Genomic imbalances associated with methotrexate resistance in human osteosarcoma cell lines detected by comparative genomic hybridization-based techniques

Chelerythrine Inhibits Stemness of Cancer Stem-Like Cells of Osteosarcoma and PI3K/AKT/mTOR Signal

Chelerythrine (CHE) is widely found in many herbs and is the main alkaloid constituent of Toddalia asiatica (L.) LAM. It has been proved to exert remarkable antitumor, antifungal, anti-inflammatory, and antiparasitic effects. In osteosarcoma, CHE is reported to inhibit proliferation and promote apoptosis. However, the effect of CHE on cancer stem-like cells (CSCs), which contribute to metastasis and recurrence in osteosarcoma, is still largely unknown. In this study, we investigated the effects of CHE on the stemness and malignant behaviors of CSCs derived from osteosarcoma cells. CSCs were enriched by culturing in serum-free medium. The effects of CHE on stemness were measured by detecting stemness factors and sphere formation ability. The effects of CHE on chemosensitivity to doxorubicin and MTX were measured by Annexin V-FITC/PI double staining. The effects of CHE on CSC malignancy were measured by performing CCK-8, colony formation, tumor formation in soft agar, migration, and invasion assays. We first enriched CSCs from osteosarcoma cells, which were characterized by upregulated stemness markers, including Oct4, Nanog, and Nestin. The addition of CHE clearly decreased malignant behaviors, including colony formation, tumor formation in soft agar, migration, and invasion. CHE also inhibited stemness and thus induced the failure of sphere formation. Moreover, CHE promoted apoptosis induced by chemo agents, including doxorubicin (DOX) and methotrexate (MTX). After CHE treatment, the protein expression of MMP-2/9 was significantly decreased, potentially inhibiting invasion. CHE also exhibited an inhibitory effect on the phosphorylation of PI3K, AKT, and mTOR, which is an upstream regulatory signaling pathway of MMP-2/9. In summary, CSCs derived from U2OS and MG-63 cells, CHE could inhibit the stemness and malignant behaviors of CSCs potentially by inhibiting the PI3K/AKT/mTOR signaling pathway.

Mechanisms of Resistance to Conventional Therapies for Osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor, mainly occurring in children and adolescents. Current standard therapy includes tumor resection associated with multidrug chemotherapy. However, patient survival has not evolved for the past decades. Since the 1970s, the 5-year survival rate is around 75% for patients with localized OS but dramatically drops to 20% for bad responders to chemotherapy or patients with metastases. Resistance is one of the biological processes at the origin of therapeutic failure. Therefore, it is necessary to better understand and decipher molecular mechanisms of resistance to conventional chemotherapy in order to develop new strategies and to adapt treatments for patients, thus improving the survival rate. This review will describe most of the molecular mechanisms involved in OS chemoresistance, such as a decrease in intracellular accumulation of drugs, inactivation of drugs, improved DNA repair, modulations of signaling pathways, resistance linked to autophagy, disruption in genes expression linked to the cell cycle, or even implication of the micro-environment. We will also give an overview of potential therapeutic strategies to circumvent resistance development.

Targeting Molecular Mechanisms Underlying Treatment Efficacy and Resistance in Osteosarcoma: A Review of Current and Future Strategies

Osteosarcoma is the most common primary malignant bone tumour in children and adolescents. Due to micrometastatic spread, radical surgery alone rarely results in cure. Introduction of combination chemotherapy in the 1970s, however, dramatically increased overall survival rates from 20% to approximately 70%. Unfortunately, large clinical trials aiming to intensify treatment in the past decades have failed to achieve higher cure rates. In this review, we revisit how the heterogenous nature of osteosarcoma as well as acquired and intrinsic resistance to chemotherapy can account for stagnation in therapy improvement. We summarise current osteosarcoma treatment strategies focusing on molecular determinants of treatment susceptibility and resistance. Understanding therapy susceptibility and resistance provides a basis for rational therapy betterment for both identifying patients that might be cured with less toxic interventions and targeting resistance mechanisms to sensitise resistant osteosarcoma to conventional therapies.

