Rhein Derivatives Research Articles

Antifungal and insecticidal activities of rhein derivatives: synthesis, characterization and preliminary structure–activity relationship studies

There is an urgent need to replace highly polluting pesticides with environmentally friendly green pesticides of high efficiency and low toxicity, because of the growing concern for quality and safety of agricultural products. To discover new pesticides with diverse chemical structures from natural products, a series of rhein derivatives 3a-9b were designed, synthesized, and evaluated for their antifungal activity and insecticidal activity. The bioassay showed that some compounds exhibited moderate antifungal activity against Rhizoctonia solani, but lower activity against the other five pathogens. Surprisingly, most compounds displayed potent insecticidal activity against Spodoptera litura and Tetranychus cinnabarinus at a concentration of 2 μmol/mL. In particular, compounds 3a, 5a and 3 b exhibited potent insecticidal activities against S. litura at 72 h, with mortality rates of 100%, 100% and 92.1%, respectively, which were equivalent to that of the insecticide fipronil (100%). Their structure-activity relationships were also discussed. The findings of this experiment provide helpful research ideas for the development of these rhein derivatives as novel natural product-based pesticides in crop protection.

Cassia sieberiana DC. leaves modulate LPS-induced inflammatory response in THP-1 cells and inhibit eicosanoid-metabolizing enzymes

Ethnopharmacological relevanceAccording to ethnobotanical surveys, Cassia sieberiana DC. (1825) is a particularly reputed species in African folk Medicine, namely due to the application of its leaves and roots for the treatment of diseases and symptomatology that appear to be related with an inflammatory background. In contrast with the roots of the plant, the leaves remain to be investigated, which prompted us to further detail mechanisms underlying their anti-inflammatory properties, by using in vitro models of disease. Aim of the studyConsidering its use in the amelioration and treatment of conditions that frequently underlie an inflammatory response, C. sieberiana leaves extract was prioritized amongst a collection of extracts obtained from plants collected in Guinea-Bissau. As such, this work aims to deliver experimental data on the anti-inflammatory properties of C. sieberiana leaf and to establish possible associations with its chemical composition, thus providing a rationale on its use in folk Medicine. Materials and methodsThe chemical profile of an hydroethanol extract obtained from the leaves of the plant was established by HPLC-DAD-ESI/MSn in order to identify bioactives. The extract and its main compound were tested towards a series of inflammatory mediators, both in enzymatic and cell-based models. The capacity to interfere with the eicosanoid-metabolizing enzymes 5-lipoxygenase (5-LOX), cyclooxygenase-1 (COX-1) and -2 (COX-2) was evaluated in cell-free systems, while the effects in interleukin 6 (IL-6) and tumour necrosis factor-α (TNF-α) levels produced by THP-1 derived macrophages were assessed through ELISA. ResultsHPLC-DAD-ESI/MSn analysis of the extract elucidated a chemical profile qualitatively characterized by a series of anthraquinones, particularly rhein derivatives, and nine flavonols, most of which 3-O-glycosylated. Considering the concentrations of the identified compounds, quercetin was detached as the main component.Effects of the hydroethanol extract obtained from C. sieberiana leaves against key enzymes of the arachidonic acid cascade were recorded, namely a concentration-dependent inhibition against 5-LOX, at concentrations ranging from 16 to 250 μg mL-1 and a selective inhibitory action upon COX-2 (IC50 = 3.58 μg mL-1) in comparison with the isoform COX-1 (IC50 = 9.10 μg mL-1).Impact on inflammatory cytokines was also noted, C. sieberiana leaf extract significantly decreasing IL-6 levels in THP-1 derived macrophages at 250 and 500 μg mL-1. In contrast, TNF-α levels were found to be increased in the same model.Quercetin appears to partially account for the observed effects, namely due to the significant inhibitory effects on the activity of the arachidonic acid metabolizing enzymes COX-2 and 5-LOX. ConclusionsThe anti-inflammatory effects herein reported provide a rationale for the use of C. sieberiana leaves in African folk practices, such as in the treatment of arthritis, rheumatism and body aches. Considering the occurrence of flavonoidic and anthraquinonic constituents, as well as the observed anti-inflammatory properties of quercetin, recorded effects must be related with the presence of several bioactives.

