Antioxidant, antiacetylcholinesterase and apoptotic effects of essential oil of Isodon wightii (Bentham) H. Hara.

Isodon wightii (Bentham) H. Hara is well known for aromatic essential oil. This is the first study aimed to evaluate antioxidant, antiacetylcholinesterase and apoptotic potential of I. wightii oil. DPPH scavenging, metal ion chelation and antiacetylcholinesterase activities were carried out for the extracted essential oil from the leaves of I. wightii. Cytotoxic effect on HeLa cells was studied by MTT assay and its apoptotic potential was determined by Acridine Orange/Ethidium Bromide and Hoechst33258 stains. A significant free radical scavenging and metal ion chelation were determined for oil. Acetylcholinesterase inhibition was recorded with IC50 value of 7.864 µg/mL. The cytotoxic effect of oil on HeLa cells was calculated with IC50 value of 13.264 µg/mL. High level of apoptosed cells were observed at 100 µg/mL oil treated cells. The results of the study emphasise the medicinal importance of I. wightii essential oil which could be a prominent plant based cancer therapeutic agent.

Diterpenoids from Isodon serra with promising anti-MRSA activities.

A series of known diterpenoids from Isodon serra (Maxim.) Hara exhibited antibacterial activities against Staphylococcus aureus and even methicillin-resistant S. aureus (MRSA). Among these diterpenoids, hebeirubescensin K (7), effusanin E (8), and nodosin (9) showed the optimal minimum inhibitory concentration (MIC) values ranging from 3.12 to 6.25 µg/mL against tested MRSA strains, and they also inhibited bacterial proliferation, biofilm formation, and key gene expressions related to adhesion and virulence of MRSA. In vivo experiments also demonstrated the antibacterial abilities of 7-9 as topical drugs and promoted wound healing caused by a MSRA infection. It is the first time that the anti-S. aureus and MRSA activities of diterpenoids from I. serra has been systematically reported. These current findings provide insight into the anti-MRSA mechanism of diterpenoids from I. serra; indicating these compounds may be used as antimicrobial agents and contribute to the development as well as application of I. serra in phytomedicine for MRSA infections.

Structurally diverse ent-clerodanoids from the aerial parts of Isodon scoparius.

Scoparodane C (1), a diterpenoid with a rare 3,4-seco-3-nor-2,11-epoxy-ent-clerodane scaffold, was obtained from the aerial parts of Isodon scoparius, along with isocopariusines A-E (2-6), five ent-clerodanoids featuring a 5/6-fused ring system, and isocopariusines F-H (7-9), three common ent-clerodanoids. The structures of these previously undescribed compounds were established by a combination of spectroscopic analysis, X-ray diffraction, chemical derivatization, and quantum chemical calculation. Remarkably, isocopariusine B (3) showed strong resistance reversal activity against fluconazole-resistant Candida albicans.

ent-Kaurane diterpenoids from Isodon henryi and their anti-inflammatory activities.

Phytochemical investigation of the 70% ethanol extract of Isodon henryi Kudô afforded fifteen ent-kaurane diterpenoids, including nine previously undescribed compounds, named isohenolides C-K (1-9). Compounds 1-6 featured an unusual 6,7;8,15-diseco-7,20-olide ent-kaurane diterpenoid scaffold, in which 1 also possessed an 11,15-lactone ring while 2-6 all contained a free α-methylene-γ-carboxylic acid. Compound 6 was also a rare 6,8-cyclo-7,20-olide ent-kauranoid. Their structures were elucidated primarily by HRESIMS, 1D and 2D NMR spectroscopy, electronic circular dichroism and X-ray diffraction (Cu Kα) methods. Additionally, most compounds were also screened for anti-inflammatory actions against lipopolysaccharide-induced RAW 264.7 cells, and compounds 9 and 13 exhibited stronger nitric oxide inhibition, with IC50 values of 15.99 ± 0.75 and 18.19 ± 0.42 µM, respectively.

Silvaticusins A-D: ent-kaurane diterpenoids and a cyclobutane-containing ent-kaurane dimer from Isodon silvaticus.

