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Open Life Sciences

formerly Central European Journal of Biology

Editor-in-Chief: Ratajczak, Mariusz


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Volume 12, Issue 1

Issues

Volume 10 (2015)

Evaluation of anticancer properties of a new α-methylene-δ-lactone DL-249 on two cancer cell lines

Dorota K. Pomorska
  • Department of Biomolecular Chemistry, Medical University of Lodz, Mazowiecka 6/8, 92-215 Lodz, Poland
  • Other articles by this author:
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/ Katarzyna Gach-Janczak
  • Department of Biomolecular Chemistry, Medical University of Lodz, Mazowiecka 6/8, 92-215 Lodz, Poland
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  • De Gruyter OnlineGoogle Scholar
/ Rafał Jakubowski
  • Institute of Organic Chemistry, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland
  • Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź, Poland
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/ Tomasz Janecki
  • Institute of Organic Chemistry, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland
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  • De Gruyter OnlineGoogle Scholar
/ Jacek Szymański / Anna Janecka
  • Corresponding author
  • Department of Biomolecular Chemistry, Medical University of Lodz, Mazowiecka 6/8, 92-215 Lodz, Poland
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Published Online: 2017-06-09 | DOI: https://doi.org/10.1515/biol-2017-0021

Abstract

Background

The anticancer activity of a new synthetic α-methylene-δ-lactone DL-249 was reported in leukemia HL-60 and breast cancer MCF-7 cells and compared with the activity of a natural α-methylene-γ-lactone from Tanacetum parthenium, parthenolide.

Methodology

The chemical synthesis of DL-249 was performed using Horner-Wadsworth-Emmons methodology. The cytotoxic activity of the tested compounds was assessed by an MTT test. The ability to induce apoptosis was studied by flow cytometry. The expression levels of genes were determined by quantitative real-time PCR.

Principal Findings/Results

DL-249 and parthenolide inhibited the growth of HL-60 and MCF-7 cells with IC50 values below 10 μM. DL-249 was a stronger apoptosis inducer than parthenolide in both cell lines and both compounds produced a more pronounced effect on HL-60 than on MCF-7 cells. DL-249 and PTL significantly up-regulated expression of Bax, caspase-9, caspase-3 and p53 genes and decreased the level of Bcl-2 and Bcl-xl genes in both cancer cell lines. Additionally DL-249 caused cell cycle arrest in the subG0/G1phase.

Conclusion/Significance

A new synthetic α-methylene-δ-lactone, DL-249 showed the anticancer activity on two cancer cell lines and seemed to be a better apoptosis inducer than parthenolide which makes this compound an attractive lead for further studies.

Keywords: cytotoxicity; apoptosis; α-methylene-δ-lactones; leukemia; breast cancer

1 Introduction

Plants have always been a primary source of pharmacological agents used not only in traditional medicine but also as lead compounds for synthetic modifications. The α-methylene-γ-lactone structural motif (Figure 1) is a well-known pharmacophoric unit present in many natural products which are abundant in plants of the Asteraceae family and possess a large spectrum of biological activities including phytotoxic, cytotoxic, antibacterial, antifungal, and anti-inflammatory properties [1]. The best known example of α-methylene-γ-lactones is parthenolide (PTL), a bioactive compound of Tanacetum parthenium, commonly known as feverfew [2], which has been extensively studied in the last decade as a potential anticancer agent [3-7].

General structure of α-methylene-γ-lactones 1 and α-methylene-δ-lactones 2 and compounds used in this study, natural γ-lactone parthenolide 3 and synthetic δ-lactone DL-249.
Figure 1

General structure of α-methylene-γ-lactones 1 and α-methylene-δ-lactones 2 and compounds used in this study, natural γ-lactone parthenolide 3 and synthetic δ-lactone DL-249.

The anticancer properties of PTL are mostly attributed to an unsaturated lactone functionality which can react with sulfhydryl (-SH) groups of cysteine residues in various cellular proteins, including enzymes and also with free intracellular glutathione, disrupting various processes in the cells (Figure 2) [8]. Other factors, such as lipophilicity, molecular geometry, and the chemical environment of the target sulfhydryl group may also influence the activity of a-methylene-g-lactones [9]. They are usually lipophilic compounds and therefore can easily penetrate cell membranes and show high cytotoxicity in vitro.

