Abstract 597: The cellular and genomic response to histone deacetylase inhibitors in diffuse large b-cell lymphoma

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Diffuse Large B-cell lymphoma (DLBCL) is the most frequent subtype of Non-Hodgkin Lymphoma (NHL) in all countries around the world and in all age groups. Several drug regimens have been used in treatment of DLBCL; however, this disease remains eventually fatal in 30 – 40% of the patients. Chemotherapy resistance can be partly explained by the fact that DLBCL is a heterogeneous group of NHLs, with the two most prevalent subtypes being “Activated B-cell Like” (ABC) and “Germinal Center B-cell like” (GCB). Patients with the ABC subtype have the poorest prognosis under the current treatment regimen. Therefore, there is a pressing need for new therapeutics that can increase survival rates in DLBCL patients. Histone deacetylase inhibitors (HDIs) have proven to be promising drugs in the treatment of blood malignancies. Even though their mechanism of action has not been fully characterized, two HDIs, (Vorinostat and Romidepsin) have been approved for the treatment of cutaneous T-cell lymphoma (CTCL). Therefore the purpose of the current study is to investigate the response of DLBCL subtypes to HDIs, with a particular focus on subtype-specific mechanisms of action. Our current working hypothesis is that a comprehensive analysis of the genomic and proteomic response to histone deacetylase inhibitors (HDIs) including gene expression and transcription factor acetylation will reveal both mechanisms and potential biomarkers of HDI action in lymphomas DLBCL. In the current study we have focused on the cellular and genomic effects of the hydroxamate HDI, Belinostat (PXD101), on cell lines representing the GCB subtype of DLBCL. We show that PXD101 inhibits growth of four GCB-type cell lines with 24 h IC50s in the low micromolar range (SUDHL6 =0.15uM, OCI Ly19 = 0.3uM, SUDHL4 = 0.45uM, DB = 0.77uM). Flow cytometry analysis has shown that three of these cell lines (SUDHL6, OCI Ly19 and DB) arrest in the G2/M phase of the cell cycle by 24 hours of treatment at the IC50 dose and then die by apoptosis. In contrast, the SUDHL4 cell line reversibly arrests in the G1 phase without undergoing cell death. Western blot analysis of PARP and caspase-3 cleavage has further confirmed the presence/absence of apoptosis. We suggest that the SUDHL4 cell line represents DLBCL tumors that are refractory to the apoptosis-inducing effects of HDIs. Thus, we are using this cell line to identify other therapeutics which could be used in combination with PXD101 to induce cell death.The mechanistic basis for the differential cellular response between the GCB type cell lines is currently under investigation using expression profiling data obtained from OCI Ly19 and SUDHL4 cells treated with PXD101. Preliminary data indicates divergent responses in expression of GADD45 and p21, the Myc/Max family of proteins, and the clock genes, Per1 and Cry2. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 597. doi:10.1158/1538-7445.AM2011-597