Oral Selinexor as Maintenance Therapy After First-Line Chemotherapy for Advanced or Recurrent Endometrial Cancer

PURPOSE

Selinexor inhibits exportin-1 (XPO1) resulting in nuclear accumulation of tumor suppressor proteins including p53 and has clinical activity in endometrial cancer (EC). The primary end point was to assess progression-free survival (PFS) with once-weekly oral selinexor in patients with advanced or recurrent EC.

PATIENTS AND METHODS

ENGOT-EN5/GOG-3055/SIENDO was a randomized, prospective, multicenter, double-blind, placebo-controlled, phase III study at 107 sites in 10 countries. Patients 18 years or older with histologically confirmed EC were enrolled. All had completed a single line of at least 12 weeks of taxane-platinum combination chemotherapy and achieved partial or complete response. Patients were assigned to receive 80 mg oral selinexor once weekly or placebo with 2:1 random assignment (ClinicalTrials.gov identifier: NCT03555422).

RESULTS

Between January 2018 and December 2021, 263 patients were randomly assigned, with 174 allocated to selinexor and 89 to placebo. The median PFS was 5.7 months (95% CI, 3.81 to 9.20) with selinexor versus 3.8 months (95% CI, 3.68 to 7.39) with placebo (hazard ratio [HR], 0.76 [95% CI, 0.54 to 1.08]; two-sided P = .126), which did not meet the criteria for statistical significance in the intent-to-treat population. Incorrect chemotherapy response stratification data for 7 (2.7%) patients were identified. In a prespecified exploratory analysis of PFS in audited stratification data, PFS for selinexor met the threshold for statistical significance (HR, 0.71; 95% CI, 0.499 to 0.996; two-sided P = .049). Furthermore, patients with the TP53 wild-type (wt) EC had a median PFS of 13.7 and 3.7 months with selinexor and placebo. The most common grade 3 treatment-related adverse events were nausea (9%), neutropenia (9%), and thrombocytopenia (7%).

CONCLUSION

The significance level for PFS was only met in the audited analysis. However, a preliminary analysis of a prespecified exploratory subgroup of patients with TP53wt EC showed promising results with selinexor maintenance therapy.

Selinexor-based regimens in patients with multiple myeloma after prior anti-B-cell maturation antigen treatment

There is a lack of consensus on therapy sequencing in previously treated multiple myeloma, particularly after anti-B-cell maturation antigen (BCMA) therapy. Earlier reports on selinexor (X) regimens demonstrated considerable efficacy in early treatment, and after anti-BCMA-targeted chimeric antigen receptor-T cell therapy. Here, we present data from 11 heavily pretreated patients who predominantly received BCMA-antibody-drug conjugate therapy. We observe that X-containing regimens are potent and achieve durable responses with numerically higher overall response and clinical benefit rates, as well as median progression free survival compared to patients' prior anti-BCMA therapies, despite being used later in the treatment course. In an area of evolving unmet need, these data reaffirm the efficacy of X-based regimens following broader anti-BCMA therapy.

Oral eltanexor treatment of patients with higher-risk myelodysplastic syndrome refractory to hypomethylating agents

Patients with higher-risk myelodysplastic syndromes (MDS) refractory to hypomethylating agents (HMAs) have limited therapeutic options and an expected overall survival (OS) of 3–5 months. Eltanexor is an investigational oral selective inhibitor of nuclear export with low central nervous system penetrance and an acceptable tolerability profile. Preclinical studies suggest that myeloid malignancies are sensitive to nuclear export inhibition. Eltanexor exhibited efficacy in hematologic models, supporting exploration in a clinical trial. This phase 1/2 study (NCT02649790) assessed single-agent activity of eltanexor in patients with higher-risk MDS and 5–19% myeloblasts. Two starting doses of eltanexor were evaluated: 20 mg (n = 15), 10 mg (n = 5), both administered on days 1–5 each week of a 28-day cycle. Twenty patients with primary HMA-refractory MDS, with a median age of 77 years (range 62–89), and a median of two prior treatment regimens (range 1–4) were enrolled. Of these, 15 were evaluated for efficacy and 20 for safety. The overall response rate (ORR) was 53.3%, with seven patients (46.7%) achieving marrow complete remission (mCR) and one additional patient achieving hematologic improvement (HI). In the 10 mg group, three patients (60%) reached mCR and two (40%) stable disease (SD), while for 20 mg, four patients (40%) had mCR and two (20%) SD. A total of three patients (20%) had HI and became transfusion independent ≥ 8 weeks. Median OS for the efficacy-evaluable patients (n = 15) was 9.86 months (7.98, NE). Overall, the most frequently reported treatment-related adverse events were nausea (45%), diarrhea (35%), decreased appetite (35%), fatigue and neutropenia (both 30%). Single-agent oral eltanexor was active, safe, and well tolerated in patients with higher-risk, primary HMA-refractory MDS.

Selinexor in Advanced, Metastatic Dedifferentiated Liposarcoma: A Multinational, Randomized, Double-Blind, Placebo-Controlled Trial

PURPOSE

Antitumor activity in preclinical models and a phase I study of patients with dedifferentiated liposarcoma (DD-LPS) was observed with selinexor. We evaluated the clinical benefit of selinexor in patients with previously treated DD-LPS whose sarcoma progressed on approved agents.

METHODS

SEAL was a phase II-III, multicenter, randomized, double-blind, placebo-controlled study. Patients age 12 years or older with advanced DD-LPS who had received two-five lines of therapy were randomly assigned (2:1) to selinexor (60 mg) or placebo twice weekly in 6-week cycles (crossover permitted). The primary end point was progression-free survival (PFS). Patients who received at least one dose of study treatment were included for safety analysis (ClinicalTrials.gov identifier: NCT02606461).

RESULTS

Two hundred eighty-five patients were enrolled (selinexor, n = 188; placebo, n = 97). PFS was significantly longer with selinexor versus placebo: hazard ratio (HR) 0.70 (95% CI, 0.52 to 0.95; one-sided P = .011; medians 2.8 v 2.1 months), as was time to next treatment: HR 0.50 (95% CI, 0.37 to 0.66; one-sided P < .0001; medians 5.8 v 3.2 months). With crossover, no difference was observed in overall survival. The most common treatment-emergent adverse events of any grade versus grade 3 or 4 with selinexor were nausea (151 [80.7%] v 11 [5.9]), decreased appetite (113 [60.4%] v 14 [7.5%]), and fatigue (96 [51.3%] v 12 [6.4%]). Four (2.1%) and three (3.1%) patients died in the selinexor and placebo arms, respectively. Exploratory RNA sequencing analysis identified that the absence of CALB1 expression was associated with longer PFS with selinexor compared with placebo (median 6.9 v 2.2 months; HR, 0.19; P = .001).

CONCLUSION

Patients with advanced, refractory DD-LPS showed improved PFS and time to next treatment with selinexor compared with placebo. Supportive care and dose reductions mitigated side effects of selinexor. Prospective validation of CALB1 expression as a predictive biomarker for selinexor in DD-LPS is warranted.

Effect of Prior Therapy and Disease Refractoriness on the Efficacy and Safety of Oral Selinexor in Patients with Diffuse Large B-cell Lymphoma (DLBCL): A Post-hoc Analysis of the SADAL Study

BACKGROUND

Despite a number of treatment options, patients with diffuse large B-cell lymphoma (DLBCL) whose disease has become refractory to treatment have a poor prognosis. Selinexor is a novel, oral drug that is approved to treat patients with relapsed/refractory DLBCL. In this post hoc analysis of the SADAL study, a multinational, open-label study, we evaluated subpopulations to determine if response to single agent selinexor is impacted by number of lines of prior treatment, autologous stem cell transplant (ASCT), response to first and most recent therapies, and time to progressive disease.

PATIENTS

Patients (n = 134) with DLBCL after 2-5 prior therapies were enrolled in SADAL and received 60mg selinexor twice weekly.

RESULTS

The median overall survival was 9.0 months and median progression free survival was 2.6 months. Patients who had the best overall response rate (ORR) and disease control rate were those who had prior ASCT (42.5% and 50.0%) or responded to last line of therapy (35.9% and 43.5%). Patients with primary refractory DLBCL also showed responses (ORR 21.8%). Adverse events between subgroups were similar to the overall study population, the most common being thrombocytopenia (29.1%), fatigue (7.5%), and nausea (6.0%).

CONCLUSION

Regardless of prior therapy and disease refractory status, selinexor treatment demonstrated results consistent with its novel mechanism of action and lack of cross-resistance. Thus, single agent oral selinexor can induce deep, durable, and tolerable responses in patients with DLBCL who have recurrent disease after several chemoimmunotherapy combination regimens.

Abstract 5519: Selinexor synergizes with anti-PD-1 antibody and inhibits tumor growth and metastasis in syngeneic mouse models of KRAS mutant colorectal cancer

Background: Colorectal cancer (CRC) is the second leading cause of cancer related death. In approximately half of all CRC cases, oncogenic KRAS mutations underlie poor prognosis and drug resistance. A previous multi-genomic analysis of 4,725 biological processes with 106 human non-small-cell lung cancer cells identified nuclear transport machinery as the sole process selectively required for the survival of KRAS mutant cells. Selinexor is a clinically approved oral inhibitor of nuclear export protein Exportin 1 (XPO1/CRM1). In preclinical studies, selinexor demonstrated robust synthetical lethality with native or engineered oncogenic KRAS both in vitro and in vivo. Clinical activity of selinexor monotherapy was observed in CRC patients with various KRAS oncogenic mutations (Razak 2016 JCO). We performed preclinical studies to evaluate the effectiveness of selinexor and the anti-PD-1 antibody RMP1-14 in syngeneic mouse models of KRAS mutant CRC.

Methods: Two syngeneic CT-26 KRAS mutant CRC mouse models were tested: 1) metastasis model with intra-hepatically injected CT-26 cells expressing luciferase (8 mice per group); and 2) subcutaneous model with CT-26 injected into the left flank (10 mice per group). Mice were allocated to four groups: vehicle control, selinexor (15 mg/kg, PO, once weekly), RMP1-14 (300 µg/mouse, IP, once weekly), or the combination of selinexor and RMP1-14. Tumor progression and body weight of test mice were monitored throughout the experiment. Tumor samples and plasma were collected at the end of the study for further analysis.

Results: Both selinexor and RMP1-14 demonstrated single agent activity against KRAS mutant CRC in the two mouse models relative to controls. In the metastasis model, tumor growth inhibition (TGI) at Day 21 was 63.5% (p=0.0001) for selinexor and 68.9% (p&lt;0.0001) for RMP1-14. The combination of selinexor and RMP1-14 significantly inhibited tumor growth and metastasis with a TGI of 98.9% (p&lt;0.0001). No tumors were detected in two mice from the combination group at the end of the study. A similar trend was observed in the subcutaneous xenograft models, at Day 17, TGIs for selinexor, RMP1-14 and combination treatment were 17.6% (p=0.0921), 26.9% (p=0.0059) and 70.4% (p&lt;0.0001), respectively.

