Cell Culture
All cells were purchased from the Peking Union Cell Bank (Beijing, China). All cells were cultured in a 37°C incubator in an atmosphere of 5% CO2. The human hepatoma cell lines (SNU182, SNU387) were cultured in RPMI-1640 medium supplemented with 10% fetal bovine serum and 10,000 U/mL penicillin-streptomycin. The HUH7, HepG2, Hep3B and LM3 cell lines were in DMEM medium supplemented with 10% fetal bovine serum and 10,000 U/mL penicillin-streptomycin cultured. The cell culture media and supplements were purchased from Gibco.
Bioinformatics
The GEPIA 2 database was used to compare and analyze the expression differences of OATP1B3 in different cancers. The 508 hepatocellular carcinoma patients were grouped based on the high and low levels of OATP1B3 mRNA expression, and survival analysis was performed using the Kaplan-Meier method according to the different patient groups. Spearman correlation test was utilized to assess the correlation between SLCO1B3 and methylase inhibitors using the TCGA-LIHC dataset[20].
Gene expression studies
Total RNA was extracted using TRIzol reagent, and cDNA was synthesized with Reverse Transcriptase. Quantitative real-time PCR was performed using SYBR GreenER qPCR SuperMix Universal(Roche, Switzerland). The threshold cycle (Ct) values for each gene were normalized to those of GAPDH, and the 2–ΔΔCt method was used for quantitative analysis.
The following primers were used:
hGAPDH-F GTCTCCTCTGACTTCAACAGCG
hGAPDH-R ACCACCCTGTTGCTGTAGCCAA
hOATP1B3-F GTCACCTTGTCTAGCAGGATGC
hOATP1B3-R GCATTCACCCAAGTGTGCTGAG
OATP1B3 (#66381-1-Ig) and GAPDH(#60004-1-Ig) antibodies were purchased from Proteintech (Rosemont, IL, USA). Using a BCA Protein Assay Reagent Kit (#PC0020, Solarbio, China). Hep3B cells were lysed by RIPA. The protein concentration was determined. Cell lysates were separated by 10% SDS-PAGE and electrotransferred onto PVDF. The PVDF were blocked with 5% Skim Milk for 40min and then incubated with antibodies against OATP1B3 (1:3000)[21], and GAPDH (1:6000) overnight at 4℃. The blots were extensively washed with Tris-buffered saline with Tween-20 (TBST) buffer. The corresponding HRP-conjugated secondary antibodies were incubated for 1h at room. Immunoreactive bands were detected by an ECL(#P0018FM, Beyotime, Shanghai, China) system using an image reader. Densitometric analysis was performed by ImageJ. The data were corrected by background subtraction and normalized against GAPDH as an internal control.
Bisulfite methylation sequencing
The SLCO1B3 promoter sequence was searched for CpG islands using a database to predict the possible methylation sites. The Genomic DNA from HCC cell lines were prepared using the proteinase K method. Bisulfite treatment was performed. Methylation-specific PCR (MSP) primers were designed according to genomic sequences inside the CpG islands in the SLCO1B3 gene promoter region. Snap Gene was compared with the sequencing results to calculate the corresponding methylation rates.
RTCA assays for cell killing
Hep3B was inoculated in E-Plate View 96-well plates (for RTCA-eSight) overnight to detect the proliferation curve. After 24 h, the medium was replaced with fresh medium containing 0, 1, 3, 10 µmol/L DAC (#HY-A0004, MCE, New Jersey, USA) or sorafenib(#HY-10201, MCE, New Jersey, USA) in 3 replicate wells, and the cell proliferation curve was monitored continuously wells and continuously monitored.Hep3B was inoculated into E-Plate View 96-well plates and the control, DAC, sorafenib and combination groups were established. The 3 replicate wells were set up and the cell proliferation curve was measured overnight. When the cell index (CI) value was around 1, the DAC and combination groups were replaced with fresh medium containing 3 µmol/L DAC, and the Control and sorafenib groups were replaced with fresh medium. After 72h incubation, the fresh medium containing 3 µmol/L sorafenib was replaced and the cell proliferation was observed. The cell survival rate was calculated after a certain period of time, and GraphPad Prism was used for graphing.
Cell viability assay
Cell viability was evaluated using MTS. Cells were seeded in a 96-well plate, and after cell treatments, MTS reagent was added according to the manufacturer’s instructions. Absorbance was measured at 490 nm using a standard instrument.
