ANTI-cancer activities of hypericin in the dark

The potent photodynamic properties of hypericin (HY) elicit a range of ligh t-dependent virucidal and tumoricidal activities. Yet, a relatively low red uction/oxidation potential endows HY with electron accepting and donating p roperties enabling it to act as both an oxidizing and a reducing agent. HY can thus compete as an electron acceptor from bioenergized reduction/oxidat ion reactions generating its excitation energy for biological activities fr om physiological reduction/oxidation reactions in the absence of light. Our studies show that HY can inhibit the growth of highly metastatic murine br east adenocarcinoma and squamous cell carcinoma tumors in culture. Furtherm ore, we show that HY can interfere with the growth of these tumors in mice reducing tumor size and prolonging animal survival in complete absence of l ight. While there is no evidence that HY induces apoptosis in these cells i n the dark, H-3-thymidine incorporation into DNA was significantly reduced indicating effects that are apparently cytostatic in nature compared to the cytocidal effects of HY with light.