Ruboxistaurin hydrochloride (LY 333531 hydrochloride) is an Isozyme-selective inhibitor of protein kinase C (PKC); competitively and reversibly inhibits PKCβI and PKCβII (IC50 values are 4.7 and 5.9 nM respectively). Selective for PKCβ over other PKC isozymes (IC50values are 0.052, 0.25, 0.30, 0.36, 0.60 and >100 μM for PKCη, -δ, -γ, -α, -ε and -ζ respectively). Exhibits selectivity for PKC over other ATP-dependent kinases, including protein kinase A, casein kinase and src).