title: Clearance and toxicity of recombinant methionyl human glial cell line-derived neurotrophic factor (r-metHu GDNF) following acute convection-enhanced delivery into the striatum.
abstract: BACKGROUND
  Despite promising early results, clinical trials involving the continuous delivery of recombinant methionyl human glial cell line-derived neurotrophic factor (r-metHuGDNF) into the putamen for the treatment of Parkinson's disease have shown evidence of poor distribution and toxicity due to point-source accumulation. Convection-enhanced delivery (CED) has the potential to facilitate more widespread and clinically effective drug distribution.
  
  
  OBJECTIVE
  We investigated acute CED of r-metHuGDNF into the striatum of normal rats in order to assess tissue clearance, toxicity (neuron loss, gliosis, microglial activation, and decreases in synaptophysin), synaptogenesis and neurite-outgrowth. We investigated a range of clinically relevant infused concentrations (0.1, 0.2, 0.6 and 1.0 µg/µL) and time points (2 and 4 weeks) in order to rationalise a dosing regimen suitable for clinical translation.
  
  
  RESULTS
  Two weeks after single dose CED, r-metHuGDNF was below the limit of detection by ELISA but detectable by immunohistochemistry when infused at low concentrations (0.1 and 0.2 µg/µL). At these concentrations, there was no associated neuronal loss (neuronal nuclei, NeuN, immunohistochemistry) or synaptic toxicity (synaptophysin ELISA). CED at an infused concentration of 0.2 µg/µL was associated with a significant increase in synaptogenesis (p<0.01). In contrast, high concentrations of r-metHuGDNF (above 0.6 µg/µL) were associated with neuronal and synaptic toxicity (p<0.01). Markers for gliosis (glial fibrillary acidic protein, GFAP) and microglia (ionized calcium-binding adapter molecule 1, Iba1) were restricted to the needle track and the presence of microglia had diminished by 4 weeks post-infusion. No change in neurite outgrowth (Growth associated protein 43, GAP43, mRNA) compared to artificial cerebral spinal fluid (aCSF) control was observed with any infused concentration.
  
  
  CONCLUSIONS
  The results of this study suggest that acute CED of low concentrations of GDNF, with dosing intervals determined by tissue clearance, has most potential for effective clinical translation by optimising distribution and minimising the risk of toxic accumulation.
authors.affiliation: School of Clinical Sciences, University of Bristol, Bristol, United Kingdom.
authors.forename: Hannah
authors.initials: H
authors.lastname: Taylor
authors.forename: Neil
authors.initials: N
authors.lastname: Barua
authors.forename: Alison
authors.initials: A
authors.lastname: Bienemann
authors.forename: Marcella
authors.initials: M
authors.lastname: Wyatt
authors.forename: Emma
authors.initials: E
authors.lastname: Castrique
authors.forename: Rebecca
authors.initials: R
authors.lastname: Foster
authors.forename: Matthias
authors.initials: M
authors.lastname: Luz
authors.forename: Christian
authors.initials: C
authors.lastname: Fibiger
authors.forename: Erich
authors.initials: E
authors.lastname: Mohr
authors.forename: Steven
authors.initials: S
authors.lastname: Gill
mesh_terms: D000818:Animals; D016923:Cell Death / Q000187:drug effects; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000633:toxicity; D006801:Humans; D007260:Infusion Pumps; D008297:Male; D008657:Metabolic Clearance Rate; D055495:Neurogenesis / Q000187:drug effects; D009457:Neuroglia / Q000378:metabolism; D010300:Parkinson Disease / Q000188:drug therapy / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity; D014018:Tissue Distribution
chemical_list: C495039:GDNF protein, human; D051100:Glial Cell Line-Derived Neurotrophic Factor; D011994:Recombinant Proteins