HDAC6 inhibition upregulates CD20 levels and increases the efficacy of anti-CD20 monoclonal antibodies

Abstract

Downregulation of CD20, a molecular target for monoclonal antibodies (mAbs), is a clinical problem leading to decreased efficacy of anti-CD20-based therapeutic regimens. The epigenetic modulation of CD20 coding gene () has been proposed as a mechanism for the reduced therapeutic efficacy of anti-CD20 antibodies and confirmed with nonselective histone deacetylase inhibitors (HDACis). Because the use of pan-HDACis is associated with substantial adverse effects, the identification of particular HDAC isoforms involved in CD20 regulation seems to be of paramount importance. In this study, we demonstrate for the first time the role of HDAC6 in the regulation of CD20 levels. We show that inhibition of HDAC6 activity significantly increases CD20 levels in established B-cell tumor cell lines and primary malignant cells. Using pharmacologic and genetic approaches, we confirm that HDAC6 inhibition augments in vitro efficacy of anti-CD20 mAbs and improves survival of mice treated with rituximab. Mechanistically, we demonstrate that HDAC6 influences synthesis of CD20 protein independently of the regulation of transcription. We further demonstrate that translation of CD20 mRNA is significantly enhanced after HDAC6 inhibition, as shown by the increase of CD20 mRNA within the polysomal fraction, indicating a new role of HDAC6 in the posttranscriptional mechanism of CD20 regulation. Collectively, our findings suggest HDAC6 inhibition is a rational therapeutic strategy to be implemented in combination therapies with anti-CD20 monoclonal antibodies and open up novel avenues for the clinical use of HDAC6 inhibitors.

HDAC inhibitors overcome immunotherapy resistance in B-cell lymphoma

“…Entinostat increases the expression of CD20 and adhesion molecules in multiple B-cell lymphomas, thereby sensitizing B-cell lymphomas to the treatment of anti-CD20 monoclonal antibodies (Frys et al, 2015). Furthermore, inhibiting HDAC 6 significantly upregulates CD20 expression in B cell tumors and enhances the efficacy of anti-CD20 monoclonal antibodies (Bobrowicz et al, 2017). HDAC inhibitors, valproic acid and romidepsin, can transactivate the CD20 gene via promoter hyperacetylation and Sp1…”

Novel HDAC inhibitor Chidamide synergizes with Rituximab to inhibit diffuse large B-cell lymphoma tumour growth by upregulating CD20

“…There were cases of CD20-deficient lymphoma relapses identified following treatment with Rituximab-associated regimens in DLBCL 6 . Rituximab-induced downregulation of CD20 expression is mainly due to deacetylation of histones by histone deacetylases (HDACs) [9][10][11] , internalization of CD20 molecule 12 and loss of CD20/Rituximab complex from cell surface 13 . Insufficient surface CD20 protein affects Rituximabinduced lipid raft domain organization and downstream signalling, leading to Rituximab resistance 14 .…”

“…The enhancer regions of MS4A1 (CD20) in DLBCL cells are H3K27ac 18 . Upregulation of CD20 expression by either specific inhibitors for HDAC6 (Tubacin and Ricolinostat) or non-specific HDAC inhibitors (Valproic acid and Romidepsin) showed sensitizing potential in Rituximab-induced cell death in malignant B cells [9][10][11] .…”

CD20 is dispensable for B-cell receptor signaling but is required for proper actin polymerization, adhesion and migration of malignant B cells

“…Furthermore, CD20 expression is highly variable and rather low on the cells of chronic lymphocytic leukemia (CLL) when compared to other B-cell malignancies or healthy B cells [3]. Notably, some experimental approaches to pharmacologically modulate CD20 expression levels were proposed, nevertheless, none of the strategies has ever been transferred into the clinical use [4,5]. So far, it is impossible to predict CD20 expression changes, as the precise molecular mechanisms of CD20 regulation and its biological function remain largely elusive.…”