Cyclin D1 is overexpressed in atypical teratoid/rhabdoid tumor with hSNF5/INI1 gene inactivation

Targeting of cyclin-dependent kinases in atypical teratoid rhabdoid tumors with multikinase inhibitor TG02

OBJECTIVE

Atypical teratoid rhabdoid tumors (ATRTs) are aggressive pediatric brain tumors with no current standard of care and an estimated median patient survival of 12 to 18 months. Previous genetic analyses have implicated cyclin D1 and enhancer of zeste homolog 2 (EZH2), a histone methyltransferase that is implicated in many cancers, as key drivers of tumorigenicity in ATRTs. Since the effects of EZH2 and cyclin D1 are facilitated by a host of cyclin-dependent kinases (CDKs), the authors sought to investigate the potential therapeutic effects of targeting CDKs in ATRTs with the multi-CDK inhibitor, TG02.

METHODS

Human ATRT cell lines BT12, BT37, CHLA05, and CHLA06 were selected for investigation. The effects of TG02 on cell viability, proliferation, clonogenicity, and apoptosis were assessed via Cell Counting Kit-8 assays, cell counting, clonogenic assays, and flow cytometry, respectively. Similar methods were used to determine the effects of TG02 combined with radiation therapy (RT) or cisplatin. Synergism indices for TG02-cisplatin combination therapy were calculated using CompuSyn software.

RESULTS

TG02 was observed to significantly impair ATRT cell growth in vitro by limiting cell proliferation and clonogenicity, and by inducing apoptosis. TG02 inhibited ATRT cell proliferation and decreased cell viability in a dose-dependent manner with nanomolar half maximal effective concentration (EC50) values (BT12, 207.0 nM; BT37, 127.8 nM; CHLA05, 29.7 nM; CHLA06, 18.7 nM). TG02 (150 nM) dramatically increased the proportion of apoptotic ATRT cells 72 hours posttreatment (TG02 8.50% vs control 1.52% apoptotic cells in BT12, p < 0.0001; TG02 70.07% vs control 15.36%, p < 0.0001). Combination therapy studies revealed that TG02 acted as a potent radiosensitizer in ATRT cells (BT12 surviving fraction, RT 51.2% vs RT + TG02 21.7%). Finally, CompuSyn analysis demonstrated that TG02 acted synergistically with cisplatin against ATRT cells at virtually all therapeutic doses. These findings were consistent in cell lines that cover all three molecular subgroups of ATRTs.

CONCLUSIONS

The results of this investigation have established that TG02 is an effective therapeutic against ATRTs in vitro. Given the lack of standard therapy for ATRTs, these findings help fill an unmet need and support further study of TG02 as a potential therapeutic option for patients with this deadly disease.

Atypical Teratoid/Rhabdoid Tumor: Revisiting Histomorphology and Immunohistochemistry With Analysis of Cyclin D1 Overexpression and MYC Amplification

Objectives. Atypical teratoid/rhabdoid tumor (AT/RT) is a rare malignant pediatric brain tumor, characterized by inactivation of INI1/hSNF5 gene and loss of its protein. We studied the histomorphological and immunohistochemical spectrum of this tumor including cyclin D1 expression and MYC gene amplification. Methods. Cases with INI1 loss by immunohistochemistry (IHC; from 2005 to 2018) were retrieved, reviewed, and evaluated for cyclin D1 expression by additional IHC and fluorescence in situ hybridization for MYC genes. Results. A total of 66 cases were identified. Age ranged from 1 to 20 years (≤3 years, 44 cases; >3 years, 22). Male to female ratio was 1.7:1. Tumor locations were as follows: posterior fossa: 30; supratentorial: 31; spinal: 5. AT/RT in patient ≤3 years was frequently located in the posterior fossa, composed of primitive embryonal morphology (P = .02), rarely had ample rhabdoid cells (P = .05), and had a negative impact on overall survival (P = .04). The rhabdoid cells was a conspicuous component of posterior fossa tumors compared with the supratentorial ones (P = .06). The supratentorial tumors (P = .06), absence of rhabdoid cells (P = .06), and the presence of immunological divergent differentiation (P = .11) had a comparatively better outcome. Cyclin D1 overexpression (n = 46) was noted in 32 cases and was frequently seen in the posterior fossa tumors (P = .02). CMYC (n = 42) amplification was seen in 1 case and the NMYC (n = 42) amplification in none. Conclusion. AT/RT can occur in the noninfantile age group, at nonconventional sites and frequently overexpress cyclin D1. The MYC alterations are almost nonexistent in AT/RT.

