BMS-214662 Eliminates CML Stem Cells and Is Active Against Blast Crisis CML and Cells Expressing BCR-ABL Kinase Mutations.

Recently, we have shown that BMS-214662, a cytotoxic farnesyltransferase inhibitor (FTI), targets primitive progenitor cells (PPC) in chronic myeloid leukaemia (CML) [Copland et al, Blood2005;106:204a]. These PPC are believed to be responsible for the molecular persistence which occurs following treatment with imatinib mesylate (IM) in CML. We have also shown that neither dasatinib (BMS-354825) nor nilotinib (AMN107) targets these PPC in vitro [Copland et al, Blood2006;107:4532; Jorgensen et al, Blood2005;106:314a]. To further investigate the efficacy of BMS-214662 against CML stem cells we performed long term culture-initiating cell (LTC-IC) assays with both chronic phase CML and normal CD34 + progenitors to assess drug selectivity. The CD34 + cells were treated for 72 hours under the following conditions no drug control, IM 5μM, dasatinib 150nM, BMS-214662 250nM, IM + BMS-214662, dasatinib + BMS-214662 before LTC-IC assay. Compared to the no drug control, CD34 + CML cells showed increased colony formation in the IM and dasatinib arms (181 and 178% respectively) indicating that, by inhibiting proliferation, these drugs exert a protective effect on CML PPC. The addition of BMS-214662 to either IM or dasatinib significantly reduced the number of colonies compared to either agent alone (P=0.045 and P=0.029 respectively). The BMS-214662 containing arms showed a dramatic reduction in total colony numbers to 0 cells in the BMS-214662 arms. The disparate effects of BMS-214662 and BMS-225975 suggest that the efficacy of BMS-214662 in CML is not via inhibition of Ras. We then determined the efficacy of BMS-214662 in Ba/F3 cells expressing different BCR-ABL kinase mutations (WT BCR-ABL, T315I, M351T and H396P) using viable cell counts and 3 H thymidine proliferation assays. BMS-214662 was equipotent in both WT BCR-ABL and mutant BCR-ABL kinase expressing cells. These results provide further evidence that BMS-214662 selectively targets CML stem cells, acts in synergy with IM or dasatinib and may prove useful in the management of IM-resistant and BC CML.