Ansamitocin p-3 (Maytansinol isobutyrate, NSC292222) is a potent tubulin polymerization inhibitor with IC50 of 3.4 μM.

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Cell lines: A31 and KB. Concentrations: Dissolved in DMSO, final concentrations ~10 μM. Incubation Time: ~24 hours. Method: After synchronized, cells are exposed to various Ansamitocin p-3 concentrations for ~24 hours. Cells are labeled with [3H]thymidine (5 Ci/mM, 1 μCi/mL) in 1 mL medium. After pulse-labeling at 37 °C for 1 hour, the cells on coverslips are fixed with methanol:acetic acid (3:1). The acidsoluble fraction is washed out from the cells, and a liquid scintillation counter is used to determine the radio activity of each coverslip. 

Polymerization inhibition assay: After the addition of 1M Tris buffer (pH 8.4, for blank) or 100 μL of various concentrations of Ansamitocin p-3 solution (GTP minus MES buffer), to 400 μL of bovine tubulin solution (1 mg/mL in cold MES buffer), maintained at 0 °C for 10 to 15 minutes, the mixture is warmed in a water bath at 37 °C for 30 to 60 minutes. Tubulin polymerization is followed by an increase in turbidity of the mixture during warming. The turbidity measurement is performed at 460 nm with a Hitachi type 101 spectrophotometer. 

 Animal Models: C57BL/6 mice bearing C1498, or B16 cells, Female DBA/2 mice bearing L1210, P815, or P388 cells, BALB/c mice bearing MOPC-104E cells, and ICR mice bearing sarcoma 180 and EAC. Dosages: about 200 μg/kg. Administration: Administered i.v. or i.p. daily. 

 Antibiotic C 15003P3 , NSC292222 , Maytansinol isobutyrate , 安丝菌素 P 3 , 安丝菌素 P 3 , NSC292222 , Maytansinol isobutyrate , Antibiotic C 15003P3 

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C₃₂H₄₃ClN₂O₉