Small Molecule Screening of Primary Human Acute Myeloid Leukemia Using Co-culture and Multiplexed FACS Analysis

Ex vivo culture of primary acute myeloid leukemia (AML) cells is notoriously difficult due to spontaneous differentiation and cell death, which hinders mechanistic and translational studies. To overcome this bottleneck, we have implemented a co-culture system, where the OP9-M2 stromal cells support the growth, but most notably limit the differentiation of primary AML cells, thus allowing for mechanistic studies in vitro. Additionally, the co-culture on OP9-M2 stromal is superior in preserving surface marker expression of primary (adult and pediatric) AML cells in comparison to stroma-free culture. Thus, by combining the co-culture with multicolor, high-throughput FACS, we can evaluate the effect of hundreds of small molecules on multi-parametric processes including: cell survival, stemness (leukemic stem cells), and myeloid differentiation on the primary AML cells at a single-cell level. This method streamlines the identification of potential therapeutic agents, but also facilitates combinatorial screening aiming, for instance, at dissecting the regulatory pathways in a patient-specific manner. Graphic abstract: Schematic representation of the ex vivo small molecule screening of primary human acute myeloid leukemia. Irradiated, sub-confluent OP9-M2 stromal cells are plated in half-area 96 wells plates 4-16 h prior to adding primary AML cells. Compounds are added 36-48 h later and effects on cell number, leukemic stem cell population, and myeloid differentiation are quantifed by FACS after 4 days of treatment.