In vitro growth inhibition of human cancer cells by novel honokiol analogs

Honokiol and magnolol: A review of structure-activity relationships of their derivatives

Honokiol (HK) and magnolol (MAG) are typical representatives of neolignans possessing a wide range of biological activities and are employed as traditional medicines in Asia. In the past few decades, HK and MAG have been proven to be promising chemical scaffolds for the development of novel neolignan drugs. This review focuses on recent advances in the medicinal chemistry of HK and MAG derivatives, especially their structure-activity relationships. In addition, it also presents a comprehensive summary of the pharmacology, biosynthetic pathways, and metabolic characteristics of HK and MAG. This review can provide pharmaceutical chemists deeper insights into medicinal research on HK and MAG, and a reference for the rational design of HK and MAG derivatives.

Semisynthesis and anti-cancer properties of novel honokiol derivatives in human nasopharyngeal carcinoma CNE-2Z cells

In this study, 21 new honokiol derivatives were synthesised, and their anti-cancer properties were investigated. Among these, compound 1g exhibited the most potent cytotoxic activity against human nasopharyngeal carcinoma CNE-2Z cells, human gastric cancer SGC7901 cells, human breast cancer MCF-7 cells, and mouse leydig testicular cancer I-10 lines with IC50 values of 6.04, 7.17, 6.83, and 5.30 μM, respectively. Compared to the parental compound, 1g displayed up to 5.18-fold enhancement of the cytotoxic effect on CNE-2Z cells. We further demonstrated that 1g inhibited cell growth, suppressed migration and invasion, and induced apoptosis of CNE-2Z cells by down-regulating HIF-1α, MMP-2, MMP-9, Bcl-2, Akt and up-regulating Bax protein levels. Transfection of CNE-2Z cells with HIF-1α siRNA reduced cell migration and invasion. In addition, in vivo experiments confirmed that 1g inhibited tumour growth in CNE-2Z cell-xenografted nude mice with low toxicity. Thus, our data suggested that 1g was a potent and safe lead compound for nasopharyngeal carcinoma therapy.

Honokiol and its analogues as anticancer compounds: Current mechanistic insights and structure-activity relationship

Lignans are plant-derived polyphenolic compounds with a plethora of biological applications. Also, regarded as phytoestrogens, the lignans offer a variety of health benefits of which the anti-cancer effects are the most attractive. Honokiol is a lignan isolated from various parts of trees belonging to the genus Magnolia. The bioactivity of honokiol is attributed to its characteristic physical properties, which include small size and the presence of two phenolic groups that may interact with proteins in cell membranes via hydrophobic interactions, aromatic pi orbital co-valency, and hydrogen bonding. The hydrophobicity of honokiol enables its rapid dissolution in lipids and the crossing of physiological barriers, including the blood-brain barrier and cerebrospinal fluid. These factors contribute towards the high bioavailability of honokiol which further support its candidature in medicinal research. Therefore, the anticancer properties of honokiol are of particular interest as many of the contemporary anticancer drugs suffer from bioavailability drawbacks, which necessitates the identification and development of novel candidate molecules directed as anticancer chemotherapeutics. The antioncogenic profile of honokiol also arises from the regulation of various signalling pathways associated with oncogenesis, arresting of the cell cycle by regulation of cyclic proteins, upregulation of epithelial markers and downregulation of mesenchymal markers leading to the inhibition of epithelial-mesenchymal transition, and preventing the metastasis by restricting cell migration and invasion due to the downregulation of matrix-metalloproteinases. In this review, we discuss the anticancer properties of honokiol.

