Differential involvement of protein kinase C in human promyelocytic leukemia cell differentiation enhanced by artemisinin

Artemisinin, a sesquiterpene lactone endoperoxide that exists in several medicinal plants, is a well-known anti-malarial agent. In this report, we investigated the effect of artemisinin on cellular differentiation in the human promyelocytic leukemia HL-60 cell culture system. Artemisinin markedly increased the degree of HL-60 leukemia cell differentiation when simultaneously combined with low doses of 1 alpha,25-dihydoxyvitamin D(3) [1,25-(OH)(2)D(3)] or all-trans retinoic acid (all-trans RA). Artemisinin by itself had very weak effects on the differentiation of HL-60 cells. Cytofluorometric analysis and cell morphologic studies indicated that artemisinin potentiated 1,25-(OH)(2)D(3)-induced cell differentiation predominantly into monocytes and all-trans RA-induced cell differentiation into granulocytes, respectively. Extracellular-regulated kinase (ERK) inhibitors markedly inhibited HL-60 cell differentiation induced by artemisinin in combination with 1,25-(OH)(2)D(3) or all-trans RA, whereas phosphatidylinositol 3-kinase (PI3-K) inhibitors did not. Particularly, protein kinase C (PKC) inhibitors inhibited HL-60 cell differentiation induced by artemisinin in combination with 1,25-(OH)(2)D(3) but not with all-trans RA. Artemisinin enhanced PKC activity and protein level of PKC beta I isoform in only 1,25-(OH)(2)D(3)-treated HL-60 cells. Taken together, these results indicate that artemisinin strongly enhanced 1,25-(OH)(2)D(3)- and all-trans RA-induced cell differentiation in which PKC is differentially involved in arteminisin-mediated enhancement of leukemia cell differentiation.     

Nargenicin enhances 1,25-dihydroxyvitamin D3- and all-trans retinoic acid-induced leukemia cell differentiation via PKCβI/MAPK pathways

A major goal in the treatment of acute myeloid leukemia (AML) is to achieve terminal differentiation and prevent drug resistance and side effects. Combined treatment with low doses of ATRA or 1,25-(OH)₂D₃ that do not induce toxicity with another drug is one useful strategy for the treatment of AML. Actinomycetes are the well known sources of antibiotics and bioactive molecules. Previously, we isolated nargenicin from the culture broth of an actinomycete isolate, Nocardia sp. CS682. In this study, we evaluated the effects of nargenicin on cellular differentiation in a human myeloid leukemia HL-60 cell system. Nargenicin inhibited cell proliferation and induced HL-60 cell differentiation when administered in combination with 1,25-(OH)₂D₃ or ATRA. In addition, western blot analyses and kinase inhibitor studies demonstrated that nargenicin primarily enhanced leukemia cell differentiation via PKCβ1/MAPK pathways. The results of this study indicate that nargenicin has the ability to induce differentiation and suggest that it may be useful for the treatment of neoplastic diseases.     

Synthesis of diacetoxy acetal derivatives of santonin and their enhancing effects on HL-60 leukemia cell differentiation

Several diacetoxy acetal analogues have been synthesized from santonin and assessed for their ability of inducing or enhancing the differentiation of human HL-60 leukemia cells. The compounds themselves had little effect on HL-60 cell differentiation. However, three analogues, 2a, 3a, and 5b, synergistically enhanced 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]-induced HL-60 cell differentiation when combined with 5 nM of dihydroxyvitamin D3 [1,25-(OH)2D3], a well-known differentiation inducer. Especially, the compound 5b profoundly enhanced the 1,25-(OH)2D3]-induced HL-60 cell differentiation.     

Induction of human promyelocytic leukemia HL-60 cell differentiation into monocytes by silibinin: involvement of protein kinase C

The effect of silibinin, an active component of Silybum marianum, on cellular differentiation was investigated in the human promyelocytic leukemia HL-60 cell culture system. Treatment of HL-60 cells with silibinin inhibited cellular proliferation and induced cellular differentiation in a dose-dependent manner. Cytofluorometric analysis and morphologic studies indicated that silibinin induced differentiation of HL-60 cells predominantly into monocytes. Importantly, strongly synergistic induction of differentiation into monocytes was observed when silibinin was combined with 5 nM 1alpha,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], a well-known differentiation inducer of HL-60 cells into the monocytic lineage. Silibinin enhanced protein kinase C (PKC) activity and increased protein levels of both PKCalpha and PKCbeta in 1,25-(OH)(2)D(3)-treated HL-60 cells. PKC and extracellular signal-regulated kinase (ERK) inhibitors significantly inhibited HL-60 cell differentiation induced by silibinin alone or in combination with 1,25-(OH)(2)D(3), indicating that PKC and ERK may be involved in silibinin-induced HL-60 cell differentiation.     

