Therapeutic Targeting of Nuclear Export Inhibition in Lung Cancer

Selinexor in combination with venetoclax and decitabine in patients with refractory myelodysplastic syndrome previously exposed to hypomethylating agents: three case reports

The management of patients with myelodysplastic syndrome (MDS) refractory to hypomethylating agents (HMAs) remains a challenge with few reliably effective treatments. Preclinical studies have shown that the inhibition of the nuclear export protein XPO1 causes nuclear accumulation of p53 and disruption of NF-κB signaling; both of which are relevant targets for MDS. Selinexor is an XPO1 inhibitor with demonstrated efficacy in MDS patients. Herein, we report three patients with MDS refractory to HMAs, however, when selinexor and venetoclax were added to the treatment regimen, the patients achieved a complete response and a significant reduction in spleen size. All patients successfully underwent hematopoietic stem cell transplantation. These cases demonstrate that the combination therapy can achieve CR and significant reductions in spleen size, offering a promising therapeutic option for patients with limited treatment choices. Combination therapy would also offer a potential way for patients to bridge to transplantation. Formal evaluations of this regimen in patients with MDS refractory to HMAs may be meaningful.

Altered RNA export by SF3B1 mutants confers sensitivity to nuclear export inhibition

SF3B1 mutations frequently occur in cancer yet lack targeted therapies. Clinical trials of XPO1 inhibitors, selinexor and eltanexor, in high-risk myelodysplastic neoplasms (MDS) revealed responders were enriched with SF3B1 mutations. Given that XPO1 (Exportin-1) is a nuclear exporter responsible for the export of proteins and multiple RNA species, this led to the hypothesis that SF3B1-mutant cells are sensitive to XPO1 inhibition, potentially due to altered splicing. Subsequent RNA sequencing after XPO1 inhibition in SF3B1 wildtype and mutant cells showed increased nuclear retention of RNA transcripts and increased alternative splicing in the SF3B1 mutant cells particularly of genes that impact apoptotic pathways. To identify novel drug combinations that synergize with XPO1 inhibition, a forward genetic screen was performed with eltanexor treatment implicating anti-apoptotic targets BCL2 and BCLXL, which were validated by functional testing in vitro and in vivo. These targets were tested in vivo using Sf3b1K700E conditional knock-in mice, which showed that the combination of eltanexor and venetoclax (BCL2 inhibitor) had a preferential sensitivity for SF3B1 mutant cells without excessive toxicity. In this study, we unveil the mechanisms underlying sensitization to XPO1 inhibition in SF3B1-mutant MDS and preclinically rationalize the combination of eltanexor and venetoclax for high-risk MDS.

XPO1 serves as a prognostic marker involving AKT/MAPK/TGFBR1 pathway in OSCC

BACKGROUND

Exportin 1 (XPO1) is a nuclear export protein that facilitates the transportation of various substances. XPO1 promotes tumor development as a poor prognostic factor in a variety of tumors and is a therapeutic target for screening inhibitors. However, the role of XPO1 in oral squamous cell carcinoma (OSCC) has yet to be determined.

METHODS

The expression patterns of XPO1 mRNA in OSCC were investigated using bioinformatics tools, and the expression levels of XPO1 protein in OSCC specimens were confirmed by immunohistochemical assays. Survival analysis was conducted to evaluate the impact of XPO1 on prognosis. GO and KEGG enrichment analyses were utilized to uncover the signaling pathways mediated by XPO1. Additionally, we examined the association between XPO1 and AKT/MAPK/TGFBR1 and immune infiltration.

RESULTS

XPO1 mRNA and protein expression levels were significantly enhanced in OSCC and associated with OSCC severity. Enhanced XPO1 expression was indicative of poor survival. Functional analysis showed that XPO1 mediated pathways associated with cell cycle and DNA replication and reduced immune infiltration in OSCC. Additionally, XPO1 mRNA and protein expression levels had significant positive relationships with AKT/MAPK/TGFBR1.

CONCLUSIONS

XPO1, as a marker of poor prognosis in OSCC, can promote OSCC through AKT/MAPK/TGFBR1.

