1. Introduction
Among the known adult malignant brain tumors, glioblastoma multiforme (GBM) is the most aggressive glioma [
1]. Despite advances in medical technologies, the average life-span of GBM patients after surgery and chemotherapy is 14-15 months [
2]. Although the annual incidence rate of GBM is about 3.19 to 4.17 cases per 100,000 people [
3], its high mortality rate and poor prognosis encourage researchers to find more effective treatments [
4].
TMZ is widely used as the first line of chemotherapy for GBM patients [
5,
6]. It is an alkylating agent [
7,
8] and induces DNA damage, cell cycle arrest and apoptosis activation [
8,
9,
10]. TMZ also induces autophagy which could have cytoprotective effects on the target cells [
9,
10,
11].
The cell fate is determined via different mechanisms including apoptosis, autophagy, and the unfolded protein response (UPR) [
12,
13]. These pathways are initiated and characterized by multiple stimuli and signaling mediators [
14,
15]. The main function of autophagy relates to the cell’s protection and survival, while under some situations it leads to cell death [
16,
17]. There are different molecular pathways for crosstalk between the apoptosis and autophagy pathways [
18,
19,
20]. Autophagy can be a pro- or anti-apoptotic mechanism based on the type of cell model, organism and the stimuli [
21,
22,
23,
24].
Statins are cholesterol lowering drugs with several pleiotropic effects including their impact on cancer [
25]. In recent years, both basic and clinical scientists have focused their investigations on the potential role of statins in cancer therapy. Recent studies have suggested that statins could have beneficial effects and impacts on the response to chemotherapy in cancer patients [
9,
26,
27,
28,
29]. A recent investigation has showed that simvastatin combined with TMZ increases the survival of GBM patients [
30]. Our team has recently discovered that simvastatin induces apoptotic cell death in glioblastoma, non-small cell lung carcinoma, breast cancer, and neuroblastoma cell lines via depletion of geranylgernaly pyrophosphate [
31,
32]. We have later showed that simvastatin sensitizes GBM tumor cell lines (U87, and U251) and primary patient derived GBM cells to TMZ-induced apoptosis via inhibition of autophagy flux [
33] and UPR [
20].
Recently, Shikonin (SHK) [
32], a highly lipophilic compound from Lithospermum erythrorhizon root that is commonly used in Chinese folklore remedies through its anti-inflammatory and pleiotropic effects, has been introduced as an antitumor agent [
34,
35,
36,
37,
38]. Besides the strong anticancer feature of Shikonin and its analogs, they also have the ability of circumventing cancer drug resistance [
39,
40]. Shikonin derivatives like Acetylshikonin (ASH) have shown cytotoxic and anti-cancer effects [
41]. A few recent investigations also showed the impact of SHK (alone or in combination with TMZ) in targeting GBM tumor cells by inducing significant apoptotic cell death and decreasing their proliferation [
42,
43].
In the current investigation, we expand our previous investigations and used triple treatments of ASH, TMZ and Simvastatin (Simva) to target GBM tumor cells (U251 and U87). We focused our investigation on the mechanism of combination therapy on GBM cells via cross talk of apoptosis and autophagy.
2. Materials and Methods
2.1. Reagents and Drugs
Acetylshikonin (CAS Number: 24502-78-1) and simvastatin (CAS Number: 79902-63-9) were purchased from Chem Face China Company. Temozolomide (CAS Number: 85622-93-1), propidium iodide (CAS Number: 25535-16-4), 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) (CAS Number: 298-93-1), Acridine Orange (CAS Number: 65-61-2), Bafilomycin A1(Cat#: B1793-10UG) and anti-rabbit LC3β antibody (Cat# L7543-100UL) were purchased from Sigma-Aldrich Co. Anti-rabbit p62 antibody (Cat#39749), anti-rabbit Beclin-1 antibody (Cat#3738), anti-mouse Bcl2 antibody (Cat#15071), anti-rabbit Mcl-1 antibody (Cat#4572), anti-rabbit Bcl-XL antibody (Cat#2762), and anti-rabbit GAPDH antibody (Cat#2118) were purchased from Cell Signaling Company. The secondary antibodies, anti-rabbit HRP-conjugate and anti-mouse HRP-conjugate were purchased from Sigma-Aldrich (Oakville, ON, Canada) as well. The enhanced chemiluminescence (ECL) (CAS Number: 12630) was acquired from Cell Signaling Technology Co. (Beverly, MA, USA). The bicinchoninic acid (BCA) protein assay kit was obtained from Thermo Fisher Scientific (Winnipeg, MB, Canada).
