Oncogenic BRAF inhibitor UAI-201 induces cell cycle arrest and autophagy in BRAF mutant glioma cells

Pediatric diffuse hemispheric glioma H3 G34-mutant with gains of the BRAF locus: An illustrative case

Diffuse hemispheric glioma, H3 G34-mutant, is a recently recognized distinct high-grade glioma with a dismal prognosis. In addition to the H3 G34 missense mutation, numerous genetic events have been identified in these malignant tumors, including ATRX, TP53, and, rarely, BRAF genes. There are only a few reports to date that have identified BRAF mutations in diffuse hemispheric glioma, H3 G34-mutant. Moreover, to our knowledge, gains of the BRAF locus have yet to be described. Here, we present a case of an 11-year-old male with a diffuse hemispheric glioma, H3 G34-mutant, found to have novel gains of the BRAF locus. Furthermore, we emphasize the current genetic landscape of diffuse hemispheric glioma, H3 G34-mutant, and implications of an aberrant BRAF signaling pathway.

Targeting RAS-RAF-MEK-ERK signaling pathway in human cancer: Current status in clinical trials

Molecular target inhibitors have been regularly approved by Food and Drug Administration (FDA) for tumor treatment, and most of them intervene in tumor cell proliferation and metabolism. The RAS-RAF-MEK-ERK pathway is a conserved signaling pathway that plays vital roles in cell proliferation, survival, and differentiation. The aberrant activation of the RAS-RAF-MEK-ERK signaling pathway induces tumors. About 33% of tumors harbor RAS mutations, while 8% of tumors are driven by RAF mutations. Great efforts have been dedicated to targeting the signaling pathway for cancer treatment in the past decades. In this review, we summarized the development of inhibitors targeting the RAS-RAF-MEK-ERK pathway with an emphasis on those used in clinical treatment. Moreover, we discussed the potential combinations of inhibitors that target the RAS-RAF-MEK-ERK signaling pathway and other signaling pathways. The inhibitors targeting the RAS-RAF-MEK-ERK pathway have essentially modified the therapeutic strategy against various cancers and deserve more attention in the current cancer research and treatment.

WAC, a novel GBM tumor suppressor, induces GBM cell apoptosis and promotes autophagy

WAC is closely related to the occurrence and development of tumors. However, its role in human glioblastoma (GBM) and its potential regulatory mechanisms have not been investigated. This study demonstrated that WAC is downregulated in GBM, and its low expression predicts a poor prognosis. We investigated the effect of WAC on the proliferation of glioma cells through a CCK-8 assay, EdU incorporation, and cell formation. The effects of WAC on apoptosis and autophagy in glioma were determined by flow cytometry, TUNEL detection, immunofluorescence, q-PCR, WB, and scanning electron microscopy. We found that overexpression of WAC inhibited the proliferation of glioma cells, promoted apoptosis, and induced autophagy. Therefore, WAC is likely to play a role as a new regulatory molecule in glioma.

Cucurbitacin IIb induces apoptosis and cell cycle arrest through regulating EGFR/MAPK pathway

Epidermal growth factor receptor (EGFR) is considered as a valid target in the clinical trials of anticancer therapy and tyrosine kinase inhibitors (TKIs) of EGFR are approved for cancer treatments. In present work, cucurbitacin IIb (CuIIb) was confirmed to exhibit the proliferation inhibitory activity in A549 cells. CuIIb induced apoptosis via STAT3 pathway, which was mitochondria-mediated and caspase-dependent. CuIIb also suppressed the cell cycle and induced G2/M phase cell cycle arrest. CuIIb was capable of suppressing the signal transmitting of the EGFR/mitogen-activated protein kinase (MAPK) pathway which was responsible for the apoptosis and cell cycle arrest. Homogeneous time-resolved fluorescence (HTRF) analysis demonstrated that the kinase activity of EGFR was inhibited by CuIIb. Molecular docking suggested that the CuIIb-EGFR binding fundamentally depends on the contribution of both hydrophobic and hydrogen-bonding interactions. Hence CuIIb may serve as a potential EGFR TKI.

