Calcium-activated potassium channels mediated blood-brain tumor barrier opening in a rat metastatic brain tumor model
© Hu et al; licensee BioMed Central Ltd. 2007
Received: 31 January 2007
Accepted: 14 March 2007
Published: 14 March 2007
The blood-brain tumor barrier (BTB) impedes the delivery of therapeutic agents to brain tumors. While adequate delivery of drugs occurs in systemic tumors, the BTB limits delivery of anti-tumor agents into brain metastases.
In this study, we examined the function and regulation of calcium-activated potassium (KCa) channels in a rat metastatic brain tumor model. We showed that intravenous infusion of NS1619, a KCa channel agonist, and bradykinin selectively enhanced BTB permeability in brain tumors, but not in normal brain. Iberiotoxin, a KCa channel antagonist, significantly attenuated NS1619-induced BTB permeability increase. We found KCa channels and bradykinin type 2 receptors (B2R) expressed in cultured human metastatic brain tumor cells (CRL-5904, non-small cell lung cancer, metastasized to brain), human brain microvessel endothelial cells (HBMEC) and human lung cancer brain metastasis tissues. Potentiometric assays demonstrated the activity of KCa channels in metastatic brain tumor cells and HBMEC. Furthermore, we detected higher expression of KCa channels in the metastatic brain tumor tissue and tumor capillary endothelia as compared to normal brain tissue. Co-culture of metastatic brain tumor cells and brain microvessel endothelial cells showed an upregulation of KCa channels, which may contribute to the overexpression of KCa channels in tumor microvessels and selectivity of BTB opening.
These findings suggest that KCa channels in metastatic brain tumors may serve as an effective target for biochemical modulation of BTB permeability to enhance selective delivery of chemotherapeutic drugs to metastatic brain tumors.
The blood-brain barrier (BBB), formed by the capillary endothelial cells surrounded by astrocytes, protects the brain, but it also poses an obstacle for the delivery of therapeutic molecules into the brain. Microvessels supplying brain tumors retain some characteristics of the BBB and form a blood-brain tumor barrier (BTB). While adequate delivery of chemotherapeutic drugs has been achieved in systemic tumors, the BTB limits such delivery to brain metastases. Therefore, understanding the biochemical modulation of BBB and BTB is critical for developing strategies to deliver therapeutic agents into metastatic brain tumors.
During the past decade, various strategies have been used to deliver therapeutic drugs selectively to brain tumors and injured brain, including, biodegradable polymers implanted into the tumor cavity , convection-enhanced delivery [2, 3], and BBB/BTB disruption [4, 5]. Our laboratory has focused on pharmacologic modulations to increase BTB permeability and increase delivery of therapeutic drugs selectively to brain tumors with little or no drug delivery to normal brain tissue [6–9]. This strategy exploits the function of certain vasomodulators that play a key role in modulation of BBB/BTB permeability. It has been demonstrated that bradykinin , leukotriene (LTC4) [11–13], nitric oxide (NO) , c-GMP , and potassium channel agonists [15, 16] can selectively increase capillary permeability in primary brain tumors, while leaving normal brain unaffected. These findings have already been translated into clinical studies to increase drug delivery selectively to tumor tissue in brain tumor patients [7, 17–19]. Modulation of critical molecules involved in selectively increasing BTB permeability could lead to the development of effective strategy to increase chemotherapy delivery to brain tumors.