2.2. Cell Lines, Culture, and Treatment
U87 and U251 human GBM cells were obtained from Bon yakhteh Company (Bon yakhteh, Tehran, Iran) and cultured in Dulbecco’s Modified Eagle’s Medium (DMEM) (Bio Idea, Tehran, Iran, Cat #: DB9696) (low-glucose, high glutamine for U87 and high-glucose for U251), supplemented with 10% Fetal Bovine Serum (FBS) (Bio Idea, Tehran, Iran, Cat #: BI-1201) and 1% penicillin–streptomycin (Bio Idea, Tehran, Iran, Cat #: BI-1203). Cells were maintained in a 5% CO2 incubator with 95% humidity at 37 °C.
2.3. Cytotoxicity Assay
To evaluate the cytotoxicity effects of Temozolomide, ASH and Simva and their combination on U87 and U251 GBM cell lines, MTT viability tests were done based on our established method [
8,
24,
31,
32,
33,
44]. Four different time points (24, 48, 72 and 96 hrs) and a range of concentrations (TMZ 50-250 µM, ASH 0.5-25 µM, Simva 0.5-20 µM) were tested. After finding the best time point and the IC50 concentration of each drug, the combination therapy of TMZ/Simva and TMZ/Simva/ASH on GBM cells was evaluated. For combination therapy, Simva was pretreated for 4 hrs. U87 and U251 cells were both briefly cultured in 96-well plates (6000 cells per well) and treated with different concentrations of the drugs. After the treatment time point, 20 µL of MTT dye, 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide was added to each well and incubated in the 37 °C incubator for 4 h. The medium was then aspirated and 200 µL of DMSO was added to each well and incubated at room temperature for 15 min in the dark. Finally, the optical absorbance was read at 570 nm by multiplate reader (Synergy, Biotek, USA).
2.4. Apoptosis Assay Using Flow Cytometry
The cell death mechanism evaluation was measured using Nicolleti method [
45,
46,
47,
48,
49]. Both cell lines were briefly cultured in 6-well plates (100,000 cells per well) and pre-treated with Simva 1 µM and 2.5 µM for U251 and U87 respectively, for 4 hrs. These were the least toxic concentrations of Simva for each cell line. Then, TMZ 100 µM and ASH 1.5 µM were added. After 72 hrs, the cells were detached by EDTA buffer to minimize cell damage and then washed with PBS. Afterward, PI lysis buffer including 0.1% Triton X-100, 40 µg/mL propidium iodide, 1% sodium citrate and 0.5 mg/mL RNase A were added to the obtained pellets and incubated at 37 °C for 35 min. Finally, sub G1 population area indicated the apoptotic nuclei levels by Flow Cytometry (FACScalibur flow cytometer, BD Biosciences, USA). All the results were acquired in 10,000 event count.
2.5. Immunoblotting
We did western blotting according to our previous investigations [
44,
50,
51,
52]. After treatment with the different compounds [TMZ-Simva-ASH, ASH, Bafilomycin A1 (Baf-A1)] at the indicated time point (72 hrs), the cells were gently washed with PBS, and the pellets were collected. The pellets were suspended in lysis buffer including NaCl 150 Mm, Triton 1%, Tris 50 Mm, protease inhibitor and Phosphatase inhibitor cocktail (Cat# P5726-Sigma) and then sonicated 5 times for 3 seconds. Equal amounts of proteins were loaded onto the electrophoresis SDS-PAGE gel. The proteins were then transferred to PVDF membranes (Sigma; # IPVH00010). The blocking step was performed in 5% fat-free milk overnight. The primary antibodies (Bax, Bcl-2, LC3β-II and p62) were also diluted based on the manufacture’s protocol to add the membranes and incubate at 4 °C overnight. The next step was the incubation of the membranes with corresponding secondary antibodies at room temperature for 90 min. Finally, the membranes were exposed to enhanced chemiluminescence (ECL) reagents and developed by the ChemiDocTM MP imaging system (Bio-Rad, Hercules, CA, USA). To quantify the intensity of the bands, Image Lab densitometry software was utilized and normalized by GAPDH protein values to correct the possible errors during protein loading.
2.6. Caspase3/7 Activation Assay
To assess the activity and catalytic function of caspase3/7 (DEVD-ase), Cayman fluorescence assay kit was used based on our adopted established protocol [
31,
33,
46]. Briefly, the cells were seeded in 96 wells plates to reach about 50% confluence to prevent high non-specific fluorescence, and were then treated with TMZ (100 µM), Simva (1 and 2.5 µM for U251 and U87 respectively), ASH (1.5 µM), TMZ/Simva and TMZ/Simva/ASH for 48 hrs based on our experimental protocol (OEP). For the combinations, Simva was pretreated for 4 h. All reagents were freshly prepared including assay buffer, caspase3/7 substrate, active caspase-3 positive control and caspase3/7 inhibitor solution. The plates were centrifuged at 800 g for 5 min, followed by aspiration of the supernatant, addition of assay buffer and another centrifugation. Later, lysis buffer was added, followed by orbital shaking and centrifuging (800 g). Caspase3/7 inhibitor, active caspase-3 positive control and caspase3/7 substrate solutions were then added (30 min, room temperature, and dark place). The fluorescence intensity of each well was measured by BioTek Cytation 3 Cell Imaging MultiMode Microplate Reader (Biotek Cytation 3, USA) (excitation wavelength: 485 nm, emission wavelength: 535 nm).
