Aurora A is differentially expressed in gliomas, is associated with patient survival in glioblastoma and is a potential chemotherapeutic target in gliomas

O 6-methylguanine DNA methyltransferase (MGMT) expression in U1242 glioblastoma cells enhances in vitro clonogenicity, tumor implantation in vivo, and sensitivity to alisertib-carboplatin combination treatment

Glioblastoma (GBM) is the most common and aggressive primary adult CNS tumor. Increased understanding of glioma biology is needed for novel treatment strategies and maximization of current therapies. The action of the widely used antiglioma drug, temozolomide (TMZ), relies on its ability to methylate DNA guanine bases leading to DNA double strand breaks and apoptosis. However, glioma cells capable of reversing guanine methylation via the repair enzyme O 6-methylguanine DNA methyltransferase (MGMT) are resistant to TMZ. GBMs exhibiting high MGMT expression, reflected by MGMT gene promoter hypomethylation, respond poorly to both chemo- and radiation therapy. To investigate possible non-canonical biological effects of MGMT and develop a tool to investigate drug sensitivity and resistance, we generated MGMT knockout (KO) U1242 GBM cells. MGMT KO U1242 cells showed substantially increased sensitivity to TMZ in vivo, and unlike wildtype U1242 cells, failed to form tumors in nude mouse brains. They also showed reduced growth in soft agar, as did wildtype U1242 and additional glioma cell lines in which MGMT expression was knocked down by siRNA. MGMT thus possesses cellular functions related to tumor cell engraftment and anchorage-independent growth beyond guanine methyltransferase repair. We additionally show that the combination of the AURKA inhibitor alisertib and carboplatin selectively induces apoptosis in high MGMT expressing wildtype U1242 cells versus MGMT KO U1242 cells and extends survival of mice orthotopically implanted with wildtype U1242 cells. This or other platinum-based drug combinations may represent a potentially effective treatment approach to chemotherapy for GBM with MGMT promoter hypomethylation.

The AURKA inhibitor alters the immune microenvironment and enhances targeting B7-H3 immunotherapy in glioblastoma

Glioblastoma (GBM) is one of the most lethal adult brain tumors with limited effective therapeutic options. Immunotherapy targeting B7-H3 (CD276) has shown promising efficacy in the treatment of gliomas. However, the response to this treatment varies among glioma patients due to individual differences. It's necessary to find an effective strategy to improve the efficacy of targeting B7-H3 immunotherapy for nonresponders. In this study, we demonstrated a strong correlation between aurora kinase A (AURKA) and CD276 expression in glioma tissue samples. Additionally, both AURKA knockdown and overexpression resulted in parallel changes in B7-H3 expression levels in glioma cells. Mechanistically, AURKA elevated B7-H3 expression by promoting epidermal growth factor receptor (EGFR) phosphorylation, which was validated in glioma cell lines and primary GBM cells. What's more, the combination of AURKA inhibitor (alisertib) and anti-B7-H3 antibody markedly reduced tumor size and promoted CD8+ T cell infiltration and activation in mouse orthotopic syngeneic glioma models. To our knowledge, this study is the first to demonstrate AURKA-mediated B7-H3 upregulation in glioma cells; moreover, it proposes a promising therapeutic strategy combining the AURKA inhibitor alisertib with B7-H3-specific blocking mAbs.

Aurora kinase A inhibition plus Tumor Treating Fields suppress glioma cell proliferation in a cilium-independent manner

Tumor Treating Fields (TTFields) extend the survival of glioblastoma (GBM) patients by interfering with a broad range of tumor cellular processes. Among these, TTFields disrupt primary cilia stability on GBM cells. Here we asked if concomitant treatment of TTFields with other agents that interfere with GBM ciliogenesis further suppress GBM cell proliferation in vitro. Aurora kinase A (AURKA) promotes both cilia disassembly and GBM growth. Inhibitors of AURKA, such as Alisertib, inhibit cilia disassembly and increase ciliary frequency in various cell types. However, we found that Alisertib treatment significantly reduced GBM cilia frequency in gliomaspheres across multiple patient derived cell lines, and in patient biopsies treated ex vivo. This effect appeared glioma cell-specific as it did not reduce normal neuronal or glial cilia frequencies. Alisertib-mediated depletion of glioma cilia appears specific to AURKA and not AURKB inhibition, and attributable in part to autophagy pathway activation. Treatment of two different GBM patient-derived cell lines with TTFields and Alisertib resulted in a significant reduction in cell proliferation compared to either treatment alone. However, this effect was not cilia-dependent as the combined treatment reduced proliferation in cilia-depleted cell lines lacking, ARL13B, or U87MG cells which are naturally devoid of ARL13B+ cilia. Thus, Alisertib-mediated effects on glioma cilia may be a useful biomarker of drug efficacy within tumor tissue. Considering Alisertib can cross the blood brain barrier and inhibit intracranial growth, our data warrant future studies to explore whether concomitant Alisertib and TTFields exposure prolongs survival of brain tumor-bearing animals in vivo.

vNARs as Neutralizing Intracellular Therapeutic Agents: Glioblastoma as a Target

Glioblastoma is the most prevalent and fatal form of primary brain tumors. New targeted therapeutic strategies for this type of tumor are imperative given the dire prognosis for glioblastoma patients and the poor results of current multimodal therapy. Previously reported drawbacks of antibody-based therapeutics include the inability to translocate across the blood-brain barrier and reach intracellular targets due to their molecular weight. These disadvantages translate into poor target neutralization and cancer maintenance. Unlike conventional antibodies, vNARs can permeate tissues and recognize conformational or cryptic epitopes due to their stability, CDR3 amino acid sequence, and smaller molecular weight. Thus, vNARs represent a potential antibody format to use as intrabodies or soluble immunocarriers. This review comprehensively summarizes key intracellular pathways in glioblastoma cells that induce proliferation, progression, and cancer survival to determine a new potential targeted glioblastoma therapy based on previously reported vNARs. The results seek to support the next application of vNARs as single-domain antibody drug-conjugated therapies, which could overcome the disadvantages of conventional monoclonal antibodies and provide an innovative approach for glioblastoma treatment.

Cellular senescence in glioma

INTRODUCTION

Glioma is the most common primary brain tumor and is often associated with treatment resistance and poor prognosis. Standard treatment typically involves radiotherapy and temozolomide-based chemotherapy, both of which induce cellular senescence-a tumor suppression mechanism.

DISCUSSION

Gliomas employ various mechanisms to bypass or escape senescence and remain in a proliferative state. Importantly, senescent cells remain viable and secrete a large number of factors collectively known as the senescence-associated secretory phenotype (SASP) that, paradoxically, also have pro-tumorigenic effects. Furthermore, senescent cells may represent one form of tumor dormancy and play a role in glioma recurrence and progression.

CONCLUSION

In this article, we delineate an overview of senescence in the context of gliomas, including the mechanisms that lead to senescence induction, bypass, and escape. Furthermore, we examine the role of senescent cells in the tumor microenvironment and their role in tumor progression and recurrence. Additionally, we highlight potential therapeutic opportunities for targeting senescence in glioma.

Drugging Hijacked Kinase Pathways in Pediatric Oncology: Opportunities and Current Scenario

Childhood cancer is considered rare, corresponding to ~3% of all malignant neoplasms in the human population. The World Health Organization (WHO) reports a universal occurrence of more than 15 cases per 100,000 inhabitants around the globe, and despite improvements in diagnosis, treatment and supportive care, one child dies of cancer every 3 min. Consequently, more efficient, selective and affordable therapeutics are still needed in order to improve outcomes and avoid long-term sequelae. Alterations in kinases' functionality is a trademark of cancer and the concept of exploiting them as drug targets has burgeoned in academia and in the pharmaceutical industry of the 21st century. Consequently, an increasing plethora of inhibitors has emerged. In the present study, the expression patterns of a selected group of kinases (including tyrosine receptors, members of the PI3K/AKT/mTOR and MAPK pathways, coordinators of cell cycle progression, and chromosome segregation) and their correlation with clinical outcomes in pediatric solid tumors were accessed through the R2: Genomics Analysis and Visualization Platform and by a thorough search of published literature. To further illustrate the importance of kinase dysregulation in the pathophysiology of pediatric cancer, we analyzed the vulnerability of different cancer cell lines against their inhibition through the Cancer Dependency Map portal, and performed a search for kinase-targeted compounds with approval and clinical applicability through the CanSAR knowledgebase. Finally, we provide a detailed literature review of a considerable set of small molecules that mitigate kinase activity under experimental testing and clinical trials for the treatment of pediatric tumors, while discuss critical challenges that must be overcome before translation into clinical options, including the absence of compounds designed specifically for childhood tumors which often show differential mutational burdens, intrinsic and acquired resistance, lack of selectivity and adverse effects on a growing organism.

