The preclinical evaluation of TIC10/ONC201 as an anti-pancreatic cancer agent

Qiangbo Zhang a, Hong Wang b, Lin Ran a, Zongli Zhang a, Runde Jiang a, *
a Department of General Surgery, Qilu Hospital, Shandong University, Jinan, China
b Department of Anesthesiology, Yidu Central Hospital, Weifang Medical University, Qingzhou, China


Here we evaluated the potential anti-pancreatic cancer activity by TIC10/ONC201, a first-in-class small- molecule inducer of tumor necrosis (TNF)-related apoptosis-inducing ligand (TRAIL). The in vitro results showed that TIC10 induced potent cytotoxic and cytostatic activities in several human pancreatic cancer cell lines (Panc-1, Mia-PaCa2, AsPC-1 or L3.6). TIC10 activated both extrinsic (TRAIL-caspase-8- dependent) and endogenous/mitochondrial (caspase-9-dependent) apoptosis pathways in the pancre- atic cancer cells. Molecularly, we showed that TIC10 inhibited Akt-Erk activation, yet induced TRAIL expression in pancreatic cancer cells. Significantly, TIC10, at a relatively low concentration, sensitized gemcitabine-induced growth inhibition and apoptosis against pancreatic cancer cells. Further, TIC10 and gemcitabine synergistically inhibited Panc-1 xenograft growth in SCID mice. The combination treatment also significantly improved mice survival. In addition, Akt-Erk in-activation and TRAIL/cleaved-caspase-8 induction were observed in TIC10-treated Panc-1 xenografts. Together, the preclinical results of the study demonstrate the potent anti-pancreatic cancer activity by TIC10, or with gemcitabine.
Keywords: Pancreatic cancer TIC10
Akt-Erk signaling Chemosensitization

1. Introduction
Pancreatic cancer is one main threat to human health [1e3]. It has become a leading cause of cancer-related mortalities [1e3]. It is an extremely aggressive cancer with very poor prognosis [1e3]. The five-year overall survival (OS) of these patients is almost dismissal [1e3]. It is characterized by rapid disease progression without distinctive symptoms [1e3]. In clinical practice, gemcitabine is only approved single-agent chemotherapeutic agent for pancreatic cancer [4]. Yet, the response to gemcitabine and gemcitabine-based regimens are far from satisfactory [1e3]. Therefore, groups are searching for alternative and more efficient anti-pancreatic cancer agents [3,5,6].
Tumor necrosis (TNF)-related apoptosis-inducing ligand (TRAIL) selectively targets cancer cells, and it has become a promising therapeutic option against human cancers [7]. Yet, the clinical development of TRAIL or TRAIL-related agents has been hampered due to several key limitations, such as the short half-life and lack of efficiency of these agents [7]. Recently, TIC10 (also named as ONC21), a first-in-class small molecule inducer of TRAIL, has been developed [8]. Preclinical studies have shown that it potently in- duces TRAIL expression [8e11]. TIC10 treatment in cancer cells blocks Akt and Erk signalings to activate Foxo3a, which transcrip- tionally up-regulates TRAIL gene [8e11].
TIC10 has displayed ideal properties as a potential anti-cancer drug, including a broad spectrum of activity, wide safety margin, robust stability, aqueous solubility, favorable pharmacokinetics, and oral activity [8e11]. The present study aims to investigate the potential anti-pancreatic cancer activity by TIC10. The associated signaling mechanisms are also analyzed.

2. Materials and methods

2.1. Chemicals and reagents
TIC10/ONC201 and gemcitabine were purchased from Sigma Chemicals (Sigma, St. Louis, MO); The caspase 3 specific inhibitor z- LEHD-fmk and the caspase-8 specific inhibitor z-IETD-fmk were provided by CalBiochem (La Jolla, CA). All kinase antibodies were from Cell Signaling Tech (Shanghai, China). All other antibodies were obtained from Santa Cruz Biotechnology (Santa Cruz, CA). Cell culture reagents were purchased from Gibco (Nanjing, China).

2.2. Cell culture
Human pancreatic cancer cell lines, including Panc-1, AsPC-1, Mia-PaCa-2 and L3.6, were provided by the Shanghai Institute of Biological Science, Chinese Academy of Science (CAS, Shanghai, China). The established cancer cells were cultured in DMEM/RPMI medium, supplemented with 10% heat-inactive fetal bovine serum (FBS).

