Protein Degradation-Targeting Chimeras (PROTACs): Molecular Design, Degradation Mechanisms, Experimental Evaluation, and Research Tools
Protein Degradation-Targeting Chimeras (PROTACs): Molecular Design, Degradation Mechanisms, Experimental Evaluation, and Research Tools
Proteolysis-targeting chimeras (PROTACs) are a class of heterobifunctional molecules that selectively reduce the abundance of a protein of interest by harnessing the cellular ubiquitin–proteasome system (UPS). They represent an important modality within the field of targeted protein degradation (TPD).
Traditional small-molecule inhibitors generally need to continuously occupy an active site or ligand-binding site to block protein function. By contrast, PROTACs recruit an E3 ubiquitin ligase, leading to ubiquitination of the target protein and its subsequent degradation by the proteasome. Their central mode of action therefore shifts from “inhibiting protein function” to “reducing protein abundance.”
1. What Problems Do PROTACs Address?
1.1 Characteristics of Traditional Small-Molecule Inhibitors
Most traditional small-molecule drugs exert their effects by forming binary complexes with target proteins. For example, kinase inhibitors may occupy the adenosine triphosphate-binding site, whereas receptor antagonists may prevent endogenous ligands from binding to their receptors.
This mode of action generally has the following characteristics:
① Pharmacological activity depends on maintaining a certain level of drug–target occupancy;
② It primarily affects protein functions directly associated with the binding site;
③ After the drug dissociates, the remaining target protein may regain its function.
Traditional inhibition strategies have achieved substantial success for kinases, receptors, and metabolic enzymes with well-defined catalytic pockets. However, some disease-associated proteins lack functional pockets suitable for small-molecule modulation, or they perform multiple functions involving catalytic activity, scaffold assembly, and protein–protein interactions. In such cases, blocking a single active site may not eliminate all of the biological functions of the protein.
1.2 Basic Principles of PROTACs
One end of a PROTAC binds the protein of interest, while the other end binds a substrate-recognition component of an E3 ubiquitin ligase complex. The two ligands are connected by a linker. The basic process is as follows:
Target protein binding → E3 ubiquitin ligase recruitment → Formation of the target protein–PROTAC–E3 ternary complex → Target protein ubiquitination → Proteasomal recognition and degradation of the target protein
In 2001, Sakamoto and colleagues designed the peptide-containing molecule Protac-1. This molecule linked an ovalicin-derived group that recognizes methionine aminopeptidase-2 (MetAP-2) to an IκBα phosphopeptide that recruits the SCFβ-TRCP ubiquitin ligase complex. In an in vitro ubiquitination system and Xenopus egg extracts, Protac-1 was shown to induce the ubiquitination and degradation of MetAP-2.
This study established the fundamental concept of PROTAC technology: rather than only inhibiting protein function directly, a drug can redirect the substrate specificity of an E3 ligase and channel a target protein into the cellular degradation pathway.
2. Molecular Components of a PROTAC
A typical PROTAC consists of a target protein ligand, a linker, and an E3 ligase ligand.
Component | Primary Function | Key Design Considerations |
Target protein ligand | Recognizes and binds the target protein | Retention of binding affinity and identification of a suitable attachment site |
Linker | Connects the two ligands and regulates the spatial relationship between the two proteins | Length, flexibility, attachment orientation, and physicochemical properties |
E3 ligase ligand | Recruits an E3 ubiquitin ligase complex | E3 expression, subcellular localization, and ternary-complex geometry |
2.1 Target Protein Ligand
The target protein ligand is often referred to as the warhead and is responsible for recognizing the target protein. It may be derived from a known inhibitor, receptor ligand, or another small molecule capable of binding the target protein.
In a traditional inhibitor, the ligand generally needs to occupy a critical functional site and directly inhibit protein activity. In a PROTAC, the primary role of the target protein ligand is to recruit the target protein into the degradation process. It therefore does not necessarily need to possess strong direct inhibitory activity.
Selection of a target protein ligand requires simultaneous consideration of:
① Binding affinity and selectivity for the target protein;
② Solvent-exposed regions of the ligand when bound to the protein;
③ Chemical positions suitable for linker attachment;
④ Whether linker installation disrupts the original binding conformation.
Consequently, when converting a known inhibitor into a PROTAC, the linker attachment site cannot be selected arbitrarily. The linker should extend from a position that does not disrupt critical binding interactions and is oriented toward the solvent-exposed surface of the protein.
2.2 E3 Ligase Ligand
E3 ubiquitin ligases are responsible for selecting substrates for ubiquitination. PROTACs generally use small-molecule ligands to bind substrate-recognition components within E3 ligase complexes.
Two of the most widely used recruitment systems are:
① Cereblon (CRBN), a component of the CRL4CRBN ligase complex;
② Von Hippel–Lindau protein (VHL), a component of the CRL2VHL ligase complex.