Adverse events reporting of XPO1 inhibitor - selinexor: a real-word analysis from FAERS database

As the world's first oral nuclear export inhibitor, selinexor is increasingly being used in clinical applications for malignant tumors. However, there is no extensive exploration on selinexor's adverse events (ADEs), necessitating a real-word assessment of its clinical medication safety. FAERS data (July 2019-June 2023) were searched for selinexor ADE reports across all indications. Use the system organ class (SOC) and preferred terms (PT) from the medical dictionary for regulatory activities (MedDRA) to describe, categorize, and statistic ADEs. Disproportionality analysis was employed through calculation of reporting odds ratio (ROR) and proportional reporting ratio (PRR). Based on total of 4392 selinexor related ADE reports as the primary suspect (PS), of which 2595 instances were severe outcomes. The predominant ADEs included gastrointestinal disorders, myelosuppression symptoms, and various nonspecific manifestations. 124 signals associated with selinexor ADE were detected, and 10 of these top 15 signals were not included into the instructions. Our study provides real-world evidence regarding the drug safety of selinexor, which is crucial for clinicians to safeguard patients' health.

HMGB1 Expression Levels Correlate with Response to Immunotherapy in Non-Small Cell Lung Cancer

Purpose

High-mobility group box 1 protein (HMGB1) is subject to exportin 1 (XPO1)-dependent nuclear export, and it is involved in functions implicated in resistance to immunotherapy. We investigated whether HMGB1 mRNA expression was associated with response to immune checkpoint inhibitors (ICI) in non-small cell lung cancer (NSCLC).

Patients and Methods

RNA was isolated from pretreatment biopsies of patients with advanced NSCLC treated with ICI. Gene expression analysis of several genes, including HMGB1, was conducted using the NanoString Counter analysis system (PanCancer Immune Profiling Panel). Western blotting analysis and cell viability assays in EGFR and KRAS mutant cell lines were carried out. Evaluation of the antitumoral effect of ICI in combination with XPO1 blocker (selinexor) and trametinib was determined in a murine Lewis lung carcinoma model.

Results

HMGB1 mRNA levels in NSCLC patients treated with ICI correlated with progression-free survival (PFS) (median PFS 9.0 versus 18.0 months, P=0.008, hazard ratio=0.30 in high versus low HMGB1). After TNF-α stimulation, HMGB1 accumulates in the cytoplasm of PC9 cells, but this accumulation can be prevented by using selinexor or antiretroviral drugs. Erlotinib or osimertinib with selinexor in EGFR-mutant cells and trametinib plus selinexor in KRAS mutant abolish tumor cell proliferation. Selinexor with a PD-1 inhibitor with or without trametinib abrogates the tumor growth in the murine Lewis lung cancer model.

Conclusion

An in-depth exploration of the functions of HMGB1 mRNA and protein is expected to uncover new potential targets and provide a basis for treating metastatic NSCLC in combination with ICI.

The nuclear export protein exportin-1 in solid malignant tumours: From biology to clinical trials

BACKGROUND

Exportin-1 (XPO1), a crucial protein regulating nuclear-cytoplasmic transport, is frequently overexpressed in various cancers, driving tumor progression and drug resistance. This makes XPO1 an attractive therapeutic target. Over the past few decades, the number of available nuclear export-selective inhibitors has been increasing. Only KPT-330 (selinexor) has been successfully used for treating haematological malignancies, and KPT-8602 (eltanexor) has been used for treating haematologic tumours in clinical trials. However, the use of nuclear export-selective inhibitors for the inhibition of XPO1 expression has yet to be thoroughly investigated in clinical studies and therapeutic outcomes for solid tumours.

METHODS

We collected numerous literatures to explain the efficacy of XPO1 Inhibitors in preclinical and clinical studies of a wide range of solid tumours.

RESULTS

In this review, we focus on the nuclear export function of XPO1 and results from clinical trials of its inhibitors in solid malignant tumours. We summarized the mechanism of action and therapeutic potential of XPO1 inhibitors, as well as adverse effects and response biomarkers.

CONCLUSION

XPO1 inhibition has emerged as a promising therapeutic strategy in the fight against cancer, offering a novel approach to targeting tumorigenic processes and overcoming drug resistance. SINE compounds have demonstrated efficacy in a wide range of solid tumours, and ongoing research is focused on optimizing their use, identifying response biomarkers, and developing effective combination therapies.

KEY POINTS

Exportin-1 (XPO1) plays a critical role in mediating nucleocytoplasmic transport and cell cycle. XPO1 dysfunction promotes tumourigenesis and drug resistance within solid tumours. The therapeutic potential and ongoing researches on XPO1 inhibitors in the treatment of solid tumours. Additional researches are essential to address safety concerns and identify biomarkers for predicting patient response to XPO1 inhibitors.

