Several mechanisms of drug resistance have been defined using cell lines selected for resistance in vitro. However, the relevance of these to tumor cell resistance in vivo remains unclear. We established tumor cell lines from biopsies of human sarcomas before and after doxorubicin therapy. One pretreatment sarcoma line, STSAR90, was 6-fold less sensitive to doxorubicin than was a normal fibroblast line, AG1522. The sensitivities of six other sarcoma lines were similar to that of AC1522. STSAR90 cells did not overexpress P-glycoprotein mRNA, by Northern analysis with the pCHPl complementary DNA fragment. Photoaffinity labeling with the vinblastine analogue N-(p-azido-3-125I-salicyl)-N-β aminoethylvindesine did not show increased P-glycoprotein concentra tions. Accumulation of |3H|daunomycin was not decreased in STSAR90 compared with a less resistant sarcoma line, STSAR11, nor was the doxorubicin sensitivity of STSAR90 increased by coincubation with verapamil. Glutathione levels were twice as high in STSAR90 as in STSAR11, and glutathione peroxidase activity was 3.5-to 6-fold higher. This was due mostly to an increase in selenium-dependent peroxidase activity. After exposure to doxorubicin, STSAR90 cells formed only half as much measurable hydroxyl radical as SISARI I, as detected by electron spin resonance spectrometry. Doxorubicin sensitivity was in creased in STSAR90 cells when intracellular glutathione levels were reduced by buthionine sulfoximine. These results indicate that multidrug resistance due to P-glycoprotein-mediated drug efflux is not the onlymechanism of doxorubicin resistance that occurs in sarcomas and that glutathione peroxidase-dependent detoxification of doxorubicin-induced oxygen radicals may contribute to clinical doxorubicin resistance.
|Original language||English (US)|
|Number of pages||7|
|State||Published - Jan 1991|
ASJC Scopus subject areas
- Cancer Research