Development of a New Monochrome Multiplex qPCR Method for Relative Telomere Length Measurement in Cancer

Excess telomere shortening has been observed in most cancer cells. The telomere quantitative polymerase chain reaction (qPCR) assay has become an important tool for epidemiological studies examining the effects of aging, stress, and other factors on the length of telomeres. Current telomere qPCR methods analyze the relative length of telomeres by amplifying telomere sequence products and normalizing with single-copy gene products. However, the current telomere qPCR does not always reflect absolute telomere length in cancer DNA. Because of genomic instability in cancer cells, we hypothesized that the use of single-copy genes (scg) is less accurate for normalizing data in cancer DNA and that new primer sets are required to better represent relative telomere length in cancer DNA. We first confirmed that cancer cells had a different copy ratio among different scg, implying that DNA is aneuploid. By using the new primer sets that amplify multiple-copy sequences (mcs) throughout the genome, the telomere qPCR results showed that the mcs primers were interchangeable with the scg primers as reference primers in normal DNA. By comparing results from the traditional southern blotting method (as kilobases) and results from monochrome multiplex qPCR using the mcs primers (as T/M ratios), we verified that the T/M ratio is highly correlated with absolute telomere length from the southern blot analysis. Together, the mcs primers were able to represent the telomere lengths accurately in cancer DNA samples. These results would allow for analyses of telomeres within cancerous DNA and the development of new, less invasive diagnostic tools for cancer.

DHFR and MDR1 upregulation is associated with chemoresistance in osteosarcoma stem-like cells

Tumor-initiating cells (TICs) are defined as a specialized subset of cells with tumor-initiating capacity that can initiate tumor growth, tumor relapse and metastasis. In the present study, osteosarcoma TICs (OS-TICs) were isolated and enriched from the osteosarcoma U2OS and MG-63 cell lines using sphere formation assays and serum-depleted media. These enriched OS-TICs showed the expression of several typical cancer stemness markers, including octamer-binding transcription factor 4, Nanog homeobox, cluster of differentiation (CD)117, Nestin and CD133, and the expression of ATP binding cassette subfamily G member 2, multidrug resistance protein 1 (MDR1) and dihydrofolate reductase (DHFR). Notably, in vitro and in vivo tumorigenic properties were enhanced in these OS-TICs. Additionally, methotrexate and doxorubicin are the most widely used anticancer agents against osteosarcoma, and the observed enhanced chemoresistance of OS-TICs to these two agents could be associated with the upregulation of DHFR and MDR1. These findings suggest that the upregulation of DHFR and MDR1 is associated with the development of chemoresistance of OS-TICs.

Pharmacogenomics of genes involved in antifolate drug response and toxicity in osteosarcoma

INTRODUCTION

Antifolates are structural analogs of folates, which have been used as antitumor drugs for more than 60 years. The antifolate drug most commonly used for treating human tumors is methotrexate (MTX), which is utilized widely in first-line treatment protocols of high-grade osteosarcoma (HGOS). In addition to MTX, two other antifolates, trimetrexate and pemetrexed, have been tested in clinical settings for second-line treatment of recurrent HGOS with patients unfortunately showing modest activity. Areas covered: There is clinical evidence which suggsest that, like other chemotherapeutic agents, not all HGOS patients are equally responsive to antifolates and do not have the same susceptibility to experience adverse drug-related toxicities. Here, we summarize the pharmacogenomic information reported so far for genes involved in antifolate metabolism and transport and in MTX-related toxicity in HGOS patients. Expert opinion: Identification and validation of genetic biomarkers that significantly impact clinical antifolate treatment response and related toxicity may provide the basis for a future treatment modulation based on the pharmacogenetic and pharmacogenomic features of HGOS patients.

The pharmacogenomics of osteosarcoma

Osteosarcoma (OS), the most common malignant tumor of bone, is presently treated with multidrug neoadjuvant chemotherapy protocols, which allow to cure 60-65% of patients but also induce toxicity events that cannot be predicted or efficiently prevented. The identification and validation of pharmacogenomic biomarkers is, therefore, absolutely warranted to provide the bases for planning personalized treatments with the aim to increase the therapeutic benefits and to avoid or limit unnecessary toxicities. As several targeted therapies against molecular and immunological markers in OS are presently under clinical investigation, it may be speculated that some new agents for innovative treatments may emerge in the next years. However, the real improvement of therapeutic perspectives for OS is strictly connected to the identification of pharmacogenomic biomarkers that may stratify patients in responders or non-responders and identify those individuals with higher susceptibility to treatment-associated toxicity. This review provides an overview of the pharmacogenomic biomarkers identified so far in OS, which appear to be promising candidates for a translation to clinical practice, after further investigation and/or prospective validation.

Hippo/YAP signaling pathway is involved in osteosarcoma chemoresistance

Background

Osteosarcoma is the most common bone malignancy in children and adolescents, and 20%–30% of the patients suffer from poor prognosis because of individual chemoresistance. The Hippo/yes-associated protein (YAP) signaling pathway has been shown to play a role in tumor chemoresistance, but no previous report has focused on its involvement in osteosarcoma chemoresistance. This study aimed to investigate the role of the Hippo/YAP signaling pathway in osteosarcoma chemoresistance and to determine potential treatment targets.

