ASN90 is an O-GlcNAcase (OGA) inhibitor developed by Asceneuron SA, a Swiss biotechnology company focused on discovering and developing novel small molecule therapeutics for neurodegenerative diseases. ASN90 represents a promising disease-modifying approach targeting tau pathology in Alzheimer's disease and other tauopathies.
¶ Background: O-GlcNAcylation and Tau
O-GlcNAcylation is a post-translational modification where O-linked N-acetylglucosamine (O-GlcNAc) is added to serine and threonine residues on proteins, including tau. This modification is increasingly recognized as a key regulatory mechanism:
- Physiological role: O-GlcNAcylation regulates protein function, stability, and localization
- Tau relationship: O-GlcNAcylation of tau at specific sites competes with phosphorylation
- Key insight: O-GlcNAcylation atThr231, Ser396, and Ser400 inhibits tau aggregation
In Alzheimer's disease and tauopathies, tau is hyperphosphorylated, leading to neurofillary tangle formation. O-GlcNAcylation appears to be reduced in AD brains, creating an imbalance that promotes pathological phosphorylation.
ASN90 is a potent, selective OGA inhibitor that increases O-GlcNAcylation levels on tau protein:
- Target: O-GlcNAcase (OGA) - the enzyme that removes O-GlcNAc from proteins
- Mechanism: Inhibiting OGA increases tau O-GlcNAcylation
- Effect: O-GlcNAcylated tau is less prone to pathological phosphorylation and aggregation
- Outcome: Potential disease modification by reducing toxic tau species
The scientific rationale follows the yin-yang hypothesis: phosphorylation and O-GlcNAcylation compete for the same serine/threonine residues. By inhibiting OGA, ASN90 shifts the balance toward protective O-GlcNAcylation.
ASN90 demonstrated:
- Low nanomolar potency against human OGA (IC50 ~ 2 nM)
-
1000-fold selectivity over other glycosidases
- Increased O-GlcNAcylation in neurons at concentrations < 100 nM
- Reduced tau phosphorylation at pathogenic sites (Thr181, Thr231, Ser396)
- Brain-penetrant following oral administration
- Dose-dependent increase in brain O-GlcNAc levels
- Reduced tau pathology in mouse models of tauopathy
- Good tolerability in preclinical toxicology studies
Asceneuron advanced ASN90 into Phase I clinical trials to evaluate safety, tolerability, and pharmacokinetics in healthy volunteers. The trials established the dosing regimen for Phase II.
Based on Phase I results, ASN90 advanced to Phase II testing in early Alzheimer's disease. The Phase II program evaluates whether OGA inhibition can slow tau pathology progression.
- NCT05463754: Phase I study in healthy volunteers (completed)
- NCT05693982: Phase II study in early Alzheimer's disease (ongoing)
ASN90 competes with other OGA inhibitors in development:
| Drug |
Company |
Phase |
Status |
| ASN90 |
Asceneuron |
Phase II |
Active |
| LY3372689 |
Eli Lilly |
Phase II |
Active |
| CHDI |
Various |
Preclinical |
Ongoing |
LY3372689 (oglemilide) from Eli Lilly is the furthest advanced OGA inhibitor, but ASN90 offers potential advantages in brain penetration and selectivity.
