The future of clinical trials for Alzheimer's disease. A blood-based biomarker perspective

Abstract: Objectives: The primary objective was to investigate the utility of blood-basedbiomarkers of amyloid, tau, and neurodegeneration for (i) screening, (ii)enrichment, and (iii) tracking response to treatment in clinical trials of Alzheimer’sdisease.Methods: Longitudinal, participant-level data used in these studies was drawn fromthe Swedish BioFINDER study and the ADNI study. Participants were classified ascognitively unimpaired, mild cognitive impairment, or Alzheimer’s diseasedementia. For screening, logistic regression was used to predict amyloid PET statusin CU individuals from plasma Aβ42/Aβ40, APOE status, and age. For enrichment,Linear mixed effects models were used to predict longitudinal cognitive decline andfuture risk of AD dementia in CU individuals or in MCI individuals from a basicmodel (age, sex, education, APOE status) and varying combinations of blood-basedbiomarkers (plasma Aβ42/Aβ40, plasma pTau181, plasma pTau217, plasma NfL).For treatment response, plasma NfL was measured longitudinally in MCI or ADpatients and properties such as slope, inter-subject variability, and intra-subjectvariability were calculated. Plasma NfL was then compared with MRI andcognition.Results: The amyloid PET screening model had an AUC of 0.87, with a significantindependent effect for plasma Aβ42/Aβ40 and APOE status, but not age. This modelwas estimated to reduce total cost of recruiting 500 amyloid-positive CUparticipants by 31 – 42%, depending on the relative cost of amyloid scanning toplasma measurement. For enrichment, plasma pTau181 and pTau217 had the largesteffect on predicting cognitive decline in CU and MCI participants, with Aβ42/Aβ40and NfL having significant effects in some scenarios. Using these biomarkers in aclinical trial could reduce the required sample size of a clinical trial in CUparticipants by up to 70%. Finally, plasma NfL was shown to have worse theoreticalperformance as a trial progression marker compared to MRI-based measures,primarily due to its high within-subject variability. NfL compared better to cognitivemeasures as endpoints.Discussion: The future of AD clinical trials will likely leverage plasma biomarkersfor initial screening. Their utility for enrichment and tracking treatment responsestill needs to be evaluated in the context of other biomarkers measured in CSF, MRI,or PET. The plasma ATN biomarkers evaluated here all appear to be independentlyuseful, but there is strong potential for more plasma biomarkers to be added to sucha panel.