Macrocycles That Inhibit the Binding between Heat Shock Protein 90 and TPR-Containing Proteins

Abstract

Heat shock protein 90 (Hsp90) accounts for 1–2% of the total proteins in normal cells and functions as a molecular chaperone that folds, assembles, and stabilizes client proteins. Hsp90 is over-expressed (3–6-fold increase) in stressed cells, including cancer cells, and regulates over 200 client and co-chaperone proteins. Hsp90 client proteins are involved in a plethora of cellular signaling events including numerous growth and apoptotic pathways. Since pathway-specific inhibitors can be problematic in drug-resistant cancers, shutting down multiple pathways at once is a promising approach when developing new therapeutics. Hsp90’s ability to modulate many growth and signaling pathways simultaneously makes this protein an attractive target in the field of cancer therapeutics. Herein we present evidence that a small molecule modulates Hsp90 via binding between the N and middle domain and allosterically inhibiting the binding interaction between Hsp90 and four C-terminal binding client proteins: IP6K2, FKBP38, FKBP52, and HOP. These last three clients contain a tetratricopeptide-repeat (TPR) region, which is known to interact with the MEEVD sequence on the C-terminus of Hsp90. Thus, this small molecule modulates the activity between co-chaperones that contain TPR motifs and Hsp90’s MEEVD region. This mechanism of action is unique from that of all Hsp90 inhibitors currently in clinical trials where these molecules have no effect on proteins that bind to the C-terminus of Hsp90. Further, our small molecule induces a Caspase-3 dependent apoptotic event. Thus, we describe the mechanism of a novel scaffold that is a useful tool for studying cell-signaling events that result when blocking the MEEVD-TPR interaction between Hsp90 and co-chaperone proteins.

Hsp70/Hsp90 Organising Protein (Hop): Beyond Interactions with Chaperones and Prion Proteins

“…Six compounds containing a 7-azapteridine ring were similarly able to inhibit the interaction between Hsp90 and Hop (Yi and Regan 2008). All of these compounds were shown to have anti-cancer activity in cell lines, demonstrating that prevention of the interaction between Hsp90 and Hop may be a viable target for anti-cancer therapies (Pimienta et al 2011;Ardi et al 2011;Yi and Regan 2008).…”

“…Unlike other inhibitors of the Hsp90 complex, this compound did not alter Hsp70 expression. It has also been possible to inhibit Hop interaction with Hsp90 via small molecules, like Sansalvamide A analogues (Ardi et al 2011) and a compound termed C9 (1,6-dimethyl-3-propylpyrimido [5,4-e] [1,2,4] triazine-5,7-dione) (Pimienta et al 2011). The Sansalvamide A analogue bound Hsp90 at a region between the N terminal and middle domains, inducing allosteric changes that blocked the binding of Hop (and two other TPR containing proteins) to the Hsp90 MEEVD.…”

Predicting the unpredictable: Recent structure–activity studies on peptide-based macrocycles

“…This cytoprotective response is usually referred to as a heat shock response (HSR). Investigation of the SM145's mechanism showed that in contrast to the classic inhibitors, SM145 did not induce this HSR [26][27][28]. This successful discovery with SM145 drove the development of new molecules that were less hydrophobic and more potent than SM145.…”

Hsp90 as a therapeutic target in endocrinology: current evidence

“…96,97 SM145 likely impacts access to the Hsp90 MEEVD C-terminal peptide by inducing or stabilizing an Hsp90 conformation that obstructs access to the TPR-docking site. SM145 was shown to induce caspase 3-dependent apoptosis, 96 interfered with the chaperoning ability of Hsp90 to refold proteins, and caused a dramatic depletion of GR in HeLa cells. 97 …”