Synergic Effect of Histone Deacetylase Inhibitor Chidamide with Doxorubicin on Diffuse Large B-Cell Lymphoma with Double BCL2/MYC Expression

Introduction

Diffuse large B-cell lymphoma (DLBCL) represents the most common neoplastic disorder of B-lymphocytes. Although great progress has been made in the treatment of DLBCL, patients with double BCL2/MYC expression have been reported to be refractory to R-CHOP regimen. In our clincial trial (NCT02753647), we found that chidamide, a histone deacetylase inhibitor, plus R-CHOP elicits favorable outcome, especially for DLBCL patients with double BCL2/MYC expression. Therefore,we set out to investigate the underlying mechanism.

Methods

Core needle biopsy of tumor samples of DLBCL with double BCL2/MYC expression were transplanted into immunodecient (NOD-SCID) mice to establish patient-derived xenograft (PDX) models. Heterotopic PDX models were maintained by passaging tumor tissues from mouse to mouse. Chidamide and doxorubicin, either alone or in combination, were applied to PDX models with low passage numbers (<10) to preserve the genetic integrity of the parental tumors. The dose and administration schedule were as follows: doxorubicin 0.6mg/kg twice a week, chidamide 12.5mg/kg/day for two weeks. RNA-seq and ATAC-seq were performed to achieve an integrative transcriptomic and epigenomic anlaysis of PDX models on Day 7 and Day 14 of treatment. The study was approved by Shanghai Rui Jin Hospital Review Board and written informed consent were obtained from patients in accordance with the Declaration of Helsinki.

Results

We observed significant growth inhibition of xenografted tumors treated with chidamide combined with doxorubicin, as compared to those of the single treatment. RNA-seq analysis revealed that chidamide and doxorubicin synergistically regulate a set of genes associated with B-cell differentiation and multiple signaling transduction pathways involved regulation of BCL2 and MYC, including the IL6-JAK-STAT and PI3K-AKT-MTOR pathways. Furthermore, accessible chroamtin region profiling by ATAC-seq indicated that chidamide and doxorubin co-repress distal cis-regulatory elements (i.e. enhancers) associated with lymphocyte development.

Conclusions

As a histone deaceltylase inhibitor, chidamide is able to synergize with doxorubicin to inhibit the growth of DLBCL expressing high levels of MYC and BCL2 in PDX models. This is, in part, due to remodeling of the landscape of accessible chromatins in lymphoma cells. Our study provides insight into how epigenetic therapeutics can sensitize DLBCL with double BCL2/MYC expression to conventional chemotherapy.