Elevated levels of opioid growth factor in the plasma of patients with pancreatic cancer

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.

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.

Opioid growth factor improves clinical benefit and survival in patients with advanced pancreatic cancer

BACKGROUND: Advanced pancreatic cancer carries the poorest prognosis of all gastrointestinal malignancies. Once the tumor has spread beyond the margins of the pancreas, chemotherapy is the major treatment modality offered to patients; however, chemotherapy does not significantly improve survival. OBJECTIVE: Opioid growth factor (OGF; [Met(5)]-enkephalin) is a natural peptide that has been shown to inhibit growth of pancreatic cancer in cell culture and in nude mice. The purpose of this study was to evaluate the effects of OGF biotherapy on subjects with advanced pancreatic cancer who failed chemotherapy. METHODS: In a prospective phase II open-labeled clinical trial, 24 subjects who failed standard chemotherapy for advanced pancreatic cancer were treated weekly with OGF 250 µg/kg intravenously. Outcomes measured included clinical benefit, tumor response by radiographic imaging, quality of life, and survival. RESULTS: Clinical benefit response was experienced by 53% of OGF-treated patients compared to historical controls of 23.8% and 4.8% for gemcitabine and 5-fluorouracil (5-FU), respectively. Of the subjects surviving more than eight weeks, 62% showed either a decrease or stabilization in tumor size by computed tomography. The median survival time for OGF-treated patients was three times that of untreated patients (65.5 versus 21 days, p < 0.001). No adverse effects on hematologic or chemistry parameters were noted, and quality of life surveys suggested improvement with OGF. LIMITATIONS: Measurements other than survival were not allowed in control patients, and clinical benefit comparisons were made to historical controls. CONCLUSION: OGF biotherapy improves the clinical benefit and prolongs survival in patients with pancreatic cancer by stabilizing disease or slowing progression. The effects of OGF did not adversely alter patient quality of life. The use of OGF biotherapy at earlier stages of disease or in combination with other chemotherapeutic agents may further improve the outcome of this malignancy.

Cancer pain and its impact on diagnosis, survival and quality of life

Cancer pain significantly affects the diagnosis, quality of life and survival of patients with cancer. During the past decade, preclinical and clinical data has begun to provide insight into the mechanisms that drive and mask cancer pain and the mechanisms by which anti-neoplastic agents induce peripheral neuropathy. Developing a mechanism-based understanding and mechanism-based therapies to treat cancer-associated pain and sensory neuropathy, and incorporating these into mainstream cancer research and therapy, will be crucial to improving the quality of life and survival of patients with cancer.

Endogenous opioids inhibit early-stage pancreatic pain in a mouse model of pancreatic cancer

BACKGROUND & AIMS

The endogenous opioid system is involved in modulating the experience of pain, the response to stress, and the action of analgesic therapies. Recent human imaging studies have shown a significant tonic modulation of visceral pain, raising the question of whether endogenous opioids tonically modulate the pain of visceral cancer.

METHODS

Transgenic mice expressing the first 127 amino acids of simian virus 40 large T antigen, under the control of the rat elastase-1 promoter, that spontaneously develop pancreatic cancer were used to investigate the role of endogenous opioids in the modulation of pancreatic cancer pain. Visceral pain behaviors were assessed as degree of hunching and vocalization.

RESULTS

Although mice with late-stage pancreatic cancer displayed spontaneous, morphine-reversible, visceral pain-related behaviors such as hunching and vocalization, these behaviors were absent in mice with early-stage pancreatic cancer. After systemic administration of the central nervous system (CNS)-penetrant opioid receptor antagonists naloxone or naltrexone, mice with early-stage pancreatic cancer displayed significant visceral pain-related behaviors, whereas systemic administration of the CNS-nonpenetrant opioid antagonist naloxone-methiodide did not induce an increase in visceral pain behaviors.

CONCLUSIONS

Our findings suggest that a CNS opioid-dependent mechanism tonically modulates early and late-stage pancreatic cancer pain. Understanding the mechanisms that mask this pain in early stage disease and drive this pain in late-stage disease may allow improved diagnosis, treatment, and care of patients with pancreatic cancer.

Detection of opioid receptors on murine lymphocytes by indirect immunofluorescence: mature normal and tumor bearing mice lymphocytes

Opioid peptides modulate immune responses via ligation to classical opioid receptors (mu, delta and kappa), expressed on immune cells, or in an indirect fashion via the central nervous system. The combination of immunofluorescent technique and flow cytometry has proven to be sensitive methods for detection of opioid receptors on leukocytes. In the current study a fluorescein isothiocyanate-conjugated naltrexone (FITC-NTX) derivative in the absence or presence of naltrexone, as a competitor, was used to detect opioid receptors on thymocytes and then on splenocytes of normal and tumor bearing Balb/c mice. Tumor bearing mice were made by intraperitoneal injection of fibrosarcoma cell line. In a two weeks interval, tumor grew and then mice splenocytes were harvested. Cells were incubated with FITC-NTX alone (direct fluorescence), or FITC-NTX followed by biotin-conjugated anti-fluorescein IgG and extravidin-R-phycoerythrin (indirect immunofluorescence). Using flow cytometry we found that, with direct fluorescence staining there is only nonspecific cell staining. In contrast, indirect staining of cells demonstrated labeling of opioid receptors. Thymocytes displayed 37.5+/-7% specific labeling by current staining procedure. However, this specific staining was 17.2+/-4% and 7.5+/-2% in splenocytes of normal and tumor bearing mice, respectively. Taken together, these results showed that, direct fluorescence staining failed to stain opioid receptors expressed on lymphocytes. These receptors can only be detected by a biotin-streptavidin amplification procedure. We also found that the level of opioid receptors on mature lymphocytes is less than that of immature ones and are even lesser in the tumor bearing mice lymphocytes.

Treatment of advanced pancreatic cancer with opioid growth factor: phase I

Opioid growth factor (OGF) is an endogenous pentapeptide that inhibits growth of human pancreatic cancer cells in culture, as well as xenografts in nude mice. To establish the maximum tolerated dose (MTD), and determine safety and toxicity of OGF, a phase I trial was performed in patients with advanced unresectable pancreatic cancer. Patients with unresectable pancreatic adenocarcinoma were treated with escalating doses of OGF for 30 min i.v. to determine the MTD. The s.c. route of administration also was evaluated. Once the MTD was established, a group of patients was treated chronically, and monitored for safety and toxicity. Hypotension was the dose-limiting toxicity, resulting in a MTD of 250 microg/kg i.v. Due to limited solubility of OGF in small volumes, a maximum dose of 50 microg/kg twice daily was determined by the s.c. route of administration. No adverse events were reported for oxygen saturation, cardiac rhythm, laboratory values or neurological status in either the acute or chronic parts of the study with the i.v. or s.c. routes. During the chronic i.v. phase, two subjects had resolution of liver metastases and one showed regression of the pancreatic tumor. Mean survival from the time of diagnosis was 8.7 months (range 2-23 months) in the i.v. group and 9.5 months (range 1-18 months) in the s.c. group. We conclude that OGF can be safely administered to patients with advanced pancreatic cancer. Further studies are needed to determine the efficacy of OGF alone or in combination with present modes of therapy for the treatment of pancreatic cancer.

Endogenous opiates: 2000

This paper is the twenty-third installment of the annual review of research concerning the opiate system. It summarizes papers published during 2000 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunological responses.