Pyrazolo[3,4-c]pyridazines as Novel and Selective Inhibitors of Cyclin-Dependent Kinases

Abstract

Pyrazolopyridazine 1a was identified in a high-throughput screening carried out by BASF Bioresearch Corp. (Worcester, MA) as a potent inhibitor of CDK1/cyclin B and shown to have selectivity for the CDK family. Analogues of the lead compound have been synthesized and their antitumor activities have been tested. A molecular model of the complex between the lead compound and the CDK2 ATP binding site has been built using a combination of conformational search and automated docking techniques. The stability of the resulting complex has been assessed by molecular dynamics simulations and the experimental results obtained for the synthesized analogues have been rationalized on the basis of the proposed binding mode for compound 1a. As a result of the SAR study, monofuryl 1o has been synthesized and is one of the most active compounds against CDK1 of this series.

The anticancer potential of various substituted pyridazines and related compounds

“…By contrast, the use of other groups capable of establishing additional hydrogen bonds with the enzyme, such as ureas 23b and 23c and hydrazine 23d, maintained the inhibitory activity. Surprisingly, compound 23a, with a hydroxyl group in the same position, proved to be inactive, while the theoretical work described later predicts a very similar orientation of compounds 16a and 23a inside the binding pocket of CDK2 (Brana et al, 2005). Finally, compounds 23f-j were designed to evaluate the effect of substitution in position 1 of the lead compound.…”

“…A molecular model of the complex between the pyrazolopyridazine compound and the CDK2 ATP binding site has been built. The stability of the resulting complex has been assessed by molecular dynamics simulations and has been rationalized on the basis of the proposed binding mode for compound (Brana et al, 2005). …”

“…As in the case of CDKs, this type of kinase is involved in cancer and neurodegenerative diseases (Knockaert et al 2002;Brana et al 2005). …”

“…Triazolo-pyridazine derivatives are used as adenine receptor ligands and evaluated as in vitro antitumor activity. The 6-substituted pyridazinone (7,8) and pyridazino-fused ring systems, triazolo [4, 3-b]pyridazinones (9)(10)(11)(12)(13)(14)(15) were exhibited in-vitro antitumor activities. The compounds 9-15 have been evaluated as cytotoxic agent against tumor cells.…”

“…Indeed, both of them failed to inhibit CDK1 at all concentrations up to 50 µM. Replacement of the aromatic rings in positions 4 and 5 of the pyrazolopyridazine system in 16a by a π-rich furan ring (16h) led to a potent CDK1/cyclin B inhibitor (IC 50 ) 1.5 µM), while an inactive compound (16i) was obtained when a ð-deficient ring was introduced (Meijer et al, 2004;Brana et al, 2005). From an electrostatic point of view, this result is in accordance with the previous observation that electron-rich aromatic rings in positions 4 and 5 have a favorable effect on the inhibitory activity.…”