Transport assays
HEK293-OATP1B3 cells were inoculated into 24 wells and incubated for 24 hours. The culture medium containing 3 µM Sorafenib was then replaced and incubated for 2 minutes in triplicate wells. The reaction was stopped using ice-cold PBS, and the cells were lysed with methanol. Sorafenib uptake was detected using LC-MS/MS. Similarly, Hep3B cells were inoculated into a 24-well plate and incubated for 24 hours. The culture medium was replaced with fresh medium containing 3 µM DAC and incubated for 72 hours. Then, fresh medium containing 10 µM Sorafenib was replaced and incubated for 1 hour in triplicate wells. The reaction was stopped using ice-cold PBS, and the cells were lysed with methanol. Sorafenib uptake was detected using LC-MS/MS.
Chromatographic conditions: ZORBAX Eclipse XDB-C18 column (50 mm×4.6 mm, 5-Micron), mobile phase A: 0.1% formic acid, B: acetonitrile, 20:80 ratio, isocratic elution. Flow rate 0.5 ml/min. Injection 2 ΜL. Column temperature 37℃. Mass spectrometry conditions: electrospray ion source with positive ion mode mass spectrometry scan with multiple reaction monitoring(MRM).
Combining DAC with Sorafenib induces Ferroptosis
Hep3B was inoculated in 96-well plates (for RTCA-eSight) overnight to detect the proliferation curve. After 24h, the medium was replaced with fresh medium containing 6µM Sorafenib, Ferroptosis inhibitor 1µM Liproxstatin-1 + 6µM Sorafenib in 3 replicate wells, and the cell proliferation curve was monitored continuously wells and continuously monitored.
Hep3B was inoculated in 12-well plates, with Control group, DAC group, Sorafenib group and combination group, triplicate wells, incubated overnight, and when the cells were wall-stabilized, the DAC group and combination group were replaced with fresh medium containing 3µM DAC. After 72h incubation, the Sorafenib group and the combination group were replaced with 3µM Sorafenib administration medium respectively. 12h later, the old culture medium was aspirated off, C11 BODIPY 581/591 (1:1000) (#HY-D1301, MCE, New Jersey, USA) was added, incubated for 20min protected from light, serum-free medium was washed three times, and cells were collected by digestion after rapid photo-preservation analysis under fluorescence microscope. Fluorescence values were detected by flow cytometric analysis.
Xenograft studies
Under SPF grade conditions, BALB/c nude mice were sterilized with alcohol in the right axilla and inoculated with Hep3B cells at 200 µL/each, 1 × 107 cells per inoculum. When the tumor volume reached 400 ~ 600 mm3, the tumor tissue was removed for passaging. When the tumor volume reached 100mm3, the mice were assigned randomly into different treatment groups (Control, DAC, Sorafenib, and DAC + Sorafenib groups).The 2.5 mg/kg of DAC was administered intraperitoneally to the DAC group and 20 mg/kg of Sorafenib was administered by gavage to the Sorafenib group. In the Control group, equal doses of Sorafenib were given intraperitoneally, and in the Control group, equal volumes of PBS were given intraperitoneally. All of the above were given on alternate days for 21 days. The tumor-bearing mice were weighed and tumor volumes were measured twice weekly. At the end of the experiment, the mice were humanely executed, the tumors were stripped and photographed, weighed. A portion of the tumors was immediately fixed in 10% buffered formalin for immunohistochemistry. The animal experiments were conducted in accordance with the Animal Ethics Committee of Tianjin Tiancheng New Drug Evaluation (Co.2021-0008) for experimental studies.
Immunohistochemical
For IHC staining, tissue slides were deparaffinized in xylene and rehydrated in alcohol. Endogenous peroxidase was blocked with 3% hydrogen peroxide. Antigen retrieval was achieved using a microwave and 0.1 M citric sodium buffer (pH 6.0). Sections were then incubated overnight at 4°C with the primary antibody. Then three PBS washes were performed, after which the slides were exposed to the secondary antibody for 1 h at room temperature. We wash 3 times with PBS, 5min each time, then with DAB color development for 5min, tap water for 10 min, hematoxylin counterstain for 2 min, tap water again for 10 min, and then routine dehydration, transparency, mounting, and microscopy. Positive expression of OATP1B3 protein as tan or brown granules. All patients complete the informed consent sign.
Data and Statistical analysis
Experimental data were statistically analyzed using GraphPad Prism 8(GraphPad Software, San Diego, CA, USA), and all experimental data were expressed as mean ± standard deviation (x ± s). Two groups were compared using independent samples t-test, and multiple comparisons were performed using one-way ANOVA, with p < 0.005 indicating significant differences.