The effects of s analgus RC-160and SMS-201-995 on tyrosine phosphatase and cell proliferation were investigated in COS-7 and NIH 3T3 cells expressing human somatostatin receptor subtype 1 or 2 (SSTR1 or SSTR2 antagonize the mitogenic effect of growth factors acting on tyrosine kinase receptors such as epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) (9-11). Furthermore, these analogues have been found to stimulate tyrosine phosphatase activity in normal and tumoral pancreatic cells (9,(12)(13)(14)(15) and to activate the dephosphorylation of EGF receptor (9, 16). The ability of somatostatin analogues to stimulate tyrosine phosphatase correlates with their inhibitory effect on pancreatic cell growth, and this correlation supports the hypothesis that the growth inhibition is mediated by dephosphorylation of tyrosine protein signals. Somatostatin analogues might suppress tumor growth by reversing the stimulatory effect of EGF on phosphorylation of EGF receptor tyrosine kinase and EGF-phosphorylated proteins (17). We also observed that a membrane tyrosine phosphatase is coeluted with somatostatin receptor, suggesting that tyrosine phosphatase may be a part ofthe signal transduction pathway promoted by somatostatin receptor occupancy (16).The somatostatin receptor subtypes and the molecular mechanism involved in the tyrosine phosphatase stimulation have been, until now, unknown (18, 19). We must better understand what physiological response every subtype elicits, how their signals are processed in the cell, and in what normal and/or pathological tissues each is expressed to choose the appropriate analogue for targeting to specific cells for therapeutic use.In the present study, we examined the effects of two somatostatin analogues, RC-160 and SMS, on binding and signal transduction pathways of the two human cloned somatostatin receptor subtypes hSSTR1 and hSSTR2 transiently expressed in COS-7 cells. We also investigated the 2315The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Several analogues of somatostatin were examined in the Mia PaCa-2 human pancreatic cancer cell line for their ability to promote tyrosine phosphatase activity affecting the receptors for the epidermal growth factor. The inhibition of growth of the Mia PaCa-2 cells in culture was also evaluated to determine the mechanism of action of somatostatin analogues and their relative effectiveness in inhibiting cancer growth. Of the analogues tested D-Phe-Cys-Tyr-D-Trp-LysVal-Cys-Trp-NH2 (RC-160) caused the greatest stimulation of tyrosine phosphatase activity. Analogue D-Phe-Cys-Tyr-DTrp-Lys-Val-Cys-Thr-NH2 (RC-121) had less effect but was more potent than somatostatin-14. Analogue D-Phe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr(ol) (SMS 201-995) produced no significant dephosphorylation. The analogues displayed the same order of activity in assays on growth inhibition of Mia PaCa-2 cells in cultures. Analogue (SMS-201-995) caused virtually no tyrosine phosphatase stimulation or growth inhibition in this cancer cell line, although it possesses a much higher antisecretory activity than somatostatin-14 in normal tissues. These observations indicate that somatostatin and some of its analogues can act as growth inhibitors in cancer cells through the activation of tyrosine phosphatase. These data reinforce the view that somatostatin analogue RC-160 and related compounds could be used for treatment of pancreatic cancer.

The traditional understanding is that an entirely new complement of digestive enzymes is secreted by the pancreas into the small intestines with each meal. This is thought to be necessary because, like food itself, these enzymes are degraded during digestion. In this review we discuss experiments that bring this point of view into question. They suggest that digestive enzymes can be absorbed into blood, reaccumulated by the pancreas, and reutilized, instead of being reduced to their constituent amino acids in the intestines. This is called an enteropancreatic circulation of digestive enzymes.

Analogues of somatostatin (SS) and luteinizing hormone-releasing hormone (LH-RH)

The exocrine pancreas and certain salivary glands of mammals secrete a variety of enzymes into the gastrointestinal tract, where they digest food. The same glands also release these enzymes into the bloodstream. This latter process has commonly been assumed to occur solely as the result of a pathological condition or as an inadvertent by-product of exocrine secretion due to the leakage of trace quantities of the enzymes into blood. However, a variety of evidence suggests that the endocrine secretion of digestive enzymes is a normal occurrence that can be of substantial magnitude in healthy individuals, is responsive to various physiological stimuli, and is distinct from exocrine secretion. Recent research has focused attention on this process as a promising means for the delivery of engineered proteins into the systemic circulation for pharmaceutical purposes. In this review, we survey research in this area and consider the evidence for the existence of an endocrine secretion of digestive enzymes, the cause of enzyme release into the bloodstream, its source within the tissue, and, finally, the physiological purposes that this secretion process might serve.

Chemotherapy is commonly used in the treatment of cancers. However, the mechanism of action of many of these agents is not well understood. We present the synthesis of a two-photon f luorophore (C625) and its biological application when chemically linked to a chemotherapeutic agent (AN-152). By using two-photon laser-scanning microscopy, the drug:f luorophore conjugate can be observed directly as it interacts with receptor-positive cell lines. The results of this project visually show the receptor-mediated entry of AN-152 into the cell cytoplasm and subsequently into the nucleus. These observations will allow for better understanding of the drug's therapeutic mechanism, which is a subject of ongoing research aimed at improving present methods for cancer therapy.Two-photon processes have been drawing a great deal of attention in the last decade because of their wide range of applications. Pioneering works by Rentzepis and coworkers (1-3) have established the utility of two-photon processes in three-dimensional data storage and microfabrication. Twophoton laser-scanning microscopy (4 -7), introduced by Webb's group, has already been shown to be a powerful technique for probing the three-dimensional structure of a cell and to have inherent optical-sectioning capability without any significant interference from autofluorescence. Our recent efforts on design and synthesis of two-photon chromophores have produced highly efficient two-photon up-converters (which emit photons of a frequency higher than that of the absorbed photons); some of them even exhibit up-conversion lasing (8-10). In this paper, we report the synthesis of a two-photon fluorophore, which was coupled to a chemotherapeutic agent and used in optical tracking of its interaction and entrance in to the target cells by two-photon laser-scanning microscopy.Chemotherapy has been used widely in the treatment of cancers. However, the cellular mechanism of these agents is often not well understood. For example, whether certain chemotherapeutic drugs attach to the membrane of a cancer cell, enter the cell, or enter the nucleus affecting the DNA replication process is not well understood. Such an understanding at the cellular and molecular level will be a major advancement in biology and will lead to ways of enhancing the efficacy of chemotherapy.Chemotherapeutic agent AN-152 was made by coupling the cytotoxic agent doxorubicin (Dox) to the luteinizing hormone-releasing hormone (LH-RH) analog, ]LH-RH (11). Its design is based on the fact that specific high-affinity membrane receptors for LH-RH have been found to be expressed in many sex-linked tissue-derived cancers (12) and expressed de novo in many other cancers (13-16). In the last decade, Schally and coworkers (17-20) have developed and tested several cytotoxic LH-RH conjugates in which a wide variety of cytotoxic agents were linked to LH-RH analogs. As one of the most widely used anticancer drugs, Dox has shown to have a broad spectrum of antitumor effects (21). Its complex cytotoxic mechanism has ...

A membrane receptor and a cytosolic receptor for somatostatin were found in a human undifferentiated pancreatic cancer cell line (MIA PaCa-2). Binding of somatostatin to this membrane receptor activates dephosphorylation of a phosphotyrosyl-membrane protein whose phosphorylation was promoted by epiderma1 growth factor (EGF). Vanadate, a purported inhibitor of dephosphorylation, interferes with the action of somatostatin. These findings suggest a possible biochemical mechanism by which somatostatin may inhibit the growth of human pancreatic cancers.

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