Methods

Using the Cell Titer-Glo Luminescent cell viability assay and flow cytometry analysis, we determined the proliferation and chemosensitivity of YAP-overexpressing and YAP-knockdown osteosarcoma cells. In addition, using western blotting and the real-time polymerase chain reaction technique, we investigated the alteration of the Hippo/YAP signaling pathway in osteosarcoma cells treated with chemotherapeutic agents.

Results

Mammalian sterile 20-like kinase 1 (MST1) degradation was increased, and large tumor suppressor kinase 1/2 (LATS1/2) total protein levels were decreased by methotrexate and doxorubicin, which increased activation and nuclear translocation of YAP. Moreover, YAP increased the proliferation and chemoresistance of MG63 cells.

Conclusions

The Hippo/YAP signaling pathway plays a role in osteosarcoma chemoresistance, and YAP is a potential target for reducing chemoresistance.

Mechanisms of methotrexate resistance in osteosarcoma cell lines and strategies for overcoming this resistance

The aim of the present study was to investigate the underlying mechanisms of methotrexate (MTX) resistance in the human osteosarcoma cell line, Saos-2/MTX4.4, and to evaluate various methods of overcoming the resistance to this chemotherapeutic agent. MMT assays were performed to determine the resistance of the primary (Saos-2) and resistant (Saos-2/MTX4.4) cell lines to MTX, cisplatin [cis-diamminedichloroplatinum II (DDP)], ifosfamide (IFO), Adriamycin (ADM), epirubicin (EPI) and theprubicin (THP). The Saos-2/MTX4.4 cells exhibited a low resistance to IFO, ADM, EPI and THP; however, no resistance to DDP was identified. Overall, the Saos-2/MTX4.4 cells exhibited a greater resistance to all the chemotherapeutic agents investigated compared with the Saos-2 cells. Rhodamine 123 (R123) fluorescence was measured in the Saos-2/MTX4.4 and Saos-2 cells 30 and 60 min after the addition of R123, and R123 plus verapamil (VER). VER administration increased the intracellular accumulation of R123. In addition, reverse transcription-quantitative polymerase chain reaction was performed to determine the mRNA expression levels of multidrug resistance gene 1 (MDR1) in the two cell lines. Although the Saos-2/MTX4.4 cells were more resistant to the chemotherapeutic agents than the Saos-2 cells, no significant difference was identified between the relative mRNA expression levels of MDR1 in the Saos-2/MTX4.4 and Saos-2 cells (0.4350±0.0354 vs. 0.3886±0.0456; P>0.05).

Reexpression of LSAMP inhibits tumor growth in a preclinical osteosarcoma model

BACKGROUND

Osteosarcomas are the most common primary malignant tumors of bone, showing complex chromosomal rearrangements with multiple gains and losses. A frequent deletion within the chromosomal region 3q13.31 has been identified by us and others, and is mainly reported to be present in osteosarcomas. The purpose of the study was to further characterize the frequency and the extent of the deletion in an extended panel of osteosarcoma samples, and the expression level of the affected genes within the region. We have identified LSAMP as the target gene for the deletion, and have studied the functional implications of LSAMP-reexpression.

METHODS

LSAMP copy number, expression level and protein level were investigated by quantitative PCR and western blotting in an osteosarcoma panel. The expression of LSAMP was restored in an osteosarcoma cell line, and differences in proliferation rate, tumor formation, gene expression, migration rate, differentiation capabilities, cell cycle distribution and apoptosis were investigated by metabolic dyes, tumor formation in vivo, gene expression profiling, time-lapse photography, differentiation techniques and flow cytometry, respectively.

RESULTS

We found reduced copy number of LSAMP in 45/76 osteosarcoma samples, reduced expression level in 25/42 samples and protein expression in 9/42 samples. By restoring the expression of LSAMP in a cell line with a homozygous deletion of the gene, the proliferation rate in vitro was significantly reduced and tumor growth in vivo was significantly delayed. In response to reexpression of LSAMP, mRNA expression profiling revealed consistent upregulation of the genes hairy and enhancer of split 1 (HES1), cancer/testis antigen 2 (CTAG2) and kruppel-like factor 10 (KLF10).

CONCLUSIONS

The high frequency and the specificity of the deletion indicate that it is important for the development of osteosarcomas. The deletion targets the tumor suppressor LSAMP, and based on the functional evidence, the tumor suppressor function of LSAMP is most likely exerted by reducing the proliferation rate of the tumor cells, possibly by indirectly upregulating one or more of the genes HES1, CTAG2 or KLF10. To our knowledge, this study describes novel functions of LSAMP, a first step to understanding the functional role of this specific deletion in osteosarcomas.

