eV-Scale Sterile Neutrino Search Using Eight Years of Atmospheric Muon Neutrino Data from the IceCube Neutrino Observatory

The results of a 3+1 sterile neutrino search using eight years of data from the IceCube Neutrino Observatory are presented. A total of 305 735 muon neutrino events are analyzed in reconstructed energy-zenith space to test for signatures of a matter-enhanced oscillation that would occur given a sterile neutrino state with a mass-squared differences between 0.01 and 100  eV^{2}. The best-fit point is found to be at sin^{2}(2θ_{24})=0.10 and Δm_{41}^{2}=4.5  eV^{2}, which is consistent with the no sterile neutrino hypothesis with a p value of 8.0%.

Characteristics of the Diffuse Astrophysical Electron and Tau Neutrino Flux with Six Years of IceCube High Energy Cascade Data

We report on the first measurement of the astrophysical neutrino flux using particle showers (cascades) in IceCube data from 2010-2015. Assuming standard oscillations, the astrophysical neutrinos in this dedicated cascade sample are dominated (∼90%) by electron and tau flavors. The flux, observed in the sensitive energy range from 16 TeV to 2.6 PeV, is consistent with a single power-law model as expected from Fermi-type acceleration of high energy particles at astrophysical sources. We find the flux spectral index to be γ=2.53±0.07 and a flux normalization for each neutrino flavor of ϕ_{astro}=1.66_{-0.27}^{+0.25} at E_{0}=100  TeV, in agreement with IceCube's complementary muon neutrino results and with all-neutrino flavor fit results. In the measured energy range we reject spectral indices γ≤2.28 at ≥3σ significance level. Because of high neutrino energy resolution and low atmospheric neutrino backgrounds, this analysis provides the most detailed characterization of the neutrino flux at energies below ∼100  TeV compared to previous IceCube results. Results from fits assuming more complex neutrino flux models suggest a flux softening at high energies and a flux hardening at low energies (p value ≥0.06). The sizable and smooth flux measured below ∼100  TeV remains a puzzle. In order to not violate the isotropic diffuse gamma-ray background as measured by the Fermi Large Area Telescope, it suggests the existence of astrophysical neutrino sources characterized by dense environments which are opaque to gamma rays.

Time-Integrated Neutrino Source Searches with 10 Years of IceCube Data

This Letter presents the results from pointlike neutrino source searches using ten years of IceCube data collected between April 6, 2008 and July 10, 2018. We evaluate the significance of an astrophysical signal from a pointlike source looking for an excess of clustered neutrino events with energies typically above ∼1  TeV among the background of atmospheric muons and neutrinos. We perform a full-sky scan, a search within a selected source catalog, a catalog population study, and three stacked Galactic catalog searches. The most significant point in the northern hemisphere from scanning the sky is coincident with the Seyfert II galaxy NGC 1068, which was included in the source catalog search. The excess at the coordinates of NGC 1068 is inconsistent with background expectations at the level of 2.9σ after accounting for statistical trials from the entire catalog. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that, collectively, correlations with sources in the northern catalog are inconsistent with background at 3.3σ significance. The southern catalog is consistent with background. These results, all based on searches for a cumulative neutrino signal integrated over the 10 years of available data, motivate further study of these and similar sources, including time-dependent analyses, multimessenger correlations, and the possibility of stronger evidence with coming upgrades to the detector.

Anti-VEGFR2 therapy delays growth of preclinical pediatric tumor models and enhances anti-tumor activity of chemotherapy

Vascular endothelial growth factor receptor 2 (VEGFR2) is an attractive therapeutic target in solid malignancies due to its central role in tumor angiogenesis. Ramucirumab (Cyramza^®, LY3009806) is a human monoclonal antibody specific for VEGFR2 approved for several adult indications and currently in a phase 1 clinical trial for pediatric patients with solid tumors (NCT02564198). Here, we evaluated ramucirumab in vitro and the anti-murine VEGFR2 antibody DC101 in vivo with or without chemotherapy across a range of pediatric cancer models. Ramucirumab abrogated in vitro endothelial cord formation driven by cancer cell lines representing multiple pediatric histologies; this response was independent of the origin of the tumor cell-line. Several pediatric cancer mouse models responded to single agent DC101-mediated VEGFR2 inhibition with tumor growth delay. Preclinical stable disease and partial xenograft regressions were observed in mouse models of Ewing’s sarcoma, synovial sarcoma, neuroblastoma, and desmoplastic small round cell tumor treated with DC101 and cytotoxic chemotherapy. In contrast, DC101 treatment in osteosarcoma models had limited efficacy alone or in combination with chemotherapeutics. Our data indicate differential efficacy of targeting the VEGFR2 pathway in pediatric models and support the continued evaluation of VEGFR2 inhibition in combination with cytotoxic chemotherapy in multiple pediatric indications.

