Protein Age Bias in Target Degradation by PROTACs.

Area of Science:

• Chemical Biology
• Molecular Biology
• Drug Discovery

Background:

• Targeted protein degradation (TPD) via PROteolysis TArgeting Chimeras (PROTACs) is a promising therapeutic strategy.
• Incomplete target clearance and rebound kinetics are common limitations of current PROTACs.
• The underlying mechanisms for these limitations are not fully understood.

Purpose of the Study:

• To investigate the role of protein age in PROTAC efficacy.
• To elucidate the mechanistic basis for incomplete target degradation and rebound kinetics.
• To identify new parameters for optimizing PROTAC design.

Main Methods:

• Utilized _CG □SLENP, a chemical genetics strategy, to differentiate and label newly synthesized and pre-existing proteins within single cells.
• Applied this method to study the degradation of the bromodomain protein BRD4 using two distinct PROTACs (dBET6 and MZ□1).
• Performed live-cell imaging and quantitative analysis across various compound concentrations and time scales.

Main Results:

• PROTACs preferentially degraded pre-existing BRD4 over newly synthesized BRD4.
• Newly synthesized BRD4 exhibited slower and incomplete degradation kinetics.
• This age-dependent degradation bias was consistent across different PROTACs, concentrations, and time points.

Conclusions:

• Protein age is a critical, previously unrecognized determinant of PROTAC efficacy.
• PROTAC-mediated degradation is influenced by the balance between protein synthesis and degradation (proteostasis).
• Understanding protein maturation state is essential for designing effective PROTACs and overcoming limitations like incomplete degradation.