Molecular mechanisms of chemoresistance in osteosarcoma (Review)

Due to the emergence of adjuvant and neoadjuvant chemotherapy, the survival rate has been greatly improved in osteosarcoma (OS) patients with localized disease. However, this survival rate has remained unchanged over the past 30 years, and the long-term survival rate for OS patients with metastatic or recurrent disease remains poor. To a certain extent, the reason behind this may be ascribed to the chemoresistance to anti-OS therapy. Chemoresistance in OS appears to be mediated by numerous mechanisms, which include decreased intracellular drug accumulation, drug inactivation, enhanced DNA repair, perturbations in signal transduction pathways, apoptosis- and autophagy-related chemoresistance, microRNA (miRNA) dysregulation and cancer stem cell (CSC)-mediated drug resistance. In addition, methods employed to circumvent these resistance mechanism have been shown to be effective in the treatment of OS. However, almost all the current studies on the mechanisms of chemoresistance in OS are in their infancy. Further studies are required to focus on the following aspects: i) Improving the delivery of efficacy through novel delivery patterns; ii) improving the understanding of the signal transduction pathways that regulate the proliferation and growth of OS cells; iii) elucidating the signaling pathways of autophagy and its association with apoptosis in OS cells; iv) utilizing high-throughput miRNA expression analysis to identify miRNAs associated with chemoresistance in OS; and v) identifying the role that CSCs play in tumor metastasis and in-depth study of the mechanism of chemoresistance in the CSCs of OS.

Array comparative genomic hybridization in osteosarcoma

Osteosarcoma, the most frequent primary bone tumor, is a malignant mesenchymal sarcoma with a peak incidence in young children and adolescents. Left untreated, it progresses relentlessly to local and systemic disease, ultimately leading to death within months. Genomically, osteosarcomas are aneuploid with chaotic karyotypes, lacking the pathognomonic genetic rearrangements characteristic of most sarcomas. The familial genetics of osteosarcoma helped in elucidating some of the etiological molecular disruptions, such as the tumor suppressor genes RB1 in retinoblastoma and TP53 in Li-Fraumeni, and RECQL4 involved in DNA repair/replication in Rothmund-Thomson syndrome. Genomic profiling approaches such as array comparative genomic hybridization (aCGH) have provided additional insights concerning the mechanisms responsible for generating complex osteosarcoma genomes. This chapter provides a brief introduction to the clinical features of conventional osteosarcoma, the predominant subtypes, and a general overview of materials and analytical methods of osteosarcoma aCGH, followed by a more detailed literature overview of aCGH studies and a discussion of emerging genes, molecular mechanisms, and their clinical implications, as well as more recent application of integrative genomics in osteosarcoma. aCHG is helping elucidate genomic events leading to tumor development and evolution as well as identification of prognostic markers and therapeutic targets in osteosarcoma.

Discovery of biomarkers for osteosarcoma by proteomics approaches

Osteosarcomas are the most common malignant bone tumors, and the identification of useful tumor biomarkers and target proteins is required to predict the clinical outcome of patients and therapeutic response as well as to develop novel therapeutic strategies. Global protein expression studies, namely, proteomic studies, can offer important clues to understanding the tumor biology that cannot be obtained by other approaches. These studies, such as two-dimensional gel electrophoresis and mass spectrometry, have provided protein expression profiles of osteosarcoma that can be used to develop novel diagnostic and therapeutic biomarkers, as well as to understand biology of tumor progression and malignancy. In this paper, a brief description of the methodology will be provided followed by a few examples of the recent proteomic studies that have generated new information regarding osteosarcomas.

Overexpression of IL-7 enhances cisplatin resistance in glioma

Cisplatin is one of the most commonly used chemotherapeutic agents for glioma patients. In this study, array comparative genomic hybridization (aCGH) was used to identify genes associated with cisplatin resistance in a human glioma cell line. The cisplatin-resistant U251/CP2 cell line was derived by stepwise selection using cisplatin. The genetic aberrations of the U251 parental cell line and the U251/CP2 cells were analyzed using aCGH. RT-PCR was used to detect the expression of the altered genes revealed by aCGH. The sensitivity of glioma cells to cisplatin was determined by using the MTT assay. Apoptosis was detected using flow cytometry and western blot analysis. The IC₅₀ value of cisplatin in U251/CP2 cells was five times higher than its IC₅₀ in U251 cells. The U251 cells lost at least one copy each of the CFHR1 and CFHR3 genes, and both CFHR1 and CFHR3 were homozygously deleted in U251/CP2 cells. The U251/CP2 cells gained two to three copies of C8orf70 and IL-7 genes. IL-7 mRNA expression was studied in 12 glioma cell lines, and expression was positively correlated with the IC₅₀ of cisplatin. Furthermore, IL-7 mRNA expression was also positively correlated with the IC₅₀ of cisplatin in 91 clinical glioma specimens. Additionally, treatment with recombinant human IL-7 (rhIL-7) enhanced cisplatin resistance and increased the relative growth rate of the glioma cells. Moreover, the apoptosis induced by cisplatin could be inhibited by IL-7. In conclusion, our results suggest that IL-7 may play an important role in cisplatin resistance in glioma.

