Inhibition of p38 MAPK Signalling Impairs the Homing of B Lineage ALL Cells to the Bone Marrow of NOD/SCID Mice.

The mechanisms regulating the migration of B lineage acute lymphoblastic leukemia (ALL) cells between the blood and bone marrow compartments remain obscure. The chemokine SDF-1 regulates the motility and proliferation of ALL cells in vitro. We have previously demonstrated that the chemotaxic response of these cells to SDF-1 requires signalling through p38 MAPK and that signalling through PI-3K and MEK/ERK pathways plays only a minor role in a subset of cases. This contrasts with normal CD34+ hematopoietic progenitors and CD34+CD19+ B cell progenitors where signalling through PI-3K is the predominant pathway required for chemotaxis. In this study we examined the requirement for SDF-1 and p38 MAPK signalling in the homing of the B lineage ALL cells to the bone marrow of NOD/SCID mice. CFSE-labelled ALL cells were pre-treated with either the specific CXCR4 antagonists AMD3100 (100μM) or TC14012 (100μM), the p38 MAPK inhibitor SB203580 (10μM), the AKT inhibitor LY294002 (6.65μM) or the MEK inhibitor PD98059 (20μM) for 0.5–1 h at 37°C. Control or inhibitor treated cells were then injected intravenously into irradiated NOD/SCID mice which were either pre-treated with control (vehicle) or the inhibitors AMD3100 (200μg/mouse), TC14012 (200μg/mouse), SB203580 (0.1 mg/mouse), the AKT inhibitor LY294002 (2 mg/mouse) or the ERK inhibitor PD98059 (0.2 mg/mouse). Homing was assessed 4 hours after the injection of cells before significant proliferation of homed cells could occur. AMD3100 and TC14012 significantly inhibited the homing of ALL cells to the bone marrow by up to 80% and 67% respectively. Inhibition of p38 MAPK also decreased the homing of ALL cells to the bone marrow of NOD/SCID mice by 40% compared with the DMSO controls (p<0.05). No inhibition of homing was observed with the inhibitors of PI-3K or MEK in ALL cells. These results support our previous in vitro findings with regards to the importance of the p38 MAPK pathway in SDF-1 induced motility of ALL cells and demonstrate that the same pathway plays an essential role in the homing of these cells to the bone marrow of NOD/SCID mice.