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

Epilepsy in the cancer patient

PURPOSE

Epileptic seizures in patients with malignancies usually occur as a consequence of brain metastases from systemic cancer or the presence of a primary brain tumor. Other less-frequent causes include metabolic disorders such as electrolyte abnormalities, hypoglycemia, hypoxia and liver failure, paraneoplastic encephalitis, leptomeningeal carcinomatosis, side effects of certain chemotherapeutic agents, central nervous system infections, and pre-existing epilepsy.

METHODS

We reviewed all published literature in the English language regarding the use of antiepileptic drugs in patients with cancer.

RESULTS

In patients with brain metastases or primary brain tumors that had never experienced seizures, prophylactic anticonvulsant treatment is justified only for a period up to 6 months postoperatively after surgical excision of a cerebral tumor, since approximately half of the patients will never develop seizures and the anti-epileptic drugs may cause toxicity and interactions with antineoplastic therapies. For brief prophylaxis, newer antiepileptic drugs such as levetiracetam and oxcarbazepine are superior to older agents like phenytoin. In patients with a malignancy and seizures, certain antiepileptic drugs that express tumor inhibitory properties should be used such as valproic acid and levetiracetam, followed by oxcarbazepine and topiramate that exhibit good tolerance, efficient seizure control and absence of significant interactions with the chemotherapy.

CONCLUSIONS

Future clinical trials in patients with cancer and epilepsy should focus on combinations of chemotherapeutic interventions with antiepileptic drugs that demonstrate antineoplastic activities.

Molecular biology of the blood-brain and the blood-cerebrospinal fluid barriers: similarities and differences

Efficient processing of information by the central nervous system (CNS) represents an important evolutionary advantage. Thus, homeostatic mechanisms have developed that provide appropriate circumstances for neuronal signaling, including a highly controlled and stable microenvironment. To provide such a milieu for neurons, extracellular fluids of the CNS are separated from the changeable environment of blood at three major interfaces: at the brain capillaries by the blood-brain barrier (BBB), which is localized at the level of the endothelial cells and separates brain interstitial fluid (ISF) from blood; at the epithelial layer of four choroid plexuses, the blood-cerebrospinal fluid (CSF) barrier (BCSFB), which separates CSF from the CP ISF, and at the arachnoid barrier. The two barriers that represent the largest interface between blood and brain extracellular fluids, the BBB and the BCSFB, prevent the free paracellular diffusion of polar molecules by complex morphological features, including tight junctions (TJs) that interconnect the endothelial and epithelial cells, respectively. The first part of this review focuses on the molecular biology of TJs and adherens junctions in the brain capillary endothelial cells and in the CP epithelial cells. However, normal function of the CNS depends on a constant supply of essential molecules, like glucose and amino acids from the blood, exchange of electrolytes between brain extracellular fluids and blood, as well as on efficient removal of metabolic waste products and excess neurotransmitters from the brain ISF. Therefore, a number of specific transport proteins are expressed in brain capillary endothelial cells and CP epithelial cells that provide transport of nutrients and ions into the CNS and removal of waste products and ions from the CSF. The second part of this review concentrates on the molecular biology of various solute carrier (SLC) transport proteins at those two barriers and underlines differences in their expression between the two barriers. Also, many blood-borne molecules and xenobiotics can diffuse into brain ISF and then into neuronal membranes due to their physicochemical properties. Entry of these compounds could be detrimental for neural transmission and signalling. Thus, BBB and BCSFB express transport proteins that actively restrict entry of lipophilic and amphipathic substances from blood and/or remove those molecules from the brain extracellular fluids. The third part of this review concentrates on the molecular biology of ATP-binding cassette (ABC)-transporters and those SLC transporters that are involved in efflux transport of xenobiotics, their expression at the BBB and BCSFB and differences in expression in the two major blood-brain interfaces. In addition, transport and diffusion of ions by the BBB and CP epithelium are involved in the formation of fluid, the ISF and CSF, respectively, so the last part of this review discusses molecular biology of ion transporters/exchangers and ion channels in the brain endothelial and CP epithelial cells.

Dual role of nanoparticles as drug carrier and drug

The conventional chemotherapeutic agents used in the treatment of human malignancies are directed nonspecifically against both malignant and nonmalignant cells, often limiting their efficacy with having serious side effects. Recent development of drug delivery vehicles has opened up the possibility of targeted drug delivery systems with the potential of achieving maximum efficacy with minimal toxicity. The possibility of using a nanomaterial as a combinational drug component is intuitively evident as it would compensate the toxicity level by enhancing drug delivery efficiency. Additionally, cell-specific cytotoxicity (reported earlier by our group) of the nanovehicle itself may potentiate a more effective targeted cell killing. In this paper, we explore the possibility of using gold nanoparticles playing the dual role of an anticancer agent and a carrier of a chemotherapeutic drug. This is demonstrated using vincristine sulfate (VS), salt of an alkaloid often used in the treatment of multiple myeloma (MM), and U266 as a test MM cell line. The drug VS shows the expected G2-M-phase arrest of cells. Notably, bare gold nanoparticle shows arrest of the S phase cells that may be particularly important in case of slow-growing malignancies like MM where most of the cells remain in G1 phase of the cell cycle. The VS conjugated gold retains the activity of both gold nanoparticle and VS leading to a synergistic rise of the apoptotic cell population.

