Home A promising naphthoquinone [8-hydroxy-2-(2-thienylcarbonyl)naphtho[2,3-b]thiophene-4,9-dione] exerts anti-colorectal cancer activity through ferroptosis and inhibition of MAPK signaling pathway based on RNA sequencing
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A promising naphthoquinone [8-hydroxy-2-(2-thienylcarbonyl)naphtho[2,3-b]thiophene-4,9-dione] exerts anti-colorectal cancer activity through ferroptosis and inhibition of MAPK signaling pathway based on RNA sequencing

  • Daneiva Caro , David Rivera , Yanet Ocampo , Klaus Müller and Luis A. Franco EMAIL logo
Published/Copyright: October 20, 2020

Abstract

Naphthoquinones are naturally occurring metabolites with recognized anti-cancer potential but limited clinical application. This study investigated the molecular mechanism of 8-hydroxy-2-(2-thenoyl)naphtho[2,3-b]thiophene-4,9-dione (1), a new candidate for colorectal cancer (CRC) treatment, using different experimental settings: MTT, clonogenic, wound healing, and cell cycle assays; as well as RNA sequencing. Naphthoquinone 1 selectively reduced the viability and migration of HT-29 cells by G2/M arrest and changes in their transcriptome signature with significant effect on cellular survival, proliferation, angiogenesis, response to interferon, oxidative stress, and immune response. Impact analysis identified ferroptosis and MAPK pathways as significantly affected. In summary, our results suggest that 1 induces the selective death of CRC cells by inducing oxidative stress, ferroptosis, and MAPK inhibition.

Graphical abstract

1 Introduction

Colorectal cancer (CRC) is a life-threatening disease documented as the third most commonly diagnosed malignancy and the fourth leading cause of cancer in the world. Historically, CRC has affected regions with a high human development index, such as North American and European countries, where incidence and mortality rates are currently stabilizing or decreasing; whereas trends are rising rapidly in many low-income and middle-income countries, including Central and South America [1,2]. The CRC burden is aggravated by the considerable socioeconomic challenges in these regions; therefore, improvements in treatment options and accessibility to better drugs are critical.

In this scenario, natural products have received great attention for CRC prevention and treatment due to their effectiveness, lack of toxicity, and affordability [3]. Among naturally occurring compounds, naphthoquinones (NQs) appear as attractive metabolites due to their biological and structural properties. Indeed, medicinal plants containing NQs, such as Tabebuia spp. (locally known as lapacho, pau-d’arco, roble, or guayacán), are employed in South America for their analgesic, anti-inflammatory, and anti-neoplastic properties. Moreover, since the seminal studies conducted by the National Cancer Institute (NCI-USA), nearly four decades ago, the clinical importance of NQs has stimulated enormous research interest along with the identification of natural and synthetic quinones with anti-proliferative activity toward a large number of human cancer cell lines, including melanoma, lymphoma, lung, breast, and CRC [4].

In the case of CRC, prominent bioactive NQs have been identified, including 5-hydroxy-2-methyl-1,4-naphthoquinone (plumbagin), 5-hydroxy-1,4-naphthoquinone (juglone), 5,8-dihydroxy-2-(1-hydroxy-4-methyl-3-pentenyl)-1,4-naphthoquinone (shikonin) and β-lapachone. Despite the encouraging experimental evidence, the clinical success of NQ derivatives has been limited mainly due to their serious and even life-threatening secondary effects [5]. Nevertheless, recent studies have demonstrated that chemical modifications to the NQ nucleus deliver new lead compounds that are both active and safe. In our previous work, it was described that the presence of a furan or thiophene ring on the naphthoquinone scaffold increases the cytotoxicity and selectivity against CRC, leading to the identification of 2-thienyl-8-hydroxynaphtho[2,3-b]thiophene-4,9-dione (1) as the most potent derivative to suppress HT-29 cells with low damaging effects against normal fibroblasts [6]. However, the molecular mechanisms underlying the cytotoxic effect of 1, as well as NQs in general, are still unclear.

In this work, we describe the effect of compound 1 on the viability, proliferation, migration, and cell cycle progression of HT-29 cells. To identify the molecular targets affected by 1, a transcriptome sequencing (RNA-sequencing) analysis was performed.

2 Materials and methods

2.1 Synthesis of test compound

The target compound 8-hydroxy-2-(2-thenoyl)naphtho[2,3-b]thiophene-4,9-dione (1) was prepared as described in ref. [7] to obtain a product with purity >95%. For experiments, stock solutions of 1 were prepared using dimethylsulfoxide (DMSO; Fisher Scientific, USA) and diluted in a complete medium when needed. The final percentage of DMSO was kept to a maximum of 0.1% (v/v).

2.2 Cell culture

HT-29 (human colorectal adenocarcinoma cell line; Cat# HTB38™; passages: 10–25), PCS-201-012 (primary dermal fibroblasts; passages: 3–8), MRC-5 (normal human fetal lung fibroblast; Cat# CCL-171; passages: 5–15), and 3T3-L1 (Mus musculus embryo fibroblasts Cat# CL-173; passages: 5–15) as cancerous or normal cells were obtained from the American Type Culture Collection (ATCC, Manassas, VA, USA). Cells were maintained routinely in McCoy’s 5A (HT-29), Dulbecco’s Modified Eagle’s medium (PCS-201-012 and 3T3-L1), or Eagle’s Minimal Essential Medium (MRC-5) (Sigma-Aldrich, St. Louis, MO, USA) supplemented with 10% fetal bovine serum (FBS; Gibco, Waltham, MA, USA or Sao Paulo, Brazil), 1.5 g/L sodium bicarbonate (Sigma-Aldrich, St. Louis, MO, USA), and low serum growth supplement (Invitrogen, Waltham, MA, USA) for PCS-201-012; at 37°C and 5% CO2.

2.3 Antiproliferative assay

The effect of test compound on cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay, following the procedures described in [6]. Cells were seeded in 96-well plate (1–1.5 × 104 cells/well) and incubated to 37°C and 5% CO2 for 24 h. After cells were treated, different concentrations of test compounds (0–40 µM) were dissolved in culture media for 48 h. Subsequently, the media was removed and replaced with MTT solution (0.25 mg/mL). At the end of 4 h, the medium was carefully dried and formazan crystals were dissolved in 100 µL of DMSO, and OD550 nm was measured using a plate reader (Multiskan Go, Thermo Scientific, Waltham, MA, USA). The values were plotted as percent relative growth of viable cells against untreated cells considered as control and expressed as the mean ± standard error of mean (SEM) of triplicate samples from three independent experiments.

2.4 Clonogenic assay

Clonogenic assay was used to evaluate the replicative capacity of CRC cells [8]. HT-29 or MRC-5 cells (750 cells/well) were plated into a 6-well plate for 6 h, and treated with 1 (0.86 and 1.73 μM), vehicle (DMSO), or Doxorubicin (1 µM) for 48 h. Then, the medium was replaced and after 7 days of culture, the colonies were fixed (acetic acid:methanol 1:7 vol/vol), stained (0.5% crystal violet), and counted with a stereomicroscope (EZ4 HD, Leica Microsystems, Singapore). A total number of three independent experiments were performed by duplicate.

2.5 Wound healing assay

The influence of 1 upon CRC cell migration was assessed using the wound healing assay. In brief, HT-29 cells (2 × 105 cells/well) were grown on 24-well plates until complete confluence. Then, a sterile pipette tip was used to scratch the monolayer, the medium was replaced for FBS-free medium, and cells were treated with 1 (0.5 and 1 μM) or vehicle (DMSO). The culture was monitored with an inverted microscope (Nikon, Melville, NY, USA) equipped with a digital camera, every 24 h for 3 days. Image analysis was performed with TScratch software (http://www.cse-lab.ethz.ch) [9]. A total number of three independent experiments were performed by duplicate.

2.6 Cell cycle analysis

To assess the effect of 1 on cell cycle distribution, HT-29 cells (2 × 105 cells/mL) were exposed to test compound (0.86 and 1.73 μM) or vehicle (DMSO) for 48 h and analyzed using the propidium iodide (PI) flow cytometry kit (ab139418; Abcam, Cambridge, UK) in accordance with the manufacturer’s instruction. Cell-cycle distribution was determined by flow cytometry (Dako, Beckman Coulter Inc., CA, USA). A total of three independent experiments were performed by duplicate.

2.7 Total RNA extraction and analysis

Total RNA of HT-29 cells treated with 1 (1.73 μM, 48 h) was extracted using a commercial kit (GeneJET™; Thermo Fisher Scientific, Vilnius, Lithuania). The concentration, purity, and integrity of the isolated RNA were assessed by Corporación CorpoGen (Bogotá, Colombia) using a NanoDrop 2000c spectrophotometer (Thermo Scientific), a Qubit® 2.0 Fluorometer (Life Technologies, Carlsbad, CA, USA), and the Agilent 2100 Bioanalyzer system (Agilent Technologies, Santa Clara, CA, USA). The concentration ranged from 49.8 to 97.6 ng/μL; the 260/280 ratios were above 1.9; and the RNA integrity number values were above 7, except for two samples.

2.8 RNA-sequencing analysis

Library preparation and sequencing were conducted at MR DNA (www.mrdnalab.com, Shallowater, TX, USA). Libraries were prepared with total RNA (150–500 ng) using the TruSeq™ RNA LT Sample Preparation kit (Illumina Inc., San Diego, CA, USA) and validated using a Qubit® dsDNA HS Assay Kit (Life Technologies) and the Agilent 2100 Bioanalyzer system, as shown in Table 2. Then, the libraries were pooled at equimolar concentration (2 nM) and 5 pM of the normalized pool was clustered using the cBOT (Illumina Inc.). Sequencing was carried out using a 2 × 150 bp paired-end configuration on the HiSeq 2500 platform for 300 cycles (Illumina Inc.)

Table 2

Summary of RNA-seq data including library construction, sequencing, and mapping results

TreatmentSampleLibrary size (average)Raw readsClean readsMapped readsMapping rate (%)GC%
Vehicle (DMSO)158812.526.53111.931.35910.537.31088.351
269614.816.82314.044.34012.334.47087.851
368014.596.73013.858.10812.218.74788.251
Compound 144769.689.7349.216.0128.030.07087.151
556812.508.59011.895.15910.410.41787.550
661610.433.1549.782.3308.609.50688.050

GC%: guanine-cytosine percentage.

2.9 Bioinformatics

Initial bioinformatics analysis was performed at Corporación CorpoGen (Bogotá, Colombia). After the quality was verified with the raw FastQC reads, Trimmomatic [10] was used to remove adapter sequences, trimming low-quality ends, and filtering low-quality reads at phred quality score Q33. Clean high-quality reads were aligned to a human reference genome (GRCh38.p7) with Tophat [11]. The expression level for each transcript was calculated as fragments per kilobase of transcript per million mapped fragments (FPKM) using Cufflinks. Differentially expressed genes (DEGs) were detected with Cuffdiff [12]. Genes were considered differentially expressed using the following threshold: log2ǀ(fold change)ǀ ≥ 0.5, p-value  ≤  0.001, and false discovery rate (FDR) q-value  ≤  0.05. iPathwayGuide online software (Advaita Corporation, Plymouth, MI, USA) was used to identify significantly impacted pathways, biological processes, molecular function, cellular components, etc.

2.10 Quantitative real-time PCR (RT-qPCR)

The transcription level of 6 DEGs (SPRR1B, HSPA6, SPRR3, IFITM1, IFI44L, and OAS2) was measured to validate the RNA-sequencing analysis. For this, 1.0 µg of RNA was employed to synthesize cDNA using the High Capacity cDNA reverse transcription kit (Applied Biosystems, Vilnius, Lithuania). RT-qPCR was performed with the LightCycler® 96 System (Roche, Mannheim, Germany) using FastStart Essential DNA Green Master (Roche) and specific primers (Table 1; Eurofins Genomics, Huntsville, USA). Gene expression was normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) or hypoxanthine phosphoribosyltransferase 1 (HPRT1) as reference genes. Duplicate cycle threshold (CT) values were analyzed by the comparative CT (ΔΔCT) method.

Table 1

Sequences of primers used for real-time qPCR analysis

Gene symbolGene IDOfficial namePrimer sequencesaTmbAmplicon Size (pb)
GAPDH2597Glyceraldehyde-3-phosphate dehydrogenaseF: TCGACAGTCAGCCGCATCTTCTTT64.6°C94
R: AACTCTACTTTGCAGAACCTCAC64.6°C
HPRT3251Hypoxanthine phosphoribosyltransferase 1F: ACCAGTCAACAGGGGACATAA58.7°C190
R: CTTCGTGGGGTCCTTTTCACC61.2°C
HSPA63310Heat shock protein family A (Hsp70) member 6F: CATCGCCTATGGGCTGGAC59.8°C94
R: GGAGAGAACCGACACATCGAA58.5°C
IFI44L10964IFN induced protein 44 likeF: ACAGAGCCAAATGATTCCCTATG58.6°C124
R: TCGATAAACGACACACCAGTTG58.9°C
IFITM18519IFN induced transmembrane protein 1F: ACTCAACACTTCCTTCCCCAA59.2°C231
R: CTTCCTGTCCCTAGACTTCACG59.8°C
OAS249392′-5′-oligoadenylate synthetase 2F: AGGTGGCTCCTATGGACGG60.8°C124
R: TTTATCGAGGATGTCACGTTGG58.5°C
SPRR1B6699Small proline-rich protein 1BF: TATTCCTCTCTTCACACCAG53.8°C155
R: TCCTTGGTTTTGGGGATG54.3°C
SPRR36707Small proline-rich protein 3F: CATGAGTTCTTACCAGCAGAAGCAG61.9°C149
R: TTCCAGGTTGTGGAACCTTTGAG60.9°C
  1. a

    F: Forward (5′ → 3′); R: Reverse (5′ → 3′).

