Pre-treatment of human osteosarcoma cells with N-methylformamide enhances P-glycoprotein expression and resistance to doxorubicin

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.

The Impact of Melatonin on Colon Cancer Cells' Resistance to Doxorubicin in an in Vitro Study

Multi-drug resistance (MDR) is the main cause of low effectiveness of cancer chemotherapy. P-glycoprotein (P-gp) is one of the main factors determining MDR. Some studies indicate the potential role of melatonin (MLT) in MDR. In this study, we examined the effect of MLT on colon cancer cell’s resistance to doxorubicin (DOX). Using the sulforhodamine B (SRB), method the effect of tested substances on the survival of LoVo (colon cancer cells sensitive to DOX) and LoVo_DX (colon cancer cells resistant to DOX) was rated. Using immunocytochemistry (ICC), the expression of P-gp in the LoVo and LoVo_DX was determined. With the real-time PCR (RT-PCR) technique, the ABCB1 expression in LoVo_DX was evaluated. Based on the results, it was found that MLT in some concentrations intensified the cytotoxicity effect of DOX in the LoVo_DX cells. In the ICC studies, it was demonstrated that certain concentrations of MLT and DOX cause an increase in the percentage of cells expressing P-gp, which correlates positively with ABCB1 expression (RT-PCR). The mechanism of overcoming resistance by MLT is probably not only associated with the expression of P-gp. It seems appropriate to carry out further research on the use of MLT as the substance supporting cancer chemotherapy.

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.

Genome Analysis of Osteosarcoma Progression Samples Identifies FGFR1 Overexpression as a Potential Treatment Target and CHM as a Candidate Tumor Suppressor Gene

Osteosarcoma (OS) is the most common primary malignant tumor of bone, showing complex chromosomal rearrangements but with few known consistent changes. Deeper biological understanding is crucial to find new therapies to improve patient survival. We have sequenced the whole exome of two primary tumors (before and after chemotherapy), one metastatic tumor and a matched normal sample from two OS patients, to identify mutations involved in cancer biology. The metastatic samples were also RNA sequenced. By RNA sequencing we identified dysregulated expression levels of drug resistance- and apoptosis-related genes. Two fusion transcripts were identified in one patient (OS111); the first resulted in p53 inactivation by fusing the first exon of TP53 to the fifth exon of FAM45A. The second fusion joined the two first exons of FGFR1 to the second exon of ZNF343. Furthermore, FGFR1 was amplified and highly expressed, representing a potential treatment target in this patient. Whole exome sequencing revealed large intertumor heterogeneity, with surprisingly few shared mutations. Careful evaluation and validation of the data sets revealed a number of artefacts, but one recurrent mutation was validated, a nonsense mutation in CHM (patient OS106), which also was the mutation with the highest expression frequency (53%). The second patient (OS111) had wild-type CHM, but a downregulated expression level. In a panel of 71 clinical samples, we confirmed significant low expression of CHM compared to the controls (p = 0.003). Furthermore, by analyzing public datasets, we identified a significant association between low expression and poor survival in two other cancer types. Together, these results suggest CHM as a candidate tumor suppressor gene that warrants further investigation.

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.

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.

bcl-2 induction of urokinase plasminogen activator receptor expression in human cancer cells through Sp1 activation: involvement of ERK1/ERK2 activity

We have previously demonstrated that Bcl-2 overexpression in human breast carcinoma and melanoma cells synergizes with hypoxia to increase angiogenesis through up-regulation of vascular endothelial growth factor. In this work we demonstrated, for the first time, that Bcl-2 overexpression in cancer cells exposed to hypoxia modulates urokinase plasminogen activator receptor (uPAR) expression through Sp1 transcription factor and that the extracellular signal-regulated kinase (ERK) pathway plays a role in Sp1 transcriptional activity. In particular, an increase in uPAR protein and mRNA expression was found in melanoma bcl-2 transfectants grown under hypoxia when compared with control cells, and a decrease of uPAR protein expression was induced by treatment of cells with specific bcl-2 antisense oligonucleotides. Up-regulation of uPAR expression was accompanied by increased Sp1 protein expression, stability, serine phosphorylation, and DNA binding activity. Treatment of cells with mitramycin A, an inhibitor of Sp1 activity, confirmed the role of Sp1 transcriptional activity in uPAR induction by Bcl-2. The contribution of the ERK pathway in Sp1-increased transcriptional activity was demonstrated by the use of chemical inhibition. In fact, ERK kinase activation was induced in Bcl-2-overexpressing cells exposed to hypoxia, and the ERK kinase inhibitor UO126 was able to down-regulate Sp1 phosphorylation and DNA binding activity. Using a human breast carcinoma line, we obtained data supporting our findings with melanoma cells and identified a link between the induction of Sp1 and uPAR expression as a common bcl-2-controlled phenomenon in human tumors. In conclusion, our results strongly indicate that up-regulation of uPAR expression by Bcl-2 in hypoxia is modulated by Sp1 DNA binding activity through the ERK signaling pathway.

