Paediatric Strategy Forum for medicinal product development of DNA damage response pathway inhibitors in children and adolescents with cancer: ACCELERATE in collaboration with the European Medicines Agency with participation of the Food and Drug Administration

DNA damage response inhibitors have a potentially important therapeutic role in paediatric cancers; however, their optimal use, including patient selection and combination strategy, remains unknown. Moreover, there is an imbalance between the number of drugs with diverse mechanisms of action and the limited number of paediatric patients available to be enrolled in early-phase trials, so prioritisation and a strategy are essential. While PARP inhibitors targeting homologous recombination-deficient tumours have been used primarily in the treatment of adult cancers with BRCA1/2 mutations, BRCA1/2 mutations occur infrequently in childhood tumours, and therefore, a specific response hypothesis is required. Combinations with targeted radiotherapy, ATR inhibitors, or antibody drug conjugates with DNA topoisomerase I inhibitor-related warheads warrant evaluation. Additional monotherapy trials of PARP inhibitors with the same mechanism of action are not recommended. PARP1-specific inhibitors and PARP inhibitors with very good central nervous system penetration also deserve evaluation. ATR, ATM, DNA-PK, CHK1, WEE1, DNA polymerase theta and PKMYT1 inhibitors are early in paediatric development. There should be an overall coordinated strategy for their development. Therefore, an academia/industry consensus of the relevant biomarkers will be established and a focused meeting on ATR inhibitors (as proof of principle) held. CHK1 inhibitors have demonstrated activity in desmoplastic small round cell tumours and have a potential role in the treatment of other paediatric malignancies, such as neuroblastoma and Ewing sarcoma. Access to CHK1 inhibitors for paediatric clinical trials is a high priority. The three key elements in evaluating these inhibitors in children are (1) innovative trial design (design driven by a clear hypothesis with the intent to further investigate responders and non-responders with detailed retrospective molecular analyses to generate a revised or new hypothesis); (2) biomarker selection and (3) rational combination therapy, which is limited by overlapping toxicity. To maximally benefit children with cancer, investigators should work collaboratively to learn the lessons from the past and apply them to future studies. Plans should be based on the relevant biology, with a focus on simultaneous and parallel research in preclinical and clinical settings, and an overall integrated and collaborative strategy.

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.

Abstract 4181: The XPO1 inhibitior, eltanexor, exhibits potent in vivo activity against a broad range of pediatric acute lymphoblastic leukemia subtypes

Introduction: Exportin 1 (XPO1/CRM1) plays a central role in the export of proteins from the nucleus including those with tumor suppressor and growth regulatory activity. Eltanexor (KPT-8602) is a second-generation Selective Inhibitor of Nuclear Export (SINE) that specifically blocks XPO1 cargo interactions and is under clinical evaluation for adults with cancer (NCT02649790). In previous Pediatric Preclinical Testing Consortium (PPTC) studies, eltanexor showed potent in vivo activity against acute lymphoblastic leukemia (ALL) patient-derived xenografts (PDXs). In an effort to understand whether eltanexor exhibited subtype-specific activity in pediatric ALL we carried out a single-mouse trial (SMT) against an intended 90 pediatric ALL PDXs.

Methods: Pediatric ALL PDXs, an orthotopic model of the disease, were inoculated into NSG mice in an SMT format (a single mouse inoculated with a single PDX was treated with a single drug). Engraftment and drug responses were assessed by weekly enumeration of the % human leukemic blasts in the peripheral blood (%huCD45+/HLA-ABC+). Treatment commenced when the median %huCD45+/HLA-ABC+ exceeded 1%, and mice received eltanexor at 12.5 mg/kg per oral daily x 5 for 4 weeks. The baseline level of the %huCD45+/HLA-ABC+ in each mouse served as its own control. PDX responses to treatment were assessed by time to event, the maximum decrease in %huCD45+/ABC+ at any point after treatment initiation, and by stringent Objective Response Measures (ORMs) modeled after the clinical setting (Houghton et al, Pediatr Blood Cancer, 2007, 49:928-40).

