Cycling hypoxia induces chemoresistance through the activation of reactive oxygen species-mediated B-cell lymphoma extra-long pathway in glioblastoma multiforme

Understanding the Significance of Hypoxia-Inducible Factors (HIFs) in Glioblastoma: A Systematic Review

BACKGROUND

The study aims to investigate the role of hypoxia-inducible factors (HIFs) in the development, progression, and therapeutic potential of glioblastomas.

METHODOLOGY

The study, following PRISMA guidelines, systematically examined hypoxia and HIFs in glioblastoma using MEDLINE (PubMed), Web of Science, and Scopus. A total of 104 relevant studies underwent data extraction.

RESULTS

Among the 104 studies, global contributions were diverse, with China leading at 23.1%. The most productive year was 2019, accounting for 11.5%. Hypoxia-inducible factor 1 alpha (HIF1α) was frequently studied, followed by hypoxia-inducible factor 2 alpha (HIF2α), osteopontin, and cavolin-1. Commonly associated factors and pathways include glucose transporter 1 (GLUT1) and glucose transporter 3 (GLUT3) receptors, vascular endothelial growth factor (VEGF), phosphoinositide 3-kinase (PI3K)-Akt-mechanistic target of rapamycin (mTOR) pathway, and reactive oxygen species (ROS). HIF expression correlates with various glioblastoma hallmarks, including progression, survival, neovascularization, glucose metabolism, migration, and invasion.

CONCLUSION

Overcoming challenges such as treatment resistance and the absence of biomarkers is critical for the effective integration of HIF-related therapies into the treatment of glioblastoma with the aim of optimizing patient outcomes.

Unveiling the mechanisms and challenges of cancer drug resistance

Cancer treatment faces many hurdles and resistance is one among them. Anti-cancer treatment strategies are evolving due to innate and acquired resistance capacity, governed by genetic, epigenetic, proteomic, metabolic, or microenvironmental cues that ultimately enable selected cancer cells to survive and progress under unfavorable conditions. Although the mechanism of drug resistance is being widely studied to generate new target-based drugs with better potency than existing ones. However, due to the broader flexibility in acquired drug resistance, advanced therapeutic options with better efficacy need to be explored. Combination therapy is an alternative with a better success rate though the risk of amplified side effects is commonplace. Moreover, recent groundbreaking precision immune therapy is one of the ways to overcome drug resistance and has revolutionized anticancer therapy to a greater extent with the only limitation of being individual-specific and needs further attention. This review will focus on the challenges and strategies opted by cancer cells to withstand the current therapies at the molecular level and also highlights the emerging therapeutic options -like immunological, and stem cell-based options that may prove to have better potential to challenge the existing problem of therapy resistance. Video Abstract.

The impact of cycling hypoxia on the phenotype of HPV-positive cervical cancer cells

Cycling hypoxia (cycH) is a prevalent form of tumor hypoxia that is characterized by exposure of tumor cells to recurrent phases of hypoxia and reoxygenation. CycH has been associated with a particularly aggressive cellular phenotype of tumor cells and increased therapy resistance. By performing comparative analyses under normoxia, physoxia, chronic hypoxia, and cycH, we here uncover distinct effects of cycH on the phenotype of human papillomavirus (HPV)-positive cervical cancer cells. We show that-other than under chronic hypoxia-viral E6/E7 oncogene expression is largely maintained under cycH as is the E6/E7-dependent regulation of p53 and retinoblastoma protein. Further, cycH enables HPV-positive cancer cells to evade prosenescent chemotherapy, similar to chronic hypoxia. Moreover, cells under cycH exhibit a particularly pronounced resistance to the proapoptotic effects of Cisplatin. Quantitative proteome analyses reveal that cycH induces a unique proteomic signature in cervical cancer cells, which includes a significant downregulation of luminal lysosomal proteins. These encompass the potentially proapoptotic cathepsins B and cathepsin L, which, however, appear not to affect the response to Cisplatin under any of the O2 conditions tested. Rather, we show that the proapoptotic Caspase 8/BH3-interacting domain death agonist (BID) cascade plays a pivotal role for the efficiency of Cisplatin-induced apoptosis in HPV-positive cancer cells under all investigated O2 conditions. In addition, we provide evidence that BID activation by Cisplatin is impaired under cycH, which could contribute to the high resistance to the proapoptotic effects of Cisplatin. Collectively, this study provides the first insights into the profound phenotypic alterations induced by cycH in HPV-positive cancer cells, with implications for their therapeutic susceptibility.

Overcoming brain barriers through surface-functionalized liposomes for glioblastoma therapy; current status, challenges and future perspective

Glioblastoma (GB) originating from astrocytes is considered a grade IV astrocytoma tumor with severe consequences. The blood-brain barrier (BBB) offers a major obstacle in drug delivery to the brain to overcome GB. The current treatment options possess limited efficacy and maximal systemic toxic effects in GB therapy. Emerging techniques such as targeted drug delivery offer significant advantages, including enhanced drug delivery to the tumor site by overcoming the BBB. This review article focuses on the status of surface-modified lipid nanocarriers with functional ligands to efficiently traverse the BBB and improve brain targeting for successful GB treatment. The difficulties with surface-functionalized liposomes and potential future directions for opening up novel treatment options for GB are highlighted.

Travelling under pressure - hypoxia and shear stress in the metastatic journey

Cancer cell invasion, intravasation and survival in the bloodstream are early steps of the metastatic process, pivotal to enabling the spread of cancer to distant tissues. Circulating tumor cells (CTCs) represent a highly selected subpopulation of cancer cells that tamed these critical steps, and a better understanding of their biology and driving molecular principles may facilitate the development of novel tools to prevent metastasis. Here, we describe key research advances in this field, aiming at describing early metastasis-related processes such as collective invasion, shedding, and survival of CTCs in the bloodstream, paying particular attention to microenvironmental factors like hypoxia and mechanical stress, considered as important influencers of the metastatic journey.

Unravelling the Glioblastoma Tumour Microenvironment: Can Aptamer Targeted Delivery Become Successful in Treating Brain Cancers?

The key challenges to treating glioblastoma multiforme (GBM) are the heterogeneous and complex nature of the GBM tumour microenvironment (TME) and difficulty of drug delivery across the blood-brain barrier (BBB). The TME is composed of various neuronal and immune cells, as well as non-cellular components, including metabolic products, cellular interactions, and chemical compositions, all of which play a critical role in GBM development and therapeutic resistance. In this review, we aim to unravel the complexity of the GBM TME, evaluate current therapeutics targeting this microenvironment, and lastly identify potential targets and therapeutic delivery vehicles for the treatment of GBM. Specifically, we explore the potential of aptamer-targeted delivery as a successful approach to treating brain cancers. Aptamers have emerged as promising therapeutic drug delivery vehicles with the potential to cross the BBB and deliver payloads to GBM and brain metastases. By targeting specific ligands within the TME, aptamers could potentially improve treatment outcomes and overcome the challenges associated with larger therapies such as antibodies.

NF-κB in Cell Deaths, Therapeutic Resistance and Nanotherapy of Tumors: Recent Advances

The transcription factor nuclear factor-κB (NF-κB) plays a complicated role in multiple tumors. Mounting evidence demonstrates that NF-κB activation supports tumorigenesis and development by enhancing cell proliferation, invasion, and metastasis, preventing cell death, facilitating angiogenesis, regulating tumor immune microenvironment and metabolism, and inducing therapeutic resistance. Notably, NF-κB functions as a double-edged sword exerting positive or negative influences on cancers. In this review, we summarize and discuss recent research on the regulation of NF-κB in cancer cell deaths, therapy resistance, and NF-κB-based nano delivery systems.

