Phase 3 randomized clinical trials of simufilam in mild-to-moderate Alzheimer's disease

Soluble amyloid β_1-42 (Aβ₄₂) signals via the α7 nicotinic acetylcholine receptor to hyperphosphorylate tau in Alzheimer's disease (AD). Simufilam disrupts this pathogenic signaling by binding filamin A and disrupts its linkages with inflammatory receptors to reduce neuroinflammation. We assessed simufilam in two Phase 3 clinical trials in mild-to-moderate AD.

Participants were age 50-87 with Stage 4 or 5 CE, a mini-mental state exam (MMSE) ≥16 and ≤27 and a Clinical Dementia Rating Global Score (CDR-GS) of 0.5, 1 or 2. The criterion supporting AD pathology was plasma phosphorylated (p)-tau181 or prior amyloid PET. RETHINK randomized participants to simufilam 100 mg or placebo for 52 weeks. REFOCUS evaluated simufilam 50 and 100 mg versus placebo for 76 weeks. Co-primary endpoints were change from baseline on ADAS-Cog12 and ADCS-ADL. Sub-studies assessed exploratory plasma biomarkers and, in REFOCUS only, CSF and imaging biomarkers.

Both trials failed to meet co-primary, secondary or exploratory biomarker endpoints. REFOCUS was terminated early, with 22% of participants still active in the trial. In the predefined mild subgroup in REFOCUS, simufilam was associated with slower cognitive decline than placebo through Week 64 (p = 0.019). This finding disappeared at Week 76 with 45% missing data and did not replicate in RETHINK. Favorable nominal exploratory post-hoc findings amongst participants with the highest half of screening plasma p-tau181 levels occurred in RETHINK but not REFOCUS. The plasma p-tau181 entry criterion did not reliably exclude amyloid PET negativity in the sub-study.

Simufilam did not meet co-primary or secondary endpoints in these Phase 3 trials. Simufilam was safe and well tolerated. Trials registered at clinicaltrials.gov: NCT04994483 and NCT05026177.