MET oncogene aberrant expression in canine osteosarcoma

Immunohistochemical Investigation into Protein Expression Patterns of FOXO4, IRF8 and LEF1 in Canine Osteosarcoma

Osteosarcoma (OSA) is the most common type of primary bone malignancy in people and dogs. Our previous molecular comparisons of canine OSA against healthy bone resulted in the identification of differentially expressed protein-expressing genes (forkhead box protein O4 (FOXO4), interferon regulatory factor 8 (IRF8), and lymphoid enhancer binding factor 1 (LEF1)). Immunohistochemistry (IHC) and H-scoring provided semi-quantitative assessment of nuclear and cytoplasmic staining alongside qualitative data to contextualise staining (n = 26 patients). FOXO4 was expressed predominantly in the cytoplasm with significantly lower nuclear H-scores. IRF8 H-scores ranged from 0 to 3 throughout the cohort in the nucleus and cytoplasm. LEF1 was expressed in all patients with significantly lower cytoplasmic staining compared to nuclear. No sex or anatomical location differences were observed. While reduced levels of FOXO4 might indicate malignancy, the weak or absent protein expression limits its primary use as diagnostic tumour marker. IRF8 and LEF1 have more potential for prognostic and diagnostic uses and facilitate further understanding of their roles within their respective molecular pathways, including Wnt/beta-catenin/LEF1 signalling and differential regulation of tumour suppressor genes. Deeper understanding of the mechanisms involved in OSA are essential contributions towards the development of novel diagnostic, prognostic, and treatment options in human and veterinary medicine contexts.

Review: The PI3K-AKT-mTOR signal transduction pathway in canine cancer

Tumors in dogs and humans share many similar molecular and genetic features, incentivizing a better understanding of canine neoplasms not only for the purpose of treating companion animals, but also to facilitate research of spontaneously developing tumors with similar biologic behavior and treatment approaches in an immunologically competent animal model. Multiple tumor types of both species have similar dysregulation of signal transduction through phosphatidylinositol 3-kinase (PI3K), protein kinase B (PKB; AKT), and mechanistic target of rapamycin (mTOR), collectively known as the PI3K-AKT-mTOR pathway. This review aims to delineate the pertinent aspects of the PI3K-AKT-mTOR signaling pathway in health and in tumor development. It will then present a synopsis of current understanding of PI3K-AKT-mTOR signaling in important canine cancers and advancements in targeted inhibitors of this pathway.

Large Scale Comparative Deconvolution Analysis of the Canine and Human Osteosarcoma Tumor Microenvironment Uncovers Conserved Clinically Relevant Subtypes

Osteosarcoma is a relatively rare but aggressive cancer of the bones with a shortage of effective biomarkers. Although less common in humans, Osteosarcomas are fairly common in adult pet dogs and have been shown to share many similarities with their human analogs. In this work, we analyze bulk transcriptomic data of 213 primary and 100 metastatic Osteosarcoma samples from 210 pet dogs enrolled in nation-wide clinical trials to uncover three Tumor Microenvironment (TME)-based subtypes: Immune Enriched (IE), Immune Enriched Dense Extra-Cellular Matrix-like (IE-ECM) and Immune Desert (ID) with distinct cell type compositions, oncogenic pathway activity and chromosomal instability. Furthermore, leveraging bulk transcriptomic data of canine primary tumors and their matched metastases from different sites, we characterize how the Osteosarcoma TME evolves from primary to metastatic disease in a standard of care clinical setting and assess its overall impact on clinical outcomes of canines. Most importantly, we find that TME-based subtypes of canine Osteosarcomas are conserved in humans and predictive of progression free survival outcomes of human patients, independently of known prognostic biomarkers such as presence of metastatic disease at diagnosis and percent necrosis following chemotherapy. In summary, these results demonstrate the power of using canines to model the human Osteosarcoma TME and discover novel biomarkers for clinical translation.

