Selinexor, a Selective Inhibitor of Nuclear Export (SINE) compound, acts through NF-κB deactivation and combines with proteasome inhibitors to synergistically induce tumor cell death

// Trinayan Kashyap 1 , Christian Argueta 1 , Amro Aboukameel 2 , Thaddeus John Unger 1 , Boris Klebanov 1 , Ramzi M. Mohammad 2 , Irfana Muqbil 2 , Asfar S. Azmi 2 , Claire Drolen 1 , William Senapedis 1 , Margaret Lee 1 , Michael Kauffman 1 , Sharon Shacham 1 , Yosef Landesman 1 1 Karyopharm Therapeutics Inc., Newton, MA, 02459, USA 2 Department of Oncology, Wayne State University School of Medicine, Detroit, MI 48201, USA Correspondence to: Trinayan Kashyap, email: tkashyap@karyopharm.com Keywords: SINE, selinexor, XPO1, NF-κB, proteasome inhibitors Received: July 25, 2016      Accepted: September 22, 2016      Published: October 04, 2016 ABSTRACT The nuclear export protein, exportin-1 (XPO1/CRM1), is overexpressed in many cancers and correlates with poor prognosis. Selinexor, a first-in-class Selective Inhibitor of Nuclear Export (SINE) compound, binds covalently to XPO1 and blocks its function. Treatment of cancer cells with selinexor results in nuclear retention of major tumor suppressor proteins and cell cycle regulators, leading to growth arrest and apoptosis. Recently, we described the selection of SINE compound resistant cells and reported elevated expression of inflammation-related genes in these cells. Here, we demonstrated that NF-κB transcriptional activity is up-regulated in cells that are naturally resistant or have acquired resistance to SINE compounds. Resistance to SINE compounds was created by knockdown of the cellular NF-κB inhibitor, IκB-α. Combination treatment of selinexor with proteasome inhibitors decreased NF-κB activity, sensitized SINE compound resistant cells and showed synergistic cytotoxicity in vitro and in vivo. Furthermore, we showed that selinexor inhibited NF-κB activity by blocking phosphorylation of the IκB-α and the NF-κB p65 subunits, protecting IκB-α from proteasome degradation and trapping IκB-α in the nucleus to suppress NF-κB activity. Therefore, combination treatment of selinexor with a proteasome inhibitor may be beneficial to patients with resistance to either single-agent.