Conclusions: Synergistic anti-cancer activity of selinexor and anti-PD-1 antibody in KRAS mutant CRC mouse models warrants further clinical investigation.

Citation Format: Hua Chang, Leah Henegar, Christopher J. Walker, Trinayan Kashyap, Marie Maloof, Feng Wang, Kathleen Martyn, Shira Orr, Michael G. Kauffman, Sharon Shacham, Yosef Landesman. Selinexor synergizes with anti-PD-1 antibody and inhibits tumor growth and metastasis in syngeneic mouse models of KRAS mutant colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5519.

Abstract 1122: Selinexor synergizes with IL-12 to inhibit tumor growth in syngeneic mouse models of melanoma

Background: Melanoma is the most deadly skin cancer and represents 4.6% of all cancers diagnosed within the US (American Cancer Society). Risk factors for melanoma are almost entirely related to pale skin color and sunburns. Selinexor is a clinically approved oral inhibitor of nuclear exportation protein Exportin 1 (XPO1/CRM1). In preclinical studies, selinexor significantly inhibited growth of A375 and CHL-1 human melanoma cell lines in vivo at well tolerated doses (Yang et al. 2014). Interleukin 12 (IL-12) is a cytokine produced by dendritic cells, macrophages, neutrophils, and human B-lymphoblastoid cells in response to antigenic stimulation. IL-12 drives the differentiation of T-cells into T helper (Th1) cells, in addition to stimulating T-cell and NK cell activity, specifically through the activation of interferon-γ (IFN-γ). IL-12 exerts antitumor activity through IFN-γ-dependent and independent mechanisms, which include modulation of the immune system and anti-angiogenesis (Zhang et al. 2016). The objective of this study was to compare the impact and scheduling of recombinant mouse IL-12 alone and in combination with selinexor on the growth of murine B16F10 melanoma cells grown as subcutaneous tumors in C57B/6 mice.

Methods: Sixty, 6-7 weeks old female C57B/6 mice were inoculated subcutaneously in the left flank with 1 x 105 B16F10 cells. Treatment was initiated when the tumors reached a mean volume of 100 mm3 (standard deviation ± 6.3 mm3). Mice were allocated to 6 groups of 10 such that mean tumor volume in each group was within the range of 11.8 to 13.4 mm3, then treated with: oral selinexor (10mg/kg, twice weekly on day 0 and 2) combined with a pre-dose of subcutaneous IL-12 (1µg/kg, once weekly on day -2); selinexor with post-dose IL-12 (1µg/kg, once weekly on day 3); selinexor alone; IL-12 alone (day -2); IL-12 alone (day 3); or vehicle. Animal weight was recorded daily, and tumors were measured 3 days a week to record percent of tumor growth inhibition (%TGI).

Results: Both selinexor and IL-12 demonstrated single agent activity against B16F10 tumor in vivo. All treatment groups showed significant tumor growth inhibition as compared to vehicle. The group receiving selinexor with pre-dose IL-12 showed the largest tumor inhibition (%TGI=92%). Significant weight loss compared to vehicle occurred only in the single agent selinexor group (p=0.039).

Conclusions: Synergistic anti-cancer activity of selinexor and IL-12 warrants further clinical investigation. Further mechanistic studies to understand the effects of IL-12 priming on increasing the effectiveness of selinexor will be undertaken.

Citation Format: Shira Orr, Leah Henegar, Christopher J. Walker, Feng Wang, Trinayan Kashyap, Marie Maloof, Kathleen Martyn, Michael G. Kauffman, Sharon Shacham, Yosef Landesman. Selinexor synergizes with IL-12 to inhibit tumor growth in syngeneic mouse models of melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1122.

Abstract 6022: Synergistic anti-cancer effects of selinexor and bevacizumab in mouse xenograft models of glioblastoma

Background: Glioblastoma (GBM) is the most common primary brain tumor with a poor prognosis. It is also one of the most vascularized human tumors. The anti-angiogenesis agent bevacizumab (BEV) is the only US FDA approved agent for recurrent GBM. Given the high resistance of GBM to current therapies and the failure of BEV to prolong overall survival, new therapeutic agents are in urgent need. Selinexor is a first-in-class oral inhibitor of nuclear export protein Exportin 1 (XPO1/CRM1), it readily crosses the blood-brain-barrier and demonstrates anti-cancer activity in various hematological and solid tumors. Selinexor can attenuate multiple cancer hallmarks simultaneously, anti-angiogenesis is one of the many anti-cancer mechanisms that selinexor has. In a phase 2 clinical trial of recurrent GBM, selinexor monotherapy demonstrated clinically relevant disease control with manageable side effects (Lassman 2021 Clin Cancer Res). We tested mouse xenograft models of GBM to evaluate the anti-GBM effects of selinexor and BEV.

Methods: Thirty-two female nude mice with subcutaneously implanted U87MG xenografts were allocated to four treatment groups of eight mice: vehicle control, selinexor, BEV, and the selinexor and BEV combination. Selinexor was given via oral gavage at 15 mg/kg once a week on Mondays, and BEV was given at 2.5 mg/kg via intraperitoneal injection every three days, starting on Monday, for four weeks. Tumor volume and body weight of test mice were monitored throughout the experiment. Xenograft tumor samples were collected at the end of the study for gene expression analysis and immunohistochemistry tests.

Results: Selinexor and BEV significantly inhibited tumor growth as single agents relative to controls, at Day 26, tumor growth inhibition (TGI) of 54.1% (p&lt;0.0001) and 64.0% (p&lt;0.0001), respectively. The combination of the two agents almost completely inhibited tumor growth, with a TGI of 95% (p&lt;0.0001). Gene expression analysis showed that genes involved in angiogenesis were significantly downregulated in tumor samples collected from mice treated with both agents and was more significant than in animals treated with BEV alone.

Conclusions: Synergistic anti-GBM effects of selinexor and BEV are likely due to the enhanced inhibition of angiogenesis related genes. An ongoing GBM clinical trial (XPORT-GBM-029, NCT04421378) is investigating the therapeutic efficacy of selinexor and BEV combination.

Citation Format: Leah Henegar, Hua Chang, Christopher J. Walker, Trinayan Kashyap, Marie Maloof, Feng Wang, Kathleen Martyn, Shira Orr, Sharon Tamir, Michael G. Kauffman, Sharon Shacham, Yosef Landesman. Synergistic anti-cancer effects of selinexor and bevacizumab in mouse xenograft models of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6022.

Abstract 5455: Nuclear export inhibitor selinexor synergizes with proteasome inhibitor marizomib in preclinical models of glioblastoma

Background: Glioblastoma (GBM) is an aggressive brain cancer with poor prognosis and limited treatment options. Selinexor is a first-in-class oral inhibitor of Exportin 1 (XPO1/CRM1) with broad anti-cancer activities and is clinically approved to treat multiple myeloma and diffuse large B cell lymphoma. In a phase 2 study of recurrent GBM, monotherapy of selinexor demonstrated clinically relevant disease control (Lassman 2021 Clin Cancer Res). Our previous preclinical studies identified synergy between selinexor and proteasome inhibitors in GBM in vitro. Among the proteasome inhibitors tested, we chose to focus on marizomib due to its ability to cross the blood-brain-barrier, supporting its use in GBM. We tested GBM cell lines and mouse xenograft models to evaluate the anti-GBM effects of selinexor and marizomib in combination.

Methods: Cytotoxic effects of selinexor and marizomib were evaluated with two GBM cell lines LN18 and U87MG. The anti-GBM effects of selinexor and marizomib were further investigated in vivo with U87MG mouse xenograft models of GBM. Female nude mice carrying U87MG subcutaneous implants were treated with vehicle, selinexor, marizomib or the combination of the two agents (six mice per treatment group). Tumor volume and body weight were monitored throughout the study. Tumor samples were collected at the end of the study for transcriptomic analysis and immunohistochemistry tests.

Results: Synergistic anti-GBM effects of selinexor and marizomib were observed in both LN18 and U87MG cells in vitro. In mouse xenograft models of U87MG, tumor growth was significantly inhibited by selinexor and marizomib single agents relative to controls, at Day 15 of the study, tumor growth inhibition (TGI) was 60.0% (p=0.0009) for selinexor (10 mg/kg, once per week), 49.2% (p=0.0069) for marizomib once weekly at 75 µg/kg, and 33.1% (p=0.0991) for marizomib once every 2 weeks at 75 µg/kg. Synergistic anti-GBM effect was observed in the combination groups, with a TGI of 99.6% (p&lt;0.0001) for selinexor with once weekly marizomib, and a TGI of 90.0% (p&lt;0.0001) for selinexor with once every other week marizomib.

Conclusions: Synergistic anti-GBM effects of selinexor and marizomib in preclinical models warrants further investigation. The synergism is likely due to enhanced inhibition of the NFκB signaling pathways as previously demonstrated for selinexor and proteasome inhibitor combination.

Citation Format: Hua Chang, Leah Henegar, Christopher J. Walker, Trinayan Kashyap, Marie Maloof, Feng Wang, Kathleen Martyn, Shira Orr, Sharon Tamir, Michael G. Kauffman, Sharon Shacham, Yosef Landesman. Nuclear export inhibitor selinexor synergizes with proteasome inhibitor marizomib in preclinical models of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5455.

A Phase II Study of the Efficacy and Safety of Oral Selinexor in Recurrent Glioblastoma

PURPOSE

Selinexor is an oral selective inhibitor of exportin-1 (XPO1) with efficacy in various solid and hematologic tumors. We assessed intratumoral penetration, safety, and efficacy of selinexor monotherapy for recurrent glioblastoma.

PATIENTS AND METHODS

Seventy-six adults with Karnofsky Performance Status ≥ 60 were enrolled. Patients undergoing cytoreductive surgery received up to three selinexor doses (twice weekly) preoperatively (Arm A; n = 8 patients). Patients not undergoing surgery received 50 mg/m2 (Arm B, n = 24), or 60 mg (Arm C, n = 14) twice weekly, or 80 mg once weekly (Arm D; n = 30). Primary endpoint was 6-month progression-free survival rate (PFS6).

