XPO1 inhibition antagonizes MCL via nuclear retention of IkB: Selinexor demonstrates antitumor activities in both ibr-sensitive and ibr-resistant tumor cells

Inhibition of BCR signaling through BTK inhibitor, ibrutinib, has generated a remarkable response in mantle cell lymphoma (MCL). However, approximately one-third of the patients do not respond well to the drug and disease relapse on ibrutinib is nearly universal. Alternative therapeutic strategies aimed to prevent and overcome ibrutinib resistance are needed. We compared and contrasted the effects of selinexor, a selective inhibitor of nuclear export, with ibrutinib in six MCL cell lines that display differential intrinsic sensitivity to ibrutinib. We found that selinexor had a broader anti-tumor activity in MCL than ibrutinib. MCL cell lines resistant to ibrutinib remained sensitive to selinexor. We showed that selinexor induced apoptosis/cell cycle arrest and XPO-1 knockdown also retarded cell growth. Further, down-regulation of the NF-B gene signature, as opposed to BCR signature, was a common feature that underlies the response of MCL to both selinexor and ibrutinib. Meanwhile, unaltered NF-B was associated with ibrutinib resistance. Mechnistically, selinexor induced nuclear retention of IB that was accompanied by the reduction of DNA binding activity of NF-B suggesting that NF-B is trapped in an inhibitory complex. Co-immunoprecipitation confirmed that p65 of NF-B and IB were physically associated. In primary MCL tumors, we further demonstrated that the number of cells with IB nuclear retention was linearly correlated with the degree of apoptosis. Our data highlight the role of NF-B pathway in drug response to ibrutinib and selinexor and show the potential of using selinexor to prevent and overcome intrinsic ibrutinib resistance through NF-B inhibition. To capture early changes in RNA transcription, JEKO1 and MAVER were treated for 6 hr with or without the inhibitors (0.4 uM for ibrutinib and 1.5 uM for selinexor) with three biological triplicates. Cells were harvested and subjected to RNA sequencing and diffrences in biological pathway perturvation were analyzed using GSEA.