The XPO1 inhibitor selinexor ameliorates bleomycin-induced pulmonary fibrosis in mice via GBP5/NLRP3 inflammasome signaling

Pulmonary fibrosis is an irreversible and progressive lung disease with limited treatments available. Selinexor (Sel), an orally available, small-molecule, selective inhibitor of XPO1, exhibits notable antitumor, anti-inflammatory and antiviral activities. However, its potential role in treating pulmonary fibrosis is unknown. C57BL/6J mice were used to establish a pulmonary fibrosis model by intratracheal administration of bleomycin (BLM). Subsequently, Sel was administered intraperitoneally. Our data demonstrated that Sel administration ameliorated BLM-induced pulmonary fibrosis by increasing mouse body weights; reducing H&E staining, Masson staining scores, and shadows in mouse lung computed tomography (CT) images, decreasing the total cell and neutrophil counts in the lung and bronchoalveolar lavage fluid (BALF); and decreasing the levels of TGF-β1. We next confirmed that Sel reduced the deposition of extracellular matrix (ECM) components in the lungs of BLM-induced pulmonary fibrosis mice. We showed that collagen I, alpha-smooth muscle actin (α-SMA), and hydroxyproline levels and the mRNA levels of Col1a1, Eln, Fn1, Ctgf, and Fgf2 were reduced. Mechanistically, tandem mass tags (TMT)- based quantitative proteomics analysis revealed a significant increase in GBP5 in the lungs of BLM mice but a decrease in that of BLM + Sel mice; this phenomenon was confirmed by western blotting and RT-qPCR. NLRP3 inflammasome signaling was significantly enriched in both the BLM group and BLM + Sel group based on GO and KEGG analyses of differentially expressed proteins between the groups. Furthermore, Sel reduced the expression of NLRP3, cleaved caspase 1, and ASC in vivo and in vitro, and decreased the levels of IL-1β, IL-18, and IFN-r in lung tissue and BALF. SiRNA-GBP5 inhibited NLRP3 signaling in vitro, and overexpression of GBP5 inhibited the protective effect of Sel against BLM-induced cellular injury. Taken together, our findings indicate that Sel ameliorates BLM-induced pulmonary fibrosis by targeting GBP5 via NLRP3 inflammasome signaling. Thus, the XPO1 inhibitor - Sel might be a potential therapeutic agent for pulmonary fibrosis.

Identifying novel inhibitors targeting Exportin-1 for the potential treatment of COVID-19

The nuclear export protein 1 (XPO1) mediates the nucleocytoplasmic transport of proteins and ribonucleic acids (RNAs) and plays a prominent role in maintaining cellular homeostasis. XPO1 has emerged as a promising therapeutic approach to interfere with the lifecycle of many viruses. In our earlier study, we proved the inhibition of XPO1 as a therapeutic strategy for managing SARS-COV-2 and its variants. In this study, we have utilized pharmacophore-assisted computational methods to identify prominent XPO1 inhibitors. After several layers of screening, a few molecules were shortlisted for further experimental validation on the in vitro SARS-CoV-2 cell infection model. It was observed that these compounds reduced spike positivity, suggesting inhibition of SARS-COV-2 infection. The outcome of this study could be considered further for developing novel antiviral therapeutic strategies against SARS-CoV-2.

Selinexor: Targeting a novel pathway in multiple myeloma

Selinexor is an orally bioavailable selective inhibitor of nuclear export compound that inhibits exportin-1 (XPO1), a novel therapeutic target that is overexpressed in multiple myeloma (MM) and is responsible for the transport of ∼220 nuclear proteins to the cytoplasm, including tumour suppressor proteins. Inhibition of this process has demonstrated substantial antimyeloma activity in preclinical studies, both alone and in combination with established MM therapeutics. Based on a clinical trial programme encompassing multiple combination regimens, selinexor-based therapy has been approved for the treatment of relapsed/refractory MM (RRMM), with selinexor-dexamethasone approved in the later-relapse setting for penta-refractory patients and selinexor-bortezomib-dexamethasone approved for patients who have received ≥1 prior therapy. Here, we provide a comprehensive review of the clinical data on selinexor-based regimens, including recent updates from the 2022 American Society of Hematology annual meeting, and summarise ongoing studies of this novel targeted agent in newly diagnosed MM and RRMM.

