title: Novel acylated steroidal glycosides from Caralluma tuberculata induce caspase-dependent apoptosis in cancer cells.
abstract: OBJECTIVE
  Pregnane glycosides are potent cytotoxic agents which may represent new leads in the development of anti-tumour drugs, particularly in the treatment of breast cancer, because of the structural similarity to estrogenic agonists. Caralluma species are natural sources of a wide variety of pregnane glycosides. The aim of the study was to isolate, using an activity-guided fractionation approach, novel pregnane glycosides for testing on breast cancer and other tumour lines.
  
  
  METHODS
  The effect of crude extracts, specific organic fractions and isolated compounds from Caralluma tuberculata was tested on the growth and viability of MCF-7 estrogen-dependent, and MDA-MB-468 estrogen-independent breast cancer cells, Caco-2 human colonic cells, HUVECs and U937 cells. Neutral red uptake and MTT assays were used. Apoptosis was detected by Western blot of poly-(ADP ribose) polymerase (PARP) as were other markers of nuclear fragmentation (DNA ladder assay, staining of cells with nuclear dye DAPI). The involvement of caspases was investigated using the pan-caspase inhibitor Z-VAD-FMK.
  
  
  RESULTS
  The ethyl acetate fraction of Caralluma tuberculata was found to be the most potent anti-proliferative fraction against all three cancer cell lines. Two novel steroidal glycosides were isolated from the active fraction after a series of chromatographic experiments. The structure of the isolated compounds was elucidated solely based on 2D-NMR (HMBC, HETCOR, DQF-COSY) and MS spectral analysis as compound 1: 12-O-benzoyl-20-O-acetyl-3β,12β,14β,20β-tetrahydroxy-pregnan-3-ylO-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1 → 4)-3-methoxy-β-D-ribopyranoside, and as compound 2: 7-O-acetyl-12-O-benzoyl-3β,7β,12β,14β-tetrahydroxy-17β-(3-methylbutyl-O-acetyl-1-yl)-androstan-3-ylO-β-D-glucopyranosyl-(1 → 4)-6-deoxy-β-D-allopyranosyl-(1 → 4)-β-D-cymaropyranosyl-(1 → 4)-β-D-cymapyranosyl-(1→ 4)-β-D-cymaropyranoside. Compound 1 (pregnane glycoside) and compound 2 (androstan glycoside) induced apoptosis at <25 μM after 48 h as assessed by cell shrinkage, PARP cleavage, DNA fragmentation, and reversal with the caspase inhibitor.
  
  
  CONCLUSIONS
  Two novel steroid glycosides isolated from Caralluma tuberculata possess moderate, micromolar cytotoxic activity on breast cancer and other cells in vitro, which may indicate a source of activity in vivo of interest to future drug design.
authors.affiliation: School of Pharmacy & Chemistry, Kingston University, Penryhn Road, Kingston Upon Thames, Surrey KT1 2EE, London, United Kingdom.
authors.forename: Abdul
authors.initials: A
authors.lastname: Waheed
authors.forename: James
authors.initials: J
authors.lastname: Barker
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Barton
authors.forename: Gul-Majid
authors.initials: GM
authors.lastname: Khan
authors.forename: Qazi
authors.initials: Q
authors.lastname: Najm-Us-Saqib
authors.forename: Manzoor
authors.initials: M
authors.lastname: Hussain
authors.forename: Sabbir
authors.initials: S
authors.lastname: Ahmed
authors.forename: Caroline
authors.initials: C
authors.lastname: Owen
authors.forename: Mark A
authors.initials: MA
authors.lastname: Carew
mesh_terms: D000215:Acylation; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000732:Androstanols / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D029062:Apocynaceae / Q000737:chemistry; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D018938:Caco-2 Cells; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D005591:Chemical Fractionation / Q000379:methods; D002845:Chromatography; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006027:Glycosides / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D015394:Molecular Structure; D009369:Neoplasms / Q000201:enzymology* / Q000473:pathology; D010946:Plants, Medicinal; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011278:Pregnanes / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D020298:U937 Cells
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000732:Androstanols; D000972:Antineoplastic Agents, Phytogenic; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D006027:Glycosides; D011278:Pregnanes; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases