GSK126 potently inhibits both wild-type and mutant EZH2 methyltransferase activity with similar potencies (Ki=0.5-3 nM) independent of substrate used, and is competitive with S-adenosyl-methionine (SAM) and non-competitive with peptide substrates. GSK126 is highly selective against other methyltransferases and multiple other protein classes (EZH1, IC50=680 nM)[1]. Treatment of three SCLC cell lines with GSK126, induces growth inhibition. SCLC cell lines (Lu130, H209, and DMS53) are treated with 0.5, 2, and 8 μM GSK126, and growth curve is analyzed by WST-8 assay. Inhibition of cellular growth by GSK126 treatment is observed at 8 μM in all the three cell lines, while Lu130 and H209 are more sensitive to GSK126, even at lower dose.
GSK126 is administered intraperitoneally at a dose volume of 0.2 mL per 20 g body weight in female beige SCID mice. GSK126 effectively inhibits the proliferation of EZH2 mutant DLBCL cell lines and markedly inhibits the growth of EZH2 mutant DLBCL xenografts in mic.
The five-member PRC2 complex (Flag-EZH2, EED, SUZ12, AEBP2, RbAp48) containing either wild-type or mutant (A677G, Y641N, Y641C, Y641H, Y641S or Y641F) EZH2 is prepared. GSK126 is dissolved in DMSO and tested at concentrations of 0.6 nM to 300 nM with a final DMSO concentration of 2.5%. In contrast to wild-type EZH2 which prefers H3K27me0 as a substrate in vitro, EZH2 Y641 mutants prefer H3K27me2 and have little activity with H3K27me0 or H3K27me1. The A677G mutant is distinct from both the wild-type and Y641 mutant forms of EZH2 in that it efficiently methylates H3K27me0, H3K27me1, and H3K27me2; therefore, histone H3 peptides (residues 21-44; 10 μM final) with either K27me0 (wild type, A677G EZH2), K27me1 (A677G EZH2), or K27me2 (A677G, Y641N, Y641C, Y641H, Y641S and Y641F EZH2) are used as methyltransferase substrates. GSK126 is added to plates followed by addition of 6 nM EZH2 complex and peptide. As the potency of GSK126 is at or near the tight binding limit of an assay run at [SAM]=Km, IC50 values are measured at a high concentration of the competitive substrate SAM relative to its Km (7.5 μM SAM where the SAM Km is 0.3 μM).
MCE has not independently confirmed the accuracy of these methods. They are for reference only.