Synergistic induction of 1,25-dihydroxyvitamin D(3)- and all-trans-retinoic acid-induced differentiation of HL-60 leukemia cells by yomogin,a sesquiterpene lactone from Artemisia princeps

Many anti-inflammatory agents are known to significantly enhance the terminal differentiation of some cancer cells such as leukemia cells. In this study, the effect of yomogin, a eudesmane sesquiterpene lactone isolated from Artemisia princeps with anti-inflammatory activity, was investigated in human promyelocytic leukemia HL-60 cells. Yomogin by itself induced small increases in cell differentiation, with less than 19 % of the cells attaining a differentiated phenotype. Importantly, yomogin synergistically enhanced differentiation of HL-60 cells in a dose-dependent manner when combined with either 5 nM 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2) D(3)] or 50 nM all- trans retinoic acid (all- trans RA). Cytofluorometric analysis and morphologic studies indicated that the combinations of yomogin and 1,25-(OH)(2) D(3) stimulated differentiation to monocytes whereas the combinations of yomogin and all- trans RA stimulated differentiation to granulocytes. These results suggest that yomogin may be useful in combination with 1,25-(OH)(2) D(3) or all- trans-RA in the differentiation therapy for myeloid leukemias. Abbreviations. 1,25-(OH)(2) D(3) :1,25-dihydroxyvitamin D(3) FITC:fluorescein isothiocyanate NBT:nitroblue tetrazolium RA:retinoic acid PE:phytoerythrin     

Differential enhancement of leukaemia cell differentiation without elevation of intracellular calcium by plant-derived sesquiterpene lactone compounds

Background and purpose:

All-trans retinoic acid (ATRA) induces complete remission in a majority of acute promyelocytic leukaemia patients, but resistance of leukaemic cells to ATRA and its toxicity, such as hypercalcaemia, lead to a limitation of treatment. Therefore, combination therapies with differentiation-enhancing agents at non-toxic concentrations of ATRA may overcome its side effects. Here, we investigated the effect of plant-derived sesquiterpene lactone compounds and their underlying mechanisms in ATRA-induced differentiation of human leukaemia HL-60 cells.

Experimental approach:

HL-60 cells were treated with four sesquiterpene lactones (helenalin, costunolide, parthenolide and sclareolide) and cell differentiation was determined by NBT reduction, Giemsa and cytofluorometric analyses. Signalling pathways were assessed by western blotting, gel-shift assay and kinase activity determinations and intracellular calcium levels were determined using a calcium-specific fluorescent probe.

Key results:

Helenalin, costunolide and parthenolide, but not sclareolide, increased ATRA-induced HL-60 cell differentiation into a granulocytic lineage. Signalling kinases PKC and ERK were involved in the ATRA-induced differentiation enhanced by all of the effective sesquiterpene lactones, but JNK and PI3-K were involved in the ATRA-induced differentiation enhanced by costunolide and parthenolide. Enhancement of cell differentiation closely correlated with inhibition of NF-κB DNA-binding activity by all three effective compounds. Importantly, enhancement of differentiation induced by 50 nM ATRA by the sesquiterpene lactones was not accompanied by elevation of basal intracellular calcium concentrations.

Conclusions and implications:

These results indicate that plant-derived sesquiterpene lactones may enhance ATRA-mediated cell differentiation through distinct pathways.     

Interferon-alpha enhances artemisinin-induced differentiation of HL-60 leukemia cells via a PKC alpha/ERK pathway

Interferon-alpha (IFN-alpha) has been used in the treatment of several cancers, including chronic myeloid leukemia. Artemisinin, a sesquiterpene lactone endoperoxide that exists in several medicinal plants, is a well known anti-malarial agent. We previously reported that artemisinin by itself caused a relatively low level of HL-60 cell differentiation. In this study, we investigated the effects of IFN-alpha in combination with artemisinin on cell growth and differentiation in HL-60 leukemia cells. Combination of IFN-alpha and artemisinin synergistically induced the levels of leukemia cell differentiation, although IFN-alpha by itself did not affect cell proliferation and differentiation. The increased cell differentiation by IFN-alpha and artemisinin was significantly suppressed by the inhibitors for protein kinase C (PKC), extracellular signal-regulated kinase (ERK) and jun N-terminal kinase (JNK), but not by the inhibitors for phosphatidylinositol 3-kinase (PI3-K) and p38 mitogen-activated protein kinase (MAPK). Furthermore, co-treatment with IFN-alpha increased levels of PKC alpha and phosphorylated ERK. Taken together, these results indicate the enhancement of artemisinin-induced HL-60 cell differentiation by IFN-alpha through the activation of a PKC alpha/ERK signaling pathway, and suggest a possible use of IFN-alpha and artemisinin in the treatment of leukemic diseases.     

