Induction of daunorubicin carbonyl reducing enzymes by daunorubicin in sensitive and resistant pancreas carcinoma cells

Daunorubicin (DRC) and other anthracyclines are valuable cytotoxic agents in the clinical treatment of certain malignancies. However, as is the case with virtually all anticancer drugs, tumor cell resistance to these agents is one of the major obstacles to successful chemotherapy. In addition to an increased energy-dependent efflux of chemotherapeutic agents, enzymatic drug-inactivating mechanisms also contribute to multidrug resistance of tumor cells. In the case of DRC, carbonyl reduction leads to 13-hydroxydaunorubicinol (DRCOL), the major metabolite of DRC with a significantly lower antineoplastic potency compared to the parent drug. In the present study, we compared two pancreas carcinoma cell lines (a DRC-sensitive parental line and its DRC-resistant subline) with respect to their capacity of DRC inactivation via carbonyl reduction. In addition, we cultured the two cell lines in the presence of increasing sublethal concentrations of DRC. Evidence is presented that DRC treatment itself leads to a concentration-dependent induction of DRC carbonyl reduction in subcellular fractions of both the sensitive and resistant pancreas carcinoma cells, resulting, surprisingly, in different susceptibilities to DRC. The principal difference between the two cell lines becomes most apparent at high-dose DRC supplementation (1 μ/mL), at which DRC resistant cells exhibited highest inducibility of DRC-inactivating enzymes, whereas respective sensitive cells already showed an impairment of cellular viability. The use of the diagnostic model substrates metyrapone and p-nitrobenzaldehyde reveals that this adaptive enhancement of DRC inactivation can be attributed to the induction of DRC carbonyl reductases different from known aldehyde and carbonyl reductases. In conclusion, these findings suggest that inactivation of anthracyclines by carbonyl reduction is inducible by the substrate itself, a fact that might be considered as one of the enzymatic mechanisms that contribute to the acquired resistance to these drugs.