Three new ent-kaurane diterpenoids, silvaticusins A-C (1-3), along with a new ent-kaurane dimer silvaticusin D (4) were isolated from the aerial parts of Isodon silvaticus. The structures of these new compounds were established mainly by comprehensive analysis of their NMR and MS data. The absolute configuration of compounds 1 and 4 were determined using a single-crystal X-ray diffraction and computational methods, respectively. Compounds 2 and 3 were found to exhibit remarkable cytotoxic effects against five human tumor cell lines (HL-60, A-549, SMMC-7721, MDA-MB-231, and SW-480), with IC50 values spanning from 1.27 ± 0.08 to 7.52 ± 0.33 µM.

The water and oridonin sources in the ice ribbons of Isodon rubescens.

To study the source and content change of oridonin in the ice ribbons, the contents of oridonin in the ice ribbons and bleeding sap of Isodon rubescens at different times were determined with RP-HPLC. The paraffin sectioning and electron microscopy imaging were performed to study the transport channel of oridonin in the stem. The results showed that there were abundant xylem rays and perfect pit pairs in the secondary xylem of I. rubescens stems. The oridonin content in the ice ribbons of I. rubescens stems was lower than that in the stem of I. rubescens and even decreased over time. The contents of oridonin in the bleeding sap of I. rubescens stems was equal to that in second-day ice ribbons and was lower than that in first-day ice ribbons. The water in the ice ribbons of I. rubescens stems originated from water absorbed by the roots from soil. This water was transported from the roots of I. rubescens to the stem and then transferred through efficient lateral conducting tissues to the surface of the stem. The oridonin in the phloem and cortex of I. rubescens stems dissolves in water originating from the soil and freezes in the form of ice ribbons below 0 °C.

Diterpenoids from the Aerial Parts of Isodon serra with Selective Cytotoxic Activity.

Four new diterpenoids, isodosins A-D (1-4), together with nine known compounds (5-13) were isolated and identified from the aerial parts of Isodon serra (Maxim.) Hara. The structures of the new diterpenoids were elucidated based on the analysis of HR-ESI-MS data, 1D/2D-NMR-spectroscopic data, and electronic circular dichroism (ECD) calculations. Cytotoxicities of compounds 2, 3, 5, 6, and 9 against the HepG2 and H1975 cell lines were evaluated with the MTT assay. As a result, compounds 2, 3, and 6 revealed higher levels of cytotoxicity against HepG2 cells than against H1975 cells. Moreover, compund 6 demonstrated the most efficacy in inhibiting the proliferation of HepG2 cells, with an IC50 value of 41.13 ± 3.49 µM. This effect was achieved by inducing apoptosis in a dose-dependent manner. Furthermore, the relationships between the structures and activities of these compounds are briefly discussed.

Abietane diterpenoids from Isodon amethystoides and their biological activities.

Seven undescribed abietane diterpenoids [abietamethinols A-G (1-7)] were isolated from the twigs and leaves of Isodon amethystoides. Their structures were elucidated on the basis of spectroscopic methods including 2D NMR, and they were further confirmed by X-ray crystallographic data. Lophanic acid was considered as the precursor of 1-7 in the biosynthesis pathway hypothesis. These compounds were evaluated for their cytotoxic, anti-bacterial and anti-AIV (avian influenza virus) activities. Compound 5 showed 42.9% inhibitory activity against the cancer cell line SMMC-7721 at the concentration of 40 µM, 3 and 4 could inhibit the bacterial growth of Streptococcus sobrinus by 55.3% and 63.2% at the concentrations of 148.6 and 141.9 µM, respectively, and 4 was demonstrated with antiviral activity against AIV with the inhibitory effect of 68.4% at 25 µM.

Six new diterpenoids with anti-inflammatory and cytotoxic activity from Isodon serra.

Diterpenoids occupy an important slot of the natural products diversity space with wide ranges of bioactivities and complex structures, providing potential applications for the development of therapeutics. In this study, we reported four new abietane-type diterpenoids viroxocin B-E (1-4), a new totarane-type diterpenoid viroxocin F (5), and a new sempervirane-type diterpenoid viroxocin G (6) along with four known compounds (7-10), isolated and identified from a widely used Traditional Chinese Medicine, Isodon serra (I. serra). Their structures were established by spectroscopic data analysis, experimental and calculated electronic circular dichroism (ECD) data, as well as X-ray diffraction analysis. Compounds 2, 5, 7, 8 and 10 exhibited promising anti-inflammatory activities in lipopolysaccharide (LPS)-induced RAW 267.4 cells, and their inhibition rates on NO production were more than 60% at 10 µM. Compound 7 showed cytotoxicity against human renal cell carcinoma 769P at 20 µM, the inhibition rate was 52.66%.

