Molecular alterations of the RB1, TP53, and MDM2 genes in primary and xenografted human osteosarcomas

Fluorescent In Situ Hybridization for TP53 in the Diagnosis of Pediatric Osteogenic Sarcoma

Osteogenic sarcoma (OS) is the most common malignant bone tumor in children and adolescents. Despite advances in molecular genetic characterization of pediatric and adult tumors, the diagnosis of OS still depends almost entirely on light microscopy. The lack of consistent genetic changes in OS has greatly hindered the development of any diagnostic molecular test. Recently, whole-genome sequencing has shown that ~50% of cases of OS have a translocation involving the TP53 gene with breakpoints confined to the first intron. We developed a 2 color break-apart fluorescent in situ hybridization (FISH) probe for intron 1 of TP53 and applied it to an archived series to assess its diagnostic utility. The study group included 37 cases of OS (including osteoblastic, chondroblastic, and fibroblastic), as well as 53 cases of non-OS pediatric sarcomas (including Ewing sarcoma, rhabdomyosarcoma, undifferentiated small cell sarcoma, CCNB3-BCOR sarcoma, CIC-DUX sarcoma, synovial sarcoma, and malignant peripheral nerve sheath tumor) and 27 cases of benign bone lesions (including osteoblastoma, chondromyxoid fibroma, fibrous dysplasia, and fibro-osseous dysplasia). A rearranged signal was found in 20/37 cases (54%) of OS and in none of the other sarcomas or benign bone lesions, giving the FISH test 100% specificity for a diagnosis of OS. p53 immunostaining was generally not predictive of the results obtained by FISH and could not substitute for this test. This FISH probe offers a simple and specific genetic test to aid in the diagnosis of OS, despite the genetic complexity of this tumor.

Osteosarcoma Overview

Osteosarcoma (OS) is the most common primary malignancy of bone and patients with metastatic disease or recurrences continue to have very poor outcomes. Unfortunately, little prognostic improvement has been generated from the last 20 years of research and a new perspective is warranted. OS is extremely heterogeneous in both its origins and manifestations. Although multiple associations have been made between the development of osteosarcoma and race, gender, age, various genomic alterations, and exposure situations among others, the etiology remains unclear and controversial. Noninvasive diagnostic methods include serum markers like alkaline phosphatase and a growing variety of imaging techniques including X-ray, computed tomography, magnetic resonance imaging, and positron emission as well as combinations thereof. Still, biopsy and microscopic examination are required to confirm the diagnosis and carry additional prognostic implications such as subtype classification and histological response to neoadjuvant chemotherapy. The current standard of care combines surgical and chemotherapeutic techniques, with a multitude of experimental biologics and small molecules currently in development and some in clinical trial phases. In this review, in addition to summarizing the current understanding of OS etiology, diagnostic methods, and the current standard of care, our group describes various experimental therapeutics and provides evidence to encourage a potential paradigm shift toward the introduction of immunomodulation, which may offer a more comprehensive approach to battling cancer pleomorphism.

A New Mutation of the p53 Gene in Human Neuroblastoma, Not Correlated with N-myc Amplification

N-myc gene amplification and/or loss of heterozygosity of chromosome 1 (LOH lp) are important criteria for prognosis and progression in human neuroblastoma (NB). Despite the high incidence of alterations of the p53 gene in human cancers, very few p53 mutations have been reported in NB. The objective of our study was to search for p53 mutations in NB and their correlation with N-myc amplification and clinical or pathologic parameters. We analyzed 14 selected cases of NB from the Spanish Protocol N-II-92. We found a missense mutation in codon 248 CGG to GGG (Arg/Gly) in one case of stage 4 NB with no N-myc amplification. Our results confirm the low incidence of p53 gene mutation in neuroblastoma and the absence of correlation with histopathologic parameters.

Investigation of osteosarcoma genomics and its impact on targeted therapy: an international collaboration to conquer human osteosarcoma

Osteosarcoma is a genetically unstable malignancy that most frequently occurs in children and young adults. The lack of progress in managing this devastating disease in the clinic has prompted international researchers to collaborate to profile key genomic alterations that define osteosarcoma. A team of researchers and clinicians from China, Finland, and the United States investigated human osteosarcoma by integrating transcriptome sequencing (RNA-seq), high-density genome-wide array comparative genomic hybridization (aCGH), fluorescence in situ hybridization (FISH), reverse transcription-polymerase chain reaction (RT-PCR), Sanger sequencing, cell culture, and molecular biological approaches. Systematic analysis of genetic/genomic alterations and further functional studies have led to several important findings, including novel rearrangement hotspots, osteosarcoma-specific LRP1-SNRNP25 and KCNMB4-CCND3 fusion genes, VEGF and Wnt signaling pathway alterations, deletion of the WWOX gene, and amplification of the APEX1 and RUNX2 genes. Importantly, these genetic events associate significantly with pathogenesis, prognosis, progression, and therapeutic activity in osteosarcoma, suggesting their potential impact on improved managements of human osteosarcoma. This international initiative provides opportunities for developing new treatment modalities to conquer osteosarcoma.

