Introduction
Liver cancer stands as a prevailing global malignancy, marked by escalating morbidity and mortality annually (Llovet et al.
2021; Mcglynn et al.
2021). The nonspecific nature of early liver cancer symptoms, coupled with the absence of effective early screening methods, contributes to delayed-stage diagnosis, thereby engendering treatment complexities. Furthermore, the high metabolic rate and the swift drug clearance, along with drug resistance and drug-induced liver damage, curtailed the effectiveness of conventional treatment modalities, including surgery, chemotherapy, and radiotherapy (Anwanwan et al.
2020; Sperandio et al.
2022). Furthermore, the intricate interplay of liver cancer's heterogeneity, complexity, and immune tolerance undermines the feasibility of achieving clinical expectations through targeted therapy and immunotherapy (Huang et al.
2020; Llovet et al.
2022; Sperandio et al.
2022). Additionally, the pronounced aggressiveness and the propensity for easy metastasis of liver cancer cells contribute significantly to the poor prognosis of liver cancer patients (Anwanwan et al.
2020). In light of the aforementioned factors, despite the swift advancement of medical expertise over the previous decade, considerable drawbacks and constraints persist in the clinical management of liver cancer. Consequently, there exists a pressing need for novel therapeutic interventions and/or more efficient pharmaceutical agents in the management of liver cancer.
Natural products have consistently been regarded as a crucial reservoir for novel drug discovery (Chopra et al.
2021; Orhan
2022; Raslan
2022; Zhang et al.
2022), particularly in the realm of anticancer drug development (Varghese et al.
2021; Naeem et al.
2022). Among these natural compounds, flavokawain derivatives have been documented to possess notable anticancer activities against a spectrum of cancer cells (Teschke et al.
2011; Abu et al.
2013; Wang et al.
2021). Notably, flavokawain A and B have demonstrated significant anticancer efficacy across a range of malignancies including breast cancer (Abu et al.
2015,
2016), lung cancer (Hseu et al.
2019; Li et al.
2020), bladder cancer (Liu et al.
2017), liver cancer (Pinner et al.
2016), and melanoma (Hseu et al.
2020a,
b). Furthermore, the fundamental anticancer mechanisms underlying flavokawain A and B primarily center around the ROS signaling pathway (Pinner et al.
2016; Chang et al.
2017; Hseu et al.
2019; Hseu et al.
2020a,
b; Hseu et al.
2020a,
b), the mTOR signaling pathway (Liu et al.
2017), and the PI3K/AKT signaling pathway (Hua et al.
2020). In contrast to flavokawain A and B, limited research has shown that flavokawain C exhibits anticancer effects specifically against colon cancer (Phang et al.
2017,
2021) and breast cancer (Lin et al.
2023). The potential of flavokawain C as a prospective drug for liver cancer treatment, along with its associated anticancer mechanisms, remains uncertain and warrants thorough investigation.
In the present study, findings revealed that flavokawain C exhibited a predilection for in vivo accumulation in liver tissues with minimal impact on normal liver tissue, and concurrently exerted substantial inhibitory effects on the proliferation and migration of liver cancer cells in vitro and in vivo by downregulating the FAK/PI3K/AKT pathway. These results underscored the promising potential of flavokawain C as a targeted therapeutic agent for liver cancer treatment.
Materials and methods
Cells culture
Liver cancer cell lines (Huh-7, Hep3B and HepG2) and normal liver cell line (MIHA) were obtained from the Chinese Academy of Sciences (CAS) and the Shanghai Academy of Biological Sciences (SABS), respectively. Huh-7 and Hep3B cells were cultured in DMEM (Gibco, USA) containing 10% FBS (PPA-GE, USA) and penicillin/streptomycin (100 U/mL). HepG2 cells were maintained in MEM (Sigma-Aldrich, USA) with 10% FBS (PPA-GE, USA) and penicillin/streptomycin (100 U/mL). MIHA cells were cultured in DMEM (Gibco, USA) containing 15% FBS (PPA-GE, USA) and penicillin/streptomycin (100 U/mL). The cell lines were maintained in a cell incubator under 37 °C with 5% CO2.
