Usnic Acid Benzylidene Analogues as Potent Mechanistic Target of Rapamycin Inhibitors for the Control of Breast Malignancies

Synthesis of aminomethyl linked (+)-usnic acid derivatives via the Mannich reaction and evaluation of their biological activities

(+)-Usnic acid (UA), a natural dibenzofuran derivative, abundantly produced by lichens and possess wide number of biomedical applications including antibacterial, anti-inflammatory, anti-oxidant and anticancer activities. In the present study, as series of usnic acid derivatives (3a-3i) were synthesised using Mannich reaction assessed for their antioxidant, α-glucosidase, and anticancer activities. The in vitro antioxidant activity showed that compound 3d displayed potent antioxidant activity by scavenging the activities of DPPH and ABTS+. The compounds 3d and 3e showed potent cytotoxic activity against HepG2 cancer cells by arresting the cell cycle at S phase and regulating the Bax/BcL2 expression and subsequently induce the apoptosis. Overall, the results clearly indicated that (+)-usnic acid derivatives bearing secondary amines are useful scaffolds for the development of drug candidates for treatment of oxidative stress mediated cancer and metabolic disorders.

Palladium-Catalyzed Defluorinative Coupling of Difluoroalkenes and Aryl Boronic Acids for Ketone Synthesis

The transition-metal-catalyzed carbonylation reaction is a useful approach for ketone synthesis. However, it is often problematic to use exogenous carbonyl reagents, such as gaseous carbon monoxide. In this manuscript, we report a novel palladium-catalyzed coupling reaction of gem-difluoroalkenes and aryl boronic acids that yields bioactive indane-type ketones with an all-carbon α-quaternary center. Characterization and stoichiometric reactions of the key intermediates RCF₂ Pd^II support a water-induced defluorination and cross-coupling cascade mechanism. The vinyl difluoromethylene motif serves as an in situ carbonyl precursor which is unprecedented in transition-metal-catalyzed coupling reactions. It is expected to raise broad research interest from the perspectives of ketone synthesis, fluoroalkene functionalization, and rational design of new synthetic protocols based on the unique reactivity of difluoroalkyl palladium(II) species.

Growth Inhibition and Apoptotic Effect of Pine Extract and Abietic Acid on MCF-7 Breast Cancer Cells via Alteration of Multiple Gene Expressions Using In Vitro Approach

In vitro anti-proliferative activity of Pinus palustris extract and its purified abietic acid was assessed against different human cancer cell lines (HepG-2, MCF-7 and HCT-116) compared to normal WI-38 cell line. Abietic acid showed more promising IC50 values against MCF-7 cells than pine extract (0.06 µg/mL and 0.11 µM, respectively), with insignificant cytotoxicity toward normal fibroblast WI-38 cells. Abietic acid triggered both G2/M cell arrest and subG0-G1 subpopulation in MCF-7, compared to SubG0-G1 subpopulation arrest only for the extract. It also induced overexpression of key apoptotic genes (Fas, FasL, Casp3, Casp8, Cyt-C and Bax) and downregulation of both proliferation (VEGF, IGFR1, TGF-β) and oncogenic (C-myc and NF-κB) genes. Additionally, abietic acid induced overexpression of cytochrome-C protein. Furthermore, it increased levels of total antioxidants to diminish carcinogenesis and chemotherapy resistance. P. palustris is a valuable source of active abietic acid, an antiproliferative agent to MCF-7 cells through induction of apoptosis with promising future anticancer agency in breast cancer therapy.

Lichens as a repository of bioactive compounds: an open window for green therapy against diverse cancers

Lichens, algae and fungi-based symbiotic associations, are sources of many important secondary metabolites, such as antibiotics, anti-inflammatory, antioxidants, and anticancer agents. Wide range of experiments based on in vivo and in vitro studies revealed that lichens are a rich treasure of anti-cancer compounds. Lichen extracts and isolated lichen compounds can interact with all biological entities currently identified to be responsible for tumor development. The critical ways to control the cancer development include induction of cell cycle arrests, blocking communication of growth factors, activation of anti-tumor immunity, inhibition of tumor-friendly inflammation, inhibition of tumor metastasis, and suppressing chromosome dysfunction. Also, lichen-based compounds induce the killing of cells by the process of apoptosis, autophagy, and necrosis, that inturn positively modulates metabolic networks of cells against uncontrolled cell division. Many lichen-based compounds have proven to possess potential anti-cancer activity against a wide range of cancer cells, either alone or in conjunction with other anti-cancer compounds. This review primarily emphasizes on an updated account of the repository of secondary metabolites reported in lichens. Besides, we discuss the anti-cancer potential and possible mechanism of the most frequently reported secondary metabolites derived from lichens.

