Clinical and molecular characteristics of XPO1 mutations in patients with chronic lymphocytic leukemia

In-depth molecular analysis of lymphomas with lymphoplasmacytic differentiation may provide more precise diagnosis and rational treatment allocation

We performed a molecular analysis of formalin-fixed paraffin embedded and decalcified bone marrow trephine biopsies of 41 patients with a B-cell disorder with lymphoplasmacytic differentiation to enable a more precise diagnosis and to describe potentially prognostic and therapeutic relevant mutations. Analysis was performed with a commercially available next-generation sequencing (NGS) lymphoma panel (Lymphoma Solution, SophiaGenetics). Results were correlated with clinical and pathological parameters. Our group covered a spectrum of B-cell disorders with plasmacytic differentiation ranging from Waldenstroem's macroglobulinemia (WM), to small-B-cell lymphomas with plasmacytic differentiation (SBCL-PC) to IgM myeloma (MM). The most helpful diagnostic criteria included morphology and immuno-phenotype as a prerequisite for the interpretation of molecular analysis. MYD88 mutation was present in nearly all WM, but also in 50% of SBCL-PCs, while MM were consistently negative. Driver mutations, such as TP53, were already detectable early in the course of the respective diseases indicating a higher risk of progression, transformation, and reduced progression-free survival. In addition, we report on a novel BIRC3 frameshift mutation in one case of a progressive WM. Our data indicate that patients with LPL/WM might benefit from thorough pathological work-up and detailed molecular analysis in terms of precise diagnosis and targeted treatment allocation.

Prognostic value and therapeutic targeting of XPO1 in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a subtype of B-cell malignancy with high heterogeneity. XPO1 is highly expressed in many hematological malignancies, which predicts poor prognosis. In the study, we aimed to explore the prognostic role of XPO1 and the therapeutic effect of Selinexor, a selective inhibitor of nuclear export, which targets XPO1. We collected 200 CLL samples in our center to confirm XPO1 mRNA expression and analyzed the correlation between XPO1 expression and prognosis. Then, we decreased XPO1 expression with Selinexor to explore the effect of proliferation inhibition, cell cycle arrest, and apoptosis in CLL cell lines. RNA-Seq was performed to explore potential mechanisms. We analyzed XPO1 expression in a cohort of 150 treatment naive patients and another cohort of 50 relapsed and refractory (R/R) patients and found that XPO1 expression was upregulated in 76% of CLL patients compared with healthy donors. Survival analysis suggested that patients with increased XPO1 expression had inferior treatment-free survival (P = 0.022) and overall survival (P = 0.032). The inhibitor of XPO1, Selinexor, induced apoptosis in primary CLL cells. We showed the effects of Selinexor on proliferation inhibition, cell cycle arrest, and apoptosis in CLL cell lines with JVM3, MEC1, and ibrutinib-resistant (MR) cells via nuclear retention of cargo proteins of IκBα, p65, p50, and FOXO3a. Moreover, downregulation of the NF-κB and FOXO pathways was a common feature of the three CLL cell lines responding to Selinexor, indicating the potential application of XPO1 inhibitor even in the high-risk CLL cells. We identified XPO1 as an unfavorable prognostic factor for CLL patients and provided a rationale for further investigation of the clinically XPO1 targeted therapeutic strategy against CLL.

Predicted Proteome Association Studies of Breast, Prostate, Ovarian, and Endometrial Cancers Implicate Plasma Protein Regulation in Cancer Susceptibility

BACKGROUND

Predicting protein levels from genotypes for proteome-wide association studies (PWAS) may provide insight into the mechanisms underlying cancer susceptibility.

METHODS

We performed PWAS of breast, endometrial, ovarian, and prostate cancers and their subtypes in several large European-ancestry discovery consortia (effective sample size: 237,483 cases/317,006 controls) and tested the results for replication in an independent European-ancestry GWAS (31,969 cases/410,350 controls). We performed PWAS using the cancer GWAS summary statistics and two sets of plasma protein prediction models, followed by colocalization analysis.

