експериментальні роботи UDC 577.152.3 + 576.38 doi: http://dx.doi.org/10.15407/ubj87.06.122 RHAMNAZIN INHIBITS PROLIFERATION AND INDUCES APOPTOSIS OF HUMAN JURKAT LEUKEMIA CELLS IN VITRO А. А. Philchenkov, М. P. Zavelevych R. e. kavetsky institute of experimental Pathology, oncology and Radiobiology, national academy of Sciences of Ukraine, kyiv; e-mail: [email protected] a ntiproliferative and apoptogenic effects of rhamnazin, a dimethoxylated derivative of quercetin, were studied in human acute lymphoblastic leukemia Jurkat cells. The cytotoxicity and apoptogenic activity of rhamnazin in vitro are inferior to that of quercetin. The apoptogenic activity of rhamnazin is realized via mitochondrial pathway and associated with activation of caspase-9 and -3. The additive apoptogenic effect of rhamnazin and suboptimal doses of etoposide, a Dna topoisomerase ii inhibitor, is demonstrated. Therefore, methylation of quercetin modifies its biological effects considerably. k e y w o r d s: acute lymphoblastic leukemia, flavonoids, cell cycle, apoptosis, caspases, flow cytometry. lavonoids constitute the largest class (over mon natural substances. Monomethylated deriva­ 6,500 compounds) of biologically active plant tives have been shown to inhibit proliferation and F polyphenols [1]. Most of them by far are de­ induce apoptosis in cancer cells [8], or to sensitize rivatives of 2-phenylbenzopyran (flavan) or 2-phe­ malignant cells to other cytotoxic agents [9]. Yet nylbenzopyran-4-one (flavone). Flavonoids display there is only a limited amount of data concerning antioxidant properties and may also induce apoptotic efficiency of rhamnazin (3′,7-dimethylquercetin), a cell death, depending on concentration [2]. It has quercetin derivative differing only by two methyl been demonstrated that the proapoptotic and cyto­ groups (Fig. 1), against infection agents [10]. An­ static activity of flavonoids could not be explained tiproliferative activity of rhamnazin has also been by their antioxidant or prooxidant properties only. demonstrated recently in vitro in human cancer cell Specific target molecules for flavonoids in tumor lines [11]. To the best of our knowledge, its effects cells are currently under spotlight. The data availab­ upon leukemia cells have not been studied. Rham­ le allows us to perceive certain flavonoids as signal nazin interaction with cytotoxic antitumor drugs is transducer analogs, which makes them especially also unknown. attractive as candidates for specific antitumor phar­ Physical­and­chemical as well as biological maceuticals. Importantly, flavonoids are also known properties of methylated derivatives of quercetin to potentiate or modify the effects of cytotoxic and may vary considerably, depending on the number antitumor agents and are thus viewed as suitable for and positions of methyl groups. There are few data adjuvant therapies. relating certain properties of quercetin derivatives, Quercetin (3,3′,4′,5,7-pentahydroxyflavone) is namely their anticancer activity, to structural char­ the most studied of flavonoids. Its well-documen- acteristics of the particular molecules [12]. The aim ted pleiotropic biological activity includes, beyond of the present work was to investigate in vitro bio­ potent antioxidant properties, an antinflammatory, logical effects of rhamnazin in human acute lympho­ antiangio genic, cytostatic, and proapoptotic effects blastic leukemia Jurkat cells, in particular its ability (as cited in [3]). Cytotoxic effects of micromolar con­ to induce apoptosis and involvement of caspases in centrations of quercetin and its derivatives towards the induction of apoptosis in these cells. The effects human leukemia cells have been demonstrated [4­7]. of rhamnazin were compared to those of quercetin, Methylated quercetin derivatives with variations in which is important for attributing biological effects the number and positions of methyl groups are com­ of flavonoids, e. g. quercetin and its dimethylated de­ 122 ISSN 2409-4943. Ukr. Biochem. J., 2015, Vol. 87, N 6 A. A. philchenkov, M. P. ZAVELEVYCH A B Fig. 1. Structure of quercetin (a) and rhamnazin (B) rivative, to their structure, and for further targeted For Western blot, cells were washed in phos­ selection and synthesis of compounds with particular phate buffer solution and lysed on ice in 20 mM properties. Tris­HCl (pH 7.4), 1% Triton X­100 and 150 mM NaCl with addition of protease inhibitor cocktail Materials and Methods (Roche Diagnostics, Germany). The lysate was cen­ Human T­cell acute lymphoblastic leukemia trifuged at 12,000 g, the supernatant was mixed with cell line Jurkat was obtained from the National Col­ Laemmli sample buffer and boiled on water bath. lection of Cell Lines of the Institute of Experimen­ Proteins were separated by electrophoresis in 12% tal Pathology, Oncology and Radiobiology (Kyiv, PAAG with SDS and transferred to Immobilon­P Ukraine). The cells were grown in RPMI­1640 polyvinylidene difluoride membrane (Millipore, medium with addition of 10% fetal bovine serum USA). The membranes were blocked for 12 h in 5% (Sigma, USA) and 