A cascade double 1,4-addition/intramolecular annulation strategy for expeditious assembly of unsymmetrical dibenzofurans

Existing synthetic routes for accessing dibenzofuran core have intrinsic regioselectivity, limiting the substitution patterns available in heteropolycyclic arene products. Here we report a double 1,4-conjugate addition/intramolecular annulation cascade reaction between propargylamines and two equivalents of imidazolium methylides that allows efficient access of structurally versatile dibenzofurans. This transition metal-free protocol proceeds smoothly under bench-top air atmosphere and offers easy manipulation of substituents on the dibenzofuran core, and also provides good-to-excellent product yields with good functional group tolerance, particularly the -Br and -Cl groups which are often incompatible with existing metal-catalyzed C-C and/or C-O bond ring-forming processes. It is worth noting that ladder-type π-systems with all-arene quarternary carbon structure can be straightforwardly generated upon simple late-stage functionalization.

Determination of Dysregulated miRNA Expression Levels by qRT-PCR after the Application of Usnic Acid to Breast Cancer

Background and Purpose:

Breast cancer still remains to be one of the most threatening cancer types in women. Recent studies have allowed scientists to better investigate the potential use of natural compounds in the treatment of breast cancers. Usnic acid is a secondary metabolite extracted from lichen species and has many biological activities. The response of microRNAs regulated by drug molecules may provide useful diagnostic and prognostic biomarkers, as well as potential therapeutics for breast cancers. Although the aberrant expression of microRNAs was observed after drug treatment, the regulatory mechanisms remain partially known. Micro RNAs (miRNAs) play an important role in gene regulation at the post-transcriptional level.

Methods:

In this study, we used quantitative Real-Time PCR (qRT-PCR) technology to demonstrate that usnic acid significantly changes the expression profile of miRNAs.

Results:

Eleven miRNAs were significantly and differentially expressed in breast cancer cells after treatment with usnic acid. Three miRNAs were up-regulated, while eight were down-regulated in usnic acid treated cells. Target prediction and GO analysis revealed many target genes and their related pathways that are potentially regulated by usnic acid regulated differentially expressed miRNAs. We found that usnic acid treatment caused significant changes in the expression of hsa-miR-5006-5p, hsa-miR-892c-3p, hsa-miR-4430, hsa-miR-5194, hsa-miR-3198, hsa-miR-3171, hsa-miR-933 and hsa-miR-185-3p in breast cancer cells.

Conclusions:

Usnic acid response miRNAs might play important regulatory roles in the tumorigenesis and development of breast cancer, and they could serve as prognostic predictors for breast cancer patients.

(+)-Usnic Acid Induces ROS-dependent Apoptosis via Inhibition of Mitochondria Respiratory Chain Complexes and Nrf2 Expression in Lung Squamous Cell Carcinoma

Lung squamous cell carcinoma (LUSC) has a poor prognosis, in part due to poor therapeutic response and limited therapeutic alternatives. Lichens are symbiotic organisms, producing a variety of substances with multiple biological activities. (+)-Usnic acid, an important biologically active metabolite of lichens, has been shown to have high anti-cancer activity at low doses. However, there have been no reports regarding the effect of (+)-usnic acid on LUSC cells. This study found that (+)-usnic acid reduced viability and induced apoptosis in LUSC cells by reactive oxygen species (ROS) accumulation. (+)-Usnic acid induced mitochondria-derived ROS production via inhibition of complex I and complex III of the mitochondrial respiratory chain (MRC). Interestingly, the elimination of mitochondrial ROS by Mito-TEMPOL only partially reversed the effect of (+)-usnic acid on cellular ROS production. Further study showed that (+)-usnic acid also induced ROS production via reducing Nrf2 stability through disruption of the PI3K/Akt pathway. The in vitro and in vivo xenograft studies showed that combined treatment of (+)-usnic acid and paclitaxel synergistically suppressed LUSC cells. In conclusion, this study indicates that (+)-usnic acid induces apoptosis of LUSC cells through ROS accumulation, probably via disrupting the mitochondrial respiratory chain (MRC) and the PI3K/Akt/Nrf2 pathway. Therefore, although clinical use of (+)-usnic acid will be limited due to toxicity issues, derivatives thereof may turn out as promising anticancer candidates for adjuvant treatment of LUSC.

