An in vitro cord formation assay identifies unique vascular phenotypes associated with angiogenic growth factors.

Vascular endothelial growth factor (VEGF) plays a dominant role in angiogenesis. While inhibitors of the VEGF pathway are approved for the treatment of a number of tumor types, the effectiveness is limited and evasive resistance is common. One mechanism of evasive resistance to inhibition of the VEGF pathway is upregulation of other pro-angiogenic factors such as fibroblast growth factor (FGF) and epidermal growth factor (EGF). Numerous in vitro assays examine angiogenesis, but many of these assays are performed in media or matrix with multiple growth factors or are driven by VEGF. In order to study angiogenesis driven by other growth factors, we developed a basal medium to use on a co-culture cord formation system of adipose derived stem cells (ADSCs) and endothelial colony forming cells (ECFCs). We found that cord formation driven by different angiogenic factors led to unique phenotypes that could be differentiated and combination studies indicate dominant phenotypes elicited by some growth factors. VEGF-driven cords were highly covered by smooth muscle actin, and bFGF-driven cords had thicker nodes, while EGF-driven cords were highly branched. Multiparametric analysis indicated that when combined EGF has a dominant phenotype. In addition, because this assay system is run in minimal medium, potential proangiogenic molecules can be screened. Using this assay we identified an inhibitor that promoted cord formation, which was translated into in vivo tumor models. Together this study illustrates the unique roles of multiple anti-angiogenic agents, which may lead to improvements in therapeutic angiogenesis efforts and better rational for anti-angiogenic therapy.

Development and characterization of a high-throughput in vitro cord formation model insensitive to VEGF inhibition.

BACKGROUND: Anti-VEGF therapy reduces tumor blood vessels, however, some vessels always remain. These VEGF insensitive vessels may help support continued tumor growth and metastases. Many in vitro assays examining multiple steps of the angiogenic process have been described, but the majority of these assays are sensitive to VEGF inhibition. There has been little focus on the development of high-throughput, in vitro assays to model the vessels that are insensitive to VEGF inhibition. METHODS: Here, we describe a fixed end-point and kinetic, high-throughput stem cell co-culture model of cord formation. RESULTS: In this system, cords develop within 24 hours, at which point they begin to lose sensitivity to VEGF inhibitors, bevacizumab, and ramucirumab. Consistent with the hypothesis that other angiogenic factors maintain VEGF-independent vessels, pharmacologic intervention with a broad spectrum anti-angiogenic antagonist (suramin), a vascular disrupting agent (combretastatin), or a combination of VEGF and Notch pathway inhibitors reduced the established networks. In addition, we used our in vitro approach to develop an in vivo co-implant vasculogenesis model that connects with the endogenous vasculature to form functional blood vessels. Similar to the in vitro system, over time these vessels become insensitive to VEGF inhibition. CONCLUSION: Together, these models may be used to identify novel drugs targeting tumor vessels that are not sensitive to VEGF inhibition.

Derivation and characterization of monoclonal antibodies against human folypolyglutamate synthetase.

Folypolyglutamate synthetase (FPGS) plays a critical role in the cellular retention of both folates and antifolates. Resistance to antifolates is in part related to changes in FPGS enzyme activity and levels of messenger RNA, or in some instances, protein as evaluated by Western blots using polyclonal antisera. The present study was designed to derive a series of monoclonal antibodies (MAb) against the native protein, to characterize them in terms of specificity and epitope mapping, and to determine kinetic constants by Biacore. We report on 3 IgG(1) kappa MAbs-namely, 4-2, 4-3, and 4-18-with epitopes localized to the carboxyl domain of the protein. These antibodies recognize a single band on Western blots of HeLa cell lysates, which is significantly reduced following RNAi knockdown. The recognition of both the native and denatured conformations of FPGS by these MAbs should provide useful reagents for FPGS quantitation in either tumor cell lysates or in tumor biopsies.

Identification of heme as the ligand for the orphan nuclear receptors REV-ERBalpha and REV-ERBbeta.

The nuclear receptors REV-ERBalpha (encoded by NR1D1) and REV-ERBbeta (NR1D2) have remained orphans owing to the lack of identified physiological ligands. Here we show that heme is a physiological ligand of both receptors. Heme associates with the ligand-binding domains of the REV-ERB receptors with a 1:1 stoichiometry and enhances the thermal stability of the proteins. Results from experiments of heme depletion in mammalian cells indicate that heme binding to REV-ERB causes the recruitment of the co-repressor NCoR, leading to repression of target genes including BMAL1 (official symbol ARNTL), an essential component of the circadian oscillator. Heme extends the known types of ligands used by the human nuclear receptor family beyond the endocrine hormones and dietary lipids described so far. Our results further indicate that heme regulation of REV-ERBs may link the control of metabolism and the mammalian clock.

