gedunin and geldanamycin

Heat shock protein 90 (Hsp90) facilitates the maturation of many newly synthesized and unfolded proteins (clients) via the Hsp90 chaperone cycle, in which Hsp90 forms a heteroprotein complex and relies upon cochaperones, immunophilins, etc., for assistance in client folding. Hsp90 inhibition has emerged as a strategy for anticancer therapies due to the involvement of clients in many oncogenic pathways. Inhibition of chaperone function results in client ubiquitinylation and degradation via the proteasome, ultimately leading to tumor digression. Small molecule inhibitors perturb ATPase activity at the N-terminus and include derivatives of the natural product geldanamycin. However, N-terminal inhibition also leads to induction of the pro-survival heat shock response (HSR), in which displacement of the Hsp90-bound transcription factor, heat shock factor-1, translocates to the nucleus and induces transcription of heat shock proteins, including Hsp90. An alternative strategy for Hsp90 inhibition is disruption of the Hsp90 heteroprotein complex. Disruption of the Hsp90 heteroprotein complex is an effective strategy to prevent client maturation without induction of the HSR. Cucurbitacin D, isolated from Cucurbita texana, and 3-epi-isocucurbitacin D prevented client maturation without induction of the HSR. Cucurbitacin D also disrupted interactions between Hsp90 and two cochaperones, Cdc37 and p23.

Topics: Benzoquinones; Cucurbitaceae; DNA-Binding Proteins; Heat Shock Transcription Factors; HSP90 Heat-Shock Proteins; Humans; Lactams, Macrocyclic; MCF-7 Cells; Molecular Chaperones; Molecular Structure; Neoplasms; Transcription Factors; Triterpenes

Several Hsp90 modulators have been identified including the N-terminal ligand geldanamycin (GDA), the C-terminal ligand novobiocin (NB), and the co-chaperone disruptor celastrol. Other Hsp90 modulators elicit a mechanism of action that remains unknown. For example, the natural product gedunin and the synthetic anti-spermatogenic agent H2-gamendazole, recently identified Hsp90 modulators, manifest biological activity through undefined mechanisms. Herein, we report a series of biochemical techniques used to classify such modulators into identifiable categories. Such studies provided evidence that gedunin and H2-gamendazole both modulate Hsp90 via a mechanism similar to celastrol, and unlike NB or GDA.

Topics: Benzoquinones; Cell Line, Tumor; Chromatography, Affinity; HSP90 Heat-Shock Proteins; Humans; Hydrolysis; Immunoprecipitation; Lactams, Macrocyclic; Models, Molecular; Novobiocin; Pentacyclic Triterpenes; Triterpenes

Although androgen receptor (AR)-mediated signaling is central to prostate cancer, the ability to modulate AR signaling states is limited. Here we establish a chemical genomic approach for discovery and target prediction of modulators of cancer phenotypes, as exemplified by AR signaling. We first identify AR activation inhibitors, including a group of structurally related compounds comprising celastrol, gedunin, and derivatives. To develop an in silico approach for target pathway identification, we apply a gene expression-based analysis that classifies HSP90 inhibitors as having similar activity to celastrol and gedunin. Validating this prediction, we demonstrate that celastrol and gedunin inhibit HSP90 activity and HSP90 clients, including AR. Broadly, this work identifies new modes of HSP90 modulation through a gene expression-based strategy.

Topics: Antibiotics, Antineoplastic; Benzoquinones; Biomarkers, Tumor; Cell Culture Techniques; Cell Line; Cell Line, Tumor; Cell Survival; ErbB Receptors; fms-Like Tyrosine Kinase 3; Fusion Proteins, bcr-abl; Gene Expression; Gene Expression Profiling; Genome, Human; HSP90 Heat-Shock Proteins; Humans; Inhibitory Concentration 50; Lactams, Macrocyclic; Limonins; Male; Metribolone; Pentacyclic Triterpenes; Prostatic Neoplasms; Receptors, Androgen; Reproducibility of Results; RNA, Messenger; Triterpenes