Mechanism of action of α-methylene-γ- and -δ-lactones.
Figure 2

Mechanism of action of α-methylene-γ- and -δ-lactones.

Another structurally related group of compounds, α-methylene-δ-lactones, that contain the same characteristic exo-methylene moiety conjugated with a carbonyl group (Figure 1), have also become of interest for synthetic and biological studies. However, when compared to α-methylene- γ-lactones, α-methylene-δ-lactones are much less abundant in nature and their biological activity is hardly recognized.

In this study we compared the anticancer potential of a new synthetic α-methylene-δ-lactone, 4-benzyl-7-methoxy-4-methyl-3-methylene-3,4-dihydro-2H-chroman-2-one (DL-249) and PTL, a representative of natural α-methylene-γ-lactones, in HL-60 promyelocytic leukemia and MCF-7 breast cancer cell lines.

2 Methods

2.1 Materials and general procedures

4-Benzyl-7-methoxy-4-methyl-3-methylene-3,4-dihydro-2H-chroman-2-one (DL-249) was synthesized as outlined in Figure 3. Heating the mixture of ethyl diethoxyphosphorylacetate (3) with triethylorthoacetate (4) in the presence of Ac2O and ZnCl2 as a catalyst at 140°C for 16 h gave desired ethyl 3-ethoxy-2-diethoxyphosphoryl-2-butenoate (5) as a mixture of E and Z isomers in reasonable, 51% yield. When 5 was reacted with 3-methoxyphenol in the presence of trifluoromethanesulfonic acid for 72 h at room temperature, Friedel-Crafts alkylation followed by intramolecular cyclization took place and 3-diethoxyphosphoryl-7-methoxy-4-methylchromen-2-one (6) was obtained in 81% yield. Next, 6 was used as a Michael acceptor in the reaction with 5 equivalents of benzylmagnesium bromide in the presence of copper iodide (CuI), to give adduct 7 in 66% yield. In the last step, adduct 7 was utilized as a Horner-Wadsworth-Emmons reagent in the olefination of formaldehyde, using sodium hydride (NaH) as a base, to yield target 3-methylenechroman-2-one 8 (DL-249) in 77% yield. The detailed procedures are described elsewhere [10].

Synthesis of DL-249 (8). Reagents and conditions: (a) Ac2O, ZnCl2, 140 °C, 16 h; (b) 3-methoxyphenol, CF3SO3H, CH2Cl2, r.t., 72 h; (c) BnMgBr 5 equivalents, CuI, THF, 0°C, then r.t., 48 h; (d) (CH2O)n, NaH, THF, r.t., 1.5 h.
Figure 3

Synthesis of DL-249 (8). Reagents and conditions: (a) Ac2O, ZnCl2, 140 °C, 16 h; (b) 3-methoxyphenol, CF3SO3H, CH2Cl2, r.t., 72 h; (c) BnMgBr 5 equivalents, CuI, THF, 0°C, then r.t., 48 h; (d) (CH2O)n, NaH, THF, r.t., 1.5 h.

PTL was obtained from Tocris Bioscience (Bristol, UK). Both tested compounds were dissolved in DMSO (Sigma-Aldrich, Louis, MO, USA) and further diluted in the culture medium to obtain less than 0.1% DMSO concentration. Controls without and with 0.1% DMSO in each experiment were performed. At used concentration DMSO had no effect on the investigated parameters.

