In vitro and in vivo killing effects of methionine enkephalin on osteosarcoma.

OBJECTIVE: This study aimed to investigate the underlying regulatory effects of methionine enkephalin (MENK) on osteosarcoma. METHODS: The Cell Counting Kit-8 assay, clone formation, wound healing, transwell assay, and flow cytometry were performed to measure the effects of MENK on the proliferation, migration, invasion, and apoptosis of MG-63 and Saos-2 cells. Opiate growth factor receptor expression (OGFr) in cells was stably knocked down using siRNA. A tumor model was established by inoculating MG-63 cells into mice. Flow cytometry was performed to identify alterations in mice bone marrow, spleen, and tumor tissue immune cells. The phenotype of tumor-associated macrophages was determined using immunohistochemistry. After OGFr knockdown or/and treatment with MENK, Bax, Bcl-2, caspase 3, caspase 9, and PARP expression levels were characterized using qRT-PCR, western blot, and WES, respectively. RESULTS: MENK could significantly inhibit the proliferation, invasion, and migration of MG-63 and Saos-2, arrest the cell cycle in the G0/G1 phase, upregulate Bax, caspase 3, caspase 9, and PARP expression, and downregulate Bcl-2 expression. Tumor size and weight were lower in the MENK group than those in the control group. MENK-treated mice exhibited a reduced ratio of CD11b + Gr-1 + myeloid-derived suppressor cells. MENK increased the ratio of M1-type macrophages and decreased the proportion of M2-type macrophages in tumor tissue. Furthermore, the level of TNF-α significantly increased while that of IL-10 decreased in MENK-treated mice. The effect of MENK could be partly reversed by OGFr knockdown. CONCLUSION: MENK reduces the abundance of myeloid-derived suppressor cells, induces M1 polarization of macrophages, and exhibits an inhibitory effect on osteosarcoma.

Methionine enkephalin suppresses lung cancer metastasis by regulating the polarization of tumor-associated macrophages and the distribution of myeloid-derived suppressor cells in the tumor microenvironment and inhibiting epithelial-mesenchymal transition.

Metastasis is one of the most difficult challenges for clinical lung cancer treatment. Epithelial-mesenchymal transition (EMT) is the crucial step of tumor metastasis. Immune cells in the tumor microenvironment (TME), such as tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs), promote cancer cell EMT. In this study, we explored the effect of methionine enkephalin (MENK) on the EMT process in vitro and in vivo, and its influence on TAMs, MDSCs, and associated cytokines in vivo. The results showed that MENK suppressed growth, migration, and invasion of lung cancer cells and inhibited the EMT process by interacting with opioid growth factor receptor. MENK reduced the number of M2 macrophages and MDSC infiltration, and downregulated the expression of interleukin-10 and transforming growth factor-ß1 in both primary and metastatic tumors of nude mice. The present findings suggest that MENK is a potential target for suppressing metastasis in lung cancer treatment.

NaV1.7 Channel Blocker [Ala5, Phe6, Leu26, Arg28]GpTx-1 Attenuates CFA-induced Inflammatory Hypersensitivity in Rats via Endogenous Enkephalin Mechanism.

Venom-derived NaV1.7 channel blockers have promising prospects in pain management. The 34-residue tarantula peptide GpTx-1 is a potent NaV1.7 channel blocker. Its powerful analog [Ala5, Phe6, Leu26, Arg28]GpTx-1 (GpTx-1-71) displayed excellent NaV1.7 selectivity and analgesic properties in mice. The current study aimed to elucidate the anti-hyperalgesic activities of GpTx-1-71 in inflammatory pain and reveal the underlying mechanisms. Our results demonstrated that intrathecal and intraplantar injections of GpTx-1-71 dose-dependently attenuated CFA-induced inflammatory hypersensitivity in rats. Moreover, GpTx-1-71-induced anti-hyperalgesia was significantly reduced by opioid receptor antagonists and the enkephalin antibody and diminished in proenkephalin (Penk) gene knockout animals. Consistently, GpTx-1-71 treatment increased the enkephalin level in the spinal dorsal horn and promoted the Penk transcription and enkephalin release in primary dorsal root ganglion (DRG) neurons, wherein sodium played a crucial role in these processes. Mass spectrometry analysis revealed that GpTx-1-71 mainly promoted the secretion of Met-enkephalin but not Leu-enkephalin from DRG neurons. In addition, the combination of subtherapeutic Met-enkephalin and GpTx-1-71 produced synergistic anti-hyperalgesia in CFA-induced inflammatory hypersensitivity. These findings suggest that the endogenous enkephalin pathway is essential for GpTx-1-71-induced spinal and peripheral analgesia in inflammatory pain. PERSPECTIVE: This article presents a possible pharmacological mechanism underlying NaV1.7 blocker-induced analgesia in inflammatory pain, which helps us to better understand and develop venom-based painkillers for incurable pain.

