BRD4-specific PROTAC inhibits basal-like breast cancer partially through downregulating KLF5 expression

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• Proteolysis-targeting chimeras (PROTACs) are emerging as a promising cancer therapy strategy.
• Bromodomain and extra terminal domain (BET) proteins, particularly BRD4, are implicated in basal-like breast cancer (BLBC) progression.
• Existing BRD4 PROTACs face challenges with bioavailability, non-selective degradation, and poor tumor targeting.

Purpose of the Study:

• To develop and evaluate a novel BRD4-specific PROTAC, compound 6b, for its efficacy against BLBC.
• To investigate the mechanism of action of 6b, including its effects on BRD4, KLF5, and BLBC cell growth.
• To assess the therapeutic potential of 6b in preclinical models of BLBC.

Main Methods:

• Synthesis and characterization of compound 6b, a BRD4-targeting PROTAC.
• In vitro assays to assess BRD4 degradation and inhibition of BLBC cell proliferation.
• Analysis of KLF5 expression and its regulation by BRD4-mediated super-enhancers.
• In vivo studies using a xenograft mouse model to evaluate tumor growth inhibition by 6b.
• Combination studies with KLF5 inhibitors to assess additive effects.

Main Results:

• Compound 6b selectively induced cereblon (CRBN)-mediated ubiquitination and proteasomal degradation of BRD4, without affecting BRD2 or BRD3.
• 6b significantly suppressed BLBC cell growth and inhibited the expression of the oncoprotein Krüppel-like factor 5 (KLF5).
• 6b demonstrated significant inhibition of HCC1806 tumor growth in a xenograft mouse model.
• The combination of 6b and KLF5 inhibitors exhibited additive effects in BLBC models.

Conclusions:

• BRD4-specific PROTACs, such as 6b, can effectively inhibit BLBC by downregulating KLF5.
• Compound 6b demonstrates potent anti-BLBC activity and warrants further investigation as a novel therapeutic agent.
• Targeting BRD4 with PROTACs offers a promising strategy for overcoming limitations of existing therapies in BLBC.