Pfizer’s Bosutinib Shows Promise in CML

Pfizer achieved positive results from a Phase III study of the investigational compound bosutinib as a first-line treatment in patients with Philadelphia chromosome positive (Ph+) chronic myeloid leukemia (CML). A significantly higher proportion of patients with newly diagnosed CML treated with bosutinib (39%) experienced a major molecular response (MMR), a secondary endpoint, compared with patients treated with imatinib (26%) in the intent-to-treat (ITT) population. However, the study did not meet its primary endpoint of superior complete cytogenetic response (CCyR) rate at one year versus imatinib (70% vs. 68%, respectively), in the ITT population.

Preliminary data show that fewer patients who took bosutinib progressed to an advanced phase of the disease (1.6%) compared to patients treated with imatinib (4%), and there were fewer deaths in the bosutinib arm (1.2%) than in the imatinib arm (3.2%). Patients responding to bosutinib achieved CCyR faster than those responding to imatinib (13 weeks vs. 25 weeks). Analysis also showed that bosutinib produced a higher rate of CCyR at one year compared to imatinib, 78% with bosutinib compared to 69% with imatinib.

Bosutinib is an investigational oral dual Src and Abl kinase inhibitor that is believed to work by dual inhibition of the Src and Abl tyrosine kinases, which may inhibit signaling in CML cells that allows the cells to grow, survive and reproduce. Based on these data, Pfizer is planning for regulatory submissions of Bosutinib in patients with CML in 2011.