Basement membrane collagen: degradation by migrating endothelial cells.

One of the first steps in neovascularization is dissolution of the basement membrane at the point of endothelial outgrowth. An assay was developed to determine whether basement membrane collagens (types IV and V) are degraded by endothelial cells migrating toward a chemotactic stimulus. Fetal bovine endothelial cells were placed on one side of a filter containing the collagen substrate, and a chemoattractant derived from retinal extracts was placed on the opposite side. Degradation of both type IV and type V collagens was observed when the retinal factor was placed on the side of the filter opposite the endothelial cells. Metalloproteinases that cleaved type IV and type V collagens could be extracted from the endothelial cells with detergents. Such endothelial cell-associated (possibly membrane-bound) proteinases may locally disrupt the basement membrane and facilitate the outgrowth of capillary sprouts toward the angiogenic stimulus.

Effect of natural protease inhibitors and a chemoattractant on tumor cell invasion in vitro.

The effect of natural protease inhibitors and a chemoattractant on tumor cell invasion were studied with the use of a new in vitro quantitative assay of tumor cell penetration of native connective tissue. Human amnion membrane denuded of its epithelium is composed of a continuous basement membrane (BM) attached to a dense avascular collagenous stroma. M5076 reticulum sarcoma cells, known to be highly invasive in vivo, were placed on the BM side of the amnion connective tissue. Tumor cells penetrating the full thickness of the connective tissue barrier were collected on the stromal side with a Millipore filter. N-Formylmethionyl-leucyl-phenylalanine (FMLP) at an optimal concentration of 10(-7) M stimulated the penetration of up to 600% more tumor cells into the connective tissue after 20 hours in comparison to the number of tumor cells spontaneously penetrating in serum-free media. Natural protease inhibitors blocked both FMLP-stimulated and spontaneous invasion. A bovine cartilage extract containing inhibitors of both serine proteinases and metalloproteinases caused a 500% decrease in invasion. Furthermore, a 500% inhibition of invasion was produced by a purified collagenase (metalloproteinase) inhibitor. In contrast, soybean trypsin inhibitor and bovine serum albumin did not significantly alter the invasion rate. The protease inhibitors were nontoxic and did not reduce tumor cell proliferation, attachment to the amnion, and the rate of tumor cell migration through Nuclepore filters. These data support the hypothesis that collagenolytic metalloproteinases play a necessary role in tumor cell invasion of native connective tissue.

In vivo treatment with antibody against IGF-1 receptor suppresses growth of human rhabdomyosarcoma and down-regulates p34cdc2.

In a previous study, we have shown that insulin-like growth factor type 2 (IGF-2) functions as an autocrine growth factor in human rhabdomyosarcoma (RMS) cell lines. In addition, we demonstrated that the inhibition of binding of IGF-2 to the IGF-1 receptor, mediated by suramin, blocked the growth of RMS cells in vitro. We now report that, in vivo, a specific IGF-1 receptor blocking antibody (alpha IR-3), but not suramin, suppresses RMS tumor growth. Both progression of tumor growth in tumor-bearing animals and formation of newly established tumors were suppressed by treatment with alpha IR-3. Histological analysis of tumors from treated animals did not reveal necrotic lesions, implying that the treatments had no cytotoxic effect. The decrease in tumor growth was associated with a decrease of p34cdc2, a cellular protein involved in cell cycle regulation, suggesting that treatment resulted in the arrest of cellular proliferation. We speculate, therefore, that agents which block the IGF signaling pathway may find application in treatment of RMS.

Type V collagen in human amnion is a 12 nm fibrillar component of the pericellular interstitium.