Recurrent LRP1-SNRNP25 and KCNMB4-CCND3 fusion genes promote tumor cell motility in human osteosarcoma

BACKGROUND

The identification of fusion genes such as SYT-SSX1/SSX2, PAX3-FOXO1, TPM3/TPM4-ALK and EWS-FLI1 in human sarcomas has provided important insight into the diagnosis and targeted therapy of sarcomas. No recurrent fusion has been reported in human osteosarcoma.

METHODS

Transcriptome sequencing was used to characterize the gene fusions and mutations in 11 human osteosarcomas.

RESULTS

Nine of 11 samples were found to harbor genetic inactivating alterations in the TP53 pathway. Two recurrent fusion genes associated with the 12q locus, LRP1-SNRNP25 and KCNMB4-CCND3, were identified and validated by RT-PCR, Sanger sequencing and fluorescence in situ hybridization, and were found to be osteosarcoma specific in a validation cohort of 240 other sarcomas. Expression of LRP1-SNRNP25 fusion gene promoted SAOS-2 osteosarcoma cell migration and invasion. Expression of KCNMB4-CCND3 fusion gene promoted SAOS-2 cell migration.

CONCLUSIONS

Our study represents the first whole transcriptome analysis of untreated human osteosarcoma. Our discovery of two osteosarcoma specific fusion genes associated with osteosarcoma cellular motility highlights the heterogeneity of osteosarcoma and provides opportunities for new treatment modalities.

Models of biobanking and tissue preservation: RNA quality in archival samples in pathology laboratories and "in vivo biobanking" by tumor xenografts in nude mice-two models of quality assurance in pathology

Tissue banks represent essential resources and platforms for biomedical research serving basic, translational, and clinical research projects. In this article, we describe 2 models of biobanking and tissue preservation with different approaches and aims. Archive tissue biobanking is described here as a resource of residual pathology tissues for translational research, which represents the huge clinical heterogeneity. In this context, managing of tissues and RNA quality in archive tissue are discussed. The other model of tissue biobanking is referred to as xenograft tissue banking, which represents an alternative method for obtaining large amounts of tissue, over an indefinite period, in so far as the tumor can be transferred in vivo over generations, maintaining the histological and genetic particularities. A description of the method and examples of the application are given with particular emphasis on sarcomas (Ewing's sarcoma/primitive neuroectodermal sarcoma, synovial sarcomas, and rhabdomyosarcomas) and early stages of tumor angiogenesis in sarcomas.

The genetics of osteosarcoma

Osteosarcoma is a primary bone malignancy with a particularly high incidence rate in children and adolescents relative to other age groups. The etiology of this often aggressive cancer is currently unknown, because complicated structural and numeric genomic rearrangements in cancer cells preclude understanding of tumour development. In addition, few consistent genetic changes that may indicate effective molecular therapeutic targets have been reported. However, high-resolution techniques continue to improve knowledge of distinct areas of the genome that are more commonly associated with osteosarcomas. Copy number gains at chromosomes 1p, 1q, 6p, 8q, and 17p as well as copy number losses at chromosomes 3q, 6q, 9, 10, 13, 17p, and 18q have been detected by numerous groups, but definitive oncogenes or tumour suppressor genes remain elusive with respect to many loci. In this paper, we examine studies of the genetics of osteosarcoma to comprehensively describe the heterogeneity and complexity of this cancer.

Osteosarcoma models: from cell lines to zebrafish

High-grade osteosarcoma is an aggressive tumor most commonly affecting adolescents. The early age of onset might suggest genetic predisposition; however, the vast majority of the tumors are sporadic. Early onset, most often lack of a predisposing condition or lesion, only infrequent (<2%) prevalence of inheritance, extensive genomic instability, and a wide histological heterogeneity are just few factors to mention that make osteosarcoma difficult to study. Therefore, it is sensible to design and use models representative of the human disease. Here we summarize multiple osteosarcoma models established in vitro and in vivo, comment on their utilities, and highlight newest achievements, such as the use of zebrafish embryos. We conclude that to gain a better understanding of osteosarcoma, simplification of this extremely complex tumor is needed. Therefore, we parse the osteosarcoma problem into parts and propose adequate models to study them each separately. A better understanding of osteosarcoma provides opportunities for discovering and assaying novel effective treatment strategies.

