minoxidil-sulfate-ester and Brain-Neoplasms

The blood-brain tumor barrier (BTB) significantly limits delivery of effective concentrations of chemotherapeutic drugs to brain tumors. Previous studies suggest that BTB permeability may be modulated via alteration in the activity of potassium channels. In this study, we studied the relationship of BTB permeability increase mediated by potassium channel agonists to channel expression in two rat brain tumor models. Intravenous infusion of KCO912 (K(ATP) agonist), minoxidil sulfate (K(ATP) agonist) or NS1619 (K(Ca) agonist) increased tumor permeability more in the 9L allogeneic brain tumor model than in the syngeneic brain tumor model. Consistently, expression of both K(ATP) and K(Ca) channels in 9L tumors was increased to a significantly greater extent in Wistar rats (allogeneic) as compared to Fischer rats (syngeneic). Furthermore, as a preliminary effort to understand clinical implication of potassium channels in brain tumor treatment, we determined the expression of K(ATP) in surgical specimens. K(ATP) mRNA was detected in glioblastoma multiforme (GBM) from nineteen patients examined, with a wide range of expression levels. Interestingly, in paired GBM tissues from seven patients before and after vaccination therapy, increased levels of K(ATP) were detected in five patients after vaccination that had positive response to chemotherapy after vaccination. The present study indicates that the effects of potassium channel agonists on BTB permeability are different between syngeneic and allogeneic models which have different expression levels of potassium channels. The expression of potassium channels in brain tumors is variable, which may be associated with different tumor permeability to therapeutic agents among patients.

Topics: Animals; Benzimidazoles; Blood-Brain Barrier; Blotting, Western; Brain Neoplasms; Capillary Permeability; Cell Line, Tumor; Female; Glioblastoma; Humans; Immunohistochemistry; Injections, Intravenous; KATP Channels; Microscopy, Confocal; Minoxidil; Neoplasm Transplantation; Neoplasms, Experimental; Potassium Channels, Calcium-Activated; Rats; Rats, Inbred F344; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Species Specificity; Vaccination

Adenosine 5'-triphosphate-sensitive potassium channel (KATP channel) activator, minoxidil sulfate (MS), can selectively increase the permeability of the blood-tumor barrier (BTB); however, the mechanism by which this occurs is still under investigation. Using a rat brain glioma (C6) model, we first examined the expression levels of occludin and claudin-5 at different time points after intracarotid infusion of MS (30 μg/kg/min) by western blotting. Compared to MS treatment for 0 min group, the protein expression levels of occludin and claudin-5 in brain tumor tissue of rats showed no changes within 1 h and began to decrease significantly after 2 h of MS infusion. Based on these findings, we then used an in vitro BTB model and selective inhibitors of diverse signaling pathways to investigate whether reactive oxygen species (ROS)/RhoA/PI3K/PKB pathway play a key role in the process of the increase of BTB permeability induced by MS. The inhibitor of ROS or RhoA or PI3K or PKB significantly attenuated the expression of tight junction (TJ) protein and the increase of the BTB permeability after 2 h of MS treatment. In addition, the significant increases in RhoA activity and PKB phosphorylation after MS administration were observed, which were partly inhibited by N-2-mercaptopropionyl glycine (MPG) or C3 exoenzyme or LY294002 pretreatment. The present study indicates that the activation of signaling cascades involving ROS/RhoA/PI3K/PKB in BTB was required for the increase of BTB permeability induced by MS. Taken together, all of these results suggested that MS might increase BTB permeability in a time-dependent manner by down-regulating TJ protein expression and this effect could be related to ROS/RhoA/PI3K/PKB signal pathway.

Topics: Animals; Blood-Brain Barrier; Brain Neoplasms; Capillary Permeability; Claudins; Dose-Response Relationship, Drug; Electric Impedance; Enzyme Inhibitors; Glioma; Horseradish Peroxidase; In Vitro Techniques; Male; Minoxidil; Neoplasm Transplantation; Phosphatidylinositol 3-Kinases; Rats; Rats, Wistar; Reactive Oxygen Species; rhoA GTP-Binding Protein; Signal Transduction; Vasodilator Agents

This study was performed to determine whether minoxidil sulfate (MS), a selective Adenosine 5'-triphosphate-sensitive potassium channel (K (ATP) channel) activator, has an effect on the expression of caveolin-1 in the rat's brain tumor tissue. Using a rat brain glioma (C6) model, we found that the expression of caveolin-1 protein at tumor sites was greatly increased after intracarotid infusion of MS at a dose of 30 μg/kg/min for 15, 30, and 60 min via Western blot analysis. And the peak value of the caveolin-1 expression was observed in rats with glioma after 15 min of MS perfusion, which was significantly attenuated by reactive oxygen species (ROS) scavenger (N-2-mercaptopropionyl glycine, MPG). In addition, MPG also significantly inhibited the increase of blood-brain tumor barrier (BTB) permeability which was induced by MS. This led to the conclusion that the MS-induced BTB permeability increase may be related to the accelerated formation of caveolin-1 protein, and could be mediated by ROS.

Topics: Animals; Blood-Brain Barrier; Brain Neoplasms; Capillaries; Caveolin 1; Disease Models, Animal; Evans Blue; Glioma; KATP Channels; Minoxidil; Permeability; Rats; Rats, Wistar; Tiopronin; Up-Regulation

Several anticancer drugs are ineffective against brain tumor and do not impact patient survival because they fail to cross the blood-brain tumor barrier (BTB) effective levels. One such agent temozolomide is commonly used in brain tumor patients, which works better when combined with radiation or other anticancer agents. Likewise, trastuzumab (Herceptin, Her-2 inhibitor), which might be effective against Her2/neu over expressing gliomas may work well when combined with temozolomide. Nonetheless, both drugs do not cross the BTB to significantly impact patient survival. Beforehand we showed that potassium channel agonists when intracarotidly administered increased carboplatin and Her-2 antibody delivery in animal glioma models by triggering formation of brain vascular endothelial transcytotic vesicles. In this study, we investigated whether, intravenously administered, ATP-sensitive potassium channel (K(ATP)) activator (minoxidil sulfate; MS) increases temozolomide and Herceptin delivery to brain tumors to induce anti-tumor activity and increase survival in nude mice with Glioblastoma multiforme (GBM) cells. The results clearly demonstrate that when given intravenously temozolomide crosses BTB at a relatively low amount while Herceptin failed to cross the BTB. However, MS co-infusion with [(14)C]-temozolomide or fluorescently labeled-Herceptin resulted in improved and selective drug delivery to brain tumor. We also showed that combination treatment with temozolomide and Herceptin has enhanced anti-tumor effect which was more prominent than that of either treatment alone in increasing the survival in mice with GBM when co-infused with MS. Therefore, brain tumor patients may be benefited when anti-neoplastic agent delivery is increased selectively to the brain tumors using KATP channel agonists.

Topics: Animals; Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Blood-Brain Barrier; Brain Neoplasms; Carbon Radioisotopes; Cell Line, Tumor; Dacarbazine; Drug Delivery Systems; Gene Expression Regulation, Neoplastic; Glioblastoma; Humans; KATP Channels; Mice; Minoxidil; Survival Rate; Temozolomide; Transplantation, Heterologous; Trastuzumab

Brain tumor microvessels/capillaries limit drug delivery to tumors by forming a blood-brain tumor barrier (BTB). The BTB overexpresses ATP-sensitive potassium (K(ATP)) channels that are barely detectable in normal brain capillaries, and which were targeted for BTB permeability modulation. In a rat brain tumor model, we infused minoxidil sulfate (MS), a selective K(ATP) channel activator, to obtain sustained, enhanced, and selective drug delivery, including various sized molecules, across the BTB to brain tumors. Glibenclamide, a selective K(ATP) channel inhibitor, significantly attenuated the MS-induced BTB permeability increase. Immunocytochemistry and glibenclamide binding studies showed increased K(ATP) channel density distribution on tumor cells and tumor capillary endothelium, which was confirmed by K(ATP) channel potentiometric assay in tumor cells and brain endothelial cells cocultured with brain tumor cells. MS infusion in rats with brain tumors significantly increased transport vesicle density in tumor capillary endothelial and tumor cells. MS facilitated increased delivery of macromolecules, including Her-2 antibody, adenoviral-green fluorescent protein, and carboplatin, to brain tumors, with carboplatin significantly increasing survival in brain tumor-bearing rats. K(ATP) channel-mediated BTB permeability increase was also demonstrated in a human, brain tumor xenograft model. We conclude that K(ATP) channels are a potential target for biochemical modulation of BTB permeability to increase antineoplastic drug delivery selectively to brain tumors.

Topics: Adenosine Triphosphate; Amino Acid Sequence; Animals; Antibodies, Monoclonal; Blood-Brain Barrier; Brain Neoplasms; Cell Membrane Permeability; Drug Synergism; Endothelium, Vascular; Female; Genetic Vectors; Glioma; Glyburide; Green Fluorescent Proteins; Humans; Luminescent Proteins; Minoxidil; Molecular Sequence Data; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Wistar; Receptor, ErbB-2; Xenograft Model Antitumor Assays