Characterization of molecular signatures of supratentorial ependymomas

Ependymomas show poor correlation between World Health Organization grade and clinical outcome. A subgroup of supratentorial ependymomas are characterized by C11orf95-RELA fusions, presumed to be secondary to chromothripsis of chromosome 11, resulting in constitutive activation of the NF-κB signaling pathway and overexpression of cyclin D1, p65, and L1 cell adhesion molecule (L1CAM). These RELA-fused ependymomas are recognized as a separate, molecularly defined World Health Organization entity and might be associated with poor clinical outcome. In this study, we show that immunohistochemistry for NF-κB signaling components, such as L1CAM, p65, and cyclin D1, can help distinguish RELA-fused from non-RELA-fused supratentorial ependymomas. Furthermore, these three markers can reliably differentiate RELA-fused ependymomas from a variety of histologic mimics. Lastly, we report that RELA-fused ependymomas may be associated with different chromosomal copy number changes and molecular alterations compared to their non-RELA-fused counterparts, providing additional insight into the genetic pathogenesis of these tumors and potential targets for directed therapies.

Atypical Teratoid Rhabdoid Tumour : From Tumours to Therapies

Atypical teratoid rhabdoid tumours (ATRTs) are the most common malignant central nervous system tumours in children ≤1 year of age and represent approximately 1–2% of all pediatric brain tumours. ATRT is a primarily monogenic disease characterized by the bi-allelic loss of the SMARCB1 gene, which encodes the hSNF5 subunit of the SWI/SNF chromatin remodeling complex. Though conventional dose chemotherapy is not effective in most ATRT patients, high dose chemotherapy with autologous stem cell transplant, radiotherapy and/or intrathecal chemotherapy all show significant potential to improve patient survival. Recent epigenetic and transcriptional studies highlight three subgroups of ATRT, each with distinct clinical and molecular characteristics with corresponding therapeutic sensitivities, including epigenetic targeting, and inhibition of tyrosine kinases or growth/lineage specific pathways.

Overexpression of TEAD4 in atypical teratoid/rhabdoid tumor: New insight to the pathophysiology of an aggressive brain tumor

BACKGROUND

Atypical teratoid/rhabdoid tumor (AT/RT) is a highly malignant embryonal brain tumor that occurs mainly in early childhood. Although most of the tumors are characterized by inactivating mutations of the tumor suppressor gene, SMARCB1, the biological basis of its tumorigenesis and aggressiveness is still unknown.

PROCEDURE

We performed high-throughput copy number variation analysis of primary cell lines generated from primary and relapsed tumors from one of our patients to identify new genes involved in AT/RT biology. The expression of the identified gene was validated in 29 AT/RT samples by gene expression profiling, quantitative real-time polymerase chain reaction, and immunohistochemistry (IHC). Furthermore, we investigated the function of this gene by mutating it in rhabdoid tumor cells.

RESULTS

TEAD4 amplification was detected in the primary cell lines and its overexpression was confirmed at mRNA and protein levels in an independent cohort of AT/RT samples. TEAD4's co-activator, YAP1, and the downstream targets, MYC and CCND1, were also found to be upregulated in AT/RT when compared to medulloblastoma. IHC showed TEAD4 and YAP1 overexpression in all samples. Cell proliferation and migration were significantly reduced in TEAD4-mutated cells.

