Blockade of MMP14 activity in murine breast carcinomas: implications for macrophages, vessels, and radiotherapy

BACKGROUND

Matrix metalloproteinase (MMP) 14 may mediate tumor progression through vascular and immune-modulatory effects.

METHODS

Orthotopic murine breast tumors (4T1 and E0771 with high and low MMP14 expression, respectively; n = 5-10 per group) were treated with an anti-MMP14 inhibitory antibody (DX-2400), IgG control, fractionated radiation therapy, or their combination. We assessed primary tumor growth, transforming growth factor β (TGFβ) and inducible nitric oxide synthase (iNOS) expression, macrophage phenotype, and vascular parameters. A linear mixed model with repeated observations, with Mann-Whitney or analysis of variance with Bonferroni post hoc adjustment, was used to determine statistical significance. All statistical tests were two-sided.

RESULTS

DX-2400 inhibited tumor growth compared with IgG control treatment, increased macrophage numbers, and shifted the macrophage phenotype towards antitumor M1-like. These effects were associated with a reduction in active TGFβ and SMAD2/3 signaling. DX-2400 also transiently increased iNOS expression and tumor perfusion, reduced tissue hypoxia (median % area: control, 20.2%, interquartile range (IQR) = 6.4%-38.9%; DX-2400: 1.2%, IQR = 0.2%-3.2%, P = .044), and synergistically enhanced radiation therapy (days to grow to 800mm(3): control, 12 days, IQR = 9-13 days; DX-2400 plus radiation, 29 days, IQR = 26-30 days, P < .001) in the 4T1 model. The selective iNOS inhibitor, 1400W, abolished the effects of DX-2400 on vessel perfusion and radiotherapy. On the other hand, DX-2400 was not capable of inducing iNOS expression or synergizing with radiation in E0771 tumors.

CONCLUSION

MMP14 blockade decreased immunosuppressive TGFβ, polarized macrophages to an antitumor phenotype, increased iNOS, and improved tumor perfusion, resulting in reduced primary tumor growth and enhanced response to radiation therapy, especially in high MMP14-expressing tumors.

Selective inhibition of matrix metalloproteinase-14 blocks tumor growth, invasion, and angiogenesis

Inhibition of specific matrix metalloproteinases (MMP) is an attractive noncytotoxic approach to cancer therapy. MMP-14, a membrane-bound zinc endopeptidase, has been proposed to play a central role in tumor growth, invasion, and neovascularization. Besides cleaving matrix proteins, MMP-14 activates proMMP-2 leading to an amplification of pericellular proteolytic activity. To examine the contribution of MMP-14 to tumor growth and angiogenesis, we used DX-2400, a highly selective fully human MMP-14 inhibitory antibody discovered using phage display technology. DX-2400 blocked proMMP-2 processing on tumor and endothelial cells, inhibited angiogenesis, and slowed tumor progression and formation of metastatic lesions. The combination of potency, selectivity, and robust in vivo activity shows the potential of a selective MMP-14 inhibitor for the treatment of solid tumors.

Revascularization of ischemic tissues by PDGF-CC via effects on endothelial cells and their progenitors

The angiogenic mechanism and therapeutic potential of PDGF-CC, a recently discovered member of the VEGF/PDGF superfamily, remain incompletely characterized. Here we report that PDGF-CC mobilized endothelial progenitor cells in ischemic conditions; induced differentiation of bone marrow cells into ECs; and stimulated migration of ECs. Furthermore, PDGF-CC induced the differentiation of bone marrow cells into smooth muscle cells and stimulated their growth during vessel sprouting. Moreover, delivery of PDGF-CC enhanced postischemic revascularization of the heart and limb. Modulating the activity of PDGF-CC may provide novel opportunities for treating ischemic diseases.

Anti-invasive, antitumoral, and antiangiogenic efficacy of a pyrimidine-2,4,6-trione derivative, an orally active and selective matrix metalloproteinases inhibitor

PURPOSE

The implication of matrix metalloproteinases (MMPs) in the major stages of cancer progression has fueled interest in the design of synthetic MMP inhibitors (MMPIs) as a novel anticancer therapy. Thus far, drugs used in clinical trials are broad-spectrum MMPIs the therapeutic index of which proved disappointingly low. The development of selective MMPIs for tumor progression-associated MMPs is, thus, likely to offer improved therapeutic possibilities.

