BCR and chronic myelogenous leukemia, BCR-ABL1 positive: PD180970 was also effective against imatinib mesylate-resistant K562 cells and Ba/F3-P210 cells expressing BCR/ABL kinase domain mutations observed in imatinib mesylate-resistant CML patients.65 Compared to imatinib mesylate, PD173955 suppressed the growth of the Bcr/Abl cell line R10(−) with an IC50 of 2.5 nM.66 PD166326 (95) was the most potent inhibitor of CD34+ CML progenitor development among the six pyridopyrimidines studied, with an IC50 around 4-fold lower than PD173955.