Description_x000D_ Packaging_x000D_ 5, 25 mg in glass bottle_x000D_ Biochem/physiol Actions_x000D_ XL388 is a potent, selective, orally bioavailable ATP-competitive inhibitor of mammalian target of rapamycin (mTOR) with an IC50 of 9.9 nM for mTOR, 8 nM for mTORC1, 166 nM for mTORC2, and 1000-fold selectivity for mTOR over the closely related PI3K kinases and a panel of 141 protein kinases tested. XL388 blocked mTORC1 phosphorylation of p70S6K (T389) with an IC50 value of 94 nM and blocked mTORC2 phosphorylationof AKT (S473) with an IC50 value of 350 nM. XL388 showed complete tumor growth inhibition in mice bearing MCF-7 xenograft tumors.