title: Constitutive and inducible Akt activity promotes resistance to chemotherapy, trastuzumab, or tamoxifen in breast cancer cells.
abstract: To evaluate the role of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in breast cancer cell survival and therapeutic resistance, we analyzed a panel of six breast cancer cell lines that varied in erbB2 and estrogen receptor status. Akt activity was constitutive in four cell lines and was associated with either PTEN mutations or erbB2 overexpression. Akt promoted breast cancer cell survival because a PI3K inhibitor, LY294002, or transient transfection of a dominant-negative Akt mutant inhibited Akt activity and increased apoptosis. When combined with therapies commonly used in breast cancer treatment, LY294002 potentiated apoptosis caused by doxorubicin, trastuzumab, paclitaxel, or etoposide. Potentiation of apoptosis by LY294002 correlated with induction of Akt by doxorubicin or trastuzumab alone that occurred before the onset of apoptosis. Similar results were observed with tamoxifen. Combining LY294002 with tamoxifen in estrogen receptor-positive cells greatly potentiated apoptosis, which was correlated with tamoxifen-induced Akt phosphorylation that preceded apoptosis. To confirm that the effects of LY294002 on chemotherapy-induced apoptosis were attributable to inhibition of Akt, we transiently transfected breast cancer cells with dominant-negative Akt and observed increased doxorubicin-induced apoptosis. Conversely, stably transfecting cells with constitutively active Akt increased Akt activity and attenuated doxorubicin-induced apoptosis. These studies show that endogenous Akt activity promotes breast cancer cell survival and therapeutic resistance, and that induction of Akt by chemotherapy, trastuzumab, or tamoxifen might be an early compensatory mechanism that could be exploited to increase the efficacy of these therapies.
authors.affiliation: Cancer Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20889, USA.
authors.forename: Amy S
authors.initials: AS
authors.lastname: Clark
authors.forename: Kip
authors.initials: K
authors.lastname: West
authors.forename: Samantha
authors.initials: S
authors.lastname: Streicher
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Dennis
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis; D001943:Breast Neoplasms / Q000188:drug therapy*; D002867:Chromones / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005047:Etoposide / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D009025:Morpholines / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D013629:Tamoxifen / Q000494:pharmacology*; D013997:Time Factors; D014162:Transfection; D000068878:Trastuzumab; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D011518:Proto-Oncogene Proteins; D013629:Tamoxifen; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D005047:Etoposide; D004317:Doxorubicin; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D000068878:Trastuzumab; D017239:Paclitaxel