Birgit Simon-Haarhaus

Inhibition of tumour cell growth by hyperforin, a novel anticancer drug from St. John's wort that acts by induction of apoptosis

Hyperforin is a plant derived antibiotic from St. Johns wort. Here we describe a novel activity of hyperforin, namely its ability to inhibit the growth of tumour cells by induction of apoptosis. Hyperforin inhibited the growth of various human and rat tumour cell lines in vivo, with IC50 values between 3–15 μM. Treatment of tumour cells with hyperforin resulted in a dose-dependent generation of apoptotic oligonucleosomes, typical DNA-laddering and apoptosis-specific morphological changes. In MT-450 mammary carcinoma cells hyperforin increased the activity of caspase-9 and caspase-3, and hyperforin-mediated apoptosis was blocked by the broad-range caspase inhibitor zVAD.fmk. When added to MT-450 cells, hyperforin, but not paclitaxel, induced a rapid loss of the mitochondrial transmembrane potential Δψm, and subsequent morphological changes such as homogenization and vacuolization of mitochondria. Monitoring of Δψm revealed that the hyperforin-mediated mitochondrial permeability transition can not be prevented by zVAD.fmk. This indicates that mitochondrial permeabilization is a cause rather than a consequence of caspase activation. Moreover, hyperforin was capable of releasing cytochrome c from isolated mitochondria. These findings suggest that hyperforin activates a mitochondria-mediated apoptosis pathway. In vivo, hyperforin inhibited the growth of autologous MT-450 breast carcinoma in immunocompetent Wistar rats to a similar extent as the cytotoxic drug paclitaxel, without any signs of acute toxicity. Owing to the combination of significant antitumour activity, low toxicity in vivo and natural abundance of the compound, hyperforin holds the promise of being an interesting novel antineoplastic agent that deserves further laboratory and in vivo exploration.

Hypericin photo-induced apoptosis involves the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and activation of caspase-8

Hypericin (HYP) is a photosensitizing pigment from Hypericum perforatum that displays cytotoxic effects in neoplastic cell lines. Therefore, HYP is presently under consideration as a new anticancer drug in photodynamic therapy. Here, we investigated the mechanism of action of HYP photo‐induced apoptosis of Jurkat cells compared to the cytostatic drug paclitaxel (PXL). Both photoactivated HYP and PXL similarly increased the activity of caspase‐8 and caspase‐3, and drug‐induced apoptosis of Jurkat cells was completely blocked by inhibitors of caspase‐8 (Z‐IETD‐FMK) and caspase‐3 (Z‐DEVD‐FMK). The involvement of death receptors was analyzed using neutralizing monoclonal antibodies against Fas (SM1/23), FasL (NOK‐2) and TNF‐R1 (MAB225), and a polyclonal rabbit anti‐human TNF‐related apoptosis‐inducing ligand (TRAIL) antiserum. TRAIL antibody blocked TRAIL‐induced and HYP photo‐induced, but not PXL‐induced apoptosis of Jurkat cells. In contrast, PXL‐induced, but not HYP‐induced apoptosis was blocked by the SM1/23 and NOK‐2 antibodies. Anti‐TNF‐R1 antibody had no effect. These findings suggest that HYP photo‐induced apoptosis of Jurkat cells is mediated in part by the TRAIL/TRAIL‐receptor system and subsequent activation of upstream caspases.