Characterization of peptide aptamers targeting Bfl-1 anti-apoptotic protein.

Bfl-1, an anti-apoptotic protein of the Bcl-2 family, has been identified as a potential therapeutic target for B-cell malignancies. We describe herein the first characterization of peptide aptamers selected against Bfl-1. We show that most of the Bfl-1 peptide aptamers do not interact with Bcl-2, Bcl-xL, or Mcl-1 in yeast and that some of them restore the pro-apoptotic activity of Bax in yeast in which Bax and Bfl-1 proteins are coexpressed. When expressed in mammalian cells, peptide aptamers interact with Bfl-1 and sensitize B-cell lines to apoptosis induced by chemotherapeutic agents. We further demonstrate that a nonconstrained peptide derived from one aptamer variable region reverses Bfl-1 anti-apoptotic activity in HeLa cells through disruption of Bax-Bfl-1 interaction. This peptide also promotes cell death in lymphoma B-cell lines expressing a high level of Bfl-1 and sensitizes these cells to drug-induced apoptosis. Taken together, these results further validate Bfl-1 as a therapeutic target for malignant B-cells and suggest that peptide aptamers may be a useful tool for guiding the identification of small compounds that target the anti-apoptotic Bfl-1 protein.