Expression of Drug Resistance Proteins Pgp, MRP1, MRP3, MRP5 AND GST-π in Human Glioma

Long-Acting Therapeutic Delivery Systems for the Treatment of Gliomas

Despite the emergence of cutting-edge therapeutic strategies and tremendous progress in research, a complete cure of glioma remains elusive. The heterogenous nature of tumor, immunosuppressive state and presence of blood brain barrier are few of the major obstacles in this regard. Long-acting depot formulations such as injectables and implantables are gaining attention for drug delivery to brain owing to their ease in administration and ability to elute drug locally for extended durations in a controlled manner with minimal toxicity. Hybrid matrices fabricated by incorporating nanoparticulates within such systems help to enhance pharmaceutical advantages. Utilization of long-acting depots as monotherapy or in conjunction with existing strategies rendered significant survival benefits in many preclinical studies and some clinical trials. The discovery of novel targets, immunotherapeutic strategies and alternative drug administration routes are now coupled with several long-acting systems with an ultimate aim to enhance patient survival and prevent glioma recurrences.

A2B Adenosine Receptor Enhances Chemoresistance of Glioblastoma Stem-Like Cells under Hypoxia: New Insights into MRP3 Transporter Function

Glioblastoma is the most common and aggressive primary brain tumor, characterized by its high chemoresistance and the presence of a cell subpopulation that persists under hypoxic niches, called glioblastoma stem-like cells (GSCs). The chemoresistance of GSCs is mediated in part by adenosine signaling and ABC transporters, which extrude drugs outside the cell, such as the multidrug resistance-associated proteins (MRPs) subfamily. Adenosine promotes MRP1-dependent chemoresistance under normoxia. However, adenosine/MRPs-dependent chemoresistance under hypoxia has not been studied until now. Transcript and protein levels were determined by RT-qPCR and Western blot, respectively. MRP extrusion capacity was determined by intracellular 5 (6)-Carboxyfluorescein diacetate (CFDA) accumulation. Cell viability was measured by MTS assays. Cell cycle and apoptosis were determined by flow cytometry. Here, we show for the first time that MRP3 expression is induced under hypoxia through the A2B adenosine receptor. Hypoxia enhances MRP-dependent extrusion capacity and the chemoresistance of GSCs. Meanwhile, MRP3 knockdown decreases GSC viability under hypoxia. Downregulation of the A_2B receptor decreases MRP3 expression and chemosensibilizes GSCs treated with teniposide under hypoxia. These data suggest that hypoxia-dependent activation of A_2B adenosine receptor promotes survival of GSCs through MRP3 induction.

Inhibiting Metastasis and Improving Chemosensitivity via Chitosan-Coated Selenium Nanoparticles for Brain Cancer Therapy

Selenium nanoparticles (SeNPs) were synthesized to overcome the limitations of selenium, such as its narrow safe range and low water solubility. SeNPs reduce the toxicity and improve the bioavailability of selenium. Chitosan-coated SeNPs (Cs-SeNPs) were developed to further stabilize SeNPs and to test their effects against glioma cells. The effects of Cs-SeNPs on cell growth were evaluated in monolayer and 3D-tumor spheroid culture. Cell migration and cell invasion were determined using a trans-well assay. The effect of Cs-SeNPs on chemotherapeutic drug 5-fluorouracil (5-FU) sensitivity of glioma cells was determined in tumor spheroids. An in vitro blood–brain barrier (BBB) model was established to test the permeability of Cs-SeNPs. SeNPs and Cs-SeNPs can reduce the cell viability of glioma cells in a dose-dependent manner. Compared with SeNPs, Cs-SeNPs more strongly inhibited 3D-tumor spheroid growth. Cs-SeNPs exhibited stronger effects in inhibiting cell migration and cell invasion than SeNPs. Improved 5-FU sensitivity was observed in Cs-SeNP-treated cells. Cellular uptake in glioma cells indicated a higher uptake rate of coumarin-6-labeled Cs-SeNPs than SeNPs. The capability of coumarin-6 associated Cs-SeNPs to pass through the BBB was confirmed. Taken together, Cs-SeNPs provide exceptional performance and are a potential alternative therapeutic strategy for future glioma treatment.

Glioblastoma, from disease understanding towards optimal cell-based in vitro models

Background

Glioblastoma (GBM) patients are notoriously difficult to treat and ultimately all succumb to disease. This unfortunate scenario motivates research into better characterizing and understanding this disease, and into developing novel research tools by which potential novel therapeutics and treatment options initially can be evaluated pre-clinically. Here, we provide a concise overview of glioblastoma epidemiology, disease classification, the challenges faced in the treatment of glioblastoma and current novel treatment strategies. From this, we lead into a description and assessment of advanced cell-based models that aim to narrow the gap between pre-clinical and clinical studies. Such invitro models are required to deliver reliable and meaningful data for the development and pre-validation of novel therapeutics and treatments.

Conclusions

The toolbox for GBM cell-based models has expanded substantially, with the possibility of 3D printing tumour tissues and thereby replicating invivo tissue architectures now looming on the horizon. A comparison of experimental cell-based model systems and techniques highlights advantages and drawbacks of the various tools available, based on which cell-based models and experimental approaches best suited to address a diversity of research questions in the glioblastoma research field can be selected.

Identification of vascular cues contributing to cancer cell stemness and function

Glioblastoma stem cells (GSCs) reside close to blood vessels (BVs) but vascular cues contributing to GSC stemness and the nature of GSC-BVs cross talk are not fully understood. Here, we dissected vascular cues influencing GSC gene expression and function to perfusion-based vascular cues, as well as to those requiring direct GSC-endothelial cell (EC) contacts. In light of our previous finding that perivascular tumor cells are metabolically different from tumor cells residing further downstream, cancer cells residing within a narrow, < 60 µm wide perivascular niche were isolated and confirmed to possess a superior tumor-initiation potential compared with those residing further downstream. To circumvent reliance on marker expression, perivascular GSCs were isolated from the respective locales based on their relative state of quiescence. Combined use of these procedures uncovered a large number of previously unrecognized differentially expressed GSC genes. We show that the unique metabolic milieu of the perivascular niche dominated by the highly restricted zone of mTOR activity is conducive for acquisition of GSC properties, primarily in the regulation of genes implicated in cell cycle control. A complementary role of vascular cues including those requiring direct glioma/EC contacts was revealed using glioma/EC co-cultures. Outstanding in the group of glioma cells impacted by nearby ECs were multiple genes responsible for maintaining GSCs in an undifferentiated state, a large fraction of which also relied on Notch-mediated signaling. Glioma-EC communication was found to be bidirectional, evidenced by extensive Notch-mediated EC reprogramming by contacting tumor cells, primarily metabolic EC reprogramming.

LINC00883 Promotes Drug Resistance of Glioma Through a microRNA-136/NEK1-Dependent Mechanism

Objective

Accumulating evidence has highlighted the roles of long noncoding RNAs (lncRNAs) as competing endogenous RNAs (ceRNAs) of microRNAs (miRNAs) through their binding sites in the progression of glioma. Hereby, we aim to explore the role of LINC00883 as a regulator of miR-136 and its target, NIMA-related kinase 1 (NEK1), thus, its involvement in the drug resistance of glioma cells.

