Establishment and characterization of a new highly metastatic human osteosarcoma cell line

Minnelide reduces tumor burden in preclinical models of osteosarcoma

Osteosarcoma is the most common bone cancer in children and adolescents with a 5-year survival rate of about 70%. In this study, we have evaluated the preclinical therapeutic efficacy of the novel synthetic drug, Minnelide, a prodrug of triptolide on osteosarcoma. Triptolide was effective in significantly inducing apoptosis in all osteosarcoma cell lines tested but had no significant effect on the human osteoblast cells. Notably, Minnelide treatment significantly reduced tumor burden and lung metastasis in the orthotopic and lung colonization models. Triptolide/Minnelide effectively downregulated the levels of pro-survival proteins such as heat shock proteins, cMYC, survivin and targets the NF-κB pathway.

HES1, a target of Notch signaling, is elevated in canine osteosarcoma, but reduced in the most aggressive tumors

BACKGROUND

Hairy and enhancer of split 1 (HES1), a basic helix-loop-helix transcriptional repressor, is a downstream target of Notch signaling. Notch signaling and HES1 expression have been linked to growth and survival in a variety of human cancer types and have been associated with increased metastasis and invasiveness in human osteosarcoma cell lines. Osteosarcoma (OSA) is an aggressive cancer demonstrating both high metastatic rate and chemotherapeutic resistance. The current study examined expression of Notch signaling mediators in primary canine OSA tumors and canine and human osteosarcoma cell lines to assess their role in OSA development and progression.

RESULTS

Reverse transcriptase - quantitative PCR (RT-qPCR) was utilized to quantify HES1, HEY1, NOTCH1 and NOTCH2 gene expression in matched tumor and normal metaphyseal bone samples taken from dogs treated for appendicular OSA at the Colorado State University Veterinary Teaching Hospital. Gene expression was also assessed in tumors from dogs with a disease free interval (DFI) of <100 days compared to those with a DFI > 300 days following treatment with surgical amputation followed by standard chemotherapy. Immunohistochemistry was performed to confirm expression of HES1. Data from RT-qPCR and immunohistochemical (IHC) experiments were analyzed using REST2009 software and survival analysis based on IHC expression employed the Kaplan-Meier method and log rank analysis. Unbiased clustered images were generated from gene array analysis data for Notch/HES1 associated genes. Gene array analysis of Notch/HES1 associated genes suggested alterations in the Notch signaling pathway may contribute to the development of canine OSA. HES1 mRNA expression was elevated in tumor samples relative to normal bone, but decreased in tumor samples from dogs with a DFI < 100 days relative to those with a DFI > 300 days. NOTCH2 and HEY1 mRNA expression was also elevated in tumors relative to normal bone, but was not differentially expressed between the DFI tumor groups. Survival analysis confirmed an association between decreased HES1 immunosignal and shorter DFI.

CONCLUSIONS

Our findings suggest that activation of Notch signaling occurs and may contribute to the development of canine OSA. However, association of low HES1 expression and shorter DFI suggests that mechanisms that do not alter HES1 expression may drive the most aggressive tumors.

Tetrandrine Suppresses Cancer Angiogenesis and Metastasis in 4T1 Tumor Bearing Mice

Metastasis remains the most deadly aspect of cancer and still evades direct treatment. Thus, there is a great need to develop new treatment regimens to suppress tumor cells that have escaped surgical removal or that may have already disseminated. We have found that tetrandrine (TET) exhibits anticolon cancer activity. Here, we investigate the inhibition effect of TET to breast cancer metastasis, angiogenesis and its molecular basis underlying TET's anticancer activity. We compare TET with chemotherapy drug doxorubicin in 4T1 tumor bearing BALB/c mice model and find that TET exhibits an anticancer metastatic and antiangiogenic activities better than those of doxorubicin. The lung metastatic sites were decreased by TET, which is confirmed by bioluminescence imaging in vivo. On the other hand, laser doppler perfusion imaging (LDI) was used for measuring the blood flow of tumor in 4T1-tumor bearing mice. As a result, the local blood perfusion of tumor was markedly decreased by TET after 3 weeks. Mechanistically, TET treatment leads to a decrease in p-ERK level and an increase in NF-κB levels in HUVECs. TET also regulated metastatic and angiogenic related proteins, including vascular endothelial growth factor, hypoxia-inducible factor-1α, integrin β5, endothelial cell specific molecule-1, and intercellular adhesion molecule-1 in vivo.