Reagents and antibodies
Flavokawain C (Catalog No. PHL83854) was purchased from sigma-Aldrich with a minimum purity of 98%. Serum alanine transferase (ALT) assay kit (Catalog No. C009-2-1) and serum aspartate aminotransferase (AST) assay kit (Catalog No. C010-2-1) were obtained from Nanjing Jiancheng Bioengineering Institute. Antibodies against Bcl2 (Catalog No. sc-7382) and Bax (Catalog No. sc-7480) were acquired from Santa Cruz Biotechnology. Antibodies against p-PI3K (Catalog No. AF3242) and PI3K (Catalog No. AF1549) were obtained from Affinity Biosciences. Antibodies against p-AKT (Catalog No. 66444-1-Ig) and GAPDH (Catalog No. 60004-1-Ig) were purchased from Proteintech. Antibodies against γ-H2AX (Catalog No. 9718), AKT (Catalog No. 4685), FAK (Catalog No. 71433), and phosphor-FAK (Catalog No. 8556) were obtained from Cell Signaling Technology. Anti-mouse lgG, HRP-linked antibody (Catalog No. 7076S) was purchased from Cell Signaling Technology.
Animal preparation and ethics statement
Kunming mice (KM) and BALB/c nude mice were procured from Beijing Vital River Laboratory Animal Technology Co., Ltd, located in Beijing, China. The mice were housed in pathogen-free facilities maintained at a controlled temperature of 22–23 °C. Adequate food and water were provided, and the animals were cared for in strict adherence to the guidelines outlined in the Guide for the Care and Use of Laboratory Animals. Ethical clearance for all animal-related experiments was obtained from the Animal Care and Use Committee of Wenzhou Medical University (Approval Document No. wydw 2023-0294).
Tissue distribution study
Twenty KM mice were randomly divided into two groups, each containing ten mice. The mice were orally administered either 20 mg/kg of flavokawain C (formulated in 10% Tween 80, 10% ethanol, and 80% saline) or normal saline. The mice were euthanized 2 h after receiving flavokawain C or normal saline. Tissues were collected, washed in normal saline, homogenized, and prepared for sampling. Subsequently, the concentration of flavokawain C was determined using UHPLC-MS/MS.
ALT and AST determination assay
Forty KM mice were randomly divided into four groups and orally administered the specified doses of flavokawain C (10, 30, 90 mg/kg) or normal saline (Control). Blood samples were collected from the ocular region 7 days after the administration of flavokawain C (formulated in 10% Tween 80, 10% ethanol, and 80% saline) or normal saline. ALT and AST activities were assessed according to the manufacturer's guidelines. Briefly, blood was centrifuged, and the resulting supernatant was collected. Substrate solution (20 μL per well) and sample (5 μL per well) were added to a 96-well plate and incubated at 37 °C for 30 min. Subsequently, 2,4-dinitrophenylhydrazine solution (20 μL per well) and sample (5 μL per well) were added and incubated for an extra 20 min. Lastly, 0.4 mol/L sodium hydroxide solution (200 μL per well) was added, and the plate was maintained at room temperature for 15 min before absorbance measurement.
Hematoxylin eosin (H&E) staining assay
The H&E staining assay was conducted following the previously described method (Shen et al.
2022). In brief, liver tissue or tumor tissue samples were fixed with 4% paraformaldehyde (Beyotime, China), embedded in paraffin, and then cut into 5 mm-thick sections. Subsequently, the sections were stained with H&E and visualized using a Nikon Ti microscope (Nikon, Japan).
Immunohistochemistry (IHC) assay
Summarily, tumors were fixed in 4% paraformaldehyde for 48 h. Subsequently, the tumors were meticulously processed, embedded in paraffin, and sectioned into 5 µm slices. After baking for 4–5 h followed by dewaxing, a subset of histological sections underwent IHC analysis, the Mouse anti-Ki67 monoclonal antibody (dilution 1:50, SANTA, China), and the Mouse anti-γ-H2AX monoclonal antibody (dilution 1:150, Millipore, USA) were incubated overnight at 4 °C. Subsequently, the sections were treated with an HRP-conjugated secondary antibody at room temperature for 1 h. Finally, the sections were stained with DAB (ZSGB-BIO, China) and counterstained with hematoxylin for enhanced visibility and analysis.
