Novel multiple tyrosine kinase inhibitor ponatinib inhibits bFGF-activated signaling in neuroblastoma cells and suppresses neuroblastoma growth in vivo

Prognosis prediction and drug guidance of ovarian serous cystadenocarcinoma through mitochondria gene-based model

BACKGROUND

Mitochondrial dysregulation contributes to the chemoresistance of multiple cancer types. Yet, the functions of mitochondrial dysregulation in Ovarian serous cystadenocarcinoma (OSC) remain largely unknown.

AIM

We sought to investigate the function of mitochondrial dysregulation in OSC from the bioinformatics perspective. We aimed to establish a model for prognosis prediction and chemosensitivity evaluation of the OSC patients by targeting mitochondrial dysregulation.

METHODS

Differentially expressed genes (DEGs) were screened from the Cancer Genome Atlas (TCGA)-OV dataset and the mitochondrial-related DEGs were identified from the Human MitoCarta 3.0 database. Prognosis-related mitochondria-related genes (MRGs) were screened to establish the MRGs-based risk score model for prognosis prediction. To validate the risk score model, the risk score model was then evaluated by IHC staining intensity and survival curves from clinical specimens of OSC patients. Migration and proliferation assays were performed to elucidate the role of carcinogenic gene ACSS3 in serous ovarian cancer cell lines.

RESULTS

Using consensus clustering algorithm, we identified 341 MRGs and two subtypes of OSC patients. Moreover, we established a novel prognostic risk score model by combining the transcription level, intensity and extent scores of MRGs for prognosis prediction purpose. The model was established using 7 MRGs (ACOT13, ACSS3, COA6, HINT2, MRPL14, NDUFC2, and NDUFV2) significantly correlated to the prognosis of OSC. Importantly, by performing the drug sensitivity analysis, we found that the OSC patients in the low-risk group were more sensitive to cisplatin, paclitaxel and docetaxel than those in the high-risk group, while the latter ones were more sensitive to VEGFR inhibitor Axitinib and BRAF inhibitors Vemurafenib and SB590885. In addition, patients in the low-risk group were predicted to have better response in anti-PD-1 immunotherapy than those in the high-risk group. The risk score model was then validated by survival curves of high-risk and low-risk groups determined by IHC staining scores of OSC clinical samples. The carcinogenic effect of ACSS3 in OSC was confirmed through the knockdown of ACSS3 in SKOV3 and HO-8910 cells.

CONCLUSION

To summarize, we established a novel 7 MRGs - based risk score model that could be utilized for prognosis prediction and chemosensitivity assessment in OSC patients.

Buparlisib and ponatinib inhibit aggressiveness of cholangiocarcinoma cells via suppression of IRS1-related pathway by targeting oxidative stress resistance

Cholangiocarcinoma (CCA) is an oxidative stress-driven liver cancer with bile duct epithelial cell phenotypes and currently lacks effective treatments, making targeted drug therapy urgently needed. Oxidative stress plays a critical role in CCA carcinogenesis, involving cells with oxidative stress resistance via upregulation of the PI3K and MEKK3 signaling pathways. In this study, we investigated the antineoplastic efficacy of a PI3K inhibitor (buparlisib) and a multi-tyrosine kinase inhibitor (ponatinib) on CCA. The cytotoxicity of the drug combination was studied in vitro using CCA cell lines and in vivo using CCA xenograft models. It was found that the drug combination suppressed growth, colony formation, and migration abilities of CCA cells and induced oxidative damage, cell cycle arrest, and autophagy by suppressing MEKK3 and YAP1 through inhibition of insulin receptor substrate 1 (IRS1) signaling. Moreover, the drugs would potentially bind to the IRS1 protein, significanly decreasing IRS1 phosphorylation. Additionally, the drug combination significantly diminished the expression of YAP1, the cell proliferation marker and an antioxidant regulator, and increased oxidative stress-responsive markers in the xenograft model. In conclusion, targeting oxidative stress resistance with combined buparlisib and ponatinib suppressed tumor growth and migration by repressing IRS1-related pathways and ultimately inducing oxidative damage, suggesting the potential for targeted therapy and clinical trials in CCA patients over the use of a single drug.

