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3-Hydrogenkwadaphnine, a novel diterpene ester from Dendrostellera lessertii, its role in differentiation and apoptosis of KG1 cells.

Abstract

3-Hydrogenkwadaphnin (3-HK) (Fig. 1) is a daphnane-type diterpene ester isolated from the leaves of Dendrostellera lessertii (Thymelaeaceae) with differentiation and apoptotic potency among several leukemic cells without any measurable adverse effects on normal cells [Moosavi, M.A., Yazdanparast, R., Sanati, M.H., Nejad, A.S., 2005a. 3-Hydrogenkwadaphnin targets inosine 5'-monophosphate dehydrogenase and triggers post-Gl arrest apoptosis in human leukemia cell lines. Int. J. Biochem. Cell Biol. 37, 2366-2379]. In this study, we evaluated differentiating and apoptotic efficiency of a second new anti-proliferating agent from the same plant relative to 3-HK using acute myeloid leukemia (AML) KG1 cell line. 3-HK at 5-30 nM inhibited proliferation of KG1 cells after 24-96 h of treatment. NBT reducing assay and expression of cell surface markers (CD11b and CD14) confirmed that the inhibition of proliferation is associated with differentiation toward macrophage-like morphology. Regarding the relatively weaker potency of 3-HK in the induction of differentiation compared to that of the crude extract, we looked for additional compound(s) with similar properties in the crude extract. This effort led to isolation of the second compound from the leaves' extract with higher differentiating potency. The new compound inhibited proliferation of KG1 cells by almost 48 [+ or -] 3.1% after 72 h of treatment with a single dose of 1.5 [micro]g/ml. The treated cells differentiated along the monocyte/macrophage lineage based on the morphological features apparent after Wright-Giemsa staining, phagocytic activity and expression of cell surface markers as analyzed by flow cytometry. On the other hand, the results indicated that exposure of KG1 cells to either 3-HK or the new compound for 3-4 days induced apoptosis as assayed qualitatively by acridine orange/ethidium bromide (Ao/EtBr) double staining, agarose gel electrophoresis and quantitatively by Annexin-V technique and sub-Gl DNA staining using flow cytometry. Based on the present data, these two active constituents of D. lessertii have the novelty of being further evaluated for pharmaceutical applications.

[FIGURE 1 OMITTED]

[C] 2008 Elsevier GmbH. All rights reserved.

Keywords: Dendrostellera lessertii; 3-Hydrogenkwadaphnine; Differentiation; KG1 cells; Leukemia

Introduction

Leukemia is a disease characterized by propagation of hematopoietic cells in an uncontrollable fashion and lack of differentiation into functional mature cells. Human acute myelogenous leukemia (AML) often arises from neoplastic transformation of pluripotent stem cells, resulting in cell immaturation at the recognizable levels of myeloblast or promyelocyte stages. The leukemic patients often die of infection because the blast cells cannot mature to functional responsive cells (Lowenberg et al., 1999). At present, differentiation induction as an alternative therapeutic approach is used in treatments of AML-M3/APL patients. For instance, treatment of APL patients with all-trans-retinoic acid (ATRA) has resulted in myeloid differentiation of leukemic blasts with improved long-term survivals (Olsson et al., 1996; Bruserud and Gjertsen, 2000). Regarding these progresses, differentiation therapy is also considered for treatment of other AML patients.