Genetic Interpretation of the Impacts of Honokiol and EGCG on Apoptotic and Self-Renewal Pathways in HEp-2 Human Laryngeal CD44high Cancer Stem Cells

Most current larynx cancer therapies are generally aimed at the global mass of tumor, targeting the non-tumorigenic cells, and unfortunately sparing the tumorigenic cancer stem cells (CSCs) that are responsible for sustained growth, metastasis, and chemo- and radioresistance. Phytochemicals and herbs have recently been introduced as therapeutic sources for eliminating CSCs. Therefore, we assessed the anti-tumor effects of two herbal ingredients, the green tea extract "Epigallocatechin-3-gallate (EGCG)" and Honokiol (HNK), on parental cells or CD44^high CSCs of the human laryngeal squamous cell carcinoma cell line HEp-2. Results revealed that EGCG had a preeminent apoptotic potential on HEp-2 laryngeal CSCs. HNK conferred higher cytotoxic impacts on parental cells mostly by necrosis induction, especially with higher doses, but apoptosis induction with lower doses was also observed. The Notch signaling pathway genes were more potently suppressed by EGCG than HNK. However, HNK surpassed EGCG in downregulating the β-catenin and the Sonic Hedgehog signaling pathways genes. On a genetic basis, both agents engaged the BCL-2 family-regulated and caspase-dependent intrinsic apoptotic pathway, but EGCG and HNK triggered apoptosis via p53-independent and p53-dependent pathways, respectively. Taken together, EGCG and HNK eradicated HEp-2 human larynx cancer cells through targeting multiple self-renewal pathways and activating diverse cell death modalities.

Novel 1,3,4-thiadiazole/oxadiazole-linked honokiol derivatives suppress cancer via inducing PI3K/Akt/mTOR-dependent autophagy

Honokiol is a bioactive biphenolic component derived from Magnoliae officinalis Cortex (known as "Hou Po" in Chinese), a traditional Chinese herbal medicine. A series of novel 1,3,4-thiadiazole/oxadiazole-linked honokiol derivatives were synthesized and tested for anticancer activity against seven human cancer cell lines in this study. Among all derivatives, 8a had the most potent cytotoxic effect on all tested cancer cells, with IC₅₀ values ranging from 1.62 ± 0.19 to 4.61 ± 0.51 µM, which were 10.38-34.36 folds more potent than the parental honokiol (IC₅₀ values of 30.96 ± 1.81-55.67 ± 0.31 µM). On A549, HCT116, and MDA-MB-231 cell lines, 8a demonstrated 5.69-fold, 5.65-fold, and 4.83-fold greater cytotoxicity than cisplatin, respectively. Compound 8a also had higher selectivity (SI values of 8.41-49.38) towards seven cancer cell lines over the normal cell lines than cisplatin (SI values of 1.24-2.52). The analysis of structure-activity relationships (SARs) revealed that honokiol derivatives bearing 1,3,4-thiadiazoles (8a-j) possessed stronger anticancer activity than those containing 1,3,4-oxadiazoles. Further mechanistic investigation indicated that 8a induced cytotoxic autophagy in cancer cells in a time- and dose-independent manner via suppressing the PI3K/Akt/mTOR pathway. Molecular docking suggested that 8a could bind to the PI3Kα active sites. Additionally, 8a inhibited the migration and invasion of A549 and MDA-MB-231 cancer cells.

Honokiol: A naturally occurring lignan with pleiotropic bioactivities

Honokiol is the dominant biphenolic compound isolated from the Magnolia tree, and has long been considered as the active constituent of the traditional Chinese herb, 'Houpo', which is widely used to treat symptoms due to 'stagnation of qi'. Pharmacological studies have shown that honokiol possesses a wide range of bioactivities without obvious toxicity. Honokiol protects the liver, kidneys, nervous system, and cardiovascular system through reducing oxidative stress and relieving inflammation. Moreover, honokiol shows anti-diabetic property through enhancing insulin sensitivity, and anti-obese property through promoting browning of adipocytes. In vivo and in vitro studies indicated that honokiol functions as an anti-cancer agent through multiple mechanisms: inhibiting angiogenesis, promoting cell apoptosis, and regulating cell cycle. A variety of therapeutic effects of honokiol may be associated with its physiochemical properties, which make honokiol readily cross the blood brain barrier and the blood-cerebrospinal fluid barrier, with high bioavailability. In the future, more clinical researches on honokiol are needed to fully authenticate its therapeutic values.

