Using NMR to identify binding regions for N and C-terminal Hsp90 inhibitors using Hsp90 domains.

We present the first NMR study of the interaction between heat shock protein 90 (Hsp90) and amino (N)-terminal inhibitors 17-AAG, and AUY922, and carboxy (C)-terminal modulators SM253, and LB51. We show that the two ATP mimics, 17-AAG and AUY922, bind deeply within the ATP binding pocket of the N-terminal domain, consistent with the crystal structures. In contrast, SM253, a C-terminal Hsp90 modulator, binds to the linker region between the N and middle domains. We also show that C-terminal inhibitor LB51 binds to the C-terminus with a more significant spectroscopic change than previously reported using NMR binding studies of C-terminal inhibitors novobiocin and silybin. These data provide key insights into how the allosteric inhibitor SM253 controls the C-terminal co-chaperones and confirms the binding domain of LB51.

Regulating the master regulator: Controlling heat shock factor 1 as a chemotherapy approach.

Described is the role that heat shock factor 1 (HSF1) plays in regulating cellular stress. Focusing on the current state of the HSF1 field in chemotherapeutics we outline the cytoprotective role of HSF1 in the cell. Summarizing the mechanism by which HSF1 regulates the unfolded proteins that are generated under stress conditions provides the background on why HSF1, the master regulator, is such an important protein in cancer cell growth. Summarizing siRNA knockdown results and current inhibitors provides a comprehensive evaluation on HSF1 and its current state. One set of molecules stands out, in that they completely obliterate the levels of HSF1, while simultaneously inhibiting heat shock protein 90 (Hsp90). These molecules are extremely promising as chemotherapeutic agents and as tools that may ultimately provide the connection between Hsp90 inhibition and HSF1 protein levels.

Chemically accessible hsp90 inhibitor that does not induce a heat shock response.

Recent cancer therapies have focused on targeting biology networks through a single regulatory protein. Heat shock protein 90 (hsp90) is an ideal oncogenic target as it regulates over 400 client proteins and cochaperones. However, clinical inhibitors of hsp90 have had limited success; the primary reason being that they induce a heat shock response. We describe the synthesis and biological evaluation of a new hsp90 inhibitor, SM253. The previous generation on which SM253 is based (SM145) has poor overall synthetic yields, low solubility, and micromolar cytotoxicity. By comparison SM253 has relatively high overall yields, good aqueous solubility, and is more cytotoxic than its parent compound. Verification that hsp90 is SM253's target was accomplished using pull-down and protein folding assays. SM253 is superior to both SM145 and the clinical candidate 17-AAG as it decreases proteins related to the heat shock response by 2-fold, versus a 2-4-fold increase observed when cells are treated with 17-AAG.

A heat shock protein 90 inhibitor that modulates the immunophilins and regulates hormone receptors without inducing the heat shock response.

When a cell encounters external stressors, such as lack of nutrients, elevated temperatures, changes in pH or other stressful environments, a key set of evolutionarily conserved proteins, the heat shock proteins (hsps), become overexpressed. Hsps are classified into six major families with the hsp90 family being the best understood; an increase in cell stress leads to increased levels of hsp90, which leads to cellular protection. A hallmark of hsp90 inhibitors is that they induce a cell rescue mechanism, the heat shock response. We define the unique molecular profile of a compound (SM145) that regulates hormone receptor protein levels through hsp90 inhibition without inducing the heat shock response. Modulation of the binding event between heat shock protein 90 and the immunophilins/homologs using SM145, leads to a decrease in hormone receptor protein levels. Unlike N-terminal hsp90 inhibitors, this hsp90 inhibitor does not induce a heat shock response. This work is proof of principle that controlling hormone receptor expression can occur by inhibiting hsp90 without inducing pro-survival protein heat shock protein 70 (hsp70) or other proteins associated with the heat shock response. Innovatively, we show that blocking the heat shock response, in addition to hsp90, is key to regulating hsp90-associated pathways.

A potential rhodium cancer therapy: studies of a cytotoxic organorhodium(I) complex that binds DNA.

Described is a novel organorhodium(I) complex that is cytotoxic to the colon cancer cell line HCT116 and alters cell migration, DNA replication, and DNA condensation. Most importantly, the mechanism observed is not seen for the parent organorhodium dimer complex [{RhCl(COD)}2], RhCl3, or the free ligand/proligands (COD and 1-(n)butyl-3-methylimidazolium chloride). Thus, the activity of this organorhodium complex is attributable to its unique structure.

Heat shock proteins 27, 40, and 70 as combinational and dual therapeutic cancer targets.

The heat shock proteins are essential players in the development of cancer and they are prime therapeutic targets. Targeting multiple hsps in dual therapies decreases the likelihood of drug resistance compared to utilizing mono-therapies. Further, employing an hsp inhibitor in combination with another therapy has proven clinically successful. Examples of efficacious strategies include the inhibition of hsp27, which prevents protein aggregation, controlling hsp40's role as an ATPase modulator, and inhibiting hsp70 from acting as a molecular chaperone. While hsp40 therapies are just in the beginning stages, hsp27 and hsp70 therapies have been successfully used in dual inhibition treatments with hsp90 inhibitors and in combinational therapy with antineoplastic drugs. Both dual and combinatorial therapies show encouraging results when used in treating chemotherapeutically resistant diseases.

An Hsp90 modulator that exhibits a unique mechanistic profile.

Described is the synthesis of two biotinylated derivatives of a cytotoxic macrocycle. Pull-down assays indicate that this macrocycle targets the N-middle domain of Hsp90. Untagged compound can effectively compete away tagged compound-Hsp90 protein complexes, confirming the binding specificity of the macrocycle for Hsp90. The macrocycle is similar in potency to other structurally-related analogs of Sansalvamide A (San A) and induces apoptosis via a caspase 3 mechanism. Unlike other San A derivatives, we show that the macrocycle does not inhibit binding between C-terminal client proteins and co-chaperones and Hsp90, suggesting that it has a unique mechanism of action.

Synthesis and evaluation of biotinylated sansalvamide A analogs and their modulation of Hsp90.

Described are the syntheses of three sansalvamide A derivatives that contain biotinylated tags at individual positions around the macrocycle. The tagged derivatives indicated in protein pull-down assays that they bind to Hsp90 at the same binding site (N-Middle domain) as the San A-amide peptide. Further, these compounds inhibit binding between Hsp90 and multiple C-terminal client proteins. This interaction is unique to the San A analogs indicating they can be tuned for selectivity against Hsp90 client/co-chaperone proteins.