RESULTS

Using Atherosclerosis Risk in Communities (ARIC) models, we identified 93 protein-cancer associations [false discovery rate (FDR) < 0.05]. We then performed a meta-analysis of the discovery and replication PWAS, resulting in 61 significant protein-cancer associations (FDR < 0.05). Ten of 15 protein-cancer pairs that could be tested using Trans-Omics for Precision Medicine (TOPMed) protein prediction models replicated with the same directions of effect in both cancer GWAS (P < 0.05). To further support our results, we applied Bayesian colocalization analysis and found colocalized SNPs for SERPINA3 protein levels and prostate cancer (posterior probability, PP = 0.65) and SNUPN protein levels and breast cancer (PP = 0.62).

CONCLUSIONS

We used PWAS to identify potential biomarkers of hormone-related cancer risk. SNPs in SERPINA3 and SNUPN did not reach genome-wide significance for cancer in the original GWAS, highlighting the power of PWAS for novel locus discovery, with the added advantage of providing directions of protein effect.

IMPACT

PWAS and colocalization are promising methods to identify potential molecular mechanisms underlying complex traits.

Construction of a Diagnostic m7G Regulator-Mediated Scoring Model for Identifying the Characteristics and Immune Landscapes of Osteoarthritis

With the increasingly serious burden of osteoarthritis (OA) on modern society, it is urgent to propose novel diagnostic biomarkers and differentiation models for OA. 7-methylguanosine (m7G), as one of the most common base modification forms in post transcriptional regulation, through which the seventh position N of guanine (G) of messenger RNA is modified by methyl under the action of methyltransferase; it has been found that it plays a crucial role in different diseases. Therefore, we explored the relationship between OA and m7G. Based on the expression level of 18 m7G-related regulators, we identified nine significant regulators. Then, via a series of methods of machine learning, such as support vector machine recursive feature elimination, random forest and lasso-cox regression analysis, a total of four significant regulators were further identified (DCP2, EIF4E2, LARP1 and SNUPN). Additionally, according to the expression level of the above four regulators, two different m7G-related clusters were divided via consensus cluster analysis. Furthermore, via immune infiltration, differential expression analysis and enrichment analysis, we explored the characteristic of the above two different clusters. An m7G-related scoring model was constructed via the PCA algorithm. Meanwhile, there was a different immune status and correlation for immune checkpoint inhibitors between the above two clusters. The expression difference of the above four regulators was verified via real-time quantitative polymerase chain reaction. Overall, a total of four biomarkers were identified and two different m7G-related subsets of OA with different immune microenvironment were obtained. Meanwhile, the construction of m7G-related Scoring model may provide some new strategies and insights for the therapy and diagnosis of OA patients.

Prognostic and therapeutic significance of XPO1 in T-cell lymphoma

T-cell lymphoma (TCL) is a highly heterogeneous group of invasive non-Hodgkin lymphoma with adverse prognosis and limited treatment options. The relationship between TCL and Exportin-1 (XPO1), a major nuclear export receptor, has not been established yet. We here investigated the prognostic role and therapeutic implication of XPO1 in TCL. We analyzed XPO1 expression in a cohort of 69 TCL tumors and found that XPO1 was over-expressed in 76.8% of TCL and correlated with decreased progression-free survival (PFS) and overall survival (OS). In vitro treatment of TCL cell lines with KPT-8602, the second-generation selective inhibitor of nuclear export (SINE), inhibited XPO1 expression and showed significant anti-proliferative, cell-cycle arrest and pro-apoptotic efficacy. In mechanism, KPT-8602 restored the localization of cytoplasmic FOXO3A, p27, p21, IκBα and PP2A into the nucleus, leading to AKT and NF-κB deactivation. Our data demonstrate for the first time that XPO1 could be an unfavorable prognostic factor for TCL, and provide a rationale for further investigation of the efficacy of KPT-8602 in TCL 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.

Up to 6.5 years (median 4 years) of follow-up of first-line ibrutinib in patients with chronic lymphocytic leukemia/small lymphocytic lymphoma and high-risk genomic features: integrated analysis of two phase 3 studies

