Activation of FGFR1beta signaling pathway promotes survival, migration and resistance to chemotherapy in acute myeloid leukemia cells

Fibroblast growth factors (FGFs) are important regulators of hematopoiesis and have been implicated in the tumorigenesis of solid tumors. Recent evidence suggests that FGF signaling through FGF receptors (FGFRs) may play a role in the proliferation of subsets of acute myeloid leukemias (AMLs). However, the precise mechanism and specific FGF receptors that support leukemic cell growth are not known. We show that FGF-2, through activation of FGFR1beta signaling, promotes survival, proliferation and migration of AML cells. Stimulation of FGFR1beta results in phosphoinositide 3-kinase (PI3-K)/Akt activation and inhibits chemotherapy-induced apoptosis of leukemic cells. Neutralizing FGFR1-specific antibody abrogates the physiologic and chemoprotective effects of FGF-2/FGFR1beta signaling and inhibits tumor growth in mice xenotransplanted with human AML. These data suggest that activation of FGF-2/FGFR1beta supports progression and chemoresistance in subsets of AML. Therefore, FGFR1 targeting may be of therapeutic benefit in subsets of AML.

Inhibition of human leukemia in an animal model with human antibodies directed against vascular endothelial growth factor receptor 2. Correlation between antibody affinity and biological activity

Vascular endothelial growth factor (VEGF) and its receptors (VEGFR) have been implicated in promoting solid tumor growth and metastasis via stimulating tumor-associated angiogenesis. We recently showed that certain 'liquid' tumors such as leukemia not only produce VEGF, but also express functional VEGFR, resulting in an autocrine loop for tumor growth and propagation. A chimeric anti-VEGFR2 (or kinase insert domain-containing receptor, KDR) antibody, IMC-1C11, was shown to be able to inhibit VEGF-induced proliferation of human leukemia cells in vitro, and to prolong survival of nonobese diabetic-severe combined immune deficient (NOD-SCID) mice inoculated with human leukemia cells. Here we produced two fully human anti-KDR antibodies (IgG1), IMC-2C6 and IMC-1121, from Fab fragments originally isolated from a large antibody phage display library. These antibodies bind specifically to KDR with high affinities: 50 and 200 pM for IMC-1121 and IMC-2C6, respectively, as compared to 270 pM for IMC-1C11. Like IMC-1C11, both human antibodies block VEGF/KDR interaction with an IC(50) of approximately 1 nM, but IMC-1121 is a more potent inhibitor to VEGF-stimulated proliferation of human endothelial cells. These anti-KDR antibodies strongly inhibited VEGF-induced migration of human leukemia cells in vitro, and when administered in vivo, significantly prolonged survival of NOD-SCID mice inoculated with human leukemia cells. It is noteworthy that the mice treated with antibody of the highest affinity, IMC-1121, survived the longest period of time, followed by mice treated with IMC-2C6 and IMC-1C11. Taken together, our data suggest that anti-KDR antibodies may have broad applications in the treatment of both solid tumors and leukemia. It further underscores the efforts to identify antibodies of high affinity for enhanced antiangiogenic and antitumor activities.

Complete inhibition of vascular endothelial growth factor (VEGF) activities with a bifunctional diabody directed against both VEGF kinase receptors, fms-like tyrosine kinase receptor and kinase insert domain-containing receptor

Vascular endothelial growth factor (VEGF) binds to and mediates its activity mainly through two tyrosine kinase receptors, VEGF receptor 1 [or fms-like tyrosine kinase receptor (Flt-1)] and VEGF receptor 2 [or kinase insert domain-containing receptor (KDR)]. Numerous studies have shown that overexpression of VEGF and its receptor plays an important role in tumor-associated angiogenesis and hence in both tumor growth and metastasis. We demonstrated previously that antagonistic antibodies to KDR specifically inhibited VEGF-stimulated receptor activation, cell migration, and endothelial cell mitogenesis. Here we constructed a recombinant bifunctional diabody that is capable of blocking both Flt-1 and KDR from binding to their ligands, including VEGF and placenta growth factor (PlGF). The diabody was expressed in Escherichia coli and purified by single-step affinity chromatography. The diabody retained the capacity to bind both KDR and Flt-1 and effectively blocked interaction between KDR and VEGF, Flt-1 and VEGF, and Flt-1 and PlGF. Furthermore, the diabody is a stronger inhibitor than its parent antibodies to VEGF-stimulated mitogenesis of human endothelial cells, as well as both VEGF- and PlGF-induced migration of human leukemia cells. Taken together, our results suggest that dual receptor blockade with the bifunctional diabody may prove to be a more efficient approach in inhibiting VEGF-stimulated angiogenesis.

Inhibition of glioma angiogenesis and growth in vivo by systemic treatment with a monoclonal antibody against vascular endothelial growth factor receptor-2

Using an orthotopic intracerebral model, we investigated whether systemic treatment with DC101, a monoclonal antibody against vascular endothelial growth factor receptor (VEGFR)-2, could inhibit angiogenesis and the growth of human glioblastoma cells in severe combined immunodeficient mice. Intraperitoneal treatment with DC101, control IgG, or PBS was initiated either on day 0 or, in another series, on day 6 after tumor cell implantation, and animals were killed approximately 2 weeks after tumor cell injection. Tumor volumes in animals treated with DC101 were reduced by 59 and 81% compared with IgG and PBS controls, respectively (P < 0.001), when treatment was initiated immediately, and similar results were obtained when treatment started on day 6. Microvessel density in tumors of DC101-treated animals was reduced by at least 40% compared with animals treated with control IgG or PBS (P < 0.01). We observed a reduction in tumor cell proliferation and an increase in apoptosis in DC101-treated animals (P < 0.001). However, in mice treated with DC101, we also noticed a striking increase in the number and total area of small satellite tumors clustered around, but distinct from, the primary. These satellites usually contained central vessel cores, and tumor cells often had migrated over long distances along the host vasculature to eventually reach the surface and spread leptomeningeally. We conclude that systemic antagonization of VEGFR-2 can inhibit glioblastoma neovascularization and growth but can lead to increased cooption of preexistent cerebral blood vessels. Therefore, a combination of different treatment modalities which also include anti-invasive therapy may be needed for an effective therapy against glioblastoma, and the use of an antibody against VEGFR-2 may be one effective component.

