Novel Inhibitors of AKT: Assessment of a Different Approach Targeting the Pleckstrin Homology Domain

E.      J. Meuillet

Abstract

Protein kinase B/AKT plays a central role in cancer. The serine/threonine kinase is over-expressed or constitutively active in many cancers and has been validated as a therapeutic target for cancer treatment. However, targeting the kinase activity has revealed itself to be a challenge due to non-selectivity of the compounds towards other kinases. This review summarizes other approaches scientists have developed to inhibit the activity and function of AKT. They consist of targeting the pleckstrin homology (PH) domain of AKT. Indeed, upon the generation of 3-phosphorylated phosphatidylinositol phosphates (PI3Ps) by PI3-kinase (PI3K), AKT translocates from the cytosol to the plasma membrane and binds to the PI3Ps via its PH domain. Thus, several analogs of PI3Ps (PI Analogs or PIAs), alkylphospholipids (APLs), such as edelfosine, and inositol phosphates (IPs) have been described that inhibit the binding of the PH domain to PI3Ps. Recently allosteric inhibitors and small molecules that do not bind the kinase domain but affect the kinase activity of AKT, presumably by interacting with the PH domain, have also been identified. Finally, several drug screening studies spawned novel chemical scaffolds that bind the PH domain of AKT. Together, these approaches have been more or less successful in vitro and to some extent translated in preclinical studies. Several of these new AKT PH domain inhibitors exhibit promising anti-tumor activity in mouse models and some of them show synergy with ionizing radiation and chemotherapy. Early clinical trials have started and results will attest to the validity and efficacy of such approaches in the near future.

Keywords: AKT, pleckstrin homology domain, rational drug design, inhibitor, allosteric, kinase, B/AKT, serine/threonine kinase, PI3-kinase