The role of toceranib phosphate in dogs with non-mast cell neoplasia: A systematic review

The use of tyrosine kinase inhibitors (TKI) has gained significant importance in veterinary cancer patients over the last decade. Toceranib phosphate has been licensed for the treatment of dogs with mast cell tumours. Its molecular similarity to sunitinib, a TKI used in human medicine, has led many veterinary oncologists to use this agent for multiple neoplastic diseases. The aim of the current study was to perform a systematic review of the evidence for the use of toceranib in dogs with non-mast cell neoplasia. Two electronic databases were searched. Publications were included if toceranib was used as a treatment option in canine patients. Studies and case reports were excluded if toceranib was used as part of a multi-modal treatment plan and response or outcome data related to toceranib therapy were not described. A total of 28 studies were included from 122 references. The most common types of neoplasias identified were neuroendocrine tumours, anal gland sac adenocarcinoma, and osteosarcoma. Multiple other neoplasias had one or two studies identified to describe the use of toceranib. Results of the study support that toceranib phosphate may have efficacy against certain types of neoplasia under certain conditions, such as neuroendocrine tumours, gastrointestinal stromal tumours and anal sac adenocarcinomas, while it is probably not effective for the management of metastatic osteosarcoma based on the findings of the review.

Roles of MET in human cancer

The MET proto-oncogene was first identified in osteosarcoma cells exposed to carcinogens. Although expressed in many normal cells, MET is overexpressed in many human cancers. MET is involved in the initiation and development of various human cancers and mediates proliferation, migration and invasion. Accordingly, MET has been successfully used as a biomarker for diagnosis and prognosis, survival, post-operative recurrence, risk assessment and pathologic grading, as well as a therapeutic target. In addition, recent work indicates that inhibition of MET expression and function has potential clinical benefit. This review summarizes the role, mechanism, and clinical significance of MET in the formation and development of human cancer.

miR-106B-25 Cluster expression: a comparative human and canine osteosarcoma study

Background

Osteosarcoma (OS) is the most common primary malignant bone tumour in dogs and human beings, characterised by similar genetic and clinical features. With the aim to define similarities and differences in the biological aspects involved in OS progression, a comparative study was performed to create a model to improve patient outcome.

Methods

First, the expression of microRNAs (miRNAs) belonging to the cluster miR-106b-25 (miR-106b, miR-25 and miR-93-5p) in human and canine OS tissue was compared.

Results

miR-25 and miR-106b presented a variable expression not significantly different from the corresponding normal bone, while miR-93-5p expression was increased in all OS specimens, with higher levels in the canine subset compared with human. Accordingly, its target p21 presented a weaker and less homogeneous immunostaining distribution in the canine group. Given the high expression of miR-93-5p in all OS specimens, the functional response of human 143B and canine DAN OS cells to miRNA inhibition was evaluated. Although p21 expression increased after miR-93-5p inhibition both at mRNA and protein level, a more significant cell response in terms of proliferation and apoptosis was seen in canine OS cells.

Conclusions

In conclusion, canine OS tissue and cell line presented higher expression levels of miR-93-5p than human OS. In addition, the introduction of miR-93-5p inhibitor caused a cell response in 143B and DAN that differed for the more intense functional impact in the canine OS cell line.

Targeted Therapies in Veterinary Oncology

Advances in molecular biology have permitted a much more detailed understanding of cellular dysfunction at the molecular and genetic levels in cancer cells. This has resulted in the identification of novel targets for therapeutic intervention, including proteins that regulate signal transduction, gene expression, and protein turnover. In many instances, small molecules are used to disrupt the function of these targets, often through competitive inhibition of ATP binding or the prevention of necessary protein-protein interactions. More than 40 small molecule inhibitors are now approved to treat a variety of human cancers, substantially impacting patient outcomes.

Integrated analysis of gene expression and copy number variations in MET proto‑oncogene‑transformed human primary osteoblasts

