XPO1 Inhibitor Research Articles

Anti-tumor activity of selinexor in combination with antineoplastic agents in chronic lymphocytic leukemia

Despite recent relevant therapeutic progresses, chronic lymphocytic leukemia (CLL) remains an incurable disease. Selinexor, an oral inhibitor of the nuclear export protein XPO1, is active as single agent in different hematologic malignancies, including CLL. The purpose of this study was to evaluate the anti-tumor effects of selinexor, used in combination with chemotherapy drugs (i.e. fludarabine and bendamustine) or with the PI3Kδ inhibitor idelalisib in CLL. Our results showed a significant decrease in CLL cell viability after treatment with selinexor-containing drug combinations compared to each single compound, with demonstration of synergistic cytotoxic effects. Interestingly, this drug synergism was exerted also in the presence of the protective effect of stromal cells. From the molecular standpoint, the synergistic cytotoxic activity of selinexor plus idelalisib was associated with increased regulatory effects of this drug combination on the tumor suppressors FOXO3A and IkBα compared to each single compound. Finally, selinexor was also effective in potentiating the in vivo anti-tumor effects of the PI3Kδ inhibitor in mice treated with the drug combination compared to single agents. Our data provide preclinical evidence of the synergism and potential efficacy of a combination treatment targeting XPO1 and PI3Kδ in CLL.

2325P Selinexor (XPO1 inhibitor) in combination with tepotinib (MET inhibitor) potentially inhibits SHOC2 and KRAS G12C in KRAS G12C mutant non-small cell lung cancer

2325P Selinexor (XPO1 inhibitor) in combination with tepotinib (MET inhibitor) potentially inhibits SHOC2 and KRAS G12C in KRAS G12C mutant non-small cell lung cancer

Targeting XPO1 Combined with Radiotherapy to Enhance Systemic Anti-tumor Effects in Non-Small Cell Lung Cancer

The combination of radiation and radiosensitizing chemotherapeutic agents have shown promising anti-tumor effects in NSCLC. Acting as an oncogenic driver, XPO1 is frequently overexpressed and/or mutated in lung cancer. Thus, suppression of XPO1-mediated nuclear export presents a unique therapeutic strategy. We hypothesize that XPO1 inhibition combined with radiotherapy (XRT) may remodel the tumor immune microenvironment (TIME) and reduce radioresistance, thus enhance systemic anti-tumor effects. Herein, we optimized a small molecule inhibitor, WJ01024, which can bind to XPO1 and antagonize its activity to inhibit nuclear export. In the C57BL/6 mouse subcutaneous tumor model, we evaluated the ability of different treatment regimens containing oral WJ01014 single or combined with XRT (one fractions of 15 Gy) in tumor control and tumor recurrence inhibition. The effects of each treatment regimen on the alterations of immunophenotypes, including the quantification, activation, proliferative capacity, exhaustion marker expression, and memory status, were evaluated by flow cytometry. In our study, we found that the overexpression of XPO1 was associated with poor prognosis and survival in radioresistant patients with NSCLC. The combination therapy of WJ01024 and XRT resulted in an increase of apoptosis and a decrease of proliferation compared to monotherapy, which was closely correlated with tumor regression and improved survival in the C57BL/6 mouse subcutaneous tumor model. Notably, we found that WJ01024 were shown to enhance the therapeutic effect of XRT by remodeling TIME. Compared with XRT, the addition of WJ01024 increased the infiltration and proliferation of radiation-stimulated CD8+ T cells, which especially promoted the production of interferon-γ and granzyme B. Moreover, the combination therapy also reversed the immunosuppressive effect of radiation on the percentage of Tregs and exhausted T cells in mouse xenografts. Thus, the TIME was significantly improved in combination therapy. Strikingly, mechanistic studies suggested that the activation of cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) signaling pathway is required to reshape TIME and produce synergistic anti-tumor effect with the combination of WJ01024 and XRT. Our findings suggest that WJ01024 might be a potential synergistic treatment for radiotherapy to control the proliferation of NSCLC cells, promote tumor regression and prolong survival in mouse model of NSCLC by activating cGAS/STING signaling, and this in turn potentiate the immune microenvironment.