CONCLUSIONS

We report the overexpression of TEAD4 in AT/RT, which is a key component of Hippo pathway. Recent reports revealed that dysregulation of the Hippo pathway is implicated in tumorigenesis and poor prognosis of several human cancers. Our results suggest that TEAD4 plays a role in the pathophysiology of AT/RT, which represents a new insight into the biology of this aggressive tumor.

The Expression of Cyclin D1, VEGF, EZH2, and H3K27me3 in Atypical Teratoid/Rhabdoid Tumors of the CNS: A Possible Role in Targeted Therapy

Atypical teratoid/rhabdoid tumor (AT/RT) is an uncommon malignancy with a dismal outcome, which responds poorly to multimodality therapies. Animal studies have revealed Cyclin D1 as a possible therapeutic target. The addition of vascular endothelial growth factor (VEGF) inhibitors to chemotherapeutic regimens has shown promising results in pediatric central nervous system tumors. Enhancer of Zeste homolog 2 (EZH2) overexpression has been implicated in various cancers, including medulloblastomas. H3K27me3 is a new marker for pediatric high-grade gliomas. However, their role in AT/RT has not been evaluated sufficiently. We retrieved cases of AT/RT, and reviewed their clinical data and histopathologic features. Immunohistochemistry for Cyclin D1, VEGF, EZH2, and H3K27me3 was performed. Follow-up was noted when available. Fourteen cases of AT/RT were identified (mean age, 3.4 y; range, 10 mo to 8 y). Cyclin D1 immunopositivity was noted in all cases [labeling index (LI): 5% to 98%; mean, 41.3%]. VEGF positivity was seen in 83.3% of the cases. All cases showed EZH2 overexpression (mean LI, 74.3%; range, 32% to 96%). Reduction of H3K27me3 expression was noted in 63% of the cases, with no correlation with EZH2 LI. Two patients died of postoperative complications. Of the rest, follow-up was available for 7 (range, 7 to 120 wk): 1 achieved clinical remission, whereas 6 developed progressive disease, including 3 deaths. Varying degrees of immunoreactivity to Cyclin D1, VEGF, and EZH2 were noted in the majority of the AT/RTs, and detection of these markers may be of value in the development of novel therapeutic agents and in determining which patients can benefit from them. AT/RTs show reduction in H3K27me3 expression, independent of EZH2 expression, indicating that their interaction requires further evaluation.

Biology and Treatment of Rhabdoid Tumor

Rhabdoid tumor is a rare, highly aggressive malignancy that primarily affects infants and young children. These tumors typically arise in the brain and kidney, although extrarenal, non-central nervous system tumors in almost all soft-tissue sites have been described. SMARCB1 is a member of the SWI/SNF chromatin-remodeling complex and functions as a tumor suppressor in the vast majority of rhabdoid tumors. Patients with germline mutations or deletions affecting SMARCB1 are predisposed to the development of rhabdoid tumors, as well as the genetic disorder schwannomatosis. The current hypothesis is that rhabdoid tumors are driven by epigenetic dysregulation, as opposed to the alteration of a specific biologic pathway. The strategies for novel therapeutic approaches based on what is currently known about rhabdoid tumor biology are presented.

Atypical teratoid/rhabdoid tumors-current concepts, advances in biology, and potential future therapies