EXPERIMENTAL DESIGN

The anti-invasive capacity of a series of pyrimidine-trione derivatives was tested in vitro in a chemoinvasion assay, and the most potent compound was further evaluated in vivo in different human tumor xenograft models. The activity of this novel selective MMPI was compared with BB-94, a broad-spectrum inhibitor.

RESULTS

Ro-28-2653, an inhibitor with high selectivity for MMP-2, MMP-9, and membrane type 1 (MT1)-MMP, showed the highest anti-invasive activity in vitro. In vivo, Ro-28-2653 reduced the growth of tumors induced by the inoculation of different cell lines producing MMPs and inhibited the tumor-promoting effect of fibroblasts on breast adenocarcinoma cells. Furthermore, Ro-28-2653 reduced tumor vascularization and blocked angiogenesis in a rat aortic ring assay. In contrast, BB-94 up-regulated MMP-9 expression in tumor cells and promoted angiogenesis in the aortic ring assay.

CONCLUSION

Ro-28-2653, a selective and orally bioavailable MMPI with inhibitory activity against MMPs expressed by tumor and/or stromal cells, is a potent antitumor and antiangiogenic agent. In contrast to broad-spectrum inhibitors, the administration of Ro-28-2653 was not associated with the occurrence of adverse side effects that might hamper the therapeutic potential of these drugs.

Multifunctional role of matrix metalloproteinases in multiple myeloma: a study in the 5T2MM mouse model

Matrix metalloproteinases (MMPs) are known to play a role in cell growth, invasion, angiogenesis, metastasis, and bone degradation, all important events in the pathogenesis of cancer. Multiple myeloma is a B-cell cancer characterized by the proliferation of malignant plasma cells in the bone marrow, increased angiogenesis, and the development of osteolytic bone disease. The role of MMPs in the development of multiple myeloma is poorly understood. Using SC-964, a potent inhibitor of several MMPs (MMP-2, -3, -8, -9, and -13), we investigated the role of MMPs in the 5T2MM murine model. Reverse transcriptase-polymerase chain reaction demonstrated the presence of mRNA for MMP-2, -8, -9, and -13 in 5T2MM-diseased bone marrow. Mice bearing 5T2MM cells were given access to food containing SC-964. The concentration of SC-964 measured in the plasma of mice after 11 days of treatment was able to inhibit MMP-9 activity in gelatin zymography. Treatment of 5T2MM-bearing mice resulted in a significant reduction in tumor burden, a significant decrease in angiogenesis, and partially protective effect against the development of osteolytic bone disease. The direct role of MMPs in these different processes was confirmed by in vitro experiments. All these results support the multifunctional role of MMPs in the development of multiple myeloma.

Plasmin‐activated doxorubicin prodrugs containing a spacer reduce tumor growth and angiogenesis without systemic toxicity

To generate doxorubicin (Dox) specifically at the tumor site, the chemotherapeutic agent was incorporated into a prodrug by linkage to a peptide specifically recognized by plasmin, which is overproduced in many cancers. ST-9905, which contains an elongated self-elimination spacer, is activated more rapidly in vitro by plasmin than is ST-9802. Prodrug activation in vitro depended on the level of urokinase produced by tumor cells and was inhibited by aprotinin, a plasmin inhibitor. Comparison of equimolar concentrations of ST-9905, ST-9802, and Dox in EF43.fgf-4 and MCF7 models revealed that both prodrugs, in sharp contrast to Dox, displayed antiproliferative and antiangiogenic activities without discernible toxicity. Although MCF7 cells are poor urokinase producers in vitro, prodrug efficacy in this model may be explained by production of plasmin by tumor-infiltrating host cells. Mice treated with equitoxic concentrations (maximum tolerated doses) of prodrugs showed 100% survival and negligible body weight loss, in contrast to results after Dox treatment. ST-9905 was substantially more effective than ST-9802 and induced similar tumor growth inhibition as Dox but without apparent toxicity. This finding may be explained by the elongated spacer, which facilitates enzymatic prodrug activation. These data validate both the use of elongated spacers in vivo and the concept of targeting anticancer prodrugs to tumor-associated plasmin.

