Optimization of the Chemistry of Hydrocarbon-Stabilized Peptides

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The stapled peptide technology has afforded a novel method for the stabilization of biologically relevant peptide helices. Thus far, it has created unique opportunities for targeting discrete components of complex signaling pathways relevant to the pathogenesis of cancer. The use of this methodology has enabled our study of the apoptotic signaling pathway and, more recently, the manipulation of transcriptional pathways restricted to the nucleus. We aim to significantly evolve the stapled peptide strategy through chemical refinement in order to expand our ability to target pathologic protein interactions implicated in cancer. The goal of these experiments is to generate more versatile stapled peptides with enhanced intracellular delivery capability. Two major approaches with distinct goals will be explored. The first makes use of chemical reactions on purified peptides to mask acidic residues contained within their primary sequence. Blocking acidic residues increases the isoelectric point (pI) of the peptide, facilitating cell permeability. Upon internalization, cellular esterases trigger hydrolysis of the protecting groups, thereby liberating the original peptide within the cell and precluding its export. The second approach aims to deliver oligomers of stapled peptides by conjugation through the hydrocarbon cross-link. The metathesis (stapling) reaction results in the formation of an olefin which is primed for functionalization. Among the stapled peptides analyzed to date, the hydrocarbon cross-link does not interfere with the biological activity of the peptide. We propose to use the cross-link as a scaffold to attach cargo covalently via disulfide bonds. The ability of stapled peptides to transport cargo into cells using this method will be evaluated. Because the reducing environment of the cytoplasm cleaves the S-S bond, subsequent to cell entry the cargo would be liberated from the stapled peptide. Potential compounds that could be introduced into the cell with the help of a staple peptide include chemotherapeutic drugs, functional nucleic acids (siRNAs and micro-RNAs) or other macromolecules. The versatility of the alkene functional group will also allow us to derivatize the side chain for other purposes including the attachment of tethers that aid in solvation or the incorporation of polyethylene glycols (PEGs) to improve the pharmacokinetic behavior of these compounds.