Synthetic lethal targeting of TET2-mutant haematopoietic stem and progenitor cells by XPO1 inhibitors

TET2 inactivating mutations serve as initiating genetic lesions in the transformation of haematopoietic stem and progenitor cells (HSPCs). In this study, we analysed known drugs in zebrafish embryos for their ability to selectively kill tet2-mutant HSPCs in vivo. We found that the exportin 1 (XPO1) inhibitors, selinexor and eltanexor, selectively kill tet2-mutant HSPCs. In serial replating colony assays, these small molecules were selectively active in killing murine Tet2-deficient Lineage-, Sca1+, Kit+ (LSK) cells, and also TET2-inactivated human acute myeloid leukaemia (AML) cells. Selective killing of TET2-mutant HSPCs and human AML cells by these inhibitors was due to increased levels of apoptosis, without evidence of DNA damage based on increased γH2AX expression. The finding that TET2 loss renders HSPCs and AML cells selectively susceptible to cell death induced by XPO1 inhibitors provides preclinical evidence of the selective activity of these drugs, justifying further clinical studies of these small molecules for the treatment of TET2-mutant haematopoietic malignancies, and to suppress clonal expansion in age-related TET2-mutant clonal haematopoiesis.

High Throughput Fluorescence-Based In Vitro Experimental Platform for the Identification of Effective Therapies to Overcome Tumour Microenvironment-Mediated Drug Resistance in AML

The interactions between Acute Myeloid Leukaemia (AML) leukemic stem cells and the bone marrow (BM) microenvironment play a critical role during AML progression and resistance to drug treatments. Therefore, the identification of novel therapies requires drug-screening methods using in vitro co-culture models that closely recreate the cytoprotective BM setting. We have developed a new fluorescence-based in vitro co-culture system scalable to high throughput for measuring the concomitant effect of drugs on AML cells and the cytoprotective BM microenvironment. eGFP-expressing AML cells are co-cultured in direct contact with mCherry-expressing BM stromal cells for the accurate assessment of proliferation, viability, and signaling in both cell types. This model identified several efficacious compounds that overcome BM stroma-mediated drug resistance against daunorubicin, including the chromosome region maintenance 1 (CRM1/XPO1) inhibitor KPT-330. In silico analysis of genes co-expressed with CRM1, combined with in vitro experiments using our new methodology, also indicates that the combination of KPT-330 with the AURKA pharmacological inhibitor alisertib circumvents the cytoprotection of AML cells mediated by the BM stroma. This new experimental model and analysis provide a more precise screening method for developing improved therapeutics targeting AML cells within the cytoprotective BM microenvironment.

One Stone, Two Birds: A Peptide-Au(I) Infinite Coordination Supermolecule for the Confederate Physical and Biological Radiosensitization in Cancer Radiation Therapy

Over half of cancer patients are subjected to radiotherapy, but owing to the deficient amount of reactive oxygen radicals (ROS) and DNA double-strand breaks (DSBs), a fair number of them suffer from radiotherapy resistance and the subsequent short-term survival opportunity. To overcome it, many successes have been achieved in radiosensitizer discovery using physical strategy and/or biological strategy, but significant challenges remain regarding developing clinically translational radiosensitizers. Herein, a peptide-Au(I) infinite coordination supermolecule termed PAICS is developed that combined both physical and biological radiosensitization and possessed pharmaceutical characteristics including adequate circulatory stability, controllable drug release, tumor-prioritized accumulation, and the favorable body eliminability. As expected, monovalent gold ion endowed this supermolecule with high X-ray absorption and the subsequent radiosensitization. Furthermore, a peptide targeting CRM1, is assembled into the supermolecule, which successfully activates p53 and apoptosis pathway, thereby further sensitizing radiotherapy. As a result, PAICS showed superior ability for radiotherapy sensitization in vivo and maintained a favorable safety profile. Thus, the PAICS reported here will offer a feasible solution to simultaneously overcome both the pharmaceutical obstacles of physical and biological radiosensitizers and will enable the development of a class of nanomedicines for tumor radiotherapy sensitization.

Guidance for Use and dosing of Selinexor in Multiple Myeloma in 2021: Consensus From International Myeloma Foundation Expert Roundtable

