Fenretinide inhibits myeloma cell growth, osteoclastogenesis and osteoclast viability.

Fenretinide (4HPR), a nontoxic analog of ATRA, has been investigated in various malignancies but not in multiple myeloma (MM), a plasma cell malignancy associated with induction of osteolytic bone disease. Here we show that 4HPR induces apoptosis through increased level of ROS and activation of caspase-8, 9 and 3, and inhibits growth of several MM cell lines in a dose-dependent manner. Serum or co-culture with the supportive osteoclasts partially protects MM cells from 4HPR-induced growth inhibition. Sphingosine-1 phosphate (S1P) significantly protects MM cells from 4HPR-induced apoptosis suggesting that as in other malignancies, this drug up-regulates ceramide in MM cells. 4HPR has no toxic effects on non-malignant cells such as blood mononucleated cells, mesenchymal stem cells and osteoblasts, but markedly reduces viability of endothelial cells and mature osteoclasts and inhibits differentiation of osteoclasts and MM-induced tube formation. 4HPR is a potential anti-MM agent, affecting MM cells and MM-induced bone disease and angiogenesis.