Hedgehog/Gli1 signaling pathway regulates MGMT expression and chemoresistance to temozolomide in human glioblastoma

Positive GLI1/INHBA feedback loop drives tumor progression in gastric cancer

GLI1, a key transcription factor of the Hedgehog (Hh) signaling pathway, plays an important role in the development of cancer. However, the function and mechanisms by which GLI1 regulates gene transcription are not fully understood in gastric cancer (GC). Here, we found that GLI1 induced the proliferation and metastasis of GC cells, accompanied by transcriptional upregulation of INHBA. This increased INHBA expression exerted a promoting activity on Smads signaling and then transcriptionally activated GLI1 expression. Notably, our results demonstrate that disrupting the interaction between GLI1 and INHBA could inhibit GC tumorigenesis in vivo. More intriguingly, we confirmed the N6-methyladenosine (m6A) activation mechanism of the Helicobacter pylori/FTO/YTHDF2/GLI1 pathway in GC cells. In conclusion, our study confirmed that the GLI1/INHBA positive feedback loop influences GC progression and revealed the mechanism by which H. pylori upregulates GLI1 expression through m6A modification. This positive GLI1/INHBA feedback loop suggests a novel noncanonical mechanism of GLI1 activity in GC and provides potential therapeutic targets for GC treatment.

Enhancing Temozolomide (TMZ) chemosensitivity using CRISPR-dCas9-mediated downregulation of O6-methylguanine DNA methyltransferase (MGMT)

PURPOSE

Glioblastoma (GBM) stands out as the most prevalent and aggressive intracranial tumor, notorious for its poor prognosis. The current standard-of-care for GBM patients involves surgical resection followed by radiotherapy, combined with concurrent and adjuvant chemotherapy using Temozolomide (TMZ). The effectiveness of TMZ primarily relies on the activity of O6-methylguanine DNA methyltransferase (MGMT), which removes alkyl adducts from the O6 position of guanine at the DNA level, thereby counteracting the toxic effects of TMZ.

METHOD

In this study, we employed fusions of catalytically-inactive Cas9 (dCas9) to DNA methyltransferases (dCas9-DNMT3A) to selectively downregulation MGMT transcription by inducing methylation at MGMT promoter and K-M enhancer.

RESULT

Our findings demonstrate a significant reduction in MGMT expression, leading to intensified TMZ sensitivity in the HEK293T cell line.

CONCLUSION

This study serves as a proof of concept for the utilization of CRISPR-based gene suppression to overcome TMZ resistance and enhance the lethal effect of TMZ in glioblastoma tumor cells.

Elucidating the Role of miRNA-326 Modulating Hedgehog Signaling in Pancreatic Carcinoma

BACKGROUND AND AIM

Pancreatic ductal adenocarcinoma (PDAC) is one of the lethal malignancies worldwide characterized by poor prognosis. MicroRNAs (miRNAs) function as the key regulators in carcinogenesis and may act as noninvasive biomarkers in various malignancies including PDAC. The present study aimed to elucidate the role of miR-326, a known modulator of hedgehog (Hh) pathway in PDAC.

MATERIALS AND METHODS

miR-326 circulating levels were assessed in 105 PDAC patients, 31 with chronic pancreatitis (CP) and 36 healthy controls by quantitative Polymerase chain reaction. The expression of miR-326 and smoothened (SMO) was checked in surgical PDAC tissue. SMO protein expression was analyzed by immunohistochemistry in different groups. Finally, the role of miR-326 as a modulator of Hh pathway was assessed in vitro.

RESULTS

Our results demonstrate that miR-326 is downregulated in both blood and tissue of PDAC patients as compared with controls. In contrast, the target gene/protein expression of SMO is upregulated in PDAC. Moreover, the tumor stromal expression of SMO was found to be clinically associated with lymph-node metastasis and vascular encasement in PDAC. Overexpression of miR-326 in Panc1 cell line was found to induce downregulation of SMO suggesting the tumor suppressor role of miR-326 in PDAC.

CONCLUSIONS

Taken together, miR-326 acts as a tumor suppressor in PDAC by modulating Hh pathway. It may be a promising target for the development of efficient drug therapies for the treatment of PDAC.

Targeting hedgehog-driven mechanisms of drug-resistant cancers

Due to the cellular plasticity that is inherent to cancer, the acquisition of resistance to therapy remains one of the biggest obstacles to patient care. In many patients, the surviving cancer cell subpopulation goes on to proliferate or metastasize, often as the result of dramatically altered cell signaling and transcriptional pathways. A notable example is the Hedgehog (Hh) signaling pathway, which is a driver of several cancer subtypes and aberrantly activated in a wide range of malignancies in response to therapy. This review will summarize the field's current understanding of the many roles played by Hh signaling in drug resistance and will include topics such as non-canonical activation of Gli proteins, amplification of genes which promote tolerance to chemotherapy, the use of hedgehog-targeted drugs and tool compounds, and remaining gaps in our knowledge of the transcriptional mechanisms at play.

Zinc finger and SCAN domain-containing 18 suppresses the proliferation, self-renewal, and drug resistance of glioblastoma cells

Elucidation of cellular and molecular mechanisms key to glioblastoma growth, self-renewal, survival, and metastasis is important for developing novel therapeutic strategies. In this study, the expression and function of zinc finger and SCAN domain-containing 18 (ZSCAN18) in human glioblastoma cell lines were characterized. Compared with normal astrocytes, ZSCAN18 was significantly down-regulated in all tested glioblastoma cell lines, with the LN-229 cell line having the lowest ZSCAN18 expression. Lentivirus-mediated ZSCAN18 overexpression suppressed glioblastoma cell proliferation, sphere formation, and SOX2 and OCT4 expression, implying the negative role of ZSCAN18 in glioblastoma development. ZSCAN18 overexpression enhanced the sensitivity of glioblastoma cells to Temozolomide. The glioblastoma implantation model showed a consistent inhibitory effect of ZSCAN18 on the proliferation and self-renewal of glioblastoma cells in vivo. Notably, ZSCAN18 overexpression resulted in the down-regulation of glioma-associated oncogene homolog 1 (GLI1) which is the terminal component of the Hedgehog signaling. Lentivirus-mediated GLI1 overexpression restored the proliferation and promoted the resistance of glioblastoma cells to Temozolomide. However, GLI1 overexpression did not affect the self-renewal of ZSCAN18-overexpressing glioblastoma cells. Taken together, this research uncovers the role of ZSCAN18 in regulating glioblastoma cell growth and maintenance. ZSCAN18 could be a potential glioblastoma biomarker.

