Opioid growth factor enhances tumor growth inhibition and increases the survival of paclitaxel-treated mice with squamous cell carcinoma of the head and neck

The Opioid Growth Factor in Growth Regulation and Immune Responses in Cancer

It has become apparent that endogenous opioids act not only as neurotransmitters and neuromodulators, but have multiple functions in the body. Activation of the opioid system by opiate drugs is associated with a risk of cancer development through direct stimulation of tumor cell proliferation and through immunosuppression. In contrast, the endogenous peptide opioid [Met5]-enkephalin, now commonly referred to as Opioid Growth Factor (OGF), negatively regulates cell proliferation in a wide number of cells during development, homeostasis, and neoplasia. This action is mediated through the opioid growth factor receptor, originally designated the zeta (ζ) opioid receptor. Further, contrary to the traditional notion of opiates as immunosuppressive, endogenous OGF has been shown to possess a number of positive immunomodulatory properties and may provide a beneficial effect in cancer by augmenting the activity of cells involved in both innate and acquired immunity. Taken together, the evidence supports consideration of opioid peptides such as OGF as new strategies for cancer therapy.

High expression of proenkephalin is associated with favorable outcomes in patients with gastrointestinal stromal tumors

Purpose

The aim of this study was to elucidate the prognostic value of proenkephalin (PENK) in gastrointestinal stromal tumors (GISTs).

Patients and methods

We collected data on 268 eligible postoperative patients diagnosed with GIST between January 1, 2002, and December 31, 2011. PENK expression was detected in GIST tissues classified using the United States National Institutes of Health (NIH) risk classification system. The associations between high PENK expression and the clinicopathological characteristics were assessed. Overall survival (OS) and recurrence-free survival (RFS) were estimated by Kaplan–Meier analysis, and the log-rank test was used to compare the differences between groups. Univariate and multivariate Cox regression analyses were conducted to assess the prognostic value of PENK in GIST patients.

Results

High PENK expression was more common in the low- and intermediate-risk GIST groups compared with the high-risk group (P<0.05). Additionally, PENK expression was associated with tumor size, mitosis count per 50 high-power fields, and tumor rupture (P<0.05). Kaplan–Meier analysis revealed that high PENK expression was associated with superior OS and RFS, while low PENK expression was associated with worse OS and RFS. Furthermore, PENK was shown to be an independent predictor of OS and RFS in the overall population (for OS, hazard ratio [HR], 1.596, 95% confidence interval [CI], 1.006–2.914, P<0.001; for RFS, HR, 1.910, 95% CI, 0.977–3.089, P<0.001).

Conclusion

PENK expression in GIST is closely associated with NIH risk grade and prognosis, indicating that PENK may act as a tumor suppressor and may serve as a new biomarker for predicting prognosis in postoperative GIST patients.

Effect of met-enkephalin on chromosomal aberrations in the lymphocytes of the peripheral blood of patients with multiple sclerosis

Endogenious opiod met-enkephalin throughout previous research manifested cytoprotective and anti-inflammatory effects. Previous research suggests that met-enkephalin has cytogenetic effects. Reducement in the frequency of structural chromosome aberrations as well as a suppressive effect on lymphocyte cell cycle is found. It also reduces apoptosis in the blood samples of the patients with immune-mediated diseases. Met-enkephalin exerts immunomodulatory properties and induces stabilization of the clinical condition in patients with multiple Sclerosis (MS). The goal of the present research was to evaluate met-enkephalin in vitro effects on the number and type of chromosome aberrations in the peripheral blood lymphocytes of patients with MS. Our research detected disappearance of ring chromosomes and chromosome fragmentations in the cultures of the peripheral blood lymphocytes treated with met-enkephalin (1.2 μg/mL). However, this research did not detect any significant effects of met-enkephalin on the reduction of structural chromosome aberrations and disappearance of dicentric chromosomes. Chromosomes with the greatest percent of inclusion in chromosome aberrations were noted as: chromosome 1, chromosome 2 and chromosome 9. Additionally, we confirmed chromosome 14 as the most frequently included in translocations. Furthermore, met-enkephalin effects on the increase of the numerical aberrations in both concentrations applied were detected. Those findings should be interpreted cautiously and more research in this field should be conducted.

