Autocrine inhibitory influences of α-melanocyte-stimulating hormone in malignant pleural mesothelioma

Melanocortin receptor agonist ACTH 1-39 protects rat forebrain neurons from apoptotic, excitotoxic and inflammation-related damage

Patients with relapsing-remitting multiple sclerosis (RRMS) are commonly treated with high doses of intravenous corticosteroids (CS). ACTH 1-39, a member of the melanocortin family, stimulates production of CS by the adrenals, but melanocortin receptors are also found in the central nervous system (CNS) and on immune cells. ACTH is produced within the CNS and may have direct protective effects on glia and neurons independent of CS. We previously reported that ACTH 1-39 protected oligodendroglia (OL) and their progenitors (OPC) from a panel of excitotoxic and inflammation-related agents. Neurons are the most vulnerable cells in the CNS. They are terminally differentiated, and sensitive to inflammatory and excitotoxic insults. For potential therapeutic protection of gray matter, it is important to investigate the direct effects of ACTH on neurons. Cultures highly enriched in neurons were isolated from 2-3 day old rat brain. After 4-7 days in culture, the neurons were treated for 24h with selected toxic agents with or without ACTH 1-39. ACTH 1-39 protected neurons from death induced by staurosporine, glutamate, NMDA, AMPA, kainate, quinolinic acid, reactive oxygen species and, to a modest extent, from rapidly released NO, but did not protect against kynurenic acid or slowly released nitric oxide. Our results show that ACTH 1-39 protects neurons in vitro from several apoptotic, excitotoxic and inflammation-related insults.

The role of interleukin-6 in malignant mesothelioma

Malignant mesothelioma (MM) still remains a dismal disease with a median overall survival between 9-12 months. During the past decade since the introduction of the multi-folate antagonist, pemetrexed, there have been no significant advances in its systemic treatment, particularly with novel therapeutics that have exhibited varying degrees of success in other solid tumours. In recent years, the pleiotropic proinflammatory cytokine, interleukin-6 (IL-6) has emerged as a mediator of pivotal processes such as cell proliferation and chemoresistance within the mesothelioma tumour microenvironment in addition to clinical symptoms commonly witnessed in this disease. This manuscript provides a brief summary on the pathophysiology and clinical management of MM, followed by the role of IL-6 in its tumourigenesis and the rationale for utilising anti-IL-6 therapeutics alongside standard chemotherapy and targeted agents in an attempt to prolong survival.

Systemic pro-opiomelanocortin expression induces melanogenic differentiation and inhibits tumor angiogenesis in established mouse melanoma

Malignant melanoma is one of the leading causes of cancer mortality worldwide, underlining the need for effective novel therapies. In this study, the therapeutic efficacy and mechanism of systemic pro-opiomelanocortin (POMC) therapy were evaluated in mice bearing established melanoma. Injection of adenovirus encoding POMC (Ad-POMC) led to hepatic POMC overexpression and elevated adrenocorticotropin (ACTH) levels in the circulation. Systemic POMC therapy significantly attenuated the growth of established melanoma and prolonged the survival of tumor-bearing mice. Histological analysis revealed that systemic POMC therapy induced melanogenic differentiation while reducing melanoma growth. In addition, POMC therapy also elicited a significant reduction in the neovascular network of melanoma. Last, we demonstrated that POMC-derived peptides, including ACTH, α-melanocyte-stimulating hormone (α-MSH), and β-MSH, are involved in POMC-mediated melanogenic differentiation and angiogenesis inhibition. In summary, systemic POMC therapy suppresses melanoma growth via induction of melanogenic differentiation and angiogenesis blockade, thereby demonstrating its potential as a novel treatment modality for melanoma.

Prophylactic proopiomelanocortin expression alleviates capsaicin-induced neurogenic inflammation in rat trachea

Neurogenic inflammation frequently causes acute plasma leakage in airways and life-threatening pulmonary edema. However, limited strategies are available to alleviate neurogenic inflammation. Proopiomelanocortin (POMC) is the precursor of anti-inflammatory melanocortins, which have been proposed of therapeutic potential for various inflammatory diseases. The present study aimed to evaluate whether peripheral POMC expression ameliorated capsaicin-induced acute neurogenic inflammation in rat trachea. Prophylactic POMC expression was achieved by intravenous injection of adenovirus encoding POMC (Ad-POMC), which led to POMC expression in livers and elevated plasma adrenocorticotropin levels for approximately 60 days. After gene delivery for 7 days, neurogenic inflammation was induced in rats by capsaicin injection. The extent of capsaicin-evoked plasma leakage in trachea was alleviated in Ad-POMC-treated rats compared with animals of control groups (P < 0.01). Moreover, the number of endothelial gaps in tracheal venules was also significantly decreased in Ad-POMC-treated animals (P < 0.01). Prophylactic POMC expression, however, did not alter the basal substance P (SP) expression or the capsaicin-induced SP elevation in trachea and circulation. Instead, cell cultures studies revealed that POMC overexpression or application of POMC-derived melanocortins potently inhibited the SP-induced migration of endothelial cells (P < 0.01), thereby possibly contributing to the attenuation of endothelial gap formation and plasma leakage. The present study indicates that the anti-inflammatory POMC gene vector or melanocortins may constitute a therapeutic alternative for neurogenic inflammation.

