Pharmacodynamic monitoring of MEK inhibition in c-kit⁺ lin^−/low cells by multi-parameter FACS. Bone marrow was obtained from WT and Mx1-Cre, Kras^G12D mice 2 hours after they received an intraperitoneal injection of vehicle control or CI-1040. The bone marrow was quickly harvested and stimulated with GM-CSF (10 ng/mL) for 10 minutes. Levels of phosphorylated ERK, STAT5, and S6 were measured in the c-kit⁺ lin^−/low subset. These data were confirmed in a second experimental group.