Broad Spectrum Activity of the Checkpoint Kinase 1 Inhibitor Prexasertib as a Single Agent or Chemopotentiator Across a Range of Preclinical Pediatric Tumor Models

PURPOSE

Checkpoint kinase 1 (CHK1) inhibitors potentiate the DNA-damaging effects of cytotoxic therapies and/or promote elevated levels of replication stress, leading to tumor cell death. Prexasertib (LY2606368) is a CHK1 small-molecule inhibitor under clinical evaluation in multiple adult and pediatric cancers. In this study, prexasertib was tested in a large panel of preclinical models of pediatric solid malignancies alone or in combination with chemotherapy.

EXPERIMENTAL DESIGN

DNA damage and changes in cell signaling following in vitro prexasertib treatment in pediatric sarcoma cell lines were analyzed by Western blot and high content imaging. Antitumor activity of prexasertib as a single agent or in combination with different chemotherapies was explored in cell line-derived (CDX) and patient-derived xenograft (PDX) mouse models representing nine different pediatric cancer histologies.

RESULTS

Pediatric sarcoma cell lines were highly sensitive to prexasertib treatment in vitro, resulting in activation of the DNA damage response. Two PDX models of desmoplastic small round cell tumor and one malignant rhabdoid tumor CDX model responded to prexasertib with complete regression. Prexasertib monotherapy also elicited robust responses in mouse models of rhabdomyosarcoma. Concurrent administration with chemotherapy was sufficient to overcome innate resistance or prevent acquired resistance to prexasertib in preclinical models of neuroblastoma, osteosarcoma, and Ewing sarcoma, or alveolar rhabdomyosarcoma, respectively.

CONCLUSIONS

Prexasertib has significant antitumor effects as a monotherapy or in combination with chemotherapy in multiple preclinical models of pediatric cancer. These findings support further investigation of prexasertib in pediatric malignancies.

Abstract B43: The CDK4 and 6 inhibitor abemaciclib induces both epigenetic and immunogenic responses in preclinical models of Ewing’s sarcoma

Ewing’s sarcoma (ES) is a rare but aggressive cancer typically occurring in the bone or soft tissue of children and adolescents. Current treatment regimens composed of surgery, radiation, and high-dose chemotherapy have improved outcomes for localized disease cases; however, ES continues to present a clinical challenge in the recurrent or metastatic setting. ES is often characterized by a chromosomal translocation that results in a chimeric EWS/ETS transcription factor. This fusion protein may contribute to tumorigenesis through modulation of downstream targets leading to cell cycle dysregulation, due in part to the overexpression of Cyclin D1. In addition, ES also has a high degree of DNA methylation when compared to other tumor types, which can lead to epigenetic silencing of key tumor suppressor genes. Abemaciclib is a small-molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4 and 6) currently under clinical evaluation for metastatic breast cancer, non-small cell lung cancer, and other adult solid tumors. Abemaciclib shows antitumor activity in preclinical models of human adult and pediatric cancer with functional Rb and high cyclin D expression, and has been reported to elicit an immune response in addition to its cell cycle effects in breast cancer. This study was designed to assess abemaciclib-induced antitumor effects, in addition to epigenetic and immunogenic changes, in preclinical ES models.

Six ES cell lines were treated with abemaciclib and the resulting changes in protein expression and methylation were evaluated by Western blot and DNA promoter methylation analysis, respectively. In addition, tumor-secreted factors from conditioned media were measured by ELISA and activation of the interferon (IFN) pathway was assessed through Western blot, qRT-PCR, and RNAseq analysis. In vivo studies of abemaciclib as a single agent or in combination with ES standard-of-care (SOC) in multiple mouse xenograft models were also performed to measure abemaciclib-mediated antitumor effects and epigenetic and immunogenic changes. Single-agent abemaciclib elicited tumor growth delay or tumor stasis, while the combination with SOC was generally superior to either monotherapy arm, often resulting in objective responses. Abemaciclib induced global DNA demethylation through the Rb-E2F-DNMT1 axis, and a ligand-independent type III IFN response. In addition, abemaciclib increased expression of the tumor cell antigen presentation protein MHC-1, and this effect was more durable than abemaciclib-dependent cell cycle effects. These data demonstrate that abemaciclib activity in ES goes beyond cell cycle arrest to include a measurable and durable immunogenic response. Therefore, the multipronged antitumor effects of abemaciclib, namely CDK4/6 inhibition, global DNA demethylation, and resulting immunogenic changes, may be a viable therapeutic option for ES patients when used in combination with appropriate chemotherapy, and additional studies to better understand this unique biology are ongoing.

