[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma (RMS) represents a rare, heterogeneous group of mesodermal malignancies
with skeletal muscle differentiation. One major subgroup of RMS tumors (so-called
“fusion-positive” tumors) carries exclusive chromosomal translocations that join the DNAbinding
domain of the PAX3 or PAX7 gene to the transactivation domain of the FOXO1
(previously known as FKHR) gene. Fusion-negative RMS represents a heterogeneous spectrum
of tumors with frequent RAS pathway activation. Overtly metastatic disease at diagnosis
is more frequently found in individuals with fusion-positive than in those with fusion-negative
tumors. RMS is the most common pediatric soft-tissue sarcoma, and approximately
60% of all children and adolescents diagnosed with RMS are cured by currently available
multimodal therapies. However, a curative outcome is achieved in ,30% of high-risk individuals
with RMS, including all those diagnosed as adults, those diagnosed with fusionpositive
tumors during childhood (including metastatic and nonmetastatic tumors), and
those diagnosed with metastatic disease during childhood (including fusion-positive
and fusion-negative tumors). This white paper outlines current challenges in RMS research
and their implications for developing more effective therapies. Urgent clinical problems
include local control, systemic disease, need for improved risk stratification, and characterization
of differences in disease course in children and adults. Biological challenges include
definition of the cellular functions of PAX-FOXO1 fusion proteins, clarification of disease
heterogeneity, elucidation of the cellular origins of RMS, delineation of the tumor microenvironment,
and identification of means for rational selection and testing of new combination
therapies. To streamline future therapeutic developments, it will be critical to improve access
to fresh tumor tissue for research purposes, consider alternative trial designs to optimize early
clinical testing of candidate drugs, coalesce advocacy efforts to garner public and industry
support, and facilitate collaborative efforts between academia and industry.
Cold Spring Harbor Perspectives in Medicine 11/2014; · 7.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Asparaginase is a chemotherapeutic agent used to induce disease remission in children with acute lymphoblastic leukemia (ALL). We describe the cases of two females with ALL who developed pseudohyponatremia as a presentation of hypertriglyceridemia following asparaginase treatment. Nine similar published cases of asparaginase-induced hypertriglyceridemia and its complications are also discussed. Possible mechanisms of action include inhibition of lipoprotein lipase, decreased hepatic synthesis of lipoprotein, and increased synthesis of VLDL. Effects of asparaginase-induced hypertriglyceridemia range from asymptomatic to transaminasemia, pancreatitis, and life-threatening thrombosis or hyperviscosity syndrome. All cases of hypertriglyceridemia described resolved following cessation of asparaginase treatment ± further treatments.
[Show abstract][Hide abstract] ABSTRACT: Alveolar rhabdomyosarcoma (aRMS) is an aggressive sarcoma of skeletal muscle characterized by expression of the paired box 3-forkhead box protein O1 (PAX3-FOXO1) fusion oncogene. Despite its discovery nearly two decades ago, the mechanisms by which PAX3-FOXO1 drives tumor development are not well characterized. Previously, we reported that PAX3-FOXO1 supports aRMS initiation by enabling bypass of cellular senescence checkpoints. We have now found that this bypass occurs in part through PAX3-FOXO1-mediated upregulation of RASSF4, a Ras-association domain family (RASSF) member. RASSF4 expression was upregulated in PAX3-FOXO1-positive aRMS cell lines and tumors. Enhanced RASSF4 expression promoted cell cycle progression, senescence evasion, and tumorigenesis through inhibition of the Hippo pathway tumor suppressor MST1. We also found that the downstream Hippo pathway target Yes-associated protein 1 (YAP), which is ordinarily restrained by Hippo signaling, was upregulated in RMS tumors. These data suggest that Hippo pathway dysfunction promotes RMS. This work provides evidence for Hippo pathway suppression in aRMS and demonstrates a progrowth role for RASSF4. Additionally, we identify a mechanism used by PAX3-FOXO1 to inhibit MST1 signaling and promote tumorigenesis in aRMS.
The Journal of clinical investigation 12/2013; · 15.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The 5-year survival for localized rhabdomyosarcoma is over 70%, but only 30% for patients presenting with metastatic disease. In this issue of Cancer Cell, Chen and colleagues performed whole-genome and RNA sequencing on human rhabdomyosarcoma and identified RAS mutations and oxidative stress as potential therapeutic targets for high-risk embryonal rhabdomyosarcoma.
