Dt Jones

Human bone marrow stromal cells prevent apoptosis and support the survival of chronic lymphocytic leukaemia cells in vitro

Leukaemic cells from most cases of B‐chronic lymphocytic leukaemia die rapidly by apoptosis in vitro unless they are cultured in the presence of interleukin‐4 or interferon α or γ. We now report prolonged survival of purified CLL cells cultured on bone marrow (BM) derived stromal cells in the absence of exogenous growth factors. In 10 cases of CLL examined 0–61% (mean 14.7%) of the cells were viable after 10 d culture in medium alone, whereas in the presence of BM stromal cells 10–102% (mean 47.0%) of cells were recovered alive (P < 0.005) in 7/10 cases of CLL, cells remained viable after 30 d of culture in BM stromal cells with cell recovery of 12–65%. These long‐term cultured CLL cells were Epstein Barr virus negative, shown by the failure to detect the ENBA‐2 and BZLF1 genes of EBV by PCR analysis. Identity between day 0 and day 30 CLL cells was demonstrated by sequence analysis of their clonal IgH CDR3 region. Adherence of CLL cells to BM stromal cell layers was critical for their protection from apoptosis. Separation of CLL cells from stroma by 0.45 μm culture filters resulted in loss of the protective effect of the stromal cells. Stromal cells were also able to protect CLL cells from hydrocortisone‐induced apoptotic cell death. Our findings provide an in vitro system that can be used to analyse the growth requirements of CLL cells and their chemosensitivity in an in vitro environment that mimics the in vivo milieu.

The sesquiterpene lactone parthenolide induces selective apoptosis of B-chronic lymphocytic leukemia cells in vitro.

We have studied the in vitro actions of the sesquiterpene lactone parthenolide (PTL) on cells isolated from patients with chronic lymphocytic leukemia (CLL). Dye reduction viability assays showed that the median LD50 for PTL was 6.2 μM (n=78). Fifteen of these isolates were relatively resistant to the conventional agent chlorambucil but retained sensitivity to PTL. Brief exposures to PTL (1–3 h) were sufficient to induce caspase activation and commitment to cell death. Chronic lymphocytic leukemia cells were more sensitive towards PTL than were normal T lymphocytes or CD34+ haematopoietic progenitor cells. The mechanism of cell killing was via PTL-induced generation of reactive oxygen species, resulting in turn in a proapoptotic Bax conformational change, release of mitochondrial cytochrome c and caspase activation. Parthenolide also decreased nuclear levels of the antiapoptotic transcription factor nuclear factor-kappa B and diminished phosphorylation of its negative regulator IκB. Killing of CLL cells by PTL was apparently independent of p53 induction. This is the first report showing the relative selectivity of PTL towards CLL cells. The data here warrant further investigation of this class of natural product as potential therapeutic agents for CLL.

Autologous plasma activates Akt/protein kinase B and enhances basal survival and resistance to DNA damage-induced apoptosis in B-chronic lymphocytic leukaemia cells

We have studied the actions of autologous plasma on both basal and DNA damage‐induced apoptosis in B‐chronic lymphocytic leukaemia (B‐CLL) cells. Apoptosis was quantified using morphological criteria and Western blot analysis for the apoptosis‐specific p85 fragment of poly(ADP ribose) polymerase. Cell viability was estimated using the methyl thiazol tetrazolium bromide dye reduction assay. Plasma cultures showed lower rates of basal apoptosis as well as a decreased cytotoxic response to chlorambucil and γ‐radiation compared with cultures in fetal calf serum. Experiments using neutralizing antibodies suggested that the protective actions of plasma could not be accounted for by interleukin 4, the interferons α or γ or stromal cell‐derived factor 1, each of which have been shown to protect B‐CLL cells from apoptosis in vitro. Plasma addition to B‐CLL cells resulted in rapid activation of the Akt protein kinase, a key signalling enzyme that has been implicated in anti‐apoptotic signalling. LY294002, an inhibitor of phosphatidylinositol 3′‐kinase, blocked Akt activation by plasma. To the best of our knowledge, this is the first report to show that factors present in plasma promote basal survival of B‐CLL cells and resistance to cytotoxic drugs via stimulation of the Akt cytoprotective‐signalling pathway. Pharmacological blockade of this pathway may have potential in the development of novel therapeutic strategies for B‐CLL treatment.

Cytotoxic drugs enhance the ex vivo sensitivity of malignant cells from a subset of acute myeloid leukaemia patients to apoptosis induction by tumour necrosis factor receptor-related apoptosis-inducing ligand

Summary. We have studied the actions of tumour‐necrosis‐factor‐related apoptosis‐inducing ligand (TRAIL) on cells isolated from patients with acute myeloid leukaemia (AML). Apoptosis induction was initially assessed by quantitative morphological analysis. Only 2/19 isolates showed a > 10% increase in apoptotic cells following TRAIL treatment. However, incubation with TRAIL combined with fludarabine, cytosine arabinoside or daunorubicin resulted in additive or super‐additive apoptosis induction in approximately half of the isolates. Molecular evidence of super‐additive apoptosis induction by TRAIL and cytotoxic agents was obtained by quantification of caspase 3 activation, detected by Western blot analysis of poly (ADP ribose) polymerase cleavage. The ability of TRAIL and daunorubicin to induce super‐additive apoptosis correlated with the ability of these agents to activate caspase 8 and to augment cellular levels of the truncated pro‐apoptotic form of the BCL‐2 family member BID. Our data suggest that co‐administration of TRAIL with conventional cytotoxic drugs may be of therapeutic value in some patients with AML.