mTORC1-Inhibition Potentiating Metabolic Block by Tyrosine Kinase Inhibitor Ponatinib in Multiple Myeloma

Simple Summary

From a screen for metabolic inhibition by a panel of approved anticancer drugs and combining the lead compound with a mammalian target of rapamycin complex 1 (mTORC1) inhibitor, we demonstrated that the combination of ponatinib and sirolimus leads to synergistic tumor growth inhibition in a mouse xenograft tumor model of multiple myeloma. The rationale of combining the two drugs was to prevent metabolic escape due to glycolysis reprogramming and residual oxidative phosphorylation (OXPHOS). The robust increases in reactive oxygen species (ROS) due to a block in glycolysis were shown to be the lead contributor of cell viability loss. The drug combination in the doses used displayed no overt toxicity in the treated animals.

Abstract

Studies in targeting metabolism in cancer cells have shown the flexibility of cells in reprogramming their pathways away from a given metabolic block. Such behavior prompts a combination drug approach in targeting cancer metabolism, as a single compound may not address the tumor intractability. Overall, mammalian target of rapamycin complex 1 (mTORC1) signaling has been implicated as enabling metabolic escape in the case of a glycolysis block. From a library of compounds, the tyrosine kinase inhibitor ponatinib was screened to provide optimal reduction in metabolic activity in the production of adenosine triphosphate (ATP), pyruvate, and lactate for multiple myeloma cells; however, these cells displayed increasing levels of oxidative phosphorylation (OXPHOS), enabling them to continue generating ATP, although at a slower pace. The combination of ponatinib with the mTORC1 inhibitor, sirolimus, blocked OXPHOS; an effect also manifested in activity reductions for hexokinase 2 (HK2) and glucose-6-phosphate isomerase (GPI) glycolysis enzymes. There were also remarkably higher levels of reactive oxygen species (ROS) produced in mouse xenografts, on par with increased glycolytic block. The combination of ponatinib and sirolimus resulted in synergistic inhibition of tumor xenografts with no overt toxicity in treated mice for kidney and liver function or maintaining weight.

The ponatinib/gossypol novel combination provides enhanced anticancer activity against murine solid Ehrlich carcinoma via triggering apoptosis and inhibiting proliferation/angiogenesis

The search for new antitumor agents or combinations that are more effective and, hopefully, provide fewer health hazards is ongoing. Therefore, this study investigated the efficacy of a novel combination of ponatinib, a multi-targeted tyrosine kinase inhibitor, and the natural phytochemical gossypol against murine solid Ehrlich carcinoma. Six groups of ten mice each received vehicle (I), ponatinib in doses of 10 and 15 mg/kg (II, III) respectively, gossypol in a dose of 4 mg/kg (IV), and ponatinib (10 or 15 mg/kg) in combination with gossypol (4 mg/kg; V, VI). All treatments started on the 12th post-Ehrlich ascites carcinoma (EAC) implantation day and were administered intraperitoneally in daily doses for 3 weeks. Treatment of EAC-bearing mice with ponatinib/gossypol combination improved anticancer efficacy over either drug alone, as demonstrated by greater decreases in tumor weight and volume, and ponatinib (10 mg/kg)/gossypol combination was more efficient than ponatinib (15 mg/kg). Mechanistically, the ponatinib/gossypol combination significantly increased apoptotic markers p53, Bax, and caspase-9 while decreasing anti-apoptotic marker Bcl-2. Furthermore, it greatly decreased proliferative and angiogenic markers, FGFR4 and VEGF, respectively. Histopathology revealed a significant decline in neoplastic cells, the majority of which have necrotic changes and numerous apoptotic bodies, as well as a decrease in mitotic figures and tumor giant cells, indicating the capacity to suppress cancer proliferation/persistence. Overall, gossypol could be used as an adjuvant medication for ponatinib in cancer treatment, possibly leading to successful dose reductions and fewer side effects; however, further research is needed before a clinical application could be feasible.