Immunoelectron microscopy was utilized to detect type V collagen in human amnion. Monospecific antibodies to type V collagen were detected with protein A-gold conjugates in tissue sections and epoxy-embedded sections of human amnion. Type V collagen was localized to the immediate vicinity of the basal lamina, but was distinct from laminin and type IV collagen, which localized only to the lamina lucida and lamina densa, respectively, of the basal lamina. At high magnification, 12 nm unbanded fibrils were seen to be labelled by anti-type V collagen antibody; these fibrils extended from the lamina densa of the basal lamina well into the interstitial matrix. In comparison, only the amorphous matrix of the lamina densa showed labelling with anti-type IV collagen antibodies. Anti-laminin antibodies labelled the lamina lucida. Quantitative analysis of grain distribution revealed the laminin labelling to be centered over the distal half of the lamina lucida (mean distance from the cell surface = 70 nm). In contrast, type IV collagen was centered over the lamina densa (mean = 115 nm). Both distributions were essentially Gaussian and distinct from the broad distribution of type V collagen. Type I collagen fibers with characteristic 67 nm periodicity were unlabelled with antibodies to type V collagen, although labelled type V fibrils were frequently enmeshed among the type I fibers. Antibodies to type I collagen labelled these fibers but not the type V fibrils. The results indicate that in human amnion, type V collagen is a 12 nm diameter, unbanded fibril which extends from the lamina densa of the basal lamina into the adjacent interstitial matrix. We hypothesize that type V collagen functions as a network of anchoring fibrils between the cell basal lamina and the extracellular matrix, especially type I collagen fibres. Type V collagen thus appears to be a unique interstitial collagen.

Tumorigenic and mitogenic capacities are reduced in transfected fibroblasts expressing mutant insulin-like growth factor (IGF)-I receptors. The role of tyrosine residues 1250, 1251, and 1316 in the carboxy-terminus of the IGF-I receptor.

Regulation of ligand-mediated signal transduction through transmembrane tyrosine kinase growth factor receptors involves phosphorylation of tyrosine residues in the intracellular domain of the receptor. The insulin-like growth factor-I (IGF-I) receptor contains three tyrosine residues in the carboxy-terminal domain at positions 1250, 1251, and 1316. Of these, only the tyrosine at position 1316 is conserved in the homologous position of the insulin receptor. Mutational analysis was used to study the role of these tyrosines in specific outcomes of IGF-I-mediated signal transduction. Mutations in the human IGF-I receptor were either replacement of tyrosines 1250 and 1251 with phenylalanine and histidine (yyFH), respectively, or replacement of the conserved distal tyrosine (position 1316) with phenylalanine (yCF). The yyFH mutation results in an IGF-I receptor with the amino acids found in the homologous position of the human insulin receptor. Cells overexpressing mutated IGF-I receptors were compared with cells expressing only endogenous IGF-I receptors or overexpressing wild-type IGF-I receptors. The ability of yyFH mutant IGF-I receptors to autophosphorylate the beta-subunit or phosphorylate insulin receptor substrate-1 was not significantly different from wild-type type IGF-I receptors. However, one or both of the proximal tyrosine residues (positions 1250 and 1251) in the carboxy-terminus of the IGF-I receptor are essential for IGF-I-stimulation of mitogenic and tumorigenic pathways. IGF-I-induced mitogenesis, measured as thymidine incorporation and cellular proliferation, was abrogated in cells overexpressing mutant IGF-I receptors with replacement of the proximal double tyrosines (positions 1250 and 1251). Fibroblasts expressing this mutant IGF-I receptor formed fewer tumors than the negative control cells, whereas cells expressing wild-type IGF-I receptors formed large tumors in all recipient mice injected. Conversely, cells expressing mutant IGF-I receptors with only the conserved distal tyrosine (position 1316) replaced had slightly reduced IGF-I-stimulated beta-subunit autophosphorylation, thymidine incorporation, and cellular proliferation when compared with cells expressing wild-type receptors. Phosphorylation of insulin receptor substrate-1 by the yCF mutant receptors was not impaired. Despite the ability of these mutant receptors to stimulate mitogenic growth, fibroblasts expressing this mutant receptor were also incapable of forming tumors in recipient nude mice. The distal tyrosine (position 1316) of the IGF-I receptor is crucial for tumor formation but is not essential for IGF-I stimulated mitogenesis. Thus, the tyrosine moieties in the carboxy-terminus of the IGF-I receptor participate in the signal transduction pathways that affect the mitogenic and tumorigenic potentials of cells expressing mutant IGF-I receptors.