Methods and Results

Mechanistic investigations by dual-luciferase reporter, RNA pull-down, and RNA-binding protein immunoprecipitation (RIP) assays indicated that LINC00883 bound to miR-136, thereby blocking miR-136-induced downregulation of NEK1. Through gain-of-function experiments in U251 cells that presented a high drug resistance, we found that ectopic expression of LINC00883 resulted in increased MRP (encoding multidrug resistance-associated protein), limited cell apoptosis, and increased proliferation. Expectedly, depleting LINC00883 yielded tumor-suppressive and anti-chemoresistance effects on U251 cells by increasing miR-136 and inhibiting NEK1. Next, drug-resistant glioma cell line SOWZ1, drug-sensitive glioma cell line SOWZ2, and drug-resistant glioma cell line SOWZ2-BCNU (SOWZ2 cultured in BCNU) were applied to validate the roles of LINC00883 in the regulation of multidrug resistance. LINC00883 knockdown suppressed the viability of SWOZ1, SWOZ2, and SWOZ2-BCNU cells.

Conclusion

In conclusion, LINC00883 knockdown reduces drug resistance in glioma. Hence, our study provides a future strategy to prevent drug resistance-induced therapeutic failure in glioma.

The role of dietary flavonoids for modulation of ATP binding cassette transporter mediated multidrug resistance

Flavonoids are widely existing compounds with enormous pharmacological effects from food and medicine. However, the low bioavailability in intestinal absorption and metabolism limits their clinical application. Intestinal efflux ABC (ATP binding cassette) transporters, including P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs), act as "pumping doors" to regulate the efflux of flavonoids from intestinal epithelial cells into the intestinal cavity or the systemic circulation. The present review describes the critical effect of ABC transporters involved in the efflux of flavonoids which depend on its efflux direction. And the role of flavonoids for modulation of intestinal ABC transporters was emphasized and several examples were given. We summarized that the resistance effect of flavonoid-mediated multidrug on ABC transporters may influence the bioavailability of drugs, bioactive ingredients and/or toxic compounds upon dietary uptake. Meanwhile, flavonoids functionalized as reversing agents of the ABC transporter may be an important mechanism for unexpected food-drug, food-toxin or food-food interactions. The overview also indicates that elucidation of the action and mechanism of the intestinal metabolic enzymes-efflux transporters coupling will lay a foundation for improving the bioavailability of flavonoids <i>in vivo</i> and increasing their clinical efficacy.

Suppression of Proliferation of Human Glioblastoma Cells by Combined Phosphodiesterase and Multidrug Resistance-Associated Protein 1 Inhibition

The paucity of currently available therapies for glioblastoma multiforme requires novel approaches to the treatment of this brain tumour. Disrupting cyclic nucleotide-signalling through phosphodiesterase (PDE) inhibition may be a promising way of suppressing glioblastoma growth. Here, we examined the effects of 28 PDE inhibitors, covering all the major PDE classes, on the proliferation of the human U87MG, A172 and T98G glioblastoma cells. The PDE10A inhibitors PF-2545920, PQ10 and papaverine, the PDE3/4 inhibitor trequinsin and the putative PDE5 inhibitor MY-5445 potently decreased glioblastoma cell proliferation. The synergistic suppression of glioblastoma cell proliferation was achieved by combining PF-2545920 and MY-5445. Furthermore, a co-incubation with drugs that block the activity of the multidrug resistance-associated protein 1 (MRP1) augmented these effects. In particular, a combination comprising the MRP1 inhibitor reversan, PF-2545920 and MY-5445, all at low micromolar concentrations, afforded nearly complete inhibition of glioblastoma cell growth. Thus, the potent suppression of glioblastoma cell viability may be achieved by combining MRP1 inhibitors with PDE inhibitors at a lower toxicity than that of the standard chemotherapeutic agents, thereby providing a new combination therapy for this challenging malignancy.

In Vivo Brain GSH: MRS Methods and Clinical Applications

Glutathione (GSH) is an important antioxidant implicated in several physiological functions, including the oxidation−reduction reaction balance and brain antioxidant defense against endogenous and exogenous toxic agents. Altered brain GSH levels may reflect inflammatory processes associated with several neurologic disorders. An accurate and reliable estimation of cerebral GSH concentrations could give a clear and thorough understanding of its metabolism within the brain, thus providing a valuable benchmark for clinical applications. In this context, we aimed to provide an overview of the different magnetic resonance spectroscopy (MRS) technologies introduced for in vivo human brain GSH quantification both in healthy control (HC) volunteers and in subjects affected by different neurological disorders (e.g., brain tumors, and psychiatric and degenerative disorders). Additionally, we aimed to provide an exhaustive list of normal GSH concentrations within different brain areas. The definition of standard reference values for different brain areas could lead to a better interpretation of the altered GSH levels recorded in subjects with neurological disorders, with insights into the possible role of GSH as a biomarker and therapeutic target.

WNT Signaling as a Therapeutic Target for Glioblastoma

The WNT (Wingless/Integrated) signaling pathway is implicated in various stages of glioblastoma, which is an aggressive brain tumor for which therapeutic options are limited. WNT has been recognized as a hallmark of therapeutic challenge due to its context-dependent role and critical function in healthy tissue homeostasis. In this review, we deeply scrutinize the WNT signaling pathway and its involvement in the genesis of glioblastoma as well as its acquired therapy resistance. We also provide an analysis of the WNT pathway in terms of its therapeutic importance in addition to an overview of the current targeted therapies under clinical investigation.

Development and Validation of a Long-Term 3D Glioblastoma Cell Culture in Alginate Microfibers as a Novel Bio-Mimicking Model System for Preclinical Drug Testing

Background: Various three-dimensional (3D) glioblastoma cell culture models have a limited duration of viability. Our aim was to develop a long-term 3D glioblastoma model, which is necessary for reliable drug response studies. Methods: Human U87 glioblastoma cells were cultured in alginate microfibers for 28 days. Cell growth, viability, morphology, and aggregation in 3D culture were monitored by fluorescent and confocal microscopy upon calcein-AM/propidium iodide (CAM/PI) staining every seven days. The glioblastoma 3D model was validated using temozolomide (TMZ) treatments 3 days in a row with a recovery period. Cell viability by MTT and resistance-related gene expression (MGMT and ABCB1) by qPCR were assessed after 28 days. The same TMZ treatment schedule was applied in 2D U87 cell culture for comparison purposes. Results: Within a long-term 3D model system in alginate fibers, U87 cells remained viable for up to 28 days. On day 7, cells formed visible aggregates oriented to the microfiber periphery. TMZ treatment reduced cell growth but increased drug resistance-related gene expression. The latter effect was more pronounced in 3D compared to 2D cell culture. Conclusion: Herein, we described a long-term glioblastoma 3D model system that could be particularly helpful for drug testing and treatment optimization.

Babao Dan Reverses Multiple-Drug Resistance in Gastric Cancer Cells via Triggering Apoptosis and Autophagy and Inhibiting PI3K/AKT/mTOR Signaling

Multidrug resistance (MDR) is a critical reason for cancer chemotherapy failure. Babaodan (BBD) is a famous traditional Chinese patent medicine reported to have antigastric cancer activity. However, the roles and molecular mechanisms of the reversal of MDR of gastric cancer by BBD have not been well described until now. Therefore, the purpose of this study was to elucidate further the role of BBD in reversing the MDR of gastric cancer cells and its specific regulatory mechanism via in vitro experiments. To verify our results, MTT, Doxorubicin (DOX) staining, Rhodamin123 (Rho123) staining, DAPI staining, Annexin V-FITC, propidium iodide (PI), Cyto-ID, and western blot assays were performed. To determine whether BBD triggers apoptosis and autophagy through the PI3K/AKT/mTOR signaling, we also applied 3-methyladenine (3-MA), chloroquine (CQ), and 740Y-P (an activator of PI3K). The results showed that BBD reversed the MDR and induced apoptosis and autophagy of SGC7901/DDP cells. Pathway analyses suggested BBD inhibits PI3K/AKT/mTOR pathway activity and subsequent apoptosis-autophagy induction. Inhibition of autophagy with 3-MA and chloroquine (CQ) was performed to confirm that BBD promoted autophagy. PI3K agonist, 740Y-P, further verified BBD inhibition of PI3K/AKT/mTOR pathway activation. In conclusion, BBD may reverse the MDR of gastric cancer cells, induce apoptosis, and promote autophagy via inactivation of the PI3K/AKT/mTOR signaling pathway.

