Induction of the monocytic differentiation of myeloid leukaemia cells by cotylenin A, a plant growth regulator

Talaromynoids A-E: Five New Fusicoccane Diterpenoids from the Endophytic Fungus Talaromyces sp. DC-26

Talaromynoids A-E (1-5), five new fusicoccane diterpenoids, were obtained from the endophytic fungus Talaromyces sp. DC-26, which was isolated from a wild leech. Talaromynoid A (1) represents the first fusicoccane diterpenoid bearing an unexpected 5-7-5 tricyclic ring system, which is possibly derived from normal 5-8-5 ones by ring contraction. Talaromynoid E (5) is characterized by an unusual oxygen bridge between C-1 and C-8 that establishes the eight-membered ring B to be a 9-oxo-bicyclo[3.3.1]nonane. Structures of 1-5 with absolute configurations were determined by extensive NMR spectral analyses, electronic circular dichroism (ECD) calculations, X-ray diffraction analyses, and acid hydrolysis.

Semisynthesis and biological evaluation of a cotylenin A mimic derived from fusicoccin A

In an effort to overcome the unavailability of cotylenin A (CN A), an anticancer agent and a stabilizer of protein-protein interactions (PPIs) mediated by 14-3-3 proteins, ISIR-050 was designed as a CN A mimic. The synthesis was accomplished via a semisynthetic approach starting from fusicoccin A. ISIR-050 showed interferon-α (IFNα)-dependent growth inhibitory activity and a PPI stabilization effect similar to those of CN A. The biochemical analysis suggested that ISIR-050 and CN A induce the same pharmacological response to IFNα-treated cancer cells and that 14-3-3 proteins play a role in the mode of action.

Antipsychotic dopamine receptor antagonists, cancer, and cancer stem cells

Cancer is one of the deadliest diseases in the world. Despite extensive studies, treating metastatic cancers remains challenging. Years of research have linked a rare set of cells known as cancer stem cells (CSCs) to drug resistance, leading to the suggestion that eradication of CSCs might be an effective therapeutic strategy. However, few drug candidates are active against CSCs. New drug discovery is often a lengthy process. Drug screening has been advantageous in identifying drug candidates. Current understanding of cancer biology has revealed various clues to target cancer from different points of view. Many studies have found dopamine receptors (DRs) in various cancers. Therefore, DR antagonists have attracted a lot of attention in cancer research. Recently, a group of antipsychotic DR antagonists has been demonstrated to possess remarkable abilities to restrain and sensitize CSCs to existing chemotherapeutics by a process called differentiation approach. In this review, we will describe current aspects of CSC-targeting therapeutics, antipsychotic DR antagonists, and their extraordinary abilities to fight cancer.

Combined treatment with cotylenin A and phenethyl isothiocyanate induces strong antitumor activity mainly through the induction of ferroptotic cell death in human pancreatic cancer cells

The treatment of pancreatic cancer, one of the most aggressive gastrointestinal tract malignancies, with current chemotherapeutic drugs has had limited success due to its chemoresistance and poor prognosis. Therefore, the development of new drugs or effective combination therapies is urgently needed. Cotylenin A (CN-A) (a plant growth regulator) is a potent inducer of differentiation in myeloid leukemia cells and exhibits potent antitumor activities in several cancer cell lines. In the present study, we demonstrated that CN-A and phenethyl isothiocyanate (PEITC), an inducer of reactive oxygen species (ROS) and a dietary anticarcinogenic compound, synergistically inhibited the proliferation of MIAPaCa-2, PANC-1 and gemcitabine-resistant PANC-1 cells. A combined treatment with CN-A and PEITC also effectively inhibited the anchorage-independent growth of these cancer cells. The combined treatment with CN-A and PEITC strongly induced cell death within 1 day at concentrations at which CN-A or PEITC alone did not affect cell viability. A combined treatment with synthetic CN-A derivatives (ISIR-005 and ISIR-042) or fusicoccin J (CN-A-related natural product) and PEITC did not have synergistic effects on cell death. The combined treatment with CN-A and PEITC synergistically induced the generation of ROS. Antioxidants (N-acetylcysteine and trolox), ferroptosis inhibitors (ferrostatin-1 and liproxstatin), and the lysosomal iron chelator deferoxamine canceled the synergistic cell death. Apoptosis inhibitors (Z-VAD-FMK and Q-VD-OPH) and the necrosis inhibitor necrostatin-1s did not inhibit synergistic cell death. Autophagy inhibitors (3-metyladenine and chloroquine) partially prevented cell death. These results show that synergistic cell death induced by the combined treatment with CN-A and PEITC is mainly due to the induction of ferroptosis. Therefore, the combination of CN-A and PEITC has potential as a novel therapeutic strategy against pancreatic cancer.

