Modulation of human neuroblastoma transplanted into nude mice by endogenous opioid systems

Preclinical and clinical studies into the bioactivity of low-dose naltrexone (LDN) for oncotherapy

Naltrexone (NTX) is a nonspecific opioid antagonist that exerts pharmacological effects on the opioid axis by blocking opioid receptors distributed in cytoplastic and nuclear regions. NTX has been used in opioid use disorder (OUD), immune-associated diseases, alcoholism, obesity, and chronic pain for decades. However, low-dose naltrexone (LDN) also exhibits remarkable inhibition of DNA synthesis, viability, and other functions in numerous cancers and is involved in immune remodeling against tumor invasion and chemical toxicity. The potential anticancer activity of LDN is a focus of basic research. Herein, we summarize the associated studies on LDN oncotherapy to highlight the potential mechanisms and prospective clinical applications.

Naltrexone's Impact on Cancer Progression and Mortality: A Systematic Review of Studies in Humans, Animal Models, and Cell Cultures

BACKGROUND

Naltrexone (NTX) is an opioid antagonist traditionally used as a treatment for alcohol and opioid use disorders, but various studies have documented its involvement in cancer progression, exploring possible anticancer potential, when administered at high doses or as low dose naltrexone (LDN). Herein we present a systematic review of cancer-related outcomes from case reports, clinical trials, and retrospective and prospective studies conducted using cell cultures, animal models, and human subjects receiving NTX/LDN.

METHODS

A systematic search of NTX in cancer therapy was conducted. Outcomes including tumor size and number, latency to tumor development, survival duration, progression of disease, and scan results were assessed in clinical and animal studies, and cell number was used as the outcome measure of culture studies.

RESULTS

Several case reports demonstrate notable survival durations and metastatic resolutions in patients with late stage cancer when administered an average LDN dose of 3-5 mg/day. Animal and cell culture studies suggest an overarching principle of NTX involvement in cancer pharmacophysiology, suggesting that high doses and continuous administration can foster cancer progression, whereas low doses and intermittent treatment may hinder cell proliferation, impede tumorigenesis, and have potential anticancer efficacy.

CONCLUSION

This review emphasizes the value of potential future research on NTX in cancer therapy, and warrants need for a better understanding of underlying mechanisms. Future controlled studies with more robust sample sizes, particularly in humans, are needed to fully elucidate its potential in cancer therapy.

Killing effect of methionine enkephalin on melanoma in vivo and in vitro

Melanoma is a common cutaneous malignancy, that is also found in specific mucosal sites, and is associated with a poor prognosis. The aim of the present study was to investigate the cytotoxicity of methionine enkephalin (MENK) for B16 melanoma cells in vivo and in vitro. The results of the present study allowed our conclusion that MENK regulates the proliferation of B16 cells, causing cell cycle arrest in the G0/G1 phase and a decrease in the percentage of cells in the S and G2/M phases. Reverse transcription-quantitative polymerase chain reaction demonstrated that MENK increased opioid receptor expression in the B16 cells. Furthermore, the tumor volume and weight in the MENK-treated group were lower than those in the control group (NS) and MENK and naltrexone (NTX)-treated groups. MENK exerted both significant antitumor activity on the growth of B16 cells and a longer survival time in mice. The mice treated with MENK exhibited an increased ratio of CD4⁺ to CD8⁺ T cells as tested by flow cytometry (FCM), resulting in a ratio of 2.03 in the control group, 3.69 in the MENK-treated group, and 2.65 in the MENK and NTX group. Furthermore, a significant increase in plasma levels of IL-2, IFN-γ and TNF-α was revealed as assessed by ELISA. In conclusion, the results of the present study indicate that MENK has a cytotoxic effect on B16 melanoma cells in vitro and in vivo, and suggest a potential mechanism for these bioactivities. Therefore, we posit that MENK should be investigated, not only as a primary therapy for melanoma, but also as an adjuvant therapy in combination with chemotherapies.

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.