In vitro biomimetic models for glioblastoma-a promising tool for drug response studies

The poor response of glioblastoma to current treatment protocols is a consequence of its intrinsic drug resistance. Resistance to chemotherapy is primarily associated with considerable cellular heterogeneity, and plasticity of glioblastoma cells, alterations in gene expression, presence of specific tumor microenvironment conditions and blood-brain barrier. In an attempt to successfully overcome chemoresistance and better understand the biological behavior of glioblastoma, numerous tri-dimensional (3D) biomimetic models were developed in the past decade. These novel advanced models are able to better recapitulate the spatial organization of glioblastoma in a real time, therefore providing more realistic and reliable evidence to the response of glioblastoma to therapy. Moreover, these models enable the fine-tuning of different tumor microenvironment conditions and facilitate studies on the effects of the tumor microenvironment on glioblastoma chemoresistance. This review outlines current knowledge on the essence of glioblastoma chemoresistance and describes the progress achieved by 3D biomimetic models. Moreover, comprehensive literature assessment regarding the influence of 3D culturing and microenvironment mimicking on glioblastoma gene expression and biological behavior is also provided. The contribution of the blood-brain barrier as well as the blood-tumor barrier to glioblastoma chemoresistance is also reviewed from the perspective of 3D biomimetic models. Finally, the role of mathematical models in predicting 3D glioblastoma behavior and drug response is elaborated. In the future, technological innovations along with mathematical simulations should create reliable 3D biomimetic systems for glioblastoma research that should facilitate the identification and possibly application in preclinical drug testing and precision medicine.

Blood-brain barrier alterations in human brain tumors revealed by genome-wide transcriptomic profiling

BACKGROUND

Brain tumors, whether primary or secondary, have limited therapeutic options despite advances in understanding driver gene mutations and heterogeneity within tumor cells. The cellular and molecular composition of brain tumor stroma, an important modifier of tumor growth, has been less investigated to date. Only few studies have focused on the vasculature of human brain tumors despite the fact that the blood-brain barrier (BBB) represents the major obstacle for efficient drug delivery.

METHODS

In this study, we employed RNA sequencing to characterize transcriptional alterations of endothelial cells isolated from primary and secondary human brain tumors. We used an immunoprecipitation approach to enrich for endothelial cells from normal brain, glioblastoma (GBM) and lung cancer brain metastasis (BM).

RESULTS

Analysis of the endothelial transcriptome showed deregulation of genes implicated in cell proliferation, angiogenesis and deposition of extracellular matrix (ECM) in the vasculature of GBM and BM. Deregulation of genes defining the BBB dysfunction module were found in both tumor types. We identified deregulated expression of genes in vessel-associated fibroblasts in GBM.

CONCLUSION

We characterize alterations in BBB genes in GBM and BM vasculature and identify proteins that might be exploited for developing drug delivery platforms. In addition, our analysis on vessel-associated fibroblasts in GBM shows that the cellular composition of brain tumor stroma merits further investigation.

In vitro function and in situ localization of Multidrug Resistance-associated Protein (MRP)1 (ABCC1) suggest a protective role against methyl mercury-induced oxidative stress in the human placenta

Methyl mercury (MeHg) is an organic highly toxic compound that is transported efficiently via the human placenta. Our previous data suggest that MeHg is taken up into placental cells by amino acid transporters while mercury export from placental cells mainly involves ATP binding cassette (ABC) transporters. We hypothesized that the ABC transporter multidrug resistance-associated protein (MRP)1 (ABCC1) plays an essential role in mercury export from the human placenta. Transwell transport studies with MRP1-overexpressing Madin-Darby Canine Kidney (MDCK)II cells confirmed the function of MRP1 in polarized mercury efflux. Consistent with this, siRNA-mediated MRP1 gene knockdown in the human placental cell line HTR-8/SVneo resulted in intracellular mercury accumulation, which was associated with reduced cell viability, accompanied by increased cytotoxicity, apoptosis, and oxidative stress as determined via the glutathione (GSH) status. In addition, the many sources claiming different localization of MRP1 in the placenta required a re-evaluation of its localization in placental tissue sections by immunofluorescence microscopy using an MRP1-specific antibody that was validated in-house. Taken together, our results show that (1) MRP1 preferentially mediates apical-to-basolateral mercury transport in epithelial cells, (2) MRP1 regulates the GSH status of placental cells, (3) MRP1 function has a decisive influence on the viability of placental cells exposed to low MeHg concentrations, and (4) the in situ localization of MRP1 corresponds to mercury transport from maternal circulation to the placenta and fetus. We conclude that MRP1 protects placental cells from MeHg-induced oxidative stress by exporting the toxic metal and by maintaining the placental cells' GSH status in equilibrium.

Thioredoxin, Glutathione and Related Molecules in Tumors of the Nervous System

BACKGROUND

Central Nervous System (CNS) tumors have a poor survival prognosis due to their invasive and heterogeneous nature, in addition to the resistance to multiple treatments.

OBJECTIVE

In this paper, the main aspects of brain tumor biology and pathogenesis are reviewed both for primary tumors of the brain, (i.e., gliomas) and for metastasis from other malignant tumors, namely lung cancer, breast cancer and malignant melanoma which account for a high percentage of overall malignant brain tumors. We review the role of antioxidant systems, namely the thioredoxin and glutathione systems, in the genesis and/or progression of brain tumors.

METHODS

Although overexpression of Thioredoxin Reductase (TrxR) and Thioredoxin (Trx) is often linked to increased malignancy rate of brain tumors, and higher expression of Glutathione (GSH) and Glutathione S-Transferases (GST) are associated to resistance to therapy, several knowledge gaps still exist regarding for example, the role of Peroxiredoxins (Prx), and Glutaredoxins (Grx).

CONCLUSION

Due to their central role in redox homeostasis and ROS scavenging, redox systems are potential targets for new antitumorals and examples of innovative therapeutics aiming at improving success rates in brain tumor treatment are discussed.

Identification of a Seven-lncRNA Immune Risk Signature and Construction of a Predictive Nomogram for Lung Adenocarcinoma

Background

The incidence of lung cancer is the highest of all cancers, and it has the highest death rate. Lung adenocarcinoma (LUAD) is a major type of lung cancer. This study is aimed at identifying the prognostic value of immune-related long noncoding RNAs (lncRNAs) in LUAD.

Materials and Methods

Gene expression profiles and the corresponding clinicopathological features of LUAD patients were obtained from The Cancer Genome Atlas (TCGA). The least absolute shrinkage and selection operator (LASSO) Cox regression algorithm was performed on the prognostic immune-related lncRNAs to calculate the risk scores, and a risk signature was constructed. Survival analysis was performed to assess the prognostic value of the risk signature. A nomogram was also constructed based on the clinicopathological features and risk signature.

Results

A total of 437 LUAD patients with gene expression data and clinicopathological features were obtained in this study, which was considered the combination set. They were randomly and equally divided into a training set and a validation set. Seven immune-related lncRNAs (AC092794.1, AL034397.3, AC069023.1, AP000695.1, AC091057.1, HLA-DQB1-AS1, and HSPC324) were identified and used to construct a risk signature. The patients were divided into the low- and high-risk groups based on the median risk score of -0.04074. Survival analysis suggested that patients in the low-risk group had a longer overall survival (OS) than those in the high-risk group (p = 1.478e − 02). A nomogram was built that could predict the 1-, 3-, and 5-year survival rates of LUAD patients (C-index of the nomogram was 0.755, and the AUCs for the 1-, 3-, and 5-year survivals were 0.826, 0.719, and 0.724, respectively). The validation and combination sets confirmed these results.