Cancer cell 12/2013; 24(6):689-691. · 25.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, whereas undifferentiated pleomorphic sarcoma (UPS) is one of the most common soft tissue sarcomas diagnosed in adults. To investigate the myogenic cell(s) of origin of these sarcomas, we used Pax7-CreER and MyoD-CreER mice to transform Pax7(+) and MyoD(+) myogenic progenitors by expressing oncogenic Kras(G12D) and deleting Trp53 in vivo. Pax7-CreER mice developed RMS and UPS, whereas MyoD-CreER mice developed UPS. Using gene set enrichment analysis, RMS and UPS each clustered specifically within their human counterparts. These results suggest that RMS and UPS have distinct and overlapping cells of origin within the muscle lineage. Taking them together, we have established mouse models of soft tissue sarcoma from muscle stem and progenitor cells.
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. Despite intergroup clinical trials conducted in Europe and North America, outcomes for high risk patients with this disease have not significantly improved in the last several decades, and survival of metastatic or relapsed disease remains extremely poor. Accrual into new clinical trials is slow and difficult, so in vitro cell-line research and in vivo xenograft models present an attractive alternative for preclinical research for this cancer type. Currently, 30 commonly used human RMS cell lines exist, with differing origins, karyotypes, histologies, and methods of validation. Selecting an appropriate cell line for RMS research has important implications for outcomes. There are also potential pitfalls in using certain cell lines including contamination with murine stromal cells, cross-contamination between cell lines, discordance between the cell line and its associated original tumor, imposter cell lines, and nomenclature errors that result in the circulation of two or more presumed unique cell lines that are actually from the same origin. These pitfalls can be avoided by testing for species-specific isoenzymes, microarray analysis, assays for subtype-specific fusion products, and short tandem repeat analysis.
[Show abstract][Hide abstract] ABSTRACT: Specificity protein (Sp) transcription factors Sp1, Sp3 and Sp4 are highly expressed in rhabdomyosarcoma (RMS) cells. In tissue arrays of RMS tumor cores from 71 patients, 80% of RMS patients expressed high levels of Sp1 protein, whereas low expression of Sp1 was detected in normal muscle tissue. The non-steroidal anti-inflammatory drug (NSAID) tolfenamic acid (TA) inhibited growth and migration of RD and RH30 RMS cell lines and also inhibited tumor growth in vivo using a mouse xenograft (RH30 cells) model. The effects of TA were accompanied by downregulation of Sp1, Sp3, Sp4 and Sp-regulated genes in RMS cells and tumors, and the role of Sp protein downregulation in mediating inhibition of RD and RH30 cell growth and migration was confirmed by individual and combined knockdown of Sp1, Sp3 and Sp4 proteins by RNA interference. TA treatment and Sp knockdown in RD and RH30 cells also showed that four genes that are emerging as individual drug targets for treating RMS, namely c-MET, insulin-like growth factor receptor (IGFR), PDGFRα and CXCR4, are also Sp-regulated genes. These results suggest that NSAIDs such as TA may have potential clinical efficacy in drug combinations for treating RMS patients.
International Journal of Cancer 07/2012; · 6.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma (RMS) is a malignancy with features of skeletal muscle, and the most common soft tissue sarcoma of childhood. Survival for high-risk groups is approximately 30% at 5 years and there are no durable therapies tailored to its genetic aberrations. During genetic modeling of the common RMS variants, embryonal RMS (eRMS) and alveolar RMS (aRMS), we noted that the receptor tyrosine kinase (RTK) fibroblast growth factor receptor 4 (FGFR4) was upregulated as an early event in aRMS. Herein, we evaluated the expression of FGFR4 in eRMS compared with aRMS, and whether FGFR4 had similar or distinct roles in their tumorigenesis.
Human RMS cell lines and tumor tissue were analyzed for FGFR4 expression by immunoblot and immunohistochemistry. Genetic and pharmacologic loss-of-function of FGFR4 using virally transduced short hairpin RNA (shRNA) and the FGFR small-molecule inhibitor PD173074, respectively, were used to study the role of FGFR4 in RMS cell lines in vitro and xenografts in vivo. Expression of the antiapoptotic protein BCL2L1 was also examined.
