Identification of CASZ1 NES reveals potential mechanisms for loss of CASZ1 tumor suppressor activity in neuroblastoma

As a transcription factor, localization to the nucleus and the recruitment of cofactors to regulate gene transcription is essential. Nuclear localization and nucleosome remodeling and histone deacetylase (NuRD) complex binding are required for the zinc-finger transcription factor CASZ1 to function as a neuroblastoma (NB) tumor suppressor. However, the critical amino acids (AAs) that are required for CASZ1 interaction with NuRD complex and the regulation of CASZ1 subcellular localization have not been characterized. Through alanine scanning, immunofluorescence cell staining and co-immunoprecipitation, we define a critical region at the CASZ1 N terminus (AAs 23-40) that mediates the CASZ1b nuclear localization and NuRD interaction. Furthermore, we identified a nuclear export signal (NES) at the N terminus (AAs 176-192) that contributes to CASZ1 nuclear-cytoplasmic shuttling in a chromosomal maintenance 1-dependent manner. An analysis of CASZ1 protein expression in a primary NB tissue microarray shows that high nuclear CASZ1 staining is detected in tumor samples from NB patients with good prognosis. In contrast, cytoplasmic-restricted CASZ1 staining or low nuclear CASZ1 staining is found in tumor samples from patients with poor prognosis. These findings provide insight into mechanisms by which CASZ1 regulates transcription, and suggests that regulation of CASZ1 subcellular localization may impact its function in normal development and pathologic conditions such as NB tumorigenesis.

Abstract 2129: Pediatric diffuse intrinsic pontine gliomas are genetically distinct from high and low grade astrocytomas

Tumors of the central nervous system constitute the most common type of solid pediatric tumors and account for the majority of mortality and morbidity in pediatric oncology. Brainstem glioma (BSG) is a type of brain tumor that arises in the medulla, pons or midbrain and accounts for approximately 10-20% of pediatric brain tumors. Diffuse gliomas of the pontine region, diffuse intrinsic pontine glioma (DIPG) are the most common type of brainstem tumor, accounting for about 58-78% of BSG and the number one cause of brain tumor related death in children with a 1-2 year survival. Despite this very little is understood about the biology of these tumors. To try to address this lack of knowledge we have undertaken genomic analysis of a series of DIPGs and compared their copy number changes to those seen in pediatric supratentorial high grade astrocytomas as well as low grade astrocytomas. Post mortem tumor and matched normal brain samples (n= 9) and surgical samples (n= 4) were collected for a series of DIPG patients. We performed high-resolution genetic analysis using whole-genome single-nucleotide polymorphism (SNP) arrays (Affymetrix 500K and 6.0). Data analysis was conducted using Partek Genome Suite and Copy Number Analysis Tool (Affymetrix). Analysis of copy number alterations returned hits in several cancer related pathways including MAPK, Wnt, prostate cancer and gliomagenesis. DIPG copy number was also compared to that of pediatric high grade (n= 20) and low grade (n= 30) astrocytomas. Unsupervised Pearson's Dissimilarity clustering resulted in 3 distinct groups. One contained 6 DIPGs; the second contained mostly LGA with a few HGA, while the third group contained mostly HGA with the remaining DIPGs clustering with this group. Although there were some similarities, DIPG are genetically distinct from supratentorial high grade and low grade astrocytomas. A better understanding of DIPG biology is needed in order to develop agents targeted more specifically towards this disease particularly given the dismal prognosis and unresponsive nature of these tumors to conventional treatment.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2129.

