The Membrane as a barrier or target in cancer chemotherapy

The overall aim of the project was to investigate the role of the cell membrane as a barrier and/or target for drug action and relate this to the development of strategies for overcoming multiple drug resistance (MDR). The effects of doxorubicin on various bacterial strains expressing different levels of anionic phospholipid were compared. Giowth of wild-type Echerichia coli (E. coli) strain MRE600 was severely affected up to 9 hours following doxorubicin treatment (15uM), but resistance occurred after 9 hours. E. coli strain FIDL1 1 was resistant to doxorubicin (1 O0piM) over 9 hours, however, increasing the anionic lipid content showed little difference in sensitivity. The mouse mammary tumour cell line (EMT6-S) and MDR sub-line (EMT6-R) were characterised with regard to growth kinetics, susceptibility to doxorubicin and membrane lipid composition. The log phase doubling times (h) were found to be 21.8 (EMT6-S)and 25.0 (EMT6-R) and the IC 50 values for doxorubicin to be 2.2 x 10-8 M and 1.8 x 10-6 M for EMT6-S and EMT6-R cells, respectively. No difference was observed between the phospholipid profiles of the two cell lines and total fatty acid composition was similar, however, the level of linoleic acid appeared to be higher in the resistant cells. The photocytotoxicity of the cationic dyes methylene blue (MB), toluidine blue (TBO) and Victoria blue BO (VBBO) against the EMT6 cell lines was compared to the cyotoxic effect of doxorubicin and cis-platinurn. The cytotoxic effect of VBBO was enhanced 10-fold by illumination (7.2 J cm2) in both EMT6-S and EMT6-R cells. In order to overcome resistance, however, the EMT6-R cells required a 10-fold greater level of the dye than the parental cells to reach an IC50 value. By contrast, doxorubicin required almost a 100-fold increase in concentration to overcome this resistance. Pre-treatment of EMT6-S and EMT6-R cells with low concentrations of VBBO resulted in a 2-fold increase in doxorubicin toxicity in both cell lines. Pre-treatment with MB and TBO resulted in a ...