Recent advances of antitumor shikonin/alkannin derivatives: A comprehensive overview focusing on structural classification, synthetic approaches, and mechanisms of action

Alkannin triggered apoptosis and ferroptosis in gastric cancer by suppressing lipid metabolism mediated by the c-Fos/SREBF1 axis

BACKGROUND

Gastric cancer (GC), one of the most common malignancies with high mortality worldwide, currently requires beneficial therapeutic strategies. Alkannin is the primary active component of Lithospermum erythrorhizon and has been shown to have potential anticancer effects on a variety of cancers. However, the specific effects and molecular mechanisms of alkannin against GC remain unknown.

PURPOSE

This study aimed to explore the detailed role and downstream effectors of alkannin in the treatment of GC.

METHODS

The functions of alkannin on the proliferation, migration and invasion of GC cells were measured via CCK-8, EdU, colony formation, LDH release, flow cytometry, wound healing, and Transwell assays. BODIPY-C11 staining, determination of cellular ferrous iron, MDA and GSH levels, and western blotting were used to evaluate alkannin-induced ferroptosis. Transcriptome sequencing was analyzed to identify differentially expressed genes. Nile red staining and cholesterol and triglyceride assays were utilized to examine changes in lipid metabolism. Transcriptional regulation was determined by real-time PCR, dual-luciferase reporter and chromatin immunoprecipitation assays. Finally, a xenograft animal model was employed to assess tumor growth in vivo.

RESULTS

Alkannin inhibited growth and motility and simultaneously triggered apoptotic and ferroptotic cell death in GC cells. Transcriptome sequencing analysis revealed that alkannin treatment downregulated c-Fos expression. The overexpression of c-Fos conferred the GC cells to tolerate alkannin in vitro and in vivo. Moreover, we confirmed that c-Fos activated SREBF1 transcription by directly binding to TPA-responsive elements within the SREBF1 promoter, leading to increased expression of lipid biosynthesis-related genes, which counteracted ferroptosis through the maintenance of cellular lipid homeostasis.

CONCLUSION

Our present study provides the first evidence that alkannin induces both apoptosis and ferroptosis in GC cells and reveals a novel mechanism by which alkannin restrains c-Fos-dependent SREBF1 transcriptional activation, leading to lipid metabolism and redox homeostasis disorders. Our findings highlight that alkannin is an available and promising natural product for the avoidance of drug resistance and the clinical treatment of GC.

The Potential Role of C4 MYH11+ Fibroblasts and the MDK-SDC2 Ligand-Receptor Pair in Lung Adenocarcinoma: Implications for Prognosis and Therapeutic Strategies

BACKGROUND

Lung adenocarcinoma (LUAD) posed a significant threat to global human health. This study employed single-cell RNA sequencing (scRNA-seq) to analyze transcriptomic data from nine LUAD patients at different stages of tumor infiltration, aiming to elucidate the tumor microenvironment and key biological processes of LUAD.

METHODS

In this study, we processed the scRNA-seq data using the Seurat package and sequentially applied principal component analysis followed by the Harmony package to effectively correct for batch effects, identifying 105,725 high-quality cells. Through cell clustering and gene expression profiling, we identified critical cell subpopulations and gene expression patterns in LUAD patients.

RESULTS

Our analysis revealed that the C4 MYH11+ Fibroblasts subtype was primarily involved in biological processes related to muscle function. Further investigations uncovered the MDK-SDC2 ligand-receptor pair as a critical regulator of tumor cell invasion, proliferation, and migration, driving LUAD progression. Additionally, we developed a gene-based prognostic model that effectively predicted patient survival, providing valuable clinical insights.

CONCLUSION

This study provided a comprehensive atlas of the LUAD tumor microenvironment, highlighted the role of the C4 MYH11+ Fibroblasts in tumor progression. It also proposed the MDK-SDC2 ligand-receptor pair as a novel mechanism, addressing a significant gap in this area of research. And presented a gene-based prognostic model as a novel perspective for research into immunotherapy and drug sensitivity in LUAD.