Identification of potential therapeutic targets in malignant mesothelioma using cell-cycle gene expression analysis

Cell-cycle defects are responsible for cancer onset and growth. We studied the expression profile of 60 genes involved in cell cycle in a series of malignant mesotheliomas (MMs), normal pleural tissues, and MM cell cultures using a quantitative polymerase chain reaction-based, low-density array. Nine genes were significantly deregulated in MMs compared with normal controls. Seven genes were overexpressed in MMs, including the following: CDKN2C, cdc6, cyclin H, cyclin B1, CDC2, FoxM1, and Chk1, whereas Ube1L and cyclin D2 were underexpressed. Chk1 is a principal mediator of cell-cycle checkpoints in response to genotoxic stress. We confirmed the overexpression of Chk1 in an independent set of 87 MMs by immunohistochemistry using tissue microarrays. To determine whether Chk1 down-regulation would affect cell-cycle control and cell survival, we transfected either control or Chk1 siRNA into two mesothelioma cell lines and a nontumorigenic (Met5a) cell line. Results showed that Chk1 knockdown increased the apoptotic fraction of MM cells and induced an S phase block in Met5a cells. Furthermore, Chk1 silencing sensitized p53-null MM cells to both an S phase block and apoptosis in the presence of doxorubicin. Our results indicate that cell-cycle gene expression analysis by quantitative polymerase chain reaction can identify potential targets for novel therapies. Chk1 knockdown could provide a novel therapeutic approach to arrest cell-cycle progression in MM cells, thus increasing the rate of cell death.

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.

Quantitative analysis of MC1R gene expression in human skin cell cultures

To address the issue of melanocortin-1 receptor (MC1R) expression in non-melanocytic cells, we have quantitatively evaluated the relative expression levels of both MC1R mRNA and protein in a subset of different cell types. Using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) at high cycle numbers, we detected MC1R mRNA in all cell types examined, including human embryonic kidney-293 (HEK 293) cells, a cell type widely used as a negative control in melanocortin expression studies. Quantitative real-time PCR revealed the highest levels of MC1R transcripts were in melanocytic cells, whereas the keratinocyte and fibroblast cell cultures examined had only a low level of expression, similar to that of HEK 293 cells. Antibody mediated detection of MC1R protein in membrane extracts demonstrated exogenous receptor in MC1R transfected cell lines, as well as endogenous MC1R in melanoma cells. However, radioligand binding procedures were required to detect MC1R protein of normal human melanocytes and no surface expression of MC1R was detected in any of the non-melanocytic cells examined. This was consistent with their low level of mRNA, and suggests that, if present, the levels of surface receptor are significantly lower than that in melanocytes. The capacity of such limited levels of MC1R protein to influence non-melanocytic skin cell biology would likely be severely compromised. Indeed, the MC1R agonist [NIe(4), D-Phe(7)] alpha-melanocyte stimulating hormone (NDP-MSH) was unable to elevate intracellular cyclic adenosine monophosphate (cAMP) levels in the keratinocyte and fibroblast cells examined, whereas a robust increase was elicited in melanocytes. Although there are a variety of cell types with detectable MC1R mRNA, the expression of physiologically significant levels of the receptor may be more restricted than the current literature indicates, and within epidermal tissue may be limited to the melanocyte.

Reduced expression of the melanocortin-1 receptor in human liver during brain death

OBJECTIVE

There is evidence that brain death has detrimental effects on peripheral organs. Clinical and experimental studies on organ donors showed marked inflammation in tissue samples of livers and kidneys collected during brain death. The inflammatory reaction is characterized by release of cytokines and inflammatory cell infiltration. Because melanocortins and their receptors are significant modulators of inflammation, we hypothesized that downregulation of melanocortin receptors during brain death could contribute to enhance inflammation.