Under-expression of the opioid growth factor receptor promotes progression of human ovarian cancer

The opioid growth factor (OGF) and its receptor, OGFr, serve as a tonically active inhibitory axis regulating the proliferation of human ovarian cancer cells. In the present study, we have investigated the repercussion on the progression of this deadly neoplasia when cells are engineered to molecularly under-express OGFr. shRNA constructs were used to knockdown OGFr in SKOV-3 cells; two clonal cell lines were examined. OGFr protein expression was decreased up to 73% in clones compared with wild-type (WT) and empty vector (EV) controls. OGFr-binding assays of clones revealed 50–55% decreases in binding capacity compared with control cells; binding affinity was comparable in all groups. Cell number in clones was increased 33–132%, and doubling times decreased 29–35%, compared with WT and EV cultures. Addition of exogenous OGF or naltrexone did not affect cell number in cultures with silenced OGFr. DNA synthesis of clonal cell lines was increased 136–146% from the WT and EV groups; no changes were noted in cell survival. Nude mice injected subcutaneously with cells under-expressing OGFr had an increased tumor incidence, decreased latency to tumor formation, increased tumor volume and decreased OGFr expression in tumors compared with WT and EV controls. OGF treatment in mice with WT or EV tumors, but not OGFr under-expressing tumors, inhibited tumor volume and weight. Collectively, these data demonstrate the critical nature of the OGF–OGFr axis as a determinant of the progression of human ovarian cancer, and suggest that attenuation of this system has an important bearing on the survival of these patients.

Low-dose naltrexone targets the opioid growth factor-opioid growth factor receptor pathway to inhibit cell proliferation: mechanistic evidence from a tissue culture model

Naltrexone (NTX) is an opioid antagonist that inhibits or accelerates cell proliferation in vivo when utilized in a low (LDN) or high (HDN) dose, respectively. The mechanism of opioid antagonist action on growth is not well understood. We established a tissue culture model of LDN and HDN using short-term and continuous opioid receptor blockade, respectively, in human ovarian cancer cells, and found that the duration of opioid receptor blockade determines cell proliferative response. The alteration of growth by NTX also was detected in cells representative of pancreatic, colorectal and squamous cell carcinomas. The opioid growth factor (OGF; [Met(5)]-enkephalin) and its receptor (OGFr) were responsible for mediating the action of NTX on cell proliferation. NTX upregulated OGF and OGFr at the translational but not at the transcriptional level. The mechanism of inhibition by short-term NTX required p16 and/or p21 cyclin-dependent inhibitory kinases, but was not dependent on cell survival (necrosis, apoptosis). Sequential administration of short-term NTX and OGF had a greater inhibitory effect on cell proliferation than either agent alone. Given the parallels between short-term NTX in vitro and LDN in vivo, we now demonstrate at the molecular level that the OGF-OGFr axis is a common pathway that is essential for the regulation of cell proliferation by NTX.

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.

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.

Opioid growth factor modulation of corneal epithelium: uppers and downers

PURPOSE

This paper presents a concise review of the role of the intrinsic opioid growth regulation system (IOGRS) in homeostasis and wound repair of the corneal epithelium.

METHODS

The article is a summary of published research on the topic.

RESULTS

The native opioid peptide, [Met(5)]-enkephalin, also termed opioid growth factor (OGF), has been demonstrated to be present in a wide variety of classes of the phylum. Chordata, and acts as an autocrine/paracrine produced, tonically active, receptor specific, negative growth modulating factor in homeostatic (uninjured) corneal epithelium in humans and non-primates. Similarly, OGF acts to down-regulate epithelial cell division and migration of corneal epithelium in the closing of corneal epithelial abrasions. Such repair can be up-regulated (hastened) in non-diabetic animals by treatment with exogenous administration of the potent opioid antagonist, naltrexone (NTX). The system also is functional in diabetic animals and can be manipulated to restore epithelial wound healing rates to normal.

CONCLUSIONS

The IOGRS plays a vital role in supporting corneal epithelial homeostasis, and in modulating closure of epithelial wounds. The system should provide opportunities for novel therapies especially for corneal epithelial wound healing disorders.

