beta-Endorphin: characterization of binding sites specific for the human hormone in human glioblastoma SF126 cells

Involvement of the Opioid Peptide Family in Cancer Progression

Peptides mediate cancer progression favoring the mitogenesis, migration, and invasion of tumor cells, promoting metastasis and anti-apoptotic mechanisms, and facilitating angiogenesis/lymphangiogenesis. Tumor cells overexpress peptide receptors, crucial targets for developing specific treatments against cancer cells using peptide receptor antagonists and promoting apoptosis in tumor cells. Opioids exert an antitumoral effect, whereas others promote tumor growth and metastasis. This review updates the findings regarding the involvement of opioid peptides (enkephalins, endorphins, and dynorphins) in cancer development. Anticancer therapeutic strategies targeting the opioid peptidergic system and the main research lines to be developed regarding the topic reviewed are suggested. There is much to investigate about opioid peptides and cancer: basic information is scarce, incomplete, or absent in many tumors. This knowledge is crucial since promising anticancer strategies could be developed alone or in combination therapies with chemotherapy/radiotherapy.

Radioendocrine Therapy of Brain Tumors with the Long Acting Opioid Antagonist Naltrexone in Association with Radiotherapy

Aims and Background

Malignant gliomas remain untreatable as the different therapeutic combinations are generally only palliative. Recent experimental evidence suggests that endogenous opioid peptides are involved in brain tumor growth. The aim of the present study was to evaluate the effect on survival of concomitant administration of the long-acting opioid antagonist naltrexone (NTX) in patients with malignant astrocytomas treated with radiotherapy (RT).

Methods

21 patients with high grade malignant gliomas were randomized to receive RT alone or RT plus NTX. The dose of RT was 60 Gy. NTX was given orally at a dose of 100 mg every other day without interruption until disease progression.

Results

The objective tumor regression rate in patients treated with RT plus NTX was higher than that of those treated with RT alone but not significantly so. On the contrary, the percentage of survivals at 1 year was significantly higher in patients treated with RT plus NTX than in those treated with RT alone (5/10 vs 1/11, P < 0.05). NTX therapy was substantially well tolerated in most patients.

Conclusions

The finding of longer survival in brain tumor patients treated with RT plus NTX than in those who received RT alone suggests in vivo involvement of endogenous opioid peptides in regulating the growth of malignant astrocytomas.

Alteration of Opioid Peptide Circadian Rhythm in Cancer Patients

Endogenous opioid peptides have been seen to play a role in regulating immunity and tumor growth. This study was carried out to investigate opioid activity in human cancer. We evaluated by radioimmunoassay β-endorphin plasma levels on blood samples collected at 9.00 a.m. from 121 cancer patients and 42 healthy subjects. In 22 cancer patients and in 12 controls, β-endorphin circadian rhythm was also investigated. Finally, in 14 cancer patients and in 10 controls GH, PRL, FSH, LH and Cortisol serum levels were measured after the administration of a metenkephalin analogue, FK 33–824 (0.3 mg i.v.). No significant differences were seen in β-endorphin mean levels between cancer patients and normal subjects. Moreover, no differences were found between patients with or without metastases, nor between those with or without chronic pain. β-Endorphin circadian rhythm appeared to be altered in 16/22 cancer patients, and anomalous hormonal responses to FK 33–824 were seen in 13/14 patients. This study shows an altered opioid activity in human neoplasms, whose clinical significance remains to be determined.