Novel treatment for triple-negative breast and ovarian cancer: endogenous opioid suppression of women's cancers

Breast and ovarian cancers are responsible for more than 500,000 female deaths worldwide each year. Fifteen percent of the 230,000 women in the USA diagnosed with breast cancer in 2013 will have triple-negative breast cancer, a disease with few options for treatment, and a twofold greater mortality risk than other breast cancers. The OGF-OGF receptor pathway is present in these cancers, and regulates cell proliferation during homeostasis and disease. OGF is a tonically active peptide that inhibits DNA synthesis by upregulation of cyclin-dependent inhibitory kinases, without disrupting cell migration, differentiation or apoptosis. OGF receptor is a determinant in the proliferation of triple-negative breast cancer and ovarian cancer, and can be genetically modified to alter neoplastic cell replication in vitro and in nude mice. Preclinical studies warrant the use of OGF alone, or in combination, for treatment of triple-negative breast and ovarian cancer patients.

Opioid growth factor - opioid growth factor receptor axis inhibits proliferation of triple negative breast cancer

Triple negative breast cancer (TNBC) represents approximately 15% of the newly diagnosed cancers worldwide and is characterized by tissue lacking in estrogen, progesterone and human epidermal growth factor receptors. TNBC disproportionately affects younger women and women of colour, and new treatments are needed. The opioid growth factor (OGF) - opioid growth factor receptor (OGFr) axis is a determinant of cell proliferation in neoplasia, and OGF is an endogenously produced pentapeptide that inhibits cell replication by interacting with OGFr and upregulating cyclin-dependent inhibitory kinase pathways thus reducing DNA synthesis. In these studies we investigated the presence and function of the OGF-OGFr axis in two human TNBC cell lines, as well as in breast cancer cell lines containing hormonal receptors. TNBC cell lines MDA-MD-231 and BT-20, as well as human breast cancer cells SK-BR-3 and MCF-7, were examined for the presence of pentapeptide and receptors, as well as their response to OGF. Specificity of peptide and receptor was confirmed by antibody neutralization and molecular studies to knockdown classical receptor protein. The requirement for protein transcription and translation and RNA transcription were investigated. Growth of TNBC cells in the presence of OGF and standard of care chemotherapeutic agent paclitaxel was evaluated to determine both efficacy and protective effects against toxicity. OGF treatment inhibited TNBC cells in a dosage related, receptor mediated, and reversible manner. OGF was the specific endogenous opioid to inhibit cell proliferation, and this was mediated by p21 cyclin dependent inhibitory kinase pathways, and required protein and RNA synthesis. OGFr was the specific receptor involved; both peptide and receptor were detected in all four cell lines. OGF treatment inhibited growth of all cancer cell lines evaluated, and reduced cell death in cultures exposed to paclitaxel. The OGF-OGFr axis is present and functioning in TNBC cell lines, and provides a novel biological pathway as potential therapy.

Targeting the opioid growth factor: Opioid growth factor receptor axis for treatment of human ovarian cancer

The opioid growth factor (OGF) – opioid growth factor receptor (OGFr) axis is a biological pathway that is present in human ovarian cancer cells and tissues. OGF, chemically termed [Met5]-enkephalin, is an endogenous opioid peptide that interfaces with OGFr to delay cells moving through the cell cycle by upregulation of cyclin-dependent inhibitory kinase pathways. OGF inhibitory activity is dose dependent, receptor mediated, reversible, protein and RNA dependent, but not related to apoptosis or necrosis. The OGF-OGFr axis can be targeted for treatment of human ovarian cancer by (i) administration of exogenous OGF, (ii) genetic manipulation to over-express OGFr and (iii) use of low dosages of naltrexone, an opioid antagonist, which stimulates production of OGF and OGFr for subsequent interaction following blockade of the receptor. The OGF-OGFr axis may be a feasible target for treatment of cancer of the ovary (i) in a prophylactic fashion, (ii) following cytoreduction or (iii) in conjunction with standard chemotherapy for additive effectiveness. In summary, preclinical data support the transition of these novel therapies for treatment of human ovarian cancer from the bench to bedside to provide additional targets for treatment of this devastating disease.

