Preferential killing of multidrug-resistant KB cells by inhibitors of glucosylceramide synthase

This study has compared the preferential killing of three multidrug-resista nt (MDR) KB cell lines, KB-CI, KB-AI and KB-V1 by two inhibitors of glucosy lceramide synthase, 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) and 1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol (PPPP), to the k illing produced by these compounds in the drug-sensitive cell line, KB-3-1. Both of the inhibitors caused much greater induction of apoptosis in each of the three MDR cell lines than in the drug-sensitive cell line, as judged by morphological assay and confirmed by poly-(ADP-ribose)-polymerase cleav age. The highest level of apoptosis was produced following 24-h exposure to 5 mu M PPPP. This treatment produced 75.8 (+/- 7.1)%, 73.6 (+/- 9.8)% and 75.3 (+/- 6.4)% apoptotic cells in the three MDR cell lines respectively, c ompared to 19.0 (+/- 9.8)% in the drug-sensitive cell line. A reduction in glucosylceramide level following inhibitor treatment occurred in KB-3-1 cel ls as well as in the MDR cell lines, suggesting that the increased apoptoti c response in the MDR cells reflected a different downstream response to ch anges in the levels of this lipid in these cells compared to that in the dr ug-sensitive cells. These results suggest that the manipulation of glucosyl ceramide levels may be a fruitful way of causing the preferential killing o f MDR cells in vitro and possibly in vivo. (C) 1999 Cancer Research Campaig n.