Inhibition of metastatic brain cancer in Sonic Hedgehog medulloblastoma using caged nitric oxide albumin nanoparticles

Medulloblastoma is a tumor of the cerebellum that metastasizes to the leptomeninges of the central nervous system (CNS), including to forebrain and to spinal cord. The inhibitory effect of polynitroxylated albumin (PNA), a caged nitroxide nanoparticle, on leptomeningeal dissemination and metastatic tumor growth was studied in a Sonic Hedgehog transgenic mouse model. PNA treated mice showed an increased lifespan with a mean survival of 95 days (n = 6, P<0.05) compared with 71 days in controls. In primary tumors, proliferation was significantly reduced and differentiation was significantly increased (P<0.001) as shown by Ki-67+ and NeuN+ immunohistochemistry, while cells in spinal cord tumors appeared unaffected. Yet, histochemical analysis of metastatic tumor in spinal cord showed that the mean total number of cells in spinal cord was significantly reduced in mice treated with PNA compared to albumin vehicle (P<0.05). Examination of various levels of the spinal cord showed that PNA treated mice had significantly reduced metastatic cell density in the thoracic, lumbar and sacral spinal cord levels (P<0.05), while cell density in the cervical region was not significantly changed. The mechanism by which PNA may exert these effects on CNS tumors is discussed.

Carbon-ion radiotherapy boost with standard dose proton radiation for incomplete-resected high-grade glioma: a phase 1 study

Background

To investigate the maximal tolerated dose (MTD) of a carbon-ion radiotherapy (CIRT) boost prior to standard dose proton radiotherapy (PRT) for newly diagnosed glioblastoma (GBM) and anaplastic astrocytoma (AA) patients with residual lesion after resection.

Methods

In total, 18 patients with high-grade glioma (HGG) (16 with GBM and 2 with AA) were enrolled in a prospective 3×3 design phase 1 trial. We investigated four dose-levels of CIRT boost [9 (starting level), 12, 15, and 18 Gy relative biological effectiveness (RBE)] delivered in three equal fractions prior to the standard dose PRT (60 Gy RBE in 30 fractions). Concurrent temozolomide (TMZ) was not provided during the CIRT boost but was initiated on the first day of PRT. Acute and late toxicities were scored based on the Common Terminology Criteria for Adverse Events (CTCAE, v 4.03). Dose-limiting toxicities (DLTs) were defined as radiation-induced severe toxicities (≥ grade 3).

Results

With a median follow-up of 17.9 months, no severe (≥ grade 3) acute or late toxicities were observed in patients treated with the first three dose levels (CIRT boost doses of 9, 12, 15 Gy RBE). Severe late toxicity (grade 3 radiation necrosis) was observed in the first patient treated with the 18 Gy RBE CIRT boost level. Therefore, this trial was terminated and the MTD of the induction CIRT boost was determined at 15 Gy RBE in 3 fractions. At the time of this analysis, both patients with AA were alive without disease progression. The progression-free survival (PFS) and overall survival (OS) for GBM at 12 months were 50.6% and 78.6%, respectively.

Conclusions

Particle beam radiotherapy consisting of a CIRT boost of 15 Gy RBE (in 3 fractions) following standard dose PRT (60 Gy RBE in 30 fractions), and used in conjunction with TMZ, is safe and potentially effective for patients with HGG.

Drug Resistance in Cancers: A Free Pass for Bullying

The cancer burden continues to grow globally, and drug resistance remains a substantial challenge in cancer therapy. It is well established that cancerous cells with clonal dysplasia generate the same carcinogenic lesions. Tumor cells pass on genetic templates to subsequent generations in evolutionary terms and exhibit drug resistance simply by accumulating genetic alterations. However, recent evidence has implied that tumor cells accumulate genetic alterations by progressively adapting. As a result, intratumor heterogeneity (ITH) is generated due to genetically distinct subclonal populations of cells coexisting. The genetic adaptive mechanisms of action of ITH include activating "cellular plasticity", through which tumor cells create a tumor-supportive microenvironment in which they can proliferate and cause increased damage. These highly plastic cells are located in the tumor microenvironment (TME) and undergo extreme changes to resist therapeutic drugs. Accordingly, the underlying mechanisms involved in drug resistance have been re-evaluated. Herein, we will reveal new themes emerging from initial studies of drug resistance and outline the findings regarding drug resistance from the perspective of the TME; the themes include exosomes, metabolic reprogramming, protein glycosylation and autophagy, and the relates studies aim to provide new targets and strategies for reversing drug resistance in cancers.

The hypoxia-driven crosstalk between tumor and tumor-associated macrophages: mechanisms and clinical treatment strategies

Given that hypoxia is a persistent physiological feature of many different solid tumors and a key driver for cancer malignancy, it is thought to be a major target in cancer treatment recently. Tumor-associated macrophages (TAMs) are the most abundant immune cells in the tumor microenvironment (TME), which have a large impact on tumor development and immunotherapy. TAMs massively accumulate within hypoxic tumor regions. TAMs and hypoxia represent a deadly combination because hypoxia has been suggested to induce a pro-tumorigenic macrophage phenotype. Hypoxia not only directly affects macrophage polarization, but it also has an indirect effect by altering the communication between tumor cells and macrophages. For example, hypoxia can influence the expression of chemokines and exosomes, both of which have profound impacts on the recipient cells. Recently, it has been demonstrated that the intricate interaction between cancer cells and TAMs in the hypoxic TME is relevant to poor prognosis and increased tumor malignancy. However, there are no comprehensive literature reviews on the molecular mechanisms underlying the hypoxia-mediated communication between tumor cells and TAMs. Therefore, this review has the aim to collect all recently available data on this topic and provide insights for developing novel therapeutic strategies for reducing the effects of hypoxia.

Cyclic Hypoxia Induces Transcriptomic Changes in Mast Cells Leading to a Hyperresponsive Phenotype after FcεRI Cross-Linking

Mast cells (MCs) play important roles in tumor development, executing pro- or antitumoral functions depending on tumor type and tumor microenvironment (TME) conditions. Cyclic hypoxia (cyH) is a common feature of TME since tumor blood vessels fail to provide a continuous supply of oxygen to the tumor mass. Here, we hypothesized that the localization of MCs in cyH regions within solid tumors could modify their transcriptional profile and activation parameters. Using confocal microscopy, we found an important number of MCs in cyH zones of murine melanoma B16-F1 tumors. Applying microarray analysis to examine the transcriptome of murine bone-marrow-derived MCs (BMMCs) exposed to interleaved cycles of hypoxia and re-oxygenation, we identified altered expression of 2512 genes. Functional enrichment analysis revealed that the transcriptional signature of MCs exposed to cyH is associated with oxidative phosphorylation and the FcεRI signaling pathway. Interestingly, FcεRI-dependent degranulation, calcium mobilization, and PLC-γ activity, as well as Tnf-α, Il-4, and Il-2 gene expression after IgE/antigen challenge were increased in BMMCs exposed to cyH compared with those maintained in normoxia. Taken together, our findings indicate that cyH causes an important phenotypic change in MCs that should be considered in the design of inflammation-targeted therapies to control tumor growth.