Emerging drugs for high-grade osteosarcoma

IMPORTANCE OF THE FIELD

Osteosarcoma (OS) is the most common primary malignant bone tumour in children and adolescents. This review focuses on the most promising therapeutic markers and drugs which may potentially be considered for innovative high-grade OS treatments.

AREAS COVERED IN THIS REVIEW

The list of drugs and compounds reviewed has been generated by taking into account those which target markers of potential clinical interest for high-grade OS and have been included in Phase I, II or III clinical trials. The literature search covers the last 40 years, starting from the first OS chemotherapy reports of the early 1970s. Particular relevance was given to reports and reviews on new targeted therapies of possible clinical usefulness for high-grade OS.

WHAT THE READER WILL GAIN

This review gives an updated overview of novel therapeutic approaches which have been or are going to be evaluated in Phase I/II/III clinical studies for high-grade OS.

TAKE HOME MESSAGE

On the basis of the information that has emerged so far, it can be predicted that in the next 5 - 10 years, new agents to be included in innovative treatment strategies for selected subgroups of high-grade OS patients may become available.

Sorafenib blocks tumour growth, angiogenesis and metastatic potential in preclinical models of osteosarcoma through a mechanism potentially involving the inhibition of ERK1/2, MCL-1 and ezrin pathways

BACKGROUND

Osteosarcoma (OS) is the most common primary bone tumour in children and young adults. Despite improved prognosis, metastatic or relapsed OS remains largely incurable and no significant improvement has been observed in the last 20 years. Therefore, the search for alternative agents in OS is mandatory.

RESULTS

We investigated phospho-ERK 1/2, MCL-1, and phospho-Ezrin/Radixin/Moesin (P-ERM) as potential therapeutic targets in OS. Activation of these pathways was shown by immunohistochemistry in about 70% of cases and in all OS cell lines analyzed. Mutational analysis revealed no activating mutations in KRAS whereas BRAF gene was found to be mutated in 4/30 OS samples from patients. Based on these results we tested the multi-kinase inhibitor sorafenib (BAY 43-9006) in preclinical models of OS. Sorafenib inhibited OS cell line proliferation, induced apoptosis and downregulated P-ERK1/2, MCL-1, and P-ERM in a dose-dependent manner. The dephosphorylation of ERM was not due to ERK inhibition. The downregulation of MCL-1 led to an increase in apoptosis in OS cell lines. In chick embryo chorioallantoic membranes, OS supernatants induced angiogenesis, which was blocked by sorafenib and it was also shown that sorafenib reduced VEGF and MMP2 production. In addition, sorafenib treatment dramatically reduced tumour volume of OS xenografts and lung metastasis in SCID mice.

CONCLUSION

In conclusion, ERK1/2, MCL-1 and ERM pathways are shown to be active in OS. Sorafenib is able to inhibit their signal transduction, both in vitro and in vivo, displaying anti-tumoural activity, anti-angiogenic effects, and reducing metastatic colony formation in lungs. These data support the testing of sorafenib as a potential therapeutic option in metastatic or relapsed OS patients unresponsive to standard treatments.

Mechanisms of gene amplification and evidence of coamplification in drug-resistant human osteosarcoma cell lines

Gene amplification and copy number changes play a pivotal role in malignant transformation and progression of human tumor cells by mediating the activation of genes and oncogenes, which are involved in many different cellular processes including development of drug resistance. Since doxorubicin (DX) and methotrexate (MTX) are the two most important drugs for high-grade osteosarcoma (OS) treatment, the aim of this study was to identify genes gained or amplified in six DX- and eight MTX-resistant variants of the human OS cell lines U-2OS and Saos-2, and to get insights into the mechanisms underlying the amplification processes. Comparative genomic hybridization techniques identified amplification of MDR1 in all six DX-resistant and of DHFR in three MTX-resistant U-2OS variants. In addition, progressive gain of MLL was detected in the four U-2OS variants with higher resistance levels either to DX or MTX, whereas gain of MYC was found in all Saos-2 MTX-resistant variants and the U-2OS variant with the highest resistance level to DX. Fluorescent in situ hybridization revealed that MDR1 was amplified in U-2OS and Saos-2/DX-resistant variants manifested as homogeneously staining regions and double minutes, respectively. In U-2OS/MTX-resistant variants, DHFR was amplified in homogeneously staining regions, and was coamplified with MLL in relation to the increase of resistance to MTX. Gene amplification was associated with gene overexpression, whereas gene gain resulted in up-regulated gene expression. These results indicate that resistance to DX and MTX in human OS cell lines is a multigenic process involving gene copy number and expression changes.