Usnic Acid Enaminone-Coupled 1,2,3-Triazoles as Antibacterial and Antitubercular Agents

(+)-Usnic acid, a product of secondary metabolism in lichens, has displayed a broad range of biological properties such as antitumor, antimicrobial, antiviral, anti-inflammatory, and insecticidal activities. Interested by these pharmacological activities and to tap into its potential, we herein present the synthesis and biological evaluation of new usnic acid enaminone-conjugated 1,2,3-triazoles 10-44 as antimycobacterial agents. (+)-Usnic acid was condensed with propargyl amine to give usnic acid enaminone 8 with a terminal ethynyl moiety. It was further reacted with various azides A1-A35 under copper catalysis to give triazoles 10-44 in good yields. Among the synthesized compounds, saccharin derivative 36 proved to be the most active analogue, inhibiting Mycobacterium tuberculosis (Mtb) at an MIC value of 2.5 μM. Analogues 16 and 27, with 3,4-difluorophenacyl and 2-acylnaphthalene units, respectively, inhibited Mtb at MIC values of 5.4 and 5.3 μM, respectively. Among the tested Gram-positive and Gram-negative bacteria, the new derivatives were active on Bacillus subtilis, with compounds 18 [3-(trifluoromethyl)phenacyl] and 29 (N-acylmorpholinyl) showing inhibitory concentrations of 41 and 90.7 μM, respectively, while they were inactive on the other tested bacterial strains. Overall, the study presented here is useful for converting natural (+)-usnic acid into antitubercular and antibacterial agents via incorporation of enaminone and 1,2,3-triazole functionalities.

Anticancer Potential of Lichens' Secondary Metabolites

Lichens produce different classes of phenolic compounds, including anthraquinones, xanthones, dibenzofuranes, depsides and depsidones. Many of them have revealed effective biological activities such as antioxidant, antiviral, antibiotics, antifungal, and anticancer. Although no clinical study has been conducted yet, there are number of in vitro and in vivo studies demonstrating anticancer effects of lichen metabolites. The main goal of our work was to review most recent published papers dealing with anticancer activities of secondary metabolites of lichens and point out to their perspective clinical use in cancer management.

Synthesis and cytotoxic evaluation of usnic acid benzylidene derivatives as potential anticancer agents

A series of usnic acid benzylidene derivatives (groups I-V) were designed, synthesized and evaluated for their anticancer activity in the search for potentially new anticancer agents. Compounds 1a, 5b, 2b, 2e and 2f exhibited the most potent cytotoxcity against K562 cell line with IC₅₀ values of 10.0 ± 3.6, 5.6 ± 0.4, 8.8 ± 1.0, 4.5 ± 0.1 and 8.4 ± 0.4 μM, respectively. It is noteworthy that compound 2e displayed potent cytotoxicity against K562 cells without any cytotoxic effect on HEK293 normal cell line.

Usnea Acid as Multidrug Resistance (MDR) Reversing Agent against Human Chronic Myelogenous Leukemia K562/ADR Cells via an ROS Dependent Apoptosis

Purpose

Multidrug resistance (MDR) is a major obstacle in chemotherapy of leukemia treatments. In this paper, we investigated Usnea Acid (UA) as MDR reversal agent on hematologic K562/ADR cells via ROS dependent apoptosis.

Methods

CCK8 assay was used to measure cell viability rate of K562/ADR. Intracellular reactive oxygen species (ROS) generation, cell cycle distribution, cell apoptosis were measured with flow cytometry, respectively. Proteins related to apoptosis were measured by Western blot. Intracellular Adriamycin accumulation was observed by confocal microscopy and measured by flow cytometry.

Results

In vitro study showed intracellular Adriamycin accumulation was remarkably increased by UA. Cell viability treated with Adr (4 μM) was decreased from 89.8%  ± 4.7 to 32%  ± 8.9 by combined with UA (4 μM). Adr-induced apoptosis and G₁/G₀ phase cell cycle arrest were remarkably increased by UA, as well as, intracellular ROS level. However, MDR reversing activity of UA was inhibited by N-acetyl cysteine (NAC), a ROS scavenger.

Conclusion

These data provide compelling evidence that UA is a promising agent against MDR in leukemia cell line and suggest a promising therapeutic approach for leukemia.

