-L-phenylalanine and 4-[211At]-L-phenylalanine and their uptake in human glioma cell cultures in-vitro.

2-[211At]-L-phenylalanine and 4-[211At]-L-phenylalanine were prepared from the corresponding iodo and bromo derivatives using the Cu(+)-assisted nucleophilic exchange. 4-[211At]-L-phenylalanine was additionally prepared by destannylation of the BOC-derivatized 4-tributylstannyl-L-phenylalanine. Radiochemical yields of 2-[211At]-L-phenylalanine and 4-[211At]-L-phenylalanine by nucleophilic exchange were 52-74% and 65-85%. Radiochemical yield of 4-[211At]-L-phenylalanine by electrophilic destannylation was 35-50%. HPLC sequence analysis showed that 2-[211At]-L-phenylalanine followed the halogen sequence (F

In vitro experimental (211)At-anti-CD33 antibody therapy of leukaemia cells overcomes cellular resistance seen in vivo against gemtuzumab ozogamicin.

PURPOSE: Monoclonal anti-CD33 antibodies conjugated with toxic calicheamicin derivative (gemtuzumab ozogamicin, GO) are a novel therapy option for acute myeloid leukaemia (AML). Key prognostic factors for patients with AML are high CD33 expression on the leukaemic cells and the ability to overcome mechanisms of resistance to cytotoxic chemotherapies, including drug efflux or other mechanisms decreasing apoptosis. Alpha particle-emitting radionuclides overwhelm such anti-apoptotic mechanisms by producing numerous DNA double-stranded breaks (DSBs) accompanied by decreased DNA repair. METHODS: We labelled anti-CD33 antibodies with the alpha-emitter (211)At and compared survival of leukaemic HL-60 and K-562 cells treated with the (211)At-labelled antibodies, GO or unlabelled antibodies as controls. We also measured caspase-3/7 activity, DNA fragmentation and necrosis in HL-60 cells after treatment with the different antibodies or with free (211)At. RESULTS: The mean labelling ratio of (211)At-labelled antibodies was 1:1,090 +/- 364 (range: 1:738-1:1,722) in comparison to 2-3:1 for GO. Tumour cell binding of (211)At-anti-CD33 was high in the presence of abundant CD33 expression and could be specifically blocked by unlabelled anti-CD33. (211)At-anti-CD33 decreased survival significantly more than did GO at comparable dilution (1:1,000). No significant differences in induction of apoptosis or necrosis or DNA DSB or in decreased survival were observed after (211)At-anti-CD33 (1:1,090) versus GO (1:1) treatment. CONCLUSION: Our results suggest that (211)At is a promising, highly cytotoxic radioimmunotherapy in CD33-positive leukaemia and kills tumour cells more efficiently than does calicheamicin-conjugated antibody. Labelling techniques leading to higher chemical yield and specific activities must be developed to increase (211)At-anti-CD33 therapeutic effects.

The first scintigraphic detection of tumor necrosis factor-alpha in patients with complex regional pain syndrome type 1.

Tumor necrosis factor (TNF)-alpha has been identified as a pathogenic factor in many immunologically based diseases and complex regional pain syndrome (CRPS). In this case series, we used radiolabeled technetium anti-TNF-alpha antibody to scintigraphically image TNF-alpha in 3 patients with type 1 CRPS. The results show that TNF-alpha was localized only in affected hands of patients with early-stage CRPS. No uptake was seen in clinically unaffected hands and late-stage CRPS. Our findings support the growing evidence for neuroimmune disturbance in patients with CRPS and may have important further implications for specific anticytokine treatment in patients with CRPS.

Modified calcium accumulation after controlled cortical impact under cyclosporin A treatment: a 45Ca autoradiographic study.