2.2 Cell culture and treatment

Human promyelocytic leukemia cell line (HL-60) and a solid tumor derived human breast adenocarcinoma cell line (MCF-7) were obtained from the European Collection of Cell Cultures (ECACC). Leukemia cells were grown in RPMI 1640 plus GlutaMax I medium (Invitrogen, Grand Island, NY, USA), supplemented with 10% heat-inactivated FBS (Biological Industries, Beit-Haemek, Israel) and antibiotics (100 μg/mL streptomycin and 100 U/mL penicillin) (Sigma-Aldrich, St. Louis, MO, USA). MCF-7 cells were grown in Minimum Essential Medium Eagle (MEME, Sigma-Aldrich, St. Louis, MO, USA) supplemented with 10% heat-inactivated fetal bovine serum (FBS) (Biological Industries, Beit-Haemek, Israel), 2 mM glutamine, Men Non-essential amino acid solution and antibiotics (100 μg/mL streptomycin and 100 U/mL penicillin), all from Sigma Aldrich (Sigma-Aldrich, St. Louis, MO, USA).

Normal human mammary gland/breast cell line (MCF-10A) and normal human umbilical vein endothelial cells (HUVECs) were obtained from the American Type Culture Collection (ATCC). MCF-10A cells were grown using MEGM Mammary Epithelial BulletKit, while HUVECs using EGM-2 Endothelial Medium BulletKit, both purchased from Lonza (Lonza, Walkersville, MD, USA). Cells were maintained at 370C in a 5% CO2 atmosphere and were grown until 80% confluent.

2.3 Metabolic activity assay (MTT)

The MTT (3-(4,5-dimethyldiazol-2-yl)-2,5 diphenyl tetrazolium bromide) assay, which measures activity of cellular dehydrogenases, was performed as described earlier [11] on four human cell lines: two cancer cell lines (i.e. breast cancer MCF-7 and leukemia HL-60) and two normal cell lines (MCF-10A and HUVEC). Cells were seeded on 96-well plates (Nunc, Roskilde, Denmark) in 100 μL of culture medium and left to grow for 24h. Tested compounds were dissolved in DMSO and diluted with the complete culture medium. To each well 100 μL of such prepared dilution was added to obtain concentration range from 10-7 to 10-3 M. After 24h of treatment, MTT (5 mg/mL in PBS) was added and cells were incubated for an additional 2 h. Afterwards, the medium was removed and insoluble blue formazan crystals were dissolved in 100 μL of DMSO. The absorbance of the formazan product was measured at 540 nm using an automated iMark Microplate reader (Bio-Rad, Hercules, CA, USA). The concentration-response curves were used for calculation of IC50 values (concentration of a drug necessary to induce 50% inhibition) of the tested compounds.

2.4 Analysis of apoptosis by APC-annexin V and propidium iodide (PI) double staining

The analysis of apoptosis was performed using APC-annexin V Apoptosis Detection Kit (BD Bioscience, San Jose, CA, USA). Briefly, the cells were seeded on 6-well plates at the density of 4.5 x 105 cells/well and 4.0 x 105 cells/well for MCF-7 and HL-60, respectively. After 24 h, the tested compounds diluted in culture medium were added to the cells at IC50 concentrations. After 24 h of treatment MCF-7 cells were trypsinized. Then both cell types were collected by centrifugation (200 x g, 5 min). Cells were stained for 15 min at room temperature with annexin V and PI. Then flow cytometry analysis was performed using BD FACSCanto II Flow Cytometer. Apoptotic cells were visualized and quantified by constructing a dot-plot with BD FACSDiva software.

2.5 Analysis of cell proliferation, apoptosis and DNA damage by flow cytometry

The analysis of cell proliferation, DNA damage and apoptotic cell death was performed using the “Apoptosis, DNA Damage, and Cell Proliferation Kit” (BD Bioscience, San Jose, CA, USA), according to the manufacturer guidelines. Briefly, cells were seeded in 25 cm2 culture flasks at a density of 8.0×104 cells/mL in 10 mL of culture medium (MCF-7) or on 6-well plates at a density of 2.0×105 cells/mL in 2 mL of culture medium (HL-60) and left to grow for 24h. Then, the tested compounds, diluted in culture medium, were added to the cells at IC50 concentrations. After 24 h of treatment, BrdU at final concentration of 10 μM was added and the cells were incubated for an additional 8 h. Then cells were harvested as described above, counted, fixed, permeabilized according to the manufacturer’s protocol. In order to expose BrdU epitopes, cells were treated with DNase (300 μg/mL in DPBS) for 1 h at 37°C and then simultaneously stained with fluorochrome-labeled anti-BrdU, H2AX (pS139), and cleaved PARP (Asp214) antibodies (20 min, room temperature). After washing, DAPI solution (1 μg/mL of the staining buffer) was used for DNA staining in order to perform cell cycle analysis. Cells were re-suspended in the staining buffer and analyzed using BD FACSCanto II Flow Cytometer. The data were visualized and quantified by constructing a dot-plot (BD FACSDiva software).