Confirming whether novel rhein derivative 4a induces paraptosis-like cell death by endoplasmic reticulum stress in ovarian cancer cells

Ovarian cancer is the leading cause of death among gynecologic cancer patients. Although platinum-based chemotherapy as a frontline treatment for ovarian cancer has been widely used in clinical settings, its clinical efficacy is not satisfactory due to the resistance of ovarian cancer cells to apoptosis. Therefore, it is of great significance to induce non-apoptotic programed cell death patterns, such as paraptosis, in ovarian cancer. In this study, we aimed to explore the potential anticancer mechanisms of novel rhein derivative 4a, which was modified with rhein as a lead compound. The results showed that a wide range of vacuoles from the endoplasmic reticulum and mitochondria appeared in ovarian SKOV3, SKOV3-PM4, and A2780 cells treated with derivative 4a, and the cell death caused by derivative 4a is a type of non-apoptotic and non-autophagic death, which is caused by expansion and damage of the endoplasmic reticulum or mitochondria, showing the characteristics of para-apoptotic death. Furthermore, derivative 4a stimulated the unfolded protein reaction of ovarian cancer cells by upregulating the expression of Bip78 and activating the PERK-eIF2α-ATF4 pathways. Notably, rhein derivative 4a-induced cell death was positively correlated with activation of p38, ERK, and JNK, and negatively correlated with Alix, a known protein that inhibits paraptosis. In addition, derivative 4a treatment also induced G2/M phase arrest in ovarian cancer cells. Taken together, our study reveals that derivative 4a induces paraptosis, and this finding can serve as a basis in developing a new strategy for the treatment of antiapoptotic ovarian cancer.

Rhein Derivative 4F Inhibits the Malignant Phenotype of Breast Cancer by Downregulating Rac1 Protein.

BackgroundTriple-negative breast cancer is a common malignant tumor with unfavorable prognosis affecting women worldwide; thus, there is an urgent need for novel therapeutic drugs with improved anti-tumor activity. Rac family small GTPase 1 (Rac1) plays an important role in malignant behavior and is a promising therapeutic target. We reported an anthraquinone compound, Rhein, and its derivative, 4F, and investigated their downregulation effects on Rac1 in breast cancer cells in vitro.MethodsThe inhibition of cell proliferation by derivative 4F was investigated in two breast cancer (MDA-MB-231 and MCF-7) and normal breast (MCF-10A) cell lines by cell counting kit-8 assay and growth curves. The role of 4F in cell migration and invasion and cytoskeletal change were assessed by Transwell chamber assay and F-actin staining, respectively. The affinity of Rhein and its derivative for Rac1 protein and the regulation of Rac1 promoter activity were evaluated by molecular docking software and luciferase reporter gene assay, respectively. Rac1 protein expression was determined by western blot assay.ResultsCompared to Rhein, derivative 4F more strongly inhibited breast cancer cell proliferation, migration, and invasion and also cause cytoskeletal changes like those in paclitaxel. Derivative 4F not only bound more stably to Rac1 but also inhibited Rac1 promoter activity in cells and downregulated Rac1 protein expression.ConclusionsRhein derivative 4F is a new anthraquinone compound with better anti-tumor activity than that of the lead compound Rhein in breast cancer. It down-regulated Rac1 expression and may be a small molecule inhibitor of Rac1.

An autophagy-dependent cell death of MDA-MB-231 cells triggered by a novel Rhein derivative 4F.