The CNS-penetrating taxane drug TPI 287 potentiates antiglioma activity of the AURKA inhibitor alisertib in vivo

INTRODUCTION

Glioblastoma (GBM) has a very poor prognosis despite current treatment. We previously found cytotoxic synergy between the AURKA inhibitor alisertib and the CNS-penetrating taxane TPI 287 against GBM tumor cells in vitro.

METHODS

We used an orthotopic human GBM xenograft mouse model to test if TPI 287 potentiates alisertib in vivo. Western blotting, immunohistochemistry, siRNA knockdown, annexin V binding, and 3-dimensional Matrigel invasion assays were used to investigate potential mechanisms of alisertib and TPI 287 treatment interactions.

RESULTS

Alisertib + TPI 287 combination therapy significantly prolonged animal survival compared to vehicle (p = 0.011), but only marginally compared to alisertib alone. Alisertib, TPI 287, and combined alisertib + TPI 287 reduced animal tumor volume compared to vehicle-treated controls. This was statistically significant for the combination therapy at 4 weeks (p < 0.0001). Alisertib + TPI 287 treatment decreased anti-apoptotic Bcl-2 protein levels in vivo and in vitro. Expression of the pro-apoptotic protein Bak was significantly increased by combination treatment (p < 0.0001). Pro-apoptotic Bim and Bak knockdown by siRNA decreased apoptosis by alisertib + TPI 287 in GB9, GB30, and U87 cells (p = 0.0005 to 0.0381). Although alisertib and TPI 287 significantly reduced GBM cell invasion (p < 0.0001), their combination was no more effective than TPI 287 alone.

CONCLUSIONS

Results suggest that apoptosis is the dominant mechanism of potentiation of GBM growth inhibition by alisertib + TPI 287, in part through effects on Bcl-2 family proteins, providing a rationale for further laboratory testing of an AURKA inhibitor plus TPI 287 as a potential therapy against GBM.

Combined inhibition of aurora kinases and Bcl-xL induces apoptosis through select BH3-only proteins

Aurora kinases (AURKs) are mitotic kinases important for regulating cell cycle progression. Small-molecule inhibitors of AURK have shown promising antitumor effects in multiple cancers; however, the utility of these inhibitors as inducers of cancer cell death has thus far been limited. Here, we examined the role of the Bcl-2 family proteins in AURK inhibition-induced apoptosis in colon cancer cells. We found that alisertib and danusertib, two small-molecule inhibitors of AURK, are inefficient inducers of apoptosis in HCT116 and DLD-1 colon cancer cells, the survival of which requires at least one of the two antiapoptotic Bcl-2 family proteins, Bcl-xL and Mcl-1. We further identified Bcl-xL as a major suppressor of alisertib- or danusertib-induced apoptosis in HCT116 cells. We demonstrate that combination of a Bcl-2 homology (BH)3-mimetic inhibitor (ABT-737), a selective inhibitor of Bcl-xL, Bcl-2, and Bcl-w, with alisertib or danusertib potently induces apoptosis through the Bcl-2 family effector protein Bax. In addition, we identified Bid, Puma, and Noxa, three BH3-only proteins of the Bcl-2 family, as mediators of alisertib-ABT-737-induced apoptosis. We show while Noxa promotes apoptosis by constitutively sequestering Mcl-1, Puma becomes associated with Mcl-1 upon alisertib treatment. On the other hand, we found that alisertib treatment causes activation of caspase-2, which promotes apoptosis by cleaving Bid into truncated Bid, a suppressor of both Bcl-xL and Mcl-1. Together, these results define the Bcl-2 protein network critically involved in AURK inhibitor-induced apoptosis and suggest that BH3-mimetics targeting Bcl-xL may help overcome resistance to AURK inhibitors in cancer cells.

Murine Central Nervous System and Bone Marrow Distribution of the Aurora A Kinase Inhibitor Alisertib: Pharmacokinetics and Exposure at the Sites of Efficacy and Toxicity

Important challenges in developing drugs that target central nervous system (CNS) tumors include overcoming barriers for CNS delivery and reducing systemic side effects. Alisertib, an aurora A kinase inhibitor, has been examined for treatment of several CNS tumors in preclinical and clinical studies. In this study, we investigated the distribution of alisertib into the CNS, the site of efficacy for brain tumors, and into the bone marrow, the site of dose-limiting toxicity leading to myelosuppression. Mechanisms influencing site-specific distribution, such as active transport mediated by the efflux proteins, p-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp), were examined. Alisertib exposure to the brain in wild-type mice was less than 1% of that in the plasma, and was evenly distributed throughout various brain regions and the spinal cord. Studies using transporter knockout mice and pharmacological inhibition show that alisertib CNS distribution is influenced by P-gp, but not Bcrp. Conversely, upon systemic administration, alisertib distribution to the bone marrow occurred rapidly, was not significantly limited by efflux transporters, and reached higher concentrations than in the CNS. This study demonstrates that, given an equivalent distributional driving force exposure in plasma, the exposure of alisertib in the brain is significantly less than that in the bone marrow, suggesting that targeted delivery may be necessary to guarantee therapeutic efficacy with minimal risk for adverse events.Therefore, these data suggest that, to improve the therapeutic index when using alisertib for brain tumors, a localized regional delivery, such as convection-enhanced delivery, may be warranted. SIGNIFICANCE STATEMENT: The CNS penetration of alisertib is limited with uniform distribution in various regions of the brain, and P-gp efflux is an important mechanism limiting that CNS distribution. Alisertib rapidly distributes into the bone marrow, a site of toxicity, with a greater exposure than in the CNS, a possible site of efficacy. These results suggest a need to design localized delivery strategies to improve the CNS exposure of alisertib and limit systemic toxicities in the treatment of brain tumors.

Centromere protein J is overexpressed in human glioblastoma and promotes cell proliferation and migration

Glioblastoma is the most common and malignant type of primary brain tumor. Previous studies have shown that alterations in centrosome amplification and its components are frequently found in treatment-resistant tumors and may be associated with tumor progression. A centrosome protein essential for centrosome biogenesis is the centromere protein J (CENPJ), known to control the proliferation of neural progenitors and hepatocarcinoma cells, and also neuronal migration. However, it remains unknown the role of CENPJ in glioblastoma. Here we show that CENPJ is overexpressed in human glioblastoma cell lines in comparison to human astrocytes. Using bioinformatics analysis, we find that high Cenpj expression is associated with poor prognosis in glioma patients. Examining Cenpj loss of function in glioblastoma by siRNA transfection, we find impairments in cell proliferation and migration. Using a Cenpj mutant version with the deleted PN2-3 or TCP domain, we found that a conserved PN2-3 region is required for glioblastoma migration. Moreover, Cenpj downregulation modulates glioblastoma morphology resulting in microtubules stabilization and actin filaments depolymerization. Altogether, our findings indicate that CENPJ controls relevant aspects of glioblastoma progression and might be a target for therapeutic intervention and a biomarker for glioma malignancy.

Astroblastomas exhibit radial glia stem cell lineages and differential expression of imprinted and X-inactivation escape genes

Astroblastomas (ABs) are rare brain tumors of unknown origin. We performed an integrative genetic and epigenetic analysis of AB-like tumors. Here, we show that tumors traceable to neural stem/progenitor cells (radial glia) that emerge during early to later brain development occur in children and young adults, respectively. Tumors with MN1-BEND2 fusion appear to present exclusively in females and exhibit overexpression of genes expressed prior to 25 post-conception weeks (pcw), including genes enriched in early ventricular zone radial glia and ependymal tumors. Other, histologically classic ABs overexpress or harbor mutations of mitogen-activated protein kinase pathway genes, outer and truncated radial glia genes, and genes expressed after 25 pcw, including neuronal and astrocyte markers. Findings support that AB-like tumors arise in the context of epigenetic and genetic changes in neural progenitors. Selective gene fusion, variable imprinting and/or chromosome X-inactivation escape resulting in biallelic overexpression may contribute to female predominance of AB molecular subtypes.