Epilepsy and brain tumors

PURPOSE OF REVIEW

To present an overview of the recent findings in pathophysiology and management of epileptic seizures in patients with brain tumors.

RECENT FINDINGS

Low-grade gliomas are the most epileptogenic brain tumors. Regarding pathophysiology, the role of peritumoral changes [hypoxia and acidosis, blood-brain barrier (BBB) disruption, increase or decrease of neurotransmitters and receptors] are of increasing importance. Tumor-associated epilepsy and tumor growth could have some common molecular pathways. Total/subtotal surgical resection (with or without epilepsy surgery) allows a seizure control in a high percentage of patients. Radiotherapy and chemotherapy as well have a role. New antiepileptic drugs are promising, both in terms of efficacy and tolerability. The resistance to antiepileptic drugs is still a major problem: new insights into pathogenesis are needed to develop strategies to manipulate the pharmakoresistance.

SUMMARY

Epileptic seizures in brain tumors have been definitely recognized as one of the major problems in patients with brain tumors, and need specific and multidisciplinary approaches.

MRP3: a molecular target for human glioblastoma multiforme immunotherapy

Background

Glioblastoma multiforme (GBM) is refractory to conventional therapies. To overcome the problem of heterogeneity, more brain tumor markers are required for prognosis and targeted therapy. We have identified and validated a promising molecular therapeutic target that is expressed by GBM: human multidrug-resistance protein 3 (MRP3).

Methods

We investigated MRP3 by genetic and immunohistochemical (IHC) analysis of human gliomas to determine the incidence, distribution, and localization of MRP3 antigens in GBM and their potential correlation with survival. To determine MRP3 mRNA transcript and protein expression levels, we performed quantitative RT-PCR, raising MRP3-specific antibodies, and IHC analysis with biopsies of newly diagnosed GBM patients. We used univariate and multivariate analyses to assess the correlation of RNA expression and IHC of MRP3 with patient survival, with and without adjustment for age, extent of resection, and KPS.

Results

Real-time PCR results from 67 GBM biopsies indicated that 59/67 (88%) samples highly expressed MRP3 mRNA transcripts, in contrast with minimal expression in normal brain samples. Rabbit polyvalent and murine monoclonal antibodies generated against an extracellular span of MRP3 protein demonstrated reactivity with defined MRP3-expressing cell lines and GBM patient biopsies by Western blotting and FACS analyses, the latter establishing cell surface MRP3 protein expression. IHC evaluation of 46 GBM biopsy samples with anti-MRP3 IgG revealed MRP3 in a primarily membranous and cytoplasmic pattern in 42 (91%) of the 46 samples. Relative RNA expression was a strong predictor of survival for newly diagnosed GBM patients. Hazard of death for GBM patients with high levels of MRP3 RNA expression was 2.71 (95% CI: 1.54-4.80) times that of patients with low/moderate levels (p = 0.002).

Conclusions

Human GBMs overexpress MRP3 at both mRNA and protein levels, and elevated MRP3 mRNA levels in GBM biopsy samples correlated with a higher risk of death. These data suggest that the tumor-associated antigen MRP3 has potential use for prognosis and as a target for malignant glioma immunotherapy.

Recombinant single-chain variable fragment antibodies against extracellular epitopes of human multidrug resistance protein MRP3 for targeting malignant gliomas

Multidrug resistance protein 3 (MRP3), a multidrug resistance protein identified by serial analysis of gene expression as a glioblastoma multiforme (GBM)-associated molecule, is highly expressed in GBM, but not in normal brain cells. Thus, MRP3 is a candidate for GBM immunotargeting, but to date, no monoclonal antibody has been isolated that can target an extracellular MRP3 epitope. By phage display, we have isolated 3 recombinant, fully human, single-chain Fv (scFv) antibodies, M25, M58 and M89, which specifically react with the extracellular N-terminus of human MRP3. In ELISA, these scFvs reacted only with the peptide used for screening and not with other MRP3-derived peptides. Flow cytometric analysis revealed that these scFv fragments bind specifically to viable human GBM cells displaying different MRP3 expression levels, but not to MRP3-null cells. Furthermore, these scFv antibodies failed to react with tumor cells overexpressing other MRP proteins, including MRP1, MRP2, MRP4 and MRP5. M25 and M58 also bound to viable neurospheres. Iodogen-labeled scFvs demonstrated a yield of 56-76%. The immunoreactive fractions of the radiolabeled M25, M58 and M89 scFvs were 32, 52 and 69%, respectively. M25 exhibited 20% internalization into D2159MG neurospheres, M58, 33% into D54MG cells and M89, 26% into D247MG. Immunohistochemical evaluation of human gliomas to determine the localization of MRP3 antigen using scFvs M25 and M58 showed a dense cytoplasmic and membranous staining pattern. These Fv-based recombinant antibodies, which possess superior tumor penetration capabilities and selectively target tumor cells that express MRP3, may potentially be used in immunotherapy and diagnosis for brain tumors and other cancers.

