Hydrocarbon peptide stapling

Bird GH, Madani N, Perry AF et al (2010) Hydrocarbon double-stapling remedies the proteolytic instability of a lengthy peptide therapeutic. Proc Natl Acad Sci USA 107 14093-14098... 

Kim Y-W, Grossmann TN, Verdine GL (2011) Synthesis of all-hydrocarbon stapled a-helical peptides by ring-closing olefin metathesis. Nat Protocol 6 761-771... 

Verdine and coworkers reported their first success with Bcl-2 family proteins using a stapled peptide analog of the proapoptotic Bid BH3 domain [37]. The hydrocarbon-crosslinked peptide was shown to bind Bcl-xL at the same binding site as wild-type Bid BH3 and with increased affinity. Importantly, the hydrocarbon crosslink rendered the stapled peptide cell permeable, where the wild-type peptide was not. In cell-based assays, stapled Bid BH3 was shown to sensitize cancer cells to Bax mediated apoptosis. In mice with leukemia xenografts, stapled Bid BH3 treatment consistently suppressed tumor growth. 

An alternative linker strategy recently employed in the synthesis of stapled peptides is through the incorporation of a triazole bridge, which was constructed through azido-acetylene click chemistry. These new stapled peptides offer enhanced chemical stability and further resistance to proteolysis [49c]. The linker length in these triazole bridge stapled peptides has a similar requirement as the hydrocarbon stapled peptide. 

Kim, Y.W. and Verdine, G.L. (2009) Stereochemical effects of all-hydrocarbon tethers in i,i + 4 stapled peptides. Bioorganic and Medicinal Chemistry Letters, 19, 2533-2536. 

Figure 9.4 Design of a,a-alkylated hydrocarbon-stapled peptides for HIV and glu-cokinase therapeutic targets.

Figure 9.7 Design of tandem hydrocarbon-stapled ( stitched ) peptides and expansion of click-stapling chemistry, including bis-triazolo-aiyl-stapling, to various intracellular targets.

Figure 9.9 3D-structural diversity of varying subclasses of hydrocarbon-stapled peptides, including double-turn, single-turn, stitch, i,i- -3 single-turn and H-bond surrogate macrocyclizations. 

Subsequent to having the desired a,a-diallq lated amino acids available, the synthesis of hydrocarbon-stapled peptides is relatively straightforward and employs solid-phase peptide chemistiy, as illustrated for ATSP-7041 (Scheme 9.2), to provide a feasible route for chemical development. As further detailed below, the hydrocarbon-stapled peptide ATSP-7041 is a dual MDM2/MDMX antagonist that exhibits high potency in vitro and efficacy in vivo in p53-dependent cancer models. 

Other noteworthy work focused on the biophysical and computational chemistry of stapled p53 peptide analogs of the SAH-p53-8 series (see compound 6) have shown a predictive correlation of a-helicity with experimental circular dichroism, and stapled p53 peptide binding to MDM2(X) further predicting direct contact between the hydrocarbon linker moiety of SAH-p53-8 (6) and the target protein. Importantly, such predictions were subsequently verified by the determination of an X-ray crystal structure of the stapled p53 peptide SAH-p53-8 bound to MDM2. Very recently,... 

Mcl-l is a recognized major resistance factor in human cancer and Mcl-l over-expression has been linked to the pathogenesis of several cancers. Its anti-apoptotic properties are mechanistically related to its neutralizing interaction with BIM, BAK, NOXA and PUMA. ° Recently, a compelling Mcl-l BH3 stapled peptide has been reported to exhibit highly specificity and affinity to bind Mcl-l as well as effectively sensitizing cancer cells to caspase-dependent apoptosis in vitroJ An X-ray structure of Mcl-l complexed with this Mcl-l BH3 stapled peptide was also determined and showed inter-molecular contact of its hydrocarbon staple moiety with Mcl-l, accounting for the specificity versus other Bcl-2 family proteins. 

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