Single-cell RNA sequencing distinctly characterizes the wide heterogeneity in pediatric mixed phenotype acute leukemia

BACKGROUND

Mixed phenotype acute leukemia (MPAL), a rare subgroup of leukemia characterized by blast cells with myeloid and lymphoid lineage features, is difficult to diagnose and treat. A better characterization of MPAL is essential to understand the subtype heterogeneity and how it compares with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). Therefore, we performed single-cell RNA sequencing (scRNAseq) on pediatric MPAL bone marrow (BM) samples to develop a granular map of the MPAL blasts and microenvironment landscape.

METHODS

We analyzed over 40,000 cells from nine pediatric MPAL BM samples to generate a single-cell transcriptomic landscape of B/myeloid (B/My) and T/myeloid (T/My) MPAL. Cells were clustered using unsupervised single-cell methods, and malignant blast and immune clusters were annotated. Differential expression analysis was performed to identify B/My and T/My MPAL blast-specific signatures by comparing transcriptome profiles of MPAL with normal BM, AML, and ALL. Gene set enrichment analysis (GSEA) was performed, and significantly enriched pathways were compared in MPAL subtypes.

RESULTS

B/My and T/My MPAL blasts displayed distinct blast signatures. Transcriptomic analysis revealed that B/My MPAL profile overlaps with B-ALL and AML samples. Similarly, T/My MPAL exhibited overlap with T-ALL and AML samples. Genes overexpressed in both MPAL subtypes' blast cells compared to AML, ALL, and healthy BM included MAP2K2 and CD81. Subtype-specific genes included HBEGF for B/My and PTEN for T/My. These marker sets segregated bulk RNA-seq AML, ALL, and MPAL samples based on expression profiles. Analysis comparing T/My MPAL to ETP, near-ETP, and non-ETP T-ALL, showed that T/My MPAL had greater overlap with ETP-ALL cases. Comparisons among MPAL subtypes between adult and pediatric samples showed analogous transcriptomic landscapes of corresponding subtypes. Transcriptomic differences were observed in the MPAL samples based on response to induction chemotherapy, including selective upregulation of the IL-16 pathway in relapsed samples.

CONCLUSIONS

We have for the first time described the single-cell transcriptomic landscape of pediatric MPAL and demonstrated that B/My and T/My MPAL have distinct scRNAseq profiles from each other, AML, and ALL. Differences in transcriptomic profiles were seen based on response to therapy, but larger studies will be needed to validate these findings.

Single-cell analysis reveals altered tumor microenvironments of relapse- and remission-associated pediatric acute myeloid leukemia

Acute myeloid leukemia (AML) microenvironment exhibits cellular and molecular differences among various subtypes. Here, we utilize single-cell RNA sequencing (scRNA-seq) to analyze pediatric AML bone marrow (BM) samples from diagnosis (Dx), end of induction (EOI), and relapse timepoints. Analysis of Dx, EOI scRNA-seq, and TARGET AML RNA-seq datasets reveals an AML blasts-associated 7-gene signature (CLEC11A, PRAME, AZU1, NREP, ARMH1, C1QBP, TRH), which we validate on independent datasets. The analysis reveals distinct clusters of Dx relapse- and continuous complete remission (CCR)-associated AML-blasts with differential expression of genes associated with survival. At Dx, relapse-associated samples have more exhausted T cells while CCR-associated samples have more inflammatory M1 macrophages. Post-therapy EOI residual blasts overexpress fatty acid oxidation, tumor growth, and stemness genes. Also, a post-therapy T-cell cluster associated with relapse samples exhibits downregulation of MHC Class I and T-cell regulatory genes. Altogether, this study deeply characterizes pediatric AML relapse- and CCR-associated samples to provide insights into the BM microenvironment landscape.

Comprehensive Genomic Profiling of High-Risk Pediatric Cancer Patients Has a Measurable Impact on Clinical Care

PURPOSE

Profiling of pediatric cancers through deep sequencing of large gene panels and whole exomes is rapidly being adopted in many clinical settings. However, the most impactful approach to genomic profiling of pediatric cancers remains to be defined.

METHODS

We conducted a prospective precision medicine trial, using whole-exome sequencing of tumor and germline tissue and whole-transcriptome sequencing (RNA Seq) of tumor tissue to characterize the mutational landscape of 127 tumors from 126 unique patients across the spectrum of pediatric brain tumors, hematologic malignancies, and extracranial solid tumors.

RESULTS

We identified somatic tumor alterations in 121/127 (95.3%) tumor samples and identified cancer predisposition syndromes on the basis of known pathogenic or likely pathogenic germline mutations in cancer predisposition genes in 9/126 patients (7.1%). Additionally, we developed a novel scoring system for measuring the impact of tumor and germline sequencing, encompassing therapeutically relevant genomic alterations, cancer-related germline findings, recommendations for treatment, and refinement of risk stratification or prognosis. At least one impactful finding from the genomic results was identified in 108/127 (85%) samples sequenced. A recommendation to consider a targeted agent was provided for 82/126 (65.1%) patients. Twenty patients ultimately received therapy with a molecularly targeted agent, representing 24% of those who received a targeted agent recommendation and 16% of the total cohort.

CONCLUSION

Paired tumor/normal whole-exome sequencing and tumor RNA Seq of de novo or relapsed/refractory tumors was feasible and clinically impactful in high-risk pediatric cancer patients.

Multicenter Analysis of Genomically Targeted Single Patient Use Requests for Pediatric Neoplasms

PURPOSE

The US Food and Drug Administration-expanded access program (EAP) uses a single patient use (SPU) mechanism to provide patient access to investigational agents in situations where no satisfactory or comparable therapy is available. Genomic profiling of de novo and relapsed or refractory childhood cancer has led to increased identification of new drug targets in the last decade. The aim of this study is to examine the SPU experience for genomically targeted therapies in patients with pediatric cancer.

PATIENTS AND METHODS

All genomically targeted therapeutic SPUs obtained over a 5-year period were evaluated at four large pediatric cancer programs. Data were collected on the type of neoplasm, agents requested, corresponding molecularly informed targets, and clinical outcomes.

