Synthesis of novel pyridazine and pyrimidine linked pyrazole derivatives as DNA ligase 1 and IV inhibitors that induce apoptosis.

Human ligase I and ligase IV have recently been recognized as potential targets and regulators of cancer. Novel pyrazole analogues were synthesized and evaluated for their anti-proliferation effects against lymphoma, breast and other cancer cell lines. The initial biological investigation resulted in the identification of lead compounds 7a and 8e. Compounds 7a and 8e were the most cytotoxic to acute lymphoblastic leukemia CEM cells, with CC50 values of 4.78 μM and 9.23 μM, respectively. Compound 8e was selected for further biological testing, whereas compound 7a was excluded from subsequent evaluations due to its poor solubility. To investigate the mechanism of action of 8e, it was tested for phosphatidylserine externalization, caspase-3 activation, mitochondrial membrane depolarization, reactive oxygen species generation (ROS) and its effects on the cell cycle. Results from these assays indicated that 8e induced the intrinsic apoptosis pathway and arrested cells in the S phase of the cell cycle. Furthermore, in silico docking and molecular dynamic simulation revealed a strong affinity of 7a and 8e for ligase I and ligase IV suggesting that the induction of apoptosis is likely due to direct inhibition of these ligases. Collectively, these findings indicate that 8e is a promising anticancer agent.