Granulocytic differentiation of leukemic cells with t(9;11)(p22;q23) induced by all-trans-retinoic acid

Acute leukemia patients with MLL (mixed linage leukemia) rearrangements tend to respond poorly to conventional therapies. We examined differentiation of human myeloid leukemia cells displaying the MLL-AF9 gene, using several differentiation agents. When MOLM-14 cells were treated with all-trans retinoic acid (ATRA) or 1beta,25-dihydroxyvitamin D3, significant induced differentiation was observed. Trichostatin A (TSA), an inhibitor of histone deacetylase, demonstrated enhance effects with ATRA in regard to growth inhibition and differentiation induction in MOLM-14 cells. Pretreatment with TSA before exposure to ATRA displayed increased effect. Based on these findings, combined treatment with ATRA and TSA may be clinically useful in therapy for acute leukemia displaying MLL-AF9 fusion gene.     

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.     

自噬在急性早幼粒细胞白血病中的研究进展

急性早幼粒细胞白血病（APL）具有特征性的t（15;17）（q22;q21）染色体易位,其表达PML-RARα融合蛋白。全反式维甲酸（ATRA）和三氧化二砷（As2O3）诱导早幼粒白血病细胞分化或凋亡,使APL成为第一种可以治愈的白血病。自噬是维持细胞稳态的重要代谢方式之一,最近有研究显示自噬在ATRA／As2O3诱导治疗中发挥重要作用,而且还可能影响APL对药物诱导凋亡作用的敏感性。因此,今后靶向自噬、调控自噬可能成为APL乃至于其他白血病治疗的一种新手段。对近年来自噬对APL的作用研究进行综述。     

Acute Myelogenous Leukemia without Maturation with a Retinoic Alpha-Receptor Deletion: A Case Report

Acute promyelocytic leukemia (APL) is characterized by a t(15;17) which fuses the 17q retinoic acid alpha-receptor sequence to the 15q PML gene sequence. The resulting fusion product plays a role in the development and maintenance of APL, and is very rarely found in other acute myeloid leukemia (AML) subtypes. Rare complex APL genomic rearrangements have retinoic acid alpha-receptor sequence deletions. Here we report a retinoic acid alpha-receptor sequence deletion in a case of AML without differentiation. To our knowledge, this is the first example of a retinoic acid alpha-receptor sequence deletion in this AML subtype.Key words: Acute myelogenous leukemia without maturation, PML/RAR?, Deletion, t(15;17)(q22;q21), Acute promyelocytic leukemia, AML-M3, AML-M1     

Interaction with RXR is necessary for NPM-RAR-induced myeloid differentiation blockade

The t(5;17)(q35;q21) APL variant results in expression of a fusion protein linking the N-terminus of nucleophosmin (NPM) to the C-terminus of the retinoic acid receptor alpha (RAR). We have previously shown that NPM-RAR is capable of binding to DNA either as a homodimer or heterodimer with RXR. To determine the biological significance of NPM-RAR/RXR interaction, we developed two mutants of NPM-RAR that showed markedly diminished ability to bind RXR. U937 subclones expressing the NPM-RAR mutants showed significantly less inhibition of vitamin D3/TGFbeta-induced differentiation, compared with NPM-RAR. These results support the hypothesis that RXR interaction is necessary for NPM-RAR-mediated myeloid maturation arrest.     

Masked t(15;17) APL with the insertion of PML–RARα fusion gene in 4q21

Most cases of acute promyelocytic leukemia (APL) are characterized by the reciprocal translocation t(15;17); however, several complex variant translocations have also been reported. Here we report complex cytogenetic abnormalities without t(15;17) assayed by the G-banding method in a 62-year-old woman with the typical morphology and clinical features of APL. Based on spectral karyotyping and FISH analyses, we confirm the insertion of a cryptic chromosomal segment containing the PML/RARα fusion gene. The patient achieved complete remission after treatment with all-trans retinoic acid (ATRA) alone. Although the mechanism of this cryptic variant insertion is not known, we conclude that the insertion of PML–RARα fusion into 4q21 seems not to alter the effectiveness of treatment with ATRA.     

Synergistic effects of clinically achievable concentrations of 12-O-tetradecanoylphorbol-13-acetate in combination with all-trans retinoic acid, 1alpha,25-dihydroxyvitamin D3, and sodium butyrate on differentiation in HL-60 cells.

