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Pancreatic cancer is an aggressive and deadly malignancy responsible for the death of over 37,000 Americans each year. Gemcitabine-based therapy is the standard treatment for pancreatic cancer but has limited efficacy due to chemoresistance. In this study, we evaluated the in vitro and in vivo effects of gemcitabine combined with the selective nuclear export (CRM1) inhibitor KPT-330 on pancreatic cancer growth. Human pancreatic cancer MiaPaCa-2 and metastatic pancreatic cancer L3.6pl cell lines were treated with different concentrations of KPT-330 and gemcitabine alone or in combination, and anchorage–dependent/independent growth was recorded. In addition, L3.6pl cells with luciferase were injected orthotopically into the pancreas of athymic nude mice, which were treated with (i) vehicle (PBS 1 mL/kg i.p., 2/week and povidone/pluronic F68 1 mL/kg p.o., 3/week), (ii) KPT-330 (20 mg/kg p.o., 3/week), (iii) gemcitabine (100 mg/kg i.p., 2/week), or (iv) KPT-330 (10 mg/kg) + gemcitabine (50 mg/kg) for 4 weeks. KPT-330 and gemcitabine alone dose-dependently inhibited anchorage-dependent growth in vitro and tumor volume in vivo compared with vehicle treatment. However, the combination inhibited growth synergistically. In combination, KPT-330 and gemcitabine acted synergistically to enhance pancreatic cancer cell death greater than each single-agent therapy. Mechanistically, KPT-330 and gemcitabine promoted apoptosis, induced p27, depleted survivin, and inhibited accumulation of DNA repair proteins. Together, our data suggest that KPT-330 potentiates the antitumor activity of gemcitabine in human pancreatic cancer through inhibition of tumor growth, depletion of the antiapoptotic proteins, and induction of apoptosis. Mol Cancer Ther; 14(7); 1570–81. ©2015 AACR.

Supplemental legend for Fig. S1

Selinexor, a selective inhibitor of nuclear export (SINE) compound targeting exportin-1, has previously been shown to inhibit melanoma cell growth in vivo. We hypothesized that combining selinexor with antibodies that block or disrupt T-cell checkpoint molecule signaling would exert superior antimelanoma activity. In vitro, selinexor increased PDCD1 and CTLA4 gene expression in leukocytes and induced CD274 gene expression in human melanoma cell lines. Mice bearing syngeneic B16F10 melanoma tumors demonstrated a significant reduction in tumor growth rate in response to the combination of selinexor and anti-PD-1 or anti-PD-L1 antibodies (P < 0.05). Similar results were obtained in B16F10-bearing mice treated with selinexor combined with anti-CTLA4 antibody. Immunophenotypic analysis of splenocytes by flow cytometry revealed that selinexor alone or in combination with anti-PD-L1 antibody significantly increased the frequency of both natural killer cells (P ≤ 0.050) and CD4+ T cells with a Th1 phenotype (P ≤ 0.050). Further experiments indicated that the antitumor effect of selinexor in combination with anti-PD-1 therapy persisted under an alternative dosing schedule but was lost when selinexor was administered daily. These data indicate that the efficacy of selinexor against melanoma may be enhanced by disrupting immune checkpoint activity. Mol Cancer Ther; 16(3); 417–27. ©2017 AACR.See related article by Tyler et al., p. 428.

Supplemental Figure S1: Effects of alternative dosing schedules for selinexor (15 mg/kg) and anti-PD-1 on systemic immune populations; Supplemental Figure S2: Effects of alternative dosing schedules for selinexor (10 mg/kg) and anti-PD-1 on systemic immune populations.

Supplementary Figure S1. Effect of KPT-330 on human normal pancreatic epithelial (HPNE) cell proliferation (MTT assay).

Background Selinexor is an oral inhibitor of the nuclear export protein Exportin 1 (XPO1) with demonstrated antitumor activity in solid and hematological malignancies. We evaluated the efficacy and safety of selinexor in heavily pretreated, recurrent gynecological malignancies. Methods In this phase 2 trial, patients received selinexor (35 or 50 mg/m2 twice-weekly [BIW] or 50 mg/m2 once-weekly [QW]) in 4-week cycles. Primary endpoint was disease control rate (DCR) including complete response (CR), partial response (PR) or stable disease (SD) ≥12 weeks. Secondary endpoints were progression-free survival (PFS), overall survival (OS) and safety. Results 114 patients with ovarian (N = 66), endometrial (N = 23) or cervical (N = 25) cancer were enrolled. Median number of prior regimens for ovarian, endometrial and cervical cancer was 6 (1–11), 2 (1–5), and 3 (1–6) respectively. DCR was 30% (ovarian 30%; endometrial 35%; cervical 24%), which included confirmed PRs in 8%, 9%, and 4% of patients with ovarian, endometrial, and cervical cancer respectively. Median PFS and OS for patients with ovarian, endometrial and cervical cancer were 2.6, 2.8 and 1.4 months, and 7.3, 7.0, and 5.0 months, respectively. Common Grade 3/4 adverse events (AEs) were thrombocytopenia (17%), fatigue (14%), anemia (10%), nausea (9%) and hyponatremia (9%). Patients with ovarian cancer receiving 50 mg/m2 QW had fewer high-grade AEs with similar efficacy as BIW treatment. Conclusions Selinexor demonstrated single-agent activity and disease control in patients with heavily pretreated ovarian and endometrial cancers. Side effects were a function of dose level and treatment frequency, similar to previous reports, reversible and mitigated with supportive care.

Selinexor, a selective inhibitor of nuclear export, has demonstrated promising activity in patients with acute myeloid leukemia (AML). This randomized, phase II study evaluated selinexor 60 mg twice weekly ( n = 118) vs. physician's choice (PC) treatment ( n = 57) in patients aged =60 years with relapsed/refractory (R/R) AML. The primary outcome was overall survival (OS). Median OS did not differ significantly for selinexor vs. PC (3.2 vs. 5.6 months; HR = 1.18 [95% CI: 0.79-1.75]; p = 0.422). Complete remission (CR) plus CR with incomplete hematologic recovery trending in favor of selinexor occurred in a minority of patients. Selinexor treated patients had an increased incidence of adverse events. The most common grade =3 adverse events were thrombocytopenia, febrile neutropenia, anemia, hyponatremia. Despite well-balanced baseline characteristics, there were numerically higher rates of TP53 mutations, prior myelodysplastic syndrome, and lower absolute neutrophil counts in the selinexor group; warranting further investigation of selinexor in more carefully stratified R/R AML patients. Registered trial: NCT02088541.

BackgroundVT1021 is a first-in-class therapeutic agent in Phase I clinical studies in solid tumors. In vivo preclinical studies demonstrated that VT1021 inhibited tumor growth via stimulation of p53 and Thrombospondin-1 (Tsp-1) in MDSCs. Moreover, induction of Tsp-1 reprogrammed the tumor microenvironment and induced apoptosis in tumor cells via its cell surface receptors CD36 and CD47. Here we report on the utility of Tsp-1 as a pharmacodynamic biomarker and its correlation with clinical response.MethodsTsp-1 protein levels in PBMCs, platelets and plasma were assessed by ELISA following SepMate-based fractionation of subject blood samples. Tsp-1 mRNA levels in peripheral blood cells were analyzed by quantitative RT-PCR following extraction of total RNA from subject whole blood samples via PAXgene Blood RNA kit. Tsp-1 levels in subject biopsy samples were analyzed by immunohistochemistry as described previously.ResultsUp-regulation of Tsp-1 protein was observed in PBMCs, platelets and plasma in all evaluable subjects following treatment with VT1021 across multiple indications in a phase 1 clinical study, indicating that Tsp-1 induction is a pharmacodynamic biomarker for VT1021 (figure 1). Induction of Tsp-1 by VT1021 was also shown at the transcriptional level via RT-PCR measurement of whole blood samples. Strikingly, maximum PBMC Tsp-1 levels induced by VT1021 were higher in subjects with glioblastoma (GBM) that had objective responses (complete or partial response) compared to subjects with stable disease (SD) or progressive disease (PD). Of note, pre-dose levels of Tsp-1 were predictive of response, as subjects with objective responses had higher basal levels of Tsp-1 than those that had stable or progressive disease. For subjects with pancreatic cancer, Tsp-1 induction was higher in SD subjects compared to PD subjects, suggesting that Tsp-1 induction in PBMCs can be a potential prognostic biomarker. In tumor biopsy samples from subjects with pancreatic cancer, increased colocalization of Tsp-1 and CD11b was observed in on-study samples, supporting a role of Tsp-1 in reprogramming the tumor microenvironment (figure 2).Abstract 375 Figure 1Up-regulation of Tsp-1 protein levels have been observed in PBMCs(A), platelets (B) and plasma (C) in all evaluable subjects post-dosing with VT1021 across multiple inductions in a phase 1 clinical study.Abstract 375 Figure 2Increased colocalization of Tsp-1 and CD11b was observed in tumor microenvironment in tumor biopsy samples from a subject with pancreatic cancer post-dosing with VT1021ConclusionsBased on both protein and mRNA levels, Tsp-1 induction has the potential to be a useful prognostic pharmacodynamic biomarker for VT1021 in various tumor types. In subjects with GBM, both basal and induced Tsp-1 levels in PBMCs are potential predictive and prognostic biomarkers, respectively. For subjects with pancreatic cancer, Tsp-1 protein induction in PBMCs is a potential prognostic biomarker. The predictive/prognostic utility coupled with the ability to measure levels in peripheral blood makes Tsp-1 a powerful biomarker to assess and predict clinical response to VT1021.