Large conductance calcium-activated potassium (KCa) channels are a unique class of ion channel coupling intracellular chemical and electrical signaling. These channels give rise to outwardly rectifying potassium currents and respond not only to changes in membrane voltage, but also to changes in intracellular calcium. Recent studies suggest that KCa channel expression levels correlate positively with the malignancy grade of glioma . KCa channels are also present in cerebral blood vessels, where they regulate cerebral blood vessel tone  and, probably, BBB/BTB permeability [15, 22]. Evidence from several studies further indicate that KCa channels play an important role in vasodilation when it is mediated by bradykinin [23, 24], NO donors , and cyclic GMP . In response to the binding of bradykinin to its type 2 receptors (B2R), intracellular Ca2+ is increased either by mobilization of Ca2+ from internal sites and influx  or by NO production from NO synthase activation . The increase in intracellular Ca2+ level activates KCa channels and alters the membrane potential of cells . Furthermore, previous studies have also shown that bradykinin-induced KCa channel activation in endothelial cells is potentiated by NS1619, a selective KCa channel agonist , and attenuated by a highly selective inhibitor, iberiotoxin (IBTX) [29–31]. We previously demonstrated that KCa channels are overexpressed in primary brain tumors and tumor microvessels, and such channels respond to NS1619, which selectively increases BTB permeability. The accelerated formation of pinocytotic vesicles appears to be the cellular mechanism by which KCa channels mediate increases in BTB permeability . Moreover, in a rat brain tumor model, we showed that the B2R expression level on brain tumors directly correlates with bradykinin-induced BTB permeability increases . Co-infusion of carboplatin with either NS1619 or a bradykinin analog, RMP-7, led to enhanced survival in intracranial tumor-bearing rats and brain tumor patients [17–19, 22, 33]. These data indicate that KCa channels serve as a convergence point in the modulation of BTB permeability in primary brain tumors.
Brain metastasis is a frequent complication in patients suffering from lung and breast cancer, and a significant cause of morbidity and mortality. Brain metastases are found in approximately 10% of lung cancer patients at the time of diagnosis, and up to 40% of all patients develop brain metastases during the course of their disease . The prognosis of brain metastases from lung cancer is poor, with median survival of 4~5 month. Lung cancer cells that spread to the brain are generally sensitive to chemotherapeutic drug compared with primary brain tumor cells. The BTB, however, prevents the delivery of non-lipid-permeable chemotherapeutic drugs and monoclonal antibodies in sufficient amounts to achieve a therapeutic benefit , especially in early stage of brain metastases. Although metastatic brain tumors have ten times more than the incidence of primary brain tumors in the United States, the role and regulation of KCa channels in metastatic brain tumors to selectively open BTB have not been elucidated. As new therapeutic agents are developed which effectively treat primary tumors, an efficient delivery of these agents selectively to metastatic brain tumors across the BTB will significantly improve treatment efficacy. Here, we studied the role of KCa channel activation in BTB permeability in a metastatic brain tumor model.
KCa channel mediates BTB permeability increase in a CRL-5904 metastatic brain tumor model
Expression of KCa channels and B2R in CRL-5904 cells, HBMEC and human tumor tissue of lung cancer brain metastases
Activity of functional KCa channels in cultured CRL-5904 cells and HBMEC
Co-culture of metastatic brain tumor and endothelial cells increases KCa Channel expression
Immuno-colocalization of KCa channel expression in a CRL5904 metastatic brain tumor animal model and human lung cancer brain metastases tissue
We have studied the presence of KCa channels and B2R in primary brain tumors, however, their occurrence and function in metastatic brain tumors remained to be investigated. In this study, we detected high level expression of KCa channels in CRL-5904 tumor and brain endothelial cells, which is consistent with previous studies showing KCa channels expression in RG2 glioma and endothelial cells . Other investigators have also demonstrated that the expression level of KCa channels correlates with the malignancy grade of glioma in human . Therefore, these data suggest there is an intimate association between KCa channel expression and brain tumor development, which remains to be fully investigated. Additionally, we detected the presence of B2R in CRL-5904 tumor and endothelial cells. Liu et al also showed that B2R are expressed in cultured RG2, C6 and 9L glioma cells, more interestingly, the expression levels of B2R in tumor cells was directly correlated with the increase of BTB permeability induced by bradykinin in a rat glioma model . Thus, the presence of KCachannels or B2R in metastatic brain tumor cells or HBMEC may play a functional role in BTB permeability of metastatic brain tumors.
