Asclepiades of Bithynia: Greek physician and medical reformer.

Asclepiades of Bithynia (124-40 BC) was a Greek physician who practised and taught Greek medicine in Rome. Among his many contributions, Asclepiades challenged the long-standing Hippocratic doctrine of the four humours. Influenced by Epicurean philosophy, he sought to construct a new theory of human disease, derived in part from atomic theories of chance and evolution earlier described by Democritus and Epicurus. In clinical practice, Asclepiades's approach to physical and mental illnesses was reasoned, humane, and, in many ways, ahead of its time. As a result of his many contributions and his overall approach to care, Asclepiades is now considered a pioneer of modern physical therapy, the progenitor of a more humane approach to mental illness, and, as highlighted by Yapijakis, the father of modern molecular medicine.

The contextual interference effect and sport skills.

During the last twenty-five years, the contextual interference effect has been thoroughly studied. This review finds that the effect is relatively robust in basic research, but considerably weaker in applied settings. Motor learning scholars have urged practitioners to develop instructional strategies based upon the inferences of the contextual interference effect. The smaller effects seem to indicate that the concept may have more limited use for the physical educator. It appears that the generalization of procedures from other domains may not adequately accommodate the complexity of motor skills. Manipulating the task difficulty, both nominal and functional, and the contextual continuum may be a promising route for the practitioner.

2-[11C]thymidine positron emission tomography reproducibility in humans.

PURPOSE: To evaluate the reproducibility of 2-[11C]thymidine positron emission tomography (PET) scanning in patients with advanced intra-abdominal malignancies. PATIENTS AND METHODS: The reproducibility of 2-[11C]thymidine PET was studied by comparing interpatient and intrapatient variability (coefficient of variability, COV) of both blood and tissue data. Arterial plasma metabolite levels were measured using on-line sampling and high-pressure liquid chromatography. 2-[11C]Thymidine retention in tissue was measured as the standardized uptake value at the end of the scan (SUV(end)), the area under the time-activity curve (AUC(0-1 hour)), and the fractional retention of thymidine (FRT). A group of seven patients were scanned 1 week apart with no intervening anticancer therapy. RESULTS: There was interpatient variability in the levels of 2-[11C]thymidine and its main metabolite, 11CO2, in plasma. Variability in 2-[11C]thymidine PET data was greater between (COV: SUV(end) = 38%, AUC(0-1 hour) = 32%, FRT = 47%) than within (COV: SUV(end) = 8%, AUC(0-1 hour) = 2%, FRT = 9%) patients. There was a borderline significant difference between the paired tumor data for SUV(end) (P = 0.041), but not for AUC(0-1 hour) (P = 0.81) or FRT (P = 0.90). There was a good correlation between paired data for SUV(end) (r = 0.98), AUC(0-1 hour) (r = 0.99), and FRT (r = 0.95). CONCLUSIONS: This is the first report showing that 2-[11C]thymidine PET scanning is reproducible in humans. Repeat scanning of tumor proliferation using 2-[11C]thymidine PET is feasible to perform in human intra-abdominal malignancies and should aid the future rapid assessment of antiproliferative tumor agents.

The uptake of 3'-deoxy-3'-[18F]fluorothymidine into L5178Y tumours in vivo is dependent on thymidine kinase 1 protein levels.

PURPOSE: The aim of this study was to investigate the role of thymidine kinase 1 (TK1) protein in 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) positron emission tomography (PET) studies. METHODS: We investigated the in vivo kinetics of [18F]FLT in TK1+/- and TK1-/- L5178Y mouse lymphoma tumours that express different levels of TK1 protein. RESULTS: [18F]FLT-derived radioactivity, measured by a dedicated small animal PET scanner, increased within the tumours over 60 min. The area under the normalised tumour time-activity curve were significantly higher for the TK1+/- compared with the -/- variant (0.89+/-0.02 vs 0.79+/-0.03 MBq ml(-1) min, P=0.043; n=5 for each tumour type). Ex vivo gamma counting of tissues excised at 60 min p.i. (n=8) also revealed significantly higher tumour [18F]FLT uptake for the TK1+/- variant (6.2+/-0.6 vs 4.6+/-0.4%ID g(-1), P=0.018). The observed differences between the cell lines with respect to [18F]FLT uptake were in keeping with a 48% higher TK1 protein in the TK1+/- tumours versus the -/- variant (P=0.043). On average, there were no differences in ATP levels between the two tumour variants (P=1.00). A positive correlation between [18F]FLT accumulation and TK1 protein levels (r=0.68, P=0.046) was seen. Normalisation of the data for ATP content further improved the correlation (r=0.86, P=0.003). CONCLUSION: This study shows that in vivo [18F]FLT kinetics depend on TK1 protein expression. ATP may be important in realising this effect. Thus, [18F]FLT-PET has the potential to yield specific information on tumour proliferation in diagnostic imaging and therapy monitoring.