The aim of the present study was to screen the potential osteosarcoma (OS)‑associated genes and to obtain additional insight into the pathogenesis of OS. Transcriptional profile (ID: GSE28256) and copy number variations (CNV) profile were downloaded from Gene Expression Omnibus database. Differentially expressed genes (DEGs) between MET proto‑oncogene‑transformed human primary osteoblast (MET‑HOB) samples and the control samples were identified using the Linear Models for Microarray Data package. Subsequently, CNV areas and CNVs were identified using cut‑off criterion of >30%‑overlap within the cases using detect_cnv.pl in PennCNV. Genes shared in DEGs and CNVs were obtained and discussed. Additionally, the Database for Annotation, Visualization and Integrated Discovery was used to identify significant Gene Ontology (GO) functions and pathways in DEGs with P<0.05. A total of 1,601 DEGs were screened out in MET‑HOBs and compared with control samples, including 784 upregulated genes, such as E2F transcription factor 1 (E2F1) and 2 (E2F2) and 817 downregulated genes, such as retinoblastoma 1 (RB1) and cyclin D1 (CCND1). DEGs were enriched in 344 GO terms, such as extracellular region part and extracellular matrix and 14 pathways, including pathways in cancer and extracellular matrix‑receptor interaction. Additionally, 239 duplications and 439 deletions in 678 genes from 1,313 chromosome regions were detected. A total of 12 genes were identified to be CNV‑driven genes, including cadherin 18, laminin subunit α 1, spectrin β, erythrocytic, ciliary rootlet coiled‑coil, rootletin pseudogene 2, β‑1,4-N-acetyl-galactosaminyltransferase 1, G protein regulated inducer of neurite outgrowth 1, EH domain binding protein 1‑like 1, growth factor independent 1, cathepsin Z, WNK lysine deficient protein kinase 1, glutathione S‑transferase mu 2 and microsomal glutathione S‑transferase 1. Therefore, cell cycle‑associated genes including E2F1, E2F2, RB1 and CCND1, and cell adhesion‑associated genes, such as CDH18 and LAMA1 may be used as diagnosis and/or therapeutic markers for patients with OS.

Blocking HSP90 Addiction Inhibits Tumor Cell Proliferation, Metastasis Development, and Synergistically Acts with Zoledronic Acid to Delay Osteosarcoma Progression

PURPOSE

Despite recent improvements in therapeutic management of osteosarcoma, ongoing challenges in improving the response to chemotherapy warrants the development of new strategies to improve overall patient survival. Among them, HSP90 is a molecular chaperone involved in the maturation and stability of various oncogenic proteins leading to tumor cells survival and disease progression. We assessed the antitumor properties of a synthetic HSP90 inhibitor, PF4942847, alone or in combination with zoledronic acid in osteosarcoma.

EXPERIMENTAL DESIGN

The effects of PF4942847 were evaluated on human osteosarcoma cells growth and apoptosis. Signaling pathways were analyzed by Western blotting. The consequence of HSP90 therapy combined or not with zoledronic acid was evaluated in mice bearing HOS-MNNG xenografts on tumor growth, associated bone lesions, and pulmonary metastasis. The effect of PF4942847 on osteoclastogenesis was assessed on human CD14(+) monocytes.

RESULTS

In osteosarcoma cell lines, PF4942847 inhibited cell growth in a dose-dependent manner (IC50 ±50 nmol/L) and induced apoptosis with an increase of sub-G1 fraction and cleaved PARP. These biologic events were accompanied by decreased expression of Akt, p-ERK, c-Met, and c-RAF1. When administered orally to mice bearing osteosarcoma tumors, PF4942847 significantly inhibited tumor growth by 80%, prolonged survival compared with controls, and inhibited pulmonary metastases by blocking c-Met, FAK, and MMP9 signaling. In contrast to 17-allylamino-17-demethoxygeldanamycin (17-AAG), PF4942847 did not induce osteoclast differentiation, and synergistically acted with zoledronic acid to delay osteosarcoma progression and prevent bone lesions.

CONCLUSIONS

All these data provide a strong rationale for clinical evaluation of PF4942847 alone or in combination with zoledronic acid in osteosarcoma. Clin Cancer Res; 22(10); 2520-33. ©2015 AACR.

miR-454 is down-regulated in osteosarcomas and suppresses cell proliferation and invasion by directly targeting c-Met

OBJECTIVES

Osteosarcoma is the most common primary bone malignancy of children and young adults. Increasing evidence has shown that microRNAs (miRNAs) are associated with cancer development, but, little is known concerning the role of miR-454 in osteosarcoma.

MATERIALS AND METHODS

qRT-PCR was performed to detect expression of miR-454 in osteosarcoma cell lines and tissues. To understand its role in osteosarcoma, we reintroduced expression of miR-454 in the MG-63 cell line by transfection with miR-454 mimics or inhibitors. CCK-8 assay and an invasion assay were used to detect the functional role of miR-454. Luciferase assay and western blot analysis were performed to detect the target gene of miR-454.

RESULTS

miR-454 was found to be down-regulated in osteosarcoma tissues and cell lines. Its over-expression inhibited tumour growth and invasion and its down-regulation promoted cell proliferation and invasion. Subsequent investigation revealed that c-Met was a direct and functional target of miR-454 in osteosarcoma. Overexpression of miR-454 impaired c-Met-induced cell proliferation and invasion. Finally, miR-454 was found to be inversely correlated to c-Met expression in human osteosarcoma tissues.