2.7. Reactive Oxygen (ROS) Assay
ROS generation was detected by Cayman ROS detection cell based Dihydroethidium (Hydroethidine, DHE) assay. The cells were cultured in the black tissue culture-treated 96-well plates, where their confluence reached about 70% after 24 hrs to avoid overgrown cells. The treatment was done at two different point times (38, 60 h). The cell-based assay buffer and DHE, N-Acetyl cysteine and Antimycin assay reagents were prepared based on the kit protocol. All wells were aspirated. The assay buffer and ROS staining buffer were then added respectively. N-Acetyl cysteine and Antimycin were used as the negative and positive controls, respectively. The kit’s instruction was followed for the incubation times, fluorescence was measured (excitation wavelength of 480–520 nm and emission wavelength of 570–620 nm) and microscopic images were taken by BioTek Cytation 3 Cell Imaging MultiMode Microplate Reader (Biotek Cytation 3, USA) and analyzed based on our established protocols [
33].
2.8. Determination of Mitochondria Membrane Potential (MMP)
Loss of mitochondria membrane potential is considered a substantial parameter of cell function. Thus, the measurement of changes in MMP is very important to follow the apoptotic process. After seeding the cells in the 96-well black culture plates and treatment for 48 hrs, Cayman JC-1 mitochondria membrane potential assay kit was used. The cells’ confluence was 80% at the time of staining. JC-1 was added to each well and the assay buffer was used after incubation. The test was performed based on the kit directions. The healthy cells with JC-1 J-aggregates were detected with Rhodamine filter (excitation/emission: 540/570) while the apoptotic cells with mainly JC-1 monomers were detectable with FITC filter (excitation/emission 485/540) by BioTek Cytation 3 Cell Imaging MultiMode Microplate Reader (Biotek Cytation 3, USA).
2.9. Acridine Orange Acidic Vacuole Assay
To detect the acidic vesicular organelles [
53], which are essential markers of late autophagy [
54], acridine orange (AO) staining assay was performed. AO induces green fluorescence in cytosolic and nuclear parts of the cells, but upon fusion into the acidic environment such as lysosomes, it becomes protonated and emits an intense red fluorescence. So, the ratio of red to green fluorescence intensity can be a suitable marker for AVO formation. Cells were seeded at 96-well plates and treated for 72 hrs. They then were stained with AO (final concentration of 1 μg/mL) and incubated at 37 °C for 10 minutes (dark and room temperature). After washing with PBS twice, the microscopic images were taken and the green and red fluorescence was read at 550 and 650 nm of emission wavelengths by BioTek Cytation 3 Cell Imaging MultiMode Microplate Reader (Biotek Cytation 3, USA), respectively.
2.10. Statistical Analysis
The results were represented as means ± SD and statistical differences were analyzed by one-way or two-way ANOVA using Graph Pad Prism 8. P-value < 0.05 implies the significance values. All the experiments were done in at least three biological replicates.
4. Discussion
Many chemotherapy approaches are not effective towards reaching the desired outcomes in GBM patient treatment [
72,
73]. Our team has recently investigated the efficiency and mechanisms of combination Simva and TMZ treatments in GBM and showed that Simva sensitizes GBM cells to TMZ-induced apoptosis [
10,
20,
22]. TMZ resistance, as a major problem in GBM patient therapeutic strategies, has been investigated for years. Moreover, several compounds and drugs were utilized to enhance the efficacy of TMZ while attenuate the resistance to TMZ to achieve the best approach to treat GBM patients [
72,
73,
74]. Recent investigations have showed that taking statins for a long period of time, could potentially increase the survival of the cancer patients (including GBM) and improve their response to different chemotherapy medications [
9,
75,
76,
77]. A significant synergistic effect of statins has been reported in combination with chemotherapy compounds including cisplatin, 5-Fluorouracil (5-FU), doxorubicin and paclitaxel [
78]. A recent investigation has also showed that lovastatin sensitizes GBM cells (U251 and U87) to TMZ-induced apoptosis via inhibition of autophagy flux [
79]. These results support our recent findings about the mechanisms of sensitization of GBM cells to TMZ-induced apoptosis using Simva [
33]. Several other investigations have showed that simvastatin induces apoptosis in breast cancer, chronic myeloid leukemia (CML) and lung cancer cells via changing the balance between pro- and anti-apoptotic Bcl2 family proteins [
78]. Co-treatment of Simva and flavons decreases chemo-resistance to doxorubicine via degradation of multi drug resistance (MDR) proteins in human colon cancer cells [
80]. In another investigation, it has been showed that liposomal Simva sensitizes C26 colon carcinoma cells to liposomal 5-FU via inhibition of tumor angiogenesis in vivo [
81]. Simvastatin also sensitizes A549 non-small cell lung cancer to Sulindac, or Pemetrexed (multi-target antifolate medication) induced caspase-dependent apoptosis via damaging mitochondria and increasing ROS [
82,
83].
