Unique proteomic features induced by a potential antiglioma agent, Nordy (dl-nordihydroguaiaretic acid), in glioma cells

Non-coding RNAs and glioma: Focus on cancer stem cells

Glioblastoma and gliomas can have a wide range of histopathologic subtypes. These heterogeneous histologic phenotypes originate from tumor cells with the distinct functions of tumorigenesis and self-renewal, called glioma stem cells (GSCs). GSCs are characterized based on multi-layered epigenetic mechanisms, which control the expression of many genes. This epigenetic regulatory mechanism is often based on functional non-coding RNAs (ncRNAs). ncRNAs have become increasingly important in the pathogenesis of human cancer and work as oncogenes or tumor suppressors to regulate carcinogenesis and progression. These RNAs by being involved in chromatin remodeling and modification, transcriptional regulation, and alternative splicing of pre-mRNA, as well as mRNA stability and protein translation, play a key role in tumor development and progression. Numerous studies have been performed to try to understand the dysregulation pattern of these ncRNAs in tumors and cancer stem cells (CSCs), which show robust differentiation and self-regeneration capacity. This review provides recent findings on the role of ncRNAs in glioma development and progression, particularly their effects on CSCs, thus accelerating the clinical implementation of ncRNAs as promising tumor biomarkers and therapeutic targets.

Utilizing Zebrafish to Identify Anti-(Lymph)Angiogenic Compounds for Cancer Treatment: Promise and Future Challenges

Cancer metastasis which predominantly occurs through blood and lymphatic vessels, is the leading cause of death in cancer patients. Consequently, several anti-angiogenic agents have been approved as therapeutic agents for human cancers such as metastatic renal cell carcinoma. Also, anti-lymphangiogenic drugs such as monoclonal antibodies VGX-100 and IMC-3C5 have undergone phase I clinical trials for advanced and metastatic solid tumors. Although anti-tumor-associated angiogenesis has proven to be a promising therapeutic strategy for human cancers, this approach is fraught with toxicities and development of drug resistance. This emphasizes the need for alternative anti-(lymph)angiogenic drugs. The use of zebrafish has become accepted as an established model for high-throughput screening, vascular biology, and cancer research. Importantly, various zebrafish transgenic lines have now been generated that can readily discriminate different vascular compartments. This now enables detailed in vivo studies that are relevant to both human physiological and tumor (lymph)angiogenesis to be conducted in zebrafish. This review highlights recent advancements in the zebrafish anti-vascular screening platform and showcases promising new anti-(lymph)angiogenic compounds that have been derived from this model. In addition, this review discusses the promises and challenges of the zebrafish model in the context of anti-(lymph)angiogenic compound discovery for cancer treatment.

NDGA-P21, a novel derivative of nordihydroguaiaretic acid, inhibits glioma cell proliferation and stemness

Nordihydroguaiaretic acid (NDGA) and its synthetic chiral analog dl-nordihydroguaiaretic acid (Nordy) show collective benefits in anti-tumor, and defending against viral and bacterial infections. Here, we synthetized a new derivative-NDGA-P21 based on NDGA structure. Regardless of the structural similarity, NDGA-P21 exhibited stronger capability in suppression of glioblastoma (GBM) cell growth as compared to Nordy. Mechanically, NDGA-P21 is able to arrest cell cycle of GBM cells in G0/G1 phase, and to block cell proliferation sequentially. It is important to note that NDGA-P21 is able to impair the stemness of glioma stem-like cells (GSLCs) via measurement of colony formation and sphere formation. Taken together, the novel NDGA-based compound NDGA-P21 exhibits potential therty -20 apeutic implications through inhibiting proliferation of glioma cells and self-renewal capability of GSLCs.

Anti-tumor effect of ultrasound-induced Nordy-loaded microbubbles destruction

BACKGROUND

Synthesized dl-Nordihydroguaiaretic acid (dl-NGDA or "Nordy") can inhibit the growth of malignant human tumors, especially the tumor angiogenesis. However, its liposoluble nature limits its in vivo efficacy in the hydrosoluble circulation of human.

PURPOSE

We tried to use the ultrasonic microbubble as the carrier and the ultrasound-induced destruction for the targeted release of Nordy and evaluate its in vitro and in vivo anti-tumor effect.

