Background
The t(9;22)(q34;q11) reciprocal translocation that creates a minute chromosome, known as the Philadelphia chromosome (Ph), is a hallmark of chronic myelogenous leukemia (CML) and also present in about 3% of pediatric B-ALL and 25% of adult B cell acute lymphoblastic leukemia (Ph
+ B-ALL) [
1]. The translocation leads to the creation and expression of the fusion gene product BCR-ABL. The ABL tyrosine kinase is activated in the BCR-ABL fusion protein and plays a central role in the pathogenesis of CML and Ph
+ B-ALL [
2].
Imatinib mesylate, a selective ABL tyrosine kinase inhibitor (TKI), has shown a remarkable clinical activity in patients with CML [
3]. Significant therapeutic effects and clinical benefits have been achieved in treating Ph
+ B-ALL, especially when combined with hematopoietic stem cell transplantation and chemotherapy [
4]. However, relapse of Ph
+ B-ALL remains a clinical problem. The second-generation ABL TKI dasatinib could yield remarkable responses in the treatment of imatinib-resistant Ph
+ B-ALL patients by co-targeting BCR-ABL and SRC family kinases [
5,
6]. Unfortunately, eventual relapse seems inevitable when leukemia cells reemerge in bone marrow with additional genetic variations and rewired survival and proliferative signaling [
7‐
9]. Besides, severe side effects such as cardiotoxicity [
10] and pulmonary hypertension [
11] are more likely to be induced by dasatinib. Thus, novel therapeutic targets are needed to treat Ph
+ B-ALL more effectively.
Mitogen-activated protein kinase (MAPK) signaling pathways play a crucial role in the regulation of tumor cell growth, proliferation, migration, and apoptosis [
12]. MAPKs belong to a diverse family of serine/threonine protein kinases, including four major subfamilies, such as c-JUN N-terminal kinase (JNK), p38 MAP kinase, extracellular signal-regulated kinase (ERK) 1/2, and ERK5 [
13]. Among them, JNK signaling is a unique MAPK pathway that is predominantly activated in cells under the stress conditions such as ROS production and inflammation [
14]. There are three JNK homologs in mammalians, JNK1/2/3, which are encoded by
MAPK8/
9/
10 genes, respectively [
15]. JNK1/2 are constitutively expressed in almost all tissues, while JNK3 restricts in brain, heart, and testis [
16]. JNK activation is through phosphorylation by MAPK kinases MKK4 and MKK7 [
17] and the activation of JNK plays an important role in cell survival, cell proliferation, cell differentiation [
14,
17], and cancer stem cell maintenance [
18]. BCR-ABL protein significantly activates the JNK signaling pathway in transformed cells [
19,
20]. More importantly, depletion of
Mapk8 mitigates the BCR-ABL-induced transformation in mouse B lymphoblasts and prolongs the survival of mice with BCR-ABL induced B-ALL [
21]. However, it is not clear how important is the JNK activation in the maintenance of Ph
+ B-ALL and whether the JNK inhibition could cooperate with BCR-ABL inhibitors in treating Ph
+ B-ALL.
In this study, using both BCR-ABL induced B-ALL mouse model and human B-ALL cells, we found that the activation of JNK could not be inhibited by BCR-ABL TKI in B-ALL cells. Targeting JNK by either RNA interference or chemical inhibitors decreased the cell viability of Ph+ B-ALL. The JNK inhibitor and BCR-ABL TKI dasatinib could synergistically kill Ph+ B-ALL cells in vitro and greatly improve the survival of mice with BCR-ABL induced B-ALL.
Material and method
Cell lines and cell culture
SUP-B15 and K562 cell lines were purchased from ATCC and cultured in RPMI 1640 (Basal Media, China) supplemented with 10% fetal bovine serum (FBS, Moregate, Batch No. 827106). Cell line identities were validated by using short tandem repeat profiling analysis according to the American National Standard ANS-0002-2011 at the laboratory of VivaCell Bioscience Co. The cell passages were limited to 15 generations for all experiments in this study. Mycoplasma contamination was excluded using the antibiotics Mycoplasmincin (InvivoGen) and periodically examined using MycoFluor Mycoplasma Detection Kit (Invitrogen, #M7006).