RESULTS

A total of 45 SPUs in 44 patients were identified. Requests were predominantly made for CNS and solid tumors (84.4%) compared with hematologic malignancies (15.6%). Lack of an available clinical trial was the main reason for SPU initiation (64.4%). The median time from US Food and Drug Administration submission to approval was 3 days (range, 0-12 days) and from Institutional Review Board submission to approval was 5 days (range, 0-50 days). Objective tumor response was seen in 39.5% (15 of 38) of all evaluable SPUs. Disease progression was the primary reason for discontinuation of drug (66.7%) followed by toxicity (13.3%).

CONCLUSION

SPU requests remain an important mechanism for pediatric access to genomically targeted agents given the limited availability of targeted clinical trials for children with high-risk neoplasms. Furthermore, this subset of SPUs resulted in a substantial number of objective tumor responses. The development of a multi-institutional data registry of SPUs may enable systematic review of toxicity and clinical outcomes and provide evidence-based access to new drugs in rare pediatric cancers.

Retrospective Diagnosis of Ataxia-Telangiectasia in an Adolescent Patient With a Remote History of T-Cell Leukemia

Ataxia-telangiectasia (A-T) is a rare autosomal recessive disorder characterized by progressive cerebellar degeneration that is typically diagnosed in early childhood. A-T is associated with a predisposition to malignancies, particularly lymphoid tumors in childhood and early adulthood. An adolescent girl with minimal neurologic symptoms was diagnosed with A-T 8 years after completing therapy for T-cell acute lymphoblastic leukemia, following a diagnosis of ATM-mutated breast cancer in her mother. We highlight the importance of recognizing ATM mutations in T-cell acute lymphoblastic leukemia, appreciating the phenotypic heterogeneity of A-T, and defining optimal cancer screening in A-T patients.

Leukoerythroblastosis as an Unusual Presentation of Parvovirus B19 Infection in a Sickle Cell Patient

Parvovirus B19 infection in pediatrics most commonly causes fifth disease, a mild viral illness. Hematologic manifestations include severe anemia, especially in patients with chronic hemolytic anemias or who are immunocompromised. Because of the shortened life span of erythrocytes in patients with sickle cell disease, parvovirus infection can cause transient aplastic crisis which can be life-threatening. However, leukocytosis and thrombocytosis are rarely seen. We report leukoerythroblastosis as an unusual presentation of acute parvovirus B19 infection in a previously splenectomized 12-year-old boy with sickle cell disease.

Very late recurrence of B-cell acute lymphoblastic leukemia masquerading as a pituitary tumor

Involvement of the pituitary gland by leukemic infiltration is exceedingly rare. Here, we describe a very late recurrence of B-cell acute lymphoblastic leukemia masquerading as a pituitary tumor and review the literature for previously reported cases. Our female patient presented 13 years after completion of therapy for B-ALL with headache, amenorrhea, galactorrhea and a pituitary mass. Subsequent studies revealed recurrence of her leukemia, and the pituitary lesion resolved after induction chemotherapy. Our case highlights the importance of considering leukemic infiltrate in the differential diagnosis of pituitary mass, particularly in a patient with a history of hematologic malignancy, sparing unnecessary surgical intervention and informing endocrine evaluation. In addition, the case also highlights difficulties with characterizing this recurrence as a very late relapse or clonal evolution of the original leukemia.

The SQSTM1-NUP214 fusion protein interacts with Crm1, activates Hoxa and Meis1 genes, and drives leukemogenesis in mice

The NUP98 and NUP214 nucleoporins (NUPs) are recurrently fused to heterologous proteins in leukemia. The resulting chimeric oncoproteins retain the phenylalanine-glycine (FG) repeat motifs of the NUP moiety that mediate interaction with the nuclear export receptor Crm1. NUP fusion leukemias are characterized by HOXA gene upregulation; however, their molecular pathogenesis remains poorly understood. To investigate the role of Crm1 in mediating the leukemogenic properties of NUP chimeric proteins, we took advantage of the Sequestosome-1 (SQSTM1)-NUP214 fusion. SQSTM1-NUP214 retains only a short C-terminal portion of NUP214 which contains FG motifs that mediate interaction with Crm1. We introduced point mutations targeting these FG motifs and found that the ability of the resulting SQSTM1-NUP214FGmut protein to interact with Crm1 was reduced by more than 50% compared with SQSTM1-NUP214. Mutation of FG motifs affected transforming potential: while SQSTM1-NUP214 impaired myeloid maturation and conferred robust colony formation to transduced hematopoietic progenitors in a serial replating assay, the effect of SQSTM1-NUP214FGmut was considerably diminished. Moreover, SQSTM1-NUP214 caused myeloid leukemia in all transplanted mice, whereas none of the SQSTM1-NUP214FGmut reconstituted mice developed leukemia. These oncogenic effects coincided with the ability of SQSTM1-NUP214 and SQSTM1-NUP214FGmut to upregulate the expression of Hoxa and Meis1 genes in hematopoietic progenitors. Indeed, chromatin immunoprecipitation assays demonstrated that impaired SQSTM1-NUP214 interaction with Crm1 correlated with impaired binding of the fusion protein to Hoxa and Meis1 genes. These findings highlight the importance of Crm1 in mediating the leukemogenic properties of SQSTM1-NUP214, and suggest a conserved role of Crm1 in recruiting oncoproteins to their effector genes.

Adolescent and Young Adult Oncology, Version 2.2018, NCCN Clinical Practice Guidelines in Oncology

This selection from the NCCN Guidelines for Adolescent and Young Adult (AYA) Oncology focuses on treatment and management considerations for AYA patients with cancer. Compared with older adults with cancer, AYA patients have unique needs regarding treatment, fertility counseling, psychosocial and behavioral issues, and supportive care services. The complete version of the NCCN Guidelines for AYA Oncology addresses additional aspects of caring for AYA patients, including risk factors, screening, diagnosis, and survivorship.

Pediatric Cancer in Northern Tanzania: Evaluation of Diagnosis, Treatment, and Outcomes

PURPOSE

The majority of new diagnoses of pediatric cancer are made in resource-poor countries, where survival rates range from 5% to 25% compared with 80% in high-resource countries. Multiple factors, including diagnostic and treatment capacities and complex socioeconomic factors, contribute to this variation. This study evaluated the available resources and outcomes for pediatric patients with cancer at the first oncology treatment center in northern Tanzania.

METHODS

Qualitative interviews were completed from July to August 2015 to determine available staff, hospital, diagnostic, treatment, and supportive care resources. A retrospective review of hospital admissions and clinic visits from January 2010 to August 2014 was completed. A total of 298 patients were identified, and data from 182 patient files were included in this review.