METHODS

Nordy-loaded lipid microbubbles were prepared by mechanical vibration. Effects of ultrasound-induced Nordy-loaded microbubbles destruction on proliferation of human umbilical vein endothelial cells (HUVECs), tumor derived endothelial cells (Td-ECs), and rabbit transplanted VX2 tumor models were evaluated.

RESULTS

The ultrasound-induced Nordy-loaded microbubbles destruction inhibited the proliferations of HUVECs and Td-ECs in vitro, and inhibited the tumor growth and the microvasculature in vivo. Its efficacy was higher than those of Nordy used only and Nordy with ultrasound exposure.

CONCLUSION

Ultrasonic microbubbles can be used as the carrier of Nordy and achieve its targeted release with improved anti-tumor efficacy in the condition of ultrasound-induced microbubbles destruction.

A synthetic dl-nordihydroguaiaretic acid (Nordy), inhibits angiogenesis, invasion and proliferation of glioma stem cells within a zebrafish xenotransplantation model

The zebrafish (Danio rerio) and their transparent embryos represent a promising model system in cancer research. Compared with other vertebrate model systems, we had previously shown that the zebrafish model provides many advantages over mouse or chicken models to study tumor invasion, angiogenesis, and tumorigenesis. In this study, we systematically investigated the biological features of glioma stem cells (GSCs) in a zebrafish model, such as tumor angiogenesis, invasion, and proliferation. We demonstrated that several verified anti-angiogenic agents inhibited angiogenesis that was induced by xenografted-GSCs. We next evaluated the effects of a synthetic dl-nordihydroguaiaretic acid compound (dl-NDGA or “Nordy”), which revealed anti-tumor activity against human GSCs in vitro by establishing parameters through studying its ability to suppress angiogenesis, tumor invasion, and proliferation. Furthermore, our results indicated that Nordy might inhibit GSCs invasion and proliferation through regulation of the arachidonate 5-lipoxygenase (Alox-5) pathway. Moreover, the combination of Nordy and a VEGF inhibitor exhibited an enhanced ability to suppress angiogenesis that was induced by GSCs. By contrast, even following treatment with 50 µM Nordy, there was no discernible effect on zebrafish embryonic development. Together, these results suggested efficacy and safety of using Nordy in vivo, and further demonstrated that this model should be suitable for studying GSCs and anti-GSC drug evaluation.

Proteomics of gliomas: initial biomarker discovery and evolution of technology

Gliomas are a group of aggressive brain tumors that diffusely infiltrate adjacent brain tissues, rendering them largely incurable, even with multiple treatment modalities and agents. Mostly asymptomatic at early stages, they present in several subtypes with astrocytic or oligodendrocytic features and invariably progress to malignant forms. Gliomas are difficult to classify precisely because of interobserver variability during histopathologic grading. Identifying biological signatures of each glioma subtype through protein biomarker profiling of tumor or tumor-proximal fluids is therefore of high priority. Such profiling not only may provide clues regarding tumor classification but may identify clinical biomarkers and pathologic targets for the development of personalized treatments. In the past decade, differential proteomic profiling techniques have utilized tumor, cerebrospinal fluid, and plasma from glioma patients to identify the first candidate diagnostic, prognostic, predictive, and therapeutic response markers, highlighting the potential for glioma biomarker discovery. The number of markers identified, however, has been limited, their reproducibility between studies is unclear, and none have been validated for clinical use. Recent technological advancements in methodologies for high-throughput profiling, which provide easy access, rapid screening, low sample consumption, and accurate protein identification, are anticipated to accelerate brain tumor biomarker discovery. Reliable tools for biomarker verification forecast translation of the biomarkers into clinical diagnostics in the foreseeable future. Herein we update the reader on the recent trends and directions in glioma proteomics, including key findings and established and emerging technologies for analysis, together with challenges we are still facing in identifying and verifying potential glioma biomarkers.