Our previous studies revealed that simvastatin triggers the intrinsic apoptosis in various human cancer cells including GBM via inhibition of the mevalonate cascade with subsequent targeting of geranylgerany pyrophosphate prenylation precursors [
84]. We later showed that the TMZ/Simva combination treatment increased apoptosis compared to the TMZ and Simva single treatments in GBM cells. Our investigations showed that Simva sensitizes GBM cells and GBM patient-derived tumor cells to TMZ-induced apoptosis via inhibition of autophagy flux and UPR induction [
33,
55].
In the current investigation, for the first time, we have assessed mechanisms of ASH-induced apoptosis and later provided mechanisms which are involved in TMZ/Simva/ASH-induced apoptosis in GBM cells. In summary, our results showed that ASH and its triple combination treatment (TMZ/Simva/ASH) increased cellular ROS, decreased mitochondrial membrane potential with subsequent caspase-dependent apoptosis induction in GBM cells. In addition, our results showed that ASH induced autophagy while TMZ/Simva/ASH partially inhibited autophagy flux in GBM cells. Furthermore, blocking autophagy flux increased ASH and TMZ/Simva/ASH-induced cell death in GBM cells which clearly shows that both ASH and TMZ/Simva/ASH-induced cell death are dependent on the autophagy pathway.
ASH induces apoptosis in a wide range of tumor cells, such as ROS-dependent apoptosis in oral squamous cell carcinoma cells (Ca9-22) [
7]. Recent investigations have shown that ASH increases ROS and nuclear damage with subsequent nuclear translocation of FOXO3 and induced caspase-dependent apoptosis in osteosarcoma U2OS, renal cell carcinoma and colorectal cancer HCT-15, and LoVo cells [
85,
86,
87]. It has also been reported that ASH induces dose-dependent apoptosis via activation of caspase-3/-7 and -9 in chondrosarcoma cell lines [
88]. They also showed that MAPK activation is involved in ASH-induced apoptosis in colorectal cancer cells [
88]. On the other hand, ASH induces caspase-dependent apoptosis via ROS and inhibition of NF-κB in K562 leukemia cells [
89]. The combination of Erlotinib and Shikonin (and its derivatives) has been recently assessed in GBM cells. The cytotoxicity results showed a synergic effect of Shikonin and its derivatives including ASH with Erlotinib in GBM cells (U87, BS153, A431 and DK-MG) [
90]. In conclusion, the ASH-induced ROS hampers tumor cell proliferation, leading to the caspase-dependent apoptosis in cancer cells including GBM cells. In addition, combination therapy with Shikonin or its derivatives improves the response of cancer cells to chemotherapy agents and induces higher apoptotic cell death compared to single chemotherapy strategies.
Previous investigations have shown that an increase of pro-apoptotic Bcl2 family proteins or decrease in anti-apoptotic Bcl2 protein expression might be involved in mitochondrial damage, increase in cellular ROS and decrease in mitochondrial membrane potential [
31,
46,
49,
70,
91,
92,
93]. It has been showed that ASH induces apoptosis in osteosarcoma U2OS cells, A498 and ACHN (human RCC cell lines), colorectal Cancer HCT-15 and LoVo cells, and human leukemia cell line K562, via changing the Bcl2 family proteins [
85,
86,
87,
89]. Interestingly, our investigations showed that ASH did not significantly change Bax, Bcl2, Bcl-XL and Mcl-1 expression while it decreased mitochondrial membrane potential, increased ROS, activated caspase-3/-7 and induced apoptosis in GBM cell lines (U87 and U251). In addition, our investigation has revealed for the first time that TMZ/Simva/ASH induces mitochondria-dependent apoptosis without significant changes in the expression of anti-apoptotic Bcl2 family proteins (Bcl2, Bcl-XL, and Mcl-1), while non-significantly increasing Bax pro-apoptotic protein in U87 and U251 cells. Therefore, our findings indicate that ASH and TMZ/Simva/ASH mitochondria-induced apoptosis in GBM cells might be dependent on other Bcl2 family proteins or could be triggered by other mitochondrial factors like Smac/Diablo, Omi/HtrA2 [
70]. Interestingly, Bafilomycin-A1 increases anti-apoptotic protein Mcl-1 in both U87 and U251 cells and Bcl-XL expression in U251 cells (which could not be mechanistically explained and needs further investigations to justify its mechanisms).