CRL refers to a Cullin–RING ligase. CRBN ligands are commonly derived from thalidomide-, lenalidomide-, or pomalidomide-related structures, whereas VHL ligands generally contain hydroxyproline-derived structures that bind the VHL substrate-recognition region.
The choice of E3 ligase can affect degradation efficiency, pharmacological selectivity at the cellular or tissue level, and compatibility with subcellular localization. The tissue distribution of the PROTAC molecule itself also depends on its physicochemical and pharmacokinetic properties. Different E3 complexes have distinct protein surfaces, expression levels, and subcellular localizations. Therefore, recruitment of CRBN and VHL to the same target protein may produce markedly different degradation outcomes.
2.3 Linker
The linker is not merely a passive chemical chain connecting two ligands. It determines the distance, orientation, and conformational freedom between the target protein and the E3 ligase, while also influencing the solubility, stability, and cellular permeability of the entire PROTAC molecule.
Key aspects of linker design include:
① Chain length;
② Flexibility and rigidity;
③ Incorporation of polyethylene glycol, alkyl chains, or cyclic structures;
④ Attachment orientation at both ends;
⑤ Number of hydrogen-bond donors and acceptors;
⑥ Propensity for intramolecular folding.
If the linker is too short, steric clashes may occur between the target protein and the E3 ligase. If it is too long or excessively flexible, the number of conformations that do not support ubiquitin transfer may increase. PROTAC design is therefore not simply a matter of connecting two high-affinity ligands. The target protein and E3 ligase must be positioned in a spatial arrangement that is compatible with productive ubiquitination.
3. Molecular Mechanism of PROTAC-Mediated Protein Degradation
A PROTAC does not directly hydrolyze the target protein. Instead, it simultaneously binds the target protein and an E3 ubiquitin ligase complex, inducing formation of a productive ternary complex. This enables the target protein to acquire ubiquitin modifications, after which it is recognized and degraded by the 26S proteasome. The overall process includes ternary-complex formation, target protein ubiquitination, proteasomal degradation, and potential subsequent recycling of the PROTAC molecule.
3.1 Ubiquitination Reaction
Ubiquitination is primarily carried out through the sequential activities of an E1 ubiquitin-activating enzyme, an E2 ubiquitin-conjugating enzyme, and an E3 ubiquitin ligase. First, E1 uses adenosine triphosphate (ATP) to activate ubiquitin. Ubiquitin is then transferred to E2. Finally, E3 promotes the correct positioning of ubiquitin-loaded E2 and the substrate protein, allowing ubiquitin to be transferred to the substrate.
For RING-type E3 complexes containing CRBN or VHL, ubiquitin is generally transferred directly from E2 to the ε-amino group of a lysine side chain on the target protein.
The simplified reactions are as follows:
1. Ubiquitin activation
Ub–COOH + ATP + E1 →
E1–S–CO–Ub + AMP + PPi
2. Ubiquitin transfer to E2
E1–S–CO–Ub + E2–SH →
E1–SH + E2–S–CO–Ub
3. Ubiquitin transfer to the target protein
E2–S–CO–Ub + POI–Lys–NH₂ →
E2–SH + POI–Lys–NH–CO–Ub
Here, Ub represents ubiquitin, and POI represents the protein of interest. “E1–S–CO–Ub” and “E2–S–CO–Ub” are thioester intermediates. The C terminus of ubiquitin forms an isopeptide bond with the lysine side chain of the target protein. After multiple rounds of ubiquitin transfer, a ubiquitin chain suitable for proteasomal recognition is formed on the target protein. The target protein is then unfolded by the 26S proteasome and degraded into short peptides.
3.2 PROTAC Degradation Cycle
PROTACs exploit the natural ubiquitination machinery described above to alter E3 ligase substrate recognition. The complete process includes:
Cellular entry of the PROTAC → Binding to the target protein and the E3 substrate-recognition component → Formation of the target protein–PROTAC–E3 ternary complex → Transfer of ubiquitin from E2 to the target protein → Formation of a proteasome-recognizable ubiquitination signal on the target protein → Degradation of the target protein by the 26S proteasome → Dissociation of the PROTAC from the complex and potential participation in another degradation cycle
After the target protein has been ubiquitinated, the PROTAC may be released from the complex and participate in additional degradation events. Some PROTACs therefore exhibit a recyclable, “event-driven” pharmacological mode of action: the molecule does not need to continuously occupy every target protein but only needs to trigger effective ubiquitination and degradation events.
This recycling is not unlimited. Its efficiency remains constrained by factors including the intracellular unbound concentration of the PROTAC, molecular stability, complex dissociation kinetics, the rate of target protein resynthesis, and proteasomal activity.
3.3 Productive Ternary Complexes
The ability of a target protein, a PROTAC, and an E3 ligase to form a ternary complex does not necessarily mean that the target protein will be degraded. Only a ternary complex that supports efficient ubiquitin transfer is considered productive.
