In vitro activity: AZ3146 also inhibits FAK, JNK1, JNK2 and Kit. AZ3146 significantly inhibits phosphorylation of Mps1 in cells. Mitotic-specific phospho forms of aurora B and BubR1 are not affected by AZ3146. AZ3146 does not inhibit Cdk1 or aurora B in mitotic cells. HeLa cells treated with nocodazole and 2 μM AZ3146 only delay mitosis briefly and then rereplicate their genomes, indicating that AZ3146 overrides the SAC. AZ3146 also inhibits an already established SAC signal, as after release from a nocodazole block, AZ3146 dramatically accelerates mitotic exit.During an otherwise unperturbed mitosis, AZ3146 reduces the time to complete mitosis from 90 minutes in controls to 32 minutes. Strikingly, ~90% of AZ3146-treated HeLa cells undergo abnormal mitoses, although ~50% enter anaphase without aligning all of their chromosomes, and ~30% exit mitosis without undergoing obvious chromosome segregation. AZ3146 has a dramatic effect on kinetochore localization of Mad2, reducing its levels to ~15%, but its effect on Mad1 is less pronounced, with levels remaining at ~60%. When Mps1 is inhibited by AZ3146 before mitotic entry, subsequent recruitment of Mad1 and Mad2 to kinetochores is abolished. However, if Mps1 is inhibited by AZ3146 after mitotic entry, the Mad1–C-Mad2 core complex remains kinetochore bound, but O-Mad2 is not recruited to the core.

Kinase Assay: His-tagged human Mps1^Cat encoding amino acids 510-857 is generated. For kinase assays, 500 ng is added to buffer (25 mM Tris-HCl, pH 7.4, 100 mM NaCl, 50 μg/mL BSA, 0.1 mM EGTA, 0.1% β-mercaptoethanol, 10 mM MgCl₂, and 0.5 μg/mL myelin basic protein), AZ3146, and 100 μM γ-[³²P]ATP (2 μCi/assay). Reactions are incubated at 30°C for 20 min, spotted onto P81 paper, washed in 0.5% phosphoric acid, and immersed in acetone. Phosphate incorporation is determined by scintillation counting. For immunoprecipitation kinase assays, HeLa cells are treated with nocodazole for 14 h, mitotic cells isolated, washed in PBS, and lysed for 30 min in 50 mM Tris-HCl, pH 7.4, 100 mM NaCl, 0.5% NP-40, 5 mM EDTA, 5 mM EGTA, 40 mM β-glycerophosphate, 0.2 mM PMSF, 1 mM DTT, 1 mM sodium orthovanadate, 20 mM sodium fluoride, 1 μM okadaic acid, and complete EDTA-free protease inhibitor cocktail. Full-length Mps1 is immunoprecipitated. Purified complexes are washed with lysis buffer containing 100 mM NaCl and assayed as described for the recombinant protein. To quantify ³²P incorporation, reactions are stopped with SDS sample buffer and separated by SDS-PAGE followed by phosphorimaging. The plate is analyzed using a phosphorimager using AIDA software. To assess the specificity of AZ3146, a single-point screen is carried using kinase profiling service. 50 kinases are selected and assayed with 1 μM AZ3146

Cell Assay: In cellular culture, if Mps1 is inhibited by AZ3146 before mitotic entry, this inhibition abloshed the subsequent recruitment of Mad1 and Mad2 to kinetochores. However, if cells were treated with AZ3146 after mitotic entry, the Mad1-C-Mad2 core complex remains kinetochore bound, but O-Mad2 is not recruited to the core. , AZ3146 interferes with chromosome alignment and overrides spindle assembly checkpoint1.

J Cell Biol. 2010 Jul 12;190(1):25-34.