Kinase experiment:

BTB-1 is prepared in DMSO. The activity of His-Kif18Amotor at increasing concentrations of ATP is monitored in the presence of 3 μM Mts and increasing concentrations of BTB-1 (0.21 μM, 0.42 μM, 0.85 μM, 1.7 μM) or DMSO as control[1].

BTB-1 is a potent, selective and reversible mitotic motor protein Kif18A inhibitor with an IC50 of 1.69 μM.

BTB-1 blocks the motility of Kif18A in a reversible manner. BTB-1 inhibits Kif18A in an adenosine triphosphate (ATP)-competitive but microtubule-uncompetitive manner and slows down the progression of cells through mitosis. 100 μM BTB-1 does not significantly inhibit any of the other tested mitotic kinesins. BTB-1 competes with ATP for Kif18A binding only when the motor-protein is associated with its pseudosubstrate microtubules. HeLa cells treated with BTB-1 accumulate in mitosis in a dose-dependent manner[1]. BTB-1 shows cell toxicity with an EC50 values of 35.8 μM. HeLa cells treated with 50 μM BTB-1 reveals severe defects in spindle morphology and chromosome alignment. Treatment with high concentrations of BTB-1 does not result in elongated spindles[2].

[1]. Catarinella M, et al. BTB-1: a small molecule inhibitor of the mitotic motor protein Kif18A. Angew Chem Int Ed Engl. 2009;48(48):9072-6. [2]. Braun J, et al. Synthesis and biological evaluation of optimized inhibitors of the mitotic kinesin Kif18A. ACS Chem Biol. 2015 Feb 20;10(2):554-60.