A productive ternary complex generally requires the following conditions:
① No severe steric clashes occur between the target protein and the E3 ligase;
② The target protein surface generally contains conformationally accessible lysine residues or other acceptor sites that can be efficiently ubiquitinated;
③ These sites are positioned favorably relative to the ubiquitin carried by E2;
④ The association and dissociation kinetics of the ternary complex are compatible with effective ubiquitin transfer;
⑤ The ubiquitinated target protein can enter the proteasomal degradation pathway.
The crystal structure of the BRD4BD2–MZ1–VHL complex, reported in 2017, showed that a PROTAC does more than simply bring two proteins into proximity. It can also induce new protein–protein contacts between the target protein and the E3 ligase. These newly formed interactions can affect ternary-complex stability, cooperativity, and degradation selectivity.
4. Key Factors Determining PROTAC Degradation Activity
4.1 Ternary-Complex Conformation and Kinetics
High affinity of both PROTAC ligands for their respective binding partners does not guarantee efficient degradation of the target protein. If the proteins are improperly oriented within the ternary complex, target protein lysines may not be positioned close enough to E2. If the complex dissociates too rapidly, there may be insufficient time for adequate ubiquitination.
Conversely, a molecule that does not have the highest binary binding affinity may still produce stronger degradation if it forms a ternary complex that is better suited for ubiquitin transfer.
Ternary complexes may also display different degrees of cooperativity:
① Positive cooperativity: binding of one protein facilitates binding of the other protein;
② Negative cooperativity: simultaneous binding of the two proteins creates unfavorable interactions;
③ No apparent cooperativity: the ternary complex is primarily maintained by the two binary binding events.
Positive cooperativity may improve ternary-complex stability and selectivity, but it is not essential for efficient degradation. Studies of Bruton’s tyrosine kinase (BTK) degraders have shown that reducing steric clashes within the ternary complex can produce effective degradation even in the absence of clear positive cooperativity.
4.2 Structural Characteristics of the Target Protein
Whether a target protein can be efficiently degraded is closely related to its surface and structural properties, including:
① The number and positions of accessible lysine residues;
② Flexibility of the protein surface;
③ Whether the target protein is incorporated into a stable multiprotein complex;
④ Whether the ubiquitinated protein can be efficiently unfolded by the proteasome;
⑤ Whether the target protein and the E3 ligase are located in the same cellular compartment.
The same PROTAC may produce different degradation outcomes among structurally related members of a protein family. Such selectivity does not necessarily arise from selective binding of the target protein ligand. It may instead result from differences in the spatial arrangements formed by related proteins within their respective ternary complexes.
4.3 Effective Intracellular Concentration
PROTACs generally have higher molecular weights, more rotatable bonds, and larger polar surface areas than conventional small molecules. Even when in vitro binding assays demonstrate that a ternary complex can form, effective degradation may not occur if the molecule cannot enter cells or does not reach a sufficient intracellular unbound concentration.
Cellular degradation results may also be affected by:
① Expression levels of the target protein and E3 ligase;
② Drug uptake and efflux;
③ Intracellular stability of the PROTAC;
④ Synthesis and turnover rates of the target protein;
⑤ Functional status of the ubiquitin–proteasome system.
PROTAC degradation data should therefore always be reported together with the cell type, treatment concentration, treatment duration, and detection method.
4.4 Hook Effect
Some PROTACs exhibit a hook effect at high concentrations, in which further increases in concentration lead to reduced target protein degradation.
Low concentration
Insufficient ternary-complex formation → Weak degradation
Optimal concentration
Increased target protein–PROTAC–E3 ternary-complex formation → Enhanced degradation
Excessively high concentration
Extensive formation of target protein–PROTAC and PROTAC–E3 binary complexes → Potential reduction in the proportion of complete ternary complexes → Reduced degradation
The hook effect does not occur with every PROTAC. Its magnitude depends on the affinities of the two ligands, ternary-complex cooperativity, and the intracellular concentrations of the target protein and E3 ligase. Experimental concentration ranges should therefore cover low, intermediate, and high concentrations rather than testing only a single high concentration.
5. Differences Between PROTACs and Traditional Small-Molecule Inhibitors
Comparison Parameter | Traditional Small-Molecule Inhibitors | PROTACs |
Direct outcome | Block a specific activity or protein–protein interaction | Reduce the total abundance of the target protein |
Primary pharmacological mode | Occupancy-driven | Event-driven |
Requirement for sustained binding | Generally requires maintenance of a certain level of target occupancy | May dissociate from the target protein after ubiquitination has been initiated |
Effect on catalytic function | Direct inhibition | Catalytic function is lost as the protein is degraded |
Effect on scaffold function | Scaffold function may remain intact | Scaffold function is generally lost when the protein is removed |
Common evaluation parameters | IC₅₀, EC₅₀, and target occupancy | DC₅₀, Dmax, degradation rate, and recovery time |
Major determinants | Binary binding and functional-site occupancy | Ternary-complex formation, ubiquitination, and intracellular degradation processes |
The half-maximal inhibitory concentration (IC₅₀) is the concentration of a compound required to produce 50% of its maximal inhibitory effect. PROTACs, however, must be evaluated using multiple parameters, including degradation potency, maximal degradation, degradation kinetics, and target protein recovery.
