KU-0063794

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]

Ku0063794 inhibits tumor growth and mTOR signaling in a preclinical renal cell carcinoma model. However, Ku0063794 was not more effective in the animal study. A possible explanation for lack of greater activity in vivo for Ku0063794^[2].

• mTOR complexes kinase assays

  HEK-293 cells are freshly lysed in Hepes lysis buffer. Lysate (1-4 mg) is pre-cleared by incubating with 5-20 μL of Protein G-Sepharose conjugated to pre-immune IgG. The lysate extracts are then incubated with 5-20 μL of Protein G-Sepharose conjugated to 5-20 μg of either anti-Rictor or anti-Raptor antibody, or pre-immune IgG. All antibodies are covalently conjugated to Protein G-Sepharose. Immunoprecipitations are carried out for 1 hour at 4 °C on a vibrating platform. The immunoprecipitates are washed four times with Hepes lysis buffer, followed by two washes with Hepes kinase buffer. For Raptor immunoprecipitates used for phosphorylating S6K1, for the initial two wash steps the buffer includes 0.5 M NaCl to ensure optimal kinase activity. GST-Akt1 is isolated from serum-deprived HEK-293 cells incubated with PI-103 (1 μM for 1 hour). GST-S6K1 is purified from serum-deprived HEK-293 cells incubated with rapamycin (0.1 μM for 1 hour). mTOR reactions are initiated by adding 0.1 mM ATP and 10 mM MgCl₂ in the presence of various concentrations of KU-0063794 and GST-Akt1 (0.5 μg) or GST-S6K1 (0.5 μg). Reaction are carried out for 30 minutes at 30 °C on a vibrating platform and stopped by addition of SDS sample buffer. Reaction mixtures are then filtered through a 0.22-μm-poresize Spin-X filter and samples are subjected to electrophoresis and immunoblot analysis with the indicated antibodies.

• Cell lines

  Wild-type and mLST8 deficient MEFs

• Concentrations

  Dissolved in DMSO, final concentration ~3 μM

• Incubation Time

  24, 48, and 72 hours

• Method

  Cells are treated with KU-0063794 for 24, 48, and 72 hours, and the medium is changed every 24 hours with freshly dissolved KU-0063794. For the measurement of cell growth, cells are washed once with PBS, and fixed in 4% (v/v) paraformaldehyde in PBS for 15 minutes. After washing once with water, the cells are stained with 0.1% Crystal Violet in 10% ethanol for 20 minutes and washed three times with water. Crystal Violet is extracted from cells with 0.5 mL of 10% (v/v) ethanoic (acetic) acid for 20 minutes. The eluate is then diluted 1:10 in water and absorbance at 590 nm is quantified. For the assessment of cell cycle distribution, cells are harvested by trypsinization, washed once in PBS, and re-suspended in ice-cold aq. 70% (v/v) ethanol. Cells are washed twice in PBS plus 1% (w/v) BSA and stained for 20 minutes in PBS plus 0.1% (v/v) Triton X-100 containing 50 g/mL propidium iodide and 50 g/mL RNase A. The DNA content of cells is determined using a FACSCalibur flow cytometer and CellQuest software. Red fluorescence (585 nm) is acquired on a linear scale, and pulse width analysis is used to exclude doublets. Cell-cycle distribution is determined using FlowJo software.

• Animal Models

  Nu/Nu nude mice

• Dosages

  8 mg/kg

• Administration

  i.p.