The effects of morphine on cell proliferation

There is increasing evidence that endogenous opioid peptides ("enkephalins") and other neurotransmitters have widespread, receptor-mediated roles as growth regulators in non-neuronal cells and tissues. For example, it is now believed that enkephalins produced in placental trophoblast giant cells have multiple roles in supporting embryo growth, and in maternal adaptation to pregnancy. Since plant and synthetic narcotics (e.g., morphine) bind to the same receptors, the questions immediately arise: Do narcotics also have actions as growth regulators? If so, do these actions have physiological significance in addicts? Recent work on the first of these questions is covered in this review. While the greatest volume of research has been focused on the proliferative effects of narcotics for cells of the immune system, the roles of opioid peptides and narcotics on the growth of a variety of other cells has come under study recently.

Cloning, sequencing, chromosomal location, and function of cDNAs encoding an opioid growth factor receptor (OGFr) in humans

The native opioid growth factor (OGF), [Met(5)]-enkephalin, is a tonic inhibitory peptide that modulates cell proliferation and tissue organization during development, cancer, cellular renewal, wound healing, and angiogenesis. OGF action is mediated by a receptor mechanism. We have cloned and sequenced cDNAs encoding multiple spliced forms of a human OGF receptor. The open reading frame in the longest cDNA was found to encode a protein of 697 amino acids, and 8 imperfect repeats of 20 amino acids each were a prominent feature. Altogether, five alternatively spliced forms were observed. The cDNA hybridized to mRNA from a variety of normal and neoplastic cells and tissues. Functional studies using antisense oligonucleotides to OGFr demonstrated an enhancement in cell growth. Fluorescent in situ hybridization (FISH) experiments showed the chromosomal location to be 20q13.3. This OGF receptor has no homology to classical opioid receptors. These results provide molecular validity for the interaction of OGF and OGF receptor in the regulation of growth processes in humans.

In vivo effects of chronic treatment with [MET5]-enkephalin on hematological values and natural killer cell activity in athymic mice

The role of endogenous opioids in immunological mechanisms was examined by subjecting athymic (nu/nu) mice to chronic injections of the opioid agonist [Met5]-enkephalin (MET) or continuous opioid receptor blockade with naltrexone (NTX). After 8 days of treatment, neither excess peptide nor deprivation of opioids from receptors had any effect on body weight, spleen index (spleen to body weight ratio), total and differential white blood cell counts, and natural killer (NK) cell activity in peripheral blood or splenic lymphocytes. At 28 days, chronic treatment with MET or NTX had no effect on any of these parameters with the exception of an elevation from controls in NK cell activity in peripheral blood in mice receiving NTX, and subnormal NK cell activity related to splenic lymphocytes in the MET group. These results suggest that chronic exposure to an opioid agonist, or persistent opioid receptor blockade, have little influence on a variety of immunological properties in athymic mice, suggesting that native opioids such as MET do not play a marked role in defense mechanisms in the athymic mouse.

Haloperidol increases spreading and nitric oxide production in macrophages from tumor-bearing mice: a possible mechanism for its antitumoral effect

Subcutaneous treatment with haloperidol (2.0 mg/kg) was found to increase both the percent of macrophage spreading and nitric oxide (NO) release in peritoneal macrophage from animals inoculated intraperitoneally with 5.0 x 10(6) Ehrlich ascites cells. This haloperidol-induced macrophage activation seems to be involved in its antitumoral effect since cotreatment with the iNOS inhibitor aminoguanidine was able to reverse the inhibitory effect of haloperidol on the development of the Ehrlich solid carcinoma.

Binding of enterostatin to the human neuroepithelioma cell line SK-N-MC

SK-N-MC cells were found to possess binding sites for enterostatin, a peptide with central effects on appetite and sympathetic activation of brown adipose tissue during high-fat feeding. Scatchard analyses of the binding indicated one high-affinity binding (Kd = 0.5-1.5 nM) and one low-affinity binding (Kd = 15-30 nM) for 3H-enterostatin (APGPR). 125I-YGGAPGPR showed similar binding parameters as for the low affinity binding of 3H-APGPR. Met-enkephalin and beta3-casomorphin1-5 were found to displace the binding of 3H-APGPR to the SK-N-MC cells. Affinity purification of solubilized cells revealed an APGPR-binding protein estimated to 53 kDa which may represent a distinct enterostatin receptor. Cross-linking of 125I-YGGAPGPR to intact cells labeled one major protein with the same molecular size. There was no binding of enterostatin to four other human neuroblastoma/neuroepithelioma cell lines, named IMR-92, LAN#5, NB-1 #14 and SH5-SY.

Hormone-defined cell system for studying G-protein coupled receptor agonist-activated growth modulation: delta-opioid and serotonin-5HT2C receptor activation show opposite mitogenic effects

G-protein-coupled receptor (GPCR) agonist-activated transformation of NIH/3T3 fibroblast cells has been documented by many workers. Our present interest is in the growth control exerted by these agonists. The mechanisms involved in GPCR agonist-activated growth regulation are not known and investigations using existing cell lines are complicated by the endogenous expression of numerous different GPCRs as well as by the fact that these cell lines are cultured in serum that contains naturally occurring agonists for these receptors. To study the agonist induced growth response of cells transfected with either delta-opioid or serotonin-5HT2C neurotransmitter receptor genes, we have developed new clonal cell lines derived from NIH/3T3 mouse fibroblast cells. These new cell lines, designated with the suffix 3T3DA, can be cultured stably in serum-free, hormone-defined medium: insulin is the only exogenous growth factor added to the culture medium of proliferating 3T3DA cell lines, and their proliferation can be stopped and started by the respective removal or addition of insulin. Micromolar concentrations of agonists were used to activate the corresponding opioid and serotonin receptors over periods extending to 6 days. We observed distinct patterns of GPCR-specific, agonist-activated growth regulation in serum-free cultures, but not in serum-supplemented cultures. At concentrations > 10 microM, morphine inhibits growth of delta-opioid receptor-expressing cells by 40% with respect to normal 3T3DA cells. Opioid agonist induced inhibition of cyclic AMP (cAMP) production as well as growth down-regulation are pertussis toxin sensitive indicating that the exogenously expressed delta-opioid receptors demonstrate classical opioid receptor signaling. The presence of 1 microM serotonin stimulates growth of serotonin-5HT2C receptor- expressing cells by approximately 100% with respect to normal 3T3DA cells. Neither the untreated nor the agonist-treated cells form colonies in soft agar, indicating that they retain anchorage-dependent growth control. These cell lines provide a simple system that could be used as a tool for probing the complex molecular mechanisms associated with GPCR agonist-activated growth control.

Opioid growth factor (OGF) inhibits human pancreatic cancer transplanted into nude mice

Nude mice inoculated with human pancreatic cancer (BxPC-3) cells and receiving 5 mg/kg of opioid growth factor ([Met5]enkephalin; OGF) three times daily exhibited a marked retardation in tumorigenicity compared to animals injected with sterile water (controls). OGF-treated animals had a delay of 43% in initial tumor appearance compared to control subjects (10.6 days). At the time when all of the control mice had tumors, 62% of the mice in the OGF group had no signs of neoplasia. Tumor tissue excised from mice after 30 days was assayed for levels of [Met5]enkephalin and zeta opioid receptors. Tumor tissue levels of [Met5]enkephalin were 24-fold greater in OGF-treated mice than controls, but plasma levels of OGF were 8.6-fold lower in animals receiving OGF. Specific and saturable binding of radiolabeled [Met5]enkephalin to nuclear homogenates of pancreatic tumor tissue was recorded, with a binding affinity (Kd) of 10 nM and a binding capacity (Bmax) of 46.8 fmol/mg protein. Binding capacity, but not affinity, of [3H-Met5]enkephalin was reduced by 58% of control levels in tumor tissue from mice of the OGF group. OGF and the zeta (zeta) opioid receptor were detected in human pancreatic tumor cells by immuno-cytochemistry. These results demonstrate that an endogenous opioid and its receptor are present in human pancreatic cancer, and act as a negative regulator of tumorigenesis in vivo.

Retinoids and the control of growth/death decisions in human neuroblastoma cell lines

Cell proliferation, the balance between mitosis and apoptosis is the result of the continuous integration of a number of different signal transduction pathways stimulated in a cell at any given point in its life. Neuroblastoma cells regulate the switch between mitosis and death, according both to intrinsic factors and extrinsic factors, such as growth factor withdrawal and action of the vitamin A derivative, retinoic acid. In this review, we describe the balance of some factors regulating growth and death of human neuroblastoma cells in vitro. These dynamic studies are necessarily-performed on cell lines, which offer controlled conditions enabling the disection of the complex stimuli mediating survival and growth (IGF, trk, BDNF) and death (transglutaminase, free radicals, Bcl-2). Although the conclusions drawn may therefore not be directly applicable to tumour cells in vivo, the results herein discussed are of sufficient significance to warrant in vivo relevance.

