Human Promyelocytic Leukemia HL-60 Research Articles

Induction of hypoxia-inducible factor-1α inhibits drug-induced apoptosis in the human leukemic cell line HL-60

BackgroundLeukemic cells originate from hypoxic bone marrow, which protects them from anti-cancer drugs. Although many factors that cause drug resistance in leukemic cells have been studied, the effect of hypoxia on drug-induced apoptosis is still poorly understood.MethodsIn this study, we examined the effect of hypoxia on anti-leukemic drug resistance in leukemic cell lines treated with cobalt chloride (CoCl2), a hypoxia-mimetic agent. Cellular proliferation was evaluated using the methyl thiazolyl tetrazolium (MTT) assay. Flow cytometry analysis and western blots were performed to investigate apoptosis-related proteins.ResultsUnlike its previously known apoptotic effect, the expression of HIF-1α increased the survival rate of human promyelocytic leukemia HL-60 cells when these cells were exposed to anti-leukemic drugs; these effects were mediated by heat-shock protein HSP70 and the pro-apoptotic protein Bax.ConclusionThese findings may provide new insights for understanding the mechanisms underlying hypoxia and for designing new therapeutic strategies for acute myeloid leukemia.

Novel microtubule-targeting agents, pyrrolo-1,5-benzoxazepines, induce apoptosis in multi-drug-resistant cancer cells

The development of multi-drug resistance (MDR) due to the expression of members of the ATP binding cassette (ABC) transporter family is a major obstacle in cancer treatment. The broad range of substrate specificities associated with these transporters leads to the efflux of many anti-cancer drugs from tumour cells. Therefore, the development of new chemotherapeutic agents that are not substrates of these transporters is important. We have recently demonstrated that some members of a novel series of pyrrolo-1,5-benzoxazepine (PBOX) compounds are microtubule-depolymerising agents that potently induce apoptosis in several cancer cell lines and impair growth of mouse breast tumours. The aim of this current study was to establish whether PBOXs were capable of inducing apoptosis in cancer cells expressing either P-glycoprotein or breast cancer resistance protein (BCRP), two of the main ABC transporters associated with MDR. We performed in vitro studies to assess the effects of PBOXs on cell proliferation, cell cycle and apoptosis in human cancer cell lines and their drug-resistant substrains expressing either P-glycoprotein or BCRP. In addition, we performed a preliminary molecular docking study to examine interactions between PBOXs and P-glycoprotein. We established that three representative PBOXs, PBOX-6, -15 and -16 were capable of inducing apoptosis in drug-resistant HL60-MDR1 cells (expressing P-glycoprotein) and HL60-ABCG2 cells (expressing BCRP) with similar potencies as in parental human promyelocytic leukaemia HL60 cells. Likewise, resistance to PBOX-6 and -16 was not evident in P-glycoprotein-expressing A2780-ADR cells in comparison with parent human ovarian carcinoma A2780 cells. Finally, we deduced by molecular docking that PBOX-6 is not likely to form favourable interactions with the substrate binding site of P-glycoprotein. Our results suggest that pro-apoptotic PBOX compounds may be potential candidates for the treatment of P-glycoprotein- or BCRP-associated MDR cancers.

Selenium Modulates Oxidative Stress-Induced Cell Apoptosis in Human Myeloid HL-60 Cells Through Regulation of Calcium Release and Caspase-3 and -9 Activities

Selenium is an essential chemopreventive antioxidant element to oxidative stress, although high concentrations of selenium induce toxic and oxidative effects on the human body. However, the mechanisms behind these effects remain elusive. We investigated toxic effects of different selenium concentrations in human promyelocytic leukemia HL-60 cells by evaluating Ca(2+) mobilization, cell viability and caspase-3 and -9 activities at different sample times. We found the toxic concentration and toxic time of H(2)O(2) as 100 microM: and 10 h on cell viability in the cells using four different concentrations of H(2)O(2) (1 microM: -1 mM: ) and six different incubation times (30 min, 1, 2, 5, 10, 24 h). Then, we found the therapeutic concentration of selenium to be 200 nM: by cells incubated in eight different concentrations of selenium (10 nM: -1 mM: ) for 1 h. We measured Ca(2+) release, cell viability and caspase-3 and -9 activities in cells incubated with high and low selenium concentrations at 30 min and 1, 2, 5, 10 and 24 h. Selenium (200 nM: ) elicited mild endoplasmic reticulum stress and mediated cell survival by modulating Ca(2+) release, the caspases and cell apoptosis, whereas selenium concentrations as high as 1 mM: induced severe endoplasmic reticulum stress and caused cell death by activating modulating Ca(2+) release, the caspases and cell apoptosis. In conclusion, these results explained the molecular mechanisms of the chemoprotective effect of different concentrations of selenium on oxidative stress-induced apoptosis.

