Multifaceted Properties of Usnic Acid in Disrupting Cancer Hallmarks

Cancer, a complex group of diseases marked by uncontrolled cell growth and invasive behavior, is characterized by distinct hallmarks acquired during tumor development. These hallmarks, first proposed by Douglas Hanahan and Robert Weinberg in 2000, provide a framework for understanding cancer's complexity. Targeting them is a key strategy in cancer therapy. It includes inhibiting abnormal signaling, reactivating growth suppressors, preventing invasion and metastasis, inhibiting angiogenesis, limiting replicative immortality, modulating the immune system, inducing apoptosis, addressing genome instability and regulating cellular energetics. Usnic acid (UA) is a natural compound found in lichens that has been explored as a cytotoxic agent against cancer cells of different origins. Although the exact mechanisms remain incompletely understood, UA presents a promising compound for therapeutic intervention. Understanding its impact on cancer hallmarks provides valuable insights into the potential of UA in developing targeted and multifaceted cancer therapies. This article explores UA activity in the context of disrupting hallmarks in cancer cells of different origins based on recent articles that emphasize the molecular mechanisms of this activity.

Hepatotoxicity of usnic acid and underlying mechanisms

Since usnic acid was first isolated in 1844 as a prominent secondary lichen metabolite, it has been used for various purposes worldwide. Usnic acid has been claimed to possess numerous therapeutic properties, including antimicrobial, anti-inflammatory, antiviral, anti-proliferative, and antipyretic activities. Approximately two decades ago, crude extracts of usnic acid or pure usnic acid were marketed in the United States as dietary supplements for aiding in weight loss as a "fat-burner" and gained popularity in the bodybuilding community; however, hepatotoxicity was documented for some usnic acid containing products. The US Food and Drug Administration (FDA) received numerous reports of liver toxicity associated with the use of dietary supplements containing usnic acid, leading the FDA to issue a warning letter in 2001 on a product, LipoKinetix. The FDA also sent a recommendation letter to the manufacturer of LipoKinetix, resulting in the withdrawal of LipoKinetix from the market. These events triggered investigations into the hepatotoxicity of usnic acid and its mechanisms. In 2008, we published a review article titled "Usnic Acid and Usnea Barbata Toxicity". This review is an updated version of our previous review article and incorporates additional data published since 2008. The purpose of this review is to provide a comprehensive summary of the understanding of the liver toxicity associated with usnic acid, with a particular focus on the current understanding of the putative mechanisms of usnic acid-related hepatotoxicity.

Bioactive Lichen Secondary Metabolites and Their Presence in Species from Chile

Lichens are symbiotic organisms composed of at least one fungal and one algal species. They are found in different environments around the world, even in the poles and deserts. Some species can withstand extreme abiotic conditions, including radiation and the vacuum of space. Their chemistry is mainly due to the fungal metabolism and the production of several secondary metabolites with biological activity, which have been isolated due to an increasing interest from the pharmaceutical community. However, beyond the experimental data, little is known about their mechanisms of action and the potential pharmaceutical use of these kinds of molecules, especially the ones isolated from lesser-known species and/or lesser-studied countries. The main objective of this review is to analyze the bibliographical data of the biological activity of secondary metabolites from lichens, identifying the possible mechanisms of action and lichen species from Chile. We carried out a bibliographic revision of different scientific articles in order to collect all necessary information on the biological activity of the metabolites of these lichen species. For this, validated databases were used. We found the most recent reports where in vitro and in vivo studies have demonstrated the biological properties of these metabolites. The biological activity, namely anticancer, antioxidant, and anti-inflammatory activity, of 26 secondary metabolites are described, as well as their reported molecular mechanisms. The most notable metabolites found in this review were usnic acid, atranorin, protolichesterinic acid, and lobaric acid. Usnic acid was the most investigated metabolite, in addition to undergoing toxicological and pharmacological studies, where a hepatotoxicity effect was reported due to uncoupling oxidative phosphorylation. Additionally, no major studies have been made to validate the pharmacological application of these metabolites, and few advancements have been made in their artificial growth in bioreactors. Despite the described biological activities, there is little support to consider these metabolites in pharmaceutical formulations or to evaluate them in clinical trials. Nevertheless, it is important to carry out further studies regarding their possible human health effects. These lichen secondary metabolites present a promising research opportunity to find new pharmaceutical molecules due to their bioactive properties.