Inhibition of both paracrine and autocrine VEGF/ VEGFR-2 signaling pathways is essential to induce long-term remission of xenotransplanted human leukemias

Antiangiogenic agents block the effects of tumor-derived angiogenic factors (paracrine factors), such as vascular endothelial growth factor (VEGF), on endothelial cells (EC), inhibiting the growth of solid tumors. However, whether inhibition of angiogenesis also may play a role in liquid tumors is not well established. We recently have shown that certain leukemias not only produce VEGF but also selectively express functional VEGF receptors (VEGFRs), such as VEGFR-2 (Flk-1, KDR) and VEGFR1 (Flt1), resulting in the generation of an autocrine loop. Here, we examined the relative contribution of paracrine (EC-dependent) and autocrine (EC-independent) VEGF/VEGFR signaling pathways, by using a human leukemia model, where autocrine and paracrine VEGF/VEGFR loops could be selectively inhibited by neutralizing mAbs specific for murine EC (paracrine pathway) or human tumor (autocrine) VEGFRs. Blocking either the paracrine or the autocrine VEGF/VEGFR-2 pathway delayed leukemic growth and engraftment in vivo, but failed to cure inoculated mice. Long-term remission with no evidence of disease was achieved only if mice were treated with mAbs against both murine and human VEGFR-2, whereas mAbs against human or murine VEGFR-1 had no effect on mice survival. Therefore, effective antiangiogenic therapies to treat VEGF-producing, VEGFR-expressing leukemias may require blocking both paracrine and autocrine VEGF/VEGFR-2 angiogenic loops to achieve remission and long-term cure.

Acquired resistance to the antitumor effect of epidermal growth factor receptor-blocking antibodies in vivo: a role for altered tumor angiogenesis

Inhibitors of epidermal growth factor receptor (EGFR) signaling are among the novel drugs showing great promise for cancer treatment in the clinic. However, the possibility of acquired resistance to such drugs because of tumor cell genetic instabilities has not yet been explored. Here we report the experimental derivation and properties of such cell variants obtained from recurrent tumor xenografts of the human A431 squamous cell carcinoma, after two consecutive cycles of therapy with one of three different anti-EGFR monoclonal antibodies: mR3, hR3, or C225. Initial response to a 2-week period of treatment was generally total tumor regression and was not significantly different among the three antibody groups. However, tumors often reappeared at the site of inoculation, generally after prolonged latency periods, and most of the tumors became refractory to a second round of therapy. Cell lines established from such resistant tumors retained high EGFR expression, normal sensitivity to anti-EGFR antibody or ligand, and unaltered growth rate when compared with the parental line in vitro. In contrast, the A431 cell variants exhibited an accelerated growth rate and a significantly attenuated response to anti-EGFR antibodies in vivo relative to the parental line. Because of the reported suppressive effect of EGFR inhibitors on vascular endothelial growth factor (VEGF) expression, and the demonstrated role of VEGF in the angiogenesis and growth of A431 tumor xenografts, relative VEGF expression was examined. Five of six resistant variants expressed increased levels of VEGF, which paralleled an increase in both angiogenic potential in vitro and tumor angiogenesis in vivo. In addition, elevated expression of VEGF in variants of A431 cells obtained by gene transfection rendered the cells significantly resistant to anti-EGFR antibodies in vivo. Taken together, the results suggest that, at least in the A431 system, variants displaying acquired resistance to anti-EGFR antibodies can emerge in vivo and can do so, at least in part, by mechanisms involving the selection of tumor cell subpopulations with increased angiogenic potential.

Preovulatory treatment of mice with anti-VEGF receptor 2 antibody inhibits angiogenesis in corpora lutea

Adult mammalian angiogenesis occurs predominantly in female reproductive organs: the ovary and the uterus. Angiogenesis is very active during corpus luteum formation. A key regulator of angiogenesis is vascular endothelial growth factor (VEGF), which is highly expressed during corpus luteum formation. Inhibition of VEGF activity can block the formation and function of the corpora lutea by preventing angiogenesis. The VEGF receptor 2 (VEGF-R2) mediates the angiogenic action of VEGF and is expressed during corpus luteum formation. We hypothesized that treatment with an antibody against VEGF-R2 would inhibit luteal angiogenesis by blocking VEGF/VEGF-R2 interaction. Immature mice were induced to superovulate with PMSG/hCG resulting in neovascularization in the corpora lutea, as evidenced by abundant staining for the endothelial-specific adhesion molecule PECAM. Multiple doses of a monoclonal antibody against the VEGF-R2 (DC101) were administered to immature mice. Treatment was initiated 2 days prior to the induction of superovulation with PMSG/hCG. This antibody inhibited luteal angiogenesis as evidenced by the lack of PECAM staining in the center of the corpora lutea. Multiple dose treatment with antibody initiated prior to gonadotropin administration could not dissociate the luteal inhibition from the consequences of inhibition of angiogenesis in the developing follicle. Administration of a single, preovulatory dose of anti-VEGF-R2 antibody, such that follicular angiogenesis would not be affected, also inhibited luteal development, demonstrating that luteal angiogenesis is required for corpus luteal development. We conclude that VEGF acting through VEGF-R2 has an obligatory role in luteal angiogenesis and corpus luteum formation.

