Significant Biological Role of Sp1 Transactivation in Myeloma: Potential Therapeutic Application.

Abstract 1841

Poster Board I-867

Sp1 is a transcription factor with an important role in regulating expression of cell cycle, cell differentiation and apoptosis related genes containing proximal GC/GT-rich promoter elements. It affects growth and metastatic potential of tumor cells. In multiple myeloma (MM), key growth and survival genes such as NF-kB p65, IGF-IR, VEGF, and IL-6 contains proximal GC-rich promoter sequences that interact with Sp proteins to control their expression. Based on this we have evaluated role of Sp1 in MM. We have observed high Sp1 expression along with increased Sp1 activity in MM cells compared to normal peripheral blood mononuclear cells. We have confirmed, by immunohistochemistry, higher nuclear localization of Sp1 in MM cells compared to other normal elements in bone marrow biopsy specimens. Moreover, we have also observed further induction of Sp1 activity shama(≥2 fold increase) after adhesion to BMSC. We next evaluated Sp1 function by analyzing the effect of Sp1 knock down in MM. Interference of Sp1 activity using siRNA showed inhibition of MM cell proliferation (≥75% inhibition) induction of apoptosis and G1 arrest. We have also used three lentiviral shRNA constructs confirming similar effects of Sp1 knock down on MM cells. We have further investigated effects of Sp1 inhibitor Terameprocol on MM cells. Terameprocol is clinical applicable small molecule that specifically competes with Sp1 for specific DNA binding domains within promoter regions. Terameprocol significantly inhibited MM cell growth in a dose-dependent fashion (IC50 beetween 5–20 μM at 24 hours) and was able to overcome the protective effects of BMSCs, inducing apoptosis, via induction of caspases activation and reduction in survivin expression at both gene and protein levels. Based on the data suggesting that both dexamethasone and Velcade increase Sp1 activity, we have combined Terameprocol with these agents and observed synergistic activity. Finally, Terameprocol treatment of nude mice bearing human myeloma xenograft resulted in tumor regression by triggering apoptosis and improving survival of mice. In conclusion, our results confirm significant biological role of Sp1 transcription factor in myeloma that can be therapeutically targeted for clinical development.