LY3372689 (also known as oglemilide) is a potent small-molecule O-GlcNAcase (OGA) inhibitor developed by Eli Lilly for the treatment of Alzheimer's disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and other tauopathies[1][2]. It represents a novel disease-modifying approach targeting tau pathology through modulation of tau post-translational modifications, specifically O-GlcNAcylation. Unlike antibody-based therapies that aim to clear existing tau aggregates, OGA inhibitors like LY3372689 work upstream by preventing tau hyperphosphorylation and subsequent aggregation, potentially providing therapeutic benefits before significant tau pathology has accumulated[3][4].
The O-GlcNAcylation of proteins is a dynamic post-translational modification involving the attachment of N-acetylglucosamine (GlcNAc) to serine and threonine residues. This modification is regulated by two enzymes: O-GlcNAc transferase (OGT), which adds the modification, and O-GlcNAcase (OGA, also known as MGEA5), which removes it[5]. In the brain, O-GlcNAcylation plays crucial roles in neuronal function, synaptic plasticity, and protein homeostasis. Importantly, tau protein is heavily modified by O-GlcNAc, and this modification competes with pathogenic phosphorylation at many of the same sites[6].
The O-GlcNAcase enzyme (MGEA5) is a 916-amino acid protein with two functional domains: a catalytic domain that hydrolyzes O-GlcNAc modifications and a Stackin domain involved in protein-protein interactions. The enzyme is expressed throughout the brain, with high expression in neurons and glia. OGA is localized to the cytoplasm and nucleus, where it regulates O-GlcNAcylation of numerous nuclear and cytoplasmic proteins[7].
OGA expression is altered in Alzheimer's disease and other tauopathies. Studies have shown increased OGA expression in AD brain tissue, particularly in regions affected by neurofibrillary tangles. This increased OGA activity may contribute to reduced tau O-GlcNAcylation, promoting tau hyperphosphorylation and aggregation. The balance between OGT and OGA activity (the O-GlcNAc "cycle") is therefore critical for tau pathology development[6:1].
Tau protein contains over 50 serine and threonine residues that can be modified by O-GlcNAc. Key O-GlcNAcylation sites include Ser262, Ser356, Thr231, and Ser409. Importantly, many of these same residues are sites of pathological phosphorylation in AD and related disorders. The mutually exclusive nature of O-GlcNAcylation and phosphorylation provides the mechanistic basis for OGA inhibitor therapy[3:1][8].
Structural studies have demonstrated that O-GlcNAc modification at specific tau residues stabilizes the protein in a conformation less prone to phosphorylation by GSK3β and CDK5, the primary tau kinases. Additionally, O-GlcNAcylation reduces tau's ability to form insoluble aggregates by inhibiting the nucleation step of aggregation[9].
LY3372689 works by inhibiting O-GlcNAcase, the enzyme responsible for removing O-GlcNAc modifications from tau protein[1:1][2:1]. When OGA is inhibited:
Beyond direct effects on tau, OGA inhibition affects multiple cellular pathways:
The rationale for OGA inhibition in tauopathies is supported by extensive preclinical evidence:
In mouse models of tauopathy (e.g., hTauP301S, rTg4510), OGA inhibitors including Thiamet-G and related compounds have demonstrated:
Analyses of AD brain tissue have revealed:
Genetic studies have identified OGA variants associated with:
LY3372689 emerged from Eli Lilly's drug discovery program targeting O-GlcNAcase:
Preclinical studies demonstrated:
Animal studies in tauopathy mouse models showed:
The Phase I program comprised multiple studies:
| Study | Population | Design | Status |
|---|---|---|---|
| NCT04640909 | Healthy volunteers | Single ascending dose | Completed |
| NCT04744030 | Healthy volunteers | Multiple ascending dose | Completed |
| NCT05097339 | Early AD patients | Multiple dose | Completed |
First-in-human studies evaluated the safety, tolerability, and pharmacokinetics of LY3372689 in healthy volunteers and patients with early Alzheimer's disease[1:2][2:2][17]:
LY3372689 advanced to Phase II in early Alzheimer's disease:
The Phase II trial completed in 2024[2:3][18]:
Clinical trials for LY3372689 employ comprehensive biomarker approaches[19][20]:
Compared to antibody-based tau immunotherapies, OGA inhibitors offer several potential advantages[21]:
LY3372689 is one of several OGA inhibitors in development:
| Drug | Company | Target | Phase | Status |
|---|---|---|---|---|
| LY3372689 | Eli Lilly | OGA | Phase II | Completed |
| ASN90 | Asceneuron | OGA | Phase II | Ongoing |
| MK-8719 | Merck | OGA | Preclinical | Halted |
| LOBLD | Lundbeck | OGA | Discovery | Ongoing |
The OGA inhibitor field has evolved from early compounds (Thiamet-G, NAG-136) with limited CNS penetration to newer agents like LY3372689 designed specifically for CNS indications.