Synergistic effect of methionine encephalin (MENK) combined with pidotimod(PTD) on the maturation of murine dendritic cells (DCs)

To gain new insight into the functional interaction between dendritic cells and methionine encephalin (MENK) combined with pidotimod (PTD), we have analyzed the effect of MENK plus PTD on the morphology, phenotype and functions of murine bone-marrow derived dendritic cells (BMDCs) in vitro. The maturation of BMDCs cultured in the presence of either MENK or PTD alone, or MENK in combination with PTD, was detected. The cell proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxy-methoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt/phenazinemethosulphate (MTS/PMS). The changes of BMDCs morphology were confirmed with light microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The BMDCs treated with MENK combined with PTD displayed a higher expression of typical maturation markers of CD40, CD80, CD83, CD86 and MHC-IIidentified by fluorescence activated cell sorting (FACS), and stronger ability to drive T cells. The decrease of the endocytic ability was assayed by DAB kit, FITC-dextran and cellular immunohistochemistry. Finally upregulation of cytokines production of IL-12 and TNF-α was determined by ELISA. These data indicate that MENK combined with PTD could exert synergistic action on BMDC maturation.

Low-dose naltrexone suppresses ovarian cancer and exhibits enhanced inhibition in combination with cisplatin

Ovarian cancer is the leading cause of death from gynecological malignancies. Although initial therapeutic modalities are successful, 65% of these women relapse with only palliative treatments available thereafter. Endogenous opioids repress the proliferation of human ovarian cancer cells in vitro, and do so in a receptor-mediated manner. The present study examined whether modulation of opioid systems by the opioid antagonist naltrexone (NTX), alone or in combination with standard of care therapies (taxol/paclitaxel, cisplatin), alters human ovarian cancer cell proliferation in tissue culture and tumor progression in mice. Administration of NTX for six hours every two days, but not continuously, reduced DNA synthesis and cell replication from vehicle-treated controls in tissue culture. Moreover, brief exposure to NTX in combination with taxol or cisplatin had an enhanced anticancer action. Mice with established ovarian tumors and treated with a low dosage of NTX (LDN), which invokes a short period of opioid receptor blockade, repressed tumor progression in a non-toxic fashion by reducing DNA synthesis and angiogenesis but not altering cell survival. The combination of LDN with cisplatin, but not taxol, resulted in an additive inhibitory effect on tumorigenesis with enhanced depression of DNA synthesis and angiogenesis. LDN combined with cisplatin alleviated the toxicity (e.g. weight loss) associated with cisplatin. LDN treatment upregulated the expression of the opioid growth factor (OGF, chemical term ([Met5]-enkephalin) and its receptor, OGFr. Previous tissue culture studies have reported that OGF is the only opioid peptide with antiproliferative activity on ovarian cancer cells, with OGF action mediated by OGFr. Thus, the common denominator of intermittent opioid receptor blockade by short-term NTX or LDN on ovarian cancer proliferation and tumorigenesis recorded herein appears to be related to the OGF–OGFr axis. These preclinical data may offer a non-toxic and efficacious pathway-related treatment that can benefit patients with ovarian cancer.

