Antibody-PROTAC Conjugates Enable HER2-Dependent Targeted Protein Degradation of BRD4

Area of Science:

• Drug Discovery
• Molecular Biology
• Oncology

Background:

• Proteolysis-Targeting Chimeras (PROTACs) are promising drug discovery tools for targeted protein degradation.
• Current PROTACs often lack tissue specificity, limiting their therapeutic application.
• Selective protein degradation in specific cell types remains a significant challenge.

Purpose of the Study:

• To design and synthesize a novel antibody-PROTAC conjugate for cell-type-specific protein degradation.
• To demonstrate selective degradation of bromodomain-containing protein 4 (BRD4) in HER2-positive cells.
• To overcome the inherent lack of selectivity in conventional PROTACs.

Main Methods:

• Design and synthesis of a trastuzumab-PROTAC conjugate (Ab-PROTAC 3).
• Utilizing antibody-mediated internalization and intracellular release of active PROTAC.
• Assessing BRD4 degradation in HER2-positive versus HER2-negative breast cancer cell lines.
• Live cell confocal microscopy to track conjugate internalization and trafficking.

Main Results:

• Ab-PROTAC 3 selectively targets and degrades BRD4 exclusively in HER2-positive cells.
• HER2-negative cells were spared from BRD4 degradation.
• Internalization and lysosomal trafficking of the conjugate were observed specifically in HER2-positive cells.
• Sufficient active PROTAC was released to induce potent BRD4 degradation.

Conclusions:

• Proof-of-concept for tissue-specific BRD4 degradation achieved using antibody-guided PROTACs.
• This strategy effectively overcomes limitations of PROTAC selectivity.
• The approach holds significant potential for targeting novel proteins in a cell-specific manner.