Progress on antiangiogenic therapy for patients with malignant glioma

Glioblastoma (GBM) is the most common primary brain tumor occurring in America. Despite recent advances in therapeutics, the prognosis for patients with newly diagnosed GBM remains dismal. As these tumors characteristically show evidence of angiogenesis (neovascularization) there has been great interest in developing anti-angiogenic therapeutic strategies for the treatment of patients with this disease and some anti-angiogenic agents have now been used for the treatment of patients with malignant glioma tumors. Although the results of these clinical trials are promising in that they indicate an initial therapeutic response, the anti-angiogenic therapies tested to date have not changed the overall survival of patients with malignant glioma tumors. This is due, in large part, to the development of resistance to these therapies. Ongoing research into key features of the neovasculature in malignant glioma tumors, as well as the general angiogenesis process, is suggesting additional molecules that may be targeted and an improved response when both the neovasculature and the tumor cells are targeted. Prevention of the development of resistance may require the development of anti-angiogenic strategies that induce apoptosis or cell death of the neovasculature, as well as an improved understanding of the potential roles of circulating endothelial progenitor cells and vascular co-option by tumor cells, in the development of resistance.

Seizures in patients with low-grade gliomas--incidence, pathogenesis, surgical management, and pharmacotherapy

Seizures complicate the clinical course of > 80% of patients with low-grade gliomas. Patients with some tumor variants almost always have epilepsy. Diffuse low-grade gliomas (LGG) are believed to cause epilepsy through partial deafferentiation of nearby brain cortex (denervation hypersensitivity). Glioneural tumors may interfere with local neurotransmitter levels and are sometimes associated with structural abnormalities of the brain which may produce seizures. The severity of tumor associated epilepsy varies considerably between patients. Some cases may present with a first seizure. Others suffer from long-standing pharmacoresistant epilepsy. Seizure control rates of > 70-80% can be expected after complete tumor resections. Patients with drug-resistant epilepsy require a comprehensive preoperative epileptological work-up which may include the placement of subdural (and intraparenchymal) electrodes or intraoperative electrocorticography (ECoG) for the delineation of extratumoral seizure foci. Partial and subtotal tumor resections are helpful in selected cases, i.e. for gliomas involving the insula. In one series, 40% of patients presented for surgery with uncontrolled seizures, i.e. medical therapy alone often fails to control tumor-related epilepsy. Use of the newer (second generation) non-enzyme inducing antiepileptic drugs (non-EIAED) is encouraged since they seem to have lesser interactions with other medications (e.g. chemotherapy). Chemotherapy and irradiation may have some minor beneficial effects on the patients' seizure disorder. Overall 60-70% of patients may experience recurrent epilepsy during long-term follow-up. Recurrent seizures (not infrequently heralding tumor recurrence) after surgery continue to pose significant clinical problems.

Circumventing tumor resistance to chemotherapy by nanotechnology

Patient relapse and metastasis of malignant cells is very common after standard cancer treatment with surgery, radiation, and/or chemotherapy. Chemotherapy, a cornerstone in the development of present day cancer therapy, is one of the most effective and potent strategies to treat malignant tumors. However, the resistance of cancer cells to the drugs remains a significant impediment to successful chemotherapy. An additional obstacle is the inability of chemotherapeutic drugs to selectively target tumor cells. Almost all the anticancer agents have severe side effects on normal tissues and organs. The toxicity of currently available anticancer drugs and the inefficiency of chemotherapeutic treatments, especially for advanced stages of the disease, have limited the optimization of clinical drug combinations and effective chemotherapeutic protocols. Nanomedicine allows the release of drugs by biodegradation and self-regulation of nanomaterials in vitro and in vivo. Nanotechnologies are characterized by effective drug encapsulation, controllable self-assembly, specificity and biocompatibility as a result of their own material properties. Nanotechnology has the potential to overcome current chemotherapeutic barriers in cancer treatment, because of the unique nanoscale size and distinctive bioeffects of nanomaterials. Nanotechnology may help to solve the problems associated with traditional chemotherapy and multidrug resistance.

Immunotherapy of pediatric brain tumor patients should include an immunoprevention strategy: a medical hypothesis paper

Adults diagnosed with Glioblastoma multiforme (GBM) are frequently faced with a 7% chance of surviving 2 years compared with pediatric patients with GBM who have a 26% survival rate. Our recent screen of possible glioma-associated antigen precursor protein (TAPP) profiles displayed from different types of pediatric brain tumors showed that pediatric patients contained a subset of the tumor antigens displayed by adult GBM patients. Adult GBM possess at least 27 tumor antigens that can potentially stimulate T cell immune responses, suggesting that these tumors are quite antigenic. In contrast, pediatric brain tumors only expressed nine tumor antigens with mRNA levels that were equivalent to those displayed by adult GBM. These tumor-associated antigens could be used as possible targets of therapeutic immunization for pediatric brain cancer patients. Children have developing immune systems that peak at puberty. An immune response mounted by these pediatric patients might account for their extended life spans, even though the pediatric brain tumors express far fewer total tumor-associated antigens. Here we present a hypothesis that pediatric brain tumor patients might be the best patients to show that immunotherapy can be used to successfully treat established cancers. We speculate that immunotherapy should include a panel of tumor antigens that might prevent the out-growth of more malignant tumor cells and thereby prevent the brain tumor relapse. Thus, pediatric brain tumor patients might provide an opportunity to prove the concept of immunoprevention.