RESULTS

Diagnostic, treatment, and supportive capacities are limited for pediatric cancer care. The most common diagnoses were Burkitt lymphoma (n = 32), other non-Hodgkin lymphoma (n = 26), and Wilms tumor (n = 25). A total of 40% of patients (n = 72) abandoned care. There was a 20% 2-year event-free survival rate, which was significantly affected by patient age, method of diagnosis, and year of diagnosis.

CONCLUSION

To our knowledge, this is the first review of pediatric cancer outcomes in northern Tanzania. The study identified areas for future development to improve pediatric cancer outcomes, which included strengthening of training and diagnostic capacities, development of registries and research databases, and the need for additional research to reduce treatment abandonment.

Wilms Tumor After Orthotopic Liver Transplant in a Patient With Alagille Syndrome

We present a case of Wilms Tumor in a patient with Alagille syndrome 10 months after liver transplant. We explore a suggested genetic connection between these 2 diseases. In children with Wilms Tumor, we propose a pathoembryologic explanation for not just the tumor, but also for the cause of associated benign ureteral and renal parenchymal aberrancies that are commonly seen in the Alagille population. We also discuss the diagnostic and therapeutic challenges that can arise in a liver transplant patient with Alagille syndrome who subsequently develops a renal mass.

A positive feedback loop between ROS and Mxi1-0 promotes hypoxia-induced VEGF expression in human hepatocellular carcinoma cells

VEGF expression induced by hypoxia plays a critical role in promoting tumor angiogenesis. However, the molecular mechanism that modulates VEGF expression under hypoxia is still poorly understood. In this study, we found that VEGF induction in hypoxic HepG2 cells is ROS-dependent. ROS mediates hypoxia-induced VEGF by upregulation of Mxi1-0. Furthermore, PI3K/AKT/HIF-1α signaling pathway is involved in ROS-mediated Mxi1-0 and VEGF expression in hypoxic HepG2 cells. Finally, Mxi1-0 could in turn regulate ROS generation in hypoxic HepG2 cells, creating a positive feedback loop. Taken together, this study demonstrate a positive regulatory feedback loop in which ROS mediates hypoxia-induced Mxi1-0 via activation of PI3K/AKT/HIF-1α pathway, events that in turn elevate ROS generation and promote hypoxia-induced VEGF expression. These findings could provide a rationale for designing new therapies based on inhibition of hepatocellular carcinoma (HCC) angiogenesis.

Abstract B32: The role of Exon 0 in mediating Mxi0 activity in neuroblastoma

Background: Neuroblastoma is the most common extracranial malignancy of childhood. The Myc family of proteins regulates cell growth and proliferation and has been implicated in the etiology of many cancers. MYCN amplified neuroblastoma is associated with a poor prognosis. Investigating specific tumor pathways will further our understanding of neuroblastoma pathogenesis and lead to future therapeutic options. Mxi1 is a member of the MAD family that inhibits N-Myc activity. Mxi0 is an alternatively spliced variant of Mxi1 with a different first exon (Exon 0) whose function has not been determined. These proteins appear to have differential functions in neuroblastoma pathogenesis.

Objective: Elucidate the impact of Mxi1 and Mxi0 expression on neuroblastoma physiology and determine the role of Exon 0 in the function of Mxi0.

Design: We created neuroblastoma cell lines with inducible expression of Mxi1 and Mxi0 to tightly control expression. Cell proliferation and survival were quantified using BrdU and MTT assays. Chemosensitivity was assessed by treating cells with doxorubicin or etoposide after induction of Mxi1 or Mxi0 expression. Cell viability was then measured by by MTT assay. To help examine the role of Exon 0, we utilized GFP tagged constructs of Mxi1, Mxi0, and Exon 0. These proteins were expressed in 293T cells and subcellular localization of Mxi1, Mxi0, and Exon 0 proteins was then detected by immunofluorescence. To assess the role of nuclear export in cell localization, cells were treated with leptomycin B.

Results: Overexpression of Mxi1 inhibits N-Myc mediated cell proliferation. Conversely, overexpression of Mxi0 in neuroblastoma cell lines leads to enhanced proliferation, suggesting that Mxi0 has a counter-regulatory role to that of Mxi1. Compared with Mxi1, expression of Mxi0 results in cells becoming more chemoresistant. Examination of Mxi1 and Mxi0 subcellular location reveals that Mxi1 resides in the nucleus while Mxi0 is found primarily in the cytoplasm. Exon 0 alone also is found in the cytoplasm, indicating that this differential localization is determined by the presence of Exon 0. Finally, treatment with leptomycin B resulted in accumulation of Mxi0 in the nucleus, suggesting that it may cycle in and out of the nucleus in response to appropriate signals.

Conclusions: Overexpression of Mxi1 in neuroblastoma cell lines leads to inhibition of N-Myc-mediated cell proliferation while Mxi0 appears to promote cell growth. Mxi1 expression enhances chemosensitivity of neuroblastoma cells, while Mxi0 has the opposite effect. Exon 0 directs the cytoplasmic localization of Mxi0 and may play an important role in its differential function. A better understanding of how the interaction between Mxi1 and Mxi0 affects neuroblastoma physiology and how Exon 0 imparts the differential function of Mxi0 may aid in developing more effective targeted therapies to improve outcomes in children with neuroblastoma.

Citation Format: Stephen J. Kirchner, James T. Bartram, D. Christian Ellis, Daniel S. Wechsler, Michael B. Armstrong. The role of Exon 0 in mediating Mxi0 activity in neuroblastoma. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr B32.

Persistent and Prolonged Parvovirus B19 Viremia in a Pediatric Patient With Acute Lymphoblastic Leukemia

Parvovirus B19 is a small single-stranded DNA virus of the Parvoviridae family. Depending on host factors, it may produce a wide array of clinical disease states. Disease severity can range from self-limited to severe, requiring significant supportive care. Immunocompromised patients are generally affected more severely but rarely develop prolonged and persistent infections. Here, we describe a patient who was diagnosed with parvovirus during maintenance therapy for acute lymphoblastic leukemia and required therapy with intravenous immunoglobulin; the patient remained parvovirus positive according to a polymerase chain reaction testing but had no clinical symptoms for 27 months off chemotherapy.