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.

The expression profiles of apoptosis-related genes induced usnic acid in SK-BR-3 breast cancer cell

This study aims to determine whether usnic acid (UA) could induce the expression of apoptosis-related genes in apoptosis pathway. The current study has enabled us to better understand the target of UA in the treatment of breast cancer. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Based on the previous study and the results of this study, UA had the most antiproliferative effect on SK-BR-3 breast cancer cell line. We examined differential expression of 88 apoptosis-related genes by quantitative real-time polymerase chain reaction using the apoptosis primary library panel in SK-BR-3 breast cancer cell. We observed a difference in the significant differential expression of 74 apoptosis-related genes in breast cancer after SK-BR-3 cells applied to UA (7.21 µM) for 48 h. The expression level of 56 of these 74 differentiated apoptosis-related genes increased ( p < 0.05), but the expression level of the other 18 related genes decreased ( p < 0.05). In order to evaluate the mechanism of apoptosis of UA, Western blot analysis was performed with Bcl-2, Bax, Caspase-3, and Caspase-9 antibodies. According to the Western blot analysis, we obtained similar results with gene-expression data. These results suggest that UA showed a cytotoxic effect in SK-BR-3 cells through activation of the mitochondrial apoptotic pathway. The obtained results from gene expression revealed that the effect of UA on apoptosis pathway is critical for clinical research.

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.

Usnic acid induces apoptosis in human gastric cancer cells through ROS generation and DNA damage and causes up-regulation of DNA-PKcs and γ-H2A.X phosphorylation

Usnic acid, a dibenzofuran derivative found in many lichen species, is reported to have anticancer activity against human gastric cancer. We investigated the molecular alterations associated with anticancer effects of usnic acid against human gastric adenocarcinoma AGS and gastric carcinoma SNU-1 cells. Usnic acid (10-25 μM) treatment to these cells caused a significant increase in mitochondrial membrane depolarization and apoptotic cells. Apoptosis induction was accompanied by an increase in the ratio of Bax:Bcl-2 expression and cleaved-PARP. Usnic acid increased the comet tail length and tail DNA in alkaline comet assay indicating DNA double-strand breaks which was also evidenced by an increase in γH2A.X (Ser139) phosphorylation. The expression of DNA damage response proteins including DNA-PKcs, pATM (Ser1981), Chk-2 and p53 were increased. Further, N-acetyl cysteine, a known reactive oxygen species (ROS) scavenger, reversed the effects of usnic acid on expression of DNA damage response proteins and γH2A.X (Ser139) phosphorylation. This reversal was also observed in comet assay in a time and dose-dependent manner suggesting that usnic acid-induced DNA damage was caused by ROS. In addition, the non-toxic concentrations (1-10 μM) of usnic acid inhibited colony forming potential of AGS cells indicating its anti-proliferation activity. More importantly, the concentration of usnic acid that caused significant death in gastric cancer cells, did not show any considerable toxicity to normal human embryonic kidney HEK293 cells, human keratinocyte HaCaT cells and mouse primary gastric cells. Collectively, these results for the first time demonstrated the selective apoptotic effect of usnic acid (10-25 μM) through ROS generation and DNA damage on human gastric cancer cells accompanied with upregulation of γH2A.X (Ser139) phosphorylation, DNA-PKcs and p53.