PDGF-R inhibition induces glioblastoma cell differentiation via DUSP1/p38MAPK signalling

Glioblastoma (GBM) is the most common and fatal primary brain tumour in adults. Considering that resistance to current therapies leads to limited response in patients, new therapeutic options are urgently needed. In recent years, differentiation therapy has been proposed as an alternative for GBM treatment, with the aim of bringing cancer cells into a post-mitotic/differentiated state, ultimately limiting tumour growth. As an integral component of cancer development and regulation of differentiation processes, kinases are potential targets of differentiation therapies. The present study describes how the screening of a panel of kinase inhibitors (KIs) identified PDGF-Rα/β inhibitor CP-673451 as a potential differentiation agent in GBM. We show that targeting PDGF-Rα/β with CP-673451 in vitro triggers outgrowth of neurite-like processes in GBM cell lines and GBM stem cells (GSCs), suggesting differentiation into neural-like cells, while reducing proliferation and invasion in 3D hyaluronic acid hydrogels. In addition, we report that treatment with CP-673451 improves the anti-tumour effects of temozolomide in vivo using a subcutaneous xenograft mouse model. RNA sequencing and follow-up proteomic analysis revealed that upregulation of phosphatase DUSP1 and consecutive downregulation of phosphorylated-p38^MAPK can underlie the pro-differentiation effect of CP-673451 on GBM cells. Overall, the present study identifies a potential novel therapeutic option that could benefit GBM patients in the future, through differentiation of residual GSCs post-surgery, with the aim to limit recurrence and improve quality of life.

Machine Learning-Based Analysis of Glioma Grades Reveals Co-Enrichment

Gliomas develop and grow in the brain and central nervous system. Examining glioma grading processes is valuable for improving therapeutic challenges. One of the most extensive repositories storing transcriptomics data for gliomas is The Cancer Genome Atlas (TCGA). However, such big cohorts should be processed with caution and evaluated thoroughly as they can contain batch and other effects. Furthermore, biological mechanisms of cancer contain interactions among biomarkers. Thus, we applied an interpretable machine learning approach to discover such relationships. This type of transparent learning provides not only good predictability, but also reveals co-predictive mechanisms among features. In this study, we corrected the strong and confounded batch effect in the TCGA glioma data. We further used the corrected datasets to perform comprehensive machine learning analysis applied on single-sample gene set enrichment scores using collections from the Molecular Signature Database. Furthermore, using rule-based classifiers, we displayed networks of co-enrichment related to glioma grades. Moreover, we validated our results using the external glioma cohorts. We believe that utilizing corrected glioma cohorts from TCGA may improve the application and validation of any future studies. Finally, the co-enrichment and survival analysis provided detailed explanations for glioma progression and consequently, it should support the targeted treatment.

Aurora-A kinase is differentially expressed in the nucleus and cytoplasm in normal Müllerian epithelium and benign, borderline and malignant serous ovarian neoplasms

Background

Aurora-A kinase is important for cellular proliferation and is implicated in the tumorigenesis of several malignancies, including of the ovary. Information regarding the expression patterns of Aurora-A in normal Müllerian epithelium as well as benign, borderline and malignant epithelial ovarian neoplasms is limited.

Methods

We investigated Aurora-A expression by immunohistochemistry in 15 benign, 19 borderline and 17 malignant ovarian serous tumors, and 16 benign, 8 borderline, and 2 malignant ovarian mucinous tumors. Twelve fimbriae from seven patients served as normal Müllerian epithelium controls. We also examined Aurora-A protein expression by western blot in normal fimbriae and tumor specimens.

Results

All normal fimbriae (n = 12) showed nuclear but not cytoplasmic Aurora-A immunoreactivity by immunohistochemistry. Benign ovarian tumors also showed strong nuclear Aurora-A immunoreactivity. Forty-eight percent (13/27) of borderline tumors demonstrated nuclear Aurora-A immunoreactivity, while the remainder (52%, 14/27) lacked Aurora-A staining. Nuclear Aurora-A immunoreactivity was absent in all malignant serous tumors, however, 47% (8/17) demonstrated perinuclear cytoplasmic staining. These results were statistically significant when tumor class (benign/borderline/malignant) was compared to immunoreactivity localization or intensity (Fisher Exact Test, p < 0.01). Western blot analysis confirmed the greater nuclear Aurora-A expression in control Müllerian epithelium compared to borderline and malignant tumors.

Conclusion

Aurora-A kinase is differentially expressed across normal Müllerian epithelium, benign and borderline serous and mucinous ovarian epithelial neoplasms and malignant serous ovarian tumors., with nuclear expression of unphosphorylated Aurora-A being present in normal and benign neoplastic epithelium, and lost in malignant serous neoplasms. Further studies of the possible biological and clinical implications of the loss of nuclear Aurora-A expression in ovarian tumors, and its role in ovarian carcinogenesis are warranted.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13000-021-01158-4.

Viability fingerprint of glioblastoma cell lines: roles of mitotic, proliferative, and epigenetic targets

Despite the use of multimodal treatment combinations, the prognosis of glioblastoma (GB) is still poor. To prevent rapid tumor recurrence, targeted strategies for the treatment of GB are widely sought. Here, we compared the efficacy of focused modulation of a set of signaling pathways in two GB cell lines, U-251 MG and T98-G, using a panel of thirteen compounds targeting cell cycle progression, proliferation, epigenetic modifications, and DNA repair mechanism. In parallel, we tested combinations of these compounds with temozolomide and lomustine, the standard chemotherapy agents used in GB treatment. Two major trends were found: within individual compounds, the lowest IC₅₀ values were exhibited by the Aurora kinase inhibitors, whereas in the case of mixtures, the addition of DNA methyltransferase 1 inhibitor azacytidine to lomustine proved the most beneficial. The efficacy of cell cycle-targeting compounds was further augmented by combination with radiation therapy using two different treatment regimes. The potency of azacytidine and lomustine mixtures was validated using a unique assay pipeline that utilizes automated imaging and machine learning-based data analysis algorithm for assessment of cell number and DNA damage extent. Based on our results, the combination of azacytidine and lomustine should be tested in GB clinical trials.

Alpelisib and radiotherapy treatment enhances Alisertib-mediated cervical cancer tumor killing

Human papilloma virus (HPV) is the main causative agent in cervical cancers. High-risk HPV cancers, including cervical cancer, are driven by major HPV oncogene, E6 and E7, which promote uncontrolled cell growth and genomic instability. We have previously shown that the presence of HPV E7 sensitizes cells to inhibition of aurora kinases (AURKs), which regulates the control of cell entry into and through mitosis. Such treatment is highly effective at eliminating early tumors and reducing large, late tumors. In addition, the presence of HPV oncogenes also sensitizes cells to inhibition of phosphoinositide 3-kinases (PI3Ks), a family of enzymes involved in cellular functions such as cell growth and proliferation. Using MLN8237 (Alisertib), an oral, selective inhibitor of AURKs, we investigated whether Alisertib treatment can improve tumor response when combined with either radiotherapy (RT) treatment or with a PI3K inhibitor, BYL719 (Alpelisib). Indeed, both RT and Alpelisib significantly improved Alisertib-mediated tumor killing, and the promising achieved results warrant further development of these combinations, and potentially translating them to the clinics.

Targeting glioma cells by antineoplastic activity of reversine

Gliomas are the most common type of primary central nervous system tumors and despite great advances in understanding the molecular basis of the disease very few new therapies have been developed. Reversine, a synthetic purine analog, is a multikinase inhibitor that targets aurora kinase A (AURKA) and aurora kinase B (AURKB). In gliomas, a high expression of AURKA or AURKB is associated with a malignant phenotype and a poor prognosis. The present study investigated reversine-related cellular and molecular antiglioma effects in HOG, T98G and U251MG cell lines. Gene and protein expression were assessed by reverse transcription-quantitative PCR and western blotting, respectively. For functional assays, human glioma cell lines (HOG, T98G and U251MG) were exposed to increasing concentrations of reversine (0.4–50 µM) and subjected to various cellular and molecular assays. Reversine reduced the viability and clonogenicity in a dose- and/or time-dependent manner in all glioma cells, with HOG (high AURKB-expression) and T98G (high AURKA-expression) cells being more sensitive compared with U251MG cells (low AURKA- and AURKB-expression). Notably, HOG cells presented higher levels of polyploidy, while T98G presented multiple mitotic spindles, which is consistent with the main regulatory functions of AURKB and AURKA, respectively. In molecular assays, reversine reduced AURKA and/or AURKB expression/activity and increased DNA damage and apoptosis markers, but autophagy-related proteins were not modulated. In conclusion, reversine potently induced mitotic catastrophe and apoptosis in glioma cells and higher basal levels of aurora kinases and genes responsive to DNA damage and may predict improved antiglioma responses to the drug. Reversine may be a potential novel drug in the antineoplastic arsenal against gliomas.