Cloning, genetic characterization, and chromosomal mapping of the mouse VDUP1 gene

VDUP1 encodes a vitamin D3-inducible gene product that has been shown to be down-regulated in chemically-induced mammary tumors in rats. It has recently been reported to negatively regulate thioredoxin expression and function. We have cloned the mouse VDUP1 gene and characterized its genomic locus. The VDUP1 coding region spans eight exons within a total length of 2.3 kb located on mouse chromosome 3. Consensus sites for polyadenylation were identified 1.3 kb downstream of the gene, defining a long 3' untranslated region. The minimal functional VDUP1 promoter contains TATA and CCAAT boxes and transcription is initiated from two major start sites downstream. A direct repeat element located proximal to the TATA with homology to the USF binding site was identified as a potential regulator of VDUP1gene expression. Expression analysis determined that VDUP1 mRNA was markedly induced in myeloma cells in high density cell culture, but not in sub-confluent cells arrested by serum deprivation. All samples of a panel of mouse immortalized or transformed cell lines were shown to express abundant levels of VDUP1 mRNA.

Monoclonal antibody strategies to block angiogenesis

Antibodies represent a unique class of therapeutics because of their high specificity towards a defined target antigen. Recent clinical success with antibody-based cancer therapeutics has led to an increase in the clinical development of these agents. Antibody therapeutics offer a promising approach for inhibiting new blood vessel formation (angiogenesis), which is associated with a variety of diseases, including cancer. In this review we will focus on angiogenesis-related mechanisms targeted by antibody-based therapeutics, with an emphasis on those studies where pre-clinical in vivo data is available.

Monoclonal antibodies directed to different regions of vascular endothelial cadherin extracellular domain affect adhesion and clustering of the protein and modulate endothelial permeability

Vascular endothelial cadherin (VE-cadherin) is an endothelial cell-specific cadherin that plays an important role in the control of vascular organization. Blocking VE-cadherin antibodies strongly inhibit angiogenesis, and inactivation of VE-cadherin gene causes embryonic lethality due to a lack of correct organization and remodeling of the vasculature. Hence, inhibitors of VE-cadherin adhesive properties may constitute a tool to prevent tumor neovascularization. In this paper, we tested different monoclonal antibodies (mAbs) directed to human VE-cadherin ectodomain for their functional activity. Three mAbs (Cad 5, BV6, BV9) were able to increase paracellular permeability, inhibit VE-cadherin reorganization, and block angiogenesis in vitro. These mAbs could also induce endothelial cell apoptosis in vitro. Two additional mAbs, TEA 1.31 and Hec 1.2, had an intermediate or undetectable activity, respectively, in these assays. Epitope mapping studies show that BV6, BV9, TEA 1.31, and Hec 1.2 bound to a recombinant fragment spanning the extracellular juxtamembrane domains EC3 through EC4. In contrast, Cad 5 bound to the aminoterminal domain EC1. By peptide scanning analysis and competition experiments, we defined the sequences TIDLRY located on EC3 and KVFRVDAETGDVFAI on EC1 as the binding domain of BV6 and Cad 5, respectively. Overall, these results support the concept that VE-cadherin plays a relevant role on human endothelial cell properties. Antibodies directed to the extracellular domains EC1 but also EC3-EC4 affect VE-cadherin adhesion and clustering and alter endothelial cell permeability, apoptosis, and vascular structure formation.

Vascular endothelial growth factor receptor-2-blocking antibody potentiates radiation-induced long-term control of human tumor xenografts

Antiangiogenic therapy can enhance radiation-induced tumor growth inhibition. However, the effects of combined antiangiogenic and radiation therapy on long-term tumor control and normal tissue response have not been reported. We treated mice bearing two different human tumor xenografts with anti-vascular endothelial growth factor receptor-2 antibody (DC101) and five dose fractions of local radiation and followed them for at least 6 months. DC101 significantly decreased the dose of radiation necessary to control 50% of tumors locally. The decrease was 1.7- and 1.3-fold for the moderately radiosensitive small cell lung carcinoma 54A and the highly radioresistant glioblastoma multiforme U87, respectively. In contrast to tumors, no increase in skin radiation reaction by the antibody was detected. Surprisingly, 44% of mice bearing 54A tumor developed clear ascites after DC101 treatment at its highest dose; this was fatal to 20% of mice. This adverse effect was seen only in mice that received whole-body irradiation 1 day before tumor implantation. The encouraging results on two human tumor xenografts suggest that vascular endothelial growth factor receptor-2 blockade merits further investigation to assess its potential as an enhancer of radiation therapy in the clinic.

Monoclonal antibody to vascular endothelial-cadherin is a potent inhibitor of angiogenesis, tumor growth, and metastasis

Vascular endothelial-cadherin (VE-cad) is an endothelial cell-specific adhesion molecule that is crucial for proper assembly of vascular tubes. Here we show that a monoclonal antibody (BV13) directed to the extracellular region of VE-cad inhibits formation of adherens junctions and capillary-like structures by endothelial cells and blocks angiogenesis in the mouse cornea and in Matrigel plugs in vivo. Systemic administration of BV13 markedly decreases the growth of s.c. Lewis lung or human A431 epidermoid tumors and strongly suppresses the growth of Lewis lung metastases. These data demonstrate that VE-cad is essential for postnatal angiogenesis and thus validate VE-cad as a novel target for antiangiogenesis agents.

cDNA cloning, chromosomal mapping, and expression analysis of human VE-Cadherin-2

Murine vascular endothelial cadherin-2 (VE-cad-2) is a cellular adhesion molecule that is distinct from vascular endothelial cadherin 1 (VE-cad-1) in that it does not interact with catenins and does not appear to affect cell migration or growth. In this study, we have cloned a full-length cDNA of the human homolog of VE-cad-2 and used it to map the chromosomal locus of the VE-cad-2 gene. Human VE-cad-2 maps to Chromosome (Chr) 5q31. The cDNA of human VE-cad-2 is highly homologous to mouse VE-cad-2, except for a C-terminal tail. The genomic structure of VE-cad-2 is strikingly similar to that reported for a large family of neuronal protocadherin genes mapped to Chr 5q, yet the amino acid sequences between VE-cad-2 and the protocadherins are substantially divergent. The promoter of human VE-cad-2 contains two TATA boxes and transcription initiates from a single site 3' to these elements. Similar to mouse VE-cad-2, the human gene is expressed primarily in highly vascularized tissues.

