title: Development of a pharmacodynamic biomarker to measure target engagement from inhibition of the NGF-TrkA pathway.
abstract: BACKGROUND
  NGF signaling through TrkA triggers pathways involved in a wide range of biological effects. Clinical trials targeting either NGF or TrkA are ongoing to treat various diseases in the areas of oncology, neuroscience, and for pain, but there is no described measure of target engagement of TrkA in these studies.
  
  
  METHODS
  We have developed custom ELISA assays to measure NGF-induced phosphorylation of TrkA specific for rodent and human receptors. Optimized tissue processing methods allow for detection in both the brain and in skin. In addition, TrkB and TrkC assays have been in established to evaluate selectivity against other neurotrophin receptors.
  
  
  RESULTS
  In a preclinical NGF-induced pain model, we show that pre-dosing with a TrkA inhibitor prevents phosphorylation of TrkA in the skin at a dose that is efficacious in reversal of thermal hypersensitivity. In addition, we show data in non-human primate and human skin supporting the potential use of this approach to enable translational target engagement. Comparison with existing methods: Existing methods involve animal models expressing TrkA tumors or injection of over-expressing TrkA recombinant cells into animals. Our method can measure target engagement in both normal and disease tissues in preclinical animal models and human skin.
  
  
  CONCLUSIONS
  We have developed methods to assess target engagement for drug programs aimed at disrupting NGF-induced TrkA signaling. This includes preclinical determination of selectivity against other neurotrophin receptors and estimation of functional peripheral restriction. Preliminary data supports this method can be translated into a clinical pharmacodynamic readout using human skin biopsies.
authors.affiliation: Departments of Neuroscience Pain and Department of Medicinal Chemistry, Merck Research Laboratories, Merck & Co., Inc, West Point, PA 19486, USA. Electronic address: eric_price2@merck.com.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Price
authors.affiliation: Departments of Neuroscience Pain and Department of Medicinal Chemistry, Merck Research Laboratories, Merck & Co., Inc, West Point, PA 19486, USA.
authors.forename: Alicja
authors.initials: A
authors.lastname: Krasowska-Zoladek
authors.affiliation: Departments of Neuroscience Pain and Department of Medicinal Chemistry, Merck Research Laboratories, Merck & Co., Inc, West Point, PA 19486, USA.
authors.forename: Kausik K
authors.initials: KK
authors.lastname: Nanda
authors.affiliation: Departments of Neuroscience Pain and Department of Medicinal Chemistry, Merck Research Laboratories, Merck & Co., Inc, West Point, PA 19486, USA.
authors.forename: Shawn J
authors.initials: SJ
authors.lastname: Stachel
authors.affiliation: Departments of Neuroscience Pain and Department of Medicinal Chemistry, Merck Research Laboratories, Merck & Co., Inc, West Point, PA 19486, USA.
authors.forename: Darrell A
authors.initials: DA
authors.lastname: Henze
mesh_terms: D000700:Analgesics / Q000493:pharmacokinetics* / Q000494:pharmacology; D000818:Animals; D054316:Biomarkers, Pharmacological / Q000378:metabolism; D001706:Biopsy; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D006801:Humans; D008253:Macaca mulatta; D008297:Male; D008875:Middle Aged; D020932:Nerve Growth Factor / Q000378:metabolism*; D010146:Pain / Q000188:drug therapy / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010865:Pilot Projects; D051381:Rats; D020917:Receptor, trkA / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D020813:Receptor, trkB / Q000378:metabolism; D020812:Receptor, trkC / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D012867:Skin / Q000187:drug effects / Q000378:metabolism
chemical_list: D000700:Analgesics; D054316:Biomarkers, Pharmacological; D020932:Nerve Growth Factor; D020917:Receptor, trkA; D020813:Receptor, trkB; D020812:Receptor, trkC
keywords: Enzyme-linked immunosorbent assays (ELISAs); NGF (nerve growth factor); Neurotrophin; Pharmacodynamic biomarker; Rodent pain model; TrkA (tropomyosin receptor kinase)