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Updated: Dec 23, 2025
Lucifer Yellow - A Robust Paracellular Permeability Marker in a Cell Model of the Human Blood-brain Barrier
Published on: August 19, 2019
Regulation of blood-brain tumor barrier permeability by calcium-activated potassium channels
Nagendra S Ningaraj1, Mamatha Rao, Kazuhiro Hashizume
1Maxine Dunitz Neurosurgical Institute, Division of Cardiology, Cedars-Sinai Medical Center, 8631 West Third Street, Los Angeles, CA 90048, USA.
Abstract:
The blood-brain tumor barrier (BTB) limits the delivery of therapeutic drugs to brain tumors. We demonstrate in a rat brain tumor (RG2) model an enhanced drug delivery to brain tumor following intracarotid infusion of bradykinin (BK), nitric oxide (NO) donors, or agonists of soluble guanylate cyclase (sGC) and calcium-dependent potassium (K(Ca)) channels. We modulated K(Ca) channels by specific agonists and agents that produce NO and cGMP in situ to obtain sustained enhancement of selective drug delivery to brain tumors. Intracarotid infusion of BK or 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619) significantly enhanced BTB permeability (K(i)) to [(14)C]alpha-aminoisobutyric acid in the brain tumor area but not in normal brain tissue. The K(i) increase achieved by BK, NS-1619, NO donors, or the sGC activator 3-(5'-hydroxymethyl-2'furyl)-1-benzylindazole (YC-1) was significantly attenuated when coinfused with a K(Ca) channel antagonist, iberiotoxin. Immunoblot and immunolocalization studies demonstrate overexpression of K(Ca) channels in tumor cells and capillaries compared with normal brain. The potentiometric assays demonstrate the functional activity of K(Ca) channels in rat brain endothelial and glioma cells. Additionally, we show that BK and NS-1619 significantly increased the density of transport vesicles in the cytoplasm of brain tumor capillary endothelia and tumor cells. The cleft indices and cleft area indices in rat tumor capillaries were significantly higher than in normal brain capillaries, and BK infusion did not alter these indices. These data demonstrate that the cellular mechanism for K(Ca) channel-mediated BTB permeability increase is due to accelerated formation of pinocytotic vesicles, which can transport drugs across BTB. We conclude that K(Ca) channels serve as a convergence point in the biochemical regulation of BTB permeability.
Insights
Targeting calcium-dependent potassium (K(Ca)) channels enhances drug delivery across the blood-brain tumor barrier (BTB). Modulating these channels increases BTB permeability selectively in tumors, offering a new strategy for brain cancer therapy.
Area of Science:
- Neuroscience
- Pharmacology
- Oncology
Background:
- The blood-brain tumor barrier (BTB) restricts therapeutic agent access to brain tumors.
- Developing strategies to enhance drug delivery across the BTB is crucial for effective brain cancer treatment.
Purpose of the Study:
- To investigate the role of calcium-dependent potassium (K(Ca)) channels in regulating BTB permeability.
- To evaluate the potential of K(Ca)) channel modulators for enhancing drug delivery to brain tumors.
Main Methods:
- Utilized a rat brain tumor (RG2) model.
- Administered intracarotid infusions of bradykinin (BK), nitric oxide (NO) donors, soluble guanylate cyclase (sGC) agonists, and K(Ca)) channel modulators.
- Assessed BTB permeability using [(14)C]alpha-aminoisobutyric acid.
- Performed immunoblot, immunolocalization, and potentiometric assays to analyze K(Ca)) channel expression and function.
- Examined changes in transport vesicle density and capillary morphology.
Main Results:
- Intracarotid infusion of BK, NO donors, sGC activators, or K(Ca)) channel agonists significantly enhanced BTB permeability specifically in the tumor area.
- K(Ca)) channel antagonists attenuated the observed increase in BTB permeability.
- Overexpression and functional activity of K(Ca)) channels were confirmed in tumor cells and capillaries.
- BK and NS-1619 increased transport vesicle density, suggesting enhanced pinocytosis as the mechanism for increased permeability.
- Tumor capillaries exhibited altered cleft morphology, but BK infusion did not affect these indices.
Conclusions:
- K(Ca)) channels play a critical role in regulating BTB permeability.
- Modulation of K(Ca)) channels offers a promising approach to enhance selective drug delivery to brain tumors.
- The mechanism involves accelerated pinocytotic vesicle formation, facilitating drug transport across the BTB.