Conclusion

Our study identified seven novel immune-related lncRNAs and generated a risk signature, as well as a nomogram, that could predict the prognosis of LUAD patients.

Interaction Between Near-Infrared Radiation and Temozolomide in a Glioblastoma Multiform Cell Line: A Treatment Strategy?

Photodynamic therapy (PDT) is a potential therapeutic modality against cancer, resulting from the interaction of a photosensitizer (PS) and radiation that generates damage to tumor cells. The use of near-infrared radiation (IR-A) is relevant because presents recognized biological effects, such as antioxidant, neuroprotective and antitumor effects. Glioblastoma is the most aggressive central nervous system (CNS) neoplasm with high proliferation and tissue invasion capacity and is resistant to radio and chemotherapy. Here, we evaluated in vitro the possible interaction of temozolomide (TMZ) with IR-A in a glioblastoma cell line (C6) and in a human keratinocyte cell line (HaCat) how non-tumor cell model, in an attempt to search for a new treatment strategy. The effects of TMZ, IR-A and the interaction between TMZ and IR-A was evaluated by viability exclusion with trypan blue. To perform the interaction experiments, we have chosen 10 μM TMZ and 4.5 J/cm² of IR-A. From this, we evaluated cytotoxicity, cell proliferation, intracellular reactive oxygen species levels (ROS), as well as the process of cell migration and the P-gp and MRP-1 activity. Cell death mainly due to apoptosis, followed by necrosis, decreased cell proliferation, increased ROS levels, decreased cell migration and decreased P-gp and MRP1 activity were observed only when there was interaction between TMZ and IR-A in the C6 cell line. The interaction between TMZ and IR-A was not able to affect cell proliferation in the HaCat non-tumor cell line. Our results suggest that this interaction could be a promising approach and that in the future may serve as an antitumor strategy for PDT application.

Alteration in the Function and Expression of SLC and ABC Transporters in the Neurovascular Unit in Alzheimer's Disease and the Clinical Significance

The neurovascular unit (NVU) plays an important role in maintaining the function of the central nervous system (CNS). Emerging evidence has indicated that the NVU changes function and molecules at the early stage of Alzheimer’s disease (AD), which initiates multiple pathways of neurodegeneration. Cell types in the NVU have become attractive targets in the interventional treatment of AD. The NVU transportation system contains a variety of proteins involved in compound transport and neurotransmission. Brain transporters can be classified as members of the solute carrier (SLC) and ATP-binding cassette (ABC) families in the NVU. Moreover, the transporters can regulate both endogenous toxins, including amyloid-beta (Aβ) and xenobiotic homeostasis, in the brains of AD patients. Genome-wide association studies (GWAS) have identified some transporter gene variants as susceptibility loci for late-onset AD. Therefore, the present study summarizes changes in blood-brain barrier (BBB) permeability in AD, identifies the location of SLC and ABC transporters in the brain and focuses on major SLC and ABC transporters that contribute to AD pathology.

ABC Transporters at the Blood-Brain Interfaces, Their Study Models, and Drug Delivery Implications in Gliomas

Drug delivery into the brain is regulated by the blood-brain interfaces. The blood-brain barrier (BBB), the blood-cerebrospinal fluid barrier (BCSFB), and the blood-arachnoid barrier (BAB) regulate the exchange of substances between the blood and brain parenchyma. These selective barriers present a high impermeability to most substances, with the selective transport of nutrients and transporters preventing the entry and accumulation of possibly toxic molecules, comprising many therapeutic drugs. Transporters of the ATP-binding cassette (ABC) superfamily have an important role in drug delivery, because they extrude a broad molecular diversity of xenobiotics, including several anticancer drugs, preventing their entry into the brain. Gliomas are the most common primary tumors diagnosed in adults, which are often characterized by a poor prognosis, notably in the case of high-grade gliomas. Therapeutic treatments frequently fail due to the difficulty of delivering drugs through the brain barriers, adding to diverse mechanisms developed by the cancer, including the overexpression or expression de novo of ABC transporters in tumoral cells and/or in the endothelial cells forming the blood-brain tumor barrier (BBTB). Many models have been developed to study the phenotype, molecular characteristics, and function of the blood-brain interfaces as well as to evaluate drug permeability into the brain. These include in vitro, in vivo, and in silico models, which together can help us to better understand their implication in drug resistance and to develop new therapeutics or delivery strategies to improve the treatment of pathologies of the central nervous system (CNS). In this review, we present the principal characteristics of the blood-brain interfaces; then, we focus on the ABC transporters present on them and their implication in drug delivery; next, we present some of the most important models used for the study of drug transport; finally, we summarize the implication of ABC transporters in glioma and the BBTB in drug resistance and the strategies to improve the delivery of CNS anticancer drugs.

ABCC3 Expressed by CD56dim CD16+ NK Cells Predicts Response in Glioblastoma Patients Treated with Combined Chemotherapy and Dendritic Cell Immunotherapy

Recently, we found that temozolomide (TMZ) can upregulate the expression of the multidrug-resistance protein ABCC3 in NK cells from both glioma-bearing mice and glioblastoma patients treated with dendritic cell immunotherapy combined with TMZ, allowing NK cells to escape apoptosis and favoring their role as antitumor effector cells. Here, we demonstrate that CD56^dim NK cells expressing CD16⁺ are predominant in patients surviving more than 12 months after surgery without disease progression. CD56^dim CD16⁺ NK cells co-expressed high levels of ABCC3 and IFN-γ. Notably, not only basal but also TMZ-induced ABCC3 expression was related to a strong, long-term NK cell response and a better prognosis of patients. The identification of the single nucleotide polymorphism (SNP) rs35467079 with the deletion of a cytosine (−897DelC) in the promoter region of the ABCC3 gene resulted associated with a better patient outcome. ABCC3 expression in patients carrying DelC compared to patients with reference haplotype was higher and modulated by TMZ. The transcription factor NRF2, involved in ABCC3 induction, was phosphorylated in CD56^dim CD16⁺ NK cells expressing ABCC3 under TMZ treatment. Thus, ABCC3 protein and the SNP −897DelC can play a predictive role in patients affected by GBM, and possibly other cancers, treated with dendritic cell immunotherapy combined with chemotherapy.

Activity and mechanism of flavokawain A in inhibiting P-glycoprotein expression in paclitaxel resistance of lung cancer

Lung cancer is one of the most common cancers, which is the leading cause of cancer-related death among various cancers worldwide. Flavokawain A (FKA), a chalcone found in the kava plant, exerts potent anticancer activity. However, the activity and mechanisms of FKA in inhibiting the viability of paclitaxel (PTX)-resistant lung cancer A549 (A549/T) have not been investigated. In the present study, the effect of FKA on the viability of A549/T and hepatotoxicity in normal liver epithelial cells was detected by Cell Counting Kit-8 assay. Flow cytometry, western blot analysis and Annexin V-FITC/PI apoptosis detection kit were used to assess cell apoptosis. The effect of FKA on permeability-glycoprotein (P-gp) expression was measured by reverse transcription-PCR and western blot analysis. The results indicated that FKA dose-dependently inhibited cell proliferation and induced cell apoptosis in PTX-resistant A549/T cells, with an IC₅₀ value of ~21 µM, while the IC₅₀ value of A549/T cells to PTX was 34.64 µM. FKA had no hepatic toxicity in liver epithelial cells. P-gp, which contributes to the chemoresistant phenotype, was not expressed in A549 cells but was remarkably enhanced in A549/T cells. FKA (30 µM) decreased P-gp protein expression at 24 h by 3-fold. Furthermore, FKA downregulated P-gp expression by blocking the PI3K/Akt pathway. These findings suggest FKA as a potential candidate for the treatment of PTX-resistant lung cancer.