“Sometimes the model is more interesting than the original disease”

PJ Hoedemaeker (1937–2007).

A tissue microarray study of osteosarcoma: histopathologic and immunohistochemical validation of xenotransplanted tumors as preclinical models

BACKGROUND

Osteosarcomas (OS) are aggressive neoplasms with a wide range of morphologic patterns.

MATERIALS AND METHODS

OS cases (primary and xenotransplanted) with paraffin blocks available were collected and included in tissue microarrays (TMAs). A morphologic evaluation including the different passages in mice was carried out according to the new WHO criteria. In addition, TMAs were analyzed with a wide panel of immunohistochemical (IHC) markers (osteonectin, osteocalcin,cytokeratin, S100, Sox-9, Ki-67, Bcl-2, p53, p16, survivin, CD99, and caveolin-1).

RESULTS

A total of 61 cases were collected. The distribution of the cases according to the histopathologic pattern was: 38 osteogenic OS, 8 primary chondrogenic OS, 2 primary telangiectatic OS, 6 parosteal OS, 2 primary small cell OS, 2 primary poorly differentiated OS, 1 primary dedifferentiated OS, and 3 primary pleomorphic MFH-like OS. The tumor morphology in xenotransplants was similar to the primary or metastatic tumor of origin and was generally maintained over the passages. The IHC results were heterogeneous and osteonectin and osteocalcin were the most expressed in original tumor and xenografts. S100 and Sox-9 were expressed in chondrogenic areas. Caveolin and survivin showed significant IHC variation between the subsequent passages. p16 displayed heterogenic expression. p53 expression increased over the passages, and Ki-67 expression was not associated with a more undifferentiated pattern, but increased over the passages.

CONCLUSIONS

An accurate morphologic evaluation using TMAs in original tumor is essential for the OS diagnosis; hence there is no IHC marker that alone distinguishes the OS subtypes. Xenografts in OS allow the study of tumor progression in this type of aggressive neoplasm.

Familial risk for histology-specific bone cancers: an updated study in Sweden

We used the nation-wide Swedish Family-Cancer Database to examine the familial risks of histology-specific bone cancers in offspring by parental or sibling probands. Adjusted standardised incidence ratios (SIRs) were used to measure the risk. Among the 1327 offspring bone cancers, only two parent-offspring pairs and one sibling pair were noted with concordant bone cancer but the SIRs were not significant. Significant associations were observed in specific histological types or specific age groups, some of which may be chance findings arising from multiple comparisons. However, the risk of early-onset (< 25 years) osteosarcoma in offspring was significantly increased when mothers presented with breast cancer (1.7) and melanoma (2.9), suggesting that Li-Fraumeni syndrome could partly explain this familial aggregation. Other associations, such as childhood osteosarcoma with parental liver cancer, Ewing's sarcoma with kidney cancer and giant cell sarcoma with maternal breast cancer, were novel findings and may be related to other familial diseases.

Deregulation of the G1 to S-phase cell cycle checkpoint is involved in the pathogenesis of human osteosarcoma

Osteosarcoma (OS) displays complex karyotypes with numerical changes as well as structural abnormalities suggesting that several oncogenes and tumor suppressor genes may be implicated in the biology of OS. The aim of our study was to investigate the possible implication of the molecular alterations of the G1 to S-phase checkpoint genes in the pathogenesis of OS. We analyzed samples from 29 patients and found molecular alterations of the RB and TP53 genes in 6 (21%) and 3 (10%) cases, respectively. Homozygous deletion of the INK4A/ARF locus and methylation of INK4A was detected in 3 (10%) and 2 (7%) cases, respectively. CDK4 and MDM2 co-amplification was observed in 1 case (3%). Cyclin D3 is differentially expressed in a greater proportion than D1- and D2-type cyclins. Cytogenetically, all cases had complex karyotypes being especially significant the losses of the chromosomes 4, 13, and 17. As a whole, 11 of 29 (38%) analyzed OS presented alterations in some of the analyzed G1 to S-phase checkpoint genes. These alterations were more frequently present in adults (P = 0.032). All patients with genetic alterations in the G1/S-phase checkpoint died during their clinical follow-up, whereas more than 53% of the remaining cases were alive in this period (P = 0.007). Hence, in the pathogenesis of human OS, deregulation of the G1/S checkpoint genes, especially RB, TP53, and INK4/ARF locus, plays an important role and defines a subgroup of patients with a poor outcome.

