Effects of mTOR inhibitors in the control of non functioning pituitary adenomas cell growth

Introduction: The main therapeutic approach for non functioning pituitary adenomas (NFA) is surgery, since radiotherapy has several important side effects and medical therapy is rarely effective. Therefore, understanding the molecular pathways regulating NFA cell proliferation is crucial for future drug development. We here explore the possible role of mTOR inhibitors, Everolimus and BEZ235 (which also inhibits the PI3 K pathway) on the effects of Insulin-like Growth Factor-1 (IGF-1) in regulating NFA cell growth in primary culture. Aims: To this aim 20 NFA primary cultures were incubated with or without IGF-1 in the presence or in the absence of Everolimus and BEZ235, which down-regulate IGF-1 signalling through the PI3 K/Akt pathway. Materials and methods: Cell viability and apoptosis were evaluated after 48 h. AKT phosphorylation was evaluated by alpha-screen. Results: Everolimus and BEZ235 significantly reduced NFA cell viability, by 30 and 40% respectively., while IGF-1 enhanced cell viability, an effect completely blocked by the presence of mTOR inhibitors. Co-incubation with an IGF-1 receptor blocking antibody enhanced the antiproliferative effects of Everolimus and BEZ235. Phosphorylation of p70S6K, a down-stream effector of mTOR in the PI3K/Akt pathway, was as well enhanced by IGF-1 and reduced by Everolimus and BEZ235, indicating that IGF-1 exerts its proliferative effects by inducing this pathway, which, in turn, can be effectively blocked by mTOR inhibitors. We also observed that AKT phosphorylation is enhanced by IGF-1 treatment and significantly reduced by treatment with BEZ235. Conclusion: In conclusion, our results indicate that IGF-I directly stimulates NFA cell viability through its own receptor. This effect is blocked by Everolimus and BEZ235 which may represent a new medical therapeutic approach for NFA.