Journal Article

RAPTOR up-regulation contributes to resistance of renal cancer cells to PI3K-mTOR inhibition

Macaulay, Valentine M., Protheroe, Andrew S., Harris, Adrian L., Earwaker, Philip, Willenbrock, Frances, Anderson, Caroline

2018

Overview

The outlook for patients with advanced renal cell cancer (RCC) has been improved by targeted agents including inhibitors of the PI3 kinase (PI3K)-AKT-mTOR axis, although treatment resistance is a major problem. Here, we aimed to understand how RCC cells acquire resistance to PI3K-mTOR inhibition. We used the RCC4 cell line to generate a model of in vitro resistance by continuous culture in PI3K-mTOR kinase inhibitor NVP-BEZ235 (BEZ235, Dactolisib). Resistant cells were cross-resistant to mTOR inhibitor AZD2014. Sensitivity was regained after 4 months drug withdrawal, and resistance was partially suppressed by HDAC inhibition, supporting an epigenetic mechanism. BEZ235-resistant cells up-regulated and/or activated numerous proteins including MET, ABL, Notch, IGF-1R, INSR and MEK/ERK. However, resistance was not reversed by inhibiting or depleting these pathways, suggesting that many induced changes were passengers not drivers of resistance. BEZ235 blocked phosphorylation of mTOR targets S6 and 4E-BP1 in parental cells, but 4E-BP1 remained phosphorylated in resistant cells, suggesting BEZ235-refractory mTORC1 activity. Consistent with this, resistant cells over-expressed mTORC1 component RAPTOR at the mRNA and protein level. Furthermore, BEZ235 resistance was suppressed by RAPTOR depletion, or allosteric mTORC1 inhibitor rapamycin. These data reveal that RAPTOR up-regulation contributes to PI3K-mTOR inhibitor resistance, and suggest that RAPTOR expression should be included in the pharmacodynamic assessment of mTOR kinase inhibitor trials.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: 1-Phosphatidylinositol 3-kinase / AKT protein / Allosteric properties / Analysis / Antineoplastic Agents - pharmacology / Antineoplastic Agents - therapeutic use / Benzamides / Biology and Life Sciences / Cancer / Cancer cells / Cancer therapies / Carcinoma, Renal Cell - drug therapy / Carcinoma, Renal Cell - metabolism / Carcinoma, Renal Cell - pathology / Cell culture / Cell Line, Tumor / Clinical trials / Continuous culture / Drug dosages / Drug resistance / Drug Resistance, Neoplasm / Enzyme inhibitors / Experiments / Extracellular signal-regulated kinase / Gene expression / Genetic aspects / Genetic regulation / Hematology / Histone deacetylase / Histone Deacetylase Inhibitors - pharmacology / Humans / Imidazoles - pharmacology / Imidazoles - therapeutic use / Inhibition / Inhibitors / Insulin-like growth factors / Kidney cancer / Kidney Neoplasms - drug therapy / Kidney Neoplasms - metabolism / Kidney Neoplasms - pathology / Kinases / Medicine and Health Sciences / Metastasis / Morpholines - therapeutic use / mRNA / Mutation / Oncology / Passengers / Pharmacodynamics / Pharmacology / Phosphoinositide-3 Kinase Inhibitors / Phosphorylation / Proteins / Pyrimidines / Quinolines - pharmacology / Quinolines - therapeutic use / Rapamycin / Regulatory-Associated Protein of mTOR - metabolism / Renal cell carcinoma / Research and Analysis Methods / Signal Transduction - drug effects / TOR protein / TOR Serine-Threonine Kinases - antagonists & inhibitors / Treatment resistance / Up-Regulation