Modulation of PICALM Levels Perturbs Cellular Cholesterol Homeostasis

PICALM (Phosphatidyl Inositol Clathrin Assembly Lymphoid Myeloid protein) is a ubiquitously expressed protein that plays a role in clathrin-mediated endocytosis. PICALM also affects the internalization and trafficking of SNAREs and modulates macroautophagy. Chromosomal translocations that result in the fusion of PICALM to heterologous proteins cause leukemias, and genome-wide association studies have linked PICALM Single Nucleotide Polymorphisms (SNPs) to Alzheimer's disease. To obtain insight into the biological role of PICALM, we performed gene expression studies of PICALM-deficient and PICALM-expressing cells. Pathway analysis demonstrated that PICALM expression influences the expression of genes that encode proteins involved in cholesterol biosynthesis and lipoprotein uptake. Gas Chromatography-Mass Spectrometry (GC-MS) studies indicated that loss of PICALM increases cellular cholesterol pool size. Isotopic labeling studies revealed that loss of PICALM alters increased net scavenging of cholesterol. Flow cytometry analyses confirmed that internalization of the LDL receptor is enhanced in PICALM-deficient cells as a result of higher levels of LDLR expression. These findings suggest that PICALM is required for cellular cholesterol homeostasis and point to a novel mechanism by which PICALM alterations may contribute to disease.

A critical role for CRM1 in regulating HOXA gene transcription in CALM-AF10 leukemias

The leukemogenic CALM-AF10 fusion protein is found in patients with immature acute myeloid and T-lymphoid malignancies. CALM-AF10 leukemias display abnormal H3K79 methylation and increased HOXA cluster gene transcription. Elevated expression of HOXA genes is critical for leukemia maintenance and progression; however, the precise mechanism by which CALM-AF10 alters HOXA gene expression is unclear. We previously determined that CALM contains a CRM1-dependent nuclear export signal (NES), which is both necessary and sufficient for CALM-AF10-mediated leukemogenesis. Here, we find that interaction of CALM-AF10 with the nuclear export receptor CRM1 is necessary for activating HOXA gene expression. We show that CRM1 localizes to HOXA loci where it recruits CALM-AF10, leading to transcriptional and epigenetic activation of HOXA genes. Genetic and pharmacological inhibition of the CALM-CRM1 interaction prevents CALM-AF10 enrichment at HOXA chromatin, resulting in immediate loss of transcription. These results provide a comprehensive mechanism by which the CALM-AF10 translocation activates the critical HOXA cluster genes. Furthermore, this report identifies a novel function of CRM1: the ability to bind chromatin and recruit the NES-containing CALM-AF10 transcription factor.

Mxi1 and mxi1-0 antagonize N-myc function and independently mediate apoptosis in neuroblastoma

Neuroblastoma (NB) is the third most common malignancy of childhood, and outcomes for children with advanced disease remain poor; amplification of the MYCN gene portends a particularly poor prognosis. Mxi1 antagonizes N-Myc by competing for binding to Max and E-boxes. Unlike N-Myc, Mxi1 mediates transcriptional repression and suppresses cell proliferation. Mxi1 and Mxi1-0 (an alternatively transcribed Mxi1 isoform) share identical Max and DNA binding domains but differ in amino-terminal sequences. Because of the conservation of these critical binding domains, we hypothesized that Mxi1-0 antagonizes N-Myc activity similar to Mxi1. SHEP NB cells and SHEP cells stably transfected with MYCN (SHEP/MYCN) were transiently transfected with vectors containing full-length Mxi1, full-length Mxi1-0, or the common Mxi domain encoded by exons 2 to 6 (ex2-6). After incubation in low serum, parental SHEP/MYCN cell numbers were reduced compared with SHEP cells. Activated caspase-3 staining and DNA fragmentation ELISA confirmed that SHEP/MYCN cells undergo apoptosis in low serum, while SHEP/MYCN cells transfected with Mxi1 or Mxi1-0 do not. However, SHEP/MYCN cells transfected with Mxi1 or Mxi1-0 and grown in normal serum showed proliferation rates similar to SHEP cells. Mxi ex2-6 did not affect cell number in low or normal serum, suggesting that amino terminal domains of Mxi1 and Mxi1-0 are critical for antagonism. In the absence of N-Myc, Mxi1 and Mxi1-0 induce apoptosis independently through the caspase-8-dependent extrinsic pathway, while N-Myc activates the caspase-9-dependent intrinsic pathway. Together, these data indicate that Mxi1 and Mxi1-0 antagonize N-Myc but also independently impact NB cell survival.

Abstract B37: The impact of modulating Mxi1 and Mxi0 expression on N-Myc-mediated neuroblastoma tumor pathogenesis and chemosensitivity

Background: Neuroblastoma is the most common extracranial malignancy of childhood. Myc family proteins regulate cell growth and proliferation in response to mitogenic stimulation, and Myc proteins are implicated in the etiology of many cancers. MYCN amplified neuroblastoma carries a poor overall survival with limited therapeutic options. Investigating specific tumor pathways will further our understanding of neuroblastoma pathogenesis and lead to future therapeutic options for children with this disease. Mxi1 is a member of the MAD family of proteins that inhibit N-Myc function. Mxi0 is an alternatively-spliced variant of Mxi1 whose function has not been determined. We hypothesize that Mxi1 and Mxi0 expression levels affect N-Myc-dependent neuroblastoma cell growth.

Objective: To determine the impact of modulating Mxi1 and Mxi0 expression on N-Myc-dependent neuroblastoma cell proliferation and survival.

Design: We expressed Mxi1 and Mxi0 in SHEP neuroblastoma cells and SHEP cells stably transfected to express high levels of MYCN (SHEP/MYCN). We also utilized native neuroblastoma cell lines with inducible expression of Mxi1 and Mxi0. Cell proliferation and survival were quantified using BrdU and MTT assays, respectively. Apoptosis was measured by propidium iodide staining and caspase-3 immunohistochemistry. Cellular localization of Mxi1 and Mxi0 proteins was detected by immunofluorescence.