Atypical teratoid/rhabdoid tumor (AT/RT) is the most common malignant CNS tumor of children below 6 months of age. The majority of AT/RTs demonstrate genomic alterations in SMARCB1 (INI1, SNF5, BAF47) or, to a lesser extent, SMARCA4 (BRG1) of the SWItch/sucrose nonfermentable chromatin remodeling complex. Recent transcription and methylation profiling studies suggest the existence of molecular subgroups. Thus, at the root of these seemingly enigmatic tumors lies a network of factors related to epigenetic regulation, which is not yet completely understood. While conventional-type chemotherapy may have significant survival benefit for certain patients, it remains to be determined which patients will eventually prove resistant to chemotherapy and thus need novel therapeutic strategies. Elucidation of the molecular consequences of a disturbed epigenome has led to the identification of a series of transduction cascades, which may be targeted for therapy. Among these are the pathways of cyclin D1/cyclin-dependent kinases 4 and 6, Hedgehog/GLI1, Wnt/ß-catenin, enhancer of zeste homolog 2, and aurora kinase A, among others. Compounds specifically targeting these pathways or agents that alter the epigenetic state of the cell are currently being evaluated in preclinical settings and in experimental clinical trials for AT/RT.

Current standards of care and future directions for "high-risk" pediatric renal tumors: Anaplastic Wilms tumor and Rhabdoid tumor

'High risk' renal tumors of childhood generally includes anaplastic Wilms tumor, rhabdoid tumor, and metastatic renal sarcomas and carcinomas. In this review, the epidemiology, biology, treatment and prognosis of anaplastic Wilms tumor and rhabdoid tumor are presented. Future directions related to management of such cancers are discussed, with insights provided into possible clinical trials in development that consider integration of novel targeted therapies.

Atypical teratoid/ rhabdoid tumor, an immunohistochemical study of potential diagnostic and prognostic markers

Atypical teratoid/rhabdoid tumor (AT/RT) is a rare tumor of the CNS mostly seen in infants and is often associated with a dismal outcome. Despite the heterogeneous morphology and/or immunoprofile, its diagnosis nowadays relies on the negative INI-1/BAF47 nuclear immunostain in tumor cells. We aim to investigate a number of immunohistochemical antibodies as potential diagnostic and prognostic markers. All AT/RT cases in patients younger than 18 years of age were included. Demographics, clinical features and outcome were collected. Immunostains tested included SALL-4, OCT3/4, CD99, FLI-1, cyclin-D1, β-catenin, P53, P16, CDX2 and WT-1. Nineteen cases (10 males) were identified at our center between 2004-2013 with a median age of 24 months. Ten (52.6%) cases were supratentorial. Six (42.9%) cases showed metastasis at time of presentation. Chemotherapy was administered to 10 (62.5%) and radiotherapy to seven (43.8%). The median overall survival was 11 months. A single long-term survival of 104 months was identified. Pathologically, most cases showed an admixture of rhabdoid cells and/or small cells and/or pale cells in variable proportions. Of all tested antibodies, only positivity for FLI-1 was associated with improved survival (P = 0.0012), while positivity for cyclin-D1 showed a trend toward improved survival (P = 0.0547). CDX2 was positive only in the single long-term survival. Interestingly, two cases showed co-expression of CD99 and FLI-1, and some were positive for SALL-4. In conclusion, FLI-1 and cyclin-D1 are potential prognostic markers associated with better outcome. Occasional AT/RT cases might co-express CD99 and FLI-1 as well as SALL-4, a potential diagnostic pitfall with Ewing sarcoma/ primitive neuroectodermal tumors and germ cell tumors, respectively.

Rhabdoid tumors: clinical approaches and molecular targets for innovative therapy

Rhabdoid tumors are rare but highly aggressive tumors with a predilection for infants and young children. The majority of these tumors harbor biallelic mutations in SMARCB1/INI1/hSNF5. Rather rare cases with mutations in other SWI/SNF core members such as BRG1 are on record. Rhabdoid tumors have only recently been registered and treated according to specifically designed treatment recommendations and in the framework of clinical trials. Within the last decade, prognosis has improved significantly but at least 50% of patients still relapse and subsequently almost inevitably succumb to their disease. This review summarizes past and current clinical approaches and presents an overview of the rationales for targeted therapy with potential for future clinical treatment trials for rhabdoid tumors.

