Relevance of in vitro leukaemia cell survival to short- and long term clinical outcome in AML

Cell viability of acute myeloid leukaemia blasts in culture correlates with treatment outcome

Despite the advances in understanding the pathophysiology of acute myeloid leukaemia (AML), the cure rate for acute myeloid leukaemia patients remains low. Cytogenetic abnormalities and age are the prognostic factors that guide treatment decisions. However, many AML patients still die. The biological factors that influence treatment outcome are largely unknown. Thus, the objective of our study was to use the in vitro viability test to correlate with treatment outcome. Acute myeloid leukaemia blasts demonstrated differing ability to survive in culture. Our examination of blast phenotype at various days in culture showed two possible growth directions. First, cells underwent maturation by increased expression of CD16 and down-regulated CD34 (a haemopoietic stem cell marker). These cells also appeared to have undergone apoptosis. Alternatively, cells continued to survive in culture and maintained high expression of CD34. An MTT assay was carried out to determine viability after three days of culture. Lower optical density values were obtained for samples that underwent apoptosis and higher values were obtained for samples that survived in culture. Apoptosis was measured by Annexin V/propidium iodide staining. A comparison between results of MTT assay and duration of disease free survival revealed that a higher viability in vitro correlated significantly with shorter survival duration in the patient (R -0.761, p=0.002, n=13). Thus, this study further supports the hypothesis that AML patients with poor survival may be related to having blasts with a biologically more immature or stem cell-like nature.

The therapy of relapsed acute leukaemia in adults

Although the cure of acute leukaemia has improved significantly, many patients will still relapse and die. The unraveling of the molecular pathogenesis of acute leukaemia has lead to the identification of new prognostic factors and improved the detection of minimal residual disease. The treatment of relapsed acute leukaemia with chemotherapy remains unsatisfactory. Allogeneic or autologous blood and marrow transplant (BMT) can cure a subset of patients with relapsed acute leukaemia. The identification of the graft-vs-leukaemia (GVL) effect has lead to the development of donor lymphocyte infusions to re-induce remission in patients with relapsed leukaemia after allogeneic BMT and also stimulated the development of the less toxic nonmyeloablative allogeneic transplant approach. The identification of molecular targets of therapy and the development of monoclonal antibody-directed therapy has generated optimism. It is possible that combinations of chemotherapy, molecularly directed therapy, and immunotherapy may be combined to cure an increasing proportion of patients with acute leukaemia.

In vitro drug sensitivity and apoptosis induction in newly diagnosed pediatric acute lymphoblastic leukemia: correlation with overall survival

The present study looked for any associations between in vitro drug sensitivity and clinical outcome in pediatric acute lymphoblastic leukemia (ALL) with the standard drugs used for leukemia therapy. A total of 72 samples were analyzed. In vitro sensitivity to drugs was tested by a methylthiazol-tetrazolium assay in 6 serial fold dilutions. Apoptosis was determined by TUNEL assay and apoptotic index was calculated for each sample. Patients sensitive to prednisone, asparginase, vincristine, and 6-mercapto purine had higher overall survival compared to patients whose tumor cells were resistant to these drugs (p < .01). For the other drugs tested, overall survival did not vary from that of the resistant patients. For doxorubicin, asparginase, vincristine, prednisone combination sensitivity, there was a significant worsening of prognosis from the extremely sensitive patients through an intermediate sensitive group to a most resistant group. The present study thus shows that in vitro drug-sensitivity testing provides significant prognostic information in childhood ALL.

Cytokine-regulated expression of survivin in myeloid leukemia

Survivin, a member of the inhibitors-of-apoptosis gene family, is expressed in a cell-cycle-dependent manner in all the most common cancers but not in normal differentiated adult tissues. Survivin expression and regulation were examined in acute myeloid leukemia (AML). Survivin was detected by Western blot analysis in all myeloid leukemia cell lines and in 16 of 18 primary AML samples tested. In contrast, normal CD34(+) cells and normal peripheral blood mononuclear cells expressed no or very low levels of survivin. Cytokine stimulation increased survivin expression in leukemic cell lines and in primary AML samples. In cultured primary samples, single-cytokine stimulation substantially increased survivin expression in comparison with control cells, and the combination of G-CSF, GM-CSF, and SCF increased survivin levels even further. Conversely, all-trans retinoic acid significantly decreased survivin protein levels in HL-60, OCI-AML3, and NB-4 cells within 96 hours, parallel to the induction of myelomonocytic differentiation. Using selective pharmacologic inhibitors, the differential involvement of mitogen-activated protein kinase kinase (MEK) and phosphatidylinositol-3 kinase (PI3K) pathways were demonstrated in the regulation of survivin expression. The MEK inhibitor PD98059 down-regulated survivin expression in both resting and GM-CSF-stimulated OCI-AML3 cells, whereas the PI3K inhibitor LY294002 inhibited survivin expression only on GM-CSF stimulation. In conclusion, these results demonstrate that survivin is highly expressed and cytokine-regulated in myeloid leukemias and suggest that hematopoietic cytokines exert their antiapoptotic and mitogenic effects, at least in part, by increasing survivin levels.

Apoptosis and drug response

Recent investigation further defines the role of p53 and of signaling events upstream and downstream of p53 in apoptosis following drug-induced DNA damage. The transcription factors NF-kappaB and AP-1 can be activated, and then directly transactivate FasL in response to chemotherapeutic agents. Death receptors for FasL (Fas) and for TRAIL (DR4, DR5) are emerging as important regulators of drug-induced apoptosis in human cancers, mediated by caspase activation. Apoptosis has been accepted as the predominant mechanism of drug-induced cell death in preclinical experimental models and in clinically sensitive tumors. However, drug-induced cell death can include acute or delayed apoptosis, necrosis, or a delayed mitotic death, and require further delineation for their relative contribution to tumor responses in vivo.

Leukaemia cell drug resistance and prognostic factors in AML

In 93 cases of acute myeloid leukaemia (AML) the extent to which prognostic factors mirrored the in vitro cellular chemotherapy resistance (to anthracyclines aclarubicin (Acla) and daunorubicin (Dau) as well as nucleoside analogue cytarabine (Ara-C)) was investigated using a 4-d MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay. We found that age at presentation and presence of secondary AML were significantly correlated to leukaemia cell Ara-C resistance. Thus, analysis of in vitro drug resistance data revealed that age at presentation and presence of secondary leukaemia were both independently correlated to cellular drug resistance, with older age being associated with higher Ara-C resistance in vitro (p=0.02 and 0.01 in univariate and multivariate analyses, respectively) and with secondary leukaemia being associated with higher Ara-C resistance (p=0.04 and 0.059 in univariate and multivariate analysis, respectively). Median LC-50 values (Ara-C) were: 178 ng/ml in paediatric cases, 356 ng/ml in younger adult cases, and 584 ng/ml in elderly (age > or = 60 yr) cases giving a resistance ratio between these age subgroups of 1:2.0:3.3. Median LC-50 values (Ara-C) was 381 ng/ml in de novo cases as opposed to 891 ng/ml (resistance ratio 1:2.3) in secondary cases. By contrast, cytogenetic findings, presenting leucocyte count, FAB-subtype, and gender were not consistently correlated to in vitro drug resistance to any of the three drugs. We conclude that at least two major adverse prognostic factors in AML (advanced age at presentation and presence of secondary leukaemia) are associated with increased leukaemia cell Ara-C resistance. High leucocyte count is not associated with increased cellular drug resistance towards Acla, Ara-C or Dau.