Targeting the Unfolded Protein Response as a Novel Therapeutic Approach in Haematological Malignancies
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The unfolded protein response (UPR) is a complex signalling pathway activated in response to endoplasmic reticulum stress. In recent years, the UPR has been implicated in cancer and chemosensitivity, particularly in solid tumours. This thesis investigated the potential value of targeting the UPR as a novel therapeutic approach in haematological malignancies using a panel of cell lines representing AML, lymphoma and myeloma. The UPR was constitutively active in these haematological cancer cell lines, with differential activation of key UPR proteins both in the panel and between the panel, peripheral blood mononuclear cells and the colorectal cancer cell line HT-29. A number of strategies were used to modulate the UPR and study chemosensitivity. Minimally toxic concentrations of the ER stress inducer thapsigargin protected cells from cytotoxic agents, with a reduction in antiproliferative drug effect. The activity of the novel small molecule versipelostatin, reported to downregulate the ER molecular chaperones GRP78 and GRP94, was also investigated, with the downregulation previously reported in solid tumour cell lines (Park et al. 2004) confirmed in HT-29 cells, but not observed in the haematological cell lines studied (although versipelostatin was an effective cytotoxic agent at low micromolar concentration). Combination experiments with the chemical chaperone 4-phenylbutyric acid (PBA) resulted in a small increase in apoptosis when PBA was combined with ER stress inducers. However, PBA also showed HDAC inhibitory activity at the concentrations used. Finally, siRNA mediated silencing of GRP78 and GRP94 in THP1 (AML) and U266 (myeloma) cells resulted in a decrease in the targeted protein, but showed only minimal effects on chemosensitivity. In conclusion, the UPR is activated in these haematological cancer cell lines and plays a complex role in chemosensitivity. In contrast to previous reports in solid tumour cells, modulating the UPR in these haematological malignancies had only a modest effect on chemosensitivity.
AuthorsMadadi, Linsey Ida
- Theses