Principles of psychoneuroendocrinoimmunotherapy of cancer

Recent advances in the knowledge of the mechanisms responsible for antitumor immunity have stimulated the elaboration of new cancer immunotherapeutic strategies. Moreover, more recent discoveries have demonstrated that immune responses are under a physiological modulatory control played by several neuroendocrine pathways, which explain the differences between the in vivo and in vitro immune responses. While until a few years ago the evaluation of the immune status of cancer patients was substantially established on the basis of clinical empirical criteria, recent discoveries of the antitumor cytokine network have allowed the biochemical bases of anticancer immunity to be defined, leading to new anticancer immunotherapeutic strategies, on the basis of patient neuroendocrine and neuroimmune status, in an attempt to correct the great number of cancer-related alterations on the basis of knowledge of the physiopathology of anticancer immunity. The rationale for cancer neuroimmunotherapy consists of the possibility to enhance the efficacy of the various immunotherapeutic strategies by a concomitant administration of antitumor cytokines (namely IL-2), in addition to neuroendocrine endogenous molecules (namely the pineal indole hormones), able to stimulate the anticancer immunoresponse by amplifying the anticancer reaction and/or by counteracting the generation of immunosuppressive events.

Endomorphin 1 and endomorphin 2 suppress in vitro antibody formation at ultra-low concentrations: anti-peptide antibodies but not opioid antagonists block the activity

Endomorphin 1 (EM-1) and endomorphin 2 (EM-2) were tested for their capacity to alter immune function. Addition of either of these peptides to murine spleen cells in vitro inhibited antibody formation to sheep red blood cells in a bi-phasic dose dependent manner. Maximal inhibition was achieved at doses in the range of 10(-13) to 10(-15)M. Neither naloxone (general opioid receptor antagonist) nor CTAP (selective mu opioid receptor antagonist) blocked the immunosuppressive effect. To show that there was specificity to the immunosuppressive activity of the peptides, affinity-purified rabbit antibodies were raised against each of the synthetic EM peptides haptenized to KLH and tested for capacity to inhibit immunosuppression. Antibody responses were monitored by a standard solid phase antibody capture ELISA, and antibodies were purified by immunochromatography using the synthetic peptides coupled to a Sepharose 6B resin. Verification of the specificity of affinity-purified antisera was performed by immunodot-blot and solid-phase RIA assays. The antisera specific for both EM-1 and EM-2 neutralized the immunosuppressive effects of their respective peptides in a dose-related manner. Control normal rabbit IgG had no blocking activity on either EM-1 or EM-2. These studies show that the endomorphins are immunomodulatory at ultra-low concentrations, but the data do not support a mechanism involving the mu-opioid receptor.

Adult human sarcomas. II. Medical oncology

Human sarcoma cells can be killed by radio- and chemotherapy, but tumor cells acquiring resistance frequently kill the patient. A keen understanding of the intracellular course of oncogenic cascades leads to the discovery of small molecular inhibitors of the involved phosphorylated kinases. Targeted therapy complements chemotherapy. Oncogene silencing is feasible by small interfering RNA. The restoration of some of the mutated or deleted tumor-suppressor genes (p53, Rb, PTEN, hSNF, INK/ARF and WT) by demethylation or reacetylation of their histones has been accomplished. Genetically engineered or naturally oncolytic viruses selectively lyse tumors and leave healthy tissues intact. Adeno- or retroviral vectors deliver genes of immunological costimulators, tumor antigens, chemo- or cytokines and/or tumor-suppressor proteins into tumor (sarcoma) cells. Suicide gene delivery results in apoptosis induction. Genes of enzymes that target prodrugs as their substrates render tumor cells highly susceptible to chemotherapy, with the prodrug to be targeted intracellularly. It will be combinations of sophisticated surgical removal of the nonencapsulated and locally invasive primary sarcomas, advanced forms of radiotherapy to the involved sites and immunotherapy with sarcoma vaccines that will cure primary sarcomas. Adoptive immunotherapy with immune lymphocytes will be operational in metastatic disease only when populations of regulatory T cells are controlled. Targeted therapy with small molecular inhibitors of oncogene cascades, the driving forces of sarcoma cells, alteration of the tumor stroma from a supportive to a tumor-hostile environment, reactivation or replacement of wild-type tumor-suppressor genes, and radio-chemotherapy (with much reduced toxicity) will eventually accomplish the cure of metastatic sarcomas.

