Addition of etoposide to initial therapy of adult acute lymphoblastic leukemia: a combined clinical and laboratory study

Central role of Fas-associated death domain protein in apoptosis induction by the mitogen-activated protein kinase kinase inhibitor CI-1040 (PD184352) in acute lymphocytic leukemia cells in vitro

Because the MAPK pathway plays important roles in cell proliferation and inhibition of apoptosis, this pathway has emerged as a potential therapeutic target for solid tumors and leukemia. At the present time there is little information about activation of this pathway and the consequences of its inhibition in acute lymphocytic leukemia cells (ALL). In the present study, constitutive MAPK pathway activation, as evidenced by phosphorylation of ERK1 and ERK2, was observed in 8 of 8 human lymphoid cell lines and 33% (8:24) of pretreatment ALL bone marrows. Inhibition of this pathway by the MEK inhibitors CI-1040 and PD098059 induced apoptosis through a unique pathway involving dephosphorylation and aggregation of Fas-associated death domain protein followed by death receptor-independent caspase-8 activation. Jurkat cell variants lacking Fas-associated death domain protein or procaspase-8 were resistant to CI-1040-induced apoptosis, as were Jurkat or Molt3 cells treated with the O-methyl ester of the caspase-8 inhibitor N-(Nalpha-benzyloxycarbonylisoleucylglutamyl) aspartate fluoromethyl ketone. In contrast, CI-1040-induced apoptosis was unaffected by blocking anti-Fas antibody, soluble tumor necrosis factor-alpha-related apoptosis-inducing ligand decoy receptor, or transfection with cDNA encoding the anti-apoptotic Bcl-2 family member Mcl-1 or dominant negative caspase-9. Collectively, these results identify the MAPK pathway as a potential therapeutic target in ALL and delineate a mechanism by which MEK inhibition triggers apoptosis in ALL cells.

Long-term follow-up of intensive ara-C-based chemotherapy followed by bone marrow transplantation for adult acute lymphoblastic leukemia: impact of induction Ara-C dose and post-remission therapy

We report single institution outcome of brief, intensive ara-C-based chemotherapy using bone marrow transplantation as primary intensification for untreated adult patients with acute lymphoblastic leukemia (ALL). Overall disease-free and overall survival were inferior to those reported with prolonged chemotherapy modeled on pediatric protocols. Survival and disease-free survival were superior for patients receiving allogeneic BMT compared with chemopurged autologous transplant or maintenance chemotherapy (patients ineligible for or declining BMT). In multivariate analysis, non-L2-FAB, higher ara-C dose, absence of CNS disease, non-Ph1+ karyotype, allogeneic BMT, T cell phenotype, and younger age were associated with improved disease-free survival. Autologous BMT was not superior to chemotherapy, and appears unlikely to provide adequate curative treatment for most adult ALL patients if not followed by maintenance.

Evaluation of Apaf-1 and procaspases-2, -3, -7, -8, and -9 as potential prognostic markers in acute leukemia

Recent studies have suggested that variations in levels of caspases, a family of intracellular cysteine proteases, can profoundly affect the ability of cells to undergo apoptosis. In this study, immunoblotting was used to examine levels of apoptotic protease activating factor-1 (Apaf-1) and procaspases-2, -3, -7, -8, and -9 in bone marrow samples (at least 80% leukemia) harvested before chemotherapy from adults with newly diagnosed acute myelogenous leukemia (AML, 42 patients) and acute lymphocytic leukemia (ALL, 18 patients). Levels of each of these polypeptides varied over a more than 10-fold range between specimens. In AML samples, expression of procaspase-2 correlated with levels of Apaf-1 (Rs = 0.52, P < .02), procaspase-3 (Rs = 0.56,P < .006) and procaspase-8 (Rs = 0.64, P < .002). In ALL samples, expression of procaspases-7 and -9 was highly correlated (Rs = 0.90,P < .003). Levels of these polypeptides did not correlate with prognostic factors or response to induction chemotherapy. In further studies, 16 paired samples (13 AML, 3 ALL), the first harvested before induction therapy and the second harvested at the time of leukemia regrowth, were also examined. There were no systematic alterations in levels of Apaf-1 or procaspases at relapse compared with diagnosis. These results indicate that levels of initiator caspases vary widely among different leukemia specimens but cast doubt on the hypothesis that this variation is a major determinant of drug sensitivity for acute leukemia in the clinical setting.

