Inhibition of p38α MAPK Reduces Tumor Burden, Prevents the Development of Myeloma Bone Disease, and Increases Survival in the 5T2 and 5T33 Murine Models of Myeloma.

The bone microenvironment plays a critical role in supporting the growth and survival of myeloma cells and the development of osteolytic bone disease. Signalling through p38 α MAPK mediates synthesis of myeloma cell survival factors by stromal cells; whereas, inhibiting p38 α MAPK reduces myeloma cell proliferation and inhibits osteoclast formation in vitro. However, it is unclear whether p38 α MAPK inhibition will prevent the growth and survival of myeloma cells and the bone disease in vivo. The aim of this study was to determine whether SCIO-469, a selective p38 α MAPK inhibitor, would inhibit myeloma growth and prevent the development of bone disease in the 5TMM syngeneic models of myeloma.

Treatment of 5TMM cells, in vitro, with SCIO-469 resulted in a clear inhibition of p38 phosphorylation, as assessed by Western blotting and an inhibition up to 35% of stromal cell induced 5T33MM proliferation.

Injection of 5T2MM murine myeloma cells into C57Bl/KaLwRij mice resulted in the growth of myeloma in bone and the development of bone disease characterized by increased osteoclast surface (p<0.05), a reduction in cancellous bone (p<0.01) and the presence of osteolytic bone lesions on x-ray (p<0.01). Treatment of 5T2MM-bearing mice with SCIO-469 (150mg/kg in the diet, therapeutical treatment from paraprotein detection) resulted in a 42% decrease in serum paraprotein and prevented development of osteolytic lesions (p<0.01). Injection of 5T33MM cells into C57Bl/KaLwRij mice also resulted in the development of myeloma but not associated bone disease. Treatment of 5T33MM-bearing mice from the time of tumor cell injection with SCIO-469 resulted in a decrease in serum paraprotein (8.8+/−1.4g/dl to 0.04+/− 0.03g/dl, p<0.001) and a reduction in the proportion of tumor cells in the bone marrow (67 +/− 8.1% to 1.09 +/− 0.58%, p<0.001). Kaplan-Meier analysis demonstrated an increase in disease-free survival (veh=27.5 days vs 96 days, p<0.001) after treatment of the mice with SCIO-469.

These data demonstrate that targeting p38 α MAPK with SCIO-469 is associated with an anti-myeloma effect, which indirectly prevents the development of myeloma bone disease.