Forms of neurohypophysial peptides generated by tumors, and factors regulating their expression

Growth Impairment of Small-Cell Cancer by Targeting Pro-Vasopressin with MAG-1 Antibody

Previously we demonstrated that human small-cell lung cancer (SCLC) seems to universally express the vasopressin gene, and this leads to the presence of a cell surface marker representing the entire pro-hormone precursor. In this study, we show this marker can be targeted with MAG-1, a mouse monoclonal antibody against a C-terminal moiety on pro-vasopressin. In vitro targeting of cell lines derived from primary and recurrent disease demonstrates attachment of antibody to the cell surface followed by internalization. In vivo targeting with ⁹⁹Tc-labeled Fab fragments of MAG-1 shows selective attachment to xenografts. In vivo treatment of tumors from classical cell line, NCI H345, with either ~1.65 mCi (~1.65 mg)/kg body weight (BW) of ⁹⁰Yttrium-labeled MAG-1, or ~1.65 mg/kg BW native MAG-1, delivered every second day for 6 days produced similar reductions in the growth rate to ~50% (p < 0.03). When dosing with native MAG-1 was escalated to daily amounts of ~3.3 mg/kg BW over 16 days, tumor growth rates fell to ~33% of saline controls (p < 0.005). Examination of tumors treated with this higher dosing demonstrated the presence in several of extensive apoptosis. Normal tissues seemed to be unaffected. A larger dosage of MAG-1 (~6.6 mg/kg BW) given daily for 14 days was used to treat xenografts of the variant cell line NCI H82 representing recurrent disease. This treatment decreased the rate of increase in tumor size by half, and doubling time ~3-fold. Increases in cleaved PARP supported increased apoptosis with antibody treatment. We believe these data provide evidence that the growth rate of SCLC tumors can be extensively reduced by treatment with MAG-1 antibody, and that a humanized form of this antibody could, in future, be potentially used for targeting therapy onto recurrent SCLC in patients.

Provasopressin expression by breast cancer cells: implications for growth and novel treatment strategies

The arginine vasopressin (AVP) gene is expressed in certain cancers such as breast cancer, where it is believed to act as an autocrine growth factor. However, little is known about the regulation of the AVP protein precursor (proAVP) or AVP-mediated signaling in breast cancer and this study was undertaken to address some of the basic issues. The cultured cell lines examined (Mcf7, Skbr3, BT474, ZR75, Mcf10a) and human breast cancer tissue extract were found to express proAVP mRNA. Western analysis revealed multiple forms of proAVP protein were present in cell lysates, corresponding to those detected in human hypothalamus extracts. Monoclonal antibodies directed against different regions of proAVP bound to intact live Mcf7 and Skbr3 cells. Dexamethasone increased the amount of proAVP-associated glycopeptide (VAG) secreted by Skbr3 cells and a combination of dexamethasone, IBMX and 8br-cAMP increased cellular levels of VAG. Exogenous AVP (1, 10, and 100 nM) elevated phospho-ERK1/2 levels, and increased cell proliferation was observed in the presence of 10 nM AVP. Concurrent treatment with the V1a receptor antagonist SR49059 reduced the effects of AVP on proliferation in Mcf7 cells, and abolished it in Skbr3 cells. Results here show that proAVP components are found at the surface of Skbr3 and Mcf7 cells and are also secreted from these cells. In addition, they show that AVP promotes cancer cell growth, apparently through a V1-type receptor-mediated pathway and subsequent ERK1/2 activation. Thus, strategies for targeting proAVP should be examined for their effectiveness in diagnosing and treating breast cancer.

Immunohistochemical detection of NRSA on small cell lung cancer with a monoclonal antibody (MAG-1) that recognizes the carboxyl terminus of provasopressin

A single monoclonal antibody (MAG-1) directed against the C-terminal 18-amino acid region (VAGc18) of provasopressin was examined as an agent for recognizing the tumor-specific NRSA marker common to small cell lung cancer (SCLC) in formalin-fixed tissues with ABC immunohistochemistry. SCLC tumors were obtained from several tissue locations and included primary, metastatic, and recurrent disease. Positive staining was found in 91% of cases (53/58). All five of the unreactive tumors were of the lungs or chest wall, and there did not appear to be an association of this negativity with disease stage, age, or sex. Alternatively, almost all primary lesions, almost all metastatic lesions, and all recurrent lesions examined gave a positive reaction with MAG-1. For this study, vasopressin-producing cells of the human anterior hypothalamus served as a positive control, while negative controls comprised normal lung tissue, tumor that received MAG-1 in the presence of an excess of antigen (VAGc18 peptide), or tumor reacted with a commercial IgG1 isotype as primary antibody. All of the results indicate that MAG-1 can be effectively used to selectively identify the NRSA marker on almost all SCLC tumors, at all disease stages, and at all locations. Since all four tumors tested showing no reactivity with MAG-1 gave a positive reaction for synaptophysin, it is proposed that a combined use of MAG-1 with synaptophysin antibodies could allow all SCLC tumors to be detected by ABC immunohistochemistry.