The effect of miR-7 on behavior and global protein expression in glioma cell lines

Malignant glioma is a common cancer of the nervous system. Despite recent research efforts in cancer therapy, the prognosis of patients with malignant glioma has remained dismal. MicroRNAs are noncoding RNAs that inhibit the expression of their targets in a sequence-specific manner, and a few have been shown to act as oncogenes or tumor suppressors. Here, we aimed at exploring the precise biological role of microRNA-7 (miR-7) and the global protein changes in glioma cell lines transiently transfected with miR-7. Transfection of miR-7 into glioma cell lines causes inhibition of cell migration and invasion and suppression of tumorigenesis. Moreover, ectopic expression of miR-7 inhibits lung metastases of glioma in vivo. Among 65 protein spots with differential expression separated by 2-DE, 37 proteins were successfully identified by MS/MS analysis. Of those, the 25 downregulated proteins, which include 14-3-3ζ, eukaryotic translation initiation factor 5A (EIF5A), and annexin A4, may be downstream targets of miR-7, a finding that could elucidate some aspects of the behavior of glioma cells at the protein level. In conclusion, the absence of miR-7 function could cause downstream molecules to switch on or off, resulting in glioma development, invasion, and metastases. MiR-7-based gene treatment may be a novel anti-invasion therapeutic strategy for malignant glioma.

Protein alterations associated with temozolomide resistance in subclones of human glioblastoma cell lines

Temozolomide (TMZ) is the standard chemotherapeutic agent for human malignant glioma, but intrinsic or acquired chemoresistance represents a major obstacle to successful treatment of this highly lethal group of tumours. Obtaining better understanding of the molecular mechanisms underlying TMZ resistance in malignant glioma is important for the development of better treatment strategies. We have successfully established a passage control line (D54-C10) and resistant variants (D54-P5 and D54-P10) from the parental TMZ-sensitive malignant glioma cell line D54-C0. The resistant sub-cell lines showed alterations in cell morphology, enhanced cell adhesion, increased migration capacities, and cell cycle arrests. Proteomic analysis identified a set of proteins that showed gradual changes in expression according to their 50% inhibitory concentration (IC₅₀). Successful validation was provided by transcript profiling in another malignant glioma cell line U87-MG and its resistant counterparts. Moreover, three of the identified proteins (vimentin, cathepsin D and prolyl 4-hydroxylase, beta polypeptide) were confirmed to be upregulated in high-grade glioma. Our data suggest that acquired TMZ resistance in human malignant glioma is associated with promotion of malignant phenotypes, and our reported molecular candidates may serve not only as markers of chemoresistance but also as potential therapeutic targets in the treatment of TMZ-resistant human malignant glioma, providing a platform for future investigations.

An inhibitor of arachidonate 5-lipoxygenase, Nordy, induces differentiation and inhibits self-renewal of glioma stem-like cells

Recent progress in cancer biology indicates that eradication of cancer stem cells (CSCs) is essential for more effective cancer therapy. Unfortunately, cancer stem cells such as glioma stem-like cells (GSLCs) are often resistant to either radio- or chemotherapy. Therefore, screening and development for novel therapeutic modalities against CSCs has been an important emerging field in cancer research. In this study, we report that a synthetic dl-nordihydroguaiaretic acid compound (dl-NDGA or "Nordy"), inhibited self-renewal and induced differentiation of GSLCs in vitro and in vivo. We found that Nordy inhibited an enzyme known to be involved in leukemia stem cell and leukemia progression, Alox-5, and attenuated the growth of GSLCs in vitro. Nordy reduced the GSLC pool through a decrease in the CD133(+) population and abrogated clonogenicity. Nordy appeared to exert its effect via astrocytic differentiation by up-regulation of GFAP and down-regulation of stemness related genes, rather than by inducing apoptosis of GSLCs. The growth inhibition of xenografted glioma by Nordy was more long-lasting compared with that of the akylating agent BCNU, which exhibited significant relapse on drug discontinuation resulting from an enrichment of GSLCs. Meanwhile, transient exposure to Nordy reduced tumorigenecity of GSLCs and induced differentiation of the xenografts. Taken together, we have identified Alox-5 as a novel target in GSLCs and its inhibition with Nordy exhibits therapeutic implications through inducing GSLC differentiation.

