Retraction Note: Inhibition effects of acridone on the growth of breast cancer cells in vivo.

The article "Inhibition effects of acridone on the growth of breast cancer cells in vivo", by Y.-F. Xia, H.-J. Chu, G.-F. Kuang, G.-J. Jiang, Y.-C. Che, published in Eur Rev Med Pharmacol Sci 2018; 22 (8): 2356-2363-DOI: 10.26355/eurrev_201804_14827-PMID: 29762857 has been retracted by the Editor in Chief for the following reasons. Following some concerns raised on PubPeer regarding a possible overlap in Figure 2, the Editor in Chief has started an investigation to assess the validity of the results as well as possible figure manipulation. The journal investigation revealed a duplication between Figures 2B and 2C. Consequently, the Editor in Chief mistrusts the results presented and has decided to retract the article. The authors have been informed about the journal's investigation but remained unresponsive. This article has been retracted. The Publisher apologizes for any inconvenience this may cause. https://www.europeanreview.org/article/14827.

Design, synthesis and evaluation of acridone-2-carbohydrazide derivatives as p-AKT Ser473 kinase inhibitors.

Aim: A series of benzylidene- and phenylethylidene-substituted acridone-2-carbohydrazide derivatives were designed, synthesized and evaluated for their cytotoxicity and response to p-AKT Ser473. Methods: The structures of the synthesized compounds were confirmed by spectroscopic techniques and evaluated for AKT enzyme inhibition activities. Molecular docking and in silico absorption, distribution, metabolism, elimination and toxicity studies were also performed. Results: Compounds 8k, 8v and 9h demonstrated good cytotoxicity against breast cancer cell lines. Especially, compounds 8v and 9h exhibited remarkable inhibition, with IC50 values of 1.75 and 2.40 µM, respectively. These compounds inhibited p-AKT Ser473 more specifically than total AKT in a dose-dependent manner. Moreover, they caused G0/G1-phase cell cycle arrest and cell apoptosis. Conclusion: This study identified compound 8v as a potent p-AKT Ser473 inhibitor.

Syntheses and evaluation of acridone derivatives as anticancer agents targeting Kras promoter i-motif structure.

Two series of novel acridone derivatives were designed and synthesized, with their anticancer activity evaluated. Most of these compounds showed potent antiproliferative activity against cancer cell lines. Among them, compound C4 with dual 1,2,3-triazol moieties exhibited the most potent activity against Hep-G2 cells with IC50 value determined to be 6.29 ± 0.93 µM. Subsequent experiments showed that C4 could bind to and destabilize Kras gene promoter i-motif structure without significant interaction with its corresponding G-quadruplex. C4 could down-regulate Kras expression in Hep-G2 cells, possibly due to its interaction with the Kras i-motif. Further cellular studies indicated that C4 could induce apoptosis of Hep-G2 cells, possibly related to its effect on mitochondrial dysfunction. These results indicated that C4 could be further developed as a promising anticancer agent.

Acridine/Acridone-Carborane Conjugates as Strong DNA-Binding Agents with Anticancer Potential.

Synthesis of acridine derivatives that act as DNA-targeting anticancer agents is an evolving field and has resulted in the introduction of several drugs into clinical trials. Carboranes can be of importance in designing biologically active compounds due to their specific properties. Therefore, a series of novel acridine analogs modified with carborane clusters were synthesized. The DNA-binding ability of these analogs was evaluated on calf thymus DNA (ct-DNA). Results of these analyses showed that 9-[(1,7-dicarba-closo-dodecaborane-1-yl)propylamino]acridine (30) interacted strongly with ct-DNA, indicating its ability to intercalate into DNA, whereas 9-[(1,7-dicarba-closo-dodecaborane-1-yl)propanamido]acridine (29) changed the B-form of ct-DNA to the Z form. Compound 30 demonstrated cytotoxicity, was able to inhibit cell proliferation, arrest the cell cycle in the S phase in the HeLa cancer cell line, and induced the production of reactive oxygen species (ROS). In addition, it was specifically localized in lysosomes and was a weak inhibitor of Topo IIα.

