Identification of an endogenous inhibitor of prostatic carcinoma cell growth.

The rate of expansion of primary prostatic carcinoma is comparatively slow, with tumours frequently taking years or decades to reach clinically relevant size. We now report the presence of an endogenous inhibitor, derived from aqueous extracts of human prostate tissue, which blocks prostatic carcinoma cell proliferation in vitro and prevents subcutaneous tumour expansion in vivo. Purification and characterization revealed the inhibitor to be spermine, a polyamine known to be locally abundant in the prostate. These results suggest that endogenous polyamine can negatively regulate the growth of prostatic carcinoma cells at their primary site in vivo and may explain the slow rate of primary tumour expansion in the prostate.

Thymosin beta 15: a novel regulator of tumor cell motility upregulated in metastatic prostate cancer.

The Dunning rat prostatic carcinoma is a model system where cell motility closely correlates with the metastatic phenotype. We have identified a novel gene, upregulated in the highly motile and metastatic Dunning cancer cell lines, that represents a new member of the thymosin-beta family, thymosin beta 15. Transfection of antisense thymosin beta 15 constructs into rat prostatic carcinoma cells demonstrates that this molecule positively regulates cell motility, a critical component of the metastatic pathway. Thymosin beta 15 levels are elevated in human prostate cancer and correlate positively with the Gleason tumor grade. Thymosin beta 15 may represent a potential new biochemical marker for human prostate cancer progression.

Stimulation of mast cell chemotaxis by interleukin 3.

PWM-activated spleen cell-conditioned medium (SCCM) and a variety of purified hematopoietic growth factors were tested for their ability to stimulate chemotaxis of mouse connective tissue mast cells (CTMC). Of the agents tested, only IL-3 and SCCM promoted mast cell chemotaxis. Neither IL-2, IL-4, GM-CSF, nor endotoxin had any significant mast cell chemotactic activity. Neutralizing antibodies to mouse IL-3 blocked greater than 90% of the chemotactic activity of SCCM, suggesting that IL-3 is the predominant mast cell chemotactic factor produced by activated spleen cells. Our results demonstrate that mature connective tissue type mast cells are capable of moving toward a gradient of spleen cell-derived IL-3 and suggest that movement of mature mast cells toward lymphokines may influence the accumulation of mast cells at sites of inflammatory or immune reactions.

Mast cell heparin stimulates migration of capillary endothelial cells in vitro.

Migration of capillary endothelial cells is an important component of angiogenesis in vivo. Increased numbers of mast cells have been associated with several types of angiogenesis. We have used a quantitative assay in vitro to demonstrate that mast cells release a factor that significantly increases bovine capillary endothelial cell migration. The factor is present in medium conditioned by mast cells as well as lysates of mast cells. The stimulatory effect of mast cells on migration is specific for capillary endothelial cells. Furthermore, mast cells have no mitogenic activity for capillary endothelial cells. Of all the secretory products of mast cells tested, only heparin stimulated capillary endothelial cell migration in vitro. Heparin preparations from a variety of sources stimulated capillary endothelial cell migration to the same degree but did not stimulate migration of several other cell types. The migration activity of heparin and mast cell conditioned medium was blocked by specific antagonists of heparin (protamine and heparinase), but not by chondroitinase ABC. The migration activity of mast cell conditioned medium was resistant to heat (100 degrees C) and incubation with proteolytic enzymes. These results suggest that the role of mast cells in angiogenesis may be to enhance migration of the endothelial cells of growing capillaries.

Metastatic potential of B16 melanoma cells after in vitro selection for organ-specific adherence.

Heterogeneous primary tumors contain subpopulations of cells that differ in ability to metastasize to specific host organs. We have used cryostat sections of host organs to select for metastatic variants of B16 melanoma cells with increased adhesion to specific syngeneic tissues. By repeating the selection procedure with lung tissue, a subpopulation of cells was isolated that demonstrated a specific increase in binding to cryostat sections of mouse lung. This altered binding was reflected by a sixfold increase in the frequency of lung metastasis 21 d after tail vein injection of the tumor cells. In contrast, B16 melanoma cells selected on cryostat sections of mouse brain showed no increase in adhesion to brain or lung tissue and the metastatic pattern in vivo was not significantly different compared with the parent cell line. When cells selected for increased adhesion to cryostat sections of lung were further examined in vitro, they showed altered morphology and increased motility but no change in growth rate. These results demonstrate that alterations in the adhesive interactions between metastatic tumor cells and a specific host tissue can directly affect the frequency of metastasis to that tissue in vivo.