18F-fluorothiols: a new approach to label peptides chemoselectively as potential tracers for positron emission tomography.

[(18)F]Fluorothiols are a new generation of peptide labeling reagents. This article describes the preparation of suitable methanesulfonyl precursors and their use in no-carrier-added radiosyntheses of (18)F-fluorothiols. The preparations of (3-[(18)F]fluoropropylsulfanyl)triphenylmethane, (2-[2-[2-(2-[(18)F]fluoroethoxy)ethoxy]ethoxy]ethylsulfanyl)triphenylmethane, and 4-[(18)F]fluoromethyl-N-[2-triphenylmethanesulfanyl)ethyl]benzamide starting from the corresponding methanesulfonyl precursors were investigated. Following the removal of the triphenylmethane protecting group, the (18)F-fluorothiols were reacted with the N-terminal chloroacetylated model peptide ClCH(2)C(O)-LysGlyPheGlyLys. The corresponding radiochemical yields of (18)F-labeled isolated model peptide, decay-corrected to (18)F fluoride, were 10%, 32%, and 1%, respectively. These results indicate a considerable potential of (18)F-fluorothiols for the chemoselective labeling of peptides as tracers for positron emission tomography (PET).

Contextual interference: a meta-analytic study.

A meta-analysis of the contextual interference effect produced 139 estimates of effect sizes from 61 studies. The average overall effect size was .38. The effect size for basic research (.57) was significantly different from applied research (.19). Significant differences were also obtained between the effect sizes for adults (.50) and those for younger learners (.10). Power for retention and transfer scores was not significantly different. The overall mean power of the studies reviewed was .43.

Radiosynthesis of 4-[(2-chloroethyl)(2-[(11)C]ethyl)amino]-phenoxycarbonyl-l-glutamic acid a half mustard prodrug as a potential probe for imaging antibody- and gene-directed enzyme prodrug therapy with positron emission tomography.

The potential antibody directed prodrug therapy half-mustard prodrug 4-[(2-chloroethyl)(2-ethyl)amino]-phenoxycarbonyl-L-glutamic acid was synthesised by reductive alkylation of 4-[(2-chloroethyl)amino]-phenoxycarbonyl-L-glutamic acid using acetaldehyde. 4-[(2-chloroethyl)[(11)C](2-ethyl)amino]phenoxycarbonyl-L-glutamic acid was synthesized with 18-22% decay corrected radiochemical yield in 45 min from EOB by reductive alkylation of 4-[(2-chloroethyl)amino]-phenoxycarbonyl-L-glutamic acid using [(11)C]acetaldehyde. [(11)C]Acetaldehyde was prepared in 60% decay corrected radiochemical yield by oxidation of [(11)C]ethanol over heated copper oxide. The radiosynthesis of [(11)C]ethanol was re-examined and optimized. 4-[(2-chloroethyl)(2-ethyl)amino]-phenoxycarbonyl-L-glutamic acid was found to have affinity for carboxypeptidase G2; the K(m) and V(max) were 99.4-115.9 microM (n=3) and 3.6-5.0 microM/min, respectively, at a carboxypeptidase G2 concentration of 0.0247 U/ml.

3'-deoxy-3'-[18F]fluorothymidine as a new marker for monitoring tumor response to antiproliferative therapy in vivo with positron emission tomography.

3'-Deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) has been proposed as a new marker for imaging tumor proliferation by positron emission tomography (PET). The uptake of [(18)F]FLT is regulated by cytosolic S-phase-specific thymidine kinase 1 (TK1). In this article, we have investigated the use of [(18)F]FLT to monitor the response of tumors to antiproliferative treatment in vivo. C3H/Hej mice bearing the radiation-induced fibrosarcoma 1 tumor were treated with 5-fluorouracil (5-FU; 165 mg/kg i.p.). Changes in tumor volume and biodistribution of [(18)F]FLT and 2-[(18)F]fluoro-2-deoxy-D-glucose ([(18)F]FDG) were measured in three groups of mice (n = 8-12/group): (a) untreated controls; (b) 24 h after 5-FU; and (c) 48 h after 5-FU. In addition, dynamic [(18)F]FLT-PET imaging was performed on a small animal scanner for 60 min. The metabolism of [(18)F]FLT in tumor, plasma, liver, and urine was determined chromatographically. Proliferation was determined by staining histological sections for proliferating cell nuclear antigen (PCNA). Tumor levels of TK1 protein and cofactor (ATP) were determined by Western blotting and bioluminescence, respectively. Tumor [(18)F]FLT uptake decreased after 5-FU treatment (47.8 +/- 7.0 and 27.1 +/- 3.7% for groups b and c, respectively, compared with group a; P < 0.001). The drug-induced reduction in tumor [(18)F]FLT uptake was significantly more pronounced than that of [(18)F]FDG. The PET image data confirmed lower tumor [(18)F]FLT retention in group c compared with group a, despite a trend toward higher radiotracer delivery for group c. Other than phosphorylation in tumors, [(18)F]FLT was found to be metabolically stable in vivo. The decrease in tumor [(18)F]FLT uptake correlated with the PCNA-labeling index (r = 0.71, P = 0.031) and tumor volume changes after 5-FU treatment (r = 0.58, P = 0.001). In this model system, the decrease in [(18)F]FLT uptake could be explained by changes in catalytic activity but not translation of TK1 protein. Compared with group a, TK1 levels were lower in group b (78.2 +/- 5.2%) but higher in group c (141.3 +/- 9.1%, P < 0.001). In contrast, a stepwise decrease in ATP levels was observed from group a to b to c (P < 0.001). In conclusion, we have demonstrated the ability to measure tumor response to antiproliferative treatment with [(18)F]FLT and PET. In our model system, the radiotracer uptake was correlated with PCNA-labeling index. The decrease in [(18)F]FLT uptake after 5-FU was more pronounced than that of [(18)F]FDG. [(18)F]FLT is, therefore, a promising marker for monitoring antiproliferative drug activity in oncology that warrants additional testing.

Metabolic activation of temozolomide measured in vivo using positron emission tomography.

The purpose of this research was to quantitate and confirm the mechanism of in vivo metabolic activation of temozolomide. The secondary aims were to evaluate the tumor, normal tissue, and plasma pharmacokinetics of temozolomide in vivo, and to determine whether such pharmacokinetics resulted in tumor targeting. [(11)C]temozolomide kinetics were studied in men using positron emission tomography (PET). It has been postulated that temozolomide undergoes decarboxylation and ring opening in the 3-4 position to produce the highly reactive methyldiazonium ion that alkylates DNA. To investigate this, a dual radiolabeling strategy, with [(11)C]temozolomide separately radiolabelled in the 3-N-methyl and 4-carbonyl positions, was used. We hypothesized that (11)C in the C-4 position of [4-(11)C-carbonyl]temozolomide would be converted to [(11)C]CO(2) if the postulated mechanism of metabolic conversion was true resulting in lower [(11)C]temozolomide tumor exposure. Paired studies were performed with both forms of [(11)C]temozolomide in 6 patients with gliomas. Another PET scan with (11)C-radiolabelled bicarbonate was performed and used to account for the metabolites of temozolomide using a data-led analytical approach. Plasma was analyzed for [(11)C]temozolomide and [(11)C]metabolites throughout the scan duration. Exhaled air was also sampled throughout the scan for [(11)C]CO(2). The percentage ring opening of temozolomide over 90 min was also calculated to evaluate whether there was a differential in metabolic breakdown among plasma, normal tissue, and tumor. There was rapid systemic clearance of both radiolabelled forms of [(11)C]temozolomide over 90 min (0.2 liter/min/m(2)), with [(11)C]CO(2) being the primary elimination product. Plasma [(11)C]CO(2) was present in all of the studies with [4-(11)C-carbonyl]temozolomide and in half the studies with [3-N-(11)C-methyl]temozolomide. The mean contributions to total plasma activity by [(11)C]CO(2) at 10 and 90 min were 12% and 28% with [4-(11)C-carbonyl]temozolomide, and 1% and 4% with [3-N-(11)C-methyl]temozolomide, respectively. There was a 5-fold increase in exhaled [(11)C]CO(2) sampled with [4-(11)C-carbonyl]temozolomide compared with [3-N-(11)C-methyl]temozolomide (P < 0.05). A decrease in tissue exposure [area under the curve between 0 and 90 min (AUC(0-90 min))] to [(11)C]temozolomide was also observed with [4-(11)C-carbonyl] temozolomide compared with [3-N-(11)C-methyl]temozolomide. Of potential therapeutic advantage was the higher [(11)C]radiotracer and [(11)C]temozolomide exposure (AUC(0-90 min)) in tumors compared with normal tissue. [(11)C]temozolomide ring opening over 90 min was less in plasma (20.9%; P < 0.05) compared with tumor (26.8%), gray matter (29.7%), and white matter (30.1%), with no differences (P > 0.05) between tumor and normal tissues. The significantly higher amounts of [(11)C]CO(2) sampled in plasma and exhaled air, in addition to the lower normal tissue and tumor [(11)C]temozolomide AUC(0-90 min) observed with [4-(11)C-carbonyl]temozolomide, confirmed the postulated mechanism of metabolic activation of temozolomide. A higher tumor [(11)C]temozolomide AUC(0-90 min) in tumors compared with normal tissue and the tissue-directed metabolic activation of temozolomide may confer potential therapeutic advantage in the activity of this agent. This is the first report of a clinical PET study used to quantify and confirm the in vivo mechanism of metabolic activation of a drug.