Development of new 1, 3-dihydroxyacridone derivatives as Akt pathway inhibitors in skeletal muscle cells.

In the present work, four new compounds based on the privileged structure acridone were efficiently synthesized following simple operational techniques and biologically tested on proliferative skeletal muscle cells (C2C12) and rhabdomyosarcoma cells (RD) showing no significant changes in the number of dead or viable cells at 1 µM during 24 or 48 h of treatment. Of relevance, acridone derivatives 3a-3d at 0.5 µM for 24 h effectively inhibited Akt activation in C2C12, while at 1 µM only compounds 3a and 3b have effect. RD cells showed a different response pattern. These cells treated with 3a (0.5 µM), 3b (0.5 µM) or 3d (0.5 or 1 µM) for 24 h shown significant Akt inhibition. In addition, 3a-3d assayed at 1 µM for 48 h were highly successful in inhibiting Akt phosphorylation. Finally, based on molecular docking and molecular dynamics simulations, we rationalize the experimental results mentioned above and propose that 3-phosphoinositide-dependent kinase-1 (PDK1) could be one of the molecular targets of this new series of 1, 3-dihydroxyacridone derivatives. Biological and in silico studies revealed that 3b could be considered as the most promising prototype for the development of new antitumor agents.

Effect of Lysine Acridone Acetate on the Level of Apoptosis and Expression of Apoptosis-Associated Proteins during Antioncogenic Therapy in Colorectal Cancer in Mice.

We studied the mechanism of action of cytostatics with the addition of lysine acridone acetate to evaluate the possibility of its use for improving the effectiveness of antioncogenic therapy in colorectal cancer. In Nude mouse model, the level of apoptosis (TUNEL) and expression of proteins CD95, p53, Bcl-2, histone H3, and Ki-67 (immunohistochemistry) were assessed in primary tumor biopsy specimens. It has been shown that cytostatic treatment led to stimulation of p53-mediated apoptosis and suppression of proliferation (Ki-67 expression) of tumor cells, and apoptosis level was increased in groups receiving lysine acridone acetate. H3 expression in the experimental groups was changed.

Acridone Derivatives from Atalantia monophyla Inhibited Cancer Cell Proliferation through ERK Pathway.

The present study aimed to investigate the effect of acridone alkaloids on cancer cell lines and elucidate the underlying molecular mechanisms. The ten acridone alkaloids from Atalantia monophyla were screened for cytotoxicity against LNCaP cell lines by a WST-8 assay. Then, the most potential acridone, buxifoliadine E, was evaluated on four types of cancer cells, namely prostate cancer (LNCaP), neuroblastoma (SH SY5Y), hepatoblastoma (HepG2), and colorectal cancer (HT29). The results showed that buxifoliadine E was able to significantly inhibit the proliferation of all four types of cancer cells, having the most potent cytotoxicity against the HepG2 cell line. Western blotting analysis was performed to assess the expression of signaling proteins in the cancer cells. In HepG2 cells, buxifoliadine E induced changes in the levels of Bid as well as cleaved caspase-3 and Bax through MAPKs, including Erk and p38. Moreover, the binding interaction between buxifoliadine E and Erk was investigated by using the Autodock 4.2.6 and Discovery Studio programs. The result showed that buxifoliadine E bound at the ATP-binding site, located at the interface between the N- and C-terminal lobes of Erk2. The results of this study indicate that buxifoliadine E suppressed cancer cell proliferation by inhibiting the Erk pathway.

A comprehensive review on acridone based derivatives as future anti-cancer agents and their structure activity relationships.

