Quantitation of resistance of leukemic cells to cytosine arabinoside from BrdUrd/DNA bivariate histograms

Valproic acid inhibits proliferation and induces apoptosis in acute myeloid leukemia cells expressing P-gp and MRP1

The multidrug resistance (MDR) phenotype, induced by the overexpression of several ABC transporters or by antiapoptotic mechanisms, has been identified as the major cause of drug resistance in the treatment of patients with acute myeloid leukemia (AML). In this study, we have shown that valproic acid (VPA) (a histone deacetylase inhibitor) can inhibit the proliferation of both P-glycoprotein (P-gp)- and MDR-associated protein 1 (MRP1)-positive and -negative cells. VPA also induced apoptosis of P-gp-positive cells. VPA induced apoptosis in K562 cells led to decrease in Flip (FLICE/caspase-8 inhibitory protein) expression with Flip cleavage, which could not be observed in HL60 cells. In HL60/MRP cell line, which proved to be resistant to apoptosis by VPA, we observed an abnormal expression of apoptotic regulatory proteins, overexpression of Bcl-2 and absence of Bax. Also, the Bcl-2 antagonist HA14-1 rapidly restored apoptosis in this cell line. Cotreatment with cytosine arabinoside induced very strong apoptosis in both K562/DOX and HL60/DNR cell lines. VPA also induced apoptosis in AML patient cells expressing P-gp and/or MRP1. Our findings show VPA as an interesting drug that should be tested in clinical trials for overcoming the MDR phenotype in AML patients.

Cell cycle regulatory protein expression in fresh acute myeloid leukemia cells and after drug exposure

Characteristics of treatment-induced cell cycle arrest are important for in vitro and in vivo sensitivity of acute myeloid leukemia (AML) cells to cytotoxic drugs. We analyzed the expression of the major G1 cell cycle regulators (p21Cip1, p27Kip1, cyclins D, cyclin E and pRb) in 41 fresh AML cell samples. The level of p27 expression was the only factor correlated with the response to chemotherapy, a high level of p27 expression being predictive of complete remission. There was a close relation between expression of pRb, cyclin D2 and FAB subtype, illustrated by the absence of both proteins in most samples having a monocytic component (M4, M5). We also assessed the expressions of pRb, cyclin E, p21 and p27 and the activity of cdk2, the major regulator of S-phase entry, after exposure to cytosine-arabinoside (AraC) and daunorubicin (DNR), and found these proteins could characterize time- and dose-dependent cellular response to each drug. We observed hyperphosphorylated pRb, increased levels of cyclin E and a high cdk2 activity, but no p21 induction, in AML cells exposed to 10(-6) M AraC. After exposure to 10(-5) M AraC, corresponding to the serum concentration reached in high-dose AraC regimens (HDAraC), a strong p21 induction was observed, associated with similarly overexpressed cyclin E and even higher cdk2 activity than after 10(-6) M AraC, while apoptosis was significantly increased. These data suggest that cdk2 activity is likely to play a role in AraC-induced apoptosis in AML cells. This mechanism may account for high efficacy of HDAraC in cells showing little sensitivity to conventional AraC doses.

Study of the apoptosis induced in vitro by antitumoral drugs on leukaemic cells

A flow cytometric method for simultaneous apoptotic cell detection and cell cycle analysis was applied on the U937 cell line. Four antitumoral drugs currently used in the treatment of acute myeloid leukaemia were studied in vitro: DNR, IDR, MITO and Ara-C. Our results show a dissociation between the cytostatic effect (the block in the cell cycle observed for low drug concentrations) and the cytotoxic effect (the induction of apoptosis induced by higher concentrations) for all the tested molecules. Low concentrations of Ara-C induced a block in the S phase while higher concentrations (>10(-7) M) induced apoptosis at the G1-S boundary. Low concentrations of anthracyclines (<40 nM DNR and <20nM IDR) induced a block in G2 without apoptosis. Apoptosis was induced in G1 and/or early S phases by higher concentrations of anthracyclines. The concentration inducing 50% apoptosis (IC50) was found to be, respectively, 200 and 40 nM for DNR and IDR. Analysis of MITO-treated cells showed a parallel increase in the percentages of S phase and apoptotic cells. However, the bivariate analysis showed that apoptosis did occur in a population with G1 DNA content. For two other drugs (CAM and COLC), apoptosis occurred for the same concentrations and in the same phase as the block (in S and G2M, respectively). The IC50 of MITO was found to be 100 nM. Cotreatment of the cells with colchicin and either Ara-C or IDR showed that the passage through mitosis was not necessary for the completion of apoptosis at the G1-S boundary. Short incubations of U937 cells with high concentrations of anthracyclines were found to be efficient in inducing further apoptosis. We conclude that, for all the assayed molecules, the cytotoxic and/or cytostatic effects of the antitumoral drugs tested greatly depend on the concentrations used and that, depending on their in vivo pharmacokinetics, the induction of apoptosis could be an important mechanism of action for some of these drugs.