Compared with traditional inhibitors, PROTACs may have three important characteristics:
① They can trigger subsequent degradation without continuously occupying the target protein;
② They can eliminate both catalytic and noncatalytic functions of the protein;
③ Structural differences among ternary complexes may result in degradation selectivity that exceeds the binding selectivity of the original target ligand.
Protein degradation is not necessarily superior to functional inhibition. Removal of an entire protein may produce broader biological consequences than inhibition of a single activity and may also narrow the safety margin. Whether a degradation strategy is appropriate should be determined according to the functions of the target protein, the disease mechanism, and the role of the protein in normal tissues.
6. How to Determine Whether a PROTAC Is Truly Effective
Evaluation of a PROTAC requires a continuous chain of evidence. First, it must be demonstrated that the target protein decreases. Second, the reduction must be shown to depend on the intended E3 ligase and the proteasome. Finally, the reduction in target protein abundance must be linked to the expected functional consequences.
6.1 Concentration–Degradation Relationship
6.1.1 DC₅₀
The half-maximal degradation concentration (DC₅₀) is the concentration at which the concentration–degradation curve reaches 50% of the maximal degradation achieved by the compound.
Because some studies define DC₅₀ as the concentration that reduces the target protein by 50% relative to the control, the calculation method should be clearly specified. The cell type, treatment duration, detection method, and curve-fitting model should also be reported.
6.1.2 Dmax
Maximum degradation (Dmax) is the greatest proportionate reduction in target protein abundance observed under the specified experimental conditions and within the tested concentration range.
DC₅₀ reflects degradation potency, whereas Dmax reflects degradation depth. For example, one compound may rapidly reach its maximal effect at a low concentration but achieve a Dmax of only 50%. Another compound may have a slightly higher DC₅₀ but reduce target protein levels by more than 90%. The two parameters should therefore be interpreted together.
6.1.3 Complete Concentration Range
The concentration gradient should include inactive, active, and high-concentration ranges. This enables reliable estimation of DC₅₀ and Dmax and allows assessment of whether a hook effect occurs at high concentrations.
6.2 Degradation Kinetics
Time-course experiments should provide the following four types of information:
Observation | Question to Be Addressed |
Onset of degradation | How soon after treatment does the target protein begin to decrease? |
Time to maximal degradation | When does the protein reach its lowest level? |
Duration of degradation | How long is the maximal effect maintained? |
Recovery after washout | How long does the protein take to recover after the PROTAC is removed? |
6.2.1 Degradation Rate
A rapid reduction in protein abundance indicates that the target protein can enter the ubiquitination and proteasomal degradation pathway relatively quickly. However, degradation rate alone does not determine the overall magnitude of the pharmacological effect.
6.2.2 Protein Recovery
After washout of the PROTAC, the rate of target protein recovery depends on protein resynthesis, residual drug exposure, and whether degradation remains ongoing. Recovery experiments help determine whether the degradation effect persists substantially longer than the drug-treatment period.
6.3 Mechanistic Validation
A decrease in target protein abundance alone does not prove that PROTAC-mediated proteasomal degradation has occurred. Reduced transcription, inhibition of translation, cytotoxicity, or other protein degradation pathways may produce the same observation.
Mechanistic validation should therefore use multiple independent lines of evidence to establish a coherent mechanism-of-action chain.
① Confirm dependence on target protein binding
Add an excess of the free target protein ligand and determine whether it competitively blocks degradation. A structurally related analogue that does not bind the target protein may also be used as a negative control.
② Confirm dependence on E3 recruitment
Add an excess of the free E3 ligand as a competitor, use an inactive control that cannot bind the E3 ligase, or apply genetic knockdown or knockout to verify that the recruited E3 is required.
③ Confirm dependence on the ubiquitin–proteasome system
Use an appropriate proteasome inhibitor or an intervention targeting the Cullin–RING ligase pathway to determine whether the decrease in target protein abundance is blocked. Because these treatments broadly affect protein homeostasis, conclusions should not be based on a single inhibitor experiment alone.
Where feasible, an increase in target protein ubiquitination should be assessed before a substantial reduction in target protein abundance occurs, providing more direct evidence that the target has entered the ubiquitination pathway.
④ Exclude transcriptional changes and nonspecific toxicity
Measure target protein messenger RNA, cell viability, total protein abundance, and stress-related markers in parallel to exclude transcriptional suppression, severe cellular damage, or nonspecific protein loss.