Results: Eltanexor was well tolerated with a mean maximum weight loss of 5.5% across all mice. SMT testing was successful in all 90 pediatric ALL PDXs representative of B-ALL (typical B-ALL, Philadelphia chromosome-positive ALL [Ph+-ALL] and Ph-like ALL), T-ALL (typical T-ALL and early T-cell precursor ALL [ETP-ALL]), and MLL-rearranged ALL (MLLr-ALL). Event-free survival (EFS) of mice ranged from 2.6-137 days, and 61 (68%) of mice experienced EFS that extended beyond the treatment window. Regressions of ≥50% from baseline were observed in 56 (62%) of mice, and these were most pronounced in T-ALL (14/18, 78%) and Ph-like ALL (11/19, 58%). ORMs classified as Complete Response (CR) or Maintained CR (MCR) were elicited in 43 (48%) of PDXs, and again these were more common in T-ALL (12/18, 67%). The ALL subtypes that exhibited the poorest responses to eltanexor were Ph+-ALL and ETP-ALL, although with relatively small sample size (n=3 and 6, respectively). ORMs in the SMT correlated highly with historical conventional drug testing (R=0.94, P<0.001, n=12).

Conclusions: Eltanexor exhibits potent single-agent in vivo activity against PDXs derived from a broad range of ALL subtypes including T-ALL and Ph-like ALL and warrants further investigation in pediatric ALL. (Supported by NCI Grants CA199222 & CA199000)

Citation Format: Richard B. Lock, Kathryn Evans, Connor D. Jones, Stephen W. Erickson, Beverly A. Teicher, TJ Unger, Yosef Landesman, Malcolm A. Smith. The XPO1 inhibitior, eltanexor, exhibits potent in vivo activity against a broad range of pediatric acute lymphoblastic leukemia subtypes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4181.

Phase 2 study of the Exportin 1 inhibitor selinexor in patients with recurrent gynecological malignancies

BACKGROUND

Selinexor is an oral inhibitor of the nuclear export protein Exportin 1 (XPO1) with demonstrated antitumor activity in solid and hematological malignancies. We evaluated the efficacy and safety of selinexor in heavily pretreated, recurrent gynecological malignancies.

METHODS

In this phase 2 trial, patients received selinexor (35 or 50 mg/m2 twice-weekly [BIW] or 50 mg/m2 once-weekly [QW]) in 4-week cycles. Primary endpoint was disease control rate (DCR) including complete response (CR), partial response (PR) or stable disease (SD) ≥12 weeks. Secondary endpoints were progression-free survival (PFS), overall survival (OS) and safety.

RESULTS

114 patients with ovarian (N = 66), endometrial (N = 23) or cervical (N = 25) cancer were enrolled. Median number of prior regimens for ovarian, endometrial and cervical cancer was 6 (1-11), 2 (1-5), and 3 (1-6) respectively. DCR was 30% (ovarian 30%; endometrial 35%; cervical 24%), which included confirmed PRs in 8%, 9%, and 4% of patients with ovarian, endometrial, and cervical cancer respectively. Median PFS and OS for patients with ovarian, endometrial and cervical cancer were 2.6, 2.8 and 1.4 months, and 7.3, 7.0, and 5.0 months, respectively. Common Grade 3/4 adverse events (AEs) were thrombocytopenia (17%), fatigue (14%), anemia (10%), nausea (9%) and hyponatremia (9%). Patients with ovarian cancer receiving 50 mg/m2 QW had fewer high-grade AEs with similar efficacy as BIW treatment.

CONCLUSIONS

Selinexor demonstrated single-agent activity and disease control in patients with heavily pretreated ovarian and endometrial cancers. Side effects were a function of dose level and treatment frequency, similar to previous reports, reversible and mitigated with supportive care.