Expression of multidrug resistance markers ABCB1 (MDR-1/P-gp) and ABCC1 (MRP-1) in renal cell carcinoma

Background

Renal cell carcinoma patients respond poorly to conventional chemotherapy, this unresponsiveness may be attributable to multidrug resistance (MDR). The mechanisms of MDR in renal cancer are not fully understood and the specific contribution of ABC transporter proteins which have been implicated in the chemoresistance of various cancers has not been fully defined in this disease.

Methods

In this retrospective study the expression of two of these transporter efflux pumps, namely MDR-1 P-gp (ABCB1) and MRP-1 (ABCC1) were studied by immunohistochemistry in archival material from 95 renal cell carcinoma patients.

Results

In the first study investigating MDR-1 P-gp and MRP-1 protein expression patterns in renal cell carcinoma patients, high levels of expression of both efflux pumps are observed with 100% of tumours studied showing MDR-1 P-gp and MRP-1 positivity.

Conclusion

Although these findings do not prove a causal role, the high frequency of tumours expressing these efflux pumps suggests that they may be important contributors to the chemoresistance of this tumour type.

Levetiracetam decreases the seizure activity and blood-brain barrier permeability in pentylenetetrazole-kindled rats with cortical dysplasia

This study investigates the effects of levetiracetam (LEV) on the functional and structural properties of blood-brain barrier (BBB) in pentylenetetrazole (PTZ)-kindled rats with cortical dysplasia (CD). Pregnant rats were exposed to 145 cGy of gamma-irradiation on embryonic day 17. In offsprings, kindling was induced by giving subconvulsive doses of PTZ three times per week for 45 days. While all kindled rats with CD died during epileptic seizures evoked by the administration of a convulsive dose of PTZ in 15 to 25 min, one week LEV (80 mg/kg) pretreatment decreased the mortality to 38% in the same setting. LEV caused a remarkable decrease (p<0.01) in extravasation of sodium fluorescein dye into the brain tissue of kindled animals with CD treated with convulsive dose of PTZ. Occludin immunoreactivity and expression remained essentially unchanged in all groups. Immunoreactivity for glial fibrillary acidic protein (GFAP) was observed to be slightly increased by acute convulsive challenge in kindled rats with CD while LEV pretreatment led to GFAP immunoreactivity comparable to that of controls. An increased c-fos immunoreactivity in kindled rats with CD exposed to convulsive PTZ challenge was also observed with LEV pretreatment. Tight junctions were ultrastructurally intact, whereas LEV decreased the increased pinocytotic activity in brain endothelium of kindled rats with CD treated with convulsive dose of PTZ. The present study showed that LEV decreased the increased BBB permeability considerably by diminishing vesicular transport in epileptic seizures induced by convulsive PTZ challenge in kindled animals with CD.

Drug interactions at the blood-brain barrier: fact or fantasy?

There is considerable interest in the therapeutic and adverse outcomes of drug interactions at the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB). These include altered efficacy of drugs used in the treatment of CNS disorders, such as AIDS dementia and malignant tumors, and enhanced neurotoxicity of drugs that normally penetrate poorly into the brain. BBB- and BCSFB-mediated interactions are possible because these interfaces are not only passive anatomical barriers, but are also dynamic in that they express a variety of influx and efflux transporters and drug metabolizing enzymes. Based on studies in rodents, it has been widely postulated that efflux transporters play an important role at the human BBB in terms of drug delivery. Furthermore, it is assumed that chemical inhibition of transporters or their genetic ablation in rodents is predictive of the magnitude of interaction to be expected at the human BBB. However, studies in humans challenge this well-established paradigm and claim that such drug interactions will be lesser in magnitude but yet may be clinically significant. This review focuses on current known mechanisms of drug interactions at the blood-brain and blood-CSF barriers and the potential impact of such interactions in humans. We also explore whether such drug interactions can be predicted from preclinical studies. Defining the mechanisms and the impact of drug-drug interactions at the BBB is important for improving efficacy of drugs used in the treatment of CNS disorders while minimizing their toxicity as well as minimizing neurotoxicity of non-CNS drugs.

Up-regulation of epithelial membrane protein-1 in the temporal neocortex of patients with intractable epilepsy

Epithelial membrane protein-1 (EMP-1), called Tumor-associated membrane protein, is the marker of a drug-resistant tumor and take part in the drug-resistant mechanism of tumor, with the relationship of epidermal growth factor receptor (EGFR). Because there are some similarities between the pathogenesis and the drug resistance mechanism of tumor and the drug resistance mechanisms in epilepsy. EMP1 expression may be connected with the drug-resistance mechanism of epilepsy. We detected EMP-1 by gene scanning and immunohistochemistry staining, comparing the IE group and the control group, and we investigated the relationship between EMP-1 and EGFR by double-label immunofluorescence staining in the IE group. We found expression of EMP-1 mRNA was higher in IE per the gene scanning, EMP-1 immunoreactivity was apparent in neurons of IE patients but not in the control group, and the expression of EMP-1 and EGFR occurred in the same neuron. We confirm EMP-1 is abnormally expressed in IE and suggest the interaction of EGFR and EMP-1 plays a role in the mechanism of drug resistance in epilepsy and may be a new gene for drug resistance.