FGFR4 is expressed in both RMS subtypes, but protein expression is higher in aRMS. The signature aRMS gene fusion product, PAX3-FOXO1, induced FGFR4 expression in primary human myoblasts. In eRMS, FGFR4 loss-of-function reduced cell proliferation in vitro and xenograft formation in vivo. In aRMS, it diminished cell survival in vitro. In myoblasts and aRMS, FGFR4 was necessary and sufficient for expression of BCL2L1 whereas in eRMS, this induction was not observed, suggesting differential FGFR4 signaling.
These studies define dichotomous roles for FGFR4 in RMS subtypes, and support further study of FGFR4 as a therapeutic target.
Clinical Cancer Research 05/2012; 18(14):3780-90. · 7.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Embryonal rhabdomyosarcoma (ERMS) is an aggressive pediatric sarcoma of muscle. Here, we show that ERMS-propagating potential is confined to myf5+ cells and can be visualized in live, fluorescent transgenic zebrafish. During early tumor growth, myf5+ ERMS cells reside adjacent normal muscle fibers. By late-stage ERMS, myf5+ cells are reorganized into distinct regions separated from differentiated tumor cells. Time-lapse imaging of late-stage ERMS revealed that myf5+ cells populate newly formed tumor only after seeding by highly migratory myogenin+ ERMS cells. Moreover, myogenin+ ERMS cells can enter the vasculature, whereas myf5+ ERMS-propagating cells do not. Our data suggest that non-tumor-propagating cells likely have important supportive roles in cancer progression and facilitate metastasis.
Cancer cell 05/2012; 21(5):680-93. · 25.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and adolescence, accounting for approximately 7% of childhood cancers. Current therapies include nonspecific cytotoxic chemotherapy regimens, radiation therapy, and surgery; however, these multimodality strategies are unsuccessful in the majority of patients with high-risk disease. It is generally believed that these tumors represent arrested or aberrant skeletal muscle development, and, accordingly, developmental signaling pathways critical to myogenesis such as Notch, WNT, and Hedgehog may represent new therapeutic targets. In this paper, we summarize the current preclinical studies linking these embryonic pathways to rhabdomyosarcoma tumorigenesis and provide support for the investigation of targeted therapies in this embryonic cancer.
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and remains refractory to combined-modality therapy in patients with high risk disease. In skeletal myogenesis, Notch signaling prevents muscle differentiation and promotes proliferation of satellite cell progeny. Given its physiologic role in myogenesis and oncogenic role in other human cancers, we hypothesized that aberrant Notch signaling may contribute to RMS tumorigenesis and present novel therapeutic opportunities.
Human RMS cell lines and tumors were evaluated by immunoblot, IHC, and RT-PCR to measure Notch ligand, receptor, and target gene expression. Manipulation of Notch signaling was accomplished using genetic and pharmacologic approaches. In vitro cell growth, proliferation, and differentiation were assessed using colorimetric MTT and BrdU assays, and biochemical/morphologic changes after incubation in differentiation-promoting media, respectively. In vivo tumorigenesis was assessed using xenograft formation in SCID/beige mice.
Notch signaling is upregulated in human RMS cell lines and tumors compared with primary skeletal muscle, especially in the embryonal (eRMS) subtype. Inhibition of Notch signaling using Notch1 RNAi or γ-secretase inhibitors reduced eRMS cell proliferation in vitro. Hey1 RNAi phenocopied Notch1 loss and permitted modest myogenic differentiation, while overexpression of an activated Notch moiety, ICN1, promoted eRMS cell proliferation and rescued pharmacologic inhibition. Finally, Notch inhibition using RNAi or γ-secretase inhibitors blocked tumorigenesis in vivo.
Aberrant Notch-Hey1 signaling contributes to eRMS by impeding differentiation and promoting proliferation. The efficacy of Notch pathway inhibition in vivo supports the development of Notch-Hey1 axis inhibitors in the treatment of eRMS.
Clinical Cancer Research 09/2011; 17(23):7324-36. · 7.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcomas (RMSs) are the most common soft tissue sarcomas of childhood and adolescence. To date, there are no effective treatments that target the genetic abnormalities in RMS, and current treatment options for high-risk groups are not adequate. Over the past two decades, research into the molecular mechanisms of RMS has identified key genes and signaling pathways involved in disease pathogenesis. In these studies, members of the receptor tyrosine kinase (RTK) family of cell surface receptors have been characterized as druggable targets for RMS. Through small molecule inhibitors, ligand-neutralizing agents, and monoclonal receptor-blocking antibodies, RTK activity can be manipulated to block oncogenic properties associated with RMS. Herein, we review the members of the RTK family that are implicated in RMS tumorigenesis and discuss both the problems and promise of targeting RTKs in RMS.
