Induction of human promyelocytic leukemia HL-60 cell differentiation into monocytes by arsenic sulphide: Involvement of serine/threonine protein phosphatases

Pharmacology, Toxicology, and Rational Application of Cinnabar, Realgar, and Their Formulations

Ethnopharmacological Relevance. Mineral medicines are widely used traditional Chinese medicines with curative effects. These medicines are used for many refractory diseases. Aim of the Review. In this review, cinnabar (HgS) and realgar (As₂S₂) serve as examples of mineral medicines, and their pharmacology, therapeutic toxicity, use in traditional medicine mixtures, and research perspectives are discussed. Materials and Methods. A search was performed for the literature on cinnabar and realgar in PubMed, the Chinese Pharmacopeia, Google, and other sources. The search included studies using single herbs, traditional formulations, or novel dosage forms. Results. Cinnabar and cinnabar formulas exhibit good efficacy for sedation, sleep improvement, anxiety alleviation, and brain protection. However, previous studies on neurotransmitters have reached different conclusions, and detailed pharmacological mechanisms are lacking. Realgar and its formulas exert promising antitumor activity through regulation of cell cycle arrest, intrinsic and extrinsic apoptosis, induction of differentiation, autophagy, metabolic reprogramming, matrix metalloproteinase-9 (MMP-9) signaling, and reactive oxygen species (ROS) generation. In addition, realgar can be used to treat a variety of refractory diseases by regulating immunity and exerting antibacterial, antiviral, and other effects. However, the existing pharmacological research on the use of realgar for epidemic prevention is insufficient, and animal experiments and research at the cellular level are lacking. Inappropriate applications of cinnabar and realgar can cause toxicity, including neurotoxicity, liver toxicity, kidney toxicity, and genotoxicity. The toxicological mechanism is complex, and molecular-level research is limited. For clinical applications, theory and clinical experience must be combined to guide scientific and rational drug use and to achieve reduced toxicity and increased efficacy through the use of modern preparation methods or combined drugs. Notably, when cinnabar and realgar are used to treat targeted diseases, these agents have a bidirectional effect of “treatment” and “toxicity” on the central nervous system in pathological and normal states. The pharmacological and toxicological mechanisms need to be elucidated in greater detail in the future. Overall, systematic research is needed to provide a basis for better promotion of the rational use of cinnabar and realgar in the clinic. Conclusion. Mineral medicines are multicomponent, multiactivity, and multitargeted substances. The pharmacology and mechanisms of the toxicity and action of realgar and cinnabar are extremely complex. A number of Chinese medicinal preparations of realgar and cinnabar have demonstrated unique efficacy in the treatment of refractory diseases.

Enhanced antitumor activity of realgar mediated by milling it to nanosize

Realgar is a poorly water-soluble compound that exhibits poor bioavailability. To improve this, the authors reduced the particle size of realgar to nanoscale by high-energy ball milling and optimized the preparation process under which (realgar weight 40 g, milling time 9 hours, milling speed 38 Hz, milling temperature −20°C) realgar nanoparticles (NPs) with an average size of 78±8.3 nm were prepared. The average particle size of realgar was characterized by laser scattering, and its apparent shape was observed by transmission electron microscopy and scanning electron microscopy. The solubility of realgar was enhanced after milling until the particles were in the nanoscale region without altering its properties, as confirmed by a scanning electron microscopy energy-dispersive spectrometer. Realgar NPs had higher cytotoxicity on the selected cell lines, namely human breast cancer (MCF7), human hepatoma (HepG2), and human lung cancer (A549) cell lines, than coarse realgar. In addition, a pharmacokinetics study performed in rats indicated that the relative bioavailability of realgar NPs was 216.9% compared with coarse realgar; a biodistribution study performed in mice showed that after intragastric administration of realgar NPs, higher arsenic concentration was reached in the tumor, heart, liver, spleen, lung, and kidney compared with the administration of coarse realgar, as confirmed by inductively coupled plasma mass spectrometry to determine the concentration of arsenic. This study indicated that high-energy ball milling is an effective way to reduce the average particle size of realgar, and compared with coarse realgar, the cytotoxicity and bioavailability of realgar NPs were significantly improved.