Background VT1021, a cyclic pentapeptide, reprograms myeloid-derived suppressor cells (MDSCs) and induces the production of thrombospondin-1 (Tsp-1) in the tumor microenvironment (TME). Tsp-1, via binding to CD36 and CD47, induces apoptosis in tumor and endothelial cells, blocks the ‘do-not-eat-me’ signal, increases the M1:M2 macrophage ratio and activates cytotoxic T lymphocytes (CTLs). Preclinical studies showed robust anti-tumor activities of VT1021 in multiple animal models. Methods This is a first-in-human, Ph 1/2, open-label, multicenter dose escalation and expansion study in advanced solid tumors. The primary objectives are to determine the recommended Phase 2 dose (RP2D) and characterize the safety and tolerability of VT1021. Secondary objectives are to characterize the adverse event (AE) profile, evaluate pharmacokinetics (PK), and describe preliminary efficacy. Exploratory objectives include evaluation of pharmacodynamic effects of VT1021 in tumor, TME, and peripheral blood. The expansion phase focuses on ovarian, pancreatic, triple negative breast cancer, glioblastoma, and a basket cohort with high CD36-expressing tumors. Results In the escalation phase, 46 subjects received between 0.5–15.6 mg/kg of VT1021 by IV infusion twice weekly. VT1021 has been well tolerated through all doses tested. One patient dosed at 1.0 mg/kg developed a grade 3 infusion reaction and 3 patients dosed at 1.0, 6.6, and 8.8 mg/kg respectively developed grade 2 infusion reactions. Other drug related AEs included grade 1–2 fatigue (n=7), nausea (n=4), constipation (n=2), increased aspartate aminotransferase (n=2) and blood bilirubin (n=2), hypomagnesaemia (n=2), and dizziness (n=2). Dose proportionality was observed in PK analysis. Among 28 evaluable subjects, one partial response (thymoma, 372+ days on treatment) and 11 stable disease (SD) in 9 different solid tumors have been observed for a disease control rate of 43%. Seven of eleven SDs had high CD36 AND high CD47 expression with an average duration of 162 days on study. VT1021 induced Tsp-1 production in peripheral blood cells at most dose levels. In addition, on-study biopsies exhibited increased Tsp-1 expression in the TME by activation of p53 in MDSCs, increased CTL infiltration, increased M1:M2 macrophage ratio, and reduced regulatory T cells in the TME. The RP2D was declared to be 11.8 mg/kg and enrollment in tumor-specific expansions is on-going. Conclusions Through all doses tested, VT1021 was safe and well tolerated, with dose proportional PK properties. In addition, VT1021 has demonstrated activities in reprogramming the TME which resulted in a high disease control rate in subjects with tumors expressing both high CD36 and high CD47. Trial Registration NCT03364400 Ethics Approval The study was approved by Northwestern University Medical School institutional review board (IRB), approval number 00000418, Horizon Oncology Center IRB, approval number 00001313, South Texas Accelerated Research Therapeutic IRB, approval number 00003657, University of Oklahoma Health Sciences Center IRB, approval number 00006075, Cleveland Clinic IRB, approval number 00000536, Florida Cancer Specialists IRB, approval number 00006075, Case Western IRB, approval number 00000536, Beth Israel Deaconess Hospital and Dana Farber Cancer Institute IRB, approval number 00000753 and MD Anderson IRB, approval number 00006023.

Introduction The goal of this study was to examine the effects of selinexor, an inhibitor of exportin-1 mediated nuclear export, on DNA damage repair and to evaluate the cytotoxic effects of selinexor in combination with DNA damaging agents (DDAs) in cancer cells. Results Selinexor reduced the expression of DNA damage repair (DDR) proteins. This did not induce significant DNA damage in tested cell lines. Inhibition of DDR protein expression resulted in enhanced cancer cell death when cells were pretreated with DDAs. In contrast, enhanced cell death was not detected in cells that were pretreated with selinexor then with DDAs. In vivo, single-agent selinexor, docetaxel, or cisplatin treatment resulted in 66.7%, 51.5%, and 26.6% tumor growth inhibition (TGI), respectively, in an MDA-MB-231 xenograft model. Consequently, combination treatment with docetaxel or cisplatin followed by selinexor in vivo resulted in 93.9% and 103.4% TGI, respectively. Immunohistochemical staining and immunoblot analysis of tumor sections confirmed reduced expression of DDR proteins. Conclusion Selinexor treatment inhibited DDR mechanisms in cancer cell lines and therefore potentiated DNA damage-based therapy. The sequential combination of DDAs followed by selinexor increased cancer cell death. This combination is superior to each individual therapy and has a mechanistic rationale as a novel anticancer strategy. Methods Cancer cells treated with selinexor ± DDAs were analyzed using reverse phase protein arrays, immunoblots, quantitative PCR and immunofluorescence. Mice bearing MDA-MB-231 tumors were treated with subtherapeutic doses of selinexor, cisplatin, docetaxel and selinexor in combination with either cisplatin or docetaxel. Tumor growth was evaluated for 25 days.

BackgroundOne barrier to treating pancreatic cancer is the immunosuppressive tumor microenvironment (TME). VT1021 is a cyclic peptide derived from prosaposin and stimulates thrombospondin-1 (Tsp-1) production in myeloid derived suppressor cells. Tsp-1 binds to CD36 on macrophages to convert M2 macrophages to anti-tumorigenic M1 macrophages; on tumor cells to induce apoptosis; and increases the CD8+/Treg ratio. Tsp-1 also binds to CD47 on tumor cells to block the ”do not eat me signal”. In a recently completed phase I/II clinical study (NCT03364400), VT1021 had no major adverse events and a predictable pharmacokinetic profile.MethodsTo evaluate potential predictive biomarkers of VT1021, CD36/CD47 levels were analyzed on pre-treatment biopsy samples and on-study tumor biopsies collected during the treatment using immunohistochemistry (IHC). Samples were stained and scored by software-based image analysis and manual review (figure 1). Induction of Tsp-1 in circulating peripheral blood mononuclear cells (PBMCs) by ELISA was correlated with Tsp-1 induction in on-study biopsy samples via IHC, and with clinical responses. To be considered ”evaluable”, subjects completed ≥1 cycle of VT1021 treatment and tumor imaging during cycle 2.ResultsIn the pancreatic cancer expansion study, 21 of 32 enrolled subjects (66%) had dual high (DH) expression of CD36/CD47. There were 5 subjects with stable diseases among 15 evaluable subjects with disease control rate of 33%. Of the 13 subjects with measurable disease, all 5 subjects with reduction of tumor burden were DH CD36/CD47 and remained on study for an average of 105 days. Moreover, paired tumor biopsies revealed increased Tsp-1 expression, CTL infiltration and M1:M2 ratio among subjects that obtained disease control with DH baseline CD36/CD47 expression.To identify other solid tumor indications that could benefit from VT1021 treatment based on CD36/CD47 expression, commercially available tumor tissue microarrays from 16 different indications were evaluated. Several indications demonstrated high percentage of DH CD36/CD47, including gastric (59%), head and neck (57%), and pancreatic cancers (56%).Abstract 369 Figure 1Expression intensities of CD36/CD47 in subjects with pancreatic cancerConclusionsPancreatic cancer subjects who were DH for CD36/CD47 were more likely to have a reduction in tumor burden and stay on study longer than non-DH subjects. Increased Tsp-1 induction in circulating PBMCs and in the TME was confirmed. Remodeling of the TME by VT1021 to be more immune sensitive via CTL and M1 accumulation was demonstrated. Based on these findings, the DH expression of CD36/CD47 could be a useful predictive biomarker to stratify subjects for inclusion in future trials in pancreatic cancer, and in other solid tumor indications.Trial RegistrationTrial RegistrationNCT03364400

XPO1 (exportin 1) is the main nuclear export protein with over 200 different protein cargos. XPO1 is overexpressed in tumor cells and high levels are correlated with poor prognosis. Selective Inhibitor of Nuclear Export (SINE) compounds block nuclear export by inhibiting XPO1. The first SINE compound, selinexor, shows promising anti-cancer activity across hematological and solid tumors in Phase 2 and 3 clinical trials. The 2nd generation SINE compound KPT-8602 is being evaluated as an anti-cancer agent in a Phase 1 clinical trial. To predict patient response to treatment and confirm the selinexor recommended phase 2 dose (RP2D), an assay based on fluorescence cross correlation spectroscopy that measures XPO1 occupancy in cancer cells was developed. Studies comparing cytotoxicity and XPO1 occupancy in cell lines treated with selinexor or KPT-8602 indicated that XPO1 occupancy by both compounds could reach saturation regardless of drug sensitivity. However, higher levels of XPO1 protein correlated with lower sensitivity to SINE compound cytotoxicity. In vivo mouse studies showed XPO1 occupancy could be measured in tumors and was dose-dependent, with >90% target saturation at 10 mg/kg (∼50 mg flat dose in humans). Drug-target occupancy was measured in a dose-response time course and full occupancy occurred by 6 hours at all doses. The duration of occupancy was dose-dependent, where 10-15 mg/kg in mice (∼ 50-75 mg human flat dose) was necessary to maintain XPO1 occupancy up to 48 hours post-dose. These findings confirm the selinexor RP2D of 60 mg for achieving target occupancy and inhibition up to 48 hours.

Selinexor, a selective inhibitor of nuclear export compound that blocks exportin 1 (XPO1) and forces nuclear accumulation and activation of tumor suppressor proteins, inhibits nuclear factor κB, and reduces oncoprotein messenger RNA translation, is a potential novel treatment for myeloma that is refractory to current therapeutic options. We administered oral selinexor (80 mg) plus dexamethasone (20 mg) twice weekly to patients with myeloma who had previous exposure to bortezomib, carfilzomib, lenalidomide, pomalidomide, daratumumab, and an alkylating agent and had disease refractory to at least one proteasome inhibitor, one immunomodulatory agent, and daratumumab (triple-class refractory). The primary end point was overall response, defined as a partial response or better, with response assessed by an independent review committee. Clinical benefit, defined as a minimal response or better, was a secondary end point. A total of 122 patients in the United States and Europe were included in the modified intention-to-treat population (primary analysis), and 123 were included in the safety population. The median age was 65 years, and the median number of previous regimens was 7; a total of 53% of the patients had high-risk cytogenetic abnormalities. A partial response or better was observed in 26% of patients (95% confidence interval, 19 to 35), including two stringent complete responses; 39% of patients had a minimal response or better. The median duration of response was 4.4 months, median progression-free survival was 3.7 months, and median overall survival was 8.6 months. Fatigue, nausea, and decreased appetite were common and were typically grade 1 or 2 (grade 3 events were noted in up to 25% of patients, and no grade 4 events were reported). Thrombocytopenia occurred in 73% of the patients (grade 3 in 25% and grade 4 in 33%). Thrombocytopenia led to bleeding events of grade 3 or higher in 6 patients. Selinexor-dexamethasone resulted in objective treatment responses in patients with myeloma refractory to currently available therapies. (Funded by Karyopharm Therapeutics; STORM ClinicalTrials.gov number, NCT02336815.).