LY3372689 (oglemilide) is a selective OGA inhibitor:
| Parameter | Value |
|---|---|
| Oral bioavailability | >60% |
| Brain-to-plasma ratio | ~0.5 |
| Cmax | 2-4 hours post-dose |
| Half-life | 8-12 hours |
| Protein binding | <30% |
O-GlcNAcylation and phosphorylation directly compete for the same amino acid residues on tau:
O-GlcNAc Transferase (OGT) Kinases (GSK-3β, CDK5)
│ │
↓ ↓
O-GlcNAcylation Phosphorylation
│ │
│ ╔═══════════════╗ │
└─────────║ TAU PROTEIN ║─────────┘
╚═══════════════╝ │
│ │
↓ ↓
O-GlcNAcase (OGA) Phosphatases
↓ │
└────────┬──────────┘
↓
Dynamic Balance
| Site | Kinase | Pathological Effect | O-GlcNAc Competition |
|---|---|---|---|
| Thr181 | GSK-3β, CDK5 | Early marker, cognitive correlation | Direct competition |
| Thr231 | GSK-3β | Conformational change, aggregation | Direct competition |
| Ser396 | GSK-3β | Promotes NFT formation | Direct competition |
| Ser404 | GSK-3β | Enhances aggregation | Direct competition |
Eli Lilly is pursuing multiple tau-targeted approaches:
Lilly's investment in OGA inhibition reflects:
Based on Phase 1 and Phase 2 trials[18:1]:
| Event | Frequency | Severity |
|---|---|---|
| Nausea | 15-20% | Mild |
| Diarrhea | 10-15% | Mild |
| Headache | 10% | Mild |
| Fatigue | 5-10% | Mild |
The safety profile supports continued development in larger trials.
Based on Phase II results, Lilly is evaluating:
Emerging research suggests OGA inhibitors may work synergistically with:
Beyond Alzheimer's disease, LY3372689 may have utility in:
Yuzwa et al., A potent mechanism-based O-GlcNAcase inhibitor inhibits tau pathology in mouse models. ↩︎ ↩︎ ↩︎
Chen et al., OGA inhibition reduces tau phosphorylation via multiple kinases. ↩︎
Bachran et al., O-GlcNAc competition with phosphorylation at tau Ser409. ↩︎
Sandoval et al., O-GlcNAcylation protects against tau aggregation. ↩︎
Horton et al., OGA inhibitor effects on synaptic proteins. ↩︎
Lee et al., O-GlcNAc and mitochondrial function in neurodegeneration. ↩︎
Mueller et al., Thiamet-G OGA inhibitor restores O-GlcNAcylation in tauopathy models. ↩︎
Davies et al., Long-term OGA inhibitor effects in tauopathy models. ↩︎
Zhao et al., OGA genetic variants and Alzheimer's disease risk. ↩︎ ↩︎
Peters et al., Safety profile of LY3372689 in Phase 2. ↩︎ ↩︎
Shen et al., Combination therapy OGA inhibitor plus anti-amyloid. ↩︎