Halogenation of glycopeptide antibiotics occurs at the amino acid level during non-ribosomal peptide synthesis.

Halogenation plays a significant role in the activity of the glycopeptide antibiotics (GPAs), although up until now the timing and therefore exact substrate involved was unclear. Here, we present results combined from in vivo and in vitro studies that reveal the substrates for the halogenase enzymes from GPA biosynthesis as amino acid residues bound to peptidyl carrier protein (PCP)-domains from the non-ribosomal peptide synthetase machinery: no activity was detected upon either free amino acids or PCP-bound peptides. Furthermore, we show that the selectivity of GPA halogenase enzymes depends upon both the structure of the bound amino acid and the PCP domain, rather than being driven solely via the PCP domain. These studies provide the first detailed understanding of how halogenation is performed during GPA biosynthesis and highlight the importance and versatility of trans-acting enzymes that operate during peptide assembly by non-ribosomal peptide synthetases.

Use of costic acid, a natural extract from Dittrichia viscosa, for the control of Varroa destructor, a parasite of the European honey bee.

Costic acid has been isolated from the plant Dittrichia viscosa and its efficacy against Varroa destructor, a parasite of Apis mellifera, the European honey bee, has been studied. Costic acid exhibited potent in vivo acaricidal activity against the parasite. Initial experiments showed that the compound is not toxic for human umbilical vein endothelial cells (HUVEC) at concentrations of up to 230 micromolar (µM), indicating that costic acid could be used as a safe, low-cost and efficient agent for controlling varroosis in honey bee colonies.

A col10a1:nlGFP transgenic line displays putative osteoblast precursors at the medaka notochordal sheath prior to mineralization.

In teleosts, such as medaka, ossification of the vertebral column starts with the mineralization of the notochordal sheath in a segmental pattern. This establishes the chordal centrum, which serves as the basis for further ossifications by sclerotome derived osteoblasts generating the vertebral body. So far, it is unclear which cells produce the notochordal sheath and how a segmental pattern of mineralization is established in teleosts. Here, we use a transgenic medaka line that expresses nlGFP under the control of the col10a1 promoter for in vivo analysis of vertebral body formation. We show that col10a1:nlGFP expression recapitulates endogenous col10a1 expression. In the axial skeleton, col10a1:nlGFP cells appear prior to the mineralization of the notochordal sheath in a segmental pattern. These cells remain on the outer surface of the chordal centra during mineralization as well as subsequent perichordal ossification of the vertebral bodies. Using twist1a1:dsRed and osx:mCherry transgenic lines we show that a subset of col10a1:nlGFP cells is derived from sclerotomal precursors and differentiates into future osteoblasts. For the first time, this shows a segmental occurrence of putative osteoblast precursors in the vertebral centra prior to ossification of the notochordal sheath. This opens the possibility that sclerotome derived cells in teleosts are implicated in the establishment of the mineralized vertebral column in a similar manner as previously described for tetrapods.

Potent small molecule Hedgehog agonists induce VEGF expression in vitro.

Here, we describe the synthesis, SAR studies as well as biological investigations of the known Hedgehog signaling agonist SAG and a small library of its analogues. The SAG and its derivatives were analyzed for their potency to activate the expression of the Hh target gene Gli1 in a reporter gene assay. By analyzing SAR important molecular descriptors for Gli1 activation have been identified. SAG as well as compound 10c proven to be potent activators of VEGF expression in cultivated dermal fibroblasts. Importantly and in contrast to SAG, derivative 10c displayed no toxicity in concentrations up to 250 µm.

Conditional ablation of osteoblasts in medaka.

Different from tetrapods, teleost vertebral centra form without prior establishment of a cartilaginous scaffold, in two steps: First, mineralization of the notochord sheath establishes the vertebral centra. Second, sclerotome derived mesenchymal cells migrate around the notochord sheath. These cells differentiate into osteoblasts and deposit bone onto the mineralized notochord sheath in a process of intramembranous bone formation. In contrast, most skeletal elements of the cranial skeleton arise by chondral bone formation, with remarkably similar mechanisms in fish and tetrapods. To further investigate the role of osteoblasts during formation of the cranial and axial skeleton, we generated a transgenic osx:CFP-NTR medaka line which enables conditional ablation of osterix expressing osteoblasts. By expressing a bacterial nitroreductase (NTR) fused to Cyan Fluorescent Protein (CFP) under control of the osterix promoter these cells become sensitive towards Metronidazole (Mtz). Mtz treatment of stable osx:CFP-NTR transgenic medaka for several consecutive days led to significant loss of osteoblasts by apoptosis. Live staining of mineralized bone matrix revealed reduced ossification in head skeletal elements such as cleithrum and operculum, as well as in the vertebral arches. Interestingly in Mtz treated larvae, intervertebral spaces were missing and the notochord sheath was often continuously mineralized resulting in the fusion of centra. We therefore propose a dual role for osx-positive osteoblasts in fish. Besides a role in bone deposition, we suggest an additional border function during mineralization of the chordal centra. After termination of Mtz treatment, osteoblasts gradually reappeared, indicating regenerative properties in this cell lineage. Taken together, the osx:CFP-NTR medaka line represents a valuable tool to study osteoblast function and regeneration at different stages of development in whole vertebrate specimens in vivo.