KPT330 promotes the sensitivity of glioblastoma to olaparib by retaining SQSTM1 in the nucleus and disrupting lysosomal function

ABSTRACT PARP (poly(ADP-ribose) polymerase) inhibitors have demonstrated promising clinical activity in multiple homologous recombination (HR) deficiency tumors. However, glioblastoma (GBM) patients have obtained little benefit from PARP inhibitors alone. PARP inhibition shows considerable promise when used together with other therapeutic agents. Thus, novel combination therapies may enhance PARP inhibitor efficacy and overcome resistance mechanisms in GBM. Herein, we report that concurrent treatment with the PARP inhibitor olaparib and XPO1 (exportin 1) inhibitor KPT330 showed synergetic anticancer effects on GBM cells. Mechanistically, in the nucleus, we show that KPT330 induced the nuclear retention of SQSTM1 (sequestosome 1) and further inhibited the ubiquitination of the DNA repair signal H2AX (H2A.X variant histone) mediated by olaparib, thus inhibiting DNA damage response and repair in GBM. Moreover, in the cytoplasm, KPT330 blocked the activation of autophagic flux caused by olaparib reagent, downregulated the expression of LAPTM4B (lysosomal protein transmembrane 4 beta) and induced the dysfunction of lysosomes, thereby preventing the degradation of autophagosome, and ultimately promoted cell death. Furthermore, in the LN229-luc mouse orthotopic xenograft model, combination treatment showed significantly increased antitumor efficacy compared to each monotherapy. These data illustrate the application prospects of combined oral administration of olaparib and KPT330 for the treatment of glioblastoma. Abbreviations AO: acridine orange; ATM: ATM serine/threonine kinase; CHEK1: checkpoint kinase 1; CHEK2: checkpoint kinase 2; CI: combination index; DMSO: dimethyl sulfoxide; DSBs: double-strand breaks; GBM: glioblastoma; HR: homologous recombination; H2AX: H2A.X variant histone; IHC: immunohistochemistry; LAPTM4B: lysosomal protein transmembrane 4 beta; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; PARP: poly(ADP-ribose) polymerase; RAD51: RAD51 recombinase; SQSTM1: sequestosome 1; SSBs: single-strand breaks; RNF168: ring finger protein 168; XPO1: exportin 1.

The development of selective XPO1 inhibitors in the treatment of acute myeloid leukemia

The development of selective XPO1 inhibitors in the treatment of acute myeloid leukemia

P-153 - Inhibition of XPO1 with Selinexor (KPT-330) triggers apoptosis in cutaneous T-cell lymphoma (CTCL) by activating the p53-p21 and p27 pathways

P-153 - Inhibition of XPO1 with Selinexor (KPT-330) triggers apoptosis in cutaneous T-cell lymphoma (CTCL) by activating the p53-p21 and p27 pathways

Cisplatin Dependent Secretion of Immunomodulatory High Mobility Group Box 1 (HMGB1) Protein from Lung Cancer Cells.

High mobility group box 1 (HMGB1) is secreted from activated immune cells, necrotic cells, and certain cancers. Previous studies have reported that different patterns of post-translational modification, particularly acetylation and oxidation, mediate HMGB1 release and confer distinct extracellular HMGB1 signaling activity. Here we report that cisplatin but not carboplatin induces secretion of HMGB1 from human A549 non-small cell lung cancer (NSCLC) cells. Cisplatin-mediated HMGB1 secretion was dose-dependent and was regulated by nuclear exportin 1 (XPO1) also known as chromosomal maintenance 1 (CRM1) rather than adenosine diphosphate (ADP)-ribosylation, acetylation, or oxidation. HMGB1, as well as lysine acetylation and cysteine disulfide oxidation of secreted HMGB1, were monitored by sensitive and specific assays using immunoprecipitation, stable isotope dilution, differential alkylation, and nano liquid chromatography parallel reaction monitoring/high-resolution mass spectrometry (nano-LC-PRM/HRMS). A major fraction of the HMGB1 secreted by low-dose cisplatin treatment of A549 NSCLC cells was found to be in the fully reduced form. In contrast, mainly oxidized forms of HMGB1 were secreted by dimethyl sulfoxide (DMSO)-mediated apoptosis. These findings suggest that inhibition of XPO1 could potentiate the anti-tumor activity of cisplatin by increasing the nuclear accumulation of HMGB1 protein, an inhibitor of cisplatin DNA-adduct repair. Furthermore, low-dose cisplatin therapy could modulate the immune response in NSCLC through the established chemokine activity of extracellular reduced HMGB1. This could potentially enhance the efficacy of subsequent immunotherapy treatment.

Selinexor With Anti-PD-1 Antibody as a Potentially Effective Regimen for Patients With Natural Killer/T-Cell Lymphoma Failing Prior L-Asparaginase and PD-1 Blockade.