CONCLUSIONS

Reduced-expression of miR-454 in osteosarcoma cells promoted tumour growth by targeting c-Met, thus miR-454 may be a potential therapy target for this tumour.

Prognostic and predictive value of MET deregulation in non-small cell lung cancer

Recent progress in cancer biology has led to the discovery of increasing number of oncogene alterations that have dramatically changed the paradigm of lung cancer treatment. MET is a tyrosine kinase receptor for the hepatocyte growth factor (HGF) that is deregulated in several malignancies, including non-small cell lung cancer (NSCLC). Abnormal MET-HGF signaling pathway activation can occur via different mechanisms, including HGF and/or MET overexpression, MET gene amplification, mutations or rearrangements. MET protein overexpression and increased MET gene number have been identified as poor prognostic factors in several series of surgically resected NSCLC making this receptor an attractive target for cancer treatment. Several clinical trials have recently evaluated the activity of a variety of anti-MET strategies in NSCLC patients with or without molecular selection with a variable degree of success, underscoring the need of establishing the best predictive biomarker for the identification of responding patients.

Kinase dysfunction and kinase inhibitors

With recent advances in molecular biology, abnormalities in cancer cells that contribute to dysregulation of cell survival and proliferation are being characterized with greater precision. Through this process, key abnormalities in cancer cells involving proteins that regulate signal transduction, migration, mitosis and other critical processes have been identified. Such abnormalities often involve a class of proteins called kinases that act to phosphorylate other proteins in the cell, resulting in activation of these proteins in the absence of appropriate stimulation/regulation. Given their role in tumour biology, substantial effort has been directed at blocking the function of these proteins. Several approaches have been used, including monoclonal antibodies and small molecule inhibitors. While antibodies are primarily directed at cell surface proteins, small molecule inhibitors, also known as kinase inhibitors, target proteins throughout the cell. A variety of kinase inhibitors have been approved for the treatment of human cancers. In some instances, these inhibitors have exhibited significant clinical efficacy, and it is likely that their biological activity will be further enhanced as combination regimens with standard treatment modalities are explored. The use of kinase inhibitors in dogs and cats is relatively recent, although two inhibitors, toceranib (Palladia; Pfizer Animal Health, Madison, NJ, USA) and masitinib (Kinavet; Catalent Pharma Solutions, Somerset, NJ, USA) have been approved by the Federal Drug Administration (USA) for use in dogs. This article reviews the biology of protein kinase dysfunction in human and animal cancers, and the application of specific kinase inhibitors to veterinary cancer patients.

Comparative analysis of the surface exposed proteome of two canine osteosarcoma cell lines and normal canine osteoblasts

Background

Osteosarcoma (OSA) is the most common primary bone tumor of dogs and carries a poor prognosis despite aggressive treatment. An improved understanding of the biology of OSA is critically needed to allow for development of novel diagnostic, prognostic, and therapeutic tools. The surface-exposed proteome (SEP) of a cancerous cell includes a multifarious array of proteins critical to cellular processes such as proliferation, migration, adhesion, and inter-cellular communication. The specific aim of this study was to define a SEP profile of two validated canine OSA cell lines and a normal canine osteoblast cell line utilizing a biotinylation/streptavidin system to selectively label, purify, and identify surface-exposed proteins by mass spectrometry (MS) analysis. Additionally, we sought to validate a subset of our MS-based observations via quantitative real-time PCR, Western blot and semi-quantitative immunocytochemistry. Our hypothesis was that MS would detect differences in the SEP composition between the OSA and the normal osteoblast cells.

Results

Shotgun MS identified 133 putative surface proteins when output from all samples were combined, with good consistency between biological replicates. Eleven of the MS-detected proteins underwent analysis of gene expression by PCR, all of which were actively transcribed, but varied in expression level. Western blot of whole cell lysates from all three cell lines was effective for Thrombospondin-1, CYR61 and CD44, and indicated that all three proteins were present in each cell line. Semi-quantitative immunofluorescence indicated that CD44 was expressed at much higher levels on the surface of the OSA than the normal osteoblast cell lines.