Synthesis of Bisphenol Neolignans Inspired by Honokiol as Antiproliferative Agents

Honokiol (2) is a natural bisphenol neolignan showing a variety of biological properties, including antitumor activity. Some studies pointed out 2 as a potential anticancer agent in view of its antiproliferative and pro-apoptotic activity towards tumor cells. As a further contribution to these studies, we report here the synthesis of a small library of bisphenol neolignans inspired by honokiol and the evaluation of their antiproliferative activity. The natural lead was hence subjected to simple chemical modifications to obtain the derivatives 3–9; further neolignans (12a-c, 13a-c, 14a-c, and 15a) were synthesized employing the Suzuki–Miyaura reaction, thus obtaining bisphenols with a substitution pattern different from honokiol. These compounds and the natural lead were subjected to antiproliferative assay towards HCT-116, HT-29, and PC3 tumor cell lines. Six of the neolignans show GI₅₀ values lower than those of 2 towards all cell lines. Compounds 14a, 14c, and 15a are the most effective antiproliferative agents, with GI₅₀ in the range of 3.6–19.1 µM, in some cases it is lower than those of the anticancer drug 5-fluorouracil. Flow cytometry experiments performed on these neolignans showed that the inhibition of proliferation is mainly due to an apoptotic process. These results indicate that the structural modification of honokiol may open the way to obtaining antitumor neolignans more potent than the natural lead.

Honokiol: A Review of Its Anticancer Potential and Mechanisms

Cancer is characterised by uncontrolled cell division and abnormal cell growth, which is largely caused by a variety of gene mutations. There are continuous efforts being made to develop effective cancer treatments as resistance to current anticancer drugs has been on the rise. Natural products represent a promising source in the search for anticancer treatments as they possess unique chemical structures and combinations of compounds that may be effective against cancer with a minimal toxicity profile or few side effects compared to standard anticancer therapy. Extensive research on natural products has shown that bioactive natural compounds target multiple cellular processes and pathways involved in cancer progression. In this review, we discuss honokiol, a plant bioactive compound that originates mainly from the Magnolia species. Various studies have proven that honokiol exerts broad-range anticancer activity in vitro and in vivo by regulating numerous signalling pathways. These include induction of G0/G1 and G2/M cell cycle arrest (via the regulation of cyclin-dependent kinase (CDK) and cyclin proteins), epithelial-mesenchymal transition inhibition via the downregulation of mesenchymal markers and upregulation of epithelial markers. Additionally, honokiol possesses the capability to supress cell migration and invasion via the downregulation of several matrix-metalloproteinases (activation of 5' AMP-activated protein kinase (AMPK) and KISS1/KISS1R signalling), inhibiting cell migration, invasion, and metastasis, as well as inducing anti-angiogenesis activity (via the down-regulation of vascular endothelial growth factor (VEGFR) and vascular endothelial growth factor (VEGF)). Combining these studies provides significant insights for the potential of honokiol to be a promising candidate natural compound for chemoprevention and treatment.

Synthesis and in vitro antitumor evaluation of honokiol derivatives

Honokiol is a natural bioactive neolignan and has been widely researched and structural modified as an anticancer agent. In this paper, 18 honokiol derivatives were synthesized and investigated for their antitumor activity. Among these, the promising compound 5a exhibited much higher anti-proliferative activity with IC₅₀ value of 10.41 μM. Transwell assays showed that 5a could significantly inhibit the invasion and migration of I-10 cells at 2.5 μM, which was further confirmed by the western blotting experiments with down-regulation of the HIF-1α and its associated downstream proteins MMP-2 and MMP-9. Overall, these results provided useful suggestion for further structural optimization of honokiol derivatives.

Anti-proliferative activity and structure-activity relationship of honokiol derivatives

As a known natural product with anti-tumor activity, honokiol has been widely researched and structural modified. Lots of honokiol derivatives have been found to possess good anti-proliferative activity and showed great potential in cancer therapy, but the SAR (structure-activity relationship) was still confused. Here in, the SAR were comprehensively researched by summary of reported derivatives and synthesis of novel derivatives. Amongst novel derivatives, the promising compounds A6 and A10 exhibited potent and selective anti-proliferative activities against K562 cell line with the IC₅₀ values of 5.04 and 7.08 μM respectively. The SAR was discussed around honokiol and 79 derivatives by the means of CoMFA and theoretical calculation, which provided useful suggestion for further structural optimization of honokiol derivatives.