Natural killer/T-cell lymphoma (NKTCL) is a rare and heterogeneous tumor type of non-Hodgkin's lymphoma (NHL) with a poor clinical outcome. There is no standardized salvage treatment failing l-asparaginase-based regimens. Here we report our retrospective results of the combined use of selinexor and PD-1 blockade (tislelizumab) in 5 patients with NKTCL who had exhausted almost all available treatments. A total of 5 patients with relapsed/refractory(R/R) NK/T-cell lymphomas failing prior l-asparaginase and anti-PD-1 antibody were retrospectively collected. They were treated with at least one cycle of XPO1 inhibitor plus the same anti-PD-1 antibody. Anti-PD-1 antibody (Tislelizumab) was administrated at 200 mg on day 1 every 3 weeks and selinexor doses and schedules ranged from 40 mg weekly for 2 weeks per 21-day cycle to 60 mg weekly per cycle. Five patients with relapsed NKTCL with extensive organ involvement including 4 central nervous system (CNS) infiltration patients were included. Four patients achieved objective responses including 3 complete responses (CR) and 1 partial response (PR). After a median follow-up time of 14.5 (range, 5-22) months, 1 patient was still in remission with CR, and the other 4 patients discontinued due to disease progression with a median progression-free survival (PFS) of 6 months and median overall survival (OS) of 12 months. Four patients with CNS involvement achieved a median OS of 8 months. Our data suggest that selinexor in combination with an anti-PD-1 antibody is a promising small molecule and immunotherapy combination regimen for patients with relapsed or refractory NKTCL.

Safety of selinexor as the only exportin 1 (XPO1) inhibitor so far: a post-marketing study based on the world Health Organization pharmacovigilance database (Vigibase).

Exportin 1 (XPO1) inhibitors are being developed as a new agent for anti-cancer therapies. This study aimed to broadly portray the adverse event (AE) profile of selinexor, an XPO1 inhibitor, in actual clinical practice. Disproportionality analyses were conducted by calculating the information component and reporting odds ratio in VigiBase over different reporting periods. All selinexor-related AEs were classified by system organ class (SOC) and preferred term (PT) according to the Medical Dictionary for Regulatory Activities. A total of 116,443 AEs were identified in 2,608 patients that received selinexor. Patients with cardiac disorders had a higher propensity for death. Thirteen SOCs and 125 PTs were identified as having a potential connection with selinexor. Notably, 29 suspected signals detected in our study were defined as significant AEs by the European Medicines Agency, including febrile neutropenia, pancytopenia, and acute kidney injury. Attention should be paid to these AEs, despite most toxicities being manageable and reversible. This study highlights a number of AEs associated with selinexor. Most toxicities are reversible but require careful management. The benefit of selinexor still outweighs the potential risks, indicating XPO1 inhibitors as promising agents.

Hub gene associated with prognosis in bladder cancer is a novel therapeutic target.

Bladder cancer is a clinical and social conundrum due to its high incidence and recurrence rate. It is urgent to find new targets for the diagnosis and treatment of bladder cancer and improve the prognosis and survival rate of bladder cancer patients. We sought a prognosis-related gene, built related models of evaluated bladder cancer and identified the function of the hub gene in bladder cancer. We downloaded the data of bladder cancer patients from the TCGA database, and used differentially expressed genes (DEGs), copy number variation (CNV) and survival analysis to scan the hub genes associated with prognosis in bladder cancer. Then, multi-factor cox regression was used to obtain the bladder cancer prognosis correlation model. Then, we analyzed the relationship between the expression of hub gene and immune microenvironment of bladder cancer. The relationship between the expression of hub gene and prognosis in bladder cancer patients was verified by immunohistochemistry. Cell proliferation assay and drug sensitivity test in vivo were used to verify the inhibition of bladder cancer by targeted inhibitors. In bladder cancer, we screened seven hub genes (ACLY, CNP, NKIRAS2, P3H4, PDIA6, VPS25 and XPO1) associated with survival. Moreover, the multifactor regression model constructed with hub gene can well distinguish the prognosis of bladder cancer. Hub gene is mostly associated with immune microenvironment. Immunohistochemical results basically confirmed the importance of XPO1 in bladder cancer. Selinexor (an inhibitor of XPO1) could effectively inhibit the proliferation of bladder cancer in the cell proliferation experiments by CCK-8 assays and it could suppress the growth of bladder cancer in mouse bladder cancer model. In this study, a prognostic model with seven hub genes has provided great help for the prognosis prediction of bladder cancer patients. And XPO1 is an important target affecting the prognosis of bladder cancer, and inhibition of XPO1 can effectively inhibit bladder cancer proliferation and growth.

