Inhibition of Multiple Myeloma Cells Growth by AS602868, a Pharmacological Inhibitor of IKK2.

The NF-κB pathway is involved in the physiological regulation of cell proliferation in many cell types as well as in the resistance of several malignancies to cell death. The pathophysiologic basis for multiple myeloma (MM) has been attributed to the dysregulation of various paracrine or autocrine growth factor loops and to perturbations in several signal transduction pathways including IKK/NF-κB. The aim of the present study was to investigate the effect of a pharmaceutical IKK2 inhibitor (IKK2-I), the anilinopyrimidine derivative AS602868 (Serono International SA), on the in vitro growth of human MM cell lines (HMCL) and primary MM cells. We evaluated the effect of AS602868 on the proliferation and the survival of 12 IL-6-dependent HCML and 2 autonomously growing HCML as well as on the survival of total bone marrow mononuclear cells from patients with newly diagnosed MM (n = 6) or with relapsing MM (n = 7). Results show that using HMCL or primary MM cells, AS602868 induces a clear dose-dependent inhibition of MM cell growth (the 50% inhibitory concentration (IC50) ranging from 0.28 to 8.3 μM, mean IC50 = 2.6 μM on HCML). It was shown using HMCL that the growth inhibition induced by AS602868 is the result of a simultaneous induction of apoptosis and inhibition of the cell cycle progression. Importantly, AS602868 does not alter the survival of other bone marrow mononuclear cells (CD138−) co-cultured with primary MM (CD138+) cells except on CD34+ hematopoietic stem cells. Interestingly, using gene expression profiling with Affymetrix microarrays on 13 HMCL, we show that the resistance (high IC50) to AS602868 inhibitor is strongly correlated to APRIL gene expression (r =.7603, p <.01). Thus, an autocrine production of APRIL confers a resistance to the AS602868 IKK2-I. This can be explained since APRIL has been shown to activate the alternative NF-κB pathway which implicates an IKK complex composed of IKK1 homodimers instead of the IKK1/IKK2/NEMO complex involved in the canonical NF-κB pathway. The results demonstrate the important role of NF-κB in maintaining survival of MM cells and suggest that a pharmacological inhibition of the NF-κB pathway by an IKK2-I, AS602868, can efficiently kill myeloma cell lines or primary myeloma cells and might represent an innovative approach for treating MM patients.