Profiling pathway-specific novel therapeutics in preclinical assessment for central nervous system atypical teratoid rhabdoid tumors (CNS ATRT): favorable activity of targeting EGFR- ErbB2 signaling with lapatinib

Despite intensifying multimodal treatments, children with central nervous system atypical teratoid/rhabdoid tumor (CNS ATRT) continue to endure unacceptably high mortality rates. At present, concerted efforts are focusing on understanding the characteristic INI1 mutation and its implications for the growth and survival of these tumors. Additionally, pharmaceutical pipeline libraries constitute a significant source of potential agents that can be taken to clinical trials in a timely manner. However, this process requires efficient target validation and relevant preclinical studies. As an initial screening approach, a panel of 129 small molecule inhibitors from multiple pharmaceutical pipeline libraries was tested against three ATRT cell lines by in vitro cytotoxicity assays. Based on these data, agents that have strong activity and corresponding susceptible cellular pathways were identified. Target modulation, antibody array analysis, drug combination and in vivo xenograft studies were performed on one of the pathway inhibitors found in this screening. Approximately 20% of agents in the library showed activity with IC(50) values of 1 μM or less and many showed IC(50) values less than 0.05 μM. Intra cell line variability was also noted among some of the drugs. However, it was determined that agents capable of affecting pathways constituting ErbB2, mTOR, proteasomes, Hsp90, Polo like kinases and Aurora kinases were universally effective against the three ATRT cell lines. The first target selected for further analysis, the inhibition of ErbB2-EGFR pathway by the small molecule inhibitor lapatinib, indicated inhibition of cell migration properties and the initiation of apoptosis. Synergy between lapatinib and IGF-IR inhibition was also demonstrated by combination index (CI) values. Xenograft studies showed effective antitumor activity of lapatinib in vivo. We present an experimental approach to identifying agents and drug combinations for future clinical trials and provide evidence for the potential of lapatinib as an effective agent in the context of the biology and heterogeneity of its targets in ATRT.

Inhibition of EZH2 suppresses self-renewal and induces radiation sensitivity in atypical rhabdoid teratoid tumor cells

INTRODUCTION

Overexpression of the Polycomb repressive complex 2 (PRC2) subunit Enhancer of Zeste 2 (EZH2) occurs in several malignancies, including prostate cancer, breast cancer, medulloblastoma, and glioblastoma multiforme. Recent evidence suggests that EZH2 may also have a role in rhabdoid tumors. Atypical teratoid/rhabdoid tumor (ATRT) is a rare, high-grade embryonal brain tumor that occurs most commonly in young children and carries a very poor prognosis. ATRTs are characterized by absence of the chromatin remodeling protein SMARCB1. Given the role of EZH2 in regulating epigenetic changes, we investigated the role of EZH2 in ATRT.

METHODS

Microarray analysis was used to evaluate expression of EZH2 in ATRT tumor samples. We used shRNA and a chemical inhibitor of EZH2 to examine the impact of EZH2 inhibition on cell growth, proliferation, and tumor cell self-renewal.

RESULTS

Here, we show that targeted disruption of EZH2 by RNAi or pharmacologic inhibition strongly impairs ATRT cell growth, suppresses tumor cell self-renewal, induces apoptosis, and potently sensitizes these cells to radiation. Using functional analysis of transcription factor activity, we found the cyclin D1-E2F axis to be repressed after EZH2 depletion in ATRT cells.

CONCLUSIONS

Our observations provide evidence that EZH2 disruption alters cell cycle progression and may be an important new therapeutic target, particularly in combination with radiation, in ATRT.

