Scientists at the University of Southern California have identified an enzyme central to inflammatory lipid signaling called calcium-dependent phospholipase A2 (cPLA2) that plays a central role in brain inflammation associated with Alzheimer’s disease (AD) among people who carry the APOE4 gene. The research was published in the Nature publication npj Drug Discovery.
“In this study, we identified compounds that act selectively on cPLA2, with minimal effects on related PLA2 enzymes that are important for normal cellular function,” said senior author Hussein Yassine, PhD, director of the Center for Personalized Brain Health at the Keck School of Medicine of USC. “Across cell-based and animal models, cPLA2 activity was reduced at low concentrations, indicating that the compounds are potent in brain-relevant systems.”
cPLA2 is a cytosolic enzyme that hydrolyzes membrane phospholipids to release arachidonic acid, a lipid that serves as a precursor of inflammation and resolution, but also supports neurotransmission. In chronic inflammation of the brain is a hallmark of AD, and cPLA2 sits upstream of pathways that generate inflammatory lipid mediators. The researchers focused on the most AD risk factor gene APOE4, noting that while not all APOE4 carriers develop Alzheimer’s, those who also show elevated cPLA2 activity generally do.
“Chronic neuroinflammation plays a key role in the progression of Alzheimer’s disease (AD), and the cytosolic calcium-dependent phospholipase A2 (cPLA2) enzyme is a critical mediator of inflammatory lipid signaling pathways,” the researchers wrote.
Previous research from the team and others has shown increased cPLA2 activity in APOE4 cellular and animal models and in postmortem brain tissue. Research has also shown elevated phosphorylated cPLA2 in astrocytes near amyloid plaques. Downregulating cPLA2 in mouse models has produced reduced glial activation and improved memory, providing further evidence that cPLA2 is a driver of inflammation linked to Alzheimer’s pathology.
While these prior studies make cPLA2 a promising target for developing AD treatments, it is essential for normal brain function, so inhibition must be selective and partial. Isoform specificity has been difficult, with off-target effects limiting earlier compounds and any targeting of cPLA2 requires a drug that can cross the blood-brain barrier, a common roadblock to developing effective therapies.
To address these challenges, the USC team used a structure-based virtual drug screening platform called V-SYNTHES2, using it to search the Enamine REAL Space of 36 billion on-demand synthesizable compounds. After two rounds of optimization for potency and selectivity, the USC team identified a lead compound, BRI-50460. In cellular assays measuring cPLA2-mediated arachidonic acid release, BRI-50460 achieved an IC50 of 0.88 nM. In vivo studies showed favorable brain-to-plasma ratios, which indicated the compound was able to penetrate the central nervous system.
Laboratory studies of the drug’s effects showed that in astrocytes and neurons derived from human induced pluripotent stem cells, BRI-50460 mitigated the effects of amyloid beta 42 oligomers on cPLA2 activation, tau hyperphosphorylation, and synaptic loss. Further studies in mouse models showed that BRI-50460 was able to cross the blood-brain barrier to modulate neuroinflammatory pathways.
The team said that the goal of their work is to determine whether modulating the cPLA2 pathway can alter Alzheimer’s risk, particularly in people who carry the APOE4 risk gene. Next steps will focus on refining the pharmacokinetics of BRI-50460, further characterizing its engagement with cPLA2, and evaluating therapeutic effects in preclinical Alzheimer’s models over longer treatment timelines. Ultimately the researchers hope to advance BRI-50460 to clinical evaluation for neuroinflammatory conditions in Alzheimer’s disease.
“This next phase focuses not on promises, but on carefully determining whether modulating this pathway is safe, feasible, and ultimately meaningful for human disease,” Yassine said.
