Drug Screening of Primary Human Pediatric Pre-B Cell Acute Lymphoblastic Leukemia (pre-B ALL) Cells in Their Stromal Niche

Abstract 4295

Pre-B cell acute lymphoblastic leukemia (pre-B ALL) is the most common leukemia in children and is treatable. However, no in vitro nor in vivo models are available to investigate their pathophysiology other than a number of established cell lines that grow in the absence of any cytokine dependence or stromal interaction. We developed a serum-free MS-5 cell (a murine bone marrow stromal cell line) co-culture system that is capable of expanding human primary pre-B ALL CD34⁺CD19⁺ cells in vitro. To define a population of pre-B ALL initiating cells, our study reveals that a sorted CD34^bright population displays a slow proliferation and maintains a high % of CD34⁺ cells. In contrast, CD34^dim cells/CD34⁻ cells fraction shows a higher proliferation but expanded cells lost CD34 antigens. A group of alkylating molecules (BO-1055, -1090, 1099, -1393 and -1509) was evaluated for proliferation of the pre-B ALL CD34⁺ cells, the pre-B ALL CD34⁻ cells, 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 (CAFC) assay with CB CD34⁺ cells. BO-1055 molecule efficiently suppressed the growth of pre-B ALL CD34⁺ cells (IC₅₀ = 0.29 μM) and CD34⁻ cells (IC₅₀ = 0.31 μM). In contrast, IC₅₀ of BMEC, MSC, CB CD34⁺ cells and CAFC are >10, >25, 8, and >5 μM, respectively. Pre-B ALL cells expressing green fluorescent protein (GFP) and luciferase (GFP-Lu-pre-B ALL) were created, and a xenograft of the GFP-Lu-pre-B ALL cells to NOD/SCID IL2R gamma null (NSG) mice was established. The in vivo effect of BO-1055 to the GFP-Lu-pre-B ALL cells in NSG mice is under investigation. Our stromal culture system supports primary pre-B ALL cells and closely recapitulates the growth of primary human pre-B ALL cells in their niche in vivo. Based on this co-culture system, we identified BO-1055 as a potential therapeutic agent with an excellent toxicity window between pre-B ALL cells and normal tissues including BMEC, MSC and hematopoietic progenitor/stem cells. The in vitro stromal co-culture system combined with the xenograft model of GFP-Lu-pre-B ALL cells provides an efficient and powerful method to screen new drugs for pre-B ALL therapy.