Naltrexone modulates tumor response in mice with neuroblastoma

Potential influence of different peri-operative analgesic regimens on tumour biology and outcome after oncologic surgery: A narrative review

The management of peri-operative pain is one of the pillars of anaesthesia and is of particular importance in patients undergoing surgery for solid malignant tumours. Amongst several options, the most commonly employed analgesic regimens involve opioids, NSAIDs and regional anaesthesia techniques with different local anaesthetics. In recent years, several research reports have tried to establish a connection between peri-operative anaesthesia care and outcome after cancer surgery. Experimental studies have indicated that certain pain management substances may influence cancer progression, mainly by modifying the tumour's response to surgical stress and peri-operative inflammation. However, these promising in-vitro and in-vivo data have yet to be confirmed by randomised clinical trials. The reason for this might lie with the nature of tumour biology itself, and in the diversity of patient and tumour phenotypes. In a translational approach, future research should therefore concentrate on patient and tumour-related factors or biomarkers, which might either influence the tumour and its microenvironment or predict potential responses to interventions, including the choice of the analgesic. This might not only be relevant for the daily practice of clinical anaesthesia, but would also be of great importance for patients undergoing cancer surgery, who might be able to receive an individualised anaesthetic regimen based on their phenotypic profile.

Naltrexone accelerated oral traumatic ulcer healing and downregulated TLR-4/NF-kB pathway in Wistar rats

OBJECTIVE

To assess the effect of naltrexone on oral mucosal healing using a traumatic ulcer model DESIGN: Wistar rats (n = 112) received distilled water (control) or naltrexone (0.5, 10, or 50 mg/kg/day). Ulcers were induced on the buccal mucosa using a round skin biopsy punch (diameter 6 mm). Euthanasia was performed on days 1, 3, 7, and 14. Healing was assessed by ulcer area, histological scores, histomorphometric analysis (number of polymorphonuclears, mononuclears, and fibroblasts), and collagen percentage. Immunohistochemistry for TLR-2, TLR-4, NF-kB, and CD31 was evaluated. Nociceptive threshold was measured daily.

RESULTS

The 50 mg/kg group showed reduced ulcer area on days 1 (p < 0.001), 3 (p < 0.05), and 14 (p < 0.01). In this group, there was, on day 14, an increase in the percentage of reepithelization (p = 0.043) and collagen (p < 0.05), an increase in connective tissue maturation (p = 0.016), and on day 7 an increase in fibroblasts (p < 0.001). The 10 mg/kg dose reduced the ulcer area on day 1 (p < 0.001). The 50 mg/kg group showed lower expression of TLR-4 (p < 0.001) on day 1, NF-kB on days 1 (p < 0.05) and 14 (p < 0.05), and CD31 on day 14 (p < 0.05). The 0.5 and 10 mg/kg doses reduced TLR-4 expression on day 1 (p < 0.05; p < 0.01, respectively). Nociceptive threshold increased in the 50 mg/kg group (p < 0.01).

CONCLUSION

Naltrexone enhanced traumatic oral ulcer healing by reducing TLR-4/NF-kB signaling and promoting fibroblast proliferation and collagen deposition. Additionally, naltrexone reduced pain in rats.

The role of bidirectional communication between the adipokines and the endogenous opioid system in an experimental mouse model of colitis-associated colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is one of the leading causes of death globally. Multiple factors may contribute to the pathogenesis of CRC, including the abnormalities in the functioning of the endogenous opioid system (EOS) or adiponectin-related signaling. The aim of our study was to evaluate if differences in the expression of opioid receptors (ORs) influence the development of CRC and if modulation of adiponectin receptors using AdipoRon, a selective AdipoR1 receptor agonist, affects colorectal carcinogenesis.

METHODS

Naltrexone, an opioid receptor antagonist, was injected intraperitoneally every second day for 2 weeks, at the dose of 1 mg/kg in healthy Balb/C mice to induce changes in ORs expression. CRC was induced by a single intraperitoneal injection of azoxymethane (AOM) and the addition of dextran sodium sulfate (DSS) into drinking water in three-week cycles. The development of CRC was assessed using macro- and microscopic scoring and molecular analysis (RT qPCR, ELISA) after 14 weeks.

RESULTS

Naltrexone significantly increased the mRNA expression of Oprm1, Oprd1, and Oprk1 in the mouse colon and in the brain (non-significantly). The pretreatment of mice with naltrexone aggravated the course of CRC (as indicated by tumor area, colon thickness, and spleen weight). The level of circulatory adiponectin was lowered in mice with CRC and increased in the colon as compared with healthy mice. The β-endorphin level was increased in the plasma of mice with CRC and decreased in the colon as compared to healthy mice. AdipoRon, AdipoR1 agonist, worsened the CRC development, and pretreatment with naltrexone enhanced this negative effect in mice. CRC did not affect the expression of the Adipor1 gene, but the Adipor1 level was increased in mice pretreated with naltrexone (AOM/DSS and healthy mice). AdipoRon did not influence the expression of opioid receptors at the mRNA level in the colon of mice with CRC. The mRNA expression of Ptgs2, Il6, Nos2, Il1b, Il18, Gsdmd, and Rela was increased in mice with CRC as compared to the healthy colon. AdipoRon significantly decreased mRNA expression of Ptgs2, Il6, Il1b, and Il18 as compared to CRC mice.

CONCLUSION

EOS and adiponectin-related signaling may play a role in the pathogenesis of CRC and these systems may present some additivity during carcinogenesis.