Adult acute leukemia

Untreated acute leukemia is a uniformly fatal disease with a median survival time shorter than 3 months. Current treatment strategies provide a significant increase in survival time for most patients, some of whom may be cured. The majority of patients with acute leukemia, however, ultimately die of the disease or complications of treatment. The effective treatment of acute leukemia requires (1) differentiation of acute myeloid leukemia (AML) from acute lymphoblastic leukemia (ALL) and recognition of clinically relevant subtypes; (2) identification of patients who are more likely or less likely than average to benefit from a conventional treatment; and (3) selection of therapy that provides a reasonable likelihood of response with acceptable risk of toxic effects. The diagnosis of acute leukemia is established in most cases by a bone marrow aspirate that demonstrates at least 30% blast cells. The traditional criteria to distinguish between AML and ALL rely on morphology and cytochemical reactions. Immunologic analysis of antigen expression and analysis for numerical or structural chromosomal abnormalities of leukemia cells are routinely feasible. Karyotypic analysis is of prognostic importance and should be performed on all diagnostic specimens of bone marrow aspirate. Immunophenotypic analysis may be useful to confirm the disease classification in selected cases. The importance of the routine immunophenotypic characterization of acute leukemia, however, is controversial. The subtypes that must be recognized because of the need for specific treatment include (a) acute promyelocytic leukemia (APL), which is the M3 subtype of AML, and (b) the L3 subtype or mature B-cell ALL. Induction therapy for acute leukemia is treatment intended to achieve induction of complete remission (CR). Complete remission is defined as the absence of morphologic evidence of leukemia after recovery of the peripheral blood cell counts. Failure to achieve CR may be attributed to death during chemotherapy-induced bone marrow hypoplasia or to drug resistance manifested either as failure to achieve hypoplasia or as persistent leukemia after recovery from hypoplasia. Postremission therapy is treatment administered in CR to prevent or delay relapse of the leukemia. However, the majority of patients have disease relapse. Intensification of therapy is a treatment strategy designed to overcome resistance to chemotherapy. Recent clinical trials of intensified induction or postremission therapy suggest improved outcome. However, the toxic effects of dose intensification can be substantial, limiting any potential benefit of this approach. Identification of prognostic factors may allow one to estimate the likelihood of an outcome, to determine an optimal treatment strategy. It is well established that age at the time of diagnosis, leukemia cell karyotype, and whether the leukemia is de novo or secondary are factors that influence treatment decisions. Patients with favorable prognostic factors should probably receive conventional therapy. Patients with unfavorable prognostic factors have shown little benefit from conventional therapy. In addition, factors that indicate poor outcome with conventional therapy are also predictive of poor outcome with intensified therapy. Consequently, these patients should be considered for investigational therapeutic strategies. The bias may be to counsel them to accept the potential increased morbidity of such treatment before there is definite evidence of the possibility of improved outcome. Induction chemotherapy for younger patients with AML (less than 55 years of age) in general consists of one or more courses of cytarabine (ara-C) and an anthracycline or an anthracycline derivative. Randomized trials have failed to confirm that treatment with either etoposide or high-dose ara-C induces disease remission. Patients with secondary AML, high levels of CD34 antigen expression, or an unfavorable karyotype, however, may benefit from ind

Effect of stem cell factor on leukemic progenitor cell growth and sensitivity to cytosine-arabinoside

Recruitment of quiescent, clonogenic blasts from patients with acute myeloid leukemia (AML) by hematopoietic growth factors (HGFs) may improve the cytotoxic effects of cell-cycle-specific drugs like cytosine-arabinoside (Ara-C). Using the culture methods described by Nara and McCulloch and making a distinction between self-renewing and post-deterministic mitoses, we analyzed the effects of stem cell factor (SCF), a growth factor acting on early hematopoietic progenitor and stem cells. First, we demonstrated that SCF, used in combination with other HGFs included in fetal calf serum (FCS) and/or in 5637 cell line supernatant (5637-CM), stimulated both colony formation and self-renewal of blast progenitors from 10 patients, unlike SCF alone. We tested the effects of SCF on the recruitment of cells in the S-phase by using a bromodeoxyuridine/DNA (BrdUrd/DNA) staining method in flow cytometry (FCM). We showed that SCF stimulated proliferation of AML cells significantly in 9/18 patients with AML. Second, we tested the influence of SCF on the sensitivity to Ara-C of self-renewing leukemic cells from 18 patients with AML. We showed that SCF was efficient in increasing the toxicity of Ara-C on the self-renewing blast progenitors, especially with high concentrations of Ara-C. However, a large patient-to-patient heterogeneity was found and the activity of SCF was not correlated with its effect on the cell cycle. These data indicate that SCF can enhance sensitivity to Ara-C of some leukemic cells with self-renewing capacity.