The development of drug resistance and severe side-effects has reduced the clinical efficacy of the existing anti-cancer drugs available in the market. Thus, there is always a constant need to develop newer anti-cancer drugs with minimal adverse effects. Researchers all over the world have been focusing on various alternative strategies to discover novel, potent, and target specific molecules for cancer therapy. In this direction, several heterocyclic compounds are being explored but amongst them one promising heterocycle is acridone which has attracted the attention of medicinal chemists and gained huge biological importance as acridones are found to act on different therapeutically proven molecular targets, overcome ABC transporters mediated drug resistance and DNA intercalation in cancer cells. Some of these acridone derivatives have reached clinical studies as these heterocycles have shown huge potential in cancer therapeutics and imaging. Here, the authors have attempted to compile and make some recommendations of acridone based derivatives concerning their cancer biological targets and in vitro-cytotoxicity based on drug design and novelty to increase their therapeutic potential. This review also provides some important insights on the design, receptor targeting and future directions for the development of acridones as possible clinically effective anti-cancer agents.

Acridone alkaloids and flavones from the leaves of Citrus reticulata.

A new acridone alkaloid, reticarcidone A (1), decorated with an oxygenated isopentenyl group between C-1 and C-2, was isolated from the leaves of Citrus reticulata Blanco, together with nine known acridone alkaloids (2-10) and fifteen flavones compounds (11-25). The structure of those compounds were confirmed by analysis of comprehensive 1D and 2D NMR, and MS data. Reticarcidone A (1) was the first pyrano[2,3-a]acridone isolated from the genus Citrus. Some of these compounds showed moderated cytotoxicity against the five human tumor cell lines MCF-7, SMMC-7721, HL-60, A549 and SW480.

Structural optimizations and bioevaluation of N-substituted acridone derivatives as strong topoisomerase II inhibitors.

Previously, an array of N-substituted acridone derivatives have been reported as potent topoisomerase II (topo II) inhibitors, and preliminary structure-activity relationship (SAR) outcomes revealed that the linker between 1-NH and N-methyl piperazine motif of the tricyclic acridone scaffold significantly affected their anti-proliferative potencies. To further explore the SARs of acridone-derived topo II inhibitors, a wider range of novel acridone derivatives were herein synthesized via two rounds of structural optimizations on two validated hits, E17 and E24. Initially, the linker length was optimized, and then influences of N-methyl piperazinyl moiety and disposition of three N atoms on the bioactivity were investigated. As a result, a newly developed topo II inhibitor 6 h was found to be more potent than E17 and E24, thereby serving as a tool compound for the follow-up mechanistic study. Compound 6 h functioned as a strong topo IIα/ß inhibitor, caused obvious DNA damage, and induced apoptosis by triggering the loss of mitochondrial membrane potential (Δψm). Further molecular docking and MD study illustrated the favorable interactions of 6 h with both topo IIα and topo IIß subtypes.

Structure-activity relationship of novel acridone derivatives as antiproliferative agents.

Unlike other DNA topoisomerase II (topo II) inhibitors, our recently identified acridone derivative E17 exerted strong cytotoxic activity by inhibiting topo II without causing topo II degradation and DNA damage, which promoted us to explore more analogues of E17 by expanding its chemical diversification and enrich the structure-activity relationship (SAR) outcomes of acridone-oriented chemotypes. To achieve this goal, 42 novel acridone derivatives were synthesized and evaluated for their antiproliferative efficacies. SAR investigations revealed that orientation and spatial topology of R3 substituents make greater contributions to the bioactivity, exemplified by compounds E24, E25 and E27, which has provided valuable information for guiding further development of acridone derivatives as promising drug candidates.

Synthesis of novel cytotoxic tetracyclic acridone derivatives and study of their molecular docking, ADMET, QSAR, bioactivity and protein binding properties.

