PROTAC BRD4 Degrader Selectivity via VHL Recruitment
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Solution Overview
Problem
Current BET inhibitors lack selectivity for individual BET family members, particularly BRD4, limiting their therapeutic potential and utility as probes for target validation due to concerns about side effects and toxicity, and they require sustained high concentrations for systemic target engagement, leading to off-target effects.
Innovation Solution
Development of PROteolysis Targeted Chimeric (PROTAC) compounds that selectively induce degradation of BRD4 by tethering a bromodomain inhibitor like JQ1 to a small molecule E3 ubiquitin ligase protein binding ligand, such as VHL, using a linker to facilitate targeted ubiquitination and degradation of BRD4 over BRD2 and BRD3.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pan-BET inhibitors like JQ1 are used to target BET proteins, then broad inhibition of BET family members (BRD2, BRD3, BRD4) is achieved, but selectivity for individual BET members is lost leading to off-target effects and toxicity
Solution Approach 1:
The PROTAC compound incorporates a specific binder that recognizes and binds selectively to BRD4, creating local selectivity within the BET family. This allows the compound to differentiate between BRD4 and other BET members (BRD2, BRD3) through targeted molecular recognition, achieving preferential degradation of BRD4 while sparing other family members.
Solution Approach 2:
The invention changes the mechanism of action from direct inhibition to proteolytic degradation. By using a PROTAC design that recruits the ubiquitin-proteasome system, the compound achieves prolonged target depletion rather than transient inhibition, fundamentally altering the pharmacological parameter from reversible binding to irreversible degradation.
2Reliability
If sustained high concentrations of BET inhibitors are maintained for systemic target engagement, then therapeutic efficacy is improved, but off-target effects and toxicity increase
Solution Approach 1:
The PROTAC compound creates a catalytic cycle where a single PROTAC molecule can facilitate the degradation of multiple target protein molecules. The PROTAC binds to the target, recruits the E3 ligase, facilitates ubiquitination, and is then released to repeat the process, amplifying the therapeutic effect at lower concentrations.
Solution Approach 2:
The PROTAC mechanism provides continuous target degradation through the catalytic cycle. Once the PROTAC initiates degradation, the process continues as long as the PROTAC remains in the system, maintaining therapeutic pressure without requiring sustained high concentrations that would cause toxicity.
3Ease of operation
If conventional BET inhibitors are used, then reversible inhibition of target proteins is achieved, but prolonged target engagement requiring sustained high concentrations is needed
Solution Approach 1:
The invention inverts the conventional approach by instead of inhibiting the target protein's function, the PROTAC induces degradation of the target protein itself. This fundamental inversion changes the duration of action from transient reversible inhibition to prolonged target depletion that persists until new protein synthesis occurs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The PROTAC compounds achieve rapid and prolonged intracellular degradation of BET proteins, demonstrating preferential degradation of BRD4, reducing the need for sustained inhibitor concentrations and minimizing off-target effects, thus offering a safer and more effective therapeutic approach.
Implementation Method 1
tethering a bromodomain inhibitor like JQ1 to a small molecule E3 ubiquitin ligase protein binding ligand, such as VHL, using a linker to facilitate targeted ubiquitination and degradation of BRD4
Data Source
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AI summary
There is provided novel small molecule E3 ubiquitin ligase protein binding ligand compounds, having utility in PROteolysis Targeted Chimeras (PROTACs), as well as processes for the preparation thereof, and use in medicine. There is particularly provided PROTACs which bind to a protein within the bromo- and Extra-terminal (BET) family of proteins, and especially to PROTACs including novel small molecule E3 ubiquitin ligase protein binding ligand compounds which selectively induce degradation of the BRD4 protein within the bromodomain of the BET family of proteins.