XPO1 inhibition sensitises CLL cells to NK cell mediated cytotoxicity and overcomes HLA-E expression

The first-in-class inhibitor of exportin-1 (XPO1) selinexor is currently under clinical investigation in combination with the BTK inhibitor ibrutinib for patients with chronic lymphocytic leukaemia (CLL) or non-Hodgkin lymphoma. Selinexor induces apoptosis of tumour cells through nuclear retention of tumour suppressor proteins and has also recently been described to modulate natural killer (NK) cell and T cell cytotoxicity against lymphoma cells. Here, we demonstrate that XPO1 inhibition enhances NK cell effector function against primary CLL cells via downregulation of HLA-E and upregulation of TRAIL death receptors DR4 and DR5. Furthermore, selinexor potentiates NK cell activation against CLL cells in combination with several approved treatments; acalabrutinib, rituximab and obinutuzumab. We further demonstrate that lymph node associated signals (IL-4 + CD40L) inhibit NK cell activation against CLL cells via upregulation of HLA-E, and that inhibition of XPO1 can overcome this protective effect. These findings allow for the design of more efficacious combination strategies to harness NK cell effector functions against CLL.

Long-term follow up of selinexor maintenance in patients with TP53wt advanced or recurrent endometrial cancer: A pre-specified subgroup analysis from the phase 3 ENGOT-EN5/GOG-3055/SIENDO study.

427956 Background: Molecular characterization is important to inform treatment decisions for patients with endometrial cancer (EC). Wild type TP53 ( TP53wt) is found in ~75% of newly diagnosed EC and 50% of advanced/recurrent tumors; there are no specific targeted therapies available for patients with TP53wt EC. Selinexor is an investigational oral XPO1 inhibitor that drives nuclear retention and functional activation of wild type tumor suppressor proteins, including p53. Methods: SIENDO (NCT03555422) was a phase 3 double-blind study evaluating selinexor vs placebo as maintenance therapy in patients with advanced/recurrent EC following response to prior systemic therapy. The primary endpoint was progression-free survival (PFS), which was previously presented at the ESMO plenary in March 2022. Preliminary analysis of a pre-specified exploratory subgroup of patients with TP53wt EC showed a decrease in risk for progression or death with a median PFS of 13.7 months with selinexor as maintenance therapy vs 3.7 months with placebo at the time of primary PFS analysis. The safety and efficacy of selinexor as maintenance therapy was now further assessed with long-term follow-up in the pre-specified subgroup of patients with TP53wt EC. Results: 113 patients with TP53wt EC were randomly assigned to receive selinexor vs placebo as maintenance therapy (selinexor, n=77/placebo, n=36). As of data cutoff on Nov 30, 2022, median follow-up was 20.3 months, with 26.3% and 22.9% patients still on selinexor and placebo treatment, respectively. Median PFS for the TP53wt subgroup was 20.8 months with selinexor vs 5.2 months with placebo (HR [Stratified by chemotherapy response CR vs PR] 0.46; 95% CI (0.27, 0.79), nominal one-sided p=0.002). Efficacy was observed regardless of MSS/MSI status. The most common adverse events (AEs) of any grade (selinexor/placebo) were nausea (90%/34%), vomiting (61%/11%) and diarrhea (38%/34%); and most common grade 3+ AEs included: neutropenia (18%/0%), nausea (12%/0%), and thrombocytopenia (9%/0%). TEAEs leading to discontinuations were reported in 15%/0% of patients, respectively. Conclusions: Long-term follow-up of a pre-specified subgroup analysis showed durable PFS benefit with selinexor maintenance in TP53wt EC, which offers the potential to prolong response to prior systemic therapy. These data suggest that TP53 status is a robust prognostic biomarker for EC and selinexor may provide meaningful benefit in patients who have TP53wt tumors. A phase 3 trial is underway to further investigate the safety and efficacy of selinexor as maintenance therapy in patients with advanced or recurrent TP53wt EC (NCT05611931). Updated PFS and results in additional molecular subtypes (MSS/MSI) of the TP53wt subgroup will be included at the time of presentation. Clinical trial information: NCT03555422 .

Dual targeting of protein translation and nuclear protein export results in enhanced antimyeloma effects.

