Potent cytotoxic effects of Calomeria amaranthoides on ovarian cancers

BACKGROUND: Ovarian cancer remains the leading cause of death from gynaecological malignancy. More than 60% of the patients are presenting the disease in stage III or IV. In spite of combination of chemotherapy and surgery the prognosis stays poor for therapy regimen. METHODS: The leaves of a plant endemic to Australia, Calomeria amaranthoides, were extracted and then fractionated by column chromatography. In vitro cytotoxicity tests were performed with fractions of the plant extract and later with an isolated compound on ovarian cancer cell lines, as well as normal fibroblasts at concentrations of 1-100 μg/mL (crude extract) and 1-10 μg/mL (compound). Cytotoxicity was measured after 24, 48 and 72 hours by using a non-fluorescent substrate, Alamar blue. In vivo cytotoxicity was tested on ascites, developed in the abdomen of nude mice after inoculation with human OVCAR(3 )cells intraperitoneally. The rate of change in abdomen size for the mice was determined by linear regression and statistically evaluated for significance by the unpaired t test. RESULTS: Two compounds were isolated by chromatographic fractionation and identified by (1)H-NMR, (13)C-NMR and mass spectrometry analyses, EPD, an α-methylene sesquiterpene lactone of the eremophilanolide subtype, and EPA, an α-methylene carboxylic acid. Cytotoxicity of EPD for normal fibroblasts at all time points IC(50 )was greater than 10 μg/mL, whereas, for OVCAR(3 )cells at 48 hours IC(50 )was 5.3 μg/mL (95% confidence interval 4.3 to 6.5 μg/mL). Both, the crude plant extract as well as EPD killed the cancer cells at a final concentration of 10 μg/mL and 5 μg/mL respectively, while in normal cells only 20% cell killing effect was observed. EPA had no cytotoxic effects. Changes in abdomen size for control versus Cisplatin treated mice were significantly different, P = 0.023, as were control versus EPD treated mice, P = 0.025, whereas, EPD versus Cisplatin treated mice were not significantly different, P = 0.13. CONCLUSIONS: For the first time both crude plant extract from Calomeria amaranthoides and EPD have been shown to have potent anti-cancer effects against ovarian cancer.