According to a wildly accepted French-American-British classification, KG1 cells belong to AML-M1 subtype, with prominent chromosomal abnormities and minimal extent of differentiation (Bennett et al., 1976; Koeffler and Golde, 1980). These leukemic cells are resistant to inducers of myeloid differentiation such as ATRA; however, after exposure to other agents such as TPA (Lotem and Sachs, 1979; Koeffler et al., 1981) and teleocidin (Fujiki et al., 1981) they differentiate to macrophage-like cells. Despite induction of differentiation, TPA and teleocidin do not have potential therapeutic values for treatment of leukemia due to their tumor-promoting activities. Thus, in recent years significant attention has been paid to discovery of suitable agents with differentiation capability and devoid of general toxicities for AML therapy. In that respect, herbal therapies have found worldwide attention as alternative therapeutic approaches. At present, almost 60% of anti-tumor agents that are clinically in use or in the late stages of development are from natural sources (Shu, 1998). Among plant-derived agents, the daphnane-type diterpene esters such as genkwadaphnin (Hall et al., 1982), gnidilatimonoein (Yazdanparast and Sadeghi, 2004), genididin, geniditrin and gnidilatin (Stanoeva et al., 2005) possess significant antileukemic activities with major metabolic effects on DNA and protein syntheses. The inhibition of inosin-5'-monopho-sphate dehydrogenase (IMPDH) activities, the rate-limiting enzyme of de novo guanine nucleotide biosyn-thetic pathway, by diterpene esters has been proposed to be the main route of action of most of these agents (Stanoeva et al., 2005; Moosavi et al., 2005a). Alterations in the activity of this enzyme have been implicated in the regulation of cellular growth, transformation, differentiation and apoptosis (Jayaram et al., 1999). In fact, several IMPDH inhibitors such as mycophenolic acid and tiazofurin have been used against many leukemia cells (Inai et al., 2000; Collart and Huberman, 1990).

It has previously been shown that 3-HK inhibits the proliferation of various cancer cells to different degrees through IMPDH activity (Moosavi et al., 2005a, b). In addition, it has been established that the anti-prolif-erative activity of 3-HK in HL-60 cells, similar to plant crude extract, was accompanied with induction of differentiation and apoptosis among the treated cells (Yazdanparast et al., 2005). Regarding the fact that these activities of 3-HK were relatively weaker on onset and potency compared to the same effects observed using the crude extract, we re-investigated the crude extract for additional active compounds with differentiation and apoptotic capabilities comparable to or stronger than 3-HK.

Materials and methods

Materials

The cell culture medium (RPMI-1640), fetal bovine serum (FBS) and penicillin-streptomycin were purchased from Gibco BRL (Life technology, Paisley, Scotland). Cell line was obtained from Pasteur Institute of Iran (Tehran, Iran). 12-O-tetradecanoyl porbol-13-acetate (TPA), propidium iodide (PI), RNase (DNase free), nitro blue tetrazolium (NBT) and sodium azide were purchased from Sigma Chem. Co. (Germany). Ethidium bromide (EtBr) and acridine orange (AO) were obtained from Pharmacia LKB Biotechnology AB Uppsala (Sweden). Annexin-V and anti CD14 and CDllb antibodies were purchased from IQ Products (Groningen, Netherlands).

Plant extraction and purification of 3-HK and the new compound

The powdered plant material (300 g) was extracted three times with methanol-water (1:1, v/v). The accumulated alcoholic extract was concentrated under reduced pressure, and the volume was adjusted to 300 ml. The crude extract was then subjected to [CHCl.sub.3] extraction for five times. The accumulated chloroform solution was concentrated under reduced pressure to a final volume of 1 ml. The 1 ml residue was fractionated on a silica gel column (1.4 x 50 cm), using diethyl ether as the eluting solvent, into six fractions. The active compounds were purified from the sixth fraction using the TLC technique. The developing system of TLC was a mixture of chloroform and diethyl ether (1:1, v/v). The relative mobilities of the 3-HK (Fig. 1) and the second compound were around 0.7 and 0.3, respectively. The characterization of 3-HK has been achieved as previously reported (Sadeghi and Yazdanparast, 2005). The purity of the second isolated compound was further confirmed using the HPLC technique. The structure elucidation of the second compound is in progress using various spectroscopic techniques.

Cell culture

The KG1 cell line was cultured in RPMI-1640 medium supplemented with FBS (20%, v/v), streptomycin (100 [micro]g/ml) and penicillin (100 U/ml). The cells were incubated under 5% [CO.sub.2] humidified atmosphere at 37 [degrees]C.

Cell viability assay

The cells (1 x [10.sup.5] cells/well) were seeded in triplicate into cell culture plates for 24 h prior to treatment. After treatments with the drugs, at different doses for various lengths of times, cell numbers were established using a hemocytometer and the cell viability was determined by the trypan blue exclusion test. The cells attached to the culture plates were trypsinized with 1 x trypsin-EDTA solution. The numbers of attached and unattached cells were determined using a hemocytometer.