The therapeutic potential of targeting p21-Activated Kinases (PAK1 - 6) for the treatment of cancer has recently gained traction in the biotech industry. Many pharmaceutically-viable ATP competitive inhibitors have been through different stages of pre-clinical development with only a single compound evaluated in human trails (PF-3758309). The best studied functional roles of PAK proteins are control of cell adhesion and migration. PAK proteins are known downstream effectors of Ras signaling with PAK expression elevated in cancer (pancreatic, colon, breast, lung and other solid tumors). In addition altered PAK expression is a confirmed driver of this disease, especially in tumors harboring oncogenic Ras. However, there are very few examples of gain-of-function PAK mutations, as a majority of the cancer types have elevated PAK expression due to gene amplification or transcriptional modifications. There is a substantial number of known substrates affected by this aberrant PAK activity. One particular substrate,#946;-catenin, has garnered interest given its importance in both normal and cancer cell development. These data place PAK proteins between two major signaling pathways in cancer (Ras and#946; -catenin), making therapeutic targeting of PAKs an intriguing approach for the treatment of a broad array of oncological malignancies.

Breast cancer is a heterogeneous disease consisting of several subtypes. Among these subtypes, triple negative breast cancer is particularly difficult to treat. This is due to a lack of understanding of the mechanisms behind the disease, and consequently a lack of druggable targets. PAK4 plays critical roles in cell survival, proliferation, and morphology. PAK4 protein levels are high in breast cancer cells and breast tumors, and the gene is often amplified in basal like breast cancers, which are frequently triple negative. PAK4 is also overexpressed in other types of cancer, making it a promising drug target. However, its inhibition is complicated by the fact that PAK4 has both kinase-dependent and -independent functions. Here we investigate a new clinical compound KPT-9274, which has been shown to inhibit PAK4 and NAMPT. We find that KPT-9274 (and its analog, KPT-8752) can reduce the steady state level of PAK4 protein in triple negative breast cancer cells. These compounds also block the growth of the breast cancer cells in vitro, and stimulate apoptosis. Most importantly, oral administration of KPT-9274 reduces tumorigenesis in mouse models of human triple negative breast cancer. Our results indicate that KPT-9274 is a novel therapeutic option for triple negative breast cancer therapy.

Introduction: Breast cancer brain metastasis (BCBM) is a devastating disease and remains largely incurable. Patients with triple negative breast cancer (TNBC) develop brain metastasis at a significantly higher incidence (46%) than patients with other breast cancer subtypes. Median survival after brain metastases in TNBC can be as short as 5 months. Selinexor is a first-in-class oral SINE (Selective Inhibitor of Nuclear Export) drug that inhibits XPO1 (exportin-1/ CRM1) activity and exhibits remarkable anti-cancer activity in advanced clinical trials. Moreover, selinexor can penetrate the blood-brain barrier and shows promising anti-tumor activity in animal models of glioblastoma and central nervous system lymphoma. Previous studies have shown that most TNBC cell lines tested in vitro and in vivo are sensitive to selinexor-induced growth inhibition and cell death. To explore the possibility of using selinexor as an effective treatment for TNBC brain metastasis, a mouse model was established and tested. Methods: TNBC cell line HCC1806 (ATCC# CRL-2335) was transformed with RediFect Red-Fluc-Puromycin and selected using puromycin to generate HCC1806-Fluc cells that expressed both puromycin resistance gene and a luciferase gene. Twenty-four nu/nu mice were inoculated intracranially with 1 x 104 HCC1806-Fluc cells. Four days post implant, mice were allocated to three groups of eight mice and treated with either vehicle, selinexor 10 mg/kg, or selinexor 15 mg/kg through oral gavage, three times per week (Mon, Wed, Fri). Body weight and condition of animals were recorded daily, and tumors were imaged twice per week (Tue and Thu). Brain tissues were collected at the end of study and analyzed by immunohistochemistry (IHC). Results: HCC1806-Fluc cells injected intracranially successfully implanted in the brains of host mice. All mice survived the duration of the study (day 16 after treatment initiation) and no significant difference in body weight was observed between different treatment groups. Mice treated with selinexor had a significant reduction in tumor area relative to vehicle controls. Tumor growth inhibition (TGI) was 103% for selinexor at 10 mg/kg and 97% for selinexor at 15 mg/kg compared to vehicle controls. IHC showed reduced tumor cell proliferation, decreased expression of Myc and Survivin, and increased nuclear expression of p21 and p27 in tumor samples from the brain of mice treated with selinexor as compared to that of controls. Decreased expression of HDAC1 and HDAC5 was also observed in brain tumor samples from selinexor-treated mice. Conclusions: Oral intake of selinexor effectively inhibited TNBC cell growth in a mouse model of brain metastasis. The anti-cancer effect is likely achieved through multiple signaling pathways, including cell cycle regulation, down-regulation of oncogenes and HDACs. Citation Format: Hua Chang, Marsha Crochiere, Sophie Debler, Trinayan Kashyap, Thaddeus J. Unger, Erkan Baloglu, William Senapedis, Sharon Shacham, Yosef Landesman. Selinexor effectively inhibits tumor growth in a triple negative breast cancer brain metastasis mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1998.

Selinexor is the first oral selective inhibitor of nuclear export compound tested for cancer treatment. Selinexor has demonstrated a safety therapy profile with broad antitumor activity against solid and hematological malignancies in phases 2 and 3 clinical trials (#NCT03071276, #NCT02343042, #NCT02227251, #NCT03110562, and #NCT02606461). Although selinexor shows promising efficacy, its primary adverse effect is high-grade thrombocytopenia. Therefore, we aimed to identify the mechanism of selinexor-induced thrombocytopenia to relieve it and improve its clinical management. We determined that selinexor causes thrombocytopenia by blocking thrombopoietin (TPO) signaling and therefore differentiation of stem cells into megakaryocytes. We then used both in vitro and in vivo models and patient samples to show that selinexor-induced thrombocytopenia is indeed reversible when TPO agonists are administered in the absence of selinexor (drug holiday). In sum, these data reveal (1) the mechanism of selinexor-induced thrombocytopenia, (2) an effective way to reverse the dose-limiting thrombocytopenia, and (3) a novel role for XPO1 in megakaryopoiesis. The improved selinexor dosing regimen described herein is crucial to help reduce thrombocytopenia in selinexor patients, allowing them to continue their course of chemotherapy and have the best chance of survival. This trial was registered at www.clinicaltrials.gov as #NCT01607905.

Selinexor, a selective inhibitor of nuclear export (SINE) compound targeting exportin-1, has previously been shown to inhibit melanoma cell growth in vivo. We hypothesized that combining selinexor with antibodies that block or disrupt T-cell checkpoint molecule signaling would exert superior antimelanoma activity. In vitro, selinexor increased PDCD1 and CTLA4 gene expression in leukocytes and induced CD274 gene expression in human melanoma cell lines. Mice bearing syngeneic B16F10 melanoma tumors demonstrated a significant reduction in tumor growth rate in response to the combination of selinexor and anti-PD-1 or anti-PD-L1 antibodies (P < 0.05). Similar results were obtained in B16F10-bearing mice treated with selinexor combined with anti-CTLA4 antibody. Immunophenotypic analysis of splenocytes by flow cytometry revealed that selinexor alone or in combination with anti-PD-L1 antibody significantly increased the frequency of both natural killer cells (P ≤ 0.050) and CD4+ T cells with a Th1 phenotype (P ≤ 0.050). Further experiments indicated that the antitumor effect of selinexor in combination with anti-PD-1 therapy persisted under an alternative dosing schedule but was lost when selinexor was administered daily. These data indicate that the efficacy of selinexor against melanoma may be enhanced by disrupting immune checkpoint activity. Mol Cancer Ther; 16(3); 417–27. ©2017 AACR. See related article by Tyler et al., p. 428.

Selinexor (KPT-330) is a selective inhibitor of nuclear export (SINE) which specifically targets XPO1 (Exportin 1)-mediated nuclear export, leading to increased nuclear retention of major tumor suppressor proteins and inducing selective apoptosis in cancer cells. Several phase I and II clinical trials demonstrate evidence of anti-cancer activity of Selinexor in solid tumors (i.e metastatic prostate cancer (PMID: 29487219), advanced refractory bone or soft tissue sarcoma (PMID: 27458288) and non-small cell lung cancer (PMID: 28647672); as well as, hematological malignancies, including non-Hodgkin lymphoma (PMID: 28468797), acute myeloid leukemia (PMID: 29304833) and multiple myeloma (MM) (PMID: 29381435). In the STORM (Selinexor Treatment of Refractory Myeloma) trial, the combination of Selinexor with dexamethasone in MM patients refractory to bortezomib, carfilzomib, lenalidomide and pomalidomide (quad-refractory), or in addition, to daratumumab (penta-refractory), has shown an overall response rate (ORR) of 21% (Vogl et al, JCO 2018). Our objective is to identify biomarkers for selection of patients at higher likelihood of clinical benefit from Selinexor salvage and understand mechanisms of Selinexor resistance. We therefore analyzed transcriptional differences using RNA sequencing in CD138+ cells from bone marrow aspirates obtained prior to treatment from 32 MM patients enrolled in STORM. The raw data (fastq) was mapped by using the tool STAR and gene-level annotated by featureCounts. Patients were split in two groups based on their progression-free survival (PFS). Differential expression analysis was performed using the tool DESeq2, which enables a more quantitative analysis of comparative RNA-seq data using shrinkage estimators for dispersion and fold change. The results revealed significant up-regulation of 13 genes in patients with PFS < 120 days (n = 21, p < 0.05) versus patients with PFS > 120 days (n=11), including the transcription factor E2F1 and its targets MYBL2, FANCA, GINS3 and SLX4 (Fig. 1). Next, we evaluated the expression of E2F1 in another set of 26 patients from the STORM trial by Affymetrix U133 gene expression microarrays. Data was analyzed using the Signal Space Transformation (SST)-Robust Multi-Chip Analysis (RMA) algorithm. Patients with PFS < 120 days (n = 19) exhibited significant up-regulation of E2F1 (p < 0.05) (Fig. 2). E2F1 is a transcription factor that regulates cell cycle G1/S progression. At rest, E2F1 is complexed with its negative regulator retinoblastoma(RB) protein. Upon phosphorylation of RB by the Cyclin D1-CDK4/6 complex, pRB is inactivated allowing E2F1 to commence transcription of target genes allowing G1/S progression. E2F transcription factors are exported by XPO1 from the nucleus to the cytoplasm. We treated RPMI8226 (IC50=150nM) and MM1S (IC50=25nM) human myeloma cell lines with Selinexor at IC50 and examined nuclear vs cytoplasmic expression of E2F1 after 24 and 48 hours by western blotting. Our results demonstrated nuclear retention of E2F1 following treatment of HMCLs with Selinexor and suggest a model where overexpression of E2F1 overwhelms the nuclear export mechanism and may result in downstream gene programming that confers a proliferative advantage in cells, manifested by rapid progression ( Our findings suggest a model where E2F1 expression may be a biomarker of Selinexor resistance. We are currently validating our findings in additional samples from patients with MM treated with Selinexor. Disclosures Crochiere: Karyopharm Therapeutics Inc: Employment. Landesman:Karyopharm Therapeutics Inc: Employment. Chari:Adaptive Biotechnology: Membership on an entity's Board of Directors or advisory committees; Array Biopharma: Research Funding; Bristol Myers Squibb: Consultancy; Pharmacyclics: Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; The Binding Site: Consultancy; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Cho:Janssen: Consultancy; Genentech Inc: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; J & J: Consultancy; Agenus Inc.: Research Funding; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees. Barlogie:Myeloma Health, LLC: Patents & Royalties: : Co-inventor of patents and patent applications related to use of GEP in cancer medicine licensed to Myeloma Health, LLC; European School of Haematology- International Conference on Multiple Myeloma: Other: travel stipend; Millenium: Consultancy, Research Funding; Dana Farber Cancer Institute: Other: travel stipend; International Workshop on Waldenström's Macroglobulinemia: Other: travel stipend; Celgene: Consultancy, Research Funding; Multiple Myeloma Research Foundation: Other: travel stipend; ComtecMed- World Congress on Controversies in Hematology: Other: travel stipend. Jagannath:Multiple Myeloma Research Foundation: Speakers Bureau; Merck: Consultancy; Novartis: Consultancy; Bristol-Myers Squibb: Consultancy; Celgene: Consultancy; Medicom: Speakers Bureau.