Pseudolaric acid B induces apoptosis in human rhabdomyosarcoma RD cells

Pseudolaric acid B (PAB) is a diterpene-type acid isolated from the root and trunk bark of Pseudolarix kaempferi Gordon of the Pinaceae family that has been demonstrated to induce apoptosis in various cell lines and autophagy in certain cell lines including murine fibrosarcoma L929, human thyroid squamous cell carcinoma SW579 and human lung fibroblast MRC5 cells. However, in human rhabdomyosarcoma RD cells, which are derived from the most common soft tissue sarcoma in children and represent a high-grade neoplasm of a skeletal myoblast type, it is not clear whether PAB induces apoptosis or autophagy. The identification of the exact mechanism of PAB is important for studying its antitumor effects and its potential application in the treatment of human rhabdomyosarcoma. To confirm the inhibitory ability of PAB on RD cells, the inhibitory ratio of PAB was analyzed, and the results of MTT assay demonstrated that PAB inhibited RD cell proliferation. Meanwhile aggregation of the microtubule fibers was found in PAB-treated RD cells compared with that in control-treated cells, which was consistent with previous studies. In addition, PAB inhibited RD cell migration, induced apoptosis and cell cycle arrest at the G2/M phase. These results suggested that the mechanism of PAB-mediated growth inhibition in RD was similar to that reported in the human breast cancer cell line MCF-7 and the neuroglioma cell line A172; however, it was different from that reported in the L929, MRC5 and SW579 cell lines. Additional experiments demonstrated that PAB regulated the activation of caspase-8 and caspase-9 to induce apoptosis and caused an upregulation of phosphorylated H2A histone family member X and cyclin B1 expression in order to induce cell cycle arrest. Therefore, PAB may be considered a potential treatment agent for human rhabdomyosarcoma.

Clinical Relevance of BRAF V600E Mutation Status in Brain Tumors with a Focus on a Novel Management Algorithm

The possible application of BRAF-targeted therapy in brain tumors is growing continuously. We have analyzed clinical strategies that address BRAF activation in primary brain tumors and verified current recommendations regarding screening for BRAF mutations. There is preliminary evidence for a range of positive responses in certain brain tumor types harboring the BRAF V600E mutation. National Comprehensive Cancer Network Guidelines for central nervous system cancers recommend screening for the BRAF V600E mutation in pilocytic astrocytoma, pleomorphic xanthoastrocytoma, and ganglioglioma. We suggest additional testing in glioblastomas WHO grade IV below the age of 30 years, especially those with epithelioid features, papillary craniopharyngiomas, and pediatric low-grade astrocytomas. BRAF-targeted therapy should be limited to the setting of a clinical trial. If the patient harboring a V600E mutation does not qualify for a trial, multimodality treatment is recommended. Dual inhibition of both RAF and MEK is expected to provide more potent and durable effects than anti-BRAF monotherapy. First-generation RAF inhibitors should be avoided. Gain-of-function mutations of EGFR and KIAA fusions may compromise BRAF-targeted therapy. BRAF alterations that result in MAPK pathway activation are common events in several types of brain tumors. BRAF V600E mutation emerges as a promising molecular target. The proposed algorithm was designed to help oncologists to provide the best therapeutic options for brain tumor patients.

ATG5 knockout promotes paclitaxel sensitivity in drug-resistant cells via induction of necrotic cell death

Autophagy regulators are often effective as potential cancer therapeutic agents. Here, we investigated paclitaxel sensitivity in cells with knockout (KO) of ATG5 gene. The ATG5 KO in multidrug resistant v-Ha-ras-transformed NIH 3T3 cells (Ras-NIH 3T3/Mdr) was generated using the CRISPR/Cas9 technology. The qPCR and LC3 immunoblot confirmed knockout of the gene and protein of ATG5, respectively. The ATG5 KO restored the sensitivity of Ras-NIH 3T3/Mdr cells to paclitaxel. Interestingly, ATG5 overexpression restored autophagy function in ATG5 KO cells, but failed to rescue paclitaxel resistance. These results raise the possibility that low level of resistance to paclitaxel in ATG5 KO cells may be related to other roles of ATG5 independent of its function in autophagy. The ATG5 KO significantly induced a G2/M arrest in cell cycle progression. Additionally, ATG5 KO caused necrosis of a high proportion of cells after paclitaxel treatment. These data suggest that the difference in sensitivity to paclitaxel between ATG5 KO and their parental MDR cells may result from the disparity in the proportions of necrotic cells in both populations. Thus, our results demonstrate that the ATG5 KO in paclitaxel resistant cells leads to a marked G2/M arrest and sensitizes cells to paclitaxel-induced necrosis.

Oncogenic BRAF Alterations and Their Role in Brain Tumors

Alterations of the v-raf murine sarcoma viral oncogene homolog B (BRAF) have been extensively studied in several tumor entities and are known to drive cell growth in several tumor entities. Effective targeted therapies with mutation-specific small molecule inhibitors have been developed and established for metastasized malignant melanoma. The BRAF V600E mutation and KIAA1549-BRAF fusion are alterations found in several brain tumors and show a distinct prognostic impact in some entities. Besides the diagnostic significance for the classification of central nervous system tumors, these alterations present possible therapy targets that may be exploitable for oncological treatments, as it has been established for malignant melanomas. In this review the different central nervous system tumors harboring BRAF alterations are presented and the diagnostic significance, prognostic role, and therapeutic potential are discussed.