Magnetic-activated cell sorting
BM cells extracted from BALB/cByJ mice were incubated with CD19 antibody conjugated microbeads (Miltenyi Biotec, #130-097-144) for 30 min and enriched by MACS separators per manufacture’s instruction.
Flow cytometry-based cell sorting and analysis
Cells from mouse peripheral blood and BM were firstly lysed with red blood cell lysis buffer and then labeled by antibodies against Mac-1-PE (Bio legend, #101208) and CD19-APC (BD Biosciences, #550992) in staining buffer (PBS, 1% FBS). After staining in dark for 15 min at room temperature, samples were washed with PBS and resuspended in staining buffer. Flow cytometry analysis and sorting were performed on an LSR II system (BD Biosciences). The cell population with given surface markers were analyzed by FlowJo software. Human cell line SUP-B15 stably infected with shJNK#1, #2, or NC were sorted based on GFP expression.
Generation of lentiviruses and retroviruses
Two distinct shRNA oligonucleotides were designed for knocking down JNKs, of which sequences are described as following: ShJNK#1 sense (TGAAAGAATGTCCTACCTTCT) and antisense (AGAAGGTAGGACATTCTTTCA); ShJNK#2 sense (GCAGAAGCAAGCGTGACAACA) and antisense (TGTTGTCACGCTTGCTTCTGC). Paired oligonucleotides were annealed and inserted into lentiviral expression vectors (pLKO.1-GFP). The JNK-targeted or scrambled non-specific control (NC) shRNA plasmids were co-transfected with the lentiviral packaging vectors, psPAX2 and pMD2G, using Lip6000 reagent (Beyotime Biotechnology) in 293 T cells to produce shJNK#1, #2, or NC lentiviruses. Likewise, BCR-ABL
p190 retroviruses were produced using MSCV-BCR/ABL
p190-IRES-GFP retroviral constructs as described previously [
22].
Bone marrow transduction and transplantation mouse model
The mouse bone marrow transduction/transplantation model for Ph
+ B-ALL was established as described previously [
22]. Briefly, bone marrow (BM) cells or CD19
+ B lymphocytes isolated from the bone marrow of 6- to 8-week-old BALB/cByJ donor mice using MACS were transduced with BCR-ABL retroviruses suspended in a cocktail medium containing 50% (vol/vol) BCR-ABL retroviral supernatant, DMEM, 5% FBS, 100 U/mL penicillin, 100 μg/mL streptomycin, 5% WEHI-3-conditioned medium, 10 ng/mL IL-7, and 8 μg/mL Polybrene (Sigma Aldrich) by spinoculation at 1200×
g for 90 min, followed by incubation at 37 °C for additional 4.5 h. Following the retroviral transduction, BM cells were washed with serum-free media and transplanted into sublethally irradiated (450 cGy) syngenic recipient mice, 10
6 cells per mouse, via tail vein. All animal experiments were approved by The Animal Care & Welfare Committee of Ruijin Hospital affiliated to Shanghai Jiao Tong University School of Medicine.
Cell viability assay
Cell viability assays were carried out using the CellTiter-Glo® Luminescent Cell Viability Assay as previously described [
23]. Cells were seeded into 96-well cell culture plates at a density of 5000 cells per well and added with indicated drugs at various concentrations. After 48 h incubation, cells were lysed by CellTiter Glo reagent (Promega, #G7573), and the luminescence signals produced by ATP molecules from live cells were measured using an Envision plate reader (PerkinElmer) after 30 min incubation at room temperature.
Western blot analysis
Western blot analysis was performed as previously described [
24]. In brief, cell samples were counted and lysed in 1× sodium dodecyl sulfate (SDS) sample loading buffer. Equal amount of protein samples was loaded on polyacrylamide gel, followed by transfer to nitrocellulose membrane. The membrane was then blotted with specific primary antibodies against p-c-Abl (Y412, #2865S), BCR (#3902S), p-stat5 (Y694, #9351S), stat5 (#9363S), AKT (#4685S), p-AKT (Ser473, #4060S), ERK (#49655S), p-ERK (T202/Y204, #4370S), p-JNK (T183/Y185, #4668S), p-c-JUN (Ser63, #2361S) (all purchased from Cell Signaling Technology), c-Myc (#ab32072, Abcam), BRD4 (#ab128874, Abcam), JNK (#66210-1-Ig), c-JUN(#66313-1-Ig), and actin-HRP (#HRP-60008) (purchased from Proteintech). After overnight incubation at 4 °C, HRP-conjugated secondary antibodies were applied and luminescence signals on membrane were detected with electrochemical luminescence (Shanghai Share-bio Biotechnology). The western blot images were taken with a LAS4000 imaging system (Fujifilm).