2.3. Methylthiazol tetrazolium (MTT) assay of cell viability
Pancreatic cancer cells were seeded onto 96-well plates at a density of 1 × 104 cells/well. Following indicated TIC10 treatment, twenty-five ml/well of MTT solution (Sigma, at a concentration of 4 mg/ml) was added for 3 h. Afterwards, DMSO (200 ml/well, Sigma) was added to dissolve the crystals. The plate was allowed to stand for 10 min, and the optic density (OD) absorbance at 590 nm was recorded. MTT OD value of treatment groups was always normal- ized to the untreated control group.

2.4. Cell death (“Trypan blue”) assay
Trypan blue can go into the cytoplasm of dead cells. Therefore, cell death was determined by trypan blue staining method. Per- centage of trypan blue positive cells (vs. total cell number) was recorded.

2.5. Clonogenic assay
Two days after applied TIC10 treatment, Panc-1 cells (one thousand cells per dish) were detached and re-suspended in 1 ml of DMEM medium plus 0.5% agar (Sigma), which were then plated onto a pre-solidified 100-mm Petri dish. Afterwards, the cells were re-fed with TIC10-containing medium every two days. After eight days, the remaining colonies were stained with crystal blue and manually counted.

2.6. Cell cycle analysis
After applied TIC10 treatment, Panc-1 cells were detached and fixed in 70% ethanol at 4 ◦C. Fixed cells were then stained with propidium iodide (PI, BD bioscience, Shanghai, China) in the pres- ence of RNase. Cells were then analyzed on a Beckman Coulter flow cytometer.

2.7. Apoptosis assay by TUNEL staining
The pancreatic cancer cell apoptosis was quantified by the TUNEL (Terminal deoxynucleotidyl transferase dUTP nick end la- beling) In Situ Cell Apoptosis Detection Kit (Roche, Shanghai, China) according to the manufacturer’s instructions. Cells were also stained with Hoechst-33342 (Sigma) to visualize the nuclei. Cell apoptosis ratio was calculated by the TUNEL percentage (TUNEL/ Hoechst-33342 × 100%) [12].

2.8. Caspase-9 and caspase-8 activity assay
After treatment, cytosolic proteins (20 mg/sample) were extracted in hypotonic cell lysis buffer [13], which were then added to the caspase assay buffer (312.5 mM HEPES, pH 7.5, 31.25% su- crose, 0.3125% CHAPS) with Ac-LEHD-AFC (10 mg/ml, CalBiochem) as the caspase-9 substrate, or Ac-IETD-AFC (10 mg/ml, CalBiochem) as the caspase-8 substrate. After incubation for 1 h under the dark, the released AFC was measured via a spectrofluorometer with excitation of 400 nm [13].

2.9. Detection of mitochondrial membrane potential (MMP) reduction
The MMP reduction, an indicator of mitochondrial apoptosis pathway activation [14,15], was measured through JC-10 dye (Invitrogen, Shanghai, China) using the protocol previously described [16]. Briefly, after treatment, cells were immediately stained with JC-10 dye for 10 min at 37 ◦C. Afterwards, cells were washed, and JC-10 green fluorescence intensity, the indicator of MMP reduction (DJm), was measured immediately by a fluores- cence microplate reader (Titertek Fluoroscan, Germany) at 485 nm wavelength [14,15].

2.10. Western blots
Cellular or xenograft tumor samples were prepared in lysis buffer [5 mM MgCl2, 137 mM KCl, 1 mM EDTA, 1 mM EGTA, 1% CHAPS, 10 mM HEPES (pH 7.5)], normalized, and boiled in SDS sample buffer. Samples were then loaded onto SDS-PAGE gels, and were transferred onto polyvinylidene difluoride (PVDF) mem- branes. The membranes were then labeled with indicated primary and secondary antibodies. Antibody binding was detected by the ECL detection kit (Amersham).