2.6 Evaluation of mitochondrial membrane potential changes

Mitochondrial membrane potential (ΔΨm) changes were analyzed using the Cell Meter™ JC-10 Mitochondrial Membrane Potential Assay Kit (AAT, Bioquest Inc., Sunnyvale, CA, USA), according to the manufacturer’s instructions. JC-10 dye exhibits potential-dependent accumulation in mitochondria, indicated by a fluorescence emission shift from green to orange when membrane potential increases. Briefly, the cells were seeded on 6-well plates at the density of 4.5 x 105 cells/well and 4.0 x 105 cells/well for MCF-7 and HL-60, respectively and left to grow for 24 h. Then, cells were treated for 24 h with the tested compounds and collected as described above. Cells were washed with PBS, stained for 45 min in the dark with JC-10 and analyzed using BD FACSCanto II Flow Cytometer. As a positive control, mitochondrial uncoupler, carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP, Sigma-Aldrich, Louis, MO, USA) was used. Changes in ΔΨm were visualized and quantified by constructing a dot-plot (BD FACSDiva software).

2.7 Quantitative real-time PCR

The changes in mRNA expression of appropriate genes were determined using qRT-PCR, as described in detail elsewhere [12]. Briefly, the cells were seeded on 6-well plates at the density of 4.5 x 105 cells/well and 4.0 x 105 cells/well for MCF-7 and HL-60, respectively and left to grow for 24 h. Then cells were incubated for 24 h with the tested compounds as described above. After treatment, cells were washed with PBS. The RNA was isolated using the Total RNA Mini Kit (A&A Biotechnology, Gdynia, Poland) [13] and the concentration of RNA was determined by measuring the absorbance at 260 and 280 nm on the UV/VIS spectrophotometer (Pharmacia, Cambridge, UK). cDNA was synthesized using the Enhanced Avian HS RT-PCR Kit and oligo(dT)12-18 primers (Sigma-Aldrich, St. Louis, MO, USA). The amplification was performed using Brilliant II SYBR Green QPCR Master Mix (Agilent Technologies, Inc. Santa Clara, CA, USA) in Mx3005P QPCR System (Agilent Technologies, Inc. Santa Clara, CA, USA) according to the manufacturer’s guidelines. The sequences of the primers are listed in Table 1. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was used as a reference. The relative mRNA expression was calculated by the 2-∆∆CT method [14].

Table 1

Primer sequences for real-time PCR reaction

2.8 Statistical analysis

All statistical calculations were performed with GraphPad Prism 4.0 (GraphPad Software Inc., San Diego, CA, USA). Results from three independent experiments performed in triplicate were expressed as mean±SEM. Data were analyzed by one-way analysis of variance (ANOVA) followed by a post-hoc multiple comparison Student-Newman-Keuls test. Statistical significance was noted when p values were equal to or less than 0.05.

Ethical approval: The conducted research is not related to either human or animals use.

3 Results

3.1 MTT assay

Cytotoxicities of DL-249 and PTL were examined by the MTT assay. The metabolic activity of HL-60 and MCF-7 cells, incubated for 24 h with increasing concentrations of the tested compounds, was measured. Both compounds were highly cytotoxic, with IC50 values below10 μM in both cancer cell lines, but DL-249 was more active than PTL in MCF-7 cells (Table 2). Cytotoxicity of both compounds on normal cells, HUVEC and MCF-10A, was also assessed. It turned out that the cytotoxicity of PTL was almost identical for cancer and normal cells. DL-249 was about 1.5 times more toxic for HL-60 and MCF-7, as compared with HUVEC and MCF-10A cells, respectively.