Looking for the Holy Grail—Drug Candidates for Glioblastoma Multiforme Chemotherapy

Glioblastoma multiforme (GBM) is the deadliest and the most heterogeneous brain cancer. The median survival time of GBM patients is approximately 8 to 15 months after initial diagnosis. GBM development is determined by numerous signaling pathways and is considered one of the most challenging and complicated-to-treat cancer types. Standard GBM therapy consist of surgery followed by radiotherapy or chemotherapy, and combined treatment. Current standard of care (SOC) does not offer a significant chance for GBM patients to combat cancer, and the selection of available drugs is limited. For almost 20 years, there has been only one drug, Temozolomide (TMZ), approved as a first-line GBM treatment. Due to the limited efficacy of TMZ and the high rate of resistant patients, the implementation of new chemotherapeutics is highly desired. However, due to the unique properties of GBM, many challenges still need to be overcome before reaching a ‘breakthrough’. This review article describes the most recent compounds introduced into clinical trials as drug candidates for GBM chemotherapy.

p53 Signaling on Microenvironment and Its Contribution to Tissue Chemoresistance

Chemoresistance persists as a significant, unresolved clinical challenge in many cancer types. The tumor microenvironment, in which cancer cells reside and interact with non-cancer cells and tissue structures, has a known role in promoting every aspect of tumor progression, including chemoresistance. However, the molecular determinants of microenvironment-driven chemoresistance are mainly unknown. In this review, we propose that the TP53 tumor suppressor, found mutant in over half of human cancers, is a crucial regulator of cancer cell-microenvironment crosstalk and a prime candidate for the investigation of microenvironment-specific modulators of chemoresistance. Wild-type p53 controls the secretion of factors that inhibit the tumor microenvironment, whereas altered secretion or mutant p53 interfere with p53 function to promote chemoresistance. We highlight resistance mechanisms promoted by mutant p53 and enforced by the microenvironment, such as extracellular matrix remodeling and adaptation to hypoxia. Alterations of wild-type p53 extracellular function may create a cascade of spatial amplification loops in the tumor tissue that can influence cellular behavior far from the initial oncogenic mutation. We discuss the concept of chemoresistance as a multicellular/tissue-level process rather than intrinsically cellular. Targeting p53-dependent crosstalk mechanisms between cancer cells and components of the tumor environment might disrupt the waves of chemoresistance that spread across the tumor tissue, increasing the efficacy of chemotherapeutic agents.

Synthetic strategy and structure-activity relationship (SAR) studies of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1, Lificiguat): a review

Since 1994, YC-1 (Lificiguat, 3-(5′-hydroxymethyl-2′-furyl)-1-benzylindazole) has been synthesized, and many targets for special bioactivities have been explored, such as stimulation of platelet-soluble guanylate cyclase, indirect elevation of platelet cGMP levels, and inhibition of hypoxia-inducible factor-1 (HIF-1) and NF-κB. Recently, Riociguat®, the first soluble guanylate cyclase (sGC) stimulator drug used to treat pulmonary hypertension and pulmonary arterial hypertension, was derived from the YC-1 structure. In this review, we aim to highlight the synthesis and structure–activity relationships in the development of YC-1 analogs and their possible indications.

Since 1994, YC-1 (Lificiguat) has been synthesized, and many targets for special bioactivities have been explored, such as stimulation of platelet-soluble guanylate cyclase, indirect elevation of platelet cGMP levels, and inhibition of HIF-1 and NF-κB.

FV-429 enhances the efficacy of paclitaxel in NSCLC by reprogramming HIF-1α-modulated FattyAcid metabolism

Solid tumors often exhibit hypoxia in their centers, which has been associated with a marked reduction in the sensitivity of the tumor cells to anti-tumor and chemotherapeutic interventions. Here, we found that the occurrence and progress of hypoxic insensitivity to paclitaxel in non-small cell lung cancer (NSCLC) are closely associated with the HIF-1α pathway. The HIF-1α protein upregulated the expression of adipose differentiation-related protein (ADRP), fatty acid synthase (FASN), and sterol regulatory element binding protein 1(SREBP1), while simultaneously downregulating carnitine palmitoyltransferase 1 (CPT1), thereby leading to a more pronounced uptake of lipids and reduced oxidation of fatty acids. Diminished levels of fatty acids led to reduced Wnt pathway activation and β-catenin nuclear translocation, leading to G2/M cell cycle arrest. In this study, FV-429, a derivative of the natural flavonoid wogonin, reprogrammed metabolism of cancer cells and decreased fatty acid levels. Moreover, paclitaxel-induced G2/M phase arrest in hypoxia-resistant NSCLC was hampered but FV-429 improved the sensitivity of these cancer cells to paclitaxel. FV-429 activated and modulated fatty acid metabolism in NSCLC cells, significantly reduced levels of fatty acids within cells and increased the oxidation of these fatty acids. The results of our study demonstrated that FV-429 could reshape fatty acid metabolism in hypoxia-induced paclitaxel-resistant NSCLC and enhance the sensitivity of NSCLC cells to paclitaxel through G2/M phase arrest deterioration, by inactivating the Wnt pathway, and suggested the possibility of using FV-429 as a promising candidate therapeutic agent for advanced NSCLC.

Biomarkers and focused ultrasound: the future of liquid biopsy for brain tumor patients

Introduction

Despite advances in modern medicine, brain tumor patients are still monitored purely by clinical evaluation and imaging. Traditionally, invasive strategies such as open or stereotactic biopsies have been used to confirm the etiology of clinical and imaging changes. Liquid biopsies can enable physicians to noninvasively analyze the evolution of a tumor and a patient’s response to specific treatments. However, as a consequence of biology and the current limitations in detection methods, no blood or cerebrospinal fluid (CSF) brain tumor-derived biomarkers are used in routine clinical practice. Enhancing the presence of tumor biomarkers in blood and CSF via brain-blood barrier (BBB) disruption with MRI-guided focused ultrasound (MRgFUS) is a very compelling strategy for future management of brain tumor patients.

Methods

A literature review on MRgFUS-enabled brain tumor liquid biopsy was performed using Medline/Pubmed databases and clinical trial registries.

Results

The therapeutic applications of MRgFUS to target brain tumors have been under intense investigation. At high-intensity, MRgFUS can ablate brain tumors and target tissues, which needs to be balanced with the increased risk for damage to surrounding normal structures. At lower-intensity and pulsed-frequency, MRgFUS may be able to disrupt the BBB transiently. Thus, while facilitating intratumoral or parenchymal access to standard or novel therapeutics, BBB disruption with MRgFUS has opened the possibility of enhanced detection of brain tumor-derived biomarkers.

Conclusions

In this review, we describe the concept of MRgFUS-enabled brain tumor liquid biopsy and present the available preclinical evidence, ongoing clinical trials, limitations, and future directions of this application.

Chronic and Cycling Hypoxia: Drivers of Cancer Chronic Inflammation through HIF-1 and NF-κB Activation: A Review of the Molecular Mechanisms

Chronic (continuous, non-interrupted) hypoxia and cycling (intermittent, transient) hypoxia are two types of hypoxia occurring in malignant tumors. They are both associated with the activation of hypoxia-inducible factor-1 (HIF-1) and nuclear factor κB (NF-κB), which induce changes in gene expression. This paper discusses in detail the mechanisms of activation of these two transcription factors in chronic and cycling hypoxia and the crosstalk between both signaling pathways. In particular, it focuses on the importance of reactive oxygen species (ROS), reactive nitrogen species (RNS) together with nitric oxide synthase, acetylation of HIF-1, and the action of MAPK cascades. The paper also discusses the importance of hypoxia in the formation of chronic low-grade inflammation in cancerous tumors. Finally, we discuss the effects of cycling hypoxia on the tumor microenvironment, in particular on the expression of VEGF-A, CCL2/MCP-1, CXCL1/GRO-α, CXCL8/IL-8, and COX-2 together with PGE₂. These factors induce angiogenesis and recruit various cells into the tumor niche, including neutrophils and monocytes which, in the tumor, are transformed into tumor-associated neutrophils (TAN) and tumor-associated macrophages (TAM) that participate in tumorigenesis.