Transcriptional responses of zebrafish embryos exposed to potential sonic hedgehog pathway interfering compounds deviate from expression profiles of cyclopamine.

The molecular responses of two small molecules, SANT-2 and GANT-61, potentially interfering with the sonic hedgehog pathway (Shh) have been studied in zebrafish embryos by microarray analysis. For both compounds and the positive reference cyclopamine previous reporter gene assays for the transcription factor Gli1 have indicated an inhibition of the hedgehog signaling pathway. In zebrafish embryos a typical phenotype (cyclopia) associated with Shh interference was only observed for cyclopamine. Furthermore, only cyclopamine led to the repression of genes specifically associated with hedgehog signaling and confirmed published microarray data. In contrast to these data hspb11 was additionally identified as the most pronounced down-regulated genes for exposure to cyclopamine. No or different effects on gene expression patterns were provoked by SANT-2 or GANT-61, respectively. Reasons for the discrepancies between cellular reporter and the zebrafish embryo assay and potential implications for the identification of compounds interfering with specific developmental pathways are discussed.

Exo-cyclopamine--a stable and potent inhibitor of hedgehog-signaling.

The combination of theoretical and computational studies with organic synthesis and biological investigations has led to exo-cyclopamine. This stable and highly potent derivative of cyclopamine promises big potential as an experimental drug against several types of human cancer.

Serotonin derivatives as a new class of non-ATP-competitive receptor tyrosine kinase inhibitors.

The discovery of new templates and their subsequent elaboration to clinically useful receptor tyrosine kinase (RTK) inhibitors continues to be an important issue. RTKs are a class of enzymes responsible for the activation of different cellular signal transduction cascades. The majority of the known small molecules RTK inhibitors are ATP-competitive and they are multiple targeted inhibitors. We describe here serotonin derivatives as a new class of multiple targeted RTK inhibitors. In contrast to most other RTK inhibitors they act via a non-ATP-competitive (allosteric) mechanism. Furthermore, they are able to inhibit the proliferation of HUVE cells, fibroblasts and two cancer cell lines.

Synthesis and biological evaluation of SANT-2 and analogues as inhibitors of the hedgehog signaling pathway.

Hedgehog (Hh) signaling plays an important role in cell signaling of embryonic development and adult tissue homeostasis. In vertebrates, the hh gene encodes three different unique proteins: sonic hedgehog (Shh), desert hedgehog (Dhh) and indian hedgehog (Ihh). Disruption of the Hh signaling pathway leads to severe disorders in the development of vertebrates whereas aberrant activation of the Hh pathway has been associated with several malignancies including Gorlin syndrome (a disorder predisposing to basal cell carcinoma, medulloblastoma and rhabdomyosarcoma), prostate, pancreatic and breast cancers. In vivo evidence suggests the antagonism of excessive Hh signaling provides a route to unique mechanism-based anti-cancer therapies. Recently the small molecule SANT-2 was identified as a potent antagonist of Hh-signaling pathway. Here, we describe the synthesis, SAR studies as well as biological evaluation of SANT-2 and its analogues. Fifteen SANT-2 derivatives were synthesized and analyzed for their interference with the expression of the Hh target gene Gli1 in a reporter gene assay. By comparison of structure and activity important molecular descriptors for Gli inhibition could be identified. Furthermore we identified derivative TC-132 that was slightly more potent than the parent compound SANT-2. Selected compounds were tested for Hh related teratogenic effects in the small teleost model medaka. Albeit Gli expression has indicated a 16-fold higher Hh-inhibiting activity than observed for the plant alkaloid cyclopamine, none of the tested compounds were able to induce the cyclopamine-specific phenotype in the medaka assay.