TYPE I BIR DOMAIN INHIBITORS IN CANCER THERAPY: SEARCHING DRUGS FOR REGULATION OF THE NF-B PATHWAY

Federica Cossu, Luca Sorrentino, Mattia Zaffaroni, Daniele Lecis, Mario Milani and Eloise Mastrangelo

Biophysics Institute, National Research Council, Milano, Italy

Abstract

The over-expression of Inhibitors of apoptosis proteins (IAPs) enhances cell survival and resistance to anticancer agents. IAPs are E3-ligases, ubiquitylating substrates for the regulation of NF-kB; furthermore, they sequester caspases to prevent apoptosis. IAPs interactions occur through Type-I and type-II BIR (Baculovirus IAP repeat) domains. Smac-mimetics (SMs), mimicking the N-terminal peptide of the natural antagonist of IAPs, interact with type-II BIRs, relieving caspases from X-linked IAP (XIAP) and leading to cellular IAPs (cIAPs) proteasomal degradation. Although SMs are currently validated candidates for cancer therapy, some cancer-cell lines retain SM-resistance due to cIAP2 overexpression and NF-B re-activation. IAPs-mediated regulation of NF-kB signaling is based on the formation of different protein complexes by Type-I BIRs, regulating ubiquitin-dependent signal transduction. We analyzed X- and cIAP-BIR1 surfaces to identify hot-spots involved in protein-protein interactions. Virtual docking selected hits able to impair BIR1-based complexes with predicted low μM affinities (i.e. NF023) that were experimentally confirmed. 3D-structural analysis of the protein-ligand complexes obtained allowed the optimization of specific and selective drug candidates. Treatment of cancer-cells with the selected compounds will validate their effects on IAPs-dependent signaling cascades. This approach represents a novel strategy to promote apoptosis in cancer, providing new insights on the regulation of NF-kB pathway.

Keywords: Structure-based drug design, in silico docking, protein-protein interaction, apoptosis, anti-cancer drugs.