Induction of eosinophilic granules, nonspecific esterase activity and CD14 expression in the human eosinophilic leukemia cell line, EOL-1

Apoptosis- and differentiation-inducing activities of jacaric acid, a conjugated linolenic acid isomer, on human eosinophilic leukemia EoL-1 cells

Conjugated linolenic acids (CLNAs) are a group of naturally occurring positional and geometrical isomers of the C18 polyunsaturated essential fatty acid, linolenic acid (LNA), with three conjugated double bonds (C18:3). Although previous research has demonstrated the growth-inhibitory effects of CLNA on a wide variety of cancer cell lines in vitro, their action mechanisms and therapeutic potential on human myeloid leukemia cells remain poorly understood. In the present study, we found that jacaric acid (8Z,10E,12Z-octadecatrienoic acid), a CLNA isomer which is present in jacaranda seed oil, inhibited the in vitro growth of human eosinophilic leukemia EoL-1 cells in a time- and concentration-dependent manner. Mechanistic studies showed that jacaric acid triggered cell cycle arrest of EoL-1 cells at the G0/G1 phase and induced apoptosis of the EoL-1 cells, as measured by the Cell Death Detection ELISAPLUS kit, Annexin V assay and JC-1 dye staining. Notably, the jacaric acid-treated EoL-1 cells also underwent differentiation as revealed by morphological and phenotypic analysis. Collectively, our results demonstrated the capability of jacaric acid to inhibit the growth of EoL-1 cells in vitro through triggering cell cycle arrest and by inducing apoptosis and differentiation of the leukemia cells. Therefore, jacaric acid might be developed as a potential candidate for the treatment of certain forms of myeloid leukemia with minimal toxicity and few side effects.

Apoptosis Induction by Retinoids in Eosinophilic Leukemia Cells: Implication of Retinoic Acid Receptor-α Signaling in All-Trans-Retinoic Acid Hypersensitivity

Hypereosinophilic syndrome (HES) has recently been recognized as a clonal leukemic lesion, which is due to a specific oncogenic event that generates hyperactive platelet-derived growth factor receptor-alpha-derived tyrosine kinase fusion proteins. In the present work, the effect of retinoids on the leukemic hypereosinophilia-derived EoL-1 cell line and on primary HES-derived cells has been investigated. We show that all-trans-retinoic acid (ATRA) inhibits eosinophil colony formation of HES-derived bone marrow cells and is a powerful inducer of apoptosis of the EoL-1 cell line. Apoptosis was shown in the nanomolar concentration range by phosphatidylserine externalization, proapoptotic shift of the Bcl-2/Bak ratio, drop in mitochondrial membrane potential, activation of caspases, and cellular morphology. Unlike in other ATRA-sensitive myeloid leukemia models, apoptosis was rapid and was not preceded by terminal cell differentiation. Use of isoform-selective synthetic retinoids indicated that retinoic acid receptor-alpha-dependent signaling is sufficient to induce apoptosis of EoL-1 cells. Our work shows that the scope of ATRA-induced apoptosis of malignancies may be wider within the myeloid lineage than thought previously, that the EoL-1 cell line constitutes a new and unique model for the study of ATRA-induced cell death, and that ATRA may have potential for the management of clonal HES.

Anti-proliferative and differentiation-inducing activities of the green tea catechin epigallocatechin-3-gallate (EGCG) on the human eosinophilic leukemia EoL-1 cell line

A novel approach for the treatment of leukemia is the differentiation therapy in which immature leukemia cells are induced to attain a mature phenotype when exposed to differentiation inducers, either alone or in combinations with other chemotherapeutic or chemopreventive drugs. Over the past decade, numerous studies indicated that green tea catechins (GTC) could suppress the growth and induce apoptosis on a number of human cancer cell lines. However, the differentiation-inducing activity of GTC on human tumors remains poorly understood. In the present study, the effect of the major GTC epigallocatechin-3-gallate (EGCG) on the proliferation and differentiation of a human eosinophilc leukemic cell line, EoL-1, was examined. Our results showed that EGCG suppressed the proliferation of the EoL-1 cells in a dose-dependent manner, with an estimated IC(50) value of 31.5 microM. On the other hand, EGCG at a concentration of 40 microM could trigger the EoL-1 cells to undergo morphological differentiation into mature eosinophil-like cells. Using RT-PCR and flow cytometry, it was found that EGCG upregulated the gene and protein expression of two eosinophil-specific granule proteins, the major basic protein (MBP) and eosinophil peroxidase (EPO), in EoL-1 cells. Taken together, our findings suggest that EGCG can exhibit anti-leukemic activity on a human eosinophilic cell line EoL-1 by suppressing the proliferation and by inducing the differentiation of the leukemia cells.