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. Despite advances in therapy, patients with a histologic variant of RMS known as alveolar (aRMS) have a 5-year survival rate of <30%. aRMS tissues exhibit a number of genetic changes, including loss-of-function of the p53 and Rb tumor suppressor pathways, amplification of MYCN, stabilization of telomeres, and most characteristically, reciprocal translocation of loci involving the PAX and FKHR genes, generating the PAX7-FKHR or PAX3-FKHR fusion proteins. We previously showed that PAX3-FKHR expression in primary human myoblasts, cells that can give rise to RMS, cooperated with loss of p16INK4A to promote extended proliferation. To better understand the genetic events required for aRMS formation, we then stepwise converted these cells to their transformed counterpart. PAX3-FKHR, the catalytic unit of telomerase hTERT, and MycN, in cooperation with down-regulation of p16INK4A/p14ARF expression, were necessary and sufficient to convert normal human myoblasts into tumorigenic cells that gave rise to aRMS tumors. However, the order of expression of these transgenes was critical, as only those cells expressing PAX3-FKHR early could form tumors. We therefore suggest that the translocation of PAX3 to FKHR drives proliferation of myoblasts, and a selection for loss of p16INK4A/p14ARF. These early steps, coupled with MycN amplification and telomere stabilization, then drive the cells to a fully tumorigenic state.
Cancer Research 01/2009; 68(23):9583-8. · 9.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. The predominant histologic variants of this disease are termed embryonal (eRMS) and alveolar (aRMS), based on their appearance under light microscopy. Of the two, aRMS is associated with an more aggressive disease pattern and a higher mortality, mandating a better understanding of this cancer at the molecular level. The PAX3-FOXO1 fusion gene, resulting from the stable reciprocal translocation of chromosomes 2 and 13, is a signature genetic change found only in aRMS, and thought to be responsible at least in part for its malignant phenotype. This review will discuss the clinical significance of the PAX3-FOXO1 fusion gene, the pertinent historical and current models used to study its oncogenic contributions, the transcriptional targets that are thought to mediate these contributions, and the cellular mechanisms impacted by PAX3-FOXO1 that ultimately lead to aRMS.
Cancer letters 06/2008; 270(1):10-8. · 5.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and adolescence. Historically, rhabdomyosarcoma has been studied by the manipulation of human cell lines derived from primary rhabdomyosarcoma tumor tissue adapted to grow in culture. Recently, mouse models have been added to the arsenal of tools to study this disease in vivo. However, given the emerging understanding of the genetic variability and mutability of human tumor-derived cell lines, and the existing differences between human and murine tumorigenesis, we sought to uniformly dissect the genetic events required to generate rhabdomyosarcoma from primary human skeletal muscle precursors. To this end, primary human skeletal muscle cells were transformed with defined genetic elements to corrupt the p53, Rb, Myc, telomerase, and Ras pathways, resulting in cells that, when assayed as subcutaneous xenografts in immunocompromised mice, formed tumors indistinguishable at the immunohistochemical level from the embryonal histologic variant of rhabdomyosarcoma. This chapter will discuss the techniques used to transform primary human skeletal muscle cells, the assays used to verify expression of the ectopically expressed genetic elements, and the methods used to evaluate the tumorigenic capacity of the resulting cell lines.
