THE IN-VITRO CYTOTOXIC EFFECT OF MITOXANTRONE IN COMBINATION WITH FLUDARABINE OR PENTOSTATIN IN B-CELL CHRONIC LYMPHOCYTIC-LEUKEMIA

Background and Objective. Clinical studies indicate that combination c hemotherapy with mitoxantrone (Mitox) and a purine analog can improve the response rate in indolent lymphoproliferative disorders. We explor ed the in vitro Mitox- fludarabine (FAMP)- and pentostatin (Pento)-ind uced cyotoxicity and their interactions in CLL. Methods. The periphera l lymphocytes of 24 CLL patients were tested at different drug concent rations, with Mitox, FAMP or their combinations in 22 cases, and with Mitox, Pento or their combinations in 20cases, 18 of which were the sa me from the FAMP group. The MTT assay was chosen for the drug-induced cell cytotoxicity and flow cytometry analysis of the DNA hypodiploid p eak for the study of the apoptotic process. Drug interactions were cal culated 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 w ere 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 wi th the multiplicative and maximum model, the combinations of Mitox+FAM P and Mitox+Pento at different drug concentrations were synergistic in 28.2% and 39.3%, respectively. At leukemic cell survival less than or equal to 50%, 11.7% and 11.1% of all combinations were synergistic in the Pento and FAMP group, respectively. The number of synergistic int eractions at a therapeutically achievable plasma-drug concentration wa s 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 c orrelation coefficient was not significant in the Pento group. Finally , as measured by the DNA hypodiploid peak, Mitox (0.25 mu g/mL) plus P ento (0.16 mu g/mL) showed a significantly enhanced apoptosis in compa rison to each single drug, while Mitox failed to demonstrate an additi ve effect with FAMP (1 mu g/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 ad junctive apoptotic effect for the Mitox-Pento association only. (C) 19 97, Ferrata Storti Foundation.