The novel PI3K inhibitor S1 synergizes with sorafenib in non-small cell lung cancer cells involving the Akt-S6 signaling.

Non-small cell lung cancer (NSCLC) has been the major cause of cancer-related deaths worldwide. Targeted therapy has been available as an additive strategy for NSCLC patients, but the inevitable resistance to mono-targeted agents has largely hampered its usage in the clinic. We have previously designed and synthesized a novel small molecule compound S1, 2-methoxy-3-phenylsulfonamino-5-(quinazolin-6-yl) benzamides and demonstrated its inhibition of PI3K and mTOR as well as the anti-tumor potential. In the present study, we have identified that S1 alone or combined with the multi-kinase inhibitor sorafenib can inhibit the in vitro cell proliferation of NSCLC cells (A549, NCI-H157 and 95D cells) and tumor growth in the A549 xenograft model. S1 alone produced inhibitory effects on the colony formation, cell migration and invasion and angiogenesis, with more pronounced inhibition when used with sorafenib. We further revealed that S1 mainly inhibited the Akt/S6 phosphorylation while sorafenib mostly decreased the phosphorylation of ERK. Together, the novel PI3K/mTOR inhibitor S1 per se exhibits strong anti-tumor effects in NSCLC cells and A549 xenograft, effects possibly via its inhibition of cell proliferation, invasion and migration and angiogenesis. The combination of S1 and sorafenib exerts potentiated anti-tumor effects, in which the underlying mechanisms may involve their differential modulation of the phosphorylation of Akt and S6 in the PI3K/Akt/mTOR cascades and ERK phosphorylation in the Raf/MEK/ERK pathways. The combination of S1 and sorafenib could be used as an additive approach in treating NSCLC in the clinic.