Combined Inhibition of Hedgehog and HDAC6: In Vitro and In Vivo Studies Reveal a New Role for Lysosomal Stress in Reducing Glioblastoma Cell Viability

Glioblastoma multiforme (GBM) is the most common and malignant brain tumor in adults. The invasiveness and the rapid progression that characterize GBM negatively impact patients’ survival. Temozolomide (TMZ) is currently considered the first-choice chemotherapeutic agent. Unfortunately, over 50% of patients with GBM do not respond to TMZ treatment, and the mutation-prone nature of GBM enables the development of resistance mechanisms. Therefore, efforts have been devoted to the dissection of aberrant pathways involved in GBM insurgence and resistance in order to identify new therapeutic targets. Among them, sphingolipid signaling, Hedgehog (Hh) pathway, and the histone deacetylase 6 (HDAC6) activity are frequently dysregulated and may represent key targets to counteract GBM progression. Given the positive correlation between Hh/HDAC6/sphingolipid metabolism in GBM, we decided to perform a dual pharmacological inhibition of Hh and HDAC6 through cyclopamine and tubastatin A, respectively, in a human GMB cell line and zebrafish embryos. The combined administration of these compounds elicited a more significant reduction of GMB cell viability than did single treatments in vitro and in cells orthotopically transplanted in the zebrafish hindbrain ventricle. We demonstrated, for the first time, that the inhibition of these pathways induces lysosomal stress which results in an impaired fusion of lysosomes with autophagosomes and a block of sphingolipid degradation in GBM cell lines. This condition, which we also recapitulated in zebrafish embryos, suggests an impairment of lysosome-dependent processes involving autophagy and sphingolipid homeostasis and might be instrumental in the reduction of GBM progression.

Re-Sensitizing Cancer Stem Cells to Conventional Chemotherapy Agents

Cancer stem cells are found in many cancer types. They comprise a distinct subpopulation of cells within the tumor that exhibit properties of stem cells. They express a number of cell surface markers, such as CD133, CD44, ALDH, and EpCAM, as well as embryonic transcription factors Oct4, Nanog, and SOX2. CSCs are more resistant to conventional chemotherapy and can potentially drive tumor relapse. Therefore, it is essential to understand the molecular mechanisms that drive chemoresistance and to target them with specific therapy effectively. Highly conserved developmental signaling pathways such as Wnt, Hedgehog, and Notch are commonly reported to play a role in CSCs chemoresistance development. Studies show that particular pathway inhibitors combined with conventional therapy may re-establish sensitivity to the conventional therapy. Another significant contributor of chemoresistance is a specific tumor microenvironment. Surrounding stroma in the form of cancer-associated fibroblasts, macrophages, endothelial cells, and extracellular matrix components produce cytokines and other factors, thus creating a favorable environment and decreasing the cytotoxic effects of chemotherapy. Anti-stromal agents may potentially help to overcome these effects. Epigenetic changes and autophagy were also among the commonly reported mechanisms of chemoresistance. This review provides an overview of signaling pathway components involved in the development of chemoresistance of CSCs and gathers evidence from experimental studies in which CSCs can be re-sensitized to conventional chemotherapy agents across different cancer types.

Fluoride in the Central Nervous System and Its Potential Influence on the Development and Invasiveness of Brain Tumours-A Research Hypothesis

The purpose of this review is to attempt to outline the potential role of fluoride in the pathogenesis of brain tumours, including glioblastoma (GBM). In this paper, we show for the first time that fluoride can potentially affect the generally accepted signalling pathways implicated in the formation and clinical course of GBM. Fluorine compounds easily cross the blood-brain barrier. Enhanced oxidative stress, disruption of multiple cellular pathways, and microglial activation are just a few examples of recent reports on the role of fluoride in the central nervous system (CNS). We sought to present the key mechanisms underlying the development and invasiveness of GBM, as well as evidence on the current state of knowledge about the pleiotropic, direct, or indirect involvement of fluoride in the regulation of these mechanisms in various tissues, including neural and tumour tissue. The effects of fluoride on the human body are still a matter of controversy. However, given the growing incidence of brain tumours, especially in children, and numerous reports on the effects of fluoride on the CNS, it is worth taking a closer look at these mechanisms in the context of brain tumours, including gliomas.

Expression analysis and regulation of GLI and its correlation with stemness and metabolic alteration in human brain tumor

GLI gene-mediated hedgehog (Hh) signaling pathway plays a substantial role in brain cancer development and growth including glioblastoma multiforme (GBM), lower-grade glioma (LGG), and medulloblastoma (MB). GLI2 and GLI3 gene expression levels are extremely enhanced in these cancers with poor patient survival. Moreover, GLI genes are correlated with stemness-related factors SOX2, SOX9, POU5F1, and NANOG that work as the driving factors for brain cancer stem cells (CSCs) progression. It's critical to find new ways to combat this deadly malignancy and CSCs. Using in silico approaches, our study explored the role of GLI genes (GLI1, GLI2, and GLI3), the primary transcription factors of the sonic hedgehog (SHH) signaling pathway, in GBM, LGG, MB, and glioblastoma stem-like cells (GSCs). Additionally, we found strong association of angiogenic-related gene VEGFA, metabolic genes ENO1, ENO2, and pluripotency-related genes SOX2, SOX9, NANOG, POU5F1 with GLI genes, suggesting their role in brain tumor initiation and progression. We also studied their transcriptional network and functional category enrichment analysis about brain tumor development to find a better therapeutic strategy against brain cancer and their stem cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03419-5.

MDK induces temozolomide resistance in glioblastoma by promoting cancer stem-like properties

Glioblastoma (GBM) is the most frequently observed and aggressive type of high-grade malignant glioma. Temozolomide (TMZ) is the primary agent for GBM treatment. However, TMZ resistance remains a major challenge. In this study, we report that MDK is overexpressed in GBM, which leads to enhanced proliferation, apoptosis inhibition, increased invasion and TMZ resistance in GBM cells. It was also determined that MDK could significantly improve the stem-like properties of GBM cells. Mechanistically, MDK enhanced p-JNK through Notch1 and subsequently increased the expression of stemness markers, such as CD133 and Nanog, thereby promoting TMZ resistance. Finally, xenograft experiments and clinical sample analysis also demonstrated that MDK knockdown could significantly inhibit tumor growth in vivo, and the expression of MDK was positively correlated with Notch1, p-JNK and CD133. This study revealed that MDK induces TMZ resistance by improving the stem-like properties of GBM by upregulating the Notch1/p-JNK signaling pathway, which provides a possible target for therapeutic intervention of GBM, especially in TMZ-resistant GBM with high MDK expression.

