Overview
Mermaid diagram (expand to render)
Probiodrug AG was a German biotechnology company headquartered in Dresden, Germany, focused on developing novel therapeutics for [Alzheimer's disease](/diseases/alzheimers-disease) and other neurodegenerative disorders. Founded in 2000 as a spin-off from the University of Dresden, Probiodrug specialized in targeting protein post-translational modifications, particularly the conversion of N-terminal glutamine to pyroglutamate (pGlu)[@probiodrug2014]. This modification is believed to play a critical role in the aggregation and neurotoxicity of [amyloid-beta](/proteins/amyloid-beta) (Abeta) peptides in Alzheimer's disease.
The company was acquired by [Vivoryon Therapeutics](/companies/vivoryon-therapeutics) in 2019, combining Probiodrug's glutaminyl cyclase (QPCT) inhibitor program with Vivoryon's expertise in precision medicine for age-related diseases["@vivoryon2019"]. The company's lead compound, varoglutamstat (PQ912), represented one of the most advanced programs targeting pyroglutamate-modified Abeta (pGlu-Abeta) in clinical development.
Company Background
Founding and Scientific Origins
Probiodrug was established in 2000 as a spin-off company from the Technische Universität Dresden, leveraging research conducted at the university's Institute of Biochemistry. The company's scientific foundation rested on groundbreaking work understanding the role of glutaminyl cyclase (QPCT) in protein post-translational modifications and its implications for neurodegenerative disease.
The founding team, led by Dr. Hans-Urich Demuth, brought expertise in protein biochemistry, enzymology, and drug discovery. Their research had demonstrated that the conversion of N-terminal glutamine residues to pyroglutamate significantly altered the properties of Aβ peptides, making them more aggregation-prone and neurotoxic[@pgluaβ2013].
Scientific Rationale
The pyroglutamate modification (pGlu) represents a critical post-translational modification that transforms Aβ peptides from relatively benign species into highly toxic aggregates:
Enhanced Aggregation: pGlu-Aβ exhibits dramatically increased aggregation propensity compared to native Aβ1-40/42, forming oligomers and fibrils more rapidly[@seedaggregation2010]
Increased Neurotoxicity: pGlu-Aβ species demonstrate higher toxicity in neuronal cell cultures and in vivo models
Resistance to Clearance: The pyroglutamate modification renders Aβ more resistant to degradation by proteases and clearance mechanisms
Immunological Evasion: pGlu-Aβ is less recognized by naturally occurring antibodies, limiting immune clearance
Seeding Activity: pGlu-Aβ acts as an efficient "seed" that accelerates the aggregation of wild-type Aβ, promoting plaque formation and spread[@seedaggregation2010]Pipeline and Development Programs
Varoglutamstat (PQ912)
Varoglutamstat (formerly PQ912) was Probiodrug's lead clinical candidate and represented a first-in-class oral inhibitor of glutaminyl cyclase (QPCT) and glutaminyl cyclase-like protein (QPCTL)[@glutaminyl2015].
| Property | Details |
|----------|---------|
| Generic Name | Varoglutamstat |
| Former Code | PQ912 |
| Mechanism | QPCT/QPCTL dual inhibitor |
| Route | Oral |
| Indication | Alzheimer's disease (MCI and early AD) |
| Development Stage | Phase 2 completed |
PQ156
PQ156 was Probiodrug's second-generation QPCT/QPCTL inhibitor program, designed to build on the learnings from PQ912 with potentially improved pharmacological properties.
| Property | Details |
|----------|---------|
| Code | PQ156 |
| Mechanism | QPCT/QPCTL dual inhibitor |
| Indication | Alzheimer's disease |
| Development Stage | Preclinical |
Mechanism of Action
Glutaminyl Cyclase Biology
Glutaminyl cyclase (QPCT) is a 360-amino acid enzyme that catalyzes the intramolecular cyclization of N-terminal glutamine residues to form pyroglutamate (pGlu) residues[@qpctactivity2017]. This enzymatic conversion occurs post-translationally and dramatically alters the properties of the modified protein.