Selinexor, a Selective Inhibitor of Nuclear Export (SINE) compound, acts through NF-κB deactivation and combines with proteasome inhibitors to synergistically induce tumor cell death

The nuclear export protein, exportin-1 (XPO1/CRM1), is overexpressed in many cancers and correlates with poor prognosis. Selinexor, a first-in-class Selective Inhibitor of Nuclear Export (SINE) compound, binds covalently to XPO1 and blocks its function. Treatment of cancer cells with selinexor results in nuclear retention of major tumor suppressor proteins and cell cycle regulators, leading to growth arrest and apoptosis. Recently, we described the selection of SINE compound resistant cells and reported elevated expression of inflammation-related genes in these cells. Here, we demonstrated that NF-κB transcriptional activity is up-regulated in cells that are naturally resistant or have acquired resistance to SINE compounds. Resistance to SINE compounds was created by knockdown of the cellular NF-κB inhibitor, IκB-α. Combination treatment of selinexor with proteasome inhibitors decreased NF-κB activity, sensitized SINE compound resistant cells and showed synergistic cytotoxicity in vitro and in vivo. Furthermore, we showed that selinexor inhibited NF-κB activity by blocking phosphorylation of the IκB-α and the NF-κB p65 subunits, protecting IκB-α from proteasome degradation and trapping IκB-α in the nucleus to suppress NF-κB activity. Therefore, combination treatment of selinexor with a proteasome inhibitor may be beneficial to patients with resistance to either single-agent.

Abstract 2899: Selinexor inhibits NF-κB activity by sequestering IkB-a in the nucleus and blocking IkB-a degradation

Background: Selinexor is a small-molecule therapeutic that inhibits XPO1 mediated nuclear export, resulting in nuclear accumulation of tumor suppressor proteins (TSPs) and subsequently cancer cell death while sparing normal cells. It has been previously demonstrated that the inhibitor of NFκB, IκB-, is localized to the cytoplasm by XPO1 in several cancer cell lines and that treatment of cancer cells with selinexor reduces NF-κB transcriptional activity. The mechanism of NF-κB inhibition by selinexor, however, is not fully understood. We hypothesized that nuclear retention of IκB- and down-regulation of IκB- kinase (IKK) in response to selinexor treatment would inhibit NF-κB transcriptional activity.

Methods: U2OS (Osteosarcoma) cells were treated with selinexor in the presence or absence of TNF stimulation and whole protein lysates were analyzed by Western blotting. IκB- localization was evaluated by immunofluorescence microscopy and NF-κB transcriptional activity by ELISA (Thermo Scientific).

Results: TNFα induced the phosphorylation of NF-κB p65 subunit on serine 536 and IκB- on serine 32/36 through IKK. This resulted in the dissociation of IκB-α from NF-κB and led to IκB-α degradation via the 26S proteasome. Free NF-κB could now migrate into the nucleus and initiate transcriptional activation supporting tumorigenicity and inflammation. The IKK kinase is a complex made of two kinases (IKKα and IKKβ) and one regulatory subunit, NEMO/IKKγ. We found that selinexor treatment blocked IKK activity through the down regulation of the IKK (IKKγ) gamma subunit protein levels. This inhibition was dose dependent and prevented IκB- phosphorylation, thereby protecting IκB- from degradation. The protection of intact IκB- from degradation and its forced nuclear accumulation through XPO1 inhibition enabled inhibition of NF-κB transcriptional activity even in the presence of TNFα. Selinexor did not alter the protein levels of IKK or IKK.

Conclusions: Selinexor blocks TNFα induced degradation of IκB- by reducing the levels of IKK. In addition, selinexor increased nuclear IκB- levels through the inhibition of nuclear export. This blocked NF-κB activity and enhanced cancer cell death. We are currently investigating the beneficial effects of combining selinexor with proteasome inhibitors, which are known to prevent IκB- degradation.

Citation Format: Trinayan Kashyap, Christian Argueta, Boris Klebanov, TJ Unger, Benjamin Link, Maxwell Werman, Margaret Lee, Sharon Shacham, Yosef Landesman. Selinexor inhibits NF-κB activity by sequestering IkB-a in the nucleus and blocking IkB-a degradation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2899.