2.11. Real-time PCR analyzing TRAIL mRNA
Total RNA was extracted with the Trizol reagents (Invitrogen, Shanghai, China), and the reverse transcription polymerase chain reaction (RT-PCR) was performed via the TOYOBO RT-PCR kit (PCR- 400, Japan). The real-time PCR was performed on a Bio-Rad IQ5 multicolor detection system via synthesized cDNA. The primers for human TRAIL were forward, 50-CCTGGGCGATAAAGTGAGAT-30 and reverse, 50-GGCCCAGCTGTATGTTGTCT-3’ [17]. After amplification, melt curve analysis was performed to analyze product melting temperature. GAPDH gene was chosen as the reference gene for normalization, and the 2—DDCt method was applied to quantify targeted mRNA change within samples.

2.12. Xenograft assay
Experiment protocols using 6-7 weeks-old female severe com- bined immunodeficiency (SCID) nu/nu mice were approved by the Ethics Committee for Animal Care according to international guidelines. Exponentially growing Panc-1 cells (1 107 cells/ mouse) were subcutaneously inoculated into right flank of each mice. Treatment began three weeks post tumor implant with intraperitoneal injection (i.p.) of gemcitabine (25 mg/kg, daily) [18] and/or oral gavage of TIC10 (30 mg/kg, daily) [19,20], for a total of 30 days [18], with 10 mice group. Tumor volumes, recorded every 10 days, were calculated using the formula: (mm3) (d2 D)/2, in which d and D were the shortest and the longest diameter, respectively. The survival data was plotted as the Kaplan Meier graph using SPSS 16.0 software, and p value was calculated. Mice body weights were also recorded every 10 days. Ten days after initial drug administration, one Panc-1 xenograft per group were isolated, and were subjected to Western blot analysis.

2.13. Statistical analysis
Statistical analysis was carried out via the SPSS 18.0 software (Chicago, IL). All values were expressed as the mean ± standard deviation (S.D.). A p-value, calculated by ANOVA, of less than 0.05 was considered statistically significant. The durations of treatment and concentrations of agents utilized were decided based on pub- lished references or pre-experiment results.

3. Results

3.1. TIC10 inhibits human pancreatic cancer cell survival and proliferation in vitro
In the current study, we are determined to evaluate the poten- tial effect of TIC10 in human pancreatic cancer cells. Panc-1 is a well-established human pancreatic cancer cell line. Therefore, Panc-1 cells were cultured in FBS-containing complete medium, and cells were treated with applied concentrations of TIC10. MTT assay results showed that TIC10 at 5e25 mM significantly decreased MTT viability OD of Panc-1 cells (Fig. 1A). The effect by TIC10 was dose-dependent, and low concentration of TIC10 (1 mM) showed no such effect (Fig. 1A). Trypan blue assay results in Fig. 1B demon- strated that TIC10 (5e25 mM) was cytotoxic when added to Panc- 1 cells, as the number of trypan blue positive cells was increased following the TIC10 (5e25 mM) treatment (Fig. 1B). A time- dependent anti-Panc-1 effect by TIC10 was also noticed (Fig. 1A and B).
Next, colony formation assay was performed to test the poten- tial effect of TIC10 on Panc-1 cell proliferation. Results showed that the number of viable Panc-1 colonies was significantly decreased following TIC10 (5e25 mM) treatment (Fig. 1C), indicating an anti- proliferative activity by TIC10. In addition, the Panc-1 cell cycle progression was also disrupted by TIC10 (5/10 mM) treatment (Fig. 1D). We noticed a significant G1-S arrest in TIC10-treated Panc-1 cells (Fig. 1D). For analyzing cell cycle, Panc-1 cells were treated with TIC10 for 24 h when only weak cytotoxicity was noticed (Fig. 1A). MTT assay results in Fig. 1E showed that TIC10 (10 mM) was cytotoxic/anti-proliferative against three other pancreatic cancer cell lines: Mia-PaCa2, AsPC-1 and L3.6. Cell cycle progression was also inhibited by TIC10 (10 mM) in these pancreatic cancer cells (Data not shown). Together, we show that TIC10 in- hibits pancreatic cancer cell survival and proliferation in vitro.

