C6-unsubstituted pyrazolo[3,4-d]pyrimidines are dual Src/Abl inhibitors effective against imatinib mesylate resistant chronic myeloid leukemia cell lines.

Docking simulations were used to predict the most favorable interaction between the T3151 mutated form of Abl (invariably assocd. with resistance to the tyrosine kinase inhibitor imatinib mesylate, IM) and C6-unsubstituted and substituted pyrazolo[3,4-d]pyrimidines previously found to be dual Src/Abl inhibitors. Two C6-unsubstituted (1 and 2) and eight C6-substituted compds. (3-10) were selected and assayed for their effects on the Ba/F3 cell line transducing the wild-type p210Bcr-Abl construct, which is IM-sensitive, or three of the most common mutations assocd. with IM resistance in vivo (T315I, Y253F, and E255K), and driven to drug resistance by satg. doses of IL-3 or by the expression of the Bcr-Abl construct coding for the p185 protein of acute lymphoblastic leukemia. Compds. 1 and 2 were active against all cell lines assayed (LD50 range: 0.7-4.3 μM), whereas C6-substituted compds. exhibited lower activity (LD50-8 μM for compd. 3 toward the T315I mutant). Notably, 1 and 2 were also effective toward the T315I mutation, which is insensitive to dual Src/Abl inhibitors. The cytotoxic effects of 1 and 2 on IM-sensitive and IM-resistant Ba/F3 cells were attributable, at least in part, to their pro-apoptotic activity. Taken together, such findings suggest that C6-unsubstituted pyrazolo[3,4-d]pyrimidines may represent useful inhibitors to target IM-resistant chronic myeloid leukemia.