MTT assay
Huh-7, HepG2, Hep3B, and MIHA cells were seeded in 96-well plates (Corning, USA) at a density of approximately 6 × 103 cells per well. The cells were incubated at 37 °C for 48 h, both with and without treatment of flavokawain C. Subsequently, MTT solution (0.5 mg/mL, 20 μL/well) was added and incubated for 4 h. After removing the culture medium, 100 μL of dimethyl sulfoxide (DMSO) was added to dissolve the formazan reaction product. The absorbance of the mixture was measured at 490 nm using a DTX880 spectrophotometer (Beckman Coulter, USA) to assess cell viability.
Huh-7, HepG2, Hep3B, and MIHA cells were seeded in 12-well plates at a density of 800 cells per well. Following attachment, the cells were incubated for 2 weeks in regular growth media with 0.01% DMSO (Control) or co-incubated with the specified concentrations of flavokavain C. The colonies were subsequently washed three times with PBS, fixed with 4% formaldehyde for 15 min, and stained with 0.04% crystal violet for 1 h. The colonies on each plate were observed under a microscope after being washed twice with ddH2O. The colony count was ascertained in three independent experiments.
EdU staining assay
The EdU staining assay was performed according to the manufacturer's guidelines. Briefly, Huh-7 and Hep3B cells were transfected and seeded in 12-well plates containing coverslip at a density of 5 × 104 cells per well. The cells then incubated overnight. Subsequently, the cells were exposed to either 0.01% DMSO (Control) or the specified concentrations of flavokawain C for 48 h. Lastly, cell proliferation was evaluated using the EdU staining proliferation kit (Beyotime, China), and the resulting stained cells were visualized under a Nikon fluorescence microscope.
Flow cytometry apoptosis assay
Apoptotic cell was identified using an apoptosis detection kit from BD Biosciences (USA). Huh-7 and Hep3B cells were incubated with either 0.01% DMSO (Control) or varying concentrations of flavokawain C (4, 8, and 16 μM) for 48 h. The cells were then stained with Annexin V and propidium iodide (PI) for 15 min. After that, Annexin V binding buffer was added to the mixture, and fluorescence was determined using a FACSC flow cytometer (BD Biosciences). The obtained data was analyzed with Flowjo 9.0 software.
Western blot assay
Cells were cultured in 6-well plates (Corning, USA) and then exposed to the specified concentrations of flavokawain C for 48 h. Subsequently, the cells were lysed, and total protein was extracted and quantified through the Bradford assay. The protein samples were electrophoresed on 10% SDS-PAGE gels and subsequently transferred to PVDF membranes (Bio-Rad). These membranes were then blocked with a 5% skim milk solution in TBST buffer and subsequently incubated with primary antibodies. After washing the PVDF membranes with TBST, an HRP-conjugated secondary antibody (CST, Danvers, MA) was applied. The immune-reactive bands were visualized by employing an enhanced chemiluminescence (ECC) reagent (Bio-Rad, USA).
Alkaline comet assay
The alkaline comet assay was performed as described method in a previous study (Shen et al.
2022). Following a 48 h treatment with either 0.01% DMSO (Control) or flavokawain C at concentrations of 4, 8, and 16 μM, cells were harvested and then placed onto slides coated with a mixture of 1.5% normal agarose and 0.5% low-melting temperature agarose. Next, the slides were subjected to lysis using a buffer comprising 0.5% Triton X-100, 2.5 M NaCl, 10 mM Tris (pH 10.0), 3% DMSO, 100 mM EDTA, and 1%
N-lauroylsarcosine. Electrophoresis was carried out at 1.5 V/cm in Tris–HCl (100 mM), 1% DMSO, and 300 mM sodium acetate buffer for 20 min. After electrophoresis, the slides were counter-stained with a solution of propidium iodide (PI) at a concentration of 0.02 mg/mL and observed under a fluorescence microscope (Nikon, Japan).
Immunofluorescence (IF) assay
The IF assay was performed as described method in a previous study (Qiu et al.
2022). Briefly, cells were seeded onto a coverslip (Corning, USA) and then fixed with 4% paraformaldehyde (Beyotime, China) for 15 min at room temperature. Subsequently, the cells were permeabilized with 0.5% Triton X-100 for 30 min. Following washing, the coverslip was incubated in a blocking solution for 1 h. Primary antibodies (53BP1 or FAK) were applied and allowed to incubate overnight. After three washes with PBST, the cells were incubated with DyLight 488-conjugated secondary antibodies for another 1.5 h. Following another round of washing with PBST, the coverslip was stained with DAPI (Beyotime, China) and then examined using a fluorescence microscope (Nikon, Japan).