Conclusions

The results of the present study identified numerous differences, and similarities, in the SEP of canine OSA cell lines and normal canine osteoblasts. The PCR, Western blot, and immunocytochemistry results, for the subset of proteins evaluated, were generally supportive of the mass spectrometry data. These methods may be applied to other cell lines, or other biological materials, to highlight unique and previously unrecognized differences between samples. While this study yielded data that may prove useful for OSA researchers and clinicians, further refinements of the described techniques are expected to yield greater accuracy and produce a more thorough SEP analysis.

A model of study for human cancer: Spontaneous occurring tumors in dogs. Biological features and translation for new anticancer therapies

Murine cancer models have been extremely useful for analyzing the biology of pathways involved in cancer initiation, promotion, and progression. Interestingly, several murine cancer models also exhibit heterogeneity, genomic instability and an intact immune system. However, they do not adequately represent several features that define cancer in humans, including long periods of latency, the complex biology of cancer recurrence and metastasis and outcomes to novel therapies. Therefore, additional models that better investigate the human disease are needed. In the pet population, with special references to the dog, cancer is a spontaneous disease and dogs naturally develop cancers that share many characteristics with human malignancies. More than 40 years ago, optimization of bone marrow transplantation protocols was undertaken in dogs and recently novel targeted therapies such as liposomal muramyl tripeptide phosphatidylethanolamine and several tyrosine kinase inhibitors, namely masitinib (AB1010) and toceranib phosphate (SU11654), have been developed to treat dog tumors which have then been translated to human clinical trials. In this review article, we will analyze biological data from dog tumors and comparative features with human tumors, and new therapeutic approaches translated from dog to human cancer.

A genome-wide approach to comparative oncology: high-resolution oligonucleotide aCGH of canine and human osteosarcoma pinpoints shared microaberrations

Molecular cytogenetic evaluation of human osteosarcoma (OS) has revealed the characteristically high degree of genomic reorganization that is the hallmark of this cancer. The extent of genomic disorder in OS has hindered identification of the genomic aberrations driving disease progression. With pathophysiological similarities to its human counterpart, canine OS represents an ideal model for comparison of conserved regions of genomic instability that may be disease-associated rather than genomic passengers. This study used high-resolution oligonucleotide array comparative genomic hybridization and a variety of informatics tools to aid in the identification of disease-associated genome-wide DNA copy number aberrations in canine and human OS. Our findings support and build upon the high level of cytogenetic complexity, through the identification of shared regions of microaberration (<500 kb) and functional analysis of possible orthologous OS-associated genes to pinpoint the cellular processes most commonly affected by aberration in human and canine OS. Aberrant regions contained previously reported genes such as CDC5L, MYC, RUNX2, and CDKN2A/CDKN2B, while expanding the gene of interest list to include ADAM15, CTC1, MEN1, CDK7, and others. Such regions of instability may thus have functional significance in the etiology of OS, the most common primary bone tumor in both species.

Animal models of osteosarcoma

Appendicular osteosarcoma (OS) is a primary mesenchymal tumor arising from malignantly transformed osteoblasts. In people, OS is the most common nonhematopoietic, primary skeletal neoplasm diagnosed in adolescents and is the second leading cause of cancer-related fatalities within this age group. Despite aggressive therapeutic management, including limb-sparing surgeries and dose-intense systemic chemotherapies, 30-40% of patients will experience progressive metastatic disease within 5 years of diagnosis. In order to reduce the fatality rate associated with recurrent or metastatic OS, a more thorough understanding of OS pathogenesis and biology is required. Towards this pursuit, comparative animal models of OS have been developed and are actively being studied to expand our fundamental understanding of OS. It is anticipated that specific animal models of OS, which most accurately recapitulate the natural disease process in people, will be most useful for advancing our understanding of OS biology, and will facilitate the discovery of disease pathogenesis and the identification of novel therapeutic strategies for managing this lethal metastatic bone sarcoma.

Oncostatin M promotes STAT3 activation, VEGF production, and invasion in osteosarcoma cell lines

Background

We have previously demonstrated that both canine and human OSA cell lines, as well as 8 fresh canine OSA tumor samples, exhibit constitutive phosphorylation of STAT3, and that this correlates with enhanced expression of matrix metalloproteinase-2 (MMP2). While multiple signal transduction pathways can result in phosphorylation of STAT3, stimulation of the cytokine receptor gp130 through either IL-6 or Oncostatin M (OSM) is the most common mechanism through which STAT3 is activated. The purpose of this study was to evaluate the role of IL-6 and OSM stimulation on both canine and human OSA cell lines to begin to determine the role of these cytokines in the biology of OSA.