Subtyping and grading of lower-grade gliomas using integrated feature selection and support vector machine

Classifying lower-grade gliomas (LGGs) is a crucial step for accurate therapeutic intervention. The histopathological classification of various subtypes of LGG, including astrocytoma, oligodendroglioma and oligoastrocytoma, suffers from intraobserver and interobserver variability leading to inaccurate classification and greater risk to patient health. We designed an efficient machine learning-based classification framework to diagnose LGG subtypes and grades using transcriptome data. First, we developed an integrated feature selection method based on correlation and support vector machine (SVM) recursive feature elimination. Then, implementation of the SVM classifier achieved superior accuracy compared with other machine learning frameworks. Most importantly, we found that the accuracy of subtype classification is always high (>90%) in a specific grade rather than in mixed grade (~80%) cancer. Differential co-expression analysis revealed higher heterogeneity in mixed grade cancer, resulting in reduced prediction accuracy. Our findings suggest that it is necessary to identify cancer grades and subtypes to attain a higher classification accuracy. Our six-class classification model efficiently predicts the grades and subtypes with an average accuracy of 91% (±0.02). Furthermore, we identify several predictive biomarkers using co-expression, gene set enrichment and survival analysis, indicating our framework is biologically interpretable and can potentially support the clinician.

Long non-coding RNA PVT1: A promising chemotherapy and radiotherapy sensitizer

The long non-coding RNA (lncRNA) PVT1 was first found to activate variant translocations in the plasmacytoma of mice. Human lncPVT1 is located on chromosome 8q24.21, at the same locus as the well-known MYC oncogene. LncPVT1 has been found to promote the progression of various malignancies. Chemoresistance and radioresistance seriously affect tumor treatment efficacy and are associated with the dysregulation of physiological processes in cancer cells, including apoptosis, autophagy, stemness (for cancer stem cells, CSC), hypoxia, epithelial–mesenchymal transition (EMT), and DNA damage repair. Previous studies have also implicated lncPVT1 in the regulation of these physiological mechanisms. In recent years, lncPVT1 was found to modulate chemoresistance and radioresistance in some cancers. In this review, we discuss the mechanisms of lncPVT1-mediated regulation of cellular chemoresistance and radioresistance. Due to its high expression in malignant tumors and sensitization effect in chemotherapy and radiotherapy, lncPVT1 is expected to become an effective antitumor target and chemotherapy and radiotherapy sensitizer, which requires further study.

Hedgehog signaling regulates the development and treatment of glioblastoma (Review)

Glioblastoma (GBM) is the most common and fatal malignant tumor type of the central nervous system. GBM affects public health and it is important to identify biomarkers to improve diagnosis, reduce drug resistance and improve prognosis (e.g., personalized targeted therapies). Hedgehog (HH) signaling has an important role in embryonic development, tissue regeneration and stem cell renewal. A large amount of evidence indicates that both normative and non-normative HH signals have an important role in GBM. The present study reviewed the role of the HH signaling pathway in the occurrence and progression of GBM. Furthermore, the effectiveness of drugs that target different components of the HH pathway was also examined. The HH pathway has an important role in reversing drug resistance after GBM conventional treatment. The present review highlighted the relevance of HH signaling in GBM and outlined that this pathway has a key role in the occurrence, development and treatment of GBM.

Differential expression of microRNAs targeting genes associated with the development of high-grade gliomas

Background

Highly malignant high-grade gliomas are tumors of the central nervous system (CNS). They are solid tumors arising from transformed cells of the brain and/or the spinal cord. In recent years, the expression of genes and regulating miRNAs in glial brain tumors has been actively studied. The present study is devoted to assessing the expression levels of miR-215-5p, miR-22-3p, miR-122-5p, miR-107, miR-324-5p, miR-34a-5p, miR-155. -5p, miR-21-5p, miR-497-5p, miR-330-3p, miR-146a-5p, miR-92a-1-5p, miR-326 and target genes EGFR, SMAD4, SMAD7, SMO, NOTCH1, NOTCH2, HIF1A, EGLIN1/3, KDM1B, KDM1A, MSI1, MSI2, TET1 in high-grade glioma tissues.

Results

As a result of the analysis of the levels of relative expression of the studied genes, there are significant changes (p < 0.05) in tumor tissue for genes: EGFR, SMAD4, SMAD7, SMO, HIF1A, EGLN1/3. We obtained data on a significant change (p < 0.05) in the levels of relative expression for microRNA: hsa-miR-215-5p, hsa-miR-22-3p, hsa-miR-122-5p, hsa-miR-107, hsa-miR-324-5p, hsa-miR-155-5p, hsa-miR-21-5p, hsa-miR-330-3p, hsa-miR-326. Data on the association of overall survival in patients with high-grade glioma and the level of relative expression of the EGFR and HIF1A genes were obtained. The obtained data demonstrate the association of overall survival of patients with high-grade glioma and the level of relative expression of EGFR, HIF1A and hsa-miR-22-3p, hsa-miR-107 and hsa-miR-330-3p.

Conclusions

The obtained data on the expression of genes and microRNAs expand the understanding of the biology of the development of high-grade glial tumors. These data demonstrate new potential therapeutic and prognostic goals in high-grade gliomas.

Tumor Heterogeneity and Molecular Characteristics of Glioblastoma Revealed by Single-Cell RNA-Seq Data Analysis

Glioblastoma multiforme (GBM) is the most common infiltrating lethal tumor of the brain. Tumor heterogeneity and the precise characterization of GBM remain challenging, and the disease-specific and effective biomarkers are not available at present. To understand GBM heterogeneity and the disease prognosis mechanism, we carried out a single-cell transcriptome data analysis of 3389 cells from four primary IDH-WT (isocitrate dehydrogenase wild type) glioblastoma patients and compared the characteristic features of the tumor and periphery cells. We observed that the marker gene expression profiles of different cell types and the copy number variations (CNVs) are heterogeneous in the GBM samples. Further, we have identified 94 differentially expressed genes (DEGs) between tumor and periphery cells. We constructed a tissue-specific co-expression network and protein-protein interaction network for the DEGs and identified several hub genes, including CX3CR1, GAPDH, FN1, PDGFRA, HTRA1, ANXA2 THBS1, GFAP, PTN, TNC, and VIM. The DEGs were significantly enriched with proliferation and migration pathways related to glioblastoma. Additionally, we were able to identify the differentiation state of microglia and changes in the transcriptome in the presence of glioblastoma that might support tumor growth. This study provides insights into GBM heterogeneity and suggests novel potential disease-specific biomarkers which could help to identify the therapeutic targets in GBM.

Transcription factors in glioblastoma - Molecular pathogenesis and clinical implications

Glioblastoma, also known as glioblastoma multiforme (GBM), is one of the most lethal human cancers, however, the molecular mechanisms driving GBM remain largely elusive. Recent studies have revealed that transcription factors are significantly involved in GBM biology. Transcription factors (TFs), which are proteins that bind DNA to regulate gene expression, have critical roles at focal points in signaling pathways, orchestrating many cellular processes, such as cell growth and proliferation, differentiation, apoptosis, immune responses, and metabolism. Dysregulated or mutated TFs are common in GBM, resulting in aberrant gene expression that promotes tumor initiation, progression, and resistance to conventional therapies. In the present Review, we focus on TFs that are implicated in GBM pathogenesis, highlighting their oncogenic or tumor suppressive functions and describing the molecular mechanisms underlying their effect on GBM cells. We also discuss their use as biomarkers for GBM prognosis and therapeutic response, as well as their targeting with drugs for GBM treatment. Deciphering the role of TFs in the biology of GBM will provide new insights into the pathological mechanisms and reveal novel biomarkers and therapeutic targets.