Cell adhesion assay
The cell adhesion assay was performed as described method in a previous study (Qiu et al.
2022). Briefly, human fibronectin (2.5 mg/mL) was dissolved in PBS (Millipore, CA) and utilized to coat a 96-well plate overnight at 4 °C. Cells were then seeded into each well at a density of 5 × 10
4 cells per well in serum-free medium. The plate was subsequently placed in a CO
2 incubator at 37 °C for cell cultivation. Following cell attachment, the medium was removed, and the cells were fixed using 4% paraformaldehyde. Subsequently, the cells were stained with crystal violet for 5 min at room temperature. The crystal violet was then dissolved in 100 mL of 33% acetic acid, and the absorbance was measured at 560 nm using a Multiskan FC automatic microplate reader (Thermo Fisher, USA). The relative number of cells adhering to the extracellular matrix was calculated using the following equation: the mean optical density (OD) of treated cells divided by the mean OD of control cells. Cells treated with a vehicle (0.1% DMSO) was used as the control.
Trans-well assay
The trans-well assay was conducted employing 24-well trans-well chambers (Corning Costar, NY) following the guidelines provided by the manufacturer. In brief, cells were cultured with either 0.01% DMSO (Control) or different concentrations of flavokawain C (4, 8, 16 μM) for 48 h. Then, a prepared cell suspension in FBS-free DMEM (100 μL) was introduced into the upper chamber at a density of 1 × 105 cells/well. In the lower chamber, 600 µL of DMEM containing 10% FBS was added. After 48 h, the lower surface of the chamber was fixed using 4% paraformaldehyde for 15 min at room temperature. Subsequently, the cells were stained with a 0.1% crystal violet solution for 5 min at room temperature. Photomicrographs were captured using a Nikon microscope. The crystal violet dye was then dissolved in 500 μL of 33% acetic acid, and the absorbance was subsequently measured at 560 nm.
RNA sequencing assay
Huh-7 cells underwent treatment with either 0.01% DMSO or 16 μM flavokawain C for 48 h. Afterward, the cells were harvested, and total RNA extraction was performed utilizing TRIzol reagent (Invitrogen, CA, USA). Paired-end sequencing was conducted at LC-BIO (Hangzhou, China) using an Illumina HiSeq 4000, following the vendor’s recommended protocol.
Molecular docking (MD) and simulations
The crystal structures for PI3K (PDB ID: 4ZOP) and FAK (PDB ID: 4GU9) were obtained from the Protein Data Bank. Molecular docking simulations were performed employing SYBYL-X 2.0 software, following the methodology described previously (Liang et al.
2021). Initially, the protein's PDB structure was acquired from the official website, and any solvent molecules and extraneous entities were removed. Subsequently, the molecular structure was optimized through energy minimization calculations. Processed protein and small molecule ligand were subjected to docking simulations, and the conformation with the highest score and the lowest energy was chosen. The resulting complex was analyzed for visualization using PyMOL. The MD simulations were carried out using Amber 20. The protein was prepared using the ff14SB force field, and the ligand was prepared using the GAFF force field with AM1-BCC charge. The MD simulation system was built using the OPC solvent model with a box shape of truncated octahedron and a margin distance of 10 Å (FAK-FKC) or 12 Å (PI3K-FKC). All systems were neutralized with explicit counterions (Na
+ or Cl
−). Simulations were run 10 ns under the condition of 300 K and 1 atm by applying periodic boundary conditions.
The Cancer Genome Atlas (TCGA) analysis
TCGA analysis was carried out using TTCGA database available at (
http://cancergenome.nih.gov/). Differential expression analysis was executed using R language (version 4.0.2) and GraphPad Prism 5.0.