Biomarkers in Osteosarcoma

Osteosarcoma is the most common primary tumor of bone and accounts for approximately 19% of all malignant tumors of bone. It is the third most common malignant tumor in teenagers. More than twenty years ago, the advent of a multidisciplinary approach that combined multi-agent chemotherapy and limb-sparing surgery greatly improved the survival rate of patients with osteosarcoma. Unfortunately, since that time, survival rates have not dramatically improved. To date, the most powerful predictors of outcome have remained the ability to detect metastatic disease at diagnosis and the histopathologic response of the tumor to preoperative chemotherapy. Presently, 80% of patients who do not have distant metastases at initial diagnosis will become long-term survivors. Unfortunately, this means that approximately 20% of patients who do not present with metastases at diagnosis will not survive. This group of patients appears to be resistant to current treatment as attempts to intensify therapy after surgery for patients with a poor histopathologic response has not significantly improved survival rates. It is these patients that are in the greatest need of additional clinically relevant markers for prognosis and who can be most helped by molecular analysis. While steady progress has been made in the identification of genetic alterations in osteosarcoma, no individual molecular marker has thus far been demonstrated to have a better prognostic significance in the treatment of osteosarcomas than the current clinical markers. Thus there is clearly a need to employ new comprehensive analysis technologies to develop significantly more informative classification systems and to identify new therapeutic targets.

Clinical impact of the methotrexate resistance-associated genes C-MYC and dihydrofolate reductase (DHFR) in high-grade osteosarcoma

BACKGROUND

Aims of this study were the validation of C-MYC involvement in methotrexate (MTX) resistance and the assessment of clinical impact of C-MYC and dihydrofolate reductase (DHFR) in osteosarcoma (OS).

MATERIALS AND METHODS

The involvement of C-MYC in MTX resistance was validated with an antisense approach. C-MYC and DHFR protein levels at diagnosis were assessed by immunohistochemistry on series of patients treated with either a MTX-based protocol (IOR/OS-1; 72 patients) or with a standard four-drug regimen (ISG/SSG 1; 61 patients).

RESULTS

Down-regulation of C-MYC significantly decreased the MTX resistance level of OS cells, demonstrating its causal involvement in this phenomenon. In clinical samples, a worse outcome was associated with increased levels of DHFR and C-MYC at diagnosis in the IOR/OS-1 patients and of C-MYC in the ISG/SSG 1 patients.

CONCLUSIONS

Meanwhile the adverse clinical impact of DHFR overexpression appeared to be closely related to the relevance of MTX in the chemotherapeutic protocol, that of C-MYC overexpression was more general and not strictly MTX related. The assessment of C-MYC and DHFR at diagnosis, together with that of other known prognostic markers, can be considered for an early identification of subgroups of OS patients with higher risk of adverse outcome.

Cancer cell lines as genetic models of their parent histology: analyses based on array comparative genomic hybridization

Tumor-derived cell lines are used as in vitro cancer models, but their ability to accurately reflect the phenotype and genotype of the parental histology remains questionable, given the prevalence of documented cell line-specific cytogenetic changes. We have addressed the issue of whether copy number alterations seen in tumor-derived cell lines reflect those observed in studies of fresh tissue by carrying out a meta-analysis of array-based comparative genomic hybridization data that considers both copy number alteration frequencies and the occurrence of cancer gene amplifications and homozygous deletions. Pairwise correlation comparisons between the data sets of seven diagnosis-specific matched tumor and cell line groups indicate that the trends in aberration frequencies are highly correlated between tumors and cell line sets of matched cancer histology relative to unmatched pairings. Despite their similarities, cell lines showed uniformly higher locus-specific alteration frequencies (P = 0.004) and several recurring cell line-specific alterations emerged. These include the previously documented losses of 13q and 9p and gains of 20q, as well as additional undescribed cell line-specific gains of 5p, 7p, and 17q and losses of 18q and 4q. These results indicate that, on average, cell lines preserve in vitro the genetic aberrations that are unique to the parent histology from which they were derived while acquiring additional locus-specific alterations. These data may enable a more predictive understanding of individual cell lines as in vitro models of cancer biology and therapy.

