Glimpsing the cause of rhabdomyosarcoma

Species-Specific Quantitative Proteomics Profiles of Sarcoma Patient-Derived Models Closely Reflect Their Primary Tumors

PURPOSE

The purpose is to examine whether patient-derived sarcoma models recapitulate the spectrum of sarcoma heterogeneity seen in patients.

EXPERIMENTAL DESIGN

To characterize patient-derived models for functional studies, proteomic comparisons with originating sarcomas representative of three intrinsic subtypes by MS are performed.

RESULTS

Human protein profiling is found to be retained with high fidelity in patient-derived models. The protein profiles of patient sarcoma tumors and mouse stroma are characterized by species-specific quantitative proteomics. Protein-expression levels in mouse stroma are affected by the primary human tumor. The levels of stromal proteins derived from tumors are lower in PDXs and cell lines, and some human stromal proteins are replaced by the corresponding mouse proteins in PDXs.

CONCLUSIONS AND CLINICAL RELEVANCE

These findings suggest that the effects of the microenvironment on drug responses may not reflect those in the primary tumor. This cross-species proteomic analysis in PDXs can potentially improve preclinical evaluation of treatment modalities and enhance the ability to predict clinical trial responses.

The role of insulin-like growth factor system in soft tissue sarcomas: from physiopathology to targeted therapeutic approaches

Purpose/Results. Although surgical, chemo- and radiotherapeutic treatment regimens in patients with soft tissue sarcomas have constantly been refined over the past two decades, the survival rate for these patients is rather low.

Discussion. There is a great need to investigate the mechanisms for oncogenesis and to identify the factors involved in malignant transformation in sarcomas. Among these factors, IGFs are thought to play a pivotal role as progression factors in various types of sarcomas. The dysregulation of the IGF-II synthesis, e.g. by loss of imprinting which occurs in most types of sarcomas, is a permissive effect through the suppression of cell death. In addition, cells that overexpress the type I IGF receptors are more susceptible to transformation by oncogenes. As TP53 suppresses the activity of IGF-II P3 and P4, as well as the type I IGF receptor promoter, mutations of TP53 in sarcomas may alternatively lead to the activation of these factors. Finally, the phenomenon of non-islet cell tumour hypoglycaemia that occurs in patients with sarcomas, and which is related to the secretion of IGF-II prohormones, is discussed. Future therapeutic strategies may be based upon the application of antibodies or antisense oligonucleotides directed against the type I IGF receptors, with the common goal of inducing apoptosis in sarcoma cells. Ultimately, these and other therapeutic approaches may lead to a better outcome in patients suffering from sarcoma.

Prenatal X-ray exposure and rhabdomyosarcoma in children: a report from the children's oncology group

The association between antenatal diagnostic X-ray exposure and risk of rhabdomyosarcoma in children was assessed in a national case-control study of 319 rhabdomyosarcoma cases and 319 matched controls. Data were collected by telephone interviews of subjects' parents. Overall, an odds ratio (OR) of 1.9 [95% confidence interval (CI), 1.1-3.4] was found for any X-ray examination of the mother during pregnancy. Risk was greatest for X-ray exposure during the first trimester (OR, 5.7; 95% CI, 1.2-27.8) and was also increased for the third trimester (OR, 2.0; 95% CI, 0.9-4.6), whereas second trimester exposure was not associated with increased risk. A nonsignificant increase in risk was found for any X-rays of the abdomen, pelvis, chest, or back. Increased risk was significantly associated with "other" X-ray exposures (relative risk, 2.9; 95% CI, 1.1-7.7), primarily composed of dental X-rays. The association was strongest between embryonal rhabdomyosarcoma and first trimester exposure (relative risk, 10.5; 95% CI, 1.5-458.4). This observation regarding embryonal rhabdomyosarcoma, and our previous report of an increased frequency of major malformations in rhabdomyosarcoma are compatible with findings from animal studies in which Ptc heterozygous knockout mice exhibited an increased risk of radiation-induced development defects and of spontaneously occurring embryonal rhabdomyosarcoma.