Hedgehog/GLI1 signaling pathway regulates the resistance to cisplatin in human osteosarcoma

Purpose: This study aimed to investigate the role and mechanism of Hedgehog/GLI1 signaling pathway in regulating the resistance to cisplatin in osteosarcoma (OS).

Materials and methods: Immunohistochemistry, western blotting and qRT-PCR assay were performed to analyze and compare the expression of GLI1 in OS tumor tissue and normal bone tissue as well as in cisplatin sensitive and resistant cell lines (SOSP-9607 and SOSP-9607/CR). Meanwhile, the biological role of GLI1 in OS was investigated by using down-regulated expression of GLI1 and functional assays, including CCK-8, colony formation assay, flow cytometry, and wound healing assay. Moreover, the relationship between GLI1 and γ-H2AX (DNA damage protein) in cells treated with GLI1 siRNA and cisplatin was examined using western blot analysis. In addition, GANT61, a inhibitor of Hedgehog pathway was used in xenograft tumor model to further verify the effect and mechanism of GLI1 on cisplatin resistance in OS.

Results: We showed that GLI1 expression was up-regulated in OS patients and cisplatin-resistant cells. Silencing GLI1 significantly restored the sensitivity of OS to cisplatin, reduced proliferation, migration and cloning capacity of cisplatin sensitive and resistant cells, and increased the apoptosis rate in vitro. Furthermore, combined administration of GANT61 and cisplatin markedly inhibitted tumor growth in the mouse model. Mechanitic studies found that γ-H2AX is involved in the cisplatin resistance, and blockade of Hedgehog/GLI1 pathway increased the expression of γ-H2AX.

Conclusion: Abnormal activation of Hedgehog-GLI1 pathway can regulate the expression of γ-H2AX, thus affecting DNA damage and repair functions, and promoting acquired cisplatin resistance of OS.

Defining the Role of GLI/Hedgehog Signaling in Chemoresistance: Implications in Therapeutic Approaches

Insight into cancer signaling pathways is vital in the development of new cancer treatments to improve treatment efficacy. A relatively new but essential developmental signaling pathway, namely Hedgehog (Hh), has recently emerged as a major mediator of cancer progression and chemoresistance. The evolutionary conserved Hh signaling pathway requires an in-depth understanding of the paradigm of Hh signaling transduction, which is fundamental to provide the necessary means for the design of novel tools for treating cancer related to aberrant Hh signaling. This review will focus substantially on the canonical Hh signaling and the treatment strategies employed in different studies, with special emphasis on the molecular mechanisms and combination treatment in regard to Hh inhibitors and chemotherapeutics. We discuss our views based on Hh signaling's role in regulating DNA repair machinery, autophagy, tumor microenvironment, drug inactivation, transporters, epithelial-to-mesenchymal transition, and cancer stem cells to promote chemoresistance. The understanding of this Achilles' Heel in cancer may improve the therapeutic outcome for cancer therapy.

GLI1: A Therapeutic Target for Cancer

GLI1 is a transcriptional effector at the terminal end of the Hedgehog signaling (Hh) pathway and is tightly regulated during embryonic development and tissue patterning/differentiation. GLI1 has low-level expression in differentiated tissues, however, in certain cancers, aberrant activation of GLI1 has been linked to the promotion of numerous hallmarks of cancer, such as proliferation, survival, angiogenesis, metastasis, metabolic rewiring, and chemotherapeutic resistance. All of these are driven, in part, by GLI1’s role in regulating cell cycle, DNA replication and DNA damage repair processes. The consequences of GLI1 oncogenic activity, specifically the activity surrounding DNA damage repair proteins, such as NBS1, and cell cycle proteins, such as CDK1, can be linked to tumorigenesis and chemoresistance. Therefore, understanding the underlying mechanisms driving GLI1 dysregulation can provide prognostic and diagnostic biomarkers to identify a patient population that would derive therapeutic benefit from either direct inhibition of GLI1 or targeted therapy towards proteins downstream of GLI1 regulation.

1-[(4-Nitrophenyl)sulfonyl]-4-phenylpiperazine treatment after brain irradiation preserves cognitive function in mice

BACKGROUND

Normal tissue toxicity is an inevitable consequence of primary or secondary brain tumor radiotherapy. Cranial irradiation commonly leads to neurocognitive deficits that manifest months or years after treatment. Mechanistically, radiation-induced loss of neural stem/progenitor cells, neuroinflammation, and demyelination are contributing factors that lead to progressive cognitive decline.

METHODS

The effects of 1-[(4-nitrophenyl)sulfonyl]-4-phenylpiperazine (NSPP) on irradiated murine neurospheres, microglia cells, and patient-derived gliomaspheres were assessed by sphere-formation assays, flow cytometry, and interleukin (IL)-6 enzyme-linked immunosorbent assay. Activation of the hedgehog pathway was studied by quantitative reverse transcription PCR. The in vivo effects of NSPP were analyzed using flow cytometry, sphere-formation assays, immunohistochemistry, behavioral testing, and an intracranial mouse model of glioblastoma.

RESULTS

We report that NSPP mitigates radiation-induced normal tissue toxicity in the brains of mice. NSPP treatment significantly increased the number of neural stem/progenitor cells after brain irradiation in female animals, and inhibited radiation-induced microglia activation and expression of the pro-inflammatory cytokine IL-6. Behavioral testing revealed that treatment with NSPP after radiotherapy was able to successfully mitigate radiation-induced decline in memory function of the brain. In mouse models of glioblastoma, NSPP showed no toxicity and did not interfere with the growth-delaying effects of radiation.

CONCLUSIONS

We conclude that NSPP has the potential to mitigate cognitive decline in patients undergoing partial or whole brain irradiation without promoting tumor growth and that the use of this compound as a radiation mitigator of radiation late effects on the central nervous system warrants further investigation.

The Role of Notch, Hedgehog, and Wnt Signaling Pathways in the Resistance of Tumors to Anticancer Therapies

Resistance to therapy is the major hurdle in the current cancer management. Cancer cells often rewire their cellular process to alternate mechanisms to resist the deleterious effect mounted by different therapeutic approaches. The major signaling pathways involved in the developmental process, such as Notch, Hedgehog, and Wnt, play a vital role in development, tumorigenesis, and also in the resistance to the various anticancer therapies. Understanding how cancer utilizes these developmental pathways in acquiring the resistance to the multi-therapeutic approach cancer can give rise to a new insight of the anti-therapy resistance mechanisms, which can be explored for the development of a novel therapeutic approach. We present a brief overview of Notch, Hedgehog, and Wnt signaling pathways in cancer and its role in providing resistance to various cancer treatment modalities such as chemotherapy, radiotherapy, molecular targeted therapy, and immunotherapy. Understanding the importance of these molecular networks will provide a rational basis for novel and safer combined anticancer therapeutic approaches for the improvement of cancer treatment by overcoming drug resistance.

