Phytochem Rev (2010) 9:425–474 DOI 10.1007/s11101-010-9183-z Saponins as cytotoxic agents: a review Irma Podolak • Agnieszka Galanty • Danuta Sobolewska Received: 13 January 2010 / Accepted: 29 April 2010 / Published online: 25 June 2010 Ó The Author(s) 2010. This article is published with open access at Springerlink.com Abstract Saponins are natural glycosides which Con A Concanavalin A possess a wide range of pharmacological properties ER Endoplasmic reticulum including cytotoxic activity. In this review, the recent ERK Extracellular signal-regulated studies (2005–2009) concerning the cytotoxic activity kinase of saponins have been summarized. The correlations GADD Growth arrest and DNA damage- between the structure and the cytotoxicity of both inducible gene steroid and triterpenoid saponins have been described GRP Glucose regulated protein as well as the most common mechanisms of action. hTERT Telomerase reverse transcriptase JAK Janus kinase Keywords Cytotoxic mechanisms Á MEK = MAPK Mitogen-activated protein kinase Glycosides Á Sar Á Steroid Á Triterpenoid MMP Matrix metalloproteinase mTOR Mammalian target of rapamycin Abbreviations NFjB Nuclear factor kappa-light-chain- AMPK AMP activated protein kinase enhancer of activated B cells BiP Binding protein NO Nitric oxide BrDU Bromodeoxyuridine PARP Poly ADP ribose polymerase CCAAT Cytidine-cytidine-adenosine- PCNA Proliferating cell nuclear antigen adenosine-thymidine PI3K Phosphoinositide-3-kinase CD Cluster of differentiation molecule PP Protein phosphatase CDK Cyclin-dependent kinase PPAR-c Peroxisome proliferator-activated CEBP CCAAT-enhancer-binding protein receptor c CHOP CEPB homology protein Raf Serine/threonine specific kinase STAT Signal transducer and activator of transcription TIMP Tissue inhibitor of metallo- proteinase TSC Tuberous sclerosis complex VEGF Vascular endothelial growth factor & I. Podolak ( ) Á A. Galanty Á D. Sobolewska XIAP X-linked inhibitor of apoptosis Department of Pharmacognosy, Jagiellonian University, Medical College, Medyczna 9, 30-688 Cracow, Poland protein e-mail: [email protected] 123 426 Phytochem Rev (2010) 9:425–474 Introduction Steroidal sapogenins (27C) can have a 6-ring spirostane or a 5-ring furostane skeleton whereas in Saponins are secondary metabolites of glycosidic the case of triterpenoid sapogenins (30C), which are nature widely distributed in higher plants but also much more structurally diverse, the basic ring system found in some animal sources, like e.g. marine is most often made of five or, more seldom, of four invertebrates. Despite their fairly large structural units. Pentacyclic triterpenoid saponins belong, in a diversity these compounds share some unique bio- majority of cases, to oleanane-type, other skeleton logical properties like the ability to lyse erythrocytes types include ursane, lupane, hopane, germanicane, or to foam (Bruneton1995; Rao and Gurfinkel 2000; dammarane (Vincken et al. 2007). The presence in Francis et al. 2002). The latter contributed to naming the polycyclic sapogenin of different substituents, this group ‘‘saponins’’, which is derived from Latin such as for example hydroxyls, hydroxymethyls, sapo meaning soap. Haemolysis of red blood cells carboxyls and acyl groups, as well as differences in seems to result from saponin ability to form com- the composition, linkage and number of sugar chains plexes with cell membrane cholesterol leading in account for significant structural diversity of saponins consequence to pore formation and cell permeabili- and also their diverse bioactivity. zation, and also to cause alterations in the negatively Saponins exert a wide range of pharmacological charged carbohydrate portions on the cell surface activities including expectorant, antiinflammatory, (Abe et al. 1981; Melzig et al. 2001; Gauthier et al. vasoprotective, hypocholesterolemic, immunomodu- 2009a). It should be mentioned however that the latory, hypoglycaemic, molluscicidal, antifungal, exact mechanism of haemolytic activity of saponins antiparasitic and many others (Sparg et al. 2004; is not clearly understood and is the subject of Sahu et al. 2008). Plants rich in saponins, like Panax discussions within the scientific community. ginseng or Glycyrrhiza glabra, have been used for Surface activity responsible for foaming proper- medicinal purposes since ancient times (Fiore et al. ties, as well as some other biological functions 2005) and to date continue to play a significant role including haemolytic activity, are attributed to char- not only in medicine but also in food and cosmetic acteristic structural features of saponins and their industry, where they are utilized as emulsifiers or amphiphilic nature which results from the presence of sweeteners (Gu¨c¸lu¨-U¨ stu¨ndag˘ and