Selinexor (KPT-330) is a small molecule inhibitor of XPO1, which mediates the transport of tumor suppressor proteins, oncogene messenger RNAs, and other proteins involved in governing cell growthfrom the cell nucleus to the cytoplasm. It is overexpressed in many cancer types. Because eukaryotic translation initiator factor 4E (eIF4E) plays a critical role in protein translation in cancer cells in multiple myeloma (MM), we evaluated the effectiveness of combined inhibition of protein translation and nuclear export in MM. Selinexor, an inhibitor of nuclear protein export, dose-dependently decreased eIF4E, IKZF1, and c-MYC protein levels. Using a doxycycline-inducible-pLKO-Tet-On vector, knockdown of eIF4E significantly enhanced the antiproliferative effects of selinexor, sensitized resistant MM cells to selinexor, and increased apoptosis in MM cells. Immunofluorescent analysis of MM cells showed that the combined treatment increased the localization of residual eIF4E to the nucleus compared with selinexor-only treatment. The overexpression of eIF4E at least partially rescued the effects of selinexor in MM cells by reducing G1 cell cycle arrest and increasing the selinexor-IC50 10-fold. Moreover, the combination of selinexor with pharmacologic inhibitors of protein translation showed synergistic anti-MM effects. These results suggest a synergistic anti-MM effect of selinexor combined with eIF4E inhibitors invitro. Our work provides a better understanding of the potential mechanism of resistance to selinexor and a rationale for combining selinexor with eIF4E inhibitors for the treatment of MM.

NPM1-mutated acute myeloid leukemia: New pathogenetic and therapeutic insights and open questions.

The nucleophosmin (NPM1) gene encodes for a multifunctional chaperone protein that is localized in the nucleolus but continuously shuttles between the nucleus and cytoplasm. NPM1 mutations occur in about one-third of AML, are AML-specific, usually involve exon 12 and are frequently associated with FLT3-ITD, DNMT3A, TET2, and IDH1/2 mutations. Because of its unique molecular and clinico-pathological features, NPM1-mutated AML is regarded as a distinct leukemia entity in both the International Consensus Classification (ICC) and the 5th edition of the World Health Organization (WHO) classification of myeloid neoplasms. All NPM1 mutations generate leukemic mutants that are aberrantly exported in the cytoplasm of the leukemic cells and are relevant to the pathogenesis of the disease. Here, we focus on recently identified functions of the NPM1 mutant at chromatin level and its relevance in driving HOX/MEIS gene expression. We also discuss yet controversial issues of the ICC/WHO classifications, including the biological and clinical significance of therapy-related NPM1-mutated AML and the relevance of blasts percentage in defining NPM1-mutated AML. Finally, we address the impact of new targeted therapies in NPM1-mutated AML with focus on CAR T cells directed against NPM1/HLA neoepitopes, as well as XPO1 and menin inhibitors.

TRLS-16. RAPID GENERATION OF EPENDYMOMA MOUSE MODELS FOR PRE-CLINICAL STUDIES

Abstract Pediatric Ependymomas are the leading cause of cancer death among children & adolescents with the 5-year progression free survival (PFS)rate being < 30%. Despite this poor prognosis there has been less success in development of targeted therapies. A major drawback in developing new therapeutics is lack of proper models of disease. Objective of out work has been to develop orthogonal models of various distinct groups of ependymoma to enable understanding of tumor microenvironment thus leading to strategies targeting potential therapeutic sites. In this regard we have developed two models of ZFTA-RELA Ependymoma: 1) In Utero Electroporation Model: DNA plasmids are transfected into developing forebrain, 2) Allograft Model: Primary tumor derived or in vitro transducer cells are allografted into various regions of brain. Further we have shown that these models molecularly resemble patient-derived tumors using RNA sequencing. Using these ZFTA-RELA mouse models we have shown that NSG mice (n=8/treatment group) treated with Selinexor (an XPO1 inhibitor) in combination with chemotherapy have lower tumor volumes by 40% as compared to vehicle or chemotherapy alone treated mice (P<0.05). Furthermore the combination therapy treated mice have improved survival by 28 days as compared to vehicle mice. In conclusion, we have shown that our novel models of ependymomas not only closely resemble disease in patients, but can also be used to develop effective targeted therapies.