Selinexor is a first in class selective inhibitor of nuclear export (SINE), blocks exportin 1 (XPO1), a protein transporter, that among other actions, shuttles cargo proteins such as tumor suppressor proteins (TSPs), the glucocorticoid receptor (GR), and oncoprotein messenger RNAs (mRNAs) across the nuclear membrane to cytoplasm. By blocking XPO1, selinexor facilitates nuclear preservation and activation of TSPs, and prevents mRNA translation of the oncoproteins leading to induction of apoptosis. The therapeutic value of selinexor in combination with dexamethasone has been successfully demonstrated in treating relapsed and/or refractory myeloma (RRMM), leading to the Food and Drug Administration (FDA) approval of selinexor in combination with dexamethasone in 2019 for the treatment of adult patients with RRMM who received at least 4 prior therapies and whose disease is refractory to at least 2 proteasome inhibitors, at least 2 immunomodulatory agents, and an anti-CD38 monoclonal antibody (mAb) - a pentarefractory myeloma. More recently, selinexor in combination with bortezomib and dexamethasone was approved by the FDA in December 2020, based on the BOSTON study among RRMM patients who had received at least one prior line of therapy. With more available safety and efficacy data supporting the increased interval between dosing of selinexor (and lesser cumulative weekly dosing) and schedule, contrary to the originally approved dose of 160 mg per week, the supportive care guidelines needed to be revisited. The current manuscript summarizes the supportive care solutions with weekly dosing of selinexor and identifies the ideal potential patient for selinexor treatment.

The molecular mechanism and challenge of targeting XPO1 in treatment of relapsed and refractory myeloma

•

Significant progress has been made on the treatment of MM during past two decades.

•

Acquired drug-resistance continues to drive early relapse in primary refractory MM.

•

XPO1 over-expression and cargo mislocalization are associated with drug-resistance.

•

XPO1 inhibitor selinexor restores drug sensitivity to subsets of RR-MM cells.

Multiple myeloma (MM) treatment regimens have vastly improved since the introduction of immunomodulators, proteasome inhibitors, and anti-CD38 monoclonal antibodies; however, MM is considered an incurable disease due to inevitable relapse and acquired drug resistance. Understanding the molecular mechanism by which drug resistance is acquired will help create novel strategies to prevent relapse and help develop novel therapeutics to treat relapsed/refractory (RR)-MM patients. Currently, only homozygous deletion/mutation of TP53 gene due to “double-hits” on Chromosome 17p region is consistently associated with a poor prognosis. The exciting discovery of XPO1 overexpression and mislocalization of its cargos in the RR-MM cells has led to a novel treatment options. Clinical studies have demonstrated that the XPO1 inhibitor selinexor can restore sensitivity of RR-MM to PIs and dexamethasone. We will elaborate on the problems of MM treatment strategies and discuss the mechanism and challenges of using XPO1 inhibitors in RR-MM therapies while deliberating potential solutions.

Selinexor and the Selective Inhibition of Nuclear Export: A New Perspective on the Treatment of Sarcomas and Other Solid and Non-Solid Tumors

Nucleocytoplasmic transport has been found dysregulated in many types of cancer and is often described as a poor prognostic factor. Specifically, Exportin-1 (XPO1) has been found overexpressed in many tumors and has become an attractive target in molecular oncology and therapeutics development. The selective inhibitor of nuclear export, Selinexor, is one of the most scientifically interesting drugs that targets XPO1 in clinical development. In this review, we summarized the most relevant preclinical and clinical results achieved for non-solid tumors, sarcomas, and other kind of solid tumors.

Phosphorylation of PED/PEA-15 at Ser116 and phosphorylation of p27 at Thr187 indicates a poor prognosis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) constitutes a deadly cancer with a high rate of recurrence and metastasis. Phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes-15 (PED/PEA-15) is a protein involved in the metabolism of glucose that regulates numerous cellular processes, including cell division, apoptosis and migration in numerous types of cancer. However, PED/PEA-15 may act as a tumor-promotor or a tumor-suppressor depending on its phosphorylation status. In the present study, the association between the phosphorylation of PED/PEA-15 at Ser116 [PED/PEA-15(S116)], the phosphorylation of P27 at Thr187 [P-p27(T187)] and the clinicopathological features and prognosis of patients with HCC was assessed. The levels of PED/PEA-15(S116) and P-p27(T187) were determined using immunohistochemistry and western blotting analysis in resected liver tumor tissues and adjacent non-cancerous tissues obtained from 60 patients with HCC as well as normal liver tissues from 12 patients with benign lesions. The association between the expression levels of these two markers and the clinicopathological features of patients with HCC was explored. Using the Kaplan-Meier method, the prognostic value of PED/PEA-15(S116) and P-p27(T187) expression levels was determined. The results demonstrated that the levels of PED/PEA-15(S116) and P-p27(T187) proteins were remarkably higher in the HCC group compared with those in the adjacent and normal tissue groups (both P<0.05). In addition, a moderate positive correlation was observed between the levels of PED/PEA-15(S116) and P-p27(T187) (r=0.434; P<0.05). The levels of these two proteins were associated with the Edmondson grade, Tumor-Node-Metastasis (TNM) stage, vascular invasion and tumor multiplicity (all P<0.05). Furthermore, the Kaplan-Meier analysis results demonstrated that patients with HCC that presented with positive expression of PED/PEA-15(S116) and P-p27(T187) exhibited a dismal prognosis compared with that in patients with negative expression regarding the overall survival (OS), as well as disease-free survival (both P<0.05). Multivariate Cox analysis revealed that the TNM stage (P<0.05), vascular invasion (P<0.05), PED/PEA-15(S116) levels (P<0.001) and P-p27(T187) levels (P<0.05) were independent prognostic factors for OS in patients with HCC. In conclusion the results of the present study demonstrated that PED/PEA-15(S116) and P-p27(T187) levels were upregulated in HCC tissues compared with those in the adjacent and normal tissues; PED/PEA-15(S116) and P-p27(T187) expression may serve as an indicator of a poor prognosis in patients with HCC, suggesting that these proteins may be prospective therapeutic targets for HCC.

