Substrate-mimetic inhibitors of Akt as potential anti-cancer therapeutics

Amplification, overexpression, and elevated activation of Akt have been detected in many human malignancies making it a critical target for cancer therapy. The substrate-binding site offers a large number of potential interactions to a small molecule derived through mimicry of the key peptide sequence, providing a good opportunity for development of Akt-selective inhibitors. This project is aimed to elucidate the critical inhibitor/Akt interactions for the development of high affinity substrate-mimetic inhibitors to be evaluated for the consequences of Akt inhibition in carcinoma cells. A simple series of peptidomimetic inhibitors was generated directly from the minimal GSK3β substrate sequence (AcGRPRTTSF) by replacement of the non-critical amino acids. Replacement of the reactive serine residue by valine (a non-nucleophilic surrogate), the central -TT- dipeptide by p-amino benzoic acid (Abz), and inclusion of a small hydrophobic group (benzyl) at the C-terminus to complement the unoccupied hydrophobic pocket afforded a lead inhibitor with an IC50 of 28 μM. Further truncation of the N-terminal Ac-GRP-tripeptide sequence produced a series of compounds with much improved lipophilicity than the initial peptides and provided the opportunity for significant structural optimization.;Further refinement towards non-peptidic, small molecule substrate-mimetics focused on the incorporation of essential binding functionalities into rigid organic scaffolds that project substituents into the corresponding Akt binding pockets to deliver improved potency and lipophilicity. Optimization of compounds, therefore, focused on the systematic rigidification and replacement of the remaining amino acid residues in the existing peptidomimetic inhibitors. The first non-peptidic substrate-mimetic inhibitors of Akt were successful in providing compounds with comparable potency to the initial peptidomimetics, while eliminating the remaining amino acid residues.;The preliminary studies demonstrated that limited structural modification of the initial peptidic substrate provided peptidomimetic inhibitors with decreasing peptidic character, possessing reasonable cellular activity. Peptidomimetic and non-peptidic inhibitors showed promising in vivo anti-cancer activity through the selective inhibition of carcinoma cell growth over normal cells and the induction of apoptosis. This strategy has been shown to possess valuable potential to provide a useful set of molecular probes to assist in the validation of Akt as a potential target for anti-cancer drug design.