Molecular mechanism of SSFA2 deletion inhibiting cell proliferation and promoting cell apoptosis in glioma

Gliomas are the most common primary brain malignant tumors in humans. Glioblastoma multiforme(GBM) is the most malignant intracranial tumor with a relatively poor prognosis. There promote us to find effective anti-cancer therapies to reduce cancer mortality. By using bioinformatic analysis, we found SSFA2 as a gene with elevated expression in the glioma tissues. We detected the expression of SSFA2 in glioma tissues and in the glioma cell lines, as well as in normal brain tissues. SSFA2 expression was higher in glioma tissues, especially in glioblastoma multiforme than normal brain tissues. Subsequently, we found that down-regulate SSFA2 in glioma cell lines can regulate the cell cycle to reduce the proliferation ability and induce the early apoptosis rate in shSSFA2 cells relative to control cells. Moreover, we found that down-regulate SSFA2 in glioma cell line U87(shSSFA2-U87) inhibited the growth effectiveness compared to the control cell line U87. These result reveals us that SSFA2 may act as oncogene to promote the progression of glioma. For further research specific mechanisms of SSFA2 in gliomas, we used the gene chip to detect the downstream gene in U87. We found that 30 genes also may be as target gene of SSFA2, and we testify the protein expression by western-blot. The result reveal that IL1A, IL1B and CDK6 as target gene of SSFA2 to regulate the progression of glioma. These finding suggest that SSFA2 could be a new therapeutic target for gliomas.

Chemical modulation of autophagy as an adjunct to chemotherapy in childhood and adolescent brain tumors

Brain tumors are the leading cause of cancer-related death in children and are the most challenging childhood cancer in relation to diagnosis, treatment, and outcome. One potential novel strategy to improve outcomes in cancer involves the manipulation of autophagy, a fundamental process in all cells. In cancer, autophagy can be thought of as having a "Janus"-like duality. On one face, especially in the early phases of cancer formation, autophagy can act as a cellular housekeeper to eliminate damaged organelles and recycle macromolecules, thus acting as tumor suppressor. On the other face, at later stages of tumor progression, autophagy can function as a pro-survival pathway in response to metabolic stresses such as nutrient depravation, hypoxia and indeed to chemotherapy itself, and can support cell growth by supplying much needed energy. In the context of chemotherapy, autophagy may, in some cases, mediate resistance to treatment. We present an overview of the relevance of autophagy in central nervous system tumors including how its chemical modulation can serve as a useful adjunct to chemotherapy, and use this knowledge to consider how targeting of autophagy may be relevant in pediatric brain tumors.

Knockout of ATG5 leads to malignant cell transformation and resistance to Src family kinase inhibitor PP2

Autophagy can either promote or inhibit cell death in different cellular contexts. In this study, we investigated the role of autophagy in ATG5 knockout (KO) cell line established using CRISPR/Cas9 system. In ATG5 KO cells, RT-PCR and immunoblot of LC3 confirmed the functional gene knockout. We found that knockout of ATG5 significantly increased proliferation of NIH 3T3 cells. In particular, autophagy deficiency enhanced susceptibility to cellular transformation as determined by an in vitro clonogenic survival assay and a soft agar colony formation assay. We also found that ATG5 KO cells had a greater migration ability as compared to wild-type (WT) cells. Moreover, ATG5 KO cells were more resistant to treatment with a Src family tyrosine kinase inhibitor (PP2) than WT cells were. Cyto-ID Green autophagy assay revealed that PP2 failed to induce autophagy in ATG5 KO cells. PP2 treatment decreased the percentage of cells in the S and G₂ /M phases among WT cells but had no effect on cell cycle distribution of ATG5 KO cells, which showed a high percentage of cells in the S and G₂ /M phases. Additionally, the proportion of apoptotic cells significantly decreased after treatment of ATG5 KO cells with PP2 in comparison with WT cells. We found that expression levels of p53 were much higher in ATG5 KO cells. The ATG5 KO seems to lead to compensatory upregulation of the p53 protein because of a decreased apoptosis rate. Taken together, our results suggest that autophagy deficiency can lead to malignant cell transformation and resistance to PP2.

Upregulation of MicroRNA-1246 Is Associated with BRAF Inhibitor Resistance in Melanoma Cells with Mutant BRAF

Purpose

Intrinsic and acquired resistance limit the therapeutic benefits of inhibitors of oncogenic BRAF in melanoma. To identify microRNAs (miRNAs) associated with resistance to a BRAF inhibitor, we compared miRNA expression levels in three cell lines with different BRAF inhibitor sensitivity.

Materials and Methods

miRNA microarray analysis was conducted to compare miRNA expression levels. Real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was performed to confirm the expression of differentially expressed miRNAs. The cellular effects of miR-1246 were further examined by MTT assay, immunoblotting analysis, cell cycle analysis, flow cytometric assay of apoptosis, and autophagy assay.

Results

The miRNA microarray analysis and qRT-PCR identified five miRNAs (miR-3617, miR-92a-1, miR-1246, miR-193b-3p, and miR-17-3p) with expression that was consistently altered in two BRAF inhibitor-resistant cell lines. Among the five miRNAs, a miR-1246 mimic significantly reduced the antiproliferative effects of the BRAF inhibitor PLX4720 in BRAF inhibitor–resistant A375P (A375P/Mdr) cells, suggesting that miR-1246 upregulation confers acquired resistance to BRAF inhibition. In particular, apoptosis was identified as a major type of cell death in miR-1246–transfected cells; however, necrosis predominated in mimic-control-transfected cells, indicating that the resistance to PLX4720 in miR-1246 mimic-transfected cells is predominantly due to a reduction in necrosis. Furthermore, we found that miR-1246 promoted G₂/M arrest through autophagy as a way to escape cell death by necrosis and apoptosis in response to PLX4720. The promotion of BRAF inhibitor resistance by miR-1246 was associated with lowered levels of p-ERK.

Conclusion

These results suggest that miR-1246 may be a potential therapeutic target in melanoma with acquired resistance to BRAF inhibitors.

Genetic biomarkers of drug response for small-molecule therapeutics targeting the RTK/Ras/PI3K, p53 or Rb pathway in glioblastoma

Glioblastoma is the most deadly and frequently occurring primary malignant tumor of the central nervous system. Genomic studies have shown that mutated oncogenes and tumor suppressor genes in glioblastoma mainly occur in three pathways: the RTK/Ras/PI3K signaling, the p53 and the Rb pathways. In this review, we summarize the modulatory effects of genetic aberrations in these three pathways to drugs targeting these specific pathways. We also provide an overview of the preclinical efforts made to identify genetic biomarkers of response and resistance. Knowledge of biomarkers will finally promote patient stratification in clinical trials, a prerequisite for trial design in the era of precision medicine.

BRAF inhibitors in BRAF-V600 mutated primary neuroepithelial brain tumors

INTRODUCTION

Primary neuroepithelial brain tumors encompass a wide variety of glial and glioneuronal neoplasms. Malignant tumors, tumors located in surgically inaccessible locations (e.g., eloquent brain areas, deep structures, brain stem) and recurrent or progressive tumors pose considerable treatment challenges and are candidates for novel therapeutics based on molecular insights. Small kinase inhibitors of v-RAF murine sarcoma viral oncogene homologue B1 (BRAF) have shown considerable antineoplastic activity in some tumor types harboring activating BRAF-V600 mutations (e.g., melanoma) and promising data are emerging on BRAF inhibitor therapy of mutation-bearing primary brain tumors.

AREAS COVERED

This review summarizes the available data on BRAF-V600 point mutations and the antineoplastic activity and toxicity profiles of BRAF inhibitors in neuroepithelial brain tumors including diffuse gliomas (glioblastomas, astrocytomas, oligodendrogliomas), pilocytic astrocytomas, pleomorphic xanthoastrocytomas and gangliogliomas.

EXPERT OPINION

Activating BRAF-V600 mutations are recurrently found in several glial and glioneuronal brain tumors and the available data indicate that BRAF inhibitors are active and well-tolerated in such tumors. Thus, BRAF inhibitors represent a novel and promising therapeutic opportunity that may alter the disease course of molecularly selected CNS neoplasms in a clinically meaningful way. However, so far the evidence is anecdotal and prospective clinical studies should be conducted.

Pseudolaric acid B inhibits proliferation in SW579 human thyroid squamous cell carcinoma

Primary squamous cell carcinoma of the thyroid is a rare and aggressive type of neoplasm, which is routinely treated with surgery; however, despite this, survival time is not commonly more than six months. Thus, the aim of the present study was to determine the efficacy of pseudolaric acid (PAB) as a therapeutic agent. PAB is an antitubulin agent, and in the present study, inhibition of the SW579 thyroid squamous cell carcinoma cell line by PAB was investigated. PAB was found to inhibit SW579 cell growth in a time- and dose-dependent manner via interference in α-tubulin polymerization. However, the inhibitory role of PAB in SW579 cells was not predominantly due to apoptosis, but was due to the cytostatic status resulting from cell cycle arrest. The present study proposes that this is the underlying mechanism of the antitumor properties of PAB. During cytostatis, autophagy was activated to sustain cell survival and SW579 cell migration was inhibited. Nuclear p53 expression was observed to be reduced, however the role of reduced p53 requires further investigation. Therefore, PAB induced cytostasis, which inhibited SW579 cell growth and therefore may function as an antitubulin therapeutic agent.