Development of selective inhibitors of the mammalian target of rapamycin

The mammalian target of rapamycin (mTOR) is a Ser/Thr protein kinase that regulates cell proliferation, size, and survival. Signaling through mTOR is hyperactivated in many human cancers and thus is an attractive target for cancer treatment. Rapamycin and its analogs selectively inhibit mTOR function and are under clinical development as anti-cancer agents.;mTOR exists in the cell as two distinct multiprotein complexes called mTORC1 and mTORC2. Rapamycin and its analogs bind to a domain of mTOR distinct from the kinase domain to block mTORC1 function, but do not affect the activity of mTORC2. Evidence indicates that compounds that inhibit both forms of mTOR, as might be achieved by directly targeting the kinase domain, should have better anticancer activity than rapamycin and its analogs.;The kinase domain of mTOR is highly homologous to the phosphatidyl inositol 3-kinases (PI3Ks) and related protein kinases. Many PI3K inhibitors are known, and most also inhibit mTOR. Two such compounds LY294002 and PI103 were used in this project as lead compounds for the development of inhibitors targeting mTOR. As the 3-D structure of mTOR has not been solved, homology modeling was performed based on a known PI3K structure to predict modifications to LY294002 to increase potency and selectivity toward mTOR. Two regions of the LY294002 structure were identified for variation, one in the region of a unique cysteine in the active site of mTOR and the other in the region of a Trp to Lys change in mTOR vs. PI3K that provides additional space in the active site for expansion of the inhibitor. A series of inhibitors have been prepared modified in each of these regions. The results of inhibition studies support the predictions based on homology modeling.;Flexible alignment of PI103 and LY294002 was used to predict the binding mode of PI103 to mTOR. Based on this alignment and the homology model, areas of PI103 were chosen for modification to increase activity toward mTOR. Compounds have been prepared and are awaiting testing. A pharmacophore model was developed based on known PI3K inhibitors and was used for virtual screening of databases of available compounds. Selected compounds have been tested as inhibitors of PI3K, resulting in the identification of new types of inhibitors of this class of enzymes. These compounds may serve as new leads for the development of more potent and selective inhibitors of mTOR.