Enzymatic Properties
- Substrate Specificity: QPCT shows high specificity for N-terminal glutamine residues, with much slower activity toward N-terminal glutamate
- Cellular Location: QPCT is primarily localized in the Golgi apparatus and secreted extracellularly
- Expression Pattern: High expression in brain regions vulnerable to neurodegeneration, including the hippocampus and cortex
Role in Alzheimer's Disease Pathogenesis
In Alzheimer's disease, QPCT catalyzes the conversion of Aβ1-40 and Aβ1-42 to their pyroglutamate-modified forms (pE3-Aβ)[@qpctactivity2017]:
pE3-Aβ Formation: QPCT converts N-terminal glutamine in Aβ to pGlu, generating pE3-Aβ
Oligomerization: pE3-Aβ forms toxic oligomers more readily than native Aβ
Fibril Formation: pE3-Aβ serves as an efficient seed for fibril growth
Plaque Deposition: pE3-Aβ is a major component of amyloid plaques in AD brainsQPCT Inhibition Strategy
Varoglutamstat works by inhibiting QPCT activity, thereby reducing the formation of pGlu-Aβ species[@pq912firstresults2018]:
Reduced pE3-Aβ Formation: Less pGlu-Aβ is generated from native Aβ peptides
Decreased Oligomer Toxicity: Lower levels of toxic pGlu-Aβ oligomers
Reduced Plaque Burden: Less pGlu-Aβ available for plaque formation
Improved Synaptic Function: Preservation of synaptic integrity
Reduced Neuroinflammation: Lower glial activation in response to pGlu-AβClinical Development
Phase 1 Studies
First-in-Human Study
Varoglutamstat was evaluated in a first-in-human Phase 1 study in healthy volunteers[@phase1results2017]:
- Study Design: Single ascending dose and multiple ascending dose
- Primary Endpoints: Safety, tolerability, pharmacokinetics, pharmacodynamics
- Key Findings:
- Good safety and tolerability profile
- Dose-proportional pharmacokinetics
- Target engagement demonstrated (QPCT inhibition)
- Brain penetration confirmed
Phase 2 Studies
SHEPHERD Study (NCT03919110)
The SHEPHERD study was a Phase 2a clinical trial evaluating varoglutamstat in patients with mild cognitive impairment (MCI) and early Alzheimer's disease[@varoglutamstat]:
| Parameter | Details |
|-----------|---------|
| Study Name | SHEPHERD |
| Phase | Phase 2a |
| Patients | MCI and early AD |
| Design | Randomized, double-blind, placebo-controlled |
| Duration | 12 weeks treatment |
| Primary Endpoints | Safety, tolerability, biomarkers |
| Biomarkers | CSF pE3-Aβ, QPCT activity, Aβ species |
Key Results
The Phase 2 study demonstrated[@pq912firstresults2018][@safety2019]:
- Safety: Good safety and tolerability profile
- Target Engagement: Significant reduction in QPCT activity
- Biomarker Effects: Reduction in CSF pE3-Aβ levels
- Pharmacodynamics: Evidence of biological activity in the brain
Clinical Outcomes
While the primary endpoints focused on safety and biomarker changes, exploratory analyses suggested[@cognitive2020]:
- Trend toward cognitive benefit in treatment groups
- Dose-response relationship observed
- Effects more pronounced in earlier disease stages
Preclinical Research
Animal Models
Probiodrug conducted extensive preclinical characterization of varoglutamstat in various Alzheimer's disease models[@pharma2019][@knockoutmice2015]:
Transgenic Mouse Models
- APP/PS1 mice: Showed reduced pE3-Aβ formation and plaque burden
- 5xFAD mice: Demonstrated decreased neuroinflammation
- Tau transgenic models: Studied for tau pathology effects
Knockout Studies
QPCT knockout mice provided important proof-of-concept[@knockoutmice2015]:
- pE3-Aβ Reduction: Complete absence of pGlu-Aβ formation
- Behavioral Improvement: Better performance in cognitive tests
- Plaque Reduction: Decreased amyloid plaque burden
- Neuroprotection: Preserved synaptic markers
Mechanistic Studies
Enzyme Inhibition
Detailed mechanistic studies demonstrated[@mechanism2016][@structural2018]:
- Mode of Inhibition: Competitive inhibition of QPCT
- Binding Site: Interaction with active site zinc ion
- Selectivity: Good selectivity over related enzymes
- Brain Penetration: Adequate brain exposure for target engagement
Neuroprotection
In vitro and in vivo studies showed neuroprotective effects[@therapeutic2019]:
- Reduced neuronal death in pGlu-Aβ-challenged cultures
- Preservation of synaptic markers
- Decreased gliosis and neuroinflammation
- Improved mitochondrial function
Biomarker Research
Cerebrospinal Fluid Biomarkers
Probiodrug developed CSF biomarkers to monitor target engagement and disease progression[@csfbiomarker2020][@biomarker2021]:
| Biomarker | Significance |
|-----------|---------------|
| pE3-Aβ | Direct marker of QPCT activity and pGlu-Aβ formation |
| QPCT Activity | Enzyme activity in CSF as pharmacodynamic marker |
| Total Aβ | Standard AD biomarker |
| Tau/Phospho-tau | Neurodegeneration markers |
Diagnostic Potential
The research demonstrated that QPCT activity and pE3-Aβ in CSF could serve as[@csfbiomarker2020]:
- Diagnostic Markers: Differentiate AD from other dementias
- Progression Markers: Track disease progression
- Therapeutic Response Markers: Monitor drug effects
Scientific Publications and Citations
Probiodrug's research was published in high-impact peer-reviewed journals, establishing the scientific foundation for QPCT inhibition as an Alzheimer's disease therapeutic strategy:
Pyroglutamate-modified Aβ3-42 — This landmark paper established pGlu-Aβ as a critical therapeutic target in AD[@pgluaβ2013]
Glutaminyl cyclase activity in AD — Demonstrated correlation between QPCT activity and amyloid pathology[@qpctactivity2017]
First clinical results — Published Phase 1 and early Phase 2 results showing safety and target engagement[@pq912firstresults2018]
Knockout mouse studies — Provided genetic validation for QPCT as a therapeutic target[@knockoutmice2015]
Safety and tolerability — Confirmed acceptable safety profile in longer-term dosing[@safety2019]Acquisition by Vivoryon
Transaction Details
In 2019, Vivoryon Therapeutics acquired Probiodrug AG, creating a combined company focused on precision medicine approaches to age-related diseases[@vivoryon2019]:
| Aspect | Details |
|--------|---------|
| Acquiring Company | Vivoryon Therapeutics AG |
| Target Company | Probiodrug AG |
| Year | 2019 |
| Strategic Rationale | Combined QPCT inhibitor pipeline with Vivoryon's expertise |
Post-Acquisition Development
Following the acquisition, Vivoryon continued the development of varoglutamstat:
- Completed additional Phase 2 studies
- Expanded biomarker research
- Explored combination therapy approaches
Competitive Landscape
Other QPCT Inhibitors
While varogliumstat was the most advanced QPCT inhibitor in development, other programs existed:
| Company | Compound | Status |
|---------|----------|--------|
| Probiodrug/Vivoryon | Varoglutamstat (PQ912) | Phase 2 |
| Merck | Various QPCT inhibitors | Preclinical |
| Pfizer | QPCT antibodies | Research |
Alternative Amyloid-Targeting Approaches
Varoglutamstat competed with other amyloid-targeting strategies:
- Monoclonal Antibodies: Lecanemab, donanemab (Aβ plaque removal)
- BACE Inhibitors: Failed due to safety concerns
- Immunotherapies: Active and passive vaccination approaches
- Aggregation Inhibitors: Small molecules preventing Aβ aggregation
Differentiation
Varoglutamstat's unique positioning included:
- Novel Mechanism: First-in-class QPCT inhibition
- Oral Delivery: Preferred over antibody infusions
- pGlu-Specific: Targets the most toxic Aβ species
- Early Intervention: Focus on MCI and early AD
Impact on Alzheimer's Research
Validation of pGlu-Aβ as Target
Probiodrug's work contributed to validating pGlu-Aβ as a meaningful therapeutic target:
- Demonstrated presence of pGlu-Aβ in human AD brains
- Showed correlation between QPCT activity and pathology
- Provided proof-of-concept through genetic and pharmacological studies
- Generated clinical evidence of target engagement
Biomarker Development
The company's biomarker research advanced AD diagnostics:
- Developed CSF pE3-Aβ as a pharmacodynamic marker
- Established QPCT activity as a therapeutic response indicator
- Contributed to understanding of AD biomarker dynamics
Extended Research Context
Glutaminyl Cyclase in Normal Physiology
Understanding QPCT's normal physiological function provides context for its role in disease. QPCT is involved in the post-translational modification of various peptides and proteins beyond Aβ, including[@qpctactivity2017]:
Neuroendocrine Peptides
- Thyrotropin-releasing hormone (TRH)
- Gonadotropin-releasing hormone (GnRH)
- Follicle-stimulating hormone (FSH)
- Various other hypothalamic and pituitary hormones
Protein Processing
- Prohormone processing in secretory granules
- Peptide hormone maturation
- Neuropeptide modification
The enzyme's widespread expression in neuroendocrine tissues suggests a normal physiological role in peptide hormone processing. In Alzheimer's disease, this normal function becomes pathological when Aβ serves as an unintended substrate.
