Cancer Therapy: Preclinical IntegrativeGenomicAnalysis of TemozolomideResistance in Diffuse Large B-Cell Lymphoma

Purpose: Despite advances, there is an urgent need for effective therapeutics for relapsed diffuse large B-cell lymphoma, particularly in elderly patients and primary central nervous system (CNS) lymphoma. Temozolomide (TMZ), an oral DNA-alkylating agent routinely used in the therapy of glioblastoma multiforme, is active in patients with primary CNS lymphoma but the response rates are low. The mechanisms contributing to TMZ resistance are unknown. Experimental Design: We undertook an unbiased and genome-wide approach to understand the genomic methylation and gene expression profiling differences associated with TMZ resistance in diffuse large B-cell lymphoma cell lines and identify mechanisms to overcome TMZ resistance. Results: TMZ was cytotoxic in a subset of diffuse large B-cell lymphoma cell lines, independent of MGMTpromotermethylation or protein expression.UsingConnectivityMap (CMAP),we identified several compounds capable of reversing the gene expression signature associated with TMZ resistance. The demethylating agent decitabine (DAC) is identified by CMAP as capable of reprogramming gene expression to overcome TMZ resistance. Treatment with DAC led to increased expression of SMAD1, a transcription factor involved in TGF-b/bone morphogenetic protein (BMP) signaling, previously shown to be epigenetically silenced in resistant diffuse large B-cell lymphoma. In vitro and in vivo treatmentwith a combination of DAC and TMZ had greater antilymphoma activity than either drug alone, with complete responses in TMZresistant diffuse large B-cell lymphoma murine xenograft models. Conclusions: Integrative genome-wide methylation and gene expression analysis identified novel genes associated with TMZ resistance and demonstrate potent synergy between DAC and TMZ. The evidence from cell line and murine experiments supports prospective investigation of TMZ in combination with demethylating agents in diffuse large B-cell lymphoma. Clin Cancer Res; 20(2); 382–92. 2013 AACR.