Strengths and limitations of Ba/F3 cells in modelling FLT3-driven AML resistance.

The Ba/F3 cell line is a widely used model in kinase drug development. Such cells are transformed to depend on a certain kinase for proliferation, and the use of an inhibitor of the kinase thus prevents their growth. We used Ba/F3 cells that expressed mutated FLT3 (FLT3-ITD), a known drug target in acute myeloid leukaemia (AML), to study drug resistance against two potent and selective inhibitors (gilteritinib and FF-10101). The cells could be made resistant to the drugs in concentrations that are similar to those in the plasma of patients, but this often required multiple secondary mutations. Several novel inhibitors, designed to be active against FLT3 mutants were tested but could not inhibit the growth of the resistant Ba/F3 cells. Several hitherto unidentified mutations in FLT3 were discovered that lead to drug resistance. These mutations were further studied using computational tools in order to understand how they lead to drug resistance. The discovery of novel mutations is significant since few patients were tested upon relapse due to lack of therapeutic options. Finally, we discuss the pros and cons of the Ba/F3 cell lines in the context of AML where patients express FLT3-ITD mutations in comparison with other cell lines, when the aim is development of drugs that overcome resistance.