Capsaicin potentiates 1,25-dihydoxyvitamin D3- and all-trans retinoic acid-induced differentiation of human promyelocytic leukemia HL-60 cells.

Human promyelocytic leukemia HL-60 cells are differentiated into monocytic or granulocytic lineage when treated with 1,25-dihydroxyvitamin D₃ [1,25-(OH)₂D₃] or all-trans retinoic acid, respectively. In this study, the effect of capsaicin, an active component of the red pepper of the genus Capsocum, on cell differentiation was investigated in a HL-60 cell culture system. Treatment of HL-60 cells with 5–30 μg/ml capsaicin for 72 h inhibited cell proliferation and induced a small increase in cell differentiation. Interestingly, synergistic induction of HL-60 cell differentiation was observed when capsaicin was combined with either 5 nM 1,25-(OH)₂D₃ or 50 nM all-trans retinoic acid. Flow cytometric analysis indicated that combinations of 1,25-(OH)₂D₃ and capsaicin stimulated differentiation predominantly to monocytes whereas combinations of all-trans retinoic acid and capsaicin stimulated differentiation predominantly to granulocytes. Capsaicin enhanced protein kinase C activity in 1,25-(OH)₂D₃- and all-trans retinoic acid-treated HL-60 cells. In addition, inhibitors for protein kinase C [bisindolylmaleimide (GF-109203X), chelerythrine, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7)] and an inhibitor for extracellular signal-regulated kinase [2-(2′-amino-3′-methoxyphenyl)-oxanaphthalen-4-one (PD-098059)] significantly inhibited HL-60 cell differentiation induced by capsaicin in combination with either 1,25-(OH)₂D₃ or all-trans retinoic acid. These results indicate that capsaicin potentiates 1,25-(OH)₂D₃- or all-trans retinoic acid-induced HL-60 cell differentiation and that both protein kinase C and extracellular signal-regulated kinase are involved in the cell differentiation synergistically enhanced by capsaicin.     

Effects of vitamin D derivatives on soft tissue calcification in neonatal and calcium mobilization in adult rats

The activity of 18 vitamin D analogs on soft tissue calcification and growth impairment in neonatal rats and their effect on bone calcium mobilization, intestinal calcium absorption and binding to intestinal 1,25-dihydroxyvitamin D₃ receptors in adult rats were compared. Depending on the chemical modification of the vitamin D parent compounds, they could be separated into active and inactive analogs. Cholecalciferol and ergocalciferol were similarly active, but epimerization of ergocalciferol at carbon 23 caused loss of activity. Hexafluorination at carbon 26 and 27 and the introduction of a double bond at carbon 22 or 23 had no or little effect on the activity. The loss of activity was caused by the introduction of a triple bond at carbon 23 and by hydroxylation at carbon 23, 26 or 28. The differentiation of human promyelocytic leukemia cells (HL-60) induced by these derivatives was used as a parameter for antitumour activity. All six analogs, which markedly affected calcium metabolism, were highly active in HL-60 cells. However, at least three derivatives were highly active in the antitumour test but failed to induce hypercalcemia. Thus, these results indicate that it could be possible to develop medically useful vitamin D derivatives devoid of hypercalcemic side-effects.     

Costunolide induces differentiation of human leukemia HL-60 cells

Costunolide has been reported to be a cytotoxic and chemopreventive agent. This work investigated the mechanism of the antiproliferative effect of costunolide and determined that it induced differentiation of the human leukemia cell line HL-60. Costunolide exhibited a potent antiproliferative activity against HL-60 cells. It was also found to be a potent inducer of differentiation in human leukemia derived HL-60 cells through the examination of differentiation markers, as assessed by the reduction of nitroblue-tetrazolium, the increase in esterase activities and phagocytic activity, morphology change and the expression of CD14 and CD66b surface antigens. These results, accompanied by a decline in the expression of c-myc protein, suggest that costunolide induces differentiation of human leukemia cells to granulocytes and monocytes/macrophages lineage.     