RESULTS

Median selinexor concentrations in resected tumors from patients receiving presurgical selinexor was 105.4 nmol/L (range 39.7-291 nmol/L). In Arms B, C, and D, respectively, the PFS6 was 10% [95% confidence interval (CI), 2.79-35.9], 7.7% (95% CI, 1.17-50.6), and 17% (95% CI, 7.78-38.3). Measurable reduction in tumor size was observed in 19 (28%) and RANO-response rate overall was 8.8% [Arm B, 8.3% (95% CI, 1.0-27.0); C: 7.7% (95% CI, 0.2-36.0); D: 10% (95% CI, 2.1-26.5)], with one complete and two durable partial responses in Arm D. Serious adverse events (AEs) occurred in 26 (34%) patients; 1 (1.3%) was fatal. The most common treatment-related AEs were fatigue (61%), nausea (59%), decreased appetite (43%), and thrombocytopenia (43%), and were manageable by supportive care and dose modification. Molecular studies identified a signature predictive of response (AUC = 0.88).

CONCLUSIONS

At 80 mg weekly, single-agent selinexor induced responses and clinically relevant PFS6 with manageable side effects requiring dose reductions. Ongoing trials are evaluating safety and efficacy of selinexor in combination with other therapies for newly diagnosed or recurrent glioblastoma.

Selinexor, bortezomib, and dexamethasone versus bortezomib and dexamethasone in previously treated multiple myeloma: Outcomes by cytogenetic risk

In the phase 3 BOSTON study, patients with multiple myeloma (MM) after 1-3 prior regimens were randomized to once-weekly selinexor (an oral inhibitor of exportin 1 [XPO1]) plus bortezomib-dexamethasone (XVd) or twice-weekly bortezomib-dexamethasone (Vd). Compared with Vd, XVd was associated with significant improvements in median progression-free survival (PFS), overall response rate (ORR), and lower rates of peripheral neuropathy, with trends in overall survival (OS) favoring XVd. In BOSTON, 141 (35.1%) patients had MM with high-risk (presence of del[17p], t[4;14], t[14;16], or ≥4 copies of amp1q21) cytogenetics (XVd, n = 70; Vd, n = 71), and 261 (64.9%) exhibited standard-risk cytogenetics (XVd, n = 125; Vd, n = 136). Among patients with high-risk MM, median PFS was 12.91 months for XVd and 8.61 months for Vd (HR, 0.73 [95% CI, (0.4673, 1.1406)], p = 0.082), and ORRs were 78.6% and 57.7%, respectively (OR 2.68; p = 0.004). In the standard-risk subgroup, median PFS was 16.62 months for XVd and 9.46 months for Vd (HR 0.61; p = 0.004), and ORRs were 75.2% and 64.7%, respectively (OR 1.65; p = 0.033). The safety profiles of XVd and Vd in both subgroups were consistent with the overall population. These data suggest that selinexor can confer benefits to patients with MM regardless of cytogenetic risk. ClinicalTrials.gov identifier: NCT03110562.

Selinexor, a novel selective inhibitor of nuclear export, reduces SARS-CoV-2 infection and protects the respiratory system in vivo

The novel coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the recent global pandemic. The nuclear export protein (XPO1) has a direct role in the export of SARS-CoV proteins including ORF3b, ORF9b, and nucleocapsid. Inhibition of XPO1 induces anti-inflammatory, anti-viral, and antioxidant pathways. Selinexor is an FDA-approved XPO1 inhibitor. Through bioinformatics analysis, we predicted nuclear export sequences in the ACE-2 protein and confirmed by in vitro testing that inhibition of XPO1 with selinexor induces nuclear localization of ACE-2. Administration of selinexor inhibited viral infection prophylactically as well as therapeutically in vitro. In a ferret model of COVID-19, selinexor treatment reduced viral load in the lungs and protected against tissue damage in the nasal turbinates and lungs in vivo. Our studies demonstrated that selinexor downregulated the pro-inflammatory cytokines IL-1β, IL-6, IL-10, IFN-γ, TNF-α, and GMCSF, commonly associated with the cytokine storm observed in COVID-19 patients. Our findings indicate that nuclear export is critical for SARS-CoV-2 infection and for COVID-19 pathology and suggest that inhibition of XPO1 by selinexor could be a viable anti-viral treatment option.

Comparison of the Effectiveness and Safety of the Oral Selective Inhibitor of Nuclear Export, Selinexor, in Diffuse Large B Cell Lymphoma Subtypes

BACKGROUND

The SADAL study evaluated oral selinexor in patients with relapsed and/or refractory diffuse large B-cell lymphoma (DLBCL) after at least 2 prior lines of systemic therapy. In this post-hoc analysis, we analyzed the outcomes of the SADAL study by DLBCL subtype to determine the effects of DLBCL subtypes on efficacy and tolerability of selinexor.

PATIENTS AND METHODS

Data from 134 patients in SADAL were analyzed by DLBCL subtypes for overall response rate (ORR), overall survival (OS), duration of treatment response, progression-free survival, and adverse events rate.

RESULTS

ORR in the entire cohort was 29.1%, and similar in patients with germinal center (GCB) versus non-GCB DLBCL (31.7% vs. 24.2%, P = 0.45); transformed DLBCL showed a trend towards higher ORR than de novo DLBCL: 38.7% vs. 26.2% (P = 0.23). Despite similar prior treatment regimens and baseline characteristics, patients with DLBCL and normal C-MYC/BCL-2 protein expression levels had a significantly higher ORR (46.2% vs.14.8%, P = 0.012) and significantly longer OS (medians 13.7 vs. 5.1 months, hazard ratio 0.43 [95% CI, 0.23-0.77], P = 0.004) as compared with those whose DLBCL had C-MYC and BCL-2 overexpression. Among patients who had normal expression levels of either C-MYC or BCL-2 and baseline hemoglobin levels ≥ 10g/dL, ORR was 51.5% (n = 47), with median OS of 15.5 months and median PFS of 4.6 months. Similar rates of adverse events were noted in all subgroups.

CONCLUSIONS

Overall, single agent oral selinexor showed strong responses in patients with limited treatment alternatives regardless of germinal center B-cell type or disease origin.

Survival among patients with relapsed/refractory diffuse large B cell lymphoma treated with single-agent selinexor in the SADAL study

Patients with RR DLBCL who have received ≥ 2 lines of therapy have limited treatment options and an expected overall survival (OS) of < 6 months. The SADAL study evaluated single-agent oral selinexor in patients with RR DLBCL and demonstrated an overall response rate (ORR) of 29.1% with median duration of response (DOR) of 9.3 months. The analyses described here evaluated a number of subpopulations in order to understand how response correlates with survival outcomes in order to identify patients who could most optimally benefit from selinexor treatment. Median age was 67 years; 44.8% of patients were ≥ 70 years of age. The median OS was 9.0 months (95% CI 6.2, 13.7) at a median follow-up of 14.8 months. The median OS was not reached in patients with a CR or PR, while patients who did not respond have a median OS of 4.9 months (p < 0.0001). Patients < 70 years had an OS of 11.1 months compared with 7.8 months in patients ≥ 70 years. Among patients with or without prior ASCT, the median OS was 10.9 and 7.8 months, respectively. Among patients with disease refractory to the most recent DLBCL treatment regimen, the median OS was 7.0 months compared with 11.1 months for disease not refractory to the most recent treatment. In a patient population in which survival is expected to be < 6 months, treatment with single-agent oral selinexor was associated with a median survival of 9 months. Increased median OS observed in patients responding to selinexor was consistent across subgroups regardless of age, prior ASCT therapy, or refractory status. Randomized studies of selinexor in combination with a variety of other anti-DLBCL agents are planned. This trial was registered at ClinicalTrials.gov (NCT02227251) on August 28, 2014. https://clinicaltrials.gov/ct2/show/NCT02227251 .

Effect of age and frailty on the efficacy and tolerability of once-weekly selinexor, bortezomib, and dexamethasone in previously treated multiple myeloma

Elderly and frail patients with multiple myeloma (MM) are more vulnerable to the toxicity of combination therapies, often resulting in treatment modifications and suboptimal outcomes. The phase 3 BOSTON study showed that once-weekly selinexor and bortezomib with low-dose dexamethasone (XVd) improved PFS and ORR compared with standard twice-weekly bortezomib and moderate-dose dexamethasone (Vd) in patients with previously treated MM. This is a retrospective subgroup analysis of the multicenter, prospective, randomized BOSTON trial. Post hoc analyses were performed to compare XVd versus Vd safety and efficacy according to age and frailty status (<65 and ≥65 years, nonfrail and frail). Patients ≥65 years with XVd had higher ORR (OR 1.77, p = .024), ≥VGPR (OR, 1.68, p = .027), PFS (HR 0.55, p = .002), and improved OS (HR 0.63, p = .030), compared with Vd. In frail patients, XVd was associated with a trend towards better PFS (HR 0.69, p = .08) and OS (HR 0.62, p = .062). Significant improvements were also observed in patients <65 (ORR and TTNT) and nonfrail patients (PFS, ORR, ≥VGPR, and TTNT). Patients treated with XVd had a lower incidence of grade ≥ 2 peripheral neuropathy in ≥65 year-old (22% vs. 37%; p = .0060) and frail patients (15% vs. 44%; p = .0002). Grade ≥3 TEAEs were not observed more often in older compared to younger patients, nor in frail compared to nonfrail patients. XVd is safe and effective in patients <65 and ≥65 and in nonfrail and frail patients with previously treated MM.

Molecular predictors of response to selinexor in advanced unresectable de-differentiated liposarcoma (DDLS)

11509

Background: Patients (pts) with recurrent inoperative DDLS have a poor prognosis and limited treatment options. Selinexor is an oral, selective inhibitor of nuclear export (SINE) compound approved for previously treated pts with myeloma and diffuse large B-cell lymphoma. SEAL was a Phase 2-3 randomized, double-blind, study of selinexor versus placebo in pts with progressive DDLS and 2-5 prior systemic therapies. SEAL showed significantly prolonged progression-free survival (PFS, HR = 0.70, p = 0.0228) with well managed toxicity. A biomarker predictive of clinical activity could be used to optimize selection of pts with DDLS for selinexor. Methods: Pts were randomized 2:1 for Phase 3: 188 received twice weekly selinexor (60mg) and 97 received placebo. Three exploratory biomarker analyses (RNA sequencing of biopsies) from selinexor-treated pts were performed: discovery set of sensitive (n = 8) or resistant (n = 9) tumors; a validation set of pts with favorable (n = 19) or poor (n = 14) tumor control based on PFS, and paired lesions from a pt who harbored both a responsive and resistant lesion. Tumor biopsies from 24 pts on placebo with short ( < 5 months, n = 18) and long ( > 6 months, n = 6) PFS were RNA sequenced. Gene expressions were compared using a negative binomial distribution with DeSeq2. Pathway analyses were performed using Gene Set Enrichment Analysis (GSEA) with MSigDB Cancer Gene Neighborhoods. Results: RNA sequencing analysis comparing 17 sensitive and resistant tumors identified 114 differentially expressed genes (adjusted p-values < 0.05). Expression of CALB1, which encodes the calcium-binding protein calbindin, was significantly lower in sensitive tumors (adjusted P [Padj] = 7.5x10-20), and expression of GRM1, which encodes a metabotropic glutamate receptor that activates phospholipase C, was higher in selinexor sensitive tumors (Padj= 0.003). These findings were confirmed in an independent validation set (Padj = 0.01 – 0.02). In the pt with paired sensitive and resistant lesions, CALB1 expression was 52-fold lower in the sensitive tumor. In a comparison of placebo-treated pts, neither CALB1 or GRM1 was differentially expressed between pts with short or long PFS, indicating they are markers of response to selinexor treatment, rather than general markers of disease aggressiveness. Gene set enrichment analyses revealed that selinexor sensitive tumors in the discovery and validation sets showed upregulation of cancer genes related to SNRK and the netrin 1 receptor tumor suppressor DCC. The resistant tumors showed upregulated EIF3S2 translation initiator-related genes. Conclusions: Selinexor sensitive DDLS tumors showed low expression of CALB1 and high GRM1. If validated, pts with DDLS whose tumors match this expression profile are especially likely to benefit from selinexor. Clinical trial information: NCT02606461.

