Induction of differentiation of human myeloid leukemia cells by 2'-deoxycoformycin in combination with 2'-deoxyadenosine

Deoxy-adenosine-monophosphate (dAMP) di-n-butylester induces apoptosis by increasing the dATP level in HL-60 cells

Deoxy-ATP is a potent inducer of apoptosis. We intended to synthesize a lipophilic dAMP derivative which, according to our working hypothesis penetrates into the cell, is converted to dAMP by intracellular esterases and to dATP by nucleotide kinases. We synthesized dAMP-di-n-butylester (DAB) and tested it. We found that it fulfills the above-described expectations. DAB treatment decreases the viability of HL-60 cells, increases the dATP concentration and induces apoptogenic cytochrome c release from mitochondria with concomitant elevation of caspase-9 activity. Our results indicate that use of dAMP derivatives with masked phosphate may be a feasible approach for pharmacological elevation of intracellular dATP and induction of apoptosis.

Human B-cell lymphoma cell lines are highly sensitive to apoptosis induced by all-trans retinoic acid and interferon-gamma

When cells were incubated in the presence of both interferon-gamma (IFN-gamma) and all-trans retinoic acid (ATRA), the concentration of IFN-gamma required to induce apoptosis of B-cell lymphoma cells was much lower than that required for myeloid or erythroid cell lines. The concentration of IFN-gamma that effectively inhibited the proliferation of BALM-3 cells was 1/40 of that required for BALM-1 cells. STAT-1 phosphorylation, IRF-1 mRNA and protein expression and RAR-beta expression were enhanced to a greater degree in BALM-3 cells treated with IFN-gamma and ATRA than in BALM-1 cells treated with IFN-gamma and ATRA, suggesting that these IFN-gamma related genes were involved in the induction of apoptosis of BALM-3 cells.

Cotylenin A--a plant growth regulator as a differentiation-inducing agent against myeloid leukemia

Acute myeloid leukemia (AML) is characterized by the arrest of differentiation leading to the accumulation of immature cells. This maturation arrest can be reversed by certain agents. Although differentiation therapy for patients with acute promyelocytic leukemia (APL) using all-trans retinoic acid (ATRA) has been established, the clinical response of AML patients other than those with APL to ATRA is limited. We must consider novel therapeutic drugs against other forms of AML for the development of a differentiation therapy for leukemia. Regulators that play an important role in the differentiation and development of plants or invertebrates may also affect the differentiation of human leukemia cells through a common signal transduction system, and might be clinically useful for treating AML. Cotylenin A, a plant growth regulator, is a potent and novel inducer of the monocytic differentiation of human myeloid leukemia cell lines and leukemia cells freshly isolated from AML patients.

A novel therapeutic strategy against monocytic leukemia with deoxyadenosine analogs and adenosine deaminase inhibitors

The adenosine deaminase inhibitor 2'-deoxycoformycin (dCF) significantly inhibits the proliferation of leukemia and lymphoma cells in the presence of either 2'-deoxyadenosine (dAdo) or its analog adenine arabinoside (araA). The concentration of dCF required to induce apoptosis of monocytoid leukemia cells is much lower than that required for myeloid, erythroid, or lymphoma cells. dATP effectively induces caspase-3 activation in cytosol from monocytoid cells, but not in that from non-monocytoid cells, suggesting that dATP-dependent caspase-3 activation is involved in the preferential induction of apoptosis in monocytoid leukemia cells. Athymic nude mice inoculated with human monocytoid leukemia U937 cells show significantly prolonged survival following combined treatment with dCF and araA. The clinical usefulness of the combination of adenosine deaminase inhibitor and dAdo analog is discussed.

Pyridinyl imidazole inhibitor SB203580 activates p44/42 mitogen-activated protein kinase and induces the differentiation of human myeloid leukemia cells

Various inhibitors of protein kinases regulate the growth and differentiation of human leukemic cell lines. The pyridinyl imidazole inhibitor SB203580 has been widely used to elucidate the role of p38 kinase in a wide array of biological systems. In the present investigation, we found that SB203580 effectively induced the granulocytic differentiation of human promyelocytic HL-60 cells. In addition to morphological differentiation, it also induced NBT-reduction, lysozyme activity and growth-inhibition. It also induced the differentiation of human myeloid leukemia HT93 and ML-1 cells, but not of other cell lines, such as NB4, U937, THP-1, K562 and HEL. This differentiation was not associated with the inhibition of p38 kinase activity, but was closely associated with the activation of extracellular signal-regulated kinase. These results demonstrate a new activity for this drug.