IGFBP5 domains exert distinct inhibitory effects on the tumorigenicity and metastasis of human osteosarcoma

Osteosarcoma (OS) is the most common primary malignancy of bone. We investigated the roles of insulin-like growth factor binding protein 5 (IGFBP5) domains in modulating OS tumorigenicity and metastasis. The N-terminal (to a lesser extent the C-terminal) domain inhibited cell proliferation and induced apoptosis while the C-terminal domain inhibited cell migration and invasion. The Linker domain had no independent effects. In vivo, the N-terminal domain decreased tumor growth without affecting pulmonary metastases while the C-terminal domain inhibited tumor growth and metastases. In summary, the N- and C-terminal domains modulated OS tumorigenic phenotypes while the C-terminal domain inhibited OS metastatic phenotypes.

Ginseng saponin metabolite 20(S)-protopanaxadiol inhibits tumor growth by targeting multiple cancer signaling pathways

Plant-derived active constituents and their semi-synthetic or synthetic analogs have served as major sources of anticancer drugs. 20(S)-protopanaxadiol (PPD) is a metabolite of ginseng saponin of both American ginseng (Panax quinquefolius L.) and Asian ginseng (Panax ginseng C.A. Meyer). We previously demonstrated that ginsenoside Rg3, a glucoside precursor of PPD, exhibits anti-proliferative effects on HCT116 cells and reduces tumor size in a xenograft model. Our subsequent study indicated that PPD has more potent antitumor activity than that of Rg3 in vitro although the mechanism underlying the anticancer activity of PPD remains to be defined. Here, we investigated the mechanism underlying the anticancer activity of PPD in human cancer cells in vitro and in vivo. PPD was shown to inhibit growth and induce cell cycle arrest in HCT116 cells. The in vivo studies indicate that PPD inhibits xenograft tumor growth in athymic nude mice bearing HCT116 cells. The xenograft tumor size was significantly reduced when the animals were treated with PPD (30 mg/kg body weight) for 3 weeks. When the expression of previously identified Rg3 targets, A kinase (PRKA) anchor protein 8 (AKAP8L) and phosphatidylinositol transfer protein α (PITPNA), was analyzed, PPD was shown to inhibit the expression of PITPNA while upregulating AKAP8L expression in HCT116 cells. Pathway-specific reporter assays indicated that PPD effectively suppressed the NF-κB, JNK and MAPK/ERK signaling pathways. Taken together, our results suggest that the anticancer activity of PPD in colon cancer cells may be mediated through targeting NF-κB, JNK and MAPK/ERK signaling pathways, although the detailed mechanisms underlying the anticancer mode of PPD action need to be fully elucidated.

Bone morphogenetic protein 4 (BMP4) is required for migration and invasion of breast cancer

Bone-morphogenetic proteins (BMPs) play an important role in development and many cellular processes. However, their functional role in the development and progression of breast cancer is not clearly understood. In the present study, we performed a systematic expression analysis of the 14 types of BMPs in 10 human breast cancer cell lines. We found that bone morphogenetic protein 4 (BMP4) was one of the most frequently expressed BMPs. Furthermore, the expression level of BMP4 was maybe correlated with the metastatic potential of the cancer lines. Accordingly, overexpression of BMP4 in the breast cancer cell lines MCF-7 and MBA-MD-231 promoted the migration and invasion phenotypes of the cancer cells, whereas RNAi-mediated knockdown of BMP4 expression inhibited the migration and invasion activities of the cancer cells. To identify the important factors that may mediate the BMP4 functions in breast cancer cells, we analyzed a panel of cancer-related genes, and found that the expression of matrix metalloproteinase-1 (MMP-1) and C-X-C chemokine receptor type 4 (CXCR4) sharply increased at both the mRNA and protein levels in the breast cancer cells overexpressing BMP4. Interestingly, when breast cancer cells MDA-MB-231 or MCF-7 were co-cultured with the osteoblast-like cells MG63 to mimic a bone metastasis microenvironment, BMP4 did not exhibit any significant effect on the expression of OPG or RANKL, two important factors in bone remodeling. BMPs antagonists, Noggin, parallel inhibited breast cancer cell migration and invasion and induced bone remodeling. Taken together, our results strongly suggest that BMP4 may promote the migration and invasion of breast cancer cells, at least in part by up-regulating the expressions of MMP-1 and CXCR4. It is conceivable that novel therapeutics for breast cancer may be developed by targeting BMP4 signaling pathway and/or its important downstream mediators in breast cancer cells.

