Scientific codes developed and used at GRS – Nuclear simulation chain

Over 60 technical experts of the reactor safety research division of the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH are developing and validating reliable methods and computer codes – summarized under the term nuclear simulation chain – for the safety-related assessment for all types of nuclear power plants (NPP) and other nuclear facilities considering the current state of science and technology. This nuclear simulation chain has to be able to simulate and assess all relevant physical processes and phenomena for all operating states and (severe) accidents. In the present contribution, the nuclear simulation chain developed and applied by GRS as well as selected examples of its application are presented. The latter demonstrate impressively the width of its scope and its performance. The GRS codes can be passed on request to other (national as well as international) organizations. This contributes to a worldwide increase of the nuclear safety standards. The code transfer is especially important for developing and emerging countries lacking the financial means and/or the necessary know-how for this purpose. At the end of this contribution, the respective course of action is described.

Mutations that disrupt PHOXB interaction with the neuronal calcium sensor HPCAL1 impede cellular differentiation in neuroblastoma

Heterozygous germline mutations in PHOX2B, a transcriptional regulator of sympathetic neuronal differentiation, predispose to diseases of the sympathetic nervous system, including neuroblastoma and congenital central hypoventilation syndrome (CCHS). Although the PHOX2B variants in CCHS largely involve expansions of the second polyalanine repeat within the C-terminus of the protein, those associated with neuroblastic tumors are nearly always frameshift and truncation mutations. To test the hypothesis that the neuroblastoma-associated variants exert their effects through loss or gain of protein-protein interactions, we performed a large-scale yeast two-hybrid screen using both wild-type (WT) and six different mutant PHOX2B proteins against over 10 000 human genes. The neuronal calcium sensor protein HPCAL1 (VILIP-3) exhibited strong binding to WT PHOX2B and a CCHS-associated polyalanine expansion mutant but only weakly or not at all to neuroblastoma-associated frameshift and truncation variants. We demonstrate that both WT PHOX2B and the neuroblastoma-associated R100L missense and the CCHS-associated alanine expansion variants induce nuclear translocation of HPCAL1 in a Ca(2+)-independent manner, while the neuroblastoma-associated 676delG frameshift and K155X truncation mutants impair subcellular localization of HPCAL1, causing it to remain in the cytoplasm. HPCAL1 did not appreciably influence the ability of WT PHOX2B to transactivate the DBH promoter, nor did it alter the decreased transactivation potential of PHOX2B variants in 293T cells. Abrogation of the PHOX2B-HPCAL1 interaction by shRNA knockdown of HPCAL1 in neuroblastoma cells expressing PHOX2B led to impaired neurite outgrowth with transcriptional profiles indicative of inhibited sympathetic neuronal differentiation. Our results suggest that certain PHOX2B variants associated with neuroblastoma pathogenesis, because of their inability to bind to key interacting proteins such as HPCAL1, may predispose to this malignancy by impeding the differentiation of immature sympathetic neurons.

Abstract 4454: The AXL tyrosine kinase receptor contributes to ALK-inhibitor resistance in neuroblastoma

The crizotinib-resistant ALKF1174L mutation occurs de novo in neuroblastoma (NB) and as an acquired mechanism of resistance in ALK translocation-driven cancers, lending impetus to the development of novel ALK inhibitors with different modes of action. One such molecule is TAE684, a structurally unrelated ATP-competitive diaminopyrimidine derivative that has shown activity against ALKF1174L in both in vitro and in vivo models of ALK-driven cancers, such as lung cancer and NB.