MDIG promotes cisplatin resistance of lung adenocarcinoma by regulating ABC transporter expression via activation of the WNT/β-catenin signaling pathway

Mineral dust-induced gene (MDIG) is a proto- oncogene associated with lung cancer that serves a key role in the biological processes of tumorigenesis. The aim of the present study was to determine whether MDIG is involved in cisplatin (DDP) resistance in lung adenocarcinoma, and to investigate the associated molecular mechanism. In the present study, MDIG-knockdown and MDIG-overexpressing A549 cells and DDP-resistant A549/DDP cells were initially constructed, and then the mRNA and protein expression levels of MDIG and ATP-binding cassette (ABC) transporters (ABCB1, ABCC1, ABCG2), and the expression levels of the major associated proteins in the WNT/β-catenin pathway were determined by reverse transcription-quantitative PCR and Western blotting experiments. The results revealed that the mRNA and protein expression levels of MDIG in A549/DDP cells were significantly higher compared with those in A549 cells, and that the protein expression levels of MDIG increased in a dose-dependent manner with increasing DDP concentrations. Overexpression of MDIG in A549 and A549/DDP cells led to an increase in the IC₅₀ value, whereas silencing of MDIG led to a clear reduction in the IC₅₀ value. The overexpression of MDIG in the A549 and A549/DDP cells markedly upregulated the mRNA and protein expression levels of ABCB1, ABCC1, ABCG2, WNT family member 5A, WNT family member 3A and active β-catenin, and these were markedly decreased following MDIG silencing. Taken together, these results demonstrated that the DDP resistance of lung adenocarcinoma may be associated with an upregulation of MDIG expression, and that the expression levels of MDIG are positively associated with the degree of DDP resistance. Furthermore, MDIG promoted the expression of ABC transporters in tumor cells by activating the WNT/β-catenin signaling pathway, which may, in turn, lead to DDP resistance in lung adenocarcinoma.

CD73 Promotes Glioblastoma Pathogenesis and Enhances Its Chemoresistance via A2B Adenosine Receptor Signaling

Glioblastoma (GB) is one of the deadliest brain cancers to afflict humans, and it has a very poor survival rate even with treatment. The extracellular adenosine-generating enzyme CD73 is involved in many cellular functions that can be usurped by tumors, including cell adhesion, proliferation, invasion, and angiogenesis. We set out to determine the role of CD73 in GB pathogenesis. To do this, we established a unique GB mouse model (CD73-FLK) in which we spatially expressed CD73 on endothelial cells in CD73^-/- mice. This allowed us to elucidate the mechanism of host CD73 versus GB-expressed CD73 by comparing GB pathogenesis in WT, CD73^-/-, and CD73-FLK mice. GB in CD73^-/- mice had decreased tumor size, decreased tumor vessel density, and reduced tumor invasiveness compared with GB in WT mice. Interestingly, GBs in CD73-FLK mice were much more invasive and caused complete distortion of the brain morphology. We showed a 20-fold upregulation of A_2B AR on GB compared with sham, and its activation induced matrix metalloproteinase-2, which enhanced GB pathogenesis. Inhibition of A_2B AR signaling decreased multidrug resistance transporter protein expression, including permeability glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1). Further, we showed that blockade of A_2B AR signaling potently increased GB cell death induced by the chemotherapeutic drug temozolomide. Together, these findings suggest that CD73 and A_2B AR play a multifaceted role in GB pathogenesis and progression and that targeting the CD73-A_2B AR axis can benefit GB patients and inform new approaches for therapy to treat GB patients.SIGNIFICANCE STATEMENT Glioblastoma (GB) is the most devastating primary brain tumor. GB patients' median survival is 16 months even with treatment. It is critical that we develop prophylaxes to advance GB treatment and improve patient survival. CD73-generated adenosine has been implicated in cancer pathogenesis, but its role in GB was not ascertained. Here, we demonstrated that host CD73 plays a prominent role in multiple areas of glioblastoma pathogenesis, including promoting GB growth, its angiogenesis, and its invasiveness. We found a 20-fold increase in A_2B adenosine receptor (AR) expression on GB compared with sham, and its inhibition increased GB chemosensitivity to temozolomide. These findings strongly indicate that blockade or inhibition of CD73 and the A_2B AR are prime targets for future GB therapy.

Overcoming the Blood–Brain Barrier. Challenges and Tricks for CNS Drug Delivery

Treatment of certain central nervous system disorders, including different types of cerebral malignancies, is limited by traditional oral or systemic administrations of therapeutic drugs due to possible serious side effects and/or lack of the brain penetration and, therefore, the efficacy of the drugs is diminished. During the last decade, several new technologies were developed to overcome barrier properties of cerebral capillaries. This review gives a short overview of the structural elements and anatomical features of the blood–brain barrier. The various in vitro (static and dynamic), in vivo (microdialysis), and in situ (brain perfusion) blood–brain barrier models are also presented. The drug formulations and administration options to deliver molecules effectively to the central nervous system (CNS) are presented. Nanocarriers, nanoparticles (lipid, polymeric, magnetic, gold, and carbon based nanoparticles, dendrimers, etc.), viral and peptid vectors and shuttles, sonoporation and microbubbles are briefly shown. The modulation of receptors and efflux transporters in the cell membrane can also be an effective approach to enhance brain exposure to therapeutic compounds. Intranasal administration is a noninvasive delivery route to bypass the blood–brain barrier, while direct brain administration is an invasive mode to target the brain region with therapeutic drug concentrations locally. Nowadays, both technological and mechanistic tools are available to assist in overcoming the blood–brain barrier. With these techniques more effective and even safer drugs can be developed for the treatment of devastating brain disorders.

ABC Family Transporters

The transport of specific molecules across lipid membranes is an essential function of all living organisms. The processes are usually mediated by specific transporters. One of the largest transporter families is the ATP-binding cassette (ABC) family. More than 40 ABC transporters have been identified in human, which are divided into 7 subfamilies (ABCA to ABCG) based on their gene structure, amino acid sequence, domain organization, and phylogenetic analysis. Of them, at least 11 ABC transporters including P-glycoprotein (P-GP/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2) are involved in multidrug resistance (MDR) development. These ABC transporters are expressed in various tissues such as the liver, intestine, kidney, and brain, playing important roles in absorption, distribution, and excretion of drugs. Some ABC transporters are also involved in diverse cellular processes such as maintenance of osmotic homeostasis, antigen processing, cell division, immunity, cholesterol, and lipid trafficking. Several human diseases such as cystic fibrosis, sitosterolemia, Tangier disease, intrahepatic cholestasis, and retinal degeneration are associated with mutations in corresponding transporters. This chapter will describe function and expression of several ABC transporters (such as P-GP, BCRP, and MRPs), their substrates and inhibitors, as well as their clinical significance.

65 YEARS OF THE DOUBLE HELIX: Treatment of pituitary tumors with temozolomide: an update

Temozolomide is an alkylating chemotherapeutic agent used in malignant neuroendocrine neoplasia, melanoma, brain metastases and an essential component of adjuvant therapy in the treatment of glioblastoma multiforme and anaplastic astrocytoma. Since 2006, it has been used for the treatment of pituitary carcinomas and aggressive pituitary adenomas. Here, we discuss the current indications and results of temozolomide therapy in pituitary tumors, as well as frequently asked questions regarding temozolomide treatment, duration of therapy, dosage, tumor recurrence and resistance.

