Decreased drug accumulation in a mitoxantrone-resistant gastric carcinoma cell line in the absence of P-glycoprotein
✍ Scribed by Udo Kellner; Lesley Hutchinson; André Seidel; Hermann Lage; Mary K. Danks; Manfred Dietel; Scott H. Kaufmann
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- French
- Weight
- 306 KB
- Volume
- 71
- Category
- Article
- ISSN
- 0020-7136
No coin nor oath required. For personal study only.
✦ Synopsis
An established gastric-carcinoma cell line, EPG85-257P, is extremely sensitive to mitoxantrone (IC 50 , 0.12 ng/ml). Stepwise selection with mitoxantrone for 3 years resulted in a cell line (EPG85-257RN) that is 7,056-fold resistant to mitoxantrone (IC 50 , 846 ng/ml) and displays cross-resistance to the topoisomerase(topo)-II poisons ametantrone (4113), etoposide (1123) and teniposide (603) as well as the topo-I poisons 7-ethyl-10-hydroxycamptothecin (3313) and topotecan (583). We now show that this resistance is multifactorial. Western blotting revealed a 5-fold decrease in topo-IIa polypeptide in the mitoxantrone-resistant cells. Immunohistochemistry and Western blotting failed to demonstrate P-glycoprotein overexpression. Formation of trapped topo-II-DNA complexes in the resistant cells required higher mitoxantrone concentrations than in parental cells, even though nuclei isolated from the EPG85-257RN cells formed cleavage complexes normally. In agreement with these observations, which suggest the possibility of a defect in mitoxantrone accumulation, examination of mitoxantrone accumulation in both cell lines by confocal laser microscopy revealed that the EPG85-257RN cells accumulate less mitoxantrone at steady state. From these results, we propose that mitoxantrone accumulation, along with alterations in topo-IIa expression, contribute to the resistance to mitoxantrone observed in these cells.