DIPG-57. TESTING FOR SYNERGY AMONG RADIATION AND HIGHLY CLINICALLY RELEVANT CHEMOTHERAPEUTIC AGENTS IN PATIENT-DERIVED MODELS OF DIFFUSE MIDLINE GLIOMA

Abstract Diffuse midline gliomas (DMG) are aggressive pediatric brain tumors with minimal long-term survival. Radiation is currently the only standard-of-care treatment and is non-curative. Several chemotherapy agents have shown preclinical and/or early clinical promise, and we hypothesize that finding effective chemoradiotherapeutic combinations is likely to be necessary to achieve long-term survival, based on experience from other previously incurable childhood cancers. We treated 8 DMG/DIPG cell lines with one, two, or three treatments among the HDAC inhibitor panobinostat, the CDK4/6 inhibitor ribociclib, the DRD2 inhibitor ONC201, the XPO1 inhibitor selinexor, the PI3K inhibitor paxalisib, and radiation. We then measured the cell survival with MTS assays. Cells were treated with drug concentrations ranging from 1 nM to 100 uM. To assess for synergy among our combinations, we used the Combination Index (CI) model, in which a score of <1 implies synergy. Of the 15 2-treatment combinations, ONC201 + radiation, ONC201 + paxalisib, ribociclib + ONC201, selinexor + paxalisib, and ribociclib + paxalisib met our criteria as successful, synergistic combinations: at least three cell lines with at least 90% cell death achieved, a CI value of 0.5 or lower at doses with at least 50% cell death, and at least 66% of dose levels with a CI value of 0.5 or lower. Early analysis suggests that ribociclib + ONC201 + paxalisib, ONC201 + paxalisib + radiation, and ONC201 + selinexor + paxalisib are the most effective three-treatment combinations. Patient-derived cell culture data in a heterogeneous pool of DMG/DIPG cell lines demonstrate synergy using several combinations of clinically relevant treatments, especially those including paxalisib. We are now optimizing treatment sequencing in synergistic combinations and testing in orthotopic xenograft models. Our goal is to find combinations that can become cycles of therapy in a multimodality clinical trial.

Correlation of comprehensive molecular mapping of pancreatic ductal adenocarcinoma with XPO1 mRNA expression levels to potential clinical targets.

4144 Background: Encouraging pre-clinical efficacy targeting Exportin-1 (XPO1) - a master regulator of tumor suppressor protein export - has been reported in pancreatic ductal adenocarcinoma (PDAC) and clinical trials are currently ongoing. However, limited data is available regarding expression and function of XPO1 in PDAC. Thus, we investigated XPO1 mRNA expression and its clinical and immune correlates in PDAC. Methods: 5,488 PDACs were tested at Caris Life Sciences (Phoenix, AZ) with NGS of DNA (WES) and RNA (WTS) . TMB-H was defined as ≥10 mutations/MB. The cohort was stratified in quartiles according to XPO1 mRNA expression status, and XPO1-high ( XPO1H) and XPO1-low ( XPO1L) expression were defined as ≥top and <bottom quartile of transcripts per million (TPM). Immune cell fraction was calculated by QuantiSeq method. Gene expression profiles were analyzed for transcriptomic signatures predictive of response to immune checkpoint inhibitors (T cell-inflamed score) and MAPK pathway activation (MPA). The Mann-Whitney U and X2 tests were applied as appropriate, with p-values adjusted for multiple comparisons. Real-world overall survival (OS) data was obtained from insurance claims. TGCA data were used to validate molecular, biological and immunological findings. Single-cell RNA analyses on a publicly available dataset were performed to elaborate cellular localization of XPO1. Results: Increased XPO1 mRNA expression was observed in metastatic lesions compared to primary tumors (p<0.001). Copy number amplification and mutation prevalence was comparable between XPO1H and XPO1L samples (p>0.05), along with similar rates of MSI-H/dMMR (1.3 vs 0.9%) and TMB-H (2.0 vs 1.3%; p>0.05). XPO1H PDACs were associated with a significant higher prevalence of T cell-inflamed tumors compared to XPO1L cases (58 vs 5%; p<0.05), consistent with higher immune cell infiltration in the XPO1H quartile as compared to XPO1L (p<0.05), except for immunosuppressive regulatory T cells and monocytes (p>0.05). XPO1H was associated with a higher MPA score as compared to XPO1L (2.4 vs -2.1 Arbitrary Units; p<0.05). XPO1H was associated with shorter OS (HR 1.09 [1.1-1.4], p=0.048). Validation studies using TCGA datasets corroborate our findings and confirmed increased immune cell infiltration as a function of XPO1. Moreover, single cell data revealed predominant and high expression of XPO1 in the tumor cell compartment. Conclusions: This is the first study comprehensively mapping XPO1 mRNA expression and immune-correlates in PDAC. We found that high XPO1 is linked to increased immune cell infiltration with a T cell-inflamed pattern. Our data provided a potential rationale to combine immune checkpoint therapy (+/- XPO1 inhibitors) in XPO1H PDACs.

