Histone Deacetylase Inhibitor Enhances the Efficacy of MEK Inhibitor through NOXA-Mediated MCL1 Degradation in Triple-Negative and Inflammatory Breast Cancer

Abstract

Purpose Inflammatory breast cancer (IBC), diagnosed clinically, and triple-negative breast cancer (TNBC), diagnosed by molecular receptor status, are the two most aggressive forms of breast cancer, and both lack effective targeted therapies. We previously demonstrated involvement of histone deacetylase (HDAC) inhibitor entinostat in regulating apoptosis in IBC and TNBC cells; here, we aimed to identify novel combination therapy candidates. Experimental Design Potential therapeutic targets were identified by mRNA expression profiling of TNBC and IBC cells treated with entinostat. Drug action and synergism were assessed by in vitro proliferation assays, tumor growth in vivo, and proteomic analyses. Gain/loss-of-expression studies were utilized to functionally validate the role of identified targets in sensitivity of TNBC and IBC cells to combination therapy. Results Entinostat induced activity of the oncogenic ERK pathway and expression of pro-apoptotic NOXA. These are known to stabilize and degrade, respectively, MCL1, an anti-apoptotic Bcl-2 protein. In breast cancer patients, high-MCL1/low-NOXA tumor expression correlated significantly with poor survival outcomes. Combination treatment of entinostat with MEK inhibitor pimasertib reduced the growth of TNBC and IBC cells in vitro and inhibited tumor growth in vivo. The synergistic action of combination therapy was observed in TNBC and IBC cell lines in which NOXA expression was induced following entinostat treatment. The therapeutic activity depended on induction of mitochondrial cell death pathways initiated by NOXA-mediated MCL1 degradation. Conclusions Our preclinical findings provide a rationale for the clinical testing of combination HDAC and MEK pathway inhibition for TNBC and IBC that exhibit elevated baseline tumor MCL1 expression.

From Inhibition to Degradation: Targeting the Anti-apoptotic Protein Myeloid Cell Leukemia 1(MCL1)

“…50 To definitively establish the CRBN dependence of this degradation mechanism, a CRBN knockout cell line of OPM2 CRBN-/was generated using CRISPR Cas9 gene editing and this In contrast, the same treatment of OPM2 CRBN-/cells with dMCL1-2 was ineffective ( Figure 7c). MCL1 levels experienced insignificant changes in abundance when CRBN is absent (lanes [15][16][17][18]. Consistent with our proposed mode of action, OPM2 CRBN-/cells no longer possess the capability to form the CUL4A-DDB1 complex and ubiquitinate MCL1, preventing any degradation from occurring, and supporting the UPP degradation mechanism of dMCL1-2.…”

“…carboxylic acid (15). To a solution of free amine 14 (0.208 g, 0.24 mmol) in THF (1.9 mL) and 13 5-((3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4yl)pentanoate (16). To a suspension of biotin (0.057 g, 0.23 mmol) in DMF (2 mL), was added Et3N (0.073 g, 0.10 mL, 0.73 mmol) under stirring at ambient temperature.…”

“…11PPIs are difficult to target with small molecule therapeutics due to their shallow and relatively featureless binding regions. 12 The majority of compounds that target MCL1 either occupy the flat binding site of the BH3 groove, 7,8,12,13 an allosteric binding site, 14 or indirectly influence MCL1 via downstream effects through tyrosine kinase and HDAC inhibition [15][16] or CDK9 degradation. 17 Nonetheless, MCL1 has gained much attention as a target for anti-cancer therapeutics, 1,2,18 and several organizations have acute programs targeting MCL1 with compounds AMG 176, AMG 397 (Amgen), AZD 5991 (Astra Zeneca), and S 64315 (Servier) currently undergoing clinical trials.…”

MGMT-activated DUB3 stabilizes MCL1 and drives chemoresistance in ovarian cancer

“…S8 A-C). The anti-tumor function of HDACis is mostly exerted via the induction of apoptosis, which activates the apoptosis cascade, including decreases in MCL1 (21,22) and BCL-2 (23). However, the immunoblotting analysis showed that the administration of HDACis to OVCA433 cells only slightly decreased the MCL1 expression levels (Fig.…”

Epigenetics and Trained Immunity

“…Histone deacetylase (HDAC) enzymes remove acetyl groups from histone tails. Thus, HAT/HDAC activity balance is an important determinant of gene regulation, and it has accordingly emerged as a potential therapeutic target for the treatment of various diseases (48,62,108,127). DNA methylation regulates gene expression.…”