Thalidomide Derivative CC-4047 Inhibits Osteoclast Formation by down Regulation of PU.1.

CC-4047 (Actimid) is an immunomodulatory analog of thalidomide that has stronger anti-myeloma and anti-angiogenic activity than thalidomide, but its effects on human osteoclast lineage are unknown. Early osteoclast progenitors are of hematopoietic origin and progressively differentiate into mature bone resorbing multinucleated osteoclasts. We investigated the effects of CC-4047 and thalidomide on human osteoclastogenesis, using in vitro receptor activator of NFκ-B ligand/M-CSF stimulated culture system of bone marrow cells. Three weeks of treatment of primary bone marrow cultures with 100 μM CC-4047 decreased osteoclast formation accompanied by complete inhibition of bone resorption. Interestingly, osteoclast formation was also inhibited when cultures were treated with CC-4047 only for the first week (90% inhibition). In contrast, inhibitory effect was greatly diminished when the drug was given for only the last week (25% inhibition), indicating that inhibition of osteoclast formation is an early event. The inhibitory effect of CC-4047 on osteoclastogenesis was not induced by cell death, but by a shift of lineage commitment to granulocyte-CFU at the expense of GM-CFU that are osteoclast progenitors. Further studies revealed that this shift is mediated through down regulation of the transcription factor PU.1, which is critical for early osteoclast formation. In contrast to CC-4047, thalidomide was a significantly less potent inhibitor of osteoclast formation and bone resorption. These results provide the first evidence that CC-4047 blocks osteoclast differentiation at the early phase of osteoclastogenesis. Therefore, CC-4047 might be a valuable drug targeting both the tumor and osteoclastic activity in patients with multiple myeloma and potentially other diseases associated with the development of osteolytic lesions.