1 alpha, 25-dihydroxy-16-ene-23-yne-26,27-hexafluorocholecalciferol (Ro24-5531) modulation of insulin-like growth factor-binding protein-3 and induction of differentiation and growth arrest in a human osteosarcoma cell line.

1 alpha,25-Dihydroxycholecalciferol [1,25-(OH)2D3] is a potent differentiating agent in a variety of tumor cell lines. However, the induction of severe hypercalcemia has limited its clinical use. Several analogs have been synthesized that retain the antiproliferative differentiating effects of 1,25-(OH)2D3, but do not have the calcitropic effect of the parent compound. One such analog, 1 alpha,25(OH)2-16-ene-23-yne-26,27-hexafluorocholecalciferol (Ro24-5531), can induce differentiation in HL-60 cells and does not induce hypercalcemia in animal models. We, therefore, evaluated the effect of Ro24-5531 on a human osteosarcoma cell line, MG-63. Compared with 1,25-(OH)2D3, the analog Ro24-5531 is 10-100 times more potent as an inhibitor of MG-63 cell proliferation, as determined by [3H]thymidine incorporation and/or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The inhibition in cell growth is accompanied by a decrease in the expression of p34cdc2 (> 4-fold), a protein critically involved in cell cycle regulation. Ro24-5531 treatment of MG-63, at a concentration of 10(-8) mol/L, induced expression of the bone differentiation markers biglycan and osteocalcin, as determined by Northern analysis. These data suggest that Ro24-5531 treatment induces growth arrest coupled with differentiation. To begin to evaluate the mechanisms by which Ro24-5531 may exert an effect, we evaluated the effect of Ro24-5531 on components of the insulin-like growth factor I (IGF-I) signaling pathway, an important regulator of normal bone growth and differentiation. The expression of IGF-binding protein (IGFBP), IGFBP-3 messenger ribonucleic acid, and protein levels are increased 20-fold after 72 h of treatment with Ro24-5531 and are associated with a marked increase in detectable binding of ligand to binding protein, as measured by RRA. These data suggest an association between Ro24-5531-induced growth arrest and increased expression of IGFBP-3.

A novel method for selection of invasive tumor cells: derivation and characterization of highly metastatic K1735 melanoma cell lines based on in vitro and in vivo invasive capacity.

Tumor cell invasion of basement membranes is required at several steps in the process of metastasis. To study the genetic and biochemical events mediating invasion, a variant cell line (TK) was selected from the metastatic M2 K1735 murine melanoma cell line. A novel selection procedure was used, based on in vitro and in vivo invasion and growth upon basement membrane and stroma. Additionally, two extrapulmonary metastases of the TK cell line, TK-Eve and TK-Liver, were established as cell lines and characterized. The TK cell line demonstrates greater metastatic potential in vivo and invasive ability in vitro than the parent M2 cell line, confirming the validity of the selection procedure. In addition, the M2 and TK cell lines were examined for other cell functions involved in the metastatic process. Cellular growth rates and sensitivity to T lymphocyte and natural killer cell lysis were not determining factors in the metastatic potentials of the M2 and selected cell lines; possible macrophage contribution to metastatic behavior was noted. [35S]methionine pulse labeling of protein synthesis and karyotypic analysis confirm the close relationship of parental and selected cell lines.

High frequency of double drug resistance in the B16 melanoma cell line.