Citation Format: Michele Dowless, Caitlin Lowery, Matthew Renschler, Wayne Blosser, Jennifer Stephens, Robert Flack, Kelly Credille, Mia Chen, Frank Dorsey, Lillian Sams, Philip Ebert, Jonathan Olsen, Terry Shackleford, Peter Houghton, Louis Stancato. The CDK4 and 6 inhibitor abemaciclib induces both epigenetic and immunogenic responses in preclinical models of Ewing’s sarcoma [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr B43.

Abemaciclib Is Active in Preclinical Models of Ewing Sarcoma via Multipronged Regulation of Cell Cycle, DNA Methylation, and Interferon Pathway Signaling

PURPOSE

Ewing sarcoma (ES) is a rare and highly malignant cancer that occurs in the bone and surrounding tissue of children and adolescents. The EWS/ETS fusion transcription factor that drives ES pathobiology was previously demonstrated to modulate cyclin D1 expression. In this study, we evaluated abemaciclib, a small-molecule CDK4 and CDK6 (CDK4 and 6) inhibitor currently under clinical investigation in pediatric solid tumors, in preclinical models of ES.

EXPERIMENTAL DESIGN

Using Western blot, high-content imaging, flow cytometry, ELISA, RNA sequencing, and CpG methylation assays, we characterized the in vitro response of ES cell lines to abemaciclib. We then evaluated abemaciclib in vivo in cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) mouse models of ES as either a monotherapy or in combination with chemotherapy.

RESULTS

Abemaciclib induced quiescence in ES cell lines via a G₁ cell-cycle block, characterized by decreased proliferation and reduction of Ki-67 and FOXM1 expression and retinoblastoma protein (RB) phosphorylation. In addition, abemaciclib reduced DNMT1 expression and promoted an inflammatory immune response as measured by cytokine secretion, antigen presentation, and interferon pathway upregulation. Single-agent abemaciclib reduced ES tumor volume in preclinical mouse models and, when given in combination with doxorubicin or temozolomide plus irinotecan, durable disease control was observed.

CONCLUSIONS

Collectively, our data demonstrate that the antitumor effects of abemaciclib in preclinical ES models are multifaceted and include cell-cycle inhibition, DNA demethylation, and immunogenic changes.

Results of a phase II trial of single-agent amrubicin (AMR) in patients with extensive disease small cell lung cancer (ED-SCLC) refractory to first-line platinum-based chemotherapy: An update

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Background: Amrubicin (AMR), a third-generation synthetic anthracycline and potent topoisomerase II inhibitor, is approved in Japan for the treatment of lung cancer. Patients (pts) with SCLC, who are refractory to first-line chemotherapy or progress within 3 months (mos) of treatment completion, are less likely to respond to additional chemotherapy and have an expected median survival of 3–5 mos. Here, we investigate the efficacy and safety of single-agent AMR in the treatment of Western pts with refractory ED-SCLC. Methods: In this phase II trial, pts with ED-SCLC refractory to prior 1st-line platinum-based chemotherapy (defined as progression (PD) while on therapy or relapse within 90 days of treatment completion) and ECOG performance status (PS) ≤2 were eligible. Patients were treated with intravenous AMR 40 mg/m2/day x 3 days every 21 days until PD or intolerable toxicity. The primary endpoint was response rate (ORR, by RECIST), with a goal to demonstrate an ORR ≥18% (point estimate). Secondary endpoints included progression-free survival (PFS) and overall survival (OS). Results: In all, 75 pts were enrolled with a median age of 63 years (range 43–88), 52% female, 17% PS 2. Response to 1st-line therapy was 5% complete remission (CR), 36% partial remission (PR) and 28% PD. Median time from completion of 1st-line therapy to PD was 1.3 mos. Sixty-nine pts received AMR for a median of 4 cycles (range 1–12). Six pts died or discontinued before receiving treatment. The primary endpoint was met with an ORR of 21% (16/75, 95% confidence interval [CI] 13.6% - 31.9%), including CR in 1 pt (1%) and PR in 15 pts (20%). Stable disease was achieved in 40% of pts. Two pts with PD as best response to 1st line chemotherapy achieved a PR. Median OS was 6.0 mos (95% CI 4.8–7.1 mos). Median PFS was 3.2 mos (95% CI 2.4–4.0 mos). The most common grade 3 or 4 adverse events were neutropenia (65%), thrombocytopenia (39%), and leukopenia (35%). Seven (10%) patients experienced febrile neutropenia. Dose reductions were required in 26 patients (38%). Conclusions: AMR shows promising activity, with an ORR of 21%, and an acceptable safety profile in patients with refractory ED-SCLC, and warrants further study in these pts.