Bufalin induces apoptosis in human osteosarcoma U-2OS and U-2OS methotrexate300-resistant cell lines

AIM

To investigate the antiproliferative activity and apoptosis-inducing effects of bufalin on human osteosarcoma cell lines.

METHODS

U-2OS and U-2OS methotrexate (MTX) 300-resistant cell lines were treated with bufalin. Cell viability was assessed using the MTT assay. Cell-cycle status, apoptosis-inducing effects, and the expression of apoptosis-related proteins were evaluated by flow cytometry, fluorescent staining, DNA fragmentation assays, and Western blotting. The effect of bufalin on dihydrofolate reductase (DHFR) expression was studied by RTPCR and Western blotting.

RESULTS

Bufalin inhibited cell growth in both U-2OS and U-2OS MTX300 cells. The induction of G2/M cell-cycle arrest was also seen in the cells treated with bufalin. The induction of apoptosis by bufalin was confirmed by increased expression of the tumor suppressor protein p53 and the increased ratio of the Bax/Bcl-2 proteins. Bufalin induced apoptosis to the same extent in both cell lines without regard to DHFR levels in the cells.

CONCLUSION

Bufalin inhibited the growth of and induced apoptosis in both MTX-sensitive and MTX-resistant human osteosarcoma U-2OS cells. The apoptosis-inducing effect of bufalin was not influenced by the presence of high levels of the DHFR protein.

Chemotherapy resistance in osteosarcoma: current challenges and future directions

For patients with osteosarcoma, the use of chemotherapy has improved survival from 11% with surgical resection alone in the 1960s, to 70% by the mid-1980s. However, survival has since plateaued, despite advances in anticancer therapy. Elucidation of the mechanisms of chemoresistance and implementation of strategies to overcome chemoresistance will likely be pivotal to improving survival. In this review, the focus is on the current understanding of the mechanisms of resistance to the most commonly used agents in the treatment of osteosarcoma and the methods employed to overcome chemotherapy resistance.

Chromosomal alterations cause the high rates and wide ranges of drug resistance in cancer cells

Conventional mutation-selection theories have failed to explain (i) how cancer cells become spontaneously resistant against cytotoxic drugs at rates of up to 10(-3) per cell generation, orders higher than gene mutation, even in cancer cells; (ii) why resistance far exceeds a challenging drug-a state termed multidrug resistance; (iii) why resistance is associated with chromosomal alterations and proportional to their numbers; and (iv) why resistance is totally dependent on aneuploidy. We propose here that cancer-specific aneuploidy generates drug resistance via chromosomal alterations. According to this mechanism, aneuploidy varies the numbers and structures of chromosomes automatically, because it corrupts the many teams of proteins that segregate, synthesize, and repair chromosomes. Aneuploidy is thus a steady source of chromosomal variation from which, in classical Darwinian terms, resistance-specific aneusomies are selected in the presence of chemotherapeutic drugs. Some of the thousands of unselected genes that hitchhike with resistance-specific aneusomies can thus generate multidrug resistance. To test this hypothesis, we determined the rates of chromosomal alterations in clonal cultures of human breast and colon cancer lines by dividing the fraction of nonclonal karyotypes by the number of generations of the clone. These rates were about 10(-2) per cell generation, orders higher than mutation. Chromosome numbers and structures were determined in metaphases hybridized with color-coded chromosome-specific DNA probes. Further, we tested puromycin-resistant subclones of these lines for resistance-specific aneusomies. Resistant subclones differed from parental lines in four to seven specific aneusomies, of which different subclones shared some. The degree of resistance was roughly proportional to the number of these aneusomies. Thus, aneuploidy is the primary cause of the high rates and wide ranges of drug resistance in cancer cells.

4-Demethoxy-3′-deamino-3′-aziridinyl-4′-methylsulphonyl-daunorubicin (PNU-159548): A promising new candidate for chemotherapeutic treatment of osteosarcoma patients