We examined KCa channel activity on metastatic tumor cells and capillary endothelial cells using a membrane potential assay, which is well-correlated with the patch-clamp method, used to measure changes in membrane potential (FLIPR application note, Molecular devices, CA). We found that NS1619 and bradykinin elicited greater hyperpolarization effects on CRL-5904 than on HBMEC. These findings may reflect a higher level of expression for KCa channels on metastatic tumor cells as compared to endothelial cells. Importantly, the membrane potential change induced by NS1619 lasted 3 times longer than that induced by bradykinin. These data further support the finding, from cellular level, that NS1619-elicited increases in BTB permeability in a glioma model last up to 60 minutes compared to the transient effect of bradykinin, which lasts for about 15~20 minutes , partially due to B2R internalization . The current data illustrates that the presence of KCa channel are functional in metastatic brain tumor and endothelial cells. Similar to our findings, Reiser et al demonstrated that bradykinin can directly activate KCa channels in rat glioma cells . Other studies have shown that bradykinin can activate KCa channels through a NO-cGMP signalling pathway . Hence, our present study indicates that bradykinin-activated downstream signals, such as activation of KCachannels, may be modulated to induce membrane potential changes on brain metastatic tumor and endothelial cells.
The presence of functional KCa channels in metastatic brain tumor and brain endothelial cells suggests that biochemical modulation of KCachannels could play an important role in therapeutic BTB opening. We further investigated whether the KCa channels agonist, NS1619 and bradykinin could selectively enhance BTB permeability in a metastatic brain tumor xenograft model. These results showed that intravenous infusion of NS1619 yielded a two-fold increase the unidirectional transport of a radiotracer into metastatic brain tumors; similar to bradykinin-induced BTB permeability increase in metastatic brain tumor-bearing rats. Our previous studies have demonstrated that higher doses of intravenous bradykinin are required to increase BTB permeability compared to intracarotid infusion of bradykinin, reflecting the influence of the first pass effect with intracarotid delivery . In a glioma model, it has been reported that the effects of bradykinin on BTB permeability mediated by B2R resulted in enhanced drug delivery to glioma ; and this effect could be attenuated by coinfusion with IBTX . In this metastatic brain tumor model, we further demonstrate the presence of B2R and confirm that the bradykinin effect on permeability is mediated via KCa channels. Consistent with previous studies , current data confirms the selective increase of BTB permeability in brain metastatic tumors but not normal brain tissue. These results suggest that biochemical modulation of KCa channel induces a selective BTB opening in metastatic brain tumor.
Confocal images showed KCa channels overexpression in tumor tissue and tumor microvessels as compared with normal brain. More importantly, the tumor capillaries showed co-localization of KCa channels and vWF in tumor area of CRL-5904 tumor and in human metastatic brain tumor tissue. To further study the interaction between tumor and endothelial cells, we co-cultured CRL-5904 metastatic brain tumors and brain endothelial cells. We show that mRNA expression of KCa channels is upregulated in co-cultured cells compared to indivdual cultures. These data suggest that increased KCa channel expression and their activity in tumor endothelial cells maybe due to the tumor micro-environment or cell-to-cell communication between tumor and microvessel endothelial cells. This is consistent with reports that brain tumor cells increase KATP channel expression in endothelial cells.
These findings support a pivotal role for KCa channels in BTB permeability regulation. Recently clinical study showed that trastuzumab, anti-HER2 antibody, while effective in treating tumors outside the brain, fails to treat brain metastases due to its inability to cross the blood brain tumor barrier . Our research has shown that KCachannel-mediated BTB permeability modulation could be a useful strategy to increase therapeutic agents, such as antibody-based therapies, delivery into metastatic brain tumors.
We present evidence that activation of KCa channels by a channel-specific agonist can selectively enhance BTB permeability in a metastatic brain tumor rat model. We show KCa channel and B2R are highly expressed in brain metastatic tumor cells, endothelial cells and lung cancer brain metastatic tissue. The expression level is correlated with KCa channel activity in these cells. In a metastatic brain tumor model, we demonstrate that NS1619 and bradykinin can selectively open BTB and significantly enhance the radiotracer delivery specifically to metastatic brain tumors. It is also demonstrated that KCa channels expression can be upregulated in the co-cultures of tumor cells and endothelial cells, as well as in the microvessel endothelia of brain metastases tissue. KCachannels may be exploited as specific target for selectively pharamacologic modulation of BTB to increase delivery of chemotherapeutic drugs to brain metastases.
