The Pitfalls of IBD Drug Discovery: 2 Strategies to Improve Reproducibility in DSS/TNBS Models
Improve the success rate of IBD drug discovery by correctly selecting between DSS and TNBS models. We explain the benefits of Pre-validated DSS and endoscopic evaluation (MEICS).
"Reproducibility issues" are frequent in IBD drug discovery. While DSS and TNBS models seem simple at first glance, slight differences in experimental conditions can drastically alter results. This article explains the scientific selection of models and strategies to increase study success rates using Pre-validated DSS and Endoscopic Evaluation (MEICS) from an expert's perspective.
1. DSS vs TNBS: Selecting the Right Model for Your Target
Choosing a model that does not match the drug's Mechanism of Action (MoA) is the biggest factor causing promising compounds to fail.
1-1. DSS Model: Epithelial Barrier and Innate Immunity
The DSS (Dextran Sulfate Sodium) model induces inflammation by damaging intestinal epithelial cells via DSS in drinking water, leading to the influx of luminal bacteria due to barrier disruption[1].
- Main Immune Response: The acute phase is dominated by innate immunity (macrophages, neutrophils). A shift to a Th2-dominant response is seen in the chronic phase.
- Recommended Drugs: Epithelial repair agents, anti-inflammatory drugs, innate immunity modulators.
1-2. TNBS Model: T-cell Dependent Adaptive Immunity
TNBS acts as a hapten (incomplete antigen), modifying self-proteins to induce T-cell mediated immunity[2].
- Main Immune Response: Characterized by Th1 (IL-12, IFN-γ) and Th17 (IL-23, IL-17) responses, similar to Crohn's disease.
- Recommended Drugs: IL-12/23 pathway (p40, p19) inhibitors, T-cell targeting drugs.
Model Comparison Quick Guide
| Feature | DSS Model | TNBS/DNBS Model |
|---|---|---|
| Human Relevance | Ulcerative Colitis (UC) | Crohn's Disease (CD) |
| Pathology | Mucosal layer, Diffuse | Transmural inflammation, Skip lesions |
| Key Cytokines | TNFα, IL-6, IL-1β | IL-12, IL-23, IFN-γ |
| Technical Difficulty | Low (Drinking water) *Note Lot diffs | High (Intrarectal procedure) |
| Best for | Mucosal protection, General anti-inflammatory | Biologics (IL-23 inhibitors etc.) |
2. Preventing the Biggest Risk: "DSS Reagent Lot Variability"
The most common cause of failure in studies using the DSS model is "Lot-to-Lot Variability of Reagents."
Why Does Lot Variability Occur?
The inflammation-inducing ability of DSS depends on its molecular weight (36-50 kDa is optimal) and degree of sulfation[1]. However, since DSS is a synthetic polymer, these properties differ slightly between manufacturing lots, even for the same catalog number from the same manufacturer. This leads to situations where "severe inflammation occurred at 2% concentration in the previous study, but inflammation doesn't occur even at 3% with this lot," losing data continuity.
Solution: Pre-validated DSS
The following protocol is effective for ensuring reproducibility:
- Secure Bulk: Secure a specific lot confirmed for performance in kilogram units.
- Dose Finding Study: Always conduct a preliminary study before the main study to determine the optimal concentration (e.g., 20% weight loss at Day 8 with 2.5%).
This ensures "expected severity" is reproduced whenever the study is conducted, minimizing noise in drug efficacy evaluation.
3. Innovation in Evaluation: Visualization with Endoscopy (MEICS)
Traditional evaluations that only "dissect and measure length" may miss the process of Mucosal Healing by drugs. Introducing small animal endoscopy dramatically improves data quality.
Quantitative Evaluation with MEICS Score
Endoscopic images are quantified using the international scoring system MEICS (Murine Endoscopic Index of Colitis Severity)[2].
- Vascularity: Evaluate loss of vascular pattern due to inflammation.
- Granularity: Evaluate mucosal surface roughness and edema.
- Fibrin: Evaluate white deposits on ulcer surfaces.
- Stool: Evaluate diarrhea and bloody stool status.
Benefits of Endoscopy
- Longitudinal Observation: Since the same individual can be tracked on Day 0, 7, and 14, "healing speed" can be measured without the influence of individual differences.
- Translationality: Evaluating with the same index as human clinical trial endpoints (Endoscopic Remission) increases clinical predictability.
Summary
In IBD drug discovery and development, the combination of "Usage of Validated Reagents" and "Advanced Evaluation Systems (Endoscopy)" is essential to avoid wasting cost and time. Do not rely on uncertain model systems; maximize the potential of candidate compounds with strategic study design.
FAQ
Q: When does inflammation peak in the DSS model? A: Typically, weight loss and DAI score peak at Day 7-10 from the start of DSS administration.
Q: What is the evaluation timing for the TNBS model? A: Acute inflammation is evaluated at Day 3-7 after intrarectal administration. Repeated administration is performed for chronic models.
Q: How long does Endoscopic Evaluation (MEICS) take? A: Non-invasive evaluation is possible in about 5-10 minutes per mouse.
Q: Is fibrosis evaluation possible? A: Yes, it is possible. Sirius Red staining is used in chronic phase models.
References