Targeting Aurora Kinase A enhances radiation sensitivity of atypical teratoid rhabdoid tumor cells

Atypical teratoid/rhabdoid tumors (ATRT) are rare, highly malignant, embryonal CNS tumors with a poor prognosis. Therapy relies on highly toxic chemotherapy and radiotherapy. To improve outcomes and decrease morbidity, more targeted therapy is required. Gene expression analysis revealed elevated expression of multiple kinases in ATRT tissues. Aurora Kinase A was one of the candidate kinases. The objective of this study was to evaluate the impact of Aurora Kinase A inhibition in ATRT cell lines. Our analysis revealed that inhibition of Aurora Kinase A induces cell death in ATRT cells and the small molecule inhibitor MLN 8237 sensitizes these cells to radiation. Furthermore, inhibition of Aurora Kinase A resulted in decreased activity of pro-proliferative signaling pathways. These data indicate that inhibition of Aurora Kinase A is a promising small molecule target for ATRT therapy.

Neurofibromatoses

The studies of familial tumor predisposition syndromes have contributed immensely to our understanding of oncogenesis. Neurofibromatosis 1, neurofibromatosis 2 and schwannomatosis are inherited autosomal dominant neurocutaneous disorders with complete penetrance. They are clinically and genetically distinct and considerable knowledge has been gathered about their pathogenesis. In this chapter, the genetics, molecular mechanism of disease, as well as clinical features, diagnosis and treatment are discussed.

Histone deacetylase inhibition decreases proliferation and potentiates the effect of ionizing radiation in atypical teratoid/rhabdoid tumor cells

Atypical teratoid/rhabdoid tumor (ATRT) is a highly malignant central nervous system neoplasm that primarily occurs in children less than 3 years of age. Because of poor outcomes with intense and toxic multimodality treatment, new therapies are urgently needed. Histone deacetylase inhibitors (HDIs) have been evaluated as novel agents for multiple malignancies and have been shown to function as radiosensitizers. They act as epigenetic modifiers and lead to re-expression of inappropriately repressed genes, proteins, and cellular functions. Because of the underlying chromatin remodeling gene mutation in ATRT, HDIs are ideal candidates for therapeutic evaluation. To evaluate the role of HDIs against ATRT in vitro, we assessed the effect of drug treatment on proliferation, apoptosis, and gene expression. In addition, we examined HDI pretreatment as a radiosensitization strategy for ATRT. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium with phenazine methosulfate electron coupling reagent (MTS) and clonogenic assays demonstrated that HDI treatment significantly reduces the proliferative capacity of BT-12 and BT-16 ATRT cells. In addition, the HDI SNDX-275 was able to induce apoptosis in both cell lines and induced p21(Waf1/Cip1) protein expression as measured by Western blot. Evaluation of differential gene expression by microarray and pathway analysis after HDI treatment demonstrated alterations of several key ATRT cellular functions. Finally, we showed that HDI pretreatment effectively potentiates the effect of ionizing radiation on ATRT cells as measured by clonogenic assay. Our findings suggest that the addition of HDIs to ATRT therapy may prove to be beneficial, especially when administered in combination with current treatment modalities, such as radiation.

p16INK4A and p14ARF tumor suppressor pathways are deregulated in malignant rhabdoid tumors

Malignant rhabdoid tumors (MRTs) are aggressive tumors associated with mutations in the SMARCB1 gene. In experimental systems, the loss of SMARCB1 is hypothesized to alter p16(INK4A) pathways resulting in the repression of tumor suppressors. To determine whether these pathways are deregulated in human MRT, we used immunohistochemistry on tissue microarrays to evaluate p16(INK4A)/E2F1/RB and p14(ARF)/MDM2/p53 pathways in 25 atypical teratoid/rhabdoid tumors (AT/RT) and 11 non-CNS MRT. p16(INK4A) was negative or showed focal weak expression. p16(INK4A) downstream targets CDK4/cyclin D1/ppRB were variably expressed at moderate to low levels; E2F1 was negative. Unexpectedly, p14(ARF) expression was seen in many cases, which correlated positively with p53 and inversely with MDM2 immunostaining in AT/RT. TP53 mutational analysis in 19 of 25 AT/RT and in 8 of 11 non-CNS MRT cases showed point mutations in only 3 AT/RT cases, suggesting that p53 expression was driven mainly by p14(ARF). Finally, nucleophosmin, a protein that stabilizes p53, was positive in most cases and colocalized with p53. Together, these data suggest that, in MRT, there is deregulation not only of p16(INK4A) but also of the p14(ARF) pathway. These results provide insights into cell cycle deregulation in the pathogenesis of human MRT and may aid in the design and evaluation of potential therapies for these tumors.