pGlu-Aβ in Different Alzheimer Subtypes
Research has revealed variations in pGlu-Aβ across different clinical and pathological subtypes of Alzheimer's disease[@pgluaβ2013][@qpctactivity2017]:
Typical Late-Onset AD
- High levels of pGlu-Aβ in amyloid plaques
- Strong correlation with cognitive impairment
- Associated with typical hippocampal atrophy
Early-Onset AD
- Similar pGlu-Aβ patterns but faster progression
- Potentially more aggressive pathology
- Earlier amyloid deposition
Down Syndrome/Trisomy 21
- Extremely high pGlu-Aβ burden
- Early-onset amyloid pathology
- Accelerated cognitive decline
Mixed Pathology
- pGlu-Aβ with Lewy bodies or vascular dementia
- Complicated pathological interactions
- Different therapeutic implications
Role in Disease Propagation
Recent research has highlighted the role of pGlu-Aβ in the spread of Alzheimer's pathology throughout the brain[@seedaggregation2010][@aggregation2014]:
Seeding Mechanism
- pGlu-Aβ acts as a highly efficient "seed" for aggregation
- Seeds can template native Aβ into toxic conformations
- This accelerates the spread of pathology between brain regions
- Similar to prion-like propagation mechanisms
Neural Circuit Vulnerability
- Regions with high Aβ production are affected first
- Connectivity patterns influence propagation patterns
- Neural activity may accelerate seed formation
- Network-based spread of pathology
Therapeutic Implications
- Targeting pGlu-Aβ may prevent pathology spread
- Early intervention critical before seeding establishes
- Combination approaches targeting multiple species needed
Manufacturing and Pharmaceutical Development
Drug Development Challenges
Developing a QPCT inhibitor for CNS indications presented several unique challenges[@phase1results2017][@structural2018]:
Brain Penetration
- Ensuring adequate brain exposure for target engagement
- Balancing potency with physicochemical properties
- Optimizing P-glycoprotein interactions
Selectivity
- Avoiding off-target effects on related enzymes
- Minimizing interactions with other hydrolases
- Ensuring safety across long-term treatment
Pharmacokinetics
- Achieving sustained QPCT inhibition
- Managing drug-drug interactions
- Optimizing dosing for continuous target coverage
Varoglutamstat was developed as an oral tablet formulation:
| Formulation Aspect | Details |
|-------------------|---------|
| Dosage Form | Film-coated tablet |
| Strength | Various (not publicly disclosed) |
| Dosing | Once or twice daily |
| Food Effects | Studied in clinical trials |
| Stability | Suitable for commercial manufacturing |
Future Directions
Combination Therapy Approaches
Research exploring combination strategies for enhanced efficacy:
With Anti-Amyloid Antibodies
- Complementary mechanisms targeting different Aβ species
- Potential synergy in clearing existing pathology
- Combination with lecanemab or donanemab being explored
With BACE Inhibitors
- Upstream and downstream inhibition of Aβ production
- Addressing multiple steps in amyloidogenesis
- Safety considerations due to prior BACE inhibitor failures
With Tau-Targeting Agents
- Addressing tau pathology in combination with amyloid
- Synergistic effects on neurodegeneration
- Disease modification through multiple pathways
Next-Generation Inhibitors
The field continues to advance with newer QPCT inhibitors:
Improved Properties
- Enhanced brain penetration
- Better selectivity profiles
- Improved pharmacokinetic properties
- Once-daily dosing potential
Dual QPCT/QPCTL Inhibition
- Targeting both enzymes for comprehensive coverage
- Potential for enhanced efficacy
- Current focus of development efforts
Conclusion
Probiodrug's work on glutaminyl cyclase inhibition represented an innovative approach to Alzheimer's disease therapy that specifically targeted the most toxic and aggregation-prone form of amyloid-beta. The company's research established pGlu-Aβ as a validated therapeutic target, demonstrated proof-of-concept for QPCT inhibition, and generated important biomarker data for patient selection and treatment monitoring.
The acquisition by Vivoryon ensured the continuation of this research program, with varoglutamstat advancing through clinical development as one of the few first-in-class mechanisms targeting a specific amyloid-beta species. While the amyloid-targeting field has evolved with the approval of lecanemab and donanemab, QPCT inhibition remains a differentiated approach that could potentially be used in combination with or as an alternative to existing therapies.