NBT reducing assay

The cells were cultured and treated with each of the drugs for various time intervals as explained in the cell viability assay. At the indicated time intervals, the cells were harvested, and the NBT reducing activity was determined by the method of Sakashita et al. (1991) with slight modification. Briefly, the cells were harvested by centrifugation and suspended in 100 [micro]l of NBT solution (4 mg/ml). After addition of 100 [micro]l of TPA solution (2 [micro]g/ml), the cell suspension was incubated at 37 [degrees]C for 30 min. The differentiated cells were identified by their intracellular blue formazan deposits. To determine the percent of differentiated cells, a minimum of 200 cells of each sample were counted using a light microscope.

Morphological evaluation of the differentiated cells

The morphology of untreated and the drug-treated cells was studied using a phase contrast microscope (Jena, Zeiss, Germany). Monocytic differentiation of the treated cells was also followed by using a light microscope following the Wright-Giemsa staining of the cells.

Latex particle phagocytosis assay

Treated and untreated control cells were assayed for their ability to phagocytize protein-coated latex particles (Sakashita et al., 1991). A protein-coated latex particle suspension, commercially marketed as a pregnancy test (Gravindex-Ortho, Omega House, UK), was used for this assay. The particle suspension was diluted 1:10 with PBS and 0.1 ml of the diluted suspension was mixed with the drug-treated and untreated KG1 cells (5 x [10.sup.4] cells) in 0.1 ml of RPMI-1640 medium supplemented with 20% FBS. The mixture was incubated for 60 min in a [CO.sub.2] incubator. Each cell sample was then washed three times with cold PBS. Each collected cell sample was resuspended in PBS. A minimum of 200 cells were counted in triplicate and those with a minimum of 10 ingested particles were considered positive.

Flow cytometry analyses of cell surface markers

The expressions of CD14 and CD11b were evaluated by flow cytometry (Partec PAS, Munich, Germany). The cells were harvested at indicated times, washed twice with PBS, then incubated for 30 min at room temperature with 10 [micro]l of mouse anti-human PE-conjugated CD14 mAb and mouse human FITC-conjugated CD11b mAb. Two parameter analyses were performed using flow cytometry.

Flow cytometry analyses of apoptotic cells with FITC-Annexin V and propidium iodide (PI) double staining

After collecting and washing twice with PBS, the treated and/or untreated cells were resuspended in the binding buffer (100 [micro]l of calcium buffer containing 10 mM HEPES/NaOH, pH 7.4, 140 mM NaCl, 2.5 mM [CaCl.sub.2]). FITC-Annexin-V (10 [micro]l) was added to the cells followed by addition of 10 [micro]l PI (50 [micro]g/ml of PBS). The samples were then incubated for 10 min in the dark at 4 [degrees]C and then subjected to flow cytometry evaluation.

Simultaneous detection of CD14 and Annexin-V binding

The cells (1 x [10.sup.5] cells/well) were treated with each drug for different time periods. After harvesting, the cells were suspended in Annexin-V binding buffer (containing 10 mM HEPES/NaOH, pH 7.4, 140 mM NaCl, 2.5 mM [CaCl.sub.2]), doubled stained with 5 [micro]l FITC-labeled Annexin-V and 10 [micro]l mouse anti-human PE-conjugated CD14 mAb, then incubated for 30 min at room temperature. After staining, the cells were washed with cold PBS and analyzed by flow cytometry.

Sub-Gl analysis by flow cytometry

DNA content was determined by propidium iodide (PI) staining using a published procedure with slight modification (Moosavi et al., 2005a). The cells (1 x [10.sup.6] cells/well) were seeded into the culture plates 24 h prior to treatments. After treatments with drug, cells were harvested and washed twice with PBS, fixed in 70% ethanol for at least 2h at 4[degrees]C. The cells were then stained with 20 [micro]g/ml propidium iodide containing 20 [micro]g/ml RNase (DNase free) for 30 min at 37 [degrees]C. The stained cells were analyzed by flow cytometry.

