- Title
- Therapeutic targeting of heat shock protein 90 in human colon cancer cells
- Creator
- Wang, Chunyan
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Colon cancer us one of the most common and deadly malignancies. Despite recent advances in early diagnosis and the development of novel treatment approaches, the overall survival of patients with metastatic colon cancers remains disappointing. This is closely related to resistance of colon cancer cells to systemic therapies resulting from oncogenic mutations of KRAS that drive activation of multiple downstream signalling pathways important for cell survival and proliferation. Indeed, active mutations of KRAS are found in up to 50% of colon cancers that are predictive of intrinsic resistance to many therapeutic drugs including antibodies against the epidermal growth factor receptor [EGFR] (Siegfried et al., 2017). Although the discovery of KRAS oncogenes has revolutionized colon cancer therapeutics, no effective therapies exist for the oncogenic driver KRAS mutation. There is a critical need for novel agents targeting KRAS mutant colon cancer. Heat shock protein 90 [HSP90] is the most abundant molecular chaperone and is essential for folding, stabilization, and activation of a large number of proteins called its ‘client’ proteins. Many of its client are effectors of KRAS, such as members of MAPKs and PI3K/Akt/mTOR pathways. As such, targeting HSP90 using small molecule inhibitors appears a promising strategy in the treatment of cancer. Currently, a number of HSP90 inhibitors have entered pre-clinical and clinical studies. But little was known about the effects of HSP90 inhibitors on colon cancer. Therefore, the aim of this thesis was to elucidate the mechanisms of HSP90 inhibitors-induced apoptosis and the resistant mechanisms of colon cancer cells to HSP90 inhibitors and thus to provide more information in identification of treatment approaches that will increase the sensitivity of colon cancer to apoptosis induced by HSP90 inhibitors. Studies in Chapter 3 show that mutant KRAS colon cancer cells are more susceptible to apoptosis induced by the HSP90 inhibitor AUY922 than those carrying wild-type KRAS. Killing of mutant KRAS colon cancer cells by AUY922 is associated with upregulation of Bim and activation of Bim is responsible for apoptosis triggered by AUY922, which is due to knockdown of Bim can abolish apoptosis induced by AUY922. Mechanistic investigations indicated that endoplasmic reticulum [ER] stress was responsible for AUY922-induced upregulation of Bim, which was inhibited by a chemical chaperone or overexpression of GRP78. Conversely, siRNA knockdown of GRP78 or XBP-1 enhanced the apoptosis induced by AUY922. Moreover, AUY922 inhibited the growth of mutant KRAS colon cancer xenografts through activation of Bim that was similarly associated with ER stress. Taken together, these results suggest that AUY922 is a promising drug in the treatment of mutant KRAS colon cancers, and the agents that enhance the apoptosis-inducing potential of Bim may be useful to improve the therapeutic efficacy. Chapter 4 describes that colon cancer cells with mutant BRAF are more resistant to the HSP90 inhibitor AUY922 and reactivation of the ERK and Akt is one of the mechanisms critical for protection of BRAF mutant colon cancer cells against HSP90 inhibitor AUY922-induced apoptosis. Reactivation of ERK was associated with the persistent expression of mutant BRAF, whereas reactivation of Akt was related to the activation of the HSP90 co-chaperone, cell division cycle [CDC37], in that knockdown of CDC37 inhibited Akt reactivation in mutant BRAF colon cancer cells treated with AUY922. Inhibition of activation of the MAPK and PI3K/Akt pathways by small molecular inhibitor and siRNA renders mutant BRAF colon cancer cells sensitive to apoptosis induced by HSP90 inhibitor AUY922. In addition, this chapter also indicated the implications of co-targeting mutant BRAF and/or CDC37 and HSP90 in the treatment of mutant BRAF colon cancers. Studies in Chapter 5 show that Mcl-1 is important for survival of colon cancer cells in the presence of AUY922. Mcl-1 was upregulated in mutant KRAS colon cancer cells selected for resistance to AUY922-induced apoptosis. This was due to its increased stability mediated by Bcl-2-associated athanogene domain 3 [BAG3], which was also increased in resistant colon cancer cells by heat shock factor 1 [HSF1] as a result of chronic endoplasmic reticulum [ER] stress. Functional investigations demonstrated that inhibition of Mcl-1, BAG3, or HSF1 triggered apoptosis in resistant colon cancer cells, and rendered AUY922-naïve colon cancer cells more sensitive to the inhibitor. Together, these results identify that the HSF1-BAG3-Mcl-1 signal axis is critical for protection of mutant KRAS colon cancer cells from AUY922-induced apoptosis, with potential implications for targeting HSF1/BAG3/Mcl-1 to improve the efficacy of AUY922 in the treatment of colon cancer. In Chapter 6 show a summary of results got in this thesis, we discussed the importance and implication of these findings. Results presented in this thesis provide new insights into mechanisms involved, and suggest the agents that enhance the induction of apoptosis-induced protein Bim, co-targeting mutant BRAF and/or CDC37 and HSP90 in mutant BRAF colon cancers cells and targeting HSF1/BAG3/Mcl-1 are potentially useful strategies to improve the therapeutic efficacy of HSP90 inhibitor to colon cancer.
- Subject
- HSP90; colon cancer; AUY922; KRAS; BRAF; Mcl-1; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1395056
- Identifier
- uon:33805
- Rights
- Copyright 2017 Chunyan Wang
- Language
- eng
- Full Text
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|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 16 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 194 KB | Adobe Acrobat PDF | View Details Download |