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

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

Rational construction of a reversible arylazo-based NIR probe for cycling hypoxia imaging in vivo

Reversible NIR luminescent probes with negligible photocytotoxicity are required for long-term tracking of cycling hypoxia in vivo. However, almost all of the reported organic fluorescent hypoxia probes reported until now were irreversible. Here we report a reversible arylazo-conjugated fluorescent probe (HDSF) for cycling hypoxia imaging. HDSF displays an off-on fluorescence switch at 705 nm in normoxia-hypoxia cycles. Mass spectroscopic and theoretical studies confirm that the reversible sensing behavior is attributed to the two electron-withdrawing trifluoromethyl groups, which stabilizes the reduction intermediate phenylhydrazine and blocks the further reductive decomposition. Cycling hypoxia monitoring in cells and zebrafish embryos is realized by HDSF using confocal imaging. Moreover, hypoxic solid tumors are visualized and the ischemia-reperfusion process in mice is monitored in real-time. This work provides an effective strategy to construct organic fluorescent probes for cycling hypoxia imaging and paves the way for the study of cycling hypoxia biology.

Stimuli-responsive hydrogels for intratumoral drug delivery

The ability of some hydrogels to exhibit a phase transition or change their structure in response to stimuli has been extensively explored for drug depot formation and controlled drug release. Taking advantage of the unique features of the tumor microenvironment (TME) or externally applied triggers, several injectable stimuli-responsive hydrogels have been described as promising candidates for intratumoral drug delivery. In this review, we provide a brief overview of the TME and highlight the advantages of intratumoral administration, followed by a summary of the reported strategies to endow hydrogels with responsiveness to physical (temperature and light), chemical (pH and redox potential), or biological (enzyme) stimuli.

Adaptive Mechanisms of Tumor Therapy Resistance Driven by Tumor Microenvironment

Cancer is a disease which frequently has a poor prognosis. Although multiple therapeutic strategies have been developed for various cancers, including chemotherapy, radiotherapy, and immunotherapy, resistance to these treatments frequently impedes the clinical outcomes. Besides the active resistance driven by genetic and epigenetic alterations in tumor cells, the tumor microenvironment (TME) has also been reported to be a crucial regulator in tumorigenesis, progression, and resistance. Here, we propose that the adaptive mechanisms of tumor resistance are closely connected with the TME rather than depending on non-cell-autonomous changes in response to clinical treatment. Although the comprehensive understanding of adaptive mechanisms driven by the TME need further investigation to fully elucidate the mechanisms of tumor therapeutic resistance, many clinical treatments targeting the TME have been successful. In this review, we report on recent advances concerning the molecular events and important factors involved in the TME, particularly focusing on the contributions of the TME to adaptive resistance, and provide insights into potential therapeutic methods or translational medicine targeting the TME to overcome resistance to therapy in clinical treatment.

Hypoxia-Induced Autophagy Enhances Cisplatin Resistance in Human Bladder Cancer Cells by Targeting Hypoxia-Inducible Factor-1α

Purpose

To investigate the effect of hypoxia on chemoresistance and the underlying mechanism in bladder cancer cells.

Methods

BIU-87 bladder cancer cell line was treated with cisplatin under hypoxic and normoxic conditions and tested using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry, and Western blotting. All the data were expressed as mean ± standard error from three independent experiments and analyzed by multiple t-tests.

Results

Apoptosis of bladder cancer cells caused by cisplatin was attenuated in hypoxic conditions. Hypoxia enhanced autophagy caused by cisplatin. The autophagy inhibitor and HIF-1α inhibitor can reverse the chemoresistance in hypoxic condition. Apoptosis and autophagy of bladder cancer cells were downregulated by HIF-1α inhibitor YC-1. Hypoxia-induced autophagy enhanced chemoresistance to cisplatin via the HIF-1 signaling pathway.

Conclusion

Resistance to cisplatin in BIU-87 bladder cancer cells under hypoxic conditions can be explained by activation of autophagy, which is regulated by HIF-1α-associated signaling pathways. The hypoxia–autophagy pathway may be a target for improving the efficacy of cisplatin chemotherapy in bladder cancer.

The Effect of Hypoxia on the Expression of CXC Chemokines and CXC Chemokine Receptors-A Review of Literature

Hypoxia is an integral component of the tumor microenvironment. Either as chronic or cycling hypoxia, it exerts a similar effect on cancer processes by activating hypoxia-inducible factor-1 (HIF-1) and nuclear factor (NF-κB), with cycling hypoxia showing a stronger proinflammatory influence. One of the systems affected by hypoxia is the CXC chemokine system. This paper reviews all available information on hypoxia-induced changes in the expression of all CXC chemokines (CXCL1, CXCL2, CXCL3, CXCL4, CXCL5, CXCL6, CXCL7, CXCL8 (IL-8), CXCL9, CXCL10, CXCL11, CXCL12 (SDF-1), CXCL13, CXCL14, CXCL15, CXCL16, CXCL17) as well as CXC chemokine receptors—CXCR1, CXCR2, CXCR3, CXCR4, CXCR5, CXCR6, CXCR7 and CXCR8. First, we present basic information on the effect of these chemoattractant cytokines on cancer processes. We then discuss the effect of hypoxia-induced changes on CXC chemokine expression on the angiogenesis, lymphangiogenesis and recruitment of various cells to the tumor niche, including myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs), regulatory T cells (T_regs) and tumor-infiltrating lymphocytes (TILs). Finally, the review summarizes data on the use of drugs targeting the CXC chemokine system in cancer therapies.

Cyclic Hypoxia: An Update on Its Characteristics, Methods to Measure It and Biological Implications in Cancer

Regions of hypoxia occur in most if not all solid cancers. Although the presence of tumor hypoxia is a common occurrence, the levels of hypoxia and proportion of the tumor that are hypoxic vary significantly. Importantly, even within tumors, oxygen levels fluctuate due to changes in red blood cell flux, vascular remodeling and thermoregulation. Together, this leads to cyclic or intermittent hypoxia. Tumor hypoxia predicts for poor patient outcome, in part due to increased resistance to all standard therapies. However, it is less clear how cyclic hypoxia impacts therapy response. Here, we discuss the causes of cyclic hypoxia and, importantly, which imaging modalities are best suited to detecting cyclic vs. chronic hypoxia. In addition, we provide a comparison of the biological response to chronic and cyclic hypoxia, including how the levels of reactive oxygen species and HIF-1 are likely impacted. Together, we highlight the importance of remembering that tumor hypoxia is not a static condition and that the fluctuations in oxygen levels have significant biological consequences.

Hypoxia, partial EMT and collective migration: Emerging culprits in metastasis

Epithelial-mesenchymal transition (EMT) is a cellular biological process involved in migration of primary cancer cells to secondary sites facilitating metastasis. Besides, EMT also confers properties such as stemness, drug resistance and immune evasion which can aid a successful colonization at the distant site. EMT is not a binary process; recent evidence suggests that cells in partial EMT or hybrid E/M phenotype(s) can have enhanced stemness and drug resistance as compared to those undergoing a complete EMT. Moreover, partial EMT enables collective migration of cells as clusters of circulating tumor cells or emboli, further endorsing that cells in hybrid E/M phenotypes may be the 'fittest' for metastasis. Here, we review mechanisms and implications of hybrid E/M phenotypes, including their reported association with hypoxia. Hypoxia-driven activation of HIF-1α can drive EMT. In addition, cyclic hypoxia, as compared to acute or chronic hypoxia, shows the highest levels of active HIF-1α and can augment cancer aggressiveness to a greater extent, including enriching for a partial EMT phenotype. We also discuss how metastasis is influenced by hypoxia, partial EMT and collective cell migration, and call for a better understanding of interconnections among these mechanisms. We discuss the known regulators of hypoxia, hybrid EMT and collective cell migration and highlight the gaps which needs to be filled for connecting these three axes which will increase our understanding of dynamics of metastasis and help control it more effectively.