OBJECTIVE: As a neuroprotective drug, cyclosporin A (CsA) has been subject of multiple experimental works in traumatic brain injury (TBI) research. It is well known that CsA inhibits calcium (Ca2+) induced mitochondrial permeability transition (mPT). The aim of this study was to investigate the influence of CsA on the alteration of Ca2+ homeostasis after experimental brain injury. METHODS: Sprague-Dawley male rats (n = 36) with a mean weight of 330 g (280-350 g) were general anesthetized with isofluran through gas mask. The anesthetized animals (n = 24) were subjected to a controlled cortical impact (CCI) over the left parietotemporal cortex using round-tip impounder with a 5 mm diameter at a velocity of approximately 3.7 m/s and a penetration depth of 2 mm. The sham group (n = 12) underwent anesthesia and craniotomy without CCI. In the CCI groups, CsA (n = 12) or vehicle (n = 12) was administered 15 minutes post-injury with a subsequent i.p. injection after 24 hours. Thirty-three hours after injury or sham craniotomy, 45calcium (45Ca) suspended in physiologic saline solution was injected in the left femoral vein. Five hours after isotope administration, animals were killed and the brain was quickly removed and placed in powdered dry ice. Coronal plane sections (20 microm thick) taken every 400 microm from the frontal cortex through the occipital cortex, were exposed to cyclotron films for 14 days at -18 degrees C. Relative optical density was utilized to provide a relative measure of 45Ca accumulation within seven different structures. RESULTS: The difference of 45Ca accumulation (measured by relative optical density) in the CsA group was greater by 30-70% in the following structures compared to vehicle treated traumatized animals: temporal cortex, CA1, anteromedial and posteromedial thalamus (p < 0.05). CONCLUSION: Post-traumatic 45Ca accumulation is modified under CsA. The crucial neuroprotective effect of CsA might be unrelated to a reduction of post-traumatic Ca2+ accumulation, especially with regard to the importance of Ca2+ as an intracellular messenger governing a large number of cellular functions.

The potential of 211Astatine for NIS-mediated radionuclide therapy in prostate cancer.

PURPOSE: We reported recently the induction of selective iodide uptake in prostate cancer cells (LNCaP) by prostate-specific antigen (PSA) promoter-directed sodium iodide symporter (NIS) expression that allowed a significant therapeutic effect of (131)I. In the current study, we studied the potential of the high-energy alpha-emitter (211)At, also transported by NIS, as an alternative radionuclide after NIS gene transfer in tumors with limited therapeutic efficacy of (131)I due to rapid iodide efflux. METHODS: We investigated uptake and therapeutic efficacy of (211)At in LNCaP cells stably expressing NIS under the control of the PSA promoter (NP-1) in vitro and in vivo. RESULTS: NP-1 cells concentrated (211)At in a perchlorate-sensitive manner, which allowed a dramatic therapeutic effect in vitro. After intraperitoneal injection of (211)At (1 MBq), NP-1 tumors accumulated approximately 16% ID/g (211)At (effective half-life 4.6 h), which resulted in a tumor-absorbed dose of 1,580+/-345 mGy/MBq and a significant tumor volume reduction of up to 82+/-19%, while control tumors continued their growth exponentially. CONCLUSIONS: A significant therapeutic effect of (211)At has been demonstrated in prostate cancer after PSA promoter-directed NIS gene transfer in vitro and in vivo suggesting a potential role for (211)At as an attractive alternative radioisotope for NIS-targeted radionuclide therapy, in particular in smaller tumors with limited radionuclide retention time.

Preparation and evaluation of 211At labelled antineoplastic antibodies.

PURPOSE: The objective of this study was to determine and verify the stability of 211At-labelled antibodies under physiological conditions and their specific cell-binding capacity for selected epitopes, in order to evaluate the potential of 211At for alpha-radioimmunotherapy. METHODS: 211At was produced at the department's cyclotron and was linked via the intermediate 3-211At-succinimidyl-benzoate (SAB) to the antineoplastic antibodies rituximab, gemtuzumab and gemtuzumab ozogamicin. The stability of the labelled antibodies was determined in serum for 21 h. Cell-binding experiments on HL-60 and CI-1 cells included kinetic, saturation and competitive binding studies. For comparison the binding to antigen-negative cells was determined. The binding specificity and affinity and the IC50-values were evaluated. RESULTS: A consistent yield of 30% and a specific activity of 3 MBq/nmol was obtained. The stability of 211At-antibodies in murine serum exceeded 85% at 37 degrees C. Cell-binding to antigen-positive cells was >25%, while binding to antigen-negative cells did not exceed the unspecific binding and was smaller than 1%. IC50 values ranged between 2 and 11 nmol/L. CONCLUSIONS: A routine preparation of 211At-labelled antibodies was established and the stability of the 211At-labelled antibodies under physiologic conditions was verified. Apparently, labelling of antibodies with 211At by the method described does not compromise the affinity and specificity to the respective epitopes.

