ISElements. Statistical Analyses Data was presented as mean 6 standard deviation. Significant differences were determined by using the Student’s t-test where p, 0.05 denotes a statistically significant difference. All the samples were measured in triplicates. DNA Fragmentation 
Analysis by Agarose Electrophoresis Cells were treated in the presence or absence of PW-M, PWH, PW-E and PPWH-7 for 48 hours, then harvested by using 500 ml lyses buffer at 65uC for 30 min on ice. Subsequent steps were carried out on ice. 100 ml of 8 M potassium acetate was added to the suspended mixtures and incubated on ice for 1 hour. The supernatant was obtained by centrifuging the lysates at 10,000 6g for 10 min and the soluble proteins were extracted by phenol/chloroform/isoamyl alcohol . Finally, DNA was precipitated using 26 volume of ice-cold absolute ethanol. To perform the DNA fragmentation assay, the DNA pellet was dissolved in 20 ml of TE buffer together with 1 ml of RNAse and 1 ml of Proteinase K and incubated at 37uC for 30 min. DNA fragmentation was analyzed by 1.5% agarose gel electrophoresis. DNA bands were observed and photographed using a Gene Flash gel documentation system. Apoptosis induction is indicated by the appearance of DNA ladder fragments of approximately 180 200 bp multiples on the agarose gel. Results Cytotoxicity of P. watsonii Extracts-NRU Assay In the present study, the potential cytotoxic effects of P. watsonii extract in methanol, hexane and ethyl acetate as well as fractions and sub-fractions of PW-H were investigated on two human gynecologic cancer cells, one colon cancer cells and one normal cells by using the NRU assay. Based on the US National Cancer Institute guidelines, a crude extract is generally considered to have in vitro cytotoxic activity if the IC50 value in carcinoma cells, following incubation between 48 and 72 hours, is #20 mg/ mL, while for a pure compound the IC50 value is #4 mg/mL. Cytotoxic activity and selectivity index of the extracts, fractions and sub-fractions are summarized in Caspase-3 Activity Assay Activity of caspase-3 was determined using the Caspase-3/ CPP32 colorimetric assay kit according to manufacturer’s protocol. The assay is based on spectrophotometric detection of the chromophore, p-nitroanilide, after its cleavage from the labeled substrate DEVD-pNA. Cells were pelleted and lysed after treatment with the 10 mg/mL of PWM, PW-H, and PW-E of P. watsonii and sub-fraction PPWH-7 for 48 hours. Assays were performed on 96-well microtiter plates by incubating 100 mg protein of cell lysate per sample in 50 ml of 26 Astragalus polysaccharide site reaction buffer. The reaction buffer is supplemented with 10 mM DTT and substrates of 4 mM DEVD-pNA in a final volume totaling to 100 ml and incubated at 37uC for 1.5 hours. Formation of p-nitroanilide was measured using the ELISA micro-plate reader at a wavelength of 405 nm and the caspase activities were expressed as percentage of enzyme activity compared with control. Bioassay-guided Fractionation-NRU Assay Column chromatography of the PW-H yielded a total of 10 fractions. PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22188834 Fractions of PW-H demonstrated stronger cytotoxic activity and higher selectivity when compared to the PW-H particularly when tested on SKOV-3 cells. On SKOV-3 cells, the fractions PWH-4, PWH-5, PWH-6, PWH-7 and PWH-8 exhibited IC50 values of 0.29 6 0.06, 0.18 6 0.06, 0.42 6 0.12, 0.77 6 0.29 and 0.36 6 0.12 mg/mL, respectively. IC50 values obtained when Ca Ski and HT-29 cells were treated with the fractions PWH-4