Multiple mechanisms confer different drug-resistant phenotypes in pancreatic carcinoma cells

Abstract

Purpose. 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 IIα and IIβ 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.