Results: Overexpression of Mxi1 inhibits N-Myc mediated cell proliferation. Additionally, in the absence of N-Myc, Mxi1 overexpression independently inhibits cell proliferation and induces cell apoptosis. Conversely, overexpression of Mxi0 in neuroblastoma cell lines leads to enhanced proliferation, suggesting that Mxi0 has a counter-regulatory role to that of Mxi1. Expression of Mxi1 increased sensitivity of the neuroblastoma cells to doxorubicin, while higher levels of Mxi0 made the cells more chemoresistant. Finally, examination of Mxi1 and Mxi0 cellular location reveals that Mxi1 resides in the nucleus while Mxi0 is found primarily in the cytoplasm.

Conclusions: Overexpression of Mxi1 in neuroblastoma cell lines leads to inhibition of N-Myc-mediated cell proliferation while Mxi0 appears to promote cell growth. Mxi1 expression enhanced chemosensitivity of neuroblastoma cells, while Mxi0 had the converse effect. A better understanding of the interaction between Mxi1 and Mxi0 and how the balance of these proteins affect neuroblastoma physiology may aid in developing more effective targeted therapies to improve outcomes in children with neuroblastoma.

Citation Format: D. Christian Ellis, R. Scott Widemon, Daniel S. Wechsler, Michael B. Armstrong. The impact of modulating Mxi1 and Mxi0 expression on N-Myc-mediated neuroblastoma tumor pathogenesis and chemosensitivity. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B37.

Successful treatment of pediatric histiocytic sarcoma using abbreviated high-risk leukemia chemotherapy

Histiocytic sarcoma (HS) is a malignant tumor composed of proliferating cells of histiocytic origin. True HS is exceedingly rare, particularly in pediatric patients. These tumors are frequently aggressive, and outcome for patients with HS has traditionally been poor. There is currently no consensus on the optimal management of these tumors, with the literature consisting largely of case reports and small case series utilizing a wide variety of therapies. We describe a case of HS in an 8-year-old female who was successfully treated with an abbreviated leukemia chemotherapy regimen.

PICALM modulates autophagy activity and tau accumulation

Genome-wide association studies have identified several loci associated with Alzheimer’s disease (AD), including proteins involved in endocytic trafficking such as PICALM/CALM (phosphatidylinositol binding clathrin assembly protein). It is unclear how these loci may contribute to AD pathology. Here we show that CALM modulates autophagy and alters clearance of tau, a protein which is a known autophagy substrate and which is causatively linked to AD, both in vitro and in vivo. Furthermore, altered CALM expression exacerbates tau-mediated toxicity in zebrafish transgenic models. CALM influences autophagy by regulating the endocytosis of SNAREs, such as VAMP2, VAMP3 and VAMP8, which have diverse effects on different stages of the autophagy pathway, from autophagosome formation to autophagosome degradation. This study suggests that the AD genetic risk factor CALM modulates autophagy, and this may affect disease in a number of ways including modulation of tau turnover.

The protein PICALM/CALM is implicated in Alzheimer’s disease (AD) pathology, but it is unclear how. In this study, the authors show that CALM regulates clearance of the protein tau, which is also implicated in AD pathology, by facilitating endocytosis-dependent autophagy.

Iron deprivation in cancer--potential therapeutic implications

Iron is essential for normal cellular function. It participates in a wide variety of cellular processes, including cellular respiration, DNA synthesis, and macromolecule biosynthesis. Iron is required for cell growth and proliferation, and changes in intracellular iron availability can have significant effects on cell cycle regulation, cellular metabolism, and cell division. Perhaps not surprisingly then, neoplastic cells have been found to have higher iron requirements than normal, non-malignant cells. Iron depletion through chelation has been explored as a possible therapeutic intervention in a variety of cancers. Here, we will review iron homeostasis in non-malignant and malignant cells, the widespread effects of iron depletion on the cell, the various iron chelators that have been explored in the treatment of cancer, and the tumor types that have been most commonly studied in the context of iron chelation.

Adolescent and young adult oncology. Clinical practice guidelines in oncology

Cancer is the leading cause of death among the adolescent and young adult (AYA) population, excluding homicide, suicide, or unintentional injury. AYA patients should be managed by a multidisciplinary team of health care professionals who are well-versed in the specific developmental issues relevant to this patient population. The recommendations for age-appropriate care outlined in these NCCN Guidelines include psychosocial assessment, a discussion of infertility risks associated with treatment and options for fertility preservation, genetic and familial risk assessment for all patients after diagnosis, screening and monitoring of late effects in AYA cancer survivors after successful completion of therapy, and palliative care and end-of-life considerations for patients for whom curative therapy fails.

Abstract LB-154: Nuclear export of CALM-AF10 is essential for leukemogenesis

Background: The t(10;11) chromosomal translocation gives rise to the CALM-AF10 fusion gene and is recurrently found in patients with aggressive and difficult-to-treat hematopoietic malignancies (AML and T-ALL). CALM-AF10 leukemias are characterized by upregulation of Hoxa cluster genes and a reduction in H3K79 methylation. The native AF10 protein localizes to the nucleus, while native CALM protein is found predominantly in the cytoplasm. It has been shown that the OM-LZ domain of AF10 interacts with the histone methyltransferase, Dot1L, and that this interaction is necessary for CALM-AF10-mediated transformation. Although it is known that CALM functions as an accessory endocytic protein, the precise role of CALM in leukemogenesis is unclear. Objective: To determine the role of CALM in CALM-AF10-mediated transformation in an effort to identify novel therapeutic targets. Results: Through structure-function analyses, we determined that a minimal region of CALM (aa 520-583) is critical for CALM-AF10-mediated transformation of murine hematopoietic progenitor cells (HPCs). Further analysis of this sequence identified a nuclear export signal (NES) encoded by CALM aa 544-553. The CALM NES mediates the cytoplasmic localization of CALM-AF10; point mutation of the CALM NES (NES*) results in exclusive CALM(NES*)-AF10 accumulation in the nucleus. In contrast to CALM-AF10, transduction of primary murine HPCs with CALM(NES*)-AF10 fails to cause in vitro transformation. Fusion of an 18 aa peptide that includes the CALM NES in frame with AF10 (NESCALM-AF10) is sufficient to induce transformation in vitro and leukemogenesis in vivo. Leukemias induced by NESCALM-AF10 recapitulated the phenotype of CALM-AF10 leukemias, including aberrant Hoxa cluster upregulation and decreased H3K79 methylation. Strikingly, fusion of the NES from different proteins, such as PKI-α and APC, to AF10 also conferred cytoplasmic localization and resulted in transformation in vitro. Finally, human CALM-AF10 leukemia cell lines (U937 and P31-FUJI) display increased sensitivity to a compound that inhibits nuclear export, Leptomycin B. Conclusions: We have determined that a CALM-derived nuclear export signal is both necessary and sufficient for CALM-AF10-mediated transformation. These findings reveal a novel mechanism by which nuclear export of CALM-AF10 mediates leukemogenesis. We postulate that nuclear export inhibitor (NEI) compounds may offer new therapeutic possibilities for patients with aggressive CALM-AF10 leukemias.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-154. doi:1538-7445.AM2012-LB-154

Synchronous occurrence of metastatic Wilms tumor and ganglioneuroma

We describe a 4-year-old female patient with a persistent paraspinal mass following chemotherapy for Wilms tumor. A discordant response to chemotherapy prompted biopsy of the persistent mass, which revealed a ganglioneuroma. This report highlights the synchronous occurrence of different tumors in the same patient, and suggests that repeat biopsies should be considered when contiguous tumor masses do not respond as expected.