In our recent investigations, our team has showed that autophagy is a regulator for apoptosis induction in different types of cells including airway mesenchymal cells [
49,
53,
71], atrial fibroblasts [
94], primary cardiac myofibroblasts [
53], human alveolar rhabdomyosarcoma cells [
8], HCT116, colorectal cancer cell line [
47,
48] and GBM cells [
33]. Recent investigations have also showed that ASH induces autophagy via PI3/AKT pathway which controls its apoptosis induction in acute myeloid leukaemia (AML) cells [
95]. Our current investigations also showed that ASH induces simultaneous autophagy and apoptosis, and autophagy flux inhibition increases ASH-induced cell death in GBM cells. For the first time, we have also showed that TMZ/Simva/ASH partially inhibits autophagy flux in GBM cells while further induction of autophagy flux inhibition significantly increased triple combination therapy-induced cell death in these cells. Overall, our investigations showed that autophagy flux plays an important role in both ASH and TMZ/Simva/ASH-induced cell death in GBM cell lines.
In our future investigations, we will try to address the impact of UPR in TMZ/Simva/ASH-induced apoptosis as it has been recently showed that UPR is involved in ASH-induced apoptosis [
96]. In addition, we will use the backbone of our recent Simva-loaded nanoparticle which specifically binds to GBM cells [
97]. We will attempt to load both Simva and ASH on these nanoparticles to increase the efficiency of targeting GBM with triple combination therapy. We will also move towards both flank and xenograft GBM animal model to test different combination therapies and investigate the impact of these approaches on animal models and be closer to clinical applications of these medications.
Figure 1.
Simvastatin, Temozolomide and Acetylshikonin induce cell death in human glioblastoma cells. U251 cells were treated with different concentrations of Simva (0.5-20µM, A–D), TMZ (50-100 µM, E–H), and ASH (0.5-25 µM, I–L) at four time points (24, 48, 72 and 96 hrs). The cytotoxicity of each treatment was measured using MTT assay. The percentage of cell viability was measured (ns= non-significant; *=P<0.05; **=P<0.01; ****=P<0.0001) compared to time match vehicle control. Simva induced significant decrease in cell viability (P<0.0001) for all concentrations at all time points except 0.5 µM at 24 and 48 hrs (P>0.05) and 1 µM at 24 hrs (P<0.01). TMZ induced significant cell death (P<0.0001) for all concentrations at all time points except 50 µM at 24 and 48 hrs (P>0.05) and 50 µM at 72 hrs (P<0.05). ASH induced significant cell death (P<0.0001) for all concentrations at all time points except 0.5 µM at 24 hrs (P<0.05). The represented findings are from 9 replicates in three independent biological assays and showed as mean ±SD.
Figure 1.
Simvastatin, Temozolomide and Acetylshikonin induce cell death in human glioblastoma cells. U251 cells were treated with different concentrations of Simva (0.5-20µM, A–D), TMZ (50-100 µM, E–H), and ASH (0.5-25 µM, I–L) at four time points (24, 48, 72 and 96 hrs). The cytotoxicity of each treatment was measured using MTT assay. The percentage of cell viability was measured (ns= non-significant; *=P<0.05; **=P<0.01; ****=P<0.0001) compared to time match vehicle control. Simva induced significant decrease in cell viability (P<0.0001) for all concentrations at all time points except 0.5 µM at 24 and 48 hrs (P>0.05) and 1 µM at 24 hrs (P<0.01). TMZ induced significant cell death (P<0.0001) for all concentrations at all time points except 50 µM at 24 and 48 hrs (P>0.05) and 50 µM at 72 hrs (P<0.05). ASH induced significant cell death (P<0.0001) for all concentrations at all time points except 0.5 µM at 24 hrs (P<0.05). The represented findings are from 9 replicates in three independent biological assays and showed as mean ±SD.
Figure 2.
Simvastatin, Temozolomide, Acetylshikonin and their combination treatments induce significant apoptotic cell death in human glioblastoma cells. U251 cells were treated with TMZ 100µM, Simva 1µM, ASH 1.5 µM, TMZ/Simva and TMZ/Simva/ASH at 24, 48, 72 and 96 hrs time points. Cell viability was measured using MTT assay and compared to time match vehicle control. Both combinations induced significant decrease in the cell viability compared to TMZ at all time points (****=P<0.0001). The cytotoxicity of TMZ/Simva/ASH was significantly higher than ASH at all time points (****=P< 0.0001) (A–D). All experiments were done in 9 replicates and three independent biological replicates. The results were shown as mean ±SD. We measured apoptosis using Nicoletti assay at 72h for U87 and U251 cells. The cell cycle pattern of each treatment is shown for both cell lines (E). The results showed a significant increase of apoptotic cell population (sub-G1) in TMZ-Simva and TMZ/Simva/ASH treated cells compared to the TMZ treatment alone in both U87 (F) and U251 (G) cells (****=P<0.0001). Moreover, apoptosis was reinforced in TMZ/Simva/ASH combination to ASH in GBM cells (****=P<0.0001) (F–G). Caspase-3/-7 activity was assessed in GBM cells which were treated with TMZ (100 µM), Simva (1µM for U251 and 2.5 µM for U87), and ASH (1.5 µM) at 48h (H,I). The activation of caspase-3/-7 was determined by Cayman fluorescence assay kit. All treatments significantly increased caspase-3/-7 activity to untreated U87 (H) and U251 (I) vehicle time match controls (****=P<0.0001). Caspase-3/-7 activation were significantly higher in both combination treatments (TMZ/Simva, TMZ/Simva/ASH) compared to TMZ and ASH treatments in both U87 (H) and U251 (I) GBM cells (****=P<0.0001).