Methotrexate (MTX) and N-(phosphonacetyl)-L-aspartate (PALA) are two agents to which cellular resistance can be conferred by gene amplification, but they do not generally show cross resistance. However, combined treatment with these two agents produced drug resistant cells in the B16 melanoma cell line at a much higher frequency than would be expected if resistance to the two agents was totally independent. An isolated doubly resistant clone, B16-F1 MP, showed a high frequency of resistance to pyrazofurin and ouabain, which are also agents to which resistance can be conferred by gene amplification. Thus MTX combined with PALA selected cells with an 'amplificator' phenotype (an increased ability to amplify parts of the genome). These B16-F1 MP cells had a decreased ability to form experimental lung metastases compared with the parent line but this difference was not found in baby hamster kidney cells with the amplificator phenotype. The mechanism underlying drug resistance may need to be considered when designing combination chemotherapy.

Astrocyte-conditioned medium stimulates HIV-1 expression in a chronically infected promonocyte clone.

Human promonocytic cells chronically infected with human immunodeficiency virus-1 (HIV-1) (clone U1.1.5) were grown in the presence of media conditioned by primary rat cortical astrocytes and HIV-1 expression was assessed by measuring reverse transcriptase activity. Media conditioned by non-stimulated and lipopolysaccharide (LPS)-stimulated astrocytes induced the expression of HIV-1 2.1-fold and 4.1-fold, respectively. LPS alone, media conditioned by the uninfected parental cell line of U1.1.5 (U937), and culture media from four other cell lines, had no effect on viral expression. The magnitude of induction was time- and dose-dependent. Tumor necrosis factor alpha (TNF-alpha) was detected in LPS-stimulated astrocyte-conditioned medium and the HIV-inducing capability of the medium was neutralized, in part, by an antibody to recombinant murine TNF-alpha. These results suggest a role for astrocytes in the induction of HIV expression and thus in the pathogenesis of HIV-1 infection in brain.

Organic thiophosphate WR-151327 suppresses expression of HIV in chronically infected cells.

Reducing agents such as glutathione (GSH), glutathione ester (GSE), and N-acetylcysteine (NAC) have been shown to suppress the induction of HIV expression in chronically infected cells stimulated by cytokines. We present data which show the effects of the organic thiophosphate WR-151327 on the expression of latent HIV in U1 cells. The chronically infected promonocytic cell line U1 constitutively expresses low levels of HIV that can be increased by 13-phorbol 12-myristate acetate (PMA), tumor necrosis factor alpha (TNF-alpha), and granulocyte/monocyte colony-stimulating factor (GM-CSF). WR-151327 suppressed, in dose-dependent fashion, the reverse transcriptase (RT) activity induced by TNF-alpha, GM-CSF, and PMA. The maximal decrease in RT activity was 70, 80, and 50%, respectively. Pretreatment with WR-151327 also suppressed the induction of total HIV protein synthesis, as shown by Western blot analysis. In addition, WR-151327 suppressed HIV-LTR-CAT activity in transfected human rhabdomyosarcoma cells (RD). Suppression of HIV expression by WR-151327 was observed in the absence of a cytotoxic or cytostatic effect. Incubation of WR-151327 with human recombinant TNF-alpha for 6 hr at 37 degrees C did not alter the capacity of TNF-alpha to induce the expression of HIV. Our observations further support the hypothesis that reducing agents are important in the control of HIV replication and that the clinical evaluation of WR-151327 may be indicated.

Novel anticancer function of inositol hexaphosphate: inhibition of human rhabdomyosarcoma in vitro and in vivo.

