In vitro activity: Previous study found that CPI-455 could potently inhibit the fulllength KDM5A in enzymatic assays with a half-maximal inhibitory concentration of 10 ± 1 nM. CPI-455 inhibited KDM5A, KDM5B and KDM5C to similar levels but showed significantly weaker potency toward KDM4C and KDM7B (~200- and 770-fold, respectively) and no detectable inhibition of KDM2B, KDM3B or KDM6A. Moreover, it was found that the CPI-455-mediated KDM5 inhibition led to a dose-dependent increase in global H3K4me3 in HeLa cells, and the removal of CPI-455 resulted in a rapid reversal of H3K4me3 increases in HeLa cells. Moreover, CPI-455 could delay the appearance of heavy H3K4me3, which was consistent with the role for KDM5 enzymes in H3K4me3 turnover, however, the turnover of H3K4me2 was only marginally altered. As expected, CPI-455 could affect the turnover of H3K4 monomethylation.

Kinase Assay: CPI-455, with high measured affinity for the target KDM5 proteins. Within 24 hours, increases in H3K4me3, but not H3K4me2, are observed after exposure to either of the two active compounds, CPI-455 and CPI-766, in a dosedependent manner.

Cell Assay: All cell lines [melanoma (M14), breast cancer (SKBR3) and NSCLC (PC9) cell lines] were treated with DMSO, CPI-4203 or CPI-455 for 5 d with two changes of medium and drug. Thereafter, the cells (PC9, Colo205, Hs888, M14, SKBR3 and EVSA-T) were plated at 2×105 cells in six-well plates in triplicate and treated for an additional 9-15 d, depending on the cell line model. The Incucyte HD imaging system was used to monitor numbers of drug-tolerant cells after cells were stained with Nuclear-ID Red stain.

Nat Chem Biol. 2016 Jul;12(7):531-8.