Placental growth factor, a member of the VEGF family, contributes to the development of choroidal neovascularization

PURPOSE

VEGF has been shown to be necessary, but not sufficient alone, for the development of subretinal pathologic angiogenesis. In the current study, the influence of placental growth factor (PlGF), a member of the VEGF family, in human and experimental choroidal neovascularization (CNV) was investigated.

METHODS

The presence of VEGF family member mRNA was evaluated by RT-PCR in neovascular membranes extracted during surgery. The spatial and temporal pattern of VEGF isoforms and PlGF mRNA expression were explored by using the laser capture catapulting technique and RT-PCR in a murine laser-induced model and in vitro. PlGF expression was also studied in human donor eyes. The influence of endogenous PlGF was evaluated in deficient mice (PlGF(-/-)) and by antibody-mediated neutralization of the PlGF receptor.

RESULTS

Human neovascular membranes consistently expressed VEGF-A, -B, and -C; PlGF; and VEGFR-1 and -2. The VEGF(120) isoform mRNA was primarily induced in early stages of angiogenesis in vivo and in vitro. PlGF mRNA expression was present in the intact choroid and significantly upregulated during the course of experimental CNV. Both deficient PlGF expression in PlGF(-/-) mice and PlGF receptor neutralization in wild-type mice prevented the development of choroidal neovascularization induced by laser.

CONCLUSIONS

These observations demonstrate the participation of PlGF in experimental CNV. They identify therefore PlGF as an additional promising target for ocular antiangiogenic strategies.

Role of plasminogen activator-plasmin system in tumor angiogenesis

New blood formation or angiogenesis has become a key target in therapeutic strategies aimed at inhibiting tumor growth and other diseases associated with neovascularization. Angiogenesis is associated with important extracellular remodeling involving different proteolytic systems among which the plasminogen system plays an essential role. It belongs to the large serine proteinase family and can act directly or indirectly by activating matrix metalloproteinases or by liberating growth factors and cytokines sequestered within the extracellular matrix. Migration of endothelial cells is associated with significant upregulation of proteolysis and, conversely, immunoneutralization or chemical inhibition of the system reduces angiogenesis in vitro. On the other hand, genetically altered mice developed normally without overt vascular anomalies indicating the possibility of compensation by other proteases in vivo. Nevertheless, they have in some experimental settings revealed unanticipated roles for previously characterized proteinases or their inhibitors. In this review, the complex mechanisms of action of the serine proteases in pathological angiogenesis are summarized alongside possible therapeutic applications.

The antitumoral effect of endostatin and angiostatin is associated with a down-regulation of vascular endothelial growth factor expression in tumor cells

Endostatin and angiostatin are known as tumor-derived angiogenesis inhibitors, but their mechanisms of action are not yet completely defined. We report here that endostatin and angiostatin, delivered by adenoviral vectors, reduced in vitro the neovessel formation in the mouse aortic ring assay by 85 and 40%, respectively. We also demonstrated in vivo that both endostatin and angiostatin inhibited local invasion and tumor vascularization of transplanted murine malignant keratinocytes, and reduced by 50 and 90% the development of highly vascularized murine mammary tumors. This inhibition of tumor growth was associated with a reduction of tumor vascularization. Expression analysis of vascular endothelial growth factor (VEGF) carried out in the mouse aortic ring model revealed a 3- to 10-fold down-regulation of VEGF mRNA expression in endostatin-treated rings. A similar down-regulation of VEGF expression at both mRNA and protein levels was also observed in the two in vivo cancer models after treatment with each angiogenesis inhibitor. This suggests that endostatin and angiostatin effects may be mediated, at least in part, by their ability to down-regulate VEGF expression within the tumor. This work provides evidence that endostatin and angiostatin act on tumor cells themselves.

Mouse Aortic Ring Assay: A New Approach of the Molecular Genetics of Angiogenesis

Angiogenesis, a key step in many physiological and pathological processes, involves proteolysis of the extracellular matrix. To study the role of two enzymatic families, serine-proteases and matrix metalloproteases in angiogenesis, we have adapted to the mouse, the aortic ring assay initially developed in the rat. The use of deficient mice allowed us to demonstrate that PAI-1 is essential for angiogenesis while the absence of an MMP, MMP-11, did not affect vessel sprouting. We report here that this model is attractive to elucidate the cellular and molecular mechanisms of angiogenesis, to identify, characterise or screen "pro- or anti-angiogenic agents that could be used for the treatment of angiogenesis-dependent diseases. Approaches include using recombinant proteins, synthetic molecules and adenovirus-mediated gene transfer.

