Bifunctional ligands allow deliberate extrinsic reprogramming of the glucocorticoid receptor

BET bromodomain ligands: Probing the WPF shelf to improve BRD4 bromodomain affinity and metabolic stability

Ligands for the bromodomain and extra-terminal domain (BET) family of bromodomains have shown promise as useful therapeutic agents for treating a range of cancers and inflammation. Here we report that our previously developed 3,5-dimethylisoxazole-based BET bromodomain ligand (OXFBD02) inhibits interactions of BRD4(1) with the RelA subunit of NF-κB, in addition to histone H4. This ligand shows a promising profile in a screen of the NCI-60 panel but was rapidly metabolised (t½ = 39.8 min). Structure-guided optimisation of compound properties led to the development of the 3-pyridyl-derived OXFBD04. Molecular dynamics simulations assisted our understanding of the role played by an internal hydrogen bond in altering the affinity of this series of molecules for BRD4(1). OXFBD04 shows improved BRD4(1) affinity (IC50 = 166 nM), optimised physicochemical properties (LE = 0.43; LLE = 5.74; SFI = 5.96), and greater metabolic stability (t½ = 388 min).

Targeted Gene Repression Using Novel Bifunctional Molecules to Harness Endogenous Histone Deacetylation Activity

Epigenome editing is a powerful method for life science research and could give rise to new therapies for diseases initiated or maintained by epigenetic dysregulation, including several types of cancers and autoimmune disorders. In addition, much is still unknown about the mechanisms by which histone-modifying proteins work in concert to properly regulate gene expression. To investigate and manipulate complex epigenetic interactions in live cells, we have developed a small molecule platform for specifically inducing gene repression and histone deacetylation at a reporter gene. We synthesized bifunctional ligands, or chemical epigenetic modifiers (CEMs), that contain two functional groups: a FK506 derivative capable of binding to a FKBP-Gal4 fusion transcription factor, and a histone deacetylase (HDAC) inhibitor that recruits HDAC-containing corepressor complexes. In our reporter cell line, which contains a GFP reporter allele upstream of a Gal4 DNA binding array in the murine Oct4 locus, our lead CEM repressed GFP expression by 50%. We also show that CEM recruitment of deacetylation activity causes marked deacetylation along our target loci. This system allowed us to detail the direct results of deacetylation to chromatin and measure the resulting gene expression in a chemically dependent and reversible manner. The CEMs system provides new insights into epigenetic gene regulation and has the potential to control disease-relevant gene regulation. The CEMs are derived from FDA-approved epigenetic modulator drugs, and use their pharmacology in a gene-specific way that avoids the toxicities and off-target effects caused by whole-cell application of these drugs.

Isoform switching of steroid receptor co-activator-1 attenuates glucocorticoid-induced anxiogenic amygdala CRH expression

Maladaptive glucocorticoid effects contribute to stress-related psychopathology. The glucocorticoid receptor (GR) that mediates many of these effects uses multiple signaling pathways. We have tested the hypothesis that manipulation of downstream factors ('coregulators') can abrogate potentially maladaptive GR-mediated effects on fear-motivated behavior that are linked to corticotropin releasing hormone (CRH). For this purpose the expression ratio of two splice variants of steroid receptor coactivator-1 (SRC-1) was altered via antisense-mediated 'exon-skipping' in the central amygdala of the mouse brain. We observed that a change in splicing towards the repressive isoform SRC-1a strongly reduced glucocorticoid-induced responsiveness of Crh mRNA expression and increased methylation of the Crh promoter. The transcriptional GR target gene Fkbp5 remained responsive to glucocorticoids, indicating gene specificity of the effect. The shift of the SRC-1 splice variants altered glucocorticoid-dependent exploratory behavior and attenuated consolidation of contextual fear memory. In conclusion, our findings demonstrate that manipulation of GR signaling pathways related to the Crh gene can selectively diminish potentially maladaptive effects of glucocorticoids.