Novel small molecule inhibitor of Kpnβ1 induces cell cycle arrest and apoptosis in cancer cells

Therapeutic targeting of nuclear export and import receptors in cancer and their potential in combination chemotherapy

Systemic modalities are crucial in the management of disseminated malignancies and liquid tumours. However, patient responses and tolerability to treatment are generally poor and those that enter remission often return with refractory disease. Combination therapies provide a methodology to overcome chemoresistance mechanisms and address dose-limiting toxicities. A deeper understanding of tumorigenic processes at the molecular level has brought a targeted therapy approach to the forefront of cancer research, and novel cancer biomarkers are being identified at a rapid rate, with some showing potential therapeutic benefits. The Karyopherin superfamily of proteins is soluble receptors that mediate nucleocytoplasmic shuttling of proteins and RNAs, and recently, nuclear transport receptors have been recognized as novel anticancer targets. Inhibitors against nuclear export have been approved for clinical use against certain cancer types, whereas inhibitors against nuclear import are in preclinical stages of investigation. Mechanistically, targeting nucleocytoplasmic shuttling has shown to abrogate oncogenic signalling and restore tumour suppressor functions through nuclear sequestration of relevant proteins and mRNAs. Hence, nuclear transport inhibitors display broad spectrum anticancer activity and harbour potential to engage in synergistic interactions with a wide array of cytotoxic agents and other targeted agents. This review is focussed on the most researched nuclear transport receptors in the context of cancer, XPO1 and KPNB1, and highlights how inhibitors targeting these receptors can enhance the therapeutic efficacy of standard of care therapies and novel targeted agents in a combination therapy approach. Furthermore, an updated review on the therapeutic targeting of lesser characterized karyopherin proteins is provided and resistance to clinically approved nuclear export inhibitors is discussed.

Exportin 1-mediated nuclear/cytoplasmic trafficking controls drug sensitivity of classical Hodgkin's lymphoma

Exportin 1 (XPO1) is the main nuclear export receptor that controls the subcellular trafficking and the functions of major regulatory proteins. XPO1 is overexpressed in various cancers and small inhibitors of nuclear export (SINEs) have been developed to inhibit XPO1. In primary mediastinal B-cell lymphoma (PMBL) and classical Hodgkin's lymphoma (cHL), the XPO1 gene may be mutated on one nucleotide and encodes the mutant XPO1E571K . To understand the impact of mutation on protein function, we studied the response of PMBL and cHL cells to selinexor, a SINE, and ibrutinib, an inhibitor of Bruton tyrosine kinase. XPO1 mutation renders lymphoma cells more sensitive to selinexor due to a faster degradation of mutant XPO1 compared to the wild-type. We further showed that a mistrafficking of p65 (RELA) and p52 (NFκB2) transcription factors between the nuclear and cytoplasmic compartments accounts for the response toward ibrutinib. XPO1 mutation may be envisaged as a biomarker of the response of PMBL and cHL cells and other B-cell hemopathies to SINEs and drugs that target even indirectly the NFκB signaling pathway.

KPNB1-mediated nuclear import in cancer

Dysregulation of nucleocytoplasmic shuttling impairs cellular homeostasis and promotes cancer development. KPNB1 is a member of karyopherin β family, mediating the transportation of proteins from the cytoplasm to the nucleus. In a variety of cancers, the expression of KPNB1 is upregulated to facilitate tumor growth and progression. Both downregulation of KPNB1 level and inhibition of KPNB1 activity prevent the entry of cancer-related transcription factors into the nucleus, subsequently suppressing the proliferation and metastasis of cancer cells. Currently, five KPNB1 inhibitors have been reported and exhibited good efficacy against cancer. This paper provides an overview of the role and mechanism of KPNB1 in different cancers and KPNB1-targeted anticancer compounds which hold promise for the future.

The Evidence That 25(OH)D3 and VK2 MK-7 Vitamins Influence the Proliferative Potential and Gene Expression Profiles of Multiple Myeloma Cells and the Development of Resistance to Bortezomib

Multiple myeloma (MM) remains an incurable hematological malignancy. Bortezomib (BTZ) is a proteasome inhibitor widely used in MM therapy whose potent activity is often hampered by the development of resistance. The immune system is vital in the pathophysiology of BTZ resistance. Vitamins D (VD) and K (VK) modulate the immune system; therefore, they are potentially beneficial in MM. The aim of the study was to evaluate the effect of BTZ therapy and VD and VK supplementation on the proliferation potential and gene expression profiles of MM cells in terms of the development of BTZ resistance. The U266 MM cell line was incubated three times with BTZ, VD and VK at different timepoints. Then, proliferation assays, RNA sequencing and bioinformatics analysis were performed. We showed BTZ resistance to be mediated by processes related to ATP metabolism and oxidative phosphorylation. The upregulation of genes from the SNORDs family suggests the involvement of epigenetic mechanisms. Supplementation with VD and VK reduced the proliferation of MM cells in both the non-BTZ-resistant and BTZ-resistant phenotypes. VD and VK, by restoring proper metabolism, may have overcome resistance to BTZ in vitro. This observation forms the basis for further clinical trials evaluating VD and VK as potential adjuvant therapies for MM patients.

Karyopherin-mediated nucleocytoplasmic transport

Efficient and regulated nucleocytoplasmic trafficking of macromolecules to the correct subcellular compartment is critical for proper functions of the eukaryotic cell. The majority of the macromolecular traffic across the nuclear pores is mediated by the Karyopherin-β (or Kap) family of nuclear transport receptors. Work over more than two decades has shed considerable light on how the different Kap family members bring their respective cargoes into the nucleus or the cytoplasm in efficient and highly regulated manners. In this Review, we overview the main features and established functions of Kap family members, describe how Kaps recognize their cargoes and discuss the different ways in which these Kap-cargo interactions can be regulated, highlighting new findings and open questions. We also describe current knowledge of the import and export of the components of three large gene expression machines - the core replisome, RNA polymerase II and the ribosome - pointing out the questions that persist about how such large macromolecular complexes are trafficked to serve their function in a designated subcellular location.