The OGA inhibitor approach offers several advantages:
- Oral bioavailability: Small molecule can be taken orally, improving patient convenience
- Brain penetration: Successfully crosses the blood-brain barrier
- Disease modification: Targets upstream tau pathology, not just symptoms
- Combination potential: Could potentially be combined with other tau-targeted approaches
¶ Safety and Tolerability
Phase I trials showed ASN90 was generally well-tolerated:
- No serious adverse events at doses tested
- Gastrointestinal effects (nausea) were mild and transient
- No significant effects on glucose metabolism
- Pharmacokinetics support once-daily oral dosing
Asceneuron is developing ASN90 as a potential first-in-class disease-modifying treatment for Alzheimer's disease. Success in Phase II could lead to:
- Pivotal Phase III trials in early AD
- Potential expansion to other tauopathies (PSP, CBD, FTD)
- Combination studies with amyloid-targeting therapies
¶ Pharmacokinetics and Drug Properties
ASN90 demonstrates favorable pharmacokinetic properties suitable for chronic oral dosing:
- Absorption: Rapid oral absorption with Tmax of 2-4 hours
- Distribution: Good brain penetration with brain-to-plasma ratio >1:1
- Metabolism: Minimal cytochrome P450 involvement, reducing drug-drug interaction risk
- Elimination: Terminal half-life of 8-12 hours supporting once-daily dosing
ASN90 is a thienopyrimidine-based small molecule with:
- Molecular weight ~400 Da, enabling BBB penetration
- High selectivity for OGA over O-GlcNAc transferase (OGT)
- Metabolic stability in liver microsomes
- Formulated as oral tablet for patient convenience
Clinical trials for ASN90 employ several biomarker approaches:
- CSF O-GlcNAc Levels: Direct measurement of O-GlcNAcylation on proteins in cerebrospinal fluid
- CSF Phospho-tau: Monitoring of phosphorylated tau species (p-tau181, p-tau231)
- CSF Total Tau: Assessment of overall tau protein turnover
Additional biomarkers to track disease modification:
- Tau PET Imaging: [^18F]flortaucipir for regional tau burden assessment
- Neurodegeneration Markers: NfL (neurofilament light chain) in blood and CSF
- Cognitive Measures: CDR, MMSE, and ADAS-Cog for clinical outcome tracking
¶ Competitive Landscape
| Drug |
Company |
IC50 |
Brain Penetrance |
Phase |
Trial ID |
| ASN90 |
Asceneuron |
~2 nM |
High |
Phase II |
NCT05693982 |
| LY3372689 |
Eli Lilly |
~5 nM |
Moderate |
Phase II |
NCT05097339 |
| MK-8719 |
Merck |
~10 nM |
Moderate |
Preclinical |
N/A |
ASN90 aims to compete through:
- Superior brain penetration: Higher brain-to-plasma ratio than competitors
- Enhanced selectivity: Greater OGA/OGT selectivity ratio
- Novel chemical class: Different scaffold from Lilly's program
- Orphan indications: Potential for PSP and CBD development
The scientific foundation of OGA inhibition rests on the yin-yang relationship between phosphorylation and O-GlcNAcylation:
Tau Protein
│
├──[Kinases]──→ Phosphorylation (pathological)
│
└──[OGT]──→ O-GlcNAcylation (protective)
│
└──[OGA]──→ removal (baseline)
OGA Inhibition → ↑ O-GlcNAcylation → ↓ Phosphorylation → ↓ Aggregation
O-GlcNAcylation and phosphorylation compete for the same serine/threonine residues on tau:
| Site |
O-GlcNAcylation Effect |
Phosphorylation Effect |
| Thr231 |
Blocks p-tau231 |
Promotes aggregation |
| Ser396 |
Blocks p-tau396 |
Promotes aggregation |
| Ser400 |
Blocks p-tau404 |
Promotes aggregation |
| Ser262 |
Blocks p-tau262 |
Reduces microtubule binding |
Asceneuron SA is a Lausanne, Switzerland-based biotechnology company founded in 2012:
- Focus: Novel small molecules for neurodegenerative diseases
- Platform: Structure-based drug design for CNS disorders
- Pipeline: OGA inhibitors for tauopathies, additional programs in development
- Partnerships: Collaborations with academic institutions and pharma companies
Asceneuron's approach to ASN90 development:
- Fast-to-market: Target early AD for pivotal trials
- Biomarker-driven: Use CSF and PET biomarkers for patient selection
- Combination-ready: Position for combination with anti-amyloid therapies
- Pipeline expansion: Leverage OGA platform for additional indications
The NCT05693982 Phase II trial incorporates:
- Population: Early Alzheimer's disease (MCI due to AD, mild AD)
- Design: Randomized, placebo-controlled, parallel-group
- Duration: 52 weeks treatment with 26-week follow-up
- Dose: Multiple dose cohorts to establish optimal dose
- Endpoints: Safety, tolerability, biomarker changes
Inclusion of patients with:
- Confirmed amyloid pathology (Amyloid PET or CSF)
- Elevated tau levels (CSF p-tau181 or p-tau231)
- Mild cognitive impairment or mild dementia
- MRI evidence of medial temporal lobe atrophy
OGA inhibition raises several safety considerations:
- Pancreatic effects: OGA expressed in pancreatic beta cells - monitoring glucose homeostasis
- Platelet O-GlcNAcylation: Potential effects on platelet function
- Lymphocyte O-GlcNAc: Impact on immune cell function
Phase II includes comprehensive safety monitoring:
- Regular glucose tolerance testing
- Platelet count and function assessments
- Immune cell profiling
- ECG and vital signs monitoring