To identify mechanisms of acquired resistance to TAE684, we established in vitro models of resistance by serially exposing TAE684-sensitive SH-SY5Y NB cells (expressing ALKF1174L) to increasing concentrations of the compound over a prolonged period (> 1 year). The resulting TAE684-resistant SY5Y-TR cells exhibited >10-fold reduced sensitivity to TAE684 compared with parental cells. Three TAE684-resistant clonal lines (TR1-TR3) were analyzed, all of which showed downregulation of pALK. In addition, TR1 cells showed downregulation of pAKT but increased expression of pERK1/2 compared to parental cells, suggesting activation of compensatory signaling pathways. To identify candidate receptor tyrosine kinases (RTKs) that may account for this observation, we analyzed TR1 cells using phospho-RTK arrays. Upregulation of the AXL RTK was seen in the resistant cells as compared to the parental cells, and this was confirmed by immunoblotting in all the resistant clones. Concurrent with the role of AXL in tumor cell invasion, TR1 cells exhibited increased invasiveness in matrigel assays. Depletion of AXL expression by shRNA knockdown in TR1 cells led to their growth inhibition. TR1 cells were more sensitive to SKI-606, a Src/Abl inhibitor with activity against AXL, than parental cells. However, exposure to an Hsp90 inhibitor led to significant cytotoxicity in all the clones (IC50s<30nM), as compared to parental cells (IC50=304nM). Inhibiting Hsp90 in the TR1 cells led to a decrease in pAXL and pERK1/2 levels with a concomitant decrease in the binding of AXL to Hsp90. Analysis of AXL in TR1 cells ruled out mutation, genomic amplification or promoter demethylation as a basis for its increased expression; however, the AXL ligand, GAS6, was increased in the resistant clones.

These studies demonstrate that AXL activation contributes to TAE684 resistance in ALKF1174L-expressing cells, and suggests that the same would be true for derivatives of TAE684 in clinical development. The finding that AXL is also involved in EGFR-targeted therapy in lung cancer suggests that AXL activation could be a general mechanism of resistance to tyrosine kinase inhibitor therapy.

Citation Format: Namrata Bhatnagar, William Luther, Bandana Sharma, Qingsong Liu, Nathanael Gray, Rani E. George. The AXL tyrosine kinase receptor contributes to ALK-inhibitor resistance in neuroblastoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4454. doi:10.1158/1538-7445.AM2013-4454

The ALK(F1174L) mutation potentiates the oncogenic activity of MYCN in neuroblastoma

The ALK(F1174L) mutation is associated with intrinsic and acquired resistance to crizotinib and cosegregates with MYCN in neuroblastoma. In this study, we generated a mouse model overexpressing ALK(F1174L) in the neural crest. Compared to ALK(F1174L) and MYCN alone, co-expression of these two oncogenes led to the development of neuroblastomas with earlier onset, higher penetrance, and enhanced lethality. ALK(F1174L)/MYCN tumors exhibited increased MYCN dosage due to ALK(F1174L)-induced activation of the PI3K/AKT/mTOR and MAPK pathways, coupled with suppression of MYCN pro-apoptotic effects. Combined treatment with the ATP-competitive mTOR inhibitor Torin2 overcame the resistance of ALK(F1174L)/MYCN tumors to crizotinib. Our findings demonstrate a pathogenic role for ALK(F1174L) in neuroblastomas overexpressing MYCN and suggest a strategy for improving targeted therapy for ALK-positive neuroblastoma.

Discovery of 3,5-Diamino-1,2,4-triazole Ureas as Potent Anaplastic Lymphoma Kinase Inhibitors

A series of novel 3,5-diamino-1,2,4-triazole benzyl ureas was identified as having potent anaplastic lymphoma kinase (ALK) inhibition exemplified by 15a, 20a, and 23a, which exhibited antiproliferative IC(50) values of 70, 40, and 20 nM in Tel-ALK transformed Ba/F3 cells, respectively. Moreover, 15a and 23a potently inhibited the growth and survival of NPM-ALK positive anaplastic large cell lymphoma cell (SU-DHL-1) and neuroblastoma cell lines (KELLY, SH-SY5Y) containing the F1174L ALK mutation. These compounds provide novel leads for the development of small-molecule ALK inhibitors for cancer therapy.

Abstract 4757: The ALK-F1174L mutation accelerates MYCN-driven tumorigenesis in a murine transgenic neuroblastoma model