Methods

RT-PCR and Western blotting were used to interrogate the consequences of OSM and IL-6 stimulation of OSA cell lines. OSA cells were stimulated with OSM and/or hepatocyte growth factor (HGF) and the effects on MMP2 activity (gel zymography), proliferation (CyQUANT), invasion (Matrigel transwell assay), and VEGF production (Western blotting, ELISA) were assessed. The small molecule STAT3 inhibitor LLL3 was used to investigate the impact of STAT3 inhibition following OSM stimulation of OSA cells.

Results

Our data demonstrate that the OSM receptor (OSMR), but not IL-6 or its receptor, is expressed by all human and canine OSA cell lines and canine OSA tumor samples; additionally, OSM expression was noted in all tumor samples. Treatment of OSA cell lines with OSM induced phosphorylation of STAT3, Src, and JAK2. OSM stimulation also resulted in a dose dependent increase in MMP2 activity and VEGF expression that was markedly reduced following treatment with the small molecule STAT3 inhibitor LLL3. Lastly, OSM stimulation of OSA cell lines enhanced invasion through Matrigel, particularly in the presence of rhHGF. In contrast, both OSM and HGF stimulation of OSA cell lines did not alter their proliferative capacity.

Conclusions

These data indicate OSM stimulation of human and canine OSA cells induces STAT3 activation, thereby enhancing the expression/activation of MMP2 and VEGF, ultimately promoting invasive behavior and tumor angiogenesis. As such, OSM and its receptor may represent a novel target for therapeutic intervention in OSA.

Prognostic and predictive biomarkers of canine osteosarcoma

Canine osteosarcoma (OS) is an aggressive tumour that accounts for approximately 90% of primary bone tumours in the dog. Although the standard treatments (including limb amputation/sparing, chemotherapy and palliative radiotherapy) have significantly increased survival rates, almost 90% of animals will eventually develop predominantly pulmonary metastases. Despite advances in various therapies, prognosis remains poor, with median survival times ranging from 3 months to 1 year and <20% of dogs survive for >2 years following diagnosis. Various clinical and epidemiological markers have facilitated decision-making with respect to therapy but no single molecular biomarker has been shown to enhance prediction of disease progression. The publication of the canine genome in 2005 raised the possibility of increasing understanding of the genetic mechanisms underpinning canine OS. This review explores the use of biomarkers within the multi-disciplinary management of dogs with OS, and highlights the few known, potential prognostic/predictive molecular markers including their potential value as 'bridging biomarkers' for human OS. Although high-throughput profiling of canine OS remains in its infancy, research within the next decade using leading-edge screening technologies has the potential to identify biomarkers that may enhance diagnostic and prognostic accuracy and result in more effective, individually tailored, treatment and management protocols for affected dogs.

Canine tumor cross-species genomics uncovers targets linked to osteosarcoma progression

BACKGROUND

Pulmonary metastasis continues to be the most common cause of death in osteosarcoma. Indeed, the 5-year survival for newly diagnosed osteosarcoma patients has not significantly changed in over 20 years. Further understanding of the mechanisms of metastasis and resistance for this aggressive pediatric cancer is necessary. Pet dogs naturally develop osteosarcoma providing a novel opportunity to model metastasis development and progression. Given the accelerated biology of canine osteosarcoma, we hypothesized that a direct comparison of canine and pediatric osteosarcoma expression profiles may help identify novel metastasis-associated tumor targets that have been missed through the study of the human cancer alone.

RESULTS

Using parallel oligonucleotide array platforms, shared orthologues between species were identified and normalized. The osteosarcoma expression signatures could not distinguish the canine and human diseases by hierarchical clustering. Cross-species target mining identified two genes, interleukin-8 (IL-8) and solute carrier family 1 (glial high affinity glutamate transporter), member 3 (SLC1A3), which were uniformly expressed in dog but not in all pediatric osteosarcoma patient samples. Expression of these genes in an independent population of pediatric osteosarcoma patients was associated with poor outcome (p = 0.020 and p = 0.026, respectively). Validation of IL-8 and SLC1A3 protein expression in pediatric osteosarcoma tissues further supported the potential value of these novel targets. Ongoing evaluation will validate the biological significance of these targets and their associated pathways.

