Altered Abundance of Barrier-Related Proteins in Brain Microvascular Endothelial Cells of the GL261 Mouse Model of Glioblastoma.

Glioblastoma multiform (GBM) is a brain cancer that has limited treatment options and a high fatality rate, due in part to limited access of chemotherapeutics to the tumor resulting from the restrictive nature of the blood-brain barrier (BBB). The present study characterized the proteome of endothelial cells forming the BBB in a mouse model of GBM, as a way to identify putative transporters that could be exploited to enhance drug delivery in GBM. Female 6-8 week old C57BL/6 mice were intracranially injected with glioma 261 (GL261) cells or underwent a sham injection. After 28-29 days, brain endothelial cells (CD31+/CD45-) from GL261 (GBM-EC) and sham-injected (control-EC) mice were isolated using magnetic-activated cell sorting, and the proteome of cells was compared by untargeted liquid chromatography dual mass spectrometry. GBM-EC had significantly lower abundance of tight junction proteins (e.g., tight junction protein 1, 0.4-fold) and drug-metabolizing enzymes (e.g., glutathione-S-transferase A4, 0.4-fold) compared to control-EC, alongside an up- and down-regulation of drug transporters (e.g., long-chain fatty acid transport protein 4, 5-fold; adenosine triphosphate binding cassette transporter subfamily B member 1A, 0.3-fold). A large, 7-fold up-regulation of the endothelial cell surface receptor melanoma cell adhesion molecule (MCAM) and scavenger receptor class B member 1 (SCARB1) were identified in GBM-EC compared to control-EC. Immunohistochemistry confirmed cerebral endothelial localization of MCAM and SCARB1 in GBM, in addition to nonvascular patterning within the GBM, suggesting these receptors may be targets that could be exploited for drug delivery. The present study identified changes to BBB markers of paracellular permeability, as well as active and receptor-mediated transcellular transport that could present novel avenues to consider to enhance the permeability and GBM access of current and future therapeutics.