Open-label phase 1 study evaluating the tolerability and anti-tumor activity of selinexor and pembrolizumab in colorectal cancer

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Background: Colorectal cancer (CRC) is the fourth leading cause of cancer-related deaths worldwide and is heterogenous in its molecular features. Checkpoint inhibitors (CPIs) are approved for only about 5% of unresectable or metastatic CRC with MSI-high (MSI-H)/deficient MMR (dMMR); however, they do not benefit the majority of advanced CRC patients. Selinexor is a first-in-class, oral selective inhibitor of nuclear export (SINE) compound with demonstrated activity in cancers with RAS mutations which are found in ̃50% of CRC. This study aims to evaluate the combination of selinexor with pembrolizumab, an anti-PD-L1 CPI, in chemotherapy refractory CRC. Methods: This phase 1/2, open-label study enrolled patients with advanced/metastatic CRC with progression after prior chemotherapy (1-3 lines for KRAS wild-type (wt), 1-2 for KRAS mutant (mut)), initially into a selinexor monotherapy period to evaluate bioavailability/bioequivalence of a new selinexor formulation, followed by a combination therapy where patients were treated with selinexor 80 mg PO QW and pembrolizumab 200 mg IV every 3 weeks. Patients were assessed for anti-tumor activity, safety, and tolerability of the combination therapy. Results: Enrollment in this study has been completed, and 29 patients have received at least 1 dose of combination therapy: median age was 56 years, 19 (65.5%) male, and 15 (51.7%) have RAS mutations. Median number of lines of prior antineoplastic therapies was 2. Median duration of combination treatment is 39 days (range: 1-246 days). Seventeen patients (58.6%) discontinued therapy mostly due to progressive disease, and 18 patients are evaluable for response. Best response was stable disease in 7 patients (6 of them (85.7%) had RAS mut CRC), and progressive disease in 11 patients (8 of them (72.7%) had RAS wt CRC. Median progression free survival (PFS) is 120 days for patients with RAS mut CRC and 41 days for those with RAS wt CRC. Notably, none of the RAS mut had MSI-H/dMMR CRC while one RAS wt with SD had MSI-H/dMMR CRC. The most common treatment-emergent adverse events (total; ≥Grade 3) were nausea (72.4%; 0%), vomiting (41.4%; 0%), decreased appetite (34.5%; 0%), and fatigue (34.5%; 10.3%). Seven patients (24.1%) had at least 1 treatment-emergent serious adverse event. Conclusions: Selinexor in combination with pembrolizumab has demonstrated disease control in patients with chemotherapy refractory advanced/metastatic CRC. Greater anti-tumor activity was observed in patients with RAS mutations despite absence of MSI-H/dMMR. The therapy was well tolerated with no unanticipated adverse events observed. These results warrant further investigation of selinexor in combination with pembrolizumab in CRC, particularly in CRC with RAS mutations. Clinical trial information: NCT04256707.

Effect of prior treatments on selinexor, bortezomib, and dexamethasone in previously treated multiple myeloma

Therapeutic regimens for previously treated multiple myeloma (MM) may not provide prolonged disease control and are often complicated by significant adverse events, including peripheral neuropathy. In patients with previously treated MM in the Phase 3 BOSTON study, once weekly selinexor, once weekly bortezomib, and 40 mg dexamethasone (XVd) demonstrated a significantly longer median progression-free survival (PFS), higher response rates, deeper responses, a trend to improved survival, and reduced incidence and severity of bortezomib-induced peripheral neuropathy when compared with standard twice weekly bortezomib and 80 mg dexamethasone (Vd). The pre-specified analyses described here evaluated the influence of the number of prior lines of therapy, prior treatment with lenalidomide, prior proteasome inhibitor (PI) therapy, prior immunomodulatory drug therapy, and prior autologous stem cell transplant (ASCT) on the efficacy and safety of XVd compared with Vd. In this 1:1 randomized study, enrolled patients were assigned to receive once weekly oral selinexor (100 mg) with once weekly subcutaneous bortezomib (1.3 mg/m2) and 40 mg per week dexamethasone (XVd) versus standard twice weekly bortezomib and 80 mg per week dexamethasone (Vd). XVd significantly improved PFS, overall response rate, time-to-next-treatment, and showed reduced all grade and grade ≥ 2 peripheral neuropathy compared with Vd regardless of prior treatments, but the benefits of XVd over Vd were more pronounced in patients treated earlier in their disease course who had either received only one prior therapy, had never been treated with a PI, or had prior ASCT. Treatment with XVd improved outcomes as compared to Vd regardless of prior therapies as well as manageable and generally reversible adverse events. XVd was associated with clinical benefit and reduced peripheral neuropathy compared to standard Vd in previously treated MM. These results suggest that the once weekly XVd regimen may be optimally administered to patients earlier in their course of disease, as their first bortezomib-containing regimen, and in those relapsing after ASCT.Trial registration: ClinicalTrials.gov (NCT03110562). Registered 12 April 2017. https://clinicaltrials.gov/ct2/show/NCT03110562 .

Once-per-week selinexor, bortezomib, and dexamethasone versus twice-per-week bortezomib and dexamethasone in patients with multiple myeloma (BOSTON): a randomised, open-label, phase 3 trial

BACKGROUND

Selinexor combined with dexamethasone has shown activity in patients with heavily pre-treated multiple myeloma. In a phase 1b/2 study, the combination of oral selinexor with bortezomib (a proteasome inhibitor) and dexamethasone induced high response rates with low rates of peripheral neuropathy, the main dose-limiting toxicity of bortezomib. We aimed to evaluate the clinical benefit of weekly selinexor, bortezomib, and dexamethasone versus standard bortezomib and dexamethasone in patients with previously treated multiple myeloma.

METHODS

This phase 3, randomised, open-label trial was done at 123 sites in 21 countries. Patients aged 18 years or older, who had multiple myeloma, and who had previously been treated with one to three lines of therapy, including proteasome inhibitors, were randomly allocated (1:1) to receive selinexor (100 mg once per week), bortezomib (1·3 mg/m2 once per week), and dexamethasone (20 mg twice per week), or bortezomib (1·3 mg/m2 twice per week for the first 24 weeks and once per week thereafter) and dexamethasone (20 mg four times per week for the first 24 weeks and twice per week thereafter). Randomisation was done using interactive response technology and stratified by previous proteasome inhibitor therapy, lines of treatment, and multiple myeloma stage. The primary endpoint was progression-free survival in the intention-to-treat population. Patients who received at least one dose of study treatment were included in the safety population. This trial is registered at ClinicalTrials.gov, NCT03110562. The trial is ongoing, with 55 patients remaining on randomised therapy as of Feb 20, 2020.

FINDINGS

Of 457 patients screened for eligibility, 402 were randomly allocated-195 (49%) to the selinexor, bortezomib, and dexamethasone group and 207 (51%) to the bortezomib and dexamethasone group-and the first dose of study medication was given between June 6, 2017, and Feb 5, 2019. Median follow-up durations were 13·2 months [IQR 6·2-19·8] for the selinexor, bortezomib, and dexamethasone group and 16·5 months [9·4-19·8] for the bortezomib and dexamethasone group. Median progression-free survival was 13·93 months (95% CI 11·73-not evaluable) with selinexor, bortezomib, and dexamethasone and 9·46 months (8·11-10·78) with bortezomib and dexamethasone (hazard ratio 0·70 [95% CI 0·53-0·93], p=0·0075). The most frequent grade 3-4 adverse events were thrombocytopenia (77 [39%] of 195 patients in the selinexor, bortezomib, and dexamethasone group vs 35 [17%] of 204 in the bortezomib and dexamethasone group), fatigue (26 [13%] vs two [1%]), anaemia (31 [16%] vs 20 [10%]), and pneumonia (22 [11%] vs 22 [11%]). Peripheral neuropathy of grade 2 or above was less frequent with selinexor, bortezomib, and dexamethasone (41 [21%] patients) than with bortezomib and dexamethasone (70 [34%] patients; odds ratio 0·50 [95% CI 0·32-0·79], p=0·0013). 47 (24%) patients in the selinexor, bortezomib, and dexamethasone group and 62 (30%) in the bortezomib and dexamethasone group died.

INTERPRETATION

A once-per-week regimen of selinexor, bortezomib, and dexamethasone is a novel, effective, and convenient treatment option for patients with multiple myeloma who have received one to three previous lines of therapy.

FUNDING

Karyopharm Therapeutics.

Integrated safety profile of selinexor in multiple myeloma: experience from 437 patients enrolled in clinical trials

Selinexor is an oral, small molecule inhibitor of the nuclear export protein exportin 1 with demonstrated activity in hematologic and solid malignancies. Side effects associated with selinexor include nausea, vomiting, fatigue, diarrhea, decreased appetite, weight loss, thrombocytopenia, neutropenia, and hyponatremia. We reviewed 437 patients with multiple myeloma treated with selinexor and assessed the kinetics of adverse events and impact of supportive care measures. Selinexor reduced both platelets and neutrophils over the first cycle of treatment and reached a nadir between 28 and 42 days. Platelet transfusions and thrombopoietin receptor agonists were effective at treating thrombocytopenia, and granulocyte colony stimulating factors were effective at resolving neutropenia. The onset of gastrointestinal side effects (nausea, vomiting, and diarrhea) was most common during the first 1-2 weeks of treatment. Nausea could be mitigated with 5-HT3 antagonists and either neurokinin 1 receptor antagonists, olanzapine, or cannbainoids. Loperamide and bismuth subsalicylate ameliorated diarrhea. The primary constitutional side effects of fatigue and decreased appetite could be managed with methylphenidate, megestrol, cannabinoids or olanzapine, respectively. Hyponatremia was highly responsive to sodium replacement. Selinexor has well-established adverse effects that mainly occur within the first 8 weeks of treatment, are reversible, and respond to supportive care.