Structurally diverse meroterpenoids from Arnebia euchroma and their anti-inflammatory effects through NF-κB pathway

Meroterpenoids in the traditional Chinese medicine Arnebia euchroma are thought to be key components in its anti-inflammatory activity. In the present study, 17 meroterpenoids including four types of structural skeletons (1-17), together with a monoterpenoid (18), were isolated from the roots of A. euchroma. HRESIMS, 1D and 2D NMR, electronic circular dichroism, and quantum computing-assisted methods were employed to determine the structures of four previously undescribed compounds (1-3, and 14). Zicaomeroterin B (2) feature with a novel benzo[b]oxepin moiety was confirmed by X-ray analysis based on the crystalline mate method. Meroterpenoids 2, 5, 6, 13, and 17 exhibited significant inhibition against the production of NO, IL-6, and TNF-α in LPS-stimulated macrophages without obvious cytotoxic effects. Furthermore, compounds 2, 5, and 6 significantly inhibited the phosphorylation activation of NF-κB p65 and its nuclear translocation in luciferase reporter test, immunoblotting, and immunofluorescence imaging, which in turn inhibited the NF-κB pathway and exerted anti-inflammatory effects. These findings suggested that meroterpenoids 2, 5, and 6 in A. euchroma are the potential lead compounds for anti-inflammatory agents based on NF-κB signaling pathway.

Shikonin Stimulates Mitochondria-Mediated Apoptosis by Enhancing Intracellular Reactive Oxygen Species Production and DNA Damage in Oral Cancer Cells

Phytotherapy has rendered a new insight towards the treatment of various cancers, including oral cancer with fewer side effects, over the traditional chemotherapeutic drugs to overcome chemoresistance. Shikonin (Shk) is a natural biologically active alkaloid found in the Lithospermum erythrorhizon plant's root. It has potent cytotoxic activities against various cancers. Our study revealed the release time and anticancer potential of Shk on the SCC9 and H357 oral cancer cell lines. We investigated the antiproliferative, antimigratory, cell cycle arresting and apoptosis promoting activity of Shk in oral cancer cells by performing MTT and morphological assay, colony, and tumor sphere formation assay, AO/EtBr and DAPI staining, Annexin V-FITC/PI staining, assay for reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) measurement, comet assay, qRT-PCR, and western blot analysis. We also checked the interaction of DNA and Shk by docking and CD spectroscopy and EtBr displacement assay. As a result, we found that Shk reduced the viability, proliferation, and tumorigenicity of SCC9 and H357 cells in a time and concentration-dependent manner. We obtained half-maximal inhibitory concentration (IC50) at 0.5 µM for SCC9 and 1.25 µM for H357. It promotes apoptosis via overexpressing proapoptotic Bax and caspase 3 via enhancing ROS that leads to MMP depletion and DNA damage and arrests cells at the G2/M & G2/S phase. The antimigratory activity of Shk was performed by analyzing the expression of markers of epithelial-mesenchymal transition like E-cadherin, ZO-1, N-cadherin, and vimentin. These overall results recommended that Shk shows potent anticancer activity against oral cancer cell lines in both in vitro and ex vivo conditions. So, it could be an excellent agent for the treatment of oral cancer.

Shikonin induces the apoptosis and pyroptosis of EGFR-T790M-mutant drug-resistant non-small cell lung cancer cells via the degradation of cyclooxygenase-2

BACKGROUND

The T790M mutation in the epidermal growth factor receptor (EGFR) gene is the primary cause of resistance to EGFR-tyrosine kinase inhibitor (TKI) therapy in non-small cell lung cancer (NSCLC) patients. Previous research demonstrated that certain traditional Chinese medicine (TCM) monomers exhibit anti-tumor effects against various malignancies. This study aims to investigate the potentials of shikonin screened from a TCM monomer library containing 1060 monomers in killing EGFR-T790M drug-resistant NSCLC cells and elucidate the underlying mechanisms.

METHODS

MTT method was used to screen for the TCM monomers with significant killing effects on H1975 cells carrying the EGFR-T790M mutation. The influences of the identified monomer shikonin on cell growth were determined by the colony formation assay. Annexin-V/PI staining and JC-1 staining were applied to detect the effects of shikonin on cell apoptosis. The influences of shikonin on cell membrane integrity were detected by lactate dehydrogenase (LDH) release assay. Reactive oxygen species (ROS) generation was analyzed using DCFH-DA as probe. The mechanisms of shikonin affecting the stability of cyclooxygenase-2 (COX-2) were evaluated by using specific inhibitors for protein degradation pathways. Western blotting was performed to assess the effects of the alteration of COX-2 expression or enzymatic activity on the related signal pathways as well as the apoptotic and pyroptotic markers.

