Effects of cis-unsaturated fatty acids on doxorubicin sensitivity in P388/DOX resistant and P388 parental cell lines

It has been reported that several cis-unsaturated fatty acids (c-UFAs) coul d increase doxorubicin (DOX) accumulation in cancer cells and hence elevate its cytotoxicity. However, some researchers showed that c-UFA pretreatment did not affect its cytotoxicity in special cell lines. It is possible that the different results occurred due to different cellular characteristics. We hypothesized that c-UFA treatment might modulate the activities of some antioxidant enzymes to affect the resistance of cells to DOX. In the presen t study, we examined how c-UFA pretreatment affected DOX cytotoxicity on mo use leukemia cell line, P388, and its resistant subline, P388/DOX, which we found to have significantly higher glutathione peroxidase (GPx) activity a s well as P-glycoprotein (p-gp) overexpression. We chose two c-UFAs, gamma- linolenic acid (GLA) (18:3n-6) and docosahexaenoic acid (DHA) (22:6n-3). Cy totoxicity was measured by MTT (3-(4,5-dimerhylthiazol-2-yl)-2,5-diphenylte trazolium bromide) and trypan blue exclusion assays. DOX accumulation and p -gp expression were measured by flow cytometry. The activities of catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), and GPx were determined for both cell lines with and without treatment with GLA or DHA. Significant DOX accumulation occurred in both cell lines with GLA or DHA pretreatment, but without any change in p-gp expression in either cell line. Sensitivity to DOX cytotoxicity was improved by GLA or DHA pretreatme nt in P388/DOX in which only SOD activity was significantly increased, but not in the parental cell line P388 in which both SOD and CAT were significa ntly increased by the pretreatment. However, combined pretreatment of GLA o r DHA with antioxidants, pyrrolidinedithiocarbamate (PDTC) or Vitamin C, co uld sensitize not only P388/DOX but also P388 cells to DOX. We conclude tha t the effects of c-UFA pretreatment on the sensitivity of cancer cells to D OX not only depend on the change in drug accumulation but also the change i n the levels of antioxidant enzyme activities, and suggest that combined ad ministration of c-UFAs, antioxidants, and DOX may be more effective in trea ting leukemia. (C) 2000 Elsevier Science Inc. All rights reserved.