Pfizer has been granted approval by the FDA for tyrosine kinase inhibitor Bosulif as an orphan drug to treat a form of chronic myelogenous leukaemia (CML) which affects around 5,500 patients in the US a year.
Bosulif (bosutinib) is indicated for patients with chronic, accelerated or blast phase Philadelphia chromosome-positive CML who are resistant to, or who cannot tolerate, other therapies, including Novartis’ Glivec/Gleevec (imatinib).
The treatment of CML was transformed by the arrival of Glivec onto the market in 2001 but, while survival improved, the development of resistance to therapy and disease progression has meant there is a need for additional lines of drug therapy.
“Despite recent advances, an unmet need remains for many CML patients who are refractory to one or more tyrosine kinase inhibitors,” said Dr Jorge Cortes of MD Anderson Cancer Centre in Texas, a lead investigator in the clinical trial programme for Bosulif.
Pfizer’s drug joins two other tyrosine kinase inhibitors used in the second-line treatment setting, namely Bristol-Myers Squibb/Otsuka’s Sprycel (dasatinib) and Novartis’ Tasigna (nilotinib).
Its approval was based on the results of a single clinical trial in 546 patients treated earlier with Glivec in which 34 per cent of patients achieved a major cytogenetic response with bosutinib after 24 weeks, compared to 27 per cent of those treated with Sprycel or Tasigna.
Of the patients who achieved a major cytogenetic response at any time, 52.8 per cent had their response last at least 18 months, according to the FDA.
In patients with accelerated CML previously treated with at least Glivec, 33 per cent had their blood counts return to normal range, known as a complete haematologic response.
All told, 55 per cent of patients achieved normal blood counts with no evidence of leukaemia – an overall haematologic response – within the first 48 weeks of treatment. And 15 per cent and 28 per cent of patients with blast phase CML achieved complete hematologic response and overall hematologic response, respectively.
Meanwhile, various other drug candidates are coming through the pipeline for CML, including Ariad’s much-fancied tyrosine kinase inhibitor ponatinib – which was filed for approval in the US in June and in Europe last week and tackles a genetic mutation in CML (T3151) that is not addressed by other therapies.
Other competition in the coming years could emerge from the likes of Cephalon/Hospira’s Omapro (omacetaxine), BioSante Pharma’s GVAX and Deciphera’s ABL inhibitor rebastinib (DCC-2036).