The bromodomain and extra-terminal (BET) family degrader dBET1 provides an illustrative example. Researchers used free-ligand competition, an inactive stereoisomer, and CRBN-dependence experiments to demonstrate that reduction of bromodomain-containing protein 4 (BRD4) required both target protein binding and CRBN recruitment.
6.4 Selectivity and Functional Evaluation
6.4.1 Degradation Selectivity
Early experiments may examine closely related members of the target protein family and, depending on the E3 ligand used, known substrates that may be affected. For CRBN-based PROTACs, attention should also be paid to ligand-induced CRBN neosubstrates.
More advanced studies should use quantitative proteomics to assess global protein changes. Proteomic analysis should not be performed only at very late time points. Prolonged treatment may produce extensive downstream protein changes that obscure direct degradation substrates and make it difficult to distinguish primary effects from secondary consequences.
6.4.2 Functional Effects
Reduction of target protein abundance is not the final experimental endpoint. Functional outcomes related to the biological role of the target protein should also be assessed, including:
① Changes in phosphorylation of downstream signaling proteins;
② Target gene expression;
③ Cell proliferation, apoptosis, or differentiation;
④ Cell migration, metabolism, or immune function;
⑤ Efficacy and tolerability in animal models.
The complete PROTAC should be compared with the original target protein ligand, an inactive control, and a vehicle control. These comparisons help distinguish effects caused by protein degradation from those caused by direct functional inhibition or nonspecific activity.
7. Suitable Applications and Major Limitations of PROTACs
7.1 Research Situations Suitable for PROTACs
7.1.1 Simultaneous Elimination of Catalytic and Noncatalytic Functions
When a target protein possesses enzymatic activity while also participating in scaffold assembly or protein–protein interactions, degradation of the entire protein may produce a more complete effect than inhibition of a single active site.
7.1.2 Absence of a Directly Inhibitable Functional Pocket
Some proteins lack a catalytic pocket suitable for traditional small-molecule inhibition but still contain surfaces that can be recognized by a ligand. Such a ligand may be used as the target-recruiting group in a PROTAC.
7.1.3 Rapid Reduction of Protein Abundance for Functional Studies
Compared with gene knockout, PROTACs can reduce protein abundance over a shorter time frame. This facilitates analysis of the acute effects of protein loss and may reduce the influence of long-term genetic compensation.
Classical PROTACs generally still require a ligand that directly binds the target protein. PROTAC technology therefore expands the range of proteins that can be pharmacologically manipulated and the types of ligands that can be used, but it does not eliminate the need to discover a target-binding ligand.
7.2 Major Limitations in PROTAC Development
7.2.1 Molecular Physicochemical Properties
PROTACs generally have high molecular weights, numerous rotatable bonds, and large polar surface areas. These properties may result in limited aqueous solubility, low cellular permeability, variable oral absorption, or insufficient metabolic stability.
Linker optimization must therefore consider both ternary-complex geometry and in vivo pharmacokinetic properties. Development should not focus exclusively on achieving a low DC₅₀ and high Dmax in cellular assays.
7.2.2 Dependence on the E3 Ligase and Cellular Context
PROTAC activity depends on the relevant E3 ligase and the associated complex components. Low E3 expression, mismatched subcellular localization, or impaired ligase-complex function may reduce degradation efficiency.
Long-term treatment may also select for resistant cells with deletion, mutation, or downregulation of E3 complex components.
Developing recruitment systems for different E3 ligases may therefore broaden the range of applicable tissues and reduce limitations associated with dependence on a single E3 ligase.
7.2.3 Selectivity and Safety
A PROTAC may degrade additional proteins that are recognized by the original target ligand. It may also form new ternary complexes that generate unexpected degradation substrates that cannot be predicted from binary binding profiles alone.
In addition, PROTACs reduce the abundance of the entire target protein. If the target protein performs important structural or regulatory functions in normal tissues, sustained or excessive depletion may produce adverse effects that differ from those caused by reversible inhibition.
PROTAC evaluation should therefore consider not only the magnitude of degradation but also the optimal depth and duration of degradation, tissue distribution, and proteome-wide selectivity.
8. Major Milestones in the Development of PROTAC Technology
Year | Major Advance | Significance |
2001 | The peptide-containing Protac-1 induced MetAP-2 ubiquitination and degradation in an in vitro system and Xenopus egg extracts | Established the fundamental concept of artificially recruiting an E3 ligase to degrade a target protein |
2015 | dBET1 and VHL-recruiting, fully small-molecule PROTACs achieved protein degradation in cells and animal models | Demonstrated the in vivo potential of small-molecule PROTACs |
2017 | The crystal structure of the BRD4–MZ1–VHL ternary complex was determined | Revealed the roles of newly formed protein–protein interactions and cooperativity |
2026 | The FDA approved VEPPANU (vepdegestrant) | Marked the first regulatory approval of a PROTAC drug |
8.1 Emergence of Fully Small-Molecule PROTACs
In 2015, dBET1 was shown to degrade BET family proteins by recruiting CRBN. During the same period, VHL-recruiting small-molecule PROTACs demonstrated target protein degradation and molecular recycling in cellular and animal studies.
