Abstract
Ovarian cancer is a heterogeneous group of diseases, often associated with
aggressive metastasis and thus with the highest case-to-fatality ratio amongst all the
gynaecological cancers. This study focusses on targeted therapy of its most common
subtype: epithelial ovarian cancer and a rare form: adult Granulosa Cell Tumour (adult
GCT). Due to lack of initial symptoms, most epithelial ovarian cancer cases are detected
at later stages when they have already metastasized, while due to distinct hormonal
activity, adult GCTs have a favourable prognosis with 90% cases detected in early stages.
However, 30% of adult GCT patients relapse and more than 90% of these relapsed cases
succumb to death. So, targeting the advanced stage metastatic disease in both types of
cancer is critical. Moreover, due to being rare, adult GCT-specific studies are limited and
not optimized in GCT cells, and most of its treatment strategies are still modelled on
treatment of epithelial ovarian cancer which is not effective.
For targeting adult GCT, two approaches have been adopted. The first one exploits
the presence of the FOXL2 mutation present in 97% of cases, facilitating protection from
cell death by apoptosis. We explored the hypothesis that overexpressing wild type
FOXL2 in the GCT representative cell line KGN might sensitize the cells to anti-cancer
therapies. However, overexpression of wild type FOXL2 showed no significant reduction
in cell viability or the IC50 value for various chemotherapeutic drugs tested, which might
be attributed to the heterozygous state of the FOXL2 gene in the KGN cell line either
masking or not being sufficient to exert its full potential effect. However, cell cycle
analysis revealed some promising effects of wild type FOXL2 overexpression. It
significantly decreased the cell population in G1 phase and increased it in Sub-G1 and
G2/M phase. All the chemotherapy drugs too, showed pronounced enhancement of the
Sub-G1 fraction of the cell population representing apoptotic cells, due to wild type
FOXL2 overexpression. So, the drug treatments in the presence of wild type FOXL2
might result in enhanced cell death by combined mechanisms of cytotoxicity, cell cycle
arrest and pro-apoptotic effects. The second approach for targeting adult GCT was to
reduce the high associated oestrogen levels, by using chemotherapy drug combinations
with aromatase inhibitors. Following the initial screening of a number of combinations,
synergy was observed for the combination of bleomycin and letrozole. Mechanistic
studies should now be undertaken to further validate this finding.
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Next, the approach undertaken to target the metastatic ability of both ovarian
cancer types was to exploit the tissue inhibitor of matrix metalloproteinase (TIMP) levels,
which are altered in cancer cells. Overexpression of each of the TIMPs in SKOV-3 and
KGN cells resulted in diminished viability and migration of the cells, by at least 40%,
and reduction in adhesion by at least 20%. Although all TIMPs resulted in reduction, it
was in varying amounts and trends and the maximum effect occurred through TIMP-3 in
both SKOV-3 and KGN cells. This reduction in viability and migration due to TIMP
overexpression might be attributed to their ability to target matrix metalloproteinase
enzymes, extracellular matrix or other functions. This, however, needs to be further
confirmed using incubation of purified TIMP protein with the cancer cells. Finally, it was
found that mesenchymal stem / stromal cells (MSCs) showed a capacity to reduce the
viability but enhance the migration and adhesion of SKOV-3 and KGN cells, by means
of cytokines secreted in their conditioned media. MSCs might therefore not be useful to
act as a delivery vehicle to the tumour site.
Overall, this thesis has explored a number of approaches to new targeted therapies
for both epithelial and GCT forms of ovarian cancer. Several novel observations have
been made, which following further in vitro or animal model studies may be able to
progress to the clinic.