The U.S. Food and Drug Administration (FDA) has approved Bosulif® (bosutinib) to treat chronic myelogenous leukemia (CML), a blood and bone marrow disease that usually affects older adults. The drug is intended for patients with chronic, accelerated or blast phase Philadelphia chromosome positive CML who are resistant to or who cannot tolerate other therapies, including imatinib.
Each year in the United States, approximately 5,000 people are diagnosed with CML. Most cases of CML are characterized by a chromosomal abnormality—the Philadelphia chromosome—in which genetic material is exchanged between chromosome 9 and chromosome 22. This exchange brings together two genes: BCRand ABL. The combination of these two genes into the single BCR-ABL gene results in the production of a protein that contributes to uncontrolled cell growth.
Recognition of the pivotal role of the BCR-ABL protein in CML led to the development of Gleevec, which blocks the activity of this protein. Gleevec produced high rates of remission among patients with chronic-phase CML and dramatically changed the treatment of this disease. Newer drugs that target the BCR-ABL protein include Tasigna® (nilotinib) and Sprycel® (dasatinib). Both Tasigna and Sprycel appear to be superior to Gleevec for the initial treatment of patients with CML and are approved by the FDA for this purpose.
Bosulif is a third-generation tyrosine kinase inhibitor that targets both Abl and Src kinases. Targeting of Src by Bosulif is thought to be important, as over-expression of Src kinases has been associated with resistance to Gleevec.
The approval of Bosulif was based on the results of a single clinical trial that included 546 adult patients with chronic, accelerated or blast phase CML. All patients had disease that progressed after treatment with imatinib or imatinib followed by dasatinib and/or nilotinib, or who could not tolerate the side effects of prior therapy. All patients in the trial were treated with Bosulif.
The results of the study showed that 34 percent of patients with chronic phase CML who had been previously treated with imatinib achieved a major cytogenetic response (MCyR) within the first 24 weeks of treatment (which was determined to be the benchmark for efficacy). Among patients who achieved MCyR at any time, 52.8 percent had their response last at least 18 months. In evaluating patients previously treated with imatinib followed by dasatinib and/or nilotinib, researchers found that 27 percent of these patients achieved MCyR within the first 24 weeks of treatment. Of those who achieved MCyR at any time, 51.4 percent had their MCyR last at least nine months.
Among patients with accelerated CML previously treated with at least imatinib, 33 percent experienced a complete hematologic response (meaning blood counts returned to the normal range) and 55 percent achieved overall hematologic response (normal blood counts with no evidence of disease) within the first 48 weeks of treatment. Among patients with blast phase CML, 15 percent achieved complete hematologic response and 28 percent achieved overall hematologic response.
The most common side effects observed with Bosulif were diarrhea, nausea, thrombocytopenia (low platelet levels), vomiting, abdominal pain, rash, anemia (low red blood cell count), fever, and fatigue.
The recommended dose and schedule for Bosulif is 500 mg orally once daily with food. Treatment is to be continued until disease progression or patient intolerance.
FDA approves new orphan drug for chronic myelogenous leukemia [FDA News Release]. U.S. Food and Drug Administration website. Available at: http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm318160.htm