RESULTS

Shikonin was identified as a potent cytotoxic compound against EGFR-T790M-mutant NSCLC cells. Shikonin induced cell apoptosis and pyroptosis by triggering the activation of the caspase cascade and cleavage of poly (ADP-ribose) polymerase and gasdermin E by elevating intracellular ROS levels. Further investigations revealed that shikonin induced the degradation of COX-2 via the proteasome pathway, thereby decreasing COX-2 protein level and enzymatic activity and subsequently inhibiting the downstream PDK1/Akt and Erk1/2 signaling pathways through the induction of ROS production. Notably, COX-2 overexpression attenuated shikonin-induced apoptosis and pyroptosis, whereas COX-2 inhibition with celecoxib enhanced the cytotoxic effects of shikonin.

CONCLUSIONS

Combination treatment with shikonin and COX-2 inhibitor may be a suitable therapeutic strategy for EGFR-T790M-mutant NSCLC treatment.

Enhanced therapeutic impact of Shikonin-encapsulated exosomes in the inhibition of colorectal cancer progression

Colorectal cancer (CRC) is a prevalent malignancy with high mortality rates and poor prognosis. Shikonin (SHK) has demonstrated extensive anti-tumor activity across various cancers, yet its clinical application is hindered by poor solubility, limited bioavailability, and high toxicity. This study aims to develop SHK-loaded exosomes (SHK-Exos) and assess their efficacy in CRC progression. Exosomes were isolated using ultracentrifugation and characterized via TEM, NTA, and western blotting. Their cellular internalization was confirmed through confocal microscopy post PKH67 labeling. Effects on cell behaviors were assessed using CCK-8 and Transwell assays. Cell cycle and apoptosis were analyzed via flow cytometry. A xenograft tumor model evaluatedin vivotherapeutic potential, and tumor tissues were examined using H&E staining andin vivoimaging. SHK-Exos demonstrated effective cell targeting and internalization in CRC cells.In vitro, SHK-Exos surpassed free SHK in inhibiting aggressive cellular behaviors and promoting apoptosis, whilein vivostudies showed substantial efficacy in reducing tumor growth with excellent tumor targeting and minimal toxicity. Employing SHK-Exos effectively impedes CRC progressionin vitroandin vivo, offering significant therapeutic potential. This research underscores the advantages of using autologous exosomes as a drug carrier, enhancing efficacy and reducing toxicity.

Exploring the Pharmacological Potential of Lithospermum officinale L.: A Review of Phytochemicals and Ethnomedicinal Uses

Exploring phytochemicals from ethnomedicinal plants for pharmacological applications is a promising research area. By studying ethnomedicine, researchers can identify plants used for centuries to treat ailments and investigate their phytochemicals. Consequently, phytochemicals can be isolated, characterized, and tested for pharmacological activities, leading to new drug development. This research also helps preserve traditional knowledge and biodiversity. Lithospermum officinale L., found in Eurasia, Argentina (South), Colombia, and the United States, is valued for its medicinal properties, including anti-inflammatory, antioxidant, and antimicrobial effects. The current review emphasizes L. officinale L. as a significant reservoir of bioactive phytochemicals, with alkaloids, quinones, glucosides, phenolics, flavonoids, and lipids identified as the principal metabolites. It also unveils the unexplored potential of this plant for future research endeavors. Continued research on L. officinale L. can unlock its full potential, providing insights into its medicinal uses and contributing to biodiversity preservation.

Naphthoquinone derivatives as potential immunomodulators: prospective for COVID-19 treatment

Inflammation plays a crucial role in COVID-19, and when it becomes dysregulated, it can lead to severe outcomes, including death. Naphthoquinones, a class of cyclic organic compounds widely distributed in nature, have attracted significant interest due to their potential biological benefits. One such naphthoquinone is 3,5,8-trihydroxy-6-methoxy-2-(5-oxohexa-1,3-dienyl)-naphthanthene-1,4-dione (3,5,8-TMON), a compound produced by fungi. Despite its structural similarity to shikonin, limited research has been conducted to investigate its biological properties. Therefore, the objective of this study was to evaluate the effects of 3,5,8-TMON and its synthetic derivatives in the context of inflammation induced by lipopolysaccharide (LPS) and SARS-CoV-2 infection in vitro using cell cultures. 3,5,8-TMON was obtained by acid treatment of crude extracts of fermentation medium from Cordyceps sp., and two derivatives were accessed by reaction with phenylhydrazine under different conditions. The results revealed that the crude extract of the fungi (C. Ex) inhibited the activity of transcription factor NF-kB, as well as the production of nitric oxide (NO) and interleukin-6 (IL-6) when LPS induced it in RAW 264.7 cells. This inhibitory effect was observed at effective concentrations of 12.5 and 3.12 μg mL-1. In parallel, 3,5,8-TMON and the new derivatives 3 and 4 demonstrated the ability to decrease IL-6 production while increasing TNF, with a specific effect depending on the concentration. These concentration-dependent agonist and antagonist effects were observed in THP-1 cells. Furthermore, 3,5,8-TMON inhibited IL-6 production at concentrations of 12.5 and 3.12 μg mL-1 in Calu-3 cells during SARS-CoV-2 viral infection. These findings present promising opportunities for further research into the therapeutic potential of this class of naphthoquinone in the management of inflammation and viral infections.