Acridone based synthetic and natural products with inherent anticancer activity advancing the research and generating a large number of structurally diversified compounds. In this sequence we have designed, synthesized a series of tetracyclic acridones with amide framework viz., 3-(alkyloyl/ aryloyl/ heteroaryloyl/ heteroaryl)-2,3-dihydropyrazino[3,2,1-de]acridin-7(1H)-ones and screened for their in vitro anti-cancer activity. The in vitro study revealed that compounds with cyclopropyl-acetyl, benzoyl, p-hydroxybenzoyl, p-(trifluoromethyl)benzoyl, p-fluorobenzoyl, m-fluorobenzoyl, picolinoyl, 6-methylpicolinoyl and 3-nicotinoyl groups are active against HT29, MDAMB231 and HEK293T cancer cell lines. The molecular docking studies performed for them against 4N5Y, HT29 and 2VWD revealed the potential ligand-protein binding interactions among the neutral aminoacid of the enzymes and carbonyl groups of the title compounds with a binding energy ranging from - 8.1394 to - 6.9915 kcal/mol. In addition, the BSA protein binding assay performed for them has confirmed their interaction with target proteins through strong binding to BSA macromolecule. The additional studies like ADMET, QSAR, bioactivity scores, drug properties and toxicity risks ascertained them as newer drug candidates. This study had added a new collection of piperazino fused acridone derivatives to the existing array of other nitrogen heterocyclic fused acridone derivatives as anticancer agents.

Cytotoxic activity of dimeric acridone alkaloids derived from Citrus plants towards human leukaemia HL-60 cells.

OBJECTIVES: Acridone alkaloids from Citrus and their derivatives show various kinds of biological activity. However, the anticancer activities of dimeric acridone alkaloids with unique structures and the molecular mechanism of these effects are poorly understood. METHODS: We investigated the cytotoxicity effects of dimeric acridone alkaloids isolated from Marsh grapefruit on human myeloid leukaemia HL-60 cells. KEY FINDINGS: Of the six dimeric acridone alkaloids tested, citbismine-E, the most potent, dose- and time-dependently decreased HL-60 cell viability by inducing apoptosis. The treatment of HL-60 cells with citbismine-E yielded a significant increase in levels of intracellular reactive oxygen species (ROS). Citbismine-E lowered the mitochondrial membrane potential and increased the activities of caspase-9 and -3. In addition, citbismine-E-induced apoptosis, decrease in mitochondrial membrane potential and caspase activation were significantly alleviated by pretreatment of the cells with antioxidant N-acetylcysteine (NAC). Citbismine-E induced intrinsic caspase-dependent apoptosis through ROS-mediated c-Jun N-terminal kinase activation. Citbismine-E-induced production of oxidative stress biomarkers, malondialdehyde and 8-hydroxy-2'-deoxyguanosine was also attenuated by pretreatment with NAC. CONCLUSIONS: Citbismine-E is a powerful cytotoxic agent against HL-60 cells that acts by inducing mitochondrial dysfunction-mediated apoptosis through ROS-dependent JNK activation. Citbismine-E also induced oxidative stress damage via ROS-mediated lipid peroxidation and DNA damage in HL-60 cells.

Lead Optimization of Second-Generation Acridones as Broad-Spectrum Antimalarials.

The global impact of malaria remains staggering despite extensive efforts to eradicate the disease. With increasing drug resistance and the absence of a clinically available vaccine, there is an urgent need for novel, affordable, and safe drugs for prevention and treatment of malaria. Previously, we described a novel antimalarial acridone chemotype that is potent against both blood-stage and liver-stage malaria parasites. Here, we describe an optimization process that has produced a second-generation acridone series with significant improvements in efficacy, metabolic stability, pharmacokinetics, and safety profiles. These findings highlight the therapeutic potential of dual-stage targeting acridones as novel drug candidates for further preclinical development.

Synthesis, biological evaluation and virtual screening of some acridone derivatives as potential anticancer agents.