Tumor xenograft model
The Laboratory Animal Resources Center of Wenzhou Medical University approved all animal experiments (Date: June 08, 2023/No: wydw2023-0294). The tumor xenograft model was conducted using 6-week-old BALB/c nude mice. Huh-7 cells (1 × 106) in PBS were subcutaneously injected into the right flank of BALB/c nude mice. Initially, six mice with good health were assigned to each group after five days of modeling. After ten days of modeling, the average tumor volume went to about 200 mm3, and some mice were excluded for the significant variations in tumor volumes, resulted in four mice per group ultimately. Then flavokawain C (16 mg/kg), which was formulated in 10% Tween 80, 10% ethanol, and 80% saline, injected intraperitoneally daily for 2 weeks. Volume of the tumor was measured every two days using calipers, and volume was calculated using V = ab2/2, where a and b are the length and width of the tumor, respectively.
Statistical analysis
Values were presented as mean ± SD. Statistical analysis was conducted using GraphPad Prism 5.0 software. Group comparisons were performed using a two-tailed, unpaired Student's t test to evaluate intergroup variations. Statistical significance was defined at a significance level of p < 0.05 (*p < 0.05, **p < 0.01, ***p < 0.001).
Discussion
Liver cancer, a substantial global health issue, has gained heightened attention due to its escalating incidence and elevated mortality rates (Anwanwan et al.
2020; Li et al.
2021). Chemotherapy and immunotherapy continue to serve as the primary therapeutic approaches for individuals with liver cancer (Anwanwan et al.
2020; Llovet et al.
2021). However, their efficacy is impeded by drug resistance, a limited response ratio, and adverse toxic effects (Anwanwan et al.
2020; Llovet et al.
2022; Sperandio et al.
2022). Thus, the imperative need arises for the exploration of novel therapeutic drugs and/or strategies to enhance clinical prognoses. Several studies have indicated that compared to synthetic small molecules, natural products might yield enhanced outcomes for cancer patients owing to diminished systemic toxicity (Anwanwan et al.
2020; Man et al.
2021). In this study, our results demonstrated that flavokawain C had stronger cytotoxicity on liver cancer cells than normal liver cells (Table
S1), suggesting it maybe act as a potential drug for liver cancer treatment.
Targeting drugs specifically to tumor tissues is expected to enhance drug efficacy, utilization, and therapeutic outcomes, while also mitigating side effects (Zhao et al.
2020). Our findings illustrate that flavokawain C exhibits selective enrichment in liver tissue in vivo (Fig.
1A). This observation provides additional evidence supporting the potential role of flavokawain C as a novel targeted drug for liver cancer treatment. The proper functioning of the liver, which serves as the central hub for metabolism and detoxification, is crucial for maintaining overall health (Trefts et al.
2017). Furthermore, drug-induced liver injury poses a significant challenge in the treatment of liver cancer patients and can ultimately result in treatment failure (Katarey et al.
2016; Kumachev et al.
2021). Our findings indicated that treatment with flavokawain C does not alter the levels of ALT and AST in the serum, nor does it affect histomorphology (Fig.
1B–D). This suggests that the administration of flavokawain C is unlikely to cause liver injury. In aggregate, these findings contribute to the enhanced potential of utilizing flavokawain C in the clinical context of liver cancer treatment.
The FAK/PI3K/AKT signaling pathway is a pivotal player in cell proliferation, metastasis, and survival processes (Guo et al.
2020; Ke et al.
2022; Chen et al.
2023; Ye et al.
2023). Our findings indicate that flavokawain C is capable of downregulating the FAK/PI3K/AKT signaling pathway through the inhibition of FAK and PI3K phosphorylation (Fig.
8). Consequently, flavokawain C markedly suppressed the proliferation and migration of liver cancer cells in vitro and in vivo (Figs.
2A,
6,
9). It is well established that natural products often exhibit a tendency toward multi-target actions (Hashem et al.
2022). Therefore, the impact of flavokawain C on the FAK/PI3K/AKT signaling pathway may involve multiple molecules. In line with this, the results suggest that the reduction in p-FAK and p-PI3K proteins could stem from gene regulation due to flavokawain C treatment, as well as a direct interaction between flavokawain C and the ATP site of the FAK and/or PI3K protein (Fig.
7A–C).
In conclusion, this study has demonstrated that flavokawain C is specifically enriched in liver tissue and effectively inhibits the proliferation and migration of liver cancer cells by downregulating the FAK/PI3K/AKT signaling pathway. Importantly, this effect is achieved while causing minimal side effects on normal liver tissues, underscoring its potential as a novel liver cancer treatment drug with broad clinical applicability.
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