Exportin-T: A Novel Prognostic Predictor and Potential Therapeutic Target for Neuroblastoma

Exportins as the key mediators of nucleocytoplasmic transport have been identified as the controllers of the passage of numerous types of crucial cancer-related proteins. Targeting exportins in cancer cells might represent an emerging strategy in cancer intervention with the potential to affect clinical outcomes. Here, we focused on the prognostic and therapeutic values of Exportin-T (XPOT) in neuroblastoma. The correlation between the expression and prognostic values of XPOT in patients with neuroblastoma was investigated based on both published transcriptome data and our clinical data. Then, decision curve analysis (DCA) was implemented to identify a XPOT risk prediction model. In addition, RNA inference was performed to silence the expression of XPOT to further investigate the specific roles of XPOT in the progression of neuroblastoma in vitro. Overexpression of XPOT mRNA was associated with poor clinical characteristics, such as age at diagnosis more than 18 months, amplification of MYCN, and advanced International Neuroblastoma Staging System (INSS) stage, and XPOT expression was identified as an independent poor prognosis factor for neuroblastoma using Cox proportional hazards model (P < .001). DCA suggested that neuroblastoma patients could benefit from XPOT risk prediction model-guided interventions (status of MYCN  +  INSS stage  +  XPOT). Experimentally, knockdown of XPOT by small interfering RNA inhibited the proliferation and migration in neuroblastoma cells. XPOT is identified as a novel prognostic predictor and potential therapeutic target for neuroblastoma patients. Further investigation should focus on the profound molecular mechanism underlying the tumor inhibition activity of XPOT inhibitors.

XPO1-dependent nuclear export as a target for cancer therapy

Cellular homeostasis requires the proper nuclear-cytoplasmic partitioning of large molecules, which is often deregulated in cancer. XPO1 is an export receptor responsible for the nuclear-cytoplasmic transport of hundreds of proteins and multiple RNA species. XPO1 is frequently overexpressed and/or mutated in human cancers and functions as an oncogenic driver. Suppression of XPO1-mediated nuclear export, therefore, presents a unique therapeutic strategy. In this review, we summarize the physiological functions of XPO1 as well as the development of various XPO1 inhibitors and provide an update on the recent clinical trials of the SINE compounds. We also discuss potential future research directions on the molecular function of XPO1 and the clinical application of XPO1 inhibitors.

Silencing KPNA2 inhibits IL-6-induced breast cancer exacerbation by blocking NF-κB signaling and c-Myc nuclear translocation in vitro

AIMS

Recently, studies indicated that inflammation could exacerbate the development of BC. Karyopherin α-2 (KPNA2) is a molecule which modulates nucleocytoplasmic transport and is involved in malignant cellular behavior and carcinogenesis. Our study aims to elucidate the role of KPNA2 in BC pathogenesis and explore the mechanism of KPNA2 in regulating inflammation-induced BC exacerbations.

MAIN METHODS

We measured the expression of KPNA2 in BC cells. Through loss-of-function experiments, the functional role of KPNA2 in MCF-7 and MDA-MB-468 cells was evaluated. SK-BR-3 cells were treated with IL-6 as an inflammatory in vitro model of BC. ELISA determination exhibited the contents of cytokines. RANKL and leptomycin B treatments activated NF-κB signaling and inhibited the nuclear translocation of c-Myc, respectively.

KEY FINDINGS

The results showed that KPNA2 was significantly up-regulated in BC and silencing KPNA2 inhibited the proliferation, migration and invasion of BC cells, while the cycle arrest was induced, via blocking NF-κB signaling and c-Myc nuclear translocation. IL-6 stimulated the secretions of IL-8 and IL-17 in BC cells, and elevated KPNA2 expression. However, KPNA2 knockdown suppressed the inflammatory responses and malignant progression of BC induced by IL-6.

SIGNIFICANCE

In conclusion, our study illustrated that KPNA2 regulated BC development, as well as IL-6-induced inflammation and exacerbation, via NF-κB signaling and c-Myc nuclear translocation. This may provide a novel target for BC therapy.

PSPC1-interchanged interactions with PTK6 and β-catenin synergize oncogenic subcellular translocations and tumor progression

Hepatocellular carcinoma (HCC) is one of the most lethal cancers worldwide due to metastasis. Paraspeckle component 1 (PSPC1) upregulation has been identified as an HCC pro-metastatic activator associated with poor patient prognosis, but with a lack of targeting strategy. Here, we report that PSPC1, a nuclear substrate of PTK6, sequesters PTK6 in the nucleus and loses its metastasis driving capability. Conversely, PSPC1 upregulation or PSPC1-Y523F mutation promotes epithelial-mesenchymal transition, stemness, and metastasis via cytoplasmic translocation of active PTK6 and nuclear translocation of β-catenin, which interacts with PSPC1 to augment Wnt3a autocrine signaling. The aberrant nucleocytoplasmic shuttling of active PTK6/β-catenin is reversed by expressing the PSPC1 C-terminal interacting domain (PSPC1-CT131), thereby suppressing PSPC1/PTK6/β-catenin-activated metastasis to prolong the survival of HCC orthotopic mice. Thus, PSPC1 is the contextual determinant of the oncogenic switch of PTK6/β-catenin subcellular localizations, and PSPC1-CT131 functions as a dual inhibitor of PSPC1 and PTK6 with potential for improving cancer therapy.

PSPC1 has a critical role in promoting EMT and metastasis. Here, the authors demonstrate that PSPC1 is the contextual determinant of the oncogenic switch of PTK6/β-catenin subcellular localizations to drive metastasis of hepatocellular carcinoma cells via a PSPC1/PTK6/β-catenin signaling.

Targeting Nuclear Exporter Protein XPO1/CRM1 in Gastric Cancer

Gastric cancer remains an unmet clinical problem in urgent need of newer and effective treatments. Here we show that the nuclear export protein, Exportin 1 (XPO1, chromosome region maintenance 1 or CRM1), is a promising molecular target in gastric cancer. We demonstrate significant overexpression of XPO1 in a cohort of histologically diverse gastric cancer patients with primary and metastatic disease. XPO1 RNA interference suppressed gastric cancer cell growth. Anti-tumor activity was observed with specific inhibitor of nuclear export (SINE) compounds (selinexor/XPOVIO), second-generation compound KPT-8602/eltanexor, KPT-185 and +ve control Leptomycin B in three distinct gastric cancer cell lines. SINE compounds inhibited gastric cancer cell proliferation, disrupted spheroid formation, induced apoptosis and halted cell cycle progression at the G1/S phase. Anti-tumor activity was concurrent with nuclear retention of tumor suppressor proteins and inhibition of colony formation. In combination studies, SINE compounds enhanced the efficacy of nab-paclitaxel in vitro and in vivo. More significantly, using non-coding RNA sequencing studies, we demonstrate for the first time that SINE compounds can alter the expression of non-coding RNAs (microRNAs and piwiRNAs). SINE treatment caused statistically significant downregulation of oncogenic miR-33b-3p in two distinct cell lines. These studies demonstrate the therapeutic significance of XPO1 in gastric cancer that warrants further clinical investigation.