Targeting Exportin 1 as treatment for cutaneous squamous cell carcinoma.

e21564 Background: Cutaneous squamous cell carcinomas (cSCC) are among the most frequent solid cancers in humans and in the U.S., cSCC cases are increasing. Molecular mechanisms transitioning premalignant lesions to cancer are not well characterized. As a result, targeted therapies need to be identified to treat these lesions. Preliminary data shows that Exportin 1 (XPO1) is one of the major proteins regulating nuclear export of proteins, helping to maintain cellular homeostasis. Previous work showed that Exportin 1 modulates the nuclear:cytoplasmic ratio of signaling proteins in skin cancer; resulting in an anti-apoptotic effect by adjusting the nuclear-cytoplasmic balance of pro-survival proteins such as CDC25A and Survivin. XPO1 expression is upregulated in many cancers, thereby affecting the nuclear:cytoplasmic ratio of many pro-survival proteins and enhancing tumorigenesis. This research project was designed to investigate the effects of XPO1 inhibition on cSCC survival. Selinexor is FDA cleared for treatment of multiple myeloma patients. Selinexor is a selective inhibitor of XPO1 regulated nuclear transport causing target molecules to remain within the cell leading to decreased cancer cell growth and decreased cancer cell survival. We hypothesize that inhibiting XPO1 with Selinexor or by CRISPRi genetic knockdown of XPO1 in cSCC cells will reduce proliferation and increase apoptosis in cSCC cells. Methods: Human cSCC cell lines SCC13 and SRB12 were seeded in 96-well plates at 8,000 cells/well density and 3,000 cells/well, respectively. Cells were treated with varying concentrations of Selinexor (0.005mM – 5mM) or DMSO as vehicle control. At 24-hour intervals, cell imaging and Neutral red staining assays were conducted to determine the IC50 concentration for Selinexor in cSCC cell lines. SCC13 cells stably expressing dCas9-KRAB and a doxycycline-inducible XPO1 guide RNA were used for CRISPRi experiments. Cells were treated with doxycycline daily and apoptosis was assayed by Caspase Glo 3/7 daily for four days. CRIPSRi enabled a doxycycline inducible XPO1 knock down on SCC13 cells allowing us to disrupt the cellular transporter protein XPO1. Results: Selinexor treatment of SRB12 cells resulted in an IC50 of 1.174 μM and 0.071 μM for SCC13. In contrast, normal human keratinocyte cell lines had higher IC50 values of 2.18 μM for HaCaT and 5.29 μM for KerCT cells. Apoptosis significantly increased after 72 and 96 hours of XPO1 knock down in SCC13 cells measured by Caspase Glo. Conclusions: These results document how XPO1 inhibition reduces proliferation and is toxic to both normal keratinocytes and cSCC cells. Additionally, cSCC cells had lower IC50 values for Selinexor, suggesting cSCC may be more sensitive to XPO1 inhibition compared to normal keratinocytes. Further, targeting XPO1 also increases apoptosis in these cells. This data supports the hypothesis that targeting XPO1 may be effective in treating cSCC.

Effectiveness of anti-B-cell maturation antigen (BCMA)-targeting therapy after selinexor treatment.

