Growth inhibition of multiple myeloma cells by a novel IκB kinase inhibitor

Abstract

Involvement of nuclear factor-κB (NF-κB) in cell survival and proliferation of multiple myeloma has been well established. In this study we observed that NF-κB is constitutively activated in all human myeloma cell lines, thus confirming the previous studies. In addition, we found the phosphorylation of p65 subunit of NF-κB in addition to the phosphorylation of IκBα and the activation of NF-κB DNA binding and that various target genes of NF-κB including bcl-xL, XIAP, c-IAP1, cyclin D1, and IL-6 are up-regulated. We then examined the effect of a novel IκB kinase inhibitor, 2-amino-6-[2-(cyclopropylmethoxy)-6-hydroxyphenyl]- 4-piperidin-4-yl nicotinonitrile (ACHP). When myeloma cells were treated with ACHP, the cell growth was efficiently inhibited with IC50 values ranging from 18 to 35 μmol/L concomitantly with inhibition of the phosphorylation of IκBα/p65 and NF-κB DNA-binding, down-regulation of the NF-κB target genes, and induction of apoptosis. In addition, we observed the treatment of ACHP augmented the cytotoxic effects of vincristine and melphalan (L-phenylalanine mustard), conventional antimyeloma drugs. These findings indicate that IκB kinase inhibitors such as ACHP can sensitize myeloma cells to the cytotoxic effects of chemotherapeutic agents by blocking the antiapoptotic nature of myeloma cells endowed by the constitutive activation of NF-κB. ©2005 American Association for Cancer Research.