Plant-derived strategies to fight against severe acute respiratory syndrome coronavirus 2

The coronavirus disease 2019 (COVID-19) pandemic has caused an unprecedented crisis, which has been exacerbated because specific drugs and treatments have not yet been developed. In the post-pandemic era, humans and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will remain in equilibrium for a long time. Therefore, we still need to be vigilant against mutated SARS-CoV-2 variants and other emerging human viruses. Plant-derived products are increasingly important in the fight against the pandemic, but a comprehensive review is lacking. This review describes plant-based strategies centered on key biological processes, such as SARS-CoV-2 transmission, entry, replication, and immune interference. We highlight the mechanisms and effects of these plant-derived products and their feasibility and limitations for the treatment and prevention of COVID-19. The development of emerging technologies is driving plants to become production platforms for various antiviral products, improving their medicinal potential. We believe that plant-based strategies will be an important part of the solutions for future pandemics.

In vitro and in vivo anticancer activity of novel Rh(III) and Pd(II) complexes with pyrazolopyrimidine derivatives

Six pyrazolopyrimidine rhodium(III) or palladium(II) complexes, [Rh(L1)(H2O)Cl3] (1), [Rh(L2)(CH3OH)Cl3] (2), [Rh(L3)(H2O)Cl3] (3), [Rh2(L4)Cl6]·CH3OH (4), [Rh(L5)(CH3CN)Cl3]·0.5CH3CN (5), and [Pd(L5)Cl2] (6), were synthesized and characterized. These complexes showed high cytotoxicity against six tested cancer cell lines. Most of the complexes showed higher cytotoxicity to T-24 cells in vitro than cisplatin. Mechanism studies indicated that complexes 5 and 6 induced G2/M phase cell cycle arrest through DNA damage, and induced apoptosis via endoplasmic reticulum stress response. In addition, complex 5 also induced cell apoptosis via mitochondrial dysfunction. Complexes 5 and 6 showed low in vivo toxicity and high tumor growth inhibitory activity in mouse tumor models. The inhibitory effect of rhodium complex 5 on tumor growth in vivo was more pronounced than that of palladium complex 6.

Recent advances on natural colorants-based intelligent colorimetric food freshness indicators: fabrication, multifunctional applications and optimization strategies

With the increasing concerns of food safety and public health, tremendous efforts have been concentrated on the development of effective, reliable, nondestructive methods to evaluate the freshness level of different kinds of food. Natural colorants-based intelligent colorimetric indicators which are typically constructed with natural colorants and polymer matrices has been regarded as an innovative approach to notify the customers and retailers of the food quality during the storage and transportation procedure in real-time. This review briefly elucidates the mechanism of natural colorants used for intelligent colorimetric indicators and fabrication methodologies of natural colorants-based food freshness indicators. Subsequently, their multifunctional applications in intelligent food packaging systems like antioxidant packaging, antimicrobial packaging, biodegradable packaging, UV-blocking packaging and inkless packaging are well introduced. This paper also summarizes several optimizing strategies for the practical application of this advanced technology from different perspectives. Strategies like adopting a hydrophobic matrix, constructing double-layer film and encapsulation have been developed to improve the stability of the indicators. Co-pigmentation, metal ion complexation, pigment-mixing and using substrates with high surface area are proved to be effective to enhance the sensitivity of the indicators. Approaches include multi-index evaluation, machine learning and smartphone-assisted evaluation have been proven to improve the accuracy of the intelligent food freshness indicators. Finally, future research opportunities and challenges are proposed. Based on the fundamental understanding of natural colorants-based intelligent colorimetric food freshness indicators, and the latest research and findings from literature, this review article will help to develop better, lower cost and more reliable food freshness evaluation technique for modern food industry.