Applications of positron-emitting halogens in PET oncology (Review).

The positron-emitting radiohalogens 18F, 75Br, 76Br, and 124I are reviewed regarding their relevance for positron emission tomography (PET) in oncology. Relevant production routes of these cyclotron-generated isotopes are given, followed by publications that deal with applications of these radiohalogens. This article tries to cover the whole literature for the non-conventional isotopes 75Br, 76Br, and 124I. From the literature on 18F, only articles since 2000 are considered. Here, the emphasis is also given to alternative biomarkers beyond [18]2-fluoro-2-deoxyglucose ([18F]FDG).

Iodine-124 labelled annexin-V as a potential radiotracer to study apoptosis using positron emission tomography.

Annexin-V is a calcium-dependent protein that binds with high affinity to phosphaditylserine exposed during apoptosis. The aim of this study was to radiolabel annexin-V with iodine-124 for use as a potential probe of apoptosis by positron emission tomography. Annexin-V was radioiodinated directly using the cyclotron-produced positron emitter iodine-124 by the chloramine-T (CAT) method and indirectly by the pre-labelled reagent N-succinimidyl 3-[124I]iodobenzoate ([124I]m-SIB). Some reaction parameters of the CAT method such as reaction time and pH were optimised to give radiochemical yields of 22.3 +/- 2.6%(n = 3, gel-filtration). After incubation with [124I]m-SIB, radiolabelled annexin-V was obtained in 14% and 25% yield by FPLC and gel-filtration, respectively. The radiochemical purities from direct and indirect labelling were 97.7 +/- 1.0%(n = 3) and 96.7 +/- 2.1%(n = 3), respectively. The new radiotracers could be stored for up to four days without significant de-iodination. The biological activity of radiolabelled annexin-V was tested in control and camptothecin-treated (i.e. apoptotic) human leukaemic HL60 cells. A significantly higher (21%) binding in treated cells was observed with [125I]m-SIB-annexin-V. The binding of [125I]m-SIB labelled annexin-V to camptothecin treated cells was blocked (68%) by a 100-fold excess of unlabelled annexin-V.

Antitumor imidazotetrazines. 40. Radiosyntheses of [4-11C-carbonyl]- and [3-N-11C-methyl]-8-carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-one (temozolomide) for positron emission tomography (PET) studies.

8-Carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-one (temozolomide, 1) is an anticancer prodrug. As part of investigations to probe its postulated mode of action using PET we have developed two rapid radiosynthetic routes for the preparation of temozolomide labeled with the short-lived positron emitter, carbon-11 (t(1/2) = 20.4 min). Reaction of 5-diazoimidazole-4-carboxamide (7) with the novel labeling agent [(11)C-methyl]methyl isocyanate (8) gave [3-N-(11)C-methyl]temozolomide (9) in 14-20% radiochemical yield from [(11)C-methyl]methyl isocyanate (8) (decay corrected). The position of radiolabeling in the 3-N-methyl group was confirmed by [(11/13)C]colabeling and subsequent carbon-13 NMR spectroscopy. Similarly, the reaction of 5-diazoimidazole-4-carboxamide (7) with [(11)C-carbonyl]methyl isocyanate (10) gave [4-(11)C-carbonyl]temozolomide (11) in 10-15% radiochemical yield from [(11)C-carbonyl]methyl isocyanate (10) (decay corrected). Apyrogenic samples of [3-N-(11)C-methyl]temozolomide (9) and [4-(11)C-carbonyl]temozolomide (11), with good chemical and radiochemical purities, have been prepared and used in human PET studies.