Loss of 13q14-q21 and gain of 5p14-pter in the progression of leiomyosarcoma

Leiomyosarcomas of soft tissues are an aggressive group of tumors with a high incidence of recurrence. Little is known about the molecular genetic changes associated with clinical outcome. Therefore, we studied 28 leiomyosarcoma samples of similar grade using comparative genomic hybridization and DNA flow cytometry and identified a difference in survival time associated with ploidy status and the number of chromosomal aberrations. The average survival time was shown to decrease with increase in chromosomal aberrations identified using comparative genomic hybridization. The average survival time was shorter in the near-tetraploid group than in the diploid and triploid group. Gain of 5p14-pter was significantly more common in near-tetraploid tumors. The survival time of patients with near-tetraploidy together with gain of 5p14-pter was reduced, and 50% died within the 1st year. Furthermore, loss of 13q14-q21 was significantly more frequent in the <5-year than in the >5-year survival group (P =.01). These results suggest that 13q14-q21 loss and 5p14-pter gain at diagnosis could be used to identify patients with leiomyosarcoma who are likely to have a shorter survival time and who might benefit from early treatment intensification.

Significance of loss of heterozygosity of the RB1 gene during tumour progression in well-differentiated liposarcomas

Tumour progression can be investigated in liposarcomas showing a transition from a low-grade well-differentiated (WD) to a high-grade dedifferentiated (DD) variant. As RB1 gene alterations are common defects in sarcomas, this study examined the frequency of RB1 loss of heterozygosity (LOH) in a group of 14 well-differentiated liposarcomas (WDLs) and 17 well-differentiated/dedifferentiated liposarcomas (WD/DDLs), using a microdissection approach (PALM laser pressure catapulting) that allows the two histological components to be separated for polymerase chain reaction (PCR) analysis. In addition, RB1 protein expression and the Mib1 proliferation index were determined by immunohistochemistry and interphase FISH was performed with an RB1 probe at 13q14. By the use of four intragenic polymorphic RB1 markers (introns 1, 17, 20, and 25) for PCR, allelic losses were found only in the DD parts, but never in the pure WDLs or in the WD components of the WD/DDLs investigated. Furthermore, DD areas characterized by a heterogeneous RB1 protein expression pattern (35-65% immunopositivity), as compared with 90-100% RB1 positivity in WD areas, showed a marked increase in Mib1 proliferation index (19.6% versus 1.8% in WD areas; p<0.001). Interphase fluorescence in situ hybridization (FISH) detected a higher RB1-LOH rate in the DD components of WD/DDLs. Considering the different detection sensitivities of the three methodologies, it is concluded that loss of RB1 function already begins in the WDL, and that the tumour cell population with RB1-LOH starts prevailing in the tumour mass during progression of a WDL.

Parental cancer as a risk factor for bone cancer: a nation-wide study from Sweden

We used the nation-wide Swedish Family-Cancer Database to analyze the risk for bone cancer in offspring by parental cancers and in siblings of bone cancer probands. Additionally, the risk of second cancer following childhood bone cancer was investigated. In offspring, 1,190 bone cancers were diagnosed between years 1958 and 1996. Groups of offspring were compared by calculating standardized incidence ratios (SIRs) for bone cancer. Most bone cancer cases occurred sporadically. Parental breast (SIR 1.7) and prostate (SIR 1.7) cancers were associated with early-onset (<25 years) osteosarcoma in offspring, probably due to Li-Fraumeni syndrome. Giant cell sarcoma was increased by parental breast cancer (SIR 2.9), and early-onset chondrosarcoma by parental kidney cancers (SIR 6.8). Bone cancers conveyed a high risk of second bone and connective tissue cancer.

[Early diagnosis of retinoblastoma: usefulness of searching for RB1 gene mutations]

BACKGROUND

Retinoblastoma, the intraocular malignancy most common in children,occurs in both familial and sporadic (bilateral or unilateral). Hereditary predisposition is caused by a germ-line mutation while non-hereditary is due to two somatic mutations in a retinal cell. This work was carried out in order to analyse genetically, the high number of families with some affected member and to go deep into the molecular mechanisms responsible of this pathology.

PATIENTS AND METHOD

59 families with one or more affected members were analysed. Cytogenetics and with polymorphic markers studies were carried out and a search for mutations was performed in DNA from white cells and from available tumoral tissue.

RESULTS

In four of the 5 familial cases, the responsible mutation was established,the same as in 9 of the 13 bilateral sporadic. In the 7% of the unilateral sporadic cases, mutation was found in leucocytary DNA. Lost of heterozygosity as a second mutational event was mainly due to mitotic recombination.

CONCLUSIONS

Among the mutations of our series, a higher frequency of punctual mutations,responsible of the first mutational event, was observed at constitutional level. Lost of heterozygosity was the mechanism observed in the majority of the tumours.