loxoribine and Leukemia--Lymphocytic--Chronic--B-Cell

Investigation of the biological actions of loxoribine in chronic lymphocytic leukemia (CLL) was undertaken because of the pervasive immunostimulatory effects of the nucleoside on normal B cells. In vitro studies with cells from a spectrum of CLL patients demonstrate that loxoribine induces B-CLL cells to enter and traverse the cell cycle. This is reflected by marked increases in DNA synthesis, by standard morphological criteria, and by flow cytometric evaluation of cell cycle status and of cell surface activation markers. Cells from about 75% of patients studied evince this response. Analysis of a variety of biological parameters indicate that only the ratio of T cells (CD4+ or CD8+) to B-CLL cells correlates with induction and degree of proliferative response. Co-stimulation with loxoribine and IL-2 results in modest proliferative synergy, presumably due to upregulation of IL-2R alpha expression on B-CLL cells by loxoribine. Prolonged exposure of B-CLL cells to stimulatory concentrations of loxoribine frequently culminates in progression of the responsive cells to apoptosis. The capacity of loxoribine to transiently approximate the reversible transformation of a low grade B cell malignancy to one of a higher grade presents the opportunity for evaluation of cycle-active drugs under these conditions. Recent studies indicate that pre-treatment of B-CLL cells with loxoribine results in synergistic killing of leukemic cells with cycle-active drugs. The ability to induce B-CLL cells into cell cycle entry and/or into either activation-induced apoptosis or into phases of the cell cycle sensitive to cytotoxic therapy opens up new perspectives for the development of potentially curative strategies for this chronic leukemia.

Topics: Adjuvants, Immunologic; Apoptosis; B-Lymphocytes; Cell Cycle; Drug Synergism; Guanosine; Humans; Immunophenotyping; Interleukin-2; Leukemia, Lymphocytic, Chronic, B-Cell; Lymphocyte Activation; Lymphocyte Count; Receptors, Interleukin-2; T-Lymphocyte Subsets; Tumor Cells, Cultured

Fludarabine has shown a definite clinical activity in B-cell chronic lymphocytic leukemia (B-CLL). Recently it has been demonstrated that loxoribine, a guanine ribonucleotide derivative, is able to increase the cytotoxicity of fludarabine in B-CLL cells, in vitro. We have here extended these findings by testing the activity of loxoribine in combination with fludarabine and mafosfamide. As we have previously demonstrated, loxoribine enhances the activity of fludarabine at all concentrations, while only lower doses of mafosfamide seem to be positively affected by loxoribine. The combination of fludarabine and mafosfamide is synergistic on CLL cells, and the cytotoxic activity is increased by the addition of loxoribine. We have also evaluated the pro-apoptotic activity of each drug, both alone and in combination; these results are concordant with the cytotoxicity data, thus demonstrating that, even though loxoribine is more active in combination with fludarabine than with mafosfamide, the efficacy of the triple combination is higher than that obtained with any other agent alone or in double combination.

Topics: Adjuvants, Immunologic; Aged; Aged, 80 and over; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Cell Division; Cyclophosphamide; Drug Screening Assays, Antitumor; Drug Therapy, Combination; Female; Guanosine; Humans; Leukemia, Lymphocytic, Chronic, B-Cell; Male; Middle Aged; Tumor Cells, Cultured; Vidarabine

Purine analogues like fludarabine have been shown to be superior to conventional therapy for B-cell chronic lymphocytic leukemia (B-CLL). In order to improve the activity of fludarabine, we tested its combination with loxoribine, a guanine ribonucleotide derivative, known to enhance the sensitivity of B-CLL cells to cytotoxic drugs. B-CLL cells from 6 patients were studied; co-incubation with loxoribine 100 microM increased the activity of fludarabine by 12% to 48%, as demonstrated by XTT colorimetric assay; while 1000 microM loxoribine exerted a protective effect. Accordingly, fludarabine-induced apoptosis was enhanced by the addition of loxoribine 1000 microM (39% increase). These results indicate that the combination of loxoribine and fludarabine could be of interest in B-CLL.

Topics: Aged; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Cell Cycle; Drug Interactions; Drug Screening Assays, Antitumor; Female; Guanosine; Humans; Leukemia, Lymphocytic, Chronic, B-Cell; Male; Middle Aged; Tumor Cells, Cultured; Vidarabine

Leukemic B cells from a majority of patients with chronic lymphocytic leukemia (CLL) enter the cell cycle upon stimulation in vitro with loxoribine, a potent 7,8-disubstituted guanine ribonucleoside immunostimulant. In the absence of added costimulants, a proportion of these cells become activated and undergo DNA synthesis and mitosis accompanied by a marked increase in expression of an array of cell surface activation antigens. The resultant activated B-CLL cells exhibit greatly enhanced sensitivity to cycle-active cytotoxic drugs. This approach may be of potential value in the therapy of CLL.

Topics: Adult; Aged; Antibodies, Monoclonal; Antigens, CD; Antineoplastic Agents; Cell Cycle; Cells, Cultured; Dose-Response Relationship, Drug; Female; Guanosine; Humans; Immunophenotyping; Leukemia, Hairy Cell; Leukemia, Lymphocytic, Chronic, B-Cell; Lymphocyte Activation; Lymphocytes; Male; Middle Aged; Mitosis