Jeffrey K. Tong

Chromatin deacetylation by an ATP-dependent nucleosome remodelling complex

The dynamic assembly and remodelling of eukaryotic chromosomes facilitate fundamental cellular processes such as DNA replication and gene transcription. The repeating unit of eukaryotic chromosomes is the nucleosome core, consisting of DNA wound about a defined octamer of histone proteins. Two enzymatic processes that regulate transcription by targeting elements of the nucleosome include ATP-dependent nucleosome remodelling and reversible histone acetylation,. The histone deacetylases, however, are unable to deacetylate oligonucleosomal histones in vitro. The protein complexes that mediate ATP-dependent nucleosome remodelling and histone acetylation/deacetylation in the regulation of transcription were considered to be different, although it has recently been suggested that these activities might be coupled. We report here the identification and functional characterization of a novel ATP-dependent nucleosome remodelling activity that is part of an endogenous human histone deacetylase complex. This activity is derived from the CHD3 and CHD4 proteins which contain helicase/ATPase domains found in SWI2-related chromatin remodelling factors, and facilitates the deacetylation of oligonucleosomal histones in vitro. We refer to this complex as the nucleosome remodelling and deacetylating (NRD) complex. Our results establish a physical and functional link between the distinct chromatin-modifying activities of histone deacetylases and nucleosome remodelling proteins.

Development of 17-allylamino-17-demethoxygeldanamycin hydroquinone hydrochloride (IPI-504), an anti-cancer agent directed against Hsp90

Heat shock protein 90 (Hsp90) is an emerging therapeutic target of interest for the treatment of cancer. Its role in protein homeostasis and the selective chaperoning of key signaling proteins in cancer survival and proliferation pathways has made it an attractive target of small molecule therapeutic intervention. 17-Allylamino-17-demethoxygeldanamycin (17-AAG), the most studied agent directed against Hsp90, suffers from poor physical-chemical properties that limit its clinical potential. Therefore, there exists a need for novel, patient-friendly Hsp90-directed agents for clinical investigation. IPI-504, the highly soluble hydroquinone hydrochloride derivative of 17-AAG, was synthesized as an Hsp90 inhibitor with favorable pharmaceutical properties. Its biochemical and biological activity was profiled in an Hsp90-binding assay, as well as in cancer-cell assays. Furthermore, the metabolic profile of IPI-504 was compared with that of 17-AAG, a geldanamycin analog currently in clinical trials. The anti-tumor activity of IPI-504 was tested as both a single agent as well as in combination with bortezomib in myeloma cell lines and in vivo xenograft models, and the retention of IPI-504 in tumor tissue was determined. In conclusion, IPI-504, a potent inhibitor of Hsp90, is efficacious in cellular and animal models of myeloma. It is synergistically efficacious with the proteasome inhibitor bortezomib and is preferentially retained in tumor tissues relative to plasma. Importantly, it was observed that IPI-504 interconverts with the known agent 17-AAG in vitro and in vivo via an oxidation-reduction equilibrium, and we demonstrate that IPI-504 is the slightly more potent inhibitor of Hsp90.

Semisynthetic cyclopamine analogues as potent and orally bioavailable hedgehog pathway antagonists.

Herein is reported the synthesis of a novel class of hedgehog antagonists derived from cyclopamine. The acid sensitive D-ring of cyclopamine was homologated utilizing a sequence of chemoselective cyclopropanation and stereoselective acid-catalyzed rearrangement. Further modification of the A/B-ring homoallylic alcohol to the conjugated ketone led to the discovery of new cyclopamine analogues with improved pharmaceutical properties and in vitro potency (EC 50) ranging from 10 to 1000 nM.

Fiber-derived butyrate and the prevention of colon cancer

Inhibition of the enzyme histone deacetylase by butyrate results in the direct transcriptional upregulation of the cyclin-dependent kinase inhibitor p21/Cip1/WAF1. We discuss a small-molecule-mediated signaling pathway to explain the suspected anti-colon-cancer properties of fiber-derived butyrate.

Dissecting Histone Deacetylase Function

Recent research describes the use of chromatin immunoprecipitation and intergenic chromosomal-DNA microarrays to analyze HDAC function genome-wide. The next step in realizing the full potential of these analyses will be to develop specific and temporal control over HDAC perturbation.

The transcriptional profile of Saccharomyces cerevisiae exposed to rapamycin mimics the profile induced by amino acid starvation

The transcriptional profile of Saccharomyces cerevisiae exposed to rapamycin mimics the profile induced by amino acid starvation