A novel EWS-WT1 gene fusion product in desmoplastic small round cell tumor is a potent transactivator of the insulin-like growth factor-I receptor (IGF-IR) gene

Desmoplastic small round cell tumor (DSRCT) is a primitive sarcoma characterized by a recurrent chromosomal translocation, t(11;22)(p13;q12), which fuses the 5' exons of the EWS gene to the 3' exons of the WT1 gene. EWS-WT1 chimeras are heterogeneous as a result of fusions of different regions of the EWS gene to the WT1 gene. We report here a rare and novel EWS-WT1 variant, EWS-WT1 5/10, in a 6-year-old boy diagnosed with DSRCT and analyze the potential transactivation effect of the fusion oncoprotein. The predicted product is comprised of the N-terminal transactivation domain of EWS and lacks any sequence derived from the WT1 gene product. Nonetheless, the truncated protein was able to stimulate expression of the insulin-like growth factor-I receptor gene, a potent antiapoptotic receptor tyrosine kinase with potentially important roles in DSRCT etiology. These findings raise the possibility that the oncogenic potential of EWS-WT1 fusions is not necessarily a consequence of the fusion protein product per se.

Patched target Igf2 is indispensable for the formation of medulloblastoma and rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children (Dagher, R., and Helman, L. (1999) Oncologist 4, 34-44), whereas medulloblastoma, a highly malignant tumor of the cerebellum, accounts for 20% of childhood brain tumors (Goodrich, L. V., and Scott, M. P. (1998) Neuron 21, 1243-1257). Both tumors are associated with a deficiency in the tumor suppressor Patched (PTCH) in Gorlin syndrome (Gorlin, R. J. (1987) Medicine (Baltimore) 66, 98-113), and they are present in the corresponding murine models. RMS in Ptch mutant mice consistently contain elevated levels of the tumor growth-promoting insulin-like growth factor 2 (Igf2). We have investigated the mechanism of Igf2 overexpression and its significance in medulloblastoma and RMS tumorigenesis. Here we report that Igf2 is indispensable for the formation of medulloblastoma and RMS in Ptch mutants. Overexpression of Igf2 in RMS in these mice does not involve loss of imprinting, uniparental disomy, amplification of the Igf2 locus, or polyploidy. Since Igf2 is also overexpressed in non-tumor tissue deficient in Ptch, these observations suggest that Ptch regulates Igf2 levels through a transcriptional mechanism. They also identify Igf2 as a potential target for medulloblastoma and RMS.

Novel genomic imbalances in embryonal rhabdomyosarcoma revealed by comparative genomic hybridization and fluorescence in situ hybridization: an intergroup rhabdomyosarcoma study

A comparative genomic hybridization (CGH) approach provides identification of genomic gains and losses in a tumor specimen in a single experiment. Only 11 embryonal rhabdomyosarcomas (E-RMS) have previously been subjected to CGH. The underlying genetic events in this histologic subtype are not well defined. In this investigation, 12 E-RMS specimens from 10 patients entered into Intergroup Rhabdomyosarcoma Study (IRS) I-IV and two local patients were analyzed by CGH and fluorescence in situ hybridization (FISH). Gains of chromosomes or chromosomal regions 2 (50%), 7 (42%), 8 (67%), 11 (42%), 12 (58%), 13q21 (33%), and 20 (33%) and losses of 1p35-36.3 (42%), 6 (33%), 9q22 (33%), 14q21-32 (25%), and 17 (25%) were most prominent. Chromosomal regions 1p35-36.3 and 9q22 represent novel regions of loss. Importantly, loss of 9q22 corresponds to the locus of a putative tumor suppressor gene (PTCH), which has been shown to play a role in rhabdomyosarcoma in a mouse model of Gorlin syndrome. Loss of 1p36 corresponds to the locus for PAX7, a paired box containing gene characteristically altered in alveolar rhabdomyosarcoma. Moreover, loss of 1p36 is prominent in another common pediatric soft tissue tumor, neuroblastoma. Gains of 2, 7, 8, 12, and 13 and loss of 14 were seen in the sole prior E-RMS CGH series; thus, these data provide important confirmatory results. In contrast to this previous study, however loss, not gain, of chromosome 17 was observed in the current study. Chromosome 17 loss correlates well with previous descriptions of frequent allelic loss of 17p (TP53) in E-RMS. In summary, CGH and FISH analyses of 12 E-RMS specimens revealed novel genomic imbalances that may be useful in directing further molecular studies for the determination of E-RMS critically involved genes.