Targeting Oncogenic Transcriptional Networks in Neuroblastoma: From N-Myc to Epigenetic Drugs

Neuroblastoma (NB) is one of the most frequently occurring neurogenic extracranial solid cancers in childhood and infancy. Over the years, many pieces of evidence suggested that NB development is controlled by gene expression dysregulation. These unleashed programs that outline NB cancer cells make them highly dependent on specific tuning of gene expression, which can act co-operatively to define the differentiation state, cell identity, and specialized functions. The peculiar regulation is mainly caused by genetic and epigenetic alterations, resulting in the dependency on a small set of key master transcriptional regulators as the convergence point of multiple signalling pathways. In this review, we provide a comprehensive blueprint of transcriptional regulation bearing NB initiation and progression, unveiling the complexity of novel oncogenic and tumour suppressive regulatory networks of this pathology. Furthermore, we underline the significance of multi-target therapies against these hallmarks, showing how novel approaches, together with chemotherapy, surgery, or radiotherapy, can have substantial antineoplastic effects, disrupting a wide variety of tumorigenic pathways through combinations of different treatments.

Synthetic Heterocyclic Derivatives as Kinase Inhibitors Tested for the Treatment of Neuroblastoma

In the last few years, small molecules endowed with different heterocyclic scaffolds have been developed as kinase inhibitors. Some of them are being tested at preclinical or clinical levels for the potential treatment of neuroblastoma (NB). This disease is the most common extracranial solid tumor in childhood and is responsible for 10% to 15% of pediatric cancer deaths. Despite the availability of some treatments, including the use of very toxic cytotoxic chemotherapeutic agents, high-risk (HR)-NB patients still have a poor prognosis and a survival rate below 50%. For these reasons, new pharmacological options are urgently needed. This review focuses on synthetic heterocyclic compounds published in the last five years, which showed at least some activity on this severe disease and act as kinase inhibitors. The specific mechanism of action, selectivity, and biological activity of these drug candidates are described, when established. Moreover, the most remarkable clinical trials are reported. Importantly, kinase inhibitors approved for other diseases have shown to be active and endowed with lower toxicity compared to conventional cytotoxic agents. The data collected in this article can be particularly useful for the researchers working in this area.

Novel Treatments and Technologies Applied to the Cure of Neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid tumour in childhood, accounting for approximately 15% of all cancer-related deaths in the paediatric population1. It is characterised by heterogeneous clinical behaviour in neonates and often adverse outcomes in toddlers. The overall survival of children with high-risk disease is around 40-50% despite the aggressive treatment protocols consisting of intensive chemotherapy, surgery, radiation therapy and hematopoietic stem cell transplantation2,3. There is an ongoing research effort to increase NB's cellular and molecular biology knowledge to translate essential findings into novel treatment strategies. This review aims to address new therapeutic modalities emerging from preclinical studies offering a unique translational opportunity for NB treatment.

Autophagic flux inhibition enhances cytotoxicity of the receptor tyrosine kinase inhibitor ponatinib

Background

Despite reported advances, acquired resistance to tyrosine kinase inhibitors still represents a serious problem in successful cancer treatment. Among this class of drugs, ponatinib (PON) has been shown to have notable long-term efficacy, although its cytotoxicity might be hampered by autophagy. In this study, we examined the likelihood of PON resistance evolution in neuroblastoma and assessed the extent to which autophagy might provide survival advantages to tumor cells.

Methods

The effects of PON in inducing autophagy were determined both in vitro, using SK-N-BE(2), SH-SY5Y, and IMR-32 human neuroblastoma cell lines, and in vivo, using zebrafish and mouse models. Single and combined treatments with chloroquine (CQ)—a blocking agent of lysosomal metabolism and autophagic flux—and PON were conducted, and the effects on cell viability were determined using metabolic and immunohistochemical assays. The activation of the autophagic flux was analyzed through immunoblot and protein arrays, immunofluorescence, and transmission electron microscopy. Combination therapy with PON and CQ was tested in a clinically relevant neuroblastoma mouse model.

Results

Our results confirm that, in neuroblastoma cells and wild-type zebrafish embryos, PON induces the accumulation of autophagy vesicles—a sign of autophagy activation. Inhibition of autophagic flux by CQ restores the cytotoxic potential of PON, thus attributing to autophagy a cytoprotective nature. In mice, the use of CQ as adjuvant therapy significantly improves the anti-tumor effects obtained by PON, leading to ulterior reduction of tumor masses.