Identification of the residues in the extracellular region of KDR important for interaction with vascular endothelial growth factor and neutralizing anti-KDR antibodies

The kinase domain receptor (KDR) of vascular endothelial growth factor (VEGF) is the main human receptor responsible for the angiogenic activity of VEGF. The extracellular region of KDR is comprised of seven immunoglobulin-like domains, of which the first three have been shown to be required for ligand binding. We have previously described antibodies directed against the extracellular region of KDR, including MAB383 and MAB664, which were shown to block the binding of VEGF to the receptor and to inhibit both VEGF-induced mitogenesis of human endothelial cells in vitro and tumor growth in vivo. Here we generated a series of KDR deletion mutants consisting of truncated extracellular regions and mapped out the domain(s) responsible for binding to VEGF and the neutralizing anti-KDR antibodies. All neutralizing antibodies were found to require domain 3 for efficient binding. Alanine-scanning mutagenesis of domain 3 identified two different sets of five residues, Ile(256), Asp(257), Glu(261), Leu(313), and Thr(315) and Tyr(262), Pro(263), Ser(264), Ser(265), and Lys(266), that were critical for binding to MAB383 and MAB664, respectively. Combination of alanine mutations affecting both MAB383 and MAB664 binding resulted in a variant that also lost binding to VEGF. These results suggest that the residues within this region of domain 3 are critical for VEGF binding. Our studies provide a basis for the mechanism of action of our anti-KDR antibodies and establish a functional foundation for the development of other classes of antagonists to the receptor.

Continuous low-dose therapy with vinblastine and VEGF receptor-2 antibody induces sustained tumor regression without overt toxicity

Various conventional chemotherapeutic drugs can block angiogenesis or even kill activated, dividing endothelial cells. Such effects may contribute to the antitumor efficacy of chemotherapy in vivo and may delay or prevent the acquisition of drug-resistance by cancer cells. We have implemented a treatment regimen that augments the potential antivascular effects of chemotherapy, that is devoid of obvious toxic side effects, and that obstructs the development of drug resistance by tumor cells. Xenografts of 2 independent neuroblastoma cell lines were subjected to either continuous treatment with low doses of vinblastine, a monoclonal neutralizing antibody (DC101) targeting the flk-1/KDR (type 2) receptor for VEGF, or both agents together. The rationale for this combination was that any antivascular effects of the low-dose chemotherapy would be selectively enhanced in cells of newly formed vessels when survival signals mediated by VEGF are blocked. Both DC101 and low-dose vinblastine treatment individually resulted in significant but transient xenograft regression, diminished tumor vascularity, and direct inhibition of angiogenesis. Remarkably, the combination therapy resulted in full and sustained regressions of large established tumors, without an ensuing increase in host toxicity or any signs of acquired drug resistance during the course of treatment, which lasted for >6 months. This article may have been published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.

Acquired antagonistic activity of a bispecific diabody directed against two different epitopes on vascular endothelial growth factor receptor 2

Bispecific antibody (BsAb) technology has been successfully used as a means to construct novel antibody (Ab) molecules with increased avidity for binding, by combining two Ab or their fragments directed against different epitopes within the same antigen. Using two single chain antibodies (scFv) isolated from a phage display library, we have constructed a bispecific diabody directed against two different epitopes on the extracellular domain (ECD) of human vascular endothelial growth factor receptor 2 (VEGFR2), the kinase-insert domain-containing receptor (KDR). Neither of the parent scFv blocks KDR/VEGF interactions or inhibits VEGF-induced receptor activation. The diabody binds to KDR with an affinity that is 1.5- to 3-fold higher than its parent scFv, mainly due to a much slower dissociation rate (k(off)), which is approximately 17- to 26-fold slower than that of the individual scFv. In addition, the diabody binds simultaneously to, and thus cross-links, the two epitopes on the receptor(s). It is rather unexpected that the diabody effectively blocked KDR/VEGF interactions, and inhibited both VEGF-induced activation of the receptor and mitogenesis of human endothelial cells. Taken together, our results suggest that the diabody is most likely to exert its effect through steric hindrance and/or causing major conformational changes of the receptor. This is the first report on the construction of a bispecific diabody with acquired novel antagonistic activity.

Antivascular endothelial growth factor receptor (fetal liver kinase 1) monoclonal antibody inhibits tumor angiogenesis and growth of several mouse and human tumors

Tumor angiogenesis is mediated by tumor-secreted angiogenic growth factors that interact with their surface receptors expressed on endothelial cells. Vascular endothelial growth factor (VEGF) and its receptor [fetal liver kinase 1 (Flk-1)/kinase insert domain-containing receptor] play an important role in vascular permeability and tumor angiogenesis. Previously, we reported on the development of anti-Flk-1 and antikinase insert domain-containing receptor monoclonal antibodies (mAbs) that potently inhibit VEGF binding and receptor signaling. Here, we report the effect of anti-Flk-1 mAb (DC101) on angiogenesis and tumor growth. Angiogenesis in vivo was examined using a growth factor supplemented (basic fibroblast growth factor + VEGF) Matrigel plug and an alginate-encapsulated tumor cell (Lewis lung) assay in C57BL/6 mice. Systemic administration of DC101 every 3 days markedly reduced neovascularization of Matrigel plugs and tumor-containing alginate beads in a dose-dependent fashion. Histological analysis of Matrigel plugs showed reduced numbers of endothelial cells and vessel structures. Several mouse tumors and human tumor xenografts in athymic mice were used to examine the effect of anti-Flk-1 mAb treatment on tumor angiogenesis and growth. Anti-Flk-1 mAb treatment significantly suppressed the growth of primary murine Lewis lung, 4T1 mammary, and B16 melanoma tumors and growth of Lewis lung metastases. DC101 also completely inhibited the growth of established epidermoid, glioblastoma, pancreatic, and renal human tumor xenografts. Histological examination of anti-Flk-1 mAb-treated tumors showed evidence of decreased microvessel density, tumor cell apoptosis, decreased tumor cell proliferation, and extensive tumor necrosis. These findings support the conclusion that anti-Flk-1 mAb treatment inhibits tumor growth by suppression of tumor-induced neovascularization and demonstrate the potential for therapeutic application of anti-VEGF receptor antibody in the treatment of angiogenesis-dependent tumors.

Cloning and functional expression of a human heparanase gene

We have cloned a gene (HSE1) from a human placental cDNA library that encodes a novel protein exhibiting heparanase activity. The cDNA was identified through peptide sequences derived from purified heparanase isolated from human SK-HEP-1 hepatoma cells. HSE1 contains an open reading frame encoding a predicted polypeptide of 543 amino acids and possesses a putative signal sequence at its amino terminus. Northern blot analysis suggested strong expression of HSE1 in placenta and spleen. Transient transfection of HSE1 in COS7 cells resulted in the expression of a protein with an apparent molecular mass of 67-72 kDa. HSE1 protein was detectable in conditioned media but was also associated with the membrane fraction following cell lysis. The HSE1 gene product was shown to exhibit heparanase activity by specifically cleaving a labeled heparan sulfate substrate in a similar manner as purified native protein.

Inhibition of vascular endothelial growth factor induced mitogenesis of human endothelial cells by a chimeric anti-kinase insert domain-containing receptor antibody

The kinase insert domain-containing receptor (KDR) is the human vascular endothelial growth factor (VEGF) receptor responsible for the mitogenic and angiogenic effects of VEGF. There is much experimental evidence to suggest that the VEGF/KDR pathway plays an important role in tumor angiogenesis, a process essential for tumor growth and metastasis. Here we produced a chimeric anti-KDR antibody (IgG1), c-p1C11, from a single chain (scFv) antibody isolated from a phage display library. C-p1C11 binds specifically to the extracellular domain of soluble as well as cell-surface expressed KDR. It effectively blocks VEGF-KDR interaction and inhibits VEGF-stimulated activation of KDR and MAP kinases p44/p42 of human endothelial cells. Furthermore, c-p1C11 efficiently neutralizes VEGF-induced mitogenesis of human endothelial cells. Our results suggest that antibodies against KDR have potential clinical applications in the treatment of cancer and other diseases where pathological angiogenesis is involved.

Inhibition of vascular endothelial growth factor-induced receptor activation with anti-kinase insert domain-containing receptor single-chain antibodies from a phage display library

A single-chain antibody phage display library was constructed from spleen cells of mice immunized with a soluble form of a human vascular endothelial growth factor (VEGF) receptor, kinase insert domain-containing receptor (KDR). After two rounds of biopanning, >90% of the clones recovered were specifically reactive to KDR. Subsequent selection identified two clones that blocked VEGF binding to KDR. The clones were expressed in Escherichia coli and purified as soluble single-chain Fv (scFv) antibodies. The affinities of the scFv for binding to KDR were determined by BIAcore analysis (2.1 x 10(-9)-5.9 x 10(-9) M). One scFv, p1C11, was shown to inhibit VEGF-induced KDR phosphorylation and VEGF-stimulated DNA synthesis in human umbilical vein endothelial cells. There is much experimental evidence to suggest that the VEGF/KDR/Flk-1 pathway plays an important role in tumor angiogenesis, a process that is essential for tumor growth and metastasis. The antibodies discussed here, which block VEGF binding to KDR, have potential clinical application in the treatment of cancer and other diseases where pathological angiogenesis is involved.

Transglutaminase forms midkine homodimers in cerebellar neurons and modulates the neurite-outgrowth response

Midkine is a prominent acyl donor substrate for the protein cross-linking enzyme transglutaminase type 2 in rat brain neurons. Transglutaminase type 2 and midkine immunoreactivity are regionally colocalized in developing cerebellar cortex. Monomeric midkine is present in the embryonic dorsal rhombic lip which gives rise to the cerebellar cortex. A high-molecular weight (29-30 kDa) midkine appears during postnatal cerebellar development. The presence of the high-molecular weight midkine in cultured cerebellar cortical interneurons is dependent upon culture conditions. Transglutaminase catalyzes the calcium-dependent cross-linking of midkine predominantly into 29-30 kDa dimers. Dimer-formation of midkine in vitro and in cultured neurons is reduced in the presence of a transglutaminase inactivator. Neurons plated onto previously cross-linked midkine exhibit larger growth cones and enhanced neurite outgrowth compared to those plated onto monomeric midkine alone.

