Arginine-glycine-aspartate (RGD)-binding a V b 3 -integrin and a V b 5 -integrin play key roles in tumor angiogenesis. We examined an 18 F-labeled small peptide (fluciclatide [United States Adopted Name (ASAN)-approved, International Nonproprietary Name (INN)-proposed name], previously referred to as AH111585) containing an RGD sequence. Fluciclatide binds with a high (nM) affinity to a V b 3 -integrin and a V b 5 -integrin, which are highly expressed on tumors and the tumor neovasculature. In this study, 18 F-fluciclatide was used to examine the response of human glioblastoma xenografts to treatment with the antiangiogenic agent sunitinib. Methods: U87-MG tumor uptake of 18 F-fluciclatide was determined by small-animal PET after longitudinal administration of the antiangiogenic agent sunitinib (a 2-wk dosing regimen). Tumor sizes were measured throughout the study, and tumor volumes were calculated. Tumor microvessel density (MVD) after therapy was also analyzed. Results: Dynamic small-animal PET of 18 F-fluciclatide uptake after administration of the clinically relevant antiangiogenic agent sunitinib revealed a reduction in the tumor uptake of 18 F-fluciclatide compared with that in vehicle-treated controls over the 2-wk dosing regimen. Skeletal muscle, used as a reference tissue, showed equivalent 18 F-fluciclatide uptake in both therapy and control groups. A reduction in tumor MVD was also observed after treatment with the antiangiogenic agent. No significant changes in tumor volume were observed in the 2 groups. Conclusion: The data demonstrated that 18 F-fluciclatide detected changes in tumor uptake after acute antiangiogenic therapy markedly earlier than any significant volumetric changes were observable. These results suggest that this imaging agent may provide clinically important information for guiding patient care and monitoring the response to antiangiogenic therapy. Int egrins are a family of cell adhesion molecules consisting of 2 noncovalently bound transmembrane subunits, a and b, that form heterodimers with distinct adhesive capabilities (1). In mammals, 18 a and 8 b subunits assemble into 24 different receptors. Integrins play important roles in several pathologic processes, such as inflammation, fibrosis, tumor metastasis, and angiogenesis (2,3).Angiogenesis, the process of forming new blood vessels from existing vessels (4), is central to normal biologic processes, such as embryogenesis, tissue remodeling, inflammation, and wound healing, and is present in numerous disease states, including rheumatoid arthritis, psoriasis, restenosis, diabetic retinopathy, and tumor growth (5-7). The interest in angiogenesis research has been fueled by the potential to develop antiangiogenic drugs as novel therapeutic agents for targeting tumors and several nononcologic diseases. a V b 3 -integrin and a V b 5 -integrin act as receptors for a variety of proteins expressing the exposed arginine-glycineaspartate (RGD) tripeptide sequence, such as vitronectin, fibronectin, fibrinogen, laminin, collagen, Von Will...

IntroductionA standardised method for quantifying β-amyloid PET tracers would allow comparison across different tracers and different sites. The development of the Centiloid scale has aimed to achieve this, applying a common scale to better aid the diagnosis and prognosis of Alzheimer’s disease (AD) and to monitor anti-amyloid therapeutic interventions. Here, we apply the Centiloid method to [18F]flutemetamol and [11C]PiB (PiB, Pittsburgh compound B) PET images and derive the scaling factor to express their binding in Centiloids.MethodsPaired PiB and [18F]flutemetamol scans for 74 subjects, including 24 young healthy controls (37 ± 5 years), were analysed using the standard Centiloid method. The same subjects were also analysed using PMOD- and FSL-based pipelines as well as SPM8. Test-retest analysis of 10 AD subjects was also performed with each pipeline.ResultsThe standard uptake value ratios (SUVR), determined using the standard SPM8 Centiloid process, showed a strong correlation between [18F]flutemetamol (Flute) and PiB binding (SUVR-Flute = 0.77 × SUVR-PiB + 0.22, R2 = 0.96). Application of the standard Centiloid process allowed the calculation of a direct conversion equation for SUVR-Flute to Centiloid units (CL) (CL = (121.42*SUVR-Flute) − 121.16). Analysis of the data via the two alternate Centiloid pipelines allowed us to derive standardised, SPM8-equivalent equations for both PMOD (CL = (115.24*SUVR-Flute) − 107.86) and FSL (CL = (120.32*SUVR-Flute) − 112.75) respectively. Test-retest analysis of 10 AD subjects showed an approximate 2% difference for each pipeline.Conclusions[18F]flutemetamol data can now be expressed in Centiloid units, enhancing its utility in clinical and research applications for β-amyloid imaging. The standard Centiloid method also demonstrates that [18F]flutemetamol has favourable performance compared with PiB and other β-amyloid tracers. Test-retest difference averaged 2%, with no difference between image processing pipelines. Centiloid scaling is robust and can be implemented on a number of platforms.