Figure 2.
Simvastatin, Temozolomide, Acetylshikonin and their combination treatments induce significant apoptotic cell death in human glioblastoma cells. U251 cells were treated with TMZ 100µM, Simva 1µM, ASH 1.5 µM, TMZ/Simva and TMZ/Simva/ASH at 24, 48, 72 and 96 hrs time points. Cell viability was measured using MTT assay and compared to time match vehicle control. Both combinations induced significant decrease in the cell viability compared to TMZ at all time points (****=P<0.0001). The cytotoxicity of TMZ/Simva/ASH was significantly higher than ASH at all time points (****=P< 0.0001) (A–D). All experiments were done in 9 replicates and three independent biological replicates. The results were shown as mean ±SD. We measured apoptosis using Nicoletti assay at 72h for U87 and U251 cells. The cell cycle pattern of each treatment is shown for both cell lines (E). The results showed a significant increase of apoptotic cell population (sub-G1) in TMZ-Simva and TMZ/Simva/ASH treated cells compared to the TMZ treatment alone in both U87 (F) and U251 (G) cells (****=P<0.0001). Moreover, apoptosis was reinforced in TMZ/Simva/ASH combination to ASH in GBM cells (****=P<0.0001) (F–G). Caspase-3/-7 activity was assessed in GBM cells which were treated with TMZ (100 µM), Simva (1µM for U251 and 2.5 µM for U87), and ASH (1.5 µM) at 48h (H,I). The activation of caspase-3/-7 was determined by Cayman fluorescence assay kit. All treatments significantly increased caspase-3/-7 activity to untreated U87 (H) and U251 (I) vehicle time match controls (****=P<0.0001). Caspase-3/-7 activation were significantly higher in both combination treatments (TMZ/Simva, TMZ/Simva/ASH) compared to TMZ and ASH treatments in both U87 (H) and U251 (I) GBM cells (****=P<0.0001).
Figure 3.
Simvastatin, Temozolomide, Acetylshikonin and their combination treatments induce mitochondrial damage in human glioblastoma cells. U251 cells were treated with TMZ 100µM, Simva 1µM, ASH 1.5 µM, TMZ/Simva and TMZ/Simva/ASH at two different time points (38 and 60 hrs). Cayman ROS detection cell based assay (DHE) was used to assess levels of ROS in different conditions. All treatments induced a significant increase of ROS at both time points compared to the time match control (****=P<0.0001). Also, both combinations treatments (TMZ/Simva, TMZ/Simva/ASH) significantly induced more ROS compared to TMZ and ASH single treatments at both time points (38 and 60 hrs) (***=P<0.001; ****=P<0.0001) (A–D). We also measured mitochondria membrane potential (MMP) in the U251 cell line. All treatments (TMZ 100µM, Simva 1µM, ASH 1.5 µM, TMZ-Simva and TMZ-Simva-ASH) induced a significant decrease in MMP compared to the time match control (****=P<0.0001) (E,F). Both combination treatments induced a decrease of MMP compared to TMZ and ASH single treatments (****=P<0.0001). All experiments have been done in 3 independent biological replicates.
Figure 3.
Simvastatin, Temozolomide, Acetylshikonin and their combination treatments induce mitochondrial damage in human glioblastoma cells. U251 cells were treated with TMZ 100µM, Simva 1µM, ASH 1.5 µM, TMZ/Simva and TMZ/Simva/ASH at two different time points (38 and 60 hrs). Cayman ROS detection cell based assay (DHE) was used to assess levels of ROS in different conditions. All treatments induced a significant increase of ROS at both time points compared to the time match control (****=P<0.0001). Also, both combinations treatments (TMZ/Simva, TMZ/Simva/ASH) significantly induced more ROS compared to TMZ and ASH single treatments at both time points (38 and 60 hrs) (***=P<0.001; ****=P<0.0001) (A–D). We also measured mitochondria membrane potential (MMP) in the U251 cell line. All treatments (TMZ 100µM, Simva 1µM, ASH 1.5 µM, TMZ-Simva and TMZ-Simva-ASH) induced a significant decrease in MMP compared to the time match control (****=P<0.0001) (E,F). Both combination treatments induced a decrease of MMP compared to TMZ and ASH single treatments (****=P<0.0001). All experiments have been done in 3 independent biological replicates.