Inhibition of ALK mutated neuroblastomas by the selective inhibitor PF-02341066

10008b

Background: Mutations in the ALK oncogene are the major cause of hereditary neuroblastoma (NB), and may offer a tractable therapeutic target. Methods: We resequenced the ALK tyrosine kinase domain in 496 primary NBs. We integrated data from 76 primary tumors analyzed using Illumina HumanHap550 SNP and Human-6 mRNA expression arrays. We stained a tissue microarray (TMA) of 134 NBs with anti-ALK and anti-pALK antibodies. We evaluated the in vitro and in vivo activity of PF-02341066, a small molecule inhibitor of ALK. Computational chemistry was used to homology map ALK interaction with PF-02341066. Results: Mutations were discovered in 38/496 NBs (8%), across the spectrum of phenotypes. R1275Q substitutions were most common (45%), followed by F1174L (15%). Evaluation of matched constitutional DNAs demonstrated 10% carried occult germline mutations. Integration of primary tumor microarrays from 76 samples showed that ALK mRNA expression was highly correlated with ALK DNA copy number (p=0.0005). ALK protein was nearly universally expressed (129/134; 93%), and there was evidence for ALK activation in 15% of tumors (pALK moderate or strong staining in 20/134), suggesting an additional and alternative pathway to ALK activation. A panel of 18 NB cell lines showed differential in vitro sensitivity to PF-2341066 dependent on ALK mutation and copy number status. A wild type (WT) amplified line and 2 lines harboring R1275Q mutations were sensitive (IC50 145 - 301 nM). Lines harboring F1174L mutations were more resistant (IC50 >950nM) as were lines with no ALK aberrations. Inhibition of proliferation was associated with abolishing phosphorylation of ALK, STAT3 and AKT. PF-02341066 caused complete regression of R1275Q xenografts, but caused only minimal growth delay in F1174L and WT xenografts. Based on homology mapping to a crystal structure of PF-02341066 bound to c-Met, the F1174L mutation is predicted to destabilize the specific conformation of the kinase activation loop required for binding PF-02341066. Conclusions: ALK pathway activation occurs in at least 15% of human neuroblastomas. PF-02341066 is a potent inhibitor of the most common ALK mutation, but there is a structural basis for resistance to F1174L mutations. Co-crystallization studies are ongoing and a phase 1 study is planned.

No significant financial relationships to disclose.

Prominent vascular endothelial proliferation in clinically aggressive neuroblastoma

10611

Background: Tumor blood vessels are disorganized and vascular endothelial cell proliferation (VEP) has been identified as a poor prognosticator in many adult cancers. To determine the clinical significance of VEP in neuroblastoma (NB), we evaluated blood vessel architecture in tumor sections from 51 children diagnosed at Children's Memorial Hospital, Chicago (CMH) and in 154 NB tumors on a Tissue Microarray (TMA) constructed at Children's Hospital of Philadelphia (CHOP). Methods: H&E-stained tumor sections were examined for the presence of structurally abnormal vessels and further characterized by immunostaining with anti-CD31 and von Willebrand factor (vWF) antibody to highlight endothelial cells. Tumors that contained vessels with disorganized walls and more than one endothelial cell layer were classified as VEP positive. Tumor sections that contained only thin walled vessels with no more than one layer of endothelial cells were classified as VEP negative. Associations between VEP and established clinico-pathologic features and outcome were assessed. Results: In the CHOP series, VEP was associated with high-risk group classification and MYCN amplification (p<0.001 and p=0.006). In the CMH series only 5 of the 10 children with MYCN amplification had VEP but 4 of these 5 patients have died, while there were no deaths in the subset of patients with MYCN amplified tumors that lacked VEP (n=5). In both study groups, VEP was significantly associated with Schwannian stroma-poor histology (CMH series: p=0.008; CHOP series: p<0.001) and decreased survival probability (CMH series: p=0.017; CHOP series: p= 0.014). Conclusions: The association between structurally abnormal vessels and poor outcome provides further support for the concept that angiogenesis plays an important role in determining the biologic behavior of NB tumors. Our results also indicate that angiogenesis is regulated differently in Schwannian stroma-rich versus stroma-poor NB tumors. Further studies investigating the activity of angiogenic inhibitors in children with clinically aggressive stroma-poor NB are warranted.

No significant financial relationships to disclose.

The expression of WT1 in the differentiation of rhabdomyosarcoma from other pediatric small round blue cell tumors

