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The goal of this study was to identify the optimal combination of magnetic resonance imaging (MRI), [18F]-fluorodeoxyglucose positron emission tomography (FDG-PET), and cerebrospinal fluid (CSF) biomarkers to predict conversion from amnestic mild cognitive impairment (aMCI) to Alzheimer's disease (AD) dementia within two years, for enriching clinical trial populations. Data from 63 subjects in the Alzheimer's Disease Neuroimaging Initiative aMCI cohort who had MRI and FDG-PET imaging along with CSF data at baseline and at least two years clinical follow-up were used. A Bayesian classification method was used to determine which combination of 31 variables (MRI, FDG-PET, CSF measurements, apolipoprotein E (ApoE) genotype, and cognitive scores) provided the most accurate prediction of aMCI to AD conversion. The cost and time trade-offs for the use of these biomarkers as inclusion criteria in clinical trials were evaluated. Using the combination of all biomarkers, ApoE genotype, and cognitive scores, we achieved an accuracy of 81% in predicting aMCI to AD conversion. With only ApoE genotype and cognitive scores, the prediction accuracy decreased to 62%. By comparing individual modalities, we found that MRI measures had the best predictive power (accuracy = 78%), followed by ApoE, FDG-PET, CSF, and the Alzheimer's disease assessment scale-cognitive subscale. The combination of biomarkers from different modalities, measuring complementary aspects of AD pathology, provided the most accurate prediction of aMCI to AD conversion within two years. This was predominantly driven by MRI measures, which emerged as the single most powerful modality. Overall, the combination of MRI, ApoE, and cognitive scores provided the best trade-off between cost and time compared with other biomarker combinations for patient recruitment in clinical trial.

IntroductionThe negative efficacy study examining the γ-secretase inhibitor semagacestat in mild to moderate Alzheimer's disease (AD) included a number of biomarkers of the disease as well as safety outcomes. We analyzed these data to explore relationships between drug exposure and pharmacodynamic effects and to examine the correlations among outcome measures.MethodsThe study was a multicenter, randomized, placebo-controlled trial of two dose regimens of semagacestat and a placebo administered for 18 months to individuals with mild to moderate AD. Changes in measures of central and peripheral drug activity were compared between the three treatment groups using one-way analysis of variance. The relationship between changes in each of the outcome measures and measures of drug exposure and peripheral pharmacodynamic effect were assessed using Spearman's correlation coefficient.ResultsAssignment to the active treatment arms was associated with reduction in plasma amyloid-β (Aβ) peptides, increase in ventricular volume, decrease in cerebrospinal fluid phosphorylated tau (p-tau) and several other laboratory measures and adverse event categories. Within the active arms, exposure to drug, as indicated by area under the concentration curve (AUC) of blood concentration, was associated with reduction in plasma Aβ peptides and a subset of laboratory changes and adverse event rates. Ventricular volume increase, right hippocampal volume loss and gastrointestinal symptoms were related to change in plasma Aβ peptide but not AUC, supporting a link to inhibition of γ-secretase cleavage of the amyloid precursor protein. Cognitive decline correlated with ventricular expansion and reduction in p-tau.ConclusionThese findings may inform future studies of drugs targeting secretases involved in Aβ generation.Trial registrationClinicalTrials.gov Identifier: NCT00594568. Registered 11 January 2008.

Tau measurements in cerebrospinal fluid (CSF) are gaining acceptance as aids to diagnosis of Alzheimer's disease (AD) and differentiation from other dementias. Two ELISA assays, the INNOTEST® hTAU Ag and the INNOTEST® PHOSPHO-TAU(181P) for quantification of t-tau and p-tau181 respectively, have been validated to regulatory standards. Validation parameters were determined by repeated testing of human CSF pools. Specimens from Phase 2 studies of the γ-secretase inhibitor semagacestat and the therapeutic antibody solanezumab at baseline and following 12-14 weeks of treatment were also tested. Estimated intra-assay CV for repeated testing of 3 CSF pools were ≤11.5% and RE varied between -14.1% and +6.4%. Inter-assay CV for t-tau was <5% and RE was within ±8%. For p-tau181, inter-assay CV was <9% and RE was within ±2.5%. Total CV (intra-assay plus inter-assay) were below 10% for both analytes. Up to 20-fold dilutional linearity was demonstrated for both analytes. Stability of t-tau and p-tau181 was demonstrated in CSF during five freeze-thaw cycles at ≤-20°C and ≤-70°C and at 18-22°C for up to 24 h. Neither semagacestat nor solanezumab interfered with either assay. Inter-individual t-tau and p-tau181 concentrations were highly variable but intra-individual variations were small. These assays are suitable for analysis of CSF t-tau and p-tau181 in a single laboratory supporting multi-center AD clinical trials. No effect of treatment with semagacestat or solanezumab was observed in response to three months of drug administration. [ABSTRACT FROM AUTHOR]

Background: Comparison of disease progression between placebo-group patients from randomised controlled trials (RCTs) and real-world patients can aid in assessing the generalisability of RCT outcomes. This analysis compared outcomes between community-dwelling patients with mild Alzheimer's disease (AD) dementia from two RCTs (pooled European (EU) data from EXPEDITION and EXPEDITION 2) and similar patients from the EU GERAS observational study. Methods: Data from placebo-group patients with mild AD dementia from the RCTs (EU countries only) were compared with data from GERAS patients with mild AD dementia. Between-group differences for changes over 18 months were analysed for cognition, functioning, neuropsychiatric symptoms, health-related quality of life (HRQoL) and caregiver time using propensity score-adjusted models. A sensitivity analysis compared EU/North American (EU/NA) EXPEDITION patients with GERAS patients. Results: EU EXPEDITION patients (n = 168) were younger than GERAS patients (n = 566) (mean (standard deviation, SD) age 71.9 (7.4) versus 77.3 (6.9) years; p < 0.001) and were more likely to use AD treatment (95% versus 84%; p < 0.001). Cognitive performance was similar at baseline in both populations, although GERAS patients showed greater functional impairment (p = 0.005) and lower HRQoL (p < 0.05). At 18 months, no statistically significant differences between EXPEDITION (n = 133) and GERAS (n = 417) patients were observed for changes in cognitive, functional, neuropsychiatric and HRQoL outcomes. Least squares mean (95% confidence interval) change in caregiver time (hours/month) spent on instrumental activities of daily living (iADL; 29.22 (19.16, 39.27) versus 3.20 (−11.89, 18.28), p = 0.001) and supervision (66.59 (47.49, 85.69) versus 3.04 (−25.39, 31.48), p < 0.001) showed greater increases in GERAS than EXPEDITION. In the sensitivity analysis, changes in neuropsychiatric and HRQoL scores and caregiver time spent on basic ADL were also significantly greater in GERAS than in EU/NA EXPEDITION patients. Conclusions: Patients with mild AD dementia participating in the EU EXPEDITION RCTs and the GERAS observational study showed a similar decline in cognitive, functional and neuropsychiatric symptoms over 18 months, whereas changes in caregiver time measures were significantly greater in GERAS. Results indicate the importance of using similar regions when comparing real-world and RCT data. Trial registration: ClinicalTrials.gov NCT00905372 EXPEDITION. Registered 18 May 2009. ClinicalTrials.gov NCT00904683 EXPEDITION 2. Registered 18 May 2009. [ABSTRACT FROM AUTHOR]