Derivation and Drug Screening of Growth Factors- and Stroma-Dependent Human Multiple Myeloma Cells

Abstract 5020

Multiple myeloma (MM) is the second most common hematological malignancy in the U. S. MM is treatable but not curable with a median survival of 5–7 years with advanced treatment. There are several established human MM cell lines that grow in the absence of any cytokine dependence or stromal interaction. However, most primary MM patient specimens are difficult to maintain or to expand in vitro for pathophysiology investigation and drug screening. To address this issue, we systemically evaluated effects of various culture parameters on the growth of primary MM cells. A serum-free MS-5 cell (a murine bone marrow stromal cell line) co-culture system containing cytokine cocktail is capable of expanding purified CD138⁺ cells from primary MM specimens in vitro. Optimal expansion of the MM CD138⁺ cells requires a combination of stromal cells, human interleukin (IL-6) and human hepatocyte growth factors (hHGF). These MM cells can be maintained and repeatedly recovered following cryopreservation. The in vitro effect of five novel alkylating agents (BO-1055, −1090, 1099, −1393 and −1509) was evaluated for an inhibition of proliferation of the MM cells, and on human mesenchymal stem cells (hMSC), murine MSC (MS-5 cells and Op9 cells), human bone marrow derived endothelial cells (BMEC), and human cord blood (CB) CD34⁺ cells, as well as for a week 5 Cobblestones area forming cells (CAFC; an in vitro surrogate assay for hematopoietic stem cells) assay with CB CD34⁺ cells. BO-1055 shows a promising therapeutic window between the MM cells and other normal tissues. For the MM cells, IC₅₀ was ∼1. 02 μM. In contrast, IC₅₀ of BMEC, MSC, CB CD34⁺ cells and CAFC was >10, >25, 8, and >5 μM, respectively. Therefore, our stromal culture system supports human primary MM cells and closely recapitulates the growth of MM cells in their niche in vivo. We also identified a novel BO-1055 molecule that inhibits primary MM cells but is well-tolerated by other normal tissues. This in vitro stromal co-culture system provides a powerful tool to dissect the pathophysiology of human MM, and to screen new drugs for MM therapy.