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- Mofers, Arjan, 1990-
(author)
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Proteasome Inhibitors against Cancer: Determining Biology and Finding Novel Compounds
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Cancer continues to be a tremendous burden on society in terms of loss of quality of life and life-years. The ubiquitin proteasome system (UPS), responsible for the bulk of protein turnover in the cell, is considered an attractive target in cancer therapy. The proteolytic subunit of the UPS, the 20S, is targeted by three clinically approved anti-cancer drugs: Bortezomib, Carfilzomib, and Ixazomib. Proteins destined for degradation by the UPS are tagged with small protein ubiquitin. The 19S regulatory cap is responsible for recognition and processing of these ubiquitinated substrates, followed by proteolysis by the 20S. Deubiquitination by proteolytic enzymes of the 19S is an essential step in the progression of substrates to progress into the 20S. Our strategy is to pharmacologically inhibit the deubiquitinating enzymes associated with the 19S with the goal of disrupting the degradation of substrates. In Paper I of this thesis, we explore the occurrence of resistance to the 19S deubiquitinating enzyme inhibitor b-AP15. We find that minimal resistance to this compound occurs, and the small observed induction of resistance is likely mediated by glutathione. We also find that cells that are slow- or non-cycling are particularly insensitive to the treatment. In Paper II we employ screening methods based on the chemical properties of b-AP15 and find that a small subset of the screened compounds are relatively selective UPS inhibitors. In Paper III we employ a different screening methods, based on the gene expression profiles associated with disruption of the UPS. This screen finds several compounds with previously described UPS inhibitory effects but also compounds with different proposed mechanisms of action. In both Paper II and Paper III we reflect on the chemical structure of the compounds and challenges that come with chemical groups that are potentially promiscuously reactive. In Paper IV we explore the validity of b-AP15 as a treatment for acute lymphoblastic leukemia, a form of cancer for which the efficacy of b-AP15 has not been fully elucidated. This thesis contributes to the body of work supporting 19S inhibition in general, and 19S inhibition with b-AP15 in particular, as a promising modality for the treatment of cancer.
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| 2. |
- Pellegrini, Paola, 1986-, et al.
(author)
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Induction of ER Stress in Acute Lymphoblastic Leukemia Cells by the Deubiquitinase Inhibitor VLX1570
- 2020
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In: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 21:13
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Journal article (peer-reviewed)abstract
- The proteasome is a validated target of cancer therapeutics. Inhibition of proteasome activity results in the activation of the unfolded protein response (UPR) characterized by phosphorylation of eukaryotic initiation factor 2 alpha (eIF2 alpha), global translational arrest, and increased expression of the proapoptotic CHOP (C/EBP homologous protein) protein. Defects in the UPR response has been reported to result in altered sensitivity of tumor cells to proteasome inhibitors. Here, we characterized the effects of the deubiquitinase (DUB) inhibitor VLX1570 on protein homeostasis, both at the level of the UPR and on protein translation, in acute lymphoblastic leukemia (ALL). Similar to the 20S inhibitor bortezomib, VLX1570 induced accumulation of polyubiquitinated proteins and increased expression of the chaperone Grp78/Bip in ALL cells. Both compounds induced cleavage of PARP (Poly (ADP-ribose) polymerase) in ALL cells, consistent with induction of apoptosis. However, and in contrast to bortezomib, VLX1570 treatment resulted in limited induction of the proapoptotic CHOP protein. Translational inhibition was observed by both bortezomib and VLX1570. We report that in distinction to bortezomib, suppression of translation by VXL1570 occurred at the level of elongation. Increased levels of Hsc70/Hsp70 proteins were observed on polysomes following exposure to VLX1570, possibly suggesting defects in nascent protein folding. Our findings demonstrate apoptosis induction in ALL cells that appears to be uncoupled from CHOP induction, and show that VLX1570 suppresses protein translation by a mechanism distinct from that of bortezomib.
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