Mechanisms of Chemoresistance in Breast Cancer Cells; Final rept

摘要

One of the most persistent factors accounting for the continuing mortality in cancer patients is the development of multidrug resistance (MDR). In this study we have shown that over expression of glucosylceramide synthase (GCS) is not a consistent characteristic in breast cancer cells. We have determined that in order for GCS to be over expressed cells must be selected to grow in the presence of anticancer agents that activate ceramide formation. This abundance of ceramide enhances GCS message which results in increases in glucosylceramide (GC). We found this to be the case with Adriamycin but not with cisplatin or etoposide. This study also showed that limiting GCS activity down regulated the expression of MDR1. In assessing P-gp status in the MCF-7- AdrR cells transfected with GCS antisense we observed a dramatic decrease in the level of MDR1 expression (80% down by RT-PCR) which translated into a similar decrease in P-gp protein levels (Western-blot). These findings demonstrated an interesting yet ambiguous relationship between GCS which regulates ceramide metabolism and the expression of P-gp. To gain insight into the relationship of GCS and MDR1 we studied the influence of sphingolipids on MDR1 expression. When cells MCF-7 and MDA-MB-231 challenged with high levels of ceramide utilize a glycosylation route to limit ceramide%s residence time this action promotes enhanced expression of the multidrug resistant phenotype in cancer cells through what we propose is a GC intermediate.