CONCLUSIONS

Collectively, these data support the strong similarities between human and canine osteosarcoma and underline the opportunities provided by a comparative oncology approach as a means to improve our understanding of cancer biology and therapies.

Expression of receptor tyrosine kinases VEGFR-1 (FLT-1), VEGFR-2 (KDR), EGFR-1, PDGFRalpha and c-Met in canine primary brain tumours

Inhibition of tumour growth and angiogenesis by targeting key growth factor receptors is a promising therapeutic strategy for central nervous system tumours. Characterization of these growth factor receptors in canine primary brain tumours has not been done. Using quantitative real-time TaqMan polymerase chain reaction (PCR), we evaluated the expression of messenger RNA (mRNA) for five tyrosine kinase growth factor receptors (vascular endothelial growth factor receptor [VEGFR]-1, VEGFR-2, endothelial growth factor receptor [EGFR]-1, platelet-derived growth factor receptor a [PDGFRa], and c-Met) relative to normal cerebral cortex in 66 spontaneous canine primary brain tumours. Increased expression of VEGFR-1 and VEGFR-2 mRNA was greatest in grade IV astrocytomas (glioblastoma multiforme) and grade III (anaplastic) oligodendrogliomas. EGFR-1 mRNA expression was more consistently increased than the other receptors in all tumour types, while increased PDGFRa mRNA expression was mostly restricted to oligodendrogliomas. The similarities in increased expression of these tyrosine kinase growth factor receptors in these canine tumours, as compared to data from their human counterparts, suggest that common molecular mechanisms may be present.

A novel small molecule Met inhibitor, PF2362376, exhibits biological activity against osteosarcoma

The receptor tyrosine kinase Met is dysregulated in several human cancers including osteosarcoma (OSA) in which overexpression is a negative prognostic indicator and enforced Met expression in normal osteoblasts leads to genomic instability and malignant transformation. Met is also known to be inappropriately expressed in canine OSA tumour samples and cell lines. The purpose of this study was to evaluate the potential utility of an orally bioavailable small molecule Met inhibitor, PF2362376, against canine OSA cell lines as a prelude to future clinical work. PF2362376 inhibited phosphorylation of Met, Gab-1, Erk and Akt, but not of Src or STAT3. Furthermore, PF2362376 inhibited proliferation of canine OSA cell lines and induced cell death at biologically achievable concentrations. Last, activities associated with Met signalling including migration, invasion, branching morphogenesis and colony formation in soft agar were blocked by PF2362376. These studies support the notion that Met is a relevant target for therapeutic intervention in OSA.

Characterization, expression and function of c-Met in canine spontaneous cancers

Aberrant expression of the proto-oncogene c-Met has been noted in a variety of human cancers. To better define the potential role of Met dysregulation in canine cancer, the canine Met, hepatocyte growth factor (HGF) and HGF activator were cloned. Inappropriate expression of Met was present in canine tumour cell lines derived from a wide variety of cancers. Furthermore, both HGF and HGF activator were also expressed in several of these cell lines, providing evidence of a possible autocrine loop of Met activation. Stimulation of tumour cell lines with recombinant human HGF induced Met autophosphorylation, as well as activation of the downstream signalling elements Gab-1, Akt and Erk1/2. Scattering of tumour cells and migration across a defect occurred in response to HGF stimulation. The Met inhibitor PHA665752 blocked both HGF-induced phosphorylation of canine Met and HGF-mediated cell cycling, scattering and migration. These studies provide evidence that Met dysregulation may play a role in the biology of canine cancer and lay the groundwork for future studies employing Met inhibitors.

Expression of hepatocyte growth factor and the proto-oncogenic receptor c-Met in canine osteosarcoma

