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

Abstract

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.

• Authors: Philip Earwaker, Caroline Anderson, Frances Willenbrock, Adrian L Harris, Andrew S Protheroe, Valentine M Macaulay
• Journal: PloS one (PLoS One) Vol. 13 Issue 2 Pg. e0191890 ( 2018) ISSN: 1932-6203 [Electronic] United States
• PMID: 29389967 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antineoplastic Agents
• Benzamides
• Histone Deacetylase Inhibitors
• Imidazoles
• Morpholines
• Phosphoinositide-3 Kinase Inhibitors
• Pyrimidines
• Quinolines
• RPTOR protein, human
• Regulatory-Associated Protein of mTOR
• vistusertib
• MTOR protein, human
• TOR Serine-Threonine Kinases
• dactolisib

Topics

• Antineoplastic Agents (pharmacology, therapeutic use)
• Benzamides
• Carcinoma, Renal Cell (drug therapy, metabolism, pathology)
• Cell Line, Tumor
• Drug Resistance, Neoplasm
• Histone Deacetylase Inhibitors (pharmacology)
• Humans
• Imidazoles (pharmacology, therapeutic use)
• Kidney Neoplasms (drug therapy, metabolism, pathology)
• Morpholines (therapeutic use)
• Phosphoinositide-3 Kinase Inhibitors
• Pyrimidines
• Quinolines (pharmacology, therapeutic use)
• Regulatory-Associated Protein of mTOR (metabolism)
• Signal Transduction (drug effects)
• TOR Serine-Threonine Kinases (antagonists & inhibitors)
• Up-Regulation