Conclusions

Together, these findings support the importance of autophagy monitoring in the treatment protocols that foresee PON administration, as this may predict drug resistance acquisition. The findings also establish the potential for combined use of CQ and PON, paving the way for their consideration in upcoming treatment protocols against neuroblastoma.

Cardiotoxicity of the BCR-ABL1 tyrosine kinase inhibitors: Emphasis on ponatinib

The advent of tyrosine kinase inhibitors (TKIs) targeted therapy revolutionized the treatment of chronic myeloid leukemia (CML) patients. However, cardiotoxicity associated with these targeted therapies puts the cancer survivors at higher risk. Ponatinib is a third-generation TKI for the treatment of CML patients having gatekeeper mutation T315I, which is resistant to the first and second generation of TKIs, namely, imatinib, nilotinib, dasatinib, and bosutinib. Multiple unbiased screening from our lab and others have identified ponatinib as most cardiotoxic FDA approved TKI among the entire FDA approved TKI family (total 50+). Indeed, ponatinib is the only treatment option for CML patients with T315I mutation. This review focusses on the cardiovascular risks and mechanism/s associated with CML TKIs with a particular focus on ponatinib cardiotoxicity. We have summarized our recent findings with transgenic zebrafish line harboring BNP luciferase activity to demonstrate the cardiotoxic potential of ponatinib. Additionally, we will review the recent discoveries reported by our and other laboratories that ponatinib primarily exerts its cardiotoxicity via an off-target effect on cardiomyocyte prosurvival signaling pathways, AKT and ERK. Finally, we will shed light on future directions for minimizing the adverse sequelae associated with CML-TKIs.

Inhibitors of Na+/K+ ATPase exhibit antitumor effects on multicellular tumor spheroids of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), one of the most common malignant cancers worldwide, is associated with substantial mortality. Because HCCs have strong resistance to conventional chemotherapeutic agents, novel therapeutic strategies are needed to improve survival in patients with HCC. The multicellular tumor spheroid (MCTS) model is a powerful method for anticancer research because of its ability to mimic the complexity and heterogeneity of tumor tissue, the three-dimensional cellular context of tumor tissue, and the pathophysiological gradients of in vivo tumors. However, it is difficult to obtain meaningful results from the MCTS model without considering the conditions of clinical tumors. We, therefore, provided a proof of concept to determine whether spheroid models simulate in vivo tumor microenvironments. Through a high-throughput screening for HCC therapy using the MCTS model, we selected inhibitors of Na⁺/K⁺-ATPase (ouabain and digoxin) that could suppress cell growth and migration via inhibition of the epithelial-mesenchymal transition of HCC in vivo and in vitro. The results showed that this model provides a new paradigm for high-throughput drug screening and will significantly improve the efficiency of identifying new drugs for HCC treatment. Through utilization of MCTS models, here we found that inhibitors of Na⁺/K⁺-ATPase may be feasible as a novel target to sensitize HCC cells.

A Combinatorial Strategy for Targeting BRAF V600E-Mutant Cancers with BRAFV600E Inhibitor (PLX4720) and Tyrosine Kinase Inhibitor (Ponatinib)

PURPOSE

Most aggressive thyroid cancers are commonly associated with a BRAF ^V600E mutation. Preclinical and clinical data in BRAF ^V600E cancers suggest that combined BRAF and MEK inhibitor treatment results in a response, but resistance is common. One mechanism of acquired resistance is through persistent activation of tyrosine kinase (TK) signaling by alternate pathways. We hypothesized that combination therapy with BRAF and multitargeting TK inhibitors (MTKI) might be more effective in BRAF ^V600E thyroid cancer than in single-agent or BRAF and MEK inhibitors.

EXPERIMENTAL DESIGN

The combined drug activity was analyzed to predict any synergistic effect using high-throughput screening (HTS) of active drugs. We performed follow-up in vitro and in vivo studies to validate and determine the mechanism of action of synergistic drugs.