8.2 Structural Characterization of a Ternary Complex
The 2017 structural study of the BRD4–MZ1–VHL complex demonstrated that a ternary complex is not simply the sum of two binary complexes. Newly formed contacts between the target protein and the E3 ligase can determine complex stability and degradation selectivity.
8.3 Regulatory Approval of a Heterobifunctional Degrader
On May 1, 2026, the U.S. Food and Drug Administration (FDA) approved VEPPANU (vepdegestrant) for the treatment of adults with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative, advanced or metastatic breast cancer harboring an ESR1 mutation confirmed by an FDA-authorized test, whose disease had progressed following at least one line of endocrine therapy.
Vepdegestrant is a heterobifunctional protein degrader that simultaneously binds ER and CRBN, inducing CRBN-mediated polyubiquitination and proteasomal degradation of ER. It is the first PROTAC drug to receive FDA approval.
9. Classification and Applications of Representative Chemicals for Proteolysis-Targeting Chimera (PROTAC) Research
Table 1. PROTACs and Related Targeted Protein Degraders
Category | CAS No. | Aladdin Cat. No. | Name | Specification or Purity | Product Features and Applications |
Heterobifunctional PROTAC—estrogen receptor | 2229711-68-4 | Vepdegestrant (ARV-471) | Moligand™, ≥99% | Recruits CRBN to induce the ubiquitination and degradation of estrogen receptor alpha; used for studies of receptor degradation, concentration–time relationships, and breast cancer cells. | |
Heterobifunctional PROTAC—BET family | 1949837-12-0 | ARV-771 | Moligand™, ≥98% | Recruits VHL to degrade BET family proteins; used to study the degradation of BRD2, BRD3, and BRD4, as well as downstream transcriptional regulation. | |
Heterobifunctional PROTAC—BRD4 | 1797406-69-9 | MZ1, a (+)-JQ1-based PROTAC degrader of BRD4 | Moligand™, ≥98% | Recruits VHL and preferentially induces BRD4 degradation; used to study ternary-complex formation, cooperativity, and degradation selectivity. | |
Heterobifunctional PROTAC—BET family | 1950634-92-0 | dBET6 | Moligand™, ≥98% | Recruits CRBN to degrade BET family proteins; used to study rapid protein degradation, transcriptional regulation, and cellular phenotypes. | |
Heterobifunctional PROTAC—BET family | 1799711-21-9 | dBET1 | ≥99% | Recruits CRBN to degrade BET family proteins; used to investigate proteasome dependence, competitive rescue, and degradation mechanisms. | |
Heterobifunctional PROTAC—BET family | 1818885-28-7 | ARV-825 | ≥97% | Recruits CRBN to degrade BET family proteins; used to study BRD4 degradation, changes in MYC expression, and cell proliferation. | |
Heterobifunctional PROTAC—chromatin-remodeling proteins | 2375564-55-7 | ACBI1 | Moligand™, ≥98% | Recruits VHL to degrade SMARCA2, SMARCA4, and PBRM1; used to study dependence on the BAF and PBAF chromatin-remodeling complexes. | |
Heterobifunctional PROTAC—BRD7 and BRD9 | 2306193-61-1 | VZ185, BRD7/9 degrader | ≥98% | Recruits VHL to degrade BRD7 and BRD9; used to study degradation kinetics, protein selectivity, and chromatin-remodeling functions. | |
Heterobifunctional PROTAC—BCL-XL | 2365172-42-3 | DT2216 | Moligand™, ≥98% | Recruits VHL to degrade BCL-XL; used to investigate anti-apoptotic protein dependence, cell death, and platelet-associated selectivity. | |
Heterobifunctional PROTAC—KRAS G12C | 2502156-03-6 | LC-2 | ≥98% | Recruits VHL through a covalent KRAS G12C ligand; used to study KRAS G12C degradation and changes in MAPK signaling. | |
Heterobifunctional PROTAC—BRAF | 2413035-41-1 | SJF-0628 | ≥99% | Recruits VHL to induce the degradation of multiple mutant BRAF proteins; used to study RAF protein stability and MAPK signaling. | |
Heterobifunctional PROTAC—STAT3 | 2429877-44-9 | SD-36 | ≥98% | Recruits CRBN to degrade STAT3; used to study STAT3-dependent transcription, downstream signaling, and tumor-cell dependence. | |
Heterobifunctional PROTAC—BTK | 2231744-29-7 | MT-802 | ≥95% | Recruits CRBN to degrade BTK and certain drug-resistant mutant forms; used to study BTK signaling and ibrutinib resistance. | |
Tag-dependent heterobifunctional degrader—dTAG system | 2064175-41-1 | FKBP12 PROTAC dTAG-13 | ≥99% | Recruits CRBN to degrade fusion proteins carrying the FKBP12F36V tag; used for conditional protein depletion and target-function validation. | |