Identification of a tumor cell receptor for VGVAPG, an elastin-derived chemotactic peptide.

Extracellular matrix proteins and their proteolytic products have been shown to modulate cell motility. We have found that certain tumor cells display a chemotactic response to degradation products of the matrix protein elastin, and to an elastin-derived peptide, VGVAPG. The hexapeptide VGVAPG is a particularly potent chemotaxin for lung-colonizing Lewis lung carcinoma cells (line M27), with 5 nM VGVAPG eliciting maximal chemotactic response when assayed in 48-microwell chemotaxis chambers. Binding of the elastin-derived peptide to M27 cells was studied using a tyrosinated analog (Y-VGVAPG) to allow iodination. Scatchard analysis of [125I]Y-VGVAPG binding to viable M27 tumor cells at both 37 and 4 degrees C indicates the presence of a single class of high affinity binding sites. The dissociation constant obtained from these studies (2.7 X 10(-9) M) is equivalent to the concentration of VGVAPG required for chemotactic activity. The receptor molecule was identified as an Mr 59,000 species by covalent cross-linking of the radiolabeled ligand to the M27 tumor cell surface and subsequent analysis of the cross-linked material by electrophoresis and size-exclusion high performance liquid chromatography. These results suggest that M27 tumor cell chemotaxis to VGVAPG is initiated by high affinity binding of the peptide to a distinct cell surface receptor.

The chemotactic response to PDGF-BB: evidence of a role for Ras.

The PDGF receptor-beta mediates both mitogenic and chemotactic responses to PDGF-BB. Although the role of Ras in tyrosine kinase-mediated mitogenesis has been characterized extensively, its role in PDGF-stimulated chemotaxis has not been defined. Using cells expressing a dominant-negative ras, we find that Ras inhibition suppresses migration toward PDGF-BB. Overexpression of either Ras-GTPase activating protein (Ras-GAP) or a Ras guanine releasing factor (GRF) also inhibited PDGF-stimulated chemotaxis. In addition, cells producing excess constitutively active Ras failed to migrate toward PDGF-BB, consistent with the observation that either excess ligand or excess signaling intermediate can suppress the chemotactic response. These results suggest that Ras can function in normal cells to support chemotaxis toward PDGF-BB and that either too little or too much Ras activity can abrogate the chemotactic response. In contrast to Ras overexpression, cells producing excess constitutively active Raf, a downstream effector of Ras, did migrate toward PDGF-BB. Cells expressing dominant-negative Ras were able to migrate toward soluble fibronectin demonstrating that these cells retained the ability to migrate. These results suggest that Ras is an intermediate in PDGF-stimulated chemotaxis but may not be required for fibronectin-stimulated cell motility.

Identification and isolation of endothelial cells based on their increased uptake of acetylated-low density lipoprotein.

Acetylated-low density lipoprotein (Ac-LDL) is taken up by macrophages and endothelial cells via the "scavenger cell pathway" of LDL metabolism. In this report, aortic and microvascular endothelial cells internalized and degraded 7-15 times more [125I]-Ac-LDL than did smooth muscle cells or pericytes. Bound [125I]-Ac-LDL was displaced by unlabeled Ac-LDL, but not unmodified LDL. The ability to identify endothelial cells based on their increased metabolism of Ac-LDL was examined using Ac-LDL labeled with the fluorescent probe 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (Dil-Ac-LDL). When cells were incubated with 10 micrograms/ml Dil-Ac-LDL for 4 h at 37 degrees C and subsequently examined by fluorescence microscopy, capillary and aortic endothelial cells were brilliantly fluorescent whereas the fluorescent intensity of retinal pericytes and smooth muscle cells was only slightly above background levels. Dil-Ac-LDL at the concentration used for labeling cells had no effect on endothelial cell growth rate. When primary cultures of bovine adrenal capillary cells were labeled with 10 micrograms/ml of Dil-Ac-LDL for 4 h at 37 degrees C, then trypsinized and subjected to fluorescence-activated cell sorting, pure cultures of capillary endothelial cells could be obtained. Utilizing this method, large numbers of early passage microvascular endothelial cells can be obtained in significantly less time than with conventional methods.

