Stapled Peptide Inhibition of Myc and the Androgen Receptor

The deregulation of transcription factors that normally promote progression through the cell cycle in response to external stimuli is one mechanism through which cancer cells acquire the capacity for autonomous proliferation. Small molecule therapeutics have not been successful in inhibiting the protein-protein interactions that are essential for transcription factor function. All-hydrocarbon stapled peptides, developed a decade ago in the Verdine Laboratory, are a new class of molecule that has been shown to disrupt intracellular protein-protein interactions in vivo.;Myc is a basic helix-loop-helix leucine zipper (bHLHz) transcription factor that is deregulated in many types of cancer. Myc heterodimerizes with Max, a homologous transcription factor, and when bound to enhancer box DNA sequences, the Myc/Max heterodimer acts to increase the expression of target genes critical for cellular proliferation. More than one hundred short (8--26 residue) alpha-helical stapled peptides intended to compete with Max for binding to Myc were designed, synthesized and tested in vitro for the ability to inhibit dimerization of Myc with Max and thereby prevent heterodimer binding to DNA. One stapled peptide inhibited this interaction with an IC50 of approximately 250nM but did not display desired activity in cell-based assays. Additional approaches to the development of stapled peptide inhibitors of Myc/Max heterodimerization provided insights into the challenges faced in attempting to disrupt the Myc/Max protein-protein interaction.;The deregulation of the activity of the androgen receptor is implicated in the development of castration-resistant prostate cancer (CRPC), the most lethal form of prostate cancer. The androgen receptor engages in a ligand-dependent interaction with short a-helical regions from a variety of transcription coactivator proteins. Nearly one hundred stapled peptides bearing the FxxLF or a related motif critical for mediating binding to the androgen receptor were designed and screened for the ability to bind to the androgen receptor in vitro and inhibit the proliferation of an AR-dependent prostate cancer cell line. A subset of the stapled peptides bound to the androgen receptor with low nanomolar affinities and lead compounds that displayed potential in the cellular proliferation assay were identified.