Novel antiangiogenic effects of the bisphosphonate compound zoledronic acid

Bisphosphonate drugs inhibit osteoclastic bone resorption and are widely used to treat skeletal complications in patients with tumor-induced osteolysis. We now show that zoledronic acid, a new generation bisphosphonate with a heterocyclic imidazole substituent, is also a potent inhibitor of angiogenesis. In vitro, zoledronic acid inhibits proliferation of human endothelial cells stimulated with fetal calf serum, basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (IC(50) values 4.1, 4.2, and 6.9 microM, respectively), and modulates endothelial cell adhesion and migration. In cultured aortic rings and in the chicken egg chorioallantoic membrane assay, zoledronic acid reduces vessel sprouting. When administered systemically to mice, zoledronic acid potently inhibits the angiogenesis induced by subcutaneous implants impregnated with bFGF [ED(50), 3 microg/kg (7.5 nmol/kg) s.c.]. These findings indicate that zoledronic acid has marked antiangiogenic properties that could augment its efficacy in the treatment of malignant bone disease and extend its potential clinical use to other diseases with an angiogenic component.

Improved quantification of angiogenesis in the rat aortic ring assay

In vitro angiogenesis assays are essential for the identification of potential angiogenic agents and screening for pharmacological inhibitors. Among these assays, the rat aortic ring model developed by Nicosia bridges the gap between in vivo and in vitro models. The quantification of angiogenesis on this system must be applicable to characterise vascular networks of various states of complexity. We present here an improved computer-assisted image analysis which allows: (1) the determination of the aortic ring area and its factor shape; (2) the number of microvessels, the total number of branchings, the maximal microvessel length and the microvessel distribution; (3) the total number of isolated fibroblast-like cells and their distribution. We show that this method is suitable to quantify spontaneous angiogenesis as well as to analyse a complex microvascular network induced by various concentrations of vascular endothelial growth factor (VEGF). In addition, by evaluating a new parameter, the fibroblast-like cell distribution, our results show that: (1) during spontaneous angiogenic response, maximal fibroblast-like cell migration delimits microvascular outgrowth; and (2) the known angiogenic inhibitor Batimastat prevents endothelial cell sprouting without completely blocking fibroblast-like cell migration. Finally, this new method of quantification is of great interest to better understand angiogenesis and to test pro- or anti-angiogenic agents.

MT1-MMP expression promotes tumor growth and angiogenesis through an up-regulation of vascular endothelial growth factor expression

Membrane type 1 metalloprotease (MT1-MMP) is a transmembrane metalloprotease that plays a major role in the extracellular matrix remodeling, directly by degrading several of its components and indirectly by activating pro-MMP2. We investigated the effects of MT1-MMP overexpression on in vitro and in vivo properties of human breast adenocarcinoma MCF7 cells, which do not express MT1-MMP or MMP-2. MT1-MMP and MMP-2 cDNAs were either transfected alone or cotransfected. All clones overexpressing MT1-MMP 1) were able to activate endogenous or exogenous pro-MMP-2, 2) displayed an enhanced in vitro invasiveness through matrigel-coated filters independent of MMP-2 transfection, 3) induced the rapid development of highly vascularized tumors when injected subcutaneously in nude mice, and 4) promoted blood vessels sprouting in the rat aortic ring assay. These effects were observed in all clones overexpressing MT1-MMP regardless of MMP-2 expression levels, suggesting that the production of MMP-2 by tumor cells themselves does not play a critical role in these events. The angiogenic phenotype of MT1-MMP-producing cells was associated with an up-regulation of VEGF expression. These results emphasize the importance of MT1-MMP during tumor angiogenesis and open new opportunities for the development of anti-angiogenic strategies combining inhibitors of MT1-MMP and VEGF antagonists.