Therapeutically targeting cyclin D1 in primary tumors arising from loss of Ini1

Rhabdoid tumors (RTs) are rare, highly aggressive pediatric malignancies with poor prognosis and with no standard or effective treatment strategies. RTs are characterized by biallelic inactivation of the INI1 tumor suppressor gene. INI1 directly represses CCND1 and activates cyclin-dependent kinase (cdk) inhibitors p16(Ink4a) and p21(CIP). RTs are exquisitely dependent on cyclin D1 for genesis and survival. To facilitate translation of unique therapeutic strategies, we have used genetically engineered, Ini1(+/-) mice for therapeutic testing. We found that PET can be used to noninvasively and accurately detect primary tumors in Ini1(+/-) mice. In a PET-guided longitudinal study, we found that treating Ini1(+/-) mice bearing primary tumors with the pan-cdk inhibitor flavopiridol resulted in complete and stable regression of some tumors. Other tumors showed resistance to flavopiridol, and one of the resistant tumors overexpressed cyclin D1, more than flavopiridol-sensitive cells. The concentration of flavopiridol used was not sufficient to down-modulate the high level of cyclin D1 and failed to induce cell death in the resistant cells. Furthermore, FISH and PCR analyses indicated that there is aneuploidy and increased CCND1 copy number in resistant cells. These studies indicate that resistance to flavopiridol may be correlated to elevated cyclin D1 levels. Our studies also indicate that Ini1(+/-) mice are valuable tools for testing unique therapeutic strategies and for understanding mechanisms of drug resistance in tumors that arise owing to loss of Ini1, which is essential for developing effective treatment strategies against these aggressive tumors.

Developmental genes and cancer in children

Childhood tumours are associated with congenital abnormalities suggesting that disruption of normal developmental processes may be linked with oncogenesis. Genetic and environmental exposures may combine to disrupt critical epigenetic processes during development, thus affecting gene-related signalling pathways and cellular function. This review examines the role of critical genes and processes regulating development such as the polycomb family and sonic hedgehog (SHH) as well as the Wnt signalling pathways and epigenetic variations (Snf5), methylation and loss of heterozygosity in controlling homeotic gene transcription and intracellular chromatin structure. The developmental and perinatal periods appears important as a window of opportunity for cancer research.

Loss of the epigenetic tumor suppressor SNF5 leads to cancer without genomic instability

There is a growing appreciation of the role that epigenetic alterations can play in oncogenesis. However, given the large number of genetic anomalies present in most cancers, it has been difficult to evaluate the extent to which epigenetic changes contribute to cancer. SNF5 (INI1/SMARCB1/BAF47) is a tumor suppressor that regulates the epigenome as a core member of the SWI/SNF chromatin remodeling complex. While the SWI/SNF complex displays potent tumor suppressor activity, it is unknown whether this activity is exerted genetically via maintenance of genome integrity or epigenetically via transcriptional regulation. Here we show that Snf5-deficient primary cells do not show altered sensitivity to DNA damaging agents, defects in gamma-H2AX induction, or an abrogated DNA damage checkpoint. Further, the aggressive malignancies that arise following SNF5 loss are diploid and genomically stable. Remarkably, we demonstrate that most human SNF5-deficient cancers lack genomic amplifications/deletions and, aside from SNF5 loss, are indistinguishable from normal cells on single-nucleotide polymorphism arrays. Finally, we show that epigenetically based changes in transcription that occur following SNF5 loss correlate with the tumor phenotype. Collectively, our results provide novel insight into the mechanisms of oncogenesis by demonstrating that disruption of a chromatin remodeling complex can largely, if not completely, substitute for genomic instability in the genesis of aggressive cancer.

