The pharmaceutical potential of AR‐65, a novel Alzheimer’s disease drug targeting the immunoproteasome

Background Previously, we reported that inhibition of the immunoproteasome (iP), which is upregulated in reactive glial cells near amyloid‐β (Aβ) deposits in the brains of patients with Alzheimer’s disease (AD), leads to improved cognitive function in an AD mouse model of Aβ amyloidosis (Tg2576) via suppression of microglia‐mediated inflammation, independent of Aβ accumulation. Method Here, we investigated the pharmaceutical properties of our lead iP inhibitor (AR‐65), a macrocyclic peptide epoxyketone, selected based on in vitro and cellulo iP inhibitory activities and cell‐based anti‐inflammatory efficacy. Specifically, the metabolic stability of AR‐65 was assessed using pooled human liver microsomes. In addition, the flux rate of AR‐65 was measured to evaluate the permeability across Caco‐2 monolayers over‐expressing ABCB1 and ABCG2, two major efflux drug transporters present in the human brain. Result The macrocyclic AR‐65 displayed improved metabolic stability (6‐fold increased half‐life), permeability, and solubility (in an injectable pharmaceutical buffer system with no cyclodextrin) compared to the FDA‐approved linear peptide epoxyketone proteasome inhibitor, carfilzomib (Kyprolis®). Finally, pilot PK studies performed using ICR mice confirmed that AR‐65 is metabolically more stable than carfilzomib and can cross the blood‐brain barrier to inhibit the brain iP. Conclusion Taken together, the results suggest that AR‐65 may hold great potential to be further investigated in clinical settings.