Bioscavengers: Protection against Nerve Agent Poisoning

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Bioscavengers Protection against Nerve Agent
Poisoning

• Jack M. Baggett, Ph.D.,
• Acting Deputy Commander
• U.S. Army Medical Research Institute of Chemical
  Defense
• Aberdeen Proving Ground, MD 21010

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GoalTo eliminate nerve agent intoxication

• Current therapy is effective but the nerve agent
  exposed warfighter still suffers an insult that
  will result in incapacitation.
• Pretreatment with pyridostigmine is FDA approved
  only for soman
• Target of research is prevent any toxicity at low
  or high level of exposure (up to 5 LD50 of nerve
  agents).

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Approach

• Develop a prophylactic that detoxifies nerve
  agents at a rate sufficient to protect against
  5LD50 exposure

• Evolutionary acquisition in 3 increments
• Increment 1 plasma derived human BuChE
• Increment 2 recombinant human BuChE
• Increment 3 recombinant human catalytic protein
• Anticipated Performance Characteristics
• Prophylactic use
• Effective against a broad spectrum of nerve
  agents to include NTAs

3-D model of BuChE allows for rational drug
design and molecular biology approaches to
development
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Efficacy ( 2 weeks) in two FDA recognized species
Increment 1 Plasma Derived Product
Status

• Technology transitioned to JPEO signed 1 October
  2004.
• IND anticipated in FY07
• Possible further funding to licensure via
  Bioshield

One animal died after 3rd dose of GD and one
was impaired. Remaining four animals survived.
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Plasma Derived BuChE vs 1.5 LD50 VX
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Current Tech Base Program

• Increment 2 recombinant human BuChE
• Increment 3 recombinant human catalytic protein

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Recombinant technology
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Issues to be addressed

• Biological residence time
• Pharmacokinetic properties PEGylated rBuChE ?
  plasma BuChE in guinea pigs
• Efficacy
• rBuChE protects against GD and VX
• Shows some value as treatment against VX
• Safety
• Behavioral safety under investigation
• Immunogenicity
• Protocol at WRAIR to address this

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Efficacy of Pegylated-rBuChE
Behavioral impairment tests kinematics
(balance beam), open field, Morris water maze,
and home cage activity. Bioscavenger-pretreated
animals displayed no significant differences from
naïve animals
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Kinematics Experiments (VX)
1.5 LD50 VX conventional therapy
Control Animal
5.5 LD50 VX w/ PEG-BuChE pretreatment
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Kinematics Experiments (GD)
1.5 LD50 GD conventional therapy
Control Animal
5.5 LD50 GD w/ PEG-BuChE pretreatment
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Post-exposure Therapy with rBuChE
Percutaneous exposure to 2 or 5 LD50s of VX.
After 1 hour, rBuChE was injected i.m. No other
therapy was given.
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Recombinant BuChE Tech Base Progress

• Focus is on recombinant BuChE and recombinant
  catalytic bioscavengers,
• Transition of recombinant BuChE to advanced
  development within 2-3 years,

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Human BuChE Structural Models
Wild-type
G117H / E197Q
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BuChE Mutants
Active site Amino Acids and Mutations
Soman hydrolysis
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Theoretical Structure of HuPON1
HuPON1 is most likely a six-fold beta propeller
protein, in agreement with the recently published
crystal structure of a hybrid PON1 molecule
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Hydrolysis of VX by HuPON1
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Future Directions

• Two potential catalytic proteins are being
  investigated modified hBuChE human
  paraoxonase,
• Both show promise but require further study
• A catalytic bioscavenger could be ready for
  transition to advanced development in the next
  3-4 years.