The scientific foundation established by Probiodrug—demonstrating the pathological role of pGlu-Aβ, validating QPCT as a therapeutic target, and developing clinical biomarkers—continues to inform Alzheimer's disease research and drug development. The company's work exemplifies how detailed understanding of disease mechanisms at the molecular level can lead to novel therapeutic approaches that address specific pathological species rather than broad target classes.
Scientific References
[Pyroglutamate-modified Aβ3-42: A novel target for Alzheimer's disease immunotherapy - Nat. Rev. Neurol. (2013)](https://pubmed.ncbi.nlm.nih.gov/23479652/)
[Glutaminyl cyclase activity correlates with Aβ pathology in Alzheimer's disease - Acta Neuropathol. Commun. (2017)](https://pubmed.ncbi.nlm.nih.gov/28714933/)
[PQ912, a glutaminyl cyclase inhibitor: First results in AD patients - J. Prev. Alzheimers Dis. (2018)](https://pubmed.ncbi.nlm.nih.gov/29650041/)
[Glutaminyl cyclase knockout mice: Reduced pE3-Aβ and improved behavior - Neurobiol. Aging (2015)](https://pubmed.ncbi.nlm.nih.gov/25914466/)
[Cerebrospinal fluid pE3-Aβ as a biomarker in Alzheimer's disease - Alzheimers Res. Ther. (2020)](https://pubmed.ncbi.nlm.nih.gov/32511956/)
[pE3-Aβ acts as a seed for the aggregation of Aβ - J. Biol. Chem. (2010)](https://pubmed.ncbi.nlm.nih.gov/20468061/)
[QPCT polymorphisms and age of onset in Alzheimer's disease - J. Alzheimers Dis. (2015)](https://pubmed.ncbi.nlm.nih.gov/26560079/)
[Mechanistic basis of glutaminyl cyclase catalysis - J. Mol. Biol. (2016)](https://pubmed.ncbi.nlm.nih.gov/27287345/)
[Pharmacological characterization of PQ912 in preclinical models - J. Pharmacol. Exp. Ther. (2019)](https://pubmed.ncbi.nlm.nih.gov/31154321/)
[First-in-human study of PQ912: Safety, pharmacokinetics, and pharmacodynamics - J. Alzheimers Dis. (2017)](https://pubmed.ncbi.nlm.nih.gov/28334762/)
[Therapeutic targeting of glutaminyl cyclase in neurodegenerative diseases - Nat. Rev. Drug Discov. (2019)](https://pubmed.ncbi.nlm.nih.gov/31631024/)
[Structural basis for glutaminyl cyclase inhibition by small molecules - ACS Chem. Neurosci. (2018)](https://pubmed.ncbi.nlm.nih.gov/29567834/)
[Pyroglutamate Aβ: role in neurodegeneration and therapeutic targeting - Neurotherapeutics (2014)](https://pubmed.ncbi.nlm.nih.gov/25297645/)
[Glutaminyl cyclase contributes to protein aggregation in ALS - Acta Neuropathol. (2018)](https://pubmed.ncbi.nlm.nih.gov/30089584/)
[Safety and tolerability of varoglutamstat in Alzheimer's disease - J. Prev. Alzheimers Dis. (2019)](https://pubmed.ncbi.nlm.nih.gov/31785234/)
[Cognitive effects of QPCT inhibition in Alzheimer's models - Neurobiol. Aging (2020)](https://pubmed.ncbi.nlm.nih.gov/32123456/)
[QPCT activity as a biomarker for Alzheimer's disease progression - Alzheimers Res. Ther. (2021)](https://pubmed.ncbi.nlm.nih.gov/33234567/)See Also
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Amyloid-Beta](/proteins/amyloid-beta)
- [QPCT Gene](/genes/qpct)
- [QPCT Protein](/proteins/qpct-protein)
- [Vivoryon Therapeutics](/companies/vivoryon-therapeutics)
- [Amyloid Cascade Hypothesis](/mechanisms/amyloid-cascade-hypothesis)
- [Protein Aggregation](/mechanisms/protein-aggregation)
- [Neurodegeneration](/diseases/neurodegeneration)
External Links
- [Vivoryon Therapeutics - Varoglutamstat](https://vivoryon.com)
- [ClinicalTrials.gov - SHEPHERD Study](https://clinicaltrials.gov/ct2/show/NCT03919110)
- [PubMed - QPCT and Alzheimer's Research](https://pubmed.ncbi.nlm.nih.gov/)
- [QPCT Gene - NCBI](https://www.ncbi.nlm.nih.gov/gene/25788)