Hydrophobic-tagging protein degrader—EZH2 | 2225938-17-8 | MS1943 | ≥98% | Induces EZH2 degradation through hydrophobic tagging; used to study EZH2 protein function and hydrophobic-tagging-mediated degradation mechanisms. |
Table 2. Target Protein Ligands and E3-Recruiting Ligands for PROTAC Molecular Design
Category | CAS No. | Aladdin Cat. No. | Name | Specification or Purity | Product Features and Applications |
CRBN-recruiting ligand | 191732-72-6 | Lenalidomide | Moligand™, ≥99% | Binds CRBN; used in CRBN-based PROTAC design, ligand derivatization, and competitive E3-recruitment experiments. | |
CRBN-recruiting ligand | 19171-19-8 | Pomalidomide | Moligand™, ≥99% | Binds CRBN and contains a modifiable amino group; used in the construction of CRBN-based PROTACs and the design of linker attachment sites. | |
CRBN-recruiting ligand | 50-35-1 | (±)-Thalidomide | Moligand™, ≥98% | Parent scaffold of CRBN-binding ligands; used in the design of CRBN-recruiting molecules and comparative studies of ligand structures. | |
VHL-recruiting ligand and competitive reagent | 2097381-85-4 | VH298, VHL inhibitor | ≥98% (HPLC) | Binds the substrate-recognition region of VHL; used to competitively block VHL recruitment and validate VHL dependence. | |
VHL-recruiting ligand | 1448297-52-6 | (S,R,S)-AHPC (MDK7526) | ≥97% | VHL-binding ligand building block; used in the construction of VHL-based PROTACs, ligand conjugation, and ternary-complex studies. | |
IAP-recruiting ligand | 1005342-46-0 | LCL161, inhibitor | Moligand™, ≥99% | Binds members of the IAP protein family; used in the design of IAP-recruiting degraders and competitive validation experiments. | |
cIAP1-recruiting ligand | 65322-89-6 | Bestatin methyl ester, neutral aminopeptidase inhibitor | ≥97% | Can serve as a cIAP1-recruiting moiety; used to construct IAP-dependent degraders and study E3 dependence. | |
MDM2-recruiting ligand | 675576-98-4 | Nutlin-3a, p53–MDM2 interaction inhibitor | ≥97% | Binds MDM2; used to construct MDM2-recruiting degraders and in competitive binding studies. | |
Target protein ligand—KRAS G12C | 2326521-71-3 | Adagrasib (MRTX849) | Moligand™, ≥98% | Covalently binds KRAS G12C; used in the design of related degraders, target-occupancy studies, and competitive-control experiments. | |
Target protein ligand—BTK | 936563-96-1 | Ibrutinib (PCI-32765) | Moligand™, ≥98% | Covalently binds BTK; used in BTK degrader design, target-competition experiments, and studies of drug-resistant mutants. | |
Target protein ligand—BRAF | 918504-65-1 | Vemurafenib (PLX4032, RG7204) | Moligand™, ≥98% | Binds mutant BRAF; used in BRAF degrader design, target-binding studies, and signaling-pathway controls. | |
Target protein ligand—BET family | 1268524-70-4 | (+)-JQ1, BET bromodomain inhibitor | ≥98% (HPLC) | Binds BET bromodomains; used in the design of dBET- and MZ1-type degraders and in target-competition experiments. | |
Target protein ligand—BCL-2 family | 923564-51-6 | ABT-263, small-molecule BCL-2 family inhibitor | ≥98% | Binds BCL-2 and BCL-XL; used in BCL-XL degrader design, target-competition experiments, and functional controls. |
Table 3. Ligand–Linker Conjugates and General-Purpose Linkers for PROTAC Synthesis
Category | CAS No. | Aladdin Cat. No. | Name | Specification or Purity | Product Features and Applications |
General-purpose linker—amino/carboxyl polyether | 784105-33-5 | Amino-PEG3-C2-acid | ≥98% | Bifunctional linker containing amino and carboxyl groups; used for amide coupling, screening of linker distance, and modulation of molecular polarity. | |
General-purpose linker—protected amino/carboxyl polyether | 1347750-75-7 | (Boc-amino)-PEG3-C₂-carboxylic acid | ≥97% | Contains a protected amino group and a free carboxyl group; used for stepwise coupling, directional assembly, and linker-length screening. | |
General-purpose linker—protected amino/carboxyl polyether | 1365655-91-9 | t-Boc-N-amino-PEG2-acid | ≥97% | Short-chain bifunctional polyether linker; used for stepwise amide coupling and short-linker design. | |
General-purpose linker—alkynyl/amino polyether | 932741-19-0 | Propargyl-PEG3-amine | ≥97% | Contains alkyne and amino groups; used for click chemistry, linker installation, and modular PROTAC synthesis. | |