  2. b

    Tm: melting temperature.

2.11 Statistical analysis

Data were represented as a mean ± SEM. Inhibitory concentration 50 (IC50) was calculated using non-linear regression. Data were analyzed by one-way analysis of variance (ANOVA) followed by Holm-Sidak’s multiple comparisons test. Statistical significance was considered at P < 0.05.

  1. Ethical approval: The conducted research is not related to either human or animal use.

3 Results

3.1 Compound 1 showed CRC-specific inhibitory activity in vitro

As we recently reported [7], the compound 8-hydroxy-2-(2-thenoyl)naphtho[2,3-b]thiophene-4,9-dione (1), exerted a selective cytotoxic effect against CRC cells (HT-29; IC50 of 1.73 ± 0.08 μM) when compared with dermal fibroblasts (PCS-201-012; IC50 = 4.59 ± 0.48 μM). Here, we confirmed the selectivity of compound 1 using fibroblasts from human (MRC-5; IC50 = 6.97 ± 0.66 μM; Figure 1a) and mouse (3T3-L1; IC50 = 14.32 ± 2.14 μM). Moreover, cytotoxic and non-cytotoxic concentrations of 1 (0.86 and 1.73 μM) inhibited the clonogenic survival of HT-29 cells, while MRC-5 fibroblast remained virtually unaffected (Figure 1b). In addition, Ames test revealed that the test compound did not induce mutagenicity even at high concentrations (4.8 and 9.6 μM, data not shown). Based on these data, the IC50 (1.73 μM) was selected as the effective concentration of 1, for further experiments.

Figure 1 Treatment with 8-hydroxy-2-(2-thenoyl)naphtho[2,3-b]thiophene-4,9-dione (1) has a CRC-specific inhibitory effect over proliferation and migration. (a) Cell viability of CRC cells (HT-29) versus fibroblasts (PCS-201-012 and MRC-5), when treated with compound 1, was determined with the MTT assay. (b) Colony formation assay confirmed the selectivity of compound 1 over CRC cells. Representative pictures of colonies were acquired with a stereomicroscope (8×). (c) Changes of the migratory potential induced by 1 were assessed by wound healing assay. The surface of migrating cells was recorded every 24 h using a microscope. Representative pictures are shown (10×). The results are expressed as the mean ± SEM of duplicate or triplicate samples from independent experiments (n = 6–12). Significant differences from the control are indicated by **p < 0.01; ***p < 0.001; ****p < 0.0001.
Figure 1

Treatment with 8-hydroxy-2-(2-thenoyl)naphtho[2,3-b]thiophene-4,9-dione (1) has a CRC-specific inhibitory effect over proliferation and migration. (a) Cell viability of CRC cells (HT-29) versus fibroblasts (PCS-201-012 and MRC-5), when treated with compound 1, was determined with the MTT assay. (b) Colony formation assay confirmed the selectivity of compound 1 over CRC cells. Representative pictures of colonies were acquired with a stereomicroscope (8×). (c) Changes of the migratory potential induced by 1 were assessed by wound healing assay. The surface of migrating cells was recorded every 24 h using a microscope. Representative pictures are shown (10×). The results are expressed as the mean ± SEM of duplicate or triplicate samples from independent experiments (n = 6–12). Significant differences from the control are indicated by **p < 0.01; ***p < 0.001; ****p < 0.0001.

To test whether compound 1 affected the migratory ability of CRC cells, the wound-healing assay was performed using a monolayer of HT-29 cells grown until confluence and scratched with a pipette tip. As shown in Figure 1c, the recovery rate of the scratched area was significantly decreased by compound 1 (0.5 and 1 μM) in a concentration-dependent manner, 48 and 72 h after treatment.

3.2 Anti-proliferative effect of compound 1 occurs by arresting cell cycle progression

Flow cytometry was employed to determine whether changes in the cell cycle distribution were involved in the reduction of HT-29 viability when exposed to compound 1. Figure 2 shows that treatment with 1 (1.73 μM) resulted in a significantly increased proportion of cells in the G2/M (2N-4N) phase, from 15.15 ± 4.62% (control – 0 μM) to 29.30 ± 6.86%. These results indicate that 1 inhibits CRC cell proliferation through cell cycle arrest at the G2/M-phase.

Figure 2 Compound 1 inhibited the proliferation of HT-29 cells by G2/M-phase arrest. Cell cycle distribution was assessed through staining with PI and flow cytometry. (a) The histogram shows the number of cells (vertical axis) vs DNA content-PI (horizontal axis-FL2 channel). (b) Percentage of cells in the indicated cell-cycle phase for the data presented in A. The results are expressed as the mean ± SEM of duplicate samples from three independent experiments (n = 6). Significant differences from the control are indicated by *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001.
Figure 2

Compound 1 inhibited the proliferation of HT-29 cells by G2/M-phase arrest. Cell cycle distribution was assessed through staining with PI and flow cytometry. (a) The histogram shows the number of cells (vertical axis) vs DNA content-PI (horizontal axis-FL2 channel). (b) Percentage of cells in the indicated cell-cycle phase for the data presented in A. The results are expressed as the mean ± SEM of duplicate samples from three independent experiments (n = 6). Significant differences from the control are indicated by *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001.

3.3 Transcriptome sequencing revealed that compound 1 reduced the carcinogenic signature of HT-29 cells and promoted cellular death through ferroptosis and inhibition of MAPK signaling

To investigate how compound 1 inhibited the viability of CRC cells, a comparative RNA sequencing (RNA-seq) analysis was conducted using HT-29 cells treated with vehicle (control) or 1 (1.73 μM). As shown in Table 2, the reads, mapping rates, and GC (guanine-cytosine) content were similar among the samples. After filtering differentially expressed transcripts (p < 0.05 and (FDR)-q value < 0.05), a total of 491 genes that significantly differed in HT-29 treated cells compared with control counterparts were identified (Figure 3a). Compound 1 significantly reduced the expression of 366 genes while increasing 125 genes. The transcriptomic analysis was validated by the significant correlation between the RNA-seq and RT-qPCR data [least-squares linear regression, p < 0.05; R2 = 0.911 (GAPDH) and R2 = 0.908 (HPRT)] when studying a selected subset of DEGs.