Naringenin enhances the anti-tumor effect of doxorubicin through selectively inhibiting the activity of multidrug resistance-associated proteins but not P-glycoprotein

PURPOSE

Naringenin has shown paradoxical results to modulate the function of multidrug resistance-associated proteins (MRPs). The aim of this study is to interpret whether naringenin can reverse intrinsic and/or acquired resistance of cancer cells to chemotherapeutic agents.

METHODS

The effects of naringenin on the uptake, retention and cytotoxicity of doxorubicin were investigated in A549, MCF-7, HepG2 and MCF-7/DOX cells. Cellular efflux pathways modulated by naringenin were assessed with their specific substrates and inhibitors. The improved antitumor activity of doxorubicin in combination with naringenin was also investigated in vivo.

RESULTS

The IC(50) values of doxorubicin in combination with naringenin in A549 and MCF-7 cells were approximately 2-fold lower than that of doxorubicin alone. The increased sensitivity to doxorubicin by naringenin in HepG2 and MCF-7/DOX cells was not observed. Naringenin increased the cellular doxorubicin accumulation through inhibiting doxorubicin efflux in the cells expressing MRPs but not P-gp. In contrast to doxorubicin alone, doxorubicin in combination with naringenin enhanced antitumor activity in vivo with low systemic toxicity.

CONCLUSION

Naringenin enhances antitumor effect of doxorubicin by selective modulating drug efflux pathways. Naringenin will be a useful adjunct to improve the effectiveness of chemotherapeutic agents in treatment of human cancers.

Pharmacotherapy for adults with tumors of the central nervous system

Tumors of the adult central nervous system are among the most common and most chemoresistant neoplasms. Malignant tumors of the brain and spinal cord collectively account for approximately 1.3% of all cancers and 2.2% of all cancer-related deaths. Novel pharmacological approaches to nervous system tumors are urgently needed. This review presents the current approaches and challenges to successful pharmacotherapy of adults with malignant tumors of the central nervous system and discusses novel approaches aimed at overcoming these challenges.

Drug delivery to brain tumors

A prerequisite for the efficacy of any cancer drug is that it reaches the tumor in therapeutic concentrations. This is difficult to accomplish in most systemic solid tumors because of factors such as variable hypoxia, intratumoral pressure gradients, and abnormal vasculature within the tumors. In brain cancer, the situation is complicated by the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier, which serve as physical and physiologic obstacles for delivery of drugs to the central nervous system. Many approaches to overcome, circumvent, disrupt, or manipulate the BBB to enhance delivery of drugs to brain tumors have been devised and are in active investigation. These approaches include high-dose intravenous chemotherapy, intra-arterial drug delivery, local drug delivery via implanted polymers or catheters, BBB disruption, and biochemical modulation of drugs.

One of the hottest topics in epileptology: ABC proteins. Their inhibition may be the future for patients with intractable seizures

One of the new topics in epileptology is the ABC proteins, which seem to control whether or not anti-epileptic drugs (AEDs) can come in contact with and affect the epileptogenic areas that cause seizures. The goal of this report is to simplify the concepts involved in these proteins and then to review the progress made in the field, especially of one protein called P-glycoprotein (P-gp). First, the ABC proteins are reviewed, mainly P-gp, which appears to alter drug permeability (like an extra blood-brain barrier). The possibility is discussed that changes in P-gp are the result of many seizures; are caused by the AEDs, or truly reflect pharmacoresistance. The different locations where these changes can be seen include the endothelial cells, glia and also neurons. The polymorphism of P-gp, called C3435T, probably has little functional significance and finally the importance of inhibitors of P-g to reverse pharmacoresistance is emphasized. Tariquidar (XR9576) is likely to be a good candidate that appears to inhibit these proteins and therefore to allow the AEDs to control the intractable seizures that may account for nearly 40% of our patients.

Comparison between cells and cancer stem-like cells isolated from glioblastoma and astrocytoma on expression of anti-apoptotic and multidrug resistance-associated protein genes

This study is to explore and compare the features of the cells and cancer stem-like cells (CSCs) isolated from both glioblastoma and astrocytoma on expression of anti-apoptotic and multidrug resistance-associated protein (MRP) genes. As a result, the mRNA expression of livin, livinalpha and MRP1 was up-regulated in human CSCs from 2 times to 85 times, but the gene expression of MRP3 was down-regulated from 0.09 times to 0.5 times. After just differentiation the mRNA expression of livin, livinalpha and MRP3 was up-regulated from 9 times to 64 times, but the mRNA expression of MRP1 was down-regulated from 0.01 times to 0.03 times. It is a rare report that glioma stem-like cells can be induced successfully from a grade 2-3 astrocytoma tissue. The properties of glioblastoma and astrocytoma stem-like cells on anti-apoptotic and MRP genes are: anti-apoptotic gene livin and survivin are elevated in CSCs but are the most increased in just differentiated CSCs; MRP1 gene is significantly increased and MRP3 is decreased in CSCs, but when differentiating the MRP3 gene starts a remarkable increase in CSCs; the expression of anti-apoptotic and MRP genes shows no differences between the CSCs isolated from glioblastoma and astrocytoma tissues.