[Table: see text]

Amrubicin (AMR) and cardiotoxicity in second-line treatment of small cell lung cancer (SCLC): A pooled analysis of left ventricular ejection fraction (LVEF) in two phase II trials

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Background: Amrubicin (AMR) is a third-generation synthetic anthracycline and a potent topoisomerase II inhibitor approved in Japan for the treatment of lung cancer. In Japanese pre and postmarking studies, AMR treatment was not associated with cardiotoxicity. The purpose of this analysis was to determine if AMR treatment of Western patients (pts) is associated with anthracycline-induced cardiomyopathy. Methods: To evaluate risk of cardiomyopathy, LVEF was measured by echocardiogram or by multiple gated acquisition (MUGA) scan and pooled from pts enrolled in 2 trials of IV AMR, 40 mg/m2/day x 3 days q 21 days for second-line treatment of sensitive or refractory SCLC. Pts with measurable disease, ECOG PS 0–2, LVEF ≥50%, and prior platinum-based treatment were assessed at baseline (BL), cycles 3, 6, then every 2 cycles, and end of treatment. Pts were to be assessed by the same method (ECHO or MUGA) throughout the study. Pts with a persistent ≥20% decrease in LVEF during treatment were to be removed from the study. Results: 112 patients were treated (sensitive n=43, median 6 cycles; refractory, n=69, median 5 cycles) and had at least 1 LVEF assessment. Median age was 63 years and median BL LVEF was 60%. Changes in LVEF from baseline were minimal ( Table ) and similar across cumulative dosing groups including 15 pts who received a cumulative dose of >1,000 mg/m2 AMR. Two refractory pts (1.8%) experienced drops in LVEF >20%. One had BL LVEF of 85%, then 60% at cycle 3, and 70% subsequently with ongoing therapy. The second, with a history of cardiomegaly, had LVEF of 55% at BL, cycle 3, and 5 by ECHO, and 29% at the time of progression after cycle 9 (cumulative AMR dose 840 mg/m2) by MUGA. The patient died due to progressive disease with no evidence of CHF. Conclusions: In this pooled analysis of SCLC pts, LVEF remained stable even in pts with cumulative AMR dosing >1,000 mg/m2. AMR for second-line treatment of SCLC does not appear to cause anthracycline-related cardiomyopathy.

[Table: see text]

[Table: see text]

Results of a randomized phase II trial of amrubicin (AMR) versus topotecan (Topo) in patients with extensive-disease small cell lung cancer (ED-SCLC) sensitive to first-line platinum-based chemotherapy

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Background: SCLC presents as ED-SCLC in 60%-70% of patients (pts). AMR, a synthetic anthracycline, is approved for these pts in Japan. We compare the efficacy and safety of single-agent AMR vs topotecan in non-Japanese pts with 2nd-line ED-SCLC sensitive to 1st-line platinum-based chemotherapy. Methods: This phase II, open-label, multicenter study enrolled pts with ED-SCLC sensitive to 1st-line platinum-based chemotherapy (recurrence or progression ≥90 days from 1st-line treatment). Pts aged ≥18 years with ECOG performance status (PS) ≤2 and only 1 prior therapy were eligible. Pts were randomized (2:1) to receive IV AMR 40 mg/m2/d (d, 1–3) or IV topotecan 1.5 mg/m2/d (d 1–5) and treated every 21 days until progression, unacceptable toxicity, or withdrawal. The primary endpoint, overall response rate (ORR, complete + partial response), used RECIST criteria. Secondary endpoints were progression-free survival (PFS), overall survival (OS), and safety. Results: In all, 76 pts were randomized to AMR (n=50) or topotecan (n=26) with AMR given for a median of 6 cycles (range 1–16) and topotecan 3 cycles (1–16). AMR significantly improved ORR rates vs topotecan (p<0.012; Table ). Median PFS/OS was 4.3 months (95% CI 2.0, 6.1)/9.3 months (95% CI 5.7, 12.0) with AMR vs 3.5 months (95% CI 2.1, 6.3)/8.9 months (95% CI 4.8, 13.8) with topotecan. There was a higher proportion of ECOG PS 2 pts in the AMR group (n=6) vs the topotecan group (n=2). A trend towards improved OS was observed in the ECOG 0–1 subgroup of 68 pts: median OS was 10.5 months with AMR vs 9.7 months with topotecan. The most common grade ≥3 adverse events with AMR vs topotecan were neutropenia (53% vs 74%), thrombocytopenia (31% vs 52%) and leukopenia (27% vs 30%). Three AMR pts (6%) and 1 topotecan pt (4%) died of neutropenic infection. Conclusions: AMR significantly improves ORR and has acceptable tolerability as 2nd-line treatment in pts with sensitive ED-SCLC.