Figure 3 Compound 1 promoted a distinctive transcriptomic change in HT-29 cells with significant effect on genes associated with cell survival and proliferation; response to virus; and ferroptosis. (a) The mRNA expression changes of HT-29 treated with 1 (1.73 μM) compared with the control are presented using a volcano plot constructed in iPathwayGuide. Positive values on the x-axis indicate up-regulation, whereas negative values indicate down-regulation, both presented as Log2 fold change (LogFC). The y-axis represents a log scale showing the adjusted p-value. Red dots (491) represent differentially expressed genes (DEGs). (b) GO analysis was performed with iPathwayGuide; cut-off p-value, p < 0.05, using weight pruning correction. Enrichment significance is displayed as bar color intensity while its height is proportional to the number of DEGs in the GO term. (c) The top five significant impacted pathways by compound 1 as categorized by iPathwayGuide, p-values are shown without correction. DEGs are highlighted in red when up-regulated or blue when down-regulated. (d) Interferome database was employed to identify the number of IRGs – type I (red) and type II (blue) – in the list of DEGs.
Figure 3

Compound 1 promoted a distinctive transcriptomic change in HT-29 cells with significant effect on genes associated with cell survival and proliferation; response to virus; and ferroptosis. (a) The mRNA expression changes of HT-29 treated with 1 (1.73 μM) compared with the control are presented using a volcano plot constructed in iPathwayGuide. Positive values on the x-axis indicate up-regulation, whereas negative values indicate down-regulation, both presented as Log2 fold change (LogFC). The y-axis represents a log scale showing the adjusted p-value. Red dots (491) represent differentially expressed genes (DEGs). (b) GO analysis was performed with iPathwayGuide; cut-off p-value, p < 0.05, using weight pruning correction. Enrichment significance is displayed as bar color intensity while its height is proportional to the number of DEGs in the GO term. (c) The top five significant impacted pathways by compound 1 as categorized by iPathwayGuide, p-values are shown without correction. DEGs are highlighted in red when up-regulated or blue when down-regulated. (d) Interferome database was employed to identify the number of IRGs – type I (red) and type II (blue) – in the list of DEGs.

Gene ontology (GO) analysis was performed using iPathwayGuide online software on all DEGs. Figure 3b shows the top-10 list of GO terms related to biological process, molecular function, and cellular components, with a bar chart presenting the p values obtained from the analysis. According to the results, a significant enrichment of terms related to cancer progression (i.e., cell proliferation, cell migration, angiogenesis, cell–cell junction, cell–cell signaling, response to oxidative stress, and immune response) terms were induced by 1. The impact analysis revealed the most influenced pathways (Figure 3c), highlighting the significant enrichment of cell adhesion molecules (KEGG: 04514) and ferroptosis (KEGG: 04216) which are linked to cellular interactions (immune response, antigen recognition, and cellular adhesion) and regulated cell death, respectively.

In particular, treatment with compound 1 resulted in significant association with terms (i.e., defense response to virus) and pathways (i.e., influenza A, herpes simplex infection, human papillomavirus infection) associated with anti-viral immune response, which is a consequence of the marked reduction of interferon regulated genes (IRGs). In fact, the Interferome database [13] predicted that 28% of the down-regulated DEGs are regulated by type I and/or type II interferon (Figure 3d). Also, 8 out of the top-10 down-regulated genes were identified as IRGs (IFITM1, IFI44L, XAF1, EPSTI1, MX2, RSAD2, and CMPK2). Interestingly, several studies report that these IRGs are overexpressed in cell lines or affected tissues from CRC patients and their up-regulation is associated with resistance to chemotherapy (Table 3). Simultaneously, the analysis of the 10-top up-regulated genes showed their association with epidermal development (SPRR1B, SPRR3, SPRR1A, and SCEL), biosynthesis of retinoic acid (DHRS9), and extreme cellular stress (HSPA6). Moreover, compound 1 induced the expression of a tumor suppressor gene (AKAP12), a cysteine proteinase inhibitor (CST1), and leucine-rich repeat neuronal 4 (LRRN4) (Table 4).

Table 3

Top-10 differentially expressed genes (down-regulated)

Gene symbolDescriptionFunctionAssociation with CRCLogFCq valueRef.
IFITM1IFN-induced transmembrane protein 1IFN-induced antiviral protein. Plays a key role in the antiproliferative action of IFN-γ (inhibition of ERK activation or arresting cell growth in G1-phase trough p53)↑ Expression in CRC tissue that is associated with an aggressive phenotype and poor prognosis−4.7690.004[36,37]
↑ Proliferation and invasiveness of SW480 and DLD-1 cells with stable/ectopic over-expression of IFITM1
↓ Migration/invasion ability of CRC cells (HT-29, LoVo, and DLD-1) with transient/stable knockdown of IFITIM1
IFI44LIFN-induced protein 44-likeExhibits a low antiviral activity against hepatitis C virus↑ Expression in HT-29 cells resistant to oxaliplatin−4.1960.004[38]
OAS22′-5′-oligoadenylate synthase 2IFN-induced, dsRNA-activated antiviral enzyme↓ mRNA expression in high pro-migratory profile cancer-associated fibroblasts from CRC patients−3.1270.004[39]
XAF1XIAP-associated factor 1Seems to function as a negative regulator of members of the IAP (inhibitor of apoptosis protein) family↓ Expression in several cell lines and CRC tissue, which is associated with advance stage and high grade of tumor−3.0590.004[40,41]
The restoration of XAF1 expression in CRC cells induces apoptosis and enhanced chemotherapy sensitivity
EPSTI1Epithelial–stromal interaction protein 1↑ Expression in sporadic and IBD-associated CRC cell lines with knockdown expression of Nkx2-3, a transcription factor down-regulated in CRC−3.0460.004[42,43]
↓ Expression in CRC cells with strong EMT phenotype
MX2IFN-induced GTP-binding protein Mx2IFN-induced dynamin-like GTPase with potent antiviral activity−2.9790.004
RSAD2IFN-inducible iron-sulfur (4FE-4S) cluster-binding antiviral proteinIFN-inducible iron-sulfur (4FE-4S) cluster-binding antiviral protein↑ Expression in CRC samples when compared with colorectal adenomas−2.9340.004[44]
PAX4Paired box protein Pax-4Plays an important role in the differentiation and development of pancreatic islet beta cells↑ mRNA levels in HCT116 cells with induced invasiveness and migration−2.9270.045[45]
FFAR2Free fatty acid receptor 2G protein-coupled receptor that is activated by the short-chain fatty acids (SCFAs)↑ mRNA and protein expression in CRC specimens−2.8240.004[46,47]
↓ mRNA and protein levels in human CRC tissue
Ffar2/ mice are more susceptible to AOM-DSS
↑ mRNA expression of FFAR2 is detected only in HT-29 cells out of 8 CRC cell lines
CMPK2UMP-CMP kinase 2, mitochondrialMay participate in dUTP and dCTP synthesis in mitochondria↓ mRNA expression is associated with a lower CRC risk score−2.7920.004[48]

LogFC: Log2 fold change.