Influence of rhGM-CSF on Ara-C sensitivity of patients with acute myeloid leukemia in relapse: a flow cytometry study

Twenty-three patients with acute myelogenous leukemia (AML) in first relapse were treated with high-dose cytosine-arabinoside (Ara-C) and amsacrine or idarubicin. To prime the cells, the patients were given rhGM-CSF. We studied the influence of 48-h infusion of rhGM-CSF on proliferation and Ara-C sensitivity of leukemic cells both ex vivo and in vitro. We found that a 48-h infusion of rhGM-CSF increased both white blood cell counts and peripheral blood blast cell percentages. Using a Bromodeoxyuridine/DNA (BrdUrd/DNA) staining in flow cytometry, we found an non-constant increase in cells in the S-phase. Ex vivo 48-h culture of leukemic cells with or without rhGM-CSF, with or without other hematopoietic growth factors (HGFs), showed a greater increase of the cells in the S-phase with GF but no correlation with the ex vivo results. We used a method of quantitation of the DNA synthesis previously described (Lacombe F., et al. (1992) Cytometry 13, 730) to monitor the Ara-C sensitivity of the cells in S-phase before and after 48-h infusion with rhGM-CSF. We observed a great variation in the Ara-C sensitivity of the leukemic cells before and after infusion with rhGM-CSF from one patient to another. The BrdUrd/DNA method seems a convenient method to study the influence of HGFs on Ara-C sensitivity of the patients.

Specific antisense oligomer anti Bcr-abl junctions in chronic myeloid leukemia: a cell cycle analysis and CFU-GM study

Antisense oligonucleotides were used to determine the role of the BCR-ABL gene in the proliferation of chronic myeloid leukaemia (CML) clonogenic cells. Peripheral blood Philadelphia chromosome positive cells were obtained from eight CML patients at diagnosis (chronic phase = 7; accelerated phase = 1). Mononuclear cells were incubated with synthetic antisense 18-mer oligonucleotides complementary to the two different junctions b2a2 or b3a2. The type of junction (b2a2 or b3a2) was previously determined by RT-PCR techniques. Cells incubated for 12 to 14 hours with or without sense oligonucleotides served as controls. After incubation with oligonucleotides, the cell DNA synthesis was analysed by flow cytometry using the BrdUrd/DNA method and the cell plating efficiency in methylcellulose was determined. In six of the seven patients in chronic phase, there was a significant inhibition of CFU-GM production which was only 68.4 +/- 19%; (p < .01) of that found in controls. The S phase index, which depends upon the percentage of S phase cells as well as the fluorescence intensity, was 48 +/- 29% (p < .01) of the control values for the seven patients in chronic phase. Interestingly, for the only CML patient in accelerated phase, antisense oligomers had no inhibitory effect on either the production of CFU-GM or the number of S phase cells. In improving the specificity of oligomers, it might be useful for gene-targeted anti-leukemic therapy and/or bone marrow purging.

Cell proliferation markers in acute leukemia

Cell proliferation of blast cells in acute myeloid leukemia (AML) plays a major role in determining response to therapy. Therefore, studies of leukemic cell growth and related factors have been very numerous involving many techniques. They have used a wide panel of proliferation markers but despite their close correlation, we consider here markers assessing cell cycle parameters and those related to cell proliferation.

Treatment of relapsed acute myeloid leukemia using GM-CSF before intensive chemotherapy

Ten patients with acute myeloblastic leukemia (AML) in first relapse were treated with high-dose cytosine-arabinoside (ara-C, 3 g/m2/12 hours x 4) and amsacrine (150 mg/m2/day x 5). In order to prime the cells, the patients were given rh-GM-CSF (3 micrograms/kg/d) for four days, the first infusion starting 48 hours before chemotherapy. Two patients died during the aplastic phase, seven patients achieved a second complete remission (CR2) and one patient remained leukemic. The median duration of aplasia was 17 days (14-21). These results were comparable to those obtained in our previous series of 27 patients treated for AML in first relapse with the same chemotherapy but without GM-CSF (66% CR2). After 48 hours of GM-CSF infusion, (before chemotherapy was started), seven patients had an increase in the white blood cell count with an increase in the absolute number of blast cells in five of these cases. Marrow blast cells percentages increased in 3 of the 8 patients analysed. Six of seven patients tested showed an increase in the percentage of cells in S-phase (studied by flow cytometry using the bromodeoxyuridine (BrdU/DNA) labelling technique and BrdU incorporation). GM-CSF used to prime leukemic cells may be safely administered but its clinical usefulness needs to be further evaluated.