RESULTS

The MTKI ponatinib and the BRAF inhibitor PLX4720 showed synergistic activity by HTS. This combination significantly inhibited proliferation, colony formation, invasion, and migration in BRAF ^V600E thyroid cancer cell lines and downregulated pERK/MEK and c-JUN signaling pathways, and increased apoptosis. PLX4720-resistant BRAF ^V600E cells became sensitized to the combination treatment, with decreased proliferation at lower PLX4720 concentrations. In an orthotopic thyroid cancer mouse model, combination therapy significantly reduced tumor growth (P < 0.05), decreased the number of metastases (P < 0.05), and increased survival (P < 0.05) compared with monotherapy and vehicle control.

CONCLUSIONS

Combination treatment with ponatinib and PLX4720 exhibited significant synergistic anticancer activity in preclinical models of BRAF ^V600E thyroid cancer, in addition to overcoming PLX4720 resistance. Our results suggest this combination should be tested in clinical trials.

Recent Studies on Ponatinib in Cancers Other Than Chronic Myeloid Leukemia

Ponatinib is a third line drug for the treatment of chronic myeloid leukemia patients, especially those that develop the gatekeeper mutation T315I, which is resistant to the first and the second line drugs imatinib, nilotinib, dasatinib and bosutinib. The compound was first identified as a pan Bcr-Abl and Src kinase inhibitor. Further studies have indicated that it is a multitargeted inhibitor that is active on FGFRs, RET, AKT, ERK1/2, KIT, MEKK2 and other kinases. For this reason, the compound has been evaluated on several cancers in which these kinases play important roles, including thyroid, breast, ovary and lung cancer, neuroblastoma, rhabdoid tumours and in myeloproliferative disorders. Ponatinib is also being tested in clinical trials to evaluate its activity in FLT3-ITD acute myelogenous leukemia, head and neck cancers, certain type of lung cancer, gastrointestinal stromal tumours and other malignancies. In this review we report the most recent preclinical and clinical studies on ponatinib in cancers other than CML, with the aim of giving a complete overview of this interesting compound.

Hitting two oncogenic machineries in cancer cells: cooperative effects of the multi-kinase inhibitor ponatinib and the BET bromodomain blockers JQ1 or dBET1 on human carcinoma cells

In recent years, numerous new targeted drugs, including multi-kinase inhibitors and epigenetic modulators have been developed for cancer treatment. Ponatinib blocks a variety of tyrosine kinases including ABL and fibroblast growth factor receptor (FGFR), and the BET bromodomain (BRD) antagonists JQ1 and dBET1 impede MYC oncogene expression. Both drugs have demonstrated substantial anti-cancer efficacy against several hematological malignancies. Solid tumors, on the other hand, although frequently driven by FGFR and/or MYC, are often unresponsive to these drugs. This is due, at least in part, to compensatory feedback-loops in the kinome and transcription network of these tumors, which are activated in response to drug exposure. Therefore, we hypothesized that the combination of the multi-kinase inhibitor ponatinib with transcription modulators such as JQ1 or dBET1 might overcome this therapeutic recalcitrance. Using ³H-thymidine uptake, cell cycle analysis, and caspase-3 or Annexin V labeling, we demonstrate that single drugs induce moderate dose-dependent growth-inhibition and/or apoptosis in colon (HCT116, HT29), breast (MCF-7, SKBR3) and ovarian (A2780, SKOV3) cancer cells. Ponatinib elicited primarily apoptosis, while JQ1 and dBET1 caused G0/G1 cell cycle arrest and very mild cell death. Phospho-FGFR and MYC, major targets of ponatinib and BET inhibitors, were downregulated after treatment with single drugs. Remarkably, ponatinib was found to sensitize cells to BET antagonists by enhancing apoptotic cell death, and this effect was associated with downregulation of MYC. In summary, our data shows that ponatinib sensitizes colon, breast, and ovarian cancer cells to BET bromodomain inhibitors. Further studies are warranted to determine the clinical value of this phenomenon.