Mapping the Evidence for Opioid-Mediated Changes in Malignancy and Chemotherapeutic Efficacy: Protocol for a Scoping Review

BACKGROUND

Numerous reports contend opioids can augment or inhibit malignancy. At present, there is no consensus on the risk or benefit posed by opioids on malignancy or chemotherapeutic activity. Distinguishing the consequences of opioid use from pain and its management is challenging. Additionally, opioid concentration data is often lacking in clinical studies. A scoping review approach inclusive of preclinical and clinical data will improve our understanding of the risk-benefit relationship concerning commonly prescribed opioids and cancer and cancer treatment.

OBJECTIVE

The aim of the study is to map diverse studies spanning from preclinical to clinical regarding opioids with malignancy and its treatment.

METHODS

This scoping review will use the Arksey six stages framework to (1) identify the research question; (2) identify relevant studies; (3) select studies meeting criteria; (4) extract and chart data; (5) collate, summarize, and report results; and (6) conduct expert consultation. An initial pilot study was undertaken to (1) parameterize the extent and scale of existing data for an evidence review, (2) identify key factors to be extracted in systematic charting efforts, and (3) assess opioid concentration as a variable for its relevance to the central hypothesis. Six databases will be searched with no filters: MEDLINE, Embase, CINAHL Complete, Cochrane Library, Biological Sciences Collection, and International Pharmaceutical Abstracts. Trial registries will include ClinicalTrials.gov, Cochrane CENTRAL, International Standard Randomised Controlled Trial Number Registry, European Union Clinical Trials Register, and World Health Organization International Clinical Trials Registry. Eligibility criteria will include preclinical and clinical study data on opioids effects on tumor growth or survival, or alteration on the antineoplastic activity of chemotherapeutics. We will chart data on (1) opioid concentration from human subjects with cancer, yielding a "physiologic range" to better interpret available preclinical data; (2) patterns of opioid exposure with disease and treatment-related patient outcomes; and (3) the influence of opioids on cancer cell survival, as well as opioid-related changes to cancer cell susceptibility for chemotherapeutics.

RESULTS

This scoping review will present results in narrative forms as well as with the use of tables and diagrams. Initiated in February 2021 at the University of Utah, this protocol is anticipated to generate a scoping review by August 2023. The results of the scoping review will be disseminated through scientific conference proceedings and presentations, stakeholder meetings, and by publication in a peer-reviewed journal.

CONCLUSIONS

The findings of this scoping review will provide a comprehensive description of the consequences of prescription opioids on malignancy and its treatment. By incorporating preclinical and clinical data, this scoping review will invite novel comparisons across study types that could inform new basic, translational, and clinical studies regarding risks and benefits of opioid use among patients with cancer.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/38167.

Opioid growth factor receptor: Anatomical distribution and receptor colocalization in neurons of the adult mouse brain

The opioid growth factor (OGF) is an endogenous peptide that binds to the nuclear-associated receptor (OGFr), and plays a significant role in the proliferation of developing, renewing, and healing tissues. The receptor is widely expressed in a variety of organs, however its distribution in the brain remains unknown. In this study, we investigated the distribution of OGFr in different brain regions of male heterozygous (-/+ Lepr ^db/J), non -diabetic mice and determined the localization of the receptor in three major brain cell types, astrocytes, microglia, and neurons. Immunofluorescence imaging revealed that the highest number of OGFr was in hippocampal CA3 subregion followed by primary motor cortex, hippocampal CA2, thalamus, caudate and hypothalamus in a descending order. Double immunostaining revealed receptor colocalization with neurons and little or no colocalization in microglia and astrocytes. The highest percentage of OGFr positive neurons was identified in the CA3. Hippocampal CA3 neurons play an important role in memory processing, learning and behavior, and motor cortex neurons are important for muscle movement. However, the significance of the OGFr receptor in these brain regions and its relevance in diseased conditions are not known. Our findings provide a basis for understanding the cellular target and interaction of the OGF- OGFr pathway in neurodegenerative diseases such as Alzheimer's, Parkinson's, and stroke where hippocampus and cortex have an important role. This foundational data may also be useful in drug discovery to modulate OGFr by opioid receptor antagonist in various CNS diseases.

An open label phase II study of safety and clinical activity of naltrexone for treatment of hormone refractory metastatic breast cancer

The opioid receptor (OR) antagonist naltrexone inhibits estrogen receptor-α (ER) function in model systems. The goal of this study was to determine the clinical activity of naltrexone in patients with ER-positive metastatic breast cancer. Patients with hormone receptor positive metastatic breast cancer were enrolled on a phase II study of naltrexone. An escalating dose scheme was used to reach the planned dose of 50 mg daily. The primary objective of the study was to evaluate response to therapy as measured by stabilization or reduction of the tumor Maximum Standardized Uptake Value (SUVmax) at 4 weeks by PET-CT scan. The secondary objectives included safety assessment and tumor SUVmax at 8 weeks. Out of 13 patients we enrolled, 8 patients had serial PET-CT scans that were evaluable for response. Of these 8 patients, 5 had stable or decreased SUVmax values at 4 weeks and 3 had clinical or imaging progression. Median time to progression was short at 7 weeks. Naltrexone was well tolerated. There were no discontinuations due to toxicity and no grade 3 or 4 toxicities were noted. Naltrexone showed modest activity in this short study suggesting the contribution of opioid receptors in ER-positive breast cancer. Our data do not support further development of naltrexone in hormone refractory breast cancer. It is possible that more potent peripherally acting OR antagonists may have a greater effect. (ClinicalTrials.gov Identifier: NCT00379197 September 21, 2006).

Thyroid, Diet, and Alternative Approaches

BACKGROUND

Increasingly, patients are asking their physicians about the benefits of dietary and alternative approaches to manage their diseases, including thyroid disease. We seek to review the evidence behind several of the vitamins, minerals, complementary medicines, and elimination diets that patients are most commonly using for the treatment of thyroid disorders.