Table 2

In vitro cytotoxic activity of DL-249 and PTL used in the IC50 concentrations on cancer (HL-60 and MCF-7) and normal cells (HUVEC and MCF-10A).

3.2 Induction of apoptosis

The ability of DL-249 and PTL to induce apoptosis was examined using APC-annexin V and PI staining. The obtained results are shown in Figure 4. In HL-60 cells, DL-249 increased the number of early and late apoptotic cells (lower and upper right quadrants) up to 29.0% and 25.4%, respectively, compared with control, while for PTL these numbers were 9.1% and 28.2%, respectively. In MCF-7 cells any of the two tested compounds changed the number of early apoptotic cells but both compounds significantly increased the number of late apoptotic cells up to 16.1% and 14%, for DL-249 and PTL, respectively.

Induction of apoptosis in HL-60 and MCF-7 cells treated for 24 h with DL-249 or PTL, at IC50 concentration. The cells were stained with APC-conjugated annexin V in a buffer containing propidium iodide and analyzed by flow cytometry. For each group of cells, the percentage of surviving cells is shown in quadrant Q3. Quadrant Q4 indicates the percentage of early apoptotic cells (annexin V-positive cells). The percentage of late apoptotic cells is shown in Q2 (annexin V- and PI-positive cells). Data represent mean±SEM of three independent experiments in triplicate. Statistical significance was assessed using one-way ANOVA and a post-hoc multiple comparison Student-Newman-Keuls test. * p < 0.05, *** p<0.001 was considered as significantly different from control.
Figure 4

Induction of apoptosis in HL-60 and MCF-7 cells treated for 24 h with DL-249 or PTL, at IC50 concentration. The cells were stained with APC-conjugated annexin V in a buffer containing propidium iodide and analyzed by flow cytometry. For each group of cells, the percentage of surviving cells is shown in quadrant Q3. Quadrant Q4 indicates the percentage of early apoptotic cells (annexin V-positive cells). The percentage of late apoptotic cells is shown in Q2 (annexin V- and PI-positive cells). Data represent mean±SEM of three independent experiments in triplicate. Statistical significance was assessed using one-way ANOVA and a post-hoc multiple comparison Student-Newman-Keuls test. * p < 0.05, *** p<0.001 was considered as significantly different from control.

3.3 Inhibition of cell proliferation, induction of DNA damage and apoptosis

Flow cytometry was used to evaluate the ability of DL-249 to inhibit cell proliferation and induce DNA damage and apoptotic cell death. Incorporation of BrdU into DNA chain is considered to be a marker of cell proliferation. PE Anti-Cleaved PARP (Asp214) conjugated antibodies which recognize an 89 kDa-cleaved fragment of PARP, served as an index of cellular apoptosis, were used for apoptosis evaluation. The DNA damage was assessed using Alexa Fluor® 647 Anti-H2AX (pS139) antibodies, directed against the phosphorylated form of H2AX protein at the pS139 residue being a biomarker of double-strand breaks (DSB) in DNA.

Incubation of HL-60 and MCF-7 cells with BrdU and DL-249 or PTL at IC50 concentrations, demonstrated that both compounds significantly inhibited cell proliferation in the tested cell lines (Figure 5A). However, the stronger inhibition was observed in MCF-7 cells. In this cell line both tested compounds decreased cell proliferation in more than 95% of cell population. In HL-60 cells DL-249 was able to inhibit proliferation in about 75% of cells, whereas PTL showed lesser effect and inhibited proliferation in 38% of cell population. As shown in Figure 5B, both tested compounds induced DNA damage. In MCF-7 cells their action was comparable and they generated DNA damage in more than 22% of MCF-7 cell population. In HL-60 cells a big difference in the activity of both compounds was noticed. DL-249 was about 2-fold more active than PTL and generated DNA damage in about 40% of cells. Similar tendency was observed for apoptosis induction (Figure 5C). In HL-60 cells DL-249 produced a 1.8-fold stronger effect than PTL and increased the number of apoptotic (cleaved PARP positive) cells up to 60%. In MCF-7 cells the effect was weaker for both tested compounds.