Gene Therapy for Drug-Resistant Glioblastoma via Lipid-Polymer Hybrid Nanoparticles Combined with Focused Ultrasound

BACKGROUND

Therapy for glioblastoma (GBM) has always been very challenging, not only because of the presence of the blood-brain barrier (BBB) but also due to susceptibility to drug resistance. Recently, the clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR/Cas9) has revolutionized gene editing technology and is capable of treating a variety of genetic diseases, including human tumors, but there is a lack of safe and effective targeting delivery systems in vivo, especially in the central nervous system (CNS).

METHODS

Lipid-polymer hybrid nanoparticles (LPHNs-cRGD) were constructed for efficient and targeting delivery of CRISPR/Cas9 plasmids targeting O6-methylguanine-DNA methyltransferase (MGMT), a drug-resistance gene to temozolomide (TMZ). Focused ultrasound (FUS)-microbubbles (MBs) were used to non-invasively and locally open the BBB to further facilitate gene delivery into glioblastoma in vivo. The gene editing efficiency and drug sensitivity changes were evaluated both in vitro and in vivo.

RESULTS

The gene-loaded LPHNs-cRGD were successfully synthesized and could protect pCas9/MGMT from enzyme degradation. LPHNs-cRGD could target GBM cells and mediate the transfection of pCas9/MGMT to downregulate the expression of MGMT, resulting in an increased sensitivity of GBM cells to TMZ. MBs-LPHNs-cRGD complexes could safely and locally increase the permeability of the BBB with FUS irradiation in vivo and facilitated the accumulation of nanoparticles at the tumor region in orthotopic tumor-bearing mice. Furthermore, the FUS-assisted MBs-LPHNspCas9/MGMT-cRGD enhanced the therapeutic effects of TMZ in glioblastoma, inhibited tumor growth, and prolonged survival of tumor-bearing mice, with a high level of biosafety.

CONCLUSION

In this work, we constructed LPHNs-cRGD for targeting delivery of the CRISPR/Cas9 system, in combination with FUS-MBs to open the BBB. The MBs-LPHNs-cRGD delivery system could be a potential alternative for efficient targeting gene delivery for the treatment of glioblastoma.

Biologically Active TNIIIA2 Region in Tenascin-C Molecule: A Major Contributor to Elicit Aggressive Malignant Phenotypes From Tumors/Tumor Stroma

Tenascin (TN)-C is highly expressed specifically in the lesions of inflammation-related diseases, including tumors. The expression level of TN-C in tumors and the tumor stroma is positively correlated with poor prognosis. However, no drugs targeting TN-C are currently clinically available, partly because the role of TN-C in tumor progression remains controversial. TN-C harbors an alternative splicing site in its fibronectin type III repeat domain, and its splicing variants including the type III-A2 domain are frequently detected in malignant tumors. We previously identified a biologically active region termed TNIIIA2 in the fibronectin type III-A2 domain of TN-C molecule and showed that this region is involved in promoting firm and persistent cell adhesion to fibronectin. In the past decade, through the exposure of various cell lines to peptides containing the TNIIIA2 region, we have published reports demonstrating the ability of the TNIIIA2 region to modulate distinct cellular activities, including survival/growth, migration, and invasion. Recently, we reported that the signals derived from TNIIIA2-mediated β1 integrin activation might play a crucial role for inducing malignant behavior of glioblastoma (GBM). GBM cells exposed to the TNIIIA2 region showed not only exacerbation of PDGF-dependent proliferation, but also acceleration of disseminative migration. On the other hand, we also found that the pro-inflammatory phenotypic changes were promoted when macrophages are stimulated with TNIIIA2 region in relatively low concentration and resulting MMP-9 upregulation is needed to release of the TNIIIA2 region from TN-C molecule. With the contribution of TNIIIA2-stimulated macrophages, the positive feedback spiral loop, which consists of the expression of TN-C, PDGF, and β1 integrin, and TNIIIA2 release, seemed to be activated in GBM with aggressive malignancy. Actually, the growth of transplanted GBM grafts in mice was significantly suppressed via the attenuation of β1 integrin activation. In this review, we thus introduce that the TNIIIA2 region has a significant impact on malignant progression of tumors by regulating cell adhesion. Importantly, it has been demonstrated that the TNIIIA2 region exerts unique biological functions through the extremely strong activation of β1-integrins and their long-lasting duration. These findings prompt us to develop new therapeutic agents targeting the TNIIIA2 region.

Revealing Temozolomide Resistance Mechanisms via Genome-Wide CRISPR Libraries

Glioblastoma is a severe type of brain tumor with a poor prognosis and few therapy options. Temozolomide (TMZ) is one of these options, however, with limited success, and failure is mainly due to tumor resistance. In this work, genome-wide CRISPR-Cas9 lentiviral screen libraries for gene knockout or activation were transduced in the human glioblastoma cell line, aiming to identify genes that modulate TMZ resistance. The sgRNAs enriched in both libraries in surviving cells after TMZ treatment were identified by next-generation sequencing (NGS). Pathway analyses of gene candidates on knockout screening revealed several enriched pathways, including the mismatch repair and the Sonic Hedgehog pathways. Silencing three genes ranked on the top 10 list (MSH2, PTCH2, and CLCA2) confirm cell protection from TMZ-induced death. In addition, a CRISPR activation library revealed that NRF2 and Wnt pathways are involved in TMZ resistance. Consistently, overexpression of FZD6, CTNNB1, or NRF2 genes significantly increased cell survival upon TMZ treatment. Moreover, NRF2 and related genes detected in this screen presented a robust negative correlation with glioblastoma patient survival rates. Finally, several gene candidates from knockout or activation screening are targetable by inhibitors or small molecules, and some of them have already been used in the clinic.

Cyclopamine sensitizes glioblastoma cells to temozolomide treatment through Sonic hedgehog pathway

AIM

Glioblastoma is an extremely aggressive glioma, resistant to radio and chemotherapy usually performed with temozolomide. One of the main reasons for glioblastoma resistance to conventional therapies is due to the presence of cancer stem-like cells. These cells could recapitulate some signaling pathways important for embryonic development, such as Sonic hedgehog. Here, we investigated if the inhibitor of the Sonic hedgehog pathway, cyclopamine, could potentiate the temozolomide effect in cancer stem-like cells and glioblastoma cell lines in vitro.

MAIN METHODS

The viability of glioblastoma cells exposed to cyclopamine and temozolomide treatment was evaluated by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay while the induction of apoptosis was assessed by western blot. The stemness properties of glioma cells were verified by clonogenic and differentiation assay and the expression of stem cell markers were measured by fluorescence microscopy and western blot.