Amyloid-β (Aβ) pathology is one of the earliest detectable brain changes in Alzheimer’s disease (AD) pathogenesis. The overall load and spatial distribution of brain Aβ can be determined in vivo using positron emission tomography (PET), for which three fluorine-18 labelled radiotracers have been approved for clinical use. In clinical practice, trained readers will categorise scans as either Aβ positive or negative, based on visual inspection. Diagnostic decisions are often based on these reads and patient selection for clinical trials is increasingly guided by amyloid status. However, tracer deposition in the grey matter as a function of amyloid load is an inherently continuous process, which is not sufficiently appreciated through binary cut-offs alone. State-of-the-art methods for amyloid PET quantification can generate tracer-independent measures of Aβ burden. Recent research has shown the ability of these quantitative measures to highlight pathological changes at the earliest stages of the AD continuum and generate more sensitive thresholds, as well as improving diagnostic confidence around established binary cut-offs. With the recent FDA approval of aducanumab and more candidate drugs on the horizon, early identification of amyloid burden using quantitative measures is critical for enrolling appropriate subjects to help establish the optimal window for therapeutic intervention and secondary prevention. In addition, quantitative amyloid measurements are used for treatment response monitoring in clinical trials. In clinical settings, large multi-centre studies have shown that amyloid PET results change both diagnosis and patient management and that quantification can accurately predict rates of cognitive decline. Whether these changes in management reflect an improvement in clinical outcomes is yet to be determined and further validation work is required to establish the utility of quantification for supporting treatment endpoint decisions. In this state-of-the-art review, several tools and measures available for amyloid PET quantification are summarised and discussed. Use of these methods is growing both clinically and in the research domain. Concurrently, there is a duty of care to the wider dementia community to increase visibility and understanding of these methods.

Introduction Two 7-fluoroimidazobenzodiazepines (AH114726 and GEH120348), analogs of flumazenil, were labeled with fluorine-18 and evaluated as alternative radioligands for in vivo imaging of the GABAA/benzodiazepine receptor by comparing them to [11C]flumazenil in rhesus monkey. Methods Radiotracers were prepared from the corresponding nitro-precursors in an automated synthesis module, and primate imaging studies were conducted on a Concorde MicroPET P4 scanner. The brain was imaged for 60 (12 × 5 min frames) or 90 min (18 × 5 min frames), and data was reconstructed using the 3D MAP algorithm. Specificity of [18F]AH114726 and [18F]GEH120348 was confirmed by displacement studies using unlabeled flumazenil. Results [18F]GEH120348 and [18F]AH114726 were obtained in 13–24% yields (end of synthesis) with high chemical (>95%) and radiochemical (>99%) purities, and high specific activities (2061 ± 985 Ci/mmol). The in vivo pharmacokinetics of [18F]AH114726 and [18F]GEH120348 were determined in a non-human primate and directly compared with [11C]flumazenil. Both fluorine-18 radioligands showed time-dependent regional brain distributions that correlated with the distribution of [11C]flumazenil and the known concentrations of GABAA/benzodiazepine receptors in the monkey brain. [18F]AH114726 exhibited maximal brain uptake and tissue time-radioactivity curves that were most similar to [11C]flumazenil. In contrast, [18F]GEH120348 showed higher initial brain uptake but very different pharmacokinetics, with continued accumulation of radioactivity into the cortical regions of high GABA/benzodiazepine receptor concentrations and very little clearance from the regions of low receptor densities. Rapid washout of both radiotracers occurred upon treatment with unlabeled flumazenil. Conclusion The ease of the radiochemical synthesis, together with in vivo brain pharmacokinetics most similar to [11C]flumazenil, support that [18F]AH114726 is a suitable option for imaging the GABAA receptor.

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ObjectiveTo evaluate a novel Aβ-PET based quantitative measure (Aβ accumulation index [Aβ-index]), including the assessment of its ability to discriminate between subjects based on Aβ-status using visual-read, CSF Aβ42/Aβ40 and post-mortem neuritic-plaque burden as standards of truth.MethodsOne thousand hundred twenty-one subjects (with and without cognitive impairment) scanned with Aβ-PET: Swedish BioFINDER, n = 392, [18F]flutemetamol; ADNI, n = 692, [18F]florbetapir; a phase-3 end-of-life study, n = 100, [18F]flutemetamol). The relationships between Aβ-index and standardized uptake values ratios (SUVR) from Aβ-PET were assessed. The diagnostic performance of Aβ-index and SUVR were compared when using visual reads, CSF Aβ42/Aβ40 and Aβ-histopathology as reference standards.ResultsStrong associations were observed between Aβ-index and SUVR (R2, BioFINDER, 0.951; ADNI, 0.943, end-of-life, 0.916). Both measures performed equally well in differentiating Aβ-positive from Aβ-negative subjects, with AUCs of 0.979–0.991 to detect abnormal visual reads, AUCs of 0.961–0.966 to detect abnormal CSF Aβ42/40 and AUCs of 0.820–0.823 to detect abnormal Aβ-histopathology. Both measures also showed a similar distribution across post-mortem based Aβ-phases (based on anti-Aβ 4G8 antibodies). By comparison to models using visual-read alone, the addition of the Aβ-index resulted in a significant increase in AUC and a decrease in Akaike information criterion to detect abnormal Aβ-histopathology.ConclusionThe proposed Aβ-index showed a tight association to SUVR and carries an advantage over the latter in that it does not require the definition of regions of interest nor the use of MRI. Aβ-index may thus prove simpler to implement in clinical settings and may also facilitate the comparison of findings using different Aβ-PET tracers.Classification of evidenceThis study provides Class III evidence that the Aβ accumulation index accurately differentiates Aβ-positive from Aβ-negative subjects when compared to Aβ-PET visual reads, CSF Aβ42/Aβ40 and Aβ-histopathology.

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