SUMMARY

Several trace elements are essential to normal thyroid function, and their supplementation has been studied in various capacities. Iodine supplementation has been implemented on national scales through universal salt iodization with great success in preventing severe thyroid disease, but can conversely cause thyroid disorders when given in excess. Selenium and zinc supplementation has been found to be beneficial in specific populations with otherwise limited generalizability. Other minerals, such as vitamin B12, low-dose naltrexone, and ashwagandha root extract, have little to no evidence of any impact on thyroid disorders. Avoidance of gluten and dairy has positive impacts only in patients with concomitant sensitivities to those substances, likely by improving absorption of levothyroxine. Avoidance of cruciferous vegetables and soy has little proven benefit in patients with thyroid disorders.

CONCLUSION

While many patients are seeking to avoid conventional therapy and instead turn to alternative and dietary approaches to thyroid disease management, many of the most popular approaches have no proven benefit or have not been well studied. It is our responsibility to educate our patients about the evidence for or against benefit, potential harms, or dearth of knowledge behind these strategies.

A repositioning screen using an FGFR2 splicing reporter reveals compounds that regulate epithelial-mesenchymal transitions and inhibit growth of prostate cancer xenografts

Research in the area of hallmarks of cancer has opened the possibility of designing new therapies based on modulating these cancer properties. We present here a screen designed to find chemicals that modulate epithelial-mesenchymal transitions (EMTs) in prostate cancer. For screening, we used a repurposing library and, as a readout, an FGFR2-based splicing reporter, which has been shown previously to be a sensor for EMTs. Various properties of cancer cells were assessed, signaling pathways investigated, and in vivo experiments in nude mice xenografts performed. The screen yielded three hit compounds (a T-type Ca channel inhibitor, an L-type Ca channel inhibitor, and an opioid antagonist) that switch FGFR2 splicing and induce an epithelial phenotype in prostate cancer cells. The compounds affected differently various properties of cancer cells, but all of them decreased cell migration, which is in line with modulating EMTs. We further present mechanistic insights into one of the compounds, nemadipine-A. The administration of nemadipine-A intraperitoneally in a nude mouse xenograft model of prostate cancer slowed tumor growth. To conclude, we show that knowledge of the molecular mechanisms that connect alternative splicing and various cancer properties may be used as a platform for drug development.

Time to initiate randomized controlled clinical trials with methadone in cancer patients

Public media coverage has fueled a demand for methadone as potential cure for cancer itself. Because patients have asked for respective prescriptions, clinical societies issued statements warning against the use of methadone as long as preclinical findings have not been supported by clinical evidence. In fact, not all preclinical data clearly support relevant effects. However, strong epidemiologic data suggest beneficial effects of methadone on cancer. Alternative explanations, namely better safety of methadone or hidden selection bias, seem less likely. This uncertainty can only be resolved by randomized controlled clinical trials. This review discusses all relevant data pertinent to methadone and cancer, uncovers supportive epidemiologic data, and suggests possible study designs.

Naltrexone at low doses (LDN) and its relevance to cancer therapy

INTRODUCTION

: Naltrexone was designed to inhibit opioid receptors without activating them, and hence used to block the stimulatory effects of morphine and heroin. It was noted that in certain patients being treated with naltrexone for an opioid addiction many reported significant secondary benefit when being weaned off naltrexone. This group of patients had chronic inflammatory and autoimmune conditions, and reported improvements whilst using the lower dosages of naltrexone. There have also been recent anecdotal reports of cancer resolution following the use of low doses of naltrexone (LDN). However, the mechanism of action is unclear.

AREAS COVERED

We review three mechanisms through which LDN can influence cancer progression; namely, a) antagonism of receptors to which LDN binds, which include toll-like receptors 7-9 that lead to IL-6 suppression b) modulation of immune function in patients; and c) direct inhibition of signalling pathways involved in cancer cell control, including the priming of pro-apoptotic pathways.

EXPERT OPINION

Considering the increase in number of anecdotal reports of activity, there will likely be a bigger drive towards using LDN in the oncological setting. These reports support clinical trials of LDN in cancer, especially when given in combination with certain chemotherapy.

Opioid Receptor-Mediated and Non-Opioid Receptor-Mediated Roles of Opioids in Tumour Growth and Metastasis

Opioids are administered to cancer patients in the period surrounding tumour excision, and in the management of cancer-associated pain. The effects of opioids on tumour growth and metastasis, and their consequences on disease outcome, continue to be the object of polarised, discrepant literature. It is becoming clear that opioids contribute a range of direct and indirect effects to the biology of solid tumours, to the anticancer immune response, inflammation, angiogenesis and importantly, to the tumour-promoting effects of pain. A common misconception in the literature is that the effect of opioid agonists equates the effect of the mu-opioid receptor, the major target of the analgesic effect of this class of drugs. We review the evidence on opioid receptor expression in cancer, opioid receptor polymorphisms and cancer outcome, the effect of opioid antagonists, especially the peripheral antagonist methylnaltrexone, and lastly, the evidence available of a role for opioids through non-opioid receptor mediated actions.