Dysregulation of ezrin phosphorylation prevents metastasis and alters cellular metabolism in osteosarcoma

Ezrin links the plasma membrane to the actin cytoskeleton where it plays a pivotal role in the metastatic progression of several human cancers; however, the precise mechanistic basis for its role remains unknown. Here, we define transitions between active (phosphorylated open) and inactive (dephosphorylated closed) forms of Ezrin that occur during metastatic progression in osteosarcoma. In our evaluation of these conformations we expressed C-terminal mutant forms of Ezrin that are open (phosphomimetic T567D) or closed (phosphodeficient T567A) and compared their biologic characteristics to full-length wild-type Ezrin in osteosarcoma cells. Unexpectedly, cells expressing open, active Ezrin could form neither primary orthotopic tumors nor lung metastases. In contrast, cells expressing closed, inactive Ezrin were also deficient in metastasis but were unaffected in their capacity for primary tumor growth. By imaging single metastatic cells in the lung, we found that cells expressing either open or closed Ezrin displayed increased levels of apoptosis early after their arrival in the lung. Gene expression analysis suggested dysregulation of genes that are functionally linked to carbohydrate and amino acid metabolism. In particular, cells expressing closed, inactive Ezrin exhibited reduced lactate production and basal or ATP-dependent oxygen consumption. Collectively, our results suggest that dynamic regulation of Ezrin phosphorylation at amino acid T567 that controls structural transitions of this protein plays a pivotal role in tumor progression and metastasis, possibly in part by altering cellular metabolism.

Cell growth inhibition and apoptotic effect of the rexinoid 6-OH-11-O-hydroxyphenantrene on human osteosarcoma and mesenchymal stem cells

Natural derivatives of vitamin A, including all-trans-retinoic acid (ATRA), commonly known as retinoids, currently produce favorable results in the treatment of many types of tumors. The rexinoid 6-OH-11-O-hydroxyphenantrene (IIF) is a synthetic derivative of ATRA. Previous in vitro and in vivo studies demonstrated that IIF is able to induce growth inhibition of various cancer cells and is a potent apoptosis-inducing agent with clinical potential. Osteosarcoma (OS) is the most common type of bone cancer, characterized by a rising aggressiveness. Recent evidences suggest that mesenchymal stem cells (MSC) may favour tumor growth and progression. Thus, it is important to investigate whether a compound with potential anti-tumoral properties such as IIF affects not only tumor cells but also MSC. The current study is an attempt to understand the mode of the potential cytotoxicity of IIF on OS cells and MSC. The response to IIF treatment of osteosarcoma SaOS-2, MG63, and U2OS cells and of bone marrow-derived MSC was the subject of investigation. The results showed that IIF significantly inhibited cell growth in OS cell lines and MSC in both a time- and dose-dependent manner, as evaluated by methylene blue assay. This was also associated with altered cell morphology and an increase in cell death with the involvement of apoptosis as demonstrated by NucleoCounter, Hoechst 33342 staining and FACS analysis. No cell death and apoptosis was found in U2OS cells. Analysis of cells treated with 20 and 40μM IIF for 24h by western blot suggests the activation of initiator caspase 9, indicating the involvement of caspases in inducing apoptosis. Furthermore, IIF upregulated the expression of the pro-apoptotic protein Bax and downregulated the anti-apoptotic protein Bcl2. For the first time, our results collectively provide an evidence for cell growth inhibition and activation of apoptosis in human OS cells and MSC by IIF. These results confirm that IIF may be an effective compound for anticancer treatment, including that of OS.

Generation of chordoma cell line JHC7 and the identification of Brachyury as a novel molecular target

OBJECT

Chordoma is a malignant bone neoplasm hypothesized to arise from notochordal remnants along the length of the neuraxis. Recent genomic investigation of chordomas has identified T (Brachyury) gene duplication as a major susceptibility mutation in familial chordomas. Brachyury plays a vital role during embryonic development of the notochord and has recently been shown to regulate epithelial-to-mesenchymal transition in epithelial-derived cancers. However, current understanding of the role of this transcription factor in chordoma is limited due to the lack of availability of a fully characterized chordoma cell line expressing Brachyury. Thus, the objective of this study was to establish the first fully characterized primary chordoma cell line expressing gain of the T gene locus that readily recapitulates the original parental tumor phenotype in vitro and in vivo.

