All-trans retinoic acid and induction of apoptosis in acute promyelocytic leukemia cells

All‑trans‑retinoic acid induces RARB‑dependent apoptosis via ROS induction and enhances cisplatin sensitivity by NRF2 downregulation in cholangiocarcinoma cells

All-trans-retinoic acid (ATRA) has been clinically used to treat acute promyelocytic leukemia and is being studied to treat other types of cancer; however, the therapeutic role and mechanism of ATRA against cholangiocarcinoma (CCA) remain unclear. The present study investigated the cytotoxic effect and underlying mechanisms of ATRA on CCA cell lines. Cell viability was evaluated by sulforhodamine B assay. Intracellular reactive oxygen species (ROS) levels were assessed by dihydroethidium assay. Apoptosis analysis was performed by flow cytometry. The pathways of apoptotic cell death induction were examined using enzymatic caspase activity assay. Proteins associated with apoptosis were evaluated by western blotting. The effects on gene expression were analyzed by reverse transcription-quantitative PCR analysis. ATRA induced a concentration- and time-dependent toxicity in CCA cells. Furthermore, when the cytotoxicity of ATRA against retinoic acid receptor (RAR)-deficient cells was assessed, it was revealed that ATRA cytotoxicity was RARB-dependent. Following ATRA treatment, there was a significant accumulation of cellular ROS and ATRA-induced ROS generation led to an increase in the expression levels of apoptosis-inducing proteins and intrinsic apoptosis. Pre-treatment with ROS scavengers could diminish the apoptotic effect of ATRA, suggesting that ROS and mitochondria may have an essential role in the induction of apoptosis. Furthermore, following ATRA treatment, an increase in cellular ROS content was associated with suppressing nuclear factor erythroid 2-related factor 2 (NFE2L2 or NRF2) and NRF2-downstream active genes. ATRA also suppressed cisplatin-induced NRF2 expression, suggesting that the enhancement of cisplatin cytotoxicity by ATRA may be associated with the downregulation of NRF2 signaling. In conclusion, the results of the present study demonstrated that ATRA could be repurposed as an alternative drug for CCA therapy.

Biological features of primary APL blasts: their relevance to the understanding of granulopoiesis, leukemogenesis and patient management

In recent years, discovery of the in vitro and in vivo differentiation of APL blasts by all-trans retinoic acid (ATRA) has modified the therapeutic approach of APL and lead to important advances in understanding the biology of APL. Since it became apparent that differentiation therapy of APL with ATRA was indeed a true model of targetted therapy, evidencing the molecular targets of retinoic acid efficacy became crucial. These molecular targets are closely related to the biological features of APL cells, some of which are well-known and have contributed to the morphological and cytogenetic definition of the leukemia, others have just been defined or re-discovered in the light of a better understanding of molecular controls of cell growth and differentiation. The aims of characterizing the biological features of APL cells should allow a better management of APL therapy and the identification of potential markers for differentiation therapies in other leukemias or solid tumors.

Cycloprodigiosin hydrochloride, H(+)/CL(-) symporter, induces apoptosis and differentiation in HL-60 cells

Cycloprodigiosin hydrochloride (cPrG * HCl), a novel H(+)/Cl(-) symporter, induces acidification of the cytosol and leads to apoptosis in rat and human liver cancer cells. In the present study, the effect of cPrG * HCl on a promyelocytic leukemia cell line (HL-60) was examined. cPrG * HCl lowered intracellular pH and induced apoptosis through up-regulation of Fas ligand, activation of stress-activated protein kinase (SAPK/JNK) and caspase. Apoptosis induced by cPrG * HCl was strongly suppressed when a cell-permeable weak base, imidazole, was present, indicating that cytosol acidification introduced by cPrG * HCl triggered caspase activation, leading to apoptosis. Concomitantly, cell differentiation into monocyte was also induced by cPrG * HCl both morphologically and functionally. However, the cPrG * HCl-induced differentiation was not suppressed by addition of imidazole, indicating that the differentiation process is unrelated to cytosol acidification. Further, the differentiation induced by cPrG * HCl was blocked by tyrosine kinase inhibitors (lavendustin A and HMA) but unaffected by the inhibitors of A-kinase (H-89) or C-kinase (H-7). Taken together, these findings suggest that cPrG * HCl, through apoptosis and differentiation induction, may be useful in leukemia treatment.

Detection of apoptosis in acute promyelocytic leukemia cells in vivo during differentiation-induction with all-trans retinoic acid in combination with chemotherapy

In two patients with acute promyelocytic leukemia (APL) treated with all-trans retinoic acid (ATRA) in combination with chemotherapy, we demonstrated that cells with apoptotic morphology were recognized in a small fraction of whole blood cells (0.2-0.4%) at the regression phase of leukocytosis with mostly maturing aberrant granulocytes of APL clone origin. Moreover, in a light-density cell fraction ( < 1.077) of peripheral blood or marrow cells obtained from three patients, DNA fragmentation was detected by agarose gel electrophoresis temporarily. These findings may suggest that, during the treatment with ATRA, a small fraction of APL cells maturing toward the stage of terminal differentiation underwent apoptosis in vivo, which might be enriched by the combination of chemotherapy to ATRA administration.