Figure 4.
Simvastatin, Temozolomide, and Acetylshikonin combination treatments change autophagy flux in human glioblastoma cells. U87 and U251 cells were treated with TMZ 100µM, Simva (2.5, 1µM respectively), ASH 1.5 µM, TMZ/Simva and TMZ/Simva/ASH for 48 hrs. The formation of acidic vesicular organelles [
53] was assessed using acridine orange (AO). The green fluorescence turned to red AVOs in the treatment conditions (white arrows) (
A,
B) [
3]. The percentage of AVO positive cells were evaluated. All treatments significantly increased the percentage of AVO positive cells in both cell lines compared to the time match vehicle control. The cells treated with TMZ/Simva/ASH showed the highest percentage of AVO positive cells (*=
P<0.05, ***=
P<0.001) (
C). We further evaluated autophagy in different experimental conditions using immunoblotting. GBM cells were treated with Bafilomycin A1 (autophagy flux inhibitor) (5 nM), ASH, Baf/ASH, TMZ/Simva/ASH and Baf/TMZ/Simva/ASH for 72hrs (all concentrations were the same as AO experiments). p62 degradation, LC3β lipidation and formation of LC3β-II and Beclin-1 expressions were evaluated using immune blotting. Ponceau S was utilized as loading control (
D). ASH increased the turnover of autophagosomes in both U87 and U251 cells, although it was not statistically significant (
E–
H,
J–
M). Baf significantly increased LC3β-II lipidation and decreased p62 degradation in both U87 and U251 cells, confirming the effect of ASH in autophagy and autophagosome turnover (
E–
H,
J–
M). TMZ/Simva/ASH partially inhibited autophagy flux, which is confirmed by the non-significant increase of LC3β-II and non-significant decrease in p62 degradation. Baf significantly induced LC3β lipidation, and accumulation of p62 in combination with TMZ/Simva/ASH treatment in both U87 and U251 cells (
E–
H,
J–
M) (
ns: non-significant; *=
P< 0.05; **=
P<0.01, ***=
P<0.001, ****=
P< 0.0001).
Figure 4.
Simvastatin, Temozolomide, and Acetylshikonin combination treatments change autophagy flux in human glioblastoma cells. U87 and U251 cells were treated with TMZ 100µM, Simva (2.5, 1µM respectively), ASH 1.5 µM, TMZ/Simva and TMZ/Simva/ASH for 48 hrs. The formation of acidic vesicular organelles [
53] was assessed using acridine orange (AO). The green fluorescence turned to red AVOs in the treatment conditions (white arrows) (
A,
B) [
3]. The percentage of AVO positive cells were evaluated. All treatments significantly increased the percentage of AVO positive cells in both cell lines compared to the time match vehicle control. The cells treated with TMZ/Simva/ASH showed the highest percentage of AVO positive cells (*=
P<0.05, ***=
P<0.001) (
C). We further evaluated autophagy in different experimental conditions using immunoblotting. GBM cells were treated with Bafilomycin A1 (autophagy flux inhibitor) (5 nM), ASH, Baf/ASH, TMZ/Simva/ASH and Baf/TMZ/Simva/ASH for 72hrs (all concentrations were the same as AO experiments). p62 degradation, LC3β lipidation and formation of LC3β-II and Beclin-1 expressions were evaluated using immune blotting. Ponceau S was utilized as loading control (
D). ASH increased the turnover of autophagosomes in both U87 and U251 cells, although it was not statistically significant (
E–
H,
J–
M). Baf significantly increased LC3β-II lipidation and decreased p62 degradation in both U87 and U251 cells, confirming the effect of ASH in autophagy and autophagosome turnover (
E–
H,
J–
M). TMZ/Simva/ASH partially inhibited autophagy flux, which is confirmed by the non-significant increase of LC3β-II and non-significant decrease in p62 degradation. Baf significantly induced LC3β lipidation, and accumulation of p62 in combination with TMZ/Simva/ASH treatment in both U87 and U251 cells (
E–
H,
J–
M) (
ns: non-significant; *=
P< 0.05; **=
P<0.01, ***=
P<0.001, ****=
P< 0.0001).
Figure 5.