Quality-of-life (QOL) analyses in patients with multiple myeloma: Results from the selinexor (KPT-330) treatment of refractory myeloma (STORM) phase IIb study

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Background: Selinexor, a novel oral selective inhibitor of nuclear export, was recently approved for use in relapsed/refractory multiple myeloma (MM). The efficacy and safety of selinexor and dexamethasone was evaluated in a phase 2b, single-arm, open-label, multicenter trial in patients with penta-exposed, triple-class refractory MM. Patient-reported outcomes were measured using the Functional Assessment of Cancer Therapy - Multiple Myeloma (FACT-MM) assessment. While minimal clinically important differences (MCID) have been established for other FACT scales, there is no known, validated definition of MCID for the FACT-MM. This study reports results of QoL analyses in patients with MM enrolled in the STORM phase 2b trial and examines two approaches to calculate MCID for the FACT-MM. Methods: FACT-MM data were collected at baseline, on day 1 of each 4-week cycle, and at end of treatment (EOT) during the STORM phase 2b trial. Change from baseline was analyzed for the FACT-MM total score, FACT-trial outcome index (TOI), FACT-General (FACT-G), and the MM-specific domain. Two approaches for evaluating MCID were explored: the first based on patient-reported assessment of meaningful change, defined as 10% of the instrument range (Ringash 2007), and the second based on mean baseline differences between ECOG groups (0 vs 1 to 2) based on patient level data. Additional analyses were performed to identify trends among treatment responders and non-responders, including a difference-in-difference (DID) analysis to compare changes between baseline and EOT. Results: Eighty patients had sufficient data to be included in longitudinal QOL analyses. MCID analyses demonstrated that most patients did not experience decline during the first six cycles of treatment; this pattern was consistent with MCID defined either as 10% of the instrument range (range 54% to 75% of patients), or as an ECOG-based anchor (range: 54% to 73% of patients). The DID analysis found that the mean change in QoL of non-responders decreased significantly between baseline and EOT, while responders had no significant change. This difference between responders and non-responders was significant for the FACT-G. Conclusions: Most patients did not experience QoL decline during the early cycles of selinexor treatment during the STORM 2b trial. The MCID decline, evaluated by two approaches, was greater among treatment non-responders than responders. A DID approach demonstrated greater decline between baseline and EOT for non-responders. Clinical trial information: NCT02336815.

PL3.5 Efficacy and safety of selinexor in recurrent glioblastoma

BACKGROUND

New treatment modalities are needed for recurrent glioblastoma (rGBM). Selinexor is a novel, oral selective inhibitor of nuclear export which forces nuclear retention of tumor suppressor proteins including p53 and p27, leading to apoptosis. We previously reported interim results showing tolerability, preliminary efficacy, and blood-brain barrier penetration in a surgical cohort (N=8). We now report updated results following completion of accrual to non-surgical cohorts (N=68).

MATERIALS AND METHODS

This is an open-label, multicenter, phase 2 study of selinexor monotherapy. Patients (pts) not undergoing surgery for measurable rGBM per response assessment neuro-oncology criteria (RANO) were enrolled in one of 3 arms encompassing different dosing schedules of selinexor (50 mg/m2 [~ 85 mg] BIW, 60 mg BIW, and 80 mg QW). Treatment was continuous, although cycles were defined as 28 days and response was assessed every other cycle by MRI. Prior treatment with radiotherapy and temozolomide was required and prior bevacizumab was exclusionary. The primary endpoint was 6-month progression free survival (6mPFS) rate, calculated by the Kaplan-Meier method.

RESULTS

76 pts were enrolled; 24, 14 and 30 pts on doses of ~85 mg BIW, 60 mg BIW, and 80 mg QW, respectively. Median age was 56 years (range 21–78). Median number of prior treatments was 2 (range 1–7)

At the end of the 6 cycles, 30.2% pts on 80 mg QW were free from progression. The 6mPFS rate on 80 mg QW was 18.9%. Best RANO-defined responses (assessed locally) among 26 evaluable pts on 80 mg QW included 1 complete response, 2 partial responses, 7 stable disease, and 16 with progressive disease. Complete and partial responses were durable: the complete and a partial responder remain on selinexor for 393 and 1093 days respectively, as of the cut-off date. Median duration of response was 10.8 months. The most common related adverse events (all grades) in pts on ~85 mg BIW/60 mg BIW/80 mg QW were nausea (42%/64%/63%), leukopenia (38%/7%/43%), fatigue (71%/71%/47%), neutropenia (29%/14%/33%), decreased appetite (46%/71%/27%), and thrombocytopenia (67%/29%/23%).

CONCLUSION

Selinexor demonstrated efficacy, with durable responses and disease stabilization in rGBM. Based on the favorable efficacy and safety profile, selinexor at a dose of 80 mg QW is recommended for further development in rGBM.

Oral Selinexor-Dexamethasone for Triple-Class Refractory Multiple Myeloma

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.).

Overall survival (OS) with oral selinexor plus low dose dexamethasone (Sd) in patients with triple class refractory-multiple myeloma (TCR-MM)

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Background: TCR-MM is defined as being refractory to immunomodulatory agents, proteasome inhibitors, and anti-CD38 mAbs, representing an urgent unmet medical need with a median OS of 3-5 months( Pick M et al, Eur J Haem 2018; Gandhi U et al, ASH 2018). Sd has shown a 26.2% overall response rate (ORR) in 122 patients (pts) with TCR-MM in the Phase 2b STORM study ( Chari A et al, ASH 2018). Here, we evaluate the OS of pts in the STORM study with Sd and in pts with bortezomib, carfilzomib, lenalidomide, pomalidomide, and daratumumab (“penta”)-exposed, TCR-MM from an observational cohort not receiving Sd. Methods: Data were drawn from STORM and a retrospective cohort from the nationally representative Flatiron Health Analytic Database (FHAD). All pts from both sources had penta-exposed TCR-MM. In order to align study populations, OS was evaluated in pts in STORM whose first therapy after their MM reached TCR status was Sd and in pts in the FHAD who received ≥1 therapy after their MM reached TCR status. The index date for this evaluation was the start date of treatment after their MM reached TCR status. A Cox proportional hazards regression model was performed to assess the survival impact of Sd. In STORM, ORR was assessed by an Independent Review Committee based on IMWG criteria. Results: In the FHAD, 69 pts with TCR-MM were identified. Characteristics of the two groups of pts were similar, except that pts in STORM were more heavily pretreated, had a higher frequency of high-risk MM, a longer time since initial diagnosis of MM, and higher baseline hemoglobin and platelet values. Among the 122 pts in STORM, 64 received Sd as their first therapy after their MM became TCR, and ORR was 32.8%. Among the 69 pts from FHAD, 37 received ≥1 therapy after their MM became TCR. Median OS (N = 64) was 10.4 months for pts receiving Sd in STORM and 5.2 months (N = 37) for pts not receiving Sd in FHAD (HR = 0.49, p = 0.0241). Conclusions: The prognosis of TCR-MM in the real-world population appears very poor. Within the limits of this analysis, median OS of pts receiving Sd as their first therapy after their MM becomes TCR is significantly better than those not receiving Sd, suggesting that Sd may be associated with an OS benefit in pts with TCR-MM. Clinical trial information: NCT02336815.

Efficacy and safety of selinexor in recurrent glioblastoma

2005

Background: New treatment modalities are needed for recurrent glioblastoma (rGBM). Selinexor (SEL) is a novel, oral selective inhibitor of nuclear export which forces nuclear retention of tumor suppressor proteins including p53 and p27, leading to apoptosis. We previously reported interim results showing tolerability, preliminary efficacy, and blood-brain barrier penetration in a surgical cohort (N = 8). We now report updated results following completion of accrual to non-surgical cohorts (N = 68). Methods: This is an open-label, multicenter, phase 2 study of SEL monotherapy. Patients (pts) not undergoing surgery for measurable rGBM (per RANO) were enrolled in one of 3 arms encompassing different dosing schedules. Treatment was continuous, although cycles were defined as 28 days and response was assessed every other cycle by MRI. Prior treatment with radiotherapy and temozolomide was required and prior bevacizumab was exclusionary. The primary endpoint was 6-month progression free survival (6mPFS) rate, calculated by the Kaplan Meier method. Results: A total of 76 pts were enrolled. Median age was 56 years (range 21-78). Median number of prior treatments was 2 (range 1-7). At the end of the 6 cycles, 30.2% patients on 80 mg QW were free from progression. The 6mPFS rate on 80 mg QW was 15.1%. Best RANO-defined responses (assessed locally) among 26 evaluable pts on 80 mg QW included 1 complete response, 2 partial responses, 7 stable disease, and 16 with progressive disease. Median duration of response was 10.8 months. The most common related adverse events in pts on ~85 mg BIW/60 mg BIW/80 mg QW were nausea (42%/64%/60%), leukopenia (38%/7%/43%), fatigue (71%/71%/43%), neutropenia (29%/14%/33%), decreased appetite (46%/71%/27%), and thrombocytopenia (67%/29%/23%). Conclusions: SEL demonstrated efficacy, with durable responses and disease stabilization in rGBM. Based on the favorable efficacy and safety profile, SEL at a dose of 80 mg QW is recommended for further development in rGBM. Clinical trial information: NCT01986348. [Table: see text]

Eltanexor (KPT-8602), a second-generation selective inhibitor of nuclear export (SINE) compound, in patients with metastatic castration-resistant prostate cancer (mCRPC)

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Background: Overexpression of exportin 1 (XPO1) in malignant cells increases the nuclear export/inactivation of tumor suppressor proteins (eg. p53), and promotes the translation of eIF4E-bound oncoprotein mRNAs (eg. c-MYC). XPO1 inhibition reduces total androgen receptor levels, including ARv7, and may re-sensitize prostate cancer (PC) cells to androgen deprivation therapy. Selinexor, the first-in-human SINE compound, showed anticancer activity in patients (pts) with mCRPC. Eltanexor (ELTA), a second-generation SINE compound, showed promising anticancer activity in preclinical models of PC, including in abiraterone (ABI) resistant cell lines. Therefore, ELTA ± ABI was evaluated in mCRPC. Methods: This was part of a phase 1/2 study to determine the safety, preliminary efficacy, and recommended phase 2 doseof ELTA in pts with advanced cancers. Pts with mCRPC received oral ELTA once daily for 5 days per week over a 28-day cycle in 4 cohorts: single-agent (20 mg; n=7 or 30 mg; n=6) or in combination with ABI (20 mg; n=13 or 30 mg; n=4). Pts may have prior exposure to chemotherapy. Pts receiving ELTA + ABI had prior response to ABI then progressed. Response was evaluated by PCWG3 / RECIST v1.1. Results: As of 17 Sept 2018, 30 pts were treated with ELTA ± ABI with a median age of 71 and a median of 4 prior regimens; (87% ABI, 60% enzalutamide, and 57% chemotherapy). Twenty-one pts with mCRPC were evaluable for efficacy: 2 partial response (10%), 15 stable disease (71%), and 4 progressive disease (19%). The median treatment duration is 75.5 days; 4 pts still on treatment. Treatment-related adverse events (TRAEs) occurring in ≥30% of the pts: fatigue (67%; 13% Gr≥3), nausea (63.3%; 0% Gr≥3), decreased appetite (57%; 0% Gr≥3), diarrhea (47%; 3% Gr≥3), weight decreased (43%; 3% Gr≥3), vomiting (37%; 7% Gr≥3), anemia (33%; 7% Gr≥3), and dysgeusia (33%; 0% Gr≥3). The 2 Gr4 TRAEs were neutropenia and elevated AST. Conclusions: ELTA± ABI is well-tolerated with AEs mostly limited to Gr 1/2 and demonstrates preliminary anti-tumor activity in patients with mCRPC. With enrollment complete, these results warrant further investigation of ELTA ± ABIin mCPRC. Clinical trial information: NCT02649790.

