AKT is a key serine/threonine kinase in the PTEN/PI3K/AKT pathway(1) and activationof AKT is often observed in human cancers. To explore the role of AKT in cell survival in different tumor cells, we tested 20 human tumor cell lines for response to knockdown of AKT by small interference RNA (siRNA) and/or a kinase-dead mutant AKT. siRNA-mediated knockdown of all three AKT isoforms in tumor cell lines led to a reduction of phosphorylation of AKT substrates. Knockdown of AKT resulted in apoptosis in six out of 11 tumor cells with activated AKT. In contrast, knockdown of AKT induced apoptosis in three out of nine cell lines with a low level of active AKT. The responsiveness of the cells to knockdown of AKT was not affected by mutational status of p53 but appeared correlated with overexpression of HER2. To assess the role of individual AKT isoforms, five of the cell lines responsive to knockdown of AKT were further characterized. In ZR-75 cells, AKT1 is the predominant isoform responsible for cell proliferation and survival. Conversely, in IGROV1 cells, AKT2 plays a major role in cell proliferation, but no single isoform is essential for cell survival. Thus, the relative importance of the AKT isoforms is cell line-specific. Our data suggest that inhibiting all three AKT isoforms is necessary to elicit maximal apoptotic response in tumor cells, and the level of activated AKT is a favorable but not always reliable biomarker for preselection of responsive tumor cell lines to AKT inhibitors.

AKT kinases are attractive targets for small molecule drug discovery because of their key role in tumor cell survival/proliferation and their overexpression/activation in many human cancers. This review summarizes studies that support the rationale for targeting AKT kinases in new drug discovery efforts. Structural features of AKT kinase in its inactive and active states, as determined by crystal structure analysis, are described. Recent efforts in the development and biological evaluation of small molecule inhibitors of AKT, and the challenges remaining are summarized. Inhibitors targeting the ATP binding site, PH domain and protein substrate binding site, as well as isoform selective allosteric inhibitors are reviewed. Structure-based design using PKA mutants as surrogates and computer modeling in the discovery of selective inhibitors is discussed. The issues and challenges facing the development of different classes of inhibitors as therapeutics are also discussed.

Chiara Urbinati, Stefania Mitola, Elena Tanghetti, Chandra Kumar, Johannes Waltenberger, Vitro and Angiogenesis In Vivo as a Target for Blocking HIV-1 Tat-Induced Endothelial Cell Activation In 3 β V α Integrin Print ISSN: 1079-5642. Online ISSN: 1524-4636 Copyright © 2005 American Heart Association, Inc. All rights reserved. Greenville Avenue, Dallas, TX 75231 is published by the American Heart Association, 7272 Arteriosclerosis, Thrombosis, and Vascular Biology doi: 10.1161/01.ATV.0000186182.14908.7b 2005; 2005;25:2315-2320; originally published online September 15, Arterioscler Thromb Vasc Biol. http://atvb.ahajournals.org/content/25/11/2315 World Wide Web at: The online version of this article, along with updated information and services, is located on the http://atvb.ahajournals.org/content/suppl/2005/09/19/01.ATV.0000186182.14908.7b.DC1.html Data Supplement (unedited) at:

The AKT1, AKT2, and AKT3 kinases have emerged as critical mediators of signal transduction pathways downstream of activated tyrosine kinases and phosphatidylinositol 3-kinase. An ever-increasing list of AKT substrates has precisely defined the multiple functions of this kinase family in normal physiology and disease states. Cellular processes regulated by AKT include cell proliferation and survival, cell size and response to nutrient availability, intermediary metabolism, angiogenesis, and tissue invasion. All these processes represent hallmarks of cancer, and a burgeoning literature has defined the importance of AKT alterations in human cancer and experimental models of tumorigenesis, continuing the legacy represented by the original identification of v-Akt as the transforming oncogene of a murine retrovirus. Many oncoproteins and tumor suppressors intersect in the AKT pathway, finely regulating cellular functions at the interface of signal transduction and classical metabolic regulation. This careful balance is altered in human cancer by a variety of activating and inactivating mechanisms that target both AKT and interrelated proteins. Reprogramming of this altered circuitry by pharmacologic modulation of the AKT pathway represents a powerful strategy for rational cancer therapy. In this review, we summarize a large body of data, from many types of cancer, indicating that AKT activation is one of the most common molecular alterations in human malignancy. We also review mechanisms of activation of AKT kinases, examples of therapeutic modulation of the AKT pathway in animal models, and the current status of efforts to target molecular components of the AKT pathway for cancer therapy and, possibly, cancer prevention. (c) 2005 Elsevier Inc.

OBJECTIVE:The transactivating factor (Tat) of HIV-1 binds to alphavbeta3 integrin present on endothelial cells contributing to neovascularization. Here, we investigated the biological consequences of Tat/alphavbeta3 interaction and the antagonist effect of an Arg-Gly-Asp (RGD)-based peptidomimetic.METHODS AND RESULTS:Binding of Tat to endothelial alphavbeta3 triggers focal adhesion kinase and nuclear factor-kappaB activation, leading to endothelial cell proliferation, membrane ruffling, and motility in vitro and neovascularization in vivo. The RGD-peptidomimetic SCH221153 inhibits Tat/alphavbeta3 interaction in a solid phase binding assay and endothelial cell adhesion to immobilized Tat with a potency higher than that of RGD-containing peptides. Accordingly, SCH221153 inhibits Tat/alphavbeta3-dependent focal adhesion kinase and nuclear factor-kappaB activation, proliferation, membrane ruffling, and motility in endothelial cells. Finally, SCH221153 inhibits the angiogenic response triggered by Tat in the chick-embryo chorioallantoic membrane without affecting physiological vascularization. SCH221153 exerts these inhibitory effects without affecting the interaction of Tat with endothelial heparan sulfate proteoglycans or with the vascular endothelial growth factor receptor-2/kinase domain-containing receptor. In all the assays the negative control SCH216687 was ineffective.CONCLUSIONS:These data provide new insights on the mechanism of endothelial cell activation by Tat and point to RGD peptidomimetics as prototypes for the development of novel Tat antagonists.