Table 4

Top ten differentially expressed genes (up-regulated)

Gene SymbolDescriptionFunctionAssociation with CRCLogFCq valueRef.
SPRR1BCornifin-BCross-linked envelope protein of keratinocytes3.5410.004
HSPA6Heat shock 70  kDa protein 6Molecular chaperone implicated in a wide variety of cellular processes↑ Expression when cell death was induced by electrohyperthermia using HT-29 CRC xenografts2.4630.004[30]
SPRR3Small proline-rich protein 3Cross-linked envelope protein of keratinocytes↑ Expression is involved in colorectal tumorigenesis, CRC proliferation, and lymphovascular invasion2.4380.012[49,50]
↑ Expression in CRC tissue and cell lines (i.e., HT-29)
AKAP12A-kinase anchor protein 12Anchoring protein that mediates the subcellular compartmentation of protein kinase A and C. (Tumor suppressor gene)↓ mRNA expression or methylation of gene promoter in CRC tissue2.3350.004[51,52]
► Represents a potential molecular biomarker for predicting CRC malignancy
► The re-expression of AKAP12 induced apoptosis, reduced colony formation and migration of LoVo cells in vitro and in vivo
SPRR1ACornifin-ACross-linked envelope protein of keratinocytes↓ mRNA expression in a mouse model of CRC2.2480.009[53]
↑Expression and ↓ methylation in CRC tissue
SCELSciellinMay function in the assembly or regulation of proteins in the cornified envelope↓ Expression in metastatic cell lines promoted CRC cell migration and invasion (↑Vimentin; ↓E-cadherin), while overexpression had the opposite effect (MET inducer?)2.1710.004[54]
↑ Expression in CRC specimens with higher clinical stage and hepatic metastasis
DHRS9Dehydrogenase/reductase SDR family member 93-Alpha-hydroxysteroid dehydrogenase that participates in dihydroxyprogesterone and retinoic acid biosynthesis↓ mRNA and protein expression in CRC clinical samples. It might represent a useful biomarker of prognosis2.1630.004[55]
LRRN4Leucine-rich repeat neuronal protein 4May play an important role in hippocampus-dependent long-lasting memoryIdentified as a low abundance protein in CRC tissues2.0090.004[56]
AKR1C1Aldo-keto reductase family 1 member C1Converts progesterone to its inactive form. In the liver and intestine may have a role in the transport of bile↓mRNA expression at the tumor center when compared to normal mucosa1.6590.004[57]
CST1Cystatin-SNCysteine proteinase inhibitors↑ mRNA levels in CRC cell lines (Caco-2 and SW480) and affected tissue from patients1.6110.004[58]
↑ Levels in urine from CRC patients

LogFC: Log2 fold change.

Since ferroptosis, an iron-dependent non-apoptotic cell death, was identified as one of the most impacted pathways by 1, a detailed analysis of the regulated genes was performed. As a result, it was found that compound 1 significantly increased the expression of genes involved with glutamate/cysteine transport (SLC3A2 and SLC7A11) and iron storage (FTH1-ferritin), which are down-regulated in CRC or dysplastic adenoma [14,15,16,17]. Alternatively, compound 1 reduced the expression of genes involved in iron efflux (SLC40A1-Ferroportin-1) and degradation of ferritin (LC3), which are interestingly overexpressed in CRC [17,18].

4 Discussion

Novel compounds that specifically and effectively target cancer cells are crucial for developing promising treatments. Molecules inspired in natural products, such as substituted naphtho[2,3-b]thiophene-4,9-diones, are proposed as leading structures with several studies and granted patents showing their strong anti-cancer effect [19,20]. In this work, we focused on the study of the 8-hydroxy-2-(2-thenoyl)naphtho[2,3-b]thiophene-4,9-dione (1), previously identified as a potent anti-proliferative compound, with IC50 values ranging from 0.29 μM (HaCaT) to 1.78 μM (HT-29) [6,7]. Consistently, we found that treatment with 1 induced selective cytotoxicity against HT-29 cells while human and mice fibroblasts from different origins (skin, lung, and embryo) were significantly less affected. Here, we also showed that 1 had a major impact on HT-29 cells proliferation and migration, as demonstrated by the absence of colony formation and the reduction of wounded area, at toxic and non-toxic concentrations. Furthermore, this derivative triggers the arrest of cell cycle progression at G2/M phase, as supported by flow cytometry analysis.

To date, it is accepted that naphthoquinone-based compounds exert their cytotoxicity inducing oxidative stress by redox cycling of the quinone through one-electron reduction by NADPH-cytochrome P-450 oxidoreductase (CPR) to the semiquinone radical, followed by a two-electron reduction by NAD(P)H:quinone oxidoreductase 1 (NQO-1) to hydroquinone [19]. Therefore, most pharmacological studies of NQs focus on the determination of the levels of superoxide and reactive oxygen species (ROS); hence, their exact molecular mechanisms still remain largely unknown. In the case of compound 1, Bannwitz et al. reported that its anti-proliferative effect was combined with low membrane-damaging effects [7]. Furthermore, they showed that several naphtho[2,3-b]thiophene-4,9-diones are activated by CPR or NQO-1; however, their ability to induce cell death was poorly correlated with the amount of superoxide, indicating that other mechanisms are involved. In our study, we profiled the transcriptomic alterations induced by compound 1 in the CRC cell line HT-29 using RNA-seq validated with RT-qPCR. The transcriptomic analysis revealed that derivative 1 promoted the differential expression of targets crucial for cellular survival, migration, signaling, and junction; immune response; oxidative stress response, among others. The detailed analysis of the top 10 DEGs, either up- or down-regulated (Tables 3 and 4), allowed us to verify that compound 1 reduced the carcinogenic signature of CRC cells since at least 50% of the DEGs were identified as altered in the opposite direction in CRC. This observation was particularly important in the case of IRGs, which were significantly down-regulated by test compound. Although interferon (IFN) signaling has traditionally been connected with pro-apoptotic tumor-suppressor functions, emerging data have revealed that in, certain contexts, IFN-activated pathways might mediate cellular growth, metastasis, and resistance to certain therapies [21]. In the case of CRC, it is described that a feature of an irinotecan-resistant cell line is the up-regulated expression of IRGs (i.e., IFIT1, G1P3, IFI35, IFITM1, OAS1, and IFIT3) [22].

Moreover, the impact analysis of the altered pathways added important information regarding the molecular mechanism underlying the cytotoxic effect of 1. This analysis evidenced that compound 1 influenced several signaling pathways that promoted cellular death (ferroptosis) or cellular proliferation and survival (MAPK and PI3K-AKT signaling pathways). Ferroptosis is a type of regulated cell death caused by the accumulation of iron-dependent lipid peroxides that are generated during excessive ROS production [23], which is triggered by (a) inhibitors of the cystine/glutamate antiporter (system Xc SLC3A2/SLC7A11) that reduce the synthesis of glutathione content causing oxidative damage; or (b) inhibitors of glutathione peroxidase 4 (GPx4) leading to uncontrolled lipid peroxidation [23]. From our transcriptomic analysis, several events might be causing the oxidative death induced by 1: (1) accumulation of intracellular iron content via increasing ferritin (FTH1) and decreasing ferroportin-1 (SLC40A1) and LC3 (MAP1LC3A) expression; (2) elevation of ROS (redox cycling) along with depletion of intracellular glutathione, which in turn leads to the observed up-regulation of glutamate cysteine ligase (GLC); or (3) decrease in Xc transport function, either by direct or indirect blockage, which is expected to decrease the levels of glutathione, which in turn will induce the expression of SLC7A11 and SLC3A2 (Figure 4). Furthermore, compound 1 also regulated the expression of several heat shock proteins (HSPs), which are involved in signaling pathways that affect iron metabolism and ferroptosis. Specifically, treatment with derivative 1 significantly reduces the expression of HSPB1 (also known as HSP-27), whose levels are often elevated and associated with chemotherapy resistance and worse clinical outcome in CRC [24]. Interestingly, a protective effect against oxidative stress by reducing iron uptake has been described for HSPB1 [23]; together with the observation that its inhibition induced the accumulation of intracellular iron leading to lipid peroxidation and injury of cancer cells when ferroptosis was induced by erastin, whereas the overexpression of HSPB1 inhibited this effect [25]. Alternatively, compound 1 up-regulated the expression of HSPA6 (HSP70B) and HSPH1 (HSP110 or HSP105), molecular chaperones which are known for improving cell survival during extreme stress. Although higher expression of HSP is not considered favorable for CRC patients [26]; it has been demonstrated that the expression of HSPH1 and HSPA6, might favor immune recognition of tumors [27,28] or inhibit the proliferation, migration, and invasion of cancer cells by cytotoxic treatments [29,30], respectively.