The chemokine CXCL12 and its receptor CXCR4 promote glioma stem cell-mediated VEGF production and tumour angiogenesis via PI3K/AKT signalling

Chemokines and their receptors are actively involved in inflammation, immune responses, and cancer development. Here we report the detection of CD133(+) glioma stem-like cells (GSCs) co-expressing a chemokine receptor CXCR4 in human primary glioma tissues. These GSCs were located in areas adjacent to tumour vascular capillaries, suggesting an association between GSCs and tumour angiogenesis. To test this hypothesis, we isolated CD133(+) GSCs from surgical specimens of human primary gliomas and glioma cell lines. As compared to CD133(-) cells, CD133(+) GSCs expressed significantly higher levels of CXCR4 mRNA and protein, and migrated more efficiently in response to the CXCR4 ligand CXCL12. In addition, CXCL12 induced vascular endothelial growth factor (VEGF) production by CD133(+) GSCs via activation of the PI3K/AKT signalling pathway. Furthermore, knocking down of CXCR4 using RNA interference or inhibition of CXCR4 function by an antagonist AMD3100 not only reduced VEGF production by CD133(+) GSCs in vitro, but also attenuated the growth and angiogenesis of tumour xenografts in vivo formed by CD133(+) GSCs in SCID mice. These results indicate that CXCL12 and its receptor CXCR4 promote GSC-initiated glioma growth and angiogenesis by stimulating VEGF production.

Proteomic studies coupled with RNAi methodologies can shed further light on the downstream effects of telomerase in glioma

A comprehensive proteomic study utilizing 2D-DIGE and MALDI-TOF was used to assess the effect of inhibiting two different regulatory mechanisms of telomerase in glioma. RNAi was used to target hTERT and hsp90α. Inhibition of telomerase activity resulted in downregulation of various cytoskeletal proteins with correlative evidence of the involvement of telomerase in regulating the expression of vimentin. Inhibition of telomerase via sihTERT resulted in the downregulation of vimentin expression in glioma cell lines in a grade-specific manner. This study identified novel downstream role of telomerase in regulating the expression of vimentin, thereby affecting tumor progression and metastasis.

Prognostic significance and therapeutic potential of eukaryotic translation initiation factor 5A (eIF5A) in hepatocellular carcinoma

Using comparative proteomic and genomic approaches, the authors identified eukaryotic translation initiation factor 5A (eIF5A) as an oncofetal molecule highly abundant in mouse embryonic livers and human hepatocellular carcinoma (HCC) cell lines. To evaluate the oncogenic role and prognostic significance of eIF5A in HCC, we investigate the expression patterns of the two isoforms (eIF5A1 and eIF5A2) in a cohort of 258 HCC cases by cDNA microarray. Both eIF5A isoforms were expressed in the tumors, and clinically correlated eIF5A1 with more numbers of tumor nodules and eIF5A2 with tumor venous infiltration in HCC. In a separate cohort of 50 HCCs, high level of eIF5A2, but not eIF5A1, was associated with elevated levels of deoxyhypusine synthase and deoxyhypusine hydroxylase that catalyze post-translational hypusination of eIF5A protein. Interestingly, N1-guanyl-1,7-diaminoheptane (GC7), which is an inhibitor for the first step of eIF5A hypusination, was shown to significantly impair the cell proliferation and invasion of primary HCC cells (HepG2 and Hep3B). To further demonstrate the tumorigenic role associated with eIF5A, a drastic reduction of cell proliferation was associated with suppression of eIF5A2 by transfecting Hep3B, H2-P and H2-M HCC cells expressing high level of this isoform using small interfering RNA (siRNA) against eIF5A2. For these assays, a milder response was usually observed in normal hepatocyte cell line. Therefore, these findings suggest that eIF5A plays an important role in HCC tumorigenesis and metastasis, and targeting eIF5A hypusination by GC7 inhibitor or eIF5A2 by RNA interference (RNAi) may offer new therapeutic alternatives to HCC patients.

Glioma proteomics: status and perspectives

High grade gliomas are the most common brain tumors in adults and their malignant nature makes them the fourth biggest cause of cancer death. Major efforts in neuro-oncology research are needed to reach similar progress in treatment efficacy as that achieved for other cancers in recent years. In addition to the urgent need to identify novel effective drug targets against malignant gliomas, the search for glioma biomarkers and grade specific protein signatures will provide a much needed contribution to diagnosis, prognosis, treatment decision and assessment of treatment response. Over the past years glioma proteomics has been attempted at different levels, including proteome analysis of patient biopsies and bodily fluids, of glioma cell lines and animal models. Here we provide an extensive review of the outcome of these studies in terms of protein identifications (protein numbers and regulated proteins), with an emphasis on the methods used and the limitations of the studies with regard to biomarker discovery. This is followed by a perspective on novel technologies and on the potential future contribution of proteomics in a broad sense to understanding glioma biology.