Low doses of methylnaltrexone inhibits head and neck squamous cell carcinoma growth in vitro and in vivo by acting on the mu-opioid receptor

The Mu-opioid receptor (MOR) has been implicated in tumorigenesis and metastasis. Methylnaltrexone (MNTX), an antagonist of MOR, has shown to inhibit tumor growth and metastasis in lung cancer cell lines. The effect of MNTX on other cell lines such as head and neck squamous cell carcinoma (HNSCC) has not been investigated. We measured the expression and activity of the receptor in different HNSCC cell lines. Then, we evaluated the impact of modulating the expression MOR and the effect of MNTX on the proliferation, clonogenic activity, invasion, and migration of two HNSCC (FaDu and MDA686Tu) cell lines expressing MOR and one cell line (UMSCC47) not expressing the receptor. We also evaluated the impact of MNTX on tumor growth and metastasis formation in vivo. Activation of the receptor with [d-Ala2,N-Me-Phe4, Gly5-ol] (DAMGO) caused a significant reduction in cyclic adenosine monophosphate levels in FaDu cells. Knockdown of MOR inhibited in vitro aggressive cell behaviors on FaDu and MDA686Tu cells and correlated with a reduction in markers of epithelial-mesenchymal transition. In vitro studies showed that MNTX strongly inhibited the proliferation, clonogenic activity, invasion, and migration of FaDu and MDA686Tu cells but has no effect on UMSCC47 cells. In vivo experiments demonstrated that MNTX suppresses tumor growth in HNSCC cell tumor-bearing mice. Our studies indicate that MOR could be considered as a therapeutic target to treat HNSCC.

Addiction and the cerebellum with a focus on actions of opioid receptors

Increasing evidence suggests that the cerebellum could play a role in the higher cognitive processes involved in addiction as the cerebellum contains anatomical and functional pathways to circuitry controlling motivation and saliency. In addition, the cerebellum exhibits a widespread presence of receptors, including opioid receptors which are known to play a prominent role in synaptic and circuit mechanisms of plasticity associated with drug use and development of addiction to opioids and other drugs of abuse. Further, the presence of perineural nets (PNNs) in the cerebellum which contain proteins known to alter synaptic plasticity could contribute to addiction. The role the cerebellum plays in processes of addiction is likely complex, and could depend on the particular drug of abuse, the pattern of use, and the stage of the user within the addiction cycle. In this review, we discuss functional and structural modifications shown to be produced in the cerebellum by opioids that exhibit dependency-inducing properties which provide support for the conclusion that the cerebellum plays a role in addiction.

Reported Benefits of Low-Dose Naltrexone Appear to Be Independent of the Endogenous Opioid System Involving Proopiomelanocortin Neurons and β-Endorphin

Naltrexone is an opioid receptor antagonist approved for the treatment of alcohol and opioid use disorders at doses of 50–150 mg/d. Naltrexone has also been prescribed at much lower doses (3–6 mg/d) for the off-label treatment of inflammation and pain. Currently, a compelling mechanistic explanation for the reported efficacy of low-dose naltrexone (LDN) is lacking and none of the proposed mechanisms can explain patient reports of improved mood and sense of well-being. Here, we examined the possibility that LDN might alter the activity of the endogenous opioid system involving proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARH) in male and female mice. Known actions of POMC neurons could account for changes in pain perception and mood. However, using electrophysiologic, imaging and peptide measurement approaches, we found no evidence for such a mechanism. LDN did not change the sensitivity of opioid receptors regulating POMC neurons, the production of the β-endorphin precursor Pomc mRNA, nor the release of β-endorphin into plasma. Spontaneous postsynaptic currents (sPSCs) onto POMC neurons were slightly decreased after LDN treatment and GCaMP fluorescent signal, a proxy for intracellular calcium levels, was slightly increased. However, LDN treatment did not appear to change POMC neuron firing rate, resting membrane potential, nor action potential threshold. Therefore, LDN appears to have only slight effects on POMC neurons that do not translate to changes in intrinsic excitability or baseline electrical activity and mechanisms beyond POMC neurons and altered opioid receptor sensitivity should continue to be explored.

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.

Successive treatment with naltrexone induces epithelial-mesenchymal transition and facilitates the malignant biological behaviors of bladder cancer cells

Naltrexone is widely used for alleviating opioid-related side effects in cancer patients. However, the effects of naltrexone on cancer progression are controversial in the literature. The present study was carried out to investigate the effects of successive treatment with clinically relevant doses of naltrexone on the malignant biological behaviors of bladder cancer cells. The human bladder cancer T24 cells and mouse bladder cancer MB49 cells were treated with naltrexone. Cell proliferation, migration, and invasion abilities were analyzed. Morphological changes of the cells were confirmed by F-actin immunofluorescence staining. Epithelial-mesenchymal transition (EMT)-related markers and transcriptional factors, as well as activation of the phosphatidylinositol 3 kinase (PI3K)/AKT signaling pathway, were analyzed. Results showed that, compared with the control group, successive treatment with naltrexone significantly promoted the proliferation and decreased the apoptosis of bladder cancer cells, together with increase in cell migration and invasion ability. Continuous treatment with naltrexone also significantly reduced the expression of epithelial markers (E-cadherin and cytokeratin 19), increased the expression of mesenchymal markers (N-cadherin and vimentin) and EMT-inducing transcription factors (Snail and Slug), and further shifted the morphological phenotype of bladder cancer cells to a mesenchymal phenotype. The PI3K/AKT signaling pathway was activated by successive treatment with naltrexone. Notably, incubation with the specific PI3K inhibitor LY294002 together with naltrexone reversed the naltrexone-induced EMT progression. In conclusion, successive treatment with naltrexone may be favorable for the progression of bladder tumors by activating the PI3K/AKT signaling pathway and inducing EMT. Long-term exposure to naltrexone should be used cautiously in patients with bladder cancer.

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.

Analysis of the Immunoexpression of Opioid Receptors and their Correlation with Markers of Angiogenesis, Cell Proliferation and Apoptosis in Breast Cancer

Objective:

Breast cancer is a disease of great concern. The prognosis of this tumor is related to its staging. Opioids are widely used to minimize pain in oncology clinics; however, the relationship between the administration of opioids and their effects on tumor cells has yet to be elucidated. Therefore, this study aimed to evaluate the immunoexpression of mu- (μ) and kappa- (κ) opioid receptors and their correlation with markers of angiogenesis, cell proliferation, and apoptosis in biopsies of breast tumors.