Eleven novel acridone derivatives were synthesized and evaluated for their anticancer activity against 60 human cancer cell lines. Five compounds 8b, 8d, 8g, 8h, and 8k displayed very good in vitro antiproliferative activities well over 95% of the panels. The most active compound is 8k (5, 7-dibromo-3-phenyl-3,4-dihydroacridin-1 (2H)-one). In addition, 8k was the most sensitive agent in all 9 panels starting with prostate (0.075 µm), leukemia (0.116 µm), non-small cell lung cancer (0.164 µm), colon cancer (0.193 µm), CNS cancer (0.264 µm), melanoma (0.317 µm), renal cancer (0.403 µm), ovarian cancer (0.410 µm), and breast cancer (0.608 µm). Virtual screening studies also revealed that nine of the eleven compounds formed good binding interaction with the active site ATPase domain of human topoisomerase IIα (PDB: 1zxm). All nine derivatives exhibited binding affinities that ranged in values from -8.5 to -7.9 kcal/mol, indicating that they could be catalytic inhibitors of the nuclear enzyme, topoisomerase.

Design, synthesis and biological evaluation of acridone glycosides as selective BChE inhibitors.

Based on structure analyses of butyrylcholinesterase (BChE), a series of 21 acridone glycosides were designed, synthesized and evaluated in vitro for their BChE and acetylcholinesterase (AChE) inhibitory activities. d-ribose derivative 6f exhibited the greatest inhibitory activity on BChE (IC50 = 6.95 µM), and was the most selective inhibitor of BChE with the IC50 ratio of AChE/BChE was 20.59. d-glucose and d-galactose derivatives 6a and 6b showed inhibitory activities against both AChE and BChE. Moreover, compounds 6a, 6b, 6f and 5t were found nontoxic on SHSY5Y neuroblastoma and HepG2 cell and exhibited remarkable neuroprotective activity. Besides, compound 6f showed mixed-type inhibition against BChE (Ki = 1.76 µM), which renders 6f a potential agent for the treatment of Alzheimer's disease. These novel acridone hybrids might be used as efficient probes to reveal the relationship between ligands and BChE and pave the way for developing selective BChE inhibitors to further study the pathogenesis of alzheimer's disease.

Design, synthesis and biological evaluation of acridone analogues as novel STING receptor agonists.

STING (Stimulator of Interferon Genes) has become a focal point in immunology research and a target in drug discovery. The discovery of a potent human-STING agonist is expected to revolutionize current anti-virus or cancer immunotherapy. Inspired by the structure and function of murine STING-specific agonists (DMXAA and CMA), we rationally designed and synthesized four series of novel compounds for the enhancement of human sensitivity. In the cell-based assay, we identified six compounds from all the synthetic small molecules: 2g, 9g, and 12b are STING agonists that are efficacious across species, and all have the skeleton of acridone; 1b, 1c, and 12c just function in the murine STING pathway. Notably, 12b exhibits the best activity among the six agonists, and its inductions of both human and murine STING-dependent signalling are similar to that of 2'3'-cGAMP, which is a well-known STING inducer. While a protein assay indicated that 2 g, 9 g, and 12b could activate the pathway by directly binding human STING, 12b also displayed the strongest binding affinity. Additionally, our studies show that 12b can induce faster, more powerful, and more durable responses of assorted cytokines in a native system than 2'3'-cGAMP. Consequently, our team is the first to successfully modify murine STING agonists to obtain human sensitivity, and these results suggest that 12b is a potent direct-human-STING agonist. Additionally, the acridone analogues demonstrate tremendous potential in the treatment of tumours or viral infections.

Meglumine acridone acetate, the ionic salt of CMA and N-methylglucamine, induces apoptosis in human PBMCs via the mitochondrial pathway.

