The in vitro cytotoxic effect of mitoxantrone in combination with fludarabine or pentostatin in B-cell chronic lymphocytic leukemia

Abstract

BACKGROUND AND OBJECTIVE: Clinical studies indicate that combination chemotherapy with mitoxantrone (Mitox) and a purine analog can improve the response rate in indolent lymphoproliferative disorders. We explored the in vitro Mitox- fludarabine (FAMP)- and pentostatin (Pento)-induced cytotoxicity and their interactions in CLL. METHODS: The peripheral lymphocytes of 24 CLL patients were tested at different drug concentrations, with Mitox, FAMP or their combinations in 22 cases, and with Mitox, Pento or their combinations in 20 cases, 18 of which were the same from the FAMP group. The MTT assay was chosen for the drug-induced cell cytotoxicity and flow cytometry analysis of the DNA hypodiploid peak for the study of the apoptotic process. Drug interactions were calculated in the MTT assay according to both multiplicative and maximum models. RESULTS: According to the lethal dose (LD) 50 values, when the three drugs were tested alone, 11 out of 22 and 8 out of 20 samples were sensitive to Mitox in the FAMP and Pento groups, respectively; on the other hand, 2 out of 22 and 0 out of 20 samples appeared sensitive to FAMP or Pento alone, respectively. Analyzing the MTT assay data with the multiplicative and maximum model, the combinations of Mitox+FAMP and Mitox+Pento at different drug concentrations were synergistic in 28.2% and 39.3%, respectively. At leukemic cell survival < or = 50%, 11.7% and 11.1% of all combinations were synergistic in the Pento and FAMP group, respectively. The number of synergistic interactions at a therapeutically achievable plasma-drug concentration was an inverse function of the Mitox concentration. In the FAMP group, a direct correlation was found between the LD50 values of both FAMP and Mitox and the number of synergistic interactions, while the Pearson correlation coefficient was not significant in the Pento group. Finally, as measured by the DNA hypodiploid peak, Mitox (0.25 microgram/mL) plus Pento (0.16 microgram/mL) showed a significantly enhanced apoptosis in comparison to each single drug, while Mitox failed to demonstrate an additive effect with FAMP (1 microgram/ml). INTERPRETATION AND CONCLUSIONS: This experience demonstrates the extent of the in vitro synergism of Mitox with FAMP and Pento in inducing cell cytotoxicity; it also shows an adjunctive apoptotic effect for the Mitox-Pento association only.