Stapled Peptide Permeability

One of the most attractive properties of stapled peptides is their improvement in cell membrane penetration, which is a well-known disadvantage of peptides and their rnimics in the application of these drugs to intracellular targets. In order to track and quantify the stapled peptide penetrating the membrane, a fluorescent tag (such as FITC) is conjugated to the N-terminus of the stapled peptide. As a control, the unstapled peptide is also labeled. Then the cellular update of FITC-labeled peptides can be examined using confocal microscopy and quantified by flow cytometry these stapled peptides are reported to be localized to the cytoplasm with minimum distribution to the nucleus when the confocal experiment is coupled with nuclear staining. 

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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. 

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