Genomic abnormalities, including del(17p)/TP53 mutation, del(11q), unmutated IGHV, and mutations in BIRC3, NOTCH1, SF3B1, and XPO1 predict poor outcomes with chemoimmunotherapy in chronic lymphocytic leukemia. To better understand the impact of these high-risk genomic features on outcomes with first-line ibrutinib-based therapy, we performed pooled analysis of two phase 3 studies with 498 patients randomized to receive ibrutinib- or chlorambucil-based therapy with median follow-up of 49.1 months. Ibrutinib-based therapy improved overall response rates (ORRs), complete response rates, and progression-free survival (PFS) versus chlorambucil-based therapy across all subgroups. In ibrutinib-randomized patients with versus without specified genomic features, ORR and PFS were comparable across subgroups. PFS hazard ratio (95% CI) for del(17p)/TP53 mutated/BIRC3 mutated: 1.05 (0.54-2.04); del(17p)/TP53 mutation, del(11q), and/or unmutated IGHV: 1.11 (0.69-1.77); unmutated IGHV: 1.79 (0.99-3.24); and NOTCH1 mutated 1.05 (0.65-1.69). This integrated analysis demonstrated efficacy of first-line ibrutinib-based treatment irrespective of cytogenetic and mutational risk features.Registered at ClinicalTrials.gov (NCT01722487 and NCT02264574).

Targeting XPO1-Dependent Nuclear Export in Cancer

Nucleocytoplasmic transport of macromolecules is tightly regulated in eukaryotic cells. XPO1 is a transport factor responsible for the nuclear export of several hundred protein and RNA substrates. Elevated levels of XPO1 and recurrent mutations have been reported in multiple cancers and linked to advanced disease stage and poor survival. In recent years, several novel small-molecule inhibitors of XPO1 were developed and extensively tested in preclinical cancer models and eventually in clinical trials. In this brief review, we summarize the functions of XPO1, its role in cancer, and the latest results of clinical trials of XPO1 inhibitors.

Therapeutic Targeting of Exportin-1 in Childhood Cancer

Overexpression of Exportin-1 (XPO1), a key regulator of nuclear-to-cytoplasmic transport, is associated with inferior patient outcomes across a range of adult malignancies. Targeting XPO1 with selinexor has demonstrated promising results in clinical trials, leading to FDA approval of its use for multiple relapsed/refractory cancers. However, XPO1 biology and selinexor sensitivity in childhood cancer is only recently being explored. In this review, we will focus on the differential biology of childhood and adult cancers as it relates to XPO1 and key cargo proteins. We will further explore the current state of pre-clinical and clinical development of XPO1 inhibitors in childhood cancers. Finally, we will outline potentially promising future therapeutic strategies for, as well as potential challenges to, integrating XPO1 inhibition to improve outcomes for children with cancer.

The nuclear export protein XPO1 - from biology to targeted therapy

Exportin 1 (XPO1), also known as chromosome region maintenance protein 1, plays a crucial role in maintaining cellular homeostasis via the regulated export of a range of cargoes, including proteins and several classes of RNAs, from the nucleus to the cytoplasm. Dysregulation of this protein plays a pivotal role in the development of various solid and haematological malignancies. Furthermore, XPO1 is associated with resistance to several standard-of-care therapies, including chemotherapies and targeted therapies, making it an attractive target of novel cancer therapies. Over the years, a number of selective inhibitors of nuclear export have been developed. However, only selinexor has been clinically validated. The novel mechanism of action of XPO1 inhibitors implies a different toxicity profile to that of other agents and has proved challenging in certain settings. Nonetheless, data from clinical trials have led to the approval of the XPO1 inhibitor selinexor (plus dexamethasone) as a fifth-line therapy for patients with multiple myeloma and as a monotherapy for patients with relapsed and/or refractory diffuse large B cell lymphoma. In this Review, we summarize the progress and challenges in the development of nuclear export inhibitors and discuss the potential of emerging combination therapies and biomarkers of response.

Selinexor, selective inhibitor of nuclear export: Unselective bullet for blood cancers

Exportin 1 (XPO1), also known as chromosome maintenance 1 protein (CRM1), is the main transporter for hundreds of proteins like tumor suppressors, growth regulatory factors, oncoprotein mRNAs and others. Its upregulation leads to the inactivation of the tumor suppressor anti-neoplastic function in many cancers and logically is associated with poor prognosis. Selective inhibitors of nuclear export (SINE) are a new generation of XPO1 inhibitors that are being investigated as a promising targeted anti-cancer therapy. Selinexor is the first generation of SINE compounds that is being evaluated in many clinical trials involving solid tumors and hematological malignancies with its two approved indications for relapsed multiple myeloma and relapsed diffuse large B-cell lymphoma. Here, we comprehensively review the current knowledge of selinexor and next generations of the SINE compounds in lymphoid and myeloid malignancies.