Abstract LB-255: Selinexor, a selective inhibitor of nuclear export (SINE) compound, shows enhanced antitumor activity in combination with the PARP inhibitor, olaparib, in models of triple-negative breast cancer

Background: Selinexor is a SINE (Selective Inhibitor of Nuclear Export) compound currently in Phase I and II clinical trails for the treatment of hematological and solid malignancies. Selinexor blocks the key nuclear export protein XPO1 to force nuclear retention of tumor suppressor proteins (TSPs), including p53, BRCA1/2, pRB and FOXO3A. Olaparib is an FDA approved therapy for BRCA1/2 mutated ovarian cancer, which inhibits Poly-ADP-Ribose Polymerase (PARP) and prevents DNA damage repair. Furthermore, olaparib is being evaluated for the treatment of Triple Negative Breast Cancer (TNBC). We hypothesized that selinexor would restore genomic surveillance through nuclear accumulation of wild type BRCA1 and therefore combination treatment with olaparib would prevent DNA damage repair to amplify cancer cell death.

Methods: The effects of selinexor alone or in combination with olaparib were tested on a panel of 7 TNBC cell lines using MTT and soft-agar colony formation assays in parallel with FACS analysis. In vivo efficacy of single-agent or combination therapy was evaluated using an MDA-MB-468 (BRCA1 wild type, TNBC) xenograft model. Combination index (CI) values were determined using the CompuSyn software and treatment was considered synergistic when CI<1.

Results: The median IC50 values for selinexor and olaparib were 1.88 μM (range: 0.27 μM to >10 μM) and 92.6 μM (range: 17.5 μM to >300 μM), respectively. Combination treatment led to synergistic inhibition of proliferation in the 7 TNBC cell lines evaluated. The median CI tested on the panel of cell lines was 0.68 (ranging from 0.4 to 0.96). FACS analysis revealed an additive effect of the selinexor and olaparib combination on S-phase inhibition and G2 arrest in BRCA1 mutated and wild type cells. Furthermore, AnnexinV/PI staining showed an additive effect on TNBC cell apoptosis regardless of BRCA1 mutational status. In the MDA-MB-468 xenograft model, 75% tumor growth inhibition (TGI) was observed in the combination group by day 22 compared to 55% and 35% TGI for single-agent selinexor and olaparib, respectively.

Conclusion: Selinexor and olaparib in combination act synergistically to induce apoptosis in TNBC cells and amplify anti-tumor effects in a TNBC xenograft model. These data provide a rationale supporting the study of selinexor/olaparib combination in clinical trials.

Citation Format: Helene Marijon, Sigal Gery, Sivan Elloul, Sharon Y. Friedlander, TJ Unger, Robert Carlson, Sharon Shacham, Michael Kauffman, Harold P. Koeffler. Selinexor, a selective inhibitor of nuclear export (SINE) compound, shows enhanced antitumor activity in combination with the PARP inhibitor, olaparib, in models of triple-negative breast cancer. [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 LB-255. doi:10.1158/1538-7445.AM2015-LB-255

Examination of behavioral deficits triggered by targeting BDNF in fetal or postnatal brains of mice

Human and animal studies have implicated brain-derived neurotrophic factor (BDNF) in the etiology of psychiatric disorders. It is expressed in limbic regions of the brain associated with the regulation of emotionality during fetal development and in the adult animal. To further our understanding of the role of BDNF in the modulation of mood and to distinguish its prenatal and postnatal functions, we investigated and contrasted behavioral changes elicited by its depletion from fetal or postnatal brains of mice. Two corresponding lines of BDNF conditional knockout mice were subjected to a battery of behavioral tests assessing locomotor, depressive, aggressive and anxiety-related behaviors. We found that both lines of mutants were dramatically hyperactive during the light and dark cycles and hyperaggressive. They also exhibited a depression-like phenotype in the tail suspension test but not in the forced swim test. Interestingly, depletion of BDNF from the fetal brain had more pronounced effects on aggressive and depressive-like behaviors and led to deficits in 5-HT(2A) receptor content in the medial frontal cortex, highlighting the importance of this neurotrophin during development. We conclude that expression of BDNF both pre- and postnatally is essential for normal modulation of behavior by neural circuits in the adult animal.