Figure 4 Compound 1 significantly impacts the expression of targets within ferroptosis pathway. iPathwayGuide online software was used to perform the impact analysis. (a) The difference in mRNA expression between HT-29 cells treated with compound 1 (1.73 μM) or vehicle (control) are shown with a heat map at the top left displayed as Log2 fold change (LogFC). Blue indicates down-regulated genes and red indicates up-regulated genes (log2 ǀ(fold change)ǀ ≥ 0.5, p-value  ≤  0.001, and q-value  ≤  0.05).
Figure 4

Compound 1 significantly impacts the expression of targets within ferroptosis pathway. iPathwayGuide online software was used to perform the impact analysis. (a) The difference in mRNA expression between HT-29 cells treated with compound 1 (1.73 μM) or vehicle (control) are shown with a heat map at the top left displayed as Log2 fold change (LogFC). Blue indicates down-regulated genes and red indicates up-regulated genes (log2 ǀ(fold change)ǀ ≥ 0.5, p-value  ≤  0.001, and q-value  ≤  0.05).

Another significantly impacted pathway by 1 was the mitogen-activated protein kinase (MAPK) pathway, including ERK, p38, and c-Jun NH2-terminal kinase (JNK), which is recognized for controlling cellular responses to the environment and regulate cell cycle, differentiation, growth, and cell senescence, all of which are critical for cancer initiation and progression [31]. Accumulating evidence has demonstrated that naphthoquinone derivatives modulate the MAPK pathway; however, studies are conflicting since some show that cell death is induced by activation of ERK, p38, and/or JNK [32,33], while others demonstrate the opposite [34]; suggesting that MAPK regulation is dependent on the compound structure or the cellular context. In HT-29 cells, we found that compound 1 significantly reduced the expression of ERK, which might explain the inhibition of cell proliferation and migration. In addition, perturbation analysis indicated that activation of JNK and p38 might also be affected by 1, which could enhance the cytotoxic effect of compound 1. Similarly, compound 1 showed a significant impact on PI3K-AKT signaling pathway that could be explained since some molecular targets are shared with the Ras/Raf/MEK/ERK pathway, highlighted as significantly impacted in the perturbation analysis. Interestingly, a recent study demonstrated a common inhibition of ERK, AKT, and STAT3 signaling pathways when cancer cells were treated with thiolated naphthoquinone derivatives [35].

Our experimental results demonstrated the value of transcriptomic sequencing as a tool to discover the molecular targets underlying the anti-proliferative effect of naphtho[2,3-b]thiophene-4,9-diones, showing that the induction ferroptosis and the inhibition of MAPK and PI3K-AKT pathways are certainly involved in the cytotoxicity promoted by 1. However, our study is limited by the lack of supporting evidence employing other molecular assays (i.e., MTT assay in the presence of ferroptosis inhibitors or western blot for ERK phosphorylation); therefore, additional studies should be performed to find the exact mechanism through which compound 1 induces cellular death and the interconnection between oxidative stress, ferroptosis, and MAPK(ERK)/PI3K-AKT activation.

In conclusion, this study demonstrated that treatment with 8-hydroxy-2-(2-thenoyl)naphtho[2,3-b]thiophene-4,9-dione (1) inhibited selectively the viability, proliferation, and migration of HT-29 CRC cell line by inducing cell cycle arrest, ferroptosis, and inhibiting the MAPK pathway, affecting specifically the activation of ERK with the consequent perturbation of the common downstream targets in the PI3K-AKT pathway. The identification of the affected molecular targets was performed through RNA-seq, confirming the utility of transcriptomic analysis to study naphthoquinone-based compounds to identify novel therapeutic targets. Indeed, this is the first report of the induction of ferroptosis, an oxidative type of cell death, by naphthoquinone-based compounds, suggesting that their targeting on oxidative stress might be linked to reprogramming of iron metabolism as an interesting mechanism for CRC therapy. Further study is necessary to elucidate the specific link between oxidative stress–ferroptosis–MAPK signaling when cell death is induced by 1, as well as the efficacy of this leading compound using in vivo models.


D. C. and D. R. should be considered joint first author.

tel: +57-5-669-9771, fax: +57-5-669-8323

Acknowledgments

This work was supported by MinCiencias and the University of Cartagena (Grants 474-2012, 597-2012, and 647-2014). The authors thank Julio Acuña and the Institute for Immunological Research for their support with flow cytometry.

  1. Conflict of interest: Authors state no conflict of interest

  2. Author contributions: LF conceived the study; LF and YO supervised the study and designed experiments; KM synthesized compound 1; DC, DR, and YO performed the experiments; YO and LF wrote the manuscript. All authors read and approved the final version of the manuscript.

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Received: 2020-02-22
Revised: 2020-07-25
Accepted: 2020-08-25
Published Online: 2020-10-20