Serotonin transporter binding in Tourette Syndrome.

Recent studies provided evidence for an involvement of the dopaminergic system in the pathophysiology of Tourette Syndrome (TS). However, little is known about possible impairment of other neurotransmitter systems. In obsessive-compulsive disorder (OCD), a common comorbidity in TS, it is suggested that the serotonergic system plays a major role in the pathogenesis. We, therefore, used [I-123]2[beta]-carbomethoxy-3[beta]-(4-iodophenyl)tropane ([123I]beta-CIT) and single photon emission computed tomography (SPECT) to investigate serotonin transporter (SERT) binding capacity in 12 patients with TS with various degrees of associated obsessive compulsive behaviour (OCB) and 16 age-matched healthy controls. Binding ratios in TS patients not receiving serotonin reuptake inhibitors (SSRI) (n=8) were significantly reduced compared to age-adjusted ratios from normal controls (2.8 versus 3.2, p=0.003). Treatment with SSRI resulted in a significant reduction of SERT availability. Performing linear regression analysis for this small group, SSRI-free patients indicated trends for a negative correlation between [123I]beta-CIT binding on SERT and OCB (r=-0.78, p=0.023) as well as complex motor tics (r=-0.68, p=0.064). In healthy controls, but not in the TS group, we found an age-related decline in SERT binding capacity (0.28% decrease per year, p=0.038). Our data are in agreement with previous results suggesting an impairment of the serotonergic system in TS. It can be speculated that the reduction in SERT binding capacity is associated with the degree of comorbid OCB.

[N-methyl 11C]meta-Hydroxyephedrine positron emission tomography in Parkinson's disease and multiple system atrophy.

Orthostatic hypotension (OH) can be present in idiopathic Parkinson's disease (IPD) as well as in atypical parkinsonian syndromes such as multiple system atrophy (MSA). According to clinical tests of sympathetic nerve function and histopathological data, OH is caused by primarily postganglionic sympathetic dysfunction in IPD and by predominantly central and preganglionic degeneration in MSA. It has been proposed that this concept of a different underlying pathogenesis for OH should be applied in the differential diagnosis of parkinsonian disorders, in the form of measurements of sympathetic myocardial innervation. In this pilot study, myocardial imaging with [ N-methyl (11)C]meta-hydroxyephedrine ((11)C-HED) and positron emission tomography (PET) was used as a quantitative tool to evaluate the feasibility of such an approach. Seven patients were included in the study. Two had MSA and OH, three had probable IPD and OH (duration of disease, >3 years), one had probable IPD without OH (disease duration, 3 years) and one had possible IPD without OH (disease duration, 2 years). Ratios of maximal (11)C-HED uptake in the myocardium to that in the liver at 5 and 40 min post injection (p.i.) and - based on kinetic modelling - tracer influx rates K(1) were calculated. Compared with MSA patients ( n=2), IPD patients with OH ( n=3) showed definitely lower uptake ratios at both 5 min p.i. (0.39-0.57 vs 0.78-0.79) and 40 min p.i. (0.21-0.60 vs 0.89-1.06), as well as lower K(1) values (0.198-0.359 vs 0.384-0.450 min(-1)). The patient with probable IPD without OH showed intermediate values (uptake ratio at 5 min: 0.65; uptake ratio at 40 min: 0.87; K(1)=0.363). In the patient with possible IPD, values (uptake ratio at 5 min: 0.96; uptake ratio at 40 min: 1.04; K(1)=0.400) did not differ from those observed in MSA. These results support the hypothesis that measurement of myocardial innervation may contribute to the differential diagnosis of parkinsonian disorders and suggest a need for quantitative pathophysiological imaging, particularly at early stages of disease.