The discovery of the amphibian skin tetradecapeptide bombesin led to the identification of several mammalian bombesin-like neuroendocrine peptides such as gastrinreleasing peptides (GRP'-27 and GRP8-27) and neuromedin B. GRP and neuromedin B are products of two distinct genes (Krane et al., 1988). Bombesin and its homologues stimulate gastric acid secretion and cause release of various peptide hormones (Dockray, 1987). Bombesin is also mitogenic, causing gastrin cell hyperplasia in rats (Lezoche et al., 1981) and stimulating proliferation of 3T3 murine fibroblasts (Rozengurt & Sinnett-Smith, 1980) and normal human bronchial epithelial cells (Willey et al., 1984) in vitro. Bombesin-like peptides may act as autocrine mitogens for small cell carcinoma of the lung (SCCL); SCCL lines secrete bombesinlike immunoreactivity (BLI) and are stimulated to proliferate by exogenous bombesin (Cuttita et al., 1985). Some SCCL lines are, however, insensitive to exogenous bombesin and do not express detectable GRP receptors (Kado-Fong & Malfroy, 1989). BLI has been found in rat mammary tumours (Gaudino et al., 1984) and in a small proportion of human breast cancer and breast carcinoid specimens (Foster & Tan, 1984; McKillop et al., 1988; Nesland et al., 1985) but is undetectable in normal breast tissue (Bostwick & Bensch, 1985). Recently, it was shown that both bombesin and GRP stimulate inositol phospholipid hydrolysis and Ca2 efflux in MCF-7 and T47D human breast cancer cells suggesting a role in mitogenic signalling (Patel & Schrey, 1990). BLI has been detected in MCF-7 and BT-20 breast cancer cell pellets (Weber et al., 1989). This suggests that a BLI-autocrine stimulatory loop may operate in some breast cancer cell lines such as is the case for SCCL cells. In the light of these observations we have investigated the effects of bombesin on the proliferation of breast cancer cells in culture. The cell lines examined were oestrogen-dependent (MCF-7), oestrogen-responsive (ZR-75-1, T47D) (Dickson & Lippman, 1986), and oestrogenindependent (MDA-MB-436) (Clarke et al., 1983). ZR-75-1, T47D and MDA-MB-436 human breast cancer cells were obtained from the European Collection of Animal Cell Cultures (Porton Down, UK), MCF-7 cells (originally from Dr M.E. Lippman, Georgetown, USA) were a gift from Dr C.R. Green, Liverpool University. All tissue culture media and foetal calf serum (FCS) were obtained from Flow Labs, Irvine, Scotland, UK. The same reserved batch of FCS was used throughout this investigation and all cells were routinely passaged in the presence of phenol red. ZR-75-1 cells were cultured in RPMI 1640 medium containing 5% FCS; MCF-7 in Eagle's minimal essential medium (MEM) with 5% FCS; T47D cells in DMEM with 10% FCS; and MDA-MB-436 cells in Liebowitz-15 medium with 10% FCS. Bombesin (Bachem, Bubendorf, Switzerland) stock solutions, made up in Earle's balanced salts solution containing 0.1% bovine serum albumin, were gassed with nitrogen to prevent oxidation and were stored frozen in liquid nitrogen. Heatand charcoal-treated foetal calf serum (DCC-FCS) was prepared by heating 100 ml of FCS, 10 g acid-washed NoritA activated charcoal and 1 g Dextran T40 at 53'C for 1 h (charcoal and dextran previously stirred at 4'C overnight). The suspension was centrifuged and then filtered through a 0.45 iLm membrane filter and finally filter-sterilised through a 0.22 pm membrane filter. To study effects of the peptides on proliferation, cells were inoculated into 24-well cluster plates (Costar, Northumbria Biologicals, UK) at 1 x 104 (MDA-MB-436) or 4 x 104 (ZR75-1, T47D, MCF-7) cells per well and incubated at 37'C in a humidified atmosphere containing 5% CO2. After 24 h, plating efficiency was determined in 8 replicate wells by electronic particle counting (Coulter counter model ZBI) of trypsinised cells. Medium was removed from the remaining wells and replaced either with medium containing 5% or 10% serum or with the same medium containing peptide, as indicated. Cells from replicate wells were detached by treatment with trypsin and counted at the times indicated; experimental and control media were either unchanged during the course of the experiment or were replaced on days 3 and 6 of incubation. In serum-free conditions, 0. 1% bovine serum albumin replaced the serum component. All growth studies were confirmed in at least three independent determinations. Bombesin did not stimulate cell proliferation of any of the lines in the presence of untreated FCS. The growth of ZR75-1 and T47D cells, however, was significantly and consistently stimulated above control in the presence of DCC-FCS (Figures 1 and 2). There were slight interexperimental variations in the effective dose-response ranges for each cell line but, under the culture conditions described, significant stimulation of cell division was always found with bombesin in the picomolar range. Bombesin stimulates proliferation of ZR-75-1 cells grown in the presence of 5% DCC-FCS, producing significant and increasing elevations above control from day 3 to day 9 of incubation (Figure la). Figure lb shows a typical dose-
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Apr 3, 2011
Giuseppe Romeo + 8
Open Access