Cell-Cycle Gene Expression in Lovastatin-Induced Medulloblastoma Apoptosis

Effects of Lovastatin on Brain Cancer Cells

Although brain tumors occur less frequently than other forms of cancer, they have one of the bleakest prognoses with low survival rates. The conventional treatment for brain tumors includes surgery, radiotherapy, and chemotherapy. However, resistance to treatment remains a problem with recurrence shortly following. The resistance to treatment may be caused by cancer stem cells (CSCs), a subset of brain tumor cells with the affinity for self-renewal and differentiation into multiple cell lineages. An emerging approach to targeting CSCs in brain tumors is through repurposing the lipid-lowering medication, lovastatin. Lovastatin is a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that impacts the mevalonate pathway. The inhibition of intermediates in the mevalonate pathway affects signaling cascades and oncogenes associated with brain tumor stem cells (BTSC). In this review, we show the possible mechanisms where lovastatin can target BTSC for different varieties of malignant brain tumors.

The multifaceted NF-kB: are there still prospects of its inhibition for clinical intervention in pediatric central nervous system tumors?

Despite advances in the understanding of the molecular mechanisms underlying the basic biology and pathogenesis of pediatric central nervous system (CNS) malignancies, patients still have an extremely unfavorable prognosis. Over the years, a plethora of natural and synthetic compounds has emerged for the pharmacologic intervention of the NF-kB pathway, one of the most frequently dysregulated signaling cascades in human cancer with key roles in cell growth, survival, and therapy resistance. Here, we provide a review about the state-of-the-art concerning the dysregulation of this hub transcription factor in the most prevalent pediatric CNS tumors: glioma, medulloblastoma, and ependymoma. Moreover, we compile the available literature on the anti-proliferative effects of varied NF-kB inhibitors acting alone or in combination with other therapies in vitro, in vivo, and clinical trials. As the wealth of basic research data continues to accumulate, recognizing NF-kB as a therapeutic target may provide important insights to treat these diseases, hopefully contributing to increase cure rates and lower side effects related to therapy.

Drug Repurposing in Medulloblastoma: Challenges and Recommendations

OPINION STATEMENT

Medulloblastoma is the most frequently diagnosed primary malignant brain tumor among children. Currently available therapeutic strategies are based on surgical resection, chemotherapy, and/or radiotherapy. However, majority of patients quickly develop therapeutic resistance and are often left with long-term therapy-related side effects and sequelae. Therefore, there remains a dire need to develop more effective therapeutics to overcome the acquired resistance to currently available therapies. Unfortunately, the process of developing novel anti-neoplastic drugs from bench to bedside is highly time-consuming and very expensive. A wide range of drugs that are already in clinical use for treating non-cancerous diseases might commonly target tumor-associated signaling pathways as well and hence be of interest in treating different cancers. This is referred to as drug repurposing or repositioning. In medulloblastoma, drug repurposing has recently gained a remarkable interest as an alternative therapy to overcome therapy resistance, wherein existing non-tumor drugs are being tested for their potential anti-neoplastic effects outside the scope of their original use.

The effect of alpha-v integrin inhibition on the malignant characteristics of medulloblastoma

OBJECT

Hypoxia induces an aggressive phenotype in some brain tumors in part due to hypoxia-inducible factor-1α (HIF-1α) and integrin expression. The importance of hypoxia in medulloblastoma is unclear and the interaction of HIF-1α and c-Myc in medulloblastoma has not been explored. The objective of this study was to determine if hypoxia induces an aggressive phenotype in human medulloblastoma cells that constitutively express high (D283 Med) or low (DAOY) levels of c-Myc and to determine if blocking α(v) integrins with the monoclonal antibody intetumumab inhibits hypoxia-induced cellular stress responses.

METHODS

Cells were grown at 21% and 1% O(2) and in the presence or absence of intetumumab. Measures of malignancy evaluated included cell proliferation, cell migration, and expression of vascular endothelial growth factor (VEGF), α(v) integrins, HIF-1α, and c-Myc.

RESULTS

Both cell lines robustly expressed α(v) integrins. Hypoxic DAOY cells showed significantly increased proliferation compared with normoxic controls (p < 0.05), whereas D283 Med cells did not. Both cell lines exhibited a dose-dependent decrease in proliferation when treated with intetumumab (p < 0.05). Hypoxia did not increase DAOY migration, but intetumumab significantly inhibited migration at both oxygen conditions (p < 0.05). Intetumumab significantly decreased VEGF levels in DAOY cells at both oxygen conditions (p < 0.05) and in normoxic D283 cells (p < 0.01). Neither cell line demonstrated increased HIF-1α expression in response to hypoxia. However, hypoxic D283 Med cells grown in the presence of intetumumab demonstrated significantly decreased c-Myc expression (p < 0.05).