Inositol hexaphosphate (IP6) is a naturally occurring polyphosphorylated carbohydrate that has been shown to suppress the growth of epithelial cancers, including those of breast and colon. The objective of this study was to investigate whether IP6 inhibits growth of rhabdomyosarcoma (RMS), a tumor of mesenchymal origin, which is the most common soft tissue sarcoma in children. We performed both in vitro and in vivo studies to evaluate the effect of IP6 on human RD cells growth. Our results show that IP6 suppresses growth of rhabdomyosarcoma cell line (RD) in vitro in a dose-dependent fashion. A 50% inhibition of cell growth (IC50) was induced by < 1.0 mM IP6. However, the removal of IP6 from the media, after 72 hours of treatment, allowed cells to recover their logarithmic growth. Exposure of RD cells to IP6 led to differentiation; cells became larger with abundant cytoplasm, expressing higher levels of muscle-specific actin. Consistent with in vitro observation, IP6 suppressed RD cell growth in vivo, in a xenografted nude mice model. When compared to controls, IP6-treated mice produced a 25 fold smaller tumors (p = 0.008), as observed after a two weeks treatment. In a second experiment, wherein the treatment period was extended to five weeks, a 49 fold (p = 0.001) reduction in tumor size was observed in mice treated with IP6. Histologically no evidence of tumor cell necrosis was observed. These data suggest a potential usefulness of this cytostatic, and non-cytotoxic, compound in novel therapeutic strategies for these types of tumor.

Association of 12 serum biochemical markers of angiogenesis, tumour invasion and bone turnover with bone metastases from breast cancer: a crossectional and longitudinal evaluation.

Complex biological pathways including angiogenesis, invasion, osteoclastic activation and bone matrix degradation are involved in the formation of bone metastasis (BM). The aim of our study was to investigate the cross-sectional and longitudinal associations of a panel of 12 serum biochemical markers reflecting biological pathways underlying BM development. In a cross-sectional study, we investigated 29 patients with primary breast carcinoma without BM (BC/BM-), 28 patients with breast carcinoma and BM (BC/BM+) and 15 healthy women. In longitudinal analyses, we investigated 34 patients for whom serum was obtained a two different time points: at the time of primary BC diagnosis and after a median time of 3 years. During this follow-up, 15 patients developed BM, whereas the other 19 remained free of BM. In patients who developed BM, the second samples were obtained before BM was documented by bone scan. The cross-sectional analyses have shown all biochemical markers to be significantly elevated in patients with BM, when compared to the patients without BM and healthy controls, except TGFbeta1 that was significantly decreased. Multivariable analyses showed that only the bone resorption markers TRACP 5b, CTX and ICTP, and the marker of angiogenesis VEGF were independently associated with BM. Those markers correctly distinguished 85% of BC patients with or without BM from normal individuals. Longitudinal analyses showed that patients with primary BC who developed BM during follow-up had higher levels of TRACP5b (+95%, P=0.08) at the time of primary diagnosis, those patients had also a higher increases of ICTP (P=0.006), MMP-7 (P=0.004) and TIMP-1 (P=0.017) during follow-up than patients who did not progress toward bone metastasis. This study provides evidence of increase and interrelationship of circulating markers of angiogenesis, invasion and bone resorption in patients with BC with and without BM. Markers of bone resorption have the highest independent diagnostic value for detecting and potentially predicting BM in breast carcinoma patients.

Human fetal glial cells constitutively produce HIV-inducing cytokines.

The capacity of two human fetal glial cell lines, SVG and POJ, to increase the expression of human immunodeficiency virus (HIV) was investigated. As a cellular model for HIV latency, a chronically infected promonocytic cell line U1 was used. This cell line constitutively expresses a low level of viral activity. To monitor the level of HIV expression in U1 cells, reverse transcriptase (RT) activity was measured in the supernatant and the level of total HIV proteins was determined in cellular lysates. It was observed that the conditioned media from SVG and POJ cells increased RT activity in U1 cells in a dose-dependent fashion. In addition, the conditioned media from fetal glial cells caused an increase in total HIV protein synthesis. The capacity of conditioned media from both fetal glial cell lines to induce the expression of HIV was reduced by 45% in the presence of antibodies against human tumor necrosis factor alpha (TNFalpha), suggesting that one of the HIV-activating factors released by these cells was TNFalpha. The presence of TNFalpha and two other HIV-activating cytokines, IL-6 and IL-1, was confirmed by ELISA. It was also observed that glutathione increased the HIV-inducing capacity of the fetal glial cell-derived conditioned media. The finding that fetal glial cells constitutively secrete soluble factors which increase the expression of HIV in vitro suggests that in vivo, during perinatally acquired infection, similar events may occur. Fetal glial cells may play an important role in the pathogenesis of HIV-related encephalopathy.