DNA fragmentation assay

DNA fragmentation was measured after extraction of the genomic DNA from a constant number of cells. After treatment of KG1 cells for 72 h with a single dose (1 [micro]g/ml) of the drug, the cells were collected and washed twice with cold PBS, resuspended in 100 [micro]l lytic solution (25 mM EDTA, 10mM Tris-HCl, pH 8, 1.0% SDS, 100 mM NaCl) and incubated with proteinase K (0.2 mg/ml) at 50 [degrees]C overnight. DNA was extracted with phenol/chloroform/isoamyl alcohol (25:24:1), washed with ethanol and resuspend in TE buffer. Aliquot of each sample was then subjected to electrophoresis in a 2% agarose gel containing ethidium bromide (0.5 [micro]g/ml) in both the gel and the running buffer (1 x TBE). The gel was run at 5 V/cm for 2 h.

Statistical analyses

Data are expressed as mean [+ or -] SD of three independent experiments and statistically analyzed using Student's t-test. Values of p <0.05 were considered significant.

Result

Morphological studies showed that a portion of KG1 cells adhered to the culture plates after treatment with 3-HK. A higher portion of the cells, however, failed to adhere and remained in suspension. The nonadherent cells had the morphology of dead cells as examined by a phase contrast microscope (Fig. 2A). In contrast, the majority of cells treated with the second isolated compound developed pseudopodia and attached to the culture plates (Fig. 2B). Further, we studied time- and dose-dependent effects of 3-HK and the new compound on proliferation of KG1 cells (Fig. 3A-D). It was found that 3-HK at 5-30 nM and the new compound at 0.5-2.5 [micro]g/ml concentrations inhibited KG1 proliferation by 17-79% and 30-80%, respectively, after 3 days of treatment (Fig. 3A and C). These effects were also time dependent. For example, after 24-96 h exposure to 15 nM 3-HK, the growth was inhibited almost by 22-68%, while proliferation was inhibited around 18-60% among the cells treated with 1.5 [micro]g/ml of the new compound (Fig. 3B and D).

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Morphological changes induced by 3-HK and the new compound are very similar to effects of a structurally related diterpene ester, TPA on inducing monocyte/ macrophage differentiation of leukemia cells (Koeffler et al., 1981; Hass et al., 1989). The differentiation-inducing capability of 3-HK and the new compound in KG1 cells were evaluated based on NBT reducing activities, Wright-Giemsa staining, phagocytic activity and the cell surface markers mainly CDllb and CD14. As shown in Fig. 4A and B, the NBT reducing activity among the 3-HK-treated cells increased in a time- and dose-dependent manner. However, this property was not observed at higher (more than 30 nM) drug concentrations, possibly due to drug toxicity at high drug concentrations. On the other hand, NBT reducing activity was also increased among the cells treated with the second compound in a time- and dose-dependent manner up to a dose of 2.5 [micro] g/ml (Fig. 4C and D). In addition, some morphological features of the monocytes such as cytoplasmic protrusion and increased cytoplasm/nuclei ratio were detectable among the KG1 cells treated with the new compound along with uptake of latex particles, which is commonly considered as a criterion of proper function of mature macrophages. Our data indicated that 30 [+ or -] 3.2% of the drug-treated cells were able to phagocytize the latex particles after 72 h of exposure to 1.5 [micro]g/ml of the new compound. However, under the same experimental conditions, only 1-3% of the control cells were able to ingest a minimum of 10 particles (Fig. 5B).

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

To confirm monocyte/macrophage differentiation of the treated cells under the influence of 3-HK and/or the new compound, the expression of cell-surface markers, such as CD11b and CD14, was also studied. Monocytic differentiation and maturation are commonly measured in terms of cell surface expression of CD14 and overexpression of CD11b confirms the myeloid differentiation of cells (Hass et al., 1989; Prudovsky et al., 2002). Treatment of the cells with the new compound resulted in enhanced expression of CD14 and CD11b by 6% and 25%, respectively, after 72h. Under the same experimental conditions, except for the drug and its concentration, we found that CD14 and CD11b expression enhanced by 18% and 5%, respectively, under the influence of 3-HK. Regarding this data, it is evident that both drugs induce myeloid differentiation among the affected cells and the new compound is more potent than 3-HK. Our results revealed that both drugs exerted profound effects on viability of the affected cells. As it is evident from Fig. 6A, treatment of the cells with a single dose of 3-HK (15 nM) resulted in a time-dependent gradual increase in Annexin-V/PI-positive cells. Parallel to these observations, the sub-Gl cell population became evident after 48 h of drug exposure and increased to 80% after 96 h (Fig. 6B, C). Treatment of KG1 cells with the second compound revealed, as shown in Fig. 7, that this compound also affected the viability of the cells leading to their DNA fragmentation and apoptosis (Fig. 7A-C).

