Mutations in PIK3CA, which encodes the p110α subunit of the insulin-activated phosphatidylinositol-3 kinase (PI3K), and loss of function mutations in PTEN, which encodes a phosphatase that degrades the phosphoinositide lipids generated by PI3K, are among the most frequent events in human cancers1,2. However, pharmacological inhibition of PI3K has resulted in variable clinical responses, raising the possibility of an inherent mechanism of resistance to treatment. As p110α mediates virtually all cellular responses to insulin, targeted inhibition of this enzyme disrupts glucose metabolism in multiple tissues. For example, blocking insulin signalling promotes glycogen breakdown in the liver and prevents glucose uptake in the skeletal muscle and adipose tissue, resulting in transient hyperglycaemia within a few hours of PI3K inhibition. The effect is usually transient because compensatory insulin release from the pancreas (insulin feedback) restores normal glucose homeostasis3. However, the hyperglycaemia may be exacerbated or prolonged in patients with any degree of insulin resistance and, in these cases, necessitates discontinuation of therapy3,4,5,6. We hypothesized that insulin feedback induced by PI3K inhibitors may reactivate the PI3K–mTOR signalling axis in tumours, thereby compromising treatment effectiveness7,8. Here we show, in several model tumours in mice, that systemic glucose–insulin feedback caused by targeted inhibition of this pathway is sufficient to activate PI3K signalling, even in the presence of PI3K inhibitors. This insulin feedback can be prevented using dietary or pharmaceutical approaches, which greatly enhance the efficacy/toxicity ratios of PI3K inhibitors. These findings have direct clinical implications for the multiple p110α inhibitors that are in clinical trials and provide a way to increase treatment efficacy for patients with many types of tumour.
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This work was supported by NIH grant R35 CA197588 (L.C.C.), R01 GM041890 (L.C.C.), U54 U54CA210184 (L.C.C.), Breast Cancer Research Foundation (L.C.C.) and the Jon and Mindy Gray Foundation (L.C.C.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We appreciate the help of the small animal imaging core at MSKCC for assistance with FDG-PET imaging and the Columbia Irving Cancer Center Flow Core Facility, funded in part through Center Grant P30CA013696.
Nature thanks V. Longo, M. Pollak, C. Rask-Madsen and the other anonymous reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
Extended Data Fig. 2 Effect of feedback levels of insulin observed in Fig. 1 on BKM120 efficacy in vitro.
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