Activation of the PI3K/Akt pathway is a common event in human cancers and is responsible for key aspects of the transformed phenotype. This pathway is activated in most breast cancers, but by different mechanisms including HER2 amplification, PI3K mutation and PTEN inactivation. Inhibition of this pathway is thus thought to be clinically useful, but the functional output of PI3K/Akt signaling and the corresponding clinical effects of its inhibition may be due to the mechanisms by which it is activated. The objective of this study was to determine the role of Akt activation in breast cancer asa function of mechanism of activation and whether inhibition of Akt signaling is a feasible approach to therapy. A selective allosteric inhibitor of Akt kinase was used to interrogate a panel of breast cancer cell lines characterized for genetic lesions that activate PI3K/Akt signaling: HER2 amplification or PI3K or PTEN mutations in order to determine the biochemical and biologic consequences of inhibition of this pathway. A variety of molecular techniques and tissue culture and in vivo xenograft models revealed that tumors with mutational activation of Akt signaling were selectively dependent on the pathway. In sensitive cells, pathway inhibition resulted in D-cyclin loss, G1 arrest and induction of apoptosis, whereas cells without pathway activation were unaffected. Most importantly, the drug effectively inhibited Akt kinase and its downstream effectors in vivo and caused complete suppression of the growth of breast cancer xenografts with PI3K mutation or HER2 amplification, including models of the latter selected for resistance to Herceptin. Furthermore, chronic administration of the drug was well-tolerated, causing only transient hyperglycemia without gross toxicity to the host despite the pleiotropic normal functions of Akt. These data demonstrate that breast cancers with PI3K mutation or HER2 amplification are selectively dependent on Akt signaling, and that effective inhibition of Akt in tumors is feasible and effective in vivo. These findings suggest that direct inhibition of Akt may represent a therapeutic strategy for breast and other cancers that are addicted to the pathway including tumors with resistant to Herceptin.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1891.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO