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Profacgen offers Small Molecule Ligands Screening, delivering high-throughput and virtual screening solutions to identify and optimize small-molecule ligands for target proteins and E3 ligases, accelerating protein degrader discovery from target validation to lead candidate.
Many biological molecules interact with small molecules, such as cofactors, metabolites, or drugs, collectively defined as ligands. Small molecule ligands not only participate in basic enzymatic reactions to build metabolic networks, but also act as extracellular and intracellular signals in regulatory networks. Screening of small molecule ligands for affinity and activity against a protein target is therefore vital in drug development and targeted protein degradation programs.
We offer two complementary screening approaches: high-throughput screening (HTS) for rapid experimental evaluation of large compound libraries, and virtual screening (VS) for cost-efficient computational identification of promising hits. Both methods are integrated with hit validation and optimization workflows to deliver actionable lead candidates.
Overview
Small molecule ligands are the foundational building blocks of heterobifunctional degraders. Their quality directly determines degrader performance across multiple dimensions:
Target engagement: High-affinity, selective binding ensures efficient target recognition and minimizes off-target effects. Ligand binding kinetics influence residence time and the duration of pharmacodynamic response
E3 recruitment: Optimized E3 ligase ligands enable selective engagement of the ubiquitin-proteasome system in specific cellular contexts, influencing tissue selectivity and degradation efficiency
Ternary complex formation: Ligand properties—binding geometry, surface complementarity, and induced-fit behavior—directly impact the stability and cooperativity of target-degrader-ligase ternary complexes
Degrader efficacy: Potent ligands with favorable physicochemical properties enable lower effective degrader doses, improved cellular permeability, and enhanced therapeutic windows
Figure 1. The process of high-throughput screening (HTS).
Our Screening Capabilities
Profacgen provides specialized screening modules tailored to diverse target classes, E3 ligase preferences, and program objectives:
Target Protein Ligand Screening
Identification of high-quality binders for disease-relevant target proteins.
Target-class expertise: Kinases, transcription factors, epigenetic regulators, and scaffold proteins
Multi-modal screening: HTS, VS, and fragment-based approaches adapted to target druggability
Validation cascade: Primary screening, counter-screening, and orthogonal confirmation
E3 Ligase Ligand Screening
Discovery of recruiters for established and emerging E3 ubiquitin ligases.
Established ligases: VHL, CRBN, MDM2, and cIAP ligands with validated clinical track records
Emerging ligases: Access to novel E3 recruiters for tissue-specific degradation programs
Modularity assessment: Evaluation of ligand compatibility with diverse linker chemistries
Fragment-Based Screening
Sensitive detection of weak-binding fragments as starting points for degrader warheads.
Fragment libraries: Diverse, rule-compliant collections (MW 150–300 Da) optimized for degrader applications
Biophysical detection: NMR, SPR, and X-ray crystallography for hit confirmation and binding mode elucidation
Fragment growing: Structure-guided elaboration to improve affinity while maintaining ligand efficiency
Hit Identification and Validation
Rigorous confirmation and prioritization of screening hits.
Hit confirmation: Dose-response validation, reproducibility assessment, and artifact exclusion
Mechanistic validation: Target engagement confirmation, binding site mapping, and competitive displacement
Prioritization: Multi-parameter scoring integrating potency, selectivity, novelty, and developability
Screening Technologies
Our platform integrates cutting-edge computational and experimental technologies to maximize screening success:
Virtual Screening: Structure-based molecular docking, pharmacophore modeling, and AI-driven hit prediction against curated compound databases. We provide VS services with E3 ligase or target protein structures. The most popular E3 ligases for screening include VHL, MDM2, cIAP, and CRBN
Structure-Based Drug Design: Homology modeling, molecular dynamics simulations, and binding free energy calculations to guide ligand optimization and predict ternary complex behavior
Biophysical Screening: Surface plasmon resonance (SPR), isothermal titration calorimetry (ITC), and bio-layer interferometry (BLI) for quantitative affinity determination and fragment detection
Functional Screening: Cell-based reporter assays, proximity-based assays, and degradation-specific readouts to validate functional activity in physiologically relevant contexts
Hit-to-Lead Optimization
Profacgen transforms validated hits into development-ready leads through systematic optimization:
Affinity optimization: Structure-guided modification of binding interactions to achieve sub-micromolar or nanomolar potency while maintaining ligand efficiency
Selectivity optimization: Counter-screening against homologs, off-target panels, and kinome-wide profiling to minimize undesired engagement and reduce safety liabilities
Structure–Activity Relationship (SAR): Iterative design-synthesize-test cycles supported by co-crystal structures, molecular modeling, and multi-parameter optimization to balance potency, selectivity, and drug-like properties
Applications
Our small molecule ligand screening platform supports diverse targeted protein degradation applications:
PROTAC Development: Identification of target warheads and E3 recruiters with compatible binding geometries, enabling rational linker design and ternary complex optimization
Molecular Glue Discovery: Screening for compounds that induce novel protein-protein interactions between target and E3 ligase, requiring sophisticated chemoproteomic and phenotypic approaches
E3 Ligase Ligand Discovery: Expansion of the E3 ligase toolbox through identification of novel recruiters with distinct tissue expression profiles and substrate specificities
Lead Optimization: Fine-tuning of ligand properties to improve cellular permeability, metabolic stability, and formulation characteristics while preserving binding affinity
Deliverables
Profacgen provides structured, decision-ready documentation aligned with your screening objectives:
Parameter
Description
Hit List
Prioritized compounds with chemical structures, screening scores, and rationale for selection
Binding Data
Kd, Ki, or IC50 values with experimental conditions, replicate statistics, and confidence intervals
SAR Analysis
Structure-activity relationship summary, optimization trajectory, and design hypotheses for next-generation compounds
Candidate Recommendations
Expert assessment of top candidates with developability scoring, risk assessment, and proposed optimization pathways
Integrated HTS and VS Platform: Complementary experimental and computational screening capabilities maximize chemical space coverage and hit discovery rates while controlling costs.
