ORIGINAL PAPER Cell cycle arrest in early mitosis and induction of caspase-dependent apoptosis in U937 cells by diallyltetrasulfide (Al2S4) Claudia Cerella Æ Christiane Scherer Æ Silvia Cristofanon Æ Estelle Henry Æ Awais Anwar Æ Corinna Busch Æ Mathias Montenarh Æ Mario Dicato Æ Claus Jacob Æ Marc Diederich Ó Springer Science+Business Media, LLC 2009 Abstract Naturally occurring organic sulfur compounds (OSCs), such as linear allylsulfides from Allium species, are attracting attention in cancer research, since several OSCs were shown to act beneficially both in chemopre- vention and in chemotherapy, while hardly exerting any harmful side effects. Hence, we investigated the possible role of different OSCs in the treatment of leukemia. Thereby, we found that the compounds tested in this study induced apoptosis in U937 cells, with an efficiency depending on the number of sulfides, and selected the most promising candidate, diallyltetrasulfide (Al2S4), for detailed mechanistic studies. Here we show that Al2S4 induced an accumulation of cells in early mitosis (G2/M phase), followed by the activation of caspase-dependent apoptosis. The compound counteracted different anti- apoptotic Bcl-2 family members (Bcl-xL, phospho-Bad and Bcl-2), promoted activation of Bax and Bak and induced the release of cytochrome c into the cytoplasm. Treatment by Al2S4 let to the identification of early apoptotic events including Bcl-xL degradation, Bak acti- vation and release of cytochrome c followed by late events including Bcl-2 proteolysis, Bax activation, Bad dephos- phorylation, caspase activation, nuclear fragmentation and phosphatidylserine exposure. Keywords Diallyltetrasulfide Á Apoptosis Á Cell cycle Á Mitosis Á Leukemia Á Bax/Bak activation Introduction Since apoptosis is the most common kind of programmed cell death of healthy cells at the end of their life span— which they undergo without affecting cells and tissues in their physiological environment [1]—induction of apopto- sis would be a suitable strategy for drug development in the field of cancer research [2–4]. If it would be possible to find compounds selectively inducing apoptosis in cancer cells [5], generally resisting programmed cell death [6], a highly efficient approach for the therapeutic treatment of patients suffering from cancer would become available. Simulta- neously, severe side effects presently related to most used approaches (chemotherapy, radiotherapy) might be avoi- ded. Consequently, drug development research makes huge efforts to find suitable compounds from different sources. This search is supported by information about medicinal activities of natural compounds from plants, being mainly provided by epidemiological studies. In this context, Allium species (especially garlic) are widely described for their positive effects on health as well as in the area of the cardiovascular system as in the area of cancer diseases [7–10]. Manifold preclinical studies in vitro and in vivo and even clinical studies were performed to assess che- mopreventive and chemotherapeutic activities of garlic Claudia Cerella and Christiane Scherer, both authors equally contributed to this work. C. Cerella Á C. Scherer Á S. Cristofanon Á E. Henry Á M. Dicato Á M. Diederich (&) Laboratoire de Biologie Mole ´culaire et Cellulaire de Cancer, Ho ˆpital Kirchberg, Rue Edward Steichen 9, 2540 Luxembourg, Luxembourg e-mail: marc.diederich@lbmcc.lu C. Scherer Á A. Anwar Á C. Jacob Division of Bioorganic Chemistry, School of Pharmacy, Saarland University, 66041 Saarbrucken, Germany C. Busch Á M. Montenarh Division of Medicinal Biochemistry and Molecular Biology, Saarland University, 66424 Homburg, Germany 123 Apoptosis DOI 10.1007/s10495-009-0328-8