A High-Content Screening of Anticancer Compounds Suggests the Multiple Tyrosine Kinase Inhibitor Ponatinib for Repurposing in Neuroblastoma Therapy

Novel druggable targets have been discovered in neuroblastoma (NB), paving the way for more effective treatments. However, children with high-risk NB still show high mortality rates prompting for a search of novel therapeutic options. Here, we aimed at repurposing FDA-approved drugs for NB treatment by performing a high-content screening of a 349 anticancer compounds library. In the primary screening, we employed three NB cell lines, grown as three-dimensional (3D) multicellular spheroids, which were treated with 10 μmol/L of the library compounds for 72 hours. The viability of 3D spheroids was evaluated using a high-content imaging approach, resulting in a primary hit list of 193 compounds. We selected 60 FDA-approved molecules and prioritized drugs with multi-target activity, discarding those already in use for NB treatment or enrolled in NB clinical trials. Hence, 20 drugs were further tested for their efficacy in inhibiting NB cell viability, both in two-dimensional and 3D models. Dose-response curves were then supplemented with the data on side effects, therapeutic index, and molecular targets, suggesting two multiple tyrosine kinase inhibitors, ponatinib and axitinib, as promising candidates for repositioning in NB. Indeed, both drugs showed induction of cell-cycle block and apoptosis, as well as inhibition of colony formation. However, only ponatinib consistently affected migration and inhibited invasion of NB cells. Finally, ponatinib also proved effective inhibition of tumor growth in orthotopic NB mice, providing the rationale for its repurposing in NB therapy. Mol Cancer Ther; 17(7); 1405-15. ©2018 AACR.

Novel multi-targeted ErbB family inhibitor afatinib blocks EGF-induced signaling and induces apoptosis in neuroblastoma

Neuroblastoma is the most common extracranial solid tumor in children. The ErbB family of proteins is a group of receptor tyrosine kinases that promote the progression of various malignant cancers including neuroblastoma. Thus, targeting them with small molecule inhibitors is a promising strategy for neuroblastoma therapy. In this study, we investigated the anti-tumor effect of afatinib, an irreversible inhibitor of members of the ErbB family, on neuroblastoma. We found that afatinib suppressed the proliferation and colony formation ability of neuroblastoma cell lines in a dose-dependent manner. Afatinib also induced apoptosis and blocked EGF-induced activation of PI3K/AKT/mTOR signaling in all neuroblastoma cell lines tested. In addition, afatinib enhanced doxorubicin-induced cytotoxicity in neuroblastoma cells, including the chemoresistant LA-N-6 cell line. Finally, afatinib exhibited antitumor efficacy in vivo by inducing apoptosis in an orthotopic xenograft neuroblastoma mouse model. Taken together, these results show that afatinib inhibits neuroblastoma growth both in vitro and in vivo by suppressing EGFR-mediated PI3K/AKT/mTOR signaling. Our study supports the idea that EGFR is a potential therapeutic target in neuroblastoma. And targeting ErbB family protein kinases with small molecule inhibitors like afatinib alone or in combination with doxorubicin is a viable option for treating neuroblastoma.

Novel Src/Abl tyrosine kinase inhibitor bosutinib suppresses neuroblastoma growth via inhibiting Src/Abl signaling

Neuroblastoma (NB) is the most common extracranial solid tumor in children. Aberrant activation of the non-receptor tyrosine kinases Src and c-Abl contributes to the progression of NB. Thus, targeting these kinases could be a promising strategy for NB therapy. In this paper, we report that the potent dual Src/Abl inhibitor bosutinib exerts anti-tumor effects on NB. Bosutinib inhibited NB cell proliferation in a dose-dependent manner and suppressed colony formation ability of NB cells. Mechanistically, bosutinib effectively decreased the activity of Src/Abl and PI3K/AKT/mTOR, MAPK/ERK, and JAK/STAT3 signaling pathways. In addition, bosutinib enhanced doxorubicin (Dox)- and etoposide (VP-16)-induced cytotoxicity in NB cells. Furthermore, bosutinib demonstrated anti-tumor efficacy in an orthotopic xenograft NB mouse model in a similar mechanism as of that in vitro. In summary, our results reveal that Src and c-Abl are potential therapeutic targets in NB and that the novel Src/Abl inhibitor bosutinib alone or in combination with other chemotherapeutic agents may be a valuable therapeutic option for NB patients.

