Probiodrug

Overview

Overview

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:

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]:

QPCT Inhibition Strategy

Varoglutamstat works by inhibiting QPCT activity, thereby reducing the formation of pGlu-Aβ species[@pq912firstresults2018]:

Clinical 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:

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

• Prohormone processing in secretory granules
• Peptide hormone maturation
• Neuropeptide modification

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

• Similar pGlu-Aβ patterns but faster progression
• Potentially more aggressive pathology
• Earlier amyloid deposition

• Extremely high pGlu-Aβ burden
• Early-onset amyloid pathology
• Accelerated cognitive decline

• 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

• Regions with high Aβ production are affected first
• Connectivity patterns influence propagation patterns
• Neural activity may accelerate seed formation
• Network-based spread of pathology

• 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

• Avoiding off-target effects on related enzymes
• Minimizing interactions with other hydrolases
• Ensuring safety across long-term treatment

• Achieving sustained QPCT inhibition
• Managing drug-drug interactions
• Optimizing dosing for continuous target coverage

Formulation Development

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

• Upstream and downstream inhibition of Aβ production
• Addressing multiple steps in amyloidogenesis
• Safety considerations due to prior BACE inhibitor failures

• 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

• 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

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)