[Analysis of chemical compositions in different parts of Isodon japonicus using UPLC-Q-TOF-MS technique combined with chemometrics].

In order to analyze the similarities and differences of chemical compositions between the roots and stems and leaves of Isodon japonicus(IJ), this study utilized UPLC-Q-TOF-MS technology to systematically characterize its chemical compositions, analyzed and identified the structure of its main compounds, and established a method for simultaneous determination of its content by refe-rence substance. A total of 34 major compounds in IJ, including 14 reference compounds, were identified or predicted online. Moreover, an UPLC-UV content determination method was developed for 11 compounds [danshensu, caffeic acid, vicenin-2,(1S,2S)-globoidnan B, rutin,(+)-rabdosiin,(-)-rabdosiin,(1S,2S)-rabdosiin, shimobashiric acid C, rosmarinic acid, and pedalitin]. The method exhibited excellent separation, stability, and repeatability, with a wide linear range(0.10-520.00 µg·mL~(-1)) and high linearity(R~2>0.999). The average recovery rates ranged from 94.72% to 104.2%. The principal component analysis(PCA) demonstrated a clear difference between the roots and stems and leaves of IJ, indicating good separation by cluster. Furthermore, the orthogonal partial least squares discriminant analysis(OPLS-DA) model was employed, and six main differentially identified compounds were identified: rosmarinic acid, shimobashiric acid C, epinodosin, pedalitin, rutin, and(1S,2S)-rabdosiin. In summary, this study established a strategy and method for distinguishing different parts of IJ, providing a valuable tool for quality control of IJ and a basis for the ratio-nal utilization and sustainable development of IJ.

Investigation of anti-nociceptive, anti-inflammatory potential and ADMET studies of pure compounds isolated from Isodon rugosus Wall. ex Benth.

The strong ethnopharmacological utilization of Isodon rugosus Wall. Ex. Benth is evident in the treatment of several types of pain and inflammation, including toothache, earache, abdominal pain, gastric pain, and generalized body pain and inflammation. Based on this background, the antinociceptive effects of the crude extract, various fractions, and essential oil have been reported previously. In this research work, we isolate and characterize pure bioactive compounds from I. rugosus and evaluate possible mechanisms using various in vivo and in vitro models. The pure compounds were analyzed for analgesic and anti-inflammatory activities through various assays. The column chromatography of the chloroform fraction of I. rugosus led to the identification of two pure compounds, i.e., 1 and 2. Compound 1 demonstrated notable inhibition (62% writhing inhibition, 72.77% COX-2 inhibition, and 76.97% 5-LOX inhibition) and anti-inflammatory potential (>50% paw edema inhibition at various intervals). The possible mechanism involved in antinociception was considered primarily, a concept that has already been elucidated through the application of naloxone (an antagonist of opioid receptors). The involvement of adrenergic receptors was investigated using a hot plate model (an adrenergic receptor antagonist). The strong ethnomedicinal analgesic background of I. rugosus, supported by previous reports and current observations, leads to the conclusion that I. rugosus is a potential source of antinociceptive and anti-inflammatory bioactive compounds. It may be concluded from the results that the isolated analgesic compounds of I. rugosus may be a possible alternative remedy for pain and inflammation management with admirable efficacy and safety profiles.

Multi-omics analysis of small RNA, transcriptome, and degradome to identify putative miRNAs linked to MeJA regulated and oridonin biosynthesis in Isodon rubescens.