2 mM of glutamine at 37 °C. nonfat dry milk in phosphate buffered saline with The cells were subcultured at density of 0.8×106 to 0.05% Tween 20 at 4 °C, then incubated with an­ 0.9×10 6 per ml. ti­caspase­9 (5B4 clone recognizing both proform Rhamnazin (99% pure, Sigma, USA) was dis­ and active form of caspase­9) or anti­caspase­8 solved in dimethyl sulfoxide. Quercetin (Merck, (5F7 clone, recognizing only procaspase­8) mono­ USA) was dissolved in ethanol. The stock solutions clonal antibodies (Immunotech, France). To confirm were stored at ­20 °C. Etoposide was purchased from equal protein loading, each membrane was probed Brystol­Myers Squibb SpA (Italy) as commercially with anti-β-actin MoAb (clone AC-15, Sigma, USA). available solution at a concentration of 20 mg/ml. Anti­mouse IgG conjugated with horseradish per­ The investigated compounds were added into oxidase (Promega, USA) was used as secondary culture medium in the beginning of the logarithmic antibody. The affinity binding bands were identified cell growth to analyze growth kinetics and cytotoxi­ with enhanced chemiluminescence Amersham ECL city. Final concentrations of ethanol or dimethyl sul­ Western Blotting Detection kit (GE Healthcare Life foxide in culture media did not exceed 0.5%. Cell Sciences, USA). viability was determined by trypan blue exclusion. The statistical analysis was performed using Cells distribution by phases of cell cycle and Student’s t-test, the results were considered signifi­ percentage of hypodiploid (apoptotic) cells [13] were cant if P < 0.05. estimated after incubating them with propidium io­ Results and Discussion dide (50 µg/ml) solution in 0.1% sodium citrate and 0.1% Triton X-100. Cell fluorescence was measured Jurkat cells were incubated with 15 µM or using FACScan flow cytometer (Becton Dickinson, 150 µM rhamnazin to evaluate its antiproliferative USA). The percentage of cells containing active activity. The cells were counted after 24 or 48 h of form of caspase-3 was assessed by flow cytometry incubation. According to the results, rhamnazin does using Caspase­3, Active Form, mAb Apoptosis Kit: not affect Jurkat cell growth kinetics at 15 µM, but FITC (BD Biosciences Pharmingen, USA) according inhibits cell growth noticeably if the concentration is to the procedure recommended by the manufacturer. increased tenfold (Fig. 2). The flow cytometry data were analyzed with ModFit As antiproliferative activity is generally reali­ LT2.0 software (Verity Software House, USA) and zed via cell cycle arrest, the next series of experi­ CELLQuest (BD Biosciences Pharmingen, USA). ments involved investigation of rhamnazin effect on ISSN 2409-4943. Ukr. Biochem. J., 2015, Vol. 87, N 6 123 експериментальні роботи 1200 showed that methylation of flavonols (including quercetin) in 3′ and 4′ position leads to significant 1000 -1 decrease or total loss of cytotoxic properties. ×ml 800 3 In order to evaluate the contribution of apopto­ sis in overall cell death induced by high rhamnazin 600 concentrations we analyzed in parallel hypodiploid 400 Control cell fraction and the content of the active form of 15 μM effector caspase­3. As demonstrated in Fig. 5, rham­ Cell count, 10 200 150 μM nazin causes apoptotic cell death (Fig. 5), and apo­ 0 ptosis induction by rhamnazin is accompanied with 0 1 2 increased number of cells with the active form of Day caspase­3. The maximum percentage of apoptotic cells and cells containing the active form of cas­ Fig. 2. Jurkat cell growth in culture incubated with pase­3 was detected after 72 h of incubation with rhamnazin rhamnazin. Delayed cell death and, probably, pro­ tracted inhibition of cell growth may in part explain the mitotic cycle of Jurkat cells. The results indicate cell cycle effects of rhamnazin in comparison to increased percentage of Jurkat cells in G2/M phase those of quercetin (see Fig. 3). if rhamnazin concentration is raised from 75 µM to As at least two main pathways have been iden­ 150 µM (Fig. 3), While the percentage of cells in tified in cells for activation of caspase-3, namely re­ G2/M induced by 150 µM rhamnazin is significant­ ceptor­mediated (via caspase­8) and mitochondrial ly less as compared to that under effect of 40 µM (via caspase­9) [15], it was important to determine quercetin, the total fraction of cells in phases S and activation of these initiator caspases in rhamnazin­ G2/M is approximately the same under both 150 µM treated cells. To this end, we used immunoblot as­ rhamnazin and 40 µM quercetin due to the partial say with monoclonal antibodies specific to procas­ arrest in S phase of the cells incubated with rham­ pase­8 or active form of caspase­9. The active form nazin. of caspase­9 was detectable in Jurkat cells incubated Rhamnazin exhibited low toxicity in Jur­ with rhamnazin or quercetin (Fig. 6, a). On the other kat cells even at the relatively high concentrations hand, the induction of apoptosis in Jurkat cells was (150 µM) with only a minor death fraction as com­ not associated with changes in procaspase­8 content pared to that induced by quercetin (Fig.