The novel, proteasome-independent NF-kappaB inhibitor V1810 induces apoptosis and cell cycle arrest in multiple myeloma and overcomes NF-kappaB-mediated drug resistance.

Evidence is increasing that aberrant NF-kappaB activation is crucial for multiple myeloma pathophysiology and a promising target for new antimyeloma therapies. In this study, we assessed the in vitro antimyeloma activity of the novel NF-kappaB inhibitor V1810. Pharmacokinetics and toxicity were studied in vivo. In mice, V1810 plasma concentrations of 10 micromol/L can be reached without relevant toxicity. At this concentration, V1810 potently induces apoptosis in all four multiple myeloma cell lines assessed (IC(50) = 5-12 micromol/L) as well as in primary multiple myeloma cells (IC(50) = 5-40 micromol/L). Apoptosis induced by V1810 is associated with proteasome-independent inhibition of NF-kappaB signaling (41% relative reduction), downregulation of Mcl-1, and caspase 3 cleavage. In OPM2, U266, and RPMI-8226 cells, induction of apoptosis is accompanied by cell cycle arrest. Western blots revealed downregulation of Cdk4 as well as cyclin D1 (U266) or cyclin D2 (OPM2, NCI-H929, RPMI-8226), but not cyclin D3. Consistently, retinoblastoma protein was found to be hypophosphorylated. Furthermore, V1810 reverses NF-kappaB activation induced by the genotoxic drugs melphalan and doxorubicin. V1810 and melphalan synergistically decrease multiple myeloma cell viability. Taken together, the novel, proteasome-independent NF-kappaB inhibitor V1810 induces apoptosis and cell cycle arrest in multiple myeloma cells at a concentration range that can be achieved in vivo. Moreover, V1810 reverses NF-kappaB activation by alkylating drugs and overcomes NF-kappaB-mediated resistance to melphalan.