CONCLUSIONS

Hypoxia did not clearly induce a more aggressive phenotype in medulloblastoma cells. Despite this result, intetumumab decreased medulloblastoma cell proliferation and migration and variably decreased VEGF and c-Myc expression in hypoxic conditions. Targeting α(v) integrins represents a promising potential adjuvant modality in the treatment of medulloblastoma, particularly subtypes that metastasize and overexpress VEGF and c-Myc.

A statin-regulated microRNA represses human c-Myc expression and function

c-Myc dysregulation is one of the most common abnormalities found in human cancer. MicroRNAs (miRNAs) are functionally intertwined with the c-Myc network as multiple miRNAs are regulated by c-Myc, while others directly suppress c-Myc expression. In this work, we identified miR-33b as a primate-specific negative regulator of c-Myc. The human miR-33b gene is located at 17p11.2, a genomic locus frequently lost in medulloblastomas, of which a subset displays c-Myc overproduction. Through a small-scale screening with drugs approved by the US Food and Drug Administration (FDA), we found that lovastatin upregulated miR-33b expression, reduced cell proliferation and impaired c-Myc expression and function in miR-33b-positive medulloblastoma cells. In addition, a low dose of lovastatin treatment at a level comparable to approved human oral use reduced tumour growth in mice orthotopically xenografted with cells carrying miR-33b, but not with cells lacking miR-33b. This work presents a highly promising therapeutic option, using drug repurposing and a miRNA as a biomarker, against cancers that overexpress c-Myc.

Statins and cancer: current and future prospects

Statins are inhibitors of 3-hydroxy-methylglutaryl (HMG) CoA reductase. They exhibit effects beyond cholesterol reduction, including anticancer activity. This review presents the effects of statins in vitro and their possible molecular anticancer mechanisms and critically discusses the data regarding the role of statins in cancer prevention. Finally, this review focuses on the use of statins combined with other chemotherapeutics to increase the effectiveness of cancer treatments. Despite rare and inconclusive clinical data, the preclinical results strongly suggest that such combined treatment could be a promising new strategy for the treatment of certain tumor types.

Intracellular distribution of beta-catenin in human medulloblastoma cell lines with different degree of neuronal differentiation

Gene mutations impairing the functions of the WNT signaling transduction pathway have been found in approximately 15% of human sporadic medulloblastomas. To understand the functional role of the WNT pathway in medulloblastoma, we have investigated the intracellular distribution of beta-catenin in a series of 17 human medulloblastomas to correlate such expression with neuronal differentiation and in cultured cell models following functional silencing of the APC gene by small-interference RNA (siRNA). Transient siRNA transfection resulted in a 50% reduction of the APC gene product levels in both DAOY and D283MED cell lines. In the former, less-differentiated cell line, beta-catenin levels remained unchanged or were slightly reduced, but beta-catenin translocated in the nucleus following APC gene siRNA silencing. In contrast, in the more differentiated D283MED cells, beta-catenin levels increased about twofold while mainly maintaining the cytoplasmic and cell membrane localization. Cytoplasmic/nuclear localization of beta-catenin was present in 12 of 17 cases of medulloblastoma with a prevalent distribution in the classic, 6/7 cases, and large cell/anaplastic variant, 4/4 cases. The nodular/desmoplastic lesions showed strongly positivity in the cell membrane mainly of intranodular cells with advanced neuronal differentiation. These observations support an important functional role of WNT/beta-catenin pathway in neuronal differentiation in medulloblastoma.

Hedgehog signaling promotes medulloblastoma survival via Bc/II

Activation of the Hedgehog (Hh) pathway has been identified in several cancers, including medulloblastoma, but the mechanisms by which this pathway affects tumor survival and growth are incompletely understood. We investigated whether Hedgehog might promote survival of medulloblastoma cells via up-regulation of BclII. We found that mRNA levels of the Hedgehog pathway effector Gli1 were significantly associated with BclII expression in medulloblastoma and that Gli1 and BclII are both present in regions of decreased apoptosis in nodular medulloblastoma. Transient overexpression of Gli1 and Gli2 in medulloblastoma cultures induced a BclII transcriptional reporter and increased BclII protein levels, whereas stable overexpression of Gli1 was associated with increased BclII mRNA. The Hedgehog antagonist cyclopamine blocked expression of the Hh pathway targets PTCH1 and Gli1, lowered BclII levels, and increased apoptosis in DAOY and UW228 medulloblastoma cells. Apoptotic induction caused by cyclopamine could be rescued in part by enforced expression of Gli1 or BclII. Hh pathway blockade also sensitized medulloblastoma to the effects of the proapoptotic agent lovastatin. These data demonstrate that BclII is an important mediator of Hh activity in medulloblastoma and suggest new strategies for combined chemotherapeutic regimens.