Triple negative breast cancer (TNBC) has very poor prognosis and no efficacious therapeutic options due to the absence of a validated molecular target. Therefore, novel therapeutic strategies against TNBC are urgently needed. Our team synthesized and screened a series of compounds derived from Rhein, of which 4F was selected for further analysis based on its ability to produce the vacuolated appearance of cells. Using Cell counting kit-8 assay, colony-formation assay, cell apoptosis and cell cycle assay, we compared the antitumor effects of 4F, Rhein and Cisplatin on a TNBC cell line MDA-MB-231 in vitro. The vacuoles in MDA-MB-231 cells were observed and analyzed by hematoxylin-eosin staining and transmission electron microscopy. Autophagy and apoptosis-related proteins including p62, Microtubule Light Chain 3 (LC3), Beclin-1 and Caspase-3 were determined by western blot. The tandem mRFP-GFP-LC3 Lentivirus was used for monitoring the maturation step of autophagosomes. Our data revealed that 4F had lower cytotoxicity to normal breast cell line MCF-10A as compared with positive drug Doxorubicin. Although 4F had better cytotoxicity than Rhein, it had no influence on cells apoptosis in 4F-treated cells. Accumulation of autolysosomes and autophagosomes was observed in 4F-treated MDA-MB-231 cells, accompanied by increased level of Beclin-1 protein. Enhanced autophagic flux was verified by higher ratio of LC3-II/LC3-I, the degradation of p62 protein and alteration in red and green fluorescence puncta. These findings suggested that the process of MDA-MB-231 cell death induced by 4F seemed rely mainly on autophagy rather than apoptosis. 4F may be an alternative drug candidate against TNBC and merits more exploration.

Probing a dipeptide-based supramolecular assembly as an efficient camptothecin delivering carrier for cancer therapy: computational simulations and experimental validations.

Short peptide-based supramolecular assemblies have drawn much attention in the field of drug delivery. However, the progress still remains limited owing to the inefficient drug loading capacity of conventional short peptide-based materials. In this study, based on coordinated intramolecular π-π stacking, we customize a dipeptide-based rhein derivative (rhein-diphenylalanine peptide, RDP), which could spontaneously form spherical nanoassemblies for drug delivery. A structure-based virtual screening of a library of small molecules is conducted to identify the suitable compounds which could be effectively delivered by this nanocarrier. Sorted by binding energy results, fifteen superior and five inferior molecules are found. Subsequently, the co-assembly capacity of high-affinity molecules (camptothecin, CPT) and low-affinity molecules (norcantharidin, NCTD) with the dipeptide-based carrier is predicted via dissipative particle dynamics (DPD) simulation. Consistent with computational results, the in vitro experimental results show that CPT-encapsulated nanoassemblies have significant advantages in the particle size distribution and recrystallization-inhibitory effect compared with NCTD. Furthermore, in vivo experiments were conducted to determine whether CPT is precisely delivered to tumor sites by using the dipeptide-based nanoassemblies. The CPT-loaded nanoassemblies show better effects in terms of drug biodistribution and in vivo anti-tumor efficacy compared to free CPT. The cooperative computational and experimental strategies (in vitro and in vivo) used in this work lay a good foundation to systematically understand short peptide-based assemblies for precise drug delivery.

A novel Rhein derivative: Activation of Rac1/NADPH pathway enhances sensitivity of nasopharyngeal carcinoma cells to radiotherapy

Radiation resistance and recurrent have become the major factors resulting in poor prognosis in the clinical treatment of patients with nasopharyngeal carcinoma (NPC). New strategies to enhance the efficacy of radiotherapy have been focused on the development of radiosensitizers and searching for directly targets that modulated tumor radiosensitivity. A novel potential radiosensitizer 1,8-Dihydroxy −3-(2′-(4″-methylpiperazin-1″-yl) ethyl-9,10-anthraquinone −3-carboxylate (RP-4) was designed and synthesized based on molecular docking technology, which was expected to regulate the radiosensitivity of tumor cells through targeting Rac1. In order to assess the radiosensitization activity of RP-4 on NPC cells, the highly differentiated CNE1 and poorly differentiated CNE2 cells NPC lines were employed. According to the results, RP-4 showed higher binding affinity toward the interaction with Rac1 than lead compounds. We found that RP-4 could inhibit cell viability and proliferation in CNE1 and CNE2 cells and significantly induced apoptosis after non-toxic concentration of RP-4 combined with 2Gy irradiation. RP-4 could effectively modulated the radiosensitivity both CNE1 cells and CNE2 cells through activating Rac1/NADPH signaling pathway and its downstream JNK/AP-1 pathway. What's more, Rac1/NADPH signaling pathway were significantly activated in Rac1-overexpressed CNE1 and CNE2 cells after treated with RP-4. Taken together, Rac1 and its downstream pathway may probably be the direct targets of RP-4 in regulating radiosensitivity of NPC cells, our finding provided a novel strategy for the development of therapeutic agents in response to tumorous radiation resistance.

