BP1 Expression in a Myeloma Cell Line: Modulation by Arsenic Trioxide and Ascorbic Acid.

BP1 belongs to a family of homeobox genes which are not expressed in normal bone marrow cells but are seen in multiple leukemic cell lineages including erythroid, myeloid, and T- and B-cell lineages, and whose modulation is important in differentiation and oncogenic transformation (Shen et al. EMBO J 1992). Multiple Myeloma (MM) is a clonal B-cell neoplasm marked by proliferation of plasma cells within bone marrow. BP1 expression has not previously been demonstrated in MM cell lineages. Recent unpublished data demonstrated elevated BP1 expression in the bone marrow of Acute Promyelocytic Leukemia (APL) patients and its down regulation with the differentiating agent ATRA. With recent data demonstrating arsenic trioxide (As₂O₃) induced remission in chemorefractory APL and MM (Grad et al. Blood 2001), we hypothesized BP1 may share a role in this response conversion.

In the current study, we treated ARH77 cells - a multiple myeloma cell line, with 0.25 – 3 uM As₂O₃ and adjuvant ascorbic acid (AA) for 24–96hrs; AA had been previously documented to potentiate As₂O₃-mediated cell death in multiple myeloma cells (Grad et al. Blood 2001). Viability, cell numbers and mRNA expression were determined at each time point. The % of viable cells at 72 and 96 hrs decreased to less than 10% of the control in cultures flasks containing 2 and 3uM; 0.25 uM had minimal effect in this assay. We then used 0.5 and 1uM, which caused growth arrest compared to controls at each interval. 1 uM caused a decrease of 12% viability at 72 hrs. A significant reduction in the expression of BP1 was seen in these cultures when balanced with beta-actin levels. Myeloma cells are marked by a myriad of antiapoptotic signaling mechanisms, which account for their acquired resistance to current chemotherapy. A better understanding of signaling pathways and genetic events may provide potential therapeutic targets and aid in correlation between genetic abnormalities and clinical outcomes.