Murine 5T multiple myeloma cells induce angiogenesis in vitro and in vivo

Multiple myeloma is a B cell malignancy. Recently, it has been demonstrated that bone marrow samples of patients with multiple myeloma display an enhanced angiogenesis. The mechanisms involved seem to be multiple and complex. We here demonstrate that the murine 5T multiple myeloma models are able to induce angiogenesis in vitro by using a rat aortic ring assay and in vivo by determining the microvessel density. The rat aortic rings cultured in 5T multiple myeloma conditioned medium exhibit a higher number of longer and more branched microvessels than the rings cultured in control medium. In bone marrow samples from 5T multiple myeloma diseased mice, a statistically significant increase of the microvessel density was observed when compared to bone marrow samples from age-matched controls. The angiogenic phenotype of both 5T multiple myeloma cells could be related, at least in part, to their capacity to produce vascular endothelial growth factor. These data clearly demonstrate that the 5T multiple myeloma models are good models to study angiogenesis in multiple myeloma and will allow to unravel the mechanisms of neovascularisation, as well as to test new putative inhibitors of angiogenesis.

The pro- or antiangiogenic effect of plasminogen activator inhibitor 1 is dose dependent

Plasminogen activator inhibitor 1 (PAI-1) is believed to control proteolytic activity and cell migration during angiogenesis. We previously demonstrated in vivo that this inhibitor is necessary for optimal tumor invasion and vascularization. We also showed that PAI-1 angiogenic activity is associated with its control of plasminogen activation but not with the regulation of cell-matrix interaction. To dissect the role of the various components of the plasminogen activation system during angiogenesis, we have adapted the aortic ring assay to use vessels from gene-inactivated mice. The single deficiency of tPA, uPA, or uPAR, as well as combined deficiencies of uPA and tPA, did not dramatically affect microvessel formation. Deficiency of plasminogen delayed microvessel outgrowth. Lack of PAI-1 completely abolished angiogenesis, demonstrating its importance in the control of plasmin-mediated proteolysis. Microvessel outgrowth from PAI-1-/- aortic rings could be restored by adding exogenous PAI-1 (wild-type serum or purified recombinant PAI-1). Addition of recombinant PAI-1 led to a bell-shaped angiogenic response clearly showing that PAI-1 is proangiogenic at physiological concentrations and antiangiogenic at higher levels. Using specific PAI-1 mutants, we could demonstrate that PAI-1 promotes angiogenesis at physiological (nanomolar) concentrations through its antiproteolytic activity rather than by interacting with vitronectin.

Histone deacetylases inhibitors as anti-angiogenic agents altering vascular endothelial growth factor signaling

Angiogenesis is a complex biological process involving the coordinated modulation of many genes. Histone deacetylases (HDAC) are a growing family of enzymes that mediate the availability of chromatin to the transcriptional machinery. Trichostatin-A (TSA) and suberoylanilide hydroxamic acid (SAHA), two HDAC inhibitors known to relieve gene silencing, were evaluated as potential antiangiogenic agents. TSA and SAHA were shown to prevent vascular endothelial growth factor (VEGF)-stimulated human umbilical cord endothelial cells (HUVEC) from invading a type I collagen gel and forming capillary-like structures. SAHA and TSA inhibited the VEGF-induced formation of a CD31-positive capillary-like network in embryoid bodies and inhibited the VEGF-induced angiogenesis in the CAM assay. TSA also prevented, in a dose-response relationship, the sprouting of capillaries from rat aortic rings. TSA inhibited in a dose-dependent and reversible fashion the VEGF-induced expression of VEGF receptors, VEGFR1, VEGFR2, and neuropilin-1. TSA and SAHA upregulated the expression by HUVEC of semaphorin III, a recently described VEGF competitor, at both mRNA and protein levels. This effect was specific to endothelial cells and was not observed in human fibroblasts neither in vascular smooth muscle cells. These observations provide a conspicuous demonstration that HDAC inhibitors are potent anti-angiogenic factors altering VEGF signaling.

Matrix and serine protease expression during leukemic cell differentiation induced by aclacinomycin and all-trans-retinoic acid