Inhibition of cell proliferation (BrdU test) (A), induction of DNA damage (H2AX test) (B) and induction of apoptosis (PARP test) (C) by DL-249 or PTL in HL-60 and MCF-7 cells. After 24 h incubation with tested compounds, BrdU was added and cells were incubated for additional 8 h. The cells were stained with PerCP-Cy™5.5 Mouse Anti-BrdU, Alexa Fluor® 647 Mouse Anti-H2AX (pS139), PE Mouse Anti-Cleaved PARP (Asp214) antibodies for 20 min at room temperature and analyzed by flow cytometry. Data represent mean ± SEM of three independent experiments in triplicate. Statistical significance was assessed using one-way ANOVA and a post-hoc multiple comparison Student-Newman-Keuls test. * p < 0.05, ** p < 0.01, *** p<0.001 was considered as significantly different from control.
Figure 5

Inhibition of cell proliferation (BrdU test) (A), induction of DNA damage (H2AX test) (B) and induction of apoptosis (PARP test) (C) by DL-249 or PTL in HL-60 and MCF-7 cells. After 24 h incubation with tested compounds, BrdU was added and cells were incubated for additional 8 h. The cells were stained with PerCP-Cy™5.5 Mouse Anti-BrdU, Alexa Fluor® 647 Mouse Anti-H2AX (pS139), PE Mouse Anti-Cleaved PARP (Asp214) antibodies for 20 min at room temperature and analyzed by flow cytometry. Data represent mean ± SEM of three independent experiments in triplicate. Statistical significance was assessed using one-way ANOVA and a post-hoc multiple comparison Student-Newman-Keuls test. * p < 0.05, ** p < 0.01, *** p<0.001 was considered as significantly different from control.

3.4 Dissipation of mitochondrial membrane potential

The transmembrane potential (ΔΨm) disruption is considered a critical step for the induction of apoptosis by the intrinsic pathway. To assess the changes in ΔΨm, cells treated with the tested compounds for 24 h at IC50 concentrations were stained with JC-10 and analyzed by flow cytometry. The majority of control cells were found within the population with high ΔΨm. FCCP was used as a positive control and as expected, this compound caused dissipation of ΔΨm in more than 99% of cells in both tested cell lines. In HL-60 cells, DL-249 decreased ΔΨm in 42.5%, while in MCF-7 in 35.7% of cell populations. PTL also significantly decreased ΔΨm. However, in MCF-7 cells its effect was much weaker as compared with DL-249 (Figure 6).

Effect of DL-249 and PTL on dissipation of the mitochondrial membrane potential (ΔΨm) in HL-60 and MCF-7 cells. Cells were treated for 24h with the tested compounds at IC50 concentrations and stained with JC-10 (5 μL/mL) for 45 min in 37°C, 5% CO2. Changes in the fluorescence were analyzed by flow cytometry. FCCP (30 μM) was used as a positive control. Data represent mean±SEM of three independent experiments in triplicate. Statistical significance was assessed using one-way ANOVA and a post-hoc multiple comparison Student-Newman-Keuls test. *p<0.05, ***p<0.001 was considered as significantly different from control.
Figure 6

Effect of DL-249 and PTL on dissipation of the mitochondrial membrane potential (ΔΨm) in HL-60 and MCF-7 cells. Cells were treated for 24h with the tested compounds at IC50 concentrations and stained with JC-10 (5 μL/mL) for 45 min in 37°C, 5% CO2. Changes in the fluorescence were analyzed by flow cytometry. FCCP (30 μM) was used as a positive control. Data represent mean±SEM of three independent experiments in triplicate. Statistical significance was assessed using one-way ANOVA and a post-hoc multiple comparison Student-Newman-Keuls test. *p<0.05, ***p<0.001 was considered as significantly different from control.