Capsaicin potentiates 1,25-dihydoxyvitamin D3- and all-trans retinoic acid-induced differentiation of human promyelocytic leukemia HL-60 cells

Human promyelocytic leukemia HL-60 cells are differentiated into monocytic or granulocytic lineage when treated with 1,25-dihydroxyvitamin D₃ [1,25-(OH)₂D₃] or all-trans retinoic acid, respectively. In this study, the effect of capsaicin, an active component of the red pepper of the genus Capsocum, on cell differentiation was investigated in a HL-60 cell culture system. Treatment of HL-60 cells with 5–30 μg/ml capsaicin for 72 h inhibited cell proliferation and induced a small increase in cell differentiation. Interestingly, synergistic induction of HL-60 cell differentiation was observed when capsaicin was combined with either 5 nM 1,25-(OH)₂D₃ or 50 nM all-trans retinoic acid. Flow cytometric analysis indicated that combinations of 1,25-(OH)₂D₃ and capsaicin stimulated differentiation predominantly to monocytes whereas combinations of all-trans retinoic acid and capsaicin stimulated differentiation predominantly to granulocytes. Capsaicin enhanced protein kinase C activity in 1,25-(OH)₂D₃- and all-trans retinoic acid-treated HL-60 cells. In addition, inhibitors for protein kinase C [bisindolylmaleimide (GF-109203X), chelerythrine, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7)] and an inhibitor for extracellular signal-regulated kinase [2-(2′-amino-3′-methoxyphenyl)-oxanaphthalen-4-one (PD-098059)] significantly inhibited HL-60 cell differentiation induced by capsaicin in combination with either 1,25-(OH)₂D₃ or all-trans retinoic acid. These results indicate that capsaicin potentiates 1,25-(OH)₂D₃- or all-trans retinoic acid-induced HL-60 cell differentiation and that both protein kinase C and extracellular signal-regulated kinase are involved in the cell differentiation synergistically enhanced by capsaicin.     

Costunolide stimulates the function of osteoblastic MC3T3-E1 cells

The effect of costunolide on the function of osteoblastic MC3T3-E1 cells was studied. Costunolide significantly increased the growth of MC3T3-E1 cells and caused a significant elevation of alkaline phosphatase (ALP) activity, collagen content, and mineralization in the cells (P<0.05). The effect of costunolide in increasing cell growth was completely prevented by the presence of ICI182780, LY294002, PD98059, rotlerin, or glibenclamide, suggesting that the effect of costunolide might be partly mediated from estrogen receptor (ER), PI3K, ERK, protein kinase C (PKC) and mitochondrial ATP-sensitive K(+) channel. The effect of costunolide in increasing ALP activity was prevented by the presence of ICI182780, PD98059, SB203580, or rotrelin, suggesting that the effect of costunolide on ALP activity might be mediated from ER, ERK, p38, and PKC. The effect of costunolide in increasing collagen content was prevented by the presence of LY294002, PD98059, SB203580, SP600125, or rotrelin, suggesting that the effect of costunolide on collagen synthesis might be mediated from PI3K, ERK, p38, JNK, and PKC. Moreover, cotreatment of ICI182780 or LY294002 inhibited costunolide-mediated upregulation of mineralization, suggesting that the induction of mineralization by costunolide is associated with increased activation of ER and PI3K. Our data indicate that the enhancement of osteoblast function by costunolide may result in the prevention for osteoporosis.     

Metabolism of 26,26,26,27,27,27-F6-1alpha,25-dihydroxyvitamin D3 by CYP24: species-based difference between humans and rats