In myeloid leukemia, immature leukemic cells are able to egress into peripheral blood to infiltrate extra-medullary organs. We therefore analyzed the migrating and invasive potential of human HL-60 and NB4 cell lines, representative of acute myelogenous leukemia, their ability to express matrix metalloproteases (MMPs), tissue inhibitors of metalloproteases (TIMPs) and urokinase plasminogen activator (uPA) in response to differentiating agents. Granulocytic differentiation by all-trans-retinoic acid (ATRA) and aclacinomycin (ACLA) strongly increased HL-60 and NB4 cell migration and invasion. At mRNA and protein levels, these cell lines produced significant amounts of MMP-9 (HL-60<NB4). Granulocytic differentiation by ACLA increased both pro and active forms of MMP-9 whereas ATRA decreased them and stimulated uPA mRNAs. TIMP-1, the physiological MMP inhibitor, increased during granulocytic differentiation whereas TIMP-2 did not significantly vary. Use of Batimastat and aprotinin suggests that ATRA was active by modulating the uPA system while ACLA interfered with MMP expression. In conclusion, our data demonstrate that HL-60 and NB4 cells express MMPs and uPA which are differentially regulated by the differentiating agents ATRA and ACLA and suggest the clinical usefulness of MMPs and serine protease inhibitors in the prophylaxis and treatment of the ATRA syndrome.

[Role of plasminogen activator inhibitor type 1 in tumor angiogenesis]

The plasminogen/plasmin system plays a key role in cancer progression, presumably via mediating extracellular matrix degradation and tumour cell migration. High levels of components of the plasminogen activation system, and paradoxically also its inhibitor, plasminogen activator inhibitor 1 (PAI-1), have been correlated with a poor prognosis for patients with cancers of different types. Recent findings clearly suggest that PAI-1 is essential for capillary sprouting during tumour angiogenesis. Moreover, there is accumulating evidence that both the urokinase receptor and PAI-1 are multifunctional proteins involved not only in extracellular matrix proteolysis but also in cellular adhesion and migration through their binding site for vitronectin. The understanding of whether PAI-1 plays a regulatory role in angiogenesis by tightly controlling proteolytic activity or by influencing cell migration could allow a new anti-angiogenic approach for tumour therapy.

Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions

Vascular endothelial growth factor (VEGF) stimulates angiogenesis by activating VEGF receptor-2 (VEGFR-2). The role of its homolog, placental growth factor (PlGF), remains unknown. Both VEGF and PlGF bind to VEGF receptor-1 (VEGFR-1), but it is unknown whether VEGFR-1, which exists as a soluble or a membrane-bound type, is an inert decoy or a signaling receptor for PlGF during angiogenesis. Here, we report that embryonic angiogenesis in mice was not affected by deficiency of PlGF (Pgf-/-). VEGF-B, another ligand of VEGFR-1, did not rescue development in Pgf-/- mice. However, loss of PlGF impaired angiogenesis, plasma extravasation and collateral growth during ischemia, inflammation, wound healing and cancer. Transplantation of wild-type bone marrow rescued the impaired angiogenesis and collateral growth in Pgf-/- mice, indicating that PlGF might have contributed to vessel growth in the adult by mobilizing bone-marrow-derived cells. The synergism between PlGF and VEGF was specific, as PlGF deficiency impaired the response to VEGF, but not to bFGF or histamine. VEGFR-1 was activated by PlGF, given that anti-VEGFR-1 antibodies and a Src-kinase inhibitor blocked the endothelial response to PlGF or VEGF/PlGF. By upregulating PlGF and the signaling subtype of VEGFR-1, endothelial cells amplify their responsiveness to VEGF during the 'angiogenic switch' in many pathological disorders.

Down-regulation of vascular endothelial growth factor by tissue inhibitor of metalloproteinase-2: effect on in vivo mammary tumor growth and angiogenesis

The tissue inhibitor of metalloproteinases-2 (TIMP-2) has at least two independent functions, i.e., regulation of matrix metalloproteinases and growth promoting activity. We investigated the effects of TIMP-2 overexpression, induced by retroviral mediated gene transfer, on the in vivo development of mammary tumors in syngeneic mice inoculated with EF43.fgf-4 cells. The EF43.fgf-4 cells established by stably infecting the normal mouse mammary EF43 cells with a retroviral expression vector for the fgf-4 oncogene, are highly tumorigenic and overproduce vascular endothelial growth factor (VEGF). Despite a promotion of the in vitro growth rate of EF43.fgf-4 cells overexpressing timp-2, the in vivo tumor growth was delayed. At day 17 post-cell injection, the volume of tumor derived from TIMP-2-overexpressing cells was reduced by 80% as compared with that obtained with control cells. Overexpression of TIMP-2 was associated with a down-regulation of VEGF expression in vitro and in vivo, a reduction of vessel size, density, and blood supply in the induced tumors. In addition, TIMP-2 completely inhibited the angiogenic activity of EF43.fgf-4 cell-conditioned medium in vitro using a rat aortic ring model. Our findings suggest that overexpression of TIMP-2 delays growth and angiogenesis of mammary carcinoma in vivo and that down-regulation of VEGF expression may play an important role in this TIMP-2-mediated antitumoral and antiangiogenic effects. Finally the in vivo delivery of TIMP-2, as assessed by i.v. injection of recombinant adenoviruses vectors, significantly reduced the growth of the EF43.fgf-4-induced tumors. This effect of TIMP-2 was shown to be equally comparable with that of angiostatin, a known potent inhibitor of angiogenesis.