3.5 Cell cycle arrest

The distribution of HL-60 and MCF-7 cells in the cell cycle was investigated after 24 h exposure of the cells to DL-249 or PTL at IC50 concentrations. In HL-60 cells, both compounds arrested the cell cycle in subG0/G1 phase (Figure 7). However, DL-249 produced a 2.5-fold stronger effect than PTL. In MCF-7 cells both compounds produced a similar effect and only slightly increased the number of cells in subG0/G1 phase and decreased in S phase.

Effect of DL-249 and PTL on cell cycle distribution in HL-60 and MCF-7 cells. Cells were treated for 24h with compounds at IC50 concentration. The percentage of cells at each stage of the cycle was analyzed by flow cytometry, following DNA staining with DAPI and compared with untreated cells regarded as control, C. The results are representative of three independent experiments. Statistical significance was assessed using one-way ANOVA and a post-hoc multiple comparison Student-Newman-Keuls test. *p<0.05,***p<0.001 was considered as significantly different from control.
Figure 7

Effect of DL-249 and PTL on cell cycle distribution in HL-60 and MCF-7 cells. Cells were treated for 24h with compounds at IC50 concentration. The percentage of cells at each stage of the cycle was analyzed by flow cytometry, following DNA staining with DAPI and compared with untreated cells regarded as control, C. The results are representative of three independent experiments. Statistical significance was assessed using one-way ANOVA and a post-hoc multiple comparison Student-Newman-Keuls test. *p<0.05,***p<0.001 was considered as significantly different from control.

3.6 Effect of DL-249 and PTL on expression levels of selected genes involved in apoptosis and cell cycle

The changes in mRNA levels of several genes engaged in regulation of apoptosis and the cell cycle were analyzed in HL-60 and MCF-7 cells, treated with DL-249 or PTL for 24h at IC50 concentrations, using quantitative real-time PCR (Table 3). Expression levels of the anti-apoptotic genes Bcl-2 and Bcl-xl were significantly down-regulated for both tested compounds in both cell lines. Up-regulation was observed for the pro-apoptotic Bax, indicating that the imbalance of the Bax/Bcl-2 ratio may be responsible for DL-249-induced apoptosis. The observed increase of caspase 9 and caspase 3 expression levels suggested that the mitochondrial pathway was engaged in apoptosis induction. DL-249 and PTL were shown to increase the mRNA levels of p53, a gene responsible for induction of cell cycle arrest or stimulation of apoptosis when DNA is damaged. In HL-60 cell line, a strong induction of this gene expression (3-fold in comparison with control) was observed. In MCF-7 the tested compounds only slightly up-regulated the expression of p53.

Table 3

The changes in expression of apoptosis- and cell cycle-related genes in MCF-7 and HL-60 cells treated with DL-249 or PTL analyzed by quantitative real-time PCR.

4 Discussion

Chemical modifications of natural products are considered an important strategy in the search for new drugs with improved pharmacological properties and often with simpler structures. Continuing our studies on compounds with exo-cyclic double bond conjugated with a carbonyl function we investigated and compared the anticancer activity of a synthetic α-methylene-δ-lactone DL-249 with PTL against HL-60 and MCF-7 cell lines, which represent leukemia and a solid tumor, respectively.

We have demonstrated that the new synthetic compound was highly cytotoxic for both examined cancer cell lines. The cytotoxic activity of DL-249 was associated with triggering apoptosis which has an essential role in chemotherapy-induced cancer cell death and can be induced by multiple events, including caspase activation, intracellular thiol depletion, mitochondrial dysfunction or induction of oxidative stress [15-18]. In this report we demonstrated and compared the pro-apoptotic activity of DL-249 and PTL in HL-60 and MCF-7 cells using Annexin V/PI staining. DL-249 was a stronger apoptosis inducer than PTL in both cell lines and both compounds produced a more pronounced effect on HL-60 than on MCF-7 cells. The pro-apoptotic activity of the tested compounds was also shown on the mRNA level. The quantitative real-time PCR analysis revealed that DL-249, as well as PTL, significantly increased expression of the pro-apoptotic (Bax) and decreased the level of anti-apoptotic (Bcl-2, Bcl-xl) genes in both cancer cell lines. Moreover, we demonstrated the up-regulation of caspase 9 and caspase 3 expression. These results were further confirmed by the PARP cleavage test, in which activation of caspase 3 was observed. The dissipation of the mitochondrial membrane potential indicated that the mitochondrial pathway of apoptosis was activated. Mitochondrial apoptotic signaling is mainly activated by pro-apoptotic Bax. Upon stimulation, the protein encoded by Bax is translocated from the cytosol to mitochondria, where it initiates the release of cytochrome c and in consequence activates caspase 9. Caspase 9 begins the caspase cascade which leads to cell death [19].

