p38MAPK Inhibitor LSN2322600 Modulates the Bone Marrow Microenvironment and Inhibits Osteoclastogenesis in Multiple Myeloma.

The interaction between multiple myeloma (MM) cells and the bone marrow (BM) microenvironment plays a crucial role not only in proliferation and survival of MM cells, but also in osteoclastogenesis. In this study, we examined diverse potential of novel p38MAPK inhibitor LSN2322600 (LSN) for MM therapy in vitro and in vivo. The cytotoxic activity of LSN against MM cell lines was modest; however, LSN significantly enhances the cytotoxicity of Bortezomib by down-regulating Bortezomib-induced heat shock protein (HSP) 27 phosphorylation. We next examined the effects of LSN on cytokine secretion in MM cells, bone marrow stromal cells and osteoclast precursor cells. LSN inhibited IL-6 secretion from long-term cultured-bone marrow stromal cells (LT-BMSCs) and bone marrow mononuclear cells (BMMNCs) from MM patients in remission. LSN also inhibited MIP-1 α secretion by fresh tumor cells, BMMNCs and CD14 positive cells. Since these cytokines mediate osteoclastogenesis, we further examined whether LSN could inhibit osteoclastogenesis. Importantly, LSN inhibited in vitro osteoclastogenesis induced by macrophage-colony stimulating factor (M-CSF) and soluble receptor activator of nuclear factor- κ B ligand (sRANKL), as well as osteoclastogenesis in the severe combined immunodeficiency (SCID)-Hu mouse model of human MM. These results suggest that LSN represents a promising novel targeted strategy to reduce skeletal complications as well as to sensitize or overcome resistance to Bortezomib.