NSC 625987 was originally reported as a cyclin-dependent kinase 4 (CDK4) inhibitor, with >500-fold selectivity compared to CDK2 (IC50
>100 μM for cdc2/cyclin A, CDK2/cyclin A and CDK2/cyclin E) [4
]. However, kinase profiling results reported by Jorda et al
. (2018) found that no kinases tested were >50% inhibited by 10 μM NSC 625987 [3
]. In addition, these authors found no evidence of CDK4 inhibition in cellular assays. Therefore, caution is advised when choosing CDK4 pharmacological tools.