Enhanced anticancer activity of glutamate prodrugs of all-trans retinoic acid

Abstract Objectives All-trans retinoic acid (ATRA), an active metabolite of vitamin A, is widely used in the treatment of acute promyelocytic leukaemia and myelodysplastic syndrome. However, its high lipophilicity is thought to be responsible for the slow dissolution and low bioavailability following oral administration. In order to obtain compounds with better solubility characteristics to improve the transportation and bioavailability of ATRA, derivatives of ATRA containing glutamic acid or its sodium salt were synthesised. Methods The ATRA derivatives synthesised – all-trans retinoyl glutamate (RAE) and all-trans retinoyl sodium glutamate (RAENa2) – were characterised in terms of melting point, optical rotation, mass spectrometry, NMR and partition coefficient. A liposomal preparation formed from RAE was characterised by particle size and zeta potential. The anti-tumour activity of RAE and RAENa2 was compared with that of ATRA in mice bearing S180 tumours and their effects on the cell cycle were determined in human pro-myelocytic leukaemia HL-60 cells. Key findings RAE and RAENa2 were more active than ATRA against tumour growth. Flow cytometry indicated that RAE and RAENa2 induced HL-60 cell cycle arrest, similar to ATRA. DNA fragmentation studies suggested that apoptosis may be one of the mechanisms responsible for the anti-tumour activities. Conclusions The two derivatives of ATRA, RAE and RAENa2, exhibited improved aqueous solubility and were more effective in mice bearing S180 tumours.

Enhanced anticancer activity of glutamate prodrugs of all-trans retinoic acid

All-trans retinoic acid (ATRA), an active metabolite of vitamin A, is widely used in the treatment of acute promyelocytic leukaemia and myelodysplastic syndrome. However, its high lipophilicity is thought to be responsible for the slow dissolution and low bioavailability following oral administration. In order to obtain compounds with better solubility characteristics to improve the transportation and bioavailability of ATRA, derivatives of ATRA containing glutamic acid or its sodium salt were synthesised. The ATRA derivatives synthesised - all-trans retinoyl glutamate (RAE) and all-trans retinoyl sodium glutamate (RAENa(2)) - were characterised in terms of melting point, optical rotation, mass spectrometry, NMR and partition coefficient. A liposomal preparation formed from RAE was characterised by particle size and zeta potential. The anti-tumour activity of RAE and RAENa(2) was compared with that of ATRA in mice bearing S(180) tumours and their effects on the cell cycle were determined in human pro-myelocytic leukaemia HL-60 cells. RAE and RAENa(2) were more active than ATRA against tumour growth. Flow cytometry indicated that RAE and RAENa(2) induced HL-60 cell cycle arrest, similar to ATRA. DNA fragmentation studies suggested that apoptosis may be one of the mechanisms responsible for the anti-tumour activities. The two derivatives of ATRA, RAE and RAENa(2), exhibited improved aqueous solubility and were more effective in mice bearing S(180) tumours.

Chrotacumines A−D, Chromone Alkaloids from Dysoxylum acutangulum

Four new chromone alkaloids, chrotacumines A-D (1-4), consisting of a 5,7-dihydroxy-2-methylchromone, an N-Me piperidine ring, and an ester side chain were isolated from Dysoxylum acutangulum, and their structures including absolute configurations were elucidated on the basis of spectroscopic data interpretation including 2D NMR, CD spectra, and X-ray analysis. The known compound rohitukine (5) showed moderate cytotoxicity against human HL-60 promyelocytic leukemia and HCT-116 colon cancer cells.

Hydroxyespintanol and schefflerichalcone: two new compounds from Uvaria scheffleri

A chemical investigation of the petroleum ether extract and chloroform extract of the root of Uvaria scheffleri Diels (Annonaceae) led to the isolation of two new compounds, named hydroxyespintanol (1) and schefflerichalcone (2), together with eight known compounds (3-10). The structural elucidation of compounds 1 and 2 by spectroscopic studies is described. The cytotoxicity of the isolated compounds against human promyelocytic leukemia HL-60 cells was studied. Among these, 2'-hydroxy-3',4',6'-trimethoxychalcone (5) exhibited cytotoxicity (IC(50) 12 microM), and espintanol (3), which was the main ingredient, also showed some cytotoxicity (IC(50) 44 microM).