Methods:

Demographic data, tumor characteristics, opioid use, and prognostic factors were collected from medical records. After the selection of the excisional biopsies, immunohistochemistry was performed for μ- and κ-opioid receptors, vascular endothelial growth factor (VEGF), Ki-67, and TUNEL.

Results:

A significant predominance of Ki-67 and μ-opioid receptor immunoexpression in the lymph nodes was observed in patients administered opioid medications. The luminal A subtype showed higher apoptosis levels (TUNEL) compared to the luminal B subtype. Patients with T4 tumor who had recurrence demonstrated a reduced expression of κ-opioid receptors at the lymph node location. Correlation analyses between the μ and κ opioid markers, VEGF, Ki-67, and TUNEL showed that these findings are likely involved in the same mechanisms the cancer of T4 stage breast cancer.

Conclusion:

The κ-opioid receptor has a lower immunoexpression in nodal tumor metastasis with recurrence, whereas the μ-opioid receptor is directly related to expression of TUNEL-positive cells in tumors and indirectly to Ki-67 in nodal metastasis. Neither of the two receptors was expressed in the primary tumor or nodal metastasis in relation to VEGF.

Low-dose naltrexone plays antineoplastic role in cervical cancer progression through suppressing PI3K/AKT/mTOR pathway

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LDN inhibited proliferation in cervical cancer.

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LDN inhibited migration and invasion in cervical cancer cells.

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LDN mediated the propagation property in cervical cancer through PI3K/AKT/mTOR signaling pathway.

The incidence of cervical cancer is increasing annually worldwide. Low-dose naltrexone (LDN) has been reported to delay tumor progression, but the mechanism remains unclear. Here, we found that low-dose naltrexone could upregulate the expression of OGFr. Additionally, LDN could suppress the abilities of colony formation, migration and invasion in cervical cancer cells. LDN could also inhibit cervical cancer progression in mice model. Moreover, LDN indirectly reduced the expressions of PI3K, pAKT and mTOR in vitro and in vivo. Therefore, LDN may be considered a potential treatment option for cervical cancer.

Low Doses Naltrexone: The Potential Benefit Effects for its Use in Patients with Cancer

Naltrexone (NTX) is an opioid antagonist that inhibits cell proliferation in vivo when administered in low doses. Naltrexone in low doses are able to reduce tumor growth by interfering with cell signalling as well as by modifying the immune system. It acts as an opioid growth factor receptor (OGFr) antagonist and the OGF-OGFr axis is an inhibitory biological pathway present in human cancer cells and tissues, being a target for treatment with naltrexone low-dose (LDN). Clinical trials have proposed a unique mechanism(s) allowing LDN to affect tumors. LDN shows promising results for people with primary cancer of the bladder, breast, liver, lung, lymph nodes, colon and rectum. This short review provides further evidence to support the role of LDN as an anticancer agent.

Supraglottic Carcinoma in Intravenous Opioid Drug Abusers: A Distinct Disease with Improved Survival

OBJECTIVES/HYPOTHESIS

Recent evidence indicates an increased prevalence of intravenous opioid drug abusers (IVDAs) among supraglottic squamous cell carcinoma (SG-SCC) patients. This study investigates whether the clinical course of SG-SCC in IVDA differs from SG-SCC in non-IVDA.

STUDY DESIGN

A retrospective case-control study conducted in a in two tertiary referral centers.

METHODS

This case-control study compares IVDA with non-IVDA patients diagnosed and treated for SG-SCC in between 2005 and 2018. Disease-free survival (DFS) and overall survival (OS) were calculated using the Kaplan-Meier estimator. Adjusted odds ratios (ORs) for mortality were calculated using multivariant analyses.

RESULTS

A total of 124 patients were included; 21% (26) were IVDA, and 79% (98) were non-IVDA. Age at diagnosis in the IVDA group versus the non-IVDA group was 53 and 66 years, respectively (P = .001). Nevertheless, the age hazard ratio for OS was calculated and found to have minimal to no effect, 1.05 (95% Cl: 1.025-1.076). Otherwise, the two groups were comparable regarding demographics, other risk factors (i.e., gender, smoking, and alcohol), and comorbidities status, as well as the comparable stage at diagnosis, histologic grading, and treatment modalities. Although the DFS was comparable in both groups, the 5-year OS was 55% in the IVDA group compared with 34% among the non-IVDA patients (P = .04). In multivariant analyses for mortality, positive IVDA history was found to be protective, adjusted OR: 0.263 (95% CI: 0.081-0.854). Similarly, within the subgroup of 100 patients with advanced-stage disease (III and IV), the adjusted OR was 0.118 (95% CI: 0.028-0.495).

CONCLUSIONS

SG-SCC in IVDA patients has a distinct clinical course, presenting at a younger age, and may have improved prognosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:E1190-E1197, 2021.

Low-dose naltrexone inhibits the epithelial-mesenchymal transition of cervical cancer cells in vitro and effects indirectly on tumor-associated macrophages in vivo

The metastasis of cervical cancer has always been a clinical challenge. We investigated the effects of low-dose naltrexone (LDN) on the epithelial mesenchymal transition of cervical cancer cells in vitro as well as its influence on macrophage polarization and associated cytokines in vivo. The results suggested that LDN supressed the proliferation, migration and invasion abilities and promote their apoptosis in Hela cells, whereas the opioid growth factor receptor (OGFr) silenced significantly reversed these effects in vitro. Knockdown the expression of OGFr, the inhibitory of LDN on EMT was weakened. LDN could inhibit cervical cancer progression in nude mice. In additon, LDN indirectly reduced the number of tumor-associated macrophages (TAMs), mainly M2 macrophages, and decreased expression of anti-inflammatory factor IL-10 in the serum of nude mice. These findings demonstrate that LDN could be a potential treatment for cervical cancer.

