The lactate salt of tozasertib, a synthetic, small-molecule Aurora kinase inhibitor with potential antitumor activity. Tozasertib binds to and inhibits Aurora kinases (AKs), thereby inducing apoptosis in tumor cells in which AKs are overexpressed. AKs, a family of serine-threonine kinases, are essential for mitotic progression, spindle formation, centrosome maturation, chromosomal segregation, and cytokinesis.