Multiple mechanisms confer different drug-resistant phenotypes in pancreatic carcinoma cells.
OBJECTIVE
Drug-resistant phenotypes of cancer cells may be caused by complex multimodal mechanisms of resistance. In order to gain further insighte into these mechanisms, a P-glycoprotein-mediated multidrug-resistant phenotype induced by daunorubicin-selection and an alternative drug resistance due to treatment with mitoxantrone were investigated in pancreatic carcinoma-derived cells.


METHODS
For assessing cross-resistance against various drugs, cell proliferation assays were performed. Drug accumulation was measured by flow cytometry. Messenger RNA expression was analyzed by Northern blot and RT-PCR, whereas protein expression was determined by Western blot. Catalytic activity of DNA-topoisomerases (Topo) II was determined by the decatenation assay.


RESULTS
In mitoxantrone-selected EPP85-181RNOV cells a decreased accumulation of mitoxantrone and daunorubicin was observed in the absence of P-glycoprotein, multidrug resistance protein or breast cancer resistance protein over-expression. An approximately twofold decrease of DNA topoisomerase II catalytic activity could be observed in both drug-resistance-exhibiting cell lines. The reduction of Topo II catalytic activity was reflected by decreased expression of Topo IIalpha and IIbeta mRNAs and proteins.


CONCLUSIONS
The decreased drug accumulation in EPP85-181RNOV cells indicates that alternative transport events are occurring. The decreased catalytic activity and expression of Topo II indicate that modulation of Topo II catalytic activity contributes to both drug-resistant phenotypes in pancreatic carcinoma cells.
Lage
Hermann
H
Humboldt University Berlin, Charité Campus Mitte, Institute of Pathology, Schumannstr. 20/21, 10117 Berlin, Germany. hermann.lage@charite.de
Dietel
Manfred
M
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000633:toxicity*; D001692:Biological Transport; D002470:Cell Survival / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D003630:Daunorubicin / Q000493:pharmacokinetics / Q000633:toxicity; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D006801:Humans; D007700:Kinetics; D008942:Mitoxantrone / Q000493:pharmacokinetics / Q000633:toxicity; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000235:genetics*; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D012333:RNA, Messenger; D008942:Mitoxantrone; D004250:DNA Topoisomerases, Type II; D003630:Daunorubicin