CRISPR-Cas9 Screening of Kaposi's Sarcoma-Associated Herpesvirus-Transformed Cells Identifies XPO1 as a Vulnerable Target of Cancer Cells

The abnormal proliferation of cancer cells is driven by deregulated oncogenes or tumor suppressors, among which the cancer-vulnerable genes are attractive therapeutic targets. Targeting mislocalization of oncogenes and tumor suppressors resulting from aberrant nuclear export is effective for inhibiting growth transformation of cancer cells. We performed a clustered regularly interspaced short palindromic repeat (CRISPR)-associated (Cas) screening in a unique model of matched primary and oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV)-transformed cells and identified genes that were growth promoting and growth suppressive for both types of cells, among which exportin XPO1 was demonstrated to be critical for the survival of transformed cells. Using XPO1 inhibitor KPT-8602 and by small interfering RNA (siRNA) knockdown, we confirmed the essential role of XPO1 in cell proliferation and growth transformation of KSHV-transformed cells and in cell lines of other cancers, including gastric cancer and liver cancer. XPO1 inhibition induced cell cycle arrest through p53 activation, but the mechanisms of p53 activation differed among the different types of cancer cells. p53 activation depended on the formation of promyelocytic leukemia (PML) nuclear bodies in gastric cancer and liver cancer cells. Mechanistically, XPO1 inhibition induced relocalization of autophagy adaptor protein p62 (SQSTM1), recruiting p53 for activation in PML nuclear bodies. Taken the data together, we have identified novel growth-promoting and growth-suppressive genes of primary and cancer cells and have demonstrated that XPO1 is a vulnerable target of cancer cells. XPO1 inhibition induces cell arrest through a novel PML- and p62-dependent mechanism of p53 activation in some types of cancer cells.IMPORTANCE Using a model of oncogenic virus KSHV-driven cellular transformation of primary cells, we have performed a genome-wide CRISPR-Cas9 screening to identify vulnerable genes of cancer cells. This screening is unique in that this virus-induced oncogenesis model does not depend on any cellular genetic alterations and has matched primary and KSHV-transformed cells, which are not available for similar screenings in other types of cancer. We have identified genes that are both growth promoting and growth suppressive in primary and transformed cells, some of which could represent novel proto-oncogenes and tumor suppressors. In particular, we have demonstrated that the exportin XPO1 is a critical factor for the survival of transformed cells. Using a XPO1 inhibitor (KPT-8602) and siRNA-mediated knockdown, we have confirmed the essential role of XPO1 in cell proliferation and in growth transformation of KSHV-transformed cells, as well as of gastric and liver cancer cells. XPO1 inhibition induces cell cycle arrest by activating p53, but the mechanisms of p53 activation differed among different types of cancer cells. p53 activation is dependent on the formation of PML nuclear bodies in gastric and liver cancer cells. Mechanistically, XPO1 inhibition induces relocalization of autophagy adaptor protein p62 (SQSTM1), recruiting p53 for activation in PML nuclear bodies. These results illustrate that XPO1 is a vulnerable target of cancer cells and reveal a novel mechanism for blocking cancer cell proliferation by XPO1 inhibition as well as a novel PML- and p62-mediated mechanism of p53 activation in some types of cancer cells.

The past, present, and future of CRM1/XPO1 inhibitors

Therapies targeted at inhibiting nucleo-cytoplasmic transport have found broad applications in the field of oncology. Chromosome region maintenance 1 (CRM1), better known as exportin 1 (XPO1), is the protein transporter responsible for the nucleo-cytoplasmic shuttling of most of the tumor suppressor proteins (TSP) and growth regulatory factors. XPO1 is also upregulated in many malignancies and associated with a poor prognosis. Its inhibition has been a target of therapy, and hence, the selective inhibitors of nuclear transport (SINE) compounds were developed as a novel class of anti-cancer agents. The most well-known SINE agent is selinexor (KPT-330) and has been widely tested in phase I and II clinical trials in both solid tumors and hematologic malignancies. This review discusses how dysregulation of XPO1 promotes tumorigenesis, the historical considerations in the development of SINE compounds, and their role in current clinical therapies.

Nuclear Export Inhibition for Pancreatic Cancer Therapy

Pancreatic cancer is a deadly disease that is resistant to most available therapeutics. Pancreatic cancer to date has no effective drugs that could enhance the survival of patients once their disease has metastasized. There is a need for the identification of novel actionable drug targets in this unusually recalcitrant cancer. Nuclear protein transport is an important mechanism that regulates the function of several tumor suppressor proteins (TSPs) in a compartmentalization-dependent manner. High expression of the nuclear exporter chromosome maintenance region 1 (CRM1) or exportin 1 (XPO1), a common feature of several cancers including pancreatic cancer, results in excessive export of critical TSPs to the incorrect cellular compartment, leading to their functional inactivation. Small molecule inhibitors of XPO1 can block this export, retaining very important and functional TSPs in the nucleus and leading to the effective killing of the cancer cells. This review highlights the current knowledge on the role of XPO1 in pancreatic cancer and how this serves as a unique and clinically viable target in this devastating and by far incurable cancer.