Apoptosis Induction by Menadione in Human Promyelocytic Leukemia HL-60 Cells

Cell death induced by menadione (vitamin K-3,2-methyl-1,4-naphthoquinone) has been investigated in human promyelocytic leukemia HL-60 cells. Menadione was found to induce both apoptosis and necrosis in HL-60 cells. Low concentration (1~50 µM) of menadione induced apoptotic cell death, which was demonstrated by typical DNA ladder patterns on agarose gel electrophoresis and flow cytometry analysis. In contrast, a high concentration of menadione (100 µM) induced necrotic cell death, which was demonstrated by DNA smear pattern in agarose gel electrophoresis. Necrotic cell death was accompanied with a great reduction of cell viability. Menadione activated caspase-3, as evidenced by both increased protease activity and proteolytic cleavage of 116 kDa poly(ADP-ribose) polymerase (PARP) into 85 kDa cleavage product. Caspase-3 activity was maximum at 50 µM of menadione, and very low at 100 µM of menadione. Taken together, our results showed that menadi-one induced mixed types of cell death, apoptosis at low concentrations and necrosis at high concentrations in HL-60 cells.

Novel events in mitchondria: Increase of poly(ADP-ribosyl)ation in human promyelocytic leukemia HL-60 cell line during differentiation by nicotinamide

Poly(ADP-ribosyl)ation, synthesized mainly by poly(ADP-ribose) polymerase-1 (PARP-1) using nicotinamide adenine dinucleotide as a substrate, has been identified as a post-translational modification of nuclear proteins in many eukaryotic cells. At present, studies on poly(ADP-ribosyl)ation have focused primarily on its roles in DNA repair, replication, transcription, and cell death. It has been suggested that poly(ADP-ribosyl)ation activity occurs in organelles, including mitochondria, but its role is not fully understood. On the other hand, it has been reported that PARP-1 and poly(ADP-ribosyl)ation play an important role in the differentiation of many cell types. Recently, we have demonstrated that niacin and its related compounds induced granulocytic differentiation in human promyelocytic leukemia HL-60 cells. In this study, we investigated changes in poly(ADP-ribosyl)ation levels during granulocytic differentiation by niacin, its related compounds and well-known granulocytic inducers. Results indicated no significant changes in expression levels and cellular localization of PARP-1 protein was observed in HL-60 cells during the differentiation. However, poly(ADP-ribosyl)ation was detected in cells treated with nicotinamide (NA) compared to the controls. Intriguingly, this phenomenon was detected in the mitochondrial fractions, but not in the nucleus. In addition, nicotinic acid, which is equivalent to NA induce neither differentiation nor the change of poly(ADP-ribosyl)ation. Because NA promotes the differentiation activities in several types of cells, these results provide important clues towards elucidating the mechanisms of NA. Additionally, these findings provide new information about mitochondrial poly(ADP-ribosyl)ation.

Difference in growth suppression and apoptosis induction of EGCG and EGC on human promyelocytic leukemia HL-60 cells

Growth suppression and apoptosis inducing effect of (-)-epigallocatechin 3-gallate (EGCG) and (-)-epigallocatechin (EGC) were studied against human promyeolcytic leukemia, HL-60 cells. EGCG showed higher growth suppression against HL-60 cells than EGC. IC(50) values for EGCG were 60.0 microM and EGC was 107.7 microM, respectively. Both EGCG and EGC induced apoptosis evidenced by nuclei fragmentation. Nuclear fragmentation was observed as a time-dependent manner and the extent of nuclear fragmentation was slightly higher in EGCG-treated cells than EGC-treated cells. The expression level of Bcl-2 was decreased and caspase-3 was activated by EGCG or EGC treatment. The extent in decrease of Bcl-2 and activation caspase-3 were more extensively occurred in EGCG-treated cells than in EGC-treated cells. These data corresponded to the growth suppression data. EGC showed no cytotoxicity to a normal V79-4 cell line and EGCG showed slight cytotoxicity at higher concentrations.