Isodon rubescens has garnered much attention due to its anti-tumor or anti-cancer properties. However, little is known about the molecular mechanism of oridonin biosynthesis leveraging the regulatory network between small RNAs and mRNAs. In this study, the regulatory networks of miRNAs and targets were examined by combining mRNA, miRNA, and degradome. A total of 348 miRNAs, including 287 known miRNAs and 61 novel miRNAs, were identified. Among them, 51 miRNAs were significantly expressed, and 36 miRNAs responded to MeJA. A total of 3066 target genes were associated with 228 miRNAs via degradome sequencing. Multi-omics analysis demonstrated that 27 miRNA-mRNA pairs were speculated to be involved in MeJA regulation, and 36 miRNA-mRNA pairs were hypothesized to be involved in the genotype-dependence of I. rubescens. Furthermore, 151 and 7 miRNA-mRNA modules were likely engaged in oridonin biosynthesis as identified by psRNATarget and degradome sequencing, respectively. Some miRNA-mRNA modules were confirmed via RT-qPCR. Moreover, miRNAs targeting plant hormone signal transduction pathway genes were identified, such as miR156, miR167, miR393, and PC-3p-19822_242. Collectively, our results demonstrate for the first time that miRNAs are identified in I. rubescens, and laid a solid foundation for further research on the molecular mechanism of oridonin biosynthesis mediated by miRNA.

The intramolecular SN2 reaction tautomeric ent-Kauranoids isolated from the aerial parts of Isodon amethystoides.

As our ongoing searching for the bioactive natural terpenoids, nine ent-kauranoids (1-9), including three previously undescribed ones (1, 2, and 9), were isolated from the aerial parts of Isodon amethystoides. Their structures were elucidated on the basis of spectroscopic data analysis, including NMR, MS, and ECD. Compounds 1 and 2 were a pair of tautomeric compounds, which was confirmed by the HPLC analysis and low temperature NMR testing. The underlying mechanism of the tautomer was proposed as an intramolecular SN2 reaction, which was explained by quantum chemical calculation. The HOMO-LUMO gap and the free energy revealed the spontaneous of the tautomeric of the 1 and 2. Additionally, the similar phenomena were also found in the two groups of known compounds 3 and 4 and 6 and 7, respectively. Apart from the tautomer, compounds 3 and 4 can be hydrolyzed into 5 through ester hydrolysis in CDCl3, while compounds 6, 7 can be hydrolyzed into 8 through ester hydrolysis. These phenomena were also confirmed through HPLC analysis and low temperature nuclear magnetic resonance tests and the mechanism was studied using quantum chemical calculation.

In Vitro and In Vivo Anti-Cancer Activity of Lasiokaurin in a Triple-Negative Breast Cancer Model.

Due to its intricate heterogeneity, high invasiveness, and poor prognosis, triple-negative breast cancer (TNBC) stands out as the most formidable subtype of breast cancer. At present, chemotherapy remains the prevailing treatment modality for TNBC, primarily due to its lack of estrogen receptors (ERs), progesterone receptors (PRs), and human epidermal growth receptor 2 (HER2). However, clinical chemotherapy for TNBC is marked by its limited efficacy and a pronounced incidence of adverse effects. Consequently, there is a pressing need for novel drugs to treat TNBC. Given the rich repository of diverse natural compounds in traditional Chinese medicine, identifying potential anti-TNBC agents is a viable strategy. This study investigated lasiokaurin (LAS), a natural diterpenoid abundantly present in Isodon plants, revealing its significant anti-TNBC activity both in vitro and in vivo. Notably, LAS treatment induced cell cycle arrest, apoptosis, and DNA damage in TNBC cells, while concurrently inhibiting cell metastasis. In addition, LAS effectively inhibited the activation of the phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway and signal transducer and activator of transcription 3 (STAT3), thus establishing its potential for multitarget therapy against TNBC. Furthermore, LAS demonstrated its ability to reduce tumor growth in a xenograft mouse model without exerting detrimental effects on the body weight or vital organs, confirming its safe applicability for TNBC treatment. Overall, this study shows that LAS is a potent candidate for treating TNBC.

Two new seco-abietane type diterpenoids from the leaves of Isodon serra.

Two new seco-abietane type diterpenoids, named as isodonserra acid A and B (1-2), along with six known compounds, angustanoic acid A (3), epipalustric acid (4), raserrane (5), 7-methoxy coumarin (6), umbelliferone (7), and (-)-loliolide (8), were obtained from the leaves of Isodon serra. The new structures of compounds 1 and 2 were elucidated by analysing their 1D NMR, 2D NMR and HR-ESI-MS spectra. Compounds 1-8 showed moderate hepatoprotective activity against APAP-induced HepG2 cell injury with a cell survival rate from 50.4% to 78.7% at a concentration of 10 µM (p < .001, bicyclol as the positive drug, 71.7%).