A Novel Rhein Derivative Modulates Bone Formation and Resorption and Ameliorates Estrogen-Dependent Bone Loss.

Osteoporosis, an osteolytic disease that affects millions of people worldwide, features a bone remodeling imbalance between bone resorption by osteoclasts and bone formation by osteoblasts. Identifying dual target-directed agents that inhibit excessive bone resorption and increase bone formation is considered an efficient strategy for developing new osteoporosis treatments. Rhein, a natural anthraquinone, can be isolated from various Asian herbal medicines. Rhein and its derivatives have been reported to have various beneficial pharmacological effects, especially their bone-targeting ability and anti-osteoclastogenesis activity. Moreover, hydrogen sulfide (H2 S) was reported to prevent ovariectomy- (OVX-) induced bone loss by enhancing bone formation, and sulfur replacement therapy has been considered a novel and plausible therapeutic option. Based on this information, we synthesized a rhein-derived thioamide (RT) and investigated its effects on bone resorption and bone formation in vitro and in vivo. It has been found that the RT-inhibited receptor activator of the nuclear factor-κB (NF-κB) ligand- (RANKL-) induced osteoclastogenesis and bone resorption in a dose-dependent manner. The expression of osteoclast marker genes was also suppressed by RT treatment. Furthermore, exploration of signal transduction pathways indicated that RT markedly blocked RANKL-induced osteoclastogenesis by attenuating MAPK pathways. However, RT treatment in an osteoblastic cell line, MC3TE-E1, indicated that RT led to an increase in the deposition of minerals and the expression of osteoblast marker genes, as demonstrated by Alizarin Red staining and alkaline phosphatase activity. Importantly, an OVX mouse model showed that RT could attenuate the bone loss in estrogen deficiency-induced osteoporosis in vivo with a smart H2 S-releasing property and that there was a considerable improvement in the biomechanical properties of bone. Accordingly, our current work highlights the dual regulation of bone remodeling by the rhein-derived molecule RT. This may be a highly promising approach for a new type of anti-osteoporosis agent. © 2018 American Society for Bone and Mineral Research.

Radiolabeled Rhein as Small-Molecule Necrosis Avid Agents for Imaging of Necrotic Myocardium.

A rapid and accurate identification of necrotic myocardium is of great importance for diagnosis, risk stratification, clinical decision-making, and prognosis evaluation of myocardial infarction. Here, we explored technetium-99m labeled rhein derivatives for rapid imaging of the necrotic myocardium. Three hydrazinonicotinic acid-linker-rhein (HYNIC-linker-rhein) derivatives were synthesized, and then, these synthetic compounds were labeled with technetium-99m using ethylenediaminediacetic acid (EDDA) and tricine as coligands [99mTc(EDDA)-HYNIC-linker-rhein]. The necrosis avidity of the three 99mTc-labeled rhein derivatives was tested in a mouse model of ethanol-induced muscular necrosis by gamma counting, histochemical staining, and autoradiography. A lead tracer for visualization of necrotic myocardium was assessed by single photon emission computed tomography/computed tomography (SPECT/CT) imaging in a rat model with reperfused myocardial infarction. The necrosis avidity mechanism of the tracer was explored by DNA binding studies in vitro and blocking experiments in vivo. Results showed that the uptake in necrotic muscles of the three 99mTc-compounds was higher than that in viable muscles (P < 0.001). Autoradiography and histochemical staining results were consistent with selective uptake of the radiotracer in the necrotic regions. Among the these tracers, 99mTc(EDDA)-HYNIC-ethylenediamine-rhein [99mTc(EDDA)-HYNIC-2C-rhein] displayed the best distribution profiles for imaging. The necrotic myocardium lesions were clearly visualized by SPECT/CT using 99mTc(EDDA)-HYNIC-2C-rhein at 1 h after injection. The necrotic-to-viable myocardium and necrotic myocardium-to-blood uptake ratios of 99mTc(EDDA)-HYNIC-2C-rhein were 4.79 and 3.02 at 1 h after injection. DNA binding studies suggested HYNIC-linker-rhein bound to DNA through intercalation. The uptake of 99mTc(EDDA)-HYNIC-2C-rhein in necrotic muscle was significantly blocked by excessive unlabeled rhein, with 77.61% decline at 1 h after coinjection. These findings suggested 99mTc(EDDA)-HYNIC-2C-rhein emerged as a "hot spot" imaging probe that has a potential for rapid imaging of necrotic myocardium. The necrosis avidity mechanism of 99mTc(EDDA)-HYNIC-linker-rhein may be due to its interaction with exposed DNA in necrotic tissues.