Therapeutic prospects of naturally occurring p38 MAPK inhibitors tanshinone IIA and pinocembrin for the treatment of SARS-CoV-2-induced CNS complications

P38 mitogen-activated protein kinase (p38 MAPK) signaling pathway is closely related to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) replication and hyperinflammatory responses in coronavirus disease 2019 (COVID-19). Therefore, blood-brain barrier-penetrating p38 MAPK inhibitors have good potential for the treatment of central nervous system (CNS) complications of COVID-19. The aim of the present study is the characterization of the therapeutic potential of tanshinone IIA and pinocembrin for the treatment of CNS complications of COVID-19. Studies published in high-quality journals indexed in databases Scopus, Web of Science, PubMed, and so forth were used to review the therapeutic capabilities of selected compounds. In continuation of our previous efforts to identify agents with favorable activity/toxicity profiles for the treatment of COVID-19, tanshinone IIA and pinocembrin were identified with a high ability to penetrate the CNS. Considering the nature of the study, no specific time frame was determined for the selection of studies, but the focus was strongly on studies published after the emergence of COVID-19. By describing the association of COVID-19-induced CNS disorders with p38 MAPK pathway disruption, this study concludes that tanshinone IIA and pinocembrin have great potential for better treatment of these complications. The inclusion of these compounds in the drug regimen of COVID-19 patients requires confirmation of their effectiveness through the conduction of high-quality clinical trials.

Necroptosis inhibits autophagy by regulating the formation of RIP3/p62/Keap1 complex in shikonin-induced ROS dependent cell death of human bladder cancer

BACKGROUND

Shikonin, a natural naphthoquinone compound, has a wide range of pharmacological effects, but its anti-tumor effect and underlying mechanisms in bladder cancer remain unclear.

PURPOSE

We aimed to investigate the role of shikonin in bladder cancer in vitro and in vivo in order to broaden the scope of shikonin's clinical application.

STUDY DESIGN AND METHODS

We performed MTT and colony formation to detect the inhibiting effect of shikonin on bladder cancer cells. ROS staining and flow cytometry assays were performed to detect the accumulation of ROS. Western blotting, siRNA and immunoprecipitation were used to evaluate the effect of necroptosis in bladder cancer cells. Transmission electron microscopy and immunofluorescence were used to examine the effect of autophagy. Nucleoplasmic separation and other pharmacological experimental methods described were used to explore the Nrf2 signal pathway and the crosstalk with necroptosis and autophagy. We established a subcutaneously implanted tumor model and performed immunohistochemistry assays to study the effects and the underlying mechanisms of shikonin on bladder cancer cells in vivo.

RESULTS

The results showed that shikonin has a selective inhibitory effect on bladder cancer cells and has no toxicity on normal bladder epithelial cells. Mechanically, shikonin induced necroptosis and impaired autophagic flux via ROS generation. The accumulation of autophagic biomarker p62 elevated p62/Keap1 complex and activated the Nrf2 signaling pathway to fight against ROS. Furthermore, crosstalk between necroptosis and autophagy was present, we found that RIP3 may be involved in autophagosomes and be degraded by autolysosomes. We found for the first time that shikonin-induced activation of RIP3 may disturb the autophagic flux, and inhibiting RIP3 and necroptosis could accelerate the conversion of autophagosome to autolysosome and further activate autophagy. Therefore, on the basis of RIP3/p62/Keap1 complex regulatory system, we further combined shikonin with late autophagy inhibitor(chloroquine) to treat bladder cancer and achieved a better inhibitory effect.

CONCLUSION

In conclusion, shikonin could induce necroptosis and impaired autophagic flux through RIP3/p62/Keap1 complex regulatory system, necroptosis could inhibit the process of autophagy via RIP3. Combining shikonin with late autophagy inhibitor could further activate necroptosis via disturbing RIP3 degradation in bladder cancer in vitro and in vivo.

