GSK-503, a potent EZH2 inhibitor, has potential antitumor activity.

EZH2:8 nM

GSK503 inhibits the methyltransferase activity of both WT and mutant EZH2 with similar potency. In a panel of seven DLBCL cell lines, GSK503 causes growth inhibition, with enhanced effects when combined with ABT737 or Obatoclax. [1]

In C57BL6 mice immunized with SRBC, GSK503 (150 mg/kg, i.p.) reduced the level of H3K27me3 in splenocytes. In male SCID mice bearing SUDHL4 and SUDHL6 tumors, GSK503 (150 mg/kg, i.p.) inhibits tumor growth. [1] In C57Bl/6 mice bearing murine B16-F10 tumors, GSK503 (150 mg/kg, i.p.) significantly reduces global H3K27me3 levels, inhibits tumor growth and virtually abolishes metastases formation. [2]

In vitro biochemical assays against histone acetylases: GSK503 is profiled to assess inhibition against a panel of histone acetylases. GSK503 is dissolved in DMSO and tested in 10-dose IC50 mode with 3-fold serial dilution starting at 100 μM, with a final DMSO concentration of 2%. Anacardic Acid is used as positive control for CBP, GCN5, and pCAF and tested in 10-dose IC50 mode with 3-fold serial dilution starting at 100 μM. Curcumin is used as positive control for KAT5, MYST2/KAT7, MYST4/KAT6B, and p300, and tested in 10-dose IC50 mode with 3-fold serial dilution starting at 100 μM. Reactions are carried out at 3.08 μM Acetyl-CoA. For CBP, GCN5, MYST2/KAT7, pCAF, and p300, the substrate used is histone H3. For KAT5 and MYST4/KAT6B the substrates used are histone H2A and histone H4, respectively.