The development of [(124)I]iodinated-VG76e: a novel tracer for imaging vascular endothelial growth factor in vivo using positron emission tomography.

The development of anticancer therapies that target the angiogenic process is an area of major growth in oncology. A method of noninvasively measuring tumor vascular endothelial growth factor (VEGF) in vivo could provide important efficacy information for VEGF-dependent antiangiogenic agents and the role of VEGF in cancer biology. We have developed a novel radiotracer for use with positron emission tomography (PET) that enables noninvasive imaging of VEGF. This radiotracer comprises an IgG1 monoclonal antibody, known as VG76e, that binds to human VEGF, labeled with a positron-emitting radionuclide, iodine-124 ([(124)I]-SHPP-VG76e). Three radiolabeling strategies were evaluated to synthesize the radiotracer with optimal radiochemical yield, purity, and immunoreactivity. To evaluate the pharmacokinetics and VEGF-specific localization of [(124)I]-SHPP-VG76e, two subclones of the HT1080 human fibrosarcoma selected on the basis of differing VEGF production (26.6 and 1/3C, the former producing 2-4-fold more in vitro) were established in culture and grown as solid tumor xenografts in immune-deficient mice. A single i.v. injection of the radiotracer into tumor-bearing mice revealed a time dependent and specific localization of [(125)I]-SHPP-VG76e to the tumor tissue. Three validation studies established the VEGF specificity and potential for use of [(124)I]-SHPP-VG76e in vivo: (a) uptake of [(125)I]-SHPP-VG76e was 1.8-fold higher in HT1080-26.6 compared with HT1080-1/3C tumors (P < 0.05); (b) uptake of [(125)I]-SHPP-VG76e in HT1080-26.6 tumors was specifically blocked by prior administration of excess unlabeled VG76e (P < 0.05); and (c) tumor uptake of the IgG1, [(125)I]-SHPP-CIP5, which has a similar molecular weight as [(125)I]-SHPP-VG76e but does not recognize VEGF, was the same for both HT1080-26.6 and HT1080-1/3C (P > 0.05). Other than tumor localization, [(125)I]-SHPP-VG76e was present in urine and blood and to a lesser extent in heart, lungs, liver, kidney, and spleen. Whole-animal PET imaging studies revealed a high tumor-to-background contrast and also revealed [(124)I]-SHPP-VG76e distributions in the major organs. These studies support further development of [(124)I]-SHPP-VG76e as a radiotracer for measuring tumor levels of VEGF in humans.

Assessment of proliferation in vivo using 2-[(11)C]thymidine positron emission tomography in advanced intra-abdominal malignancies.

The purpose of this study was to determine the relationship between 2-[(11)C]thymidine positron emission tomography (PET) in vivo-derived parameters and the ex vivo Ki-67 index of proliferation in human tumors. The study comprised 17 treatment-naïve patients with advanced intra-abdominal malignancies. Tumor thymidine kinetics were measured using 2-[(11)C]thymidine PET. Tissue data were analyzed to give the standardized uptake value, the area under the time activity curve, and the fractional retention of thymidine (FRT) obtained by kinetic modeling. For the latter, the contribution of labeled metabolites was accounted for by measuring thymidine metabolites in arterial plasma. To examine the influence of tumor blood flow on the thymidine PET data, a perfusion scan using inhaled [(15)O]CO(2) was carried out in a subset of 11 patients. Biopsies were stained with a MIB1 antibody to obtain a Ki-67 index, and correlations with the PET-derived parameters were investigated. There was no relationship between tumor blood flow and the thymidine PET data, showing that the retention of 2-[(11)C]thymidine in tumors was independent of tumor perfusion. There was no correlation between the Ki-67 index and either standard uptake value or area under the curve. There was a correlation between the Ki-67 index and FRT (r = 0.58; P = 0.01). The correlation between the Ki-67 index and FRT in this dataset was not influenced by the interval between biopsy and imaging (0.1-126 weeks), the origin of the biopsy for Ki-67 staining (primary tumor or metastasis), or whether the biopsy was from an imaged or a nonimaged tumor. This is the first report in human tumors showing that 2-[(11)C]thymidine PET-derived parameters correlate with the level of tumor proliferation measured using Ki-67 immunohistochemistry. The study shows that the in vivo measurement of 2-[(11)C]thymidine in tumors using PET can provide a surrogate marker of proliferation and supports the potential use of the technique in the early assessment of response to antiproliferative cancer treatment.