The quantification of Target Occupancy (TO) in cells after application of an inhibitor is an important parameter to correlate the biochemical features of a drug with its in vivo efficacy. Experimental evidence of TO is a robust support of the target hypothesis and helps to identify optimal dosing of the drug. The sensitive correlation spectroscopy methods (FCS and FCCS) have been used successfully in the past to analyze drug- target interactions. The technology is fast, specific and allows detection of drug target interactions in smallest sample volumes. Here we adopted the FCCS method to quantify the occupancy of the XPO1 target in cells and tumors treated with the Selective Inhibitor of Nuclear Export (SINE) compound Selinexor (KPT-330), currently in advanced clinical trials in patients with hematological and solid cancers. We used a fluorescently labeled tracer (Leptomycin B -Cy5; LMB-Cy5) to quantify the loading of XPO1 with Selinexor and confirmed target specificity of the signal using a fluorescent labeled antibody detecting native XPO1 protein. The amount of Antibody-XPO1-tracer complex was determined by FCCS. Occupancy of XPO1 target with Selinexor decreases the amount of tracer-target complexes in a dose and time dependent manner. Target occupancy studies of XPO1 were carried out in different cancer relevant cell lines and xenograft tumors retrieved from treated animals. As such the approach can be applied to study target occupancy in vitro and in vivo. Citation Format: Frank Becker, Kerrin Hansen, Marsha Crochiere, Yosef Landesmann, Stefan Hannus. Application of Fluorescence Correlation Spectroscopy as a novel tool to quantify target occupancy in cells and tumor tissue [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B09.

Selective Inhibitor of Nuclear Export (SINE) compounds are a family of small-molecules that inhibit nuclear export through covalent binding to cysteine 528 (Cys528) in the cargo-binding pocket of Exportin 1 (XPO1/CRM1) and promote cancer cell death. Selinexor is the lead SINE compound currently in phase I and II clinical trials for advanced solid and hematological malignancies. In an effort to understand selinexor-XPO1 interaction and to establish whether cancer cell response is a function of drug-target engagement, we developed a quantitative XPO1 occupancy assay. Biotinylated leptomycin B (b-LMB) was utilized as a tool compound to measure SINE-free XPO1. Binding to XPO1 was quantitated from SINE compound treated adherent and suspension cells in vitro, dosed ex vivo human peripheral blood mononuclear cells (PBMCs), and PBMCs from mice dosed orally with drug in vivo. Evaluation of a panel of selinexor sensitive and resistant cell lines revealed that resistance was not attributed to XPO1 occupancy by selinexor. Administration of a single dose of selinexor bound XPO1 for minimally 72 hours both in vitro and in vivo. While XPO1 inhibition directly correlates with selinexor pharmacokinetics, the biological outcome of this inhibition depends on modulation of pathways downstream of XPO1, which ultimately determines cancer cell responsiveness.

Pancreatic cancer is an aggressive and deadly malignancy responsible for the death of over 37,000 Americans each year. Gemcitabine-based therapy is the standard treatment for pancreatic cancer but has limited efficacy due to chemoresistance. In this study, we evaluated the in vitro and in vivo effects of gemcitabine combined with the selective nuclear export (CRM1) inhibitor KPT-330 on pancreatic cancer growth. Human pancreatic cancer MiaPaCa-2 and metastatic pancreatic cancer L3.6pl cell lines were treated with different concentrations of KPT-330 and gemcitabine alone or in combination, and anchorage–dependent/independent growth was recorded. In addition, L3.6pl cells with luciferase were injected orthotopically into the pancreas of athymic nude mice, which were treated with (i) vehicle (PBS 1 mL/kg i.p., 2/week and povidone/pluronic F68 1 mL/kg p.o., 3/week), (ii) KPT-330 (20 mg/kg p.o., 3/week), (iii) gemcitabine (100 mg/kg i.p., 2/week), or (iv) KPT-330 (10 mg/kg) + gemcitabine (50 mg/kg) for 4 weeks. KPT-330 and gemcitabine alone dose-dependently inhibited anchorage-dependent growth in vitro and tumor volume in vivo compared with vehicle treatment. However, the combination inhibited growth synergistically. In combination, KPT-330 and gemcitabine acted synergistically to enhance pancreatic cancer cell death greater than each single-agent therapy. Mechanistically, KPT-330 and gemcitabine promoted apoptosis, induced p27, depleted survivin, and inhibited accumulation of DNA repair proteins. Together, our data suggest that KPT-330 potentiates the antitumor activity of gemcitabine in human pancreatic cancer through inhibition of tumor growth, depletion of the antiapoptotic proteins, and induction of apoptosis. Mol Cancer Ther; 14(7); 1570–81. ©2015 AACR.

Introduction: Selective Inhibitor of Nuclear Export (SINE) compounds are a new class of oral anti-cancers drugs that block nuclear export by inhibiting the exportin XPO1 (also known as CRM1). The most advanced compounds in this class are selinexor and KPT-8602, which are being evaluated in clinical trials for the treatment of hematological malignancies (clinicaltrials.gov). XPO1 is commonly overexpressed in cancer and high levels of XPO1 are correlated with poor prognosis. Based on Phase I efficacy and safety studies, the recommended Phase 2 dose (RP2D) of selinexor is 60 mg twice weekly on days 1 and 3. We have previously reported the development of a pharmacodynamics (PD) assay to measure XPO1 target occupancy by selinexor in cancer cells based on Fluorescence Cross Correlation Spectroscopy (FCCS). Here we report proof of concept studies to determine the level of XPO1 occupancy associated with the selinexor RP2D regimen. Methods: Z138 cells in culture were treated with 1 µM selinexor either continuously for up to 32 hours or for 6 hours followed by drug removal and culture for up to 72 hours post-wash out. Cell were treated in culture for 4 hours with either 0-10 µM selinexor, KPT-8602, or Leptomycin B (LMB). Cells were harvested, lysed, and cleared by ultracentrifugation. Total protein was measured from lysates for Western blot with α-XPO1, α-GAPDH, and α-β-tubulin and for FCCS analysis. In vivo, nude mice were inoculated in both flanks with Z138 cells. Once tumors reached approximately 250 mm3, mice were administered a single dose of 0, 5, 10, 15, or 20 mg/kg selinexor. Tumors were harvested at 6, 24, 48, 72, and 96 hours post-dose, lysed, and cleared by ultracentrifugation. Cell line or tumor supernatants were incubated with a fluorescently labeled antibody (Ab) recognizing XPO1 and fluorescently labeled LMB. To allow binding of labeled Ab and LMB to XPO1, samples were measured by FCCS after 15, 120, and 1200 minutes. Results: XPO1 protein dynamics were evaluated in Z138 cells treated with selinexor either continuously or after drug removal. Selinexor treatment resulted in the reduction of XPO1 protein by 26% as early as 4 hours of treatment and reduced XPO1 levels by 93% with continuous drug exposure up to 32 hours. However, cells treated with selinexor for only 6 hours followed by drug washout showed nearly full restoration of XPO1 expression by 72 hours, indicating that continuous presence of drug is required to sustain reduced XPO1 protein levels. Measurements by FCCS showed that brief exposure to selinexor (6 hours) resulted in rapid XPO1 occupancy, and drug washout resulted in sustained occupancy that was not relieved until 72 hours post-selinexor wash out. To determine whether the second generation SINE compound clinical candidate, KPT-8602, had a similar XPO1 occupancy profile as selinexor, a panel of hematologic cell lines were treated with either compound and analyzed by FCCS. FCCS was also measured from cells treated with LMB, a natural product inhibitor of XPO1. FCCS analysis confirmed that KPT-8602 treatment resulted in a dose-dependent increase in drug-target occupancy with increasing drug concentration similar to that of selinexor, while LMB showed complete occupancy at very low levels of compound. Lastly, to confirm the level of target engagement in the RP2D regimen for selinexor, drug-target occupancy was measured in Z138 xenograft tumors from mice treated with a single oral dose of 0, 5, 10, 15, or 20 mg/kg selinexor. Tumors were collected at 6, 24, 48, 72, and 96 hours post-single dose. The FCCS results showed that full occupancy occurred by 6 hours at all doses, but the duration of occupancy was dose-dependent. XPO1 occupancy was relieved by 24 hours at 5 and 10 mg/kg, 48 hours at 15 mg/kg, and 72 hours at 20 mg/kg selinexor. This finding supports the RP2D dosing regimen, where 10-15 mg/kg in mice (approximately equivalent to 50-75 mg flat dose in humans) is necessary to maintain XPO1 occupancy for up to 48 hours post-dose, thus requiring the twice weekly dosing for continuous target occupancy. Conclusions: Using an FCCS based PD assay developed to measure the dynamics of XPO1 target occupancy by selinexor, our studies support the selinexor RP2D dosing regimen for patients with heavily pretreated hematologic and solid tumors. Future studies are planned to measure XPO1 occupancy in CD138+ cells isolated from patients with advanced multiple myeloma following treatment with selinexor or KPT-8602. Disclosures Crochiere: Karyopharm Therapeutics Inc: Employment, Other: stockholder. Hannus:Intana Bioscience GmbH: Consultancy. Hansen:Intanat Bioscience GmbH: Consultancy. Becker:Intana Bioscience GmbH: Consultancy. Baloglu:Karyopharm Therapeutics Inc: Employment, Other: stockholder. Kauffman:Karyopharm Therapeutics Inc: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Landesman:Karyopharm Therapeutics Inc: Employment, Other: stockholder.