METHODS

Using an intraoperatively obtained tumor sample from a 61-year-old woman with primary sacral chordoma, a chordoma cell line (JHC7, or Johns Hopkins Chordoma Line 7) was established. Molecular characterization of the primary tumor and cell line was conducted using standard immunostaining and Western blotting. Chromosomal aberrations and genomic amplification of the T gene in this cell line were determined. Using this cell line, a xenograft model was established and the histopathological analysis of the tumor was performed. Silencing of Brachyury and changes in gene expression were assessed.

RESULTS

The authors report, for the first time, the successful establishment of a chordoma cell line (JHC7) from a patient with pathologically confirmed sacral chordoma. This cell line readily forms tumors in immunodeficient mice that recapitulate the parental tumor phenotype with conserved histological features consistent with the parental tumor. Furthermore, it is demonstrated for the first time that silencing of Brachyury using short hairpin RNA renders the morphology of chordoma cells to a more differentiated-like state and leads to complete growth arrest and senescence with an inability to be passaged serially in vitro.

CONCLUSIONS

This report represents the first xenograft model of a sacral chordoma line described in the literature and the first cell line established with stable Brachyury expression. The authors propose that Brachyury is an attractive therapeutic target in chordoma and that JHC7 will serve as a clinically relevant model for the study of this disease.

Insulin-like growth factor binding protein 5 suppresses tumor growth and metastasis of human osteosarcoma

Osteosarcoma (OS) is the most common primary malignancy of bone. There is a critical need to identify the events that lead to the poorly understood mechanism of OS development and metastasis. The goal of this investigation is to identify and characterize a novel marker of OS progression. We have established and characterized a highly metastatic OS subline that is derived from the less metastatic human MG63 line through serial passages in nude mice via intratibial injections. Microarray analysis of the parental MG63, the highly metastatic MG63.2 subline, as well as the corresponding primary tumors and pulmonary metastases revealed insulin-like growth factor binding protein 5 (IGFBP5) to be one of the significantly downregulated genes in the metastatic subline. Confirmatory quantitative RT-PCR on 20 genes of interest demonstrated IGFBP5 to be the most differentially expressed and was therefore chosen to be one of the genes for further investigation. Adenoviral mediated overexpression and knockdown of IGFBP5 in the MG63 and MG63.2 cell lines, as well as other OS lines (143B and MNNG/HOS) that are independent of our MG63 lines, were employed to examine the role of IGFBP5. We found that overexpression of IGFBP5 inhibited in vitro cell proliferation, migration and invasion of OS cells. Additionally, IGFBP5 overexpression promoted apoptosis and cell cycle arrest in the G1 phase. In an orthotopic xenograft animal model, overexpression of IGFBP5 inhibited OS tumor growth and pulmonary metastases. Conversely, siRNA-mediated knockdown of IGFBP5 promoted OS tumor growth and pulmonary metastases in vivo. Immunohistochemical staining of patient-matched primary and metastatic OS samples demonstrated decreased IGFBP5 expression in the metastases. These results suggest 1) a role for IGFBP5 as a novel marker that has an important role in the pathogenesis of OS, and 2) that the loss of IGFBP5 function may contribute to more metastatic phenotypes in OS.

Lysophosphatidic acid acyltransferase β (LPAATβ) promotes the tumor growth of human osteosarcoma

Background

Osteosarcoma is the most common primary malignancy of bone with poorly characterized molecular pathways important in its pathogenesis. Increasing evidence indicates that elevated lipid biosynthesis is a characteristic feature of cancer. We sought to investigate the role of lysophosphatidic acid acyltransferase β (LPAATβ, aka, AGPAT2) in regulating the proliferation and growth of human osteosarcoma cells. LPAATβ can generate phosphatidic acid, which plays a key role in lipid biosynthesis as well as in cell proliferation and survival. Although elevated expression of LPAATβ has been reported in several types of human tumors, the role of LPAATβ in osteosarcoma progression has yet to be elucidated.

Methodology/Principal Findings

Endogenous expression of LPAATβ in osteosarcoma cell lines is analyzed by using semi-quantitative PCR and immunohistochemical staining. Adenovirus-mediated overexpression of LPAATβ and silencing LPAATβ expression is employed to determine the effect of LPAATβ on osteosarcoma cell proliferation and migration in vitro and osteosarcoma tumor growth in vivo. We have found that expression of LPAATβ is readily detected in 8 of the 10 analyzed human osteosarcoma lines. Exogenous expression of LPAATβ promotes osteosarcoma cell proliferation and migration, while silencing LPAATβ expression inhibits these cellular characteristics. We further demonstrate that exogenous expression of LPAATβ effectively promotes tumor growth, while knockdown of LPAATβ expression inhibits tumor growth in an orthotopic xenograft model of human osteosarcoma.

