The synergistic interaction between CD20 monoclonal antibodies and histone deacetylase inhibitors in B cell Non Hodgkin's Lymphoma

Recent improvements in molecular sub typing of Non Hodgkin’s lymphomas have resulted in targeted therapies becoming incorporated into treatment paradigms. The anti-CD20 monoclonal antibody, Rituximab, has resulted in dramatic improvements in survival for patients with B cell Non Hodgkin’s lymphoma. Histone deacetylase inhibitors are a novel class of anti cancer agents targeting epigenetic regulation. This thesis addresses the interaction between histone deacetylase inhibitors and anti-CD20 monoclonal antibodies, including Rituximab, both in vitro and in vivo. The initial approach identified synergistic induction of apoptosis in a number of B cell lines. In a Ramos xenograft model, combination treatment with suberoylanilide hydroxamic acid (SAHA) and Rituximab reduced tumour growth compared to either agent alone, without discernable toxicity. This effect appears specific to CD20 since monoclonal antibodies directed to other surface molecules (CD32b, CD22, CD37) did not exhibit cooperative effect. Analysis of apoptotic pathways demonstrated that PARP cleavage and caspase processing is significantly higher in cells receiving both treatments. Co-treatment of Ramos cells with the pan caspase inhibitor QVD-OPH abolished the synergy observed with CD20 monoclonal antibodies, suggesting that caspase processing is necessary for synergy. Treatment of Ramos cells stably transfected to overexpress Bcl-2 resulted in loss of synergy with Rituximab, but not with the type II CD20 mAb B1 (Tositumomab). Gene expression array analysis of Ramos cells was performed. Geneset enrichment analysis identified significant regulation of NFқB target genes in some genesets (Rituximab Vs control, p