Vitamin K2 and cotylenin A synergistically induce monocytic differentiation and growth arrest along with the suppression of c-MYC expression and induction of cyclin G2 expression in human leukemia HL-60 cells

Although all-trans retinoic acid (ATRA) is a standard and effective drug used for differentiation therapy in acute promyelocytic leukemia, ATRA-resistant leukemia cells ultimately emerge during this treatment. Therefore, the development of new drugs or effective combination therapy is urgently needed. We demonstrate that the combined treatment of vitamin K2 and cotylenin A synergistically induced monocytic differentiation in HL-60 cells. This combined treatment also synergistically induced NBT-reducing activity and non-specific esterase-positive cells as well as morphological changes to monocyte/macrophage-like cells. Vitamin K2 and cotylenin A cooperatively inhibited the proliferation of HL-60 cells in short-term and long-term cultures. This treatment also induced growth arrest at the G1 phase. Although 5 µg/ml cotylenin A or 5 µM vitamin K2 alone reduced c-MYC gene expression in HL-60 cells to approximately 45% or 80% that of control cells, respectively, the combined treatment almost completely suppressed c-MYC gene expression. We also demonstrated that the combined treatment of vitamin K2 and cotylenin A synergistically induced the expression of cyclin G2, which had a positive effect on the promotion and maintenance of cell cycle arrest. These results suggest that the combination of vitamin K2 and cotylenin A has therapeutic value in the treatment of acute myeloid leukemia.

Synergistic combination therapy with cotylenin A and vincristine in multiple myeloma models

Multiple myeloma is a malignant proliferative disease of plasma cells in the bone marrow and remains largely incurable. Cotylenin A, a fusicoccane diterpene glycoside with a complex sugar moiety, was isolated as a plant-growth regulator. Cotylenin A has been shown to inhibit the growth of various cancer cells. Herein, we examined the anti-myeloma effects of cotylenin A using five human myeloma cell lines (RPMI-8226, KMS-11, KMS-26, KMS-12 PE and KMS-12 BM) and xenografts in immunodeficient mice. Cotylenin A and vincristine synergistically inhibited the growth and induced apoptosis in myeloma cells. While other microtubule-disturbing agents also showed co-operative effects with cotylenin A, other anticancer agents, such as doxorubicin, cisplatin, camptothecin, methotrexate, gemcitabine and 5-fluorouracil, did not show such co-operation with cotylenin A. These differences might be attributed to the effects on autophagic responses. Combined treatment with cotylenin A and vincristine induced autophagy (formation of LC3-II and degradation of p62 protein). However, doxorubicin did not enhance the autophagy induced by cotylenin A. A colony-forming assay indicated that the combined treatment with cotylenin A and vincristine more effectively suppressed the formation of large colonies, which have higher self-renewal activity than vincristine alone. Expression of pluripotency-associated transcription factor Sox2 mRNA in RPMI-8226 myeloma cells was significantly suppressed by treatment with cotylenin A. Combined treatment with cotylenin A and vincristine significantly inhibited the growth of KMS-26 myeloma cells as xenografts. Our results suggest that the combination of cotylenin A and vincristine may have therapeutic value. Recently, it was reported that cotylenin A modulates the 14-3-3 intracellular signaling pathway. The 14-3-3 proteins may be novel targets in treating myeloma. However, our study could not explain how the sensitization to vincristine is related to the effects of cotylenin A on the 14-3-3 signaling pathway and further studies will be needed.