Spinal activation of delta opioid receptors alleviates cancer-related bone pain

Over the past few years, significant progress has been made in cancer therapy. Indeed, the lifespan of cancer patients has significantly increased. Although patients live longer, cancer-related pain remains a daily problem affecting their quality of life, especially when metastases reach the bone. In patients coping with cancer-induced bone pain, morphine and NSAIDs, often used in combination with other medications, are the most commonly used drugs to alleviate pain. However, these drugs have dose-limiting side effects. Morphine and other routinely used opioids are mu opioid receptor (MOPR) agonists. The MOPR is responsible for most opioid-related adverse effects. In the present study, we revealed potent analgesic effects of an intrathecally-administered selective delta opioid receptor (DOPR) agonist, deltorphin II, in a recently developed rat bone cancer model. Indeed, we found that deltorphin II dose-dependently reversed mechanical allodynia 14 days post-surgery in this cancer pain model, which is based on the implantation of mammary MRMT-1 cells in the femur. This effect was DOPR-mediated as it was completely blocked by naltrindole, a selective DOPR antagonist. Using the complete Freund's adjuvant model of inflammatory pain, we further demonstrated that deltorphin II was equipotent at alleviating inflammatory and cancer pain (i.e. similar ED50 values). Altogether, the present results show, for the first time, that activation of spinal DOPRs causes significant analgesia at doses sufficient to reduce inflammatory pain in a rat bone cancer pain model. Our results further suggest that DOPR represents a potential target for the development of novel analgesic therapies to be used in the treatment of cancer-related pain.

The opioid growth factor (OGF) and low dose naltrexone (LDN) suppress human ovarian cancer progression in mice

OBJECTIVE

The opioid growth factor (OGF) and its receptor, OGFr, serve as a tonically active inhibitory axis regulating cell proliferation in normal cells and a variety of cancers, including human ovarian cancer. Blockade of OGF and OGFr with the nonselective opioid receptor antagonist naltrexone (NTX) upregulates expression of OGF and OGFr. Administration of a low dosage of NTX (LDN) blocks endogenous opioids from opioid receptors for a short period of time (4-6 h) each day, providing a window of 18-20 h for the upregulated opioids and receptors to interact. The present study investigated the repercussions of upregulating the OGF-OGFr axis by treatment with OGF or LDN on human ovarian tumorigenesis in vivo.

METHODS

Female nude mice were transplanted intraperitoneally with SKOV-3 human ovarian cancer cells and treated on a daily basis with OGF (10 mg/kg), LDN (0.1 mg/kg), or an equivalent volume of vehicle (saline). Tumor burden, as well as DNA synthesis, apoptosis, and angiogenesis was assessed in tumor tissue following 40 days of treatment.

RESULTS

OGF and LDN markedly reduced ovarian tumor burden (tumor nodule number and weight). The mechanism of action was targeted to an inhibition of tumor cell proliferation and angiogenesis; no changes in cell survival were noted.

CONCLUSIONS

This study shows that a native opioid pathway can suppress human ovarian cancer in a xenograft model, and provides novel non-toxic therapies for the treatment of this lethal neoplasia.

Regulation of cell proliferation by the opioid growth factor receptor is dependent on karyopherin β and Ran for nucleocytoplasmic trafficking

