KU-0063794S1226

Compared with the mTOR inhibitor PP242, KU-0063794 exhibits higher specificity for mTOR, as being inactive against PI3Ks or 76 other kinases. In HEK-293 cells, KU-0063794 at 30 nM is sufficient to rapidly ablate S6K1 activity by blocking the phosphorylation of the hydrophobic motif (Thr³⁸⁹) and subsequently the phosphorylation of the T-loop residue (Thr²²⁹). In case of IGF1 stimulation of serum-starved HEK-293 cells, 300 nM of KU-0063794 is needed to inhibit the S6K1 activity by ~90%. KU-0063794 at 100-300 nM also completely inhibits the amino-acid-induced phosphorylation of S6K1 and S6 protein. Similar to S6K1, KU-0063794 inhibits the phosphorylation of mTORC1 at Ser²⁴⁴⁸ and mTORC2 at Ser²⁴⁸¹ in a dose-dependent and time-dependent manner. In the presence of serum or following IGF1 stimulation, KU-0063794 induces a dose-dependent inhibition of the activity and phosphorylation of Akt at Ser⁴⁷³ and unexpected Thr³⁰⁸ as well as the phosphorylation of the Akt substrates PRAS40 at Thr²⁴⁶, GSK3α/GSK3β at Ser²¹/Ser⁹ and Foxo-1/3a at Thr²⁴/Thr³². KU-0063794 but not rapamycin inhibits SGK1 activity and Ser⁴²² phosphorylation as well as its physiological substrate NDGR1 in a dose-dependent manner, to the same extent as S6K1 and Akt phosphorylation, whereas KU-0063794 dose not inhibit phorbol ester induced ERK or RSK phosphorylation and RSK activation. Compared with rapamycin, KU-0063794 exhibits more significant potency to induce the complete dephosphorylation of 4E-BP1 at Thr³⁷, Thr⁴⁶ and Ser⁶⁵. KU-0063794 inhibits cell growth of both wild-type and mLST8-deficient MEFs and induces a G1 cell cycle arrest, more significantly than rapamycin. ^[1]