Bcl-2 overexpression in human melanoma cells increases angiogenesis through VEGF mRNA stabilization and HIF-1-mediated transcriptional activity

The aim of this paper was to study the molecular mechanisms by which bcl-2 increases hypoxia-induced vascular endothelial growth factor (VEGF) expression. We demonstrated that bcl-2 overexpression in M14 human melanoma cell line enhances hypoxia-induced VEGF mRNA stability and promoter activation. In particular, the half-life of the message was longer in bcl-2 transfectants (approximately 330 min) than in control cells (approximately 180 min). In addition, bcl-2 overexpression increased VEGF promoter activity through the hypoxia-inducible factor-1 (HIF-1) transcription factor. Increased HIF-1a protein expression and DNA binding activity were detected in bcl-2 overexpressing cells compared with control cells. An enhanced functional activity of secreted VEGF was found both in in vitro and in vivo angiogenic assays, and the use of VEGF specific antibodies validated the role of VEGF on bcl-2-induced angiogenesis. Taken together our results indicate that bcl-2 plays an important role in melanoma angiogenesis, and that VEGF mRNA stabilization and HIF-1-mediated transcriptional activity are two important control points in bcl-2/hypoxia-induced VEGF expression.

Cytotoxic and cytostatic effects induced by 4-hydroxynonenal in human osteosarcoma cells

Several studies point to the existence of an inverse correlation between cellular lipid peroxidation and both cell proliferation and neoplastic transformation. Furthermore, numerous results demonstrate that lipid peroxidation products affect central biochemical pathways and intracellular signalling at physiological concentrations. 4-Hydroxynonenal (HNE) is one of the most active products of lipid peroxidation. This work has focused on the evaluation of HNE nuclear content, so far never directly measured, by electrospray-ionization-mass-spectrometry (ESI/MS) and on the correlation between its concentration and the induced effects after exogenous administration. In a human osteosarcoma cell line (SaOS2), HNE exhibited an early cytotoxic effect characterized by apoptosis, cytostatic and differentiating effects characterized by slow growth, increase in alkaline phosphatase (ALP), and alpha5 integrin subunit content with decrease in tumorigenicity.

Simultaneous paired analysis of numerical chromosomal aberrations and DNA content in osteosarcoma

Relatively little is known about the biologic relevance of numerical chromosomal changes in relation to DNA content in osteosarcoma. In this study, by using a series of human osteosarcoma cell lines, we standardized a method for the assessment, on the same nuclei specimen, of both specific chromosome copy numbers by fluorescence in situ hybridization (FISH) and the DNA content by static cytofluorometry or image cytometry. On the same cell lines, we also evaluated the DNA content by using flow cytometry and the chromosome number distribution by metaphase analysis. Comparison between these different methods showed that DNA ploidy level as determined by FISH or metaphase analysis is frequently lower than the ploidy pattern as defined by cytometric methods. By using comparative genomic hybridization, we were able to demonstrate that these discrepancies were due to the presence of several unbalanced chromosome aberrations, specifically gains and high-level amplifications, which affect the total DNA content with less effect on the total chromosome number. Thus, evaluation of DNA ploidy in osteosarcoma cells is needed for a correct interpretation of FISH or cytogenetic data concerning numerical chromosomal changes. Evaluation of tumor ploidy in a series of clinical samples demonstrated that in high-grade osteosarcoma, flow cytometry sometimes may give false results because of the presence of high proportions of contaminating, nonneoplastic cells that cannot be excluded from the flow cytometric assessment but that do not interfere with the evaluation of DNA ploidy by static cytofluorometry or image cytometry, in which only tumor cells are selected for the analysis. The possibility of using this method to evaluate, on the same nuclei sample, both specific chromosomal aberrations and DNA ploidy may allow a better determination of numerical chromosomal changes that may be relevant for the biologic behavior of osteosarcoma.

Actin organization associated with the expression of multidrug resistant phenotype in osteosarcoma cells and the effect of actin depolymerization on drug resistance

We have previously reported that P-glycoprotein (Pgp)-overexpressing multidrug resistant (MDR) osteosarcoma cells were functionally more differentiated than their parent cells. The present study showed that in the parent cells, the actin filaments were sparsely distributed or were diffusely spread throughout the cytoplasm, whereas the MDR osteosarcoma cells exhibited a remarkable increase in well-organized actin stress fibers. Furthermore, dihydrocytochalasin B, a specific inhibitor of actin polymerization, dramatically disrupted this network of stress fibers, increased the intracellular accumulation of doxorubicin (DOX) and modified the resistance against DOX. These results indicate that the organization of actin filaments associated with cellular differentiation may be involved in the expression of Pgp function in the MDR osteosarcoma cells.