Alqathama, Aljawharah; (2017) Bioguided isolation and pharmacological studies of cytotoxic principles from medicinal plants against malignant melanoma. Doctoral thesis (Ph.D), UCL (University College London).

Abstract

Background and purpose: Malignant melanoma is the most aggressive form of skin cancer and natural products are an important source of anticancer lead compounds. The aim of this study is to search for agents with antimelanoma activity by studying 20 Saudi plants on human melanoma cells (A375). Methods: Bioguided isolation of active principles was performed utilising chromatographic methods and their characterisation was performed by NMR, MS and IR. Cell viability, proliferation and further mechanistic studies were conducted, including caspase-3/7, LDH, cell cycle analysis, AnnexinV/PI staining, cell morphology and Bax/Bcl-2 expression. Furthermore, the effect of drug combinations on melanoma migration was evaluated using B16-F10 cell lines in scratch and Transwell chamber assays. Results: Nine out of twenty plants showed significant cytotoxicity. Four cytotoxic lignans; justicidin A, justicidin B, tuberculatin and tuberculatin acetate were isolated from H. tuberculatum. They induced apoptosis due to the elevation of sub-G1 and AnnexinV positive populations and the activation of caspase-3/7. All lignans upregulated the Bax expression, but interestingly, justicidin A only downregulated the expression of Bcl-2 protein, suggesting the role of methyl substitution in this effect. Ursolic acid acetate, ursolic acid and quercetin were obtained from C. edulis. Ursolic acid acetate induced apoptosis (activating caspase-3/7, elevating AnnexinV positive population and Bax/Bcl-2 ratio), and caused cell cycle arrest at S phase. Morphological changes were stronger than those caused by ursolic acid, indicating that the acetyl group may potentiate the cytotoxicity. Combination studies showed synergistic antimigratory effects of ursolic acid and quercetin in melanoma migration at very low concentrations. Conclusion: This is the first time that cytotoxicity for most of the selected plants has been reported. This study sheds light on the mechanisms by which these extracts affect melanoma cells. Bioguided isolation did not afford new cytotoxic secondary metabolites, but allowed the study of the structure-activity relationship of important cytotoxic compounds like pentacyclic triterpenoids and arylnaphatalene lignans.

Download activity - last month

Export as JSONCSVXML

Download activity - last 12 months

Export as CSVXMLJSON

Downloads by country - last 12 months

Export as XMLCSVJSON

Archive Staff Only

View Item