The Pleckstrin homology (PH) domain is a modular structurally conserved protein superfold that binds to plasma membrane phosphoinositide (PtdIns)-3 phosphates causing the host proteins to move to the plasma membrane where they initiate signal transduction cascades critical to cell growth and survival. Ptdlns binding PH domains provide a rich and, as yet, unmined family of unique target sites for anticancer drug discovery. Akt (protein kinase B) is a PH domain containing serine/threonine kinase that is a key component of the PtdIns-3-kinase cell survival signaling pathway. Downstream protein targets phosphorylated by Akt act to inhibit apoptosis and are a major reason cancer cells are resistant to apoptosis. The hypothesis upon which our work is based is that the Ptdlns binding PH domain of Akt provides a novel signaling pathway important for cancer cell survival, and these agents will have antitumor and chemosensitizing activity. This is a novel approach to cancer drug discovery that seeks to block a specific protein/lipid interaction, and thus, prevent the subcellular translocation of the target signaling protein. Using the crystal structure of the PH domain of human Akt and Ins(l,3,4,5)P4, we have conducted in silico screening to identify four novel classes of small molecules that bind selectively to the PH domain of Akt compared to PH domains of other proteins. The lead compounds have been shown to inhibit Akt activation in cancer cells. The objectives of the proposed studies are to obtain molecular validation for Akt relative to other PH domain proteins as a cancer drug target, to use molecular docking and rational drug design to identify specific Akt PH domain inhibitors, to use an iterative process to improve the selectivity of the compounds for the PH domain of Akt, and to identify lead compounds with in vivo antitumor activity for preclinical development. We will focus our studies on pancreatic cancer, a devastating disease for which new treatments are urgently needed. The PtdIns-3-kinase/Akt signaling pathway is upregulated in many pancreatic cancers making it an ideal target for drugs to treat the disease.
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