Alterations in the SMARCB1 (INI1) tumor suppressor gene in familial schwannomatosis

Schwannomatosis is a third major form of neurofibromatosis that has recently been linked to mutations in the SMARCB1 (hSnf5/INI1) tumor suppressor gene. We analyzed the coding region of SMARCB1 by direct sequencing and multiplex ligation-dependent probe amplification (MLPA) in genomic DNA from 19 schwannomatosis kindreds. Microsatellite markers in the SMARCB1 region were developed to determine loss of heterozygosity (LOH) in associated tumors. We detected four alterations in conserved splice acceptor or donor sequences of exons 3, 4 and 6. Two alterations that likely affect splicing were seen in introns 4 and 5. An additional four alterations of unclear pathogenicity were found to segregate on the affected allele in eight families including two non-conservative missense alterations in three families. No constitutional deletions or duplications were detected by MLPA. Nine of 13 tumors examined showed partial LOH of the SMARCB1 region consistent with 'second hits.' Alterations were detected in tumors both with and without somatic NF2 gene changes. These findings support the hypothesis that SMARCB1 is a tumor suppressor for schwannomas in the context of familial disease. Further work is needed to determine its role in other multiple and single tumor syndromes.

Rhabdoid choroid plexus carcinoma: a rare histological type

Primary central nervous system atypical teratoid/rhabdoid tumors mostly occur during early childhood and are almost invariably fatal. These tumors show similar histological and radiological features to primitive neuroectodermal tumor, meduloblastoma and choroid plexus carcinoma, but present different biological behaviors. We present the case of an 18 year-old man who presented headache, vomiting and ataxia. CT-scan and MRI revealed a posterior fossa tumor. A gross total resection was performed. An intraoperative study showed papillary-like tumors with large cells and mitotic features. Histological examination showed two different main growth patterns: solid sheets of undifferentiated polygonal cells with papillary features and rhabdoid cells. Immunohistochemically, these rhabdoid cells were positive for vimentin, epithelial membrane antigen, smooth-muscle actin, cytokeratin, S-100 protein, and glial fibrillary acidic protein. Electro-microscopically, the typical rhabdoid cells contained whorled bundles of intermediate filaments in their cytoplasm. A rhabdoid tumor is a clinicalpathological entity and emphasizes the necessity to distinguish this unique tumor from other pediatric central nervous system neoplasms. Cytopathological features, immunohistochemistry and electro-microscopy differential diagnoses are discussed.

Mutation of the INI1 gene in composite rhabdoid tumor of the endometrium

Composite rhabdoid tumors are typically adult tumors that contain a component of rhabdoid cells, which are characteristic of the aggressive childhood malignant rhabdoid tumor. Pediatric rhabdoid tumors are characterized by the inactivation of the hSNF5/INI1/SMARCB1 gene, with subsequent loss of expression of the protein. In contrast, only a single composite rhabdoid tumor has demonstrated involvement of the INI1 gene. In our study, INI1 protein expression was studied in 2 uterine carcinosarcomas with rhabdoid components (composite rhabdoid tumors). The rhabdoid component of 1 tumor showed lack of immunoreactivity for the INI1 protein and strong positivity for cyclin D1, whereas the adenocarcinomatous component of the tumor and both components of the second tumor were immunoreactive for the INI1 protein and negative for cyclin D1. Loss of one INI1 allele and a mutation in exon 7 of the remaining allele were detected in the first tumor, consistent with the immunohistochemistry results. Our results demonstrate that deletions and mutations of the INI1 gene can occur also in rare composite rhabdoid tumors of adulthood. Further studies are necessary, however, to determine the prognostic significance of this finding.