Cotylenin A and arsenic trioxide cooperatively suppress cell proliferation and cell invasion activity in human breast cancer cells

Arsenic trioxide (ATO) is an approved treatment for acute promyelocytic leukemia (APL). It has also shown potential for treatment of multiple myeloma and various solid tumors including breast cancer. The requirement of high, toxic concentrations for the induction of apoptosis in non-APL and solid tumor cells is a major limitation for its use in other hematological malignancies and solid tumors. We have examined whether inducers of differentiation of leukemia cells can control the growth of solid tumor cells. In the present study, we found that cotylenin A, a plant growth regulator and a potent inducer of differentiation in myeloid leukemia cells, significantly potentiated both ATO-induced inhibition of cell growth in a liquid culture, and ATO-induced inhibition of anchorage-independent growth in a semi-solid culture in human breast cancer MCF-7 and MDA-MB-231 cells. ISIR-005 (a synthetic cotylenin A-derivative) was also able to enhance ATO-induced growth inhibition. The combined treatment with cotylenin A and ATO induced cleaved caspase-7 in MCF-7 cells at the concentrations which ATO alone scarcely induced and cotylenin A alone only weakly induced. Expression of survivin in MCF-7 cells was markedly decreased with the presence of both cotylenin A and ATO, although the expression of survivin was only slightly decreased by cotylenin A or ATO alone. The pretreatment with N-acetylcysteine significantly reduced the combination treatment-induced cell growth inhibition. These data suggest that induction of cleaved caspase-7, inhibition of survivin and oxidative responses are important events in the corporative inhibition in the growth of MCF-7 cells induced by both cotylenin A and ATO. Furthermore, we found that the combined treatment with cotylenin A and ATO also could be effective in suppressing the invasive capacity of MDA-MB-231 cells determined with the impedance-based xCELLigence Real-Time Cell Analysis technology. These results suggest that cotylenin A is an attractive enhancer for the ATO-induced anticancer activities in human breast cancer.

Cotylenin A, a new differentiation inducer, and rapamycin cooperatively inhibit growth of cancer cells through induction of cyclin G2

Cotylenin A, a plant growth regulator, and rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), are potent inducers of differentiation of myeloid leukemia cells. Recently, we found that cotylenin A and rapamycin effectively inhibited the proliferation of several human breast cancer cell lines including MCF-7. Herein, we demonstrate that cotylenin A and rapamycin rapidly and markedly induced the cyclin G2 gene expression in several cancer cells including MCF-7 cells. The growth arrest of the MCF-7 cells at the G1 phase, induced by the treatment with cotylenin A and rapamycin or the culture in low serum medium, markedly induced the cyclin G2 gene expression. Anticancer drugs including doxorubicin, etoposide and 5-fluorouracil also induced cyclin G2 expression during induction of growth arrest of the MCF-7 cell at the G1 phase or G2/M phase. Ectopically inducible cyclin G2 expression potently inhibited the proliferation of MCF-7 cells. Furthermore, cyclin G2 knockdown induced by cyclin G2 small interfering RNA markedly reduced the potency of cotylenin A plus rapamycin to induce growth inhibition. Taken together, our results suggest that cotylenin A and rapamycin induce inhibition of cancer cell growth through the induction of cyclin G2.

Induction of differentiation of myeloid leukemia cells in primary culture in response to lithocholic acid acetate, a bile acid derivative, and cooperative effects with another differentiation inducer, cotylenin A

Lithocholic acid (LCA) acetate induced the differentiation of human leukemia cells. Treatment with a combination of LCA acetate and cotylenin A, an inducer of the differentiation of leukemia cells, was more effective than that with LCA acetate or cotylenin A alone at inducing monocytic differentiation. LCA acetate activated mitogen-activated protein kinase (MAPK) before inducing differentiation. Cotylenin A did not activate MAPK, suggesting that cotylenin A has a different mode of action. The cooperative effects of LCA acetate and cotylenin A on inducing differentiation were, at least partly, due to the enhancement of LCA acetate-induced MAPK activation by cotylenin A.

