Matrix metalloproteinases in multiple myeloma.

Multiple myeloma is a deadly malignancy characterized by plasma cell infiltration of bones. The resulting effect is painful "punched-out" lesions where bone is eroded and filled with myeloma cells that suppress and replace the normal marrow components. Recently it has been shown that myeloma cells produce matrix-metalloproteinase-9 (MMP-9) and MMP-2 and that accumulation of MMP-9 protein is suppressed upon expression of the heparan sulfate proteoglycan, syndecan-1. In this review, we briefly consider the potential roles for MMPs in the pathogenesis of multiple myeloma. MMPs likely have major roles in: 1) the infiltration of bone and other tissues by the myeloma cells; 2) the osteolytic bone destruction caused by overly active osteoclasts, 3) extracellular matrix remodeling by bone marrow stromal cells; 4) promoting the invasion of the endothelial cells that form neoangiogenic blood vessels necessary to sustain tumor foci; and 5) promoting the growth of myeloma cells. Effective and safe synthetic inhibitors of MMPs are available and these may prove useful in limiting the growth and spread of myeloma cells. In addition, recent insights into the suppression of MMP-9 by syndecan-1 may suggest new strategies for treatment of myeloma.