New functions of stromal proteases and their inhibitors in tumor progression

Acquisition of invasive metastatic potential through protease expression is a key event in tumor progression. In carcinomas, the production of metalloproteinases and serine proteinases is regulated by a cross talk between stromal cells and cancer cells. Paradoxically, high rather than low levels of their inhibitors predict poor survival of patients suffering from a variety of cancers. Recent observations suggest a much more complex role of these inhibitors in tumor progression than expected initially.

Emerging roles for proteinases in cancer

Metalloproteinases and serine proteinases have been associated with tumor invasion and formation of metastasis which represent the major obstacles to cancer cure. The contribution of proteinases in these processes was initially thought to be the destruction of extracellular matrices. However, recent evidence suggests that they mainly affect tumor growth rather than invasion. Proteinases can indeed generate active matrix protein fragments, influence the release, the activation and the bioavailability of growth factors, and consequently modulate tumor cell growth, apoptosis and angiogenesis. Additionally, proteinases, their receptors and/or inhibitors can be directly involved in cell migration and in the processing or shedding of cell surface proteins. Further elucidation of the functions of proteinases is essential for the development of novel anticancer strategies.

Induction of endothelial cell apoptosis by solid tumor cells

The mechanisms by which tumor cells extravasate to form metastasis remain controversial. Previous studies performed in vivo and in vitro demonstrate that the contact between tumor cells and the vascular wall impairs endothelium integrity. Here, we investigated the effect of breast adenocarcinoma MCF-7 cells on the apoptosis of human umbilical vein endothelial cells (HUVEC). TUNEL labeling, nuclear morphology, and DNA electrophoresis indicated that MCF-7 cells induced a two- to fourfold increase in HUVEC apoptosis. Caspase-3 activity was significantly enhanced. Neither normal cells tested (mammary epithelial cells, fibroblasts, leukocytes) nor transformed hematopoietic cells tested (HL60, Jurkat) induced HUVEC apoptosis. On the contrary, cells derived from solid tumors (breast adenocarcinoma, MDA-MB-231 and T47D; fibrosarcoma, HT 1080) had an effect similar to that of MCF-7 cells. The induction of apoptosis requires cell-to-cell contact, since it could not be reproduced by media conditioned by MCF-7 cells cultured alone or cocultured with HUVEC. Our results suggest that cells derived from solid tumors may alter the endothelium integrity by inducing endothelial cell apoptosis. On the contrary, normal or malignant leukocytes appear to extravasate by distinct mechanisms and do not damage the endothelium. Our data may lead to a better understanding of the steps involved in tumor cell extravasation.

Production and activation of matrix metalloprotease-9 (MMP-9) by HL-60 promyelocytic leukemia cells

Human promyelocytic HL-60 cells have been used as a model of acute leukemia to investigate the expression and the regulation of matrix metalloproteases (MMPs), known to contribute to the degradation of extracellular matrix components. As shown by gelatin zymography, HL-60 cells constitutively released significant amounts of proMMP-9 (92 kDa) and moderate amounts of proMMP-2 (72 kDa). Furthermore, casein zymography confirmed the presence of serine proteases in the form of pro-urokinase. Activation of proMMP-9 was dependent on the plasminogen activator/plasmin (PA/plasmin) system and was inhibited by aprotinin. MMP-9 was only detected in cellular extracts or conditioned media incubated with HL-60 cells, indicating that cells are essential to the activation process. Addition of plasminogen increased by 3-fold the basal invasive rate of these cells across a matrigel layer (2.1% versus 0.7% in control cells after 4 h of incubation). Taken together, these results indicate that HL-60 cells exhibit an autocrine activation mechanism of proMMP-9 via the PA/plasmin system and that activation of proMMP-9 increases their invasive potential.