Isolation and amino-terminal sequence of a novel cellular growth inhibitor (inhibitory diffusible factor 45) secreted by 3T3 fibroblasts

A growth inhibitory protein named inhibitory diffusible factor 45 (IDF45) has been purified to homogeneity from medium conditioned by dense cultures of mouse 3T3 cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of fast protein liquid chromatography-purified bioactive material showed a single band corresponding to a protein of 45 kDa. The molecule is a monomer. The pI of the molecule, as determined by isoelectric focusing, is about 6.5. The amino-terminal sequence of the protein was established as Ser-Ala-Gly-Ala-Val-Gly-Ala-Gly-Pro-Val-Val-Arg. The protein inhibits DNA synthesis in chicken embryo fibroblasts in a dose-dependent manner (ED50: 40 ng/ml, approximately 1 nM). The chemical properties of IDF45, i.e. molecular weight and amino-terminal sequence, clearly distinguish it from other known growth inhibitory proteins.

An improved method for the purification of human insulin-like growth factors I and II

Insulin-like growth factors (IGFs) I and II have been purified from Cohn fraction IV-1 of human plasma. After acid-ethanol extraction, the consecutive use of conventional gel filtration and reverse phase liquid chromatography has permitted the rapid isolation of these polypeptides. Purification was monitored by the use of specific RIAs. In both chromatography systems, separation was optimized by performing it on the same stationary phase but successively with mobile phases of different pH or different solute selectivity. The two polypeptides were shown to be pure by their unique amino acid composition, particularly by the absence of specific amino acids (histidine, tryptophan, and methionine), and their unique amino-terminal sequences. In addition, the lack of cross-contamination of the two growth factors with each other was established by the unique isoelectric focusing patterns of IGF-I at pI 8.25 and IGF-II at pI 6.5. From 900 g Cohn fraction IV-1, which is equivalent to 66 liters human plasma, approximately 100 micrograms of each IGF can be obtained by our procedure, which can easily be carried out in a clinical research laboratory.

Evidence for FGF-like growth factor in adult bovine retina: analogies with EDGF I

Eye Derived Growth Factor (EDGF) is the genus name for growth factor activities found in several ocular tissues. Purification from bovine retina by Cibacron blue affinity chromatography has previously given a fraction which can induce target cell proliferation at doses of 30 ng per ml of culture medium. Radioimmunoassay using a labelled synthetic decapeptide [Tyr 10]--FGF (1-10) including the 9 N terminal amino acids of brain Fibroblast Growth Factor (FGF) indicated that EDGF contained a FGF-like material. Further purification of Cibacron blue purified EDGF with heparin sepharose chromatography yielded two active fractions after elution with a sodium chloride gradient. One fraction named EDGF I eluted between 1.3 and 1.5 M NaCl and accounted for over 50% of the input biological activity and comigrated with purified FGF on SDS PAGE at a molecular weight of 16,000 d as a single band. FGF competed with EDGF I for binding to specific receptors on bovine epithelial lens cells. We conclude that retina contains a growth factor activity (EDGF I) similar if not identical to FGF.

Isolation of fibroblast growth factor from bovine adrenal gland: physicochemical and biological characterization

The angiogenic growth factors present in the bovine adrenal gland have been purified by a combination of differential salt precipitation, ion exchange chromatography, and heparin-Sepharose chromatography. They consist of 2 single chain polypeptides with apparent mol wt of 16,000 and 15,000. Sequence analysis of the first 14 residues of both peptides identified the sequences as Pro-Ala-Leu-Pro-Glu-Asp-Gly-Gly-Ser-Gly-Ala-Phe-Pro-Pro for 1 of the peptides and His-Phe-Lys-Asp-Pro-Lys-Arg-Leu-Tyr-x-Lys-Asn-Gly-Gly for the other. The first sequence is identical to residues 1-14 of bovine pituitary and brain fibroblast growth factor (FGF), while the second is identical to residues 1-14 of the corpus luteum (CL) FGF, which is an amino-terminally truncated form of FGF and is otherwise similar, if not identical, to FGF. The biological activity of adrenal FGF is indistinguishable from that of pituitary or brain FGF and CL FGF. They are highly active in triggering the proliferation of culture bovine vascular endothelial cells derived from either large vessels (aortic arch) or CL and adrenal cortex capillaries (half-maximal stimulation at 20-40 pg/ml and saturation at 400-600 pg/ml). In vivo implants containing 50 ng to 1 microgram adrenal-derived growth factors stimulate neovascularization in the chorioallantoic membrane of the chick embryo. In addition to being mitogenic for vascular endothelial cells, adrenal FGFs stimulate the proliferation of a wide variety of mesoderm- and neuroectoderm-derived cells, including vascular smooth muscle cells, granulosa and adrenal cortex cells, rabbit costal chondrocytes, and corneal endothelial cells.

In situ hybridization histochemistry for the analysis of gene expression in the endocrine and central nervous system tissues: a 3-year experience

We report our experience in development of the in situ hybridization (ISH) procedure to detect messenger RNAs (mRNAs) coding for various molecules involved in endocrine glands and central nervous system activity, including mRNAs coding for endorphin precursors [preproenkephalin A (PPA), pro-opiocortin (POMC)], vasopressin, and transferrin. Various conditions of fixation and handling of the tissues were tested to establish optimal parameters for mRNA detection. Double-stranded DNA probes labeled by nick translation, synthetic oligonucleotides labeled at their 5' end, as well as single-stranded RNA probes were used, after incorporation of 32P- or 35S-labeled nucleotides. Specific requirements for efficient and reproducible ISH investigations are discussed. Cells expressing the PPA gene in the adrenal medulla and in the brain were detected by ISH. The results show that ISH is as sensitive as immunohistochemistry in detecting peptide-producing cells in the adrenal and that it allows detection of PPA cell bodies in brain in conditions in which they are inconstantly detected by immunohistochemistry. Unilateral destruction of substantia nigra provokes a dramatic decrease in the number of neurons expressing the PPA gene in the contralateral striatum. Cells expressing the POMC gene were detected in the pituitary of various species including man and in the rat arcuate nucleus. Neurons containing vasopressin mRNA were visualized in the supraoptic paraventricular and suprachiasmatic nucleus of the adult rat by using a synthetic oligonucleotide probe. Transferrin gene expression was shown in the central nervous system of the rat brain in two cell populations, the oligodendrocytes and the epithelial cells of the choroid plexus, by demonstration of simultaneous presence in them of transferrin immunoreactivity together with transferrin mRNA. These results show that the ISH procedure is a technique that can be routinely used to investigate gene transcription anatomically in complex heterocellular tissues such as the endocrine glands and the nervous system.

Corpus luteum angiogenic factor is related to fibroblast growth factor

An angiogenic growth factor present in bovine corpus luteum (CL) has been purified to apparent homogeneity by a combination of differential salt precipitation, ion exchange chromatography, and heparin-Sepharose chromatography. It is a single chain polypeptide with an apparent mol wt of 15,000 and an amino acid composition similar to that previously reported for pituitary and brain fibroblast growth factor (FGF). Sequence analysis of the first 17 residues of the CL-derived growth factor identified the sequence; His-Phe-Lys-Asp-Pro-Lys-Arg-Leu-Tyr-X-Lys-Asn-Gly-Gly-X-Phe-Leu. This sequence is identical to residues 16-33 of bovine pituitary and brain FGF, indicating that the CL-derived growth factor is an amino-terminally truncated form of FGF and is otherwise similar, if not identical, to FGF. The biological activity of CL FGF is indistinguishable from that of pituitary or brain FGF. It is highly active in triggering the proliferation of cultured bovine vascular endothelial cells derived either from large vessels (aortic arch) or from corpus luteum and adrenal cortex capillaries (half-maximal stimulation at 20-40 pg/ml and saturation at 400-600 pg/ml). In vivo implants containing 50 ng to 1 microgram CL-derived growth factor stimulate neovascularization in the chorioallantoic membrane of the chick embryo. In addition to being mitogenic for vascular endothelial cells, CL FGF also stimulates the proliferation of a wide variety of mesoderm- and neuroectoderm-derived cells, including vascular smooth muscle cells, granulosa and adrenal cortex cells, rabbit costal chondrocytes, and corneal endothelial cells.

Somatostatin-28 [1-12]-like peptides

The search for a peptide corresponding to the NH2-terminus of somatostatin-28 (SS-28) in tissues has led to the isolation and characterization of somatostatin-28[1-12] from pancreas and hypothalamus. Somatostatin-28[1-12]-like immunoreactivity [SS-28 [1-12]-LI] is widely distributed throughout the central nervous system and the digestive system of rodents and primates, reaching levels comparable to those of somatostatin-14 (SS-14). Antibodies directed against the C-terminal end of the dodecapeptide are more specific and constitute excellent markers for the "prosomatostatin" system in mammalian tissues. In rat brain, SS-28[1-12]-LI material is highly concentrated in nerve fibres and terminals, especially in the median eminence, layer I of neocortex, the outer molecular layer of the dentate gyrus and the striatum. Additionally, immunoreactivity is observed in large multipolar or occasionally pyramidal-like neurons of the neocortex. SS-28[1-12] is secreted from hypothalamus and amygdala by a calcium dependent mechanism. No biological role is presently known for the dodecapeptide. Two other peptides of Mr = 8000 (8 K) and Mr = 5000 (5 K) which contain SS-28[1-12] at their carboxy-termini are present in acid extracts from rat pancreas, brain and spinal cord. These two peptides were isolated from an acid extract of rat brains using ion-exchange chromatography, gel permeation chromatography and reverse-phase HPLC. Results from amino acid analysis and partial sequencing were compared to the sequence of the cDNA encoding rat pre-prosomatostatin (prepro-SS) and revealed that the 8 K peptide is a 76 amino acid molecule corresponding to prepro-SS[25-100] and that the 5K peptide, which contains 44 amino acids, corresponds to prepro-SS [57-100]. The 5 K peptide was generated after cleavage of a Leu-Leu bond at position 56-57 of prepro-SS. The four most predominant peptides of the "prosomatostatin system" presently characterized are: SS-14, SS-28[1-12], SS-28 and prepro-SS[25-100]. Studies on pooled perfusates from rat hypothalamic tissue show that prepro-SS[25-100] is released with SS-28[1-12] in vitro and accounts for 22% of the total SS-28[1-12]-like immunoreactive material released during depolarization. The 5 K peptide is apparently not secreted. The presence of prepro-SS[25-100] in brain implies that, first, prosomatostatin can serve as an immediate precursor for SS-14 without going through SS-28 as an intermediate step and second, other peptides could conceivably be derived from the cryptic portion of the precursor.

Isolation and characterization of the bovine hypothalamic corticotropin-releasing factor

A 41 amino acid peptide with high intrinsic corticotropin-releasing activity was isolated from 1000 bovine hypothalami by means of immunoaffinity chromatography, gel filtration, and two steps of reverse phase HPLC. The primary structure of the amino terminal 39 amino acids was characterized by gas phase sequence analysis. The sequence of the amidated carboxyl terminal dipeptide was established by digestion of the intact natural product with Staphylococcus aureus V8 protease, dansylation of the digest and comparative reverse phase liquid chromatography studies with the synthetic dansylated dipeptides Ile-Ala-NH2, Ile-Ala-OH, Ala-Ile-NH2 and Ala-Ile-OH. The complete structure of the bovine corticotropin-releasing factor was established as: Ser-Gln-Glu-Pro-Pro-Ile-Ser-Leu-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Glu-Val- Leu- Glu-Met-Thr-Lys-Ala-Asp-Gln-Leu-Ala-Gln-Gln-Ala-His-Asn-Asn-Arg-Lys-Leu- Leu- Asp-Ile-Ala-NH2 using approximately 650 pmol of material.