Design, synthesis, and characterization of rhein analogs as novel inhibitors of scavenger receptor A

Scavenger receptor A (SRA) has been known as an immunosuppressive factor and therefore therapeutic inhibition of SRA may be potentially exploited for cancer immunotherapy. Our previously work suggested that rhein may act as an inhibitor of SRA in reversing immunosuppression of SRA during T cells activation. Herein, three deconstruction analogs of rhein, compound 1, 2, and 3, were further studied as inhibitors of SRA. These three compounds, particularly compound 1, also known as a natural product danthron, enhanced T cells activation, indicated by increased transcriptional activation of interleukin 2 (Il2) gene, production of IL-2 protein, and proliferation of T cells. Additionally, the interaction between these compounds and SRA was studied by molecular modeling. Compound 1 showed a favorable binding mode with the cysteine rich domain of SRA protein compared to compound 2 and 3. Collectively, those results would provide insight for future design and development of next generation rhein derivatives as SRA inhibitors.

Synthesis and biological evaluation of rhein amides as inhibitors of osteoclast differentiation and bone resorption

Approaches of targeting excessive activation and differentiation of osteoclasts were considered as an effective treatment option for osteoporosis or osteopenia. In the present work, a series of rhein derivatives were synthesized and employed for their cytotoxicity screening against bone marrow-derived macrophages cells (BMMs) and their inhibition effects on osteoclasts activation and differentiation in vitro using an MTT assay and a TRAP activity assay respectively. Two rhein derivatives d6 and d11 inhibited BMMs activation and differentiation with 98% and 85% inhibitory activity respectively, without showing any cytotoxicity on BMMs. Subsequently, the most potent compound d6 was further validated for its inhibitory effects on the formation of TRAP-positive multinucleated cells and bone resorption as evaluated by TRAP staining and bone resorption assay. The regulation by d6 of osteoclast marker genes assay revealed that treatment of BMMs with M-CSF and RANKL resulted in the stimulation of mRNA expressions of NFATc1, c-fos, TRAP, MMP-9 and cathepsin K which were highly related with osteoclast activation and differentiation, while d6 decreased mRNA expressions of these genes. It was indicated that d6 might regulate osteoclasts activity through RANKL/RANK/NFATc1 pathway. Thus our current work is expected to provide a highly promising approach for the development of a new type of anti-osteoporosis agent.

Design, synthesis and biological evaluation of rhein derivatives as anticancer agents

A series of novel derivatives of rhein were synthesized and evaluated for their in vitro antiproliferative activity against six kinds of tumor cell lines. All derivatives displayed more potent anti-tumor activity than rhein, and most of them were even stronger than 5-FU. Compound 4v was the most promising candidate among the investigated compounds.

Synthesis and Multitarget Biological Profiling of a Novel Family of Rhein Derivatives As Disease-Modifying Anti-Alzheimer Agents

We have synthesized a family of rhein-huprine hybrids to hit several key targets for Alzheimer's disease. Biological screening performed in vitro and in Escherichia coli cells has shown that these hybrids exhibit potent inhibitory activities against human acetylcholinesterase, butyrylcholinesterase, and BACE-1, dual Aβ42 and tau antiaggregating activity, and brain permeability. Ex vivo studies with the leads (+)- and (-)-7e in brain slices of C57bl6 mice have revealed that they efficiently protect against the Aβ-induced synaptic dysfunction, preventing the loss of synaptic proteins and/or have a positive effect on the induction of long-term potentiation. In vivo studies in APP-PS1 transgenic mice treated ip for 4 weeks with (+)- and (-)-7e have shown a central soluble Aβ lowering effect, accompanied by an increase in the levels of mature amyloid precursor protein (APP). Thus, (+)- and (-)-7e emerge as very promising disease-modifying anti-Alzheimer drug candidates.