Recurrent XPO1 mutations alter pathogenesis of chronic lymphocytic leukemia

BACKGROUND

Exportin 1 (XPO1/CRM1) is a key mediator of nuclear export with relevance to multiple cancers, including chronic lymphocytic leukemia (CLL). Whole exome sequencing has identified hot-spot somatic XPO1 point mutations which we found to disrupt highly conserved biophysical interactions in the NES-binding groove, conferring novel cargo-binding abilities and forcing cellular mis-localization of critical regulators. However, the pathogenic role played by change-in-function XPO1 mutations in CLL is not fully understood.

METHODS

We performed a large, multi-center retrospective analysis of CLL cases (N = 1286) to correlate nonsynonymous mutations in XPO1 (predominantly E571K or E571G; n = 72) with genetic and epigenetic features contributing to the overall outcomes in these patients. We then established a mouse model with over-expression of wildtype (wt) or mutant (E571K or E571G) XPO1 restricted to the B cell compartment (Eµ-XPO1). Eµ-XPO1 mice were then crossed with the Eµ-TCL1 CLL mouse model. Lastly, we determined crystal structures of XPO1 (wt or E571K) bound to several selective inhibitors of nuclear export (SINE) molecules (KPT-185, KPT-330/Selinexor, and KPT-8602/Eltanexor).

RESULTS

We report that nonsynonymous mutations in XPO1 associate with high risk genetic and epigenetic features and accelerated CLL progression. Using the newly-generated Eµ-XPO1 mouse model, we found that constitutive B-cell over-expression of wt or mutant XPO1 could affect development of a CLL-like disease in aged mice. Furthermore, concurrent B-cell expression of XPO1 with E571K or E571G mutations and TCL1 accelerated the rate of leukemogenesis relative to that of Eµ-TCL1 mice. Lastly, crystal structures of E571 or E571K-XPO1 bound to SINEs, including Selinexor, are highly similar, suggesting that the activity of this class of compounds will not be affected by XPO1 mutations at E571 in patients with CLL.

CONCLUSIONS

These findings indicate that mutations in XPO1 at E571 can drive leukemogenesis by priming the pre-neoplastic lymphocytes for acquisition of additional genetic and epigenetic abnormalities that collectively result in neoplastic transformation.

Circ-XPO1 upregulates XPO1 expression by sponging multiple miRNAs to facilitate osteosarcoma cell progression

Circular RNAs (circRNAs) act as a key role in mediating carcinogenesis. Nevertheless, the functions and mechanisms of circRNAs in osteosarcoma (OS) are still not fully understood. In the present study, we aim to investigate the functions of circ-XPO1 in OS and its potential mechanism underlying OS progression. CircRNA microarray indicated elevation of circ-XPO1 in OS specimens relative to normal samples. Elevation of circ-XPO1 and XPO1 mRNA was identified in OS tissue specimens and cells by qRT-PCR. In addition, enhanced expression of circ-XPO1 and XPO1 mRNA both correlated with poor prognosis for the patients with OS, as estimated by Kaplan-Meier analysis. Functionally, circ-XPO1 and XPO1 both facilitated the growth and invasion and decreased the apoptosis of OS cells. Moreover, we constructed the circ-XPO1-miRNAs-XPO1 3'-UTR interaction network and verified that circ-XPO1 could sponge miR-23a-3p, miR-23b-3p, miR-23c, and miR-130a-5p to regulate XPO1 expression. Furthermore, rescue assay indicated that the effect of circ-XPO1 on cell progression was partly relying on these miRNAs. Taken together, we found that circ-XPO1 regulated the expression of XPO1 through sponging miRNAs as a competing endogenous (ceRNA), providing the possibility that circ-XPO1 might play as a new therapeutic target for OS.

