Clinical Effects of Tramiprosate in APOE4/4 Homozygous Patients with Mild Alzheimer's Disease Suggest Disease Modification Potential

BACKGROUND: Alzheimer's Disease (AD) patients homozygous for the APOE4 allele (APOE4/4) have a distinct clinical and biological phenotype with high levels of beta amyloid (AN pathology and toxic A beta oligomers. Tramiprosate, an oral agent that inhibits A beta monomer aggregation into toxic oligomers, was evaluated in two Phase 3 Mild to Moderate AD studies which did not show efficacy in the overall population. Re-analyses of these trials showed the most consistent clinical benefits in APOE4/4 patients. We analyzed efficacy in the APOE4/4 patients with Mild disease. OBJECTIVES: To determine the optimal stage of AD for future trials in APOE4/4 homozygotes. DESIGN: Two randomized, double-blind, placebo-controlled parallel-arm multi-center studies of 78-weeks duration. SETTING: Academic Alzheimer's disease centers, community based memory dines, and neuropsychiatric research sites. PARTICIPANTS: Participants included 2,025 AD patients with MMSE 16-26. Approximately 13-15% had APOE4/4 genotype (N= 147 and 110 per study), mean age 71.1 years, 56% females. Almost all were on stable symptomatic drugs. INTERVENTION: Randomized subjects received oral placebo, 100mg BID, or 150mg BID of tramiprosate. MEASUREMENTS: Co-primary outcomes were change from baseline in the ADAS-cogll and CDR-SB. Disability assessment for dementia (DAD) was a secondary outcome. RESULTS: In APOE4/4 homozygotes receiving 150mg BID tramiprosate, efficacy in the traditional Mild AD patients (MMSE 20-26) was higher than the overall group (MMSE 16-26) and efficacy in the Mild patients (MMSE 22-26) was highest. Tramiprosate benefits compared to placebo on ADAS-cog, CDR-SB, and DAD were 125%, 81% and 71%, respectively (p<0.02). The Mild subgroup (MMSE 22-26) showed cognitive stabilization with no decline over 78 weeks, both ADAS-cog and DAD effects increased over time. Tramiprosate safety in APOE4/4 patients was favorable. Most common adverse events were nausea, vomiting, depression and decreased weight. CONCLUSIONS: The Mild subgroup of APOE4/ 4 AD patients (MMSE 22-26) showed larger benefits on the high dose of tramiprosate than the overall Mild and Moderate group. Consistent with its preclinical effects on A beta oligomers, tramiprosate seemed to stabilize cognitive performance, supporting its disease modification potential. Confirmatory studies using ALZ-801, an improved pro-drug formulation of tramiprosate, will target APOE4/4 patients with Mild AD.