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

Regarding our present data, both drugs induced differentiation and apoptosis among the affected cells. To verify that apoptosis is the final destiny of the induced differentiation, we subjected the drug-affected cells to simultaneous analyses of their CD14 content and their response to Annexin-V staining. As shown in Fig. 8, after 72 h of exposure to 3-HK, the majority of cells (21%) were CD14 positive and Annexin-V negative. However, by 96 h of drug exposure, the main population of cells became apoptotic (meaning that they were CD14 negative and Annexin-V positive) while the remaining minority of cells were CD14 and Annexin-V positive, meaning that they are non-apoptotic differentiated cells.

[FIGURE 8 OMITTED]

Discussion

The primary objective in AML-patient therapies is to induce remission and thereafter to prevent the disease relapse. One ideal approach in that regard would be to use differentiation-inducing agents with no or minimal biological adverse effects. In this investigation we evaluated the differentiation potencies of two antiproliferative compounds isolated from D. lessertii using human KG1 cells. Our results indicated that inhibition of proliferation was the most prominent effect of 3-HK and the new compound following 24 h exposure to the drugs. These results indicate that both drugs are cytostatic rather than cytotoxic at early treatment times, though massive cell death were recorded at longer exposures using either of the two compounds.

It has previously been shown that 3-HK arrests the leukemic cells in G0/G1 phase of their growth progression cycle (Moosavi et al., 2005a). Our present data document the fact that 3-HK and the new compound are capable of inducing differentiation among the KG1 drug-treated cells. Occurrence of differentiation following the growth arrest of the cells at G1 phase is in accordance with the literature data.

On the other hand, differentiation of the drug-treated KG1 cells was accompanied with gradual attachments of the cells to the culture plates. This cell-behavior variation might indicate the arrest and progress of differentiation along the monocyte/macrophage lineage. This prediction was further confirmed by observing more CD11b-positive cells along the progress of differentiation which is finally associated with higher levels of CD14-bearing cells, indicating the maturation of the affected KG1 cells to monocytes/macrophages. In that regard, the new compound seems to be more effective relative to 3-HK (Fig. 5C).

Differentiation of KG1 cells under the influences of 3-HK and the new compound has always been associated with occurrence of apoptosis, a similar event also observed among the 3-HK-treated HL-60 cells (Yaz-danparast et al., 2005). The interesting observation concerning this event is the down regulation of CD14 expression among the differentiated cells at the onset of apoptosis. This observation is apparently in accordance with Heidenreich et al.'s (1997) report. They have indicated that down regulation or removal of CD14 receptors triggers apoptosis among the monocytes. Consisted with this report, we also have found that following drug-mediated monocytic differentiation of KG1 cells, a massive apoptosis, associated with down regulation of CD14 levels, occurs.

In conclusion the results of this investigation clearly indicate that both 3-HK and the new compound, whose structural elucidation is under investigation, are capable of inducing differentiation and apoptosis among the differentiation-resistance KG1 cells. Therefore, these two new agents might be valuable candidates for pharmaceutical purposes.

Acknowledgment

The authors appreciate the financial support of this investigation by the research council of University of Tehran.

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Yazdanparast, R., Moosavi, M.A., Mahdavi, M., Sanati, M.H., 2005. 3-Hydrogenkwadaphnin from Dendrostellera lessertii induces differentiation and apoptosis in HL-60 cells. Planta Med. 71, 1112-1117.

Razieh Yazdanparast *, Azadeh Meshkini

Institute of Biochemistry and Biophysics, P.O. Box 13145-1384, University of Tehran, Tehran, Iran

* Corresponding author. Tel.: +98 2166956976; fax: +98 2166404680.

E-mail address: yazdan@ibb.ut.ac.ir (R. Yazdanparast).
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Author:Yazdanparast, Razieh; Meshkini, Azadeh
Publication:Phytomedicine: International Journal of Phytotherapy & Phytopharmacology
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Date:Mar 1, 2009
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