Background & Objective: Oldenlandia diffusa (Bai Hua She She Cao) is one of the herbs most commonly used in traditional Chinese medicine for treating cancer. Various studies using the herb alone or in combination with other therapy plans have evidenced the effectiveness of the herb in the management of cancers of different tissue origin. However, the mechanisms underlying its anti-cancer activity are unknown. In the present study, we attempted to investigate the apoptotic activity of crude extracts of the herb as well as the possible molecular pathways. Methods:We incubated human promyelocytic leukemia cell line HL60 cells with ethanol or aqueous extracts of the herb, and determined the levels of intracellular superoxide at 2 and 4 hours as well as caspase activity at 3, 6 and 8 hours using photospectrometry. Cancer cell survival and apoptosis were quantified at 24 hours by using MTT and flow cytometry analyses respectively.Results: We found that it dose-dependently inhibited the cancer cell growth in MTT assay. Flow cytometry analysis revealed that it elicited significant production of sub-G₁ population of the cells, indicating the extract-evoked cell apoptotic death. The LD₅₀ of the ethanol extract was estimated to be approximately 320 μg/ml. Moreover, treatment of the cancer cells with the ethanol component markedly increased the production of superoxide within few hours. Significant elevation in the protease activities of caspases-2 and -3 were detected at as early as 3 and 6 hours respectively. Conclusion: Our results show that the ethanol extract of the herb effectively evokes cancer cell apoptosis, possibly through burst-mediated caspase activation.

Key words: Oldenlandia diffusa, Cancer, Superoxide, Caspase, Apoptosis