XPO1 is a critical player for bortezomib resistance in multiple myeloma: A quantitative proteomic approach

Among the blood cancers, 13% mortality is caused by Multiple myeloma (MM) type of hematological malignancy. In spite of therapeutic advances in chemotherapy treatment, still MM remains an incurable disease is mainly due to emergence of chemoresistance. At present time, FDA approved bortezomib is the first line drug for MM treatment. However, like other chemotherapy, MM patients are acquiring resistance against bortezomib. The present study aims to identify and validate bortezomib resistant protein targets in MM using iTRAQ and label free quantitative proteomic approaches. 112 differentially expressed proteins were commonly found in both approaches with similar differential expression pattern. Exportin-1 (XPO1) protein was selected for further validation as its significant high expression was observed in both iTRAQ and label free analysis. Bioinformatic analysis of these common differentially expressed proteins showed a clear cluster of proteins such as SMC1A, RCC2, CSE1, NUP88, NUP50, TPR, HSPA14, DYNLL1, RAD21 and RANBP2 being associated with XPO1. Functional studies like cell count assay, flow cytometry assay and soft agar assay proved that XPO1 knock down in RPMI 8226R cell line results in re-sensitization to bortezomib drug. The mass spectrometry data are available via ProteomeXchange with identifier PXD013859. BIOLOGICAL SIGNIFICANCE: Multiple myeloma (MM) is a type of hematological malignancy which constitutes about 13% of all blood cell related malignancies. Chemoresistance is one of the major obstacles for the successful treatment for MM. Bortezomib is a first proteasome inhibitor drug, widely used in MM treatment. The present study aims to identify and validate bortezomib resistant protein targets in MM. Here, we identified 112 candidate proteins to be associated with bortezomib resistance using global quantitative proteomic analysis. Among these candidate proteins, we show that XPO1 plays crucial role in emerging bortezomib resistance using functional studies like cell count assay, flow cytometry assay and soft agar assay. XPO1 could be a potential therapeutic target for MM and development of inhibitors of XPO1 might help to cure MM.

XPO1 Expression Is a Poor-Prognosis Marker in Pancreatic Adenocarcinoma

Pancreatic adenocarcinoma (PAC) is one of the most aggressive human cancers and new systemic therapies are urgently needed. Exportin-1 (XPO1), which is a member of the importin-β superfamily of karyopherins, is the major exporter of many tumor suppressor proteins that are involved in the progression of PAC. Promising pre-clinical data using XPO1 inhibitors have been reported in PAC, but very few data are available regarding XPO1 expression in clinical samples. Retrospectively, we analyzed XPO1 mRNA expression in 741 pancreatic samples, including 95 normal, 73 metastatic and 573 primary cancers samples, and searched for correlations with clinicopathological and molecular data, including overall survival. XPO1 expression was heterogeneous across the samples, higher in metastatic samples than in the primary tumors, and higher in primaries than in the normal samples. "XPO1-high" tumors were associated with positive pathological lymph node status and aggressive molecular subtypes. They were also associated with shorter overall survival in both uni- and multivariate analyses. Supervised analysis between the "XPO1-high" and "XPO1-low" tumors identified a robust 268-gene signature, whereby ontology analysis suggested increased XPO1 activity in the "XPO1-high" tumors. XPO1 expression refines the prognostication in PAC and higher expression exists in secondary versus primary tumors, which supports the development of XPO1 inhibitors in this so-lethal disease.

NOTCH1 Aberrations in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is an incurable B-cell neoplasm characterized by highly variable clinical outcomes. In recent years, genomic and molecular studies revealed a remarkable heterogeneity in CLL, which mirrored the clinical diversity of this disease. These studies profoundly enhanced our understanding of leukemia cell biology and led to the identification of new biomarkers with potential prognostic and therapeutic significance. Accumulating evidence indicates a key role of deregulated NOTCH1 signaling and NOTCH1 mutations in CLL. This review highlights recent discoveries that improve our understanding of the pathophysiological NOTCH1 signaling in CLL and the clinical impact of NOTCH1 mutations in retrospective and prospective trials. In addition, we discuss the rationale for a therapeutic strategy aiming at inhibiting NOTCH1 signaling in CLL, along with an overview on the currently available NOTCH1-directed approaches.