Methods in Enzymology 02/2008; 438:419-27. · 2.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and adolescence. Despite advances in therapy, patients with a histologic variant of rhabdomyosarcoma known as alveolar rhabdomyosarcoma (ARMS) have a 5-year survival of <30%. ARMS is characterized by a chromosomal translocation generating the PAX3-FKHR fusion gene. However, ectopic expression of PAX3-FKHR often induces inhibition of cell proliferation, or cell death, when expressed in nonmuscle cells. This prompted us to explore the effect of expressing PAX3-FKHR in more relevant cells, specifically primary human skeletal muscle cells because these cells can be converted to a tumorigenic state that mimics rhabdomyosarcoma. PAX3-FKHR expression promoted both fetal and postnatal primary human skeletal muscle cell precursors to bypass the senescence growth arrest checkpoint. This bypass was accompanied by epigenetic DNA methylation of the p16(INK4A) promoter and correspondingly a loss of expression of this tumor suppressor. Knockdown of p16(INK4A) cooperated with PAX3-FKHR to drive proliferation past senescence, whereas reintroduction of wild-type p16(INK4A) in post-senescent cells caused growth arrest. Thus, PAX3-FKHR acts in concert with loss of p16(INK4A) to promote inappropriate proliferation of skeletal muscle cells. This association between PAX3-FKHR expression and p16(INK4A) loss was seen in human ARMS tumor tissue, as both human rhabdomyosarcoma cell lines and tissue microarrays showed a trend toward down-regulation of p16(INK4A) protein in alveolar subsets. We surmise that the generation of the PAX3-FKHR fusion protein may require loss of p16(INK4A) to promote malignant proliferation of skeletal muscle cells as an early step in ARMS tumorigenesis.
Cancer Research 08/2007; 67(14):6691-9. · 8.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although great progress has been made at identifying and characterizing individual genes involved in cancer, less is known about how the combination of such genes collaborate to form tumors in humans. To this end, we sought to genetically recreate tumorigenesis in normal human cells using genes altered in human cancer. We now show that expression of mammalian proteins that inactivate the tumor suppressors Rb and p53 in conjunction with the oncoproteins Ras and Myc and the telomerase subunit hTERT is sufficient to drive a number of normal human somatic cells to a tumorigenic fate. This provides a blueprint of the events that lead to human cancer, allowing different cancers to be genetically modeled from normal human cells.
Cancer Research 12/2005; 65(21):9824-8. · 8.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhabdomyosarcoma, a malignancy showing features of skeletal muscle differentiation, is the most common soft tissue sarcoma of childhood. The identification of distinct clinical presentation patterns, histologic tumor types, and risk groups suggests that rhabdomyosarcoma is a collection of highly related sarcomas rather than a single entity. In an effort to understand this seemingly heterogeneous malignancy, we constructed a genetically defined but malleable model of rhabdomyosarcoma by converting less differentiated human skeletal muscle cell precursors (SkMC) and committed human skeletal muscle myoblasts (HSMM) into their malignant counterparts by targeting pathways altered in rhabdomyosarcoma. Whereas the two cell types were both tumorigenic, SkMCs gave rise to highly heterogeneous tumors occasionally displaying features of rhabdomyosarcoma, whereas HSMMs formed rhabdomyosarcoma-like tumors with an embryonal morphology, capable of invasion and metastasis. Thus, despite introducing the same panel of genetic changes, altering the skeletal muscle cell of origin led to different tumor morphologies, suggesting that cell of origin may dictate rhabdomyosarcoma tumor histology. The ability to now genetically induce human rhabdomyosarcoma-like tumors provides a representative model to dissect the molecular mechanisms underlying this cancer.
Cancer Research 07/2005; 65(11):4490-5. · 8.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The protein hPot1 shares homology with telomere-binding proteins in lower eukaryotes and associates with single-stranded telomeric DNA in vitro as well as colocalizing with telomere-binding proteins in vivo. We now show that hPot1 is coimmunoprecipitated with telomeric DNA and that stable expression of this protein in telomerase-positive cells results in telomere elongation, supporting the idea that hPot1 is a bona fide mammalian telomere-binding protein. We previously found that mutations in the N-terminal DAT domain of the hTERT catalytic subunit of telomerase rendered the enzyme catalytically active but unable to elongate telomeres in vivo. This phenotype could be partially rescued by fusion with the double-stranded telomeric protein hTRF2. Given that hPot1 binds to single-stranded DNA in vitro (at the same site that hTERT binds to in vivo), we addressed whether fusion of hPot1 can rescue the DAT mutations more efficiently than that of hTRF2. We now report that a DAT mutant of hTERT is indeed efficiently rescued upon fusion to hPot1. However, this rescue depended on the ability of hPot1 to localize to telomeres rather than binding to DNA per se. These data support a model whereby the DAT domain of hTERT is implicated in telomere-telomerase associations.
Molecular and Cellular Biology 05/2004; 24(8):3552-61. · 5.04 Impact Factor