Role of glioblastoma stem cells in cancer therapeutic resistance: a perspective on antineoplastic agents from natural sources and chemical derivatives

Glioblastoma (GBM) is the highest-grade form of glioma, as well as one of the most aggressive types of cancer, exhibiting rapid cellular growth and highly invasive behavior. Despite significant advances in diagnosis and therapy in recent decades, the outcomes for high-grade gliomas (WHO grades III-IV) remain unfavorable, with a median overall survival time of 15–18 months. The concept of cancer stem cells (CSCs) has emerged and provided new insight into GBM resistance and management. CSCs can self-renew and initiate tumor growth and are also responsible for tumor cell heterogeneity and the induction of systemic immunosuppression. The idea that GBM resistance could be dependent on innate differences in the sensitivity of clonogenic glial stem cells (GSCs) to chemotherapeutic drugs/radiation prompted the scientific community to rethink the understanding of GBM growth and therapies directed at eliminating these cells or modulating their stemness. This review aims to describe major intrinsic and extrinsic mechanisms that mediate chemoradioresistant GSCs and therapies based on antineoplastic agents from natural sources, derivatives, and synthetics used alone or in synergistic combination with conventional treatment. We will also address ongoing clinical trials focused on these promising targets. Although the development of effective therapy for GBM remains a major challenge in molecular oncology, GSC knowledge can offer new directions for a promising future.

Targeting MYCN in Molecularly Defined Malignant Brain Tumors

Misregulation of MYC genes, causing MYC overexpression or protein stabilization, is frequently found in malignant brain tumors highlighting their important roles as oncogenes. Brain tumors in children are the most lethal of all pediatric malignancies and the most common malignant primary adult brain tumor, glioblastoma, is still practically incurable. MYCN is one of three MYC family members and is crucial for normal brain development. It is associated with poor prognosis in many malignant pediatric brain tumor types and is focally amplified in specific adult brain tumors. Targeting MYCN has proved to be challenging due to its undruggable nature as a transcription factor and for its importance in regulating developmental programs also in healthy cells. In this review, we will discuss efforts made to circumvent the difficulty of targeting MYCN specifically by using direct or indirect measures to treat MYCN-driven brain tumors. We will further consider the mechanism of action of these measures and suggest which molecularly defined brain tumor patients that might benefit from MYCN-directed precision therapies.

MicroRNA-based regulation of Aurora A kinase in breast cancer

The involvement of non-coding RNAs (ncRNAs) in cellular physiology and disease pathogenesis is becoming increasingly relevant in recent years specifically in cancer research. Breast cancer (BC) has become a health concern and accounts for most of the cancer-related incidences and mortalities reported amongst females. In spite of the presence of promising tools for BC therapy, the mortality rate of metastatic BC cases is still high. Therefore, the genomic exploration of the BC subtype and the use of ncRNAs for possible regulation is pivotal. The expression and prognostic values of AURKA gene were assessed by Oncomine, GEPIA, KM-plotter, and bc-GenExMiner v4.4, respectively. Associated proteins and functional enrichment were evaluated by Cytoscape and DAVID databases. Additionally, molecular docking approach was employed to investigate the regulatory role of hsa-miR-32-3p assisted argonaute (AGO) protein of AURKA gene in BC. AURKA gene was highly expressed in patients with BC relative to normal counterpart and significantly correlated with poor survival. The docking result suggested that AURKA could be regulated by hsa-miR-32-3p as confirmed by the reported binding energy and specific interactions. The study gives some insights into role of AURKA and its regulation by microRNAs through AGO protein. It also provides exciting opportunities for cancer therapeutic intervention.

Disentangling the therapeutic tactics in GBM: From bench to bedside and beyond

Glioblastoma multiforme (GBM) is one of the most common and malignant form of adult brain tumor with a high mortality rate and dismal prognosis. The present standard treatment comprising surgical resection followed by radiation and chemotherapy using temozolomide can broaden patient's survival to some extent. However, the advantages are not palliative due to the development of resistance to the drug and tumor recurrence following the multimodal treatment approaches due to both intra- and intertumoral heterogeneity of GBM. One of the major contributors to temozolomide resistance is O⁶ -methylguanine-DNA methyltransferase. Furthermore, deficiency of mismatch repair, base excision repair, and cytoprotective autophagy adds to temozolomide obstruction. Rising proof additionally showed that a small population of cells displaying certain stem cell markers, known as glioma stem cells, adds on to the resistance and tumor progression. Collectively, these findings necessitate the discovery of novel therapeutic avenues for treating glioblastoma. As of late, after understanding the pathophysiology and biology of GBM, some novel therapeutic discoveries, such as drug repurposing, targeted molecules, immunotherapies, antimitotic therapies, and microRNAs, have been developed as new potential treatments for glioblastoma. To help illustrate, "what are the mechanisms of resistance to temozolomide" and "what kind of alternative therapeutics can be suggested" with this fatal disease, a detailed history of these has been discussed in this review article, all with a hope to develop an effective treatment strategy for GBM.

Elevated levels of Drosophila Wdr62 promote glial cell growth and proliferation through AURKA signalling to AKT and MYC

WD40-Repeat Protein 62 (WDR62) is required to maintain neural and glial cell populations during embryonic brain growth. Although elevated expression of WDR62 is frequently associated with several tumour types, potential effects of excess WDR62 on proliferative growth remain undefined. Here, we demonstrate that glia specific overexpression of WDR62 in Drosophila larval brains resulted in increased cell size, over-proliferation and increased brain volume, without overt disruption of tissue organization. We further demonstrate WDR62 promoted over-proliferation and brain overgrowth by activating AURKA and pAKT signalling to increase MYC function in glial cells. Together these data suggest WDR62 normally functions in the glial lineage to activate oncogenic signalling networks, promoting proliferation and brain overgrowth.

The therapeutic potential of Aurora kinases targeting in glioblastoma: from preclinical research to translational oncology

Glioblastoma is the most common aggressive primary brain tumor. Standard care includes maximal safe surgical resection, radiation, and chemotherapy with temozolomide. However, the impact of this therapeutic approach on patient survival is disappointing and poor outcomes are frequently observed. Therefore, new therapeutic targets are needed to treat this potentially deadly tumor. Aurora kinases are one of today's most sought-after classes of therapeutic targets to glioblastoma therapy. They are a family of proteins composed of three members: Aurora-A, Aurora-B, and Aurora-C that play different roles in the cell division through regulation of chromosome segregation. Deregulation of these genes has been reported in glioblastoma and a progressive number of studies have shown that inhibition of these proteins could be a promising strategy for the treatment of this tumor. This review discusses the preclinical and early clinical findings on the potential use of the Aurora kinases as new targets for the treatment of glioblastoma. KEY MESSAGES: GBM is a very aggressive tumor with limited therapeutic options. Aurora kinases are a family of serine/threonine kinases implicated in GBM pathology. Aurora kinases are critical for glioblastoma cell growth, apoptosis, and chemoresistance. Inhibition of Aurora kinases has a synergistic or sensitizing effect with chemotherapy drugs, radiotherapy, or with other targeted molecules in GBM. Several Aurora kinase inhibitors are currently in clinical trials.

BET and Aurora Kinase A inhibitors synergize against MYCN-positive human glioblastoma cells

Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor in adults. Patients usually undergo surgery followed by aggressive radio- and chemotherapy with the alkylating agent temozolomide (TMZ). Still, median survival is only 12–15 months after diagnosis. Many human cancers including GBMs demonstrate addiction to MYC transcription factor signaling and can become susceptible to inhibition of MYC downstream genes. JQ1 is an effective inhibitor of BET Bromodomains, a class of epigenetic readers regulating expression of downstream MYC targets. Here, we show that BET inhibition decreases viability of patient-derived GBM cell lines. We propose a distinct expression signature of MYCN-elevated GBM cells that correlates with significant sensitivity to BET inhibition. In tumors showing JQ1 sensitivity, we found enrichment of pathways regulating cell cycle, DNA damage response and repair. As DNA repair leads to acquired chemoresistance to TMZ, JQ1 treatment in combination with TMZ synergistically inhibited proliferation of MYCN-elevated cells. Bioinformatic analyses further showed that the expression of MYCN correlates with Aurora Kinase A levels and Aurora Kinase inhibitors indeed showed synergistic efficacy in combination with BET inhibition. Collectively, our data suggest that BET inhibitors could potentiate the efficacy of either TMZ or Aurora Kinase inhibitors in GBM treatment.

Activation of Aurora A kinase increases YAP stability via blockage of autophagy

Transcription cofactor Yes-associated protein (YAP) plays an important role in cancer progression. Here, we found that Aurora A kinase expression was positively correlated with YAP in lung cancer. Aurora A depletion suppresses lung cancer cell colony formation, which could be reversed by YAP ectopic overexpression. In addition, activation of Aurora A increases YAP protein abundance through maintaining its protein stability. Consistently, the transcriptional activity of YAP is increased upon Aurora A activation. We further showed that shAURKA suppressed YAP expression in the absence of Lats1/2, indicating that Aurora A regulates YAP independently of Hippo pathway. Instead, Aurora A induced blockage of autophagy to up-regulate YAP expression. Collectively, our findings provide insights into regulatory mechanisms of YAP expression in lung cancer development.

Cytotoxic synergy between alisertib and carboplatin versus alisertib and irinotecan are inversely dependent on MGMT levels in glioblastoma cells

INTRODUCTION

Glioblastoma remains difficult to treat and patients whose tumors express high levels of O⁶-methylguanine DNA methyltransferase (MGMT) usually respond poorly to standard temozolomide chemotherapy. We have previously shown that the selective AURKA inhibitor alisertib potently inhibits growth of glioblastoma cells.

METHODS

We used colony formation assays, annexin V binding, and western blotting to examine the effects of alisertib on the antiproliferative capabilities of carboplatin and irinotecan in glioblastoma cells.

RESULTS

In colony formation assays, alisertib potentiated the antiproliferative effects of both carboplatin and irinotecan, often synergistically, including against glioblastoma tumor stem-like cells, as demonstrated by Chou-Talalay and Bliss statistical analyses. Western blotting showed that high MGMT expression in cell lines correlated with more pronounced potentiation of carboplatin's growth inhibitory effects by alisertib, while low MGMT expression correlated with stronger potentiation of irinotecan by alisertib. This pattern was also observed when these drug combinations were tested for their ability to induce apoptosis via annexin V binding assays. MGMT knockdown increased apoptosis caused by combined alisertib and irinotecan, while exogenous MGMT overexpression increased apoptosis from alisertib and carboplatin combination treatment.

CONCLUSIONS

These results suggest that tumor MGMT expression levels may be predictive of patient response to these drug combinations, and importantly that the combination of alisertib and carboplatin may be selectively effective in glioblastoma patients with high tumor MGMT who are resistant to standard therapy. Since clinical experience with alisertib, carboplatin and irinotecan as single agents already exists, these findings may provide rationale for the design of clinical trials for their use in combination treatment regimens.

Selective BCL-XL inhibition promotes apoptosis in combination with MLN8237 in medulloblastoma and pediatric glioblastoma cells

Background

CNS tumors, including medulloblastoma and pediatric glioblastoma (pGBM) account for the majority of solid pediatric malignancies. There remains an unmet need to identify novel treatment approaches in poor prognosis and relapsed pediatric brain tumors, where therapeutic options are limited. Small-molecule B-cell lymphoma 2 (BCL-2) family inhibitors may enhance tumor cell killing when combined with conventional and targeted chemotherapeutic agents. We investigated the effect of disrupting BCL-2 and B cell lymphoma-extra large (BCL-XL) protein function using ABT-263, ABT-199 and WEHI-539 in medulloblastoma and pGBM cells following treatment with MLN8237, an Aurora kinase inhibitor under investigation as a novel agent for the treatment of malignant brain tumors.

Methods

Tumor cell growth and viability were determined by MTT/WST-1 assays and flow cytometry. Effects on cell phenotype, cell cycle progression, and ploidy were determined by live cell imaging and DNA content analysis. Apoptosis was determined by annexin V/propidium iodide staining and time-lapse microscopy and confirmed by measuring caspase-3/7 activity and western blotting and by short interfering RNA (siRNA) knockdown of BCL-2 associated X protein/BCL-2 antagonist killer (BAX/BAK).

Results

ABT-263, in combination with MLN8237, reduced mitotic slippage and polyploidy and promoted the elimination of mitotically defective cells via a BAX/BAK-dependent, caspase-mediated apoptotic pathway. The BCL-XL antagonist, WEHI-539, significantly augmented tumor cell killing when used in combination with MLN8237, as well as sensitized resistant brain tumor cells to a novel BAX activator, SMBA1. In addition, siRNA-mediated knockdown of BCL-XL sensitized pGBM and medulloblastoma cells to MLN8237 and mimicked the effect of combination drug treatment.

Conclusion

Selective small-molecule inhibitors of BCL-XL may enhance the efficacy of MLN8237 and other targeted chemotherapeutic agents.

Role of senescence induction in cancer treatment

Cellular senescence is a form of permanent cell cycle arrest that can be triggered by a variety of cell-intrinsic and extrinsic stimuli, including telomere shortening, DNA damage, oxidative stress, and exposure to chemotherapeutic agents and ionizing radiation. Although the induction of apoptotic cell death is a desirable outcome in cancer therapy, mutations and/or deficiencies in the apoptotic signaling pathways have been frequently identified in many human cancer types, suggesting the importance of alternative apoptosis-independent therapeutic approaches for cancer treatment. A growing body of evidence has documented that senescence induction in tumor cells is a frequent response to many anticancer modalities including cyclin-dependent kinases 4/6 small molecule inhibitor-based targeted therapeutics and T helper-1 cytokine-mediated immunotherapy. This review discusses the recent advances and clinical relevance of therapy-induced senescence in cancer treatment.

Potential Strategies Overcoming the Temozolomide Resistance for Glioblastoma

Glioblastoma (GBM) is a highly malignant type of primary brain tumor with a high mortality rate. Although the current standard therapy consists of surgery followed by radiation and temozolomide (TMZ), chemotherapy can extend patient's post-operative survival but most cases eventually demonstrate resistance to TMZ. O6-methylguanine-DNA methyltransferase (MGMT) repairs the main cytotoxic lesion, as O6-methylguanine, generated by TMZ, can be the main mechanism of the drug resistance. In addition, mismatch repair and BER also contribute to TMZ resistance. TMZ treatment can induce self-protective autophagy, a mechanism by which tumor cells resist TMZ treatment. Emerging evidence also demonstrated that a small population of cells expressing stem cell markers, also identified as GBM stem cells (GSCs), contributes to drug resistance and tumor recurrence owing to their ability for self-renewal and invasion into neighboring tissue. Some molecules maintain stem cell properties. Other molecules or signaling pathways regulate stemness and influence MGMT activity, making these GCSs attractive therapeutic targets. Treatments targeting these molecules and pathways result in suppression of GSCs stemness and, in highly resistant cases, a decrease in MGMT activity. Recently, some novel therapeutic strategies, targeted molecules, immunotherapies, and microRNAs have provided new potential treatments for highly resistant GBM cases. In this review, we summarize the current knowledge of different resistance mechanisms, novel strategies for enhancing the effect of TMZ, and emerging therapeutic approaches to eliminate GSCs, all with the aim to produce a successful GBM treatment and discuss future directions for basic and clinical research to achieve this end.

An Aurora kinase inhibitor, AMG900, inhibits glioblastoma cell proliferation by disrupting mitotic progression

The Aurora kinase family of serine/threonine protein kinases comprises Aurora A, B, and C and plays an important role in mitotic progression. Several inhibitors of Aurora kinase have been developed as anti‐cancer therapeutics. Here, we examined the effects of a pan‐Aurora kinase inhibitor, AMG900, against glioblastoma cells. AMG900 inhibited proliferation of A172, U‐87MG, and U‐118MG glioblastoma cells by upregulating p53 and p21 and subsequently inducing cell cycle arrest and senescence. Abnormal cell cycle progression was triggered by dysregulated mitosis. Mitosis was prolonged due to a defect in mitotic spindle assembly. Despite the presence of an unattached kinetochore, BubR1, a component of the spindle assembly checkpoint, was not recruited. In addition, Aurora B was not recruited to central spindle at anaphase. Abnormal mitotic progression resulted in accumulation of multinuclei and micronuclei, a type of chromosome missegregation, and ultimately inhibited cell survival. Therefore, the data suggest that AMG900‐mediated inhibition of Aurora kinase is a potential anti‐cancer therapy for glioblastoma.

Aurora A plays a dual role in migration and survival of human glioblastoma cells according to the CXCL12 concentration

Primary glioblastoma is the most frequent human brain tumor in adults and is generally fatal due to tumor recurrence. We previously demonstrated that glioblastoma-initiating cells invade the subventricular zones and promote their radio-resistance in response to the local release of the CXCL12 chemokine. In this work, we show that the mitotic Aurora A kinase (AurA) is activated through the CXCL12–CXCR4 pathway in an ERK1/2-dependent manner. Moreover, the CXCL12–ERK1/2 signaling induces the expression of Ajuba, the main cofactor of AurA, which allows the auto-phosphorylation of AurA.

We show that AurA contributes to glioblastoma cell survival, radio-resistance, self-renewal, and proliferation regardless of the exogenous stimulation with CXCL12. On the other hand, AurA triggers the CXCL12-mediated migration of glioblastoma cells in vitro as well as the invasion of the subventricular zone in xenograft experiments. Moreover, AurA regulates cytoskeletal proteins (i.e., Actin and Vimentin) and favors the pro-migratory activity of the Rho-GTPase CDC42 in response to CXCL12. Altogether, these results show that AurA, a well-known kinase of the mitotic machinery, may play alternative roles in human glioblastoma according to the CXCL12 concentration.

Aurora kinase A interacts with H-Ras and potentiates Ras-MAPK signaling

In cancer, upregulated Ras promotes cellular transformation and proliferation in part through activation of oncogenic Ras-MAPK signaling. While directly inhibiting Ras has proven challenging, new insights into Ras regulation through protein-protein interactions may offer unique opportunities for therapeutic intervention. Here we report the identification and validation of Aurora kinase A (Aurora A) as a novel Ras binding protein. We demonstrate that the kinase domain of Aurora A mediates the interaction with the N-terminal domain of H-Ras. Further more, the interaction of Aurora A and H-Ras exists in a protein complex with Raf-1. We show that binding of H-Ras to Raf-1 and subsequent MAPK signaling is enhanced by Aurora A, and requires active H-Ras. Thus, the functional linkage between Aurora A and the H-Ras/Raf-1 protein complex may provide a mechanism for Aurora A's oncogenic activity through direct activation of the Ras/MAPK pathway.

Concurrent Inhibition of Neurosphere and Monolayer Cells of Pediatric Glioblastoma by Aurora A Inhibitor MLN8237 Predicted Survival Extension in PDOX Models

Purpose: Pediatric glioblastoma multiforme (pGBM) is a highly aggressive tumor in need of novel therapies. Our objective was to demonstrate the therapeutic efficacy of MLN8237 (alisertib), an orally available selective inhibitor of Aurora A kinase (AURKA), and to evaluate which in vitro model system (monolayer or neurosphere) can predict therapeutic efficacy in vivoExperimental Design: AURKA mRNA expressions were screened with qRT-PCR. In vitro antitumor effects were examined in three matching pairs of monolayer and neurosphere lines established from patient-derived orthotopic xenograft (PDOX) models of the untreated (IC-4687GBM), recurrent (IC-3752GBM), and terminal (IC-R0315GBM) tumors, and in vivo therapeutic efficacy through log rank analysis of survival times in two models (IC-4687GBM and IC-R0315GBM) following MLN8237 treatment (30 mg/kg/day, orally, 12 days). Drug concentrations in vivo and mechanism of action and resistance were also investigated.Results: AURKA mRNA overexpression was detected in 14 pGBM tumors, 10 PDOX models, and 6 cultured pGBM lines as compared with 11 low-grade gliomas and normal brains. MLN8237 penetrated into pGBM xenografts in mouse brains. Significant extension of survival times were achieved in IC-4687GBM of which both neurosphere and monolayer were inhibited in vitro, but not in IC-R0315GBM of which only neurosphere cells responded (similar to IC-3752GBM). Apoptosis-mediated MLN8237 induced cell death, and the presence of AURKA-negative and CD133⁺ cells appears to have contributed to in vivo therapy resistance.Conclusions: MLN8237 successfully targeted AURKA in a subset of pGBMs. Our data suggest that combination therapy should aim at AURKA-negative and/or CD133⁺ pGBM cells to prevent tumor recurrence. Clin Cancer Res; 24(9); 2159-70. ©2018 AACR.

The CNS penetrating taxane TPI 287 and the AURKA inhibitor alisertib induce synergistic apoptosis in glioblastoma cells

Glioblastoma is a highly malignant disease in critical need of expanded treatment options. The AURKA inhibitor alisertib exhibits antiproliferative activity against glioblastoma in vitro and in vivo. Unlike current clinically used taxane drugs, the novel taxane TPI 287 penetrates the CNS. We tested for interactions between three selective AURKA inhibitors and TPI 287 against standard U87 and U1242 cells and primary glioblastoma neurospheres using colony formation assays. Bliss and Chou-Talalay analyses were utilized to statistically test for synergism. Morphological analysis, flow cytometry and annexin V binding were employed to examine cell cycle and apoptotic effects of these drug combinations. TPI 287 not only potentiated the cytotoxicity of the AURKA inhibitors alisertib, MLN8054 and TC-A2317, but was often potently synergistic. Morphologic and biochemical analysis of the combined effects of alisertib and TPI 287 consistently revealed synergistic induction of apoptosis. While each agent alone induces a mitotic block, slippage occurs allowing some tumor cells to avoid apoptosis. Combination treatment greatly attenuated mitotic slippage, committing the majority of cells to apoptosis. Alisertib and TPI 287 demonstrate significant synergism against glioblastoma cells largely attributable to a synergistic effect in inducing apoptosis. These results provide compelling rationale for clinical testing of alisertib and/or other AURKA inhibitors for potential combination use with TPI 287 against glioblastoma and other CNS neoplasms.

G2/M inhibitors as pharmacotherapeutic opportunities for glioblastoma: the old, the new, and the future

Glioblastoma (GBM) is one of the deadliest tumors and has a median survival of 3 months if left untreated. Despite advances in rationally targeted pharmacological approaches, the clinical care of GBM remains palliative in intent. Since the majority of altered signaling cascades involved in cancer establishment and progression eventually affect cell cycle progression, an alternative approach for cancer therapy is to develop innovative compounds that block the activity of crucial molecules needed by tumor cells to complete cell division. In this context, we review promising ongoing and future strategies for GBM therapeutics aimed towards G2/M inhibition such as anti-microtubule agents and targeted therapy against G2/M regulators like cyclin-dependent kinases, Aurora inhibitors, PLK1, BUB, 1, and BUBR1, and survivin. Moreover, we also include investigational agents in the preclinical and early clinical settings. Although several drugs were shown to be gliotoxic, most of them have not yet entered therapeutic trials. The use of either single exposure or a combination with novel compounds may lead to treatment alternatives for GBM patients in the near future.