KPT-330 inhibition of chromosome region maintenance 1 is cytotoxic and sensitizes chronic myeloid leukemia to Imatinib

As tyrosine kinase inhibitors (e.g., Imatinib, IM) fail to induce long-term response in some chronic myeloid leukemia (CML), novel therapies targeting leukemia-dysregulated pathways are necessary. Nuclear-cytoplasmic trafficking of proteins play a key role in the development of leukemia and drug resistance. KPT-330 (Selinexor), an inhibitor of chromosome region maintenance 1 (CRM1, nuclear receptor exportin 1, XPO1), demonstrated activities against a few hematological malignancies. We examined the anti-leukemic efficacy of KPT-330 in IM-resistant CML. Cell viability was examined by MTS assay. Apoptosis and cell cycle were assessed by flow cytometry. CRM1 mRNA was detected by PCR. Expression of CRM1 protein and its cargo proteins were determined by western blot or immunofluorescent staining. Furthermore, we engrafted nude mice subcutaneously with IM-resistant CML K562G. Mice were treated with IM, KPT-330 alone or in combination. Expression of CRM1 in CML were markedly higher than control. KPT-330 inhibited proliferation, induced cell cycle arrest and apoptosis of K562 and K562G. IC50 of IM on K562G was reduced by KPT-330. Mechanistically, KPT-330 inhibited CRM1 and increased the nuclear/cytoplasm ratio of BCR-ABL and P27. p-AKT was downregulated while p-STAT1 and caspase-3 were upregulated. Furthermore, KPT-330 showed anti-leukemic effect in primary IM-resistant CML with T315I mutation in CRM1-dependent manner. In K562G xenograft mice model, KPT-330 inhibited tumor growth and sensitized K562G to IM in vivo. To conclude, KPT-330 showed anti-leukemic activity and sensitized CML to IM in CRM1-dependent manner in vitro and in vivo. KPT-330 represents an alternative therapy for IM-refractory CML, warranting further investigation of CRM1 as therapeutic target.

XPO1 in B cell hematological malignancies: from recurrent somatic mutations to targeted therapy

Many recent publications highlight the large role of the pivotal eukaryotic nuclear export protein exportin-1 (XPO1) in the oncogenesis of several malignancies, and there is emerging evidence that XPO1 inhibition is a key target against cancer. The clinical validation of the pharmacological inhibition of XPO1 was recently achieved with the development of the selective inhibitor of nuclear export compounds, displaying an interesting anti-tumor activity in patients with massive pre-treated hematological malignancies. Recent reports have shown molecular alterations in the gene encoding XPO1 and showed a mutation hotspot (E571K) in the following two hematological malignancies with similar phenotypes and natural histories: primary mediastinal diffuse large B cell lymphoma and classical Hodgkin's lymphoma. Emerging evidence suggests that the mutant XPO1 E571K plays a role in carcinogenesis, and this variant is quantifiable in tumor and plasma cell-free DNA of patients using highly sensitive molecular biology techniques, such as digital PCR and next-generation sequencing. Therefore, it was proposed that the XPO1 E571K variant may serve as a minimal residual disease tool in this setting. To clarify and summarize the recent findings on the role of XPO1 in B cell hematological malignancies, we conducted a literature search to present the major publications establishing the landscape of XPO1 molecular alterations, their impact on the XPO1 protein, their interest as biomarkers, and investigations into the development of new XPO1-targeted therapies in B cell hematological malignancies.

Heterozygous mutation of cysteine528 in XPO1 is sufficient for resistance to selective inhibitors of nuclear export

Exportin-1 (CRM1/XPO1) is a crucial nuclear export protein that transports a wide variety of proteins from the nucleus to the cytoplasm. These cargo proteins include tumor suppressors and growth-regulatory factors and as such XPO1 is considered a potential anti-cancer target. From this perspective, inhibition of the XPO1-mediated nuclear export by selective inhibitor of nuclear export (SINE) compounds has shown broad-spectrum anti-cancer activity. Furthermore, the clinical candidate SINE, selinexor, is currently in multiple phase I/II/IIb trials for treatment of cancer. Resistance against selinexor has not yet been observed in the clinic, but in vitro selection of resistance did not reveal any mutations in the target protein, XPO1. However, introduction of a homozygous mutation at the drug's target site, the cysteine 528 residue inside the XPO1 cargo-binding pocket, by genetic engineering, confers resistance to selinexor. Here we investigated whether this resistance to selinexor is recessive or dominant. For this purpose we have engineered multiple leukemia cell lines containing heterozygous or homozygous C528S substitutions using CRISPR/Cas9-mediated genome editing. Our findings show that heterozygous mutation confers similar resistance against selinexor as homozygous substitution, demonstrating that SINE resistance can be obtained by a single and dominant mutation of the cysteine528 residue in XPO1.