Emerging role of NRF2 in ROS-mediated tumor chemoresistance

Chemoresistance is a central cause for the tumor management failure. Cancer cells disrupt the redox homeostasis through reactive oxygen species (ROS) regulatory mechanisms, leading to tumor progression and chemoresistance. The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of neutralizing cellular ROS and restoring redox balance. Understanding the role of NRF2 in ROS-mediated chemoresistance can be helpful in the development of chemotherapy strategies with better efficiency. In this review, we sum up the roles of ROS in the development of chemoresistance to classical chemotherapy agents including cisplatin, 5-fluorouracil, gemcitabine, oxaliplatin, paclitaxel, and doxorubicin, and how to overcome ROS-mediated tumor chemoresistance by targeting NRF2. Finally, we propose that targeting NRF2 might be a promising strategy to resist ROS-driven chemoresistance and acquire better efficacy in cancer treatment.

Hypoxia Alters the Expression of CC Chemokines and CC Chemokine Receptors in a Tumor-A Literature Review

Hypoxia, i.e., oxygen deficiency condition, is one of the most important factors promoting the growth of tumors. Since its effect on the chemokine system is crucial in understanding the changes in the recruitment of cells to a tumor niche, in this review we have gathered all the available data about the impact of hypoxia on β chemokines. In the introduction, we present the chronic (continuous, non-interrupted) and cycling (intermittent, transient) hypoxia together with the mechanisms of activation of hypoxia inducible factors (HIF-1 and HIF-2) and NF-κB. Then we describe the effect of hypoxia on the expression of chemokines with the CC motif: CCL1, CCL2, CCL3, CCL4, CCL5, CCL7, CCL8, CCL11, CCL13, CCL15, CCL16, CCL17, CCL18, CCL19, CCL20, CCL21, CCL22, CCL24, CCL25, CCL26, CCL27, CCL28 together with CC chemokine receptors: CCR1, CCR2, CCR3, CCR4, CCR5, CCR6, CCR7, CCR8, CCR9, and CCR10. To better understand the effect of hypoxia on neoplastic processes and changes in the expression of the described proteins, we summarize the available data in a table which shows the effect of individual chemokines on angiogenesis, lymphangiogenesis, and recruitment of eosinophils, myeloid-derived suppressor cells (MDSC), regulatory T cells (T_reg), and tumor-associated macrophages (TAM) to a tumor niche.

Overcoming the Blood-Brain Barrier: Successes and Challenges in Developing Nanoparticle-Mediated Drug Delivery Systems for the Treatment of Brain Tumours

High-grade gliomas are still characterized by a poor prognosis, despite recent advances in surgical treatment. Chemotherapy is currently practiced after surgery, but its efficacy is limited by aspecific toxicity on healthy cells, tumour cell chemoresistance, poor selectivity, and especially by the blood–brain barrier (BBB). Thus, despite the large number of potential drug candidates, the choice of effective chemotherapeutics is still limited to few compounds. Malignant gliomas are characterized by high infiltration and neovascularization, and leaky BBB (the so-called blood–brain tumour barrier); surgical resection is often incomplete, leaving residual cells that are able to migrate and proliferate. Nanocarriers can favour delivery of chemotherapeutics to brain tumours owing to different strategies, including chemical stabilization of the drug in the bloodstream; passive targeting (because of the leaky vascularization at the tumour site); inhibition of drug efflux mechanisms in endothelial and cancer cells; and active targeting by exploiting carriers and receptors overexpressed at the blood–brain tumour barrier. Within this concern, a suitable nanomedicine-based therapy for gliomas should not be limited to cytotoxic agents, but also target the most important pathogenetic mechanisms, including cell differentiation pathways and angiogenesis. Moreover, the combinatorial approach of cell therapy plus nanomedicine strategies can open new therapeutical opportunities. The major part of attempted preclinical approaches on animal models involves active targeting with protein ligands, but, despite encouraging results, a few number of nanomedicines reached clinical trials, and most of them include drug-loaded nanocarriers free of targeting ligands, also because of safety and scalability concerns.

Repetitively hypoxic preconditioning attenuates ischemia/reperfusion-induced liver dysfunction through upregulation of hypoxia-induced factor-1 alpha-dependent mitochondrial Bcl-xl in rat

Repetitive hypoxic preconditioning (HP) enforces protective effects to subsequently severe hypoxic/ischemic stress. We hypothesized that HP may provide protection against ischemia/reperfusion (I/R) injury in rat livers via hypoxia-induced factor-1 alpha (HIF-1α)/reactive oxygen species (ROS)-dependent defensive mechanisms. Female Wistar rats were exposed to hypoxia (15 h/day) in a hypobaric hypoxic chamber (5500 m) for HP induction, whereas the others were kept in sea level. These rats were subjected to 45 min of hepatic ischemia by portal vein occlusion followed by 6 h of reperfusion. We evaluated HIF-1α in nuclear extracts, MnSOD, CuZnSOD, catalase, Bad/Bcl-xL/caspase 3/poly-(ADP-ribose)-polymerase (PARP), mitochondrial Bcl-xL, and cytosolic cytochrome C expression with Western blot and nitroblue tetrazolium/3-nitrotyrosine stain. Kupffer cell infiltration and terminal deoxynucleotidyl transferase-mediated nick-end labeling method apoptosis were determined by immunocytochemistry. The ROS value from liver surface and bile was detected by an ultrasensitive chemiluminescence-amplification method. Hepatic function was assessed with plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. HP increased nuclear translocation of HIF-1α and enhanced Bcl-xL, MnSOD, CuZnSOD, and catalase protein expression in a time-dependent manner. The response of HP enhanced hepatic HIF-1α, and Bcl-xL expression was abrogated by a HIF-1α inhibitor YC-1. Hepatic I/R increased ROS levels, myeloperoxidase activity, Kupffer cell infiltration, ALT and AST levels associated with the enhancement of cytosolic Bad translocation to mitochondria, release of cytochrome C to cytosol, and activation of caspase 3/PARP-mediated apoptosis. HP significantly ameliorated hepatic I/R-enhanced oxidative stress, apoptosis, and mitochondrial and hepatic dysfunction. In summary, HP enhances HIF-1α/ROS-dependent cascades to upregulate mitochondrial Bcl-xL protein expression and to confer protection against I/R injury in the livers.

