GRK6-IN-1 (Compound 18) is the inhibitor for G protein-coupled receptorkinase 6 (GRK6) with an IC50 of 3.8-8 nM. GRK6-IN-1 also inhibits GRK7, GRK5, GRK4 and GRK1 with IC50s of 6.4, 12, 22 and 52 nM, respectively. GRK6-IN-1 has the potential for the research of multiple myeloma[1].