Control of proliferation of human vascular endothelial cells. Characterization of the response of human umbilical vein endothelial cells to fibroblast growth factor, epidermal growth factor, and thrombin.

Because the response of human endothelial cells to growth factors and conditioning agents has broad implications for our understanding of wound healing angiogenesis, and human atherogenesis, we have investigated the responses of these cells to the fibroblast (FGF) and epidermal growth factors (EGF), as well as to the protease thrombin, which has been previously shown to potentiate the growth response of other cell types of FGF and EGF. Because the vascular endothelial cells that form the inner lining of blood vessels may be expected to be exposed to high thrombin concentrations after trauma or in pathological states associated with thrombosis, they are of particular interest with respect to the physiological role of this protease in potentiating cell proliferation. Our results indicate that human vascular endothelial cells respond poorly to either FGF or thrombin alone. In contrast, when cells are maintained in the presence of thrombin, their proliferative response to FGF is greatly increased even in cultures seeded at a density as low as 3 cells/mm2. Human vascular endothelial cells also respond to EGF and thrombin, although their rate of proliferation is much slower than when maintained with FGF and thrombin. In contrast, bovine vascular endothelial cells derived from vascular territories as diverse as the bovine heart, aortic arch, and umbilical vein respond maximally to FGF alone and neither respond to nor bind EGF. Furthermore, the response of bovine vascular endothelial cells to FGF was not potentiated by thrombin, indicating that the set of factors controlling the proliferation of vascular endothelial cells could be species-dependent. The requirement of cultured human vascular endothelial cells for thrombin could explain why the human cells, in contrast to bovine endothelial cells, are so difficult to maintain in tissue culture. Our results demonstrate that by using FGF and thrombin one can develop cultures of human vascular endothelial cells capable of being passage repeatedly while maintaining a high mitotic index. The stock cultures used for these studies have been passed weekly with a split ratio of 1 to 10 and are currently in their 30th passage. These cultures are indistinguishable from earlier passages when examined for the presence of Weibel-Palade bodies or Factor VIII antigen. We conclude that the use of FGF and thrombin can prevent the precocious senescence observed in most human endothelial cells cultures previously described.

Inhibition of cell motility by interferon.

Interferon derived from human leukocytes, human fibroblasts, and mouse fibroblasts was found to inhibit the motility of cultured cells. It inhibits the tumor-induced motility of capillary endothelial cells as well as the spontaneous migration of other cell types. The ability of a given preparation of interferon to inhibit the motility of a given cell type is proportional to its antiviral activity in that particular cell type. Antiserum to human leukocyte interferon neutralizes both the motility-inhibitory activity and the antiviral activity of this preparation.

Organ-specific adhesion of metastatic tumor cells in vitro.

Binding of tumor cells to cryostat sections of host organs was studied. B16-F10 melanoma cells and reticulum cell sarcoma cells demonstrated an organ specificity in their binding in vitro that reflected the organ specificity of their metastatic distribution 25 days after intravenous injection. These results provide evidence for specific binding of tumor cells to the tissues that they selectively colonize in vivo.

In vitro and in vivo consequences of VLA-2 expression on rhabdomyosarcoma cells.

Cloned integrin alpha 2 subunit complementary DNA was expressed on human rhabdomyosarcoma (RD) cells to give a functional VLA-2 (alpha 2 beta 1) adhesion receptor. The VLA-2-positive RDA2 cells not only showed increased adhesion to collagen and laminin in vitro, but also formed substantially more metastatic tumor colonies in nude mice after either intravenous or subcutaneous injection. These results show that a specific adhesion receptor (VLA-2) can markedly enhance both experimental and spontaneous metastasis. In contrast to the metastasis results, there was no difference in either the in vitro growth rate or apparent in vivo tumorigenicity of RD and RDA2 cells.

Stimulation of human prostatic carcinoma cell growth by factors present in human bone marrow.