Gene regulation of vasopressin and vasopressin receptors in cancer

It is proposed that neuropeptide production by tumours is an important part of a special process of oncogenic transformation rather than a pre-existing condition of progenitor cells; this concept is called Selective Tumour gene Expression of Peptides essential for Survival (STEPS). All small-cell lung cancers and breast cancers evidently express the vasopressin gene, and this gene seems to be structurally normal in all but exceptional cases. Vasopressin gene expression in cancer cells leads to the production of both normal and abnormal forms of tumour vasopressin mRNA and proteins. Although the necessary post-translational processing enzymes are expressed in these cells, most processing seems to be extragranular, and most of the protein products become components of the plasma membrane. Small-cell lung cancer and breast cancer cells also express normal genes for all vasopressin receptors and produce normal vasopressin receptor mRNAs and V1a and V1b receptor proteins, and the vasopressin-activated calcium mobilising (VACM) protein; plus both normal and abnormal forms of the V2 receptor. Through these receptors, vasopressin exercises multifaceted effects on tumour growth and metabolism. A normal protein vasopressin gene promoter seems to be present in small-cell lung cancer cells, and this promoter contains all of the transcriptional elements known to be involved in gene regulation within hypothalamic neurones. Since these elements largely account for regulation of tumour gene expression observed in vitro, it is likely that as yet unknown factors are selectively produced by tumours in vivo to account for the observed seemingly autonomous or unregulated production of hormone in tumour patients. Promoter elements thought to be responsible for selective vasopressin gene expression in small-cell lung cancer probably include an E-box and a neurone restrictive silencer element close to the transcription start site. It is possible that transcription factors acting at these same elements can explain selective vasopressin expression, not only in small-cell tumours, but also in all other tumours such as breast cancer. By extrapolation, similar mechanisms might also be responsible for the expression of additional features that characterize the 'neuroendocrine' profile of these cancers.

The thymic repertoire of neuroendocrine-related self antigens: biological role in T-cell selection and pharmacological implications

Thymic epithelium, including nurse cells (TEC/TNC), as well as other thymic stromal cells (macrophages and dentritic cells), express a repertoire of polypeptide belonging to various neuroendocrine protein families (such as the neurophypophysial, tachykinin, neurotensin and insulin families). A hierarchy of dominance exists in the organization of the thymic repertoire of neuroendocrine precursors. Oxytocin (OT) is more expressed in the TEC/TNC than vasopressin (VP); insulin-like growth factor 2 (IGF-2) thymic expression predominates over IGF-1, and much more over (pro)insulin. Thus, OT was proposed to be the self antigen of the neurohypophysial family, and IGF-2 the self antigen precursor of the insulin family. The dual role of the thymus in T-cell life and death is recapitulated at the level of the thymic neuroendocrine protein repertoire. Indeed, thymic polypeptides behave as accessory signals involved in T-cell development and positive selection according to the cryptocrine model of signaling. Moreover, thymic neuroendocrine polypeptides are the source of self antigens presented by thymic MHC molecules to developing pre-T cells. This presentation might induce the negative selection of T cells bearing a randomly rearranged antigen receptor (TCR) oriented against neuroendocrine families. Using an animal model of autoimmune type 1 diabetes (BB rat), we have shown a defect in intrathymic expression of the self antigen of the insulin family (IGF-2) and in IGF-2-mediated T-cell education to recognize and tolerate the insulin family. Altogether these studies have enlightened the crucial role played by the thymus in the induction of the central self tolerance of neuroendocrine families. The tolerogenic properties of thymic self peptides could be used in a novel type of vaccination for the prevention of autoimmune diseases.