Enhanced liver-targeting via coadministration of 10-Hydroxycamptothecin polymeric micelles with vinegar baked Radix Bupleuri

BACKGROUND

Vinegar baked Radix Bupleuri (VBRB) is a wildly used traditional Chinese medicine, it could be used as a meridian guided drug to enhance liver targeting efficiency of the delivered drug in addition to its therapeutic effect.

PURPOSE

To investigate the liver targeting effect induced by VBRB via coadministration with 10-Hydroxycamptothecin loaded polymeric micelles.

METHODS

First of all, the inhibitory effect of VBRB on the activity of glutathione S-transferase (GST) was investigated in vitro to select the most effective extract. After oral administration of 10-Hydroxycamptothecin (HCPT) polymeric micelles with low, medium and high doses of VBRB, pharmacokinetic parameters, including the ratio of Cmax in the liver (Ce) and the relative uptake efficiency (RUE), were employed to assess the liver targeting efficiency.

RESULTS

It was found that VBRB extract BC1 has the strongest inhibition effect on GST activity in the five extracts. By coadministration of HCPT loaded micelles with three doses of BC1, the AUC_0-t of HCPT in the liver raised by 42.5%, 23.0%, -0.2%, with RUE 1.45, 1.23, 1.02 for low, medium and high dose groups, respectively, indicating that low and medium dose of BC1 presented better liver-targeting enhancing effect than that of the high dose, which corresponded to the commonly used dose of VBRB in traditional Chinese medicine formulae.

CONCLUSIONS

VBRB could effectively enhance the liver-targeting efficiency of HCPT loaded polymeric micelles after oral coadministration. Such a simple but effective strategy may enlighten on the potential use of meridian guided drug together with modern drug delivery system to achieve better active drug targeting.

IDH1 R132H mutation regulates glioma chemosensitivity through Nrf2 pathway

Purpose

Numerous studies have reported that glioma patients with isocitrate dehydrogenase 1(IDH1) R132H mutation are sensitive to temozolomide treatment. However, the mechanism of IDH1 mutations on the chemosensitivity of glioma remains unclear. In this study, we investigated the role and the potential mechanism of Nrf2 in IDH1 R132H-mediated drug resistance.

Methods

Wild type IDH1 (R132H-WT) and mutant IDH1 (R132H) plasmids were constructed. Stable U87 cells and U251 cells overexpressing IDH1 were generated. Phenotypic differences between IDH1-WT and IDH1 R132H overexpressing cells were evaluated using MTT, cell colony formation assay, scratch test assay and flow cytometry. Expression of IDH1 and its associated targets, nuclear factor-erythroid 2-related factor 2 (Nrf2), NAD(P)H quinine oxidoreductase 1 (NQO1), multidrug resistant protein 1 (MRP1) and p53 were analyzed.

Results

The IDH1 R132H overexpressing cells were more sensitive to temozolomide than WT and the control, and Nrf2 was significantly decreased in IDH1 R132H overexpressing cells. We found that knocking down Nrf2 could decrease resistance to temozolomide. The nuclear translocation of Nrf2 in IDH1 R132H overexpressing cells was lower than the WT and the control groups after temozolomide treatment. When compared with WT cells, NQO1 expression was reduced in IDH1 R132H cells, especially after temozolomide treatment. P53 was involved in the resistance mechanism of temozolomide mediated by Nrf2 and NQO1.

Conclusions

Nrf2 played an important role in IDH1 R132H-mediated drug resistance. The present study provides new insight for glioma chemotherapy with temozolomide.

Forkhead box K2 inhibits the proliferation, migration, and invasion of human glioma cells and predicts a favorable prognosis

Purpose

Forkhead box K2 (FOXK2) is a member of the forkhead box family of transcription factors. Recently, researchers discovered that overexpression of FOXK2 inhibits the proliferation and metastasis of breast cancer, non-small cell lung cancer, and colorectal cancer, and is related to the clinical prognosis. However, in hepatocellular carcinoma, FOXK2 results in the opposite phenotypes. Currently, the contribution of FOXK2 to glioma pathogenesis is not clear.

Patients and methods

We evaluated the expression of FOXK2 in 151 glioma patients using immunohistochemistry assays. The associations among the expression of FOXK2, clinicopathological parameters, and the prognosis of glioma patients were statistically analyzed. We downregulated and upregulated the level of FOXK2 in glioma cells by transfections with small interfering RNA and plasmids. Then, we investigated the effects on tumor cell behavior in vitro by Cell Counting Kit-8 assays, colony-formation assay, transwell assay, and the epithelial-to-mesenchymal transition (EMT) biomarker levels.

Results

The clinical data showed that expression of FOXK2 gradually decreased with increasing World Health Organization (WHO) grades and a low level of FOXK2 indicates a poor prognosis. FOXK2 expression is negatively correlated with Ki67 expression and the WHO degree but is not correlated with other clinicopathological parameters, including sex, age, Karnofsky Performance Status, tumor diameter, O-6-methylguanine-DNA methyltransferase, and glutathione S-transferase pi. FOXK2 knockdown enhances glioma cell proliferation, migration, invasion, and EMT process, and, in contrast, FOXK2 overexpression inhibits glioma cell proliferation, migration, invasion, and the EMT process.

Conclusion

Expression of FOXK2 gradually decreases with increasing WHO grades. FOXK2 inhibits tumor proliferation, migration, and invasion. FOXK2 is a critical mediator of the EMT process.

Adenosine A3 receptor elicits chemoresistance mediated by multiple resistance-associated protein-1 in human glioblastoma stem-like cells

MRP1 transporter correlates positively with glioma malignancy and the Multiple Drug Resistance (MDR) phenotype in Glioblastoma Multiforme (GBM). Evidence shows that the MRP1 transporter is controlled by the adenosine signalling axis. The aim of this study was to identify the role of adenosine on the MDR phenotype in Glioblastoma Stem-like Cells (GSCs), the cell population responsible for the tumorigenic and chemoresistance capabilities of this tumour. We found that GSCs have increased intrinsic capacity to generate extracellular adenosine, thus controlling MRP1 transporter expression and activity via activation of the adenosine A3 receptor (A3AR). We showed PI3K/Akt and MEK/ERK1/2 signaling pathways downstream A3AR to control MRP1 in GSCs. In vitro pharmacological blockade of A3AR had a chemosensitizing effect, enhancing the actions of antitumour drugs and decreasing cell viability and proliferation of GSCs. In addition, we produced an in vivo xenograft model by subcutaneous inoculation of human GSCs in NOD/SCID-IL2Rg null mice. Pharmacological blockade of A3AR generated a chemosensitizing effect, enhancing the effectiveness of the MRP1 transporter substrate, vincristine, reducing tumour size and the levels of CD44 and Nestin stem cell markers as well as the Ki-67 proliferation indicator. In conclusion, we demonstrated the chemosensitizing effect of A3AR blockade on GSCs.

Temozolomide and Pituitary Tumors: Current Understanding, Unresolved Issues, and Future Directions

Temozolomide, an alkylating agent, initially used in the treatment of gliomas was expanded to include pituitary tumors in 2006. After 12 years of use, temozolomide has shown a notable advancement in pituitary tumor treatment with a remarkable improvement rate in the 5-year overall survival and 5-year progression-free survival in both aggressive pituitary adenomas and pituitary carcinomas. In this paper, we review the mechanism of action of temozolomide as alkylating agent, its interaction with deoxyribonucleic acid repair systems, therapeutic effects in pituitary tumors, unresolved issues, and future directions relating to new possibilities of targeted therapy.

