Novel acylated steroidal glycosides from Caralluma tuberculata induce caspase-dependent apoptosis in cancer cells

Waheed, Abdul, Barker, James, Barton, Stephen J., Khan, Gul-Majid, Najm-Us-Saqib, Qazi, Hussain, Manzoor, Ahmed, Sabbir, Owen, Caroline and Carew, Mark A. (2011) Novel acylated steroidal glycosides from Caralluma tuberculata induce caspase-dependent apoptosis in cancer cells. Journal of Ethnopharmacology, 137(3), pp. 1189-1196. ISSN (print) 0378-8741


AIM OF THE STUDY: 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. MATERIALS AND 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 <25μM after 48h 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.

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