Detection of the messenger RNA coding for preproenkephalin A in bovine adrenal by in situ hybridization

The messenger RNA (mRNA) coding for the adrenal precursor of enkephalins (preproenkephalin-A) has been detected in bovine adrenal medulla cells using in situ hybridization with 32P-labelled preproenkephalin A (PPA) complementary DNA. In formaldehyde- and Carnoy-fixed tissue sections, an intense elective labelling restricted to the cells located at the periphery of the adrenal medulla can be detected after hybridization procedure, using X-ray film and classical autoradiographic procedure. Adequate controls show that this labelling is obtained only using PPA complementary DNA, inserted or not in its vector. Distribution of PPA mRNA appears identical to that of its immunoreactive end products, namely Met-enkephalin and BAM22 peptide, detected by immunohistochemistry. Norepinephrine, detectable using monoamine histofluorescence, appears restricted to the cells of the center of the gland unlabelled for PPA mRNA and its end-products. Cultured bovine adrenomedullary cells that exhibited enkephalin immunoreactivity also contain PPA mRNA located in their cytoplasm.

Immunohistochemical detection of growth hormone-releasing factor in brain

The concept of a hypothalamic neurohumoral control for anterior pituitary secretion postulates the existence of a growth hormone-releasing factor (GRF) of neuronal origin that stimulates the pituitary gland to release growth hormone (GH). Such a compound has not yet been isolated and characterized from the brain, although there is extensive physiological and biochemical evidence for its existence (reviewed in ref. 2). However, a 44-amino-acid amidated peptide having the physiological properties of GRF as well as chemical similarities was recently isolated from a human pancreatic tumour that had caused acromegaly. Two shorter biologically active fragments of 40 and 37 residues were also isolated. The synthetic replicates of these human pancreas GRF (hpGRF) peptides specifically stimulate GH release in vitro and in vivo. Assuming similarity or identity between the putative hypothalamic GRF and the tumour-derived hpGRF, we have used immunohistochemistry to search for hpGRF-like immunoreactivity in the brain. We report here that antisera against the hpGRF1-40 peptide specifically stain neuronal cell bodies in the arcuate nucleus of the primate hypothalamus, with fibres projecting to the median eminence and ending in contact with portal vessels. This topography is characteristic of a neuronal system elaborating a releasing factor. These results provide evidence that hypothalamic GRF is very similar, if not identical, to hpGRF.

Isolation and characterization of a full-length expressible cDNA for human hypoxanthine phosphoribosyl transferase

We have cloned a full-length 1.6-kilobase cDNA of a human mRNA coding for hypoxanthine phosphoribosyltransferase (HPRT; IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) into a simian virus 40-based expression vector and have determined its full nucleotide sequence. The inferred amino acid sequence agrees with a partial amino acid sequence determined for authentic human HPRT protein. Transfection of HPRT-deficient mouse LA9 cells with the purified plasmid leads to the expression of human HPRT enzyme activity in cells stably transfected and selected for enzyme activity in hypoxanthine/aminopterin/thymidine medium.

Selective effects of somatostatin-14, -25 and -28 on in vitro insulin and glucagon secretion

The widely occurring tetradecapeptide somatostatin (SRIF-14) has been variously implicated as a neurotransmitter, a neurohormone, a cybernin (local regulatory factor) and a hormone. In the first isolation of SRIF-14 from hypothalamic extracts and subsequent extracts of other tissues, peptides of higher molecular weight but with similar activity have been noted. Recently two such peptides have been characterized as the 28-amino acid SRIF-28 (from porcine gastro-intestinal tract and porcine and ovine hypothalamus and the 25-amino acid SRIF-25 (from ovine hypothalamus), each of which consists of an N-terminal extension of SRIF-14. We now report that SRIF-28 and SRIF-25 are more potent than SRIF-14 in the inhibition of insulin release, but that SRIF-14 preferentially inhibits glucagon release. This suggests that SRIF-28 and SRIF-25 are not mere biosynthetic precursors of SRIF-14 and that their differential release may be physiologically important.

Isolation and characterization of rat hypothalamic somatostatin-14

A peptide with somatostatin-like immuno- and bioactivity has been isolated from 1165 rat hypothalami by using antisomatostatin affinity chromatography, gel filtration and reverse-phase high-performance liquid chromatography. The isolated peptide is indistinguishable from synthetic somatostatin-14 with respect to chromatographic properties and amino acid composition. We therefore propose that rat hypothalamic somatostatin-14 is identical in structure to somatostatin-14 found in other species.

[High biological activity of the synthetic counterparts of hypothalamic somatostatin-28 and somatostatin-25]

We have isolated from extracts of ovine hypothalamus two molecules characterized as somatostatin-28 and somatostatin-4-28 (referred to as somatostatin-25). They were reproduced by synthesis. In equimolar ratios and depending upon the experimental conditions, synthetic somatostatin-28 and somatostatin-25 are 3 to 14 times more potent than somatostatin-14 to inhibit the basal in vitro secretion of growth hormone. These results suggest that somatostatin-14 as originally isolated, is a biologically active fragment of a larger molecule of greater specific activity, rather than somatostatin-28 being a precursor of the tetradecapeptide.

Skin polyamine levels in psoriasis: the effect of dithranol therapy

Concentrations of putrescine, spermidine and spermine were determined in biopsies of skin of eight control subjects and of uninvolved skin and skin lesions of eight psoriatic patients before and after topical therapy with dithranol. Mean spermidine and spermine concentrations in uninvolved skin of psoriatic patients were normal, but putrescine concentration was elevated. In psoriatic skin lesions all three amines were significantly elevated. Chemotherapy effectively reduced polyamine concentrations in involved skin touards normal. This decrease in polyamine levels correlated with reduction of the proliferative activity of the epidermis and with clinical improvement of the patients.