Induction of the monocytic differentiation of myeloid leukaemia cells by cotylenin A, a plant growth regulator

Regulators that play an important role in the differentiation and development of plants or invertebrates may also affect the differentiation of human leukaemia cells through a common signal transduction system, and might be clinically useful for treating acute myeloid leukaemia. Cotylenin A has been isolated as a plant growth regulator. We examined the effects of cotylenin A on the differentiation of several myelogenous leukaemia cells, and found that cotylenin A is a potent and novel inducer of the monocytic differentiation of human myeloid leukaemia cells. Cotylenin A induced the functional and morphological differentiation of myeloblastic and promyelocytic leukaemia cells, but did not effectively induce the differentiation of monocytoid leukaemia cells. Cotylenin A-induced differentiation was not affected by several inhibitors of signal transduction, suggesting that this inducer exhibits a unique mode of action.

Sensitization by 5-aza-2'-deoxycytidine of leukaemia cells with MLL abnormalities to induction of differentiation by all-trans retinoic acid and 1alpha,25-dihydroxyvitamin D3

Most chromosomal abnormalities associated with breakage at 11q23 in acute leukaemia involve the MLL gene, and the presence of this breakage strongly predicts a poor clinical outcome. We assessed the possibility of differentiation-inducing therapy for acute leukaemias with chromosomal translocations involving 11q23. Among the cell lines with MLL translocations that we examined, KOCL48 and KOPN-1 cells were induced to differentiate into granulocytes by all-trans retinoic acid (ATRA) or into monocytes by 1alpha,25-dihydroxyvitamin D3 (VD3). These cells expressed p16 mRNA before treatment with 5-aza-2'-deoxycytidine (5-AZA), an inhibitor of DNA methylation. On the other hand, differentiation was not induced in SN-1, KOCL33, KOCL51 or KOCL44 cells by ATRA or VD3, and these cells did not express mRNA of this gene. However, these cells were effectively induced to differentiate by ATRA or VD3 in the presence of 5-AZA, and concomitantly exhibited p16 gene expression, suggesting an association between DNA demethylation and restoration of sensitivity to differentiation-inducing activity of ATRA or VD3 in leukaemia cells with MLL abnormalities. Based on these findings, combined treatment with ATRA or VD3 plus 5-AZA may be clinically useful in therapy for acute leukaemia with MLL abnormalities.

Vidarabine and 2-deoxycoformycin as antileukemic agents against monocytic leukemia

Although 2'-deoxycoformycin (dCF) has been reported in clinical trials to be less effective against myeloid than lymphoid malignancies, it may be useful for treating monocytic leukemia with the aid of 2'-deoxyadenosine (dAd) analogs. In the presence of 10 microM dAd, the concentration of dCF required to inhibit the viability of monocytoid leukemia cells was much lower than that required on normal or non-monocytoid malignant cells in primary culture. Among the dAd analogs, 9-beta-D-arabinofuranosyladenine (AraA) was also effective in combination with dCF. Although dCF alone slightly but significantly prolonged the survival of mice inoculated with U937 monocytic leukemia cells, combined treatment with dCF and AraA markedly prolonged the survival. These results suggest that the combination of dCF and AraA may be useful for the clinical treatment of acute monocytic leukemia.

Myeloid and monocytoid leukemia cells have different sensitivity to differentiation-inducing activity of deoxyadenosine analogs

The differentiation-inducing effect of clinically applicable analogs of deoxyadenosine on myelomonocytic leukemia cells was examined. Monocytoid leukemia cells were more sensitive to the analogs than were erythroid or myeloid leukemia cells based on the inhibition of cell growth and induction of cell differentiation. Monocytoid leukemia cells were highly sensitive to combined treatment with 2'-deoxycoformycin (dCF) and 9-beta-D-arabinofuranosyladenine (Ara A) for inducing cell differentiation. Ara A induced the differentiation of monocytoid leukemia U937 and THP-1 cells at concentrations which were 1/1000-10000 of that at which it induced the differentiation of other cell lines in the presence of dCF. In combination with a low concentration of 1alpha,25-dihydroxyvitamin D3 (VD3), the induction of the monocytic differentiation was greater in monoblastic U937 cells. Adenosine deaminase-resistant analogs such as fludarabine (FLU) and cladribine (CdA) also induced the differentiation of human myelomonocytic leukemia cells, and these analogs synergistically enhanced the differentiation induced by all-trans retinoic acid (ATRA) or VD3. CdA was the most potent analog for inducing the differentiation of myeloid leukemia NB4 and HL-60 cells in the presence or absence of ATRA. These findings indicate that dCF + Ara A and CdA may be effective for the therapy of acute monocytoid and myeloid leukemia, respectively.