Small molecule inhibitor regorafenib inhibits RET signaling in neuroblastoma cells and effectively suppresses tumor growth in vivo

Neuroblastoma (NB), the most common extracranial pediatric solid tumor, continues to cause significant cancer-related morbidity and mortality in children. Dysregulation of oncogenic receptor tyrosine kinases (RTKs) has been shown to contribute to tumorigenesis in various human cancers and targeting these RTKs has had therapeutic benefit. RET is an RTK which is commonly expressed in NB, and high expression of RET correlates with poor outcomes in patients with NB. Herein we report that RET is required for NB cell proliferation and that the small molecule inhibitor regorafenib (BAY 73-4506) blocks glial cell derived neurotrophic factor (GDNF)-induced RET signaling in NB cells and inhibits NB growth both in vitro and in vivo. We found that regorafenib significantly inhibited cell proliferation and colony formation ability of NB cells. Moreover, regorafenib suppressed tumor growth in both an orthotopic xenograft NB mouse model and a TH-MYCN transgenic NB mouse model. Finally, regorafenib markedly improved the overall survival of TH-MYCN transgenic tumor-bearing mice. In summary, our study suggests that RET is a potential therapeutic target in NB, and that using a novel RET inhibitor, like regorafenib, should be investigated as a therapeutic treatment option for children with NB.

Wip1 inhibitor GSK2830371 inhibits neuroblastoma growth by inducing Chk2/p53-mediated apoptosis

Neuroblastoma (NB) is the most common extracranial tumor in children. Unlike in most adult tumors, tumor suppressor protein 53 (p53) mutations occur with a relatively low frequency in NB and the downstream function of p53 is intact in NB cell lines. Wip1 is a negative regulator of p53 and hindrance of Wip1 activity by novel inhibitor GSK2830371 is a potential strategy to activate p53’s tumor suppressing function in NB. Yet, the in vivo efficacy and the possible mechanisms of GSK2830371 in NB have not yet been elucidated. Here we report that novel Wip1 inhibitor GSK2830371 induced Chk2/p53-mediated apoptosis in NB cells in a p53-dependent manner. In addition, GSK2830371 suppressed the colony-formation potential of p53 wild-type NB cell lines. Furthermore, GSK2830371 enhanced doxorubicin- (Dox) and etoposide- (VP-16) induced cytotoxicity in a subset of NB cell lines, including the chemoresistant LA-N-6 cell line. More importantly, GSK2830371 significantly inhibited tumor growth in an orthotopic xenograft NB mouse model by inducing Chk2/p53-mediated apoptosis in vivo. Taken together, this study suggests that GSK2830371 induces Chk2/p53-mediated apoptosis both in vitro and in vivo in a p53 dependent manner.

Novel proteasome inhibitor ixazomib sensitizes neuroblastoma cells to doxorubicin treatment

Neuroblastoma (NB) is the most common extracranial malignant solid tumor seen in children and continues to lead to the death of many pediatric cancer patients. The poor outcome in high risk NB is largely attributed to the development of chemoresistant tumor cells. Doxorubicin (dox) has been widely employed as a potent anti-cancer agent in chemotherapeutic regimens; however, it also leads to chemoresistance in many cancer types including NB. Thus, developing novel small molecules that can overcome dox-induced chemoresistance is a promising strategy in cancer therapy. Here we show that the second generation proteasome inhibitor ixazomib (MLN9708) not only inhibits NB cell proliferation and induces apoptosis in vitro but also enhances dox-induced cytotoxicity in NB cells. Ixazomib inhibits dox-induced NF-κB activity and sensitizes NB cells to dox-induced apoptosis. More importantly, ixazomib demonstrated potent anti-tumor efficacy in vivo by enhancing dox-induced apoptosis in an orthotopic xenograft NB mouse model. Collectively, our study illustrates the anti-tumor efficacy of ixazomib in NB both alone and in combination with dox, suggesting that combination therapy including ixazomib with traditional therapeutic agents such as dox is a viable strategy that may achieve better outcomes for NB patients.