Methionine enkephalin inhibits colorectal cancer by remodeling the immune status of the tumor microenvironment.

There is evidence that methionine enkephalin (MENK), an opioid peptide, promotes anti-tumor immune responses. In this study, the effect of MENK on colorectal cancer (CRC) and its mechanisms of action were examined in vivo. The intraperitoneal administration of 20 mg/kg MENK effectively inhibited MC38 subcutaneous colorectal tumor growth in mice. MENK inhibited tumor progression by increasing the immunogenicity and recognition of MC38 cells. MENK down-regulated the oncogene Kras and anti-apoptotic Bclxl and Bcl2, suppressed Il1b, Il6, iNOS, and Arg1 (encoding inflammatory cytokines), and increased Il17a and Il10 levels. MENK promoted a tumor suppressive state by decreasing the immune checkpoints Pd-1, Pd-l1, Lag3, Flgl1, and 2b4 in CRC. MENK also altered the immune status of the tumor immune microenvironment (TIME). It increased the infiltration of M1-type macrophages, CD8+T cells, and CD4+T cells and decreased the proportions of G-MDSCs, M-MDSCs, and M2-type macrophages. MENK accelerated CD4+TEM and CD8+TEM cell activation in the TIME and up-regulated IFN-γ, TNF-α, and IL-17A in CD4+T cells and Granzyme B in CD8+T cells. In addition, analyses of PD-1 and PD-L1 expression indicated that MENK promoted the anti-tumor immune response mediated by effector T cells. Finally, OGFr was up-regulated at the protein and mRNA levels by MENK, and the inhibitory effects of MENK on tumor growth were blocked by NTX, a specific blocker of OGFr. These finding indicate that MENK remodels the TIME in CRC to inhibit tumor progression by binding to OGFr. MENK is a potential therapeutic agent for CRC, especially for improving the efficacy of immunotherapy.

Methionine enkephalin inhibited cervical carcinoma via apoptosis promotion and reduction of myeloid derived suppressor cell infiltrated in tumor.

Immunotherapy for cervical carcinoma is becoming increasingly important recently. In these studies methionine enkephalin (menk) is shown to inhibit cervical tumor cell proliferation in vitro in association with an increase in the expression of apoptosis markers and mediators, including an increase in fas, caspase 8, and caspase 3 expression and intrinsic expression of the signaling pathway mediator bax. In vivo, tumor growth was restrained in mice xenotransplant model with typical pathological features of apoptosis. Furthermore, myeloid derived suppressor cells (MDSCs) had a significant decrease in circulation and in tumor site. In brief, these findings showed menk could inhibit tumor growth in vitro and in vivo, providing direction of further research and clinical application prospect.

The paradoxical role of methionine enkephalin in tumor responses.

Methionine enkephalin (MENK) is an opioid peptide composed of five amino acids with multiple biological activities. Since its discovery, MENK has become prominent in neuroregulation and immunoregulation. Tumors have increasingly been a spotlight because of their terrible trends and refractory characteristic. The therapeutic potential of MENK was investigated on a large scale, and there are numerous evidences that MENK exerts anti-tumor effects via two mechanisms. The first mechanism explains the enhanced anti-tumor immune effects of MENK. The second mechanism shows that MENK directly inhibits tumor cell proliferation. However, numerous reports have clarified the pro-tumor role of MENK by inhibiting T and B cell proliferation, promoting tumor cell growth by binding to opioid receptors, leading to desensitization of lymphocytes, and inducing tolerance. It is particularly intriguing that dual reactions are triggered when MENK combines with its opioid receptors; thus, anti-tumor response of the whole body is influenced. This review will expound the dual roles of MENK in tumor responses based on immune cells, cytokines, and tumor cells to provide better suggestions for its application in tumor treatment.

