title: Anti-angiogenic effects of the tubulysin precursor pretubulysin and of simplified pretubulysin derivatives.
abstract: OBJECTIVE
  The use of tubulin-binding compounds, which act in part by inhibiting tumour angiogenesis, has become an integral strategy of tumour therapy. Recently, tubulysins were identified as a novel class of natural compounds of myxobacterial origin, which inhibit tubulin polymerization. As these compounds are structurally highly complex, the search for simplified precursors [e.g. pretubulysin (Prt)] and their derivatives is mandatory to overcome supply problems hampering clinical development. We tested the anti-angiogenic efficacy of Prt and seven of its derivatives in comparison to tubulysin A (TubA).
  
  
  METHODS
  The compounds were tested in cellular angiogenesis assays (proliferation, cytotoxicity, cell cycle, migration, chemotaxis, tube formation) and in vitro (tubulin polymerization). The efficacy of Prt was also tested in vivo in a murine subcutaneous tumour model induced with HUH7 cells; tumour size and vascularization were measured.
  
  
  RESULTS
  The anti-angiogenic potency of all the compounds tested ran parallel to their inhibition of tubulin polymerization in vitro. Prt showed nearly the same efficacy as TubA (EC(50) in low nanomolar range in all cellular assays). Some modifications in the Prt molecule caused only a moderate drop in potency, while others resulted in a dramatic loss of action, providing initial insight into structure-activity relations. In vivo, Prt completely prevented tumour growth and reduced vascular density to 30%.
  
  
  CONCLUSIONS
  Prt, a chemically accessible precursor of some tubulysins is a highly attractive anti-angiogenic compound both in vitro and in vivo. Even more simplified derivatives of this compound still retain high anti-angiogenic efficacy.
authors.affiliation: Department of Pharmacy--Center for Drug Research, Butenandtstr, 5-13, 81377 Munich, Germany. stefan.zahler@cup.unimuenchen.de
authors.forename: S
authors.initials: S
authors.lastname: Rath
authors.forename: J
authors.initials: J
authors.lastname: Liebl
authors.forename: R
authors.initials: R
authors.lastname: Fürst
authors.forename: A
authors.initials: A
authors.lastname: Ullrich
authors.forename: J L
authors.initials: JL
authors.lastname: Burkhart
authors.forename: U
authors.initials: U
authors.lastname: Kazmaier
authors.forename: J
authors.initials: J
authors.lastname: Herrmann
authors.forename: Rolf
authors.initials: R
authors.lastname: Müller
authors.forename: M
authors.initials: M
authors.lastname: Günther
authors.forename: L
authors.initials: L
authors.lastname: Schreiner
authors.forename: E
authors.initials: E
authors.lastname: Wagner
authors.forename: A M
authors.initials: AM
authors.lastname: Vollmar
authors.forename: S
authors.initials: S
authors.lastname: Zahler
mesh_terms: D020533:Angiogenesis Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002633:Chemotaxis / Q000187:drug effects; D005260:Female; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D009369:Neoplasms / Q000098:blood supply / Q000188:drug therapy / Q000473:pathology; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000473:pathology; D009842:Oligopeptides / Q000494:pharmacology* / Q000627:therapeutic use; D014404:Tubulin / Q000378:metabolism; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D020533:Angiogenesis Inhibitors; D009842:Oligopeptides; D014404:Tubulin; C510756:tubulysin A; C575012:pretubulysin