Background. Both basal-like subtype and BRCA1-related breast cancers tend to have a poor overall prognosis and lack of effective treatments. Given that the lung cancer drug gefitinib and the leukemia drug dasatinib inhibit proteins also belonging to the molecular signature of this subtype, we and others hypothesized that they might be useful therapies for those two breast cancer subgroups. / Methods. Eight breast cancer cell lines were characterized by immunohistochemistry and western blotting and were treated with both drugs. Response was measured by using the sulphorhodamine B (SRB) assay. / Results. Two out of six basal-like cell lines were sensitive to gefitinib and five of six to dasatinib. BRCA1-related breast cancers were also responsive to dasatinib (three out of four). Moreover, EGFR and caveolin-1 act as markers for dasatinib sensitivity, but do not appear to be the primary targets of this drug. The presence of SRC but not ABL is necessary to achieve a response to dasatinib. / Conclusion. Dasatinib is more effective in the treatment of basal-like breast cancers than gefitinib and acts by inhibiting SRC and other molecules that are yet to be determined.

[Truncated abstract] In recent years a better understanding of the biology of PPAR , a nuclear transcription factor, has emerged, leading to a resurgence in targeting PPAR for chemotherapy. The family of synthetic PPAR agonists, the thiazolidinediones (TZDs), and non-steroidal anti-inflammatory drugs (NSAIDs) have been implicated in the inhibition of cell proliferation, apoptosis and cell cycle arrest of androgen-sensitive (LNCaP) and androgen-independent (PC-3 and DU145) prostate cancer cells generating much interest in their use for potential curative cancer therapies. In light of the potential use of TZDs and NSAIDs in prostate cancer prevention and their ability to induce inhibitory effects in vitro and in vivo, the first aim of this project was to undertake a comprehensive study of the effects of ciglitazone (TZD) and indomethacin (NSAID) on the androgen-independent prostate cancer cell line DU145, using standardised concentrations and time-points to compare the effects of TZDs and NSAIDs on cell proliferation, cell cycle and apoptosis. Treating the cells with either 10 µM ciglitazone or 10 µM indomethacin resulted in a time-dependent decrease in DU145 cell proliferation. The anti-proliferative effects were found to be in-part attributed to the slowing of cell progression through the G1/S-phase checkpoint of the cell cycle, and in the case of ciglitazone, apoptosis also played a role in its anti-proliferative effects in this cell line. Interestingly, although indomethacin failed to induce apoptosis, its antiproliferative effects were more potent than ciglitazone. The second aim of this project was to further investigate the underlying mechanisms responsible for the anti-proliferative effects of ciglitazone and indomethacin by evaluating their ability to modulate PPAR mRNA and protein expression, and to induce PPAR transcriptional activity. ... In addition, ligandinduced regulation of secreted frizzled related protein 4 (sFRP4) expression, a Wnt/ - catenin antagonists, was investigated. It was demonstrated that both ciglitazone and indomethacin attenuated Wnt/ -catenin signalling via the down-regulation of total - catenin levels within the cells, inhibition or slowing of the translocation of cytoplasmic -catenin into the nucleus and inhibition of cyclin–D1 expression An inverse relationship between PPAR and -catenin protein levels was also detected, suggesting that PPAR may directly bind to -catenin itself. sFRP4 expression was transiently upregulated by ciglitazone and indomethacin-treatment, suggesting that the antiproliferative effects of the ligands may be mediated in part through regulation of sFRP4 mRNA and protein levels. In summary, the anti-proliferative effects of ciglitazone and indomethacin on the androgen-independent prostate cancer cell line, DU145, described in this thesis are progressive steps in characterising the role of PPAR in prostate cancer cell proliferation. The identification of indomethacin as a more potent PPAR agonist than ciglitazone represents a novel target for the development of preventative strategies for advanced disease, and the relationship between PPAR and the Wnt/ -catenin signalling pathway provide an insight into the mechanisms involved in the anti-proliferative effects of ciglitazone and indomethacin. Further studies into this relationship would advance help identify novel preventative and curative therapeutic strategies for advanced prostate cancer.

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