Isolated from Hypericum perforatum, St. John’s Wort. Hypericin has been shown to display antiviral and antiretroviral activity. A potent and selective inhibitor of protein kinase C (IC₅₀ = 3.4 µM). Also known to inhibit Casein Kinase II (CKII), MAP Kinase, Insulin R, EGFR, PI-3 Kinase. Displays antineoplastic and antitumor actitities. Most activities require light activation. Induces apoptosis in neuroblastoma cells at 1 µM or above (IC₅₀ = 0.1 µM at 29 mW/cm2 (tungsten light)). Used in photodynamic treatment of tumors and has been reported to be cytotoxic to some tumor cell lines when Hypericin is photoactivated.