CRL-5904 cells (human non-small cell lung cancer; metastatic site: brain poorly differentiated carcinoma) and human brain microvessel endothelial cells (HBMEC) were obtained from the American tissue culture collection (ATCC, VA) and maintained in RPMI 1640 with 10% fetal bovine serum. Both cell lines were maintained in the common tissue culture condition. For co-culture of CRL-5904 cells with HBMEC, the same number of CRL-5904 cells and HBMEC were co-cultured in growth medium and allowed to achieve 90% confluence. Then, the co-culture and single cultures of cells were harvested for protein or RNA extraction.
Membrane Potential Assay
The functional activity of KCa channels in CRL-5904 cells and HBMEC was measured using the FLIPR Membrane Potential Assay Kit on a FLEXstation (Molecular Devices, Sunnyvale, CA) as described previously . This kit provided a fast, simple and consistent mix-and read procedure. In brief, the cells were seeded in sterile, clear bottom, black 96-well plates (Corning Inc., MA) at density of 2 × 103 cells/well to achieve monolayer within 24 h. The monolayer cells were incubated with the membrane potential assay kits reagents for 30 min before loading the compounds. The anionic potentiometric dye that transverses between cells and extracellular solution in a membrane potential-dependent manner serves as an indicator of vasomodulator-induced voltage changes across the cell membrane. Dose response studies were performed with 0 to 50 μM NS1619 or bradykinin with or without IBTX (20 nM). The FLEXstation was set up using the following parameters: excitation 530 nm, emission 565 nm, and emission cut of 550 nm wavelengths. Observations and recordings were made for 300 seconds after adding the compounds. NS1619, bradykinin and IBTX were obtained from Sigma (St. Louis, MO).
In Vivo BBB/BTB Permeability
All of the animals used were conducted in accordance with the Institutional Animal Care and Usage Committee in force at Cedars-Sinai Medical Center. A metastatic brain tumor xenograft model was established using athymic nude rats (180–200 g; Charles River Laboratories, Inc., MA) for BBB/BTB permeability studies. Athymic nude rats were anesthetized with i.p. ketamine and xylazine, and stereotactically implanted with CRL-5904 cells (2 × 105) in 4 μl of 1.2% methylcellulose/PBS using a Hamilton syringe into the right striatum. The Coordinates were 3.4 mm lateral to bregma and 5.0 mm deep from dura. Ten days after tumor implantation, the femoral arteries of rats were cannulated to measure blood pressure and collect blood, and the femoral vein was also cannulated to administer the drugs and radiotracer. Body temperature was maintained at 37°C. Arterial blood gases, blood pressure and hematocrit were monitored. Animals with abnormal physiological parameters were eliminated from this study. In regional permeability studies, either intravenous drug or PBS was infused into the femoral vein at a rate of 66.7 μl/min for 15 minutes. Five minutes after the start of the intravenous infusion, 50 μCi/kg of the radiotracer [14C] sucrose was injected as an intravenous bolus. Arterial blood pressure was monitored throughout the experimental period with a blood pressure monitor (DigiMed, KY). The unilateral transport constant Ki (μl/g/min), which is an initial rate for blood-to-brain transfer of radiotracer, was calculated as described by Ohno et al. The Ki was determined by radiotracer [14C] sucrose in the tumor core, tumor-adjacent brain tissue, and contralateral brain tissue using the quantitative autoradiographic (QAR) method as describe previously . Quantitative analysis of the regional radioactivity was performed using a computer (Power Macintosh 7100) and Image 1.55 software (National Institutes of Health, Bethesda, MD). An optimum dose (120 μg/kg/min, i.v.) of bradykinin established previously was used for Ki measurements. To establish the optimal and safe dose range that would result in selective increase in BTB permeability without appreciably altering system blood pressure, various doses (0~120 μg/kg/min, i.v.) of NS1619 were administered in metastatic brain tumor bearing-nude rats. Additional experiments were performed by coinfusing of NS1619 with IBTX (1.0 μg/kg/min) to investigate whether inhibition of KCa channels by IBTX has any effects on NS1619-induced permeability increase.