Anti-inflammatory and metabolic reprogramming effects of MENK produce antitumor response in CT26 tumor-bearing mice.

Methionine enkephalin (MENK), an endogenous opioid peptide, has a role in nervous system, immune system, and anticancer therapy. Inflammation, metabolism and cancer are closely intertwined with each other. This study is to identify the correlation of the antitumor effects of MENK with systemic inflammation, liver metabolism, and immune cells as myeloid-derived suppressor cells (MDSCs). We established a subcutaneous CT26 colon carcinoma model and a cyclophosphamide-induced immunosuppressive model subjected to MENK. AML12 and MDSCs were used as in vitro models. The results showed that MENK treatment degraded tumor growth and inhibited proinflammatory cytokines both in tumor tissues and serum. The MENK-treated tumor mice showed normalized liver function with glycolipid metabolic homeostasis. No inhibitory effect on CT26 tumor cell in vitro, but only reduced lipid synthesis in AML12 were presented by MENK. Meanwhile, MENK invigorated immune response in both two animal models by markedly suppressing MDSCs and enhancing T cells response. In vitro MENK-treated MDSCs showed reduced glycolysis and less ROS production, which was mediated by PI3K/AKT/mTOR pathway. Opioid receptor antagonist naltrexone reversed most of the regulation. These results illustrate that MENK preventing development of colon carcinoma might be correlated with the suppression of inflammation, improving metabolism in liver as well as in MDSCs partly through opioid receptor, which brings new elements supporting the adjuvant therapy for tumor by MENK.

Methionine enkephalin inhibits influenza A virus infection through upregulating antiviral state in RAW264.7 cells.

MENK, as an immune adjuvant, has potential immune-regulatory activity on innate and adaptive immune cells. The aim of this work was to investigate the antiviral effect of MENK on influenza virus-infected murine macrophage cells (RAW264.7) and its underlying mechanisms. The results showed that MENK markedly inhibited influenza A virus (H1N1) replication in pre- and post-MENK treatment, especially in pre-MENK treatment. The mechanisms exploration revealed that MENK (10 mg/mL) significantly inhibited the nucleoprotein (NP) of influenza virus and up-regulated levels of IL-6, TNF-α and IFN-ß compared with those in H1N1 control group. Further experiments confirmed that antiviral effects of MENK was associated with promotion of opioid receptor (MOR) as well as activation of NF-κB p65 inducing cellular antiviral status. The data suggest that MENK should be potential candidate for prophylactic or therapeutic treatment against H1N1 influenza virus.

Interaction of opioid growth factor (OGF) and opioid antagonist and their significance in cancer therapy.

Endogenous opioids are neuro-peptides with multifunctional properties. Historically, opioids are used to mediate pain; however, excess opiate consumption can lead to addiction. One endogenous opioid, methionine enkephalin (MENK), was reported to modulate cell growth, MENK was identified as an opioid growth factor (OGF) that interacts with the OGF receptor (OGFr) and regulates cell proliferation. Further, opioid antagonists, including naltrexone and naloxone are widely used to reverse drug and alcohol overdoses. Naltrexone (NTX) acts on all opioid receptors, blocking the interaction between OGF and OGFr, and thus influencing cell growth. During the last decades, insights have been made concerning the interaction between OGF and OGFr, confirming that both opioids and opioid antagonists have an important role in balancing host homeostasis, host immunity and mediating cancer therapy. This review provides insight into the interactions between OGF and OGFr in the treatment of cancers.

Methionine enkephalin (MENK) inhibits human gastric cancer through regulating tumor associated macrophages (TAMs) and PI3K/AKT/mTOR signaling pathway inside cancer cells.

This study was to explore the effect and mechanisms of anti- human gastric cancer by MENK in vitro and in vivo. The results showed in MENK-treated xenograft tissue, the percentage of M2-type macrophages decreased while M1-type macrophages increased. MENK increased the expression of M1-related cytokine TNF-α and attenuated the expression of M2-related cytokine IL-10 expression. MENK upregulated the expression of opioid receptor (OGFr), while it inhibited HGC27 and SGC7901 cells through blocking PI3K/AKT/mTOR signal pathway in vitro and in vivo. These effects of MENK could be cancelled when OGFr was knockdown. This indicates that binding to OGFr by MENK appears to be essential for the anti- GC cells. Therefore, it is concluded that MENK might skew macrophage toward M2 phenotype from M1 phenotype within tumor and induce cells apoptosis though blocking OGFr/PI3K/AKT/mTOR signaling pathway.