Mazza 2007). a hydrophilic sugar moiety and a hydrophobic genin Another important application of saponins is their (called sapogenin). Saponins can possess from one to use as adjuvants in the production of vaccines (Sun three straight or branched sugar chains, most often et al. 2009b). Steroidal sapogenins since many years composed of D-glucose, L-rhamnose, D-galactose, have served as economically important raw materials D-glucuronic acid, L-arabinose, D-xylose or D-fucose. for the pharmaceutical industry in the production of The sugar chain can contain from one to several steroidal hormones (Blunden et al. 1975;Gu¨c¸lu¨- monosaccharide residues, and is usually attached at U¨ stu¨ndag˘ and Mazza 2007). C-3 (Vincken et al. 2007). Many reviews summarized different aspects The aglycone may have steroid or triterpenoid related to saponins, some of the more recent tackled structure according to which saponins are usually biosynthesis (Haralampidis et al. 2002; Kalinowska classified. Steroidal compounds are less common and et al. 2005), distribution (Henry 2005; Vincken et al. usually found among the Liliopsida (former Mono- 2007), structures (Vincken et al. 2007; Sahu et al. cotyledones) in members of such families as Lilia- 2008), biological and pharmacological activities of ceae, Dioscoreaceae, Agavaceae, while triterpenoid saponins (Sparg et al. 2004; Yang et al. 2006; Wang saponins are more widely distributed and typical of et al. 2007; Sun et al. 2009b), application and the Magnoliopsida families (former Dicotyledones), processing (Gu¨c¸lu¨-U¨ stu¨ndag˘ and Mazza 2007), meth- e.g. Primulaceae, Sapotaceae, Caryophyllaceae and ods employed in their analysis (Oleszek and Bialy others. In rare cases both types of saponins may 2006; Sahu et al. 2008) and chemical synthesis of accumulate in a plant, like for example in Avena sp. saponins (Yu et al. 2007; Yu and Sun 2009; Gauthier (monocotyledonous Poaceae) (Osbourn 2003)or et al. 2009b). Lysimachia paridiformis (dicotyledonous Myrsina- Cytotoxicity and the chemopreventive role of ceae) (Xu et al. 2007b). saponins was also discussed in a number of review 123 Phytochem Rev (2010) 9:425–474 427 papers (Rao and Sung 1995; Konoshima 1996; As far as cytotoxicity data are concerned the Shibata 2001; Kerwin 2004;Kim2008; Bachran following observations can be made. Most studies et al. 2008; Fuchs et al. 2009). While most of these were performed on a relatively narrow range of cell focus on triterpenoids, and especially on ginseng and lines, usually from one to five, sometimes up to ten. soy saponins, chemopreventive and cancer control The most notable exceptions in this respect are the activity of a steroidal sapogenin—diosgenin has been reports, in which isolated compounds were assayed by recently summarized (Raju and Mehta 2009). Cyto- National Cancer Institute (NCI) in anticancer drug toxicity of dioscins was also discussed in a review on discovery screen. For example, Zhang (Zhang and Li bioactive steroid saponins from the Dioscorea genus 2007) tested triterpenoid saponins isolated from (Sautour and Mitaine-Offer 2007). Bachran et al. Aesculus pavia against a panel of 59 cell lines from (Bachran et al. 2008) in their review of saponins nine different human cancers such as leukemia, non- playing a role in tumor therapy focused on certain small cell lung, colon, CNS, melanoma, ovarian, renal, groups of compounds, such as dioscins, saikosapo- prostate and breast. Similarly, cytotoxicity of seven nins, julibrosides, avicins, soy and ginseng saponins, steroid saponins, isolated from Dioscorea collettii var. and on combinations of saponins and conventional hypoglauca, was compared on such a wide panel of anti-tumorigenic drugs. cancer cell lines (Sautour and Mitaine-Offer 2007). This review focuses on the studies from the last One of the saponins, furostanol protoneodioscin 5 years referring to saponins for which cytotoxic (NSC-698789) isolated from the rhizomes of this activity in vitro against human cancer cell lines was plant, showed high activity against leukemia lines reported. Some data from animal models are also (CCRF-CEM, K562 and MOLT-4), colon cancer lines presented. (HCT-15, KM12), CNS cancer line (SNB-75), mela- Due to enormous number of reports that appear noma line (M14), renal cancer line (CAKI-1), prostate worldwide in which some reference to cytotoxicity is cancer (DU-145) and breast cancer line (MDA-MB- -1 made we had to set some limits. Thus, literature 435) with GI50 B 2.0 lmol l . Leukemia, CNS can- searches were conducted in the following electronic cer, and prostate cancer appeared the most sensitive databases: MEDLINE/PubMed, SCOPUS/Elsevier, subpanels to protoneodioscin. A comparison with Springer/ICM, INSPEC/ICM, SCI-Ex/ICM. The other compounds in the NCI’s