Intermittent blockade of OGFr and treatment of autoimmune disorders

IMPACT STATEMENT

This mini-review presents information on the intermittent blockade of the opioid growth factor (OGF)-OGF receptor (OGFr) axis by low-dose naltrexone (LDN), and the role of enkephalin (i.e. OGF) in autoimmune disorders, specifically multiple sclerosis, Crohn's, and fibromyalgia. Clinical reports on subjects taking LDN have documented reduced fatigue, few side-effects, and improved overall health. Preclinical studies on mice with experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis, revealed that immunization for EAE reduces serum OGF. Intermittent OGFr blockade with LDN restores serum enkephalin levels that correlate with reduced behavioral and pathological signs of EAE; LDN also increases enkephalin levels in naïve mice. The interplay between LDN, and the onset and treatment of autoimmune diseases, chronic pain, and other addictive behaviors requires further investigation, but highlights a central role for enkephalins and intermittent blockade of the OGF-OGFr pathway in pathogenesis and treatment of these disorders.

Low-Dose Naltrexone (LDN)-Review of Therapeutic Utilization

Naltrexone and naloxone are classical opioid antagonists. In substantially lower than standard doses, they exert different pharmacodynamics. Low-dose naltrexone (LDN), considered in a daily dose of 1 to 5 mg, has been shown to reduce glial inflammatory response by modulating Toll-like receptor 4 signaling in addition to systemically upregulating endogenous opioid signaling by transient opioid-receptor blockade. Clinical reports of LDN have demonstrated possible benefits in diseases such as fibromyalgia, Crohn’s disease, multiple sclerosis, complex-regional pain syndrome, Hailey-Hailey disease, and cancer. In a dosing range at less than 1 μg per day, oral naltrexone or intravenous naloxone potentiate opioid analgesia by acting on filamin A, a scaffolding protein involved in μ-opioid receptor signaling. This dose is termed ultra low-dose naltrexone/naloxone (ULDN). It has been of use in postoperative control of analgesia by reducing the need for the total amount of opioids following surgery, as well as ameliorating certain side-effects of opioid-related treatment. A dosing range between 1 μg and 1 mg comprises very low-dose naltrexone (VLDN), which has primarily been used as an experimental adjunct treatment for boosting tolerability of opioid-weaning methadone taper. In general, all of the low-dose features regarding naltrexone and naloxone have been only recently and still scarcely scientifically evaluated. This review aims to present an overview of the current knowledge on these topics and summarize the key findings published in peer-review sources. The existing potential of LDN, VLDN, and ULDN for various areas of biomedicine has still not been thoroughly and comprehensively addressed.

Regional anesthesia and analgesia in cancer care: is it time to break the bad news?

PURPOSE OF REVIEW

There is ongoing controversy regarding the tumor-protective effects of regional anesthesia in patients undergoing cancer surgery. Evidence of up-to-date systematic reviews will be presented alongside recent updates on the effects of opioids and local anesthetics.

RECENT FINDINGS

In recent years, the literature regarding the effects of regional anesthesia techniques on cancer recurrence has raised many unanswered questions. Ongoing randomized controlled trials may not be able to shed light on the controversial discussion regarding the tumor protective effects of regional anesthesia because the expected effect size and event rate in those studies may be overstated.Recent more refined animal data, provides no evidence to suggest that opioids promote cancer recurrence or facilitate the development of metastatic disease.In addition, local anesthetics have promising preclinical anticarcinogenic effects that extend beyond their voltage-gated sodium channel blocking properties and could be of therapeutic value.

SUMMARY

Cancer recurrence in patients undergoing surgery remains a global burden. Current evidence suggests that regional techniques, opioid analgesia and local anesthetics in onco-anesthesia may require a tailored individual approach due to the phenotypic and genotypic heterogeneity within and between different tumors. The authors surmise that future or ongoing randomized controlled trials regarding regional anesthesia techniques and cancer outcome may not be able to reproduce clear results, as it will be challenging to prove the efficacy of one single intervention (e.g. regional anesthesia) in an otherwise complex multifactorial perioperative oncological setting.

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.

Topical Naltrexone Is a Safe and Effective Alternative to Standard Treatment of Diabetic Wounds

Objective: Diabetes affects more than 29 million individuals in the United States, resulting in healthcare costs approaching $245 billion. Approximately 15% of these individuals will develop a chronic, non-healing foot ulcer (diabetic foot ulcer [DFU]) that, if untreated, may lead to amputation. The current treatments for DFU are expensive, have significant side-effects, and often result in non-compliance. A new topical treatment is described that accelerates cutaneous wound repair and is disease modifying by targeting underlying aberrant diabetic pathways. Approach: The efficacy of naltrexone (NTX), an opioid receptor antagonist, and Regranex® was compared in preclinical studies using type 1 diabetic rats. Dorsal cutaneous wounds were treated topically with 0.03% NTX, Regranex, or moisturizing cream alone. Wound closure, DNA synthesis, and cytokine production were monitored. Results: Wound closure rates with topical NTX in type 1 diabetic rats were comparable to Regranex. Topical NTX accelerated DNA synthesis, as measured by BrdU incorporation, increased mast cells, and enhanced expression of platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF), a marker for angiogenesis. Regranex had little effect on DNA synthesis, mast cells, and VEGF expression relative to vehicle-treated wounds, and it only temporarily increased PDGF expression. Fibroblast growth factor expression was not altered by either treatment. Innovation: Topical application of 0.03% NTX cream accelerates diabetic wound closure. Conclusion: Blockade of the opioid growth factor (OGF)-OGF receptor (OGFr) axis utilizing 0.03% NTX cream is comparable to standard care in preclinical studies, and it provides a safe, inexpensive, and effective alternative for treatment of diabetic wounds.

