Prostaglandin E2 induces growth inhibition, apoptosis and differentiation in T and B cell-derived acute lymphoblastic leukemia cell lines (CCRF-CEM and Nalm-6)

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Abstract

Despite advances in the treatment of ALL, in most patients long-term survival rates remain unsatisfactory. The objective of the present study was to investigate the anti-cancer effects of Prostaglandin E2 (PGE2) in two different ALL cell lines (CCRF-CEM (T-ALL) and Nalm-6 (B-ALL)). The anti-leukemic effects of PGE2 were also compared with two epigenetic compounds (trichostatin A and 5-aza-2´-deoxycytidine). MTT assay was used to assess growth inhibition by anti-cancer drugs in these cells. All three compounds were shown to induce apoptosis in both ALL cell lines using flow cytometry and Western blotting. To evaluate the differentiation induction by these agents, the expressions of CD19 and CD38 markers on Nalm-6 cell line and CD7 marker on CCRF-CEM cell line were assayed. Surprisingly, the flow cytometric analysis showed a significant increase in CD markers expression in response to PGE2 treatments. We, for the first time, provide evidences that PGE2 has anti-leukemic effects and induces differentiation at micromolar ranges in both T- and B-cell derived ALL cell lines. Since T-ALL cells are insensitive to current chemotherapies, these findings may help the designing of new protocols for T-ALL differentiation therapy in the future.

Introduction

Acute lymphoblastic leukemia (ALL) is a malignant disorder of blood progenitor cells that affects both children and adults. Despite advances in the treatment of ALL, in most patients long-term survival rates remain unsatisfactory. Moreover, the drugs most frequently used to treat this malignancy often have several toxic side effects [1]. For this reason, either new chemotherapeutic agents or refinements of old ones are needed to improve the ALL patients' outcomes. There are an increasing number of biological agents that target several characteristics of cells such as differentiation, proliferation, DNA repair, and apoptosis [1], [2], [3], [4].

Prostaglandins (PGs) are a family of oxygenated metabolites of arachidonic acid. PGs have a wide range of activities depending on the PG type and targeted cells [5]. The presence of PGs has been demonstrated in the processes of carcinogenesis and inflammation. PGs are divided into two groups, conventional PGs such as PGE2, PGF2α and PGD2 and cyclopentenone PGs such as PGJ2, PGA1 and PGA2 [5]. Prostaglandin E2 (PGE2) is a metabolite of cyclooxygenase-2 (COX-2) that has been demonstrated to induce apoptosis in various cell systems including normal and cancerous cells [6], [7], [8], [9].

Epigenetic alterations such as deacetylation of histones are known to be involved in the development of cancer [10]. Histone deacetylase inhibitors (HDACIs) promote several anti-cancer mechanisms, such as apoptosis, cell cycle arrest, differentiation and are currently used in clinical trials [11], [12]. One of the most potent inhibitors of histone deacetylases is trichostatin A (TSA). TSA has been used in many cancerous cells including leukemia to induce cell differentiation [13], cell cycle arrest [13] or apoptosis [14]. TSA has opened the way to assess its effects on leukemic cells and has exhibited variable responses toward different types of leukemic cells [15].

Another well-described component of epigenetic silencing in human cells is cytosine DNA methylation in CpG-rich promoters [16]. In recent years, the relationship between the development of various cancers and hypermethylation of the promoter regions of tumor suppressor genes has been demonstrated. Reversal of this epigenetic process using specific demethylating agents (e.g. 5-aza-2´-deoxycytidine) has become a new targeted approach for cancer therapy [17]. 5-Aza-2´-deoxycytidine (5-Azadc) has been shown to have promising preclinical in vivo anti-tumor activity, and it is currently undergoing clinical evaluations [18], [19], [20], [21].

Although many studies have examined the anti-cancer effects of these compounds (especially trichostatin A and 5-aza-2´-deoxycytidine) in various cancers including leukemias, very few studies have evaluated the anti-leukemic effects of PGE2 in T-cell and B-cell derived acute lymphoblastic leukemia cell lines. In light of the above, the aim of the present study is to evaluate induction of growth inhibition, cell cycle arrest, apoptosis and differentiation in two acute lymphoblastic leukemia cell lines (CCRF-CEM [T-ALL] and Nalm-6 [B-ALL]) exposed to PGE2, TSA and 5-Azadc.

Significantly, we provide evidence that PGE2 induces growth inhibition and apoptosis at micromolar range in both T- and B-cell derived human ALL cell lines. Moreover, we, for the first time, demonstrate that PGE2 can markedly promote differentiation in Nalm-6 and CCRF-CEM cell lines. These may have significant clinical applications especially for the treatment of T-ALL patients due to their insensitivity to current chemotherapies.

Section snippets

Leukemia cell lines

The acute lymphoblastic leukemia (ALL) cell lines (CCRF-CEM, Nalm-6) were purchased from the cell bank (Pasteur Inst. Iran, Tehran). CCRF-CEM and Nalm-6 are derived from T and B lymphocytes, respectively. Human leukemic cell lines were grown in RPMI 1640 culture medium (GIBCO, Grand Island, NY) supplemented with 10% fetal bovine serum (FBS, Gibco, invitrogen, South America), 1% glutamine, 1% antibiotics (penicillin–streptomycin), and 1% nonessential amino acids. Cells were maintained at 37 °C

Effects of anti-cancer compounds on proliferation in ALL cell lines

To examine the effects of anti-cancer drugs on the growth of ALL cell lines, we cultured these cells in the presence of various concentrations of either PGE2 (5–25 μM), TSA (0.1–1 μM), or 5-Azadc (0.05–5 μM). Cell viability was assessed using the MTT assay 24, 48, and 72 h post treatment, and the results were graphed. Six samples were tested for each drug concentration and each experiment was repeated three times prior to MTT analysis. Results are represented in Fig. 1. The results shown in Fig. 1a

Acknowledgment

This work was supported by a grant from Monoclonal Antibody Research Center at Avicenna Research Institute. We thank Mr. Torkabadi for his help in flow cytometry analyses, Mr. Lakpour, Mr. Bayat, Miss. Einy, and Mrs. Ghaempanah for their technical assistants and Dr. Qahremani for his statistical consultancy. We specially thank Dr. Jedi Tehrani for his support throughout this study.

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