Western Blot Analysis
The extracted protein samples were quantified to determine total protein concentrations using a protein assay kit (BioRad, CA). Same amount of each sample was fractionated on 10% SDS-polyacrylamide gel and then transferred to a nitrocellulose membrane. The membrane was probed with primary antibodies anti-MaxiKá (1:200; Santa Cruz Biotechnology, CA) and β-actin (1:5000; Sigma, MO), followed by peroxidase-conjugated secondary antibodies. The signals were detected with an enhanced chemiluminescence kit (Amersham Biosciences Corp., NJ). β-actin served as an internal control.
The extracted RNA was reverse transcripted using a Bioscript kit (Bioline) and Oligo (dT) 12–18 primer (Invitrogene). The resulting cDNA products were used as templates for PCR assay. The genes of the KCa channels were concurrently amplified with internal control β-actin in the same reaction tube as described previously . Sequence specific primers were used for amplification of KCa channels (forward: 5'-tccaaaacaaccaggctctc-3'; reverse: 5'- gggggagatgttgtgaagaa-3') and β-actin (forward: 5'- gcaccacaccttctacaatgagc-3'; reverse: 5'- ttgaaggtagtttcgtggatgcc-3'). PCR products were identified using agarose gel electrophoresis and ethidium bromide staining.
CRL-5904 cells and HBMEC were fixed with 4% paraformoldehyde for 15 min, and then incubated with anti-B2R (1:200; BD Bioscience, NJ) or anti-MaxiKα (1:200; Santa Cruz, CA) antibodies. The signals were detected with FITC-conjugated secondary antibodies (1:200; Jackson ImmnoResearch, CA). The cells were counterstained with 4', 6-diamidino-2-phenylindole (DAPI; Vector Laboratories, CA) and cover-slipped. Paraffin-embedded, metastatic brain tumor samples from lung cancer were deparaffinized and rehydrated. The slides were incubated with primary anti-MaxiKá and anti-B2R antibodies, and followed by biotinylated secondary antibodies (1:1000; Jackson ImmunoResearch, CA). Biotinylated conjugates were detected with avidin-biotin peroxide complex (Vector Laboratories), and then developed with 3, 3'-Diaminobenzidine (DAB) method. The sections were counterstained with hematoxylin. For the double staining, the sections were incubated with primary antibodies, anti-MaxiKá and anti-von Willebrand Factor (1:200; Chemicon, CA), and then subjected to FITC-and Tex-Red-conjugated secondary antibodies. The slides were examined under confocal microscopy. Negative control experiments were performed on all the corresponded specimens by deleting of primary antibodies.
This research was supported by National Institutes of Health grants NS32103, NS25554, RR13707, a Jacob Javits Award (KLB), and an American Cancer Society grant (NSN).