Discovery of novel (+)-Usnic acid derivatives as potential anti-leukemia agents with pan-Pim kinases inhibitory activity

Usnic acid (UA) is the main secondary metabolite isolated from lichens, with moderate anticancer activity. A small group of (+)-UA derivatives characterized with flavanone moiety was designed and synthesized, and their anticancer activities were evaluated in leukemia cells. It was demonstrated that (+)-UA derivatives 6a-6g inhibited the proliferation of leukemia cells HL-60 and K562 with low micromolar IC₅₀ values. Mechanisms of action were investigated to find that 6g induced apoptosis in HL-60 and K562 cell lines, and affected the expression of MNK/eIF4E axis-related proteins, such as Mcl-1, p-eIF4E, p-4E-BP1. Finally, kinase inhibition assay suggested 6g was a potential inhibitor of pan-Pim kinases. Meanwhile, the blocking of phosphorylation of BAD and 4E-BP1 by 6g, together with the proposed binding mode of 6g with Pim-1 further confirmed its Pim inhibition effects. Our finding provides the sight towards the potential mechanism of (+)-UA derivatives 6g as anti-leukemia agents.

Synergistic effects of hormone therapy drugs and usnic acid on hormone receptor-positive breast and prostate cancer cells

The aim of this study was to investigate the combined effects of usnic acid (UA) and Tamoxifen (Tam) or Enzalutamide (Enz) on hormone receptor-positive breast and prostate cancer (BC and PC), respectively. The antiproliferative and apoptotic effects of Tam or Enz alone and in combination with UA on MCF7 and LNCaP cancer cells were detected. The results of the WST-1 assay indicated that UA was a promising anticancer compound that significantly enhanced the effectiveness of hormone therapy drugs compared with each drug alone (combination index < 1). In addition, the combination of UA with Tam or Enz remarkably induced more cell cycle arrest at the G0/G1 phase and apoptosis than only drug-treated cells (P < 0.01). Consequently, our findings suggest that the combination of UA with Tam or Enz may be a potential therapeutic approach for the treatment of BC and PC and further studies are required to exploit the potential mechanisms of synergistic effects.

Structure of a new usnic acid derivative from a deacylating Mannich reaction: NMR studies supported by theoretical calculations of chemical shifts

In a conventional Mannich reaction using piperidine, hydroxypiperidines, morpholine, and N-methylpiperazine with usnic acid, a deacetylation was observed resulting in a substitution at C-2, a loss of an acetyl group, and a Mannich base with a stabilized enol. The enol has a hydrogen bond to the nitrogen of the secondary amine. The structure was investigated by nuclear magnetic resonance and deuterium isotope effects on ¹³ C chemical shifts as well as with density functional theory calculations to study the changed hydrogen bond pattern. It was found that the hydrogen bond involving the OH-9 group in chloroform forms a strong hydrogen bond than in usnic acid itself and that this hydrogen bond becomes even stronger in the more polar solvent, dimethylsulfoxide. Tautomerism was observed in the Mannich base as demonstrated by deuterium isotope effects on chemical shifts. The position of the tautomeric equilibrium depends on the solvent, and the position of the equilibrium governs the strength of the OH-9…O═C hydrogen bond.

Gram-scale production of carrier-free fluorescent berberine microrods for selective liver cancer therapy

Berberine, a widely used isoquinoline alkaloid in traditional Chinese medicine, has been proved to be a potential candidate in liver cancer therapy. However, the low therapeutic dose in the tumor target which is due to the poor solubility and oral bioavailability has limited its clinical application. In this study, fluorescent self-carried Berberine microrods (Ber-MRs) were prepared in gram-scale through a facile and cheap antisolvent precipitation method. Ber-MRs exhibited good optical properties, pH-responsive drug release behavior and selective and safe antitumor performance in vitro and in vivo without obvious toxicity. These findings have demonstrated that Ber-MRs are promising for efficient and safe liver cancer therapy. © 2018 BioFactors, 44(5):496-502, 2018.

In vitro cytotoxic and antiproliferative effects of usnic acid on hormone-dependent breast and prostate cancer cells

The aim of the current study was first to investigate cytotoxic activity of usnic acid (UA) on hormone-dependent breast and prostate cancer, and normal cells. Cells were treated with increasing concentrations (25 to 150 µM) of UA for 48 hours and cell viability, quantitative and morphological analysis of cell death, and cell cycle analysis were performed. UA was shown to have selective cytotoxicity on hormone-dependent cancer cells with the IC₅₀ levels of 71.4 and 77.5 µM for MCF7 and LNCaP cells, respectively. UA induced apoptotic cell death and G0/G1 cell cycle arrest without damaging normal cells. MCF7 cells were more sensitive to UA than LNCaP cells. Our results first revealed that UA is a promising candidate as an alternative agent for hormone-dependent breast and prostate cancers. However, molecular mechanism underlying the UA-mediated cell death in cancer cells should be investigated further.

