1. ¹UMR 736 INSERM/Université Paris VI, Centre de Recherches Biomédicales des Cordeliers, Paris, France
2. ²Laboratory of Galenic and Industrial Pharmacy, Faculty of Pharmacy, Marseille, France

Correspondence: Dr J-P Kolb, UMR 736 INSERM/Université Paris VI, Centre de recherches Biomedicales des Cordeliers, 15 rue de l'Ecole de Medecine, Paris Cedex 06 75270, France. E-mail: jpkolb@bhdc.jussieu.fr

Received 18 July 2005; Revised 10 November 2005; Accepted 1 December 2005; Published online 19 January 2006.

Abstract

The effects of the hyperforin (HF), a natural phloroglucinol purified from Hypericum perforatum, were investigated ex vivo on leukemic cells from patients with B-cell chronic lymphocytic leukemia (B-CLL). HF was found to promote apoptosis of B-CLL cells, as shown by time- and dose-dependent stimulation of phosphatidylserine externalization and DNA fragmentation, by disruption of the mitochondrial transmembrane potential, caspase-3 activation and cleavage of the caspase substrate PARP-1. Moreover, HF-induced downregulation of Bcl-2 and Mcl-1, two antiapoptotic proteins that control mitochondrial permeability. HF also downregulated two proteins which are overexpressed by B-CLL patients' cells, the cell cycle inhibitor p27^kip1 through caspase-dependent cleavage into a p23 form, and the nitric oxid (NO) synthase of type 2 (inducible NO synthase). This latter was accompanied by reduction in the production of NO known to be antiapoptotic in B-CLL cells. Preventing effects of the general caspase inhibitor z-VAD-fmk indicated that HF-promoted apoptosis of B-CLL cells was mostly caspase dependent. Furthermore, normal B lymphocytes purified from healthy donors appeared less sensitive to HF-induced apoptosis than B-CLL cells. These results indicate that HF may be of interest in the development of new therapies for B-CLL based on the induction of apoptosis and combination with cell cycle-dependent antitumor drugs.