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.

Ultraviolet A eye irradiation ameliorates colon carcinoma induced by azoxymethane and dextran sodium sulfate through β-endorphin and methionine-enkephalin

BACKGROUND

We previously reported that ultraviolet (UV) A eye irradiation reduces the ulcerative colitis induced by dextran sodium sulfate (DSS). This study examined the effects of UVA on colon carcinoma induced by azoxymethane (AOM) and DSS.

METHODS

We irradiated the eyes of ICR mice with UVA at a dose of 110 kJ/m² using an FL20SBLB-A lamp for the experimental period.

RESULTS

In mice treated with these drugs, the symptom of colon carcinoma was reduced by UVA eye irradiation. The levels of interleukin (IL)-6 and tumor necrosis factor (TNF)-α in the blood were increased in AOM + DSS-treated mice; however, those levels were reduced by UVA eye irradiation. The expression of β-endorphin, methionine-enkephalin (OGF), μ-opioid receptor, and opioid growth factor receptor (OGFR) of the colon was increased in the AOM + DSS-treated mice, and these levels were increased further following UVA eye irradiation. When β-endorphin inhibitor was administered, the ameliorative effect of UVA eye irradiation was reduced, and the effect of eye irradiation disappeared entirely following the administration of naltrexone (inhibitor of both opioid receptor and OGFR).

CONCLUSIONS

These results suggested that UVA eye irradiation exerts major effects on AOM + DSS-induced colon carcinoma.

The Long-term Survival of a Patient With Pancreatic Cancer With Metastases to the Liver After Treatment With the Intravenous α-Lipoic Acid/Low-Dose Naltrexone Protocol

The authors describe the long-term survival of a patient with pancreatic cancer without any toxic adverse effects. The treatment regimen includes the intravenous α-lipoic acid and low-dose naltrexone (ALA-N) protocol and a healthy lifestyle program. The patient was told by a reputable university oncology center in October 2002 that there was little hope for his survival. Today, January 2006, however, he is back at work, free from symptoms, and without appreciable progression of his malignancy. The integrative protocol described in this article may have the possibility of extending the life of a patient who would be customarily considered to be terminal. The authors believe that life scientists will one day develop a cure for metastatic pancreatic cancer, perhaps via gene therapy or another biological platform. But until such protocols come to market, the ALA-N protocol should be studied and considered, given its lack of toxicity at levels reported. Several other patients are on this treatment protocol and appear to be doing well at this time.

The mu opioid receptor: A new target for cancer therapy?

Mu opioids are among the most widely used drugs for patients with cancer with both acute and chronic pain as well as in the perioperative period. Several retrospective studies have suggested that opioid use might promote tumor progression and as a result negatively impact survival in patients with advanced cancer; however, in the absence of appropriate prospective validation, any changes in recommendations for opioid use are not warranted. In this review, the authors present preclinical and clinical data that support their hypothesis that the mu opioid receptor is a potential target for cancer therapy because of its plausible role in tumor progression. The authors also propose the hypothesis that peripheral opioid antagonists such as methylnaltrexone, which reverses the peripheral effects of mu opioids but maintains centrally mediated analgesia and is approved by the US Food and Drug Administration for the treatment of opioid-induced constipation, can be used to target the mu opioid receptor.

Association of opioid requirement and cancer pain with survival in advanced non-small cell lung cancer

BACKGROUND

Pain is associated with shorter survival in non-small cell lung cancer (NSCLC). Lung cancer cells express opioid receptors. Opioids promote angiogenesis, tumour growth, and metastases, and shorten survival in animal models.

METHODS

We examined retrospectively if long-term opioid requirement, independently of chronic pain, is associated with reduced survival in 209 patients with stage IIIB/IV NSCLC. Opioid doses were converted to average oral morphine equivalents (OME). Patients were stratified by proportion of time they reported severe pain, and required <5 or ≥5 mg day^-1 OME. Effects of pain, opioid requirement, and known prognostic variables on overall survival were analysed.

RESULTS

Severe pain before chemotherapy initiation was associated with shorter survival (hazards ratio 1.39, 95% confidence interval, 1.02-1.87, P=0.035). The magnitude of pain and opioid requirement during first 90 days of chemotherapy were predictive of shorter survival: patients with no/mild pain and requiring <5 mg day^-1 OME had 12 months longer median survival compared with those requiring more opioids, experiencing more pain, or both (18 compared with 4.2-7.7 months, P≤0.002). Survival differences (16 compared with 5.5-7.8 months, P<0.001) were similar when chronic pain and opioid requirement were assessed until death or last follow-up. In multivariable models, opioid requirement and chronic pain remained independent predictors of survival, after adjustment for age, stage, and performance status.

CONCLUSIONS

The severity of chronic cancer-related pain or greater opioid requirement is associated with shorter survival in advanced NSCLC, independently of known prognostic factors. While pain adversely influences prognosis, controlling it with opioids does not improve survival. Prospective studies should determine if pain control using equi-analgesic opioid-sparing approaches can improve outcomes.