The compound 26,26,26,27,27,27-F(6)-1alpha,25(OH)(2)D(3) is a hexafluorinated analog of the active form of Vitamin D(3). The enhanced biological activity of F(6)-1alpha,25(OH)(2)D(3) is considered to be related to a decreased metabolic inactivation of the compound in target tissues such as the kidneys, small intestine, and bones. Our previous study demonstrated that CYP24 is responsible for the metabolism of F(6)-1alpha,25(OH)(2)D(3) in the target tissues. In this study, we compared the human and rat CYP24-dependent metabolism of F(6)-1alpha,25(OH)(2)D(3) by using the Escherichia coli expression system. In the recombinant E. coli cells expressing human CYP24, bovine adrenodoxin and NADPH-adrenodoxin reductase, F(6)-1alpha,25(OH)(2)D(3) was successively converted to F(6)-1alpha,23S,25(OH)(3)D(3), F(6)-23-oxo-1alpha,25(OH)(2)D(3), and the putative ether compound with the same molecular mass as F(6)-1alpha,25(OH)(2)D(3). The putative ether was not observed in the recombinant E. coli cells expressing rat CYP24. These results indicate species-based difference between human and rat CYP24 in the metabolism of F(6)-1alpha,25(OH)(2)D(3). In addition, the metabolite with a cleavage at the C(24)z.sbnd;C(25) bond of F(6)-1alpha,25(OH)(2)D(3) was detected as a minor metabolite in both human and rat CYP24. Although F(6)-1alpha,23S,25(OH)(3)D(3) and F(6)-23-oxo-1alpha,25(OH)(2)D(3) had a high affinity for Vitamin D receptor, the side-chain cleaved metabolite and the putative ether showed extremely low affinity for Vitamin D receptor. These findings indicate that human CYP24 has a dual pathway for metabolic inactivation of F(6)-1alpha,25(OH)(2)D(3) while rat CYP24 has only one pathway. Judging from the fact that metabolism of F(6)-1alpha,25(OH)(2)D(3) in rat CYP24-harboring E. coli cells is quite similar to that in the target tissues of rat, the metabolism seen in human CYP24-harboring E. coli cells appear to exhibit the same metabolism as in human target tissues. Thus, this recombinant system harboring human CYP24 appears quite useful for predicting the metabolism and efficacy of Vitamin D analogs in human target tissues before clinical trials.     

Structure-specific control of differentiation and apoptosis of human promyelocytic leukemia (HL-60) cells by A-ring diastereomers of 2-methyl- 1α,25-dihydroxyvitamin D3 and its 20-epimer

1α,25-Dihydroxyvitamin D₃ (1α,25(OH)₂D₃) has been shown to modulate not only proliferation and differentiation but also apoptosis of malignant cells, indicating that it would be useful for the treatment of hyperproliferative diseases such as cancer and psoriasis. Little information is available concerning structural motifs of the 1α,25(OH)₂D₃ molecule responsible for modulation of differentiation and apoptosis. We synthesized all possible A-ring diastereomers of the 2-methyl-1α,25(OH)₂D₃ and its 20-epimer and evaluated their biological activities in human promyelocytic leukemia (HL-60) cells. Surprisingly, the potent analogues could be clearly divided into two groups: (i) those bearing the 1α- and 3β-hydroxyl groups on the A-ring were potent inducers of differentiation and growth inhibitors of HL-60 cells and (ii) those bearing the 1β-hydroxyl group together with either 3α- or 3β-hydroxyl groups on the A-ring were potent stimulators of apoptosis in these cells. We have clearly identified for the first time the structural motifs on the basis of the stereochemistry of both hydroxyl groups at positions 1 and 3 of the A-ring of the 1α,25(OH)₂D₃ molecule responsible for the induction of differentiation and apoptosis of HL-60 cells. These findings provide useful information not only for structure–function studies of 1α,25(OH)₂D₃ analogues but also for the development of therapeutic agents for the treatment of leukemia and other cancers.     

Induction of human leukemia HL-60 cell differentiation via a PKC/ERK pathway by helenalin, a pseudoguainolide sesquiterpene lactone

Helenalin, a cell-permeable pseudoguainolide sesquiterpene lactone, is a potent anti-inflammatory agent that inhibits nuclear factor-kappa B (NF-kappa B) DNA binding activity. In this report, we investigated the effect of helenalin on cellular differentiation in the human promyelocytic leukemia HL-60 cell culture system. Helenalin by itself markedly induced HL-60 cell differentiation in a concentration-dependent manner. Cytofluorometric analysis and cell morphologic studies indicated that helenalin induced cell differentiation predominantly into granulocytes. Protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) inhibitors significantly inhibited HL-60 cell differentiation induced by helenalin, while p38 mitogen-activated protein kinase (MAPK) inhibitors did not. Moreover, helenalin enhanced PKC activity and protein level of PKC beta I and PKC beta II isoforms, and also increased the level of pERK in a concentration-dependent manner. In addition, the enhanced levels of cell differentiation closely correlated with the decreased levels of NF-kappa B binding activity by helenalin. These results indicate that PKC, ERK, and NF-kappa B may be involved in HL-60 cell differentiation induced by helenalin.