Introduction: Selinexor, a Selective Inhibitor of Nuclear Export (SINE) compound, is an anti-cancer drug that is currently being evaluated in Phase I and II clinical trials for the treatment of solid and hematological malignancies (clinicaltrials.gov). XPO1 (exportin 1/CRM1), the target of selinexor, is commonly overexpressed in cancer. XPO1 is the main nuclear export protein with over 200 different protein cargos which include tumor suppressor and growth regulatory proteins. Binding of selinexor to XPO1 inhibits the nuclear export of TSPs and GRPs and induces cell cycle arrest followed by cancer cell apoptosis.Certain cancers are more sensitive to selinexor than others. We hypothesized that part of the inherent differences in sensitivities are attributed to different levels of target inactivation upon selinexor binding. To predict patient response to treatment, we developed a binding assay based on Fluorescence Cross Correlation Spectroscopy (FCCS) to measure XPO1 target occupancy in cancer cells. Methods: Cells were treated in culture for 4 hours with 0-10 µM selinexor. Cells were harvested, lysed, and cleared by ultracentrifugation. In vivo, nude mice were inoculated in both flanks with Z-138 tumor cells. Once tumors reached approximately 250 mm3, mice were administered a single dose of 0, 5, 10, 15, or 20 mg/kg selinexor. Tumors were harvested 6 hours post-dose, lysed, and cleared by ultracentrifugation. Cell or tumor supernatants were incubated with a fluorescently labeled antibody (Ab) against XPO1 and fluorescently labeled Leptomycin B (LMB). To allow binding of labeled Ab and LMB to XPO1, samples were measured by FCCS after 15, 120, and 1200 minutes. FCCS measures signal fluctuations induced by fluorescent molecules diffusing through an illuminated microscopic detection spot. The approach allows simultaneous monitoring of 2 different fluorescently labeled molecules and extracts information on particle concentration, size, binding state, and molecular brightness. Interacting particles are scored by codiffusion. FCCS measurements were performed to quantify the concentration of dually labeled XPO1 molecules in prepared lysates. In the absence of selinexor, complexes of XPO1, the labeled antibody (aXPO1ABATTO488), and the red labeled LMB (LMBDY647) are formed and indicate low target occupancy. XPO1 molecules occupied by selinexor cannot bind to the labeled tracer and decrease the number of dually labeled particles. Accordingly, loss of complex formation is a measure of target occupancy in cells and tumor samples. Results: Comparison of cytotoxicity and XPO1 binding in hematological cell lines treated with increasing concentrations of selinexor in vitro indicated that XPO1 occupancy by selinexor occurred to the same extent regardless of drug sensitivity (Table 1). However, there were two observations that distinguished the selinexor-resistant cell line THP-1 from the other 3 sensitive cell lines (Table 1): 1. Untreated THP-1 cells had the highest XPO1 occupancy of fluorescently labeled LMB compared to lower values in more sensitive cells, and 2. Treatment of THP-1 cells with very low dose selinexor (10 nM) demonstrated lower saturation of XPO1 protein, while treatment of MV-4-11, Z-138, and MM.1S with 10 nM selinexor resulted in marked XPO1 occupancy. These results suggest that high levels of XPO1 proteins might lead to resistance to XPO1 inhibition. We are currently testing whether these two observations are general predictors of resistance in other cell lines. Mouse studies showed that XPO1 target occupancy could be measured in tumors and that there was a dose-dependent effect of selinexor on complex formation with >90% target saturation at 10 mg/kg selinexor (estimated Cmax ~2400 ng/ml). Conclusions: For the first time, the FCCS method permits the direct measurement XPO1 occupancy by selinexor in cells and tumors following treatment. Here, we demonstrate XPO1 occupancy saturation at 10 mg/kg (30 mg/m2) in mice, a dose active against xenografts, and consistent with doses of selinexor that show anti-cancer activity in patients with heavily pretreated hematologic and solid tumors. Table 1. Cytotoxicity and FCCS values for cell lines. Cell Line MTT IC50 (nM) FCCS IC50 (nM) FCCS Complex without selinexor (nM) FCCS Complex with 10 nM selinexor (nM) THP-1 1060 35.5 3.95 3.19 MV-4-11 20 56.2 2.55 1.9 Z-138 40 24.0 0.72 0.66 MM.1S 20 20.4 2.25 1.64 Disclosures Crochiere: Karyopharm: Employment. Hannus:Intana: Employment. Hansen:Intana: Employment. Becker:Intana: Employment. Ellis:Karyopharm Therapeutics Inc: Employment. Lee:Karyopharm Therapeutics Inc: Employment. Landesman:Karyopharm: Employment.

Exportin-1 (XPO1) is a nuclear export protein with >220 cargo proteins, including tumor suppressors and cell cycle modulators. Selinexor is a SINE (Selective Inhibitor of Nuclear Export) compound that has been administered to >900 cancer patients in Phase I and II trials to date, with evidence of efficacy and tolerability. Selinexor blocks nuclear export of NFAT1c, STAT1 and STAT3, which are implicated in regulating the inhibitory T cell receptor PD-1 and its ligand, PD-L1. We hypothesized that selinexor would upregulate T cell checkpoint molecule expression, and that combination treatment with anti-PD-1 or anti-PD-L1 would thereby enhance the ability of selinexor to elicit antitumor activity. Selinexor increased PD-1 gene expression by ~2-fold in normal lymphocytes and induced PD-L1 gene expression in tumor cell lines. Mice bearing syngeneic colon tumors (colon26) treated with selinexor and anti-PD-1 for 2 weeks demonstrated a significant reduction in tumor growth rate (P < 0.05), while monotherapy with either agent had no significant effect on tumor growth. Similar results were obtained in mice bearing syngeneic B16F10 melanoma tumors, whereby combined treatment with selinexor + anti-PD-1 was superior to either single agent alone (p < 0.034). Combined therapy of mice bearing B16F10 tumors with selinexor and anti-PD-L1 was similarly effective, with significantly smaller tumors at the study endpoint (p < 0.001). No weight loss or signs of toxicity were evident in any in vivo study. Immunophenotypic analysis by flow cytometry revealed that selinexor alone or in combination with anti-PD-1/anti-PD-L1 significantly increased the percentage of splenic NK cells (p≤0.050), while selinexor ± anti-PD-L1 significantly increased the percentage of splenic Th1 T cells (p≤0.011), all compared to vehicle treated mice. Interestingly, combining selinexor with anti-PD-L1 significantly decreased the percentage of splenocytes that expressed PD-L1 (p < 0.001). These data indicate that the efficacy of selinexor may be enhanced by disrupting the pre-existing PD-1/PD-L1 signaling in effector cells (T and NK cells). Altogether, these data suggest that the efficacy of selinexor in combination with anti-PD-1 or anti PD L1 in mouse syngeneic tumor models may be due to both disrupting immunosuppressive PD-1/PD-L1 signaling and increasing the frequency of potentially tumor reactive NK cells and Th1 T cells. This provides a rational basis for this treatment combination as a novel therapeutic approach for advanced cancer.

Background: The primary nuclear export protein, Exportin 1 (XPO1/CRM1), is overexpressed in most cancers, which is frequently correlated with poor prognosis. SINE compounds are small-molecule bioavailable drugs that bind covalently to XPO1, which leads to nuclear retention of major tumor suppressor proteins, such as p53, FOXO and IκB, resulting in selective cancer cell death. Selinexor is the most advanced SINE with >500 hematological and solid tumor cancer patients treated to date in Phase I/II clinical trials. Glucocorticoid Receptor (GR) is an XPO1 cargo and dexamethasone (Dex) acts through GR agonism and inhibition of NF-κB activity. The combination of selinexor with Dex seems likely to have enhanced anti-tumor potency and this hypothesis was tested in multiple myeloma models. Methods: Total RNA and whole protein cell lysates from multiple myeloma cell line (MM1S) treated with selinexor with or without dexamethasone were analyzed by quantitative PCR and by immunoblots. Localization of GR was evaluated by immunofluorescence. GR and NF-κB transcriptional activity was analyzed using ELISA assays. MM1S xenograft model in NOD-SCID mice were treated with selinexor with or without dexamethasone to evaluate the effect on tumor growth. Results: In MM.1S cells, we found Dex, but not selinexor, induced phosphorylation of GR resulting in GR nuclear localization. Selinexor prevented nuclear export of phosphorylated GR, leading to the synergistic induction of GR-dependent transcriptional activity. RNA levels of GR regulated genes such as MNK2 were induced by this combination treatment. Interestingly, between the two MNK2 isomers, the combination treatment increased the expression of MNK2α, which is a tumor suppressor protein but not the MNK2β isoform. NF-κB transcriptional activity was inhibited additively by this treatment in MM1S cells. The combination treatment of suboptimal doses of selinexor (5 mg/kg; 60% TGI) and Dex (1 mg/kg; 47% TGI) led to nearly complete growth suppression (91% TGI) in the MM1.S multiple myeloma xenografts. Conclusions: We confirmed the hypothesized synergistic anti-tumor activity for the combination of selinexor with dexamethasone and provided evidence that this synergy is mediated through enhanced GR transcriptional activity, inhibition NF-κB and upregulation of the tumor suppressor MNK2α. This work provides a rationale basis for conducting clinical trials of combinations of selinexor with dexamethasone against cancers known to be sensitive to dexamethasone, such as multiple myeloma. Promising anti tumor activity for the combination of selinexor and dexamethasone in patients with relapsed/refractory MM was reported in the ongoing Phase 1 study (NCT01607892). Citation Format: Yosef Landesman, Trinayan Kashyap, Boris Klebanov, Sivan Elloul, Marsha Crochiere, Sharon Friedlander, William Senapedis, Robert Carlson, Michael Kauffman, Sharon Shacham. Selective inhibitor of nuclear export (SINE) compounds show synergistic anti-tumor activity in combination with dexamethasone in multiple myeloma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2074. doi:10.1158/1538-7445.AM2015-2074