Molecular pathology of soft tissue and bone tumors. A review

OBJECTIVE

To present recent concepts on the molecular pathogenesis of tumors of soft tissue and bone, and on the use of molecular genetic methods, including their significance as diagnostic markers and prognostic indicators.

DATA SOURCES AND STUDY SELECTION

Reports on tumors of bone and/or soft tissue published in the English language literature and observations made using specimens available at the Departments of Pathology at Albany Medical College and Loyola University Medical Center.

DATA EXTRACTION AND SYNTHESIS

Studies on bone and soft tissue tumors containing chromosomal or genetic evaluation were selected for further analysis. Specific chromosomal abnormalities, such as numerical aberrations or translocations with production of fusion genes, were classified according to the tumor of origin. Data were also collected on mutations in tumor suppressor genes, genes coding for growth factors or their receptors, and genes coding for tyrosine kinases. Also noted were mutations of uncertain significance, for which the pathogenic connection between tumor production and mutated gene function is still unclear.

CONCLUSIONS

In general, the mutations reported interfere with the action of peptide growth factors coordinating mesenchyme proliferation and differentiation, although membrane-bound receptors expressing the intracellular signaling modifier, tyrosine kinase activity, have also been involved. Functional types of genes most commonly affected include tumor suppressors, oncogenes, and nuclear transcription factors. Thus, the mutations involved in the pathogenesis of soft tissue and bone tumors have affected multiple genes. Moreover, aberrant fusion gene products may be formed in tumoral tissue and may then act as transcription regulators stimulating cellular proliferation. Cytogenetic studies help at the clinical level by demonstrating aneuploidy and increased ploidy, which may correlate with malignant behavior. Diagnostic tumor-specific chromosomal translocations may be detected with Southern hybridization analysis, polymerase chain reaction, reverse-transcription polymerase chain reaction, or with the fluorescence in situ hybridization technique. Notably, early metastatic disease may be detectable in blood specimens using polymerase chain reaction or reverse-transcription polymerase chain reaction techniques.

Rhabdomyosarcoma--working out the pathways

Rhabdomyosarcomas constitute a collection of childhood malignancies thought to arise as a consequence of regulatory disruption of skeletal muscle progenitor cell growth and differentiation. Our understanding of the pathogenesis of this neoplasm has recently benefited from the study of normal and malignant myogenic cells in vitro, facilitating the identification of diagnostic cytogenetic markers and the elucidation of mechanisms by which myogenesis is regulated. It is now appreciated that the delicate balance between proliferation and differentiation, mutually exclusive yet intimately associated processes, is normally controlled in large part through the action of a multitude of growth factors, whose signals are interpreted by members of the MyoD family of helix - loop - helix proteins, and key regulatory cell cycle factors. The latter have proven to be frequent targets of mutational events that subvert myogenesis and promote the development of rhabdomyosarcoma. Although significant progress has been made in the treatment of rhabdomyosarcoma, patients presenting with metastatic disease or certain high risk features are still faced with a dismal prognosis. Only now are genetically engineered mouse models becoming available that are certain to provide fresh insights into the molecular/genetic pathways by which rhabdomyosarcomas arise and progress, and to suggest novel avenues of therapeutic opportunity.