A comparative investigation of catalytic mechanism and domain between catechol-O-methyltransferase isoforms by isomeric shikonin and alkannin

The differences in catalytic mechanism and domain between the soluble (S-COMT) and membrane-bound catechol-O-methyltransferase (MB-COMT) are poorly documented due to the unavailable crystal structure of MB-COMT. Considering the enzymatic nature of S-COMT and MB-COMT, the challenge could be solvable by probing the interactions between the enzymes with the ligands with minor differences in structures. Herein, isomeric shikonin and alkannin bearing a R/S -OH group in side chain at the C2 position were used for domain profiling of COMTs. Human and rat liver-derived COMTs showed the differences in inhibitory response (human's IC₅₀ and K_i values for S-COMT < rat's, 5.80-19.56 vs. 19.56-37.47 μM; human's IC₅₀ and K_i values for MB-COMT > rat's) and mechanism (uncompetition vs. noncompetition) towards the two isomers. The inhibition of the two isomers against human and rat S-COMTs was stronger than those for MB-COMTs (S-COMT's IC₅₀ and K_i values < MB-COMT's, 5.80-37.47 vs. 40.01-111.8 μM). Additionally, the inhibition response of alkannin was higher than those of shikonin in no matter human and rat COMTs. Molecular docking stimulation was used for analysis. The inhibitory effects observed in in vitro and in silico tests were confirmed in vivo. These findings would facilitate further COMT-associated basic and applied research.

Targeting regulated cell death with plant natural compounds for cancer therapy: A revisited review of apoptosis, autophagy-dependent cell death, and necroptosis

Regulated cell death (RCD) refers to programmed cell death regulated by various protein molecules, such as apoptosis, autophagy-dependent cell death, and necroptosis. Accumulating evidence has recently revealed that RCD subroutines have several links to many types of human cancer; therefore, targeting RCD with pharmacological small-molecule compounds would be a promising therapeutic strategy. Moreover, plant natural compounds, small-molecule compounds synthesized from plant sources, and their derivatives have been widely reported to regulate different RCD subroutines to improve potential cancer therapy. Thus, in this review, we focus on updating the intricate mechanisms of apoptosis, autophagy-dependent cell death, and necroptosis in cancer. Moreover, we further discuss several representative plant natural compounds and their derivatives that regulate the above-mentioned three subroutines of RCD, and their potential as candidate small-molecule drugs for the future cancer treatment.

Recruitment of chalcone's potential in drug discovery of anti-SARS-CoV-2 agents

Chalcone is an interesting scaffold found in the structure of many naturally occurring molecules. Medicinal chemists are commonly interested in designing new chalcone-based structures because of having the α, β-unsaturated ketone functional group, which allows these compounds to participate in Michael's reaction and create strong covalent bonds at the active sites of the targets. Some studies have identified several natural chalcone-based compounds with the ability to inhibit the severe acute respiratory syndrome coronavirus and Middle East respiratory syndrome coronavirus proteases. A few years after the advent of the coronavirus disease 2019 pandemic and the publication of many findings in this regard, there is some evidence that suggests chalcone scaffolding has great potential for use in the design and development of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inhibitors. Artificial placement of this scaffold in the structure of optimized anti-SARS-CoV-2 compounds can potentially provide irreversible inhibition of the viral cysteine proteases 3-chymotrypsin-like protease and papain-like protease by creating Michael interaction. Despite having remarkable capabilities, the use of chalcone scaffold in drug design and discovery of SARS-CoV-2 inhibitors seems to have been largely neglected. This review addresses issues that could lead to further consideration of chalcone scaffolding in the structure of SARS-CoV-2 protease inhibitors in the future.

Recent Advancements in Natural Plant Colorants Used for Hair Dye Applications: A Review

There is an on-going demand in recent years for safer and "greener" hair coloring agents with the global consumer awareness of the adverse effects of synthetic hair dyes. The belief in sustainability and health benefits has focused the attention of the scientific community towards natural colorants that serve to replace their synthetic toxic counterparts. This review article encompasses the historical applications of a vast array of natural plant hair dyes and summarizes the possible coloration mechanisms (direct dyeing and mordant dyeing). Current information on phytochemicals (quinones, tannins, flavonoids, indigo, curcuminoids and carotenoids) used for hair dyeing are summarized, including their botanical sources, color chemistry and biological/toxicological activities. A particular focus is given on research into new natural hair dye sources along with eco-friendly, robust and cost-effective technologies for their processing and applications, such as the synthetic biology approach for colorant production, encapsulation techniques for stabilization and the development of inorganic nanocarriers. In addition, innovative in vitro approaches for the toxicological assessments of natural hair dye cosmetics are highlighted.