[Isodopharicin C inhibits NLRP3 inflammasome activation and alleviates septic shock in mice].

OBJECTIVE: To investigate the effect of Isodopharicin C (Iso C), a traditional Chinese herbal medicine extract, on NLRP3 inflammasome activation and lipopolysaccharide (LPS)-induced septic shock in mice. METHODS: Murine bone marrow-derived macrophages (BMDM) and human monocytic THP-1 cells were stimulated with LPS before treatment with different NLRP3 inflammasome agonists to activate canonical NLRP3 inflammasomes. The non-canonical NLRP3 inflammasomes were activated by intracellular LPS transfection, and AIM2 inflammasomes were activated with poly A: T. The cleavage of caspase-1 induced by NLRP3 activation was measured using Western blotting. The levels of NLRP3-dependent and -independent pro-inflammatory cytokines in the cell culture supernatant were detected using ELISA, and the intracellular potassium ion concentration was measured using ICP-OES. In the animal experiment, C57BL/6J mouse models of septic shock (induced by intraperitoneal LPS injection) were treated with Iso C, and the levels of IL-1ß, TNF-α and IL-6 in the serum and peritoneal lavage fluid were detected using ELISA. The survival time of the mice was observed within 48 h after LPS injection and a survival curve was plotted. RESULTS: In BMDM cells, Iso C dose-dependently inhibited the activation of canonical NLRP3 inflammasomes and non-canonical NLRP3 inflammasomes (P<0.05) without obviously affecting the secretion levels of TNF-α and IL-6 (P>0.05), the activation of AIM2 inflammasomes (P>0.05), or K + efflux, the upstream signaling of NLRP3 activation (P>0.05). Iso C inhibited the activation of canonical NLRP3 inflammasomes in human THP-1 cells. In septic C57BL/6J mice, Iso C treatment significantly reduced IL-1ß levels in the serum and peritoneal lavage fluid, and prolonged the survival time of the mice (P<0.05). CONCLUSION: Iso C specifically inhibits NLRP3 inflammasome activation and alleviates septic shock in mice, and can serve as a potential small molecule compound for treatment of inflammatory diseases.

Guidongnins I-J: Two New 6,7-seco-7,20-Olide-ent-kaurene Diterpenes with Unusual Structures from Isodon rubescens.

Two undescribed ent-kaurene diterpenes, named guidongnins I (1) and J (2), were isolated from the medicinal plant Isodon rubescens. Compound 1 was determined to contain an unprecedented 23 carbons in the skeleton by bearing an extra isopropyl group at C-17 out of the diterpenoid parent structure, and compound 2 was the first example of 6,7-seco-7,20-olide-ent-kaurenes with two fused-tetrahydrofuran rings formed between C-6 and C-19/C-20 through oxygen bridges. Their structures, including their absolute configurations, were determined using the analyses of the spectroscopic and X-ray diffraction data. Guidongnins I (1) and J (2) were assessed for their anti-cancer activities against the growth of various cancer cell lines, and 2 displayed cytotoxic potency against HepG2 at IC50 27.14 ± 3.43 µM.

Network Pharmacology and Molecular Docking Reveal the Mechanism of Isodon ternifolius (D. Don) Kudo Against Liver Fibrosis.

Aim: Many studies have demonstrated the hepatoprotective or anti-fibrotic effects of Isodon ternifolius, but its pharmacological basis and mechanism remain unclear. In this study, we used in vitro models to validate the predicted results and revealed the potential mechanism of action and active ingredients through network pharmacology methods and molecular docking. Methods: The chemical components of Isodon ternifolius were identified by literatures. Potential targets of Isodon ternifolius were predicted by Swiss Target Prediction. The disease targets were collected through the databases of Gene Card. Common targets of Isodon ternifolius and liver fibrosis were obtained by online tool Venny 2.1. PPI protein interaction network was obtained using String database, and target protein interaction network was drawn using Cytoscape software. Signaling pathway enrichment analysis was performed on drug-disease targets with of DAVID database. Results: Twenty-one potential active ingredients and 298 potential targets were predicted by Swiss Target Prediction platform. Ninety pathways related to liver fibrosis were obtained by KEGG enrichment. The TLR4, MAPK and PI3K-Akt signaling pathways are mostly associated with liver fibrosis. Molecular docking techniques were used to validate the core target proteins TNF, Akt1, MAPK1, EGFR and TLR4 binding to the ingredients of Isodon ternifolius, which showed that a multitude of ingredients of Isodon ternifolius were able to bind to the above target proteins, especially 2α-hydroxy oleanolic acid and (-)-Lambertic acid. Our experimental validation results showed that Isodon ternifolius inhibited the activation of PI3K-Akt and ERK1/2 signaling pathways. Conclusion: Through a network pharmacology approach and in vitro cell assay, we predicted and validated the active compounds of Isodon ternifolius and its potential targets for LF treatment. The results suggest that the mechanism of Isodon ternifolius treating LF by inhibiting angiogenesis may be related to the ERK1/2 and PI3K/Akt signaling pathways.

