Two major pharmacological hurdles severely limit the widespread use of small
peptides as
therapeutics: poor proteolytic stability and membrane permeability. Importantly, low aqueous solubility also impedes the development of
peptides for clinical use. Various elaborate side chain stapling chemistries have been developed for α-helical
peptides to circumvent this problem, with considerable success in spite of inevitable limitations. Here we report a novel
peptide stapling strategy based on the dithiocarbamate chemistry linking the side chains of residues Lys(i) and Cys(i + 4) of unprotected
peptides and apply it to a series of dodecameric
peptide antagonists of the p53-inhibitory oncogenic
proteins MDM2 and MDMX. Crystallographic studies of
peptide-MDM2/MDMX complexes structurally validated the chemoselectivity of the dithiocarbamate staple bridging Lys and Cys at (i, i + 4) positions. One dithiocarbamate-stapled PMI derivative, DTCPMI, showed a 50-fold stronger binding to MDM2 and MDMX than its linear counterpart. Importantly, in contrast to PMI and its linear derivatives, the DTCPMI
peptide actively traversed the cell membrane and killed HCT116
tumor cells in vitro by activating the
tumor suppressor protein p53. Compared with other known stapling techniques, our
solution-based DTC stapling chemistry is simple, cost-effective, regio-specific and environmentally friendly, promising an important new tool for the development of
peptide therapeutics with improved pharmacological properties including aqueous solubility, proteolytic stability and membrane permeability.