BRD4 inhibition leads to MDSC apoptosis and enhances checkpoint blockade therapy
Himanshu Savardekar, … , Kari L. Kendra, William E. Carson III
Himanshu Savardekar, … , Kari L. Kendra, William E. Carson III
Published August 5, 2025
Citation Information: J Clin Invest. 2025;135(19):e181975. https://doi.org/10.1172/JCI181975.
View: Text | PDF
Research Article Immunology Oncology

BRD4 inhibition leads to MDSC apoptosis and enhances checkpoint blockade therapy

Abstract

BRD4 is an epigenetic reader protein that regulates oncogenes such as myc in cancer. However, its additional role in shaping immune responses via regulation of inflammatory and myeloid cell responses is not yet fully understood. This work further characterized the multifaceted role of BRD4 in antitumor immunity. Nanostring gene expression analysis of EMT6 tumors treated with a BRD4 inhibitor identified a reduction in myeloid gene expression signatures. Additionally, BRD4 inhibition significantly reduced myeloid-derived suppressor cells (MDSCs) in the spleens and tumors of mice in multiple tumor models and also decreased the release of tumor-derived MDSC growth and chemotactic factors. Pharmacologic inhibition of BRD4 in MDSCs induced apoptosis and modulated expression of apoptosis regulatory proteins. A BRD4 myeloid–specific knockout model suggested that the dominant mechanism of MDSC reduction after BRD4 inhibition was primarily through a direct effect on MDSCs. BRD4 inhibition enhanced anti–PD-L1 therapy in the EMT6, 4T1, and Lewis lung carcinoma tumor models, and the efficacy of the combination treatment was dependent on CD8+ T cells and on BRD4 expression in the myeloid compartment. These results identify BRD4 as a regulator of MDSC survival and provide evidence to further investigate BRD4 inhibitors in combination with immune-based therapies.

Authors

Himanshu Savardekar, Andrew Stiff, Alvin Liu, Robert Wesolowski, Emily Schwarz, Ian C. Garbarine, Megan C. Duggan, Sara Zelinskas, Jianying Li, Gabriella Lapurga, Alexander Abreo, Lohith Savardekar, Ryan Parker, Julia Sabella, Mallory J. DiVincenzo, Brooke Benner, Steven H. Sun, Dionisia Quiroga, Luke Scarberry, Gang Xin, Anup Dey, Keiko Ozato, Lianbo Yu, Merve Hasanov, Debasish Sundi, Richard C. Wu, Kari L. Kendra, William E. Carson III

×

Figure 5

PLX51107 modulates apoptotic proteins in MDSCs.

Options: View larger image (or click on image) Download as PowerPoint
PLX51107 modulates apoptotic proteins in MDSCs. (A) MSC2 cells treated f...
(A) MSC2 cells treated for 24 h with DMSO control or indicated dose of PLX51107 (PLX). Protein lysates of treated cells were probed with antibodies for caspase-9, cleaved caspase-9, caspase-8, cleaved caspase-8, and β-actin. (B) Single-cell RNA-Seq dataset of peripheral blood mononuclear cells of 16 patients at baseline. Dot plot of relative gene expression of select apoptosis genes across all cell types. (C) MSC2 cells treated as in A and probed for BCL2A1, MCL1, XIAP, and β-actin. (D) Splenic murine MDSCs were isolated from 4T1 tumor–bearing mice and treated for 48 h with DMSO control or the indicated dose of PLX51107 with media supplemented with 10 ng/mL IL-6 and GM-CSF. Relative gene expression of Bcl2a1a across treatment groups normalized to β-actin; P < 0.05 DMSO versus 250 nM PLX51107, paired 2-tailed Student’s t test. (E) Splenic murine MDSCs from 4T1 tumor–bearing mice treated as in D. Protein lysates from each condition probed with BCL2A1 or β-actin. (F) CD33+/CD11b+/HLA-DRlo/– MDSCs were isolated from the peripheral blood of patients with melanoma by FACS. Cells were cultured in HAB media supplemented with 10 ng/mL IL-6 and GM-CSF and treated with DMSO or the indicated concentration of PLX51107. After 48 h, RNA was isolated from cells, and relative gene expression of BCL2A1 across treatment groups was normalized to 18S; P < 0.05 for DMSO versus 250 nM PLX51107, paired 2-tailed Student’s t test. (G) MSC2 cells treated as in A and probed for BIM. (H) Splenic murine MDSCs for 4T1 tumor–bearing mice treated as in D and probed for BIM. (I) Relative gene expression of BIMEL in human MDSCs treated as in F across treatment groups normalized to 18S; P < 0.05 for DMSO versus 250 nM PLX51107, paired 2-tailed Student’s t test. (J) Gr1+/CD11b+ MDSCs were isolated from spleens of 4T1 tumor–bearing female mice by negative selection and treated with DMSO vehicle control (blue) or 125 nM PLX51107 (red) for 24 h. BRD4 enrichment was assayed by ChIP-Seq using input control. Control and inhibitor groups were normalized by Drosophila chromatin spike-in. Track heights indicate relative enrichment, and each group represents pooled cells from 3–4 mice. H3K27ac (gray) enrichment was determined from a public dataset (38).