Chemoresistance in gliomas

Despite improved knowledge and advanced treatments of gliomas, the overall survival rate for glioma patients remains low. Gliomas comprise of significant cell heterogeneity that contains a large number of multidrug resistant (MDR) phenotypes and cancer stem cells (CSCs), a combination that may contribute to the resistance to treatment. This article reviews the MDR related genes, major-vault protein (MVP), anti-apoptotic protein (Bcl-2) and the molecular mechanisms that may contribute to chemoresistance, in addition to the upregulated MDR phenotypes present in CSCs that has recently been identified in gliomas. Moreover, future potential therapies that modulate MDR phenotypes and CSCs are also reviewed. An improved understanding of MDR may lead to a combined treatment, targeting both CSCs and their protective MDR phenotypes leading eventually to attractive strategies for the treatment of gliomas.

The role of membrane transporters in drug delivery to brain tumors

Most brain tumors are highly resistant to chemotherapy because many chemotherapeutic drugs poorly cross the blood-brain barrier, the blood-cerebrospinal-fluid barrier, and the plasma membrane of the tumor cells. This restricted drug delivery is largely due to the presence of integral plasma membrane proteins belonging to the solute carriers (SLCs) and to the ATP-binding cassette (ABC) superfamily of transporters that decisively determine substance uptake and efflux, respectively, by the barrier-forming cells and the tumor cells. This review focuses on the localization and function of drug-transporting members of both transporter groups in human brain.

Epilepsy in patients with brain tumours: epidemiology, mechanisms, and management

Epilepsy is common in patients with brain tumours and can substantially affect daily life, even if the tumour is under control. Several factors affect the mechanism of seizures in brain tumours, including tumour type, tumour location, and peritumoral and genetic changes. Prophylactic use of antiepileptic drugs is not recommended, and potential interactions between antiepileptic and chemotherapeutic agents persuades against the use of enzyme-inducing antiepileptic drugs. Multidrug-resistance proteins prevent the access of antiepileptic drugs into brain parenchyma, which partly explains why seizures are frequently refractory to treatment. Lamotrigine, valproic acid, and topiramate are first-line treatments of choice; if insufficient, add-on treatment with levetiracetam or gabapentin can be recommended. On the basis of clinical studies, we prefer to start treatment with valproic acid, adding levetiracetam if necessary. Risks of cognitive side-effects with antiepileptic drugs can add to previous damage by surgery or radiotherapy, and therefore appropriate choice and dose of antiepileptic drug is crucial.

Drug distribution in tumors: Mechanisms, role in drug resistance, and methods for modification

Distribution of antineoplastic agents within tumors remains one of the major challenges in cancer chemotherapy because distribution is hampered by several factors related to the drug (its physicochemical characteristics) and to the neoplastic tissue (blood and lymphatic vasculature, cell density, extracellular matrix composition, and interstitium). The inhomogeneous distribution and structure of tumor vasculature lead to large avascular and hypoxic areas with low pH and high interstitial oncotic pressure. In these critical conditions, the gradient of drug concentrations from the vessels to the inner parts of the tumor is not sufficient to promote diffusion of pharmacologic agents. Again, cellular sequestration and binding to extracellular matrix represent further factors that limit drug distribution and reduce tumor sensitivity to chemotherapy. Several strategies have been investigated to circumvent drug resistance. The evaluation of liposomal and nanoparticle formulations and the characterization of newer bioreductive agents and drugs that should normalize tumor vasculature are in progress.

Quantitative PCR analysis of the expression profile of genes related to multiple drug resistance in tumors of the central nervous system

OBJECTIVES

To evaluate and compare the profile of expression of genes related to drug resistance in brain tumors and to analyze the impact of the increased expression of these genes on overall survival.

METHODS

Eighty microdissected brain tumor samples from 79 patients were analyzed by RQ-PCR for the genes MDR1, MRP1, MRP3, LRP and BCRP. Protein expression was assessed by immunohistochemistry for MRP1 and LRP genes. Pediatric cases (0 to 20 years): 46 (17F:29M, median age 7.3 +/- 5.9 years); adult tumors: 33 (17F:16M, median age 46.6 +/- 14.5 years). Histological diagnoses: 21 astrocytomas I and II, 28 astrocytomas III and glioblastomas, 17 medulloblastomas, 8 ependymomas, and 6 oligodendrogliomas.