Hepatocyte growth factor (HGF) and the proto-oncogenic receptor c-Met are implicated in growth, invasion, and metastasis in human cancer. Little information is available on the expression and role of both gene products in canine osteosarcoma. We hypothesized that the expression of c-Met is associated with malignant histologic characteristics, a short survival time, and a reduced disease-free interval in canine osteosarcoma. Quantitative real-time polymerase chain reaction was used to analyze the messenger RNA (mRNA) expression of both HGF and c-Met in 59 canine osteosarcoma samples. The relationship between HGF and c-Met expression, patient outcome, and histologic characteristics of the tumor were studied. Western blot analysis was performed to investigate the presence of active HGF protein. The expression pattern of c-Met in 16 slides of canine osteosarcoma was identified by immunohistochemistry. Coexpression of HGF and c-Met mRNA in all canine osteosarcoma samples suggested autocrine or paracrine receptor activation. A significant, moderately positive correlation was found between c-Met and HGF mRNA expression. c-Met mRNA expression was not associated with survival time or disease-free interval. Expression of c-Met was significantly associated with metastasis via the lymphogenic route. Immunolabeling with c-Met revealed a cytoplasmic staining pattern in all osteosarcoma cell types. In this study, c-Met mRNA expression in canine osteosarcoma was found to be of no influence on survival time and disease-free interval. Further studies are necessary to confirm the involvement of the c-Met pathway in the lymphogenic route of metastasis.

Molecular Cloning of the Canine c-Met/HGF Receptor and Its Expression in Normal and Regenerated Liver

The c-Met proto-oncogene is the receptor for hepatocyte growth factor (HGF), which is a member of the tyrosine kinase family. Activation of the HGF/c-Met signal pathway leads to cell proliferation, motility, regeneration, and morphogenesis. In this study, the complete nucleotide sequence of complementary DNA (cDNA) of canine c-Met was cloned, and its distribution was determined in tissues. The canine c-Met cDNA clone had an open reading frame of 4419 bp that encoded a putative polypeptide of 1383 amino acids. The c-Met mRNA was expressed in a variety of canine tissues including peripheral blood mononuclear cells (PBMC), bone marrow, liver, kidney, lung, stomach, uterus, testis, thymus, lymph node, small intestine, colon, adrenal gland, thyroid gland, heart, muscle, skin, pancreas, ovary, prostate, spleen, fat, cerebrum, and cerebellum. In addition, the c-Met mRNA expression in normal and regenerated liver was examined. The levels of the mRNA increased 2-fold in regenerated liver compared to that found in normal liver, indicating that c-Met is involved in various functions including remodeling of canine hepatocytes.

c-Met tyrosine kinase receptor expression and function in human and canine osteosarcoma cells

To further characterize the role of hepatocyte growth factor-scatter factor (HGF-SF) and its receptor (c-Met) in osteosarcoma (OS), human OS cell lines with low (SAOS-2) and high (SAOS-LM2) metastatic potential, and cell lines derived from spontaneous canine OS were studied. All cell lines were evaluated for c-Met and HGF-SF expression and receptor activation using Northern, RT-PCR, and Western blot analyses, respectively. Functional activity of receptor-ligand interaction was measured using c-Met phosphorylation status, proliferation assays (anchorage-dependent and -independent), Matrigel invasion, modulation of urokinase plasminogen activator (uPA) expression, and cell dispersion (scattering). All cell lines exhibited steady-state mRNA expression of c-Met. The canine OS cell lines also expressed HGF-SF mRNA as determined by RT-PCR analysis. Western analysis showed c-Met protein expression and HGF-stimulated (human) or constitutive (canine) receptor autophosphorylation. Treatment with recombinant human HGF resulted in enhanced proliferation in 3 of 5 OS cell lines and enhanced colony formation in 2 of 5 OS cell lines. Matrigel invasion was significantly enhanced in 3 of the cell lines and uPA levels were significantly increased in the SAOS-2 cells following HGF treatment. Scattering was enhanced in both the SAOS-2 and SAOS-LM2 cells. These data support the involvement of c-Met and HGF-SF in the growth and progression of human and canine OS, and may offer new targets for the development of therapeutic strategies for OS.

Update on the biology and management of canine osteosarcoma

Osteosarcoma (OSA) is the most common primary bone tumor diagnosed in dogs. Our understanding of the risk factors and genetic changes in canine OSA patients is growing, but specific, innovative therapeutic strategies are slow in coming. Appendicular skeletal osteosarcoma, the most frequent form of this disease, is typically seen in large to giant breeds, with males being overrepresented in most reports. Axial skeletal OSA is less common than appendicular OSA, but the biologic behavior of the disease is equally aggressive in all skeletal sites except for the mandible. Though the current standard of care for dogs with osteosarcoma remains surgical resection of the affected site, followed by chemotherapy with either a platinum- (cisplatin or carboplatin) or doxorubicin-based protocol, novel therapies are being actively investigated.