KEY FINDINGS

The glioblastoma viability was reduced by cyclopamine treatment. Cyclopamine potentiated temozolomide treatment in glioblastoma cell lines by inducing apoptosis through activation of caspase-3 cleaved. Conversely, the combined treatment of cyclopamine and temozolomide potentiated the stemness properties of glioblastoma cells by inducing the expression of SOX-2 and OCT-4.

SIGNIFICANCE

Cyclopamine plays an effect on glioblastoma cell lines but also sensibilize them to temozolomide treatment. Thus, first-line treatment with Sonic hedgehog inhibitor followed by temozolomide could be used as a new therapeutic strategy for glioblastoma patients.

MGMT expression affects the gemcitabine resistance of pancreatic cancer cells

Pancreatic cancer is a malignant cancer with poor prognosis. This study aimed to explore how O6-methylguanine-DNA methyltransferase (MGMT) affects the gemcitabine resistance of pancreatic cancer cells by the regulatory role of SHH/GLI signaling pathway. MGMT inhibition induced by lomeguatrib (LM) suppressed the proliferation, invasion, migration and autophagy, promoted the apoptosis of PanC-1/GEM cells and up-regulated the GEM inhibition rates for PanC-1/GEM cells. Moreover, MGMT inhibition increased the expression of Caspase-3 and Bax and decreased the expression of Bcl-2, Beclin1 and Atg5 in PanC-1/GEM cells. PVT1 silencing could also produce the similar effects of MGMT inhibition induced by LM on PanC-1/GEM cells. And, PVT1 silencing could inhibit the SHH/GLI signaling pathway in PanC-1/GEM cells by regulating the MGMT expression. miR-409 was demonstrated to be a potential target of PVT1 and SHH was demonstrated to be a potential target of miR-409. Furthermore, GLI overexpression could reverse the effects of PVT1 silencing. In the xenograft model of pancreatic cancer, nude mice were treated with GEM. MGMT inhibition suppressed the tumor growth and autophagy and promoted the apoptosis in tumor tissues. And, PVT1 silencing could inhibit the SHH/GLI signaling pathway in tumor tissues. In conclusion, MGMT inhibition could suppress the proliferation, invasion, migration and autophagy and promote the apoptosis of PanC-1/GEM cells in vitro and in vivo. PVT1 silencing may affect the PanC-1/GEM cells through changing the MGMT expression by inhibiting the SHH/GLI signaling pathway.

Wnt-β-catenin Signaling Pathway, the Achilles' Heels of Cancer Multidrug Resistance

BACKGROUND

Most of the anticancer chemotherapies are hampered via the development of multidrug resistance (MDR), which is the resistance of tumor cells against cytotoxic effects of multiple chemotherapeutic agents. Overexpression and/or over-activation of ATP-dependent drug efflux transporters is a key mechanism underlying MDR development. Moreover, enhancement of drug metabolism, changes in drug targets and aberrant activation of the main signaling pathways, including Wnt, Akt and NF-κB are also responsible for MDR.

METHODS

In this study, we have reviewed the roles of Wnt signaling in MDR as well as its potential therapeutic significance. Pubmed and Scopus have been searched using Wnt, β-catenin, cancer, MDR and multidrug resistance as keywords. The last search was done in March 2019. Manuscripts investigating the roles of Wnt signaling in MDR or studying the modulation of MDR through the inhibition of Wnt signaling have been involved in the study. The main focus of the manuscript is regulation of MDR related transporters by canonical Wnt signaling pathway.

RESULT AND CONCLUSION

Wnt signaling has been involved in several pathophysiological states, including carcinogenesis and embryonic development. Wnt signaling is linked to various aspects of MDR including P-glycoprotein and multidrug resistance protein 1 regulation through its canonical pathways. Aberrant activation of Wnt/β- catenin signaling leads to the induction of cancer MDR mainly through the overexpression and/or over-activation of MDR related transporters. Accordingly, Wnt/β-catenin signaling can be a potential target for modulating cancer MDR.

CDK4/6 inhibition suppresses tumour growth and enhances the effect of temozolomide in glioma cells

In adults, glioma is the most commonly occurring and invasive brain tumour. For malignant gliomas, the current advanced chemotherapy includes TMZ (temozolomide). However, a sizeable number of gliomas are unyielding to TMZ, hence, giving rise to an urgent need for more efficient treatment choices. Here, we report that cyclin-dependent kinases 4 (CDK4) is expressed at significantly high levels in glioma cell lines and tissues. CDK4 overexpression enhances colony formation and proliferation of glioma cells and extends resistance to inhibition of TMZ-mediated cell proliferation and induction of apoptosis. However, CDK4 knockdown impedes colony formation and cell proliferation, and enhances sensitivity of glioma cells to TMZ. The selective inhibition of CDK4/6 impedes glioma cell proliferation and induces apoptotic induction. The selective inhibitors of CDK4/6 may enhance glioma cell sensitivity to TMZ. We further showed the possible role of RB phosphorylation mediated by CDK4 for its oncogenic function in glioma. The growth of glioma xenografts was inhibited in vivo, through combination treatment, and corresponded to enhanced p-RB levels, reduced staining of Ki-67 and enhanced activation of caspase 3. Therefore, CDK4 inhibition may be a favourable strategy for glioma treatment and overcomes TMZ resistance.

Exploring Novel Molecular Targets for the Treatment of High-Grade Astrocytomas Using Peptide Therapeutics: An Overview

Diffuse astrocytomas are the most aggressive and lethal glial tumors of the central nervous system (CNS). Their high cellular heterogeneity and the presence of specific barriers, i.e., blood–brain barrier (BBB) and tumor barrier, make these cancers poorly responsive to all kinds of currently available therapies. Standard therapeutic approaches developed to prevent astrocytoma progression, such as chemotherapy and radiotherapy, do not improve the average survival of patients. However, the recent identification of key genetic alterations and molecular signatures specific for astrocytomas has allowed the advent of novel targeted therapies, potentially more efficient and characterized by fewer side effects. Among others, peptides have emerged as promising therapeutic agents, due to their numerous advantages when compared to standard chemotherapeutics. They can be employed as (i) pharmacologically active agents, which promote the reduction of tumor growth; or (ii) carriers, either to facilitate the translocation of drugs through brain, tumor, and cellular barriers, or to target tumor-specific receptors. Since several pathways are normally altered in malignant gliomas, better outcomes may result from combining multi-target strategies rather than targeting a single effector. In the last years, several preclinical studies with different types of peptides moved in this direction, providing promising results in murine models of disease and opening new perspectives for peptide applications in the treatment of high-grade brain tumors.