Met-enkephalin improves metabolic syndrome in high fat diet challenged mice through promotion of adipose tissue browning.

Obesity and its related metabolic disorders including insulin resistance and fatty liver become major public health concerns in both developed and developing countries. Brown adipose tissue (BAT), a critical organ of energy expenditure due to thermogenesis, has been considered as an attractive target for prevention or treatment of obesity and obesity related diseases. Previous studies indicate Met-enkephalin (MetEnk) has the potential on adipocyte browning, however, whether MetEnk displays the impact on adipocyte browning in vivo to improve obesity associated morbidities is still unclear. In the present study, we showed that MetEnk effectively prevented high fat diet (HFD) induced C57BL/6J mice weight gain, clearly enhanced glucose tolerance and insulin sensitivity, and dramatically reduced hepatic steatosis in HFD fed mice. Mechanically, MetEnk restored protein kinase A (PKA) signaling pathway in HFD challenged mice and promoted subcutaneous white adipose tissue (WAT) browning. Our study suggests that MetEnk can be considered as a potential therapeutic peptide for diet-induced obesity and metabolic disorders.

Novel effect of methionine enkephalin against influenza A virus infection through inhibiting TLR7-MyD88-TRAF6-NF-κB p65 signaling pathway.

The morbidity and mortality associated with influenza A virus infections, have stimulated the search for novel prophylactic and therapeutic drugs. The purpose of this study was to investigate the prophylactic and therapeutic effect of synthetic methionine enkephalin (MENK) on mice infected by A/PR/8/34 influenza virus (H1N1) in vivo. The results showed that MENK could exert both prophylactic and therapeutic influences on infected mice, significantly improve the survival rate, relieve acute lung injury and decrease cytokine (IFN-α, IFN-ß, TNF-α, IL-6, and IL-1ß) levels. MENK also inhibited virus replication on day 4 post infection (p.i.) through upregulating opioid receptors (MOR, DOR) and suppressing TLR7-MyD88-TRAF6-NF-κB p65 signaling pathways. These results suggest that MENK, given via intranasal administration, could provide a novel drug with a new mode of action as a nonspecific anti-influenza agent or vaccine adjuvant.

Methionine enkephalin (MENK) mounts antitumor effect via regulating dendritic cells (DCs).

MENK, an endogenous opioid peptide has been reported to have many immunological and antitumor activities. So far the detailed mechanisms of antitumor through regulating DCs by MENK have not been elucidated yet. The aim of this work was to investigate the antitumor mechanisms of MENK via regulating DC. The monitoring methods, such as ELISA, MTS assay, CFSE, Real-time PCR and Western blot were included in our research. We found bone marrow derived dendritic cells (BMDCs) in 36 female C57BL/6 mice treated with MENK enhanced expression of key surface molecules, increased production of critical cytokines reduced endocytosis of FITC-dextran, upregulated TLR4 through MyD88/NF-κB signaling pathway and mounted higher antitumor activity. These observations were further supported by an enhancement of nuclear translocation of the p65NF-κB subunit involved in this process. Surprisingly, mu-opioid receptors were the main participants of this kind of activation, not delta-opioid receptors nor kappa-opioid receptors, and these interactions could be partly blocked by Naltrexone (a kind of opioid antagonist). In vivo study the activated CD4+, CD8+T cells and decreased ability to induce differentiation of Foxp3+ regulatory T cells were detected post treatment of MENK. Thus, it is concluded that MENK could exert antitumor effect through precisely regulating opioid receptor mediated functions of DCs. In addition, MENK treated DCs may serve as a new immunotherapy approach against tumor.

Opioid growth factor and the treatment of human pancreatic cancer: a review.