Human Exportin-1 (XPO1) is the key nuclear-cytoplasmic transport protein that exports a variety of different cargo proteins out of the cell's nucleus. Inhibition of XPO1-mediated protein export results in nuclear retention of cargo proteins including tumour suppressor proteins and is a novel therapeutic strategy for cancer. Selinexor, an orally bioavailable XPO1 inhibitor, effectively demonstrates potent activity against multiple types of cancer. Here we directly demonstrate the high selectivity of selinexor for XPO1 inside living cells. Selinexor binds to the cargo-binding pocket of XPO1 and inhibits the formation of XPO1-cargo complex. The binding of selinexor to XPO1 involves a slowly reversible Michael addition type interaction of its acrylate moiety with cysteine 528 residue of XPO1. Using CRISPR/Cas9 genome editing we have now created a homozygous Jurkat T-ALL cell line carrying a Cys528Ser mutation in XPO1. This cell line was used to study the specificity of selinexor for XPO1 inside the cancer cell. Selinexor was highly toxic to wild-type Jurkat cells in the low nanomolar range while the mutant cells were resistant up to micromolar concentrations. These results were confirmed by resistance to induction of caspase dependent apoptosis as well as cell cycle arrest in mutant cells. The single Cys528Ser mutation thus confers resistance to selinexor. In addition, selinexor failed to accumulate cargo proteins in the nucleus of mutant cells. Moreover, the Cys528Ser substitution conferred resistance to the direct interaction of this drug to XPO1 in cells. In conclusion, these results validate XPO1 as the selinexor's prime target and pinpoint its unique selectivity to the Cys528 residue of XPO1. Our findings also demonstrate the general utility of CRISPR/Cas9 genome editing for introducing point mutations in the genome of cancer cells for drug-target specificity validation. Citation Format: Jasper E. Neggers, Thomas Vercruysse, Maarten Jacquemyn, Els Vanstreels, Erkan Baloglu, Sharon Shacham, Marsha Crochiere, William Senapedis, Yosef Landesman, Dirk Daelemans. XPO1 is selinexor prime target: validation by mutating cysteine 528 on both XPO1 alleles using CRISPR/Cas9 genome editing. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2442. doi:10.1158/1538-7445.AM2015-2442

Background: The primary nuclear export protein, Exportin 1 (XPO1/CRM1) is overexpressed in most cancers, which frequently correlates with poor prognosis. SINE compounds are a family of small-molecule bioavailable drugs that bind covalently to XPO1 leading to nuclear retention of major tumor suppressor proteins such as p53 and IκB, resulting in selective tumor cell death. Selinexor is the most advanced SINE with >500 hematological and solid tumor cancer patients treated to date in Phase I/II clinical trials. Here we investigated the role of NF-κB transcriptional deactivation in SINE induced anti tumor activity by nuclear retention of IκB. We report the results of combining selinexor or related SINE compounds with proteasome inhibitors, for which inhibition of NF-κB has also been shown to be an important mechanism for cancer cell killing. Methods: Whole protein cell lysates from solid and hematological cancer cell lines treated with selinexor with or without proteasome inhibitors were analyzed by immunoblots. IκB localization was evaluated by immunofluorescence. Cytotoxic effects of SINE compounds were evaluated in the presence or absence of proteasome inhibitors. NF-κB transcriptional activity was analyzed using an ELISA assay. H929 multiple myeloma xenografts in NOD-SCID mice were treated with selinexor alone or in combination with carfilzomib to determine effects on tumor growth. Results: NF-κB transcriptional activity was upregulated in SINE resistant sarcoma cell lines HT1080R (IC50 = 2.4 μM versus HT1080 parental IC50 = 0.03 μM) and ASPS-KY (IC50>10μM). In those resistant lines, combination of the proteasome inhibitors bortezomib or carfilzomib with SINE compound showed dramatic synergistic cytotoxic potency of more than 10 folds. Also, the combination of bortezomib with selinexor led to synergistic nuclear retention of IκB. Furthermore, IκB silencing by siRNA led to reduced selinexor cytotoxic potency, increasing IC50 from 58 nM to 830 nM (9-fold) in IM-9 multiple myeloma cells and from 27 nM to 1.9 μM (66-fold) in U2OS osteosarcoma cells. Finally, the combination of selinexor with carfilzomib was synergistic in reducing tumor growth in the H929 multiple myeloma xenograft model. Conclusion: Inhibition of NF-κB transcriptional activity through forced nuclear retention of IκB appears to be an important mechanism in the selective tumor cell cytotoxicity of selinexor and related SINE compounds. Furthermore, the combination of selinexor and proteasome inhibitors, which are also known to act at least in part through inhibition of NF-κB, leads to synergistic activity in vitro and in vivo, suggesting that such combinations may provide clinically more effective than the single agents. A Phase 1 trial to study the safety and efficacy of selinexor in combination with carfilzomib in multiple myeloma is ongoing (NCT02199665). Citation Format: Yosef Landesman, Trinayan Kashyap, Marsha Crochiere, Boris Klebanov, Sharon Friedlander, William Senapedis, Robert Carlson, Michael Kauffman, Sharon Shacham. Selinexor, a selective inhibitor of nuclear export (SINE), acts through NF-κB deactivation and combines with proteasome inhibitors to synergistically induce tumor cell death. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5472. doi:10.1158/1538-7445.AM2015-5472

Introduction: Many hematological cancers have been successfully treated through identification of specialized targets in each specific tumor subtype (e.g. BTK inhibition in NHL or proteasome inhibition in multiple myeloma). The p21-Activated Kinase 4 (PAK4) is critical to cellular signaling and may represent a new target for therapy in many hematologic malignancies. PAK4 is a member of the PAK family of proteins that regulate cell survival, cell division and apoptosis. The six members of the PAK family are divided into two groups; Group I (PAK1, 2, 3) and Group II (PAK4, 5, 6), based upon their sequence homology and regulatory mechanisms. PAK4 is a member of the group II family of PAKs and is amplified or mutated in many cancer types. PAK4 is also a key downstream effector of the K-Ras pathway. Methods: Flow cytometry and CellTiter AQueous One (MTS) assays were used to determine compound effects on cell cycle distribution, proliferation and viability. Immunoblots were used to measure effects of compounds on protein steady state levels and phosphorylation. The T-cell ALL cell line, MOLT-4, and the mantle cell lymphoma cell line, Z-138, were used in xenograft models in mice to test the in vivo efficacy of these compounds. Results: We have identified selective, orally bioavailable, small molecule PAK4 allosteric modulators {PAMs; e.g. KPT-8752 (mw: 585.6), KPT-9274 (mw: 610.6), and KPT-9331 (mw: 628.6)} which demonstrated selective anti-tumor activity in a variety of hematological cancer cell lines (IC50 values = 0.005 – 1 mM). Treatment of cancer cells with these small molecules resulted in the reduction of PAK4 steady state levels and reduced phosphorylation of key growth signaling proteins such as Akt, β-catenin, cofilin, p21, and cyclin D1. There was a measurable increase in phospho-AMPK indicative of autophagy and stress. These allosteric modulators induced apoptosis through the activation of caspases 3 and 8 and subsequent cleavage of PARP. In MOLT-4 and Z-138 xenograft mouse models, daily treatment with oral PAMs resulted in near elimination of small (100 mm3) and large (800 mm3) tumors in the absence of any clinical signs of toxicity within the animals. Additional cell line and primary tumor models are currently being explored. Conclusions: PAK4 represents a novel anti-cancer target as a major downstream effector of the Ras oncogene. We have identified selective, orally-bioavailable small molecule PAK4 allosteric modulators which induce potent cytotoxicity in multiple leukemia and lymphoma cell lines with minimal toxicity to normal cell in vitro and clear anti-tumor activity with excellent tolerability in in vivo models of hematological cancers. These compounds inactivate PAK4 by directly inducing PAK4 destabilization. This represents a novel mechanism of the protein kinase inactivation involving degradation of PAK4 rather than direct inhibition of the kinase activity. Based on the in vitro and in vivo activity, these PAK4 allosteric modulators show promising results for the treatment of a wide variety of hematological cancers. Disclosures Senapedis: Karyopharm: Employment. George:Karyopharm: Employment. McCauley:Karyopharm Therapeutics: Employment, Equity Ownership. Ellis:Karyopharm: Employment. Crochiere:Karyopharm: Employment. Savona:Karyopharm: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees. Shacham:Karyopharm Therapeutics: Employment. Landesman:Karyopharm Therapeutics: Employment. Baloglu:Karyopharm: Employment.

Introduction: SINE are a family of small molecules that selectively inhibit nuclear export by forming a slowly reversible covalent bond with Cysteine 528 (Cys528) in the cargo binding pocket of Exportin 1 (XPO1/CRM1). SINE binding to XPO1 leads to forced nuclear retention and activation of major tumor suppressor proteins (TSPs) such as p53, FOXO, pRB and IkB, resulting in selective death of cancer cells. Selinexor is an orally bioavailable SINE compound currently in human phase I and II clinical trials for advanced hematological and solid cancers. Oral selinexor demonstrates maximal pharmacokinetic exposure at 1-2 hours in humans with associated increases in pharmacodynamic markers of XPO1 inhibition in 2-4 hours that last for up to 48 hours. The goal of this study was to develop a binding assay that would enable quantification of XPO1 occupancy in PBMCs from patients following oral administration of selinexor. Methods: To measure the binding of SINE to XPO1, biotinylated leptomycin B (LMB) was utilized. Biotinylated LMB binds covalently and irreversibly to Cys528 in the cargo-binding site of free XPO1 with activity confirmed to be similar to that of unmodified LMB in cytotoxicity assays. To measure SINE binding to XPO1 in vitro, cancer cell lines and PBMCs from normal human donors were treated with SINE compounds prior to treatment with biotinylated LMB. Any XPO1 that did not bind SINE instead binds to biotinylated LMB and can be quantified. In in vivo studies, mice were treated with selinexor, followed by collection of PBMCs for treatment with biotinylated LMB. After incubation with biotinylated LMB, cells were harvested, lysed, and protein lysates were subjected to pull-down experiments with streptavidin-conjugated beads followed by immunoanalysis of XPO1. Results: To evaluate selinexor-XPO1 binding kinetics in vitro, MM.1S, AML2, AML3, and HEL cells were treated with 0 - 10 µM of SINE compounds and unbound XPO1 was pulled down from cell lysates treated with biotinylated LMB. Immunoanalysis showed that 50% XPO1 occupancy with selinexor was achieved at 0.07 µM in MM.1S, 0.1 µM in AML2, 0.03 µM in AML3, and 0.12 µM in HEL cells. Selinexor-XPO1 occupancy experiments using human PBMCs isolated from donor whole blood showed 50% XPO1 occupancy at 0.05 µM. In mice, 50% XPO1 occupancy in PMBCs was achieved after 4 hours treatment with 1.2 mg/kg (3.6 mg/m2) selinexor, while 90% XPO1 occupancy was achieved at 8.1 mg/kg (24.3 mg/m2). Mice treated with a single dose of selinexor from 1.5 to 10 mg/kg for 4-96 hours revealed sustained, dose dependent XPO1 occupancy in PBMCs for up to 72 hours. Conclusions: We have developed a sensitive and robust assay to measure selinexor binding to XPO1 that can be used to evaluate drug exposure following treatment with oral selinexor in preclinical and clinical studies. Studies are ongoing to determine whether there is a correlation between XPO1 occupancy (pharmacodynamics measurement) with disease response in patients with solid and hematological malignancies. Disclosures Crochiere: Karyopharm: Employment. Klebanov:Karyopharm Therpeutics: Employment. Baloglu:Karyopharm: Employment. Kalid:Karyopharm Therapeutics: Employment. Kashyap:Karyopharm Therapeutics: Employment. Senapedis:Karyopharm: Employment. del Alamo:Karyopharm: Employment. Rashal:Karyopharm Therapeutics: Employment. Tamir:Karyopharm: Employment. McCauley:Karyopharm Therapeutics: Employment, Equity Ownership. Carlson:Karyopharm Therapeutics: Employment. Savona:Karyopharm: Consultancy, Equity Ownership; Gilead: Consultancy; Incyte: Consultancy; Celgene: Consultancy. Kauffman:Karyopharm Therapeutics, Inc: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Shacham:Karyopharm Therapeutics, Inc: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Landesman:Karyopharm Therapeutics: Employment.