[Table: see text]

[Table: see text]

Improvement in neurocognitive function (NCF) correlates with tumor regression after whole brain radiation therapy (WBRT) for brain metastases (BM)

1504

Background: Few prospective trials have explored the neurocognitive impact of WBRT in BM patients (pts), complicated by competing effects between benefit from WBRT and deterioration due to disease progression. Methods: 208 pts from the WBRT alone arm (30 Gy) of a phase III trial (PCYC-9801) evaluating motexafin gadolinium in BM were analyzed. NCF was assessed by 8 tests of memory, executive function and fine motor coordination, and correlated to BM volume change by MRI, using Spearman’s rank correlation. Pts with tumor shrinkage below and above the median (45%) were compared for survival and NCF deterioration using Kaplan-Meier analysis. Results: 135 pts (65%) were evaluable for BM volume at baseline and 2 months (mo). Pts were divided into “good” and “poor” responders based on % volume reduction at 2 mo above or below the population median of 45%. The uni-directional hypothesis of improved survival in good responders was significant (P = 0.03, median survival (MS) 300±26 days (d) vs 240±19 d). For all 8 tests, the median time to NCF deterioration was longer in good responders than in poor responders. Largest gains were for an executive function test Trailmaking B (131 d gain, P=0.02), fine motor tests Pegboard non-dominant hand (110 d gain, P=0.05) and Pegboard dominant hand (93 d gain, P=0.02). In 15 mo survivors, statistically significant correlation between tumor shrinkage and NCF preservation was seen for 4/8 NCF tests (r = 0.68–0.88), especially for executive function and fine motor coordination. At early follow-up, the population mean NCF scores were dominated by pts with progressive disease, as reflected by a sharp drop in the mean NCF scores at 4 mo. 15-mo survivors had stable or improving scores, associated with greater reduction in BM volume in the 15 versus 4 mo survivors. Conclusions: WBRT-induced tumor shrinkage correlates with better survival and NCF preservation. NCF is stable or improved in long-term BM survivors. The adverse impact of tumor growth on neurocognitive function appears greater than that of WBRT.

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Phases IB and II multidose trial of gadolinium texaphyrin, a radiation sensitizer detectable at MR imaging: preliminary results in brain metastases

PURPOSE

To evaluate magnetic resonance (MR) imaging results after administration of gadolinium texaphyrin, a tumor-selective radiation sensitizer that is detectable at MR imaging, and to determine an appropriate intravenous dose of gadolinium texaphyrin for repeated injections during radiation therapy, the dose-limiting toxicity of reiterated doses of gadolinium texaphyrin, the maximal tolerated dose, the biolocalization of gadolinium texaphyrin (as assessed at MR examinations), and the response to treatment.

MATERIALS AND METHODS

Ten daily intravenous injections of gadolinium texaphyrin, each followed by whole-brain radiation therapy (total of 10 fractions, 30 Gy), were administered to patients with brain metastases in a multicenter study. At the study institution, 11 patients underwent MR imaging before and after the first injection, after the 10th injection, and 8 weeks after entry into the study.

RESULTS

MR imaging revealed selective drug uptake in metastases, without enhancement of normal brain tissue. In 10 patients, tumor uptake was higher after the 10th injection than after the first injection, which indicated accumulation of gadolinium texaphyrin in metastases. One lesion was visible only after the 10th injection and not at the pretherapeutic MR examination with injection of conventional gadolinium-based contrast material. Response to treatment was defined as a reduction in the size of the metastases between the preinjection MR study and the last MR study; seven patients achieved partial remission with tumor regression exceeding 50% of the initial size, and four achieved a minor response with less than 50% tumor regression.

CONCLUSION

These preliminary results indicate that gadolinium texaphyrin is tumor selective and that brain metastases can be depicted at MR imaging long after the administration of gadolinium texaphyrin.