METHODS

Using real-time polymerase chain reaction (PCR) analysis, we determined expression of melanocortin receptors in liver biopsies obtained from brain-dead organ donors before cold ischemia and in normal liver tissue during resection of benign focal lesions of the liver. Tissue biopsies were also analyzed for expression of intercellular adhesion molecule-1 (ICAM-1), which has a central function in inflammatory cell migration.

RESULTS

Expression of melanocortin-1 receptor (MC1R) mRNA was markedly reduced in liver samples obtained from brain-dead organ donors compared to hepatic tissue collected during resection of benign focal lesions of the liver. Conversely, expression of the adhesion molecule ICAM-1 was significantly increased in livers of brain-dead organ donors.

CONCLUSIONS

Disruption of the endogenous anti-inflammatory circuit based on MC1R could contribute to tissue damage during brain death.

Gene transfer of pro-opiomelanocortin prohormone suppressed the growth and metastasis of melanoma: involvement of alpha-melanocyte-stimulating hormone-mediated inhibition of the nuclear factor kappaB/cyclooxygenase-2 pathway

Pro-opiomelanocortin (POMC) is a prohormone of various neuropeptides, including corticotropin, alpha-melanocyte-stimulating hormone (alpha-MSH), and beta-endorphin (beta-EP). POMC neuropeptides are potent inflammation inhibitors and immunosuppressants and may exert opposite influences during tumorigenesis. However, the role of POMC expression in carcinogenesis remains elusive. We evaluated the antineoplastic potential of POMC gene delivery in a syngenic B16-F10 melanoma model. Adenovirus-mediated POMC gene delivery in B16-F10 cells increased the release of POMC neuropeptides in cultured media, which differentially regulated the secretion of pro- and anti-inflammatory cytokines in lymphocytes. POMC gene transfer significantly reduced the anchorage-independent growth of melanoma cells. Moreover, pre- or post-treatment with POMC gene delivery effectively retarded the melanoma growth in mice. Intravenous injection of POMC-transduced B16-F10 cells resulted in reduced foci formation in lung by 60 to 70% of control. The reduced metastasis of POMC-transduced B16-F10 cells could be attributed to their attenuated migratory and adhesive capabilities. POMC gene delivery reduced the cyclooxygenase-2 (COX-2) expression and prostaglandin (PG) E(2) synthesis in melanoma cells and tumor tissues. In addition, application of NS-398, a selective COX-2 inhibitor, mimicked the antineoplastic functions of POMC gene transfer in melanoma. The POMC-mediated COX-2 down-regulation was correlated with its inhibition of nuclear factor kappaB (NFkappaB) activities. Exogenous supply of alpha-MSH inhibited NFkappaB activities, whereas application of the alpha-MSH antagonist growth hormone-releasing peptide-6 (GHRP-6) abolished the POMC-induced inhibition of NFkappaB activities and melanoma growth in mice. In summary, POMC gene delivery suppresses melanoma via alpha-MSH-induced inhibition of NFkappaB/COX-2 pathway, thereby constituting a novel therapy for melanoma.

Suppression of Melanotroph Carcinogenesis Leads to Accelerated Progression of Pituitary Anterior Lobe Tumors and Medullary Thyroid Carcinomas in Rb+/− Mice

Mice with a single copy of the retinoblastoma gene (Rb+/−) develop a syndrome of multiple neuroendocrine neoplasia. They usually succumb to fast-growing, Rb-deficient melanotroph tumors of the pituitary intermediate lobe, which are extremely rare in humans. Thus, full assessment of Rb role in other, more relevant to human pathology, neoplasms is complicated. To prevent melanotroph neoplasia while preserving spontaneous carcinogenesis in other types of cells, we have prepared transgenic mice in which 770-bp fragment of pro-opiomelanocortin promoter directs expression of the human RB gene to melanotrophs (TgPOMC-RB). In three independent lines, transgenic mice crossed to Rb+/− background are devoid of melanotroph tumors but develop the usual spectrum of other neoplasms. Interestingly, abrogation of melanotroph carcinogenesis results in accelerated progression of pituitary anterior lobe tumors and medullary thyroid carcinomas. A combination of immunologic tests, cell culture studies, and tumorigenicity assays indicates that α-melanocyte–stimulating hormone, which is overproduced by melanotroph tumors, attenuates neoplastic progression by decreasing cell proliferation and inducing apoptosis. Taken together, we show that cell lineage–specific complementation of Rb function can be successfully used for refining available models of stochastic carcinogenesis and identify α-melanocyte–stimulating hormone as a potential attenuating factor during progression of neuroendocrine neoplasms.