e20034 Background: Multiple myeloma (MM) remains incurable, with the disease typically becoming refractory to three main classes of standard therapies: immunomodulatory drugs (IMiDs), proteasome inhibitors (PIs) and anti-CD38 monoclonal antibodies (αCD38 mAbs). Treatments with novel mechanisms of action, including the XPO1 inhibitor selinexor and T-cell engaging anti-B-cell maturation antigen (αBCMA)-agents (antibody drug conjugates [ADC], bi-specific antibodies [BiS]), are increasingly used for treatment of relapsed and/or refractory MM (RRMM) after standard therapies have failed. Emerging data suggests a deleterious impact on T cell function with certain MM treatments, including alkylators and PIs, leading to inferior clinical outcomes. The influence of selinexor-based treatment on T cell function, which may alter the efficacy of αBCMA agents following selinexor treatment, is unknown. Methods: We analyzed the effectiveness of non-cellular αBCMA (NCA) therapies in pts with MM treated in 4 clinical studies (STORM [NCT02336815]; STOMP [NCT02343042]; BOSTON [NCT03110562], XPORT-MM-028 [NCT04414475]) with selinexor + dexamethasone (Xd), with or without PIs, IMiDs, or αCD38 mAbs, followed by therapy with NCA. After end of treatment with selinexor, survival follow-up data was collected every 3 months for 1 (STORM, STOMP, XPORT-MM-028) to 5 years (BOSTON). Results: Across the 4 clinical studies, 724 pts received selinexor, 404 of which had therapy post-selinexor documented. Thirty-seven pts (median age: 68, range: 40-87) received NCA therapy at any time following a selinexor regimen (Xd, n = 12; Xd + bortezomib, n = 9; Xd + pomalidomide, n = 6; Xd + daratumumab, n = 3; Xd + carfilzomib, n = 5; Xd + ixazomib, n = 2). NCAs included the ADC belantamab mafodotin (n = 28), the BiS teclistamab (n = 2), SEA-BCMA (n = 2), AMG 701 (n = 1), elranatamab (n = 1), MEDI2228 (n = 1), and investigational (n = 3; 2 had αBCMA bispecific antibodies and 1 had αBCMA BITE) (1 pt received 2 NCAs, belantamab and teclistamab). For the selinexor-based regimens, the median number of previous lines of therapy was 5 (range: 2-11) and 21 (56.8%) pts had triple-class refractory MM including 8 (21.6%) with penta-refractory MM. Median time from last dose of selinexor to NCA was 8 weeks (range: 2-117). Median time to treatment discontinuation with NCA was 4.4 months (95% CI: 2.1, NE). The median overall survival from initiation of NCA was 12.0 months (95% CI: 9.4, NE) with a median follow-up of 7.8 months. Conclusions: In this cohort of heavily-pretreated pts with MM who received a selinexor regimen prior to NCA, overall survival was in the range of 1 year, akin to historical results seen with ADCs. The 8-week median time between administration of selinexor and NCAs suggests that selinexor, with various partner agents, did not negatively impact overall survival with subsequent NCA therapy.

ENGOT-EN20/GOG-3083/xport-EC-042: A phase 3, randomized, placebo-controlled, double-blind, multicenter trial of selinexor in maintenance therapy after systemic therapy for patients with P53 wild-type, advanced or recurrent endometrial carcinoma.

TPS5627 Background: Patients (pts) with first-line metastatic or recurrent endometrial cancer (EC) have a poor prognosis. Selinexor is an oral XPO1 inhibitor, which leads to nuclear accumulation of tumor suppressor proteins, including p53. Selinexor is FDA-approved for use in multiple myeloma and diffuse large B-cell lymphoma, and has shown clinical activity in previously treated, advanced EC. Molecular characterization of EC is critical in directing treatment for advanced and recurrent disease. Of the EC molecular subtypes, TP53 wild type (wt) tumors represent 50% of advanced and recurrent tumors. A recent phase 3 study in maintenance after chemotherapy found that, despite the primary endpoint (PFS) not reaching statistical significance, prolonged PFS of oral once-weekly selinexor versus placebo (13.7 months and 3.7 months, respectively) was observed in a prespecified exploratory subgroup analysis of patients with advanced or recurrent TP53wt EC. Methods: XPORT-EC-042 (NCT05611931) is a Phase 3 randomized, double-blind, placebo-controlled study designed to evaluate the efficacy and safety of selinexor as maintenance therapy in pts with TP53wt advanced or recurrent EC, who have achieved a partial response or complete response per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 after completing at least 12 weeks of platinum combination chemotherapy ±immunotherapy for primary stage IV or recurrent disease. Eligible pts must be ≥18 years of age, have histologically confirmed EC, and TP53 wt disease based on NGS sequencing assessed by Foundation Medicine. Pts will be randomized 1:1 with either selinexor 60 mg or placebo once weekly in 28-day cycles until progressive disease, toxicity, or 3 years if in complete response. A total of 220 pts will be enrolled at sites across the United States, Canada, Europe, and Israel. The primary objective is to compare PFS in pts treated with selinexor compared to placebo based on RECIST v1.1 criteria as assessed by the Investigator. Key secondary objective is overall survival. Other secondary objectives are safety, time to first subsequent therapy, time to second subsequent therapy, time from randomization until the second progression event (PFS2), and PFS by a blinded independent central review. Patient enrollment is ongoing. Clinical trial information: NCT05611931 .