The expression of the p53 gene, named “guardian of the genome”, was up-regulated similarly by both tested compounds but the effect was 2-fold stronger in HL-60 than in MCF-7 cells. The protein produced by this gene acts as a tumor suppressor that keeps cells from dividing and growing too fast or in an uncontrolled way [20, 21]. The p53 protein plays a significant role in the modulation of the cell cycle by inducing the G1-, S-, or G2-phase arrest or stimulating apoptosis when DNA is damaged. Transactivation of p21 is required for the p53-dependent G1 checkpoint. The cell cycle analysis of HL-60 cells treated with DL-249 revealed the arrest of the cycle in subG0/G1 phase.

The obtained results showed that in cancer cells, DL-249 caused activation of Bax, inactivation of Bcl-2 and disruption of the mitochondrial outer membrane, leading to cytochrome c release, induction of caspase cascade and apoptosis. The graph in Figure 8 shows possible pathways leading to HL-60 and MCF-7 cell apoptosis induced by DL-249.

The possible mechanisms of apoptosis induction by DL-249 in HL-60 and MCF-7 cells.
Figure 8

The possible mechanisms of apoptosis induction by DL-249 in HL-60 and MCF-7 cells.

As previously documented, high reactivity of compounds with exo-cyclic double bond conjugated with a carbonyl function, as in DL-249, is responsible for the simultaneous activation of several processes which means that such products can affect multiple targets in cancer cells [5]. On one hand, this may be advantageous in cancer therapy and increase its effectiveness, but on the other, compounds with such motif show low specificity of action and target not only cancer but also normal cells [22]. However, this problem is common for most anticancer drugs that have already found their place in cancer therapy and explains the serious side-effects that always accompany administration of anticancer agents.

The toxicity of PTL against leukemia and HUVEC cells and against MCF-7 and MCF-10A cells was similar. The new synthetic δ-lactone, DL-249, showed some small selectivity in cancer versus normal cells. Therefore, the observed anticancer activity makes this new synthetic δ-lactone an attractive lead structure for further modifications and shows that simple, easy to synthesize compounds can be valuable and often much cheaper substitutes of complex natural products isolated from plants.

5 Conclusions

In this study, we demonstrated the anticancer activity of a simple synthetic compound with an α-methylene-δ-lactone motif and we compared it to the activity of a plant-derived α-methylene-γ-lactone, PTL, extensively studied as a potential anti-leukemic drug. We have shown that DL-249 can induce stronger pro-apoptotic effect than PTL in HL-60 and MCF-7 cells. The cytotoxicity of DL-249 was related to the intrinsic apoptotic pathway and was correlated with the imbalance between Bax and Bcl-2 and with dissipation of the mitochondrial membrane potential. Promising anticancer properties of DL-249 show the enormous potential that cheap and easy to produce synthetic compounds hold in the search for novel chemotherapeutics.

Acknowledgments

The authors would like to acknowledge the financial supported from the Medical University of Lodz (No 502-03/1-156-02/502-14-241 and No 502-03/1-156-02/502-14-191) and from the National Science Center (No 2015/17/D/NZ3/02226).

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Footnotes

    About the article

    Received: 2017-03-08

    Accepted: 2017-04-11

    Published Online: 2017-06-09


    Conflict of interest: Authors state no conflict of interest.


    Citation Information: Open Life Sciences, Volume 12, Issue 1, Pages 178–189, ISSN (Online) 2391-5412, DOI: https://doi.org/10.1515/biol-2017-0021.

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    © 2017 Dorota K. Pomorska et al.. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License. BY-NC-ND 3.0

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