Expression of Heat Shock Proteins after Ultrasound Exposure in HL-60 Cells

One of the important cellular defense mechanisms against stress is the induction of heat shock proteins (HSPs). We have recently demonstrated that a low frequency electromagnetic field is unable to induce the heat shock response (HSR). In the present study, we expanded our investigations to the induction of HSPs, particularly Hsp72, by ultrasound (US). Human promyelocytic leukemia HL-60 cells were exposed in suspension to US at 1, 3 and 10 MHz, as well as combinations of two of these frequencies. The ability of US to induce Hsp72 was tested for different frequencies, intensities and exposure times. In addition, the water bath temperature was varied from 30 to 36°C. The Hsp72 protein expression was determined 4 and 24 h after treatment. We found that the amount of Hsp72 increased with increasing US frequency, reaching its highest level of about 1800%, induced by 10 MHz. After increasing the temperature of the water bath, the amount of Hsp72 in the treated cells was also increased, whereas no induction was observed at 30°C. For all treatment conditions, ultrasound of 1 MHz was unable to significantly induce Hsp72. At 10 MHz, the exposure time was varied from 0 to 20 min. We found that the induction of Hsp72 took place after 5 min of exposure. For a fixed level of absorbed US energy, the continuous regime, as well as a pulsation of 1:2 (5 ms on and 5 ms off) induced the same Hsp72 level. Pulsation of 1:5 (2 ms on and 8 ms off) and 1:10 (1 ms on and 9 ms off) did not show any effect. A single sonication of 20 min, as well as a fractionated sonication of two 10 min exposures induced the same level of Hsp72, whereas four exposures of 5 min reduced the Hsp72 level. At the optimum exposure conditions (10 MHz, 10 min), the concentration of other HSPs was also determined. Hsp27 showed no effect but Hsp32, Hsp40 and Hsp72 were induced. Taken together, these results suggest a synergistic interaction between heat and US. (E-mail: werner.sontag@ibg.fzk.de)

Gene expression analysis of human promyelocytic leukemia HL-60 cell differentiation and cytotoxicity induced by natural and synthetic retinoids

Aims This study analyzed gene expression profiles of human promyelocytic leukemia HL-60 cells treated with natural and synthetic retinoids ( ATRA, RII and R9158), in an attempt to investigate the structure–function relationship of the retinoids in inducing cell differentiation and cytotoxicity. Main methods Flow cytometry was used to determine cell cycle changes in HL-60 cells following treatment (1.0 μM) with natural and synthetic retinoids ( ATRA, RII and R9158), and cDNA microarrays were used to monitor the gene expression profiles of HL-60 cells treated with the various retinoids. Key findings Consistent with retinoid-induced cell differentiation, treatment with these three retinoids correlated with an increase in the percentage of cells arrested in the G1/G0 phase of the cell cycle. Microarray analysis showed upregulation of known differentiation genes, adhesion molecules, and the oxidase activation pathway following retinoid treatment. Differential expression of several genes was observed in HL-60 cells treated with the three retinoids. For example, tissue remodeling protein genes, ubiquitin genes, and signal transduction genes were highly expressed in ATRA- and R9158-treated HL-60 cells, but remained unchanged in HL-60 cells treated with RII. Significance The above findings suggest that the differentiation of HL-60 cells induced by the three retinoids occurs through similar pathways, and that there exists a structure–function relationship regarding retinoids and the induction of cell differentiation and cytotoxicity.

Ellagitannins from Terminalia calamansanai induced apoptosis in HL-60 cells

Terminalia calamansanai (Blanco) Rolf. (Combretaceae) is used medicinally as lithontriptic in Philippines. The 70% acetone extracts of T. calamansanai leaves inhibited the viability of human promyelocytic leukemia HL-60 cells. 1-α- O-Galloylpunicalagin, punicalagin, 2- O-galloylpunicalin, sanguiin H-4, and methyl gallate were the main components isolated from T. calamansanai with the IC 50 values of 65.2, 74.8, 42.2, 38.0 and >100 μM, respectively, for HL-60 cells. Apoptosis of HL-60 cells treated with 1-α- O-galloylpunicalagin, punicalagin, 2- O-galloylpunicalin, and sanguiin H-4 was noted by the appearance of a sub-G 1 peak in flow cytometric analysis and DNA fragmentation by gel electrophoresis. 2- O-Galloylpunicalin and sanguiin H-4 induced a decrease of the human poly(ADP-ribose)polymerase (PARP) cleavage-related procaspase-3 and elevated activity of caspase-3 in HL-60 cells, but not normal human peripheral blood mononuclear cells (PBMCs), suggesting that both compounds may be new candidates for drug development in the prevention and treatment of cancer.