Structure-Activity Relationships and Docking Studies of Hydroxychavicol and Its Analogs as Xanthine Oxidase Inhibitors

Hydroxychavicol (HC), which is obtained from the leaves of Piper betle LINN. (Piperaceae), inhibits xanthine oxidase (XO) with an IC₅₀ value of 16.7 µM, making it more potent than the clinically used allopurinol (IC₅₀=30.7 µM). Herein, a structure-activity relationship analysis of the polar part analogs of HC was conducted and an inhibitor was discovered with a potency 13 times that of HC. Kinetic studies have revealed that HC and its active analog inhibit XO in an uncompetitive manner. The binding structure prediction of these inhibitor molecules to the XO complex with xanthine suggested that both compounds (HC and its analog) could simultaneously form hydrogen bonds with xanthine and XO.

Bioactive Neolignans and Other Compounds from Magnolia grandiflora L.: Isolation and Antiplasmodial Activity

Bioassay-guided fractionation of a methanol extract of Magnolia grandiflora against Plasmodium falciparum yielded two new (1 and 2) and six known (3 - 8) bioactive compounds. The structures of the new compounds were assigned by mass spectrometric and 1D- and 2D-NMR data. Known compounds were identified by comparison of ¹ H-NMR and MS data with literature data. The two known neolignans 3 and 4 showed moderate antiplasmodial activity with the IC₅₀ values of 2.8 ± 0.1 and 3.4 ± 0.1 μm, respectively. Weak antiplasmodial activity was recorded for compounds 1, 2, 5, 6, 7, and 8, with the IC₅₀ values of 38 ± 2, 23 ± 2, 16.5 ± 0.2, 86 ± 1, 44 ± 4, and 114 ± 9 μm, respectively.

Chemoenzymatic Synthesis and α-Glucosidase Inhibitory Activity of Dimeric Neolignans Inspired by Magnolol

A chemoenzymatic synthesis of a small library of dimeric neolignans inspired by magnolol (1) is reported. The 2-iodoxybenzoic acid (IBX)-mediated regioselective ortho-hydroxylation of magnolol is described, affording the bisphenols 6 and 7. Further magnolol analogues (12, 13, 15-17, 19-23) were obtained from eugenol (3), tyrosol (4), and homovanillic alcohol (5), through horseradish peroxidase (HRP)-mediated oxidative coupling and regioselective ortho-hydroxylation or ortho-demethylation in the presence of IBX, followed by reductive treatment with Na₂S₂O₄. A chemoselective protection/deprotection of the alcoholic group of 4 and 5 was carried out by lipase-mediated acetylation/deacetylation. The dimeric neolignans, together with 1 and honokiol (2), were evaluated as inhibitors of yeast α-glucosidase, in view of their possible utilization and optimization as antidiabetic drugs. The synthetic analogues of magnolol showed a strong inhibitory activity with IC₅₀ values in the range 0.15-4.1 μM, much lower than those of honokiol and the reference compounds quercetin and acarbose. In particular, a very potent inhibitory activity, with an IC₅₀ of 0.15 μM, was observed for 1,1'-dityrosol-8,8'-diacetate (15), and comparable inhibitory activities were also shown by bisphenols 6 (0.49 μM), 13 (0.50 μM), and 22 (0.86 μM). A kinetic study showed that 15 acts as a competitive inhibitor, with a K_i value of 0.86 μM.

