Batch release testing for GLP-1 agonists: Building confidence from API to prefilled syringe

Introduction

The rapid growth of GLP-1 receptor agonists such as semaglutide, liraglutide, dulaglutide, and emerging dual/triple agonists in treating type-II diabetes has increased the importance of robust bioanalytical strategies to ensure product quality, potency, safety, and efficacy. As the industry scales manufacturing capacity globally, bioassay-based batch release testing has become a critical component of the control strategy for APIs, finished products, and prefilled syringe presentations.

Unlike conventional small molecules, GLP-1 agonists require demonstration of biological activity in addition to physicochemical characterisation. Regulatory expectations emphasise validated analytical procedures and potency assays that are scientifically justified, accurate, reproducible, and suitable for their intended use.

Why bioassays matter for GLP-1 agonists

A bioassay measures the functional activity of a drug substance/product against its biological target. For GLP-1 receptor agonists, potency is typically evaluated through receptor activation assays that measure downstream signalling pathways such as cAMP generation, CRE-luciferase reporter activity, or other mechanism-of-action relevant cellular responses.

These assays provide direct evidence that the molecule retains its expected biological function throughout:

• API release
• Drug product formulation
• Storage and stability lifecycle
• Commercial batch release testing

Batch release testing across the product lifecycle

1. API testing 

   For GLP-1 APIs, quality control typically includes:

• Identity confirmation
• Purity and impurity profiling
• Peptide content assay
• Related substances
• Biological potency evaluation

The potency assay confirms that the active peptide maintains its receptor-binding and signaling capability after synthesis, purification, and storage.

2. Finished product testing

Finished dosage forms require additional assessment because formulation components can potentially impact biological activity.

Typical release tests include:

• Potency/Bioactivity
• Assay and content uniformity
• Aggregation profile
• Degradation products
• pH and appearance
• Sterility and endotoxin testing

A validated bioassay provides assurance that formulation processes have not altered the molecule’s biological performance.

3. Prefilled syringe testing

Prefilled syringe presentations introduce additional variables:

• Siliconisation effects
• Container closure interactions
• Adsorption to contact surfaces
• Mechanical stress during filling

Consequently, potency monitoring becomes particularly important to demonstrate that biological activity remains unchanged from bulk drug product through final container closure systems.

Method development strategy

Successful bioassay development begins with a clear understanding of the molecule’s mechanism of action.

For GLP-1 agonists, commonly employed platforms include:

cAMP functional assays

Measure intracellular cAMP accumulation following GLP-1 receptor activation.

Advantages:

• Direct MOA relevance
• High sensitivity
• Well-established platform

Reporter gene assays

CRE-Luciferase systems convert receptor activation into a quantifiable luminescent signal.

Advantages:

• Excellent throughput
• Robust response window
• Suitability for QC environments

Receptor activation assays

These cell-based assays directly evaluate functional receptor engagement and downstream signaling.

Critical development considerations include:

• Cell line selection
• Reference standard qualification
• Dynamic assay range
• Signal-to-noise ratio
• Data fitting model
• Assay robustness and transferability

Method validation: Key regulatory expectations

According to ICH Q2(R2) and USP <1033>, bioassays used for release testing must be validated to demonstrate fitness for purpose. The key validation parameters are listed below.

Accuracy

Accuracy demonstrates agreement between measured and expected potency values.

For GLP-1 bioassays, accuracy is commonly evaluated through:

• Recovery studies
• Relative potency samples
• Spiked preparations

Acceptance criteria are established based on intended assay use and manufacturing variability.

Precision

Precision measures closeness between independent test results.

Repeatability (Intra-assay precision)

Evaluates variability within a single run.

Typical factors:

• Same analyst
• Same equipment
• Same day
• Multiple replicates

Intermediate precision

Evaluates:

• Different analysts
• Different days
• Different reagent lots
• Different instruments

Reproducibility

Measures performance across laboratories and during method transfer activities.

For global GLP-1 manufacturing networks, reproducibility is often a key indicator of assay readiness for commercial implementation.

Linearity

Linearity demonstrates that assay response remains proportional to concentration across the intended operating range.

For GLP-1 potency assays, evaluation typically includes:

• 50% to 150% relative potency range
• Multiple concentration levels
• Dose-response modeling

Results should show consistent relative potency estimation throughout the validated range.

Range

The validated range represents concentrations over which acceptable:

• Accuracy
• Precision
• Linearity

have been demonstrated.

An appropriately defined range minimises out-of-specification investigations and supports routine QC operations.

Specificity

Specificity confirms that the assay measures the intended biological activity and is not influenced by:

• Excipients
• Degradation products
• Process impurities
• Matrix effects

This is particularly important for finished product and prefilled syringe testing.

Robustness

Robustness studies demonstrate assay reliability under small deliberate variations such as:

• Incubation time
• Cell density
• Reagent lot changes
• Temperature variations

Robust methods significantly reduce analytical risk during commercial manufacturing.

Dose formulation analysis

Dose formulation analysis ensures the administered dose accurately reflects the labelled claim and intended biological activity.

For GLP-1 products, dose formulation assessments typically include:

• Concentration verification
• Potency confirmation
• Homogeneity evaluation
• Stability assessment during use

These studies are especially important during development, clinical manufacturing, and comparability exercises following process changes.

The future of GLP-1 bioassay testing

As the market expands beyond semaglutide into dual and triple agonist platforms in type-II diabetes treatment, analytical strategies must evolve to support increasingly complex mechanisms of action. Advanced cell-based assays, digital data analytics, lifecycle validation approaches, and globally harmonised potency standards are expected to become central pillars of next-generation batch release programs.

Why partner with Adgyl Lifesciences?

With experience & expertise Adgyl supports bioassays across diverse therapeutic areas, including GLP-1 agonists. Our key capabilities include:

GLP-1 agonist-specific capabilities

• End-to-end bioassay support – Capability to support GLP-1 agonist programs from API/drug substance through formulated drug product and prefilled syringe, enabling consistent potency assessment across the product lifecycle.
• Relevant cell-based potency platforms – Experience in developing and executing mechanism-of-action-aligned functional bioassays, including receptor-mediated signaling and downstream response assays relevant to GLP-1 agonists

Bioassay support across therapeutic areas

• Method development to routine batch release – Integrated support covering assay development, optimisation, qualification/validation, method transfer, and routine GMP batch-release testing.
• GLP & GMP testing infrastructure – Quality systems and laboratory infrastructure supporting regulated bioanalytical testing, with an emphasis on data integrity, traceability, controlled documentation, and reproducibility.
• API-to-drug-product comparability – Bioassay strategies designed to demonstrate consistent biological activity across API, formulated product, and device-presented product, helping identify potential impacts of formulation, manufacturing, or presentation.
• Lifecycle and stability support – Potency testing to support release, stability programs, formulation/process changes, investigations, and comparability exercises.
• Fit-for-purpose assay strategy – Assays tailored around the molecule’s mechanism of action, intended product stage, specifications, and regulatory objective, rather than a one-size-fits-all testing approach.
• Strong scientific and regulatory focus – Experienced scientific teams supporting assay troubleshooting, investigation of atypical/OOS results, method robustness, and regulatory-facing documentation.

Summary

For GLP-1 agonists, bioassays are the scientific bridge connecting molecular design to patient outcomes. A well-developed and thoroughly validated potency assay enables reliable batch release decisions, supports manufacturing consistency, and ultimately safeguards product efficacy from API through finished product and prefilled syringe delivery.

In an increasingly competitive GLP-1 landscape, analytical excellence will remain a key differentiator for organisations committed to quality, compliance, and patient trust.