Anticancer drugs from traditional toxic Chinese medicines

Many anticancer drugs are obtained from natural sources. Nature produces a variety of toxic compounds, which are often used as anticancer drugs. Up to now, there are at least 120 species of poisonous botanicals, animals and minerals, of which more than half have been found to possess significant anticancer properties. In spite of their clinical toxicity, they exhibit pharmacological effects and have been used as important traditional Chinese medicines for the different stages of cancer. The article reviews many structures such as alkaloids of Camptotheca acuminata, Catharanthus roseus and Cephalotaxus fortunei, lignans of Dysosma versipellis and Podophyllum emodi, ketones of Garcinia hanburyi, terpenoids of Mylabris and Ginkgo biloba, diterpenoids of Tripterygium wilfordii, Euphorbia fischeriana, Euphorbia lathyris, Euphorbia kansui, Daphne genkwa, Pseudolarix kaempferi and Brucea javanica, triterpenoids of Melia toosendan, steroids of Periploca sepium, Paris polyphylla and Venenum Bufonis, and arsenic compounds including Arsenicum and Realgar. By comparing their related phytochemistry, toxic effects and the recent advances in understanding the mechanisms of action, this review puts forward some ideals and examples about how to increase antitumour activity and/or reduce the side effects experienced with Chinese medicine.

The medicinal use of realgar (As₄S₄) and its recent development as an anticancer agent

ETHNOPHARMACOLOGICAL RELEVANCE

Arsenicals have been known as poisons and paradoxically as therapeutic agents. In the early 1970s, Chinese physicians from Harbin revived the medicinal use of arsenicals as anticancer agents. Notable success was observed in the treatment of acute promyelocytic leukemia (APL) with arsenic trioxide (ATO). The FDA approved ATO injection in the year 2000 for the treatment of APL. In contrast, the clinical use of the other arsenical, realgar (As₄S₄), is currently much less established, though it has also long been used in medical history. According to ancient medical records and recent findings in clinical trials, realgar was found as effective as ATO, but with relatively good oral safety profiles even on chronic administration. These give realgar an advantage over ATO in maintenance treatment. Though there is increasing understanding on the mechanisms of action and metabolic profiles of ATO, similar aspects of realgar are unclear to date.

MATERIALS AND METHODS

We outline the use of realgar in traditional medicines, especially in traditional Chinese medicines (TCM) from ancient times to present. The clinical and experimental observations on realgar as a therapeutic agent are described with an emphasis on those findings that may imply the rationale and future directions of realgar as a potential anticancer drug candidate.

RESULTS

There is an increasing understanding in the mechanisms of action of realgar as an antileukemic agent. However, there is still sparse information on its metabolism and toxicity profiles.

CONCLUSIONS

Realgar is poorly soluble in water. Recently, several types of realgar nanoparticles (NPs) have been developed. Some of these realgar NPs also possess the unique optical properties of quantum dots. The activities and bioavailability of realgar NPs are much influenced by their sizes, making realgar an interesting biomedical and pharmaceutical research candidate.

PP2A impaired activity is a common event in acute myeloid leukemia and its activation by forskolin has a potent anti-leukemic effect

Protein phosphatase 2A (PP2A) is a human tumor suppressor that inhibits cellular transformation by regulating the activity of several signaling proteins critical for malignant cell behavior. PP2A has been described as a potential therapeutic target in chronic myeloid leukemia, Philadelphia chromosome-positive acute lymphoblastic leukemia and B-cell chronic lymphocytic leukemia. Here, we show that PP2A inactivation is a recurrent event in acute myeloid leukemia (AML), and that restoration of PP2A phosphatase activity by treatment with forskolin in AML cells blocks proliferation, induces caspase-dependent apoptosis and affects AKT and ERK1/2 activity. Moreover, treatment with forskolin had an additive effect with Idarubicin and Ara-c, drugs used in standard induction therapy in AML patients. Analysis at protein level of the PP2A activation status in a series of patients with AML at diagnosis showed PP2A hyperphosphorylation in 78% of cases (29/37). In addition, we found that either deregulated expression of the endogenous PP2A inhibitors SET or CIP2A, overexpression of SETBP1, or downregulation of some PP2A subunits, might be contributing to PP2A inhibition in AML. In conclusion, our results show that PP2A inhibition is a common event in AML cells and that PP2A activators, such as forskolin or FTY720, could represent potential novel therapeutic targets in AML.