The effectiveness of the alkycycline 4-demethoxy-3'-deamino-3'-aziridinyl-4'-methylsulphonyl-daunorubicin (PNU-159548, ladirubicin), a new drug with high antitumour activity against a broad range of neoplasms, was evaluated by using a panel of 32 human osteosarcoma cell lines, including cell lines resistant to doxorubicin, methotrexate, or cisplatin. PNU-159548 resulted to be highly active in all cell lines. No cross-resistance was found with conventional drugs, being PNU-159548 active also in cells resistant to doxorubicin and with a multidrug resistance phenotype (associated with MDR1 gene/P-glycoprotein overexpression), as well as in cells resistant to methotrexate or to cisplatin. Analysis of drug-drug interactions showed that PNU-159548 could be successfully used in combination with all the most important drugs currently used in OS chemotherapy. In fact, the simultaneous administration of PNU-159548 and doxorubicin, methotrexate, or cisplatin produced mostly additive or synergistic effects. Sequential exposure to PNU-159548 followed immediately by doxorubicin, methotrexate, or cisplatin was the most effective sequence of administration, invariably resulting in additive or synergistic effects in both drug-sensitive and drug-resistant osteosarcoma cell lines. In conclusion, the high in vitro effectiveness, the absence of cross-resistance with doxorubicin, methotrexate, or cisplatin and the possibility to be successfully used in combination with these drugs indicate PNU-159548 as a promising candidate to be considered for planning new therapeutic regimens for osteosarcoma patients, who show a decreased response to conventional chemotherapy.

Chromosomal imbalances associated with drug resistance and thermoresistance in human pancreatic carcinoma cells

Resistance to therapeutic treatment is the major obstacle to advances in the successful management of pancreatic cancer. To characterize chromosomal alterations associated with different phenotypes of acquired multidrug resistance (MDR) and thermoresistance, comparative genomic hybridization (CGH) was applied to compare human pancreatic carcinoma-derived cells. This panel of cell lines consists of the parental, drug- and thermosensitive pancreatic carcinoma cell line EPP85 - 181P, its atypical MDR variant EPP85-181RNOV, the classical MDR subline EPP85-181RDB, and their thermoresistant counterparts EPP85-181P-TR, EPP85-181RNOV-TR, and EPP85 - 181RDB-TR, respectively. CGH using genomic DNA prepared from these cell lines as probes successfully identified genomic gains and/or losses in chromosomal regions encoding putative genes associated with drug resistance and/or thermoresistance. These genes included 23 members of the family of ABC transporters, 27 members of the family of cytochrome P450 (CYP) monooxygenases, various molecular chaperones, DNA repair enzymes, and factors involved in the regulation of cell cycle and apoptosis. The importance of these cell variant-specific genomic imbalances in the development of MDR and thermoresistance is discussed and remains to be elucidated.

Genetic analysis of fibrosarcoma of bone, a rare tumour entity closely related to osteosarcoma and malignant fibrous histiocytoma of bone

Fibrosarcoma (FS) of bone is an extremely rare and genetically uncharacterised malignant tumour arising in the skeleton. On the basis of clinicopathologic features it appears to be closely related to either fibroblastic osteosarcoma (OS) or malignant fibrous histiocytoma (MFH) of bone. In this study, 27 decalcified, paraffin-embedded FS of bone were collected for genetic and immunohistochemical characterisation. Good quality DNA, suitable for genetic analyses, was isolated from nine cases (7 primary tumours, 1 local recurrence, and 1 lung metastasis), which were analysed by comparative genomic hybridisation (CGH) on chromosomes and DNA microarrays. DNA sequence copy number changes were found in five out of seven primary tumours (72%), as well as in both, the local recurrence and the metastatic lesion, by CGH on chromosomes. The most frequent aberration was gain of the chromosomal region 22q, which was present in four out of the five primary tumours with genetic changes, in the local recurrence and, as the sole genetic aberration, in the lung metastasis. DNA microarray analysis showed that gain of the platelet-derived growth factor beta (PDGF-B) gene (located at 22q12.3-q13.1) was the most frequent gene imbalance, which was present in three out of the five analysed tumours. In these three cases, real-time PCR revealed a 2.1- to 2.7-fold increase of PDGF-B gene copy numbers. By immunohistochemistry, a positive reaction for B-chain-containing PDGF proteins was revealed in all the cases showing gain of 22q. A more extensive immunohistochemical analysis identified the presence of PDGF-B proteins in 8/20 primary FS of bone (40%), 3/3 lung metastases and in 1/2 local recurrences. A simultaneous positive reaction for PDGF-B proteins and PDGF receptors was found in two third of PDGF-B-positive cases (8/12). Taken together, the genetic and immunohistochemical data indicate that over-representation of the chromosomal region 22q, including particularly the PDGF-B gene, may be important for the pathogenesis of FS of bone. Our results also demonstrate that CGH on chromosomes and DNA microarrays are suitable for the genetic characterisation of decalcified, paraffin-embedded tumour tissue samples and may facilitate, combined with other techniques, the rapid acquisition of data providing insight into the molecular genetic and biologic basis of rare bone sarcomas. Moreover, these findings suggest the possible presence of an autocrine loop in FS of bone, which might be taken into account for planning innovative therapeutic strategies for patients unresponsive to conventional treatments.