The role of phytochemicals in modulating breast cancer resistance protein at the blood-brain barrier and the blood-tumour barrier

  • Basma Elbakary

Student thesis: Doctoral ThesisDoctor of Philosophy


The blood-brain barrier (BBB) and the blood-tumour barrier (BTB) represent insidious
obstacles for the delivery of anti-cancer agents to solid brain tumours, not only because
of their morphological features, but also due to the presence of the drug efflux transporter
breast cancer resistant protein (BCRP), localised at both the BBB and BTB. This efflux
transporter restricts the permeation of anti-cancer agents across both barriers leading to
suboptimal concentrations of drugs at the intended site of action.
This work examined 13 naturally occurring phytochemicals, which were screened for
their dual ability to modulate the efflux function of BCRP in addition to their anti-cancer
properties in human LN229 glioblastoma cells, namely: (i) inhibition of cellular migration;
(ii) activation of apoptosis; (iii) reactive oxygen species (ROS) production and (iv)
activation of caspase pathways. Phytochemicals displayed minimal cytotoxicity, were
able to modulate BCRP which led to enhancing the permeability of the fluorescent probe
substrate H33342, in addition to inhibiting cellular migration. Hesperetin and baicalin
displayed the optimal modulatory potential and demonstrated a similar ability to generate
ROS and activate Caspase-3/7 when compared to the anti-cancer agents methotrexate
and temozolomide. Subsequently, hesperetin was progressed as the optimal candidate,
and its ability to permeate across the BBB was confirmed after conducting a permeability
study using an in-vitro primary porcine brain microvascular endothelial cell (PBMEC)
BBB model. We demonstrated that hesperetin was highly permeable across the BBB,
can modulate the efflux function of BCRP and overall enhance the apparent permeability
(Papp) of mitoxantrone and methotrexate. Thereafter, we assessed the impact of shear
stress fashioned by laminal flow on the morphology of PBMEC using a Quasi Vivo 600®
perfusion system. The results displayed a significant increase in Transepithelial
Electrical Resistance (TEER) values, improved formation of zonula occludens-1 (ZO-1),
and higher expression of efflux transporter proteins, suggesting the formation of a better
in-vitro BBB model with hesperetin still being highly permeable across the barrier further
confirming its ability to bypass the BBB and reach the BTB. This work highlights the anticancer and BCRP modulatory capabilities of phytochemicals as well as the ability of
hesperetin to bypass the BBB.
Date of Award2021
Original languageEnglish
SupervisorRaj Badhan (Supervisor) & Michael Coleman (Supervisor)

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