Use of an ex vivo model of human colorectal tumours to study response to the MEK1/2 inhibitor AZD6244
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Date
29/11/2013Item status
Restricted AccessAuthor
Novo, Sonia Marisa
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Abstract
Colorectal cancer is the second most common cause of cancer death in
Western Europe and North America. Current therapies are largely ineffective and are
associated with considerable morbidity. Activating mutations in KRAS and BRAF
genes are frequent in colorectal cancer, especially at later stages of the disease, and
result in constitutive activity of the MAPK pathway, leading to increased
proliferation and tumour survival. The MEK1/2 inhibitor AZD6244, that targets the
MAPK pathway downstream of these mutations, has been tested as novel therapy for
colorectal cancer. However, clinical trials have been disappointing due to an apparent
intrinsic and/or acquired resistance to treatment. Mechanisms underlying this
resistance have been studied using cell lines and tumour xenografts. However, the
relevance of these data to advanced human colorectal cancer is unclear.
One of the difficulties in testing and developing novel therapies for colorectal
cancer is the lack of representative models of human disease. Thus, the initial aim of
my PhD was to develop a method to culture human colorectal cancers ex vivo in
order to use this as a platform for investigating response to AZD6244 and other
therapies. These studies indicated that regardless of growth conditions, colonic
tumour explants suffered extensive apoptosis in the first 24h in culture, which limited
their application in drug response assays. Therefore, as an alternative to long term
culture of human colorectal explants, I tested the effects of AZD6244 using acute
treatments. Twenty three fresh colonic tumours were obtained from patients and
treated for 1h with AZD6244 ex vivo in dose response studies. In all samples,
MEK1/2 inhibition occurred within 1h of treatment. In one group of particularly
sensitive tumours, the drug also had a distinct phenotypic effect. In these tumours, I
found that the agent induced a dose-dependent decrease in proliferation and increase
in apoptosis within 1h of treatment. Analysis of markers for this sensitivity indicated
it was not clearly dependent of the presence of KRAS or BRAF mutations, which
have previously been shown to confer sensitivity. Other markers of sensitivity /
resistance were also examined. In addition to studies with AZD6244 alone, I
examined the combined effects of this agent and aspirin in colon cancer cells lines
and in tumour explants, with promising results. Whilst the use of fresh patient
tumour tissue has some technical and logistical challenges, these data suggest that
such methodologies are worthy of further investigation as a means to examine
determinants of sensitivity and resistance to novel therapies, or their likely activity in
combination.