Discovery at the interface: novel anti-cancer agents targeting human estrogen receptor/S100 interactions
Lee, David Hudson
MetadataShow full item record
For the past four decades, endocrine ligand-based inhibitor, Tamoxifen (TaM) has been administered as an effective treatment for ERα positive breast tumors of both premenopausal stage and postmenopausal stage. However, many ERα positive breast tumors are intrinsically resistant to TaM and other endocrine therapies, despite the tumor having high expression of ERα, and the tumors that are not intrinsically resistant will eventually acquire resistance in advanced stage of tumor progression. The mechanisms of resistance has not been clearly understood, but it is suggested that coregulator proteins of ERα may play a crucial role in ligand-independent pathways of ERα transactivation. It has been shown that (i) calmodulin, a ubiquitous Ca2+ sensor protein, is significantly overexpressed in breast tumors; (ii) ERα and ERE complex formation requires calmodulin directly binding to ERα, and is also required for the activation of an estrogen responsive promoter. The hinge region of ERα has been shown to participate as an allosteric binding site in the interaction between Estrogen Receptor alpha and calmodulin. Ca2+ -calmodulin directly binds to ER alpha in the hinge region, residues 298 - 317. In search of a novel anti-cancer agent, a library of interaction profiles of human ER-EF hand protein complexes was generated, and S100P was identified as potential targets due to the finding that S100P shares a high degree of sequence and structural homology with Calmodulin. Our objective is to develop peptidomimetics and small molecules to block ER-S100P interactions using drug discovery approach. A series of S100P peptides were designed and synthesized based on the interaction profiles of ER-EF hand protein complexes. Using the fold information and contact regions obtained in silico, 3D structures of ER-S100P protein complexes were reconstructed. These structures of ER best represent the conformational state sensed by the specific interacting partner. ER-S100P complex is distinct from CaM. The lack of the connective peptidic region between the EF hand pairs in S100P attributed to less interaction coverage than CaM. The identified ER conformation-sensing regions of the interacting EF hand proteins were used to develop a library of top peptidomimetics targeting the interfaces of ER-S100P interactions. We have evaluated their ability to block specific ER-S100 interactions inhibit cancer cell proliferation and ER-mediated transcription of target genes. The peptide P1 (GGGFIVFVG) derived from S100P 74-78 significantly decreased estrogen induced cell proliferation of MCF-7 cells, whereas, peptide P2 derived from S100P 74-81 (GGGFIVFVAAIG) did not. Pharmacophores from peptide P1-ER interactions was used to design high-affinity peptidomimetics and small molecules. The ensemble of ER-EF hand protein complexes generated by our integrated proteomics-assisted protein interaction profiling will shed light on the linger issue of hormone independent activation of ER at the molecular level and novel therapeutics targeting ER-S100P interactions, and warrants further studies with respect to its prognostic, predictive and potentially therapeutic value.