Autophagy flux inhibition increases Simvastatin, Temozolomide, Acetylshikonin and triple combination treatment-induced cell death. U251 cells were treated with different concentrations of chloroquine (CQ) (25–200 µM) at 24, 48 and 72 hrs. Cell viability was assessed via MTT test (
A–
C). CQ induced significant cell death for all concentrations at all time points (****=
P<0.0001) except 25 and 50 µM concentrations at 24 hrs (
P>0.05). We used CQ 50 µM in combination with Simva 1 µM (
D–
F), TMZ 100 µM (
G–
I) [
98], ASH 1.5 µM (
J–
L) and TMZ/Simva/ASH (
M–
O) for 24, 48, and 72 hrs. CQ decreased cell viability in combination with all treatments (****=
P<0.0001), which showed that TMZ, Simva, ASH, and TMZ/Simva/ASH-induced cell death is dependent on autophagy flux. All experiments have been done in 9 replicates and three independent biological replicates and are showed as mean ±SD.
Figure 5.
Autophagy flux inhibition increases Simvastatin, Temozolomide, Acetylshikonin and triple combination treatment-induced cell death. U251 cells were treated with different concentrations of chloroquine (CQ) (25–200 µM) at 24, 48 and 72 hrs. Cell viability was assessed via MTT test (
A–
C). CQ induced significant cell death for all concentrations at all time points (****=
P<0.0001) except 25 and 50 µM concentrations at 24 hrs (
P>0.05). We used CQ 50 µM in combination with Simva 1 µM (
D–
F), TMZ 100 µM (
G–
I) [
98], ASH 1.5 µM (
J–
L) and TMZ/Simva/ASH (
M–
O) for 24, 48, and 72 hrs. CQ decreased cell viability in combination with all treatments (****=
P<0.0001), which showed that TMZ, Simva, ASH, and TMZ/Simva/ASH-induced cell death is dependent on autophagy flux. All experiments have been done in 9 replicates and three independent biological replicates and are showed as mean ±SD.
Figure 6.
Effect of Autophagy Flux inhibition on pro and anti- apoptotic proteins expressions in GBM cells. We used Bafilomycin A1 (Baf) 5 nM in combination with ASH 1.5 µM and TMZ/Simva/ASH (Simva 1 µM, U251 and Simva 2.5 µM, U87). We evaluated pro- (Bax) and anti- apoptotic Bcl2 (Bcl2, Bcl-XL, Mcl-1) family proteins in different experimental conditions using immunoblotting at 72 hrs. GAPDH was utilized as loading control (A). TMZ/Simva/ASH non-significantly increased Bax expression (P>0.05) while TMZ/Simva/ASH/Baf significantly increased Bax expression in U87 cells (***=P<0.001), (B). All treatments did not significantly change Bcl2 (C) and Bcl-XL (D) expressions in U87 cells. The Baf treatment significantly increased Mcl-1 expression in both ASH (P<0.01) and TMZ/Simva/ASH (*=P<0.05) treatments in U87 cells (E). TMZ/Simva/ASH and its combination with Baf non-significantly increased Bax expression (P>0.05) in U251 cells (F). All treatments did not significantly change Bcl2 (G) expression in U251 cells. Baf treatment significantly increased Bcl-XL (H) expression in U251 cells (single Baf treatment, P<0.05, Baf-TMZ/Simva/ASH, P<0.001). Baf treatment significantly increased Mcl-1 (I) expression in U251 cells (single Baf treatment, P<0.01, Baf-TMZ/Simva/ASH, P<0.05). All experiments have been done in 9 replicates and three independent biological replicates and are shown as mean ±SD.
Figure 6.
Effect of Autophagy Flux inhibition on pro and anti- apoptotic proteins expressions in GBM cells. We used Bafilomycin A1 (Baf) 5 nM in combination with ASH 1.5 µM and TMZ/Simva/ASH (Simva 1 µM, U251 and Simva 2.5 µM, U87). We evaluated pro- (Bax) and anti- apoptotic Bcl2 (Bcl2, Bcl-XL, Mcl-1) family proteins in different experimental conditions using immunoblotting at 72 hrs. GAPDH was utilized as loading control (A). TMZ/Simva/ASH non-significantly increased Bax expression (P>0.05) while TMZ/Simva/ASH/Baf significantly increased Bax expression in U87 cells (***=P<0.001), (B). All treatments did not significantly change Bcl2 (C) and Bcl-XL (D) expressions in U87 cells. The Baf treatment significantly increased Mcl-1 expression in both ASH (P<0.01) and TMZ/Simva/ASH (*=P<0.05) treatments in U87 cells (E). TMZ/Simva/ASH and its combination with Baf non-significantly increased Bax expression (P>0.05) in U251 cells (F). All treatments did not significantly change Bcl2 (G) expression in U251 cells. Baf treatment significantly increased Bcl-XL (H) expression in U251 cells (single Baf treatment, P<0.05, Baf-TMZ/Simva/ASH, P<0.001). Baf treatment significantly increased Mcl-1 (I) expression in U251 cells (single Baf treatment, P<0.01, Baf-TMZ/Simva/ASH, P<0.05). All experiments have been done in 9 replicates and three independent biological replicates and are shown as mean ±SD.