An orally bioavailable, selective inhibitor of the serine/threonine-protein kinase monopolar spindle 1 (Mps1; TTK), with potential antineoplastic activity. Upon administration, the Mps1 inhibitor BOS172722 binds to and inhibits the activity of Mps1, a core component of the spindle assembly checkpoint (SAC). Inhibition of Mps1 activity compromises spindle assembly checkpoint, increases chromosome missegregation errors and decreases cancer cell viability. Mps1, a dual-specificity protein kinase expressed in proliferating normal tissues and aberrantly overexpressed in certain tumor types, is activated during mitosis and is essential in proper SAC function and chromosomal alignment.