Expression of multidrug resistance proteins in retinoblastoma

AIM

To elucidate the mechanism of multidrug resistance in retinoblastoma, and to acquire more insights into in vivo drug resistance.

METHODS

Three anticancer drug resistant Y79 human RB cells were generated against vincristine, etoposide or carboplatin, which are used for conventional chemotherapy in RB. Primary cultures from enucleated eyes after chemotherapy (PCNC) were also prepared. Their chemosensitivity to chemotherapeutic agents (vincristine, etoposide and carboplatin) were measured using MTT assay. Western blot analysis was performed to evaluate the expression of p53, Bcl-2 and various multidrug resistant proteins in retinoblastoma cells.

RESULTS

Following exposure to chemotherapeutic drugs, PCNC showed less sensitivity to drugs. No significant changes observed in the p53 expression, whereas Bcl-2 expression was found to be increased in the drug resistant cells as well as in PCNC. Increased expression of P-glycoprotein (P-gp) was observed in drug resistant Y79 cells; however there was no significant change in the expression of P-gp found between primary cultures of primarily enucleated eyes and PCNC. Multidrug resistance protein 1 (Mrp-1) expression was found to be elevated in the drug resistant Y79 cells as well as in PCNC. No significant change in the expression of lung resistance associated protein (Lrp) was observed in the drug resistant Y79 cells as well as in PCNC.

CONCLUSION

Our results suggest that multidrug resistant proteins are intrinsically present in retinoblastoma which causes treatment failure in managing retinoblastoma with chemotherapy.

Glioblastoma entities express subtle differences in molecular composition and response to treatment

Glioblastoma (GBM) is a grade IV astrocytoma. GBM patients show resistance to chemotherapy such as temozolomide (TMZ), the gold standard treatment. In order to simulate the molecular mechanisms behind the different chemotherapeutic responses in GBM patients we compared the cellular heterogeneity and chemotherapeutic resistance mechanisms in different GBM cell lines. We isolated and characterized a human GBM cell line obtained from a GBM patient, named GBM11. We studied the GBM11 behaviour when treated with Tamoxifen (TMX) that, among other functions, is a protein kinase C (PKC) inhibitor, alone and in combination with TMZ in comparison with the responses of U87 and U118 human GBM cell lines. We evaluated the cell death, cell cycle arrest and cell proliferation, mainly through PKC expression, by flow cytometry and western blot analysis and, ultimately, cell migration capability and f-actin filament disorganization by fluorescence microscopy. We demonstrated that the constitutive activation of p-PKC seems to be one of the main metabolic implicated on GBM malignancy. Despite of its higher resistance, possibly due to the overexpression of P-glycoprotein and stem-like cell markers, GBM11 cells presented a subtle different chemotherapeutic response compared to U87 and U118 cells. The GBM11, U87, U118 cell lines show subtle molecular differences, which clearly indicate the characterization of GBM heterogeneity, one of the main reasons for tumor resistance. The adding of cellular heterogeneity in molecular behaviour constitutes a step closer in the understanding of resistant molecular mechanisms in GBM, and can circumvents the eventual impaired therapy.

Multidrug resistance in glioblastoma stem-like cells: Role of the hypoxic microenvironment and adenosine signaling

Glioblastoma multiforme (GBM) is considered the most common and aggressive tumour of the central nervous system and is characterized for being highly chemoresistant. This property is mainly due to the activation of Multiple Drug Resistance (MDR) mechanisms that protect cancer cells from structurally and morphologically different drugs. Overexpression and increased ABC transporters activity is one of the most important MDR mechanisms at the clinical level, and both its expression and activity are elevated in GBM cells. Within the tumour, there is a subpopulation called glioblastoma stem-like cells (GSCs), which due to its high tumourigenic capacity and chemoresistance, have been postulated as the main responsible for tumour recurrence. The GSCs inhabit hypoxic tumour zones, niches that apart from maintaining and promoting stem phenotype have also been correlated with high chemoresistance. Of the signalling pathways activated during hypoxia, purinergic signalling has been highly associated to the induction of MDR mechanisms. Through its receptors, the nucleoside adenosine has been shown to promotes the chemoresistance mediated by ABC transporters. Therefore, targeting its components is a promising alternative for GBM treatment. In this review, we will discuss chemoresistance in GSCs and the effect of the hypoxic microenvironment and adenosine on MDR mechanisms.

Mitochondrial serine hydroxymethyltransferase 2 is a potential diagnostic and prognostic biomarker for human glioma

OBJECTIVE

Scholars have gradually come to appreciate the relevance of serine and glycine metabolism. Recently, researchers have discovered that mitochondrial serine hydroxymethyltransferase 2 (SHMT2) is overexpressed in various types of cancer. However, the function of SHMT2 in glioma is not clear. In this study, we sought to examine the expression of SHMT2 in glioma, the association between SHMT2 expression and clinicopathological characteristics, and the association of SHMT2 expression with prognosis in glioma patients.

METHODS

We evaluated the expression of SHMT2, Ki67, O-6-methylguanine-DNA methyltransferase (MGMT), and Glutathione S Transferase pi (GST-pi) in 150 glioma patients using immunohistochemistry assays. The associations among the expression of SHMT2, clinicopathological parameters, and outcome of glioma patients were statistically analysed.

RESULTS

The expression of SHMT2 was increased in gliomas compared to normal brain tissue and gradually increased with increasing WHO grade. The SHMT2 expression was positively correlated with Ki67 expression and WHO degree (p<0.01) but was not correlated with other clinicopathological parameters, including sex, age, Karnofsky Performance Status (KPS), tumour diameter, MGMT, and GST-pi (p>0.05). Kaplan-Meier survival curves and Cox regression analyses showed that SHMT2 expression and the WHO grade were independent prognostic indicators for glioma patients.

CONCLUSION

The expression of SHMT2 in glioma was significantly increased compared to normal brain tissue. SHMT2 promoted tumour proliferation, and there was no association between SHMT2 and drug resistance mechanisms of glioma. SHMT2 may be a novel and valuable biomarker for the diagnosis of glioma and an independent prognostic parameter of glioma.

Role of Glutathione-S-transferases in neurological problems

INTRODUCTION

Role of Glutathione-S-transferases (GSTs) has been well explored in the cellular detoxification process, regulation of redox homeostasis and S-glutothionylation of target proteins like JNK, ASK1 etc. However, altered levels or functions of this enzyme or their subtypes have emerged in the development of several pathologies diseases such as Alzheimer's disease, Parkinson's disease, cancer and related conditions. Oxidative stress is one of the possible pathological events that contributes significantly to activation of degenerating cascades inside neuronal cells. The central nervous system is highly sensitive to oxidative stress because of low levels or capacities of antioxidant enzymes. The brain is highly metabolic in nature making it susceptible to oxidative stress. Areas covered: The present review provides a comprehensive overview of the multiple connections of GSTs within diverse neurological diseases including cancer. Furthermore, the authors have made significant efforts to discuss the regulation of different GST isoforms that have been associated with various pathological processes such as glioblastoma, Alzheimer's disease, Parkinson's disease, stroke and epilepsy. Expert opinion: Though GSTs have been one of the key areas of scientific research over the last few decades, much remains to be elucidated about their physiological functions as well as pathological involvement of GSTs and their polymorphic variants.