Flow-Encoded Oxygen Control to Track the Time-Dependence of Molecular Changes Induced by Static or Cycling Hypoxia

Detecting the effects of low oxygen on cell function is often dependent on monitoring the expression of a number of hypoxia markers. The time dependence of the appearance and stability of these markers varies between cell lines. Assessing cellular marker dynamics is also critical to determining how quickly cells respond to transient changes in oxygen levels that occurs with cycling hypoxia. We fabricated a manifold designed to use flow-encoding to produce sequential changes in gas mixtures delivered to a permeable-bottom 96-well plate. We show how this manifold and plate design can be used to expose cells to either static or cycling hypoxic conditions for eight different time periods thereby facilitating the study of the time-response of cells to altered oxygen environments. Using this device, we monitored the time-dependence of molecular changes in human PANC-1 pancreatic carcinoma and Caco-2 colon adenocarcinoma cells exposed to increasing periods of static or cycling hypoxia. Using immunohistochemistry, both cell lines show detectable levels of the marker protein hypoxia-inducible factor-1α (HIF-1α) after 3 h of exposure to static hypoxia. Cycling hypoxia increased the expression level of HIF-1α compared to static hypoxia. Both static and cycling hypoxia also increased glucose uptake and aldehyde dehydrogenase activity. This new device offers a facile screening approach to determine the kinetics of cellular alterations under varying oxygen conditions.

Long-term monitoring in a microfluidic system to study tumour spheroid response to chronic and cycling hypoxia

We demonstrate the application of a microfluidic platform combining spatiotemporal oxygen control and long-term microscopy monitoring to observe tumour spheroid response to hypoxia. The platform is capable of recreating physiologically-relevant low and cycling oxygen levels not attainable in traditional cell culture environments, while image-based monitoring visualizes cell response to these physiologically-relevant conditions. Monitoring spheroid cultures during hypoxic exposure allows us to observe, for the first time, that spheroids swell and shrink in response to time-varying oxygen profiles switching between 0% and 10% O₂; this swelling-shrinkage behaviour appears to be driven by swelling of individual cells within the spheroids. We also apply the system to monitoring tumour models during anticancer treatment under varying oxygen conditions. We observe higher uptake of the anticancer agent doxorubicin under a cycling hypoxia profile than under either chronic hypoxia or in vitro normoxia, and the two-photon microscopy monitoring facilitated by our system also allows us to observe heterogeneity in doxorubicin uptake within spheroids at the single-cell level. Combining optical sectioning microscopy with precise spatiotemporal oxygen control and 3D culture opens the door for a wide range of future studies on microenvironmental mechanisms driving cancer progression and resistance to anticancer therapy. These types of studies could facilitate future improvements in cancer diagnostics and treatment.

Acute vs. Chronic vs. Cyclic Hypoxia: Their Differential Dynamics, Molecular Mechanisms, and Effects on Tumor Progression

Hypoxia has been shown to increase the aggressiveness and severity of tumor progression. Along with chronic and acute hypoxic regions, solid tumors contain regions of cycling hypoxia (also called intermittent hypoxia or IH). Cyclic hypoxia is mimicked in vitro and in vivo by periodic exposure to cycles of hypoxia and reoxygenation (H-R cycles). Compared to chronic hypoxia, cyclic hypoxia has been shown to augment various hallmarks of cancer to a greater extent: angiogenesis, immune evasion, metastasis, survival etc. Cycling hypoxia has also been shown to be the major contributing factor in increasing the risk of cancer in obstructive sleep apnea (OSA) patients. Here, we first compare and contrast the effects of acute, chronic and intermittent hypoxia in terms of molecular pathways activated and the cellular processes affected. We highlight the underlying complexity of these differential effects and emphasize the need to investigate various combinations of factors impacting cellular adaptation to hypoxia: total duration of hypoxia, concentration of oxygen (O2), and the presence of and frequency of H-R cycles. Finally, we summarize the effects of cycling hypoxia on various hallmarks of cancer highlighting their dependence on the abovementioned factors. We conclude with a call for an integrative and rigorous analysis of the effects of varying extents and durations of hypoxia on cells, including tools such as mechanism-based mathematical modelling and microfluidic setups.

Combination chemotherapy of valproic acid (VPA) and gemcitabine regulates STAT3/Bmi1 pathway to differentially potentiate the motility of pancreatic cancer cells

BACKGROUND

Gemcitabine is the standard first-line chemotherapy regimen for pancreatic cancer. However, its therapeutic value is substantially limited in pancreatic cancer patients due to occurrence of resistance towards gemcitabine. A strategy of combined chemo-regimens is widely employed in clinical settings in attempt to reduce the chance of developing therapeutic resistance. Valproic acid (VPA) has been reported as a promising anticancer drug in various clinical trials and studies. However, the clinical value and potential dose-effect of VPA in combination with gemcitabine for pancreatic cancer treatment are under investigated.

RESULTS

In this study, we determined the synergistic effect of VPA and gemcitabine and found that high-dose VPA significantly and dose-dependently enhanced the sensitivity of pancreatic cancer cells to gemcitabine. Intriguingly, low-dose VPA potentiated the migration and invasion of pancreatic cancer cells that already showed gemcitabine-induced motility. Moreover, low-dose VPA increased the reactive oxygen species (ROS) production, which activated AKT to further stimulate the activation of STAT3, Bmi1 expression and eventually promoted the migration and invasion of pancreatic cancer cells induced by gemcitabine. Whereas high-dose VPA stimulated excessive ROS accumulation that promoted p38 activation, which suppressed the activation of STAT3 and Bmi1.

CONCLUSION

Pancreatic cancer cells respond differentially towards low- or high-dose of VPA in combination with gemcitabine, and a low VPA further potentiate pancreatic cancer cell to migrate and invade. Our results suggest that STAT3/Bmi1 signaling cascade, which is regulated by ROS-dependent, AKT- or p38-modulated pathways, primarily mediated the sensitivity and motility of pancreatic cancer cells towards combined gemcitabine and VPA regimen. These findings suggest a highly clinically relevant new mechanism of developing resistance against combined chemo-regimens, warranting further mechanistic and translational exploration for VPA in combination with gemcitabine and other chemotherapies.

Distinct Tumor Microenvironment at Tumor Edge as a Result of Astrocyte Activation Is Associated With Therapeutic Resistance for Brain Tumor

Tumor vasculatures and hypoxia are critical tumor micro-environmental factors associated with tumor response to the therapy and heterogeneous in both time- and location-dependent manner. Using a murine orthotopic anaplastic astrocytoma model, ALTS1C1, this study showed that brain tumor edge had a very unique microenvironment, having higher microvascular density (MVD) and better vessel function than the tumor core, but on the other hand was also positive for hypoxia markers, such as pimonidazole (PIMO), hypoxia inducible factor-1α (HIF-1α), and carbonic anhydrase IV (CAIX). The hypoxia at tumor edge was transient, named as peripheral hypoxia, and caused by different mechanisms from the chronic hypoxia in tumor core. The correlation of CAIX staining with astrocyte activation marker, glial fibrillary acid protein (GFAP), at the tumor edge indicated the involvement of astrocyte activation on the development of peripheral hypoxia. Peripheral hypoxia was a specific trait of orthotopic brain tumors at tumor edge, regardless of tumor origin. The hypoxic cells were resistant to the therapy, regardless of their location. Surviving cells, particularly those at the hypoxic region of tumor edge, are likely the cause of tumor recurrence after the therapy. New therapeutic platform that targets cells in tumor edge is likely to achieve better treatment outcomes.

Tumor microenvironment-driven non-cell-autonomous resistance to antineoplastic treatment

Drug resistance is of great concern in cancer treatment because most effective drugs are limited by the development of resistance following some periods of therapeutic administration. The tumor microenvironment (TME), which includes various types of cells and extracellular components, mediates tumor progression and affects treatment efficacy. TME-mediated drug resistance is associated with tumor cells and their pericellular matrix. Noninherent-adaptive drug resistance refers to a non-cell-autonomous mechanism in which the resistance lies in the treatment process rather than genetic or epigenetic changes, and this mechanism is closely related to the TME. A new concept is therefore proposed in which tumor cell resistance to targeted therapy may be due to non-cell-autonomous mechanisms. However, knowledge of non-cell-autonomous mechanisms of resistance to different treatments is not comprehensive. In this review, we outlined TME factors and molecular events involved in the regulation of non-cell-autonomous resistance of cancer, summarized how the TME contributes to non-cell-autonomous drug resistance in different types of antineoplastic treatment, and discussed the novel strategies to investigate and overcome the non-cell-autonomous mechanism of cancer non-cell-autonomous resistance.

