PI3K inhibition results in enhanced HER signaling and acquired ERK dependency in HER2-overexpressing breast cancer

• Published in: Oncogene Vol. 30; no. 22; pp. 2547 - 2557
• Main Authors: Serra, V, Scaltriti, M, Prudkin, L, Eichhorn, P J A, Ibrahim, Y H, Chandarlapaty, S, Markman, B, Rodriguez, O, Guzman, M, Rodriguez, S, Gili, M, Russillo, M, Parra, J L, Singh, S, Arribas, J, Rosen, N, Baselga, J
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 02-06-2011; Nature Publishing Group
• Subjects: 631/67/1059; 631/80/86; 692/699/67/1347; Analysis; Apoptosis; Biological and medical sciences; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - enzymology; Cancer therapies; Cell Biology; Cell Line, Tumor; Cell physiology; Cell transformation and carcinogenesis. Action of oncogenes and antioncogenes; Cellular signal transduction; Development and progression; Extracellular Signal-Regulated MAP Kinases - metabolism; Female; Fundamental and applied biological sciences. Psychology; Gene expression; Genetic aspects; Gynecology. Andrology. Obstetrics; Human Genetics; Humans; Internal Medicine; Kinases; Mammary gland diseases; Medical sciences; Medicine; Medicine & Public Health; Molecular and cellular biology; Monoclonal antibodies; Oncology; Original; original-article; Phosphoinositide-3 Kinase Inhibitors; Physiological aspects; Protein Kinase Inhibitors - therapeutic use; Protein kinases; Proto-Oncogene Proteins c-akt - metabolism; Receptor, ErbB-2 - metabolism; Receptor, ErbB-3 - metabolism; TOR Serine-Threonine Kinases - antagonists & inhibitors; Tumors; Spain; feedback; BEZ235; PI3K/mTOR; HER2; ERK; Breast disease; Extracellular signal-regulated protein kinase; Enzyme; Breast cancer; Malignant tumor; Carcinogenesis; Mammary gland diseases; Feedback; C-Onc gene; Inhibition; Cancer
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/onc.2010.626

There is a strong rationale to therapeutically target the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway in breast cancer since it is highly deregulated in this disease and it also mediates resistance to anti-HER2 therapies. However, initial studies with rapalogs, allosteric inhibitors of mTORC1, have resulted in limited clinical efficacy probably due to the release of a negative regulatory feedback loop that triggers AKT and ERK signaling. Since activation of AKT occurs via PI3K, we decided to explore whether PI3K inhibitors prevent the activation of these compensatory pathways. Using HER2-overexpressing breast cancer cells as a model, we observed that PI3K inhibitors abolished AKT activation. However, PI3K inhibition resulted in a compensatory activation of the ERK signaling pathway. This enhanced ERK signaling occurred as a result of activation of HER family receptors as evidenced by induction of HER receptors dimerization and phosphorylation, increased expression of HER3 and binding of adaptor molecules to HER2 and HER3. The activation of ERK was prevented with either MEK inhibitors or anti-HER2 monoclonal antibodies and tyrosine kinase inhibitors. Combined administration of PI3K inhibitors with either HER2 or MEK inhibitors resulted in decreased proliferation, enhanced cell death and superior anti-tumor activity compared with single agent PI3K inhibitors. Our findings indicate that PI3K inhibition in HER2-overexpressing breast cancer activates a new compensatory pathway that results in ERK dependency. Combined anti-MEK or anti-HER2 therapy with PI3K inhibitors may be required in order to achieve optimal efficacy in HER2-overexpressing breast cancer. This approach warrants clinical evaluation.