– GRK6 inhibitor 18 is a potent, and selective GRK6 inhibitor with IC50 of 8 nM.GRK6 inhibitor 18 displays >1,000-fold selectivity over Aurora A, as well as high selectivity against a panel of 85 kinases.GRK6 inhibitor 18 has potent cellular target engagement and antiproliferative activity against MM cells (IC50=0.4-0.46 uM) and is synergistic with bortezomib.