HEMATOLOGIC SAFETY OF A BRAIN PENETRATING ERYTHROPOIETIN-TRANSFERRIN RECEPTOR ANTIBODY FUSION PROTEIN IN A MOUSE MODEL OF ALZHEIMER’S DISEASE

Erythropoietin (EPO) acts primarily to stimulate erythroid cell production and is clinically used to treat anemia. Recent studies show that EPO is a promising neurotherapeutic for Alzheimer's disease (AD). However, penetration of the blood-brain barrier (BBB) and negative hematopoietic effects are the two challenges for the therapeutic development of EPO for AD. One approach to deliver EPO for AD is by fusing EPO to a chimeric monoclonal antibody targeting the BBB transferrin receptor (TfRMAb), which ferries the EPO into the brain via the transvascular route and enables rapid peripheral clearance of EPO. Our previous work shows the protective effects of this BBB-penetrating EPO in AD mice, but the hematologic effects of the BBB-penetrating EPO have not been studied. The current study investigated the hematologic safety of the BBB-penetrating EPO following chronic dosing in AD mice. 9.5 months old male APPswe PSEN1dE9 transgenic mice were treated with saline (n=11), BBB-penetrable EPO, cTfRMAb-EPO, (3 mg/kg, n=7), or recombinant human EPO (rhu-EPO; 0.6 mg/kg, n=10) 2 days/week subcutaneously for 6 weeks, compared to same-aged C57BL/6 wild-type mice treated with saline (n=10). Six-weeks following treatment initiation, functional memory was assessed with the open-field and Y-maze test, and brains were evaluated for Aβ load. Blood was collected at baseline, 4-, 6- and 8-weeks for complete blood count and white blood cell (WBC) differential. Chronic treatment with cTfRMAb-EPO caused a significant transient increase in reticulocytes after 4 weeks of treatment without changing any other hematologic parameter. rhu-EPO caused a transient increase in hematocrit, RBC count and hemoglobin at 4-weeks, followed by a significant decrease in all hematologic parameters studied (hematocrit, reticulocytes, red blood cells, mean corpuscular volume and hemoglobin) at 8-weeks following treatment initiation. WBC counts did not differ between any experimental groups. cTfRMAb-EPO caused a significant reduction in brain Aβ load and notably, brain Aβ(1-42) was significantly higher in the rhu-EPO treated mice compared with cTfRMAb-EPO group. Overall, chronic treatment with cTfRMAb-EPO resulted in better safety and therapeutic indices compared with rhu-EPO, which supports the development of this BBB-penetrating-EPO for AD.