Targeting Oncogenic Nuclear Factor Kappa B Signaling with Redox-Active Agents for Cancer Treatment

SIGNIFICANCE

Nuclear factor kappa B (NF-κB) signaling is essential under physiologically relevant conditions. However, aberrant activation of this pathway plays a pertinent role in tumorigenesis and contributes to resistance. Recent Advances: The importance of the NF-κB pathway means that its targeting must be specific to avoid side effects. For many currently used therapeutics and those under development, the ability to generate reactive oxygen species (ROS) is a promising strategy.

CRITICAL ISSUES

As cancer cells exhibit greater ROS levels than their normal counterparts, they are more sensitive to additional ROS, which may be a potential therapeutic niche. It is known that ROS are involved in (i) the activation of NF-κB signaling, when in sublethal amounts; and (ii) high levels induce cytotoxicity resulting in apoptosis. Indeed, ROS-induced cytotoxicity is valuable for its capabilities in killing cancer cells, but establishing the potency of ROS for effective inhibition of NF-κB signaling is necessary. Indeed, some cancer treatments, currently used, activate NF-κB and may stimulate oncogenesis and confer resistance.

FUTURE DIRECTIONS

Thus, combinatorial approaches using ROS-generating agents alongside conventional therapeutics may prove an effective tactic to reduce NF-κB activity to kill cancer cells. One strategy is the use of thiosemicarbazones, which form redox-active metal complexes that generate high ROS levels to deliver potent antitumor activity. These agents also upregulate the metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1), which functions as an NF-κB signaling inhibitor. It is proposed that targeting NF-κB signaling may proffer a new therapeutic niche to improve the efficacy of anticancer regimens.

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.

A novel 3D in vitro model of glioblastoma reveals resistance to temozolomide which was potentiated by hypoxia

Purpose

Glioblastoma (GBM) is the most common invasive malignant brain tumour in adults. It is traditionally investigated in vitro by culturing cells as a monolayer (2D culture) or as neurospheres (clusters enriched in cancer stem cells) but neither system accurately reflects the complexity of the three-dimensional (3D) chemoresistant microenvironment of GBM.

Materials and methods

Using three GBM cell-lines (U87, U251, and SNB19), the effect of culturing cells in a Cultrex-based basement membrane extract (BME) [3D Tumour Growth Assay (TGA)] on morphology, gene expression, metabolism, and temozolomide chemoresistance was investigated.

Results

Cells were easily harvested from the 3D model and cultured as a monolayer (2D) and neurospheres. Indeed, the SNB19 cells formed neurospheres only after they were first cultured in the 3D model. The expression of CD133 and OCT4 was upregulated in the neurosphere and 3D assays respectively. Compared with cells cultured in the 2D model, cells were more resistant to temozolomide in the 3D model and this resistance was potentiated by hypoxia.

Conclusion

Taken together, these results suggest that micro-environmental factors influence GBM sensitivity to temozolomide. Knowledge of the mechanisms involved in temozolomide resistance in this 3D model might lead to the identification of new strategies that enable the more effective use of the current standard of care agents.

Electronic supplementary material

The online version of this article (10.1007/s11060-019-03107-0) contains supplementary material, which is available to authorized users.

Nanotechnology for Treatment of Glioblastoma Multiforme

Glioblastoma multiforme (GBM), a grade IV astrocytoma as defined by the World Health Organization (WHO) criteria, is the most common primary central nervous system tumor in adults. After treatment with the current standard of care consisting of surgical resection, concurrent temozolomide (TMZ), and radiation, the median survival is only 15 months. The limited and less-effective treatment options for these highly aggressive GBMs call for the development of new techniques and the improvement of existing technologies. Nanotechnology has shown promise in treating this disease, and some nanomaterials have demonstrated the ability to cross the blood–brain barrier (BBB) and remain in GBM tissues. Although the retention of nanoparticles (NPs) in GBM tissue is necessary to elicit an antitumor response, the delivery of the NP needs to be enhanced. Current research in nanotechnology is directed at increasing the active targeting of GBM tissue not only for the aid of chemotherapeutic drug delivery but also for imaging studies. This review is aimed at describing advancements in increasing nanotechnology specificity to GBM tissue.

Exosome-related tumor microenvironment

The tumor microenvironment (tumor cells are located in the internal and external environment) is vital for the occurrence, growth and metastasis of tumors. An increasing number of studies have shown that exosomes are closely related to the tumor microenvironment. The mechanisms involved, however, are unclear. The focus of this review is on the exosome-related tumor microenvironment and other relevant factors, such as hypoxia, inflammation and angiogenesis. Many studies have suggested that exosomes are important mediators of metastasis, angiogenesis, and immune modulation in the tumor microenvironment. Additionally, exosomes can be isolated from bodily fluids of cancer patients, including urine, blood, saliva, milk, tumor effusion, cerebrospinal fluid, amniotic fluid and so on. Consequently, exosomes are potential biomarkers for clinical predictions and are also good drug carriers because they can cross the biofilm without triggering an immune response. Collectively, these findings illustrate that exosomes are crucial for developing potential targets for a new generation of pharmaceutical therapies that would improve the tumor microenvironment.

Hypoxia-induced autophagy promotes gemcitabine resistance in human bladder cancer cells through hypoxia-inducible factor 1α activation

Overcoming the chemoresistance of bladder cancer is a pivotal obstacle in clinical treatments. Hypoxia widely exists in solid tumors and has been demonstrated to contribute to chemoresistance through hypoxia-inducible factor 1α (HIF‑1α)-mediated autophagy in several types of cancer. However, it is unclear whether HIF‑1α-mediated autophagy and chemoresistance occur in bladder cancer. The present study demonstrated that HIF‑1α was overexpressed in 20 bladder cancer tissues compared with matched paracarcinoma tissues. Gemcitabine-induced apoptosis during hypoxia was significantly reduced compared with that observed under normoxic conditions. In addition, hypoxia activated autophagy and enhanced gemcitabine-induced autophagy. Combined treatment using gemcitabine and an autophagy inhibitor (3-methyladenine) under hypoxia significantly increased gemcitabine cytotoxicity. Furthermore, it was demonstrated that hypoxia-activated autophagy depended on the HIF‑1α/BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3)/Beclin1 signaling pathway. Suppressing HIF‑1α inhibited autophagy, BNIP3 and Beclin1, as well as enhanced gemcitabine-induced apoptosis in bladder cancer cells under hypoxic conditions. Consequently, the results of the present study demonstrated that hypoxia-induced cytoprotective autophagy counteracted gemcitabine-induced apoptosis through increasing HIF‑1α expression. Therefore, targeting HIF‑1α-associated pathways or autophagy in bladder cancer may be a successful strategy to enhance the sensitivity of bladder cancer chemotherapy.

