Expression of the pro-opiomelanocortin gene in lung neuroendocrine tumours: in situ hybridization and immunohistochemical studies

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.

Local pulmonary opioid network in patients with lung cancer: a putative modulator of respiratory function

Recently, there has been growing interest in the opioid regulation of physiological respiratory function. However, evidence for a local opioid network that includes endogenous opioid peptides and their receptors is scarce. Tissue samples from patients with lung cancer were examined by immunohistochemistry to identify the components of the opioid network: beta-endorphin (END); its precursor, proopiomelanocortin (POMC); the key processing enzymes prohormone convertase 1 and 2; carboxypeptidase E; and END's corresponding opioid receptor, the mu-opioid receptor (MOR). Additionally, we tested pulmonary function parameters in a patient with advanced lung cancer after inhalation of nebulized morphine. Confocal immunofluorescence microscopy revealed that the opioid precursor POMC colocalizes with its active peptide END, key processing enzymes and MOR in alveolar macrophages, submucosal glands, cancerous cells, and pulmonary neuroendocrine cells within the bronchial epithelium. In addition, MOR was identified on sensory nerve endings within the bronchial epithelium. Furthermore, nebulized morphine improved pulmonary function parameters in advanced lung cancer. These findings provide evidence of a local opioid network in functionally important anatomical structures of the respiratory system; this network consists of all the machinery required for POMC processing into active peptides, such as END, and contains the receptors for END. Our findings indicate a need for further clinical trials to elucidate the modulatory function of peripheral endogenous opioids in the human lung.

In situ hybridization and its diagnostic applications in pathology

In situ hybridization (ISH) is a technique by which specific nucleotide sequences are identified in cells or tissue sections. These may be endogenous, bacterial or viral, DNA or RNA. On the basis of research applications, the technique is now being translated into diagnostic practice, mainly in the areas of gene expression, infection and interphase cytogenetics. Diagnostic applications are most often based on short nucleotide sequences (oligomers) labelled with non-isotopic reporter molecules, and sites of binding may be localized by histochemical or immunohistochemical methods. The technique can be applied to routinely fixed and processed tissues; with some targets, it is even possible to obtain hybridization in autopsy material. ISH has been used to detect messenger RNA (mRNA) as a marker of gene expression, where levels of protein storage are low; for example, to confirm an endocrine tumour as the source of excess hormone production. Its application in infectious diseases has to date been mainly in viral infections, such as the typing of human papillomavirus (HPV) or the detection of Epstein-Barr virus by the presence of small nuclear RNAs (EBERs). The expression of mRNAs for histone proteins has been used to detect cells in S phase, and related methods may be applied to detect apoptotic cells. Using probes to chromosome-specific sequences, it is possible to detect aneuploidy, and to document changes in specific chromosomes, which may have prognostic significance in some tumours, such as B-cell chronic lymphatic leukaemia. Using sequence-specific probes, translocations can be identified, such as the t(11;12) of Ewing's sarcoma. This review presents an outline of the technique of in situ hybridization and discusses areas of current and potential diagnostic application.

Small cell carcinoma of the vagina causing Cushing's syndrome by ectopic production and secretion of ACTH: a case report

BACKGROUND

Small cell carcinomas of pulmonary or extrapulmonary origin are neuroendocrine tumors classically associated with ectopic hormone production, particularly ACTH secretion resulting in Cushing's syndrome. However, ectopic Cushing's syndrome has not previously been reported in the setting of small cell carcinoma of the vagina.

METHODS

A primary vaginal tumor with hepatic metastases was evaluated with light microscopy. Serum cortisol and plasma ACTH levels were evaluated by radioimmunoassay and immunoradiometric assay, respectively, during a standard high-dose (8 mg) overnight dexamethasone suppression test.

RESULTS

Vaginal small cell carcinoma with hepatic metastases was demonstrated. Electrolyte abnormalities, elevated cortisol and ACTH levels, and failure to suppress ACTH secretion during high-dose dexamethasone administration confirmed the diagnosis of ectopic ACTH syndrome.

CONCLUSIONS

This case report establishes a clinical association between vaginal small cell carcinoma and ectopic Cushing's syndrome, confirming the neuroendocrine potential of this malignancy and features common to small cell neoplasms originating in other sites.

Neuroendocrine differentiation in lung cancer

The human lung has a resident population of neuroendocrine (NE) cells. These are characterised by the presence of neurosecretory granules and by a number of histochemical and immunocytochemical reactions. NE differentiation is a defining feature of classical and atypical carcinoid tumours and is seen in most small cell lung cancers (SCLC). Such differentiation has also been described in up to one third of non-small cell lung cancers (NSCLC). As demonstrated in an accompanying paper in this issue of the Journal, the reporting of NE differentiation varies with the technical approach used and with the nature of the tissue specimen. This phenomenon is a reflection of the histological and biological heterogeneity of lung cancer and has not been shown to be of clinical utility.

In situ hybridization techniques for the analysis of gene expression: applications in tumor pathology

In situ hybridization (ISH) has emerged over the past decade as an extraordinarily sensitive technique for the detection of gene expression at the cellular level. Advances in probe preparation and labeling methods have facilitated the transfer of this technology from the research laboratory to the clinical arena. In contrast to immunohistochemistry, which is dependent on the protein content of cells, ISH analyses permit the identification of cells on the basis of their contents of specific messenger RNAs (mRNAs) encoding the products of interest. These methods provide a critical approach for the analysis of heterogeneity in tumors that typically contain cells at different phases of neoplastic progression and at multiple levels of differentiation and functional activity. In situ hybridization methods have been of particular value for studies of mRNAs encoding oncogenes, hormones, secretory proteins, cytokines, and a wide variety of other cellular products. Advances in ISH technology, including polymerase chain reaction (PCR) based methods, offer particular promise for examining genes with low levels of expression at the cellular level.

Proopiomelanocortin mrna expression by small cell bladder carcinoma associated with cushing's syndrome: diagnostic contribution of in situ hybridization

A case of ectopic ACTH secretion by primary small-cell carcinoma of the urinary bladder is described. The patient, a 38-year-old woman, presented with Cushing's syndrome. Although immunocytochemistry of the tumor for ACTH and corticotropin-releasing factor yielded negative results, in situ hybridization demonstrated a conclusive signal for proopiomelanocortin messenger RNA. This case report shows the value of in situ hybridization in diagnostic pathology.