Cytotoxic activity of sanguinarine and dihydrosanguinarine in human promyelocytic leukemia HL-60 cells

The benzo[ c]phenanthridine alkaloid sanguinarine has been studied for its antiproliferative activity in many cell types. Almost nothing however, is known about the cytotoxic effects of dihydrosanguinarine, a metabolite of sanguinarine. We compared the cytotoxicity of sanguinarine and dihydrosanguinarine in human leukemia HL-60 cells. Sanguinarine produced a dose-dependent decline in cell viability with IC 50 (inhibitor concentration required for 50% inhibition of cell viability) of 0.9 μM as determined by MTT assay after 4 h exposure. Dihydrosanguinarine showed much less cytotoxicity than sanguinarine: at the highest concentration tested (20 μM) and 24 h exposure, dihydrosanguinarine decreased viability only to 52%. Cytotoxic effects of both alkaloids were accompanied by activation of the intrinsic apoptotic pathway since we observed the dissipation of mitochondrial membrane potential, induction of caspase-9 and -3 activities, the appearance of sub-G 1 DNA and loss of plasma membrane asymmetry. This aside, sanguinarine also increased the activity of caspase-8. As shown by flow cytometry using annexin V/propidium iodide staining, 0.5 μM sanguinarine induced apoptosis while 1–4 μM sanguinarine caused necrotic cell death. In contrast, dihydrosanguinarine at concentrations from 5 μM induced primarily necrosis, whereas apoptosis occurred at 10 μM and above. We conclude that both alkaloids may cause, depending on the alkaloid concentration, both necrosis and apoptosis of HL-60 cells.

Contribution of stress-activated MAP kinases to nivalenol-caused cytotoxicity and interleukin-8 secretion in HL60 cells

To elucidate the molecular mechanism underlying the toxicity of the Fusarium mycotoxin nivalenol, we investigated the involvement of stress-activated MAP kinases (SAPKs; c-Jun Nterminal kinases (JNKs) and p38s) in nivalenol-caused cytotoxicity and interleukin (IL) -8 secretion in human promyelocytic leukemia HL60 cells. Nivalenol treatment for 24 h increased the phosphorylated (i.e., the active-form) JNKs with maximum effect at 1 μg/mL; when nivalenol was given at this concentration in a time-series experiment, phosphorylated JNK quantity peaked at 12 h and then decreased. Essentially the same results were obtained for phosphorylated (active-form) p38s. To elucidate the functions of SAPKs, we investigated the effects of the JNK-specific inhibitor SP600125 and the p38-specific inhibitor SB203580 on nivalenol-caused cytotoxicity and IL-8 secretion. Nivalenol hindered cell proliferation regardless of the presence or absence of SAPK-specific inhibitors. However, co-treatment with SAPK inhibitors reduced this effect, indicating that JNKs and p38s play roles in nivalenolassociated retardation of cell proliferation. SP600125 significantly reduced nivalenol-induced IL-8 secretion, indicating that JNKs contribute to this phenomenon. SB203580 moderately lessened nivalenol-elicited IL-8 secretion, however, the contribution of p38s to nivalenolinduced IL-8 secretion appears to be meaningful, because SB203580 alone markedly increased IL-8 secretion.

Indoleacetic Acid Falcarindiol Ester Induces Granulocytic Differentiation of the Human Leukemia Cell Line HL-60

Indoleacetic acid falcarindiol ester (compound 1) has previously been isolated and purified using an SiO2 column and ODS HPLC from an acetone extract of Japanese ivy (Hedera rhombea). Here we investigate the differentiation-inducing activity of compound 1 using the human promyelocytic leukemia HL-60 cell line. The effect of compound 1 on HL-60 cell viability and proliferation was determined at different treatment times using the 3-(4,5-dimethythiazol-2-yl)-2,5-diohenyl-2 H-tetrazolium bromide (MTT) assay and flow cytometry analysis. Also cell cycle kinetics were examined using propidium iodide staining of DNA. Cell differentiation was assessed by specific and non-specific esterase double staining assays, and by detection of the cell surface differentiation markers CD11b and CD14 using flow cytometry. The results showed HL-60 cell growth inhibition at 0.1 and 1.0 microg/mL compound 1, whereas 10 microg/mL was cytotoxic. The growth suppression induced by compound 1 was accompanied by G0/G1 phase arrest in the cell cycle at 1.0 microg/mL. Moreover, staining and immunochemical analysis indicated that compound 1 induced granulocytic differentiation in HL-60 cells. This is the first report describing granulocytic differentiation activity of a falcarindiol derived polyacetylenic compound on leukemia cells.