FOXM1: a potential therapeutic target in human solid cancers

Introduction: FOXM1 is one of the most frequently overexpressed proteins in human solid cancers. Here, we discuss novel direct targets of FOXM1 as well as new pathways involving FOXM1, through which this protein exerts its oncogenic activity.Areas covered: We give a detailed review of FOXM1 transcriptional targets involved in 16 different types of human cancer as published in the literature in the last 5 years. We also discuss a novel positive feedback loop between FOXM1 and AKT - both well-established master regulators of cancer.Expert opinion: Despite the discovery of several FOXM1 inhibitors over the years (by our team and others), their therapeutic use is limited by their adverse off-target effects.Newly-discovered proteins regulated by FOXM1 present a promising alternative approach to target its pro-cancer activity. In addition, targeting regulating proteins that take part in the positive feedback loop between FOXM1/AKT has the double advantage of suppressing both, and can lead to developing novel anti-cancer drugs.

IKBKE enhances TMZ-chemoresistance through upregulation of MGMT expression in glioblastoma

PURPOSE

Glioblastoma multiforme (GBM) is the most common and aggressive malignant type of brain tumor. Despite advances in diagnosis and therapy, the prognosis of patients with GBM has remained dismal. Multidrug resistance and high recurrence are two of the major challenges in successfully treating brain tumors. IKBKE (inhibitor of nuclear factor kappa-B kinase subunit epsilon) is a major oncogenic protein in tumors and can inhibit glioblastoma cell proliferation, migration, and tumorigenesis. Our study aimed to investigate the mechanism of IKBKE enhancing the resistance of glioma cells to temozolomide.

METHODS

For the in vitro experiments, LN18 and U118 glioblastoma cells were treated with a combination of sh/oe-IKBKE lentivirus and TMZ. Cell proliferation was determined by the EdU assay and colony formation assays. Apoptosis was analyzed by the TUNEL assay. In vivo, LN18 NC and LN18 sh-IKBKE cells were implanted into the cerebrums of nude mice to detect the effect of combination therapy. The protein and mRNA levels were assayed by western blot, immunohistochemistry, and qRT-PCR.

RESULTS

In this study, we demonstrated that IKBKE enhances the resistance of glioblastoma cells to temozolomide (TMZ) by activating the AKT/NF-κB signaling pathway to upregulate the expression of the DNA repair enzyme o6-methylguanine-dna methyltransferase (MGMT). In glioblastoma cells, IKBKE knockdown enhances apoptosis and suppresses cell proliferation, clone formation, and tumor development in vivo induced by TMZ. However, overexpression of IKBKE reduces the effects of TMZ.

CONCLUSION

Our studies suggest that inhibition of IKBKE can enhance the therapeutic effect of TMZ on GBM in vitro and in vivo, providing new research directions and therapeutic targets for the treatment of GBM.

Cancer Stem Cells: Powerful Targets to Improve Current Anticancer Therapeutics

A frequent observation in several malignancies is the development of resistance to therapy that results in frequent tumor relapse and metastasis. Much of the tumor resistance phenotype comes from its heterogeneity that halts the ability of therapeutic agents to eliminate all cancer cells effectively. Tumor heterogeneity is, in part, controlled by cancer stem cells (CSC). CSC may be considered the reservoir of cancer cells as they exhibit properties of self-renewal and plasticity and the capability of reestablishing a heterogeneous tumor cell population. The endowed resistance mechanisms of CSC are mainly attributed to several factors including cellular quiescence, accumulation of ABC transporters, disruption of apoptosis, epigenetic reprogramming, and metabolism. There is a current need to develop new therapeutic drugs capable of targeting CSC to overcome tumor resistance. Emerging in vitro and in vivo studies strongly support the potential benefits of combination therapies capable of targeting cancer stem cell-targeting agents. Clinical trials are still underway to address the pharmacokinetics, safety, and efficacy of combination treatment. This review will address the main characteristics, therapeutic implications, and perspectives of targeting CSC to improve current anticancer therapeutics.

Downregulation of MGMT promotes proliferation of intrahepatic cholangiocarcinoma by regulating p21

BACKGROUND

Intrahepatic cholangiocarcinoma (ICC) is one of the most devastating cancers of the gastrointestinal tract. It is crucial to determine the accurate prognostic factors and find new therapeutic strategies. Meanwhile, O⁶-methylguanine-DNA methyltransferase (MGMT) is associated with malignant tumor progression. Thus, further studies are needed to investigate whether MGMT plays a similar role in ICC.

MATERIALS AND METHODS

Quantitative real-time PCR, western blot, and immunohistochemistry staining were used to detect the expression of MGMT in ICC tissues. The correlations between MGMT expression and clinicopathologic features were analyzed. The cell-proliferation assay and colony-formation assay were applied to evaluate proliferation ability, while methylation-specific PCR were used to detect the methylation status of the MGMT promoter CpG island in ICC tissues and cells.

RESULTS

Our study found that the expression of MGMT was decreased in ICC tissues when compared with paired normal tissues. In addition, we demonstrated that MGMT expression was positively correlated with overall survival rates and tumor histological grade. Silencing of MGMT significantly promoted cell proliferation in ICC. Further research showed that silencing of MGMT induced cells to enter S phase by inhibiting p21, p27, and Cyclin E expression, ultimately promoting ICC proliferation. We also demonstrated that the MGMT promoter was highly methylated in ICC, and the levels of MGMT and p21 mRNA increased after DNA demethylation. In addition, the levels of MGMT and p21 protein were positively correlated in ICC tissues.

CONCLUSION

MGMT may play a critical role in carcinogenesis and the development of ICC, and provides a new marker of clinical prognosis and target for ICC treatment.

Aggressive Progression in Glioblastoma Cells through Potentiated Activation of Integrin α5β1 by the Tenascin-C-Derived Peptide TNIIIA2

Tenascin-C is a member of the matricellular protein family, and its expression level is correlated to poor prognosis in cancer, including glioblastoma, whereas its substantial role in tumor formation and malignant progression remains controversial. We reported previously that peptide TNIIIA2 derived from the cancer-associated alternative splicing domain of tenascin-C molecule has an ability to activate β1-integrin strongly and to maintain it for a long time. Here, we demonstrate that β1-integrin activation by TNIIIA2 causes acquisition of aggressive behavior, dysregulated proliferation, and migration, characteristic of glioblastoma cells. TNIIIA2 hyperstimulated the platelet-derived growth factor-dependent cell survival and proliferation in an anchorage-independent as well as -dependent manner in glioblastoma cells. TNIIIA2 also strongly promoted glioblastoma multiforme cell migration, which was accompanied by an epithelial-mesenchymal transition-like morphologic change on the fibronectin substrate. Notably, acquisition of these aggressive properties by TNIIIA2 in glioblastoma cells was abrogated by peptide FNIII14 that is capable of inducing inactivation in β1-integrin activation. Moreover, FNIII14 significantly inhibited tumor growth in a mouse xenograft glioblastoma model. More importantly, FNIII14 sensitized glioblastoma cells to temozolomide via downregulation of O⁶-methylguanine-DNA methyltransferase expression. Consequently, FNIII14 augmented the antitumor activity of temozolomide in a mouse xenograft glioblastoma model. Taken altogether, the present study provides not only an interpretation for the critical role of tenascin-C/TNIIIA2 in aggressive behavior of glioblastoma cells, but also an important strategy for glioblastoma chemotherapy. Inhibition of the tenascin-C/β1-integrin axis may be a therapeutic target for glioblastoma, and peptide FNIII14 may represent a new approach for glioblastoma chemotherapy. SIGNIFICANCE: These findings provide a proposal of new strategy for glioblastoma chemotherapy based on integrin inactivation.