Chalcone-amide, a privileged backbone for the design and development of selective SARS-CoV/SARS-CoV-2 papain-like protease inhibitors

The newly emerged coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that caused the COVID-19 pandemic, is the closest relative of SARS-CoV with high genetic similarity. The papain-like protease (PLpro) is an important SARS-CoV/SARS-CoV-2 nonstructural protein that plays a critical role in some infection processes such as the generation of the functional replication complex, maturation of crude polyproteins, and regulation of the host antiviral immune responses. Therefore, the research to discover SARS-CoV-2 PLpro inhibitors could be a sensible strategy to obtain therapeutic agents for the treatment of COVID-19. Aiming to find SARS-CoV/SARS-CoV-2 PLpro inhibitors, various high throughput screenings (HTS) have been performed over the past two decades. Interestingly, the result of these efforts is the identification of hit/lead compounds whose structures have one important feature in common, namely having a chalcone-amide (N-benzylbenzamide) backbone. Structure-activity relationship (SAR) studies have shown that placing an (R)-configurated methyl group on the middle carbon adjacent to the amide group creates a unique backbone called (R)-methyl chalcone-amide, which dramatically increases PLpro inhibitory potency. Although this scaffold has not yet been introduced by medicinal chemists as a specific skeleton for the design of PLpro inhibitors, structural considerations show that the most reported PLpro inhibitors have this skeleton. This review suggests the (R)-methyl chalcone-amide scaffold as a key backbone for the design and development of selective SARS-CoV-2 PLpro inhibitors. Understanding the SAR and binding mode of these inhibitors in the active site of SARS-CoV-2 PLpro can aid the future development of anti-COVID-19 agents.

Deoxyshikonin Mediates Heme Oxygenase-1 Induction and Apoptotic Response via p38 Signaling in Tongue Cancer Cell Lines

Deoxyshikonin (DSK), a phytochemical constituent, has been documented to elicit various oncostatic properties alone or in combination with established therapeutics. However, its role in restraining oral squamous cell carcinoma (OSCC) is mostly unclear. Here, we examined the tumor-suppressive effect of DSK and explored the molecular mechanisms underlying DSK’s activities on controlling oral cancer. Our results showed that DSK dose-dependently lessened the cell viability of tongue cancer cell lines, involving induction of cell cycle arrest at the sub-G1 phase and apoptotic cell death. Moreover, a unique signature of apoptosis-related proteins, including augmented nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) expression and caspase activation, was observed in DSK-treated tongue cancer cell lines. Furthermore, DSK-mediated upregulation of HO-1 and cleavage of caspase-9 and -3 were significantly inhibited by pharmacological blockage of p38 kinase. Collectively, these data revealed that DSK halted cell cycle progression and elicited cell apoptosis in tongue cancer cell lines, reshaping a p38-dependent profile of apoptotic proteome. Our findings provided novel insights into the therapeutic implications of a natural compound on the management of OSCC.

Different Aspects of Emetine's Capabilities as a Highly Potent SARS-CoV-2 Inhibitor against COVID-19

In the global movement to find the appropriate agents to fight the coronavirus disease of 2019 (COVID-19), emetine is one of the strongest anti-SARS-CoV-2 compounds with sub-micromolar EC50 values, identified in several studies and high-throughput screening efforts. The reported anti-SARS-CoV-2 mechanisms indicate the effect of this compound on both virus-based and host-based targets. In addition to having excellent antiviral effects, emetine can relieve COVID-19 patients by reducing inflammation through inhibitory activity against NF-κB by the mechanism of IκBα phosphorylation inhibition; it can also limit the lipopolysaccharide-induced expression of pro-inflammatory cytokines TNFα, IL-1β, and IL-6. Emetine also can well reduce pulmonary arterial hypertension as an important COVID-19 complication by modulating a variety of cellular processes such as the Rho-kinase/CyPA/Bsg signaling pathway. The therapeutic value of emetine for combating COVID-19 was highlighted when in vivo pharmacokinetic studies showed that the concentration of this compound in the lungs increases significantly higher than the EC50 of the drug. Despite its valuable therapeutic effects, emetine has some cardiotoxic effects that limit its use in high doses. However, high therapeutic capabilities make emetine a valuable lead compound that can be used for the design and development of less toxic anti-COVID-19 agents in the future. This Review provides a collection of information on the capabilities of emetine and its potential for the treatment of COVID-19, along with structural analysis which could be used for further research in the future.