Functional vasopressin V1 type receptors are present in variant as well as classical forms of small-cell carcinoma

Vasopressin and other neuropeptides are believed to serve as autocrine growth factors for small-cell carcinoma of the lung (SCCL), and these mitogenic influences are reported to involve increases in intracellular Ca2+. Of the classical and variant forms of SCCL, the latter is not only more drug-resistant but also refractory to vasopressin, and other peptides, with respect to changes in intracellular Ca2+. It is currently unclear if this refractiveness of variant SCCL is due to the absence of involved peptide receptors, to the production of abnormal receptors, or to abnormalities in components of induced transduction cascades. In this study, the presence of structurally-normal and functional vasopressin V1a receptors, was examined in a classical SCCL cell line (NCI H345) that is Ca(2+)-responsive to vasopressin, and a variant SCCL cell line (NCI H82) that is unresponsive in this regard to the peptide. Both cell lines were shown to express an mRNA of 1.9 Kb for the vasopressin V1a receptor. RT-PCR, cloning, and DNA sequencing revealed the structure of the mRNA was identical for both cell lines, and, in turn, identical to the mRNA expressed for this receptor by human liver cells. In both cell lines and liver, this mRNA was shown by Western analysis and RIA to generate major protein products of approximately 70,000 and 43,000 daltons. Vasopressin action on NCI H82 cells resulted in a substantial rise in the levels of total inositol phosphates. However, it was reaffirmed that these changes in inositol phosphates were not accompanied by a rise in Ca2+ levels. All of these data indicate that variant SCCL, as well as classical SCCL, expresses structurally-normal and functional vasopressin V1a receptors, but their activation in variant SCCL raises IP3 levels without a corresponding rise in intracellular Ca2+. This difference between the two SCCL sub-types therefore involves either steps in the inositol triphosphate cascade beyond the activation of phospholipase C, or alternatively, components of other transduction events that might be involved with changes in intracellular Ca2+.

The immunological impairment of arcuate neuropeptide Y neurons by ricin A chain produces persistent decrease of food intake and body weight

Neuropeptide Y is demonstrated as a potent orexigenic peptide when injected into the rat hypothalamic paraventricular nuclei. The neuropeptide Y innervation of paraventricular nuclei originates from both hypothalamic arcuate nuclei and brainstem neurons, whose specific role in the control of food intake is still under discussion. To assess the role of the arcuate neuropeptide Y in the regulation of food intake, we propose a new method for immunologically impairing the neuronal secretion of neuropeptide Y from a unique brain site. The monoclonal antibody to the neuropeptide Y precursor epitope, the C-flanking peptide, was microinjected with two cellular toxins (the ricin A chain and the monensin) into the hypothalamic arcuate nuclei or paraventricular nuclei. One microinjection into the arcuate nuclei reduced the food intake and body weight gain for 10 days. It prevented the food intake stimulation usually induced by a 12 h food deprivation. This decrease of food intake was not due to the aversive properties of monoclonal antibody or cellular toxins, or the immunoneutralization of the biologically active neuropeptide Y, because (i) the acute effect of the microinjection into the arcuate nuclei promoted a transient increase of the food intake likely induced by a strong release of neuropeptide Y from the arcuate neurons which were immunologically damaged, and (ii) the C-flanking peptide monoclonal antibody binds neither neuropeptide Y nor its receptors. The microinjection was inefficient when C-flanking peptide monoclonal antibody was replaced by non-specific rat immunoglobulins or when the C-flanking peptide monoclonal antibody/toxins mixture was injected into the paraventricular nuclei. The data bring further arguments in two domains.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors regulating the production of vasopressin-associated human neurophysin by small-cell carcinoma of the lung: evaluation by computer-enhanced quantitative immunocytochemistry

Expression of the vasopressin gene appears to be a property common to all small-cell lung tumours. For some cultures of small-cell lung carcinoma (SCCL), Northern and Western Blot analyses have revealed that expression of this gene and its protein products are regulated by cAMP and glucocorticoids. In this study, these evaluations have been extended by examining the production of vasopressin-associated human neurophysin (VP-HNP) by computer-enhanced quantitative immunocytochemistry in a classical cell-line (H69) of SCCL, and defining the amount of protein in cells by area of positive staining above an arbitrarily set threshold. Intracellular cAMP was raised by incubating cells with either 8,Br-cAMP (0.5 mM) and IBMX (0.5 mM), or with forskolin (25 microM) and IBMX (0.5 mM). Both of these treatments caused a significant increase in the amount of positive VP-HNP immunoreactivity in the cells, an increase that was further enhanced by simultaneous administration of dexamethasone (0.1 microM). Addition of dexamethasone alone, however, caused a significant decrease in VP-HNP levels. Results confirm earlier findings from Western Blot analysis revealing the influence these agents have on production of vasopressin gene-related proteins by H69 cells, and indicate that computer-enhanced quantitative immunocytochemistry can be effectively used to provide a suitable index of this production.