Cotylenin A-induced differentiation is independent of the transforming growth factor-beta signaling system in human myeloid leukemia HL-60 cells

Cotylenin A, which has been isolated as a plant growth regulator, potently induces the differentiation of human myeloid leukemia cells. Treatment of HL-60 cells with a combination of transforming growth factor (TGF)-beta and 1alpha, 25-dihydroxyvitamin D(3) (VD3) resulted in increased differentiation compared to separate treatments, but TGF-beta did not affect the cotylenin A-induced differentiation of HL-60 cells. It is possible that the signal transduction pathway used by cotylenin A for inducing the differentiation of leukemia cells is the same as that used by TGF-beta. However, cotylenin A did not affect the expression of TGF superfamily or Smad genes in HL-60 cells. Treatment with neutralizing anti-TGF-beta antibody or an inhibitor of TGF-beta signaling did not inhibit cotylenin A-induced differentiation, although VD3-induced differentiation was significantly suppressed by these treatments. The subcellular distribution of Smad3 was also unaffected by cotylenin A. These results suggest that the cotylenin A-induced differentiation of leukemia cells is independent of the TGF-beta signaling system, although TGF-beta acts as an autocrine mediator of the growth arrest and differentiation of leukemia cells induced by VD3 and other inducers.

Preparation, biological activity and endogenous occurrence of N6-benzyladenosines

Cytokinin activity of forty-eight 6-benzyladenosine derivatives at both the receptor and cellular levels as well as their anticancer properties were compared in various in vitro assays. The compounds were prepared by the condensation of 6-chloropurine riboside with corresponding substituted benzylamines and characterized by standard collection of physico-chemical methods. The majority of synthesized derivatives exhibited high activity in all three of the cytokinin bioassays used (tobacco callus, wheat leaf senescence and Amaranthus bioassay). The highest activities were observed in the senescence bioassay. For several of the compounds tested, significant differences in activity were found between the bioassays used, indicating that diverse recognition systems may operate. This suggests that it may be possible to modulate particular cytokinin-dependent processes with specific compounds. In contrast to their high activity in bioassays, the tested compounds were recognized with only very low sensitivity in both Arabidopsis thaliana AHK3 and AHK4 receptor assays. The prepared derivatives were also investigated for their antiproliferative properties on cancer and normal cell lines. Several of them showed very strong cytotoxic activity against various cancer cell lines. On the other hand, they were not cytotoxic for normal murine fibroblast (NIH/3T3) cell line. This anticancer activity of cytokinin ribosides may be important, given that several of them occur as endogenous compounds in different organisms.

Effects of combined treatment with rapamycin and cotylenin A, a novel differentiation-inducing agent, on human breast carcinoma MCF-7 cells and xenografts

INTRODUCTION

Rapamycin, an inhibitor of the serine/threonine kinase target of rapamycin, induces G1 arrest and/or apoptosis. Although rapamycin and its analogues are attractive candidates for cancer therapy, their sensitivities with respect to growth inhibition differ markedly among various cancer cells. Using human breast carcinoma cell line MCF-7 as an experimental model system, we examined the growth-inhibitory effects of combinations of various agents and rapamycin to find the agent that most potently enhances the growth-inhibitory effect of rapamycin.

METHOD

We evaluated the growth-inhibitory effect of rapamycin plus various agents, including cotylenin A (a novel inducer of differentiation of myeloid leukaemia cells) to MCF-7 cells, using either MTT assay or trypan blue dye exclusion test. The cell cycle was analyzed using propidium iodide-stained nuclei. Expressions of several genes in MCF-7 cells with rapamycin plus cotylenin A were studied using cDNA microarray analysis and RT-PCR. The in vitro results of MCF-7 cells treated with rapamycin plus cotylenin A were further confirmed in vivo in a mouse xenograft model.

RESULTS

We found that the sensitivity of rapamycin to MCF-7 cells was markedly affected by cotylenin A. This treatment induced growth arrest of the cells at the G1 phase, rather than apoptosis, and induced senescence-associated beta-galactosidase activity. We examined the gene expression profiles associated with exposure to rapamycin and cotylenin A using cDNA microarrays. We found that expressions of cyclin G2, transforming growth factor-beta-induced 68 kDa protein, BCL2-interacting killer, and growth factor receptor-bound 7 were markedly induced in MCF-7 cells treated with rapamycin plus cotylenin A. Furthermore, combined treatment with rapamycin and cotylenin A significantly inhibited the growth of MCF-7 cells as xenografts, without apparent adverse effects.

CONCLUSION

Rapamycin and cotylenin A cooperatively induced growth arrest in breast carcinoma MCF-7 cells in vitro, and treatment with rapamycin and cotylenin A combined more strongly inhibited the growth of MCF-7 cells as xenografts in vivo than treatment with rapamycin or cotylenin A alone, suggesting that this combination may have therapeutic value in treating breast cancer. We also identified several genes that were markedly modulated in MCF-7 cells treated with rapamycin plus cotylenin A.