The role of usnic acid-induced apoptosis and autophagy in hepatocellular carcinoma

Usnic acid (UA) is a multifunctional bioactive lichen secondary metabolite with potential anti-cancer properties. Although the promising therapeutic effects of UA have been investigated in different cancer cell lines, the mechanism driving UA-induced cell death has yet to be elucidated. As the type of cell death (apoptosis or autophagy) induced by UA may vary depending on the cancer cell type, we first studied the cytotoxic effects of UA in HEPG2 (HBV(−)) and SNU-449(HBV(+)) hepatocellular carcinoma (HCC) cell lines. HCC cell viability was considerably reduced in a dose-dependent manner at 12, 24, and 48 h after treatment with UA ( p < 0.05). However, SNU-449 cells were more sensitive to UA than HEPG2 cells. UA also induced apoptotic cell death in HCC cells with cell cycle arrest at G0/G1 and G2/M phase depending on the genetic profile of each cell type. On the other hand, we observed acidic vesicular organelles in HCC cells after 36 h of UA treatment. Taken together, these findings suggest that UA stimulates apoptosis and autophagy in HEPG2 and SNU-449 cells without damaging normal control cells. Thus, UA might be a potential therapeutic compound for HCC treatment. However, there is a need for further studies investigating the death-promoting or preventing roles for autophagy and the molecular signaling mechanisms induced by UA treatment.

Anticancer effects of ginsenoside Rk3 on non-small cell lung cancer cells: in vitro and in vivo

Ginsenoside Rk3 (Rk3) is present in the roots of processed Panax notoginseng herbs and it exerts anti-platelet aggregation, pro-immunogenic and cardioprotective effects. However, little is known regarding the anticancer activities of this compound, especially in lung cancer. This study was designed to investigate the anticancer effects of Rk3 on non-small cell lung cancer (NSCLC) cells and in an H460 xenograft tumor model. Our results showed that Rk3 reduced cell viability, inhibited both cell proliferation and colony formation, and induced G1 phase cell cycle arrest by downregulating the expression of cyclin D1 and CDK4 and upregulating the expression of P21. Rk3 also induced apoptosis in a concentration-dependent manner in H460 and A549 cells by Annexin V/PI staining, TUNEL assay and JC-1 staining, resulting in a change in the nuclear morphology. Moreover, Rk3 induced the activation of caspase-8, -9, and -3, promoted changes in mitochondrial membrane potential, decreased the expression of Bcl-2, increased the expression of Bax, and caused the release of cytochrome c, which indicated that the apoptosis-inducing effects of Rk3 were triggered via death receptor-mediated mitochondria-dependent pathways. Furthermore, Rk3 significantly inhibited the growth of H460 xenograft tumors without an obvious effect on the body weight of the treated mice. Histological analysis indicated that Rk3 inhibited tumor growth by altering the proliferation and morphology of tumor cells. In addition, we confirmed that Rk3 inhibited angiogenesis via CD34 staining and chick embryo chorioallantoic membrane (CAM) assay in vivo. Taken together, our findings revealed not only the anticancer effect of Rk3 on NSCLC cells but also a new promising therapeutic agent for human NSCLC.

