AMN107, Novel Aminopyrimidine Inhibitor of Bcr-Abl, Is Significantly More Potent Than Imatinib Mesylate Against Philadelphia Chromosome Positive Acute Lymphoblastic Leukemia Cells.

Imatinib mesylate is effective against Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL) but, when used as a single agent, responses are transient and most patients relapse within 4–6 months. AMN107 is a novel oral aminopyrimidine ATP-competitive inhibitor of the protein tyrosine kinase activity of Bcr-Abl. Following oral administration to animals, AMN107 is well absorbed, has a good pharmacokinetic profile, and is well tolerated. The activity of AMN107, relative to imatinib, in both Ph-positive (Z-119 and Z-181) and Ph-negative (Z-138) ALL cell lines was studied. Z-119 and Z-181 cells were derived from Ph-positive ALL patients and retained typical B-cell characteristics and phenotypes of the original leukemia, including cytogenetic abnormality t(9;22) and p190 Bcr/Abl kinase. Z-138, a Ph-negative cell line, was derived from a patient with chronic lymphocytic leukemia and supervening ALL. Treatment with AMN107 or imatinib for 3 days (MTS assay) inhibited proliferation of Z-119 cells with the IC₅₀ values of 19.3 nM and 620.0 nM, respectively, revealing AMN107 to be 32 fold more potent than imatinib. Treatment of Z-181 cell line lasted for 4 days (MTS assay) because of lower growth rate of these cells: IC₅₀ for AMN107 and imatinib were 1.6 nM and 63.9 nM, respectively, showing AMN107 to be 40 fold more potent than imatinib. Neither drug showed activity against Ph-negative Z-138 cells. We also compared the activity of AMN107 in Ph-positive ALL cell lines expressing p190 Bcr/Abl protein to that in Ph-positive chronic myeloid leukemia cell lines KBM5 and KBM7 expressing p210 Bcr/Abl protein. The activity was similar with IC₅₀ in KBM5 cells of 11.3 nM and in KBM7 cells of 4.3 nM. In experiments focused on cell cycle analysis we found that at equipotent doses (as determined by MTS assay) both drugs induced cell accumulation in G0/G1 phase in Z-119 but not in Z-181. We demonstrated that increasing equipotent concentrations of AMN107 and imatinib induced activation of caspase-3 that resulted in apoptosis, as assessed by propidium iodide staining, in Z-119 cells, while Z-181 cells showed lack of apoptotic response. Following treatment with a broad range of AMN107 and imatinib doses for 3 hrs, Bcr/Abl expression and phosphorylation were determined in Z-119 cells by immunoprecipitation and Western blotting: Bcr/Abl phosphorylation was inhibited completely with AMN107 at 125.0 nM, and with imatinib at 2500 nM, confirming again the higher potency of AMN107. Finally, similar differential effect of AMN107 and imatinib on Bcr/Abl protein expression and phosphorylation was observed in leukemic cells obtained from blood of Ph-positive ALL patients. We conclude that AMN107 has significant activity against Ph-positive ALL cells and warrants investigation in patients with Ph-positive ALL.