Effect of haloperidol on the development of the solid Ehrlich tumor in mice

We determined the effect of 13 days of treatment with 2.0 mg/kg haloperidol (s.c) on the development of the Ehrlich solid carcinoma, after inoculation of 1.5 x 10(6) Ehrlich ascites tumor cells into the left footpad of mice. The footpad thickness of haloperidol treated animals was significantly smaller than control from day two after tumor inoculation, to the end of the experiment. Histopathological examination showed that haloperidol treated mice apparently presented less necrotic areas within the tumor mass as well as less invasion of subepithelial connective tissue and other adjacent structures. In particular, in comparison with the control group, no nerve bundles were invaded by neoplastic cells in experimental mice. The possible mechanism underlying these results is discussed in light of the specific pharmacological properties of this neuroleptics drug.

Inhibition of human colon cancer by intermittent opioid receptor blockade with naltrexone

Nude mice inoculated with human colon cancer (HT-29) and receiving 0.1 mg/kg naltrexone (NTX) beginning immediately after tumor cell injection exhibited a marked retardation in tumorigenicity. This dosage of NTX, which blocked opioid receptors for 6-8 h/day, resulted in a delay of 2.4-fold in tumor appearance compared to control subjects. At the time (10 days) when all control mice had tumors, 80% of the mice in the 0.1 mg/kg NTX group had no signs of neoplasia. Binding capacity, but not affinity, of [3H][Met5]-enkephalin was reduced 85% of control levels in tumor tissue from mice of the 0.1 NTX group. Plasma, but not tumor tissue levels of [Met5]-enkephalin were elevated (2.5-fold) in contrast to control values. These results suggest that daily intermittent opioid receptor blockade with NTX provokes the interaction of opioids and receptors in the interval following drug availability, with opioids serving to inhibit tumorigenicity of human colon cancer.

Co-localization of mu and delta opioid receptors on SK-N-SH cells detected by fluorescence microscopy using labeled anti-idiotypic antibodies

Selective fluorescence labeling of opioid receptor subclasses on SK-N-SH cultured cells has been accomplished using labeled polyclonal anti-idiotypic antibodies along with subclass-selective opioid agonists (DPDPE, delta-selective; DAMGO, mu-selective) as blocking reagents. Labeling of the cells was examined using conventional fluorescence microscopy. Co-localization of mu- and delta-opioid receptors on SK-N-SH cells has been studied by double labeling fluorescence experiments. In agreement with our own, and other workers', previous observations on NG108-15 cells, a subpopulation of viable cells in asynchronous cultures are labeled. Among those SK-N-SH cells that are labeled, both subclasses of receptors are seen. On the basis of sequential blocking experiments we interpret our combined results to be consistent with a model where mu- and delta- binding sites reside on different subunits of a multimeric complex.

The effect of chronic treatment with naltrindole, a selective delta-opioid antagonist, on mu-opioid receptor-mediated antinociception in diabetic mice

The effects of chronic treatment with naltrindole (NTI), a selective delta-opioid receptor antagonist, on the antinociceptive effects of mu-opioid agonists, such as morphine and [D-Ala2, N-MePhe4, Gly-ol(5)]enkephalin (DAMGO) were examined in diabetic mice. Antinociception induced by morphine (10 micrograms, ICV) and DAMGO (0.5 microgram, ICV) was significantly lower in diabetic mice than in non-diabetic mice. The low sensitivities to the antinociceptive potencies of ICV morphine (10 micrograms) and DAMGO (0.5 micrograms) in diabetic mice were reversed compared with those in saline-treated non-diabetic mice when diabetic mice had been pretreated with NTI (2 mg/kg per day, SC) for 14 days. Naive mice which had been injected with spleen mononuclear cells from saline-treated diabetic mice were less sensitive to DAMGO-induced antinociception. However, adoptive transfer of spleen mononuclear cells from NTI-treated diabetic mice to naive mice had no effect on the recipients' antinociceptive sensitivity to DAMGO. These results suggest that the effect of NTI on the sensitivity to mu-opioid agonists in diabetic mice may be due to the immunosuppressive effects of NTI.