Abstract 3952: CALM deficiency in fit1 embryonic cells alters expression and rate of endocytosis of growth factor receptors

Background: Gene rearrangements involving the Clathrin Assembly Lymphoid Myeloid Leukemia (CALM) and Mixed-Lineage Leukemia (MLL) or AF10 genes have been identified in aggressive leukemias and lymphomas. Expression of CALM-containing fusion proteins immortalizes murine hematopoietic cells in vitro, correlating with leukemogenesis in vivo. Disruption of normal CALM, MLL or AF10 protein function as a result of these translocations likely contributes to transformation, although the precise mechanisms are unknown. The native CALM protein is involved in clathrin-mediated endocytosis (CME); it localizes to the cytoplasmic side of endocytic vesicles, interacts with both membrane elements and clathrin, and when over- or under-expressed, disrupts endocytosis. To better understand the effects of altered CALM activity, we have focused our studies on mutant fit1 mice that lack CALM expression. Previous studies have shown that these mice have iron deficiency, defective hematopoiesis and ultimately premature death. Here we examine CALM's role in endocytosis and cellular function using cells derived from fit1 mice.

Objective: To examine the effect of CALM deficiency on cell surface receptor expression and endocytosis using mouse embryonic fibroblasts (MEFs) and fetal liver cells derived from normal and CALM-deficient mice.

Design: Day 14 MEFs were generated from normal, heterozygous, and mutant fit1 embryos. Immortalized MEFs were compared in terms of quantity of cell surface and total cellular receptors (by flow cytometry and Western blotting), receptor mRNA levels, and rate of endocytosis. Receptors were also measured in fetal liver derived from the same embryos.

Results: When compared to their normal counterparts, cells lacking full length CALM showed altered cell surface receptor expression: transferrin receptor (TfR) protein levels measured by flow cytometry were increased two-fold, while EGF receptor (EGFR) levels were reduced two-fold. These results correlated with increased total cellular TfR protein and mRNA levels and decreased total EGFR protein levels. Whereas the rate of internalization of TfR was similar, the rate of endocytosis of EGFR was significantly reduced in CALM-deficient compared with wildtype cells. Elevated TfR levels were also identified in CALM-deficient fetal liver cells.

Conclusions: CALM deficiency in fit1-derived cells results in increased TfR surface expression; this is consistent with the iron deficiency phenotype of fit1 mice. The reduced surface expression of EGFR seen in fit1 cells may be a compensatory mechanism that counteracts the increased growth factor receptor signaling that is associated with impaired endocytosis. Since CALM haploinsufficiency is a feature of CALM-AF10 and MLL-CALM leukemias, our results suggest that the perturbation of normal growth factor biology may contribute to transformation in these malignancies.

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 3952.

Treatment with sirolimus results in complete responses in patients with autoimmune lymphoproliferative syndrome

We hypothesized that sirolimus, an mTOR inhibitor, may be effective in patients with autoimmune lymphoproliferative syndrome (ALPS) and treated patients who were intolerant to or failed other therapies. Four patients were treated for autoimmune cytopenias; all had a rapid complete or near complete response. Two patients were treated for autoimmune arthritis and colitis, demonstrating marked improvement. Three patients had complete resolution of lymphadenopathy and splenomegaly and all patients had a reduction in double negative T cells, a population hallmark of the disease. Based on these significant responses, we recommend that sirolimus be considered as second-line therapy for patients with steroid-refractory disease.

Consensus on a core curriculum in American training programs in pediatric hematology-oncology: a report from the ASPHO Training Committee

The Training Committee (TC) of the American Society of Pediatric Hematology/Oncology created a foundation of common goals and objectives that could provide a structure for fellowship programs. The TC conducted a survey of program directors for input into the structure of their programs and training methods and the results are presented here. Additionally, a suggested core program is outlined, taking into account the new common requirements as stipulated by the ACGME and ABP, and additional suggestions from the program directors. This paper highlights the suggested training objectives and educational opportunities that should be afforded all fellows in this sub-specialty. The goal of this consensus statement is to provide a model curriculum to improve quality and consistency of training and achieve compliance with new requirements while simultaneously recognizing the importance of alternative approaches that emphasize each program's unique strengths and character.

Aortobronchial Fistula in a Pediatric Patient With Massive Hemoptysis: Treatment by Means of an Aortic Endograft

We present an 11-year-old girl with acute myelogenous leukemia and hemoptysis from abscess erosion into the descending thoracic aorta. We report a pediatric case of an aortobronchial fistula treated with an aortic endograft and discuss the technical limitations and potential complications of this procedure.

Testicular chloroma in a nonleukemic infant

Extramedullary myeloid cell tumors (EMCT) are localized collections of immature myeloid cells that occur outside of the bone marrow. Usually observed concurrently with bone marrow disease, EMCT also may occur in the absence of overt marrow leukemia. In this report, we describe an infant with a testicular mass that was identified as an EMCT after orchiectomy. Unlike the only previously reported case of infantile testicular chloroma, this patient did not exhibit bone marrow disease at diagnosis. Because systemic chemotherapy is considered to be superior to local control (surgery, radiation therapy), the patient was treated with intensively timed induction chemotherapy followed by 3 cycles of maintenance treatment (according to CCG protocol #2891) but no radiation therapy. The patient remains disease-free 18 months after diagnosis.