HIV-1 modulates the expression of gelatinase A and B in monocytic cells.

The levels of mRNA of both gelatinases A and B were dramatically decreased in HIV-infected cells, when compared to uninfected cells. The expression of gelatinase A in HIV-infected cells was selectively increased by tumor necrosis factor (TNF alpha) while the expression of gelatinase B was not affected. In contrast, in uninfected cells TNF alpha down regulated gelatinase B mRNA level, without affecting the gelatinase A. N-acethylcysteine (NAC) increased the levels of mRNA of both gelatinases. The conditioned media from HIV-infected and uninfected cells had comparable level of secreted gelatinase A protein. These data suggest that in monocytic cells different regulatory pathways control gelatinases A and B and that HIV could modulate in vivo the expression of these proteolytic enzymes, critically involved in regulation of invasion of basement membrane.

Suppression of rhabdomyosarcoma growth by fumagillin analog TNP-470.

The purpose of our study was to investigate a novel therapeutic approach for rhabdomyosarcoma (RMS) in an animal model. The pursuit of new therapeutic modalities for RMS is critically important since this type of tumor is the most common soft tissue sarcoma in children and because patients with metastatic disease may not be cured with current therapeutic modalities. We studied whether RMS growth may be suppressed by TNP-470, an analog of fumagillin, which was found to inhibit neoangiogenesis. Our data had shown that animals treated with TNP-470 (60 mg/kg), over a specific period of time, had approximately 50% smaller tumors than controls. Consistent with previous observations, treatment with TNP-470 decreases the level of the cyclin D1. Tumors dissected from TNP-470-treated animals had also considerable necrotic areas. In addition, TNP-470 had a direct cytotoxic effect on RMS cells in vitro. Our study has shown, therefore, that RMS in an animal model and in vitro responds to treatment with TNP-470, which suggests that the inhibitors of angiogenesis may be useful in a novel therapeutic design for RMS.

Suppression of human immunodeficiency virus expression in chronically infected monocytic cells by glutathione, glutathione ester, and N-acetylcysteine.

The effects of glutathione (GSH), glutathione ester (GSE), and N-acetyl-L-cysteine (NAC) on the induction of human immunodeficiency virus (HIV) expression were investigated in the chronically infected monocytic U1 cell line, a previously described cellular model for HIV latency. U1 cells constitutively express low levels of virus, which can be increased by phorbol 12-myristate 13-acetate (PMA), tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), and other inducers. GSH, GSE, and NAC suppressed in a dose-dependent fashion the induction of HIV expression mediated by PMA, TNF-alpha, and IL-6, in the absence of cytotoxic or cytostatic effects. Reverse transcriptase activity, inducible by PMA, TNF-alpha, or IL-6, was decreased by 80-90% after pretreatment with GSH, GSE, or NAC. The induction of total HIV protein synthesis was also decreased appreciably after pretreatment with GSH, GSE, or NAC. The accumulation of HIV mRNA was substantially suppressed after pretreatment with NAC but to a lesser extent after pretreatment with GSH or GSE. Although PMA induces the expression of TNF-alpha in U1 cells, the suppressive effect of GSH, GSE, and NAC on PMA-induced HIV expression in U1 cells was not associated with the inhibition of TNF-alpha expression. The present findings, which elucidate relationships between cellular GSH and HIV expression, suggest that therapy with thiols may be of value in the treatment of HIV infection.