Exportin 1 (XPO1) inhibition leads to restoration of tumor suppressor miR-145 and consequent suppression of pancreatic cancer cell proliferation and migration

Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer related deaths in the United States with a majority of these patients dying from aggressively invasive and metastatic disease. There is growing evidence that suggests an important role for microRNAs (miRNAs) in the pathobiology of aggressive PDAC. In this study, we found that the expression of miR-145 was significantly lower in PDAC cells when compared to normal pancreatic duct epithelial cells. Here we show that inhibition of the nuclear exporter protein exportin 1 (XPO1; also known as chromosome maintenance region 1 [CRM1]) by siRNA knockdown or by the Selective Inhibitor of Nuclear Export (SINE) compound (KPT-330; selinexor) increases miR-145 expression in PDAC cells resulting in the decreased cell proliferation and migration capacities. A similar result was obtained with forced expression of miR-145 in PDAC cells. To this end, SINE compound treatment mediated the down-regulation of known miR-145 targets genes including EGFR, MMP1, MT-MMP, c-Myc, Pak4 and Sox-2. In addition, selinexor induced the expression of two important tumor suppressive miRNAs miR-34c and let-7d leading to the up-regulation of p21^WAF1. These results are the first to report that targeted inhibition of the nuclear export machinery could restore tumor suppressive miRNAs in PDAC that warrants further clinical investigations.

Abstract CT132: A Phase 2b randomized study of selinexor in patients with relapsed/refractory Diffuse Large B-Cell Lymphoma (DLBCL) demonstrates durable responses in both GCB & Non-GCB subtypes

Intro: Patients with DLBCL after at least two lines of therapy have limited effective treatments options. The nuclear export protein exportin 1 (XPO1) is upregulated in hematologic malignancies including DLBCL with pleiotropic effects on tumorigenesis such as functional downregulation of tumor suppressor proteins (TSPs) as well as increased export and translation of mRNAs for oncoproteins c-Myc and key survival proteins such as Bcl-2. Selinexor (SEL), an oral XPO1 inhibitor, causes sequestration of TSPs including p53, p21, and IκBα, the latter of which serves to suppress NF-κB driven transcription, along with reductions in c-Myc and Bcl family proteins. SEL has shown activity in canine and rodent models of non-Hodgkin’s lymphoma (NHL), as well as in phase 1 clinical studies including DLBCL. Pts with relapsed/refractory (R/R) DLBCL treated with SEL, had an overall response rate (ORR) of 32% including 4 CRs. Interestingly, 2 of these pts remain in CR for &gt;1 yr. In this clinical study we assess the utility of single agent SEL in pts with R/R DLBCL after ≥2 prior regimens.

Methods: Pts with R/R DLBCL were randomized to 60 or 100 mg of SEL twice weekly (8 doses) per 28-day cycle. Pts were also grouped by DLBCL subtype (GCB or non-GCB). The primary objectives are to determine the ORR, and safety of 60 v 100 mg doses. Disease response was assessed using the Lugano Classification (Cheson, 2014). Pt tissue samples were also collected to evaluate cytogenetics.

Results: In 67 pts (33 pts 60 mg, 34 pts 100 mg) enrolled; the most common related adverse effects (AEs) across both dosing groups (Grade 1/2) were: nausea (46%), anorexia (43%), vomiting (36%), and fatigue (34%). Common Grade 3/4 AEs were: thrombocytopenia (39%), fatigue (18%), neutropenia (16%), and anemia (10%). These were managed with dose interruption/reduction, platelet stimulators, and/or standard supportive care. Grade 3/4 fatigue (13% v 4%) and thrombocytopenia (22% v 16%) were higher in 100 mg arm as compared to the 60 mg arm. Among 65 evaluable pts, the ORR was 21.5%. Responders had a median of 3 prior treatment regimens. 8 pts (12.3%) had a complete response (CR) and 6 pts (9.2%) achieved a partial response. 9 responders, including 7 CR, remain on treatment. Median time on study for CR is 8.8+ mos. ORR by subtype: GCB 23.5%, non-GCB 19.3%. The ORR (26.4%) in the 60 mg arm was higher than 100 mg arm (16.1%), possibly due to better tolerability and less time without drug exposure.

Conclusion: SEL monotherapy shows anti-cancer activity in pts with R/R DLBCL including in pts with GCB subtype. 60 mg SEL twice weekly was more tolerable than 100 mg twice weekly, with less dosing interruptions due to toxicity and a trend towards higher response rates. Objective responses to SEL were durable, suggesting these responses were associated with clinical benefit. Molecular predictors of response are being evaluated.

Citation Format: Marie Maerevoet, Jason Westin, Catherine Thieblemont, Josee Zijlstra, Brian T. Hill, Fatima De La Cruz Vicente, Sylvain Choquet, Paolo Caimi, Jason Kaplan, Miguel Albendea Canales, John Kuruvilla, George Follows, Eric Van den Neste, Julie Meade, Brendan Wrigley, Marissa Devlin, Conny Nippgen, Humphrey Gardner, Sharon Shacham, Michael G. Kauffman, Rene-Olivier Casasnovas. A Phase 2b randomized study of selinexor in patients with relapsed/refractory Diffuse Large B-Cell Lymphoma (DLBCL) demonstrates durable responses in both GCB & Non-GCB subtypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT132. doi:10.1158/1538-7445.AM2017-CT132

XPO1 Inhibition Preferentially Disrupts the 3D Nuclear Organization of Telomeres in Tumor Cells

Previous work has shown that the three-dimensional (3D) nuclear organization of telomeres is altered in cancer cells and the degree of alterations coincides with aggressiveness of disease. Nuclear pores are essential for spatial genome organization and gene regulation and XPO1 (exportin 1/CRM1) is the key nuclear export protein. The Selective Inhibitor of Nuclear Export (SINE) compounds developed by Karyopharm Therapeutics (KPT-185, KPT-330/selinexor, and KPT-8602) inhibit XPO1 nuclear export function. In this study, we investigated whether XPO1 inhibition has downstream effects on the 3D nuclear organization of the genome. This was assessed by measuring the 3D telomeric architecture of normal and tumor cells in vitro and ex vivo. Our data demonstrate for the first time a rapid and preferential disruption of the 3D nuclear organization of telomeres in tumor cell lines and in primary cells ex vivo derived from treatment-naïve newly diagnosed multiple myeloma patients. Normal primary cells in culture as well as healthy lymphocyte control cells from the same patients were minimally affected. Using both lymphoid and non-lymphoid tumor cell lines, we found that the downstream effects on the 3D nuclear telomere structure are independent of tumor type. We conclude that the 3D nuclear organization of telomeres is a sensitive indicator of cellular response when treated with XPO1 inhibitors. J. Cell. Physiol. 231: 2711-2719, 2016. © 2016 Wiley Periodicals, Inc.

Next-generation XPO1 inhibitor shows improved efficacy and in vivo tolerability in hematological malignancies

The nuclear export receptor, Exportin 1 (XPO1), mediates transport of growth-regulatory proteins, including tumor suppressors, and is overactive in many cancers, including chronic lymphocytic leukemia (CLL), acute myeloid leukemia (AML) and aggressive lymphomas. Oral selective inhibitor of nuclear export (SINE) compounds that block XPO1 function were recently identified and hold promise as a new therapeutic paradigm in many neoplasms. One of these compounds, KPT-330 (selinexor), has made progress in Phase I/II clinical trials, but systemic toxicities limit its administration to twice-per-week and requiring supportive care. We designed a new generation SINE compound, KPT-8602, with a similar mechanism of XPO1 inhibition and potency but considerably improved tolerability. Efficacy of KPT-8602 was evaluated in preclinical animal models of hematological malignancies, including CLL and AML. KPT-8602 shows similar in vitro potency compared with KPT-330 but lower central nervous system penetration, which resulted in enhanced tolerability, even when dosed daily, and improved survival in CLL and AML murine models compared with KPT-330. KPT-8602 is a promising compound for further development in hematological malignancies and other cancers in which upregulation of XPO1 is seen. The wider therapeutic window of KPT-8602 may also allow increased on-target efficacy leading to even more efficacious combinations with other targeted anticancer therapies.

Abstract 19: Antitumor activity of selective inhibitors of XPO1/CRM1-mediated nuclear export in diffuse malignant peritoneal mesothelioma: the role of survivin

Survivin, which is highly expressed and promotes cell survival in diffuse malignant peritoneal mesothelioma (DMPM), exclusively relies on the nuclear exportin 1 (XPO1/CRM1) to be released in the cytoplasm and perform its anti-apoptotic function. Here, we explored the efficacy of selective inhibitors of nuclear export (SINEs) in patient-derived DMPM preclinical models. Exposure to individual SINE (KPT-251, KPT-276, KPT-330) was able to induce a time- and dose-dependent inhibition of the growth of two DMPM cell lines without affecting normal cell proliferation. Such a cell growth inhibition was preceded by a decline in the nuclear XPO1/CRM1 levels and an increase in the nuclear accumulation of its cargo proteins p53 and p21, which led to a cell cycle arrest at G1-phase. Our results also indicated that survivin is an essential component of the downstream signaling pathway of XPO1/CRM1 inhibition in DMPM cells. In fact, in both cell lines, exposure to SINEs led to a time-dependent reduction of cytoplasmic survivin levels and, after an initial survivin nuclear accumulation, also to a progressive decrease in the nuclear protein abundance, through the ubiquitin-proteasomal degradation pathway, leading to the complete depletion of total survivin levels. In both DMPM cell models, according to survivin anti-apoptotic activity, drug-induced reduction of cytoplasmic survivin levels correlated with the onset of caspase-dependent apoptosis. We further observed that SINEs can be combined with other survivin inhibitors, such as the survivin suppressant YM155 to achieve enhanced growth inhibition in DMPM cells. Initial in vivo experiments with orally administered KPT-251, KPT-276 and the orally available, clinical stage KPT-330 (selinexor) indicated that each compound was able to significantly reduce the growth of early-stage subcutaneous DMPM xenografts. Interestingly, additional experiments carry out with selinexor demonstrated that the compound was also able to inhibit the growth of late-stage subcutaneous DMPM xenografts in nude mice. Most importantly, oral administration of selinexor to SCID mice reduced the growth of orthotopic DMPM xenografts, which properly recapitulate the dissemination pattern in the peritoneal cavity of human DMPM and, for this reason, represent a valuable model for investigating novel therapeutic approaches for the disease. Consistent with an important role of survivin as a determinant of anti-cancer activity of SINE compounds, a reduction of the protein expression was observed in tumor specimens obtained from selinexor treated mice. Overall, our results (i) demonstrate a marked efficacy of SINEs in DMPM preclinical models, which is, at least in part, dependent on the interference with survivin intracellular distribution and function, and (ii) suggest SINE-mediated XPO1/CRM1 inhibition as a novel therapeutic option for the disease.

