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.