Alisertib induces G2/M arrest, apoptosis, and autophagy via PI3K/Akt/mTOR- and p38 MAPK-mediated pathways in human glioblastoma cells

Glioblastoma (GBM) is the most common brain tumor with poor response to current therapeutics. Alisertib (ALS), a second-generation selective Aurora kinase A (AURKA) inhibitor, has shown potent anticancer effects on solid tumors in animal studies. This study aimed to investigate the killing effect of ALS on GBM cell line DAOY and the possible underlying mechanisms using both bioinformatic and cell-based approaches. Our molecular docking showed that ALS preferentially bound AURKA over AURKB via hydrogen bond formation, charge interaction, and π-π stacking. ALS also bound key regulating proteins of cell cycle, apoptosis and autophagy, such as cyclin-dependent kinase 1 (CDK1/CDC2), CDK2, cyclin B1, p27 Kip1, p53, cytochrome C, cleaved caspase 3, Bax, Bcl-2, Bcl-xl, phosphatidylinositol 3-kinase (PI3K), protein kinase B (Akt), mammalian target of rapamycin (mTOR), 5'-adenosine monophosphate-activated protein kinase (AMPK), p38 mitogen-activated protein kinase (MAPK), beclin 1, phosphatase and tensin homolog (PTEN), and microtubule-associated protein light chain 3 (LC3). ALS exhibited potent growth-inhibitory, pro-apoptotic, and pro-autophagic effects on DAOY cells in a concentration-dependent manner. Notably, ALS remarkably induced G₂/M arrest mainlyvia regulating the expression of CDK1/CDC2, CDK2, cyclin B1, p27 Kip1, and p53 in DAOY cells. ALS significantly induced the expression of mitochondria-mediated pro-apoptotic proteins such as Baxbut inhibited the expression of anti-apoptotic proteins such as Bcl-2 and Bcl-xl, with a significant increase in the release of cytochrome C and the activation of caspases 3 and 9. ALS also induced PI3K/Akt/mTOR and p38 MAPK signaling pathways while activating the AMPK signaling pathway. Taken together, these findings indicate that ALS exerts a potent inhibitory effect on cell proliferation and induces mitochondria-dependent apoptosis and autophagy with the involvement of PI3K/Akt/mTOR- and p38 MAPK-mediated signaling pathways in DAOY cells. ALS is a promising anticancer agent for GBM treatment.

Dual Inhibition of PDK1 and Aurora Kinase A: An Effective Strategy to Induce Differentiation and Apoptosis of Human Glioblastoma Multiforme Stem Cells

The poor prognosis of glioblastoma multiforme (GBM) is mainly attributed to drug resistance mechanisms and to the existence of a subpopulation of glioma stem cells (GSCs). Multitarget compounds able to both affect different deregulated pathways and the GSC subpopulation could escape tumor resistance and, most importantly, eradicate the stem cell reservoir. In this respect, the simultaneous inhibition of phosphoinositide-dependent kinase-1 (PDK1) and aurora kinase A (AurA), each one playing a pivotal role in cellular survival/migration/differentiation, could represent an innovative strategy to overcome GBM resistance and recurrence. Herein, the cross-talk between these pathways was investigated, using the single-target reference compounds MP7 (PDK1 inhibitor) and Alisertib (AurA inhibitor). Furthermore, a new ligand, SA16, was identified for its ability to inhibit the PDK1 and the AurA pathways at once, thus proving to be a useful tool for the simultaneous inhibition of the two kinases. SA16 blocked GBM cell proliferation, reduced tumor invasiveness, and triggered cellular apoptosis. Most importantly, the AurA/PDK1 blocker showed an increased efficacy against GSCs, inducing their differentiation and apoptosis. To the best of our knowledge, this is the first report on combined targeting of PDK1 and AurA. This drug represents an attractive multitarget lead scaffold for the development of new potential treatments for GBM and GSCs.

Alisertib demonstrates significant antitumor activity in bevacizumab resistant, patient derived orthotopic models of glioblastoma

Aurora A kinase (AURKA), a member of the serine/threonine kinase family, plays a critical role in cell division, and it is widely overexpressed in a variety of tumors including glioblastoma (GBM). Alisertib (MLN8237) is an orally administered selective AURKA inhibitor with potent antiproliferative activity, currently undergoing clinical testing in different tumor types. In vitro evaluation of alisertib against the primary GBM lines, GBM6, GBM10, GBM12 and GBM39 showed significant antitumor activity with IC_50s ranging between 30 and 95 nM. Orthotopic xenografts of GBM10 and the bevacizumab resistant lines GBM6 and GBM39 were established by implantating 3 × 10⁵ cells in the caudate nucleus of nude mice; animals were randomized to treatment with either alisertib 30 mg/kg/day or vehicle. In all three models, treatment with alisertib resulted in a statistically significant prolongation of survival (p < 0.0001). In addition, alisertib administration in these mice decreased phosphorylated aurora-A, induced mitotic arrest and significantly decreased histone H3 phosphorylation in tumors. In conclusion, alisertib displays significant antitumor activity against primary GBM lines and xenografts, including patient derived GBM lines resistant to bevacizumab; these data support clinical translation in GBM.

The Ski Protein is Involved in the Transformation Pathway of Aurora Kinase A

Oncogenic kinase Aurora A (AURKA) has been found to be overexpresed in several tumors including colorectal, breast, and hematological cancers. Overexpression of AURKA induces centrosome amplification and aneuploidy and it is related with cancer progression and poor prognosis. Here we show that AURKA phosphorylates in vitro the transcripcional co-repressor Ski on aminoacids Ser326 and Ser383. Phosphorylations on these aminoacids decreased Ski protein half-life. Reduced levels of Ski resulted in centrosomes amplification and multipolar spindles formation, same as AURKA overexpressing cells. Importantly, overexpression of Ski wild type, but not S326D and S383D mutants inhibited centrosome amplification and cellular transformation induced by AURKA. Altogether, these results suggest that the Ski protein is a target in the transformation pathway mediated by the AURKA oncogene.

Aurora-A Kinase: A Potent Oncogene and Target for Cancer Therapy

The Aurora kinase family is comprised of three serine/threonine kinases, Aurora-A, Aurora-B, and Aurora-C. Among these, Aurora-A and Aurora-B play central roles in mitosis, whereas Aurora-C executes unique roles in meiosis. Overexpression or gene amplification of Aurora kinases has been reported in a broad range of human malignancies, pointing to their role as potent oncogenes in tumorigenesis. Aurora kinases therefore represent promising targets for anticancer therapeutics. A number of Aurora kinase inhibitors (AKIs) have been generated; some of which are currently undergoing clinical evaluation. Recent studies have unveiled novel unexpected functions of Aurora kinases during cancer development and the mechanisms underlying the anticancer actions of AKIs. In this review, we discuss the most recent advances in Aurora-A kinase research and targeted cancer therapy, focusing on the oncogenic roles and signaling pathways of Aurora-A kinases in promoting tumorigenesis, the recent preclinical and clinical AKI data, and potential alternative routes for Aurora-A kinase inhibition.

Activation of Aurora A kinase through the FGF1/FGFR signaling axis sustains the stem cell characteristics of glioblastoma cells

Fibroblast growth factor 1 (FGF1) binds and activates FGF receptors, thereby regulating cell proliferation and neurogenesis. Human FGF1 gene 1B promoter (-540 to +31)-driven SV40 T antigen has been shown to result in tumorigenesis in the brains of transgenic mice. FGF1B promoter (-540 to +31)-driven green fluorescent protein (F1BGFP) has also been used in isolating neural stem cells (NSCs) with self-renewal and multipotency from developing and adult mouse brains. In this study, we provide six lines of evidence to demonstrate that FGF1/FGFR signaling is implicated in the expression of Aurora A (AurA) and the activation of its kinase domain (Thr288 phosphorylation) in the maintenance of glioblastoma (GBM) cells and NSCs. First, treatment of FGF1 increases AurA expression in human GBM cell lines. Second, using fluorescence-activated cell sorting, we observed that F1BGFP reporter facilitates the isolation of F1BGFP(+) GBM cells with higher expression levels of FGFR and AurA. Third, both FGFR inhibitor (SU5402) and AurA inhibitor (VX680) could down-regulate F1BGFP-dependent AurA activity. Fourth, inhibition of AurA activity by two different AurA inhibitors (VX680 and valproic acid) not only reduced neurosphere formation but also induced neuronal differentiation of F1BGFP(+) GBM cells. Fifth, flow cytometric analyses demonstrated that F1BGFP(+) GBM cells possessed different NSC cell surface markers. Finally, inhibition of AurA by VX680 reduced the neurosphere formation of different types of NSCs. Our results show that activation of AurA kinase through FGF1/FGFR signaling axis sustains the stem cell characteristics of GBM cells.

IMPLICATIONS

This study identified a novel mechanism for the malignancy of GBM, which could be a potential therapeutic target for GBM.