Pyrrospirones A and B, apoptosis inducers in HL-60 cells, from an endophytic fungus, Neonectria ramulariae Wollenw KS-246

Pyrrospirones A and B have been isolated from unpolished rice cultures of the endophytic fungus Neonectria ramulariae Wollenw KS-246. Their absolute stereostructures (1 and 2) were elucidated through spectroscopic methods using 1D and 2D NMR techniques and chemical transformations, including the modified Mosher’s method. The compounds exhibited cytotoxicity and induced apoptosis in human promyelocytic leukemia HL-60 cells.

Identification of Novel Endogenous Cytochrome P450 Arachidonate Metabolites with High Affinity for Cannabinoid Receptors

Arachidonic acid is an essential constituent of cell membranes that is esterified to the sn-2-position of glycerophospholipids and is released from selected lipid pools by phospholipase cleavage. The released arachidonic acid can be metabolized by three enzymatic pathways: the cyclooxygenase pathway forming prostaglandins and thromboxanes, the lipoxygenase pathway generating leukotrienes and lipoxins, and the cytochrome P450 (cP450) pathway producing epoxyeicosatrienoic acids and hydroxyeicosatetraenoic acids. The present study describes a novel group of cP450 epoxygenase-dependent metabolites of arachidonic acid, termed 2-epoxyeicosatrienoylglycerols (2-EG), including two regioisomers, 2-(11,12-epoxyeicosatrienoyl)glycerol (2-11,12-EG) and 2-(14,15-epoxyeicosatrienoyl)glycerol (2-14,15-EG), which are both produced in the kidney and spleen, whereas 2-11,12-EG is also detected in the brain. Both 2-11,12-EG and 2-14,15-EG activated the two cannabinoid (CB) receptor subtypes, CB1 and CB2, with high affinity and elicited biological responses in cultured cells expressing CB receptors and in intact animals. In contrast, the parental arachidonic acid and epoxyeicosatrienoic acids failed to activate CB1 or CB2 receptors. Thus, these cP450 epoxygenase-dependent metabolites are a novel class of endogenously produced, biologically active lipid mediators with the characteristics of endocannabinoids. This is the first evidence of a cytochrome P450-dependent arachidonate metabolite that can activate G-protein-coupled cell membrane receptors and suggests a functional link between the cytochrome P450 enzyme system and the endocannabinoid system.

Smenospongine, a Sesquiterpene Aminoquinone from Marine Sponge, Induces G1 Arrest or Apoptosis in Different Leukemia Cells

Smenospongine, a sesquiterpene aminoquinone isolated from the marine sponge Dactylospongia elegans, was previously reported by us to induce erythroid differentiation and G1 phase arrest of K562 chronic myelogenous leukemia cells. In this study, we investigated the effect of smenospongine on the cell cycles of other leukemia cells, including HL60 human acute promyelocytic leukemia cells and U937 human histiocytic lymphoma cells by flow cytometric analysis. Smenospongine induced apoptosis dose-dependently in HL60 and U937 cells. The smenospongine treatment increased expression of p21 and inhibited phosphorylation of Rb in K562 cells, suggesting the p21-Rb pathway play an important role in G1 arrest in K562 cells. However, the p21 promoter was not activated by the smenospongine treatment based on a luciferase assay using the transfected K562 cells. Smenospongine might induce p21 expression via another mechanism than transactivation of p21 promoter.

The protozoan toxin climacostol inhibits growth and induces apoptosis of human tumor cell lines

Climacostol (5-( Z)-non-2-enyl-benzene-1,3-diol) is a natural toxin isolated from the freshwater ciliated protozoan Climacostomum virens and belongs to the group of resorcinolic lipids, compounds that show antimicrobial, antiparasitic and antitumor activities. We investigated the cytotoxic activity of the chemically synthesized toxin on: (1) human tumor squamous carcinoma A431 cells, (2) human promyelocytic leukaemia HL60 cells, and (3) human non-tumor endothelial EA.hy926 cells. The results showed that climacostol effectively inhibited the growth of tumor cell lines in a dose-dependent manner by inducing programmed cell death, with non-tumor cells proving significantly more resistant to the toxin.