Opioid growth factor (OGF), chemically termed [Met5]-enkephalin, and its receptor, OGF receptor (OGFr), form a biological axis that tonically regulates cell proliferation by delaying the G1/S interface of the cell cycle under homeostatic conditions or in neoplasia. Modulation of the OGF-OGFr pathway mediates the course of pancreatic cancer, with exogenous OGF or upregulation of OGFr repressing growth of human pancreatic cancer cells in culture and in nude mice. OGF therapy alone or in combination with standard chemotherapies such as gemcitabine and 5-fluorouracil results in enhanced inhibition of DNA synthesis and tumor growth. Molecular manipulation of OGFr confirms that the receptor is specific for OGF's inhibitory action. Preclinical studies have warranted Phase I and Phase II clinical trials using OGF infusions as a treatment for patients with advanced, unresectable pancreatic cancers. OGF, an endogenous neuropeptide, is a safe, non-toxic, and effective biotherapy that utilizes the OGF-OGFr axis to mediate pancreatic tumor progression.

Opioid growth factor (OGF) for hepatoblastoma: a novel non-toxic treatment.

Hepatoblastoma is the most common liver malignancy in children, typically diagnosed before age 2. The survival rate for hepatoblastoma has increased dramatically in the last 30 years, but the typical chemotherapeutic agents used for treatment are associated with significant toxicity. In this report, the authors present two cases of hepatoblastoma treated with surgical resection and a novel biotherapeutic regimen that included opioid growth factor (OGF). Case #1 is an infant diagnosed with a large mass on prenatal ultrasound. After subsequent diagnosis of hepatoblastoma, she was treated with one course of neoadjuvant chemotherapy at approximately 1 week of age. Following significant complications from the chemotherapy (neutropenic fever, pneumonia and sepsis), the patient's parents declined further chemotherapy, and the infant was treated with surgical resection and opioid growth factor (OGF)/low dose naltrexone (LDN). She is currently at close to 10 years disease-free survival. Case #2 is a child diagnosed with a liver mass on ultrasound at 20 months of age, later biopsy-proven to represent hepatoblastoma. Due to existing co-morbidities including autosomal recessive polycystic kidney disease and hypertension, and indications from the biopsy that the tumor might be insensitive to chemotherapy, the parents elected not to proceed with neoadjuvant chemotherapy. The patient was treated with surgical resection and OGF/LDN, and is currently at more than 5 years disease-free survival. This case series highlights the need for less toxic treatment options than conventional chemotherapy. Modulation of the OGF-OGF receptor axis represents a promising safe and therapeutic avenue for effective treatment of hepatoblastoma.

Supraspinal peroxynitrite modulates pain signaling by suppressing the endogenous opioid pathway.

Peroxynitrite (PN, ONOO(-)) is a potent oxidant and nitrating agent that contributes to pain through peripheral and spinal mechanisms, but its supraspinal role is unknown. We present evidence here that PN in the rostral ventromedial medulla (RVM) is essential for descending nociceptive modulation in rats during inflammatory and neuropathic pain through PN-mediated suppression of opioid signaling. Carrageenan-induced thermal hyperalgesia was associated with increased 3-nitrotyrosine (NT), a PN biomarker, in the RVM. Furthermore, intra-RVM microinjections of the PN decomposition catalyst Fe(III)-5,10,15,20-tetrakis(N-methyl-pyridinium-4-yl)porphyrin (FeTMPyP(5+)) dose-dependently reversed this thermal hyperalgesia. These effects of FeTMPyP(5+) were abrogated by intra-RVM naloxone, implicating potential interplay between PN and opioids. In support, we identified NT colocalization with the endogenous opioid enkephalin (ENK) in the RVM during thermal hyperalgesia, suggesting potential in situ interactions. To address the functional significance of such interactions, we exposed methionine-enkephalin (MENK) to PN and identified the major metabolite, 3-nitrotyrosine-methionine-sulfoxide (NSO)-MENK, using liquid chromatography-mass spectrometry. Next, we isolated, purified, and tested NSO-MENK for opioid receptor binding affinity and analgesic effects. Compared to MENK, this NSO-MENK metabolite lacked appreciable binding affinity for δ, µ, and κ opioid receptors. Intrathecal injection of NSO-MENK in rats did not evoke antinociception, suggesting that PN-mediated chemical modifications of ENK suppress opioid signaling. When extended to chronic pain, intra-RVM FeTMPyP(5+) produced naloxone-sensitive reversal of mechanical allodynia in rats following chronic constriction injury of the sciatic nerve. Collectively, our data reveal the central role of PN in RVM descending facilitation during inflammatory and neuropathic pain potentially through anti-opioid activity.