Citation Format: Nadia Zaffaroni, Michelandrea De Cesare, Denis Cominetti, Valentina Doldi, Alessia Lopergolo, Marcello Deraco, Paolo Gandellini, Yosef Landesman, Sharon Friedlander, Michael G. Kauffman, Sharon Shacham, Marzia Pennati. Antitumor activity of selective inhibitors of XPO1/CRM1-mediated nuclear export in diffuse malignant peritoneal mesothelioma: the role of survivin. [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 19. doi:10.1158/1538-7445.AM2015-19

Anti-tumor activity of selective inhibitors of XPO1/CRM1-mediated nuclear export in diffuse malignant peritoneal mesothelioma: the role of survivin

Survivin, which is highly expressed and promotes cell survival in diffuse malignant peritoneal mesothelioma (DMPM), exclusively relies on exportin 1 (XPO1/CRM1) to be shuttled into the cytoplasm and perform its anti-apoptotic function. Here, we explored the efficacy of Selective Inhibitors of Nuclear Export (SINE), KPT-251, KPT-276 and the orally available, clinical stage KPT-330 (selinexor), in DMPM preclinical models. Exposure to SINE induced dose-dependent inhibition of cell growth, cell cycle arrest at G1-phase and caspase-dependent apoptosis, which were consequent to a decrease of XPO1/CRM1 protein levels and the concomitant nuclear accumulation of its cargo proteins p53 and CDKN1a. Cell exposure to SINE led to a time-dependent reduction of cytoplasmic survivin levels. In addition, after an initial accumulation, the nuclear protein abundance progressively decreased, as a consequence of an enhanced ubiquitination and proteasome-dependent degradation. SINE and the survivin inhibitor YM155 synergistically cooperated in reducing DMPM cell proliferation. Most importantly, orally administered SINE caused a significant anti-tumor effect in subcutaneous and orthotopic DMPM xenografts without appreciable toxicity. Overall, we have demonstrated a marked efficacy of SINE in DMPM preclinical models that may relay on the interference with survivin intracellular distribution and function. Our study suggests SINE-mediated XPO1/CRM1 inhibition as a novel therapeutic option for DMPM.

Abstract 3808: Preclinical efficacy of the novel, oral Selective Inhibitor of Nuclear Export (SINE) Selinexor (KPT-330) on castration resistant prostate cancer

Exportin 1/ Chromosomal Maintenance Protein 1 (XPO1/CRM1) is a key nuclear export protein whose inhibition leads to the nuclear accumulation of tumor suppressor proteins such as p53, FOXO, PTEN, pRB and I-κB. Selinexor is an orally bioavailable XPO1 inhibitor that represents a novel class of small molecule compounds with potent activity against a wide variety of cancers. Here we report the activity of Selinexor against Castration resistant prostate cancer (CRPC).

CRPC progression is mediated by activation of various adaptive Androgen Receptor (AR) signaling pathways. These pathways are currently being targeted by novel anti-androgen therapies such as abiraterone acetate and enzalutamide with favorable outcomes. However, resistance to anti-androgen therapy can be developed through deregulation of tumor suppressor pathways. XPO-1 is highly expressed in prostate cancer cells and therefore we tested the effects of Selinexor on CRPC cells and tumors models. Treatment of the C4-2B prostate cancer cell line with Selinexor in vitro significantly inhibited cell proliferation and resulted in nuclear accumulation of p53 and p21. In addition, Selinexor inhibited expression of the tumor-promoting gene Ubiquitin-Conjugating Enzyme E2C (UBE2C), which is activated by AR in these cells. Selinexor was also tested in tumor graft models of two patient tumors in castrated male mice. The MDA-PCa-133 tumor is an adenocarcinoma derived from a clinical CRPC bone metastasis. Subcutaneous MDA-PCa-133 tumors in castrated male mice express full-length AR and Prostate-Specific Antigen (PSA) but lack expression of p53. The MDA-PCa-144-13 tumor is a small cell carcinoma derived from a lethal variant of prostate cancer with anaplastic clinical phenotype and does not express AR or PSA but expresses a gain-of-function p53 mutant. Vehicle or Selinexor treatment (10 mg/kg p.o. QoDX3 M/W/F) of MDA-PCa-133 tumors for 34 days resulted in almost complete inhibition of tumor growth with a 30-fold reduction of PSA (p&lt;0.001). Treatment of MDA-PCa-144-13 tumors for 22 days also resulted in significant reduction of tumor volume (&gt;8 fold compared to vehicle only; p&lt;0.0047). Immunohistochemical analysis of MDA-PCa-133 tumors showed that Selinexor induced nuclear accumulation of XPO1 cargos FOXO3a and p27 with concomitant reduction in the proliferation marker KI67.

In conclusion, Selinexor demonstrated robust inhibition of CRPC tumor growth and activated multiple tumor suppressors in prostate cancer cells. Selinexor is now being evaluated in Phase 1 clinical studies in patients with advanced hematological and solid tumor cancers, and preliminary results show adequate tolerability with evidence of anti cancer activity. Future clinical studies in patients with CRPC are planned and will provide more information on the use of Selinexor as monotherapy and in combination with anti-androgen therapy of CRPC.

Citation Format: Sankar Narayan Maity, Guanglin Wu, Jing-Fang Lu, Anh Hoang, Yosef Landesman, Dilara McCauley, Sharon Shacham, Michael G. Kauffman, Ana M. Aparicio, Eleni Efstathiou, John C. Araujo, Christopher J. Logothetis. Preclinical efficacy of the novel, oral Selective Inhibitor of Nuclear Export (SINE) Selinexor (KPT-330) on castration resistant prostate cancer. [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 3808. doi:10.1158/1538-7445.AM2014-3808

Biologic activity of the novel orally bioavailable selective inhibitor of nuclear export (SINE) KPT-335 against canine melanoma cell lines

BACKGROUND

Exportin 1 (XPO1, also known as CRM1), is a chaperone protein responsible for the export of over 200 target proteins out of the nucleus. The expression and activity of XPO1 is upregulated in several human cancers and its expression is also linked to the development of chemotherapy resistance. Recent studies using both human and murine cancer cell lines have demonstrated that XPO1 is a relevant target for therapeutic intervention. The present study sought to characterize the biologic activity of an orally bioavailable selective inhibitor of nuclear export (SINE), KPT-335, against canine melanoma cell lines as a prelude to future clinical trials in dogs with melanoma.

RESULTS

We evaluated the effects of KPT-335 on 4 canine malignant melanoma cell lines and found that KPT-335 inhibited proliferation, blocked colony formation, and induced apoptosis of treated cells at biologically relevant concentrations of drug. Additionally, KPT-335 downregulated XPO1 protein while inducing a concomitant increase in XPO1 messenger RNA. Lastly, KPT-335 treatment of cell lines upregulated the expression of both protein and mRNA for the tumor suppressor proteins p53 and p21, and promoted their nuclear localization.

CONCLUSIONS

KPT-335 demonstrates biologic activity against canine melanoma cell lines at physiologically relevant doses, suggesting that KPT-335 may represent a viable treatment option for dogs with malignant melanoma.

XPO1 (CRM1) inhibition represses STAT3 activation to drive a survivin-dependent oncogenic switch in triple-negative breast cancer

Inhibition of XPO1 (CRM1)-mediated nuclear export of multiple tumor suppressor proteins has been proposed as a novel cancer therapeutic strategy to turn off oncogenic signals and enhance tumor suppression. Survivin is a multifunctional protein with oncogenic properties when expressed in the cytoplasm that requires the XPO1-RanGTP complex for its nuclear export. We investigated the antitumor mechanisms of the drug-like selective inhibitors of nuclear export (SINE) XPO1 antagonists KPT-185, KPT-251 KPT-276, and KPT-330 in estrogen receptor-positive and triple-negative breast cancer (TNBC) cell lines and xenograft models of human breast tumors. KPT compounds significantly inhibited breast cancer cell growth and induced tumor cell death, both in vitro and in vivo. These drugs initially promoted survivin accumulation within tumor cell nuclei. However, their major in vitro effect was to decrease survivin cytoplasmic protein levels, correlating with the onset of apoptosis. XPO1 inhibition repressed Survivin transcription by inhibiting CREB-binding protein-mediated STAT3 acetylation, and blocking STAT3 binding to the Survivin promoter. In addition, caspase-3 was activated to cleave survivin, rendering it unavailable to bind X-linked inhibitor of apoptosis protein and block the caspase cascade. Collectively, these data demonstrate that XPO1 inhibition by SINE compounds represses STAT3 transactivation to block the selective oncogenic properties of survivin and supports their clinical use in TNBC.