Derivation and characterization of a monoclonal antibody against human glycinamide ribonucleotide formyltransferase.

Glycinamide ribonucleotide formyltransferase (GARFT) is a trifunctional enzyme involved in purine biosynthesis. Its central role in folate metabolism has made it an obvious target for the development of GARFT inhibitors, primarily for oncology. While the crystal structure, enzyme kinetics, and mechanism of action of GARFT inhibitors are reasonably well understood, GARFT regulation at the protein level remains unclear. The present study reports the development and characterization of a monoclonal antibody (MAb) specific for human GARFT. This MAb, an IgG1kappa, designated PHR1, recognizes human GARFT by both Western blot and by immunohistochemistry from non-small-cell lung carcinoma and colon adenocarcinoma tissue biopsies, has a KD of 1.14 x 10(10) M, and has been epitope mapped at residues 59-78 of the GARFT functional domain. The ability of PHR1 to recognize both sodium dodecyl sulfate (SDS)-denatured as well as native GARFT should make this MAb an important research tool in determining GARFT protein levels in both normal and neoplastic tissues.

Biochemical regulation of mammalian AMP-activated protein kinase activity by NAD and NADH.

AMP-activated protein kinase (AMPK) serves as an energy-sensing protein kinase that is activated by a variety of metabolic stresses that lower cellular energy levels. When activated, AMPK modulates a network of metabolic pathways that result in net increased substrate oxidation, generation of reduced nucleotide cofactors, and production of ATP. AMPK is activated by a high AMP:ATP ratio and phosphorylation on threonine 172 by an upstream kinase. Recent studies suggest that mechanisms that do not involve changes in adenine nucleotide levels can activate AMPK. Another sensor of the metabolic state of the cell is the NAD/NADH redox potential. To test whether the redox state might have an effect on AMPK activity, we examined the effect of beta-NAD and NADH on this enzyme. The recombinant T172D-AMPK, which was mutated to mimic the phosphorylated state, was activated by beta-NAD in a dose-dependent manner, whereas NADH inhibited its activity. We explored the effect of NADH on AMPK by systematically varying the concentrations of ATP, NADH, peptide substrate, and AMP. Based on our findings and established activation of AMPK by AMP, we proposed a model for the regulation by NADH. Key features of this model are as follows. (a) NADH has an apparent competitive behavior with respect to ATP and uncompetitive behavior with respect to AMP resulting in improved binding constant in the presence of AMP, and (b) the binding of the peptide is not significantly altered by NADH. In the absence of AMP, the binding constant of NADH becomes higher than physiologically relevant. We conclude that AMPK senses both components of cellular energy status, redox potential, and phosphorylation potential.

Biochemical and kinetic characterization of BACE1: investigation into the putative species-specificity for beta- and beta'-cleavage sites by human and murine BACE1.

Beta-amyloid peptides (Abeta) are produced by a sequential cleavage of amyloid precursor protein (APP) by beta- and gamma-secretases. The lack of Abeta production in beta-APP cleaving enzyme (BACE1)(-/-) mice suggests that BACE1 is the principal beta-secretase in mammalian neurons. Transfection of human APP and BACE1 into neurons derived from wild-type and BACE1(-/-) mice supports cleavage of APP at the canonical beta-secretase site. However, these studies also revealed an alternative BACE1 cleavage site in APP, designated as beta', resulting in Abeta peptides starting at Glu11. The apparent inability of human BACE1 to make this beta'-cleavage in murine APP, and vice versa, led to the hypothesis that this alternative cleavage was species-specific. In contrast, the results from human BACE1 transgenic mice demonstrated that the human BACE1 is able to cleave the endogenous murine APP at the beta'-cleavage site. To address this discrepancy, we designed fluorescent resonance energy transfer peptide substrates containing the beta- and beta'-cleavage sites within human and murine APP to compare: (i) the enzymatic efficiency; (ii) binding kinetics of a BACE1 active site inhibitor LY2039911; and (iii) the pharmacological profiles for human and murine recombinant BACE1. Both BACE1 orthologs were able to cleave APP at the beta- and beta'-sites, although with different efficiencies. Moreover, the inhibitory potency of LY2039911 toward recombinant human and native BACE1 from mouse or guinea pig was indistinguishable. In summary, we have demonstrated, for the first time, that recombinant BACE1 can recognize and cleave APP peptide substrates at the postulated beta'-cleavage site. It does not appear to be a significant species specificity to this cleavage.