(+)-Usnic Acid Inhibits Migration of c-KIT Positive Cells in Human Colorectal Cancer

Inhibition of tumor cell migration is a treatment strategy for patients with colorectal cancer (CRC). SCF-dependent activation of c-KIT is responsible for migration of c-KIT positive [c-KIT(+)] cells of CRC. Drug resistance to Imatinib Mesylate (c-KIT inhibitor) has emerged. Inhibition of mTOR can induce autophagic degradation of c-KIT. (+)-usnic acid [(+)-UA], isolated from lichens, has two major functions including induction of proton shuttle and targeting inhibition of mTOR. To reduce hepatotoxicity, the treatment concentration of (+)-UA should be lower than 10 μM. HCT116 cells and LS174 cells were employed to investigate the inhibiting effect of (+)-UA (<10 μM) on SCF-mediated migration of c-KIT(+) CRC cells. HCT116 cells were employed to investigate the molecular mechanisms. The results indicated that firstly, 8 μM (+)-UA decreased ATP content via uncoupling; secondly, 8 μM (+)-UA induced mTOR inhibition, thereby mediated activation suppression of PKC-A, and induced the autophagy of the completed autophagic flux that resulted in the autophagic degradation and transcriptional inhibition of c-KIT and the increase in LDH release; ultimately, 8 μM (+)-UA inhibited SCF-mediated migration of CRC c-KIT(+) cells. Taken together, 8 μM could be determined as the effective concentration for (+)-UA to inhibit SCF-mediated migration of CRC c-KIT(+) cells.

Graviola (Annona muricata) Exerts Anti-Proliferative, Anti-Clonogenic and Pro-Apoptotic Effects in Human Non-Melanoma Skin Cancer UW-BCC1 and A431 Cells In Vitro: Involvement of Hedgehog Signaling

Non-melanoma skin cancers (NMSCs) are the leading cause of skin cancer-related morbidity and mortality. Effective strategies are needed to control NMSC occurrence and progression. Non-toxic, plant-derived extracts have been shown to exert multiple anti-cancer effects. Graviola (Annona muricata), a tropical fruit-bearing plant, has been used in traditional medicine against multiple human diseases including cancer. The current study investigated the effects of graviola leaf and stem extract (GLSE) and its solvent-extracted fractions on two human NMSC cell lines, UW-BCC1 and A431. GLSE was found to: (i) dose-dependently suppress UW-BCC1 and A431 cell growth, motility, wound closure, and clonogenicity; (ii) induce G₀/G₁ cell cycle arrest by downregulating cyclin/cdk factors while upregulating cdk inhibitors, and (iii) induce apoptosis as evidenced by cleavage of caspases-3, -8 and PARP. Further, GLSE suppressed levels of activated hedgehog (Hh) pathway components Smo, Gli 1/2, and Shh while inducing SuFu. GLSE also decreased the expression of pro-apoptotic protein Bax while decreasing the expression of the anti-apoptotic protein Bcl-2. We determined that these activities were concentrated in an acetogenin/alkaloid-rich dichloromethane subfraction of GLSE. Our data identify graviola extracts and their constituents as promising sources for new chemopreventive and therapeutic agent(s) to be further developed for the control of NMSCs.

Usnic Acid Induces Cycle Arrest, Apoptosis, and Autophagy in Gastric Cancer Cells In Vitro and In Vivo

Background

Usnic acid (UA), a secondary metabolite, is mainly derived from certain lichen species. Growing evidence suggests that UA has antitumor, anti-oxidative, anti-inflammatory, and other activities in a variety of cancer cells. However, the antitumor effect of UA in gastric cancer cells (GC) is unclear. The aim of this investigation was to assess the antitumor effect of UA in GC cells in vitro and in vivo, and to explore the underlying mechanisms.

Material/Methods

Cell proliferation was measured by CCK8 assay, the arrest of cell cycle was assessed by flow cytometry, and cellular apoptosis was observed via Hoechst 33258 staining assay. Expression levels of apoptosis-related proteins (activated caspase-3 and PARP, Bax, Bcl2) and autophagy-associated proteins (LC3-II and p62) were verified through Western blot analysis. H&E staining and immunohistochemistry were carried out in the subcutaneously implanted BGC823 tumor model in a nude mouse experiment.

Results

In vitro, we demonstrated that UA was significantly effective in inducing morphological changes, inhibiting the cell proliferation dose- and time-dependently, arresting the cell cycle phase, promoting cancer cellular apoptosis, and inducing autophagy activity. In vivo, compared to mice treated with 5-FU alone, UA treatment was significantly more effective in suppressing the tumor growth without affecting body weight, and in regulating the amount of Bax and Bcl2 in tumor tissues.

Conclusions

UA induces cell cycle arrest and autophagy and exerts anti-proliferative and apoptotic effects by modulating expression of apoptosis-related proteins in stomach neoplasm cells, and has a better antitumor effect compared to 5-Fu in the xenograft model.