Interleukin-6 and corticotrophin-releasing hormone mRNA are modulated during differentiation of human neuroblastoma cells

Two cell clones [BE(2)-C and BE(2)-M17] derived from the human neuroblastoma cell line SK-N-BE(2) express corticotrophin-releasing hormone as well as interleukin-6 mRNA. Both genes are overexpressed, although with a different time course, following exposure to 5 microM retinoic acid, in parallel to the induction of neuroblastic differentiation. On the contrary, we are unable to detect interleukin-1 beta mRNA in these cell lines. Both cytokines are known to increase hypothalamic CRH mRNA. The production of cytokines and neuropeptides by neuroblastoma cells indicate a complex dialogue between tumour cells and anti-tumour immunity.

Isolation of a growth and mitosis inhibitory peptide from mouse liver

The isolation of a liver peptide that inhibits the growth, mitosis rate and thymidine incorporation in regenerating liver is described. The peptide has the structure Pyroglu-gln-gly-ser-asn, and the deamidated forms are also active. The peptide probably belongs to a class of growth inhibitors with a high degree of tissue specificity. Two such peptides have previously been isolated from the epidermis (Reichelt et al. 1987) and from colonic tissue (Skraastad et al. 1987).

Adult and developing human cerebella exhibit different profiles of opioid binding sites

The binding of [3H][D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO), [3H][D-Pen2,5]enkephalin (DPDPE), [3H]ethylketocyclazocine (EKC), and [3H][Met5]enkephalin (MET) was used to examine mu-, delta-, kappa-, and zeta-receptors, respectively, in the developing (birth to postnatal day 19) and adult human cerebellum. Specific and saturable binding of all ligands was recorded in developing brains, and of [3H]DAGO, [3H]DPDPE, and [3H]EKC in adult cerebellum; all data fit a single homogeneous binding site for each ligand. However, the ontogenic profile of opioid receptor subtypes differed. Delta- and kappa-receptor capacities were 7.8- and 3.6-fold, respectively, greater in infant cerebellum than in adults. The mu-receptor decreased over 7-fold in both binding affinity and capacity after day 2; by adulthood, the binding affinity was the same as in newborns but only one-half the binding capacity was recorded. The concentration of zeta-receptors was 20-fold greater in subjects 2-19 days of age than in newborns. These data demonstrate the presence, and distinct developmental profiles, of opioid receptors in human cerebellum. Although the function of mu-, delta-, and kappa-receptors in human cerebellum are unclear, the growth-related zeta-receptor is present at a time of cell replication and differentiation but is not detected in mature cerebellum.

Sigma and opioid receptors in human brain tumors

Human brain tumors (obtained as surgical specimens) and nude mouse-borne human neuroblastomas and gliomas were analyzed for sigma and opioid receptor content. Sigma binding was assessed using [3H]1,3-di-o-tolylguanidine (DTG), whereas opoid receptor subtypes were measured with tritiated forms of the following: mu, [D-ala2,mePhe4,gly-ol5]enkephalin (DAMGE); kappa, ethylketocyclazocine (EKC) or U69,593; delta, [D-pen2,D-pen5]enkephalin (DPDPE) or [D-ala2,D-leu5]enkephalin (DADLE) with mu suppressor present. Binding parameters were estimated by homologous displacement assays followed by analysis using the LIGAND program. Sigma binding was detected in 15 of 16 tumors examined with very high levels (pmol/mg protein) found in a brain metastasis from an adenocarcinoma of lung and a human neuroblastoma (SK-N-MC) passaged in nude mice. kappa opioid receptor binding was detected in 4 of 4 glioblastoma multiforme specimens and 2 of 2 human astrocytoma cell lines tested but not in the other brain tumors analyzed.