- Guerin C, Olivi A, Weingart JD, Lawson HC, Brem H: Recent advances in brain tumor therapy: local intracerebral drug delivery by polymers. Invest New Drugs. 2004, 22 (1): 27-37. 10.1023/B:DRUG.0000006172.65135.3eView ArticlePubMedGoogle Scholar
- Kunwar S: Convection enhanced delivery of IL13-PE38QQR for treatment of recurrent malignant glioma: presentation of interim findings from ongoing phase 1 studies. Acta Neurochir Suppl. 2003, 88: 105-111.PubMedGoogle Scholar
- Li C, Hall WA, Jin N, Todhunter DA, Panoskaltsis-Mortari A, Vallera DA: Targeting glioblastoma multiforme with an IL-13/diphtheria toxin fusion protein in vitro and in vivo in nude mice. Protein Eng. 2002, 15 (5): 419-427. 10.1093/protein/15.5.419View ArticlePubMedGoogle Scholar
- Bhattacharjee AK, Nagashima T, Kondoh T, Tamaki N: Quantification of early blood-brain barrier disruption by in situ brain perfusion technique. Brain Res Brain Res Protoc. 2001, 8 (2): 126-131. 10.1016/S1385-299X(01)00094-0View ArticlePubMedGoogle Scholar
- Siegal T, Rubinstein R, Bokstein F, Schwartz A, Lossos A, Shalom E, Chisin R, Gomori JM: In vivo assessment of the window of barrier opening after osmotic blood-brain barrier disruption in humans. J Neurosurg. 2000, 92 (4): 599-605.View ArticlePubMedGoogle Scholar
- Black KL, Baba T, Pardridge WM: Enzymatic barrier protects brain capillaries from leukotriene C4. J Neurosurg. 1994, 81 (5): 745-751.View ArticlePubMedGoogle Scholar
- Black KL, Cloughesy T, Huang SC, Gobin YP, Zhou Y, Grous J, Nelson G, Farahani K, Hoh CK, Phelps M: Intracarotid infusion of RMP-7, a bradykinin analog, and transport of gallium-68 ethylenediamine tetraacetic acid into human gliomas. J Neurosurg. 1997, 86 (4): 603-609.View ArticlePubMedGoogle Scholar
- Sugita M, Black KL: Cyclic GMP-specific phosphodiesterase inhibition and intracarotid bradykinin infusion enhances permeability into brain tumors. Cancer Res. 1998, 58 (5): 914-920.PubMedGoogle Scholar
- Matsukado K, Nakano S, Bartus RT, Black KL: Steroids decrease uptake of carboplatin in rat gliomas--uptake improved by intracarotid infusion of bradykinin analog, RMP-7. J Neurooncol. 1997, 34 (2): 131-138. 10.1023/A:1005706329630View ArticlePubMedGoogle Scholar
- Nomura T, Inamura T, Black KL: Intracarotid infusion of bradykinin selectively increases blood-tumor permeability in 9L and C6 brain tumors. Brain Res. 1994, 659 (1-2): 62-66. 10.1016/0006-8993(94)90863-XView ArticlePubMedGoogle Scholar
- Black KL, Hoff JT, McGillicuddy JE, Gebarski SS: Increased leukotriene C4 and vasogenic edema surrounding brain tumors in humans. Ann Neurol. 1986, 19 (6): 592-595. 10.1002/ana.410190613View ArticlePubMedGoogle Scholar
- Black KL, Chio CC: Increased opening of blood-tumour barrier by leukotriene C4 is dependent on size of molecules. Neurol Res. 1992, 14 (5): 402-404.PubMedGoogle Scholar
- Hashizume K, Black KL: Increased endothelial vesicular transport correlates with increased blood-tumor barrier permeability induced by bradykinin and leukotriene C4. J Neuropathol Exp Neurol. 2002, 61 (8): 725-735.PubMedGoogle Scholar
- Nakano S, Matsukado K, Black KL: Increased brain tumor microvessel permeability after intracarotid bradykinin infusion is mediated by nitric oxide. Cancer Res. 1996, 56 (17): 4027-4031.PubMedGoogle Scholar
- Ningaraj NS, Rao M, Hashizume K, Asotra K, Black KL: Regulation of blood-brain tumor barrier permeability by calcium-activated potassium channels. J Pharmacol Exp Ther. 2002, 301 (3): 838-851. 10.1124/jpet.301.3.838View ArticlePubMedGoogle Scholar
