Potent, selective and photo-dependent inhibitor of protein kinase C that targets the regulatory domain (IC50 = 50 nM). Displays > 1000-fold selectivity over other protein kinases such as cAMP-dependent protein kinase and tyrosine-specific protein kinase. Inhibits cell proliferation of malignant glioma cells in light-treated conditions in vitro (IC50 ~ 40 - 60 nM).