Emerging role of NRF2 in chemoresistance by regulating drug-metabolizing enzymes and efflux transporters

Chemoresistance is a disturbing barrier in cancer therapy, which always results in limited therapeutic options and unfavorable prognosis. Nuclear factor E2-related factor 2 (NRF2) controls the expression of genes encoding cytoprotective enzymes and transporters that protect against oxidative stress and electrophilic injury to maintain intrinsic redox homeostasis. However, recent studies have demonstrated that aberrant activation of NRF2 due to genetic and/or epigenetic mutations in tumor contributes to the high expression of phase I and phase II drug-metabolizing enzymes, phase III transporters, and other cytoprotective proteins, which leads to the decreased therapeutic efficacy of anticancer drugs through biotransformation or extrusion during chemotherapy. Therefore, a better understanding of the role of NRF2 in regulation of these enzymes and transporters in tumors is necessary to find new strategies that improve chemotherapeutic efficacy. In this review, we summarized the recent findings about the chemoresistance-promoting role of NRF2, NRF2-regulated phase I and phase II drug-metabolizing enzymes, phase III drug efflux transporters, and other cytoprotective genes. Most importantly, the potential of NRF2 was proposed to counteract drug resistance in cancer treatment.

Epithelial-mesenchymal transition contributes to docetaxel resistance in human non-small cell lung cancer

Lung cancer is an aggressive malignancy with high morbidity and mortality. Chemotherapy has always been the principal treatment measure, but its acquired resistance becomes a critical problem. In the current study, we established a new docetaxel-resistant human non-small lung cancer (NSCLC) cell line A549/Docetaxel. The resistance index (RI) of A549/Docetaxel cells and A549 induced by TGF-β to docetaxel were 8.91 and 11.5, respectively. Compared to the parental A549 cells, the multiplication time of A549/Docetaxel was prolonged, the proportion of the cell cycle in the S phase decreased while that in the G1 phase increased, and apoptotic rate was much lower. The morphology of the resistant cells eventuated epithelial-mesenchymal transition (EMT), which was confirmed by the higher expression of fibronectin, vimentin (mesenchymal markers), and lower expression of E-cadherin (epithelial marker) at mRNA and proteins levels. Furthermore, the representative markers for docetaxel resistance were examined, including ABCB1 (MDR1), Bcl-2, Bax, and tubulin, to figure out the mechanisms of the resistance of A549/Docetaxel. In summary, we have established a typical docetaxel-resistant human NSCLC cell line A549/Docetaxel, and it was suggested that the multidrug resistance of A549/Docetaxel was related to EMT.

Cytokine-induced killer cells induce apoptosis and inhibit the Akt/nuclear factor-κB signaling pathway in cisplatin-resistant human glioma U87MG cells

Despite advances in the development of treatment methods, glioma remains among the cancer types with a high rate of mortality. Therefore, significant efforts are made to develop novel strategies for the treatment of glioma. Ineffective, long-term cancer chemotherapy can lead to multidrug resistance (MDR), which is one of the most common reasons for the failure of chemotherapy. The present study investigated the effects of cytokine‑induced killer cells (CIK) on reversing MDR in cisplatin-resistant U87MG cells (U87MG/DDP). Mononuclear cells were isolated from the peripheral blood of healthy individuals and cultured in vitro in the presence of a combination of cytokines to generate CIK for the treatment of U87MG/DDP. An MTS assay, flow cytometric analysis of apoptosis, ELISA, western blotting and reverse transcription quantitative polymerase chain reaction were used to investigate the MDR-reversing effects of CIK as well as the underlying mechanisms. The results showed that cisplatin sensitivity and the apoptotic rate following cisplatin treatment were increased, P‑glycoprotein expression was decreased and the intracellular rhodamine‑123 content was increased in U87MG/DDP co‑cultured with CIK. In addition, the present study also identified increased mRNA and protein expression levels of MDR gene 1 (MDR1), MDR‑associated protein 1 (MRP1), B-cell lymphoma 2, Survivin and glutathione S-transferase‑π, while the phosphorylation of AKT and the transcriptional activity of nuclear factor‑κB in CIK co‑cultured U87MG/DDP was decreased. These results indicated that pre‑treatment with CIK reversed the MDR of U87MG/DDP, and that CIK‑induced apoptosis of U87MG/DDP was associated with the inhibition of Akt/NF‑κB. These findings suggested that treatment with CIK may be an effective method to enhance the sensitivity of patients with glioma to chemotherapy.

Nanoparticle-mediated drug delivery for treating melanoma

Melanoma originated from melanocytes is the most aggressive type of skin cancer with limited treatment options. New targeted therapeutic options with the discovery of BRAF and MEK inhibitors have shown significant survival benefits. Despite the recent progress, development of chemoresistance and systemic toxicity remains a challenge for treating metastatic melanoma. While the response from the first line of treatment against melanoma using dacarbazine remains only 5-10%, the prolonged use of targeted therapy against mutated oncogene BRAF develops chemoresistance. In this review, we will discuss the nanoparticle-based strategies for encapsulation and conjugation of drugs to the polymer for maximizing their tumor distribution through enhanced permeability and retention effect. We will also highlight photodynamic therapy and design of melanoma-targeted nanoparticles.

Acetate supplementation as a means of inducing glioblastoma stem-like cell growth arrest

Glioblastoma (GBM), the most common primary adult malignant brain tumor, is associated with a poor prognosis due, in part, to tumor recurrence mediated by chemotherapy and radiation resistant glioma stem-like cells (GSCs). The metabolic and epigenetic state of GSCs differs from their non-GSC counterparts, with GSCs exhibiting greater glycolytic metabolism and global hypoacetylation. However, little attention has been focused on the potential use of acetate supplementation as a therapeutic approach. N-acetyl-l-aspartate (NAA), the primary storage form of brain acetate, and aspartoacylase (ASPA), the enzyme responsible for NAA catalysis, are significantly reduced in GBM tumors. We recently demonstrated that NAA supplementation is not an appropriate therapeutic approach since it increases GSC proliferation and pursued an alternative acetate source. The FDA approved food additive Triacetin (glyceryl triacetate, GTA) has been safely used for acetate supplementation therapy in Canavan disease, a leukodystrophy due to ASPA mutation. This study characterized the effects of GTA on the proliferation and differentiation of six primary GBM-derived GSCs relative to established U87 and U251 GBM cell lines, normal human cerebral cortical astrocytes, and murine neural stem cells. GTA reduced proliferation of GSCs greater than established GBM lines. Moreover, GTA reduced growth of the more aggressive mesenchymal GSCs greater than proneural GSCs. Although sodium acetate induced a dose-dependent reduction of GSC growth, it also reduced cell viability. GTA-mediated growth inhibition was not associated with differentiation, but increased protein acetylation. These data suggest that GTA-mediated acetate supplementation is a novel therapeutic strategy to inhibit GSC growth.

Involvement of p38 MAPK in the Drug Resistance of Refractory Epilepsy Through the Regulation Multidrug Resistance-Associated Protein 1

Increased expression of multidrug-resistance associated protein 1 in brain tissue has been reported which lead to multidrug resistance of refractory epilepsy. However, the mechanism of up-regulated expression is still unclear. In our previous study, we have found that the MAPK signaling pathway mediated the expression of P-glycoprotein. So in this study, we used a rat model of refractory epilepsy to examine whether p38 MAPK affect the expression of MRP1 and the concentrations of AEDs in the brain. The expression of MRP1 and p38 MAPK was detected by immunofluorescence, Western-blot and real time-PCR, while the concentration of AEDs was measured by microdialysis and HPLC. The result showed that SB202190, the specific inhibitor of p38 MAPK, could down-regulate the expression of MRP1, while increase the concentrations of valproate and lamotrigine in hippocampus extracellular fluid of refractory epileptic rat. We demonstrate that p38 MAPK signaling pathway may be involved in drug resistance of refractory epilepsy by regulating MRP1.