Effects of methylprednisolone on human myeloid leukemic cells in vitro

We have demonstrated previously that high-dose methylprednisolone treatment induces differentiation and apoptosis of leukemic cells in patients with different morphological subtypes of acute myeloblastic leukemia (AML) in vivo. In the present study, we investigated the in vitro effects of high (10(-3) M) and low (10(-6) M) concentrations of methylprednisolone (MP) on freshly isolated bone marrow leukemic cells from nine newly diagnosed patients with AML by light and electron microscopy (EM) and agarose gel electrophoresis. A marked increase in MP-induced apoptosis of leukemic cells, with a maximum effect at 24 hr of exposure to both low and high concentrations of MP (10(-6) M and 10(-3) M), was demonstrated by light microscopy in cultures of four (three with AML-M1 and one with AML-M7) of the nine patients. In three cases, the increase in the number of apoptotic cells induced by high-concentration MP was approximately twice that observed when the lower concentration was used. A few apoptotic cells were detected in the cultures from the other five patients. However, a typical DNA ladder pattern of apoptosis was observed on gel electrophoresis of MP-treated leukemic cells from one patient (AML-M1) after 2 hr of incubation with both high- and low-MP concentrations. In two patients, a nonspecific DNA smear was observed only when high-concentration MP was used. The increase in differentiated leukemic cells induced by MP was also dose dependent, and was observed in cultures from all but one patient. Morphological features of apoptosis and differentiation were also confirmed by EM studies. The results of the present study, together with our previous clinical experience, suggest that MP, especially at high doses, could have a significant role in the treatment of some AML patients by inducing apoptosis and differentiation of leukemic cells.

The PML/RARalpha fusion protein inhibits tumor necrosis factor-alpha-induced apoptosis in U937 cells and acute promyelocytic leukemia blasts

We investigated the effect of the acute promyelocytic leukemia (APL) specific PML/RARalpha fusion protein on the sensitivity to TNF-alpha-mediated apoptosis. The U937 leukemia cell line was transduced with PML/RARalpha cDNA. PML/RARalpha expression caused a markedly reduced sensitivity to TNF-alpha, even if apoptosis was triggered by agonistic antibodies to TNF-alpha receptors I and II (TNF-alphaRI, II). PML/RARalpha induced a 10-20-fold decrease of the TNF-alpha-binding capacity via downmodulation of both TNF-alphaRI and TNF-alphaRII: this may mediate at least in part the reduced sensitivity to TNF-alpha. Furthermore, the fusion protein did not modify Fas expression (CD95) or sensitivity to Fas-mediated apoptosis. The pathophysiological significance of these findings is supported by two series of observations. (a) Fresh APL blasts exhibit no TNF-alpha binding and are resistant to TNF-alpha-mediated apoptosis. Conversely, normal myeloblasts-promyelocytes show marked TNF-alphaR expression and are moderately sensitive to TNF-alpha-mediated cytotoxicity. Similarly, blasts from other types of acute myeloid leukemia (AML M1, M2, and M4 FAB types) show an elevated TNF-alpha binding. (b) The NB4 APL cell line, which is PML/RARalpha+, shows low TNF-alphaR expression capacity and is resistant to TNF-alpha-triggered apoptosis; conversely a PML/RARalpha- NB4 subclone (NB4.306) exhibits detectable TNF-alpha-binding capacity and is sensitive to TNF-alpha-mediated cytotoxicity. These studies indicate that the PML/RARalpha fusion protein protects against TNF-alpha-induced apoptosis, at least in part via downmodulation of TNF-alphaRI/II: this phenomenon may play a significant role in APL, which is characterized by prolonged survival of leukemic blasts.

Reduction of heat-shock protein-70 after prolonged treatment with retinoids: biological and clinical implications

Heat shock proteins (HSPs) are a group of highly conserved polypeptides involved in cellular response to heat or other physical or chemical stresses. It has been recently reported that HSPs could play a role in cellular differentiation. In this study we have evaluated, by a cytofluorimetric method, the presence of HSP-70 in HL-60 cells during treatment with all-trans retinoic acid (ATRA), 9-cis retinoic acid (9-cis RA), and 13-cis retinoic acid (13-cis RA). After 1 and 3 days of incubation at 10(-7) M, HSP-70 did not show any variation compared to control; prolonging the exposure, together with the appearance of cellular differentiation along the granulocytic pathway and apoptosis, a progressive decrease of HSP-70 was observed that, after 8 days of treatment, was reduced by 40% with ATRA and by 28% with 9-cis RA compared to untreated samples, while only minimal changes were evident by incubating the cells with 13-cis RA. Reduction of HSP-70 was not associated with decreased protein synthesis, as demonstrated by [3H] leucine incorporation. Double labeling with propidium iodide showed a decrease in HSP-70 in all the phases of the cell cycle concomitant with a reduced percentage of cycling cells in ATRA-treated samples. Dot blot and Northern blot analysis demonstrated no change in HSP-70 mRNA after retinoid treatment, thus suggesting a post-transcriptional regulation of the phenomenon. This reduced production of HSP-70 caused by ATRA and by 9-cis RA, though to a lesser extent, could render the cells more sensitive to cytotoxic agents and could provide the rationale for the efficacy of ATRA + chemotherapy combinations.