Our recent studies demonstrated that 12-O-tetradecanoylphorbol-13-acetate (TPA) has pharmacological activity for the treatment of acute myelocytic leukemia patients. In the present study, we investigated the potential synergistic effect of all-trans retinoic acid (RA), 1alpha,25-dihydroxyvitamin D3 (VD3), and sodium butyrate (NaB) on TPA-induced differentiation in HL-60 human promyelocytic leukemia cells. The cells were treated once with these agents for 48 h or treated every 24 h for 96 h. Treatment of HL-60 cells once with TPA, RA, VD3, or NaB for 48 h resulted in concentration-dependent growth inhibition and cell differentiation. At clinically achievable concentrations, TPA (0.16 nM) increased the number of adherent cells and RA (0.1-1 microM) increased the number of nitroblue tetrazolium (NBT)-positive cells. The combinations of TPA (0.16 nM) with RA (0.1-1 microM), VD3 (1 nM), or NaB (100 microM) for 48 h synergistically increased differentiation as measured by the formation of adherent cells (P < or = 0.01). Moreover, cells treated with various combinations of low concentrations of TPA, RA, VD3, and NaB every 24 h for 96 h resulted in a further decrease in cell growth and an increase in differentiation. At clinically achievable concentrations, the strongest stimulation of differentiation was achieved in cells treated with a "cocktail" that combined TPA, RA, VD3, and NaB. The synergistic effect of combinations of TPA with RA or NaB at clinically effective concentrations on HL-60 cell differentiation suggests that the combination of these agents may improve the therapeutic efficacy of TPA for the treatment of acute promyelocytic leukemia (APL) patients. A differentiation "cocktail" that combines TPA, RA, VD3, and NaB may provide an even more effective strategy for improving the therapeutic efficacy of TPA and RA.     

Induction of differentiation of acute promyelocytic leukemia cells by a cytidine deaminase-resistant analogue of 1-beta-D-arabinofuranosylcytosine, 1-(2-deoxy-2-methylene-beta-D-erythro-pentofuranosyl)cytidine

Since the establishment of all-trans retinoic acid (ATRA) differentiation therapy, the prognosis of acute promyelocytic leukemia (APL) has improved, and APL has become a curable subtype of acute myelocytic leukemia. Complete remission can be achieved with ATRA alone, but disease-free survival is still too short because of relapse. To overcome this drawback, ATRA has been used in combination with chemotherapeutic agents such as 1-beta-D-arabinofuranosylcytosine (araC) and daunorubicin. However, growth of the APL cell lines NB4 and HT93 is less sensitive to araC than to that of other myeloid leukemia cell lines such as HL-60 and U937. ATRA effectively induced granulocytic differentiation of NB4 and HT93 cells, whereas araC did not, even in a high concentration. A cytidine deaminase-resistant analogue of araC, 1-(2-deoxy-2-methylene-beta-D-erythro-pentofuranosyl)cytidine (DMDC), inhibited the growth of NB4 and HT-93 cells and was also effective on HL-60 and U937 cells. The promyelocytic cell lines were induced to differentiate by DMDC and other cytidine deaminase-resistant analogues. Among them, DMDC was the most potent in inducing differentiation and inhibiting the growth of NB4 cells. The ATRA-induced differentiation of NB4 cells was not augmented by araC, whereas combined treatment with ATRA and DMDC had more than additive effects in inducing the differentiation of NB4 cells. Similar results were observed in a primary culture of leukemia cells that had been freshly isolated from APL patients. These results suggest that DMDC may play a role in the treatment of APL.     

All trans retinoic acid induces apoptosis in acute promyelocytic NB4 cells when combined with isoquinolinediol, a poly(ADP-ribose) polymerase inhibitor

NB4 cells, a model of acute promyelocytic leukemia have been shown to undergo granulocytic differentiation in response to all trans retinoic acid (ATRA), or monocytic differentiation in response to 1alpha,25 dihydroxyvitamin D(3) (1,25 D(3)) and phorbol ester. We have shown previously that the expression of poly(ADP-ribose) polymerase (PARP) is dramatically increased during monocytic differentiation and completely down-regulated during neutrophilic differentiation. Here we show that NB4 cells simultaneously treated with ATRA and isoquinolinediol (Iso-Q), a specific PARP inhibitor, fail to differentiate into neutrophils. Nitroblue tetrazolium (NBT) dye reduction was inhibited by 48% and neutrophil formation was reduced by 75%. NB4 cells treated with ATRA and Iso-Q instead showed features of apoptosis including nuclear condensation, DNA fragmentation, and PARP cleavage yielding a 85 kDa fragment. NB4 cells treated with ATRA in combination with 1,25 D(3), a monocytic differentiation inducer, while continuing to reduce NBT also failed to mature into neutrophils or monocytes and again showed features of apoptosis. Down-regulation of Bcl-2 protein expression was evident in NB4 cells treated with ATRA and ATRA in combination with Iso-Q or 1,25 D(3), but not in cells treated with a classic chemotherapeutic agent, arabinosycytosine, suggesting that Bcl-2 down-regulation is neither necessary, nor specific for apoptosis in this model.