Anthracyclines as tumor cell differentiating agents: effects on the regulation of erythroid gene expression

Tumor cells, and particularly leukemic cells, can be considered as maturation-arrested cells which have escaped some normal control and continue to proliferate. This maturation arrest can be reversed by differentiation agents such as antitumor drugs currently used in conventional cytotoxic chemotherapy. In this respect, anthracyclines have been shown to trigger the differentiation of leukemic and solid tumor cells, but the molecular mechanisms by which such drugs lead to the differentiating phenotype are still poorly understood. Using human leukemic multipotent K562 cells, we have demonstrated that subtoxic concentrations of aclacinomycin (ACLA) and doxorubicin (DOX) preferentially stimulate the hemoglobinic pathway (globins and heme synthesis) and the expression of mRNAs of globins and of porphobilinogen deaminase (PBGD). However, our results indicate that both drugs exert this differentiating effect along distinct regulatory pathways. Indeed, only ACLA and not DOX induces the expression of erythropoietin receptor (EpoR) mRNAs and of membrane EpoR, as well as an overexpression of the erythroid transcription factors GATA-1 and NF-E2 known to play a central role in erythroid gene regulation. Similarly, using transfection assays, ACLA but not DOX activates the regulatory regions (promoters and enhancers) of GATA-1, EpoR, PBGD, epsilon- and gamma-globin genes. Finally, results of run-on assays indicate that ACLA induces an enhancement of the transcription rate of these erythroid genes whereas DOX preferentially increases stability of GATA-1, NF-E2 and PBGD mRNAs. In conclusion, ACLA mainly acts at the transcriptional level via specific activation of erythroid regulatory regions whereas DOX rather acts at the posttranscriptional level by increasing the half-lives of erythroid mRNAs.

P53 protein expression in human multidrug-resistant CEM lymphoblasts

A role for p53 in the regulation of multidrug-resistance (MDR) has been postulated as wild-type p53 suppresses and mutant p53 specifically activates the mdr1 promoter. Moreover, changes in p53 expression and/or functions could be implicated in drug resistance. As the parental lymphoblastic CCRF-CEM cell line has been described as expressing a mutated form of p53, we have examined p53 and mdm2 protein levels in the human multidrug-resistant CEM-VLB cell line variant. These drug-resistant CEM-VLB cells, which have increased expressions of mdr1 and P-glycoprotein, displayed p53 and mdm2 protein expressions similar to those observed in their sensitive CCRF-CEM counterparts. Treatment of these drug-resistant cells with non-toxic doses of the resistance-inducing drug vinblastin induced a strong increase in p53 protein and mRNA but was ineffective on mdm2 protein expression, or mdr1 mRNA expression. These data indicate that mutant p53 protein was not overexpressed in these MDR cells. This overexpression could be induced by microtubule-active drug treatment, but, as previously observed in other sensitive cell lines, mutant p53 from these MDR cells was unable to positively regulate mdm2 gene product expression.

Evidence for distinct regulation processes in the aclacinomycin- and doxorubicin-mediated differentiation of human erythroleukemic cells

Human erythroleukemic K 562 cells were induced to were induced to differentiate along the erythroid lineage by anthracycline antitumor drugs, such as aclacinomycin (ACLA) and doxorubicin (DOX). Subsequent stimulation of heme and globin synthesis led to a differential quantitative expression of hemoglobins. Gower 1 (epsilon2, zeta2) was the major type for ACLA and X (epsilon2, gamma2) for DOX. Although ACLA and DOX increased both the expression of gamma-globin and porphobilinogen deaminase mRNAs, striking differences were observed in the expression of erythropoietin receptor mRNAs and in erythroid transcription factors GATA-1 and NF-E2, known to play a key role in erythroid gene regulation. Indeed, ACLA induces an increase either in the binding capacity of GATA-1 and NF-E2 or in the accumulation of erythropoietin receptor, GATA-1 and NF-E2 transcripts. In contrast, their expression with DOX was not significantly modified compared to uninduced cells, except for a slight decrease in NF-E2 expression on day 3. In conclusion, these data show that: 1. increased expression of erythroid transcription factors and erythroid genes are associated only with ACLA treatment, and 2. although cytotoxicity of both ACLA and DOX is certainly dependent on DNA intercalation, regulation of differentiation processes by these two drugs involves distinct mechanisms.