Endogenous opioids and neural cancer: an immunoelectron microscopic study

[Met5]-enkephalin, an endogenous opioid peptide derived from proenkephalin A, participates in tumorigenic events by serving as a natural trophic factor that inhibits cell replication. In order to understand how endogenous opioids function in modulating neoplasia, the present study examined the fine structural association of enkephalin with the cellular components of a tumor cell. Immunoelectron microscopic studies were undertaken using antibodies recognizing [Met5]-enkephalin-like substances, and murine S20Y neuroblastoma cells that are known to be responsive to endogenous opioid modulation. Enkephalin was found throughout the cell body and process. Immunoreactivity was associated with the plasma membrane, outer nuclear envelope, and a variety of organelles. With the exception of aggregates of immunoreactivity subjacent to the inner nuclear envelope, the nucleus was not reactive. These results establish that growth-related enkephalins are localized discretely within neuroblastoma cells. Since neuroblastoma cells produce and secrete enkephalins, and enkephalins interact with receptors to mediate actions on cell replication, this study examined enkephalins involved in two different patterns of traffic; further work will be needed to examine each aspect.

Characterization of zeta (zeta): a new opioid receptor involved in growth

Endogenous opioid systems (i.e., opioids and opioid receptors) are known to play a role in neural cancer. Using [3H]-[Met5]enkephalin, a potent ligand involved in growth, specific and saturable binding was detected in homogenates of S20Y neuroblastoma transplanted into A/Jax mice; the data fit a single binding site. Scatchard analysis yielded a Kd of 0.49 nM and a binding capacity of 5.32 fmol/mg protein. Binding was dependent on protein concentration, time, temperature, and pH, and was sensitive to Na+ and guanine nucleotides. Optimal binding required protease inhibitors, and pretreatment of the tumor homogenates with trypsin markedly reduced [3H]-[Met5]enkephalin binding, suggesting that the binding site was proteinaceous in character. Displacement experiments indicated that [Met5]enkephalin was the most potent displacer of [3H]-[Met5]enkephalin; other ligands selective for mu, delta, kappa, epsilon, and sigma were not highly competitive. Given the functional significance of [Met5]enkephalin as a potent regulator of normal and abnormal growth, and that the receptor recognized by [Met5]enkephalin does not resemble any previously described, the present study has demonstrated the presence of a new opioid receptor termed zeta (zeta) (from the Greek 'Zoe', life) related to the proliferation of cells and tissues.

Opioid antagonist modulation of murine neuroblastoma: a profile of cell proliferation and opioid peptides and receptors

The endogenous opioids and their receptors are known to play a major role in neoplasia. In the present study, naltrexone (NTX), a potent opioid antagonist, was utilized to explore the interactions of opioids and opioid receptors in mice with transplanted neuroblastoma (S20Y). Tumors from mice subjected to either intermittent (4-6h/day; 0.1 mg/kg NTX) or complete (24 h/day; 10 mg/kg NTX) opioid receptor blockade exhibited an up-regulation of DADLE and Met-enkephalin binding sites, as well as tissue levels of beta-endorphin and Met-enkephalin. Binding affinity to [D-Ala2,D-Leu5]enkephalin (DADLE) or ethylketocyclazocine (EKC), the levels of plasma beta-endorphin, and the anatomical location and quantity of Met- and Leu-enkephalin and cytoskeletal components (i.e. tubulin, actin, brain spectrin (240/235) were similar in NTX and control tumor-bearing animals. Tissue viability of the 0.1 NTX group was increased compared to controls. Both mitotic and labeling indexes were increased during the period of opioid receptor blockade, but decreased in the period subsequent to receptor blockade. NTX treatment produced a 2-fold increased in sensitivity to opioids. Met-enkephalin (10 mg/kg) produced a depression in both mitotic and labeling indexes in tumor-bearing mice that could be reversed by naloxone (10 mg/kg) administration. Thus, the endogenous opioids are trophic agents that inhibit growth by suppressing cell proliferation. The duration of receptor blockade by opioid antagonists modulates these actions, affecting both tumor incidence and survival time. Complete opioid receptor block prevents the interaction of increased levels of putative growth-related peptides with a greater number of opioid receptors, thereby increasing cell proliferation and accelerating tumor growth. With intermittent blockade, an enhanced opioid-receptor interaction occurs during the interval when the opioid antagonist is no longer present, producing an exaggerated inhibitory action on cell proliferation and the repression of tumorigenic events.