The WT1 gene encodes a transcription factor implicated in normal and neoplastic development. The purpose of this study was to evaluate the diagnostic utility of a commercial WT1 antibody on a variety of pediatric small round blue cell tumors (SRBCT). A mouse monoclonal antibody (clone: 6F-H2, DAKO) raised against the N-terminal amino acids 1-181 of the human WT1 protein was tested. Microscopic sections from 66 specimens were stained using an antigen retrieval protocol with trypsin. The tumors included peripheral neuroectodermal tumors (PNET/Ewing's), neuroblastomas, desmoplastic small round cell tumors (DSRCT), lymphomas, Wilms' tumors, and rhabdomyosarcomas (RMS). One RMS case was investigated by Western blot analysis and RT-PCR to confirm the antibody specificity. A strong cytoplasmic staining was demonstrated in all RMS (11/11). The Western blot analysis confirmed the WT1 protein in the tissue, and the RT-PCR confirmed the presence of WT1 mRNA in the peripheral blood and tissue of one RMS patient. The Wilms' tumors had a variable nuclear and/or cytoplasmic positivity in most (17/24) cases. All PNET/Ewing's were negative. The nuclei of two lymphoblastic lymphomas stained strongly. A weak nuclear or cytoplasmic staining was reported in a few DSRCT (3/5), lymphomas (2/10), and neuroblastomas (2/8). This is a useful antibody in the differentiation of RMS from other SRBCTs. A strong cytoplasmic staining favors an RMS, and a strong nuclear staining is suggestive of a Wilms' tumor. A role for WT1 in the pathogenesis of rhabdomyosarcomas is raised. The limited sampling precludes any conclusions regarding the value of tissue or peripheral blood analysis for WT1 mRNA in patients with rhabdomyosarcoma.

Angiogenesis inhibitor TNP-470 during bone marrow transplant: safety in a preclinical model

High-dose therapy with stem cell rescue is a treatment option for patients with advanced solid tumors. Although this approach has promise for some pediatric cancers, especially neuroblastoma, it is limited by the risk of relapse posttransplant as well as concern about possible reinfused tumor cells in autologous stem cell products. Antiangiogenic agents given during and after recovery from high-dose therapy with stem cell rescue may decrease the risk of relapse. TNP-470 is an antiangiogenic agent now in clinical trials. Although it inhibits the growth of bone marrow (BM) colony-forming cells in vitro, no significant hematological toxicity has been seen in Phase I trials. To assess the feasibility of using antiangiogenic agents during the period of posttransplant hematopoietic engraftment, we have developed a model of stem cell transplant in mice. Mice were lethally irradiated and then rescued with stem cells containing a transgene expressed in the hematopoietic lineage. Mice were then treated with TNP-470 or placebo, and assessed for survival, successful engraftment, and kinetics of engraftment. Both treated and control mice demonstrated reliable multilineage engraftment as well as normal lymphoid maturation with no excess mortality in the treated group. WBCs were lower but still within the normal range at d+28 in mice treated with bolus TNP-470, but not in those treated with continuous infusion TNP-470, compared with controls. These data indicate that inhibitors of angiogenesis do not adversely impact engraftment after stem cell transplantation.

A case of acute monocytic leukemia with lysozyme-positive leukemic monocytes and normal serum lysozyme levels

We report a case of acute monocytic leukemia with normal serum lysozyme but with immunoperoxidase positivity for lysozyme in the leukemic blasts. The diagnosis of acute monocytic leukemia was made on the basis of cellular morphology, immunocytochemistry and cytochemistry. Discrepancy between serum lysozyme and intracytoplasmic lysozyme has not previously been reported in the literature. Levels of serum lysozyme may be misleading in cases of acute monocytic leukemia (FAB classification M5).

Arteriopathy in children with acquired immune deficiency syndrome

Pathologic features of the arteries of different organs (heart, lungs, kidneys, spleen, intestine, brain) seen at autopsy in 6 children with acquired immune deficiency syndrome (AIDS) are described. Small and medium-sized arteries, which were the most commonly involved, showed intimal fibrosis with fragmentation of elastic tissue, fibrosis and calcification of media with variable luminal narrowing, and a vasculitis or perivasculitis that was seen only in the brain in association with AIDS encephalopathy. In 1 case aneurysms of the right coronary artery with thrombosis and myocardial infarction were seen. Vascular inflammation, seen only in the brain, may be related to the agent associated with AIDS encephalopathy. The fibrocalcific arterial lesions most closely resemble idiopathic arterial calcification of infancy, but because of differences in age incidence, clinicopathologic and immunologic features, and the size and distribution of the involved arteries, the arterial lesions of pediatric AIDS appear to constitute a distinctive arteriopathy. Infection, secondary to immunodeficiency and resulting in increased exposure to endogenous and exogenous elastases, may be the pathogenesis. Luminal narrowing caused by arterial lesions may play a contributory role in the pathogenesis of the atrophy, cell depletion, scarring, and necrosis or infarction found in organs of children with AIDS. Pediatricians should be alerted to the possibility of arterial involvement in pediatrics AIDS.