Overcoming imatinib resistance using Src inhibitor CGP76030, Abl inhibitor nilotinib and Abl/Lyn inhibitor INNO-406 in newly established K562 variants with BCR-ABL gene amplification

Because imatinib (IM) resistance in chronic myeloid leukemia is primarily caused by the re-establishment of AN kinase, new inhibitors may be efficacious. We evaluated 3 new agents against 2 new K562 variants, IM-R1 and IM-R2 cells, which were developed having 7- and 27-fold greater IM resistance, respectively, than the parental K562 cells. Both variants possessed BCR-ABL gene amplification along with elevated levels of its transcript and protein. Greater BCR-ABL gene amplification was observed in IM-R2 cells than in IM-RI cells, which was consistent with the higher mRNA and protein levels of Bcr-Abl, and ultimately correlated with the greater IM resistance in IM-R2 cells. No mutation in the AbI kinase domain was detected in either variant. Despite the absence of Lyn overexpression, the Src kinase inhibito CGP76030 showed positive cooperability with IM in inhibiting c 11 growth of not only K562 cells but also these 2 variants. This might be because of the augmented inhibition of Erkl/2 phosphorylation. The new AbI kinase inhibitor nilotinib was 10-fold more potent than IM in inhibiting the growth of K562 cells. Nilotinib inhibited the growth of IM-RI and IM-R2 cells as potently as K562 cells. The combination of nilotinib with CGP76030 showed little additivity, because the potency of nilotinib masked the efficacy of CGP76030. The new dual Abl/Lyn inhibitor INNO-406 (formerly NS-187) was slightly more potent than nilotinib in inhibiting the growth of all 3 cell lines. Because BCR-ABL gene amplification occurs in blast crisis, these inhibitors might overcome IM resistance in such patients' leukemia. (c) 2008 Wiley-Liss, Inc.