Recurrent Glioblastomas Reveal Molecular Subtypes Associated with Mechanistic Implications of Drug-Resistance

Previously, transcriptomic profiling studies have shown distinct molecular subtypes of glioblastomas. It has also been suggested that the recurrence of glioblastomas could be achieved by transcriptomic reprograming of tumors, however, their characteristics are not yet fully understood. Here, to gain the mechanistic insights on the molecular phenotypes of recurrent glioblastomas, gene expression profiling was performed on the 43 cases of glioblastomas including 15 paired primary and recurrent cases. Unsupervised clustering analyses revealed two subtypes of G1 and G2, which were characterized by proliferation and neuron-like gene expression traits, respectively. While the primary tumors were classified as G1 subtype, the recurrent glioblastomas showed two distinct expression types. Compared to paired primary tumors, the recurrent tumors in G1 subtype did not show expression alteration. By contrast, the recurrent tumors in G2 subtype showed expression changes from proliferation type to neuron-like one. We also observed the expression of stemness-related genes in G1 recurrent tumors and the altered expression of DNA-repair genes (i.e., AURK, HOX, MGMT, and MSH6) in the G2 recurrent tumors, which might be responsible for the acquisition of drug resistance mechanism during tumor recurrence in a subtype-specific manner. We suggest that recurrent glioblastomas may choose two different strategies for transcriptomic reprograming to escape the chemotherapeutic treatment during tumor recurrence. Our results might be helpful to determine personalized therapeutic strategy against heterogeneous glioma recurrence.

A phase I trial of AT9283 (a selective inhibitor of aurora kinases) in children and adolescents with solid tumors: a Cancer Research UK study

PURPOSE

A phase I trial of AT9283 (a multitargeted inhibitor of Aurora kinases A and B) was conducted in children and adolescents with solid tumors, to identify maximum-tolerated dose (MTD), safety, efficacy, pharmacokinetics, and pharmacodynamic (PD) activity.

EXPERIMENTAL DESIGN

AT9283 was administered as a 72-hour continuous intravenous infusion every 3 weeks. A rolling-six design, explored six dose levels (7, 9, 11.5, 14.5, 18.5, and 23 mg/m(2)/d). Pharmacokinetic and PD assessments, included inhibition of phospho-histone 3 (pHH3) in paired skin punch biopsies.

RESULTS

Thirty-three patients were evaluable for toxicity. There were six dose-limiting toxicities and the MTD was 18.5 mg/m(2)/d. Most common drug-related toxicities were hematologic (neutropenia, anemia, and thrombocytopenia in 36.4%, 18.2%, and 21.2% of patients), which were grade ≥3 in 30.3%, 6.1%, and 3% of patients. Nonhematologic toxicities included fatigue, infections, febrile neutropenia and ALT elevation. One patient with central nervous system-primitive neuroectodermal tumor (CNS-PNET) achieved a partial response after 16 cycles and 3 cases were stable for four or more cycles. Plasma concentrations were comparable with those in adults at the same dose level, clearance was similar although half-life was shorter (4.9 ± 1.5 hours, compared with 8.4 ± 3.7 hours in adults). Inhibition of Aurora kinase B was shown by reduction in pHH3 in 17 of 18 patients treated at ≥11.5 mg/m(2)/d.

CONCLUSION

AT9283 was well tolerated in children and adolescents with solid tumors with manageable hematologic toxicity. Target inhibition was demonstrated. Disease stabilization was documented in intracranial and extracranial pediatric solid tumors and a phase II dose determined.

Radiotherapy followed by aurora kinase inhibition targets tumor-propagating cells in human glioblastoma

Glioblastoma (GBM) is the most common malignant primary brain tumor. Radiotherapy fails to eliminate subpopulations of stem-like tumor-propagating cells (TPC), resulting in tumor regrowth. To identify kinases that promote TPC self-renewal rather than increasing proliferation in human GBM cultures, we screened a library of 54 nonselective tool compounds and determined their kinase inhibitor profiles in vitro. Most compounds inhibited aurora kinase (AURK) activity and blocked TPC self-renewal, while inducing GBM cell polynucleation and apoptosis. To prevent regrowth by TPCs, we used a priming dose of radiation followed by incubation with the pan-AURK inhibitor VX680 to block self-renewal and induce apoptosis in GBM cultures. In mice xenografted with human GBM cells, radiotherapy followed by VX680 treatment resulted in reduced tumor growth and increased survival relative to either monotherapy alone or VX680 treatment before radiation. Our results indicate that AURK inhibition, subsequent to radiation, may enhance the efficacy of radiotherapy by targeting radioresistant TPCs in human GBMs.

Signal transducer and activator of transcription 5b drives malignant progression in a PDGFB-dependent proneural glioma model by suppressing apoptosis

Signal transducer and activator of transcription 5b (STAT5b) is likely the relevant STAT5 isoform with respect to the process of malignant progression in gliomas. STAT5b is a latent cytoplasmic protein involved in cell signaling through the modulation of growth factors, apoptosis, and angiogenesis. Previous in vitro studies have shown increased STAT5b expression in glioblastomas relative to low-grade tumors and normal brain. We recently demonstrated that phosphorylated STAT5b associates with delta epidermal growth factor receptor in the nucleus and subsequently binds the promoters of downstream effector molecules, including aurora kinase A. Analysis of TCGA dataset reveals that STAT5b is predominantly expressed in proneural (PN) gliomas relative to mesenchymal and neural gliomas. Here, we modeled ectopic expression of STAT5b in vivo using a platelet-derived growth factor subunit B (PDGFB)-dependent mouse model of PN glioma to determine its effect on tumor formation and progression. We showed that coexpression of STAT5b and PDGFB in mice yielded a significantly higher rate of high-grade gliomas than PDGFB expression alone. We also observed shorter survival in the combined expression set. High-grade tumors from the STAT5b + PDGFB expression set were found to have a lower rate of apoptosis than those from PDGFB alone. Furthermore, we showed that increased expression of STAT5b + PDGFB led to increased expression of downstream STAT5b targets, including Bcl-xL, cyclin D1 and aurora kinase A in high-grade tumors when compared to tumors derived from PDGFB alone. Our findings show that STAT5b promotes the malignant transformation of gliomas, particularly the PN subtype, and is a potential therapeutic target.

Aurora-A inhibition offers a novel therapy effective against intracranial glioblastoma

Glioblastoma remains a devastating disease for which novel therapies are urgently needed. Here, we report that the Aurora-A kinase inhibitor alisertib exhibits potent efficacy against glioblastoma neurosphere tumor stem-like cells in vitro and in vivo. Many glioblastoma neurosphere cells treated with alisertib for short periods undergo apoptosis, although some regain proliferative activity upon drug removal. Extended treatment, however, results in complete and irreversible loss of tumor cell proliferation. Moreover, alisertib caused glioblastoma neurosphere cells to partially differentiate and enter senescence. These effects were also observed in glioma cells treated with the Aurora-A inhibitor TC-A2317 or anti-Aurora-A siRNA. Furthermore, alisertib extended median survival of mice bearing intracranial human glioblastoma neurosphere tumor xenografts. Alisertib exerted similar effects on glioblastoma neurosphere cells in vivo and resulted in markedly reduced activated phosphoThr288Aurora-A and increased abnormal mitoses and cellular ploidy, consistent with on-target activity. Our results offer preclinical proof-of-concept for alisertib as a new therapeutic for glioma treatment.

WWOX modulates the gene expression profile in the T98G glioblastoma cell line rendering its phenotype less malignant

The aim of the present study was to assess the influence of WWOX gene upregulation on the transcriptome and phenotype of the T98G glioblastoma cell line. The cells with high WWOX expression demonstrated a significantly different transcription profile for approximately 3,000 genes. The main cellular pathways affected were Wnt, TGFβ, Notch and Hedgehog. Moreover, the WWOX-transfected cells proliferated at less than half the rate, exhibited greatly lowered adhesion to ECM, increased apoptosis and impaired 3D culture formation. They also demonstrated an increased ability for crossing the basement membrane. Our results indicate that WWOX, apart from its tumor-suppressor function, appears to be a key regulator of the main cellular functions of the cell cycle and apoptosis. Furthermore, our results showed that WWOX may be involved in controlling metabolism, cytoskeletal structure and differentiation.