of cell cycle distribution in the presence of PW-H and PPWH-7 in SKOV-3, Ca Ski and HT-29 cells by flow cytometry. Interestingly, SKOV-3 cells exhibited a dramatic accumulation of cells in S and G2/M phases and a concomitant decrease of the percentage of cells in G0/G1 phase, suggesting that both PW-H and PPWH-7 induced SKOV-3 cell cycle arrest at S and G2/M phases. Significant increment from 5.5 6 0.50% to 26.4 6 0.87% and 0.8 6 0.20% to 12.3 6 0.64% were observed in S Apoptosis Induction of Phyllanthus watsonii possessed a significant cytotoxic activity if the IC50 value is #4 mg/mL. The IC50 values established for PPWH-7 ranged from 0.660.83 mg/mL, a highly cytotoxic activity when considering a pure compound and these findings strongly suggest the promising potential of P. watsonii to be developed as an anti cancer drug. Variations in the cytotoxic activities among the fractions and sub-fractions against the cancer cells studied were also observed and this could be attributed to the distribution of the several AG-1478 identified cytotoxic compounds in different fractions/subfractions. In the present study, it also been clearly observed that fraction PWH-4, PWH-5, PWH-6 and PWH-8 exhibited a higher degree of cytotoxic acivity than purified sub-fraction PPWH-7 9 Apoptosis Induction of Phyllanthus watsonii towards SKOV-3 cells. While sub-fraction PPWH-7 demonstrated an increased cytotoxic activity and higher selectivity towards Ca Ski and PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22189346 HT-29 cells, the reason for the decreased cytotoxic activity towards SKOV-3 cells remains to be determined. Synergism between the components and/or the presence of other minor active compound is more likely to have caused the observed cytotoxicity of the fractions and sub-fraction. Further experiments are required to confirm this hypothesis with the cytotoxic activity of the fractions and sub-fraction of P. watsonii towards SKOV-3 cells. 10 Apoptosis Induction of Phyllanthus watsonii 11 Apoptosis Induction of Phyllanthus watsonii At present, LC-MS is one of the most sensitive analytical methods to yield information about the molecular weight as well as the structure of the analyst. Analysis of the PPWH-7 using LC-MS/MS indicated the presence of trimethyl ether of ellagic acid, methyl ester of geraiinic acid, glochidone, betulin, Phyllanthin sodium salt, Phyllanthin potassium salt and sterol glucoside and some of these detected 
compounds have been shown to have anti cancer activities. Based on this information, we conjecture that the observed cytotoxic activity in P. watsonii may be due to the presence of some of these compounds. Plantderived ellagic acid has previously been identified as a potent anti cancer agent with suggested molecular targets for ellagic acid effects being NF-kB, cyclin D1, p21cip1/waf1 and p53. Many studies have shown that ellagic acid possessed growth-inhibiting and apoptosis promoting activities against various human cancer cell lines representing different tissues such as Ca Ski cervical carcinoma cells, Caco-2 colon cells, MCF-7 breast cells and Hs 578T breast cells, DU 145 prostatic cells and SH-SY5Y neuroblastoma cells. Anti cancer potential of geraiinic acid, a compound under the chemical class of monoterpene has not been reported but there are numerous studies on the cytotoxicity of monoterpenes and its derivatives. Anti tumor activity of betulin, also known as betulinol, betuline and betulinic acid and its derivatives could be therapeutically important, because these compounds ex