Featured Article: Selective blockade of the OGF–OGFr pathway by naltrexone accelerates fibroblast proliferation and wound healing

Naltrexone (NTX) is an opioid receptor antagonist that acts at classical and non-classical opioid receptors including the opioid growth factor receptor (OGFr). Animal models of type 1 and type 2 diabetes, as well as normal rodents, have shown that topical NTX enhances the healing rates of corneal epithelium and full-thickness cutaneous wounds. The mechanism of this general opioid antagonist on growth, and in particular the specific receptor pathway involved, is not understood. Tissue culture studies using NIH 3T3 fibroblasts and primary rat auricular fibroblasts were established to evaluate growth following opioid receptor antagonist treatment. Treatment of cells with CTOP, naltrindole, or nalmefene, selective antagonists for mu, delta, and kappa opioid receptors, respectively, did not accelerate cell replication. Addition of the classical opioid receptor peptides DAMGO, DPDPE, or EKC did not alter cell growth, suggesting that the classical opioid receptors were not involved in cutaneous wound healing. However, NTX (10−6 M) increased the growth of NIH 3T3 fibroblasts in culture over a 96-h period, and the specific ligand OGF decreased cell growth, supporting that the OGF-OGFr axis is tonically active and constitutively expressed in fibroblasts, the primary cell type in granulation tissue of the skin. Transfection of NIH 3T3 cells with OGFr siRNA reduced receptor protein; subsequent treatment with NTX did not accelerate cell proliferation. These data indicate that blockade of the OGFr pathway enhances proliferation of fibroblasts in vitro, and in a primary culture of auricular fibroblasts, suggesting that the effect of NTX on growth is mediated through the OGF-OGFr axis. Finally, antagonists for classical opioid receptors as well as NTX were topically applied to cutaneous wounds in type 1 diabetic rats; only NTX accelerated wound closure. These studies indicate that the mechanistic pathway underlying the effects of NTX to enhance cutaneous wound closure in diabetic and nondiabetic subjects is specific blockade of the OGF–OGFr regulatory axis.

Topical Naltrexone as Treatment for Type 2 Diabetic Cutaneous Wounds

Objective: Type 2 diabetes (T2D) is associated with impaired cutaneous wound healing and can result in ulceration, infection, and/or amputation. More than 25 million people in the United States have T2D and are vulnerable to epithelial-related complications. Current therapies are limited in their efficacy. New treatments for full-thickness cutaneous wounds that focus on underlying diabetic pathways are needed. Approach: Topical application of the opioid receptor antagonist naltrexone (NTX) dissolved in cream reverses delayed wound closure in type 1 diabetic rat by the acceleration of reepithelialization and enhancement of angiogenesis and remodeling. NTX blocks the opioid growth factor (OGF)-OGF receptor (OGFr) axis and upregulates DNA synthesis and cell proliferation. To investigate whether NTX is an effective therapy for T2D wound closure, genetically obese mice (db/db) and normal C57Bl/6J mice received full-thickness cutaneous wounds. Wounds (5 mm in diameter) were treated topically three times daily with 10-5 M NTX or sterile saline dissolved in cream and photographed every 2 days. Results: Wounds in db/db mice treated with saline were 11-92% larger than those in normal mice throughout the 2-week observation. Topical NTX therapy in T2D mice reduced the residual wound size by 13-30% between days 8 and 14 relative to diabetic mice receiving saline. Reepithelialization and DNA synthesis, as analyzed by epithelial thickness and BrdU labeling indexes, respectively, were accelerated in NTX-treated wounds. Innovation and Conclusion: These data suggest that the OGF-OGFr axis plays a role in epithelial-related complications of T2D and that blockade of this pathway by NTX may be an effective treatment for wound repair.

Ex vivo studies for the passive transdermal delivery of low-dose naltrexone from a cream; detection of naltrexone and its active metabolite, 6β-naltrexol, using a novel LC Q-ToF MS assay

Naltrexone (NTX) is a long-acting opiate antagonist. Low-dose naltrexone (LDN) therapy has shown promising results in the treatment of several autoimmune disorders. Our aim was to formulate NTX into a cream for the delivery of LDN and develop an analytical technique for the quantification of NTX and its active metabolite 6-β-naltrexol (NTXol) during transdermal diffusion cell permeation studies. A 1% w/w NTX cream was formulated and drug permeation was examined over 24 h using static Franz diffusion cells mounted with pig skin. A Liquid Chromatography Quadrupole-Time of Flight Mass Spectrometry (LC-MS Q-ToF) method was developed for the detection of NTX and NTXol in the receptor solution, skin membrane and residual cream on the donor chamber after completion of the diffusion studies. The cream formulation exhibited steady state release of NTX over 24 h after an initial lag time of 2.74 h. The bioconversion of NTX to NTXol in the skin membrane was 1.1%. It was concluded that the cream may be an effective formulation for the sustained transdermal delivery of LDN. The novel LC Q-ToF MS method allowed the accurate measurement of NTX and NTXol levels across the diffusion cell assemblies and the quantification of NTX metabolism in the skin.

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

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

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.

G protein-coupled receptors as therapeutic targets for multiple sclerosis

G protein-coupled receptors (GPCRs) mediate most of our physiological responses to hormones, neurotransmitters and environmental stimulants. They are considered as the most successful therapeutic targets for a broad spectrum of diseases. Multiple sclerosis (MS) is an inflammatory disease that is characterized by immune-mediated demyelination and degeneration of the central nervous system (CNS). It is the leading cause of non-traumatic disability in young adults. Great progress has been made over the past few decades in understanding the pathogenesis of MS. Numerous data from animal and clinical studies indicate that many GPCRs are critically involved in various aspects of MS pathogenesis, including antigen presentation, cytokine production, T-cell differentiation, T-cell proliferation, T-cell invasion, etc. In this review, we summarize the recent findings regarding the expression or functional changes of GPCRs in MS patients or animal models, and the influences of GPCRs on disease severity upon genetic or pharmacological manipulations. Hopefully some of these findings will lead to the development of novel therapies for MS in the near future.

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

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

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.