3.2. TIC10 activates both extrinsic and endogenous apoptosis pathways in human pancreatic cancer cells
Next, we focused on the role of TIC10 on pancreatic cancer cell apoptosis. As shown in Fig. 2A, the number of TUNEL positive Panc-1 cells was significantly increased following TIC10 (5e25 mM) treatment, indicating apoptosis activation. TIC10 is a known TRAIL inducer [11], which stimulates TRAIL expression to induce extrinsic apoptosis pathway activation [11]. Here, we showed that TRAIL mRNA expression was significantly increased in TIC10 (5e25 mM)- treated Panc-1 cells (Fig. 2B). As a result, the caspase-8 activity was also enhanced (Fig. 2C). These results suggest extrinsic apoptosis pathway activation by TIC10. Significantly, caspase-9 activity, the indicator of endogenous or mitochondrial apoptosis pathway acti- vation [21], was also increased in TIC10-treated Panc-1 cells (Fig. 2D). Further studies showed that TIC10 treatment in Panc- 1 cells induced MMP reduction, the latter was confirmed by JC-10 dye assay (See method, Fig. 2E). These results indicated simulta- neous mitochondrial apoptosis pathway activation by TIC10 in Panc-1 cells.
To dissect the role of extrinsic or endogenous apoptosis pathway in TIC10-mediated actions, we utilized the caspase-9 specific in- hibitor z-LEHD-fmk and the caspase-8 specific inhibitor z-IETD- fmk. Treatment with z-LEHD-fmk or z-IETD-fmk alone only exerted a relatively weak (but significant) inhibition on TIC10-induced Panc-1 cell apoptosis (Fig. 2F), viability reduction (Fig. 2G), and cell death (Fig. 2H). Remarkably, z-LEHD-fmk and z-IETD-fmk combination almost abolished TIC10-induced cytotoxicity in Panc- 1 cells (Fig. 2FeH). The concurrent caspase-8 and caspase-9 inhi- bition was significantly more potent than single inhibition (Fig. 2FeH). These results indicate that both extrinsic (caspase-8 dependent) and endogenous (caspase-9 dependent) apoptosis pathways may participate in TIC10-exerted actions against Panc- 1 cells. As shown in Fig. 2I, caspase-9 activity (upper panel) and TRAIL mRNA expression (lower panel) were both increased in TIC10-treated other pancreatic cancer cells (Mia-PaCa2, AsPC-1 and L3.6).

3.3. TIC10 inhibits Akt-Erk signaling and sensitizes gemcitabine’s activity in pancreatic cancer cells
Previous studies have shown that TIC10 blocks Akt and Erk activation in cancer cells [8]. We then tested these two signalings in TIC10-treated pancreatic cancer cells. Western blot results in Fig. 3A showed that TIC10 (5/10 mM) significant inhibited Akt and Erk activation in Panc-1 cells. Note that Akt activation was reflected by phosphorylation (p-) Akt (Thr-308), and Erk activation was tested by p-Erk1/2 (Fig. 3A). Similar results were also observed in TIC10- treated Mia-PaCa2 pancreatic cancer cells (Fig. 3B). Based on these results, we speculated that this compound may improve the activity of gemcitabine in pancreatic cancer cells. As a matter of fact, we showed that co-treatment with a relatively low concentration (5 mM, see Fig. 1) of TIC10 could significantly potentiate gemcitabine-induced Panc-1 cell viability reduction (Fig. 3C) and cell death (Fig. 3D). In another word, gemcitabine-induced cyto- toxicity against Panc-1 cells was dramatically potentiated in the presence of TIC10 (Fig. 3C and D). We also repeated the above ex- periments in Mia-PaCa2 cells, and similar gemcitabine- sensitization activity by TIC10 was obtained (Fig. 3E and F).

3.4. The in vivo anti-pancreatic cancer activity by TIC10, either alone or in combination with gemcitabine
Finally, we evaluated the anti-pancreatic cancer activity by TIC10 in vivo, using the SCID mice Panc-1 xenograft model. As described, a large amount of Panc-1 cells (1 107 cells/mouse) were inoculated into the right flanks of SCID mice, and xenograft pancreatic tumors were established after three weeks. When analyzing tumor growth, we showed that oral gavage of a single dose of TIC10 (30 mg/kg, daily) significantly inhibited Panc-1 tumor growth in SCID mice (Fig. 4A). More importantly, gemcitabine- induced anti-Panc-1 tumor activity was enhanced following TIC10 co-administration (Fig. 4A). In another word, TIC10 and gemcitabine synergistically inhibited Panc-1 xenograft growth in SCID mice, more potently than either single agent (Fig. 4A). Further, TIC10 and gemcitabine co-administration significantly improved the survival of tumor-bearing SCID mice (Fig. 4B). The combined activity was again more potent than either single treatment (Fig. 4B). Note that mice body weights were not affected by above TIC10 and/or gemcitabine (Fig. 4C). We failed to notice any signs of tox- icities in these animals. These results indicated that SCID mice were well-tolerated to the TIC10 and/or gemcitabine treatment regi- mens. The above in vitro signaling was also tested in the xeno- grafted tumors (one xenograft tumor per group, ten days after initial drug treatment). Western blot results showed that, in TIC10- treated tumor tissues, Akt-Erk phosphorylation was inhibited, yet TRAIL and cleaved-caspase-9 expression was dramatically enhanced (Fig. 4D). Gemcitabine co-administration showed almost no effect on the above signaling (Fig. 4D). Thus, the in vitro signaling changes by TIC10 in pancreatic cancer cells were also observed in TIC10-treated xenograft tumors.

