Unique Pharmacokinetic Self-Potentiation of Idarubicin through Induction of Carbonyl Reducing Enzymes in Contrast to Other Anthracyclines, Pharmacologic and Clinical Study

Idarubicin (IDA) is one of the key drugs for treating hematological malignancies. Severe myelosuppression is one of the major adverse events of IDA. Interestingly, when IDA is administered in 2 consecutive courses of therapy, IDA tends to exert a stronger bone marrow suppressive effect in the second course compared with the first course while other anthracyclines such as daunorubicin tend to milder suppressive effect in the second course compared with the first course (Wiernik PH et al, Blood, 1992). In order to clarify this unique characteristics, in vivo and in vitro studies regarding the pharmacokinetic behavior were performed. When RLN-B2 (a rat liver cell line) was precultured in the presence of IDA, higher carbonyl reducing enzymes (CREs) activity was observed compared with non-precultured cells, suggesting the anthracycline-reducing enzymes was induced in the cells incubated in the presence of IDA. We examined the in vivo effects of IDA administration on the induction of CREs and subsequent enhanced formation of the 13-OH metabolite, idarubicinol (IDAol) which is more active compared with IDA and has a remarkably long half-life in the blood. The rats (F344) preadministered IDA showed higher enzymatic activity than that from non-preadministered rats (p < 0.05). At 4 hours after IDA administration, the production of IDAol was facilitated in the preadministered group compared with the non preadministered group (p < 0.05). Clinically, the duration of leucopenia was compared between IDA and mitoxantrone, an CREs independent anthraquinone, in combination with enocytabine, 6-mercaptopurine and etoposide. In 2 consecutive therapy, namely remission-induction and first consolidation therapy, in 30 cases of acute myelogenous leukemias, the duration of leucopenia was substantially equal in IDA group while it was substantially shorter in consolidation therapy compared with induction therapy in mitoxantrone group. These results suggest that CREs was induced by IDA pretreatment in vitro and in vivo, resulting in increased IDAol, which could potentiate the myelosuppressive and probably antitumor effects of IDA in contrast to other anthracyclines. This unique PK/PD characteristics of pharmacokinetic self-potentiation could be important in the safe and effective use of IDA in the therapy for hematological malignancies.