[Effect of Isodon ternifolius-medicated serum on hepatic stellate cells based on TLR4/NF-κB/NLRP3 signaling pathway].

The present study aimed to investigate the inhibitory effect and mechanism of Isodon terricolous-medicated serum on lipopolysaccharide(LPS)-induced hepatic stellate cell(HSC) activation. LPS-induced HSCs were divided into a blank control group, an LPS model group, a colchicine-medicated serum group, an LPS + blank serum group, an I. terricolous-medicated serum group, a Toll-like receptor 4(TLR4) blocker group, and a TLR4 blocker + I. terricolous-medicated serum group. HSC proliferation was detected by methyl thiazolyl tetrazolium(MTT) assay. Enzyme-linked immunosorbent assay(ELISA) was used to measure type Ⅰ collagen(COL Ⅰ), COL Ⅲ, transforming growth factor-ß1(TGF-ß1), intercellular adhesion molecule-1(ICAM-1), α-smooth muscle actin(α-SMA), vascular cell adhesion molecule-1(VCAM-1), cysteinyl aspartate-specific proteinase-1(caspase-1), and monocyte chemotactic protein-1(MCP-1). Real-time PCR(RT-PCR) was used to detect mRNA expression of TLR4, IκBα, and NOD-like receptor thermal protein domain associated protein 3(NLRP3), nuclear factor-κB(NF-κB) p65, gasdermin D(GSDMD), and apoptosis-associated speck-like protein containing a CARD(ASC) in HSCs. Western blot(WB) was used to detect the protein levels of TLR4, p-IκBα, NF-κB p65, NLRP3, ASC, and GSDMD in HSCs. The results showed that I. terricolous-medicated serum could inhibit the proliferation activity of HSCs and inhibit the secretion of COL Ⅰ, COL Ⅲ, α-SMA, TGF-ß1, caspase-1, MCP-1, VCAM-1, and ICAM-1 in HSCs. Compared with the LPS model group, the I. terricolous-medicated serum group, the colchicine-medicated serum group, and the TLR4 blocker group showed down-regulated expression of p-IκBα, NLRP3, NF-κB p65, GSDMD, and ASC, and up-regulated expression of IκBα. Compared with the TLR4 blocker group, the TLR4 blocker + I. terricolous-medicated serum group showed decreased expression of TLR4, p-IκBα, NLRP3, NF-κB p65, GSDMD, and ASC, and increased expression of IκBα. In conclusion, I. terricolous-medicated serum down-regulates HSC activation by inhibiting the TLR4/NF-κB/NLRP3 signaling pathway.

Antiproliferative Activities of Diterpenes from Leaves of Isodon trichocarpus against Cancer Stem Cells.

Two new diterpenes named trichoterpene I (1) and trichoterpene II (2) were isolated from the extract from the leaves of Isodon trichocarpus together with 19 known diterpenes. Their chemical structures were elucidated on the basis of chemical and physicochemical properties. Among them, oridonin (3), effusanin A (4), and lasiokaurin (9) with the α,ß-unsaturated carbonyl moiety showed antiproliferative activities against breast cancer MDA-MB-231 and human astrocytoma U-251 MG cells [i.e., non-cancer stem cells (non-CSCs)] and their cancer stem cells (CSCs) isolated by sphere formation. In particular, compound 4 (IC50 = 0.51 µM) showed a higher antiproliferative activity against MDA-MB-231 CSCs than against MDA-MB-231 non-CSCs. The antiproliferative activity toward CSCs of compound 4 was equal to adriamycin (positive control, IC50 = 0.60 µM).