Eleven known compounds were separated from Oldenlandia diffusa using the bioassay-guided methods. Among which, heptatriacontane and stearic acid (SA) were isolated from this herb for the first time. The anti-proliferative activities of ursolic acid (UA) and SA, as well as the anti-proliferative and immunomodulatory activities of quercetin, kaempferol, quercetin-3-O-D-glucoside, kaempferol-3-O-D-glucoside and kaempferol-3-O-D-galactoside, are responsible for the anti-hepatomatic effect of OD, to which UA might be the major contributor due to relatively high content in OD and potent cytotoxicity. / In conclusion, our findings provided a better elucidation on phytochemical basis responsible for the anti-cancer activities of OD and AU, and also suggested the potential of UA, SB and SD as new chemotherapeutic agents for the treatment of liver cancer in further studies. / Mechanistic study indicated that anti-proliferative effects of SB and SD due to induction of apoptosis on both HepG2 and R-HepG2 cells were established by sub-G1 accumulation in cell cycle profile and cell population with PS externalization, which were confirmed by activation of apoptosis mediators PARP and caspase-3. The induction of apoptosis was suggested to be mediated by both extrinsic and intrinsic pathways, as evidenced by activation of caspase-8 and -9, up-regulation of Bcl-XS, dysfunction of mitochondria and release of cytochrome c during SB and SD treatment. Besides, Bcl-2 and Bax expression levels were notably different on SB/SD-treated HepG2 and R-HepG2 cells, which implied that Bcl-2 and Bax might play a role in SB and SD modulation of drug resistance on R-HepG2 cells. / Motivated by the serious health hazard worldwide caused by hepatoma and side effects of chemotherapeutic agents in clinical treatment, we have initiated a research project to isolate and characterize bioactive compounds from Oldenlandia diffusa (OD) and Androsace umbellata (AU) as well as to study the molecular mechanisms of their anti-proliferative effects on human hepatoma cells. / On the other hand, phytochemical study of Androsace umbellata led to isolation of two novel triterpenoid sapogenins and five known compounds (3-O-D-glucosyl-(1→2)-L-arabinosyl cyclamiretin A, primulanin, saxifragifolin B, saxifragifolin C and saxifragifolin D). Their anti-tumor effects were firstly reported here, where saxifragifolin B (SB) and saxifragifolin (SD) showed the most potent cytotoxicities on human hepatoma cells. Structure-activity relationship study revealed that introduction of glucosyl moiety might be useful for the enhancement of cytotoxicity of this chemotype. / The action mechanism of UA has been intensively investigated. Our results showed that UA was not a substrate of p-glycoprotein, and it could bypass multidrug resistance of R-HepG2 cells. Furthermore, UA treatment also resulted in apoptotic cell death which was indicated by cell morphology observation, cell cycle analysis, DNA fragmentation and Annexin V-FITC/PI double staining assay. UA-induced apoptosis was associated with the extrinsic (death receptor-mediated) pathway, which was suggested by increase of FasL expression, activation of caspase-8 and caspase-3 as well as cleavage of PARP. Besides, changes implying the intrinsic (mitochondria-mediated) apoptotic pathway, including up-regulation of p53 and Bax, down-regulation of Bcl-2, cleavage of Bid, collapse of Deltapsi m, leakage of cytochrome c and AIF as well as activation of caspase-9, were also observed on R-HepG2 cells after UA treatment. Moreover, elevation of cytosolic calcium concentration, generation of reactive oxygen species and activation of MAPKs pathway were involved in UA-induced apoptosis. Proteomic analysis exhibited significant changes in the expression level of twelve proteins which were involved in tumor cell proliferation, invasion and apoptosis. / Zhang, Dongmei. / "September 2007." / Adviser: Kwok-Pui Fung. / Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4744. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 239-263). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.