Pharmacodynamic and stage-dependent therapeutic efficacy of SFRP1 neutralization in a mouse model of Alzheimer's disease.

INTRODUCTION

Alzheimer's disease (AD) is characterized by early synaptic dysfunction followed by progressive amyloid beta (Aβ) accumulation, neuroinflammation, and cognitive decline. We previously identified secreted frizzled-related protein 1 (SFRP1) as a multifactorial contributor to AD pathogenesis and provided initial evidence that its neutralization ameliorates pathological AD-like traits in mice. Here we evaluate the pharmacodynamics, biodistribution, and therapeutic window of an anti-SFRP1 monoclonal antibody (α-SFRP1) in double transgenic amyloid precursor protein (APP) and presenilin-1 (PS1) mice (APP/PS1).

METHODS

Pharmacokinetics and target engagement of α-SFRP1 were assessed in groups of both male and female APP/PS1 mice using biotinylated or Zirconium-89 labeled (89Zr) antibodies, with tissue distribution and α-SFRP1 levels quantified by in-house enzyme-linked immunosorbent assay (ELISA) or positron emission tomography/computed tomography (PET/CT). Therapeutic efficacy was evaluated by administering α-SFRP1 or the SFRP1 inhibitor WAY-316606 at different stages of disease progression via retro-orbital injection, followed by analysis of AD-like pathology using ELISA and quantitative immunofluorescence assays and statistical analysis.

RESULTS

Using 89Zr-labeled antibodies, we show that intravenously administered α-SFRP1 engages its target systemically and reaches the brain, although at substantially lower levels and with a rapid 24-h clearance. Treatment with α-SFRP1 had no apparent systemic side effects or sex-dependent differences, but its therapeutic efficacy against AD-like brain pathology was strongly dependent on disease stage. Although early administration reduced amyloid pathology in previous studies, treatment initiated at intermediate or advanced stages showed minimal benefit at standard doses. Higher antibody doses reduced amyloid burden and dystrophic neurites but were associated with increased mortality. Pharmacological inhibition of SFRP1 using a small-molecule inhibitor similarly failed to ameliorate pathology at intermediate stages.

DISCUSSION: Together, these findings demonstrate that SFRP1 remains a relevant therapeutic target in AD, but its effective modulation is constrained by limited brain exposure and a narrow therapeutic window, underscoring the importance of early intervention and prompting the search for improved brain-targeted delivery strategies.