Targeting MYC with modular synthetic transcriptional repressors derived from bHLH DNA-binding domains.

Despite unequivocal roles in disease, transcription factors (TFs) remain largely untapped as pharmacologic targets due to the challenges in targeting protein-protein and protein-DNA interactions. Here we report a chemical strategy to generate modular synthetic transcriptional repressors (STRs) derived from the bHLH domain of MAX. Our synthetic approach yields chemically stabilized tertiary domain mimetics that cooperatively bind the MYC/MAX consensus E-box motif with nanomolar affinity, exhibit specificity that is equivalent to or beyond that of full-length TFs and directly compete with MYC/MAX protein for DNA binding.

Versatile Peptide Macrocyclization with Diels-Alder Cycloadditions.

Macrocyclization can improve bioactive peptide ligands through preorganization of molecular topology, leading to improvement of pharmacologic properties like binding affinity, cell permeability, and metabolic stability. Here we demonstrate that Diels-Alder [4 + 2] cycloadditions can be harnessed for peptide macrocyclization and stabilization within a range of peptide scaffolds and chemical environments. Diels-Alder cyclization of diverse diene-dienophile reactive pairs proceeds rapidly, in high yield and with tunable stereochemical preferences on solid-phase or in aqueous solution.

Steroid receptor/coactivator binding inhibitors: An update.

The purpose of this review is to highlight recent developments in small molecules and peptides that block the binding of coactivators to steroid receptors. These coactivator binding inhibitors bind at the coregulator binding groove, also known as Activation Function-2, rather than at the ligand-binding site of steroid receptors. Steroid receptors that have been targeted with coactivator binding inhibitors include the androgen receptor, estrogen receptor and progesterone receptor.

Recent structural advances in constrained helical peptides.

Given the ubiquity of the ⍺-helix in the proteome, there has been much research in developing mimics of ⍺-helices, and most of this study has been toward developing protein-protein interaction inhibitors. A common strategy for mimicking ⍺-helices has been through the use of constrained, helical peptides. The addition of a constraint typically provides for conformational and proteolytic stability and, in some cases, cell permeability.

Using Tumor Explants for Imaging Mass Spectrometry Visualization of Unlabeled Peptides and Small Molecules.

Matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) imaging mass spectrometry has emerged as a powerful, label-free technique to visualize penetration of small molecules and , including in 3D cell culture spheroids; however, some spheroids do not grow sufficiently large to provide enough area for imaging mass spectrometry. Here, we describe an method for visualizing unlabeled peptides and small molecules in tumor explants, which can be divided into pieces of desired size, thus circumventing the size limitations of many spheroids. As proof-of-concept, a small molecule drug (4-hydroxytamoxifen), as well as a peptide drug (cyclosporin A) and peptide chemical probe, can be visualized after incubation with tumor explants so that this technique may provide a solution to robing cell penetration by unlabeled peptides.

A "cross-stitched" peptide with improved helicity and proteolytic stability.

A new computational approach to obtain quantitative energy profiles for helix folding was used in the design of orthogonal hydrocarbon and lactam bicyclic peptides. The proteolytically stable, "cross-stitched" peptide SRC2-BCP1 shows nanomolar affinity for estrogen receptor α and X-ray crystallography confirms a helical binding pose.

A Cell-Permeable Stapled Peptide Inhibitor of the Estrogen Receptor/Coactivator Interaction.

We and others have proposed that coactivator binding inhibitors, which block the interaction of estrogen receptor and steroid receptor coactivators, may represent a potential class of new breast cancer therapeutics. The development of coactivator binding inhibitors has been limited, however, because many of the current molecules which are active in in vitro and biochemical assays are not active in cell-based assays. Our goal in this work was to prepare a coactivator binding inhibitor active in cellular models of breast cancer.

Stapled Peptides with γ-Methylated Hydrocarbon Chains for the Estrogen Receptor/Coactivator Interaction.

"Stapled" peptides are typically designed to replace two non-interacting residues with a constraining, olefinic staple. To mimic interacting leucine and isoleucine residues, we have created new amino acids that incorporate a methyl group in the γ-position of the stapling amino acid S5. We have incorporated them into a sequence derived from steroid receptor coactivator 2, which interacts with estrogen receptor α.