Activating mutations in the anaplastic lymphoma receptor tyrosine kinase gene (ALK) have been identified in neuroblastoma and represent a novel therapeutic target in this childhood tumor of the sympathetic nervous system. The ALK-F1174L mutation, in particular, occurs at a higher frequency in tumors with MYCN gene amplification, is associated with a worse prognosis and with resistance to pharmacologic ALK inhibitors in adults with ALK-translocated cancers. To investigate the role of mutated ALK in MYCN-driven neuroblastoma, we generated transgenic mice that overexpress ALK-F1174L in neural crest-derived cells under the control of the tyrosine hydroxylase (TH) promoter, and performed genetic crosses against TH-MYCN transgenic mice. Doubly transgenic TH-ALK-F1174L/TH-MYCN animals developed aggressive tumors of the adrenal glands and abdominal and thoracic sympathetic ganglia, with 100% penetrance and a very short latency (31 days). In contrast, TH-MYCN littermates failed to develop tumors by this time. Furthermore, TH-ALK-F1174L hemizygote or homozygote animals failed to initiate tumors in the absence of MYCN expression. On histologic examination, ALK-F1174L/MYCN tumors were stroma poor and displayed undifferentiated small round blue cells with numerous apoptotic figures and scattered mitoses, and exhibited strong expression of both MYCN and aberrant ALK-F1174L transcripts and protein. Taken together, our studies demonstrate that the ALK-F1174L mutation plays a potent and significant role in the genesis of neuroblastoma, cooperating with MYCN to drive tumor formation. To our knowledge, this is the first mouse model available for investigations into the role of mutant ALK in neuroblastoma, especially its interaction with MYCN, and should provide a valuable new tool for development of ALK-targeted therapeutics in neuroblastoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4757. doi:10.1158/1538-7445.AM2011-4757

Activating mutations in ALK provide a therapeutic target in neuroblastoma

Neuroblastoma, an embryonal tumor of the peripheral sympathetic nervous system, accounts for approximately 15% of all deaths due to childhood cancer1. High-risk neuroblastomas, prevalent in the majority of patients, are rapidly progressive; even with intensive myeloablative chemotherapy, relapse is common and almost uniformly fatal2,3. Here we report the detection of previously unknown mutations in the ALK gene, which encodes a receptor tyrosine kinase, in 8% of primary neuroblastomas. Five non-synonymous sequence variations were identified in the kinase domain of ALK, of which three were somatic and two were germline. The most frequent mutation, F1174L, was also identified in three different neuroblastoma cell lines. ALK cDNAs encoding the F1174L and R1275Q variants, but not the wild-type ALK cDNA, transformed IL-3-dependent murine hematopoietic Ba/F3 cells to cytokine-independent growth. Ba/F3 cells expressing these mutations were sensitive to a small-molecule inhibitor of ALK, TAE6844. Furthermore, two human neuroblastoma cell lines harboring the F1174L mutation were sensitive to the inhibitor. Cytotoxicity was associated with increased levels of apoptosis as measured by TUNEL-labeling. shRNA-mediated knockdown of ALK expression in neuroblastoma cell lines with the F1174L mutation also resulted in apoptosis and impaired cell proliferation. Thus, activating alleles of the ALK receptor tyrosine kinase are present in primary neuroblastoma tumors and in established neuroblastoma cell lines, and confer sensitivity to ALK inhibition with small molecules, providing a molecular rationale for targeted therapy of this disease.

The effect of stress level, amino acid formula, and nitrogen dose on nitrogen retention in traumatic and septic stress

Eighty-seven patients were entered into a randomized, prospective, double-blind, six-center study to evaluate the effect of amino acid loading and a formula that was branched chain enriched (50%) on nitrogen retention in metabolic stress. The patients had varying levels of metabolic stress (0-3) after major surgery, polytrauma, or surgical sepsis. The study was isocaloric and isonitrogenous and lasted for 7 days. The patients received either a standard amino acid formula (SAA) (Travasol) or a 50% branched chain enriched formula that was equimolar, leucine, isoleucine, and valine (MAA) (Travasol + Branchamin concentrate) at a dose of 1.0-2.0 g/kg/day in a fixed ratio with 114 glucose calories per gram of nitrogen administered. The nitrogen retention was proportionate to the nitrogen (and, therefore, caloric) load in both groups. The MAA group, however, had better nitrogen retention, reached nitrogen equilibrium at a lower dose of amino acids, and had less urinary nitrogen excretion per gram of nitrogen administered. Since the groups were isonitrogenous and the calorie to nitrogen ratios were fixed, it appears that nitrogen equilibrium in surgical stress is proportionate to the amino acid load over a range of 0.05-0.4 g/kg/day of nitrogen; and that MAA are more efficient at inducing nitrogen retention and a reduction in urea excretion. These effects on nitrogen retention were more significant at level 2 stress or greater. At these higher stress levels, a dose of 2 +/- 0.2 g/kg/day of MAA seemed most efficient in promoting nitrogen retention.