Modulation of murine melanoma growth by naloxone

The present study was undertaken to determine the effect of the opioid receptor antagonist, naloxone, on the growth of B16 melanoma, a murine tumor known to possess opioid receptors. Naloxone inhibited the growth of B16 melanoma in vitro when monolayer cultures were continuously exposed to concentrations of greater than or equal to 0.25 mg/ml. Tumor cell proliferation as measured by [3H]thymidine ([3H]Tdr) incorporation is reduced by a continuous 48-h treatment with greater than or equal to 0.025 mg/ml but slightly enhanced by a 6-h treatment. The administration of naloxone to mice caused a transient inhibition of subcutaneous local tumor growth at doses of 0.1, 1 and 10 mg/kg daily. At a dose of 10 mg/kg daily, naloxone caused a slight reduction in the number of pulmonary metastases following the intravenous inoculation of tumor cells. The mechanism by which naloxone inhibits tumor growth in vivo is not clear, but factors other than direct cytotoxicity may also be involved. The results further support the role of the endogenous opioid system in the modulation of tumor growth.

Endogenous opiates: 1987

This paper is the tenth installment of our annual review of the research during the past year involving the endogenous opiate system. It covers the nonanalgesia and behavioral studies of the opiate peptides published in 1987. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal activity; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical activity; locomotor activity; sex, pregnancy, and development; immunology and cancer; and other behavior.

Endogenous opioid systems and neural cancer: transmission and scanning electron microscopic studies of murine neuroblastoma in tissue culture

Endogenous opioid systems participate in carcinogenic events. To understand further the action of opioids on growth, S20Y neuroblastoma cells in tissue culture were exposed to i) [Met5]-enkephalin, a naturally occurring opioid pentapeptide, at a concentration (10(-6) M) that inhibits cell replication by 66% of control levels, ii) [Met5]-enkephalin (10(-6) M) and the opioid antagonist naloxone (10(-6) M) which blocks opioid agonist action, or iii) naltrexone (10(-6) M), a potent antagonist that disrupts endogenous opioid-opioid receptor interaction and increased cell number 76% above control values. The morphology of cells exposed to these agents for 2-4 days were similar to controls (i.e., exposed to sterile water) as determined by scanning and transmission electron microscopy. These results support the hypothesis that endogenous opioid systems act as trophic factors as they regulate growth; their effects on cell growth and survival, however, do not alter the basic ultrastructural morphology of the cells. Moreover, these data strengthen the validity of paradigms and therapeutic regimens that utilize opioid agonists and antagonists to modulate the relationship of endogenous opioid-opioid receptor interactions in neural cancer.

Characterization of opioid binding sites in murine neuroblastoma

The binding of [3H] [D-Ala2, MePhe4, Gly-ol5]enkephalin ([3H]DAGO), [3H]D-Ala2,D-Leu5]enkephalin ([3H]DADLE) and (+/-)-[3H]ethylketocyclazocine ([3H]EKC) to neurotumor tissues derived from S20Y neuroblastoma cells transplanted into A/Jax mice was examined. Specific and saturable binding to [3H]DADLE and [3H]EKC was detected, and the data fit a single homogeneous binding site for each ligand. Scatchard analysis for [3H]DADLE and [3H]EKC yielded Kd values of 0.65 and 0.45 nM, respectively, and Bmax values of 9.2 and 116 fmol/mg protein. Binding was dependent on time, temperature, and pH, and was sensitive to Na+ and guanine nucleotides. Pretreatment of the tumor homogenates with trypsin markedly reduced binding to both ligands, suggesting that the binding sites were proteinaceous in character. Displacement experiments indicated that delta (delta) receptor related compounds (e.g. DPDPE, ICI 174,864) avidly displaced [3H]DADLE, whereas kappa (kappa) related compounds (e.g. U50,488, dynorphin) markedly competed with [3H]EKC. Mu (mu) receptor drugs (e.g. DAGO, beta-FNA, morphine) were not potent in displacing either [3H]DADLE or [3H]EKC. These results are the first to characterize opioid binding sites in tumor tissue. The function of these sites is unclear, but previous evidence as to the growth regulatory properties of endogenous opioid systems may suggest that either one, or both, binding sites may be involved in carcinogenic events.