Immediate up-regulation of the calcium-binding protein S100P and its involvement in the cytokinin-induced differentiation of human myeloid leukemia cells

Cytokinins are important purine derivatives that act as redifferentiation-inducing hormones to control many processes in plants. Cytokinins such as isopentenyladenine (IPA) and kinetin are very effective at inducing the granulocytic differentiation of human myeloid leukemia HL-60 cells. We examined the gene expression profiles associated with exposure to IPA using cDNA microarrays and compared the results with those obtained with other inducers of differentiation, such as all-trans retinoic acid (ATRA), 1 alpha,25-dihydroxyvitamin D3 (VD3) and cotylenin A (CN-A). Many genes were up-regulated, and only a small fraction were down-regulated, upon exposure to the inducers. IPA and CN-A, but not ATRA or VD3, immediately induced the expression of mRNA for the calcium-binding protein S100P. The up-regulation of S100P was confirmed at the protein expression level. We also examined the expression of other S100 proteins, including S100A8, S100A9 and S100A12, and found that IPA preferentially up-regulated S100P at the early stages of differentiation. IPA-induced differentiation of HL-60 cells was suppressed by treatment with antisense oligonucleotides against S100P, suggesting that S100P plays an important role in cell differentiation.

Induction of CCAAT/enhancer binding protein-delta by cytokinins, but not by retinoic acid, during granulocytic differentiation of human myeloid leukaemia cells

Cytokinins, purine derivatives that act as hormones to control many processes in plants, are very effective at inducing the granulocytic differentiation of human myeloid leukaemia cells. Isopentenyladenine (IPA), a potent cytokinin, significantly induced the expression of CCAAT/enhancer-binding protein (C/EBP)delta, but not C/EBP alpha protein, whereas all-trans retinoic acid, a well-known inducer of granulocytic differentiation, induced C/EBP alpha but not C/EBP delta protein. Antisense oligonucleotide for C/EBP delta, but not C/EBP alpha or C/EBP beta, effectively suppressed IPA-induced differentiation, suggesting that the expression of C/EBP delta protein is necessary for cytokinin-induced differentiation. Although C/EBP alpha is known to be crucial for granulocytic differentiation, the function of C/EBP delta has not been well documented in the regulation of haematopoiesis. The role of C/EBP delta in the granulocytic differentiation of myeloid leukaemia cells is discussed.

Treatment of human promyelocytic leukemia in the SCID mouse model with cotylenin A, an inducer of myelomonocytic differentiation of leukemia cells

Cotylenin A has differentiation-inducing activity in human myeloid leukemia cell lines and leukemic cells that were freshly isolated from acute myeloid leukemia (AML) patients in primary culture. Injection of the human promyelocytic leukemia cell line NB4 into SCID mice resulted in the death of all mice due to leukemia. Administration of cotylenin A significantly prolonged the survival of mice inoculated with NB4 cells. In an in vivo analysis, cotylenin A induced the differentiation of leukemia cells in a retinoid-resistant leukemia model. Cotylenin A may be useful for differentiation therapy of retinoid-resistant leukemia.

The catalytic DNA topoisomerase II inhibitor ICRF-193 and all-trans retinoic acid cooperatively induce granulocytic differentiation of acute promyelocytic leukemia cells: candidate drugs for chemo-differentiation therapy against acute promyelocytic leukemia

OBJECTIVE

Although all-trans retinoic acid (ATRA) can bring about complete remission of acute promyelocytic leukemia (APL), the incidence of early recurrence is considerably high. Thus, chemotherapeutic agents, such as anthracycline agents or cytosine arabinoside (AraC), are generally co-administered with ATRA. The therapeutic outcome of APL patients has significantly improved by chemo-differentiation therapy. Late-phase toxicities, such as cardiotoxicity and secondary carcinogenesis, are becoming clinically important. Therefore, we must identify the most suitable chemotherapeutic agents for the treatment of APL.

METHODS

We examined the effects of ICRF-193 and several other anticancer drugs on the growth and differentiation of APL cell lines (NB4 and HT-93) and other myeloid leukemia cell lines (HL-60 and U937).