- Ningaraj NS, Rao MK, Black KL: Adenosine 5'-triphosphate-sensitive potassium channel-mediated blood-brain tumor barrier permeability increase in a rat brain tumor model. Cancer Res. 2003, 63 (24): 8899-8911.PubMedGoogle Scholar
- Gregor A, Lind M, Newman H, Grant R, Hadley DM, Barton T, Osborn C: Phase II studies of RMP-7 and carboplatin in the treatment of recurrent high grade glioma. RMP-7 European Study Group. J Neurooncol. 1999, 44 (2): 137-145. 10.1023/A:1006379332212View ArticlePubMedGoogle Scholar
- Ford J, Osborn C, Barton T, Bleehen NM: A phase I study of intravenous RMP-7 with carboplatin in patients with progression of malignant glioma. Eur J Cancer. 1998, 34 (11): 1807-1811. 10.1016/S0959-8049(98)00155-5View ArticlePubMedGoogle Scholar
- Prados MD, Schold SJS, Fine HA, Jaeckle K, Hochberg F, Mechtler L, Fetell MR, Phuphanich S, Feun L, Janus TJ, Ford K, Graney W: A randomized, double-blind, placebo-controlled, phase 2 study of RMP-7 in combination with carboplatin administered intravenously for the treatment of recurrent malignant glioma. Neuro-oncol. 2003, 5 (2): 96-103. 10.1215/15228517-5-2-96PubMed CentralPubMedGoogle Scholar
- Liu X, Chang Y, Reinhart PH, Sontheimer H: Cloning and characterization of glioma BK, a novel BK channel isoform highly expressed in human glioma cells. J Neurosci. 2002, 22 (5): 1840-1849.PubMedGoogle Scholar
- Kitazono T, Faraci FM, Taguchi H, Heistad DD: Role of potassium channels in cerebral blood vessels. Stroke. 1995, 26 (9): 1713-1723.View ArticlePubMedGoogle Scholar
- Ningaraj NS, Rao M, Black KL: Calcium-dependent potassium channels as a target protein for modulation of the blood-brain tumor barrier. Drug News Perspect. 2003, 16 (5): 291-298. 10.1358/dnp.2003.16.5.878815View ArticlePubMedGoogle Scholar
- Sobey CG, Heistad DD, Faraci FM: Mechanisms of bradykinin-induced cerebral vasodilatation in rats. Evidence that reactive oxygen species activate K+ channels. Stroke. 1997, 28 (11): 2290-4; discussion 2295.View ArticlePubMedGoogle Scholar
- Berg T, Koteng O: Signalling pathways in bradykinin- and nitric oxide-induced hypotension in the normotensive rat; role of K+-channels. Br J Pharmacol. 1997, 121 (6): 1113-1120. 10.1038/sj.bjp.0701246PubMed CentralView ArticlePubMedGoogle Scholar
- Bolotina VM, Najibi S, Palacino JJ, Pagano PJ, Cohen RA: Nitric oxide directly activates calcium-dependent potassium channels in vascular smooth muscle. Nature. 1994, 368 (6474): 850-853. 10.1038/368850a0View ArticlePubMedGoogle Scholar
- Lohse MJ, Forstermann U, Schmidt HH: Pharmacology of NO:cGMP signal transduction. Naunyn Schmiedebergs Arch Pharmacol. 1998, 358 (1): 111-112. 10.1007/PL00005230View ArticlePubMedGoogle Scholar
- Hall JM: Bradykinin receptors. Gen Pharmacol. 1997, 28 (1): 1-6.View ArticlePubMedGoogle Scholar
- Miura H, Liu Y, Gutterman DD: Human coronary arteriolar dilation to bradykinin depends on membrane hyperpolarization: contribution of nitric oxide and Ca2+-activated K+ channels. Circulation. 1999, 99 (24): 3132-3138.View ArticlePubMedGoogle Scholar
- Faraci FM, Heistad DD: Regulation of the cerebral circulation: role of endothelium and potassium channels. Physiol Rev. 1998, 78 (1): 53-97.PubMedGoogle Scholar
- Ransom CB, Sontheimer H: BK channels in human glioma cells. J Neurophysiol. 2001, 85 (2): 790-803.PubMedGoogle Scholar
- Wanner SG, Koch RO, Koschak A, Trieb M, Garcia ML, Kaczorowski GJ, Knaus HG: High-conductance calcium-activated potassium channels in rat brain: pharmacology, distribution, and subunit composition. Biochemistry. 1999, 38 (17): 5392-5400. 10.1021/bi983040cView ArticlePubMedGoogle Scholar