Evaluation of Apaf-1 and procaspases-2, -3, -7, -8, and -9 as potential prognostic markers in acute leukemia

Recent studies have suggested that variations in levels of caspases, a family of intracellular cysteine proteases, can profoundly affect the ability of cells to undergo apoptosis. In this study, immunoblotting was used to examine levels of apoptotic protease activating factor-1 (Apaf-1) and procaspases-2, -3, -7, -8, and -9 in bone marrow samples (at least 80% leukemia) harvested before chemotherapy from adults with newly diagnosed acute myelogenous leukemia (AML, 42 patients) and acute lymphocytic leukemia (ALL, 18 patients). Levels of each of these polypeptides varied over a more than 10-fold range between specimens. In AML samples, expression of procaspase-2 correlated with levels of Apaf-1 (Rs = 0.52, P < .02), procaspase-3 (Rs = 0.56,P < .006) and procaspase-8 (Rs = 0.64, P < .002). In ALL samples, expression of procaspases-7 and -9 was highly correlated (Rs = 0.90,P < .003). Levels of these polypeptides did not correlate with prognostic factors or response to induction chemotherapy. In further studies, 16 paired samples (13 AML, 3 ALL), the first harvested before induction therapy and the second harvested at the time of leukemia regrowth, were also examined. There were no systematic alterations in levels of Apaf-1 or procaspases at relapse compared with diagnosis. These results indicate that levels of initiator caspases vary widely among different leukemia specimens but cast doubt on the hypothesis that this variation is a major determinant of drug sensitivity for acute leukemia in the clinical setting.

Quantitation of DNA topoisomerase IIalpha and beta in human leukaemia cells by immunoblotting

DNA topoisomerase II (topo II) is an essential nuclear enzyme and is the target for etoposide, which is used in the therapy of childhood acute lymphoblastic leukaemia (ALL). Topo II exists as two isoforms referred to as topo IIalpha and topo IIbeta. To determine whether cellular levels of topo IIalpha and beta are an important factor in determining drug sensitivity/resistance requires accurate, precise measurements of the two isoforms. We have developed a quantitative Western blotting method to accurately measure the absolute amounts of human topo IIalpha and beta, using recombinant human topo IIalpha and beta as standards. This quantitative method has been used to assess the efficiency of several commonly used topo II extraction protocols. The extractable amount of topo IIalpha and beta was found to be salt-dependent. However extraction using the optimal salt concentration was found to be as efficient as extraction with DNase I/Rnase A digestion and SDS solubilisation. Using the optimum extraction procedure and the quantitative immunoblotting method, topo IIalpha and beta was quantified in cell lines, peripheral blood lymphocytes and in lymphoblasts from children with newly diagnosed ALL.

Clinical resistance to topoisomerase-targeted drugs

This review describes topoisomerase (topo)-mediated drug resistance and topo expression in human tissues and cancers. In some in vitro studies a relation has been observed between topo I, IIalpha or IIbeta expression and sensitivity to topo inhibitors. Drug resistance to topo inhibitors may, however, be multifactorial. Several topo inhibitors are substrates for drug membrane transporters. As most topo inhibitors are cell cycle specific, disturbances in cell cycle regulation can also confer resistance, and downstream events following DNA damage induced by topo inhibitors may be involved in regulating cell death or survival. Several studies in patient specimens have shown a relation between topo IIalpha expression and the proliferative state of the tumor, higher topo IIalpha levels being seen in more highly proliferating tumor types. In contrast, topo IIbeta appears to be expressed in both proliferating and quiescent cells. Furthermore, higher topo I levels were observed in some tumors when compared to their normal counterparts. In some studies a reduced topo IIalpha level was seen in samples taken after chemotherapy treatment, as compared with specimens prior to treatment. No unequivocal relation was observed, however, between expression or activity of the topo genes and response to chemotherapy; nonetheless only a few studies have properly addressed this question. This review summarizes the results of the clinical studies performed so far, and analyzes the critical issues in performing studies on patient material.

Topoisomerase II and the response to antileukemic therapy

A number of recent studies have investigated the expression of topoisomerase II in clinical leukemia specimens. Here we outline the rationale for these studies, identify potential pitfalls, summarize recent results, and discuss unanswered questions in this area.

Elevated Expression of the Apoptotic Regulator Mcl-1 at the Time of Leukemic Relapse