RESULTS

If anticancer agents were available that not only inhibited the proliferation of APL cells but also induced their differentiation, they would be very useful for the treatment of APL. DNR slightly induced the differentiation of APL cells. On the other hand, other DNA topoisomerase II inhibitors, such as ICRF-154 and ICRF-193, significantly induced the differentiation of APL cell lines and leukemia cells freshly isolated from APL patients. These drugs effectively cooperated with ATRA in inhibiting the growth and inducing the differentiation of APL cells, whereas DNR did not. The incidence of cardiotoxicity and secondary carcinogenesis associated with ICRF-193 are much lower than that with DNR.

CONCLUSION

These results suggest that ICRF-193 may be useful in the treatment of patients with APL.

Differentiation of human myeloid leukemia cells by plant redifferentiation-inducing hormones

Although differentiation therapy for patients with acute promyelocytic leukemia (APL) using all-trans retinoic acid (ATRA) has now been established, acute myeloid leukemia (AML) patients with other than APL only show a limited clinical response to ATRA. We must consider novel therapeutic drugs against other AML to develop a differentiation therapy for leukemia. Regulators that play an important role in the differentiation and development of plants may also affect the differentiation of human leukemia cells through a common signal transduction system, and might be clinically useful for treating AML. Cytokinins are important purine derivatives that serve as hormones that control many processes in plants. Cytokinins such as kinetin, isopentenyladenine (IPA) and benzyladenine were very effective at inducing nitroblue tetrazolium (NBT) reduction and morphological changes in human myeloid leukemia cells into mature granulocytes. On the other hand, cytokinin ribosides such as kinetin riboside, isopentenyladenosine (IPAR) and benzyladenine riboside were the most potent for inhibiting growth and inducing apoptosis. When the cells were incubated with cytokinin ribosides in the presence of an O2- scavenger, antioxidant or caspase inhibitor, apoptosis was significantly reduced and differentiation was greatly enhanced. These results suggest that both cytokinins and cytokinin ribosides can induce the granulocytic differentiation of HL-60 cells, but cytokinin ribosides also induce apoptosis prior to differentiation. Cotylenin A has been isolated as a plant growth regulator exhibits cytokinin-like activity. Although it has a different structure than cytokinins, it also induces the differentiation of human myeloid leukemia cells. These results suggest that there is an association between the action of plant redifferentiation-inducing hormones and the mechanism of the differentiation of human leukemia cells.

Cotylenin A--a plant growth regulator as a differentiation-inducing agent against myeloid leukemia

Acute myeloid leukemia (AML) is characterized by the arrest of differentiation leading to the accumulation of immature cells. This maturation arrest can be reversed by certain agents. Although differentiation therapy for patients with acute promyelocytic leukemia (APL) using all-trans retinoic acid (ATRA) has been established, the clinical response of AML patients other than those with APL to ATRA is limited. We must consider novel therapeutic drugs against other forms of AML for the development of a differentiation therapy for leukemia. Regulators that play an important role in the differentiation and development of plants or invertebrates may also affect the differentiation of human leukemia cells through a common signal transduction system, and might be clinically useful for treating AML. Cotylenin A, a plant growth regulator, is a potent and novel inducer of the monocytic differentiation of human myeloid leukemia cell lines and leukemia cells freshly isolated from AML patients.

Differentiation of human acute myeloid leukaemia cells in primary culture in response to cotylenin A, a plant growth regulator

Cotylenin A, which has a diterpenoid tricarbocyclic skeleton, has been isolated as a plant growth regulator, has been shown to affect several physiological processes of higher plants and have differentiation-inducing activity in several myeloid leukaemia cell lines. We examined the effect of cotylenin A on the differentiation of leukaemic cells that were freshly isolated from acute myeloid leukaemia (AML) patients in primary culture. Cotylenin A significantly stimulated both functional and morphological differentiation of leukaemia cells in 9 out of 12 cases. This differentiation-inducing activity was more potent than those of all-trans retinoic acid and 1alpha,25-dihydroxyvitamin D3 (VD3). Treatment with a combination of cotylenin A and VD3 was more effective than cotylenin A or VD3 alone at inducing the monocytic differentiation of AML cells.