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

(+)-Usnic acid (1) is a common bioactive lichen-derived secondary metabolite with a characteristic dibenzofuran scaffold. It displayed low micromolar antiproliferative activity levels and, notably, induced autophagy in a panel of diverse breast cancer cell lines, suggesting the mechanistic (formerly "mammalian") target of rapamycin (mTOR) as a potential macromolecular target. The cellular autophagic markers were significantly upregulated due to the inhibition of mTOR downstream effectors. Additionally, 1 showed an optimal binding pose at the mTOR kinase pocket aided by multiple interactions to critical amino acids. Rationally designed benzylidene analogues of 1 displayed excellent fitting into a targeted deep hydrophobic pocket at the core of the kinase cleft, through stacking with the phenolic side chain of the Tyr2225 residue. Several potent analogues were generated, including 52, that exhibited potent (nM concentrations) antiproliferative, antimigratory, and anti-invasive activities against cells from multiple breast cancer clonal lines, without affecting the nontumorigenic MCF-10A mammary epithelial cells. Analogue 52 also exhibited potent mTOR inhibition and autophagy induction. Furthermore, 52 showed potent in vivo antitumor activity in two athymic nude mice breast cancer xenograft models. Collectively, usnic acid and analogues are potential lead mTOR inhibitors appropriate for future use to control breast malignancies.

Secondary metabolites from cetrarioid lichens: Chemotaxonomy, biological activities and pharmaceutical potential

BACKGROUND

Lichens, as a symbiotic association of photobionts and mycobionts, display an unmatched environmental adaptability and a great chemical diversity. As an important morphological group, cetrarioid lichens are one of the most studied lichen taxa for their phylogeny, secondary chemistry, bioactivities and uses in folk medicines, especially the lichen Cetraria islandica. However, insufficient structure elucidation and discrepancy in bioactivity results could be found in a few studies.

PURPOSE

This review aimed to present a more detailed and updated overview of the knowledge of secondary metabolites from cetrarioid lichens in a critical manner, highlighting their potentials for pharmaceuticals as well as other applications. Here we also highlight the uses of molecular phylogenetics, metabolomics and ChemGPS-NP model for future bioprospecting, taxonomy and drug screening to accelerate applications of those lichen substances.

CHAPTERS

The paper starts with a short introduction in to the studies of lichen secondary metabolites, the biological classification of cetrarioid lichens and the aim. In light of ethnic uses of cetrarioid lichens for therapeutic purposes, molecular phylogeny is proposed as a tool for future bioprospecting of cetrarioid lichens, followed by a brief discussion of the taxonomic value of lichen substances. Then a delicate description of the bioactivities, patents, updated chemical structures and lichen sources is presented, where lichen substances are grouped by their chemical structures and discussed about their bioactivity in comparison with reference compounds. To accelerate the discovery of bioactivities and potential drug targets of lichen substances, the application of the ChemGPS NP model is highlighted. Finally the safety concerns of lichen substances (i.e. toxicity and immunogenicity) and future-prospects in the field are exhibited.

CONCLUSION

While the ethnic uses of cetrarioid lichens and the pharmaceutical potential of their secondary metabolites have been recognized, the knowledge of a large number of lichen substances with interesting structures is still limited to various in vitro assays with insufficient biological annotations, and this area still deserves more research in bioactivity, drug targets and screening. Attention should be paid on the accurate interpretation of their bioactivity for further applications avoiding over-interpretations from various in vitro bioassays.

Studies on the structures, cytotoxicity and apoptosis mechanism of 8-hydroxylquinoline rhodium(iii) complexes in T-24 cells

Two rhodium(iii) complexes showed good cytotoxicity. The underlying investigation of the apoptosis mechanism suggested that the mitochondrial apoptotic pathway was involved.

The genus Usnea: a potent phytomedicine with multifarious ethnobotany, phytochemistry and pharmacology

The genusUsneaAdans. (Parmeliaceae; lichenized Ascomycetes) is a typical group of mostly pale grayish-green fruticoselichens that grow as leafless mini-shrubs.

Usnic acid is a novel Pim-1 inhibitor with the abilities of inhibiting growth and inducing apoptosis in human myeloid leukemia cells

Usnic acid, a potent Pim-1 inhibitor, represents a lead compound for developing effective therapeutics for myeloid leukemia treatment.

Cadmium induced apoptosis in mouse primary hepatocytes: the role of oxidative stress-mediated ERK pathway activation and the involvement of histone H3 phosphorylation

Time-delayed apoptosis induced by cadmium in primary hepatocytes through DNA damage, histone modification and ERK signaling cascade, which are all mediated by oxidative stress.