Honokiol Inhibits DNA Polymerases β and λ and Increases Bleomycin Sensitivity of Human Cancer Cells

A major concept to sensitize cancer cells to DNA damaging agents is by inhibiting proteins in the DNA repair pathways. X-family DNA polymerases play critical roles in both base excision repair (BER) and nonhomologous end joining (NHEJ). In this study, we examined the effectiveness of honokiol to inhibit human DNA polymerase β (pol β), which is involved in BER, and DNA polymerase λ (pol λ), which is involved in NHEJ. Kinetic analysis with purified polymerases showed that honokiol inhibited DNA polymerase activity. The inhibition mode for the polymerases was a mixed-function noncompetitive inhibition with respect to the substrate, dCTP. The X-family polymerases, pol β and pol λ, were slightly more sensitive to inhibition by honokiol based on the Ki value of 4.0 μM for pol β, and 8.3 μM for pol λ, while the Ki values for pol η and Kf were 20 and 26 μM, respectively. Next we extended our studies to determine the effect of honokiol on the cytotoxicity of bleomycin and temozolomide in human cancer cell lines A549, MCF7, PANC-1, UACC903, and normal blood lymphocytes (GM12878). Bleomycin causes both single strand DNA damage that is repaired by BER and double strand breaks that are repaired by NHEJ, while temozolomide causes methylation damage repaired by BER and O6-alkylguanine-DNA alkyltransferase. The greatest effects were found with the honokiol and bleomycin combination in MCF7, PANC-1, and UACC903 cells, in which the EC50 values were decreased 10-fold. The temozolomide and honokiol combination was less effective; the EC50 values decreased three-fold due to the combination. It is hypothesized that the greater effect of honokiol on bleomycin is due to inhibition of the repair of the single strand and double strand damage. The synergistic activity shown by the combination of bleomycin and honokiol suggests that they can be used as combination therapy for treatment of cancer, which will decrease the therapeutic dosage and side effects of bleomycin.

Synthesis of 2,2′-biphenols through direct C(sp2)–H hydroxylation of [1,1′-biphenyl]-2-ols

A novel synthesis of diversely substituted 2,2′-biphenols through Pd(ii)-catalyzed,^tBuOOH-oxidized, and hydroxyl-directed C(sp²)–H hydroxylation of [1,1′-biphenyl]-2-ols has been developed.

KRT6B, a key mediator of notch signaling in honokiol-induced human hepatoma cell apoptosis

The study was performed to investigate the relationship between KRT6B and Notch1 in the development and progress of hepatocellular carcinoma. The cell viability was detected by CCK8 assay. The cell apoptosis was assessed by annexin V-PI double-labeling staining on a flow cytometry. Expression of genes and proteins were analyzed by real-time PCR and Western blotting, respectively. KRT6B gene was overexpressed using a lentiviral expression vector in a human hepatoma cell line in vitro, in order to explore the mechanism by which the KRT6B promoted cell growth. The results of CCK8 and immunohistochemistry showed that honokiol induced cell death in a concentration- dependent manner, and suppressed human hepatoma cells' proliferation. The mRNA and protein expression of Notch1 was significantly lower in human hepatoma cells with honokiol treatment than that in the untreatment group. Activation of Notch-1 by exogenous transfection of Notch1 intracellular domain increased KRT6B expression in human hepatoma cells. Furthermore, cells were transfected with the wild type pLenti-KRT6B vector, the protein expression of KRT6B and NOTCH1 was significantly upregulated in human hepatoma cells with honokiol treatment. Overexpression of KRT6B promoted hepatoma cells' proliferation and showed anti-apoptosis effect. This study demonstrated that honokiol could induce human hepatoma cells' apoptosis. KRT6B, a key mediator of Notch signaling, was downregulated in honokiol-induced hepatocellular carcinoma apoptosis, suggesting that KRT6B might be a novel therapeutic target for the treatment of hepatocellular carcinoma.

Honokiol induces cell cycle arrest and apoptosis in human gastric carcinoma MGC-803 cell line

OBJECTIVE

Gastric carcinoma is a malignant tumor that responds poorly to both chemotherapy and radiation therapy. In our study, we investigated the anti-cancer effect of honokiol, an active component isolated and purified from the Magnolia officinalis, in human gastric carcinoma MGC-803 cell line.

METHODS

The cell viability was detected by the CCK8 assay. The cell apoptosis and cell cycle arrest were assessed by flow cytometer. The protein expression of cell cycle regulators and tumor suppressors were analyzed by western blotting.