© 2020 Daneiva Caro et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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  26. Study on the interaction between catechin and cholesterol by the density functional theory
  27. Analysis of some pharmaceuticals in the presence of their synthetic impurities by applying hybrid micelle liquid chromatography
  28. Two mixed-ligand coordination polymers based on 2,5-thiophenedicarboxylic acid and flexible N-donor ligands: the protective effect on periodontitis via reducing the release of IL-1β and TNF-α
  29. Incorporation of silver stearate nanoparticles in methacrylate polymeric monoliths for hemeprotein isolation
  30. Development of ultrasound-assisted dispersive solid-phase microextraction based on mesoporous carbon coated with silica@iron oxide nanocomposite for preconcentration of Te and Tl in natural water systems
  31. N,N′-Bis[2-hydroxynaphthylidene]/[2-methoxybenzylidene]amino]oxamides and their divalent manganese complexes: Isolation, spectral characterization, morphology, antibacterial and cytotoxicity against leukemia cells
  32. Determination of the content of selected trace elements in Polish commercial fruit juices and health risk assessment
  33. Diorganotin(iv) benzyldithiocarbamate complexes: synthesis, characterization, and thermal and cytotoxicity study
  34. Keratin 17 is induced in prurigo nodularis lesions
  35. Anticancer, antioxidant, and acute toxicity studies of a Saudi polyherbal formulation, PHF5
  36. LaCoO3 perovskite-type catalysts in syngas conversion
  37. Comparative studies of two vegetal extracts from Stokesia laevis and Geranium pratense: polyphenol profile, cytotoxic effect and antiproliferative activity
  38. Fragmentation pattern of certain isatin–indole antiproliferative conjugates with application to identify their in vitro metabolic profiles in rat liver microsomes by liquid chromatography tandem mass spectrometry
  39. Investigation of polyphenol profile, antioxidant activity and hepatoprotective potential of Aconogonon alpinum (All.) Schur roots
  40. Lead discovery of a guanidinyl tryptophan derivative on amyloid cascade inhibition
  41. Physicochemical evaluation of the fruit pulp of Opuntia spp growing in the Mediterranean area under hard climate conditions
  42. Electronic structural properties of amino/hydroxyl functionalized imidazolium-based bromide ionic liquids
  43. New Schiff bases of 2-(quinolin-8-yloxy)acetohydrazide and their Cu(ii), and Zn(ii) metal complexes: their in vitro antimicrobial potentials and in silico physicochemical and pharmacokinetics properties
  44. Treatment of adhesions after Achilles tendon injury using focused ultrasound with targeted bFGF plasmid-loaded cationic microbubbles
  45. Synthesis of orotic acid derivatives and their effects on stem cell proliferation
  46. Chirality of β2-agonists. An overview of pharmacological activity, stereoselective analysis, and synthesis
  47. Fe3O4@urea/HITh-SO3H as an efficient and reusable catalyst for the solvent-free synthesis of 7-aryl-8H-benzo[h]indeno[1,2-b]quinoline-8-one and indeno[2′,1′:5,6]pyrido[2,3-d]pyrimidine derivatives
  48. Adsorption kinetic characteristics of molybdenum in yellow-brown soil in response to pH and phosphate
  49. Enhancement of thermal properties of bio-based microcapsules intended for textile applications
  50. Exploring the effect of khat (Catha edulis) chewing on the pharmacokinetics of the antiplatelet drug clopidogrel in rats using the newly developed LC-MS/MS technique
  51. A green strategy for obtaining anthraquinones from Rheum tanguticum by subcritical water
  52. Cadmium (Cd) chloride affects the nutrient uptake and Cd-resistant bacterium reduces the adsorption of Cd in muskmelon plants
  53. Removal of H2S by vermicompost biofilter and analysis on bacterial community
  54. Structural cytotoxicity relationship of 2-phenoxy(thiomethyl)pyridotriazolopyrimidines: Quantum chemical calculations and statistical analysis
  55. A self-breaking supramolecular plugging system as lost circulation material in oilfield
  56. Synthesis, characterization, and pharmacological evaluation of thiourea derivatives
  57. Application of drug–metal ion interaction principle in conductometric determination of imatinib, sorafenib, gefitinib and bosutinib
  58. Synthesis and characterization of a novel chitosan-grafted-polyorthoethylaniline biocomposite and utilization for dye removal from water
  59. Optimisation of urine sample preparation for shotgun proteomics
  60. DFT investigations on arylsulphonyl pyrazole derivatives as potential ligands of selected kinases
  61. Treatment of Parkinson’s disease using focused ultrasound with GDNF retrovirus-loaded microbubbles to open the blood–brain barrier
  62. New derivatives of a natural nordentatin
  63. Fluorescence biomarkers of malignant melanoma detectable in urine
  64. Study of the remediation effects of passivation materials on Pb-contaminated soil
  65. Saliva proteomic analysis reveals possible biomarkers of renal cell carcinoma
  66. Withania frutescens: Chemical characterization, analgesic, anti-inflammatory, and healing activities
  67. Design, synthesis and pharmacological profile of (−)-verbenone hydrazones
  68. Synthesis of magnesium carbonate hydrate from natural talc
  69. Stability-indicating HPLC-DAD assay for simultaneous quantification of hydrocortisone 21 acetate, dexamethasone, and fluocinolone acetonide in cosmetics
  70. A novel lactose biosensor based on electrochemically synthesized 3,4-ethylenedioxythiophene/thiophene (EDOT/Th) copolymer
  71. Citrullus colocynthis (L.) Schrad: Chemical characterization, scavenging and cytotoxic activities
  72. Development and validation of a high performance liquid chromatography/diode array detection method for estrogen determination: Application to residual analysis in meat products
  73. PCSK9 concentrations in different stages of subclinical atherosclerosis and their relationship with inflammation
  74. Development of trace analysis for alkyl methanesulfonates in the delgocitinib drug substance using GC-FID and liquid–liquid extraction with ionic liquid
  75. Electrochemical evaluation of the antioxidant capacity of natural compounds on glassy carbon electrode modified with guanine-, polythionine-, and nitrogen-doped graphene
  76. A Dy(iii)–organic framework as a fluorescent probe for highly selective detection of picric acid and treatment activity on human lung cancer cells
  77. A Zn(ii)–organic cage with semirigid ligand for solvent-free cyanosilylation and inhibitory effect on ovarian cancer cell migration and invasion ability via regulating mi-RNA16 expression
  78. Polyphenol content and antioxidant activities of Prunus padus L. and Prunus serotina L. leaves: Electrochemical and spectrophotometric approach and their antimicrobial properties
  79. The combined use of GC, PDSC and FT-IR techniques to characterize fat extracted from commercial complete dry pet food for adult cats
  80. MALDI-TOF MS profiling in the discovery and identification of salivary proteomic patterns of temporomandibular joint disorders
  81. Concentrations of dioxins, furans and dioxin-like PCBs in natural animal feed additives
  82. Structure and some physicochemical and functional properties of water treated under ammonia with low-temperature low-pressure glow plasma of low frequency
  83. Mesoscale nanoparticles encapsulated with emodin for targeting antifibrosis in animal models
  84. Amine-functionalized magnetic activated carbon as an adsorbent for preconcentration and determination of acidic drugs in environmental water samples using HPLC-DAD
  85. Antioxidant activity as a response to cadmium pollution in three durum wheat genotypes differing in salt-tolerance
  86. A promising naphthoquinone [8-hydroxy-2-(2-thienylcarbonyl)naphtho[2,3-b]thiophene-4,9-dione] exerts anti-colorectal cancer activity through ferroptosis and inhibition of MAPK signaling pathway based on RNA sequencing
  87. Synthesis and efficacy of herbicidal ionic liquids with chlorsulfuron as the anion
  88. Effect of isovalent substitution on the crystal structure and properties of two-slab indates BaLa2−xSmxIn2O7