RESULTS

glial tumors expressed higher MDR1 (P = 0.003) and BCRP (P = 0.03) levels than embryonic tumors. Low-grade astrocytomas expressed high MDR1 (P = 0.001), MRP3 (P = 0.01) and LRP (P = 0.02) levels. The MRP1 gene was preferentially expressed by medulloblastomas (P = 0.04) and ependymomas (P = 0.04); ependymomas also presented an increase of LRP (P = 0.02). The mRNA levels of MRP1 and LRP genes were associated to protein expression. The profile of gene expression of primary pilocytic astrocytomas of the hypothalamus and of the other locations was similar. Increased expression of resistance genes, separately or jointly, was not correlated with shorter overall survival in patients with medulloblastomas/PNET and malignant gliomas.

CONCLUSIONS

Drug resistance genes do not explain the higher sensitivity of gliomas of the hypothalamus/pituitary/optic pathways to chemotherapy. The increased expression of resistance genes had no impact on the overall survival of patients with medulloblastomas/PNET and high grade gliomas. High MDR1, MRP3 and LRP levels may be implicated in the primary resistance of pilocytic astrocytomas to chemotherapy.

Expression of glutathione S-transferase pi and glutathione synthase correlates with survival in early stage non-small cell carcinomas of the lung

The glutathione S-transferase (GST) family of genes encode for detoxification enzymes that protect against reactive oxygen species and influence host susceptibility to carcinogens, including tobacco smoke. It has not been determined whether isoenzyme GST-pi or glutathione synthase (GSH2) expression by tumor cells bears a relationship to survival. A total of 201 non-small cell lung cancers (NSCLC) with long-term follow-up were immunostained with antibodies to GST-pi and GSH2 using standard immunostaining techniques. Results were graded semiquantitatively using a scale of 0 to 3 (0 < or = 10%; 1 = 10%-50%; 2 = 51%-80%; 3 > or = 80%) for both nuclear and cytoplasmic staining. Results were correlated with patient survival using Kaplan-Meier analysis. Nuclear staining with GST-pi in greater than 10% of the cells was closely associated with decreased survival (P = .02) in stage I and II squamous cell carcinomas (n = 40). Cytoplasmic staining showed a similar trend that did not reach statistical significance. No significant correlation between GST-pi staining and survival was determined for other histologic types of NSCLC. Cytoplasmic GSH2 staining in greater than 80% of tumor cells was associated with a trend toward improved survival for stage I adenocarcinoma (P = .08) but did not show a relationship to survival for other histologic types of NSCLC. GST-pi expression predicts prognosis in stage I and II squamous cell lung carcinoma, and GSH2 expression may indicate better survival in early stage adenocarcinoma of the lung. Manipulation of GST-pi and GSH2 may be a potential basis for treatment of some NSCLC.

Glioblastoma-derived tumorospheres identify a population of tumor stem-like cells with angiogenic potential and enhanced multidrug resistance phenotype

We investigated in vitro the properties of selected populations of cancer stem-like cells defined as tumorospheres that were obtained from human glioblastoma. We also assessed their potential and capability of differentiating into mature cells of the central nervous system. In vivo, their tumorigenicity was confirmed after transplantation into the brain of non-obese diabetic/severe combined immunodeficient (NOD-SCID) mice. The angiogenic potential of tumorospheres and glioblastoma-derived cells grown as adherent cells was revealed by evaluating the release of angiogenic factors such as vascular endothelial growth factor and CXCL12 by ELISA, as well as by rat aortic ring assay. The proliferative response of tumorospheres in the presence of CXCL12 was observed for the first time. Multidrug resistance-associated proteins 1 and 3 as well as other molecules conferring multidrug resistance were higher when compared with primary adherent cells derived from the same tumor. Finally, we obtained cells from the tumor developing after grafting that clearly expressed the putative neural stem cell marker CD133 as shown by FACS analysis and also nestin and CXCR4. The cells' positivity for glial fibrillary acidic protein was very low. Moreover these cells preserved their angiogenic potential. We conclude that human glioblastoma could contain tumor cell subsets with angiogenic and chemoresistance properties and that this chemoresistance potential is highly preserved by immature cells whereas the angiogenic potential is, to a higher extent, a property of mature cells. A better understanding of the features of these cell subsets may favor the development of more specifically targeted therapies.