Conclusions: These studies reveal no evidence for an allosteric trapping mechanism and indicate that all PARP inhibitors examined trap PARP1 via catalytic inhibition. The potency of PARP inhibitors with respect to trapping and catalytic inhibition is linearly correlated in biochemical systems. In cells, trapping potency is related to concentrations required for potentiation in animal models. Detection of PARP trapping in cells requires supraphysiologic conditions that exhaust cellular NAD and PAR, exceed concentrations required to elicit synergism and are not tolerated in vivo. In addition trapping potency appears to be inversely correlated with tolerability. Quantitation of the degree of trapping that is tolerable and is required for therapeutic benefit is under active investigation. Disclosures: All authors are employees of AbbVie. The design, study conduct, and financial support for this research were provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the publication.

Chromosomal Region Maintenance Protein 1/Exportin 1 (CRM1/XPO1) is a key nuclear export protein whose inhibition leads to the nuclear accumulation of Tumor Suppressor Proteins (TSPs) and renders cancer cells susceptible to apoptosis. Selinexor is orally bioavailable and represents a novel class of small molecule compounds with potent activity against a wide variety of cancers. Selinexor is currently in Phase 1 clinical studies in hematological and solid cancer patients (Clinicaltrials.gov NCT01607892 and NCT01607905). We tested the activity of Selinexor in a soft tissue sarcoma – ASPS that is resistant to traditional chemotherapy and irradiation treatment. Here we report in vitro activity of Selinexor against ASPS and in vivo efficacy results in xenograft models. Methods We used MTT, FACS, qPCR, immunofluorescence, immunostaining and immunoblots to measure the in vitro and in vivo effects of KPT-330 on the ASPS-KY cell line and in xenograft models. Results The IC50 of the ASPS-KY cell line treated with Selinexor for 72 hours was 10 μM. This concentration induced nuclear accumulation of p53, p21, IκB and FOXO3A within 4 hours of treatment, and by 24 hours cells stopped DNA synthesis and were arrested at G1 phase of the cell cycle. By 72 hours, 25% of the cells died. Prior to cell death, the drug reduced the survival protein BCL2 as well as other pro-proliferative proteins such as CDK4, Cyclin D and E2F. In addition, Selinexor induced dephosphorylation of pRb activating its tumor suppressor activity and also induced Caspase 3/7 and PARP cleavage. To assess the in vivo activity of Selinexor in a xenograft model of ASPS, we treated mice with 10 or 20 mg/kg of KPT-330 using a 3 times weekly oral dosing schedule. Following a week of treatment, tumors showed accumulation of TSPs as well as significant reduction of the proliferation marker Ki-67. Following treatment with Selinexor for 40 days, tumor growth was inhibited by 70% at 10 mg/kg and by 80% at 20 mg/kg compared with vehicle treated animals. Analysis of immunoblots from these tumors showed induction of p21, with corresponding reduction of the pro-survival and proliferation markers c-Jun, c-Met, survivin, ERK and HSP70. Histological analysis revealed apoptosis and large areas of fibrosis in treated tumors. These results indicated that Selinexor not only inhibited tumor growth, but also induced ASPS cell death in vivo. Conclusions Our results demonstrated that Selinexor is effective against ASPS in vivo as a single agent and further support the development of SINE-based therapies for alveolar soft part sarcoma that has currently no cure. We will perform further studies to test Selinexor in drug combination studies to identify synergism with other therapies. Citation Format: Marsha L. Crochiere, Trinayan Kashyap, Boris Klebanov, William Senapedis, Diego del Alamo, Sharon Tamir, Erkan Baloglu, Dilara McCauley, Robert Carlson, Michael Kauffman, Sharon Shacham, George Demetri, Andrew Wagner, Ewa Sicinska, Prafulla Gokhale, Nancy Kohl, Amy Saur, Yosef Landesman. Selinexor (KPT-330), a novel selective inhibitor of nuclear export (SINE), shows single agent efficacy against alveolar soft part sarcoma (ASPS) in vivo. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3810. doi:10.1158/1538-7445.AM2014-3810

P21-Activated Kinase 4 (PAK4) is a member of the PAK family of proteins that regulate cell survival, cell division and apoptosis. The six members of the PAK family are divided into two groups; Group I (PAK1, 2, 3) and Group II (PAK4, 5, 6), based upon their sequence homology and regulatory mechanisms. PAK4 is a member of the group II family of PAKs and is amplified or mutated in many cancer types. PAK4 is also a key downstream effector of the K-Ras pathway. Methods: Flow cytometry, CellTiter AQueous One assay (MTS) and colony formation assays were used to determine compound effects on cell cycle distribution, proliferation and viability. Immunoblots were used to measure effects of compounds on protein steady state levels and phosphorylation. The breast cancer cell line, MDA-MB-468, and the mantle cell lymphoma line, Z-138, were used in xenograft models in mice to test the in vivo efficacy of these compounds. Results: We have identified selective, orally bioavailable small molecule PAK4 allosteric modulators, which demonstrated anti-tumor activity in a variety of cancer cell lines (IC50 values = 0.005 - 1 μM). Treatment of cancer cells with these small molecules resulted in the reduction of PAK4 steady state levels and reduced phosphorylation of key growth signaling proteins such as Akt, ERK1/2, p90RSK, β-catenin, cofilin, p21, and cyclin D1. These allosteric modulators induced apoptosis through the activation of caspases 3 and 8 and subsequent cleavage of PARP. After 48 hours of compound treatment, it was found that the cancer cells were arrested at the G1 and G2 phases of the cell cycle. In addition, we have observed anti-tumor activity against Z-138 and MDA-MB-468 xenografts in mice at a daily oral dose of 10 mg/kg in the absence of any clinical signs of toxicity up to 200 mg/kg daily dose. Conclusions: PAK4 represents a novel anti-cancer target as a major downstream effector of Ras oncogene. We have identified selective, orally-bioavailable small molecule PAK4 allosteric modulators with anti-tumor activity both in vitro and in vivo. These compounds inactivate PAK4 by directly inducing PAK4 destabilization. This represents a novel mechanism of the protein kinase inactivation involving degradation of PAK4 rather than direct inhibition of the kinase activity. Moreover, these allosteric modulators induce tumor cell growth arrest and apoptosis. Based on the in vitro and in vivo activity, these PAK4 allosteric modulators show promising results for the treatment of a wide variety of cancers. Citation Format: William Senapedis, Erkan Baloglu, Natalie Pursell, Marsha Crochiere, Dilara McCauley, Joel Ellis, Trinayan Kashyap, Boris Klebanov, Robert Carlson, Ori Kalid, Michael Kauffman, Sharon Shacham, Yosef Landesman. Novel selective orally bioavailable small molecule PAK4 allosteric modulators display antitumor activity and induce apoptosis in vitro and in vivo. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 748. doi:10.1158/1538-7445.AM2014-748

SINE (Selective Inhibitors of Nuclear Export) are novel small molecule drugs in phase I clinical trials for advanced cancers. SINEs inhibit nuclear export through covalent binding to Exportin 1 (XPO1/CRM1) leading to forced nuclear retention of major tumor suppressor proteins (TSPs) such as p53, FOXO, pRB and IkB, resulting in selective death of cancer cells. Resistant cells were created by treating the sensitive fibrosarcoma cell line HT1080 with increasing concentrations of SINE over 10 months. Gene chip analysis of parental-sensitive and drug-resistant cells treated with SINE demonstrated activation of distinct pathways that mediate either cell death or survival. In addition, SINE resistance was overcome by drug combination with proteasome inhibition. Methods: Resistant cells were generated with selection in increasing concentrations of SINE. Cell viability was assayed by MTT. Immunofluorescence was used to compare nuclear export of TSPs. FACS and immunoblots were used to measure effects on cell cycle, protein expression and cell death. RNA from nai[[Unable to Display Character: ̈]]ve and drug treated sensitive/resistant cells was analyzed by Affymetrix microarrays and qPCR. A drug combination study was performed to evaluate whether resistance to SINE could be overcome with proteasome inhibition. Results: Treatment of SINE-sensitive fibrosarcoma cell line HT1080 (IC50 = 13.6nM) with gradually increasing concentrations of SINE for 10 months resulted in > 100 fold decrease in sensitivity to SINE cytotoxicity (IC50 = 1.7μM). Resistant cells displayed prolonged cell cycle (∼72 vs 24 hrs) compared to parental cells. Resistant cells did not show increased MDR1 and MRP1 activity, suggesting that resistance to SINE was not mediated by induction of the multidrug resistance mechanism. Sequencing of XPO-1 from the SINE resistant cells revealed no mutations in the SINE / cargo binding pocket including the reactive Cys528. Upon exposure to SINE, resistant cells had reduced nuclear accumulation of p53, p21, FOXO1A, IkB, p27, and PP2A proteins compared with SINE-sensitive cells. SINE treatment of both sensitive and resistant cells resulted in pRB de-phosphorylation and induction of p53 and its downstream target p21. In addition, SINE treatment reduced the levels of the anti-apoptotic protein Mcl-1, and induced the apoptotic markers Caspase 3 and PARP cleavage. Microarray analysis revealed changes in cell survival and cell death pathways, which were confirmed by qPCR. In spite of the changes, resistant cells continue to show synergistic death effects induced by SINE in combination with proteasome inhibition. Conclusions: The extensive selection time (10 months) needed to achieve drug resistance suggests that generation of resistance may be difficult and that drug response may be prolonged. However such a resistance would be overcome by drug combination treatment. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A188. Citation Format: Marsha L. Crochiere, Trinayan Kashyap, Jean-Richard Saint-Martin, Sharon Shechter, Ori Kalid, Eran Shacham, William Senapedis, Boris Klebanov, Sharon Tamir, Diego del Alamo, Mwanasha Hamuza, Gali Golan, Erkan Baloglu, Dilara McCauley, Michael Kauffman, Sharon Shacham, Yosef Landesman. SINE resistant fibrosarcoma cells reveal changes in profile of gene expression, but continue to be sensitive to combination treatment by proteasome inhibition. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A188.

