Pharmacologically impeding glioblastoma tumour motility through simultaneous inhibition of aquaporin-1 and ion channels
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(Thesis)
Date
2023
Authors
Varricchio, Alanah
Editors
Advisors
Yool, Andrea J.
Ramesh, Sunita A. (Flinders University)
Ramesh, Sunita A. (Flinders University)
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Thesis
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Abstract
Glioblastoma multiforme (GBM) is an invasive tumour derived from neuroglial progenitor stem
cells. Despite increasingly intricate treatment strategies, rapid infiltration of glioma cells into
healthy brain tissue remains a major clinical challenge.
I hypothesise that therapies which target cellular motility pathways could effectively slow tumour
dispersal and widen the time window for administration of frontline treatments aimed at direct
eradication of primary tumours. The array of signal transduction pathways that control cellular
motility include aquaporins and ion channels. These protein classes could therefore be prime
candidates as pharmacological targets to restrain cell motility in glioblastoma.
Identifying optimal combinations of inhibitory agents to use against selected channel targets, and
developing drug delivery systems that have minimal side effects in the complex environment of
the brain, could control glioblastoma motility without disrupting finely tuned activities of neuroglial
networks.
This thesis explores a selection of ion channel and aquaporin channel blockers as putative
inhibitors of in vitro glioblastoma invasion. Results here define novel agents that potently impair
GBM cell motility. Natural compounds (xanthurenic acid and caelestine C) and semi-synthetic
amides (SN00756563, SN00756564 and SN00756565) decreased invasion in U87-MG and
U251-MG glioblastoma cell lines, revealing previously unknown anti-invasive activities of these
agents. When combined with the aquaporin-1 inhibitor AqB013, xanthurenic acid and caelestine
C produced a synergistic block of invasion in both U87-MG and U251-MG. Ion channel blockers
nifedipine, amiloride, apamin, 4-aminopyridine, and AMPA/kainate receptor inhibitor
cyanquixaline significantly decreased invasion in U87-MG and U251-MG, effects that were
additively enhanced upon co-treatment with AqB013. Interestingly, when solid tumour spheroids
of U87-MG and U251-MG were treated with the same agents, no significant additive or
synergistic effects were observed.
Some combinations of inhibitors blocked invasion in U87-MG more effectively than in U251-
MG and vice versa. This differential effect could reflect the array of protein factors that affect the motility of glioblastoma tumour cells, including unique expression patterns of aquaporins and ion
channels.
This work presents the novel finding that these pharmacological inhibitors, natural compounds,
or semi-synthetics, administered at low doses either individually or in combinations, produced no
significant cytotoxicity in cultured glioblastoma cells or astrocytes. This could indicate the
capacity to minimise off-target effects associated with these agents.
Implementation of site-specific drug delivery systems could further reduce off-target effects. pHsensitive
gating mechanisms in many channel proteins is attributable to pore-lining histidine
residues. Site-directed mutagenesis experiments described in this thesis identified sites within
AQP1 where introduction or removal of histidine residues potentiated or abolished cGMPinduced
ionic currents in the presence of Ni2+. Histidine could serve as a promising pH-sensing
agent to be incorporated into the design of drug delivery systems that are activated by the hallmark
acidity of the tumour microenvironment.
Impeding glioblastoma tumour dispersal by targeting enriched signalling proteins with functions
in key cellular motility pathways could constitute a powerful adjunct therapy when applied in
parallel with existing procedures. Additionally, coupling these novel inhibitors of glioblastoma
invasion to carrier molecules containing pH-sensitive histidine residues could maximise
controlled release of treatment agents to glioblastoma tumour cells and limit off-target effects.
School/Discipline
Adelaide Medical School
Dissertation Note
Thesis (M.Phil.) -- University of Adelaide, Adelaide Medical School, 2023
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