Membrane transporter proteins: a challenge for CNS drug development

Drug transporters are membrane proteins present in various tissues such as the lymphocytes, intestine, liver, kidney, testis, placenta, and central nervous system. These transporters play a significant role in drug absorption and distribution to organic systems, particularly if the organs are protected by blood-organ barriers, such as the blood-brain barrier or the maternal-fetal barrier. In contrast to neurotransmitters and receptor-coupled transporters or other modes of interneuronal transmission, drug transporters are not directly involved in specific neuronal functions, but provide global protection to the central nervous system. The lack of capillary fenestration, the low pinocytic activity, and the tight junctions between brain capillary and choroid plexus endothelial cells represent further gatekeepers limiting the entrance of endogenous and exogenous compounds into the central nervous system. Drug transport is a result of the concerted action of efflux and influx pumps (transporters) located both in the basolateral and apical membranes of brain capillary and choroid plexus endothelial cells. By regulating efflux and influx of endogenous or exogenous substances, the blood-brain barrier and, to a lesser extent, the blood-cerebrospinal barrier in the ventricles, represents the main interface between the central nervous system and the blood, ie, the rest of the body. As drug distribution to organs is dependent on the affinity of a substrate for a specific transport system, membrane transporter proteins are increasingly recognized as a key determinant of drug disposition. Many drug transporters are members of the adenosine triphosphate (ATP)-binding cassette (ABC) transporter superfamily or the solute-linked carrier (SLC) class. The multidrug resistance protein MDR1 (ABCB1), also called P-glycoprotein, the multidrug resistance-associated proteins MRP1 (ABCC1) and MRP2 (ABCC2), and the breast cancer-resistance protein BCRP (ABCG2) are ATP-dependent efflux transporters expressed in the blood-brain barrier. They belong to the superfamily of ABC transporters, which export drugs from the intracellular to the extracellular milieu. Members of the SLC class of solute carriers include, for example, organic ion transporting peptides, organic cation transporters, and organic ion transporters. They are ATP-independent polypeptides principally expressed at the basolateral membrane of brain capillary and choroid plexus endothelial cells that also mediate drug transport through central nervous system barriers.

Genetic alterations associated with acquired temozolomide resistance in SNB-19, a human glioma cell line

Gliomas are highly lethal neoplasms that cannot be cured by currently available therapies. Temozolomide is a recently introduced alkylating agent that has yielded a significant benefit in the treatment of high-grade gliomas. However, either de novo or acquired chemoresistance occurs frequently and has been attributed to increased levels of O6-methylguanine-DNA methyltransferase or to the loss of mismatch repair capacity. However, very few gliomas overexpress O6-methylguanine-DNA methyltransferase or are mismatch repair-deficient, suggesting that other mechanisms may be involved in the resistance to temozolomide. The purpose of the present study was to generate temozolomide-resistant variants from a human glioma cell line (SNB-19) and to use large-scale genomic and transcriptional analyses to study the molecular basis of acquired temozolomide resistance. Two independently obtained temozolomide-resistant variants exhibited no cross-resistance to other alkylating agents [1,3-bis(2-chloroethyl)-1-nitrosourea and carboplatin] and shared genetic alterations, such as loss of a 2p region and loss of amplification of chromosome 4 and 16q regions. The karyotypic alterations were compatible with clonal selection of preexistent resistant cells in the parental SNB-19 cell line. Microarray analysis showed that 78 out of 17,000 genes were differentially expressed between parental cells and both temozolomide-resistant variants. None are implicated in known resistance mechanisms, such as DNA repair, whereas interestingly, several genes involved in differentiation were down-regulated. The data suggest that the acquisition of resistance to temozolomide in this model resulted from the selection of less differentiated preexistent resistant cells in the parental tumor.

The molecular mechanism of resistance to methotrexate in mouse methotrexate-resistant cells by cancer drug resistance and metabolism SuperArray

Drug resistance is often a limiting factor in successful chemotherapy. Understanding of the molecular mechanism of resistance to methotrexate is important for optimal use as well as for the development of new drugs. Using standard cytogenetic techniques, double minutes (DMs) were detected in mouse methotrexate-resistant cell lines inducted in vitro in this study. Moreover, functional SuperArray, determining the regulation of gene expression corresponding to 96 genes involved in the metabolism of and the development of resistance to cancer drugs was used to study in detail the molecular mechanism of resistance to methotrexate. Significant higher expressions of many genes especially dhfr, mrp5, atm and p53 were detected in methotrexate-resistant cells than in normal mouse cells by SuperArray analysis and corresponding excessive expressions of DHFR, MRP5, ATM, and P53 proteins in methotrexate-resistant cells were also confirmed by Western blot analysis. The results in this study indicated that DHFR, MRP5, ATM, and P53 could play important roles in resistance to methotrexate and some of them would be new potential drug targets.

Multidrug Resistance-Associated Proteins: Expression and Function in the Central Nervous System

Drug delivery to the brain is highly restricted, since compounds must cross a series of structural and metabolic barriers to reach their final destination, often a cellular compartment such as neurons, microglia, or astrocytes. The primary barriers to the central nervous system are the blood-brain and blood-cerebrospinal fluid barriers. Through structural modifications, including the presence of tight junctions that greatly limit paracellular transport, the cells that make up these barriers restrict diffusion of many pharmaceutically active compounds. In addition, the cells that comprise the blood-brain and blood-cerebrospinal fluid barriers express multiple ATP-dependent, membrane-bound, efflux transporters, such as members of the multidrug resistance-associated protein (MRP) family, which contribute to lowered drug accumulation. A relatively new concept in brain drug distribution just beginning to be explored is the possibility that cellular components of the brain parenchyma could act as a "second" barrier to brain permeation of pharmacological agents via expression of many of the same transporters. Indeed, efflux transporters expressed in brain parenchyma may facilitate the overall export of xenobiotics from the central nervous system, essentially handing them off to the barrier tissues. We propose that these primary and secondary barriers work in tandem to limit overall accumulation and distribution of xenobiotics in the central nervous system. The present review summarizes recent knowledge in this area and emphasizes the clinical significance of MRP transporter expression in a variety of neurological disorders.