A cyclic peptide inhibitor of HIF-1 heterodimerization that inhibits hypoxia signaling in cancer cells.

Hypoxia inducible factor-1 (HIF-1) is a heterodimeric transcription factor that acts as the master regulator of cellular response to reduced oxygen levels, thus playing a key role in the adaptation, survival, and progression of tumors. Here we report cyclo-CLLFVY, identified from a library of 3.2 million cyclic hexapeptides using a genetically encoded high-throughput screening platform, as an inhibitor of the HIF-1α/HIF-1ß protein-protein interaction in vitro and in cells. The identified compound inhibits HIF-1 dimerization and transcription activity by binding to the PAS-B domain of HIF-1α, reducing HIF-1-mediated hypoxia response signaling in a variety of cell lines, without affecting the function of the closely related HIF-2 isoform. The reported cyclic peptide demonstrates the utility of our high-throughput screening platform for the identification of protein-protein interaction inhibitors, and forms the starting point for the development of HIF-1 targeted cancer therapeutics.

A cyclic peptide inhibitor of C-terminal binding protein dimerization links metabolism with mitotic fidelity in breast cancer cells.

Identification of direct modulators of transcription factor protein-protein interactions is a key challenge for ligand discovery that promises to significantly advance current approaches to cancer therapy. Here, we report an inhibitor of NADH-dependent dimerization of the C-terminal binding protein (CtBP) transcriptional repressor, identified by screening genetically encoded cyclic peptide libraries of up to 64 million members. CtBP dimers form the core of transcription complexes associated with epigenetic regulation of multiple genes that control many characteristics of cancer cells, including proliferation, survival and migration. CtBP monomers also have distinct and critical cellular function, thus current experimental tools that deplete all forms of a targeted protein (e.g. siRNA) do not allow the cellular consequences of this metabolically regulated transcription factor to be deciphered. The most potent inhibitor from our screen (cyclo-SGWTVVRMY) is demonstrated to disrupt CtBP dimerization in vitro and in cells. This compound is used as a chemical tool to establish that the NADH-dependent dimerization of CtBPs regulates the maintenance of mitotic fidelity in cancer cells. Treatment of highly glycolytic breast cancer cell lines with the identified inhibitor significantly reduced their mitotic fidelity, proliferation and colony forming potential, whereas the compound does not affect mitotic fidelity of cells with lower glycolytic flux. This work not only links the altered metabolic state of transformed cells to a key determinant of the tumor cell phenotype, but the uncovered compound also serves as the starting point for the development of potential therapeutic agents that target tumors by disrupting the CtBP chromatin-modifying complex.