All-trans retinoic acid is capable of inducing folate receptor β expression in KG-1 cells

The high expression of folate receptor (FR) on cancer cells might be a potential target for cancer therapy. In this study, the FR-β expression and the modulation effect of all-trans retinoic acid (ATRA) in a number of cancer cell lines were analyzed. The gateway of ATRA activity on FR-β expression was further studied by a panel of retinoid activators and inhibitors. The results revealed that ATRA was capable of upregulating the expression of FR-β protein in KG-1 cells in a dosage-dependent manner, not in KG-1a, NB4, HL60, 293, L1210, JAR, and Hela cells. FR-β mRNA expression in KG-1 cells was higher when ATRA was present in culture medium at 10⁻⁶ mol/L for 5 days, and it went down to baseline when ATRA was removed from the medium, vice versa. The upregulation of FR-β expression in KG-1 cells by ATRA was not associated with cell proliferation and differentiation. In addition, activators of retinoid acid receptor (RAR)α and RARγ, CD336, and CD2781 also induced FR-β expression. The induction of FR-β expression by CD336 could be inhibited by RARγ antagonist CD2665; RARβ agonist CD-417 and CD-2314 as well as retinoid X receptor (RXR) agonist LG100364 could not induce FR-β expression. These results indicate that ATRA within a certain range of concentration could reversibly induce the expression of FR-β in a dosage- and cell type-dependent manner, and its action in KG-1 cells might be associated with the signal transduction of retinoid receptor RARα and RARγ, rather than RARβ and RXRs.

Arsenic in cancer treatment: challenges for application of realgar nanoparticles (a minireview)

While intensive efforts have been made for the treatment of cancer, this disease is still the second leading cause of death in many countries. Metastatic breast cancer, late-stage colon cancer, malignant melanoma, multiple myeloma, and other forms of cancer are still essentially incurable in most cases. Recent advances in genomic technologies have permitted the simultaneous evaluation of DNA sequence-based alterations together with copy number gains and losses. The requirement for a multi-targeting approach is the common theme that emerges from these studies. Therefore, the combination of new targeted biological and cytotoxic agents is currently under investigation in multimodal treatment regimens. Similarly, a combinational principle is applied in traditional Chinese medicine, as formulas consist of several types of medicinal herbs or minerals, in which one represents the principal component, and the others serve as adjuvant ones that assist the effects, or facilitate the delivery, of the principal component. In Western medicine, approximately 60 different arsenic preparations have been developed and used in pharmacological history. In traditional Chinese medicines, different forms of mineral arsenicals (orpiment—As₂S₃, realgar—As₄S₄, and arsenolite—arsenic trioxide, As₂O₃) are used, and realgar alone is included in 22 oral remedies that are recognized by the Chinese Pharmacopeia Committee (2005). It is known that a significant portion of some forms of mineral arsenicals is poorly absorbed into the body, and would be unavailable to cause systemic damage. This review primary focuses on the application of arsenic sulfide (realgar) for treatment of various forms of cancer in vitro and in vivo.

Anticancer effect of realgar nanoparticles on mouse melanoma skin cancer in vivo via transdermal drug delivery

Realgar has been used successfully to treat diseases for thousands of years, but its poor water solubility and high toxicity hampered its further medical uses. Here, we first applied transdermal drug delivery system to deliver realgar nanoparticles to investigate its anticancer effect and toxicity in vivo. In this study, MTT assay and flow cytometry analysis demonstrated that realgar significantly suppressed the proliferation and induced apoptosis of B16 melanoma cells in a dose-dependent manner. Transdermal penetration studies in vitro showed realgar nanoparticles could be delivered efficiently through skin. Tests on tumor-bearing C57BL/6 mice displayed that realgar could decrease the tumor volume markedly via transdermal drug delivery compared with the intraperitoneal administration and the control. Hematoxylin-eosin and immunohistochemical staining revealed that it could inhibit angiogenesis. The monitoring of the hepatic injury, body weight, feeding behavior, motor activity, and skin irritation of each animal indicated little toxicity of realgar to mice. The results demonstrated that realgar nanoparticles can be dermally delivered to achieve high efficacy against menaloma in vivo with low toxicity.