Adenosine analogs as possible differentiation-inducing agents against acute myeloid leukemia

Several adenosine analogs induce the functional and morphological differentiation of myelomonocytic leukemia cells. They can be classified into two types; i.e., those that do/do not require phosphorylation to induce the differentiation of leukemia cells. Neplanocin A, a potent S-adenosylhomocysteine hydrolase inhibitor, induces the differentiation of some leukemia cells without phosphorylation. On the other hand, deoxycoformycin (dCF), a potent adenosine deaminase inhibitor, also induces the myelomonocytic differentiation of leukemia cells when it is treated with deoxyadenosine (dAdo). This differentiation is inhibited by 5'-amino-deoxyadenosine, an inhibitor of (deoxy)adenosine kinase, suggesting that kinase-dependent phosphorylation is involved in the differentiation-inducing effect of dCF plus dAdo. Retinoids induce the differentiation of NB4 cells, a cell line derived from human promyelocytic leukemia. When used in combination with all-trans retinoic acid (ATRA), both NPA and dCF plus dAdo greatly enhance the granulocytic differentiation of NB4 cells. This enhancing effect is greatest when the cells are pretreated with NPA and then with ATRA. On the other hand, pre-exposure of NB4 cells to ATRA greatly potentiates the differentiation induced by dCF plus dAdo, while pretreatment with dCF plus dAdo before exposure to ATRA is less effective. The ATRA-induced differentiation of NB4 cells is effectively augmented by clinically applicable concentrations of these analogs. A clinical strategy that combines intermittent treatment with these analogs and a low dose of ATRA may increase the clinical response and decrease the adverse effects of ATRA.

Human Monocytoid Leukemia Cells Are Highly Sensitive to Apoptosis Induced by 2′-Deoxycoformycin and 2′-Deoxyadenosine: Association With dATP-Dependent Activation of Caspase-3

The adenosine deaminase (ADA) inhibitor 2′-deoxycoformycin (dCF) significantly inhibits the proliferation of leukemia and lymphoma cell lines. When cells were incubated in the presence of both dCF and 2′-deoxyadenosine (dAd), the concentration of dCF required to induce apoptosis of monocytoid leukemia cells was much lower than that required for myeloid, erythroid, or lymphoma cell lines. Among the cell lines tested, U937 cells were the most sensitive to this treatment. The concentration of dCF that effectively inhibited the proliferation of U937 cells was 1/1,000 of that required for lymphoma cell lines, on a molar basis. However, the uptake of dCF or dAd in U937 cells was comparable with that in other leukemia and lymphoma cell lines. The intracellular accumulation of dATP in U937 cells was only slightly higher than that in other leukemia cells in dCF-treated culture. Treatment with dCF plus dAd induced apoptosis in U937 cells at low concentrations, and this apoptosis was reduced by treatment with caspase inhibitors. Induction of caspase-3 (CPP32) activity accompanied the apoptosis induced by dCF plus dAd. No activation of CPP32 was observed in cytosol prepared from exponentially growing leukemia and lymphoma cells. However, dATP effectively induced CPP32 activation in cytosol from monocytoid cells, but not in that from nonmonocytoid cells, suggesting that dATP-dependent CPP32 activation is at least partly involved in the preferential induction of apoptosis in monocytoid leukemia cells. The combination of dCF and dAd may be useful for the clinical treatment of acute monocytic leukemia.

© 1998 by The American Society of Hematology.

Human Monocytoid Leukemia Cells Are Highly Sensitive to Apoptosis Induced by 2′-Deoxycoformycin and 2′-Deoxyadenosine: Association With dATP-Dependent Activation of Caspase-3

The adenosine deaminase (ADA) inhibitor 2′-deoxycoformycin (dCF) significantly inhibits the proliferation of leukemia and lymphoma cell lines. When cells were incubated in the presence of both dCF and 2′-deoxyadenosine (dAd), the concentration of dCF required to induce apoptosis of monocytoid leukemia cells was much lower than that required for myeloid, erythroid, or lymphoma cell lines. Among the cell lines tested, U937 cells were the most sensitive to this treatment. The concentration of dCF that effectively inhibited the proliferation of U937 cells was 1/1,000 of that required for lymphoma cell lines, on a molar basis. However, the uptake of dCF or dAd in U937 cells was comparable with that in other leukemia and lymphoma cell lines. The intracellular accumulation of dATP in U937 cells was only slightly higher than that in other leukemia cells in dCF-treated culture. Treatment with dCF plus dAd induced apoptosis in U937 cells at low concentrations, and this apoptosis was reduced by treatment with caspase inhibitors. Induction of caspase-3 (CPP32) activity accompanied the apoptosis induced by dCF plus dAd. No activation of CPP32 was observed in cytosol prepared from exponentially growing leukemia and lymphoma cells. However, dATP effectively induced CPP32 activation in cytosol from monocytoid cells, but not in that from nonmonocytoid cells, suggesting that dATP-dependent CPP32 activation is at least partly involved in the preferential induction of apoptosis in monocytoid leukemia cells. The combination of dCF and dAd may be useful for the clinical treatment of acute monocytic leukemia.

© 1998 by The American Society of Hematology.