High-risk surgically resected pediatric melanoma and adjuvant interferon therapy

BACKGROUND

Pediatric patients with high-risk surgically resected melanoma are at risk for relapse, yet little is known about these young patients and how they tolerate high-dose interferon therapy.

PROCEDURE

We reviewed medical records of patients (< or =18 years) with high-risk melanoma referred to the University of Michigan Pediatric Hematology-Oncology service between January 1989 and July 2003.

RESULTS

Fourteen patients were identified with high-risk resected melanoma. The median age at diagnosis was 8.5 years. The median time to establish diagnosis was 9 months. Primary lesions were diagnosed as unequivocal melanoma, atypical epithelioid melanocytic proliferations, or atypical Spitz tumor with indeterminate malignant potential. Twelve patients had a positive sentinel lymph node (SLN) biopsy or a palpable regional lymph node and underwent regional lymph node dissection (LND). Two patients with unequivocal melanoma with Breslow depth >4 mm had negative SLN biopsies. Twelve patients received adjuvant high-dose interferon. The following toxicities were observed: constitutional symptoms, gastrointestinal symptoms, depression or neuropsychiatric symptoms, myelosuppression, elevated AST or ALT, hypothyroidism, and hypertension. Grade 3 or 4 toxicities were uncommon with exception of neutropenia, resulting in modification of therapy in one patient. All patients are alive and free of disease at follow-up (median 24.5 months).

CONCLUSIONS

Invasive melanoma can occur in very young children. Despite early signs of malignancy, there is often a delay in diagnosis. Histologically, diagnosis may be difficult because of overlap with Spitz nevi. Pediatric patients tolerated adjuvant high-dose interferon well and may be less likely than adults to require therapy modification secondary to toxicities.

Mxi1-0, an alternatively transcribed Mxi1 isoform, is overexpressed in glioblastomas

The c-Myc transcription factor regulates expression of genes related to cell growth, division, and apoptosis. Mxi1, a member of the Mad family, represses transcription of c-Myc-regulated genes by mediating chromatin condensation via histone deacetylase and the Sin3 corepressor. Mxi1 is a c-Myc antagonist and suppresses cell proliferation in vitro. Here, we describe the identification of Mxi1-0, a novel Mxi1 isoform that is alternatively transcribed from an upstream exon. Mxi1-0 and Mxi1 have different amino-terminal sequences, but share identical Max- and DNA-binding domains. Both isoforms are able to bind Max, to recognize E-box binding sites, and to interact with Sin3. Despite these similarities and in contrast to Mxi1, Mxi1-0 is predominantly localized to the cytoplasm and fails to repress c-Myc-dependent transcription. Although Mxi1-0 and Mxi1 are coexpressed in both human and mouse cells, the relative levels of Mxi1-0 are higher in primary glioblastoma tumors than in normal brain tissue. This variation in the levels of Mxi1-0 and Mxi1 suggests that Mxi1-0 may modulate the Myc-inhibitory activity of Mxi1. The identification of Mxi1-0 as an alternatively transcribed Mxi1 isoform has significant implications for the interpretation of previous Mxi1 studies, particularly those related to the phenotype of the mxi1 knockout mouse.

Metastatic neuroblastoma presenting with binocular blindness from intracranial compression of the optic nerves

A 2-year-old boy with blindness as an isolated symptom was found to have no light perception binocularly because of compression of both optic nerves by a neuroblastoma infiltrating the walls of the optic canals and medial sphenoid bone. Imaging disclosed a primary tumor near the kidney and multiple osseous metastases. Although neuroblastoma commonly causes blindness by metastasis to the orbit, it rarely causes bilateral blindness from intracranial compression of the optic nerves. This is the first report of bilateral blindness as the presenting feature.

Characterization of gene expression profiles associated with glioma progression using oligonucleotide-based microarray analysis and real-time reverse transcription-polymerase chain reaction

Diffuse astrocytoma of World Health Organization (WHO) grade II has an inherent tendency to spontaneously progress to anaplastic astrocytoma (WHO grade III) and/or glioblastoma (WHO grade IV). The molecular basis of astrocytoma progression is still poorly understood, in particular with respect to the progression-associated changes at the mRNA level. Therefore, we compared the transcriptional profile of approximately 6800 genes in primary WHO grade II gliomas and corresponding recurrent high-grade (WHO grade III or IV) gliomas from eight patients using oligonucleotide-based microarray analysis. We identified 66 genes whose mRNA levels differed significantly (P < 0.01, > or =2-fold change) between the primary and recurrent tumors. The microarray data were corroborated by real-time reverse transcription-polymerase chain reaction analysis of 12 selected genes, including 7 genes with increased expression and 5 genes with reduced expression on progression. In addition, the expression of these 12 genes was determined in an independent series of 43 astrocytic gliomas (9 diffuse astrocytomas, 10 anaplastic astrocytomas, 17 primary, and 7 secondary glioblastomas). These analyses confirmed that the transcript levels of nine of the selected genes (COL4A2, FOXM1, MGP, TOP2A, CENPF, IGFBP4, VEGFA, ADD3, and CAMK2G) differed significantly in WHO grade II astrocytomas as compared to anaplastic astrocytomas and/or glioblastomas. Thus, we identified and validated a set of interesting candidate genes whose differential expression likely plays a role in astrocytoma progression.

Refractory iron deficiency anemia as the primary clinical manifestation of celiac disease

In the absence of dietary insufficiency, iron deficiency is usually caused by chronic blood loss or intestinal malabsorption. Celiac disease is one of the most common causes of intestinal malabsorption during childhood, and its association with insulin-dependent diabetes mellitus has been previously reported. Here the authors describe an otherwise asymptomatic diabetic adolescent boy with iron deficiency anemia that was not responsive to oral iron therapy. A diagnosis of celiac disease was made based on both anti-endomysial antibody titers and small intestinal biopsy. Institution of a gluten-free diet resulted in correction of the anemia. These observations emphasize the importance of considering a diagnosis of celiac disease in patients with nonresponsive iron deficiency anemia, particularly in the setting of insulin-dependent diabetes mellitus.