Automation and Data Integrity: Our HTS platform is fully integrated with industry-leading informatics for data fidelity, compound tracking, and full audit trails across data, samples, and operations.
State-of-the-Art Software Tools: We deploy advanced molecular docking, free energy perturbation, and AI-based prediction algorithms to identify innovative hits with improved hit rates.
TPD-Specific Expertise: Deep understanding of degrader pharmacology ensures ligand selection criteria are aligned with downstream ternary complex formation and cellular degradation requirements.
Collaborative Execution: We work closely with customers at every stage, from assay design and library selection through data interpretation and hit prioritization.
Representative Program Scenarios
Scenario 1: HTS for E3 Ligase Recruiter Discovery
Program Context:
A targeted protein degradation program required a novel E3 ligase recruiter with distinct tissue specificity compared to established VHL and CRBN ligands. The team sought to expand the E3 toolbox for a tissue-restricted degradation application.
Objective:
To identify small molecule binders for an emerging E3 ligase through high-throughput screening, validate binding specificity, and assess compatibility with degrader linker attachment.
Approach:
Profacgen developed a biochemical assay for the target E3 ligase and screened a diverse library of 350,000 compounds using automated liquid handling and plate-based detection. Primary hits were triaged through counter-screens against closely related ligases and orthogonal validation by SPR. Confirmed binders were evaluated for cellular permeability, metabolic stability, and linker compatibility. Top candidates were advanced to co-crystallization for structure-guided optimization.
Outcome:
The screen identified 8 validated hits with sub-micromolar affinity and >20-fold selectivity over related E3 family members. Two candidates demonstrated favorable cellular activity and were successfully incorporated into functional PROTACs, validating the new E3 ligase as a viable degrader recruitment platform.
Scenario 2: Virtual Screening for Kinase Warhead Optimization
Program Context:
A kinase degrader program possessed a weakly binding fragment hit and required rapid expansion into a potent, selective warhead suitable for PROTAC assembly. Traditional medicinal chemistry was constrained by limited structural information.
Objective:
To leverage virtual screening and structure-based design to identify novel chemical scaffolds with improved affinity and selectivity, and to generate structural data for rational optimization.
Approach:
Profacgen generated a homology model of the target kinase and performed virtual screening of 5 million compounds from commercial and proprietary libraries. Top-ranked hits were evaluated by docking score, pharmacophore fit, and predicted binding free energy. Selected compounds were purchased and validated by biochemical assay and SPR. A novel chemotype was identified and optimized through iterative structure-based design, yielding a candidate with confirmed co-crystal structure.
Outcome:
The optimized warhead achieved 200-fold improvement in binding affinity over the original fragment, with exceptional selectivity against the kinome. The co-crystal structure enabled rational linker placement, and the resulting PROTAC demonstrated potent cellular degradation, supporting progression to lead optimization.
Q: What is the difference between HTS and virtual screening?
A: HTS experimentally tests large compound libraries against a biological target using automated robotics and detection systems, generating direct activity data. Virtual screening computationally evaluates compounds against target structures, predicting binding affinity and identifying promising hits without experimental testing. HTS provides experimental validation but requires more resources; VS is faster and more cost-efficient but requires subsequent experimental confirmation. We recommend combining both approaches for optimal coverage.
Q: Which E3 ligases do you support for ligand screening?
A: We routinely screen against established E3 ligases including VHL, CRBN, MDM2, and cIAP. We also support emerging ligases based on specific program requirements. Our platform includes validated assays and structural models for multiple E3 ligases, enabling selection of the optimal recruiter for your target biology and therapeutic context.
Q: Can you screen targets without crystal structures?
A: Yes. We employ homology modeling and molecular dynamics to generate reliable structural models for virtual screening when experimental structures are unavailable. For HTS, biochemical assays do not require structural information. We validate model quality through retrospective enrichment studies and cross-validation before initiating virtual screening campaigns.
Q: What is the typical timeline for a screening campaign?
A: Virtual screening campaigns typically require 4–6 weeks from target preparation to hit list delivery. HTS campaigns range from 8–12 weeks depending on library size, assay complexity, and validation requirements. Hit-to-lead optimization timelines vary based on starting point quality and optimization scope, typically 3–6 months.
Q: How do you ensure data quality in HTS?
A: Our HTS platform integrates industry-leading informatics for real-time data monitoring, automated quality control, and compound tracking. We implement strict assay validation including Z'-factor determination, replicate consistency checks, and hit confirmation thresholds. Full audit trails ensure data integrity and regulatory compliance.
Q: Can existing inhibitors be repurposed as degrader warheads?
A: Yes. Known inhibitors with defined binding modes can be evaluated for warhead suitability, including linker attachment vector identification and affinity assessment. This approach significantly accelerates timelines by leveraging existing SAR data. We also support de novo discovery when no suitable inhibitor exists.
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Figure 1. The process of high-throughput screening (HTS).