Plasma PTau181 Predicts Clinical Progression in a Phase 2 Randomized Controlled Trial of the 11β-HSD1 Inhibitor Xanamem® for Mild Alzheimer's Disease

Background: Blood biomarkers are proposed as a diagnostic alternative to amyloid PET or cerebrospinal fluid (CSF) analyses for the diagnosis of Alzheimer's disease (AD). Relatively little is known of the natural history of patients identified by different blood biomarkers.

Objective: To identify patients with elevated plasma phosphorylated tau (pTau)181 from a prior Phase 2a trial, and explore the natural histories of their clinical progression, and potential efficacy of Xanamem, a selective inhibitor of 11beta-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in these patients.

Methods: A prespecified, double-blind analysis was conducted in 72 participants with clinically diagnosed AD and available plasma samples from baseline and Week 12 of the "XanADu" Phase 2a trial of Xanamem versus placebo. The analysis prespecified plasma pTau181 > median to identify patients more likely to have AD ("H", > 6.74 pg/mL, n = 34). Cohen's d (d) of≥0.2 defined potential clinical significance.

Results: In the placebo group, H patients showed greater clinical progression compared to L patients (pTau181≤median) on ADCOMS (d = 0.55, p < 0.001), CDR-SB (d = 0.63, p < 0.001), MMSE (d = 0.52, p = 0.12), and ADAS-Cog14 (d = 0.53, p = 0.19). In H patients, a potentially clinically meaningful Xanamem treatment effect compared to placebo was seen in the CDR-SB (LS mean difference 0.6 units, d = 0.41, p = 0.09) and Neuropsychological Test Battery (NTB; LS mean difference 1.8 units, d = 0.26, p = 0.48) but not ADCOMS or ADAS-Cog14.

Conclusions: This trial demonstrates that elevated plasma pTau181 identifies participants more likely to have progressive AD and is a suitable method for enrichment in AD clinical trials. Xanamem treatment showed evidence of potential clinically meaningful benefits.