Glioblastoma expression of vitronectin and the alpha v beta 3 integrin. Adhesion mechanism for transformed glial cells

Glioblastoma multiforme, the most malignant astroglial-derived tumor, grows as an adherent mass and locally invades normal brain. An examination of adult cerebral glioblastoma biopsy material for the expression of adhesive proteins that might potentiate adhesion and invasion demonstrated tumor cell-associated vitronectin (5/5). In contrast, vitronectin was not detected associated with glial cells in low grade astroglial tumors (0/4), reactive astrogliosis (0/4), or in normal adult cortex and cerebral white matter (0/5). Also, a wide variety of other adhesive ligands were absent from the glioblastoma tumor parenchyma. The alpha v beta 3 integrin was the only vitronectin receptor identified in glioblastoma tumors in situ, and was also not expressed on low grade astroglial-derived tumors, reactive astrogliosis, or on glia or neurons in normal adult cortex and cerebral white matter. In a cell attachment assay, cultured glioblastoma cells attached to the parenchyma of glioblastoma tumor cryostat sections at the sites of vitronectin expression, but failed to attach to normal brain. This adhesion was inhibited by antibodies directed against vitronectin, the alpha v beta 3 integrin, and with an Arg-Gly-Asp-containing peptide. These data provide evidence for a cell adhesion mechanism in glioblastoma tumors that might potentiate glioblastoma cell invasion of normal brain.

Preparation of [125I-Tyr27,Leu5]beta h-endorphin and its use for crosslinking of opioid binding sites in human striatum and NG108-15 neuroblastoma-glioma cells

A radioligand suitable for crosslinking studies to opioid receptors has been obtained by radioiodination and purification of the monoiodotyrosine-27 derivative of the synthetic human beta-endorphin (beta h-endorphin) analogue [5-leucine]beta h-endorphin. The derivative, [27-[125I]monoiodotyrosine,5-leucine]beta h-endorphin, was crosslinked to human striatal (caudate and putamen) and NG108-15 neuroblastoma-glioma cell membranes by using disuccinimidyl suberate. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis under reducing conditions revealed four specifically labeled bands at 68, 40, 30, and 25 kDa for both human caudate and putamen, whereas NG108-15 cell membranes gave specifically labeled bands at 92, 56, 38, and 23 kDa.

Characterization of solubilized human and rat brain beta-endorphin-receptor complex

Opioid receptors have been solubilized from human striatal and rat whole-brain membranes by use of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). Tritiated human beta-endorphin (3H-beta h-EP) binding revealed high-affinity competition by morphine, naloxone, and various beta-EP analogues, suggesting predominantly mu-type binding. Lack of high-affinity competition by (+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneaceta mide methanesulfonate (U50-488, Upjohn) indicated that kappa sites were not labeled by 3H-beta h-EP under these conditions. Affinities were similar in both soluble and membrane preparations except for [Met]enkephalin, which appears to be rapidly degraded by the solubilized extract. Size differences between human and rat solubilized 3H-beta h-EP-receptor complexes were revealed by exclusion chromatography.

Human retinoblastomas have binding sites for the COOH-terminal segment of human beta-endorphin

Two human retinoblastoma cell lines (Y79 and McA) were evaluated for the presence of binding sites for human beta-endorphin (beta h-EP). Using tritiated beta h-EP (3H-beta h-EP) and synthetic beta-EP analogues, it was possible to demonstrate binding sites for 3H-beta h-EP with an ED50 of 3.5 nM in Y79 cells and 8 nM in McA cells respectively. The non-opioid segment [beta h-EP-(6-31)] retained about 20% relative potency in Y79 and 40% in McA in displacing the tritiated hormone when compared with beta h-EP. Camel beta-EP had a relative potency of less than 1% and beta h-EP-(1-27) was inactive in both cells in doses as high as 4 microM. Taken together with previous reports on similar binding sites in human neuroblastoma and glioblastoma cell lines, it appears that cell lines of neural origin have binding sites for the COOH-terminal of human beta-EP.