Summary of recent advancesHerein we review contemporary synthetic and protein design strategies to stabilize the α-helical motif in short peptides and miniature proteins. Advances in organometallic catalyst design, specifically for the olefin metathesis reaction, enable the use of hydrocarbon bridges to either crosslink side chains of specific residues or mimic intramolecular hydrogen bonds with carbon-carbon bonds. The resulting hydrocarbon-stapled and hydrogen bond surrogate α-helices provide unique synthetic ligands for targeting biomolecules. In the protein design realm, several classes of miniature proteins that display stable helical domains have been engineered and manipulated with powerful in vitro selection technologies to yield libraries of sequences that retain their helical folds. Rational re-design of these scaffolds provide distinctive reagents for the modulation of protein-protein interactions.

Designed ligands that inhibit hypoxia-inducible gene expression could offer new tools for genomic research and, potentially, drug discovery efforts for the treatment of neovascularization in cancers. We report a stabilized alpha-helix designed to target the binding interface between the C-terminal transactivation domain (C-TAD) of hypoxia-inducible factor 1alpha (HIF-1alpha) and cysteine-histidine rich region (CH1) of transcriptional coactivator CBP/p300. The synthetic helix disrupts the structure and function of this complex, resulting in a rapid downregulation of two hypoxia-inducible genes (VEGF and GLUT1) in cell culture.

Selective blockade of gene expression by designed small molecules is a fundamental challenge at the interface of chemistry, biology, and medicine. Transcription factors have been among the most elusive targets in genetics and drug discovery, but the fields of chemical biology and genetics have evolved to a point where this task can be addressed. Herein we report the design, synthesis, and in vivo efficacy evaluation of a protein domain mimetic targeting the interaction of the p300/CBP coactivator with the transcription factor hypoxia-inducible factor-1α. Our results indicate that disrupting this interaction results in a rapid down-regulation of hypoxia-inducible genes critical for cancer progression. The observed effects were compound-specific and dose-dependent. Gene expression profiling with oligonucleotide microarrays revealed effective inhibition of hypoxia-inducible genes with relatively minimal perturbation of nontargeted signaling pathways. We observed remarkable efficacy of the compound HBS 1 in suppressing tumor growth in the fully established murine xenograft models of renal cell carcinoma of the clear cell type. Our results suggest that rationally designed synthetic mimics of protein subdomains that target the transcription factor-coactivator interfaces represent a unique approach for in vivo modulation of oncogenic signaling and arresting tumor growth.helix mimetics | synthetic inhibitors of transcription | rational design | hydrogen bond surrogate helices

No abstract

Selective blockade of hypoxia-inducible gene expression by designed small molecules would prove valuable in suppressing tumor angiogenesis, metastasis and altered energy metabolism. We report the design, synthesis, and biological evaluation of dimeric epidithiodiketopiperazine (ETP) small molecule transcriptional antagonist targeting the interaction of the p300/CBP coactivator with the transcription factor HIF-1α. Our results indicate that disrupting this interaction results in rapid downregulation of hypoxia-inducible genes critical for cancer progression. The observed effects are compound-specific and dose-dependent. Controlling gene expression with designed small molecules targeting the transcription factor-coactivator interface may represent a new approach for arresting tumor growth.

Scheme I. Reaction equation for the aldol condensation.

Hypoxia-Inducible Factor (HIF-1) is a heterodimeric transcriptional activator which plays a critical role in tumorigenesis and therefore is an important therapeutic target. Transcriptional activation of HIF-1 is known to involve the interaction between cysteine-histidine rich region1 (CH1) of a coactivator protein p300 or Creb Binding Protein (CBP) and C-terminal activation domain (C-TAD) of its α-subunit (HIF-1α C-TAD). Based on the hydrogen bond surrogate (HBS) approach, we have rationally designed stabilized alpha helix that can disrupt the binding interface between C-TAD domain of HIF-1α and CH1 domain of p300/CBP. We have shown by fluorescence polarization that such stabilized alpha helix mimetics can directly bind to the CH1 domain of p300 and also can disrupt the HIF-1α/p300 complex. HBS helix mimetics are also shown to selectively downregulate the hypoxia inducible genes in cell culture. Thus, orthosteric inhibition of the HIF-1 transcriptional complex by rationally designed helix mimetics offers a novel approach to downregulate the expression of key hypoxia inducible genes responsible for tumor progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 289. doi:1538-7445.AM2012-289

Table 1 shows incorrect placement of crosslinks in sequences 1-3. The pentenoic acid residue (X) was crosslinked to the fourth residue (alanine) rather than glutamic acid, which is the fifth residue in the sequence. The corrected Table is shown below.