The cytotoxicity of vincristine in vitro was investigated in B chronic lymphocytic leukemia (CLL) cells and in normal peripheral blood mononuclear cells. An approximately 25-fold selectivity towards leukemic vs. normal lymphocytes was demonstrated. Cells from patients having a mature subtype (CLL or CLL/mix) or a slowly progressing form of CLL were significantly more sensitive to vincristine in vitro than the cases with a CLL/PL phenotype or faster-progressing disease. Depending on the vincristine dose, the number of dead CLL cells accumulated slowly during the 4-d observation period. Our data indicate a marked individual variation in vincristine susceptibility among individual CLL cells. Vincristine induced annexin positivity, nuclear blebbing and DNA fragmentation in CLL cells. These indicate an "apoptosis-like" cell death. Since CLL cells are in the G0/G1 phase of the cell cycle, the only known mode of anticancer action of vinca alkaloids, i.e. anti-mitotic action, cannot explain the death of CLL cells. Furthermore, similar cellular uptake and efflux of vincristine by normal and CLL cells excluded pharmacokinetic differences as a cause of selectivity of vincristine towards leukemic lymphocytes. Immunostaining of filamentous structures of CLL cells revealed that vincristine brings about selective changes in alpha-tubulin but not in beta-actin or vimentin. Although the antitubulin action of vinca alkaloids in the biochemical sense is well demonstrated, this kind of anticancer effect has not previously been shown. Vincristine is used in several regimens for CLL, but its efficacy in CLL has never been demonstrated in a clinical context and its value in routine CLL chemotherapy has been questioned. The present data strongly support the need for further evaluation of the role and mode of action of vincristine in chemotherapy of CLL and other cancers as well.
Chronic lymphocytic leukemia (CLL) is a clonal B-cell disorder, which has recently been divided into 2 subtypes based on the somatic hypermutation status of the immunoglobulin heavy chain (IgVH) genes. In patients with unmutated tumor cells the survival time is approximately half of that in mutated cases, but the reason for this difference is poorly understood. Since infections are the major cause of mortality in CLL, we investigated the effect of the mutation status on host immunity and proneness to infections in patients with CLL. As expected, the disease progression seemed to be faster and the disease more advanced (Binet B and C) among unmutated patients than in the mutated ones. Surprisingly, no differences in humoral immunity [immunoglobulin G (IgG), IgM, IgA, IgG subclasses, anti-ABO blood group antibodies and mannan-binding lectin (MBL)] or immune responses (Haemophilus influenzae serotype b conjugate vaccination) were detected between these 2 patient groups. Furthermore, UM-patients were not more prone to infections compared to M-patients, and therapy had no impact on the incidence and pattern of infections in either of the patient groups. The current findings within this patient cohort reveal that the worse outcome in the unmutated subgroup is not caused by more severe defects in immunity and increased susceptibility to infections when compared with the hypermutated group. It is thus conceivable that active immunization procedures such as vaccination can successfully be applied on patients with unmutated IgVH gene and advanced disease stage.
Drug resistance is a major problem in chemotherapy of chronic lymphocytic leukemia (CLL). The genetic basis and molecular pathogenesis of drug resistance in CLL remain poorly understood. Here, we have investigated the association between chromosomal aberrations and cellular resistance of CLL cells against seven drugs, gamma and ultraviolet irradiation. Samples were obtained from 35 patients having a classical form of B-CLL. Chromosomal aberrations were first analyzed by traditional karyotyping improved by using optimized mitogen combinations. DNA sequence copy number changes throughout the genome were next screened by comparative genomic hybridization. Finally, fluorescence in situ hybridization was used to detect trisomy 12 and loss of Rb and deletions at chromosome 11. The cellular sensitivity in vitro was assessed by the reduction of macromolecular protein synthesis measured as incorporation of radioactive L-leucine as an endpoint. The overall analysis disclosed a statistically highly significant difference in cellular drug resistance between patients having at least three aberrations compared with patients with fewer or no aberrations. This strongly indicates that complex rather than simple molecular mechanisms are responsible for the drug and irradiation resistance in CLL. According to published results, complex aberrations are constantly associated with poor prognosis in CLL. We demonstrated here that complex chromosomal aberrations were associated with cellular irradiation and drug resistance, which, on the other hand, may be responsible for the poor clinical outcome in CLL.
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