Conclusions/Significance

Our results strongly suggest that LPAATβ expression may be associated with the aggressive phenotypes of human osteosarcoma and that LPAATβ may play an important role in regulating osteosarcoma cell proliferation and tumor growth. Thus, targeting LPAATβ may be exploited as a novel therapeutic strategy for the clinical management of osteosarcoma. This is especially attractive given the availability of selective pharmacological inhibitors.

Tetrandrine inhibits Wnt/β-catenin signaling and suppresses tumor growth of human colorectal cancer

As one of the most common malignancies, colon cancer is initiated by abnormal activation of the Wnt/β-catenin pathway. Although the treatment options have increased for some patients, overall progress has been modest. Thus, there is a great need to develop new treatments. We have found that bisbenzylisoquinoline alkaloid tetrandrine (TET) exhibits anticancer activity. TET is used as a calcium channel blocker to treat hypertensive and arrhythmic conditions in Chinese medicine. Here, we investigate the molecular basis underlying TET's anticancer activity. We compare TET with six chemotherapy drugs in eight cancer lines and find that TET exhibits comparable anticancer activities with camptothecin, vincristine, paclitaxel, and doxorubicin, and better than that of 5-fluorouracil (5-FU) and carboplatin. TET IC₅₀ is ≤5 μM in most of the tested cancer lines. TET exhibits synergistic anticancer activity with 5-FU and reduces migration and invasion capabilities of HCT116 cells. Furthermore, TET induces apoptosis and inhibits xenograft tumor growth of colon cancer. TET treatment leads to a decrease in β-catenin protein level in xenograft tumors, which is confirmed by T-cell factor/lymphocyte enhancer factor and c-Myc reporter assays. It is noteworthy that HCT116 cells with allelic oncogenic β-catenin deleted are less sensitive to TET-mediated inhibition of proliferation, viability, and xenograft tumor growth. Thus, our findings strongly suggest that the anticancer effect of TET in colon cancer may be at least in part mediated by targeting β-catenin activity. Therefore, TET may be used alone or in combination as an effective anticancer agent.

Synergistic antitumor effect of the activated PPARgamma and retinoid receptors on human osteosarcoma

PURPOSE

Osteosarcoma is the most common primary malignancy of bone. The long-term survival of osteosarcoma patients hinges on our ability to prevent and/or treat recurrent and metastatic lesions. Here, we investigated the activation of peroxisome proliferator-activated receptor gamma (PPARgamma) and retinoid receptors as a means of differentiation therapy for human osteosarcoma.

EXPERIMENTAL DESIGN

We examined the endogenous expression of PPARgamma and retinoid receptors in a panel of osteosarcoma cells. Ligands or adenovirus-mediated overexpression of these receptors were tested to inhibit proliferation and induce apoptosis of osteosarcoma cells. Osteosarcoma cells overexpressing the receptors were introduced into an orthotopic tumor model. The effect of these ligands on osteoblastic differentiation was further investigated.

RESULTS

Endogenous expression of PPARgamma and isotypes of retinoic acid receptor (RAR) and retinoid X receptor (RXR) is detected in most osteosarcoma cells. Troglitazone, 9-cis retinoic acid (RA), and all-trans RA, as well as overexpression of PPARgamma, RARalpha, and RXRalpha, inhibit osteosarcoma cell proliferation and induce apoptosis. A synergistic inhibitory effect on osteosarcoma cell proliferation is observed between troglitazone and retinoids, as well as with the overexpression pairs of PPARgamma/RARalpha, or PPARgamma/RXRalpha. Overexpression of PPARgamma, RARalpha, RXRalpha, or in combinations inhibits osteosarcoma tumor growth and cell proliferation in vivo. Retinoids (and to a lesser extent, troglitazone) are shown to promote osteogenic differentiation of osteosarcoma cells and mesenchymal stem cells.

CONCLUSIONS

Activation of PPARgamma, RARalpha, and RXRalpha may act synergistically on inhibiting osteosarcoma cell proliferation and tumor growth, which is at least partially mediated by promoting osteoblastic differentiation of osteosarcoma cells.