NVP-BEZ235, A Dual Inhibitor of Phosphoinositol-3-Kinase (PI3K) and Mammalian Target of Rapamycin (mTOR), Is a Potent Inhibitor of Lymphoma Cell Growth and Survival

Abstract 4965

The Phosphatidylinositol-3-kinase (PI3K)/AKT/mTOR pathway is frequently deregulated in Hodgkin (HL) and non-Hodgkin lymphoma (NHL), and has been linked with tumor cell growth and survival. Although several proteins/enzymes in this pathway can be targeted by a variety of small molecules in vitro and in vivo, it remains unclear which protein target is the ideal for clinical testing. Previous studies demonstrated that the clinical activity of mTOR inhibitors may be attenuated by a negative feedback loop that involves activation of AKT, suggesting that a dual inhibition of AKT and mTOR activation may produce a better therapeutic outcome. To test this hypothesis, we evaluated the in vitro activity of NVP-BEZ235, a dual inhibitor of PI3K and mTOR, in a panel of 13 HL and NHL cell lines. NVP-BEZ235 inhibited cell growth and induced apoptosis in lymphoma cell lines in a time and dose dependent manner. After 48 hours of incubation, the IC50 ranged between 50 and 100 nM, and it was equally effective in ABC and GCB-derived DLBCL cell lines. NVP-BEZ235 induced cell death was primarily due to induction of apoptosis, as evident by the annexin-V and PI dual staining method, and the induction of caspase 3 and PARP cleavage. NVP-BEZ235 effectively inhibited the activation of the PI3K pathway at several steps, including decreasing the phosphorylation level of p-Akt (Ser473), p-Akt (Thr308), p-mTOR, p-4-EBPI and pP70S6K. Because lymphoma cells frequently depend on multiple activated signaling pathways to promote their survival, including the JAK/STAT pathway, we investigated the potential synergy between PI3K and JAK/STAT pathway inhibitors. Lymphoma cells were variably sensitive to the JAK1/2 inhibitor INCB16562 in vitro. Submaximal concentrations of NVP-BEZ235 demonstrated a synergistic activity with INCB16562. Collectively, our data show that the PI3K/mTOR inhibitor NVP-BEZ235 is highly effective against a wide range of lymphoma cell lines, and warrants evaluating it alone and in combination with JAK/STAT inhibitors in phase I/II clinical trials in patients with relapsed lymphoma.