Abstract SINE are novel small molecules in human phase I clinical trials for advanced cancers. SINEs inhibit nuclear export through covalent binding to Exportin 1 (XPO1/CRM1) leading to forced nuclear retention of major tumor suppressor proteins (TSPs) such as p53, FOXO, PTEN, pRB and IKB, leading to selective death of cancer cells. Resistant cells were created by treating the sensitive fibrosarcoma cell line HT1080 with increasing concentrations of SINE over 12 months. Gene chip analysis of parental-sensitive and drug-resistant cells that were treated with SINE resulted in activation of distinct pathways that mediate mechanisms of response and drug resistance. Methods Resistant cells were generated by selection in increasing concentrations of SINE. Cell viability was assayed by MTT. Immunofluorescence was used to compare nuclear export of TSPs. FACS, qPCR and immunoblots were used to measure effects on cell cycle, gene expression and cell death. RNA from naïve and drug treated sensitive/resistant cells was analyzed by Affymetrix microarrays. Results Treatment of SINE-sensitive fibrosarcoma cell line HT1080 (IC50 = 13.6nM) with gradually increasing concentrations of SINE for ∼1 year resulted with > 100 fold decrease in sensitivity to SINE cytotoxicity (IC50 = 1.7μM). Resistant cells displayed prolonged cell cycle (∼72 vs 24hrs) compared to parental cells. Resistant cells did not show increased PgP activity, suggesting that resistance to SINE was not the result of the induction of the multidrug resistance mechanism. Sequencing of CRM1 from the SINE resistant cells revealed no mutations in the SINE / cargo binding pocket including the reactive Cys528. Upon exposure to SINE, resistant cells had reduced nuclear accumulation of p53, p21, FOXO1A, IKB and p27 compared with SINE-sensitive cells. Interestingly, in SINE-sensitive cells, but not in resistant cells, SINE treatment resulted in potent pRB dephosphorylation (growth suppressive form of pRB), nuclear localization and the activation of p53 as measured by the induction of p53-downstream targets p21 and MIC1 (GDF15). In addition, SINE reduced levels of the anti-apoptotic protein Mcl-1, and induced the apoptotic markers Caspase 3 and PARP cleavage in sensitive but not in SINE resistant cells. Genes involved in cell adhesion, cytoskeleton formation, tight junctions, vesicle transport, cell cycle, and apoptosis were identified as key pathways correlating with drug response and resistance. Conclusions This study identified key pathways and genes that are likely mediating response and resistance to SINE antagonists. The extensive selection time (∼1 year) needed to achieve drug resistance suggests that generation of resistance may be difficult and that drug response may be prolonged. Citation Format: Yosef Landesman, Sharon Shechter, Jean-Richard Saint-Martin, Trinayan Kashyap, Marsha Crochiere, William Senapedis, Paul Ippolitti, Boris Klebanov, Sharon Tamir, Diego del Alamo, Mwanasha Hamuza, Gali Golan, Ori Kalid, Erkan Baloglu, Dilara McCauley, Michael Kauffman, Sharon Shacham. Deciphering mechanisms of drug sensitivity and resistance to Selective Inhibitors of Nuclear Export (SINE). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 875. doi:10.1158/1538-7445.AM2013-875

Abstract Chromosomal Maintenance Protein 1/Exportin 1 (CRM1/XPO1) is a key nuclear export protein whose inhibition leads to the nuclear accumulation of Tumor Suppressor Proteins (TSPs) such as p53, FOXO, PTEN, pRB and I-κB. SINE are a novel class of compounds currently in clinical development for a variety of cancers. SINE irreversibly block CRM1-dependent nuclear export and force the nuclear retention of TSPs, inducing apoptosis in cancer cells. Here we report in vitro activity of SINE on a broad range of cancer cell lines and in vivo efficacy results in NCI-N87 gastric and HCT-116 colorectal carcinoma murine tumor xenograft models. Methods MTT cytotoxicity assays were used to determine IC50s of KPT-SINE on various cell lines. The effects of SINE on the cell cycle and gene expression were investigated by FACS and quantitative RT/PCR respectively. Inhibition of CRM1 nuclear export was determined by immunofluorescence of CRM1 cargos. The effects of SINE treatment on tumor growth in vivo were assessed by measuring tumor volumes and by imaging with FluoroThymidine Positron Emission Tomography (FLT-PET). In tumors, gene expression was analyzed and immunohistochemistry performed to detect TSP, proliferation and apoptosis markers. Results SINE showed potent cytotoxicity on the majority of the cell lines tested with IC50 values 80%. Treated tumor samples showed very low levels of Ki67 and increased TUNEL staining consistent with induction of cell cycle arrest and apoptosis in SINE-treated groups. Also, marked upregulation of the TSPs p53 and p21 was observed, indicating that SINE induced nuclear localization of these proteins in situ. In the NCI-N87 gastric carcinoma xenograft model, oral SINE treatment inhibited tumor growth >75% compared with vehicle- treated animals. Immunofluorescence analysis with biomarkers of proliferation, along with FLT-PET results, indicated significant inhibition of proliferation in tumors. Histological analysis of the tumors confirmed in vitro observations of cytotoxic effects on tumors, induction of apoptosis and the replacement of cancer cells with fibrotic tissue. Conclusions These studies demonstrate potent in vitro and in vivo efficacy of single agent SINE CRM1 inhibitors against NCI-N87 and HCT-116 xenografts. These data further support the development of SINE-based therapies for gastric and colorectal cancers. Citation Format: Dilara McCauley, Trinayan Kashyap, Mwanasha Hamuza, Yosef Landesman, Paul Ippolitti, Sharon Shechter, Jean Richard Saint-Martin, Marsha Crochiere, William Senapedis, Boris Klebanov, Sharon Tamir, Diego Del Alamo, Erkan Baloglu, Giulio Draetta, Michael Kauffman, Sharon Shacham. Selective inhibitors of nuclear export (SINE) display single agent efficacy against gastric (NCI-N87) and colon (HCT-116) xenografts. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4336. doi:10.1158/1538-7445.AM2013-4336

Background Exportin 1 (XPO1) is a well-characterized nuclear export protein whose expression is up-regulated in many types of cancers and functions to transport key tumor suppressor proteins (TSPs) from the nucleus. Karyopharm Therapeutics has developed a series of small-molecule Selective Inhibitor of Nuclear Export (SINE) compounds, which have been shown to block XPO1 function both in vitro and in vivo. The drug candidate, selinexor (KPT-330), is currently in Phase-II/IIb clinical trials for treatment of both hematologic and solid tumors. The present study sought to decipher the mechanisms that render cells either sensitive or resistant to treatment with SINE compounds, represented by KPT-185, an early analogue of KPT-330. Methods Using the human fibrosarcoma HT1080 cell line, resistance to SINE was acquired over a period of 10 months of constant incubation with increasing concentration of KPT-185. Cell viability was assayed by MTT. Immunofluorescence was used to compare nuclear export of TSPs. Fluorescence activated cell sorting (FACS), quantitative polymerase chain reaction (qPCR), and immunoblots were used to measure effects on cell cycle, gene expression, and cell death. RNA from naïve and drug treated parental and resistant cells was analyzed by Affymetrix microarrays. Results Treatment of HT1080 cells with gradually increasing concentrations of SINE resulted in > 100 fold decrease in sensitivity to SINE cytotoxicity. Resistant cells displayed prolonged cell cycle, reduced nuclear accumulation of TSPs, and similar changes in protein expression compared to parental cells, however the magnitude of the protein expression changes were more significant in parental cells. Microarray analyses comparing parental to resistant cells indicate that a number of key signaling pathways were altered in resistant cells including expression changes in genes involved in adhesion, apoptosis, and inflammation. While the patterns of changes in transcription following drug treatment are similar in parental and resistant cells, the extent of response was more robust in the parental cells. Conclusions These results suggest that SINE resistance is conferred by alterations in signaling pathways downstream of XPO1 inhibition. Modulation of these pathways could potentially overcome the resistance to nuclear export inhibitors. Electronic supplementary material The online version of this article (doi:10.1186/s12885-015-1790-z) contains supplementary material, which is available to authorized users.

SummaryValidation of drug-target interaction is essential in drug discovery and development. The ultimate proof for drug-target validation requires the introduction of mutations that confer resistance in cells, an approach that is not straightforward in mammalian cells. Using CRISPR/Cas9 genome editing, we show that a homozygous genomic C528S mutation in the XPO1 gene confers cells with resistance to selinexor (KPT-330). Selinexor is an orally bioavailable inhibitor of exportin-1 (CRM1/XPO1) with potent anticancer activity and is currently under evaluation in human clinical trials. Mutant cells were resistant to the induction of cytotoxicity, apoptosis, cell cycle arrest, and inhibition of XPO1 function, including direct binding of the drug to XPO1. These results validate XPO1 as the prime target of selinexor in cells and identify the selectivity of this drug toward the cysteine 528 residue of XPO1. Our findings demonstrate that CRISPR/Cas9 genome editing enables drug-target validation and drug-target selectivity studies in cancer cells.