Prognostic significance of O6-methylguanine-DNA-methyltransferase (MGMT) promoter methylation and isocitrate dehydrogenase-1 (IDH-1) mutation in glioblastoma multiforme patients: A single-center experience in the Middle East region

OBJECTIVES

To determine the prevalence and prognostic value of MGMT promoter methylation and IDH1 mutation in glioblastoma multiforme (GBM) patients from the Middle East.

PATIENTS AND METHODS

Records of patients diagnosed between 2003 and 2015 were reviewed. MGMT promoter methylation was measured using methylation-specific polymerase chain reaction and IDH-1 mutation was reported. The primary endpoint was overall survival (OS).

RESULTS

A total of 110 patients were included. The median age was 51 years and 71 patients (64.5%) were males. The median diameter of GBM was 4.6 cm and 29 patients (26.4%) had multifocal disease. Gross total resection was achieved in 38 patients (24.9%). All patients received adjuvant radiation therapy, and 96 patients (91.4%) received concomitant temozolomide. At a median follow up of 13.6 months, the median OS was 17.2 months, and the OS at 1 and 2 years were 71.6% and 34.8%, respectively. On multivariate analysis, age at diagnosis (HR 1.019; P = 0.044) and multifocality (HR 2.373; P = 0.001) were the only independent prognostic variables. MGMT promoter methylation was found in 28.2% of patients but did not significantly correlate with survival (HR 1.160; P = 0.635). IDH-1 mutation was found in 10% of patients was associated with a non-significant trend for survival improvement (HR 0.502; P = 0.151).

CONCLUSION

Patients with GBM from the Middle East have adequate survival outcomes when given the optimal treatment. In our patient population, MGMT promoter methylation did not seem to correlate with outcomes, but patients with IDH1 mutation had numerically higher survival outcomes.

Oroxylin A increases the sensitivity of temozolomide on glioma cells by hypoxia-inducible factor 1α/hedgehog pathway under hypoxia

Microenvironmental hypoxia-mediated drug resistance is responsible for the failure of cancer therapy. To date, the role of the hedgehog pathway in resistance to temozolomide (TMZ) under hypoxia has not been investigated. In this study, we discovered that the increasing hypoxia-inducible factor 1α (HIF-1α) activated the hedgehog pathway in hypoxic microenvironment by promoting autocrine secretion of sonic hedgehog protein (Shh), and then upregulating transfer of Gli1 to the nucleus, finally contributed to TMZ resistance in glioma cells. Oroxylin A (C16H12O5), a bioactive flavonoid, could induce HIF-1α degradation via prolyl-hydroxylases-VHL signaling pathway, resulting in the inactivation of the hedgehog. Besides, oroxylin A increased the expression of Sufu, which is a negative regulator of Gli1. By this mechanism, oroxylin A sensitized TMZ on glioma cells. U251 intracranial transplantation model and GL261 xenograft model were used to confirm the reversal effects of oroxylin A in vivo. In conclusion, our results demonstrated that HIF-1α/hedgehog pathway conferred TMZ resistance under hypoxia, and oroxylin A was capable of increasing the sensitivity of TMZ on glioma cells in vitro and in vivo by inhibiting HIF-1α/hedgehog pathway and depressing the activation of Gli1 directly.

Role of GLI Transcription Factors in Pathogenesis and Their Potential as New Therapeutic Targets

GLI transcription factors have important roles in intracellular signaling cascade, acting as the main mediators of the HH-GLI signaling pathway. This is one of the major developmental pathways, regulated both canonically and non-canonically. Deregulation of the pathway during development leads to a number of developmental malformations, depending on the deregulated pathway component. The HH-GLI pathway is mostly inactive in the adult organism but retains its function in stem cells. Aberrant activation in adult cells leads to carcinogenesis through overactivation of several tightly regulated cellular processes such as proliferation, angiogenesis, EMT. Targeting GLI transcription factors has recently become a major focus of potential therapeutic protocols.

CAT3, a prodrug of 13a(S)-3-hydroxyl-6,7-dimethoxyphenanthro[9,10-b]-indolizidine, circumvents temozolomide-resistant glioblastoma via the Hedgehog signaling pathway, independently of O6-methylguanine DNA methyltransferase expression

PURPOSE

Glioblastoma multiforme (GBM) is a malignant high-grade glioma with a poor clinical outcome. Temozolomide (TMZ) is the first-line GBM chemotherapy; however, patients commonly develop resistance to its effects.

MATERIALS AND METHODS

We investigated the antitumor activity of CAT3 in TMZ-resistant glioblastoma cell lines U251/TMZ and T98G. Orthotopic and subcutaneous mice tumor models were used to investigate the effects of various treatment regimes.

RESULTS

We found that PF403, the active metabolite of CAT3, inhibited proliferation of both cell lines. PF403 repressed the Hedgehog signaling pathway in the U251/TMZ cell line, reduced O6-methylguanine DNA methyltransferase (MGMT) expression, and abolished the effects of the Shh pathway. Moreover, PF403 blocked the Hedgehog signaling pathway in T98G MGMT-expressing cells and downregulated the expression of MGMT. CAT3 suppressed growth in the U251/TMZ orthotopic and T98G subcutaneous xenograft tumor models in vivo. We also demonstrated that inhibition of the Hedgehog pathway by PF403 counteracted TMZ resistance and enhanced the antitumor activity of TMZ in vitro and in vivo.

CONCLUSION

These results indicate that CAT3 is a potential therapeutic agent for TMZ-resistant GBM.

A highlight on Sonic hedgehog pathway

Hedgehog (Hh) signaling pathway plays an essential role during vertebrate embryonic development and tumorigenesis. It is already known that Sonic hedgehog (Shh) pathway is important for the evolution of radio and chemo-resistance of several types of tumors. Most of the brain tumors are resistant to chemotherapeutic drugs, consequently, they have a poor prognosis. So, a better knowledge of the Shh pathway opens an opportunity for targeted therapies against brain tumors considering a multi-factorial molecular overview. Therefore, emerging studies are being conducted in order to find new inhibitors for Shh signaling pathway, which could be safely used in clinical trials. Shh can signal through a canonical and non-canonical way, and it also has important points of interaction with other pathways during brain tumorigenesis. So, a better knowledge of Shh signaling pathway opens an avenue of possibilities for the treatment of not only for brain tumors but also for other types of cancers. In this review, we will also highlight some clinical trials that use the Shh pathway as a target for treating brain cancer.