A systems biology understanding of the synergistic effects of arsenic sulfide and Imatinib in BCR/ABL-associated leukemia

In this study, we show that combined use of Imatinib (IM) and arsenic sulfide [As(4)S(4) (AS)] exerts more profound therapeutic effects in a BCR/ABL-positive mouse model of chronic myeloid leukemia (CML) than either drug as a single agent. A systematic analysis of dynamic changes of the proteome, phosphoproteome, and transcriptome in K562 cells after AS and/or IM treatment was performed to address the mechanisms underlying this synergy. Our data indicate that AS promotes the activities of the unfolded protein reaction (UPR) and ubiquitination pathway, which could form the biochemical basis for the pharmacological effects of this compound. In this CML model, AS targets BCR/ABL through the ubiquitination of key lysine residues, leading to its proteasomal degradation, whereas IM inhibits the PI3K/AKT/mTOR pathway. Combination of the 2 agents synergistically arrests the cell cycle, decreases activity of BCR/ABL, and leads to activation of intrinsic and extrinsic apoptosis pathways through complex modifications to both transcription and protein levels. Thus, these results suggest potential clinical benefits of IM/AS combination therapy for human CML.

Roles of PI3-K/Akt pathways in nanoparticle realgar powders-induced apoptosis in U937 cells

AIM

To study the mechanism by which nanoparticle realgar powders (NRP) induce human histocytic lymphoma U937 cell apoptosis.

METHODS

After the U937 cells were treated with various doses of NRP, the viability of the NRP-induced U937 cells was detected by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Granular apoptotic bodies with membrane blebbing and condensed nuclei were observed by fluorescence microscopy. The apoptotic ratio induced by NRP was measured by lactate dehydrogenase (LDH) activity-based assay. Caspase-3 and the expressions of Akt, p-Akt, a nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase (SIRT1), p53, and p-p53 were detected by Western blot analysis.

RESULTS

The growth-inhibitory activity of NRP for U937 cells was in a time- and dose-dependent manner. After treatment with various concentrations of NRP for 24 h, the majority of U937 cells underwent apoptosis as measured by LDH assay. In the presence of NRP, wortmannin, the inhibitor of phosphoinositide 3-kinase (PI3-K), and Akt inhibitor KP372-1 augmented the NRP-induced cell apoptosis. When the U937 cells were treated with NRP for the indicated time periods, procaspase-3 was gradually degraded and the activated caspase-3 was significantly increased. The expressions of anti-apoptotic proteins Akt and p-Akt were downregulated. Importantly, the inhibition of SIRT1 contributed to the activation of p53 and the inactivation of the PI3-K/Akt signaling pathway increased the expression of the p53 protein and downregulated the SIRT1 protein expression.

CONCLUSION

The PI3-K/Akt signaling pathway plays an important role in NRP-induced U937 cell apoptosis. The reduced SIRT1 expression and activated p53 might be partially due to the inhibition of the PI3-K/Akt pathway triggered by the NRP-induced initiation of U937 cell apoptosis.

Retinoic acid enhances differentiation of v-myb-transformed monoblasts induced by okadaic acid

Differentiation of various leukemic cells can be induced by liganded retinoic acid receptors and protein phosphatase inhibitors. In this study, we explored the effects of okadaic acid (OA), the phosphatase inhibitor, and retinoic acid (RA) in v-myb-transformed monoblasts BM2. OA induced differentiation of BM2 monoblasts into macrophage-like cells, as documented by analyses of cell morphology, cell cycle, phagocytic activity, non-specific esterase activity, production of reactive oxygen species and expression of vimentin and Mo-1. In contrast to many other leukemic cell lines, BM2 cells do not respond to retinoic acid. However, once exposed to OA and RA simultaneously, BM2 cells differentiate along monocyte/macrophage pathway more efficiently. We conclude that RA enhances differentiation of v-myb-transformed monoblasts induced by protein phosphorylation.