Methionine enkephalin (MENK) improved the functions of bone marrow-derived dendritic cells (BMDCs) loaded with antigen.

The aim of this investigation is to look at whether MENK could improve antitumor effect of CD8+T cell elicited by BMDCs. We investigated the effects of MENK on the differentiation, maturation, and functions of murine BMDC loaded with Rac-1 antigens (RG) and CTL of tumor specific immune response elicited by the BMDC in vitro and in vivo. The production of cytokine IL-12 and TNF-α secreted by BMDCs in the presence of MENK was assayed with ELISA and key surface markers of CD40, CD86, CD83 and MHC-II on the BMDCs were analyzed with use of flow cytometry (FCM). In addition, the activities to induce CD8+ T cell proliferation, along with displayed cytotoxicity of the CD8+T cells(CTL) by the BMDCs after treatment with MENK were determined with use of FCM as well as MTS. Our results indicated that MENK induced phenotypic and functional maturation of BMDC loaded with RG antigen, as evidenced by higher level of expression of key surface markers and more production of cytokines. Subsequently, the BMDC activated by MENK intensified immune responses mounted by CTL, resulting in stronger antitumor activity. Our results suggest that MENK could be working as an effective immune adjuvant in vaccine preparation for cancer fight and other immune related diseases. We concluded that MENK could be a positive immune modulator in the improved functions of BMDCs loaded with antigen as well as in CD8+T cell mediated anti-tumor responses.

The opioid growth factor-opioid growth factor receptor axis: homeostatic regulator of cell proliferation and its implications for health and disease.

The opioid growth factor (OGF), chemically termed [Met(5)]-enkephalin, is an endogenous opioid peptide that interacts with the OGF receptor (OGFr) to delay the G(1)/S interface of the cell cycle by modulating cyclin-dependent inhibitory kinase (CKI) pathways. The OGF-OGFr axis is a tonically active, inhibitory pathway that is an important regulator during homeostasis and re-epithelialization, and plays a role in the onset and progression of autoimmune diseases and cancer. Modulation of the OGF-OGFr axis can be accomplished by a variety of pharmacological and molecular approaches including use of intermittent or continuous exposure to the opioid antagonist naltrexone, genetic manipulation of OGFr expression, and antibody neutralization of OGF. Clinically, OGF is a biological therapy that has potential application for treatment of cancer. Currently, naltrexone at low dosages is being evaluated for treatment of autoimmune diseases such as Crohn's and multiple sclerosis. High dosages of naltrexone are effective in reversing dry eye and accelerating the repair of corneal abrasions in normal and diabetic rats; these studies are under investigation in the clinical setting. Naltrexone also enhances full-thickness wound closure in animal models of Type 1 or Type 2 diabetes, and translation of this knowledge to the clinic is planned. In summary, understanding the OGF-OGFr axis as a homeostatic regulator of proliferation has substantial implications for maintaining human health and treatment of disease.

Macrophage polarization induced by neuropeptide methionine enkephalin (MENK) promotes tumoricidal responses.

The aim of this study is to investigate macrophages polarization induced by methionine enkephalin (MENK) that promotes tumoricidal responses in vivo and in vitro. Both phenotypic and functional activities of macrophages were assessed by the quantitative analysis of key surface molecules on macrophages with flow cytometry, immunofluorescent staining, and the production of cytokines with enzyme-linked immunosorbent assay and reverse transcriptase-polymerase chain reaction. Our results showed that MENK could down-regulate the expression of CD206 and the production of arginase-1 (the markers of alternatively activated (M2) macrophage) in tumor-associated macrophages in vivo, meanwhile it could significantly up-regulate the expression of CD64, MHC-II, and the production of induced nitric oxide synthase (the markers of classically activated (M1) macrophages). Furthermore, the studies on bone marrow-derived macrophages treated with MENK (10(-12) M) in vitro had demonstrated that MENK could markedly increase tumoricidal activity. MENK could also enhance the release of reactive oxidant species and the production of interleukin-12p40, tumor necrosis factor-α, while decrease the production of interleukin-10. In conclusion, MENK could effectively induce M2 macrophages polarizing to M1 macrophages, sequentially to modulate the Th1 responses of the host immune system. Our results suggest that MENK might have great potential as a new therapeutic agent for cancer.