Patient sample preparation
Heparinized bone marrow samples were collected from 6 patients with newly diagnosed Ph
+ B-ALL (detailed information for these patients are provided in Supplementary Table
S2). Mononuclear cells (MNCs) were then separated by density gradient centrifugation using Lymphoprep reagent (Stemcell Technologies). Subsequently, MNCs were cultured in StemSpan basic media (Stemcell Technologies) supplemented with 10 ng/mL human stem cell factor, 10 ng/mL human IL-3, 10 ng/mL human IL-6 (all above cytokines were purchased from R&D Systems), 100 U/mL penicillin, and 100 μg/mL streptomycin (both from BBI Life Sciences). This study was approved by the Institutional Review Board of the Ruijin Hospital affiliated to Shanghai Jiao Tong University School of Medicine. Informed consent for the in vitro drug testing studies was obtained in accordance with the Declaration of Ruijin Hospital affiliated to Shanghai Jiao Tong University School of Medicine.
Compounds and in vivo drug testing
JNK-IN-8, SP600125, JQ-1, imatinib, and dasatinib were all purchased from Selleck Chemicals. For the treatment of BCR-ABL+ B-ALL mouse model, mice were randomly separated into four groups, for comparing the effects of the vehicle control, dasatinib, JNK-IN-8, and both drugs in combination. Drugs or vehicle was administered after 10 days post BMT. The consecutive treatment was conducted in the following 18 days. Dasatinib was dissolved in 80 mM sodium citrate (pH 3.1) and administrated through oral gavage at the dosage of 2 mg/kg/day. JNK-IN-8 was dissolved successively in 2% DMSO, 30% PEG 300, 5% Tween 80, and deionized water and injected intraperitoneally at 20 mg/kg once a day. To monitor leukemia progress in mice, peripheral blood was collected via retro-orbital plexus and analyzed by using a pocH-100iV Diff hemocytometer (Sysmex Corporation) and flow cytometer. After 10 days post treatment, representative mice were sacrificed and autopsied, and samples from selected organs were obtained and stained with hematoxylin and eosin (H&E).
KiNativ profiling
SUP-B15 cells were treated with DMSO or 0.3 μM of imatinib or dasatinib for 2 h and cell lysates were extracted to detect kinase activity using Pierce™ Kinase Enrichment Kits and ActivX™ Probes according to the manufacturer’s instruction (Thermo scientific). Samples were analyzed by Q-Exactive liquid chromatography-mass spectrometry-tandem mass spectrometry with a linear ion trap mass spectrometer (LC-MS/MS, Thermo Scientific).
Statistical analysis
GraphPad Prism 7 software was used for statistical data analysis. Two-tailed unpaired Student’s
t test was used for mean comparison between two groups, whereas the Kaplan-Meier survival curve and log-rank test were used for survival analysis. Calcusyn v2.0 software was used for calculating the “combination index” (CI) of the drug combination treatment to depict synergism (CI < 1), addictive effect (CI = 1), or antagonism (CI > 1) [
25].
P values < 0.05 were considered statistically significant, and different levels were denoted as *
P < 0.05, **
P < 0.01, and ***
P < 0.001, respectively.
Discussion
The application of BCR-ABL tyrosine kinase inhibitor dasatinib in Ph
+ B-ALL has largely improved the initial complete remission rate. However, many patients without secondary BCR-ABL mutations ended up with relapse after treatment [
8,
34], implying the contribution of alternative survival pathways to the dasatinib resistance. Therefore, eradication of Ph
+ B-ALL cells requires inhibition of additional targets beyond BCR-ABL.