Malignant prostatic carcinoma, a major cause of cancer mortality in males, most often metastasizes to secondary sites in bone. Frequently, the growth rate of the secondary tumor in bone marrow is considerably greater than that of the slowly growing primary prostatic tumor. We now report that two lines of human prostatic carcinoma cells proliferate in response to conditioned media from unstimulated human, rat, or bovine bone marrow. Nonprostatic tumor cell lines showed little or no growth response to the same medium. The proliferative activity found in bone marrow was not duplicated by any of a variety of purified growth factors including epidermal growth factor (EGF), acidic or basic fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), transforming growth factor (TGF) alpha or beta, interleukins 1, 2, 3, 4 or 6, granulocyte (G), macrophage (M) or granulocyte-macrophage (GM) colony stimulating factor (CSF). Whereas a mixture of G-CSF, M-CSF, and IL 3 produced a mitogenic response in the prostatic carcinoma cells, these three factors were not present in our bone marrow samples in sufficient quantities to promote the observed proliferative response. To further identify the cellular source of the proliferative activity present in bone marrow-conditioned medium, we tested conditioned media made from human bone marrow stromal cells. The stromal cell conditioned medium stimulated increased growth of the prostatic carcinoma cells to levels equivalent to those observed with the bone marrow conditioned medium. These results suggest that novel mitogenic factors that are produced by bone marrow stromal cells and remain in the bone marrow cavity may account, in part, for the preferential growth of prostatic metastases in bone.

Capillary endothelial cell migration: stimulating activity of aqueous humor from patients with ocular cancers.

In double-masked studies, various concentrations of aqueous humor (AH) from 157 patients (208 samples) with ocular cancers, nonmalignant ocular lesions, and normal eyes were added to bovine capillary endothelial (BCE) cells plated onto gold-coated cover slips. The phagokinetic tracks made by 100 cells at each concentration were traced, and the mean area of migration plus or minus the standard error of the mean was determined. Data are expressed as the percentages of increase in mean track area made by 100 cells incubated in medium that contained AH samples beyond the mean area of 100 cells incubated in medium alone. The percentage increases in migration-stimulating activity were as follows: a) malignant ocular disease--retinoblastoma (30 samples), 34 +/- 2; malignant melanoma (55 samples), 37 +/- 3; b) nonmalignant ocular disease--cataracts, glaucoma, pseudoglioma, and diabetic retinopathy (36 samples), 14 +/- 2; c) control AH--no ocular disease (51 samples), 9 +/- 1; normal eyes and systemic cancer (36 samples), 38 +/- 6. The percentage increase in endothelial cell migration was as great in cases of systemic cancer as it was in cases of ocular cancer. The endothelial cell migration-stimulating activity in AH from patients with intraocular cancers was significantly higher than the levels in the other groups of patients having no systemic cancer (P much less than .001). In addition, when the results were compared in the control group and the group with benign ocular disease, no significant differences were detected (P greater than .01).

Laminin regulates a tumor cell chemotaxis receptor through the laminin-binding integrin subunit alpha 6.

Chemotaxis of the M27 variant of Lewis lung carcinoma to VGVAPG, an elastin-derived chemoattractant, is restricted by the basement membrane glycoprotein laminin. Laminin does not inhibit random migration of M27 tumor cells, nor does it inhibit M27 cell chemotaxis to a second chemotactic peptide, fMLF. The laminin sensitivity of VGVAPG chemotaxis appears to be independent of adhesion to laminin, and it is not due to competitive inhibition of VGVAPG receptor binding. Preincubation of M27 cells with laminin reduces the affinity of VGVAPG-specific binding without altering the number of available VGVAPG receptors. Reduced VGVAPG receptor affinity was previously observed: (a) a nonresponsive Lewis lung carcinoma variant, H59, expresses low-affinity VGVAPG binding and (b) maintenance of high-affinity VGVAPG receptors on M27 tumor cells is correlated with elevated protein kinase C activity in the particulate cell fraction (C. H. Blood and B. R. Zetter, J. Biol. Chem., 264: 10614-10620, 1989). The negative regulation of VGVAPG chemotaxis by laminin is consistent with these observations: laminin coordinately inhibits VGVAPG chemotaxis, reduces VGVAPG receptor affinity, and decreases protein kinase C activity in the particulate fraction of M27 cells. These parameters are not affected by a second glycoprotein, fibronectin. Anti-alpha 6 antibodies neutralize the laminin inhibition of both VGVAPG chemotaxis and protein kinase C activity. The results demonstrate that laminin can modulate cell behavior by regulating cell surface receptors for biologically active ligands.

