BRD4 inhibition suppresses PD-L1 expression in triple-negative breast cancer

Area of Science:

• Oncology
• Immunology
• Molecular Biology

Background:

• Programmed death-ligand 1 (PD-L1) expression on tumor cells promotes immune evasion in advanced triple-negative breast cancer (TNBC).
• While anti-PD-L1 therapy combined with nab-paclitaxel shows benefits in TNBC, immune-related adverse effects (irAEs) limit its use.
• The role of Bromodomain and extra-terminal domain 4 (BRD4) in TNBC, particularly its immune regulation and impact on PD-L1, remains largely unexplored.

Purpose of the Study:

• To investigate the influence of BRD4 on PD-L1 expression in TNBC.
• To explore BRD4's role in regulating the tumor immune microenvironment in TNBC.

Main Methods:

• Utilized JQ1, a specific BET inhibitor, and small interfering RNAs (siRNAs) targeting BRD4.
• Assessed the impact of BRD4 inhibition on PD-L1 expression in TNBC cells, including its modulation by interferon-gamma (IFN-γ).
• Conducted in vivo experiments in tumor-bearing mice to evaluate systemic effects of JQ1 on PD-L1 levels and T lymphocyte subsets.

Main Results:

• BRD4 inhibition significantly suppressed PD-L1 expression in TNBC.
• BRD4 inhibition counteracted PD-L1 upregulation induced by IFN-γ.
• In vivo, JQ1 reduced PD-L1 levels and altered splenic T lymphocyte subsets, suggesting a relief of immunosuppression.

Conclusions:

• BRD4 plays a crucial role in regulating PD-L1 expression in TNBC.
• Targeting BRD4 presents a potential therapeutic strategy to modulate the PD-1/PD-L1 immune checkpoint in TNBC.
• BRD4 inhibition may offer an alternative or complementary approach to overcome immunotherapy resistance and irAEs in TNBC.