Biological and clinical significance of in vitro prednisolone resistance in adult acute lymphoblastic leukaemia

It has been reported that in vitro prednisolone (PDN) resistance provides a prognostic value in childhood acute lymphoblastic leukaemia (ALL). This study aimed at investigating the biological and clinical significance of in vitro PDN resistance in adult ALL. Blast cells from 30 patients were exposed to PDN (0.1 microM-35 microM) and cytotoxicity was determined by the soluble tetrazolium formazan 2,3-bis (2-methoxy-4-nitro-5-sulphophenyl)-5-[(phenylamino) carbamyl]-2H-tetrazolium hydroxyde (XTT) colorimetric assay. The IC50 (defined as the drug concentration that results in 50% growth inhibition) varied greatly among the samples, from 0.3 microM to > 35 microM; 15 microM was subsequently chosen as IC50-cut-off point between in vitro resistant and sensitive cases. PDN-induced cytotoxicity was significantly related to apoptosis, as demonstrated by regression analysis; in sensitive cases, however, the percentage of apoptotic cells after in vitro PDN treatment was significantly increased compared with control (p = 0.002). Immunofluorescence evaluation of intracellular BCL-2 protein showed an equal percentage of positive cells in the two groups, but in resistant cells a higher mean fluorescence intensity (p = 0.04) was demonstrated. In vitro sensitive and resistant patients did not display differences in clinical characteristics, in cytological, karyotypic and immunophenotypic features and in the outcome of induction therapy. Disease-free survival (DFS), however, was significantly better in sensitive patients (p = 0.02).

Apoptosis in acute myeloblastic leukemia: follow-up study on trephine biopsies of the bone marrow

A clinicopathological study on 87 adult patients presenting with "de novo" acute myeloblastic leukemia (AML) was performed to assess the rate of apoptosis before and during chemotherapy and its predictive impact on clinical course. Evaluation included trephine biopsies of the bone marrow and the situ end-labeling technic (ISEL) for the identification of programmed cell death in large and intact hemopoietic tissue areas. In comparison with a control group of 21 patients without any hematological disorder, morphometric analysis revealed no significantly different numbers of apoptotic cells in AML at the onset of disease and following sequential examinations at intervals ranging between 10 to 19 months. Moreover, the incidence of programmed cell death was not associated with the subgroups of the FAB classification and statistics failed to show a relationship with survival or remission status. In conclusion, these findings are in keeping with the assumption that apoptosis occurs with the same frequency in recovering normal hemopoiesis in complete or partial remission, in manifest AML and relapse. In the latter conditions, enhancement of proliferation is not associated with an increase in the apoptotic index.

Tretinoin. A review of its pharmacodynamic and pharmacokinetic properties and use in the management of acute promyelocytic leukaemia

Tretinoin (all-trans retinoic acid), a vitamin A derivative, induces cellular differentiation in several haematological precursor cell lines and cells from patients with acute promyelocytic leukaemia. Drug treatment with tretinoin is associated with morphological and functional maturation of leukaemic promyelocytes and a progressive reduction in the occurrence of the characteristic t(15;17) chromosomal translocation. Recent therapeutic trials indicate that tretinoin induces remission in 64 to 100% of patients with acute promyelocytic leukaemia. In newly diagnosed patients, remission induction treatment with tretinoin followed by intensive chemotherapy resulted in a significant reduction in relapse rate and prolongation of event-free and overall survival compared with chemotherapy alone in 1 comparative trial. Tretinoin alone does not totally eradicate the leukaemic clone and consolidation chemotherapy is recommended as follow-up. The use of reverse transcription polymerase chain reaction (RT-PCR) provides a sensitive and specific technique to assist in prediction and monitoring of a patient's response to treatment and to help detect the presence of residual or recurrent disease. The use of tretinoin is potentially limited by the rapid and almost universal development of drug resistance and occurrence of the often severe retinoic acid syndrome. Useful strategies have been described to manage these effects but current and future efforts must be directed at elucidating the mechanisms involved and determining the optimum therapeutic management. In summary, results to date indicate that the combination of tretinoin and intensive chemotherapy is more effective than chemotherapy alone and appears to improve the prognosis of newly diagnosed patients with acute promyelocytic leukaemia. Further information on the relative efficacy of various induction and post-remission strategies in subsets of patients will help determine optimum use of this promising agent in the management of acute promyelocytic leukaemia.