  89. Synthesis, spectral and thermo-kinetics explorations of Schiff-base derived metal complexes
  90. An improved reduction method for phase stability testing in the single-phase region
  91. Comparative analysis of chemical composition of some commercially important fishes with an emphasis on various Malaysian diets
  92. Development of a solventless stir bar sorptive extraction/thermal desorption large volume injection capillary gas chromatographic-mass spectrometric method for ultra-trace determination of pyrethroids pesticides in river and tap water samples
  93. A turbidity sensor development based on NL-PI observers: Experimental application to the control of a Sinaloa’s River Spirulina maxima cultivation
  94. Deep desulfurization of sintering flue gas in iron and steel works based on low-temperature oxidation
  95. Investigations of metallic elements and phenolics in Chinese medicinal plants
  96. Influence of site-classification approach on geochemical background values
  97. Effects of ageing on the surface characteristics and Cu(ii) adsorption behaviour of rice husk biochar in soil
  98. Adsorption and sugarcane-bagasse-derived activated carbon-based mitigation of 1-[2-(2-chloroethoxy)phenyl]sulfonyl-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl) urea-contaminated soils
  99. Antimicrobial and antifungal activities of bifunctional cooper(ii) complexes with non-steroidal anti-inflammatory drugs, flufenamic, mefenamic and tolfenamic acids and 1,10-phenanthroline
  100. Application of selenium and silicon to alleviate short-term drought stress in French marigold (Tagetes patula L.) as a model plant species
  101. Screening and analysis of xanthine oxidase inhibitors in jute leaves and their protective effects against hydrogen peroxide-induced oxidative stress in cells
  102. Synthesis and physicochemical studies of a series of mixed-ligand transition metal complexes and their molecular docking investigations against Coronavirus main protease
  103. A study of in vitro metabolism and cytotoxicity of mephedrone and methoxetamine in human and pig liver models using GC/MS and LC/MS analyses
  104. A new phenyl alkyl ester and a new combretin triterpene derivative from Combretum fragrans F. Hoffm (Combretaceae) and antiproliferative activity
  105. Erratum
  106. Erratum to: A one-step incubation ELISA kit for rapid determination of dibutyl phthalate in water, beverage and liquor
  107. Review Articles
  108. Sinoporphyrin sodium, a novel sensitizer for photodynamic and sonodynamic therapy
  109. Natural products isolated from Casimiroa
  110. Plant description, phytochemical constituents and bioactivities of Syzygium genus: A review
  111. Evaluation of elastomeric heat shielding materials as insulators for solid propellant rocket motors: A short review
  112. Special Issue on Applied Biochemistry and Biotechnology 2019
  113. An overview of Monascus fermentation processes for monacolin K production
  114. Study on online soft sensor method of total sugar content in chlorotetracycline fermentation tank
  115. Studies on the Anti-Gouty Arthritis and Anti-hyperuricemia Properties of Astilbin in Animal Models
  116. Effects of organic fertilizer on water use, photosynthetic characteristics, and fruit quality of pear jujube in northern Shaanxi
  117. Characteristics of the root exudate release system of typical plants in plateau lakeside wetland under phosphorus stress conditions
  118. Characterization of soil water by the means of hydrogen and oxygen isotope ratio at dry-wet season under different soil layers in the dry-hot valley of Jinsha River
  119. Composition and diurnal variation of floral scent emission in Rosa rugosa Thunb. and Tulipa gesneriana L.
  120. Preparation of a novel ginkgolide B niosomal composite drug
  121. The degradation, biodegradability and toxicity evaluation of sulfamethazine antibiotics by gamma radiation
  122. Special issue on Monitoring, Risk Assessment and Sustainable Management for the Exposure to Environmental Toxins
  123. Insight into the cadmium and zinc binding potential of humic acids derived from composts by EEM spectra combined with PARAFAC analysis
  124. Source apportionment of soil contamination based on multivariate receptor and robust geostatistics in a typical rural–urban area, Wuhan city, middle China
  125. Special Issue on 13th JCC 2018
  126. The Role of H2C2O4 and Na2CO3 as Precipitating Agents on The Physichochemical Properties and Photocatalytic Activity of Bismuth Oxide
  127. Preparation of magnetite-silica–cetyltrimethylammonium for phenol removal based on adsolubilization
  128. Topical Issue on Agriculture
  129. Size-dependent growth kinetics of struvite crystals in wastewater with calcium ions
  130. The effect of silica-calcite sedimentary rock contained in the chicken broiler diet on the overall quality of chicken muscles
  131. Physicochemical properties of selected herbicidal products containing nicosulfuron as an active ingredient
  132. Lycopene in tomatoes and tomato products
  133. Fluorescence in the assessment of the share of a key component in the mixing of feed
  134. Sulfur application alleviates chromium stress in maize and wheat
  135. Effectiveness of removal of sulphur compounds from the air after 3 years of biofiltration with a mixture of compost soil, peat, coconut fibre and oak bark
  136. Special Issue on the 4th Green Chemistry 2018
  137. Study and fire test of banana fibre reinforced composites with flame retardance properties
  138. Special Issue on the International conference CosCI 2018
  139. Disintegration, In vitro Dissolution, and Drug Release Kinetics Profiles of k-Carrageenan-based Nutraceutical Hard-shell Capsules Containing Salicylamide
  140. Synthesis of amorphous aluminosilicate from impure Indonesian kaolin
  141. Special Issue on the International Conf on Science, Applied Science, Teaching and Education 2019
  142. Functionalization of Congo red dye as a light harvester on solar cell
  143. The effect of nitrite food preservatives added to se’i meat on the expression of wild-type p53 protein
  144. Biocompatibility and osteoconductivity of scaffold porous composite collagen–hydroxyapatite based coral for bone regeneration
  145. Special Issue on the Joint Science Congress of Materials and Polymers (ISCMP 2019)
  146. Effect of natural boron mineral use on the essential oil ratio and components of Musk Sage (Salvia sclarea L.)
  147. A theoretical and experimental study of the adsorptive removal of hexavalent chromium ions using graphene oxide as an adsorbent
  148. A study on the bacterial adhesion of Streptococcus mutans in various dental ceramics: In vitro study
  149. Corrosion study of copper in aqueous sulfuric acid solution in the presence of (2E,5E)-2,5-dibenzylidenecyclopentanone and (2E,5E)-bis[(4-dimethylamino)benzylidene]cyclopentanone: Experimental and theoretical study
  150. Special Issue on Chemistry Today for Tomorrow 2019
  151. Diabetes mellitus type 2: Exploratory data analysis based on clinical reading
  152. Multivariate analysis for the classification of copper–lead and copper–zinc glasses
  153. Special Issue on Advances in Chemistry and Polymers
  154. The spatial and temporal distribution of cationic and anionic radicals in early embryo implantation
  155. Special Issue on 3rd IC3PE 2020
  156. Magnetic iron oxide/clay nanocomposites for adsorption and catalytic oxidation in water treatment applications
  157. Special Issue on IC3PE 2018/2019 Conference
  158. Exergy analysis of conventional and hydrothermal liquefaction–esterification processes of microalgae for biodiesel production
  159. Advancing biodiesel production from microalgae Spirulina sp. by a simultaneous extraction–transesterification process using palm oil as a co-solvent of methanol
  160. Topical Issue on Applications of Mathematics in Chemistry
  161. Omega and the related counting polynomials of some chemical structures
  162. M-polynomial and topological indices of zigzag edge coronoid fused by starphene
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