Longitudinal pharmacokinetic and safety studies for dose optimization of a brain- penetrating erythropoietin for Alzheimer's disease.

Background: Erythropoietin (EPO) is a potential therapeutic for Alzheimer's disease (AD), but has limited brain penetration, requiring high systemic doses that lead to hematopoietic side effects. To overcome this, EPO was conjugated with a transferrin receptor monoclonal antibody (TfRMAb) to enhance blood-brain barrier transport. This study assessed the pharmacokinetics (PK), safety, and efficacy of this modified EPO after repeated dosing in mice.

Methods: For the PK and safety study, a multidose design was employed with 10-week-old C57 male mice (n=4-5/dose) receiving low (1 mg/kg), mid (3 and 6 mg/kg), or high (20 mg/kg) doses SQ for 4 weeks, aimed to evaluate the dose-dependent plasma concentrations and biodistribution, and metabolic and hematologic safety of the modified EPO. The dose that resulted in the highest safety and sustained plasma exposure was then dosed SQ to 5.5-month-old male APP_SAA KI mice (n=6) for 14 weeks. Controls included vehicle-treated APP_SAA KI and APP wild-type mice (n=4-5/group). The effect of modified EPO on Aβ load by immunoassays and spatial memory via the Y-maze test were assessed.

Results: The 1 mg/kg dose showed no adverse effects and sustained brain and plasma exposure following repeated dosing, making it suitable for longitudinal treatment. Mid and high doses reduced plasma and brain exposure, and altered hematocrit, TfR expression, and spleen weight; changes that were largely reversible upon treatment cessation. Reduced plasma exposure at mid and high doses was not completely explained by increased TfR expression, anti-drug antibodies, tissue sequestration, or EPO receptor expression. Subsequently, 5.5-month-old APP_SAA KI mice received 1 mg/kg TfRMAb-EPO SQ for 14 weeks. Modified EPO significantly reduced brain Aβ load (70-80%, p<0.001) and aggregated Aβ (p<0.05), and improved spatial memory, indicated by a higher discrimination index in the Y maze test (p<0.05).

Conclusions: With the advancement of TfRMAb-based therapeutics into clinical trials for AD, these findings are particularly significant. They offer essential preclinical data to guide dose optimization in longitudinal studies using TfRMAb-based therapeutics, specifically modified-EPO, and show the robust therapeutic potential of low-dose brain-penetrating EPO in the APP_SAA KI AD mouse model.