- Liu Y, Hashizume K, Chen Z, Samoto K, Ningaraj N, Asotra K, Black KL: Correlation between bradykinin-induced blood-tumor barrier permeability and B2 receptor expression in experimental brain tumors. Neurol Res. 2001, 23 (4): 379-387. 10.1179/016164101101198596View ArticlePubMedGoogle Scholar
- Matsukado K, Inamura T, Nakano S, Fukui M, Bartus RT, Black KL: Enhanced tumor uptake of carboplatin and survival in glioma-bearing rats by intracarotid infusion of bradykinin analog, RMP-7. Neurosurgery. 1996, 39 (1): 125-33; discussion 133-4. 10.1097/00006123-199607000-00025View ArticlePubMedGoogle Scholar
- Rizzi A, Tondini M, Rocco G, Rossi G, Robustellini M, Radaelli F, Della Pona C: Lung cancer with a single brain metastasis: therapeutic options. Tumori. 1990, 76 (6): 579-581.PubMedGoogle Scholar
- Doolittle ND, Peereboom DM, Christoforidis GA, Hall WA, Palmieri D, Brock PR, Campbell KC, Dickey DT, Muldoon LL, O'Neill B P, Peterson DR, Pollock B, Soussain C, Smith Q, Tyson RM, Neuwelt EA: Delivery of chemotherapy and antibodies across the blood-brain barrier and the role of chemoprotection, in primary and metastatic brain tumors: report of the eleventh annual blood-brain barrier consortium meeting. J Neurooncol. 2007, 81 (1): 81-91. 10.1007/s11060-006-9209-yView ArticlePubMedGoogle Scholar
- Pizard A, Blaukat A, Muller-Esterl W, Alhenc-Gelas F, Rajerison RM: Bradykinin-induced internalization of the human B2 receptor requires phosphorylation of three serine and two threonine residues at its carboxyl tail. J Biol Chem. 1999, 274 (18): 12738-12747. 10.1074/jbc.274.18.12738View ArticlePubMedGoogle Scholar
- Greiser E, Soehring K: [On the transport of pentobarbital through biological membranes and its influencing by ethanol]. Arzneimittelforschung. 1967, 17 (2): 207-214.PubMedGoogle Scholar
- Zhou XB, Schlossmann J, Hofmann F, Ruth P, Korth M: Regulation of stably expressed and native BK channels from human myometrium by cGMP- and cAMP-dependent protein kinase. Pflugers Arch. 1998, 436 (5): 725-734. 10.1007/s004240050695View ArticlePubMedGoogle Scholar
- Matsukado K, Sugita M, Black KL: Intracarotid low dose bradykinin infusion selectively increases tumor permeability through activation of bradykinin B2 receptors in malignant gliomas. Brain Res. 1998, 792 (1). 10.15.View ArticlePubMedGoogle Scholar
- Ningaraj NS, Rao M, Groysman L, Black KL: Role of Ca2+-dependent and ATP-sensitive potassium channels in blood-brain barrier permeability after transient focal ischemia/reperfusion in rats. Stroke. 2002, 33 (1): 361-Google Scholar
- Okita R, Saeki T, Takashima S, Aogi K, Ohsumi S: Progressive central nervous system metastases in responder patients for outside central nervous system metastases on trastuzumab-based therapy--report of two cases of refractory breast cancer. Hiroshima J Med Sci. 2005, 54 (1): 35-38.PubMedGoogle Scholar
- Ohno K, Pettigrew KD, Rapoport SI: Lower limits of cerebrovascular permeability to nonelectrolytes in the conscious rat. Am J Physiol. 1978, 235 (3): H299-307.PubMedGoogle Scholar
- Sugita M, Hunt GE, Liu Y, Black KL: Nitric oxide and cyclic GMP attenuate sensitivity of the blood-tumor barrier permeability to bradykinin. Neurol Res. 1998, 20 (6): 559-563. 10.1159/000017358PubMedGoogle Scholar
- Yuan X, Curtin J, Xiong Y, Liu G, Waschsmann-Hogiu S, Farkas DL, Black KL, Yu JS: Isolation of cancer stem cells from adult glioblastoma multiforme. Oncogene. 2004, 23 (58): 9392-9400. 10.1038/sj.onc.1208311View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.