Drug Discovery Pipeline
Overview of the drug discovery process from initial concept through target selection, hit identification, lead optimization, and candidate selection.
## The Drug Development Timeline
Bringing a new drug from concept to market typically takes 10-15 years and costs $1-2 billion on average, including the cost of failures. The process follows a sequential pipeline with high attrition at every stage: for every 5,000-10,000 compounds entering discovery, approximately one reaches the market.
The pipeline consists of discovery (3-5 years), preclinical development (1-2 years), clinical trials (6-7 years), and regulatory review (1-2 years).
## Discovery Phase Stages
**Target identification**: Selecting a biological molecule (protein, receptor, enzyme, gene product) whose modulation will alter disease course. Targets emerge from genomic studies, disease biology research, competitor analysis, and clinical observations.
**Target validation**: Confirming that modulating the target will produce therapeutic benefit. Methods include genetic knockdown/knockout models, tool compounds, human genetic evidence (e.g., loss-of-function mutations that protect against disease), and biomarker studies.
**Hit identification**: Screening compound libraries against the validated target to identify molecules with measurable activity. High-throughput screening (HTS) tests 100,000-2,000,000 compounds using automated assays. Fragment-based screening uses smaller, simpler molecules (MW 120-250) at higher concentrations. Virtual screening applies computational docking to prioritize compounds.
**Hit-to-lead**: Confirmed hits are optimized through iterative medicinal chemistry to improve potency, selectivity, and basic drug-like properties. Structure-activity relationships (SAR) guide systematic modification of the chemical scaffold.
## Lead Optimization to Candidate
Lead optimization transforms early leads into drug candidates suitable for preclinical development. Medicinal chemists balance multiple parameters simultaneously:
- **Potency**: IC50/EC50 in the low nanomolar range
- **Selectivity**: Minimal off-target activity (selectivity panels of 50+ targets)
- **ADME properties**: Oral bioavailability, metabolic stability, permeability
- **Safety**: No genotoxicity (Ames test), acceptable hERG liability, clean safety pharmacology
- **Physicochemical properties**: Lipinski's Rule of Five compliance, solubility, stability
The output is a **preclinical candidate** (PCC) with a complete data package supporting advancement to GLP toxicology studies and IND-enabling work.
## Attrition and Failure Modes
Most drug programs fail. Common failure points include:
- **Lack of efficacy** (40-50% of Phase II failures): Target hypothesis was wrong or compound exposure was insufficient
- **Safety/toxicity** (30% of failures): Unacceptable adverse effects in animals or humans
- **Pharmacokinetic issues** (10%): Poor oral absorption, rapid metabolism, distribution problems
- **Commercial/strategic** (10-15%): Market changes, competitor approvals, portfolio prioritization
De-risking strategies include biomarker-driven patient selection, adaptive trial designs, and platform technologies that accelerate screening cycles.
## Key Takeaways
- Drug discovery spans 10-15 years with >99.9% compound attrition
- Target validation using human genetic evidence reduces late-stage failure risk
- Lead optimization balances potency, selectivity, ADME, and safety simultaneously
- Lack of efficacy is the leading cause of clinical-stage drug program failure