Bcl-2, Bcl-xL, and Mcl-1 are three related intracellular polypeptides that have been implicated as negative regulators of apoptosis. In contrast, the partner protein Bax acts as a positive regulator of apoptosis. Based on the observation that all four of these polypeptides are expressed in a variety of acute myelogenous leukemia (AML) and acute lymphocytic leukemia (ALL) cell lines, cellular levels of these polypeptides were examined by immunoblotting in bone marrow samples harvested from 123 adult AML patients and 36 adult ALL patients before initial antileukemic therapy. Levels of Bcl-2, Mcl-1, Bcl-xL, and Bax each varied over a more than 10-fold range in different pretreatment leukemia specimens. When the 54 AML and 23 ALL samples that contained greater than 80% malignant cells were examined in greater detail, it was observed that pretreatment levels of Bcl-2 and Mcl-1 correlated with each other (R = .44,P < .001 for AML and R = .79,P < .0001 for ALL). In addition, a weak negative correlation between Bax expression and age was observed in AML samples (R = −0.35, P < .02) but not ALL samples. There was no relationship between pretreatment levels of these polypeptides and response to initial therapy. However, examination of 19 paired samples (the first harvested before chemotherapy and the second harvested 23 to 290 days later at the time of leukemic recurrence) revealed a greater than or equal to twofold increase in Mcl-1 levels in 10 of 19 pairs (7 of 15 AML and 3 of 4 ALL) at recurrence. In contrast, 2 of 19 pairs contained twofold less Mcl-1 at the time of recurrence. Approximately equal numbers of samples showed twofold increases and decreases in Bcl-2 (5 increases, 3 decreases) and Bcl-xL (1 increase, 4 decreases) at recurrence. Bax levels did not show a twofold decrease in any patient. These results, coupled with recent observations that cells overexpressing Mcl-1 are resistant to a variety of chemotherapeutic agents, raise the possibility that some chemotherapeutic regimens might select for leukemia cells with elevated levels of this particular apoptosis inhibitor.

Elevated Expression of the Apoptotic Regulator Mcl-1 at the Time of Leukemic Relapse

Bcl-2, Bcl-xL, and Mcl-1 are three related intracellular polypeptides that have been implicated as negative regulators of apoptosis. In contrast, the partner protein Bax acts as a positive regulator of apoptosis. Based on the observation that all four of these polypeptides are expressed in a variety of acute myelogenous leukemia (AML) and acute lymphocytic leukemia (ALL) cell lines, cellular levels of these polypeptides were examined by immunoblotting in bone marrow samples harvested from 123 adult AML patients and 36 adult ALL patients before initial antileukemic therapy. Levels of Bcl-2, Mcl-1, Bcl-xL, and Bax each varied over a more than 10-fold range in different pretreatment leukemia specimens. When the 54 AML and 23 ALL samples that contained greater than 80% malignant cells were examined in greater detail, it was observed that pretreatment levels of Bcl-2 and Mcl-1 correlated with each other (R = .44,P < .001 for AML and R = .79,P < .0001 for ALL). In addition, a weak negative correlation between Bax expression and age was observed in AML samples (R = −0.35, P < .02) but not ALL samples. There was no relationship between pretreatment levels of these polypeptides and response to initial therapy. However, examination of 19 paired samples (the first harvested before chemotherapy and the second harvested 23 to 290 days later at the time of leukemic recurrence) revealed a greater than or equal to twofold increase in Mcl-1 levels in 10 of 19 pairs (7 of 15 AML and 3 of 4 ALL) at recurrence. In contrast, 2 of 19 pairs contained twofold less Mcl-1 at the time of recurrence. Approximately equal numbers of samples showed twofold increases and decreases in Bcl-2 (5 increases, 3 decreases) and Bcl-xL (1 increase, 4 decreases) at recurrence. Bax levels did not show a twofold decrease in any patient. These results, coupled with recent observations that cells overexpressing Mcl-1 are resistant to a variety of chemotherapeutic agents, raise the possibility that some chemotherapeutic regimens might select for leukemia cells with elevated levels of this particular apoptosis inhibitor.

Altered Formation of Topotecan-Stabilized Topoisomerase I-DNA Adducts in Human Leukemia Cells

Topotecan (TPT) is a topoisomerase I (topo I) poison that has shown promising antineoplastic activity in solid tumors and acute leukemia. In the present study, a band depletion assay was used to evaluate the ability of TPT to stabilize topo I-DNA adducts in human leukemia cell lines and in clinical leukemia samples ex vivo. This assay showed that 50% of the cellular topo I in HL-60 human myelomonocytic leukemia cells became covalently bound to DNA at an extracellular TPT concentration of 4 μmol/L. In contrast, in 13 clinical specimens of human leukemia harvested before treatment of patients with TPT, the TPT concentration required to stabilize 50% of the cellular topo I in topo I-DNA complexes ranged from 3 to greater than 100 μmol/L (median, 30 μmol/L). Flow microfluorimetry showed that cellular TPT accumulation varied over only a twofold range and failed to provide evidence for transport-mediated resistance in the clinical samples. These observations raise the possibility that formation of topo I-DNA adducts is diminished in many specimens of refractory/relapsed acute leukemia by a mechanism that might alter topo I sensitivity to TPT.