Target Validation Using PROTACs: Applying the Four Pillars Framework.

Area of Science:

• Drug discovery and development
• Chemical biology
• Pharmacology

Background:

• Proteolysis targeting chimeras (PROTACs) are heterobifunctional molecules that induce targeted protein degradation via ubiquitination and proteasomal pathways.
• Targeted protein depletion offers therapeutic advantages over mere inhibition, but PROTACs face challenges in oral bioavailability and complex pharmacology.
• The development of orally bioavailable PROTACs is crucial for advancing targeted protein degradation therapies.

Purpose of the Study:

• To introduce a translational pharmacology framework, the "four pillars," to expedite PROTAC development.
• To enhance pharmacokinetic-pharmacodynamic (PKPD) understanding and structure-activity relationship (SAR) elucidation for PROTACs.
• To provide guidance for developing robust PROTAC molecules as chemical probes for target validation.

Main Methods:

• Review of experimental methods to assess drug exposure at the site of action (Pillar 1).
• Evaluation of methods for measuring target engagement (Pillar 2).
• Assessment of techniques to link target engagement to functional pharmacological effects (Pillar 3) and phenotypic outcomes (Pillar 4).

Main Results:

• The "four pillars" framework integrates PKPD and SAR to streamline PROTAC development.
• Experimental methods are outlined to comprehensively evaluate PROTAC performance from exposure to phenotype.
• The framework facilitates the understanding of complex PROTAC pharmacology.

Conclusions:

• The presented translational pharmacology framework aids in overcoming challenges in PROTAC development, particularly oral bioavailability.
• Application of the "four pillars" can accelerate the discovery and optimization of PROTACs.
• This guidance aims to establish PROTACs as reliable chemical probes for target validation in drug discovery.