Influence of c-Src on hypoxic resistance to paclitaxel in human ovarian cancer cells and reversal of FV-429

SRC family kinase was documented to have vital roles in adjusting cancer cell malignant behaviors. To date, the role of c-Src, a member of SRC family kinase, in resistance to paclitaxel in human ovarian cancer cells under hypoxia has not been investigated. In the present study, we discovered that hypoxic environment suppressed paclitaxel-induced G2/M phase arrest and blockade of c-Src improved ovarian cancer cells’ sensitivity to paclitaxel. FV-429, a derivative of natural flavonoid wogonin, could suppress gene expression and activation of c-Src, followed by deteriorated Stat3 nuclear translocation and its binding to HIF-1α, resulting in paclitaxel resistance reversal through G2/M arrest potentiation. Our study demonstrated that c-Src contributed to hypoxic microenvironment-rendered paclitaxel resistance in human epithelial ovarian cancer cells by G2/M phase arrest deterioration, and through c-Src suppression, FV-429 was capable of reversing the resistance by blocking c-Src/Stat3/HIF-1α pathway.

Targeting tumor microenvironment to curb chemoresistance via novel drug delivery strategies

INTRODUCTION

Tumor is a heterogeneous mass of malignant cells co-existing with non-malignant cells. This co-existence evolves from the initial developmental stages of the tumor and is one of the hallmarks of cancer providing a protumorigenic niche known as tumor microenvironment (TME). Proliferation, invasiveness, metastatic potential and maintenance of stemness through cross-talk between tumors and its stroma forms the basis of TME.

AREAS COVERED

The article highlights the developmental phases of a tumor from dysplasia to the formation of clinically detectable tumors. The authors discuss the mechanistic stages involved in the formation of TME and its contribution in tumor outgrowth and chemoresistance. The authors have reviewed various approaches for targeting TME and its hallmarks along with their advantages and pitfalls. The authors also highlight cancer stem cells (CSCs) that are resistant to chemotherapeutics and thus a primary reason for tumor recurrence thereby, posing a challenge for the oncologists.

EXPERT OPINION

Recent understanding of the cellular and molecular mechanisms involved in acquired chemoresistance has enabled scientists to target the tumor niche and TME and modulate and/or disrupt this communication leading to the transformation from a tumor-supportive niche environment to a tumor-non-supporting environment and give synergistic results towards an effective management of cancer.

Temporal stability of MGMT promoter methylation in glioblastoma patients undergoing STUPP protocol

Epigenetic silencing of O-6-methylguanine-DNA methyltransferase (MGMT) promoter via methylation in a glioblastoma (GBM), has been correlated with a more favourable response to alkylating chemotherapeutic agents such as temozolomide. The use of global methylation surrogates such as Long Interspersed Nucleotide Element 1 (LINE1) may also be valuable in order to fully understand these highly heterogeneous tumours. In this study, we analysed both original and recurrent GBMs in 22 patients (i.e. 44 tumours), for both MGMT and LINE1 methylation status. In the 22 patients: 14 (63.6%) displayed MGMT methylation stability in the recurrent GBM versus 8 (36.4%), with instability of methylation status. No significant differences in overall and progression free survival was evident between these two groups. LINE1 methylation status remained stable for 12 (54.5%) of recurrent GBM patients versus 9 (41%) of the patients with instability in LINE1 methylation status (p = 0.02), resulting in an increase in overall survival of the stable LINE1 group (p = 0.04). The results obtained demonstrated major epigenetic instability of GBMs treated with temozolomide as part of the STUPP protocol. GBMs appear to undergo selective evolution post-treatment, and have the ability to recur with a newly reprogrammed epigenetic status. Selective targeting of the altered epigenomes in recurrent GBMs may facilitate the future development of both prognostic biomarkers and enhanced therapeutic strategies.

1,2-Dichloroethane Induces Reproductive Toxicity Mediated by the CREM/CREB Signaling Pathway in Male NIH Swiss Mice

1,2-Dichloroethane (1,2-DCE) is a widely used chlorinated organic toxicant but little is known about the reproductive disorders induced by its excessive exposure. To reveal 1,2-DCE-induced male reproductive toxicity and to elucidate the underlying mechanisms, we exposed male National Institutes of Health Swiss mice to 1,2-DCE by inhalation at 0, 100, 350, and 700 mg/m3 for 6 h/day, for 1 and 4 weeks. Our findings showed a significant decrease in body weight with increased testis/body weight ratio, reduced sperm concentration and induced malformation of spermatozoa, and vacuolar degeneration of germ cells in the seminiferous tubules of testes in mice exposed to 1,2-DCE. Cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB) and cAMP-response element modulator (CREM) were significantly inhibited by 1,2-DCE. This is consistent with the declines in the transducer of regulated CREB activity 1 and activator of CREM in testis, which results in the decrease in lactate dehydrogenase C and testis-specific kinase 1 in the testes. Moreover, the activation of p53 and Bax with the inhibition of Bcl-2 might be the reason for the upregulation of caspase-3 in the apoptosis, as detected by TdT-mediated dUTP nick-end labeling assay in the testes induced by 1,2-DCE. Finally, elevated testosterone levels were found along with increased levels of gonadotropin-releasing hormone, cAMP, luteinizing hormone (LH), and LH receptors in the testes. These findings suggest that 1,2-DCE inhibits CREM/CREB signaling cascade and subsequently induces apoptosis associated with p53 activation and mitochondrial dysfunction. This also results in induced malformation of spermatozoa, reduced sperm concentration, and pathological impairment of the testes.

Intermittent hypoxia and cancer: Undesirable bed partners?

The deleterious effects of intermittent hypoxia (IH) on cancer biology have been primarily evaluated in the context of the aberrant circulation observed in solid tumors which results in recurrent intra-tumoral episodic hypoxia. From those studies, IH has been linked to an accelerated tumor progression, metastasis and resistance to therapies. More recently, the role of IH in cancer has also been studied in the context of obstructive sleep apnea (OSA), since IH is a hallmark characteristic of this condition. Such recent studies are undoubtedly adding more information regarding the role of IH on tumor malignancy. In terms of the IH patterns associated with OSA, this altered oxygenation paradigm has been recently proposed as a determinant factor in fostering cancer incidence and progression from both in vitro and in vivo experimental models. Here, we summarize all the available evidence to date linking IH effects on several types of cancer.

Coiled-coil domain containing 109B is a HIF1α-regulated gene critical for progression of human gliomas

Background

The coiled-coil domain is a structural motif found in proteins that participate in a variety of biological processes. Aberrant expression of such proteins has been shown to be associated with the malignant behavior of human cancers. In this study, we investigated the role of a specific family member, coiled-coil domain containing 109B (CCDC109B), in human gliomas.

Methods and results

We confirmed that CCDC109B was highly expressed in high grade gliomas (HGG; WHO III–IV) using immunofluorescence, western blot analysis, immunohistochemistry (IHC) and open databases. Through Cox regression analysis of The Cancer Genome Atlas (TCGA) database, we found that the expression levels of CCDC109B were inversely correlated with patient overall survival and it could serve as a prognostic marker. Then, a serious of cell functional assays were performed in human glioma cell lines, U87MG and U251, which indicated that silencing of CCDC109B attenuated glioma proliferation and migration/invasion both in vitro and in vivo. Notably, IHC staining in primary glioma samples interestingly revealed localization of elevated CCDC109B expression in necrotic areas which are typically hypoxic. Moreover, small interfering RNA (siRNA) and specific inhibiters of HIF1α led to decreased expression of CCDC109B in vitro and in vivo. Transwell assay further showed that CCDC109B is a critical factor in mediating HIF1α-induced glioma cell migration and invasion.

Conclusion

Our study elucidated a role for CCDC109B as an oncogene and a prognostic marker in human gliomas. CCDC109B may provide a novel therapeutic target for the treatment of human glioma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1266-9) contains supplementary material, which is available to authorized users.