The opioid growth factor (OGF; [Met5]-enkephalin) and the OGF receptor (OGFr) form an endogenous and tonically active growth-regulating system that modulates cell proliferation by upregulating the cyclin-dependent kinase inhibitory pathway. Previous reports have documented that nucleocytoplasmic trafficking of the OGF–OGFr axis is dependent on nuclear localization signals. This study determined the specific transport factors required for the import of the OGF–OGFr complex from the cytoplasm to the nucleus using a probe of full-length OGFr fused to enhanced green fluorescent protein (eGFP) and knockdown of karyopherin α1, α2, α3, α4 or α6, karyopherin β1 or Ran with small interfering RNA (siRNA). A human squamous cell carcinoma of the head and neck cell line (squamous cell carcinoma-1, SCC-1) that was downregulated for karyopherin β1 or Ran did not have transport of OGFr-eGFP into the nucleus. Moreover, there was an increase of 44% in bromodeoxyuridine (BrdU)-labeled cells in cultures of SCC-1 that were transfected with siRNAs to karyopherin β1 or Ran compared with cells transfected with scrambled siRNA. No alteration in distribution of OGFr-eGFP or BrdU labeling indexes was recorded in cultures treated with siRNAs to karyopherin α1, α2, α3, α4 or α6. These results indicate that the regulation of cell proliferation by the OGF–OGFr axis is dependent on nucleocytoplasmic transport by karyopherin β1 as well as the gradient of RanGTP/RanGDP across the nuclear envelope, but is not reliant on adaptor molecules related to karyopherin α. Thus, the passage of the OGF–OGFr complex has controlled entry from the cytoplasm to the nucleus, and the timely and faithful translocation of this cargo across the nuclear envelope is critical to cell proliferation. These hierarchical levels of nuclear import provide multiple pathways for the subtle regulation of OGF–OGFr as it relates to the control of cell proliferative events.

Opioid growth factor-opioid growth factor receptor axis is a physiological determinant of cell proliferation in diverse human cancers

The opioid growth factor (OGF) regulates cell proliferation of human cancer cells through the cyclin-dependent kinase inhibitory pathway, with mediation of this action by the OGF receptor (OGFr). The ubiquity of the OGF-OGFr axis in human cancer is unknown. We used 31 human cancer cell lines, representative of more than 90% of neoplasias occurring in humans, and found that OGF and OGFr were detected in the cytoplasm and nucleus by immunohistochemistry. The addition of OGF to cultures depressed cell number up to 41%, whereas naltrexone (NTX) increased cell proliferation by up to 44%, a total of 85% in the modulating capacity for the OGF-OGFr axis. Neutralization of OGF by specific antibodies led to a marked increase in cell number. Knockdown of OGFr by OGFr-siRNA resulted in a significant increase in the number of cells, even in the face of the addition of exogenous OGF. The cultures to which NTX was added and subjected to OGFr-siRNA were similar to those with OGF-siRNA alone. The OGF-OGFr axis, a physiological determinant of cell-proliferative activity, is a ubiquitous feature of human cancer cells. The identification of this native biological system in neoplasia may be important in understanding the pathophysiology of neoplasia, and in designing treatment modalities that utilize the body's own chemistry.

Evaluation of a novel aminopeptidase N inhibitor, in vitro, using two assay systems

The activities of the novel aminopeptidase N inhibitor (APNI), beta-Amino-alpha-Hydroxyl-Phenyl butanic acid-Valine (AHPA-Val), were compared with APNI (amastatin). AHPA-Val and amastatin produced competitive inhibition of the hydrolysis of Tyr-Gly in the guinea-pig striatal membrane preparation, with K(i) equal to 14.06 microM and 12.48 microM respectively. Met-enkephalin-induced twitch inhibition of the guinea-pig ileum preparation was enhanced by AHPA-Val and amastatin with pA(1/2) values (the negative logarithm concentration of APNI that decreased the IC(50) of Met-enkephalin by half), of 7.08 and 7.79 respectively. These results suggest that AHPA-Val has good activity as an APNI and that these two assay systems are useful for evaluating the potency of novel APNIs.