In this study, we found BCR-ABL TKI dasatinib is unable to inhibit the abnormally activated JNK pathway in BCR-ABL+ B-ALL. Furthermore, the expression of p-JNK was increased in Ph+ B-ALL cells after treated with dasatinib. JNK inhibition by either genetic or chemical intervention could potently kill human BCR-ABL+ B-ALL cells. More importantly, JNK inhibition can effectively treat BCR-ABL+ B-ALL synergistically with dasatinib. These results indicate that JNK is a key signaling for dasatinib resistance in Ph+ B-ALL.
It is previously reported that JNK deficiency in mice delays the onset of B-ALL induced by BCR-ABL [
21]. But the probability and feasibility of JNK-targeting therapy in BCR-ABL
+ B-ALL was not unclear. Here we demonstrate that JNK plays an important role in the maintenance of Ph
+ B-ALL and it is an effective target for combination therapy of BCR-ABL
+ B-ALL together with BCR-ABL TKI dasatinib.
Side effects of dasatinib such as weight loss [
35], cardiotoxicity [
10], and pulmonary hypertension [
11] are frequently encountered. In this study, we reduced the dose of dasatinib to 2 mg/kg QD instead of the standard dose (5 mg/kg QD). Our results show that the combined treatment with JNK-IN-8 and dasatinib exhibits a better therapeutic effect in prolonging the life of BCR-ABL
+ B-ALL mice than that by either JNK inhibitor or dasatinib alone.
It was shown that JNK activation plays a crucial role in the induction of apoptosis of CML cells [
36,
37]. Consistently, our data show that JNK inhibition has no therapeutic effect in CML cells. These findings indicate that JNK plays a context-dependent function in BCR-ABL
+ B-ALL Vs. CML. The differential requirement of certain pathways in BCR-ABL
+ B-ALL and CML has also been shown previously. As an example, Src kinases Lyn, Hck, and Fgr are required for BCR-ABL-induced B-ALL but not in CML [
38]. In addition, the noncanonical Wnt pathway controlled by ɣ-catenin has recently been identified to be selectively required in the initiation and maintenance of Ph
+ B-ALL cells but not in CML [
32].
It has been shown that JNK activation also plays an important role in the survival of B cell lymphoma [
30] and T cell acute lymphoblastic leukemia [
39]. The significant therapeutic effects of JNK inhibitor in a B cell lymphoma mouse model was demonstrated [
30]. A number of JNK inhibitors with various activity and selectivity to JNK kinases have been developed. JNK-IN-8 is a potent and specific JNK inhibitor that can covalently bind the Cys 116 residue of all three JNK kinases and inhibit them in an irreversible way [
28]. In this study, we chose JNK-IN-8 to treat Ph
+ B-ALL in combination with dasatinib in vivo. JNK-IN-8 showed therapeutic activity both alone and, to a much larger extent, in combination with dasatinib in treating BCR/ABL
+ B-ALL.
It has been shown that JNK inhibitors exerted their therapeutic effect in tumor through regulating the downstream effectors, such as c-Myc [
29,
30], and that c-MYC plays a critical role in the proliferation of Ph
+ B-ALL cells [
32]. Here we show that the JNK-IN-8 treatment or JNK knocking down dramatically downregulates the expression of c-MYC (Supplementary Fig.
S3a). The BRD4 inhibitor JQ-1 that downregulates c-MYC expression and inhibits the proliferation of Ph
+ B-ALL cells in a dose-dependent manner (Supplementary Fig.
S3c, d and e). Interestingly, the dasatinib treatment also reduced c-MYC expression, but the effect was much more dramatic when used in combination with JNK-IN-8 (Supplementary Fig.
S3f). Consistent with the synergy between JNK-IN-8 and dasatinib, JQ-1 also enhanced the effect of dasatinib in inhibiting the proliferation of SUP-B15 (Supplementary Fig.
S3g). These results suggest that dasatinib and JNK-IN-8 suppress Ph
+ B-ALL synergistically at least partially through downregulating the c-MYC expression.
In conclusion, we demonstrate that targeting JNK signaling pathway could synergistically treat Ph+ B-ALL with BCR-ABL TKI, providing a new therapeutic strategy for Ph+ B-ALL.
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