¹Department of Medical Oncology, LeBow Institute for Myeloma Therapeutics, Jerome Lipper Multiple Myeloma Center, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, USA

Correspondence: Dr KC Anderson or Dr I Breitkreutz, Department of Medical Oncology, LeBow Institute for Myeloma Therapeutics, Jerome Lipper Multiple Myeloma Center, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA. E-mails: Kenneth_Anderson@dfci.harvard.edu or Iris_Breitkreutz@dfci.harvard.edu

Received 28 February 2008; Revised 27 May 2008; Accepted 30 May 2008; Published online 3 July 2008.

Abstract

Osteolytic bone disease in multiple myeloma (MM) is caused by enhanced osteoclast (OCL) activation and inhibition of osteoblast function. Lenalidomide and bortezomib have shown promising response rates in relapsed and newly diagnosed MM, and bortezomib has recently been reported to inhibit OCLs. We here investigated the effect of lenalidomide on OCL formation and osteoclastogenesis in comparison with bortezomib. Both drugs decreased V3-integrin, tartrate-resistant acid phosphatase-positive cells and bone resorption on dentin disks. In addition, both agents decreased receptor activator of nuclear factor-B ligand (RANKL) secretion of bone marrow stromal cells (BMSCs) derived from MM patients. We identified PU.1 and pERK as major targets of lenalidomide, and nuclear factor of activated T cells of bortezomib, resulting in inhibition of osteoclastogenesis. Furthermore, downregulation of cathepsin K, essential for resorption of the bone collagen matrix, was observed. We demonstrated a significant decrease of growth and survival factors including macrophage inflammatory protein-, B-cell activating factor and a proliferation-inducing ligand. Importantly, in serum from MM patients treated with lenalidomide, the essential bone-remodeling factor RANKL, as well as the RANKL/OPG ratio, were significantly reduced, whereas osteoprotegerin (OPG) was increased. We conclude that both agents specifically target key factors in osteoclastogenesis, and could directly affect the MM-OCL-BMSCs activation loop in osteolytic bone disease.