The opioid growth factor (OGF)-OGF receptor axis uses the p16 pathway to inhibit head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) represents 5.5% of malignancies worldwide, with approximately 30,000 new cases and approximately 11,000 deaths reported in the United States annually. The opioid growth factor (OGF; [Met(5)]-enkephalin) and the OGF receptor (OGFr) form an endogenous growth regulating system; the OGF-OGFr axis influences the G(0)-G(1) phase of the cell cycle in HNSCC. Cells treated with small interfering RNA (siRNA) for OGFr no longer responded to the growth inhibitory effects of OGF or the growth stimulatory effects of naltrexone, indicating that these activities are entirely mediated by OGFr. In this investigation, we examined the precise target of OGF in the cell cycle. Using SCC-1 cells, OGF decreased the phosphorylation of retinoblastoma protein. This change was correlated with reduced Cdk4, but not Cdk2, kinase activity. OGF treatment increased cyclin-dependent kinase inhibitor p16 protein expression. Importantly, p16 complexed with Cdk4 was increased by OGF treatment at all time points, consistent with the hypothesis that OGF mediated growth inhibition through p16. Blockade of OGF-OGFr interactions with naloxone abolished the increased expression of p16 protein by OGF. Inhibition of p16 (INK4a) activation by p16-specific siRNA blocked OGF's repressive action on proliferation of SCC-1, CAL-27, and SCC-4 HNSCC cells. These data are the first to reveal that the target of cell proliferative inhibitory action of OGF in human HNSCC is a cyclin-dependent kinase inhibitory pathway, and this may be useful in the diagnosis and treatment of HNSCC.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

Enhanced growth inhibition of squamous cell carcinoma of the head and neck by combination therapy of fusaric acid and paclitaxel or carboplatin

Combination of a single dose of paclitaxel with three different dosages of FA resulted in significant (P<0.001) reductions in cell number from controls, paclitaxel alone, and FA treatments alone at four different time points. Combination of a single dose of carboplatin with three different dosages of FA resulted in significant (P<0.001) reductions in cell number from controls and carboplatin treatment alone at 72 and 96 h. Our data suggest that these combinations may provide an enhanced anti-tumor effect with respect to HNSCC. Since, FA can be administered orally, this regimen may introduce a paradigm change in chemotherapy for HNSCC.

Combination chemotherapy with gemcitabine and biotherapy with opioid growth factor (OGF) enhances the growth inhibition of pancreatic adenocarcinoma

Gemcitabine is the standard of care for advanced pancreatic neoplasia, and exerts its effect through inhibition of DNA synthesis. However, gemcitabine has limited survival benefits. Opioid growth factor (OGF) is an autocrine-produced peptide that interacts with the nuclear receptor, OGFr, to inhibit cell proliferation but is not cytotoxic or apoptotic. The present study was designed to examine whether a combination of chemotherapy with gemcitabine and biotherapy with OGF is more effective than either agent alone in inhibiting pancreatic cancer growth in vitro and in vivo. The combination of OGF (10(-6) M) and gemcitabine (10(-8) M) reduced MIA PaCa-2 cell number from control levels by 46% within 48 h, and resulted in a growth inhibition greater than that of the individual compounds. OGF in combination with 5-fluorouracil also depressed cell growth more than either agent alone. The action of OGF, but not gemcitabine, was mediated by a naloxone-sensitive receptor, and was completely reversible. OGF, but no other endogenous or exogenous opioids, altered pancreatic cancer growth in tissue culture. The combination of OGF and gemcitabine also repressed the growth of another pancreatic cancer cell line, PANC-1. MIA PaCa-2 cells transplanted into athymic mice received 10 mg/kg OGF daily, 120 mg/kg gemcitabine every 3 days; 10 mg/kg OGF daily and 120 mg/kg gemcitabine every 3rd day, or 0.1 ml of sterile saline daily. Tumor incidence, and latency times to tumor appearance, of mice receiving combined therapy with OGF and gemcitabine, were significantly decreased from those of the control, OGF, and gemcitabine groups. Tumor volumes in the OGF, gemcitabine, and OGF/gemcitabine groups were markedly decreased from controls beginning on days 14, 12, and 8, respectively, after tumor cell inoculation. Tumor weight and tumor volume were reduced from control levels by 36-85% in the OGF and/or gemcitabine groups on day 45 (date of termination), and the group of mice exposed to a combination of OGF and gemcitabine had decreases in tumor size of 70% and 63% from the OGF or the gemcitabine alone groups, respectively. This preclinical evidence shows that combined chemotherapy (e.g. gemcitabine) and biotherapy (OGF) provides an enhanced therapeutic benefit for pancreatic cancer.