RESULTS

Treatment of human gastric carcinoma cells with honokiol induced cell death in a dose-and time-dependent manner by using CCK8 assay. Consistent with the CCK8 assay, the flow cytometry results showed that the proportion of apoptosis cells had gained when the cells were exposed to honokiol. Moreover, Cyclin B1, CDC2 and cdc25C were downregulated, and the expression of p-CDC2 and p-cdc25c was significantly upregulated upon honokiol treatment. P53 and p21 were significantly upregulated by honokiol treatment. Treatment of MGC-803 cells with honokiol significantly increased the pro-apoptotic Bax level and decreased the anti-apoptotic Bcl-2 level.

CONCLUSIONS

These results confirmed that honokiol could induce apoptosis and cell cycle arrest, the underlying molecular mechanisms, at least partially, through activation p53 signaling and downregulation CDC2/cdc25C expression.

13C stable isotope labeling followed by ultra-high performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UHPLC/Q-TOF MS) was applied to identify the metabolites of honokiol in rat small intestines

Honokiol, as a pharmacological active small-molecule, has received significant attention for its strong pharmacological effects without remarkable toxicity.

FT-IR, molecular structure, HOMO-LUMO, MEP, NBO analysis and first order hyperpolarizability of Methyl 4,4″-difluoro-5'-methoxy-1,1':3',1″-terphenyl-4'-carboxylate

Methyl 4,4″-difluoro-5'-methoxy-1,1':3',1″-terphenyl-4'-carboxylate was prepared by the aromatization of a cyclohexenone derivative, Methyl 4,6-bis(4-fluorophenyl)-2-oxocyclohex-3-ene-1-carboxylate using iodine and methanol at reflux conditions. The structure of the compound was confirmed by IR and single crystal X-ray diffraction studies. FT-IR spectrum was recorded and analyzed. The crystal structure is also described. The vibrational wavenumbers are calculated using HF and DFT methods and are assigned with the help of potential energy distribution. The geometrical parameters of the title compound obtained from XRD studies are in agreement with the calculated (DFT) values. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. According to the MEP analysis, negative region (red) is mainly over the carbonyl group showing large activity. The calculated hyperpolarizability of the title compound is greater than that of the standard NLO material urea and the title compound is an attractive object for future studies of nonlinear optical properties.

Synthesis of tetrahydrohonokiol derivates and their evaluation for cytotoxic activity against CCRF-CEM leukemia, U251 glioblastoma and HCT-116 colon cancer cells

Biphenyl neolignans such as honokiol and magnolol, which are the major active constituents of the Asian medicinal plant Magnolia officinalis, are known to exert a multitude of pharmacological and biological activities. Among these, cytotoxic and tumor growth inhibitory activity against various tumour cell lines are well-documented. To further elucidate the cytotoxic effects of honokiol derivatives, derivatizations were performed using tetrahydrohonokiol as a scaffold. The derivatizations comprised the introduction of functional groups, e.g., nitro and amino groups, as well as alkylation. This way, 18 derivatives, of which 13 were previously undescribed compounds, were evaluated against CCRF-CEM leukemia cells, U251 glioblastoma and HCT-116 colon cancer cells. The results revealed no significant cytotoxic effects in any of the three tested cell lines at a test concentration of 10 µM.

Honokiol analogs: a novel class of anticancer agents targeting cell signaling pathways and other bioactivities

Honokiol (3,5-di-(2-propenyl)-1,1-biphenyl-2,2-diol) is a natural bioactive neolignan isolated from the genus Magnolia. In recent studies, honokiol has been observed to have anti-angiogenic, anticancer, anti-inflammatory, neuroprotective and GABA-modulating properties in vitro and in preclinical models. Honokiol and its analogs target multiple signaling pathways including NF-κB, STAT3, EGFR, mTOR and caspase-mediated common pathway, which regulate cancer initiation and progression. Honokiol and its targets of action may be helpful in the development of effective analogs and targeted cancer therapy. In this review, recent data describing the molecular targets of honokiol and its analogs with anticancer and some other bioactivities are discussed.