Preclinical and clinical efficacy of XPO1/CRM1 inhibition by the karyopherin inhibitor KPT-330 in Ph+ leukemias

As tyrosine kinase inhibitors (TKIs) fail to induce long-term response in blast crisis chronic myelogenous leukemia (CML-BC) and Philadelphia chromosome-positive (Ph(+)) acute lymphoblastic leukemia (ALL), novel therapies targeting leukemia-dysregulated pathways are necessary. Exportin-1 (XPO1), also known as chromosome maintenance protein 1, regulates cell growth and differentiation by controlling the nucleocytoplasmic trafficking of proteins and RNAs, some of which are aberrantly modulated in BCR-ABL1(+) leukemias. Using CD34(+) progenitors from CML, B-ALL, and healthy individuals, we found that XPO1 expression was markedly increased, mostly in a TKI-sensitive manner, in CML-BC and Ph(+) B-ALL. Notably, XPO1 was also elevated in Ph(-) B-ALL. Moreover, the clinically relevant XPO1 inhibitor KPT-330 strongly triggered apoptosis and impaired the clonogenic potential of leukemic, but not normal, CD34(+) progenitors, and increased survival of BCR-ABL1(+) mice, 50% of which remained alive and, mostly, became BCR-ABL1 negative. Moreover, KPT-330 compassionate use in a patient with TKI-resistant CML undergoing disease progression significantly reduced white blood cell count, blast cells, splenomegaly, lactate dehydrogenase levels, and bone pain. Mechanistically, KPT-330 altered the subcellular localization of leukemia-regulated factors including RNA-binding heterogeneous nuclear ribonucleoprotein A1 and the oncogene SET, thereby inducing reactivation of protein phosphatase 2A tumor suppressor and inhibition of BCR-ABL1 in CML-BC cells. Because XPO1 is important for leukemic cell survival, KPT-330 may represent an alternative therapy for TKI-refractory Ph(+) leukemias.

Abstract A19: KPT0127, a novel, potent, and selective inhibitor of Crm1-mediated nuclear export shows selective cytotoxicity for neoplastic over normal cells and is well tolerated in animals

CRM1 (Xpo1) is the major export factor for proteins from the nucleus to the cytoplasm, including tumor suppressors (TSPs) and other modulators of proliferative responses such as p53, FOXO, c-Abl, pRB and IκB. Leptomycin B (LMB), a non-drug like natural product is a potent inhibitor of CRM1-mediated nucleocytoplasmic transport. LMB and related analogs trap TSPs and other proteins in the nucleus, forcing neoplastic cells into apoptosis while normal cells undergo reversible cell cycle arrest. However, LMB has limited efficacy in vivo due to its severe gastrointestinal toxicity. Here, we describe our lead compound KPT-0127 a novel small molecule, water soluble, drug-like, selective, irreversible CRM1 antagonist. Like LMB, KPT-0127 forms a covalent bond with Cys528 in the CRM1 cargo-binding pocket, abrogating most, but not all, export functions of CRM1. KPT-0127 exerts a potent (EC50 300-400nM) and prolonged inhibition of CRM1- mediated HIV-1 Rev, forkhead (FOXO), and p53 nuclear export in a variety of normal and transformed cell lines. In cytotoxicity assays, KPT-0127 showed high potency in most hematologic cancer cell lines (EC50 &lt;500nM, with leukemia and lymphoma lines often &lt;100nM) and variable activity in solid tumor cell lines (EC50 90-2000nM), with colon and melanoma cells being the most sensitive (EC50&lt; 100 nM). By contrast, normal cells were largely unaffected by treatment with KPT-0127 (EC50 &gt;5-10µM). Studies in the HCT-116 colon cancer cell line suggested that KPT-0127 dose dependently increases the nuclear levels of p53 and appears to induce cell cycle arrest at both the G1/S and G2/M checkpoints, prior to inducing apoptosis. In normal peripheral blood mononuclear cells (PBMCs) and in Hut78 leukemia cells, KPT-0127 potently increased the nuclear levels of IκB. However, KPT-0127 induced cell death of Hut78 cells with no effect on normal PBMCs. In drug combination studies, KPT-0127 showed additive or synergistic cytotoxicity activity with either 5-FU, carboplatin, or doxorubicin. Mechanism of action studies demonstrated that the Cys528 residue in the cargo-binding pocket of CRM1 is essential for the inhibitory effect of KPT-0127. Mutagenesis of Cys528 to a Ser completely abrogated KPT-0127 inhibition. KPT-0128, the transisomer of KPT-0127, shows little effect on both HIV-Rev nuclear export and in cytotoxicity assays (EC50s &gt; 10μM), supporting the specificity of KPT-0127 for CRM1. Moreover, the selectivity of KTP-0127 was demonstrated across a panel of 37 proteins including several cysteine proteases.

In single dose mouse toxicology studies, KPT-0127 was generally well tolerated (oral or SC) up to 560 mg/kg, and no deaths were observed. SC dosing daily for 5 days up to 100mg/kg (the highest dose tested) showed no behavioral, clinical chemistry, or hematogical effects in mice; Pharmacokinetics of KPT-0127 is adequate and in vivo efficacy studies are currently being performed; results will be presented. All together, these data demonstrate that KPT-0127 represents a novel, tumor selective, and well-tolerated irreversible Crm1 inhibitor which may be suitable for clinical development both as a single agent and in combination with standard therapies.

Citation Information: Clin Cancer Res 2010;16(14 Suppl):A19.

Mutations in the thymidine kinase gene that allow expression of the enzyme in quiescent (G0) cells

Thymidine kinase (TK) is a nucleotide salvage pathway enzyme whose activity is highly dependent on the growth state and cell cycle phase of a cell. Cells in the resting or quiescent (G0) phase express very low levels of TK mRNA and protein. When quiescent cells are stimulated to enter the cell cycle by the addition of serum, TK mRNA, activity and polypeptide increase coordinately after about 10-15 h, at the beginning of S phase. When growth-independent heterologous promoters are substituted for the natural TK promoter, TK mRNA can be expressed in quiescent cells. Despite the presence of TK mRNA in such G0 cells, there is little expression of TK polypeptide; the normal increase in enzyme at S phase is observed following serum stimulation. Deletion of the introns and 3' untranslated sequences does not affect the expression of the TK gene in serum stimulation experiments. In contrast, deletion of the C-terminal 40 amino acids or fusion of a small segment of a beta-galactosidase to the C-terminus overcomes the block to expression of the TK polypeptide in G0 cells. These C-terminal alterations are the same as those which lead to constitutive expression of TK during the cell cycle of proliferating cells, suggesting that mechanisms which control the levels of TK in cycling cells may also operate in quiescent cells.

Cell cycle regulation of thymidine kinase: residues near the carboxyl terminus are essential for the specific degradation of the enzyme at mitosis

The level of human thymidine kinase (TK) polypeptide is subject to cell cycle regulation. The enzyme is barely detectable in G1 phase but increases 10- to 20-fold by M phase. The low level of human TK in G1 phase is due primarily to the specific degradation of the protein during cell division. Substitution of heterologous promoters, removal of the introns, and deletion of all of the 3' untranslated region from the human TK gene do not affect cell cycle regulation of the enzyme. However, deletion of the carboxyl-terminal 40 amino acids or fusion of beta-galactosidase to the carboxyl terminus of human TK completely abolishes cell cycle regulation and stabilizes the protein throughout the cell cycle. These alterations do not significantly alter the specific enzymatic activity of TK. Changing the carboxyl terminus or deletion of the last 10 amino acids does not alter cell cycle regulation. These data demonstrate that residues near the carboxyl terminus of TK are essential for the cell cycle phase-specific degradation of the enzyme.

Isolation of cell cycle fractions by counterflow centrifugal elutriation

Counterflow centrifugal elutriation (CCE) has been used to fractionate cell populations on the basis of sedimentation properties, with minimal perturbation of metabolic function. Therefore, it is an ideal method for the isolation of cell cycle phase specific populations. We present modifications of the standard Beckman centrifugal elutriation system which permit standardization of the elutriation procedure and eliminate inter-run variability. We provide elutriation parameters for the cell cycle fractionation of a variety of cultured cell lines and suggest ways to improve the quality of the cell separations. In addition, we describe protocols for the fractionation of up to 3.50 X 10(8) cells in the small (JE-6B) Beckman elutriation system. This represents a four- to eight-fold increase in cell numbers over current cell fractionation procedures. Cell cycle populations containing greater than 95% G1, greater than 80% S, and greater than 70% G2/M were consistently obtained using these protocols. Finally, we analyzed phase-enriched fractions from several cultured cell lines for the cell cycle regulation of the enzyme thymidine kinase. The data confirm previous findings that CCE is an excellent means of obtaining physiologically unperturbed cell cycle phase specific fractions.

Activation of SV40 DNA replication in vitro by cellular protein phosphatase 2A

We have made use of the cell-free SV40 DNA replication system to identify and characterize cellular proteins required for efficient DNA synthesis. One such protein, replication protein C (RP-C), was shown to be involved with SV40 large T antigen in the early stages of viral DNA replication in vitro. We demonstrate here that RP-C is identical to the catalytic subunit of cellular protein phosphatase 2A (PP2Ac). The purified protein dephosphorylates specific phosphoamino acid residues in T antigen, consistent with the hypothesis that SV40 DNA replication is regulated by modulating the phosphorylation state of the viral initiator protein. We also show that purified RP-C/PP2Ac preferentially stimulates SV40 DNA replication in extracts from early G1 phase cells. This finding suggests that the activity of a cellular factor that influences the net phosphorylation state of T antigen is cell cycle dependent.

Accessory cells in immune suppression. II. Evidence for presentation of idiotype-specific suppressor factors to B cell targets by I-A+ accessory cells

The functional suppression of two BALB/c myelomas, MOPC315 and MOPC460, by idiotype-specific suppressor T cells is mediated by secreted factors (TsF). Idiotype-specific TsF only functions in the presence of accessory cells (AC) that can be low density splenocytes or cells of BALB/c B lymphoma A20-2J. Such AC are I-A+ but do not have to be histocompatible with the myeloma targets or the source of TsF. A20-2J cells incubated with soluble idiotype and TsF also are capable of suppressing the relevant myeloma target. The effect of TsF-pulsed A20-2J cells is idiotype specific, and these cells do not secrete immunosuppressive mediators. Finally, TsF-pulsed A20-2J cells suppress myeloma targets when the two are cultured on the same side of a cell-impermeable membrane but not when they are separated by the membrane. These results indicate that I-A+ cells are capable of concentrating and/or presenting TsF to suppressible targets, and they demonstrate a novel role for Ia-bearing cells in immune regulation.

Accessory cells in immune suppression. II. Evidence for presentation of idiotype-specific suppressor factors to B cell targets by I-A+ accessory cells

The functional suppression of two BALB/c myelomas, MOPC315 and MOPC460, by idiotype-specific suppressor T cells is mediated by secreted factors (TsF). Idiotype-specific TsF only functions in the presence of accessory cells (AC) that can be low density splenocytes or cells of BALB/c B lymphoma A20-2J. Such AC are I-A+ but do not have to be histocompatible with the myeloma targets or the source of TsF. A20-2J cells incubated with soluble idiotype and TsF also are capable of suppressing the relevant myeloma target. The effect of TsF-pulsed A20-2J cells is idiotype specific, and these cells do not secrete immunosuppressive mediators. Finally, TsF-pulsed A20-2J cells suppress myeloma targets when the two are cultured on the same side of a cell-impermeable membrane but not when they are separated by the membrane. These results indicate that I-A+ cells are capable of concentrating and/or presenting TsF to suppressible targets, and they demonstrate a novel role for Ia-bearing cells in immune regulation.