Stimulation of rat peritoneal mast cell migration by tumor-derived peptides.

The accumulation of mast cells is characteristic of a number of pathological states. We demonstrate here the directional motility of mast cells in vitro in response to tumor-derived peptides. Rat peritoneal mast cells were isolated on Percoll gradients and maintained in serum-free medium containing transferrin, albumin, soybean lipid, and cholesterol. The isolated mast cells migrated under agarose in response to medium conditioned by any of eight tumor cell lines but not to medium conditioned by any of a variety of nontumorigenic cell types. The tumor-derived activity is dialyzable (cutoff, Mr 3500), stable to trypsin treatment and to heating at 56 degrees, but destroyed by heating to 100 degrees or by treatment with Streptomyces griseus protease or carboxypeptidase A. Ultrafiltration suggests a molecular weight of 300 to 1000. Two tripeptides, glycylhistidyllysine and N-formylmethionylleucylphenylalanine, were also found to be potent chemoattractants for mast cells. N-Formylmethionylphenylalanine and valylglycylserylglutamic acid (eosinophil chemotactic Factor A) had significantly less chemoattractant activity over the same range of concentrations. Several peptide analogues of glycylhistidyllysine were tested and found to have no activity. The growth of capillary blood vessels toward a growing tumor is generally preceded by an accumulation of mast cells at the tumor site. Based on the results presented here and previous data from our laboratory on mast cell stimulation of capillary endothelial cell migration, we propose an hypothesis that the chemoattraction of mast cells by tumor-derived peptides may be an important early event in tumor neovascularization.

Sensitivity to polyamine-induced growth arrest correlates with antizyme induction in prostate carcinoma cells.

High local polyamine concentrations may suppress cell growth of primary prostatic carcinomas. When cell growth assays were conducted in defined serum-free medium, spermine inhibited the growth of poorly metastatic rat prostate carcinoma cells, causing cell cycle arrest in the G1 phase. In contrast, highly metastatic prostate carcinoma cells were resistant to the growth inhibitory activity of spermine. Ornithine decarboxylase antizyme levels, measured by Western blotting, were elevated 1-2 h after spermine treatment of spermine-sensitive cells but not spermine-resistant cells. Spermine uptake was similar in both the sensitive and resistant cell lines. These results suggest that failure to induce antizyme correlates with spermine resistance in prostate carcinoma.

Inhibition of cell motility after nm23 transfection of human and murine tumor cells.

Abstract nm23 gene expression has been inversely correlated with tumor metastatic potential in certain tumors including melanomas, breast carcinomas, and hepatocellular carcinomas. The cellular mechanisms by which the nm23 protein may directly or indirectly modulate the metastatic phenotype is not yet known. Because cell motility plays an essential role in metastatic dissemination, we have studied whether tumor cells transfected with nm23 complementary DNA have any alterations in their ability to migrate. Our results demonstrate that nm23 transfection inhibits the ability of murine melanoma and human breast carcinoma cells to migrate in response to serum or to defined factors such as platelet derived growth factor or insulin-like growth factor 1. Random, unstimulated cell motility was not depressed in the nm23 transfectants. The results suggest that the nm23 gene product may interact with intracellular molecules that are essential for stimulated cell motility in two different tumor cell systems.

Stimulation of increased capillary endothelial cell motility by chondrosarcoma cell-derived factors.

The ability of chondrosarcoma cell-derived preparations to stimulate an increase in the motility of bovine capillary endothelial (BCE) cells was quantitated using a phagokinetic track assay which measures the area of tracks produced by BCE cells after ingestion of gold particles. Chondrosarcoma preparations stimulated a 2-fold increase in the mean track area produced by BCE cells in an 18-hr incubation period. The motility-stimulating activity of chondrosarcoma was purified about 120-fold. The most highly purified fractions had molecular weights between 16,000 and 20,000 and stimulated a 2-fold increase in BCE cell motility at concentrations of 10 to 20 ng/ml.