Synthetic Peptide P33 Cuts Amyloid Beta Release Over 50% in Neurons, Plaque Area 35.6% in APP/PS1 Mice

The study screened a 50-member library of cis-γ-amino-L-proline peptides for selective interference with BACE1-mediated APP cleavage. P33 emerged with >50% reduction in Aβ secretion, >50% drop in BACE1 activity, and minimal effect on the closely related BACE2 enzyme or cell viability in vitro. In vivo, eight-week intraperitoneal dosing in plaque-bearing mice produced the 35.6% plaque-area decrease without detectable organ toxicity or inflammatory-marker shifts.

Prior BACE1 inhibitors such as verubecestat achieved near-complete enzymatic blockade yet failed phase 3 trials because of cognitive worsening and other on-target toxicities. P33’s partial, selective slowing of BACE1 activity illustrates a narrower therapeutic window that may avoid those liabilities while still lowering Aβ production.

Key gaps remain: brain exposure was not quantified, memory endpoints were exploratory only, and the cohort size was modest. The next required studies are dose-ranging pharmacokinetics in larger mouse cohorts followed by GLP toxicology before any human testing can be considered.