A novel chromosomal inversion at 11q23 in infant acute myeloid leukemia fuses MLL to CALM, a gene that encodes a clathrin assembly protein

Rearrangements involving the MLL gene at chromosome band 11q23 are common in infant acute myeloid leukemias (AMLs). We recently encountered an infant patient with rapidly progressive AML whose leukemic cells harbored a previously undescribed MLL rearrangement involving an inversion of 11q [inv(11)(q14q23)]. We used panhandle PCR to determine that this rearrangement juxtaposed the MLL (Mixed-Lineage Leukemia) gene to the CALM (Clathrin Assembly Lymphoid Myeloid leukemia) gene at 11q14-q21. The CALM protein participates in recruitment of clathrin to internal membrane surfaces, thereby regulating vesicle formation in both endocytosis and intracellular protein transport. Intriguingly, CALM has been identified in other cases of AML as a translocation partner for the AF10 gene, which has independently been found to be an MLL partner in AML. We identified the MLL-CALM fusion transcript (but not the reciprocal CALM-MLL transcript) in leukemia cell RNA by RT-PCR. The predicted 1803 amino acid MLL-CALM fusion protein includes amino-terminal MLL domains involved in transcriptional repression, and carboxy-terminal CALM-derived clathrin-binding domains. The genomic breakpoint in MLL is in the 7th intron (within the breakpoint cluster region); the corresponding CALM breakpoint is in the 7th CALM intron. In contrast, breakpoints in CALM-AF10 translocations lie in the 17th-19th CALM introns (30 kb downstream); also, in these translocations, CALM provides the 5' end of the fusion transcript. Together with its previously recognized association with AF10 in AML, the identification of CALM as an MLL fusion partner suggests that interference with clathrin-mediated trafficking pathways may be an underappreciated mechanism in leukemogenesis.

Mediastinal seminoma in a patient with Wiskott-Aldrich syndrome

Shortness of breath developed in an 18-year-old man with Wiskott-Aldrich syndrome, and he was found to have a large mediastinal mass. The gallium scan was positive, and biopsy indicated a seminoma. After treatment with four cycles of chemotherapy, the mass completely resolved. Despite severe thrombocytopenia, he required only two platelet transfusions during therapy. Although lymphomas make up the vast majority of mediastinal tumors in patients with Wiskott-Aldrich syndrome, a positive gallium scan should not preclude the diagnosis of seminoma or the need for confirmatory tissue diagnosis. This report shows the possibility of uneventful and successful treatment of malignancy in a patient with Wiskott-Aldrich syndrome and severe thrombocytopenia.

Mxi1, a Myc antagonist, suppresses proliferation of DU145 human prostate cells

BACKGROUND

Mxi1, an antagonist of c-Myc, maps to human chromosome 10q24-q25, a region altered in a substantial fraction of prostate tumors. Mice deficient for Mxi1 exhibit significant prostate hyperplasia. We studied the ability of Mxi1 to act as a growth suppressor in prostate tumor cells.

METHODS

We infected DU145 prostate carcinoma cells with an Mxi1-expressing adenovirus (AdMxi1) in vitro, and measured Mxi1 expression, cell proliferation, soft agar colony formation, and cell cycle distribution. To explore mechanisms of Mxi1-induced growth arrest, we performed gene expression analysis.

RESULTS

AdMxi1 infection resulted in reduced cell proliferation, reduced soft agar colony formation, and a higher proportion of cells in the G(2)/M phase of the cell cycle. This G(2)/M growth arrest was associated with elevated levels of cyclin B, and reduced levels of c-MYC and MDM2.

CONCLUSIONS

The ability of AdMxi1 to suppress prostate tumor cell proliferation supports a role for Mxi1 loss in the pathogenesis of a subset of human prostate cancers. Prostate 47:194-204, 2001.

Expression of MXI1, a Myc antagonist, is regulated by Sp1 and AP2

MXI1, a member of the MAD family of Myc antagonists, encodes a transcription factor whose expression must be tightly regulated to maintain normal cell growth and differentiation. To more closely investigate the transcriptional regulation of the human MXI1 gene, we have cloned and characterized the MXI1 promoter. After clarification of the 5'- and 3'-untranslated regions of the cDNA (indicating that the true length of the MXI1 transcript is 2643 base pairs), we identified two transcription initiation sites. We subsequently isolated the MXI1 promoter, which is GC-rich and lacks a TATA box. Although it contains at least six potential initiator sequences, functional studies indicate the proximal two initiator sequences in combination with nearby Sp1 and MED-1 sites together account for virtually all promoter activity. We also demonstrate that MXI1 promoter activity is repressed by high levels of AP2. These studies provide further insight into the complex regulatory mechanisms governing MXI1 gene expression and its role in cellular differentiation and tumor suppression.

MXI1, a putative tumor suppressor gene, suppresses growth of human glioblastoma cells

The Mxi1 protein functions in a regulatory network with members of the c-Myc family, in which c-Myc activates transcription and stimulates cell proliferation, and Mxi1 negatively regulates these actions. Inactivation of the MXI1 gene could, therefore, inhibit differentiation and enhance proliferation in the presence of normal levels of c-Myc, and thus MXI1 is a potential tumor suppressor gene. We and others have previously mapped the MXI1 gene to the distal portion of chromosome 10q, a region that is rearranged or affected by allelic loss in many astrocytic brain tumors. Using a newly described polymorphic CA microsatellite repeat in the third MXI1 intron, we show that 7 of 11 informative glioblastomas demonstrated MXI1 allelic loss. Sequence analysis revealed no somatic mutations in any of the six MXI1 coding exons, similar to findings in prostate tumors with MXI1 allelic loss. To determine whether MXI1 can indeed function as a suppressor of growth, we have introduced a steroid-inducible MXI1 expression vector into the U87MG cell line, a glioblastoma cell line lacking endogenous MXI1 expression. Induction of MXI1 expression resulted in a decreased growth rate and distinct morphological changes. Furthermore, cell cycle analysis demonstrated that induction of MXI1 results in accumulation of cells in the G2-M phase. Thus, these studies support the notion that MXI1 normally functions to suppress cell growth and suggest that loss of MXI1 function may play a role in human glioblastoma development.

Hemolysis following coil embolization of a patent ductus arteriosus

We describe the development of hemolysis from moderate residual shunting across a patent ductus arteriosus following coil embolization. The fall in hemoglobin levels from 11.6 to 6.0 gm/dl necessitated a second coil procedure which resulted in complete closure of the residual shunting and resolution of hemolysis. Therefore, appearance of anemia following coil embolization of patent ductus arteriosus should be monitored closely; however, repeat coil embolization with elimination of residual shunt will lead to prompt recovery of normal hemoglobin levels.