Rutamarin, an Active Constituent from Ruta angustifolia Pers., Induced Apoptotic Cell Death in the HT29 Colon Adenocarcinoma Cell Line

BACKGROUND: Ruta angustifolia Pers. is a perennial herb that is cultivated worldwide, including Southeast Asia, for the treatment of various diseases as traditional medicine. OBJECTIVE: The purpose of the study was to identify an active principle of R. angustifolia and to investigate its effect on the HT29 cell death. MATERIALS AND METHODS: The methanol and fractionated extracts (hexane, chloroform, ethyl acetate, and water) of R. angustifolia Pers. were initially investigated for their cytotoxic activity against two human carcinoma cell lines (MCF7 and HT29) and a normal human colon fibroblast cell line (CCD-18Co) using sulforhodamine B cytotoxicity assay. Eight compounds including rutamarin were isolated from the active chloroform extract and evaluated for their cytotoxic activity against HT29 human colon carcinoma cell line and CCD-18Co noncancer cells. Further studies on the induction of apoptosis such as morphological examinations, biochemical analyses, cell cycle analysis, and caspase activation assay were conducted in rutamarin-treated HT29 cells. RESULTS: Rutamarin exhibited remarkable cytotoxic activity against HT29 cells (IC(50) value of 5.6 μM) but was not toxic to CCD-18Co cells. The morphological and biochemical hallmarks of apoptosis including activation of caspases 3, 8, and 9 were observed in rutamarin-treated HT29 cells. These may be associated with cell cycle arrest at the G0/G1 and G2/M checkpoints, which was also observed in HT29 cells. CONCLUSIONS: The present study describes rutamarin-induced apoptosis in the HT29 cell line for the first time and suggests that rutamarin has the potential to be developed as an anticancer agent. SUMMARY: Rutamarin was cytotoxic to HT29 colon cancer cells but exerted no damage to normal colon cells. Rutamarin induced morphological and biochemical hallmarks of apoptosis in HT29 cells. Rutamarin induced cell cycle arrest at the G0/G1 and G2/M checkpoints in a dose-dependent manner in HT29 cells. Rutamarin activated caspases 3, 8, and 9 in a dose-dependent manner in HT29 cells. Abbreviations used: ACN: Acetonitrile, ANOVA: One-way analysis of variance, BrdU: Bromodeoxyuridine, 13C-NMR: Carbon-13 Nuclear magnetic resonance, CAD: Caspase-activated endonuclease, CCD-18Co: Human colon normal, DLD1: Human Duke's type C colorectal adenocarcinoma, DMRT: Duncan's multiple range test, DMSO: Dimethyl sulfoxide, DNA: Deoxyribonucleic acid, DR4/5: Death receptor 4/5 protein, EMEM: Eagle's minimum essential media, FBS: Fetal bovine serum, FITC Annexin V: Annexin V conjugated with fluorescein isothiocyanate, FITC-DEVD-FMK: Fluorescein isothiocyanate conjugate of caspase inhibitor Asp-Glu-Val-Asp-fluoromethyl ketone, FITC-IETD-FMK: Fluorescein isothiocyanate conjugate of caspase inhibitor Ile-Glu-Thr-Asp-fluoromethyl ketone, FITC-LEHD-FMK: Fluorescein isothiocyanate conjugate of caspase inhibitor Leu-Glu-His-Asp-fluoromethyl ketone, G0: Quiescent phase of cell cycle, G1: Gap 1 phase of cell cycle, G2: Gap 2 phase of cell cycle, GC-MS: Gas chromatography-mass spectrometry, HeLa: Human cervical adenocarcinoma, HPLC: High performance liquid chromatography, HT29: Human colon adenocarcinoma, Huh7.5: Human hepatocellular carcinoma, IC50: Half maximal inhibitory concentration, KSHV: Kaposi's sarcoma-associated herpesvirus, M phase: Mitotic phase of cell cycle, MCF7: Human breast adenocarcinoma, NMR: Nuclear magnetic resonance, PBS: Phosphate-buffered saline, PI: Propidium iodide, RNase: Ribonuclease, rt: Retention time, S phase: Synthesis phase of cell cycle, SD: Standard deviation, SRB: Sulforhodamine B, TCA: Trichloroacetic acid, TLC: Thin layer chromatography, TNF-R1: Tumor necrosis factor receptor 1 protein, TUNEL: Terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling, UV: Ultraviolet.