The phosphoinositide-3 kinase/mammalian target of rapamycin (PI3K/mTOR) pathway has been identified as a master regulator of cell growth, proliferation and survival.Ongoing clin. trials with mTOR or dual PI3K/mTOR inhibitors showed unmet need for a better, more tolerable mTOR inhibitor with addnl. tolerable activity on the PI3K.FP-208, an imidazoquinolinone derivative with flexible arms, showed well-balanced activities between mTOR (0.3 nM) and PI3K alpha (4.5 nM).The compound is soluble in water with a good oral PK profile and excellent bioavailability in mice, rats and monkeys.In vitro and in vivo studies showed clear activities against biomarkers specific for mTORC1 and mTORC2 signaling pathways.The antitumor activities of FP-208 were evaluated in human cancer xenograft models as well.Oral administration of the compound in tumor bearing mice strongly inhibited tumor growth as a single agent.Further anal. demonstrated that treatment with FP-208 inhibited phosphorylation of S6 and AKTS473 in mTORC1/2 pathways in the tumors.GLP toxicol. experiments showed that FP-208 was safe for rats and monkeys in a wide range of dosage.In summary, FP-208 is a good clin. candidate with well-balanced activities on mTOR and PI3K alpha, improved safety and tolerability, strong inhibition on xenograft tumors.