4. Discussions
TIC10/ONC201 is currently under early-phase clinical testing for various malignancies [22e24]. For example, a very recent study by Ishizawa et al., has implied the clinical potential of TIC10 in he- matological malignancies [22]. Ishizawa’s study showed that TIC10 induced integrated stress responses (ISR), yet p53-independent apoptosis in mantle cell lymphoma (MCL) and acute myeloid leu- kemia (AML) cells [22]. Similarly, Kline et al., demonstrated that ONC201 induced death of solid tumor cells via ISR-dependent TRAIL pathway [23]. In the present study, we showed that TIC10 induced potent cytotoxic and cytostatic/anti-proliferative activities against a number of human pancreatic cancer cell lines. TIC10 activated both extrinsic (TRAIL/caspase-8-dependent) and mito- chondrial (caspase-9-dependent) apoptosis pathways in the pancreatic cancer cells. Significantly, TIC10 potentiated gemcitabine-induced anti-pancreatic cancer activity in vitro. Further, TIC10 displayed a potent anti-pancreatic cancer activity in xenograft nude mice model, alone or in combination with gemci- tabine. All these results point out a potent anti-pancreatic cancer activity by this first-in-class small molecule.
The complexity of the cellular signaling network in pancreatic cancer cells opens the opportunity to combined inhibition of multiple pro-cancer pathways [25], which might lead to superior anti-cancer activity [25]. Akt is the central member of the phos- phatidylinositol-3-kinase (PI3K)/Akt and the mammalian target of rapamycin (mTOR) pathway, which is vital for regulating cancer cell survival, apoptosis-resistance and proliferation as well as metas- tasis and angiogenesis [26,27]. Constitutively active Akt and other components of this pathway are seen in many pancreatic cancers, which promote cancer transformation and development [28e30]. At the meantime, over-activation of KRAS/MEK/Erk pathway is seen in over 90% of patients, which is known as a major contributor of pancreatic cancer progression and resistance [31,32]. In the current study, we showed that TIC10 simultaneously blocked Akt and Erk activation in pancreatic cancer cells both in vitro and in vivo. These signaling changes, along with the TRAIL induction and extrinsic/ endogenous apoptosis activation, could explain its superior activity against these cancer cells.
Currently, gemcitabine is only approved single cytotoxic chemodrug for the clinical treatment of pancreatic cancer, yet its activity in increasing patients’ survival is not ideal [33]. As a result, groups are looking for gemcitabine sensitizers. Yet, the fast majority of phase III clinical trials studying gemcitabine-based combination strategies have been failed, the only expectance is erlotinib [34]. The results of current study demonstrate that co-administration of TIC10 could significantly increase gemcitabine’s anti-pancreatic cancer activity both in vivo and in vitro. Therefore, further studies may further explore TIC10 as a gemcitabine sensitizer/adjuvants. Pancreatic cancer is the fourth most common cancer, and will soon be the second leading cause of cancer-related mortality [35]. New treatment paradigms are desperately needed. The results of study indicate that TIC10 has a significant therapeutic potential against human pancreatic cancer, as a mono-agent or in combina- tion with gemcitabine.

Financial support of the study
This work was supported by the National Natural Science Foundation of China.

Competing financial interests
The authors declare no competing interests.

Transparency document
Transparency document related to this article can be found online at http://dx.doi.org/10.1016/j.bbrc.2016.05.106.

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