Omacetaxine: a protein translation inhibitor for treatment of chronic myelogenous leukemia.

Chronic myelogenous leukemia (CML) is driven by the Bcr-Abl fusion protein, which is a result of a (9;22) chromosomal translocation. Imatinib, dasatinib, and nilotinib (tyrosine kinase inhibitors, TKI) have revolutionized how CML is treated. Although the majority of patients respond to these kinase inhibitors, a subset becomes resistant to these therapeutics. Synribo (omacetaxine mepesuccinate) was recently approved by the U.S. Food and Drug Administration for Philadelphia-positive CML either in the chronic or the accelerated phase whose disease failed two prior TKIs. With omacetaxine 1.25 mg/m(2) twice daily for 14 days during induction and for 7 days during maintenance, a major cytogenetic response occurred in 20% of patients in the chronic phase and major hematologic response in 27% of patients in the accelerated phase. Laboratory investigations unraveled the mechanism of action and effectiveness of this agent. Bcr-Abl protein is intrinsically programmed to turn over with a short half-life that makes it susceptible to protein translation inhibitors. Omacetaxine (homoharringtonine) inhibits total protein biosynthesis by binding to A-site cleft of ribosomes. As a corollary to this action, there is a diminution of short-lived proteins, such as Bcr-Abl, followed by cell death. Approval of this first-in-class protein translation inhibitor opens up new avenues for its use in other diseases as well as mechanism-based combinations.