Abstract 288: Targeting Sp1 transactivation in Waldenstrom's macroglobulinemia: A novel therapeutic option

Waldenstrom's macroglobulinemia (WM) is a low-grade non-Hodgkin lymphoma, characterized by bone marrow infiltration and abnormal production of monoclonal immunoglobulin M protein (IgM). Whereas recent gene expression and proteomics studies have advanced our understanding of WM pathogenesis and identified potential therapeutic targets, WM remains incurable, with a 5-year survival rate of 50%. Therefore, there is a need for the development of novel chemotherapeutic agents targeting deregulated signaling pathways specifically present in WM. We have here evaluated role of Sp1 transcription factor and its aberrant activation in WM based on our prior results suggesting its growth and survival effects in multiple myeloma (MM). We observed high nuclear Sp1 expression along with increased Sp1 activity in WM cells compared to normal cells. Moreover, adhesion of WM cells to bone marrow stromal cells (BMSC) further induced Sp1 activity in WM cells. Binding Sp1 to promoter regions of important genes such as survivin and VEGF, was observed in WM cell lines as compared with resting and activated B lymphocytes from healthy donors as assessed by chromatin immunoprecipitation (ChIP) assay and interference with Sp1 activity induced cell cycle arrest, decreased survivin and VEGF expression. Based on these data, we investigated the efficacy of Terameprocol (TMP), a small molecule inhibitor of Sp1 transactivation suitable for clinical application. TMP specifically competes with Sp1-specific DNA binding domains within gene promoter regions. We have confirmed inhibition of both basal and BMSC-induced binding and transcriptional activity of Sp1 in WM cells using an ELISA assay specific for measuring Sp1 binding activity and using Sp1-sensitive luciferase reporter plasmid. Importantly, TMP significantly inhibited the growth of all three WM cell lines (WMWSU, BCWM.1 and the novel IgM-secreting, immunoglobulin light chain-restricted cell line, MWCL-1), as well as IgM-secreting low grade lymphoma cell lines (RL and MEC-1) in a dose-dependent fashion, overcoming the growth promoting affect of BMSC or cytokines such as interleukin-6 (IL6). Moreover, inhibition of Sp1 activity by TMP decreased IgM secretion in MWCL-1 culture supernatant after 6 hours following treatment. Finally, TMP had in vivo activity in a murine xenograft model of WM. ChIP assay showed that TMP treatment for 24 hours significantly decreased the binding of Sp1 to the promoters of Survivin and VEGF, as well as other kn