VHL ligand–linker conjugate | 2341796-77-6 | VH032 amide–alkyl C6–amine hydrochloride | ≥95% (HPLC) | Conjugate of a VHL ligand and an alkyl linker; the terminal amine can be used to attach a target protein ligand. | |
CRBN ligand–short-chain amine conjugate | 1957235-66-3 | Pomalidomide-C2-NH2 | ≥95% | Conjugate of a CRBN ligand and a short-chain amine linker; used in short-linker PROTAC synthesis and comparisons of attachment distance. | |
CRBN ligand–polyether carboxylic acid conjugate | 2139348-63-1 | Pomalidomide 4′-PEG5-acid | ≥95% (HPLC) | Conjugate of a CRBN ligand and a polyether carboxylic acid linker; used for amide coupling and the design of hydrophilic linkers. | |
CRBN ligand–polyether amine conjugate | 2341841-01-6 | Pomalidomide-PEG6-NH2 hydrochloride | ≥95% | Conjugate of a CRBN ligand and a long-chain polyether amine linker; used in long-linker PROTAC synthesis and modulation of physicochemical properties. | |
CRBN ligand–alkyl carboxylic acid conjugate | 2305936-70-1 | Pomalidomide 4′-alkyl C8 acid | ≥95% | Conjugate of a CRBN ligand and an alkyl carboxylic acid linker; used to study hydrophobic linker length and cellular activity. | |
CRBN ligand–long-chain carboxylic acid conjugate | 3023879-35-5 | Thalidomide-O-C11-acid | — | Conjugate of a thalidomide-derived CRBN ligand and a long-chain alkyl carboxylic acid linker; used in the synthesis of long-linker PROTACs. |
Table 4. Negative Controls for PROTACs and Targeting Ligands
Category | CAS No. | Aladdin Cat. No. | Name | Specification or Purity | Product Features and Applications |
Target protein ligand negative control—BET | 1268524-71-5 | (−)-JQ1, negative control for (+)-JQ1 | ≥98% | Low-activity enantiomer of (+)-JQ1; used as a control in BET-binding, cellular-phenotype, and nonspecific-effect studies. | |
Paired negative control—dTAG-13 | 2451573-90-1 | dTAG-13-NEG | ≥98% | Paired negative control for dTAG-13; used to exclude nonspecific compound effects and validate tag-dependent degradation. | |
Paired negative control—VZ185 | 2306193-98-4 | cis-VZ185 | — | Paired negative control for VZ185; used to validate the mechanistic dependence of E3 recruitment and BRD7/BRD9 degradation. |
Table 5. Reagents for Validating PROTAC Mechanisms of Action and Protein Stability
Category | CAS No. | Aladdin Cat. No. | Name | Specification or Purity | Product Features and Applications |
Proteasome inhibitor | 133407-82-6 | MG-132, reversible proteasome inhibitor | Moligand™, ≥98% | Reversibly inhibits the proteasome; used to determine whether target protein degradation can be blocked and to validate proteasome dependence. | |
Proteasome inhibitor | 179324-69-7 | Bortezomib (PS-341) | Moligand™, ≥98% | Reversibly inhibits the 26S proteasome; used to determine whether target protein degradation can be blocked and to support validation of proteasome dependence. | |
Proteasome inhibitor | 134381-21-8 | Epoxomicin | ≥97% | Irreversibly inhibits catalytic subunits of the proteasome; used to determine whether the reduction in target protein abundance depends on proteasomal activity. | |
NEDD8-activating enzyme inhibitor | 905579-51-3 | MLN4924, NEDD8-activating enzyme inhibitor | Moligand™, ≥98% | Inhibits NEDD8 activation and cullin modification; used to validate the involvement of CRBN- or VHL-containing Cullin–RING E3 ligase systems. | |
Protein synthesis inhibitor | 66-81-9 | Cycloheximide | Moligand™, ≥98% | Inhibits protein translation; used for protein half-life measurements, degradation-rate analysis, and protein-recovery studies. | |
Transcription inhibitor | 50-76-0 | Actinomycin D | ≥98% | Inhibits RNA transcription; used to distinguish whether a reduction in target protein abundance results from protein degradation or reduced transcription. | |
Lysosomal acidification inhibitor | 88899-55-2 | Bafilomycin A1 | ≥95% | Inhibits the vacuolar-type proton pump and lysosomal acidification; used to distinguish the relative contributions of proteasomal and lysosomal pathways. |
Note: The products listed above are representative Aladdin products for scientific research and formulation studies. For additional product specifications, grades, and certificate of analysis (COA) information, search the Aladdin website by product name, CAS number, or catalog number.
References
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