Meglumine acridone acetate (MA) is used in Russia for the treatment of influenza and other acute respiratory viral infections. It was assumed, until recently, that its antiviral effect was associated with its potential ability to induce type I interferon. Advanced studies, however, have shown the failure of 10-carboxymethyl-9-acridanone (CMA) to activate human STING. As such, MA's antiviral properties are still undergoing clarification. To gain insight into MA's mechanisms of action, we carried out RNA-sequencing analysis of global transcriptomes in MA-treated (MA+) human peripheral blood mononuclear cells (PBMCs). In response to treatment, approximately 1,223 genes were found to be differentially expressed, among which 464 and 759 were identified as either up- or down-regulated, respectively. To clarify the cellular and molecular processes taking place in MA+ cells, we performed a functional analysis of those genes. We have shown that evident MA subcellular localizations are: at the nuclear envelope; inside the nucleus; and diffusely in perinuclear cytoplasm. Postulating that MA may be a nuclear receptor agonist, we carried out docking simulations with PPARα and RORα ligand binding domains including prediction and molecular dynamics-based analysis of potential MA binding poses. Finally, we confirmed that MA treatment enhanced nuclear apoptosis in human PBMCs. The research presented here, in our view, indicates that: (i) MA activity is mediated by nuclear receptors; (ii) MA is a possible PPARα and/or RORα agonist; (iii) MA has an immunosuppressive effect; and (iv) MA induces apoptosis through the mitochondrial signaling pathway.

A new acridone with antifungal properties against Candida spp. and dermatophytes, and antibiofilm activity against C. albicans.

AIM: The increase in the number of fungal infections worldwide, coupled with the limitations of current antifungal chemotherapy, demand the development of safe and effective new antifungals. Here, we presented the synthesis of a novel acridone (M14) and its antifungal properties against Candida and dermatophytes species. METHODS AND RESULTS: A series of 17 acridones was designed, synthesized and tested for its antifungal activity. The minimum inhibitory concentration (MIC) was determined by the broth microdilution method. Only the acridone M14 showed growth-inhibitory activity against reference strains and clinical isolates of Candida and dermatophytes, with MIC range of 7·81-31·25 µg ml-1 . Moreover, M14 exhibited fungicidal activity and prevented biofilm formation by C. albicans as well as reduced the viability of preformed biofilms, even at sub-MICs. The confocal laser scanning microscopy analysis revealed that C. albicans hyphal growth was completely inhibited in the presence of M14. Similarly, there was a severe inhibition on hyphal growth of Trichophyton rubrum. We also found that M14 has relatively low toxicity to human fibroblasts. CONCLUSIONS: The new acridone M14 has antifungal properties against Candida spp. and dermatophytes, and antibiofilm activity against C. albicans. In addition, M14 is relatively selective to fungal cells compared to human normal cells. SIGNIFICANCE AND IMPACT OF THE STUDY: Because of its in vitro antifungal activity, anti-Candida biofilm effect and moderate cytotoxicity towards normal human cell, M14 may serve as a valuable lead compound to develop a new antifungal agent.

Assessment of DNA Topoisomerase I Unwinding Activity, Radical Scavenging Capacity, and Inhibition of Breast Cancer Cell Viability of N-alkyl-acridones and N,N'-dialkyl-9,9'-biacridylidenes.

The anticancer activity of acridone derivatives has attracted increasing interest, therefore, a variety of substituted analogs belonging to this family have been developed and evaluated for their anti-cancer properties. A series of N-alkyl-acridones 1-6 and N,N'-dialkyl-9,9'-biacridylidenes 7-12 with variable alkyl chains were examined for their topoisomerase I activity at neutral and acidic conditions as well as for their binding capacity to calf thymus and possible radical trapping antioxidant activity. It was found that at a neutral pH, topoisomerase I activity of both classes of compounds was similar, while under acidic conditions, enhanced intercalation was observed. N-alkyl-acridone derivatives 1-6 exhibited stronger, dose-dependent, cytotoxic activity against MCF-7 human breast epithelial cancer cells than N,N'-dialkyl-9,9'-biacridylidenes 7-12, revealing that conjugation of the heteroaromatic system plays a significant role on the effective distribution of the compound in the intracellular environment. Cellular investigation of long alkyl derivatives against cell migration exhibited 40-50% wound healing effects and cytoplasm diffusion, while compounds with shorter alkyl chains were accumulated both in the nucleus and cytoplasm. All N,N'-dialkyl-9,9'-biacridylidenes showed unexpected high scavenging activity towards DPPH or ABTS radicals which may be explained by higher stabilization of radical cations by the extended conjugation of heteroaromatic ring system.